Did You Know?

Prosopagnosia

2011-01-29T13:12:00.000+08:00

Prosopagnosia (Greek: "prosopon" = "face", "agnosia" = "inability to recognize/identify") is a disorder of fac e perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact. The term originally referred to a condition following acute brain damage, but recently a congenital form of the disorder has been proposed, which may be inherited by about 2.5% of the population. The specific brain area usually associated with prosopagnosia is the fusiform gyrus.
Few successful therapies have so far been developed for affected people, although individuals often learn to use 'piecemeal' or 'feature by feature' recognition strategies. This may involve secondary clues such as clothing, hair color, body shape, and voice. Because the face seems to function as an important identifying feature in memory, it can also be difficult for people with this condition to keep track of information about people, and socialize normally with others.
Some also use the term prosophenosia, which refers to the inability to recognize faces following extensive damage of both occipital and temporal lobes.

Overview

Selective inabilities to recognize faces were reported throughout the 19th century, and included case studies by Hughlings Jackson and Charcot. However, it was not named until the term prosopagnosia was first used in 1947 by Joachim Bodamer, a German neurologist. He described three cases, including a 24-year-old man who suffered a bullet wound to the head and lost his ability to recognize his friends, family, and even his own face. However, he was able to recognize and identify them through other sensory modalities such as auditory, tactile, and even other visual stimuli patterns (such as gait and other physical mannerisms). Bodamer gave his paper the title Die Prosop-Agnosie, derived from classical Greek πρόσωπον (prosopon) meaning "face" and αγνωσία (agnosia) meaning "non-knowledge".
The study of prosopagnosia has been crucial in the development of theories of face perception. Because prosopagnosia is not a unitary disorder (i.e., different people may show different types and levels of impairment), it has been argued that face perception involves a number of stages, each of which can be separately damaged. This is reflected not just in the amount of impairment displayed, but also in the qualitative differences in impairment that a person with prosopagnosia may present with.
This sort of evidence has been crucial in supporting the theory that there may be a specific face perception system in the brain. This is counterintuitive to many people, as they do not experience faces as 'special' or perceived in a different way from other objects in the rest of the world.
A recent case report described a closely related condition called prosop amnesia, in which the subject, from birth, could perceive faces normally, but had a severely impaired ability to remember them.
It has also been argued that prosopagnosia may be a general impairment in understanding how individual perceptual components make up the structure or gestalt of an object. Psychologist Martha Farah has been particularly associated with this view.
Until late in the 20th century, prosopagnosia was thought to be quite rare and solely associated with brain injury or neurological illness affecting specific areas of the brain. However, recently a form of congenital prosopagnosia has been proposed, in which people are born with an impairment in recognizing and perceiving faces, as well as other objects and visual scenes.
Dr Jane Whittaker, writing in 1999, described the case of a Mr. C. and referred to other similar cases (De Haan & Campbell, 1991, McConachie, 1976 and Temple, 1992). The reported cases suggest that this form of the disorder may be heritable and much more common than previously thought (about 2.5% of the population may be affected), although this congenital disorder is commonly accompanied by other forms of visual agnosia, and may not be "pure" prosopagnosia. It has been suggested that very mild cases of face blindness are much more common, perhaps affecting 10% of the population, although there have not been any studies confirming this. The inability to keep track of the identity of characters in movies is a common complaint.
A classic case of a prosopagnosia is presented by "Dr. P." in Oliver Sacks' 1985 book The Man Who Mistook His Wife for a Hat, though this is more properly considered "agnosia." Although Dr. P. could not recognize his wife from her face, he was able to recognize her by her voice. His recognition of pictures of his family and friends appeared to be based on highly specific features, such as his brother's square jaw and big teeth.

Subtypes

Apperceptive prosopagnosia
Apperceptive prosopagnosia is thought to be a disorder of some of the earliest processes in the face perception system. People with this disorder cannot make any sense of faces and are unable to make same-different judgments when they are presented with pictures of different faces. They may also be unable to work out attributes such as age or gender from a face. However, they may be able to recognize people based on non-face clues such as their clothing, hairstyle or voice.

Associative prosopagnosia
Associative prosopagnosia is thought to be an impairment to the links between early face perception processes and the semantic information we hold about people in our memories. People with this form of the disorder may be able to say whether photos of people's faces are the same or different and derive the age and gender from a face (suggesting they can make sense of some face information) but may not be able to subsequently identify the person or provide any information about them such as their name, occupation, or when they were last encountered. They may be able to recognize and produce such information based on non-face information such as voice, hair, or even particularly distinctive facial features (such as a distinctive moustache) that does not require the structure of the face to be understood. Typically such people do not report that 'faces make no sense' but simply that they do not look distinctive in any way.

Developmental prosopagnosia
Developmental prosopagnosia (DP) is a face-recognition deficit that is lifelong, manifesting in early childhood, and that cannot be attributed to acquired brain damage. However, a number of studies have found functional deficits in DP both on the basis of EEG measures and fMRI. It has been suggested that a genetic factor is responsible for the condition.
There seem to be two categories of DP patients:- patients who are impaired in basic face processing (age estimation, judgment of facial affect) and also show deficits on other forms of visual processing;- patients with pure face-recognition impairments in the presence of intact basic visual processing.The first group of patients fail to obtain view-centered descriptions. According to the Bruce and Young model of face recognition, these are precursors of the more abstract expression-independent descriptions. View-centered descriptions do not seem to be specific for faces, as the patients with impairments of processing the physical aspects of faces also show difficulties in non-facial tasks like object recognition or tests of visuo-spatial abilities.However, there is as yet only limited evidence for a classification into different subtypes. There are many developmental disorders that incorporate within themselves an increased likelihood that the person will have differences in face perception, of which the person may or may not be aware. That is to say, the person may or may not have insight in the clinical sense of the word. However, the mechanism by which these effects take place is largely unknown. A partial list of some disorders that often have prosopagnosiac components would include nonverbal learning disorder, Williams syndrome, and autism spectrum disorders in general. However, these types of disorders are very complicated, so arbitrary assumptions should be avoided.

Unconscious face recognition

One particularly interesting feature of prosopagnosia is that it suggests both a conscious and unconscious aspect to face recognition. Experiments have shown that when presented with a mixture of familiar and unfamiliar faces, people with prosopagnosia may be unable to successfully identify the people in the pictures, or even make a simple familiarity judgement ("this person seems familiar / unfamiliar"). However, when a measure of emotional response is taken (typically a measure of skin conductance), there tends to be an emotional response to familiar people even though no conscious recognition takes place.
This suggests emotion plays a significant role in face recognition, perhaps unsurprising when basic survival (particularly security) relies on identifying the people around you.
It is thought that Capgras delusion may be the reverse of prosopagnosia. In this condition people report conscious recognition of people from faces, but show no emotional response, perhaps leading to the delusional belief that their relative or spouse has been replaced by an impostor.

Prosopagnosia in Children

Developmental Prosopagnosia can be a difficult thing for a child to both understand and cope with. Many adults with Developmental Prosopagnosia report for a long time they had no idea that they had a deficit in face processing, unaware that others could distinguish people solely on facial differences.
Children with Prosopagnosia can be hard to find. They may just appear to be very shy or slightly odd due to their inabilities to recognize faces. Children with prosopagnosia may have a hard time making friends, as they may not recognize their classmates. They often make friends with children with other distinguishing features, for example the only white student in class or the very tall girl.
Children with prosopagnosia may also have difficulties following the plots of television shows and movies, as they have trouble recognizing the different characters. They tend to gravitate towards cartoons, where the characters always wear the same thing and have other distinguishing features. Prosopagnosiac children may also have a hard time telling family members apart or recognizing people out of context (i.e. the teacher in a grocery store).
Additionally, those children with Prosopagnosia can have a difficult time with the public school system, as many school professionals are not well versed in Prosopagnosia, if they are aware of the disorder at all. It is one of the goals of the Yonas Perception Lab to draw public attention to this disorder, in order to better educate school professionals on the topic so that children can receive appropriate interventions and assistance.

Wind

2010-12-20T00:06:00.000+08:00

Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer s p ace, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space. Winds are commonly classified by their spatial scale, their speed, the types of forces that cause them, the regions in which they occur, and their effect. The strongest observed winds on a planet in our solar system occur on Neptune and Saturn.

In meteorology, winds are often referred to according to their strength, and the direction from which the wind is blowing. Short bursts of high speed wind are termed gusts. Strong winds of intermediate duration (around one minute) are termed squalls. Long-duration winds have various names associated with their average strength, such as breeze, gale, storm, hurricane, and typhoon. Wind occurs on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hours, to global winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two main causes of large scale atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet (Coriolis effect). Within the tropics, thermal low circulations over terrain and high plateaus can drive monsoon circulations. In coastal areas the sea breeze/land breeze cycle can define local winds; in areas that have variable terrain, mountain and valley breezes can dominate local winds.
In human civilization, wind has inspired mythology, influenced the events of history, expanded the range of transport and warfare, and provided a power source for mechanical wor k, electricity, and recreation. Wind has powered the voyages of sailing ships across Earth's oceans. H ot air balloons use the wind to take short trips, and powered flight uses it to increase lift and reduce fuel consumption. Areas of wind shear caused by various weather phenomena can lead to dangerous situations for aircraft. When winds become strong, trees and man-made structures are damaged or destroyed.
Winds can shape landforms, via a variety of Aeolian processes such as the formation of fertile soils, such as loess, and by erosion. Dust from large deserts can be moved great distances from its source region by the prevailing winds; winds that are accelerated by rough topography and associated with dust outbreaks have been assigned regional names in various parts of the world because of their significant effects on those regions. Wind affects the spread of wildfires. Winds disperse seeds from various plants, enabling the survival and dispersal of those plant species, as well as flying insect populations. When combined with cold temperatures, wind has a negative impact on livestock. Wind affects animals' food stores, as well as their hunting and defensive strategies.

Cause

Wind is caused by differences in pressure. When a difference in pressure exists, the air is accelerated from higher to lower pressure. On a rotating planet the air will be deflected by the Coriolis effe ct, except exactly on the equator. Globally, the two major driving factors of large scale winds (the atmospheric circulation) are the differential heating between the equator and the poles (difference in absorption of solar energy leading to buoyancy forces) and the rotation of the planet. Outside the tropics and aloft from frictional effects of the surface, the large-scale winds tend to approach geostrophic balance. Near the Earth's surface, friction causes the wind to be slower than it would be otherwise. Surface friction also causes winds to blow more inward into low pressure areas.
Winds defined by an equilibrium of physical forces are used in the decomposition and analysis of wind profiles. They are useful for simplifying the atmospheric equations of moti on and for making qualitative arguments about the horizontal and vertical distribution of winds. The geostrophic wind component is the result of the balance between Coriolis force and pressure gradient force. It flows parallel to isobars and approximates the flow above the atmospheric boundary layer in the midlatitudes. The thermal wind is the difference in the geostrophic wind between two levels in the atmosphere. It exists only in an atmosphere with horizontal temperature gradients. The ageostrophic wind component is the difference between actual and geostrophic wind, which is responsible for air "filling up" cyclones over time. The gradient wind is similar to the geostrophic wind but also includes centrifugal force (or centripetal acceleration).

Usage of wind

Transportation

There are many different forms of sailing ships, but they all have certain basic things in common. Except for rotor ships using the Magnus effect, every sailing ship has a hull, rigging and at least one mast to hold up the sails that use the wind to power the ship. Ocean journeys by sailing ship can take many months, and a common hazard is becoming becalmed because of lack of wind, or being blown off course by severe storms or winds that do not allow progress in the desired direction. A severe storm could lead to shipwreck, and the loss of all hands. Sailing ships can only carry a certain quantity of supplies in their hold, so they have to plan long voyage s carefully to include appropriate provisions, including fresh water.
While aircraft usually travel under an internal power source, tail winds affect groundspeed and in the case of hot air balloons and other lighter-than-air vehicles, wind may play a significant role in their movement and ground track. In addition, the direction of wind plays a role in the takeoff and landing of fixed-wing aircraft and airfield runways are usually aligned to take the direction of wind into account. Of all factors affecting the direction of flight operations at an airport, wind direction is considered the primary governing factor. While taking off with a tailwind may be permissible under certain circumstances, it is generally considered the least desirable choice because of performance and safety considerations, with a headwind the desirable choice. A tailwind will increase takeoff distance and decrease climb gradient such that runway length and obstacle clearance may become limiting factors. An airship, or dirigible, is a lighter-than-air aircraft that can be steered and propelled through the air using rudders and propellers or other thrust. Unlike other aerodynamic aircraft such as fixed-wing aircraft and helicopters, which produce lift by moving a wing, or airfoil, through the air, aerostatic aircraft, such as airships and hot air balloons, stay aloft by filling a large cavity, such as a balloon, with a lifting gas. The main types of airship are non-rigid (or blimps), semi-rigid and rigid. Blimps are small airships without internal skeletons. Semi-rigid airships are slightly larger and have some form of internal support such as a fixed keel. Rigid airships with full skeletons, such as the massive Zeppelin transoceanic models, all but disappeared after several high-profile catastrophic accidents during the mid-20th century.

Power source

Historically, the ancient Sinhalese of Anuradhapura and in other cities around Sri Lanka used the monsoon winds to power furnaces as early as 300 BCE. The furnaces were constructed on the path of the monsoon winds to exploit the wind power, to bring the temperatures inside up to 1,200 °C (2,190 °F). An early historical reference to a rudimentary windmill was used to power an organ in the first century CE. The first practical windmills were later built in Sistan, Afghanistan, from the 7th century CE. These were vertical-axle windmills, which had long vertical driveshafts with rectangle shaped blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn and draw up water, and were used in the gristmilling and sugarcane industries. Horizontal-axle windmills were later used extensively in Northwestern Europe to grind flour beginning in the 1180s, and many Dutch windmills still exist. High altitude wind power is the focus of over 30 companies worldwide using tethered technology rather than ground-hugging compressive-towers. Oil is being saved by using wind for powering cargo ships by use of the mechanical energy converted from the wind's kinetic energy using very large kites.

Recreation

Wind figures prominently in several popular sports, including recreational hang gliding, hot air ballooning, kite flying, snowkiting, kite landboarding, kite surfing, paragliding, sailing, and windsurfing. In gliding, wind gradients just above the surface affect the takeoff and landing phases of flight of a glider. Wind gradient can have a noticeable effect on ground launches, also known as winch launches or wire launches. If the wind gradient is significant or sudden, or both, and the pilot maintains the same pitch attitude, the indicated airspeed will increase, possibly exceeding the maximum ground launch tow speed. The pilot must adjust the airspeed to deal with the effect of the gradient. When landing, wind shear is also a hazard, particularly when the winds are strong. As the glider descends through the wind gradient on final approach to landing, airspeed decreases while sink rate increases, and there is insufficient time to accelerate prior to ground contact. The pilot must anticipate the wind gradient and use a higher approach speed to compensate for it.

Ice

2010-07-12T22:04:00.000+08:00

Ice, technically, is one of the 15 known crystalline phases of water. In non-scientific contexts, the term usually mea ns ice Ih, which is known to be the most abundant of these solid phases. It can appear transparent or opaque bluish-white colour, depending on the presence of impurities or air inclusions. The addition of other materials such as soil may further alter the appearance.
The most common phase transition to ice Ih occurs when liquid water is cooled below 0°C (273.15K, 32°F) at standard atmospheric pressure. It can also deposit from vapour with no intervening liquid phase, such as in the formation of frost.
Ice appears in nature in forms of precipitation as varied as snowflakes, h ail, icicles, g laciers, pack ice, and entire polar ice caps. It is an important component of the global climate, and plays an important role in the water cycle. Furthermore, ice has numerous cultural applications, from ice cooling of drinks to winter sports and the art of ice sculpting.
The word is derived from Old English ís, which in turn stems from Proto-Germanic *isaz.

Formation

Ice that is found at sea may be in the form of sea ice, pack ice, or icebergs. The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the cryosphere. Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and snowpacks are an important storage mechanism for fresh water; over time, they may sublimate or melt. Snowmelt is often an important source of seasonal fresh water.
Rime is a type of ice formed on cold objects when drops of water crystallize on the m. This can be observed in foggy weather, when the temperature drops during the night. S oft rime contains a high proportion of trapped air, making it appear white rather than transparent, and giving it a density about one quarter of that of pure ice. Hard rime is comparatively denser.
Aufeis is layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick. Ice can also form icicles, similar to stalactites in appearance, or stalagmite-like forms as water drips and re-freezes.
Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice. Pancake ice is a formation of ice generally created in areas with less calm conditions.
Candle Ice is a form of Rotten Ice that develops in columns perpendicular to the surface of a lake.
Ice discs are circular formations of ice surrounded by water in a river.

Ice and transportation

Ice can also be an obstacle; for harbours near the poles, being ice-free is an important advantage; ideally, all year long. Examples are Murmansk (Russia), Petsamo (Russia, formerly Finland) and Vardø (Norway). Harbours which aren't ice-free are opened up using icebreakers.
Ice forming on roads is a dangerous winter hazard. Black ice is very difficult to see, because it lacks the expected frosty surface. Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the windows of vehicles. Driving safely requires the removal of the ice build-up. Ice scrapers are tools designed to break the ice free and clear the windows, though removing the ice can be a long and laborious process.
Far enough below the freezing point, a thin layer of ice crystals can form on the inside surface of windows. This usually happens when a vehicle has been left alone after being driven for a while, but can happen while driving, if the outside temperature is low enough. Moisture from the driver's breath is the source of water for the crystals. It is troublesome to remove this form of ice, so people often open their windows slightly when the vehicle is parked in order to let the moisture dissipate, and it is now common for cars to have rear-window defrosters to solve the problem. A similar problem can happen in homes, which is one reason why many colder regions require double-pane windows for insulation.
When the outdoor temperature stays below freezing for extended periods, very thick layers of ice can form on lakes and other bodies of water, although places with flowing water require much colder temperatures. The ice can become thick enough to drive onto with automobiles and trucks. Doing this safely requires a thickness of at least 30 centimetres (one foot).
For ships, ice presents two distinct hazards. Spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, and to require it to be hacked off or melted with steam hoses. And icebergs — large masses of ice floating in water (typically created when glaciers reach the sea) — can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous probably being the Titanic.

For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. During the first non-stop flight of the Atlantic, the British aviators Captain John Alcock and Lieutenant Arthur Whitten Brown encountered such icing conditions - Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the Vickers Vimy aircraft they were flying.
A particular icing vulnerability associated with reciprocating internal combustion engines is the carburetor. As air is sucked through the carburettor into the engine, the local air pressure is lowered, which causes adiabatic cooling. So, in humid near-freezing conditions, the carburettor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. For this reason, aircraft reciprocating engines with carburettors are provided with carburettor air intake heaters. The increasing use of fuel injection—which does not require carburettors—has made "carb icing" less of an issue for reciprocating engines.
Jet engines do not experience carb icing, but recent evidence indicates that they can be slowed, stopped, or damaged by internal icing in certain types of atmospheric conditions much more easily than previously believed. In most cases, the engines can be quickly restarted and flights are not endangered, but research continues to determine the exact conditions which produce this type of icing, and find the best methods to prevent, or reverse it, in flight.

Unidentified flying object

2010-06-17T21:25:00.000+08:00

Unidentified flying object (commonly abbreviated as UFO or U.F.O.) is the popular term for any apparent aerial phenomenon whose cause cannot be easily or immediately identified by the observer. The United States Air Force, which coined the term in 1952, initially defined UFOs as those objects that remain unidentified after scrutiny by expert investigators, though today the term UFO is colloquially used to refer to any unidentifiable sighting regardless of whether it has been investigated. UFO reports increased precipitously after the first widely publicized U.S. sighting, reported by private pilot Kenneth Arnold in 1947, that gave rise to the popular terms "flying saucer" and "flying disc." The term UFO is popularly taken as a synonym for alien spacecraft and generally most discussions of UFOs revolve around this presumption. UFO enthusiasts and devotees have created organizations, religious cults have adopted extraterrestrial themes, and in general the UFO concept has evolved into a prominent mythos in modern culture. Some investigators now prefer to use the broader term unidentified aerial phenomenon (or UAP), to avoid the confusion and speculative associations that have become attached to UFO. Another widely known acronym for UFO in Spanish, French, Portuguese and Italian is OVNI (Objeto Volador No Identificado, with variant regional spellings).
Studies have established that the majority of UFOs are observations of some real but conventional object—most commonly aircraft, balloons, or astronomical objects such as meteors or bright planets—that have been misidentified by the observer as anomalies, while a small percentage of reported UFOs are hoaxes. Only between 5% to 20% of anomalous sightings can be classified as unidentified in the strictest sense.
The possibility that all UFO sightings are misidentifications of known natural phenomena inspired some debate in the scientific community about whether scientific investigation was warranted given the paucity of available empirical data. Very little peer-reviewed literature has been published in which scientists have proposed, studied or supported non-prosaic explanations for UFOs. Nevertheless, UFOs as a cultural phenomenon continues to be the subject of serious academic research and amateur investigators continue to advocate that UFOs represent real and unexplained events, usually associated with alien encounters.

Identification of UFOs
Studies show that after careful investigation, the majority of UFOs can be identified as ordinary objects or phenomena. The most commonly found identified sources of UFO reports are:
a) Astronomical objects (bright stars, planets, meteors, re-entering man-made spacecraft, artificial satellites, and the moon)
b) Aircraft (Aerial advertising and other aircraft, missile launches)
c) Balloons (weather balloons, prank balloons, large research balloons)
d) Other atmospheric objects and phenomena (birds, unusual clouds, kites, flares)
e) Light phenomena (mirages, Fata Morgana, moon dogs, searchlights and other ground lights, etc.)
f) Hoaxes

A 1952–1955 study by the Battelle Memorial Institute for the US Air Force included these categories as well as a "psychological" one. However, the scientific analysts were unable to come up with prosaic explanations for 21.5 % of the 3200 cases they examined and 33 % of what were considered the best cases remained unexplained, double the number of the worst cases. (See full statistical breakdown in Identification studies of UFOs). Of the 69 % identifieds, 38 % were deemed definitely explained while 31 % were thought to be "questionable." About 9 % of the cases were considered to have insufficient information to make a determination.
The official French government UFO investigation (GEPAN/SEPRA/GEIPAN), run within the French space agency CNES between 1977 and 2004, scientifically investigated about 6000 cases and found that 13.5 % defied any rational explanation, 46 % were deemed definitely or likely identifiable, while 41 % lacked sufficient information for classification.
An individual 1979 study by CUFOS researcher Allan Hendry found, as did other investigations, that only a small percentage of cases he investigated were hoaxes and that most sightings were actually honest misidentifications of prosaic phenomena. Hendry attributed most of these to inexperience or misperception. However, Hendry's figure for unidentified cases was considerably lower than many other UFO studies such as Project Blue Book or the Condon Report that have found rates of unidentified cases ranging from 6 % to 30 %. Hendry found that 88.6 % of the cases he studied had a clear prosaic explanation, and he discarded a further 2.8 % due to unreliable or contradictory witnesses or insufficient information. The remaining 8.6 % of reports could not definitively be explained by prosaic phenomena, although he felt that a further 7.1 % could possibly be explained, leaving only the very best 1.5 % without plausible explanation.

UFO hypotheses
To account for unsolved UFO cases, several hypotheses have been proposed.
1) The extraterrestrial hypothesis (ETH) is defined by Edward U. Condon in the 1968 Condon Report as "The idea that some UFOs may be spacecraft sent to Earth from another civilization, or on a planet associated with a more distant star", further attributing the popularity of the idea to Donald Keyhoe's UFO book from 1950, though the idea clearly predated Keyhoe, appearing in newspapers and various government documents. This is probably the most popular theory among Ufologists. Some private or governmental studies, some secret, have concluded in favor of the ETH, or have had members who disagreed with official conclusions against the conclusion by committees and agencies to which they belonged.
2) The interdimensional hypothesis (IDH or IH) says that UFOs are objects crossing over from other dimensions or parallel universe, popularly proposed by Jacques Vallée, though also predating him.
3) The paranormal/occult hypothesis is a variant of the interdimensional hypothesis, invoked to explain so-called paranormal aspects sometimes associated with UFO reports.
4) The psychosocial hypothesis, that what people report as UFO experiences is the result of psychological misperception mechanisms and is strongly influenced by popular culture.
5) That UFOs represent poorly understood or still unknown natural phenomena, such as ball lightning or sprites.
6) The earthquake lights/tectonic strain hypothesis: UFOs are caused by strains in Earth's crust near earthquake faults, which can also supposedly induce hallucinations.
That UFOs are military flying saucers, top secret or experimental aircraft unfamiliar to most people.

Hiccup

2010-06-02T21:32:00.000+08:00

A hiccup or hiccough (pronounced /ˈhɪkʌp/ HICK-up) is a contraction of the diaph rag m that repeats several times per minute. In humans, the abrupt rush of air into the lungs causes the epiglottis to close, creating a "hic" sound.
In medicine it is known as synchronous diaphragmatic flutter (SDF), or singultus, from the Latin singult, "the act of catching one's breath while sobbing". The hiccup is an involuntary action involving a reflex arc. A bout of hiccups, in general, resolves itself without intervention, although many home remedies claim to shorten the duration, and medical treatment is occasionally necessary in cases of chronic hiccups.

Causes

Hiccups are caused by many central and peripheral nervous system disorders, all from injury or irritation to the phrenic and vagus nerves, as well as toxic or metabolic disorders affecting the aforementioned systems. Hiccups often occur after drinking carbonated beverages or alcohol or ingesting spicy foods. Prolonged lau ghter is also known to cause hiccups. Eating too fast can also cause the hiccups. Persistent or intractable hiccups may be caused by any condition which irritates or damages the relevant nerves. Chemotherapy—which can include a huge number of different drugs—has been implicated in hiccups (some data states 30 percent of patients), while other studies have not proven such a relationship. Many times chemotherapy is applied to tumors sitting at places that are by themselves prone to cause hiccups, if irritated.

Treatment

Ordinary hiccups are cured easily without medical intervention. However, there are a number of anecdotal treatments for casual cases of hiccups. Some of the more common home remedies include giving the afflicted a fright or shock, eating peanut butter, taking a teaspoon of vinegar, drinking water (sometimes in an unorthodox manner), holding one's breath and altering one's breathing patterns. A solution involving sugar placed on or under the tongue was cited in the December 23, 1971 issue of the New England Journal of Medicine.
Hiccups are treated medically only in severe and persistent (termed "intractable") cases, such as in the case of a 15-year-old girl who, in 2007, hiccuped continuously for five weeks.

Haloperidol (Haldol, an anti-psychotic and sedative), metoclopramide (Reglan, a gastrointestinal stimulant), and chlorpromazine (Thorazine, an anti-psychotic with strong sedative effects) are used in cases of intractable hiccups. In severe or resistant cases, ba clofen, an anti-spasmodic, is sometimes required to suppress hiccups. Effective treatment with sedatives often requires a dose that renders the person either unconscious or highly lethargic. Hence, medicating singultus is done short-term, as the affected individual cannot continue with normal life activities while taking the medication.
Persistent and intractable hiccups due to electrolyte imbalance (hypokalemia, hyponatremia) may benefit from drinking a carbonated beverage containing salt to normalize the potassium-sodium balance in the nervous system. The carbonation promotes quicker absorption. Carbonated beverages by themselves may have a tendency to provoke hiccups in some people.
The administration of intranasal vinegar was found to ease the chronic and severe hiccups of a three-year old Japanese girl. Vinegar may stimulate the dorsal wall of the nasopharynx, where the pharyngeal branch of the glossopharyngeal nerve (the afferent of the hiccup reflex arc) is located.
Dr. Bryan R. Payne, a neurosurgeon at the Louisiana State University Health Sciences Center in New Orleans, has had some success with an experimental procedure in which a vagus nerve stimulator is implanted in the upper chest of patients with an intractable case of hiccups. "It sends rhythmic bursts of electricity to the brain by way of the vagus nerve, which passes through the neck. The Food and Drug Administration approved the vagus nerve stimulator in 1997 as a way to control seizures in some patients with epilepsy".

Getting the wind knocked out of you

Getting the wind knocked out of you is a phrase and a commonly used idiom that mainly refers to a kind of diaphragm spasm that occurs when sudden force is applied to the abdomen which puts pressure on the solar plexus. It results in a temporary paralysis of the diaphragm that makes it difficult to breathe for a short period of time. It can also occur from a strong blow to the back.
When the abdomen is struck, a large difference in pressure occurs across the diaphragm. The diaphragm then stretches, which also stretches the diaphragm's nerves. The resulting mechanical force puts the diaphragm into a muscle spasm, comparable to having a charley horse in the leg. It takes a few seconds for the diaphragm to relax again before breathing can resume normally. Martial artists are often taught to breathe out heavily when struck in the stomach, to minimize this effect.
Often, the laryngeal muscles contract during diaphragm spasm producing an inspiratory sound known as stridor which can be heard for several cycles as breathing resumes.
Singultus, commonly known as the hiccups, is also a form of diaphragm spasm, although much milder. A singultus episode impairs voluntary breathing control for brief moments (measured in milliseconds) rather than for several seconds.
It may also be referred to as Rat Gut, getting winded or just winded.

Society and culture

American man Charles Osborne had the hiccups for 68 years, from 1922 to 1990, and was entered in the Guinness World Records as the man with the longest attack of hiccups.
In 2007, a teenager from Washington State in the United States named Cheyenne Motland hiccuped around 50 times a minute for more than five weeks. After her hiccups returned, her neurologist suggested that she may have Tourette syndrome, and the hiccups may be a "tic" caused by Tourette's.
Christopher Sands from the UK had hiccups for a period of almost three years which was eventually discovered to be due to a tumor located on the part of the brain that controls vascular activities, once 2/3 of the tumor was removed the hiccups appeared to settle and Sands no longer suffers from his condition.

Anemia

2010-05-23T23:51:00.000+08:00

Anemia (pronounced /əˈniːmiə/, also spelled anaemia and anæmia; from Ancient Greek ἀναιμία anaimia, meaning lack of blood) is a decrease in normal number of red blood cells (RBCs) or less than the normal quantity of hemoglo bin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin deficiency.
Because hemoglobin (found inside RBCs) normally carries oxygen from the lungs to the tissues, anemia leads to hypoxia (lack of oxygen) in organs. Because all human cells depend on oxygen for survival, varying degrees of anemia can have a wide range of clinical consequences.
Anemia is the most common disorder of the blood. There are several kinds of anemia, produced by a variety of underlying causes. Anemia can be classified in a variety of ways, based on the morphology of RBCs, underlying etiologic mechanisms, and discernible clinical spectra, to mention a few. The three main classes of anemia include excessive blood loss (acutely such as a hemorrhage or chronically through low-volume loss), excessive blood cell destruction (hemolysis) or deficient red blood cell production (ineffective hematopoiesis).
There are two major approaches: the "kinetic" approach which involves evaluating production, destruction and loss, and the "morphologic" approach which groups anemia by red blood cell size. The morphologic approach uses a quickly available and cheap lab test as its starting point (the MCV). On the other hand, focusing early on the question of production may allow the clinician more rapidly to expose cases where multiple causes of anemia coexist.

Signs and symptoms

Anemia goes undetected in many people, and symptoms can be minor or vague. The signs and symptoms can be related to the anemia itself, or the underlying cause.
Most commonly, people with anemia report non-specific symptoms of a feeling of weakness, or fatigue, general malaise and sometimes poor concentration. They may also report shortness of breath, dyspnea, on exertion. In very severe anemia, the body may compensate for the lack of oxygen carrying capability of the blood by increasing cardiac output. The patient may have symptoms related to this, such as palpitations, angina (if preexisting heart disease is present), intermittent claudication of the legs, and symptoms of heart failure.
On examination, the signs exhibited may include pallor (pale skin, mucosal linings and nail beds) but this is not a reliable sign. There may be signs of specific causes of anemia, e.g., koilonychia (in iron deficiency), jaundice (when anemia results from abnormal break down of red blood cells — in hemolytic anemia), bone deformities (found in thalassaemia major) or leg ulcers (seen in sickle cell disease).
In severe anemia, there may be signs of a hyperdynamic circulation: a fast heart rate (tachycardia), flow murmurs, and cardiac enlargement. There may be signs of heart failure.
Pica, the consumption of non-food based items such as dirt, paper, wax, grass, ice, and hair, may be a symptom of iron deficiency, although it occurs often in those who have normal levels of hemoglobin.
Chronic anemia may result in behavioral disturbances in children as a direct result of impaired neurological development in infants, and reduced scholastic performance in children of school age.
Restless legs syndrome is more common in those with iron deficiency anemia.
Less common symptoms may include swelling of the legs or arms, chronic heartburn, vague bruises, vomiting, increased sweating, and blood in stool.

Possible complications

Anemia diminishes the capability of affected individuals to perform physical activities, a result of one's muscles being forced to depend on anaerobic metabolism. The lack of iron associated with anemia can cause many complications, including hypoxemia, brittle or rigid fingernails, cold intolerance, and possible behavioral disturbances in children. Hypoxemia resulting from anemia can worsen the cardio-pulmonary status of patients with pre-existing chronic pulmonary disease. Cold intolerance occurs in one in five patients with iron deficiency anemia, and becomes visible through numbness and tingling.

Treatments

There are many different treatments for anemia and the treatment depends on severity and the cause.
Iron deficiency from nutritional causes is rare in non-menstruating adults (men and post-menopausal women). The diagnosis of iron deficiency mandates a search for potential sources of loss such as gastrointestinal bleeding from ulcers or colon cancer. Mild to moderate iron deficiency anemia is treated by oral iron supplementation with ferrous sulfate, ferrous fumarate, or ferrous gluconate. When taking iron supplements, it is very common to experience stomach upset and/or darkening of the feces. The stomach upset can be alleviated by taking the iron with food; however, this decreases the amount of iron absorbed. Vitamin C aids in the body's ability to absorb iron, so taking oral iron supplements with orange juice is of benefit.
Vitamin supplements given orally (folic acid) or subcutaneously (vitamin B-12) will replace specific deficiencies.
In anemia of chronic disease, anemia associated with chemotherapy, or anemia associated with renal disease, some clinicians prescribe recombinant erythropoietin, epoetin alfa, to stimulate red cell production.
In severe cases of anemia, or with ongoing blood loss, a blood transfusion may be necessary.

Blood transfusions

Doctors attempt to avoid blood transfusion in general, since multiple lines of evidence point to increased adverse patient clinical outcomes with more intensive transfusion strategies. The physiological principle that reduction of oxygen delivery associated with anemia leads to adverse clinical outcomes is balanced by the finding that transfusion does not necessarily mitigate these adverse clinical outcomes.
In severe, acute bleeding, transfusions of donated blood are often lifesaving. Improvements in battlefield casualty survival is attributable, at least in part, to the recent improvements in blood banking and transfusion techniques.
Transfusion of the stable but anemic hospitalized patient has been the subject of numerous clinical trials, and transfusion is emerging as a deleterious intervention.
Four randomized controlled clinical trials have been conducted to evaluate aggressive versus conservative transfusion strategies in critically ill patients. All four of these studies failed to find a benefit with more aggressive transfusion strategies.
In addition, at least two retrospective studies have shown increases in adverse clinical outcomes with more aggressive transfusion strategies.

Hyperbaric oxygen

Treatment of exceptional blood loss (anemia) is recognized as an indication for hyperbaric oxygen (HBO) by the Undersea and Hyperbaric Medical Society. The use of HBO is indicated when oxygen delivery to tissue is not sufficient in patients who cannot be transfused for medical or religious reasons. HBO may be used for medical reasons when threat of blood product incompatibility or concern for transmissible disease are factors.
In 2002, Van Meter reviewed the publications surrounding the use of HBO in severe anemia and found that all publications report a positive result.

Ibn Bajjah

2010-05-20T22:01:00.000+08:00

Abū-Bakr Muhammad ibn Yahya ibn al-Sāyigh (Arabic أبو بكر محمد بن يحيى بن الصائغ), known as Ibn Bājjah (Arabic: ابن باجة‎), was an Andalusian-Arab Muslim polymath: an astronomer, logician, musician, philosopher, physician, physicist, psychologist, Botany, poet and scientist. He was known in the West by his Latini zed name, Avempace. He was born in Zarago za in what is today Spain and died in Fes, Morocco in 1138. Avempace worked as vizir for Abu Bakr ibn Ibrahim Ibn Tîfilwît, the Almoravid governor of Saragossa. Avempace also wrote poems (panegyrics and 'muwasshahat') for him, and they both enjoyed music and wine. Avempace joined in poetic competitions with the poet al-Tutili. He later worked, for some twenty years, as the vizir of Yahyà ibn Yûsuf Ibn Tashufin, another brother of the Almoravid Sultan Yusuf Ibn Tashufin (died 1143) in Morocco. He was the famous author of the Kitab al-Nabat (The Book of Plants), a popular work on B otany, which defined the sex of Plants.
His philosophic ideas had a clear effect on Ibn Rushd and Albertus Magnus. Most of his writings and book were not completed (or well organized) because of his early death. He had a vast knowledge of Medicine, Mathematics and Astronomy. His main contribution to Islamic Philosophy is his idea on Soul Phenomenology, but unfortunately not completed.
His beloved expressions were Gharib غريب and Mutawahhid متوحد, two approved and popular expressions of Islamic Gnostics.
Ibn Bajjah was also a renowned poet. In his explanation of the Zajal E.G. Gomes writes: "There is some evidence for the belief that it was invented by the famous philosopher and musician known as Avempace. Its chief characteristic being that it is written entirely in the vernacular. ” (Emilio Gracia Gomes in his essay “Moorish Spain")
Though many of his works have not survived, his theories on astronomy and physics were preserved by Maimonides and Averroes respectively, which had a subsequent influence on later astronomers and physicists in the Islamic civilization and Renaissance Europe, including Galileo Galilei.

Astronomy

In Islamic astronomy, Maimonides wrote the following on the planetary model proposed by Ibn Bajjah:

"I have heard that Abu Bakr [Ibn Bajja] discovered a system in which no epicycles occur, but ecce ntric spheres are not excluded by him. I have not heard it from his pupils; and even if it be correct that he discovered such a system, he has not gained much by it, for eccentricity is likewise contrary to the principles laid down by Aristotle.... I have explained to you that these difficulties do not concern the astronomer, for he does not profess to tell us the existing properties of the spheres, but to suggest, whether correctly or not, a theory in which the motion of the stars and planets is uniform and circular, and in agreement with observation."

In his commentary on Aristotle's Meteorology, Ibn Bajjah presented his own theory on the Milky Way galaxy. Aristotle believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions." On the other hand, Aristotle's Arabic commentator Ibn al-Bitriq considered "the Milky Way to be a phenomenon exclusively of the heavenly spheres, not of the upper part of the atmosphere" and that the "light of those stars makes a visible patch because they are so close." Ibn Bajjah's view differed from both, as he considered "the Milky Way to be a phenomenon both of the spheres above the moon and of the sublunar region." The Stanford Encyclopedia of Philosophy describes his theory and observation on the Milky Way as follows:

"The Milky Way is the light of many stars which almost touch one another. Their light forms a “continuous image” (khayâl muttasil) on the surface of the body which is like a “tent” (takhawwum) under the fierily element and over the air which it covers. Avempace defines the continuous image as the result of refraction (in‛ikâs) and supports its explanation with an observation of a conjunction of two planets, Jupiter and Mars which took place in 500/1106-7. He watched the conjunction and “saw them having an elongate figure” although their figure is circular."

Ibn Bajjah also reported observing "two planets as black spots on the face of the Sun." In the 13th century, the Maragha astronomer Qotb al-Din Shirazi identified this observation as the transit of Venus and Mercury. However, Ibn Bajjah cannot have observed a Venus transit, as there were no Venus transits in his lifetime.

Physics

In Islamic physics, Ibn Bajjah's law of motion was equivalent to the principle that uniform motion implies absence of action by a force. This principle would later form the basis of modern mechanics and have a subsequent influence on the classical mechanics of physicists such as Galileo Galilei. Ibn Bajjah's definition of velocity was also equivalent to Galileo's definition of velocity:

Velocity = Motive Power - Material Resistance

where the motive power is measured by the specific gravity of the mobile body and the material resistance is the resisting medium whose resistive power is measured by its specific gravity.
Ibn Bajjah was among the first to state that there is always a reaction force for every force exerted, a precursor to Gottfried Leibniz's idea of force which underlies Newton's third law of motion or law of reciprocal actions. However,the history of the principle of action and reaction can be traced as far as Aristotle.

Ibn Bajjah also had an influence on Thomas Aquinas' analysis of motion. In his Systeme du Monde, the pioneering historian of medieval science, Pierre Duhem, stated:
"For the first time we have seen human reason distinguish two elements in a heavy body: the motive force, that is, in modern terms, the weight; and the moved thing, the corpus quantum, or as we say today, the mass. For the first time we have seen the notion of mass being introduced in mechanics, and being introduced as equivalent to what remains in a body when one has suppressed all forms in order to leave only the prime matter quantified by its determined dimensions. Saint Thomas Aquinas's analysis, completing Ibn Bajja's, came to distinguish three notions in a falling body: the weight, the mass, and the resistance of the medium, about which physics will reason during the modern era....This mass, this quantified body, resists the motor attempting to transport it from one place to another, stated Thomas Aquinas."

Psychology

In Islamic psychology, Ibn Bajjah "based his psychological studies on physics." In his essay, Recognition of the Active Intelligence, he wrote that active intelligence is the most important ability of human beings, and he wrote many other essays on sensations and imaginations. He concluded that "knowledge cannot be acquired by senses alone but by Active Intelligence, which is the governing intelligence of nature." He begins his discussion of the soul with the definition that "bodies are composed of matter and form and intelligence is the most important part of man—sound knowledge is obtained through intelligence, which alone enables one to attain prosperity and build character." He viewed the unity of the rational soul as the principle of the individual identity, and that by its contact with the Active Intelligence, it "becomes one of those lights that gives glory to God." His definition of freedom is "that when one can think and act rationally". He also writes that "the aim of life should be to seek spiritual knowledge and make contact with Active Intelligence and thus with the Divine."

Pan-STARRS

2010-05-16T22:09:00.000+08:00

Pan-STARRS (an acronym for Panoramic Survey Telescope And Rapid Response System) is a planned astronomical survey that will conduct astrometry and photometry of much of the entire sky on a continuous basis. By detecting any differences from previous observations of the same areas of the sky, it is expected to discover a very large number of new asteroids, comets, variable stars and other celestial objects. Its primary mission is to detect near-Earth objects that threaten to cause impact events. It is expected to create a database of all objects visible from Hawaii (three-quarters of the entire sky) down to apparent magnitude 24.
Pan-STARRS' first telescope, called PS1, is located at the summit of Haleakala in Maui Island, and went online on December 6, 2008, under the administration of the University of Hawaii. The other three telescopes completing the array will be completed by 2012 at a total cost of USD 100 million for the entire array.
The Pan-STARRS is a collaboration between the University of Hawaii Institute for Astronomy, MIT Lincoln Laboratory, Maui High Perform ance Computing Center and Science Applications International Corporation. Telescope construction is funded by the US Air Force. Once PS1 reaches the milestone of passing its Operational Readiness Review, expected Fall 2008, the Pan-STARRS Project will focus on building PS4.
The operations for the first Pan-STARRS telescope (PS1) are funded by The PS1 Science Consort ium or PS1SC a consortium including the Max Planck Society in Germany, National Central University in Taiwan, Edinburgh, Durham and Queen's Belfast Universities in the UK, and Johns Hopkins and Harvard Universities in the USA and the Las Cumbres Observatory Global Telescope Network.

Science
Systematically surveying the entire sky on a continuous basis is an unprecedented project and is expected to produce a dramatically larger number of discoveries of various types of celestial objects. For instance, the current leading asteroid discovery project Catalina Sky Survey only goes down to apparent magnitude 20-20.5 and concentrates its searches mostly near the ecliptic; Pan-STARRS will go four magnitudes fainter and cover the entire sky visible from Hawaii. The ongoing survey will also complement the efforts to map the infrared sky by the NASA WISE orbital telescope, with the results of one survey complementing and extending the other.

Solar system
In addition to the large number of expected discoveries in the main asteroid belt, Pan-STARRS is expected to detect at least 100,000 Jupiter Trojan asteroids (compared to 2900 known as of end-2008); at least 20,000 Kuiper belt objects (compared to 800 known as of mid-2005); thousands of Trojan asteroids of Saturn, Uranus and Neptune (currently six Neptune Trojans are known, and none for the other planets excluding Mars and Jupiter); and large numbers of Centaurs and comets.
Apart from drastically adding to the number of known solar system objects, Pan-STARRS will remove or mitigate the observational bias inherent in many current surveys. For instance, among currently known objects there is a bias favoring low orbital inclination, and thus an object such as Makemake escaped detection until recently despite its bright apparent magnitude of 17, which is not much fainter than Pluto. Also, among currently known comets there is a bias favoring those with short perihelion distances. Reducing the effects of this observational bias will enable a more complete picture of solar system dynamics. For instance it is expected that the number of Jupiter Trojans larger than 1 km may in fact roughly match the number of main asteroid belt objects, although the currently known population of the latter is several orders of magnitude larger.
One intriguing possibility is that Pan-STARRS may detect "interstellar debris" or "interstellar interlopers" flying through the solar system. During the formation of a planetary system it is thought that a very large number of objects are ejected due to gravitational interactions with planets (as many as 1013 such objects in the case of our solar system). Objects ejected by planetary systems around other stars might plausibly be flying throughout the galaxy and some may pass through our solar system.
Another intriguing possibility is that Pan-STARRS may actually detect collisions involving small asteroids. These are quite rare and none have yet been observed, but with the drastically larger number of asteroids that will be discovered it is expected from statistical considerations that some collision events may be observed.
Pan-STARRS will also likely detect a number of Kuiper belt objects the size of Pluto or larger, similar to Eris.

Beyond the solar system
It is expected that Pan-STARRS will discover an extremely large number of variable stars, including such stars in other nearby galaxies; in fact, this may lead to the discovery of hitherto unknown dwarf galaxies. In discovering a large number of Cepheid va riables and ec lipsing binary stars, it will help determine distances to nearby galaxies with greater precision. It is expected to discover a large number of Type Ia supernovae in other galaxies, which are important in studying the effects of dark energy, and also optical afterglows of gamma ray bursts.
Because very young stars (such as T Tauri stars) are usually variable, Pan-STARRS should discover a large number of these and improve our understanding of them. It is also expected that Pan-STARRS may discover a large number of extrasolar planets by observing their transits across their parent stars, as well as gravitational microlensing events.
Pan-STARRS will also measure proper motion and parallax and should thereby discover a large number of brown dwarfs and white dwarfs and other nearby faint objects, and it should be able to conduct a complete census of all stars within 100 parsecs of the Sun. Prior proper motion and parallax surveys often did not detect faint objects such as the recently-discovered Teegarden's star, which are too faint for projects such as Hipparcos.
Also, by identifying stars with large parallax but very small proper motion for followup radial velocity measurements, Pan-STARRS may even be able to permit the detection of hypothetical Nemesis-type objects if these actually exist.

Discovery
SN 2008id (type 1a supernova), confirmed by Keck observatory via redshift.

Paracetamol

2010-05-09T23:59:00.000+08:00

Paracetamol (INN) (pronounced /ˌpærəˈsiːtəmɒl, ˌpærəˈsɛtəmɒl/) or acetaminophen (/əˌsiːtəˈmɪnɵfɨn/ ( listen)) (USAN) is a widely used over-the-counter analgesic (pain reliever) and antipyretic (fever reducer).
It is commonly used for the relief of headaches, and other minor aches and pains, and is a major ingredient in numerous cold and flu remedies. In combination with opioid analgesics, paracetamol could be used also in the management of more severe pain (such as in advanced cancer).
While generally safe for use at recommended doses (1,000 mg per single dose and up to 4,000 mg per day for adults, up to 2,000 mg per day if drinking alcohol), acute overdoses of paracetamol can cause potentially fatal liver damage and, in rare individuals, a normal dose can do the same; the risk is heightened by alcohol consumption. Paracetamol toxicity is the foremost cause of acute liver failure in the Western world, and accounts for most drug overdoses in the United States, the United Kingdom, Australia and New Zealand.
Paracetamol is part of the class of drugs known as "aniline analgesics"; it is the only such drug still in use today. It is the active metabolite of phenacetin, once popular as an analgesic and antipyretic in its own right, but unlike phenacetin and its combinations, paracetamol is not considered to be carcinogenic at therapeutic doses. The words acetaminophen (used in the United States, Canada, Hong Kong, Iran, Colombia and other Latin American countries) and paracetamol (used elsewhere) both come from chemical names for the compound: para-acetylaminophenol and para-acetylaminophenol. In some contexts, it is simply abbreviated as APAP, for N-acetyl-para-aminophenol.
There is confusion in terminology of paracetamol. It could be considered a nonsteroidal antiinflammatory drug (NSAID), but paracetamol has very little anti-inflammatory effect in many tissues. However, aspirin, paracetamol and other NSAIDs all act by the same mechanism (inhibition of prostaglandin (PG) synthesis) and all show varying levels of analgesic, anti-inflammatory, antipyretic and antiplatelet actions.

Indications

The World Health Organization (WHO) recommends that paracetamol be given to children with fever higher than 38.5 °C (101.3 °F).
Paracetamol is much more effective than aspirin, especially in patients where excessive gastric acid secretion or prolongation of bleeding time may be a concern. While paracetamol has analgesic and antipyretic properties comparable to those of aspirin, its anti-inflammatory effects are weak. Because paracetamol is well tolerated, available without a prescription, and lacks the gastric side effects of aspirin, it has in recent years increasingly become a common household drug.
Acetaminophen is used for the relief of fevers, aches and pains associated with many parts of the body. Acetaminophen relieves pain in mild arthritis but has no effect on the underlying inflammation, redness, and swelling of the joint. If the pain is not due to inflammation, acetaminophen is as effective as aspirin. It is as effective as the non-steroidal antiinflammatory drug ibuprofen (Motrin) in relieving the pain of osteoarthritis of the knee. Unless directed by physician, acetaminophen should not be used for longer than 10 days.

Efficacy and side effects

Paracetamol, unlike other common analgesics such as aspirin and ibuprofen, has relatively little anti-inflammatory activity, so it is not considered to be a non-steroidal anti-inflammatory drug (NSAID).

Efficacy
Regarding comparative efficacy, studies show conflicting results when compared to NSAIDs. A randomized controlled trial of chronic pain from osteoarthritis in adults found similar benefit from paracetamol and ibuprofen.
A randomized controlled trial of acute musculoskeletal pain in children found that the standard OTC dose of ibuprofen gives greater relief of pain than the standard dose of paracetamol. Another study has questioned the benefits of this drug as an antipyretic in children

Adverse effects
In recommended doses, paracetamol does not irritate the lining of the stomach, affect blood coagulation as much as NSAIDs, or affect function of the kidneys. However, some studies have shown that high dose-usage (greater than 2,000 mg per day) does increase the risk of upper gastrointestinal complications such as stomach bleeding. The researchers found that heavy use of aspirin or paracetamol - defined as 300 grams a year (1 g per day on average) - was linked to a condition known as small, indented and calcified kidneys (SICK). Paracetamol is safe in pregnancy, and does not affect the closure of the fetal ductus arteriosus as NSAIDs can. Unlike aspirin, it is safe in children, as paracetamol is not associated with a risk of Reye's syndrome in children with viral illnesses.
Like NSAIDs and unlike opioid analgesics, paracetamol has not been found to cause euphoria or alter mood in any way. In 2008, the largest study to date on the long term side effects of paracetamol in children was published in The Lancet. Conducted on over 200,000 children in 31 countries, the study found that the use of paracetamol for fever in the first year of life was associated with an increase in the incidence of asthmatic symptoms at 6–7 years, and that paracetamol use, both in the first year of life and in children aged 6–7 years, was associated with an increased incidence of rhinoconjunctivitis and eczema. The authors acknowledged that their "findings might have been due to confounding by indication", i.e. that the association may not be causal but rather due to the disease being treated with paracetamol, and emphasized that further research was needed. Furthermore a number of editorials, comments, correspondence and their replies have been published in The Lancet concerning the methodology and conclusions of this study. The UK regulatory body the Medicines and Healthcare products Regu latory Agency, also reviewed this research and published a number of concerns over data interpretation, and offer the following advice for healthcare professionals, parents, and carers: "The results of this new study do not necessitate any change to the current guidance for use in children. Paracetamol remains a safe and appropriate choice of analgesic in children. There is insufficient evidence from this research to change guidance regarding the use of antipyretics in children."

Time travel

2010-04-29T23:44:00.001+08:00

Time travel is the concept of moving between different points in time in a manner analogous to moving between different points in space, either sending objects (or in some cases just information) backwards in time to some moment before the present, or sending objects forward from the present to the future without the need to experience the intervening period (at least not at the normal rate).
Although time travel has been a common plot device in fiction since the 19th century, and one-way travel into the future is arguably possible given the phenomenon of time dilation based on velocity in the theory of special relativity (exemplified by the twin paradox), as well as gravitational time dilation in the theory of general relativity, it is currently unknown whether the l aws of physics would allow backwards time travel.
Any technological device, whether fictional or hypothetical, that is used to achieve time travel is commonly known as a time machine.
Some interpretations of time travel also suggest that an attempt to travel backwards in time might take one to a parallel universe whose history would begin to diverge from the traveler's original history after the moment the traveler arrived in the past.

Time travel in theory
Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime, or specific types of motion in space, might allow time travel into the past and future if these geometries or motions are possible. In technical papers, physicists generally avoid the commonplace language of "moving" or "traveling" through time ('movement' normally refers only to a change in spatial position as the time coordinate is varied), and instead discuss the possibility of closed timelike curves, which are worldlines that form closed loops in spacetime, allowing objects to return to their own past. There are known to be solutions to the equations of general relativity that describe spacetimes which contain closed timelike curves (such as Gödel spacetime), but the physical plausibility of these solutions is uncertain.
Relativity states that if one were to move away from the Earth at relativistic velocities and return, more time would have passed on Earth than for the traveler, so in this sense it is accepted that relativity allows "travel into the future" (although according to relativity there is no single objective answer to how much time has 'really' passed between the departure and the return). On the other hand, many in the scientific community believe that backwards time travel is highly unlikely. Any theory which would allow time travel would require that problems of causality be resolved. The classic example of a problem involving causality is the "grandfather paradox": what if one were to go back in time and kill one's own grandfather before one's father was conceived? But some scientists believe that paradoxes can be avoided, either by appealing to the Novikov self-consistency principle or to the notion of branching parallel universes.

Tourism in time

Stephen Hawking once suggested that the absence of tourists from the future constitutes an argument against the existence of time travel—a variant of the Fermi paradox. Of course this would not prove that time travel is physically impossible, since it might be that time travel is physically possible but that it is never in fact developed (or is cautiously never used); and even if it is developed, Hawking notes elsewhere that time travel might only be possible in a region of spacetime that is warped in the right way, and that if we cannot create such a region until the future, then time travelers would not be able to travel back before that date, so "This picture would explain why we haven't been over run by tourists from the future." Carl Sagan also once suggested the possibility that time travelers could be here, but are disguising their existence or are not recognized as time travelers.

General relativity

However, the theory of general relativity does suggest scientific grounds for thinking backwards time travel could be possible in certain unusual scenarios, although arguments from semiclassical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed. These semiclassical arguments led Hawking to formulate the chronology protection conjecture, suggesting that the fundamental laws of nature prevent time travel, but physicists cannot come to a definite judgment on the issue without a theory of quantum gravity to join quantum mechanics and general relativity into a completely unified theory.

Time travel to the past in physics

Using wormholes

Wormholes are a hypothetical warped spacetime which are also permitted by the Einstein field equations of general relativity, although it would be impossible to travel through a wormhole unless it was what is known as a traversable wormhole.
A proposed time-travel machine using a traversable wormhole would (hypothetically) work in the following way: One end of the wormhole is accelerated to some significant fraction of the speed of light, perhaps with some advanced propulsion system, and then brought back to the point of origin. Alternatively, another way is to take one entrance of the wormhole and move it to within the gravitational field of an object that has higher gravity than the other entrance, and then return it to a position near the other entrance. For both of these methods, time dilation causes the end of the wormhole that has been moved to have aged less than the stationary end, as seen by an external observer; however, time connects differently through the wormhole than outside it, so that synchronized clocks at either end of the wormhole will always remain synchronized as seen by an observer passing through the wormhole, no matter how the two ends move around. This means that an observer entering the accelerated end would exit the stationary end when the stationary end was the same age that the accelerated end had been at the moment before entry; for example, if prior to entering the wormhole the observer noted that a clock at the accelerated end read a date of 2007 while a clock at the stationary end read 2012, then the observer would exit the stationary end when its clock also read 2007, a trip backwards in time as seen by other observers outside. One significant limitation of such a time machine is that it is only possible to go as far back in time as the initial creation of the machine; in essence, it is more of a path through time than it is a device that itself moves through time, and it would not allow the technology itself to be moved backwards in time. This could provide an alternative explanation for Hawking's observation: a time machine will be built someday, but has not yet been built, so the tourists from the future cannot reach this far back in time.
According to current theories on the nature of wormholes, construction of a traversable wormhole would require the existence of a substance with negative energy (often referred to as "exotic matter") . More technically, the wormhole spacetime requires a distribution of energy that violates various energy conditions, such as the null energy condition along with the weak, strong, and dominant energy conditions. However, it is known that quantum effects can lead to small measurable violations of the null energy condition, and many physicists believe that the required negative energy may actually be possible due to the Casimir effect in quantum physics. Although early calculations suggested a very large amount of negative energy would be required, later calculations showed that the amount of negative energy can be made arbitrarily small.
In 1993, Matt Visser argued that the two mouths of a wormhole with such an induced clock difference could not be brought together without inducing quantum field and gravitational effects that would either make the wormhole collapse or the two mouths repel each other. Because of this, the two mouths could not be brought close enough for causality violation to take place. However, in a 1997 paper, Visser hypothesized that a complex "Roman ring" (named after Tom Roman) configuration of an N number of wormholes arranged in a symmetric polygon could still act as a time machine, although he concludes that this is more likely a flaw in classical quantum gravity theory rather than proof that causality violation is possible.

Ibn Khaldun

2010-04-24T17:23:00.000+08:00

Ibn Khaldūn or Ibn Khaldoun (full name, Arabic: أبو زيد عبد الرحمن بن محمد بن خلدون الحضرمي ‎, Abū Zayd ‘Abdu r-Raḥman bin Muḥammad bin Khaldūn Al-Hadrami, (May 27, 1332 AD/732 AH – March 19, 1406 AD/808 AH) was an Arab polymath — an astronomer, economist, historian, Islamic jurist, Islamic lawyer, Islamic scholar, Islamic theologian, hafiz, mathematician, military strategist, nutritionist, phil osopher, social scientist and statesman—born in North Africa in present-day Tunisia. He is considered a forerunner of several social scientific disciplines: demography, cultural history, historiography, the philosophy of history, and sociology. He is also considered one of the forerunners of modern economics, alongside the earlier Indian scholar Chanakya. Ibn Khaldun is considered by many to be the father of a number of these disciplines, and of social sciences in general, for anticipating many elements of these disciplines centuries before they were founded in the West. He is best known for his Muqaddimah (known as Prolegomenon in English), the first volume of his book on universal history, Kitab al-Ibar.

Works

Ibn Khaldūn has left behind few works other than his history of the world, al-Kitābu l-ʕibār. Significantly, such writings are not alluded to in his autobiography, suggesting perhaps that Ibn Khaldūn saw himself first and foremost as a historian and wanted to be known above all as the author of al-Kitābu l-ʕibār. From other sources we know of several other works, primarily composed during the time he spent in North Africa and Al-Andalus. His first book, Lubābu l-Muhassal, a commentary on the Islamic theology of Fakhr al-Din al-Razi, was written at the age of 19 under the supervision of his teacher al-Ābilī in Tunis. A work on Sufism, Sifā'u l-Sā'il, was composed around 1373 in Fes, Morocco. Whilst at the court of Muhammed V, Sultan of Granada, Ibn Khaldūn composed a work on logic, ʕallaqa li-l-Sultān.
The Kitābu l-ʕibār (full title: Kitābu l-ʕibār wa Diwānu l-Mubtada' wa l-Ħabar fī Ayyāmu l-ʕarab wa l-Ājam wa l-Barbar wa man ʕĀsarahum min ĐawIu s-Sultānu l-Akbār "Book of Evidence, Record of Beginnings and Events from the Days of the Arabs, Persians and Berbers and their Powerful Contemporaries"), Ibn Khaldūn's main work, was originally conceived as a history of the Berbers. Later, the focus was widened so that in its final form (including its own methodology and anthropology), to represent a so-called "universal history". It is divided into seven books, the first of which, the Muqaddimah, can be considered a separate work. Books two to five cover the history of mankind up to the time of Ibn Khaldūn. Books six and seven cover the history of the Berber peoples and the Maghreb, which remain invaluable to present-day historians, as they are based on Ibn Khaldūn's personal knowledge of the Berbers.
Concerning the discipline of sociology, he conceived a theory of social conflict. He developed the dichotomy of sedentary life versus nomadic life as well as the concept of a "generation," and the inevitable loss of power that occurs when desert warriors conquer a city. Following a contemporary Arab scholar, Sati' al-Husri, the Muqaddimah may be read as a sociological work: six books of general sociology. Topics dealt with in this work include politics, urban life, economics, and knowledge. The work is based around Ibn Khaldun's central concept of 'asabiyyah, which has been translated as "social cohesion", "group solidarity", or "tribalism." This social cohesion arises spontaneously in tribes and other small kinship groups; it can be intensified and enlarged by a religious ideology. Ibn Khaldun's analysis looks at how this cohesion carries groups to power but contains within itself the seeds - psychological, sociological, economic, political - of the group's downfall, to be replaced by a new group, dynasty or empire bound by a stronger (or at least younger and more vigorous) cohesion. Ibn Khaldun has been cited as a racist, but his theories on the rise and fall of empires had no racial component, and this reading of his work has been claimed to be the result of mistranslations.
Perhaps the most frequently cited observation drawn from Ibn Khaldūn's work is the notion that when a society becomes a great civilization (and, presumably, the dominant culture in its region), its high point is followed by a period of decay. This means that the next cohesive group that conquers the diminished civilization is, by comparison, a group of barbarians. Once the barbarians solidify their control over the conquered society, however, they become attracted to its more refined aspects, such as literacy and arts, and either assimilate into or appropriate such cultural practices. Then, eventually, the former barbarians will be conquered by a new set of barbarians, who will repeat the process. Some contemporary readers of Khaldun have read this as an early business cycle theory, though set in the historical circumstances of the mature Islamic empire.
Some readings posit an anticipation of Marx's labour theory of value in Ibn Khaldun's work. Ibn Khaldun asserts that all value (profit) comes from labour, as Marx was later to write. He outlines an early (possibly even the earliest) example of political economy. He describes the economy as being composed of value-adding processes; that is, labour is added to techniques and crafts and the product is sold at a higher value. He also made the distinction between "profit" and "sustenance", in modern political economy terms, surplus and that required for the reproduction of classes respectively. He also calls for the creation of a science to explain society and goes on to outline these ideas in his major work the Muqaddimah

Legacy

Ibn Khaldun was first brought to the attention of the Western world in 1697, when a biography of him appeared in Barthélemy d'Herbelot de Molainville's Bibliothèque Orientale. Ibn Khaldun began gaining more attention from 1806, when Silvestre de Sacy's Chrestomathie Arabe included his biography together with a translation of parts of the Muqaddimah as the Prolegomena. In 1816, de Sacy again published a biography with a more detailed description on the Prolegomena. More details on and partial translations of the Prolegomena emerged over the years until the complete Arabic edition was published in 1858, followed by a complete French translation a few years later by de Sacy. Since then, the work of Ibn Khaldun has been extensively studied in the Western world with special interest.
a) British historian Arnold J. Toynbee called the Muqaddimah "a philosophy of history which is undoubtedly the greatest work of its kind that has ever yet been created by any mind in any time or place." Much of his own work on world history was inspired by Ibn Khaldun.
b) The British philosopher Robert Flint wrote the following on Ibn Khaldun: "As a theorist on history he had no equal in any age… Plato, Aristotle and Augustine were not his peers."
c) Abderrahmane Lakhsassi writes: "No historian of the Maghreb since and particularly of the Berbers can do without his historical contribution."
d) The British philosopher-anthropologist Ernest Gellner considered Ibn Khaldun's definition of government, "an institution which prevents injustice other than such as it commits itself", the best in the history of political theory.
e) Egon Orowan, who termed the concept of socionomy, developed the writings of Ibn Khaldun to forecast an eventual failure of market demand.
f) Arthur Laffer, whom the Laffer curve is named after, noted that, among others, some of Ibn Khaldun's ideas precede his own.
g) In 2006, the Atlas Economic Research Foundation launched an annual essay contest for Muslim students named in Ibn Khaldun's honor. The theme of the contest is "how individuals, think tanks, universities and entrepreneurs can influence government policies to allow the free market to flourish and improve the lives of its citizens based on Islamic teachings and traditions."
h) In 2006, Spain commemorated the 600th anniversary of the death of Ibn Khaldun.

Coral

2010-04-19T19:40:00.000+08:00

Corals are marine organisms in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans, which secrete calcium carbonate to form a hard skeleton.
A coral "head," which appears to be a single organism, is a colony of myriad genetically identical polyps. Each polyp is typically only a few millimeters in diameter. Over many generations the colony secretes a skeleton that is characteristic of the species. Individual heads grow by asex ual reproduction of individual polyps. Corals also breed sexually by spawning. Polyps of the same species release gametes simultaneously over a period of one to several nights around a full moon.
Although corals can catch small fish and animals such as plankton using stinging cells on their tentacles, most corals obtain most of their energy and nutrients from photosynthetic unicellular algae called zooxanthellae. Such corals require sunlight and grow in clear, shallow water, typically at depths shallower than 60 metres (200 ft). Corals can be major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia. Other corals do not have associated algae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3,000 metres (9,800 ft). Examples live on the Darwin Mounds located north-west of Cape Wrath, Scotland. Corals coordinate behavior by communicating with each other.

Taxonomy

Corals divide into two subclasses, depending on the number of tentacles or lines of symmetry, and a series of orders corresponding to their exoskeleton, nematocyst type and mitochondrial genetic analysis. Those with eight tentacles are called octocorallia or Alcyonaria and comprise soft corals, sea fans and sea pens. Those with more than eight in a multiple of six are called hexacorallia or Zoantharia. This group includes reef-building corals (Scleractinians), sea anemones and zoanthids.

Anatomy

Initially believed to be a plant, William Herschel used a microscope to establish in the 18th Century that Coral had the characteristic thin cell membranes of an animal.
While a coral head appears to be a single organism, it is actually a group of many individual, yet genetically identical, polyps. The polyps are multicellular organisms. Polyps are usually a few millimeters in diameter, and are formed by a layer of outer epithelium and inner jellylike tissue known as the mesoglea. They are radially symmetrical with tentacles surrounding a central mouth, the only opening to the stomach or coelenteron, through which food is ingested and waste expelled.
The stomach closes at the base of the polyp, where the epithelium produces an exoskeleton called the basal plate or calicle (L. small cup). The calicle is formed by a thickened calcareous ring (annular thickening) with six supporting radial ridges. These structures grow vertically and project into the base of the polyp. When a polyp is physically stressed, its tentacles contract into the calyx so that virtually no part is exposed above the skeletal platform. This protects the organism from predators and the elements.
The polyp grows by extension of vertical calices which occasionally septate to form a new, higher, basal plate. Over many generations this extension forms the large calcareous structures of corals and ultimately coral reefs.
Formation of the calcareous exoskeleton involves deposition of the mineral aragonite by the polyps from calcium and carbonate ions they acquire from seawater. The rate of deposition, while varying greatly across species and environmental conditions, can be as much as 10 g / m² of polyp / day (0.3 ounce / sq yd / day). This is light dependent, with night-time production 90% lower than that during the middle of the day.

Nematocysts are stinging cells at the tips of the calices that carry poison which they rapidly release in response to contact with another organism. The tentacles also bear a contractile band of epithelium called the pharynx. Jellyfish and sea anemones also carry nematocysts.
The polyps interconnect by a complex and well developed system of gastrovascular canals allowing significant sharing of nutrients and symbiotes. In soft corals these range in size from 50–500 micrometres (0.0020–0.020 in) in diameter and allow transport of both metabolites and cellular components.

Many corals as well as other cnidarian groups such as sea anemones (e.g. Aiptasia), form a symbiotic relationship with a class of algae, zooxanthellae, of the genus Symbiodinium. Aiptasia, while considered a pest among coral reef aquarium hobbyists, serves as a valuable model organism in the study of cnidarian-algal symbiosis. Typically a polyp harbors one species of algae. Via photosynthesis, these provide energy for the coral, and aid in calcification. The algae benefit from a safe environment, and consume the carbon dioxide and nitrogenous waste produced by the polyp. Due to the strain the algae can put on the polyp, stress on the coral often drives the coral to eject the algae. Mass ejections are known as coral bleaching, because the algae contribute to coral's brown coloration; other colors, however, are due to host coral pigments, such as GFPs (green fluorescent protein). Ejection increases the polyp's chances of surviving short-term stress—they can regain algae at a later time. If the stressful conditions persist, the polyp eventually dies.

Feeding

Polyps feed on a variety of small organisms, from microscopic plankton to small fish. The polyp's tentacles immobilize or kill prey using their nematocysts. The tentacles then contract to bring the prey into the stomach. Once digested, the stomach reopens, allowing the elimination of waste products and the beginning of the next hunting cycle.
These poisons are usually too weak to harm humans. An exception is fire coral.

Robotics

2010-04-08T21:24:00.001+08:00

Robotics is the engineering science and technology of robots, and their design, manufacture, application, and structural disposition. Robotics is related to electronics, mechanics, and software. The word robot was introduced to the public by Czech writer Karel Čapek in his play R.U.R. (Rossum's Universal Robots), published in 1920. The term "robotics" was coined by Isaac Asimov in his 1941 science fiction short-story "Liar!".

Origins
Stories of artificial helpers and companions and attempts to create them have a long history, but fully autonomous machines only appeared in the 20th century. The first digitally operated and programmable robot, the Unimate, was installed in 1961 to lift hot pieces of metal from a die casting machine and stack them. Today, commercial and industrial robots are in widespread use performing jobs more cheaply or more accurately and reliably than humans. They are also employed in jobs which are too dirty, dangerous, or dull to be suitable for humans. Robots are widely used in manufacturing, assembly, and packing; transport; earth and space exploration; surgery; weaponry; laboratory research; safety; and mass production of consumer and industrial goods.

Robot research
Much of the research in robotics focuses not on specific industrial tasks, but on investigations into new types of robots, alternative ways to think about or design robots, and new ways to manufacture them but other investigations, such as MIT's cyberflora project, are almost wholly academic.
A first particular new innovation in robot design is the opensourcing of robot-projects. To describe the level of advancement of a robot, the term "Generation Robots" can be used. This term is coined by Professor Hans Moravec, Principal Research Scientist at the Carnegie Mellon University Robotics Institute in describing the near future evolution of robot technology. First generation robots, Moravec predicted in 1997, should have an intellectual capacity comparable to perhaps a lizard and should become available by 2010. Because the first generation robot would be incapable of learning, however, Moravec predicts that the second generation robot would be an improvement over the first and become available by 2020, with an intelligence maybe comparable to that of a mouse. The third generation robot should have an intelligence comparable to that of a monkey. Though fourth generation robots, robots with human intelligence, professor Moravec predicts, would become possible, he does not predict this happening before around 2040 or 2050.
The second is Evolutionary Robots. This is a methodology that uses evolutionary computation to help design robots, especially the body form, or motion and behavior controllers, In a similar way to natural evolution, a large population of robots is allowed to compete in some way, or their ability to perform a task is measured using a fitness function. Those that perform worst are removed from the population, and replaced by a new set, which have new behaviors based on those of the winners. Over time the population improves, and eventually a satisfactory robot may appear. This happens without any direct programming of the robots by the researchers. Researchers use this method both to create better robots, and to explore the nature of evolution. Because the process often requires many generations of robots to be simulated, this technique may be run entirely or mostly in simulation, then tested on real robots once the evolved algorithms are good enough. Currently, there are about 1 million industrial robots toiling around the world, and Japan is the top country having high density of utilizing robots in its manufacturing industry.

Education and training
Robotics is a common undergraduate area of study. Some universities offer degrees in robotics.
Robots recently became a popular tool in raising interests in computing for middle and high school students. First year computer science courses at several universities were developed which involves the programming of a robot instead of the traditional software engineering based coursework. Some Master courses in the field of Robotics are also offered.
As the number of robots increases, robotics-related jobs grow. Some jobs require existing job skills, such as building cables, assembling parts, and testing.

Healthcare
Script Pro manufactures a robot designed to help pharmacies fill prescriptions that consist of oral solids or medications in pill form. The pharmacist or pharmacy technician enters the prescription information into its information system. The system, upon determining whether or not the drug is in the robot, will send the information to the robot for filling. The robot has 3 different size vials to fill determined by the size of the pill. The robot technician, user, or pharmacist determines the needed size of the vial based on the tablet when the robot is stocked. Once the vial is filled it is brought up to a conveyor belt that delivers it to a holder that spins the vial and attaches the patient label. Afterwards it is set on another conveyor that delivers the patient’s medication vial to a slot labeled with the patient's name on an LED read out. The pharmacist or technician then checks the contents of the vial to ensure it’s the correct drug for the correct patient and then seals the vials and sends it out front to be picked up. The robot is a very time efficient device that the pharmacy depends on to fill prescriptions.
McKesson’s Robot RX is another healthcare robotics product that helps pharmacies dispense thousands of medications daily with little or no errors. The robot can be ten feet wide and thirty feet long and can hold hundreds of different kinds of medications and thousands of doses. The pharmacy saves many resources like staff members that are otherwise unavailable in a resource scarce industry. It uses an electromechanical head coupled with a pneumatic system to capture each dose and deliver it to its either stocked or dispensed location. The head moves along a single axis while it rotates 180 degrees to pull the medications. During this process it uses barcode technology to verify its pulling the correct drug. It then delivers the drug to a patient specific bin on a conveyor belt. Once the bin is filled with all of the drugs that a particular patient needs and that the robot stocks, the bin is then released and returned out on the conveyor belt to a technician waiting to load it into a cart for delivery to the floor.

Carbon chauvinism

2010-04-02T22:22:00.000+08:00

Carbon chauvinism is a relatively new term meant to disparage the assumption that extraterrestrial life will resemble life on Earth.

Concept
Carbon chauvinism is applied to those who assume that the molecules responsible for the chemical processes of life must be constructed primarily from carbon. It suggests that human beings, as carbon-based life forms who have never encountered any life that has evolved outside the earth’s environment, may find it difficult to envision radically different biochemistries. The term was used as early as 1973, when Carl Sagan described it and other human chauvinisms that limit imagination of possible extraterrestrial life in his Cosmic Connection.
In a 1999 Reason magazine article discussing the theory of a fine-tuned universe, Kenneth Silber quotes astrophysicist Victor J. Stenger using the term:

"There is no good reason, says Stenger, to "assume that there's only one kind of life possible" - we know far too little about life in our own universe, let alone "other" universes, to reach such a conclusion. Stenger denounces as "carbon chauvinism" the assumption that life requires carbon; other chemical elements, such as silicon, can also form molecules of considerable complexity. Indeed, Stenger ventures, it is "molecular chauvinism" to assume that molecules are required at all; in a universe with different properties, atomic nuclei or other structures might assemble in totally unfamiliar ways".

Criticism
Carbon has unique features that make it suitable for life possessed by no other element. Only two elements, carbon and silicon, can create molecules that are sufficiently large enough to carry biological information. However, carbon, unlike silicon has the important property that it can form chemical bonds with diverse types of other atoms and so create the chemical versatility needed to enable the chemical reactions needed for biology such as metabolism. Elements creating organic functional groups with carbon include hydrogen, oxygen, nitrogen, phosphorus, sulfur, and diverse metals, such as iron, magnesium, and zinc. The only alternative, silicon, interacts with very few other types of atoms. Moreover, where it does it creates molecules that "are monotonous compared with the combinatorial universe of organic macromolecules."

Carbon-based life
Carbon forms the backbone of biology for all life on Earth. Complex molecules are made up of carbon bonded with other elements, especially oxygen, hydrogen and nitrogen, and carbon is able to bond with all of these because of its four valence electrons. It is often assumed in astrobiology that if life exists somewhere else in the universe, it will also be carbon based. This assumption is referred to by critics as carbon chauvinism.
In cinematic and literary science fiction, a moment when man-made machines cross from nonliving to living, is often posited, this new form would be the first example of non-carbon-based life. Since the advent of the microprocessor in the late 1960s, these machines are often classed as computers (or computer-guided robots) and filed under "silicon-based life", even though the silicon backing matrix of these processors is not nearly as fundamental to their operation as carbon is for "wet life".

Characteristics of carbon as a basis for life
The two most important characteristics of carbon as a basis for the chemistry of life, are that it has four valence bonds and that the energy required to make or break a bond is just at an appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the building of arbitrarily long and complex molecules.
There are not many other elements which appear to be even promising candidates for supporting life-like behavior, but the most frequent alternative suggested is silicon. This is in the same group in the Periodic Table of elements and therefore also has four valence bonds. It also bonds to itself, but generally in the form of crystal lattices, less amenable to a complete source of life, rather than long chains. However, its compounds are generally highly stable and do not support the ability to readily re-combine in different permutations in a manner that would plausibly support life-like processes.
This speculation of a life based on the chemistry of silicon is clearly distinct from "silicon-based life" in the above sense of artificial intelligence based on electronic processes utilizing silicon integrated circuits.

Key carbon-based molecules in the life processes
The most notable groups of chemicals used in the processes of living organisms include:
a) Proteins, which are the building blocks from which the structures of living organisms are constructed (this includes almost all enzymes, which catalyse organic chemical reactions
b) Nucleic acids, which carry genetic information
c) Carbohydrates, which store energy in a form that can be used by living cells
d) Fats, which also store energy, but in a more concentrated form, and which may be stored for extended periods in the bodies of animals.

Alhazen

2010-03-23T19:24:00.000+08:00

Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham (Arabic: ابو علي، الحسن بن الحسن بن الهيثم, Persian: ابن هیثم, Latinized: Alhacen or (deprecated) Alhazen) (965 in Basra - c. 1039 in Cairo) was an Arab or Persian scientist and polymath. He made significant contributions to the principles of optics, as well as to physics, anatomy, astronomy, en gineering, mathematics, medicine, ophthalmology, philosophy, psychology, visual perception, and to science in general with his early application of the scienti fic method. He is sometimes called al-Basri (Arabic: البصري), after his birthplace in the city of Basra. He was also nicknamed Ptolemaeus Secundus ("Ptolemy the Second") or simply "The Physicist" in medieval Europe.
Ibn al-Haytham is regarded as the "father of modern optics" for his influential Book of Optics which proved the intromission theory of vision and refined it into essentially its modern form. He is also recognized so for his experiments on optics, including experiments on lenses, mirrors, refraction, reflection, and the dispersion of light into its constituent colours. He studied binocular vision and the Moon illusion, described the finite speed of light, and argued that it is made of particles travelling in straight lines. Due to his formulation of a modern quantitative and empirical approach to physics and science, he is considered the pioneer of the modern scientific method and the originator of the experimen tal nature of physics and science. Author Bradley Steffens describes him as the "first scientist". He is also considered by A. I. Sabra to be the founder of experimental psychology for his approach to visual perception and optical illusions, and a pioneer of the philosophical field of phenomenology or the study of consciousness from a first-person perspective. His Book of Optics has been ranked with Isaac Newton's Philosophiae Naturalis Principia Mathematica as one of the most influential books in the history of physics, for starting a revolution in optics and visual perception.
Ibn al-Haytham's achievements include many advances in physics and mathematics. He gave the first clear description and correct analysis of the camera obscura. He enunciated Fermat's principle of least time and the concept of inertia (Newton's first law of motion), and developed the concept of momentum. He described the attraction between masses and was aware of the magnitude of acceleration due to gravity at-a-distance. He stated that the heavenly bodies were accountable to the laws of physics and also presented a critique and reform of Ptolemaic astronomy. He was the first to state Wilson's theorem in number theory, and he formulated the Lambert quadrilateral and a concept similar to Playfair's axiom now used in non-Euclidean geometry. Moreover, he formulated and solved Alhazen's problem geometrically using early ideas related to infinitesimal calculus and mathematical induction.

Legacy
Ibn al-Haythem made significant improvements in optics, physical science, and the scientific method which influenced the development of science for over five hundred years after his death. Ibn al-Haytham's work on optics is credited with contributing a new emphasis on experiment. His influence on physical sciences in general, and on optics in particular, has been held in high esteem and, in fact, ushered in a new era in optical research, both in theory and practice. The scientific method is considered to be so fundamental to modern science that some—especially philosophers of science and practising scientists—consider earlier inquiries into nature to be pre-scientific.
Richard Powers nominated Ibn al-Haytham's scientific method and scientific skepticism as the most influential idea of the second millennium. Recipient of the Nobel Prize in Physics Abdus Salam considered Ibn-al-Haytham "one of the greatest physicists of all time." George Sarton, the father of the history of science, wrote that "Ibn Haytham's writings reveal his fine development of the experimental faculty" and considered him "not only the greatest Muslim physicist, but by all means the greatest of mediaeval times." Robert S. Elliot considers Ibn al-Haytham to be "one of the ablest students of optics of all times." The author Bradley Steffens considers him to be the "first scientist", and Professor Jim Al-Khalili also considers him the "world's first true scientist". The Biographical Dictionary of Scientists wrote that Ibn al-Haytham was "probably the greatest scientist of the Middle Ages" and that "his work remained unsurpassed for nearly 600 years until the time of Johannes Kepler." At a scientific conference in February 2007 as a part of the Hockney-Falco thesis, Charles M. Falco argued that Ibn al-Haytham's work on optics may have influenced the use of optical aids by Renaissance artists. Falco said that his and David Hockney's examples of Renaissance art "demonstrate a continuum in the use of optics by artists from circa 1430, arguably initiated as a result of Ibn al-Haytham's influence, until today." The Latin translation of his main work, Kitab al-Manazir (Book of Optics), exerted a great influence on Western science: for example, on the work of Roger Bacon, who cites him by name, and on Johannes Kepler. It brought about a great progress in experimental methods. His research in catoptrics (the study of optical systems using mirrors) centred on spherical and parabolic mirrors and spherical aberration. He made the observation that the ratio between the angle of inc idence and refraction does not remain constant, and investigated the magnifying power of a lens. His work on catoptrics also contains the problem known as "Alhazen's problem". Meanwhile in the Islamic world, Ibn al-Haytham's work influenced Averroes' writings on optics, and his legacy was further advanced through the 'reforming' of his Optics by Persian scientist Kamal al-Din al-Farisi (d. ca. 1320) in the latter's Kitab Tanqih al-Manazir (The Revision of [Ibn al-Haytham's] Optics). The correct explanations of the rainbow phenomenon given by al-Fārisī and Theodoric of Freiberg in the 14th century depended on Ibn al-Haytham's Book of Optics. The work of Ibn al-Haytham and al-Fārisī was also further advanced in the Ottoman Empire by polymath Taqi al-Din in his Book of the Light of the Pupil of Vision and the Light of the Truth of the Sights (1574). He wrote as many as 200 books, although only 55 have survived, and many of those have not yet been translated from Arabic. Even some of his treatises on optics survived only through Latin translation. During the Middle Ages his books on cosmology were translated into Latin, Hebrew and other languages. The crater Alhazen on the Moon is named in his honour, as was the asteroid "59239 Alhazen".

George Town, Penang

2010-03-17T18:57:00.000+08:00

George Town World Heritage Site

THE World Heritage Committee meeting in Quebec City added George Town to UNESCO’s World Heritage List on the morning of 7 July 2008. George Town's built heritage comprises architectural traditions adapted to local conditions from both East and West. Its historic core has the largest concentration of pre-World War II architecture in Southeast Asia. Over the last 222 years, a unique way of life based upon East-West exchanges has developed here. The influences of Asia and Europe have endowed the city with a specific multicultural heritage.

George Town is one of three great historic settlements along the Straits of Malacca. The other settlements are Malacca, also a World Heritage Site, and Singapore. The island of Penang, in north-west Malaysia, was the first of these three British colonies to be established, and George Town is its capital.

In 1786, Ca ptain Francis Light established an English East India Company (EIC) trading post here. However, Light was not the first settler and his role as “founder” is much contested, for Penang was, until then, part of the ancient Kedah Sultanate.

Achenese traders had already settled along the Pinang River when Francis Light arrived. Chinese tombstones in Tanjong Tokong allegedly predate Light’s arrival. In those days, however, Penang Island was very sparsely populated. After Francis Light arrived, George Town soon attracted migrants from all over Asia and Europe, contributing to a rapidly burgeoning multicultural identity.

In 1805, the British government designated the colony as an Indian Presidency, under the administration of Bengal, and a multiethnic Committee of Assessors was established to set rates and help manage the city. This was the precursor to the George Town Municipal Council, and the first in Malaysia.

In its early days, George Town attracted traders from India and Indonesia because it was a major port for textiles and pepper within the region, and later nutmeg. These commodities were of great importance financially. But the big money was in the China trade that passed through the Malacca Straits. It was based almost entirely upon tea, but included silk and ceramics.

In the opposite direction, ships carried opium and silver, and sundry other items that were of interest to the Chinese. However, Penang never became the main port for the China trade, because its role was soon usurped by Singapore (est 1819), which was fast developing under the administration of Stamford Raffles, who had the ear of the British Government.

In 1826, George Town became the capital of the British Straits Settlements comprising Penang, Malacca and Singapore. But by 1832, Singapore had taken over George Town’s administrative role. With declining trade and disease threatening its pepper and nutmeg plantations, the city’s future was bleak.

This decline was stemmed 10 years later by the discovery of tin in the neighbouring Malay States. Migrants from south-eastern China soon arrived, adding to the city’s cosmopolitan character. The Triads, fighting men affiliated with Chinese clans and dialect groups, accompanied them.

In 1857, competition amongst the Chinese over the monopoly for opium and tin trading exploded into open warfare. The Penang Riots resulted in the end of indirect rule. Up till then, the British had ruled through local headmen called “Kapitans”. In their place, the British established an inspectorate of police that enforced British laws throughout the colony.

By 1869, the year the Suez Canal opened, George Town had developed into the region’s chief entrepot port. Wealth from trade, tin mining and commercial agriculture resulted in the largest conglomeration of pre-World War II architecture in Southeast Asia.

By the turn of the 20th century, George Town had become a regional education and intellectual centre through its English schools and lively modern press. It became a haven for religious reformers, revolutionaries and proto-nationalists. It was also a modern city with electric tram-cars and a funicular railway linking the city to the Penang Hills. As with so many major ports in the 1930s, George Town was a centre not just for trade and finance, but also for recreation, with its Great World Parks, jazz bands and cabarets.

In 1941, this cosmopolitan society was shattered by the bombing raids of the Japanese Imperial Air Force and nearly extinguished by the brutal three and a half year occupation that followed. Rebuilding went on in earnest after the war ended in 1945, but George Town’s role as an imperial port city was played out as the post-war British Empire was quickly dismantled, to be replaced by the looser affiliations of the Commonwealth.

On 1 January 1957, George Town was granted city status by HRH Queen Elizabeth II. It was now settling into its new role as the second city in the new Malaysian Federation. In the 1960s, as entrepot trade declined further, George Town also declined. A decade later, with a shift away from trade, manufacturing and mass tourism took over, creating new townships. Manufacturing concentrated in the south-west, with tourism to the north.

Reference: http://www.igeorgetownpenang.com/

Chikungunya

2010-03-12T21:26:00.000+08:00

Chikungunya (in the Makonde language "that which bends up") virus (CHIKV) is an insect-borne virus, of the genus Alphavirus, that is transmitted to humans by virus-carrying Aedes mosquitoes. There have been recent outbreaks of CHIKV associated with severe illness. CHIKV causes an illness with symptoms similar to dengue fever. CHIKV manifests itself with an acute febrile phase of the illness lasting only two to five days, followed by a prolonged arthralgic disease that affects the joints of the extremities. The pain associated with CHIKV infection of the joints persists for weeks or months, or in some cases years.

Signs and symptoms
The incubation period of Chikungunya disease is from two to four days. Symptoms of the disease include a fever up to 40 °C (104 °F), a petechial or maculopapular rash of the trunk and occasionally the limbs, and arthralgia or arthritis affecting multiple joints. Other nonspecific symptoms can include headache, conjunctival Injection, and slight photophobia. Typically, the fever lasts for two days and then ends abruptly. However, other symptoms—namely joint pain, intense headache, insomnia and an extreme degree of prostration—last for a variable period; usually for about 5 to 7 days. Patients have complained of joint pains for much longer time periods depending on their age.

Causes
Chikungunya virus is indigenous to tropical Africa and Asia, where it is transmitted to humans by the bite of infected mosquitoes, usually of the genus Aedes. Chikungunya virus belongs to alpha-virus under Togaviridae family. It is an "Arbovirus" (Ar-arthropod, bo-borne). CHIK fever epidemics are sustained by human-mosquito-human transmission. The word "chikungunya" is thought to derive from description in local dialect of the contorted posture of patients afflicted with the severe joint pain associated with this disease. The main virus reservoirs are monkeys, but other species can also be affected, including humans.

Treatment
There are no specific treatments for Chikungunya. There is no vaccine currently available. A Phase II vaccine trial, sponsored by the US Government and published in the American Journal of Tropical Medicine and Hygiene in 2000, used a live, attenuated virus, developing viral resistance in 98% of those tested after 28 days and 85% still showed resistance after one year.
A serological test for Chikungunya is available from the University of Malaya in Kuala Lumpur, Malaysia.
Chloroquine is gaining ground as a possible treatment for the symptoms associated with Chikungunya, and as an anti-inflammatory agent to combat the arthritis associated with Chikungunya virus. A University of Malaya study found that for arthritis-like symptoms that are not relieved by aspirin and non-steroidal anti-inflammatory drugs (NSAID), chloroquine phosphate (250 mg/day) has given promising results. Research by an Italian scientist, Andrea Savarino, and his colleagues together with a French government press release in March 2006 have added more credence to the claim that chloroquine might be effective in treating chikungunya. Unpublished studies in cell culture and monkeys show no effect of chloroquine treatment on reduction of chikungunya disease. The fact sheet on Chikungunya advises against using aspirin, ibuprofen, naproxen and other NSAIDs that are recommended for arthritic pain and fever.

Epidemiology
Chikungunya virus is an alphavirus closely related to the O'nyong'nyong virus, the Ross River virus in Australia, and the viruses that cause eastern equine encephalitis and western equine encephalitis.
Chikungunya is generally spread through bites from Aedes aegypti mosquitoes, but recent research by the Pasteur Institute in Paris has suggested that Chikungunya virus strains in the 2005-2006 Reunion Island outbreak incurred a mutation that facilitated transmission by Aedes albopictus (Tiger mosquito). Concurrent studies by arbovirologists at the University of Texas Medical Branch in Galveston, Texas, confirmed definitively that enhanced chikungunya virus infection of Aedes albopictus was caused by a point mutation in one of the viral envelope genes (E1). Enhanced transmission of chikungunya virus by Aedes albopictus could mean an increased risk for chikungunya outbreaks in other areas where the Asian tiger mosquito is present. A recent epidemic in Italy was likely perpetuated by Aedes albopictus.
In Africa, chikungunya is spread via a sylvatic cycle in which the virus largely resides in other primates in between human outbreaks.
On 28 May 2009 in Changwat Trang of Thailand where the virus is endemic, the provincial hospital decided to deliver by Caesarean section a male baby from his Chikungunya-infected mother—Khwanruethai Sutmueang, 28, a Trang native—in order to prevent mother-foetus virus transmission. However, after delivering the baby, the physicians discovered that the baby was infected with Chikungunya virus, and put him into intensive care because the infection had left the baby unable to breathe by himself or to drink milk. The physicians presumed that Chikungunya virus might be able to be transmitted from a mother to her foetus; however, there is no laboratory confirmation for this presumption.

Geomagnetic storm

2010-03-07T14:57:00.001+08:00

A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in space weather. Associated with solar coronal mass ejections (CME), coronal holes, or solar flares, a geomagnetic storm is caused by a solar wind shock wave which typically strikes the Earth's magne ti c field 24 to 36 hours after the event. This only happens if the shock wave travels in a direction toward Earth. The solar wind pressure on the magnetosphere will increase or decrease depending on the Sun's activity. These solar wind pressure changes modify the electric currents in the ionosphere. Magnetic storms usually last 24 to 48 hours, but some may last for many days. In 1989, an electromagnetic storm disrupted power throughout most of Quebec—it caused auroras as far south as Texas.

Radiation hazards to humans
Intense solar flares release very-high-energy particles that can cause radiation poisoning to humans (and mammals in general) in the same way as low-energy radiation from nuclear blasts.
Earth's atmosphere and magnetosphere allow adequate protection at ground level, but astronauts in space are subject to potentially lethal doses of radiation. The penetration of high-energy particles into living cells can cause chromosome damage, cancer, and a host of other health problems. Large doses can be fatal immediately.
Solar protons with energies greater than 30 MeV are particularly hazardous. In October 1989, the Sun produced enough energetic particles that an astronaut wearing only a space suit and caught out in the brunt of the storm, would probably have died; the expected dose would be about 7000 rem. Note that Astronauts who had time to gain safety in a shelter beneath moon soil would have absorbed only slight amounts of radiation.
The cosmonauts on the Mir station were subjected to daily doses of about twice the yearly dose on the ground, and during the solar storm at the end of 1989 they absorbed their full-year radiation dose limit in just a few hours.
Solar proton events can also produce elevated radiation aboard aircraft flying at high altitudes. Although these risks are small, monitoring of solar proton events by satellite instrumentation allows the occasional exposure to be monitored and evaluated, and eventually the flight paths and altitudes adjusted in order to lower the absorbed dose of the flight crews.

Disrupted systems - Communications
Many communication systems use the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect radio communication at all latitudes. Some radio frequencies are absorbed and others are reflected, leading to rapidly fluctuating signals and unexpected propagation paths. TV and commercial radio stations are little affected by solar activity, but ground-to-air, ship-to-shore, shortwave broadcast, and amateur radio (mostly the bands below 30 MHz) are frequently disrupted. Radio operators using HF bands rely upon solar and geomagnetic alerts to keep their communication circuits up and running.
Some military detection or early warning systems are also affected by solar activity. The over-the-horizon radar bounces signals off the ionosphere to monitor the launch of aircraft and missiles from long distances. During geomagnetic storms, this system can be severely hampered by radio clutter. Some submarine detection systems use the magnetic signatures of submarines as one input to their locating schemes. Geomagnetic storms can mask and distort these signals.
The Federal Aviation Administration routinely receives alerts of solar radio bursts so that they can recognize communication problems and forego unnecessary maintenance. When an aircraft and a ground station are aligned with the Sun, jamming of air-control radio frequencies can occur. This can also happen when an Earth station, a satellite, and the Sun are in alignment.
The telegraph lines in the past were affected by geomagnetic storms as well. The telegraphs used a long wire for the data line, stretching for many miles, using ground as the return wire and being fed with DC power from a battery; this made them (together with the power lines mentioned below) susceptible to being influenced by the fluctuations caused by the ring current. The voltage/current induced by the geomagnetic storm could have led to diminishing of the signal, when subtracted from the battery polarity, or to overly strong and spurious signals when added to it; some operators in such cases even learned to disconnect the battery and rely on the induced current as their power source. In extreme cases the induced current was so high the coils at the receiving side burst in flames, or the operators received electric shocks. Geomagnetic storms affect also long-haul telephone lines, including undersea cables unless they are fiber optic.
Damage to communications satellites can disrupt non-terrestrial telephone, television, radio, and Internet links.

Disrupted systems - Geologic exploration
Earth's magnetic field is used by geologists to determine subterranean rock structures. For the most part, these geodetic surveyors are searching for oil, gas, or mineral deposits. They can accomplish this only when Earth's field is quiet, so that true magnetic signatures can be detected. Other surveyors prefer to work during geomagnetic storms, when the variations to Earth's normal subsurface electric currents help them to see subsurface oil or mineral structures. For these reasons, many surveyors use geomagnetic alerts and predictions to schedule their mapping activities.

Antenna (biology)

2010-03-01T18:52:00.000+08:00

Antennae (singular: antenna) in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in many cell types of eukaryotes.
In arthropods, antennae are connected to the front-most segments. In c rustaceans, they are biramous and present on the first two segments of the head, with the smaller pair known as antennules. All other arthropod groups, except chelicerates, proturans and arachnids which have none, have a single, uniramous pair of antennae. These antennae are jointed, at least at the base, and generally extend forward from the head. They are sensory organs, although the exact nature of what they sense and how they sense it is not the same in all groups, nor always clear. Functions may variously include sensing touch, air motion, heat, vibration (sound), and especially olfaction (smell) or gustation (taste).

Insects

Antenna are the primary olfactory sensors of an insect and are accordingly well-equipped with a wide variety of sensilla (singular : sensillum). Paired, mobile, and segmented, they are located between the eyes on the forehead. Embryologically, they represent the appendages of the second head segment.
All insects have antenna though these may be greatly reduced in the larval forms. Amongst the non-insect classes of Hexapoda, Collembola and Diplura have antenna, but Protura do not.

Structure

The three basic segments of the typical insect antenna are the scape (base), the pedicel (stem), and finally the flagellum, which often comprises many units known as flagellomeres.
Muscles are only present in the two first segments, the scape and pedicel. The scape is surrounded by a membranous region of the head. It pivots on a single marginal point called the antennifer, allowing it to move in any direction.
The number of flagellomeres can vary greatly, and is often of diagnostic importance. True flagellomeres have a membranous articulation between them, but in many insects, especially the more primitive groups, the flagellum is entirely or partially composed of a flexible series of small annuli, which are not true flagellomeres.
In many beetles and in the chalcidoid wasps, the apical flagellomeres form a club, and the collective term for the segments between the club and the antennal base is the funicle; for traditional reasons, in beetles it is the segments between the club and the scape, but in wasps, it is the segments between the club and the pedicel.
In the groups with more uniform antennae (for example: Diplopoda), all segments are called antennomeres. Some groups have a simple or variously modified apical or subapical bristle called an arista (this may be especially well-developed in various Diptera).

Functions

Olfactory receptors on the antennae bind to odour molecules, including pheromones. The neurons that possess these receptors signal this binding by sending action potent ia ls down their axons to the antennal lobe in the brain. From there, neurons in the antennal lobes connect to mushroom bodies that identify the odour. The sum of the electrical potentials of the antenna to a given odor can be measured using an electroantennogram.
In the case of the Monarch, it has been shown that antennae are necessary for proper time-compensated Sun compass orientation during migration, that antennal clocks exist in monarchs, and that they likely provide the primary timing mechanism for Sun compass orientation.

Crustaceans

Crustaceans bear two pairs of antennae. The first pair are uniramous and are often referred to as antennules, while the second pair are biramous, meaning that each antenna is composed of two parts, joined at their base. In most adults, the antenna are sensory organs, but they are used by the nauplius larva for swimming. In some groups of crustaceans, such as the spiny lobsters and slipper lobsters, the second antennae are enlarged, while in others, such as crabs, the antennae are reduced in size.

Cellular antennae

Within the biological and medical disciplines, recent discoveries have noted that primary cilia in many types of cells within eukaryotes serve as cellular antennae. These cilia play important roles in chemosensation, mechanosensation, and thermosensation. The current scientific understanding of primary cilia organelles views them as "sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation."

Solid-fuel rocket

2010-02-21T23:11:00.000+08:00

A solid rocket or a solid-fuel rocket is a rocket with a motor that uses solid propellants (fuel/oxidizer). The earliest rockets were solid fueled and powered by gunpowder; they were used by the Chinese, Mongols and Arabs in warfare as early as the 13th century. All rockets used some form of solid or powdered propellant up until the 20th century, when liquid rockets and hybrid rockets offered more efficient and controllable alternatives. Solid rockets are still used today in model rockets and on larger applications for their simplicity and reliability. Since solid fuel rockets can remain in storage for long periods—and then reliably launch on short notice—they have been frequently used in military applications such as missiles. Solid fuel rockets are unusual as primary propulsion in modern space exploration, but are commonly used as booster rockets.

Basic concepts

A simple solid rocket motor consists of a casing, nozzle, grain (propellant charge), and igniter.
The grain behaves like a solid mass, burning in a predictable fashion and producing exhaust gases. The nozzle dimensions are calculated to maintain a design chamber pressure, while producing thrust from the exhaust gases.
Once ignited, a simple solid rocket motor cannot be shut off, because it contains all the ingredients necessary for combustion within the chamber that they are burned in. More advanced solid rocket motors can not only be throttled but can be extinguished and then re-ignited by controlling the nozzle geometry or through the use of vent ports. Also, pulsed rocket motors which burn in segments and which can be ignited upon command are available.
Modern designs may also include a steerable nozzle for guidance, avionics, recovery hardware (parachutes), self-destruct mechanisms, APUs, controllable tactical motors, controllable divert and attitude control motors and thermal management materials.

Design

Design begins with the total impulse required, this determines the fuel/oxidizer mass. Grain geometry and chemistry are then chosen to satisfy the required motor characteristics.
The following are chosen or solved simultaneously. The results are exact dimensions for grain, nozzle and case geometries;

1. The grain burns at a predictable rate, given its surface area and chamber pressure.
2. The chamber pressure is determined by the nozzle orifice diameter and grain burn rate.
3. Allowable chamber pressure is a function of casing design.
4. The length of burn time is determined by the grain 'web thickness'.

The grain may be bonded to the casing, or not. Case-bonded motors are much more difficult to design, since the deformation, under operating conditions, of the case and the grain must be compatible.
Common modes of failure in solid rocket motors include fracture of the grain, failure of case bonding, and air pockets in the grain. All of these produce an instantaneous increase in burn surface area and a corresponding increase in exhaust gas and pressure, which may potentially induce rupture of the casing.
Another failure mode is casing seal design. Seals are required in casings that have to be opened to load the grain. Once a seal fails, hot gas will erode the escape path and result in failure. This was the cause of the Space Shuttle Challenger disaster.

Hobby and amateur rocketry

Solid fuel rocket motors can be bought for use in model rocketry; they are normally small cylinders of black powder fuel with an integral nozzle and sometimes a small charge that is set off when the propellant is exhausted after a time delay. This charge can be used to trigger a camera, or deploy a parachute. Without this charge and delay, the motor may ignite a second stage (black powder only).
In mid- and high power rocketry, commercially made APCP motors are widely used. They can be designed as either single use or reloadables. These motors are available in impulse ranges from "D" to "O", from several manufacturers. They are manufactured in standardized diameters, and varying lengths depending on required impulse. Standard motor diameters are 18, 24, 29, 38, 54, 75, 98, and 150 millimeters. Different propellant formulations are available to produce different thrust profiles, as well as "special effects" such as colored flames, smoke trails, or large quantities of sparks (produced by adding titanium sponge to the mix).
Designing solid rocket motors is particularly interesting to amateur rocketry enthusiasts. The design of a successful solid fuel motor requires application of continuum mechanics, combustion chemistry, materials science, fluid dynamics (including compressible flow), heat transfer, geometry (particle spectrum packing), and machining. The vast majority of amateur-built rocket motors utilize a composite propellant, most commonly APCP

Langkawi Geopark

2010-02-18T21:26:00.000+08:00

On June 1, 2007, Langkawi Island has been given a World Geopark status by UNESCO. Three of its main conservation area in Langkawi Geopark; Machincang Cambrian Geoforest Park, Kilim Karst Geoforest Park and Dayang Bunting Marble Geoforest park. (Island of the Pregnant Maiden Lake). These three parks are the most popular tourism area within Langkawi Geopark.
Langkawi Geopark is made up of 99 tropical islands off the northwestern coast of Peninsular Malaysia covering an area of about 478 square kilometer. These rocky tropical legendary islands are rich in geodiversity, many of which have scientific value of national and regional significant. Langkawi Geopark highlights the region's most complete Palaeozoic geological history and outstanding beauty of tropical island karst landscape. The Palaeozoic rocks of Langkawi Geopark contain among others the oldest strata in the region, complete Palaeozoic succession from Cambrian to Permian, and best sedimentological and palaeontological evidences affiliating Langkawi and the surrounding region with Gondwanaland. Langkawi Geopark portrays a rich mixtures of surface water, ground water and ocean wave originated karstic landscape including some rare formation of islands and hills, ridges and pinnacles; gorges, wangs and doline lakes; caves, tunnels and their diverse cave deposit landforms; and sea-notches, sea-caves, sea-tunnels, sea-arches and sea-stacks. Langkawi Geopark geoheritage sites are mostly protected within the Malaysian holistic nature conservation concept of Geoforest Park where rock conservation is equally treated as biological conservation and other nature conservation components. Three geoforest parks of Langkawi are the Machinchang Cambrian, Kilim Karst and Dayang Bunting Marble Geoforest Parks, each of which highlighting its own unique geology and geological landscape. Other smaller conservation areas are the Recreational Forest and State Permanent Forest Reserves, which hosted several protected geoheritage sites and geological monuments outside the geoforest parks.

Geoheritage of Langkawi
Langkawi possesses rich geodiversity in terms of rocks, minerals, fossils, geological structures, geomorphological and landscape features, with heritage value of national and regional significant. Geoheritage of Langkawi mostly occurred within rocky coasts, cliffs, peaks and waterfalls as well as in caves. Some highly significant exposures have been classified as geoheritage sites, containing one or more geodiversities of high heritage value. There are more than 90 geoheritage sites identified throughout the Langkawi Geopark, some of which have been proposed into the National Geological Heritage Lists. Despite of its rich geodiversity, Langkawi Geopark will only highlight two major geological attractions, that are: complete Palaeozoic geological records, incorporating oldest rocks and fossils in the region, best preserved sedimentary structures and fossils, best sedimentological and palaeontological evidences for affiliation with Gondwanaland, most beautiful island karst landscape in the region featuring unique hills, ridges, islands and pinnacles, beautiful caves, tunnels and arches and the magnificent rare mangrove association with limestone bedrock.

Geoforest Park
Geoforest park is essentially chosen in area where most of the rocks are permanently or seasonally exposed, hence the coverage of the three geoforest parks in Langkawi shows that nearly 40 percent of the islands are half-barren. This also indicates why most of Langkawi geheritage sites fall within these geoforest parks. Geoforest park is a special conservation areas within PRFs with outstanding geological and biological resources where protection and wise utilization of these resources are geared towards sustainable recreation, promoting multidisciplinary research and enriching community awareness about the natural integration of various forest resources. Three geoforest parks of Langkawi are: Machinchang Cambrian Geoforest Park which highlights region's oldest sandstone that bears beautifully preserved sedimentary structures and oldest fossils of the region. Competent Machinchang Cambrian sandstone produced outstanding and beautiful landscapes of mountain peaks, cliffs, waterfalls, remnant islands and rocky beaches, while detailed sculpture on some of the rocks produced amazing tafoni and other erosional features.

Kilim Karst Geoforest Park features breathtaking landscape of nearly vertical karstic hills, ridges and islands with pinnacles of various shapes and sizes formed on thinly bedded flat to very gently dipping limestone of Setul Formation. Kilim karstic hills bear many beautiful cave, while karstic coastlines are provided with much more varied and colourful karstic features including sea notches, sea tunnels, sea caves, sea arches, sea stacks and remnant islands. The limestone of Kilim is also very rich in fossils, particularly those at Pulau Langgun. The region's highest (23m above m.s.l.) Holocene (circa 7000m.a.) sea level was also recorded within this geoforest park.

Dayang Bunting Marble Geoforest Park exhibits karst landscapes developed mostly on marble of Chuping Formation. This geoforest park has fine cave features developed in Gua Pasir Dagang, beautiful sea-arches and caves at Pulau Lima and Pulau Dua, sea-stacks and other wave-related features. The famous Tasik Dayang Bunting (or Lake of Pregnant Maiden) is the biggest natural fresh water lake in Langkawi Islands, and is thought to be of doline origin.

Reference : http://www.globalgeopark.org/publish/portal1/tab128/info2293.htm

Abu Rayhan Biruni

2010-02-14T21:35:00.000+08:00

Abū Rayhān Muhammad ibn Ahmad Bīrūnī (Persian: ابوریحان محمد بن احمد بیرونی), often known as Alberuni, Al Beruni or variants, (born 5 September 973 in Kath, Khwarezm (now in Uzbekistan), died 13 December 1048 in Ghazni, today's Afghanistan) was a Persian scholar and polymath of the 11th century.
He was a scientist and physicist, an anthropologist and comparative sociologist, an astronomer and chemist, a critic of alchemy and astrology, an encyclopedist and historian, a geo grapher and traveler, a geodesist and geologist, a mathematician, a pharm acist and psychologist, an Islamic philosopher and theologian, and an scholar and teacher.
He was the first Muslim scholar to study India and the Brahminical tradition, and has been described as the founder of Indology, the father of geodesy, and "the first anthropologist". He was also one of the earliest leading exponents of the experimental scientific method, and was responsible for introducing the experimental method into mechanics and mineralogy, a pioneer of comparative sociology and experimental psychology, and the first to conduct elaborate experiments related to astronomical phenomena.
George Sarton, the father of the history of science, described Biruni as "one of the very greatest scientists of Islam, and, all considered, one of the greatest of all times." A. I. Sabra described Biruni as "one of the great scientific minds in all history."
The crater Al-Biruni on the Moon is named after him. Tashkent Technical University (formerly Tashkent Polytechnic Institute) is also named after Abu Rayhan al-Biruni and a university founded by Ahmad Shah Massoud in Kapisa is named after him.

Astronomy

Will Durant wrote the following on al-Biruni's contributions to Islamic astronomy:
"He wrote treatises on the astrolabe, the planisphere, the armillary sphere; and formulated astronomical tables for Sultan Masud. He took it for granted that the earth is round, noted “the attraction of all things towards the center of the earth,” and remarked that astronomic data can be explained as well by supposing that the earth turns daily on its axis and annually around the sun, as by the reverse hypothesis."

Experimental observations

Biruni was the first to conduct elaborate experiments related to astronomical phenomena.

He supposed the Milky Way galaxy to be a collection of numerous nebulous stars, and in Khorasan, he observed and described the solar eclipse on 8 April 1019, and the lunar eclipse on 17 September 1019, in detail, and gave the exact latitudes of the stars during the lunar eclipse.
In 1031, Biruni completed his extensive astronomical encyclopaedia Kitab al-Qanun al-Mas'udi (Latinized as Canon Mas’udicus), in which he recorded his astronomical findings and formulated astronomical tables. The book introduces the mathematical technique of analysing the acceleration of the planets, and first states that the motions of the solar apogee and the precession are not identical. Biruni also discovered that the distance between the Earth and the Sun is larger than Ptolemy's estimate, on the basis that Ptolemy disregarded the annual solar eclipses.

Philosophy of science

Scientific method

In early Islamic philosophy, Biruni discussed the philosophy of science and introduced an early scientific method in nearly every field of inquiry he studied. For example, in his treatise on mineralogy, Kitab al-Jawahir (Book of Precious Stones), he is "the most exac t of experimental scientists", while in the introduction to his study of India, he declares that "to execute our project, it has not been possible to follow the geometric method" and develops comparative sociology as a scientific method in the field. He was also responsible for introducing the experimental method into mechanics, the first to conduct elaborate experiments related to astronomical phenomena, and a pioneer of experimental psychology.
Unlike his contemporary Avicenna's scientific method where "general and universal questions came first and led to experimental work", Biruni developed scientific methods where "universals came out of practical, experimental work" and "theories are formulated after discoveries." In his debate with Avicenna, Biruni made the first real distinction between a scientist and a philosopher, referring to Avicenna as a philosopher and considering himself to be a mathematical scientist.
Biruni's scientific method was similar to the modern scientific method in many ways, particularly his emphasis on repeated experimentation. Biruni was concerned with how to conceptualize and prevent both systematic errors and random errors, such as "errors caused by the use of small instruments and errors made by human observers." He argued that if instruments produce random errors because of their imperfections or idiosyncratic qualities, then multiple observations must be taken, analyzed qualitatively, and on this basis, arrive at a "common-sense single value for the constant sought", whether an arithmetic mean or a "reliable estimate."

Stockholm syndrome

2010-02-07T14:01:00.000+08:00

In psychology, the Stockholm syndrome is a term used to describe a paradoxical psychological phenomenon wherein hostages express adulation and have positive feelings towards their captors that appear irrational in light of the danger or risk endured by the victims. While uncommon, the FBI’s Hostage Barricade Database System shows that roughly 27% of victims show evidence of Stockholm syndrome. The syndrome is named after the Norrmalmstorg robbery of Kreditbanken at Norrmalmstorg in Stockholm, in which the bank robbers held bank employees hostage from August 23 to August 28, 1973. In this case, the victims became emotionally attached to their captors, and even defended them after they were freed from their six-day ordeal. The term "Stockholm Syndrome" was coined by the criminologist and psychiatrist Nils Bejerot, who assisted the police during the robbery, and referred to the syndrome in a news broadcast. It was originally defined by psychiatrist Frank Ochberg to aid the management of hostage situations.

Development

While there is still disagreement as to what factors characterize incidents that contribute to the development of Stockholm syndrome, research has suggested that hostages may exhibit the condition in situations that feature captors who do not abuse the victim, a long duration before resolution, continued contact between the perpetrator and hostage, and a high level of emotion. In fact, experts have concluded that the intensity, not the length of the incident, combined with a lack of physical abuse more likely will create favorable conditions for the development of Stockholm syndrome.
The following are viewed as the conditions necessary for the Stockholm syndrome to occur.

a) Hostages who develop Stockholm syndrome often view the perpetrator as giving life by simply not taking it. In this sense, the captor becomes the person in control of the captive’s basic needs for survival and the victim’s life itself.
b) The hostage endures isolation from other people and has only the captor’s perspective available. Perpetrators routinely keep information about the outside world’s response to their actions from captives to keep them totally dependent.
c) The hostage taker threatens to kill the victim and gives the perception of having the capability to do so. The captive judges it safer to align with the perpetrator, endure the hardship of captivity, and comply with the captor than to resist and face murder.
d) The captive sees the perpetrator as showing some degree of kindness. Kindness serves as the cornerstone of Stockholm syndrome; the condition will not develop unless the captor exhibits it in some form toward the hostage. However, captives often misinterpret a lack of abuse as kindness and may develop feelings of appreciation for this perceived benevolence. If the captor is purely evil and abusive, the hostage will respond with hatred. But, if perpetrators show some kindness, victims will submerge the anger they feel in response to the terror and concentrate on the captors’ “good side” to protect themselves

In cases where Stockholm syndrome has occurred, the captive is in a situation where the captor has stripped nearly all forms of independence and gained control of the victim’s life, as well as basic needs for survival. Some experts say that the hostage regresses to, perhaps, a state of infancy; the captive must cry for food, remain silent, and exist in an extreme state of dependence. In contrast, the perpetrator serves as a mother ﬁgure protecting her child from a threatening outside world, including law enforcement’s deadly weapons. The victim then begins a struggle for survival, both relying on and identifying with the captor. Possibly, hostages’ motivation to live outweighs their impulse to hate the person who created their dilemma.

Historically explanations

Historically raptio (e.g., Rape of the Sabine women) and bride kidnapping have been (and still are in some places) very common practices. Women who were kidnapped and consistently fought back were likely to be killed or imprisoned and thus not have children. But women who bonded with and submitted to their captors were more likely to have children and their children were more likely to receive the genes that made their mothers more passive and bonding towards their captors. And over several generations, this made the population of humans more genetically prone to submission and bonding when kidnapped.
In many cases, capture may also involve the killing (or threat of killing) of the captive's relatives, thereby isolating the captive. The captive is subjected to isolation and so sees even a small act, such as providing amenities, as a great favour. Such captives may side with their captors while believing their captors have conferred on them great importance and love. Furthermore, captives who perceive themselves as the only members of their group not to have been killed may believe that they have been shown a special interest.

Psychoanalytic explanations

The Stockholm syndrome is a psychological shift that occurs in captives when they are threatened gravely but are shown acts of kindness by their captors. Captives who exhibit the syndrome tend to sympathize with and think highly of their captors, at times believing that the captors are showing them favor stemming from inherent kindness. Such captives fail to recognize that their captors' choices are essentially self-serving. When subjected to prolonged captivity, these captives can develop a strong bond with their captors, in some cases including a sexual interest.
Psychiatrist Frank Ochberg, widely credited with Stockholm Syndrome's psychiatric definition, describes it as "a primitive gratitude for the gift of life," not unlike that felt by an infant.
According to the psychoanalytic view of the syndrome, this tendency might be the result of employing the strategy evolved by newborn babies to form an emotional attachment to the nearest powerful adult in order to maximize the probability that this adult will enable—at the very least—the survival of the child, if not also prove to be a good parental figure. This syndrome is considered a prime example for the defense mechanism of identification.

Metamorphic rock

2010-02-01T22:47:00.000+08:00

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure (temperatures greater than 150 to 200 °C and pressures of 1500 bars) causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior.
The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides us with very valuable information about the temperatures and pressures that occur at great depths within the Earth's crust.
Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite.

Metamorphic minerals
Metamorphic minerals are those that form only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet.
Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks, but are not necessarily the result of the process of metamorphism. These minerals formed during the crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are stable only within certain limits, and the presence of some minerals in metamorphic rocks indicates the approximate temperatures and pressures at which they formed.
The change in the particle size of the rock during the process of metamorphism is called recrysta llization. For instance, the small calcite crystals in the sedimentary rock limestone change into larger crystals in the metamorphic rock marble, or in metamorphosed sandstone, recrystallisation of the original quartz sand grains results in very compact quartzite, in which the often larger quartz crystals are interlocked. Both high temperatures and pressures contribute to recrystallization. High temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact.

Foliation
The layering within metamorphic rocks is called foliation (derived from the Latin word folia, meaning "leaves"), and it occurs when a rock is being shortened along one axis during recrystallization. This causes the platy or elongated crystals of minerals, such as mica and chlorite, to become rotated such that their long axes are perpendicular to the orientation of shortening. This results in a banded, or foliated, rock, with the bands showing the colors of the minerals that formed them.
Textures are separated into foliated and non-foliated categories. Foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage. For example, slate is a foliated metamorphic rock, originating from shale. Non-foliated rock does not have planar patterns of strain.
Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with distinctive growth habits, will not be foliated. Slate is an example of a very fine-grained, foliated metamorphic rock, while phyllite is medium, schist coarse, and gneiss very coarse-grained. Marble is generally not foliated, which allows its use as a material for sculpture and architecture.
Another important mechanism of metamorphism is that of chemical reactions that occur between minerals without them melting. In the process atoms are exchanged between the minerals, and thus new minerals are formed. Many complex high-temperature reactions may take place, and each mineral assemblage produced provides us with a clue as to the temperatures and pressures at the time of metamorphism.
Metasomatism is the drastic change in the bulk chemical composition of a rock that often occurs during the processes of metamorphism. It is due to the introduction of chemicals from other surrounding rocks. Water may transport these chemicals rapidly over great distances. Because of the role played by water, metamorphic rocks generally contain many elements absent from the original rock, and lack some that originally were present. Still, the introduction of new chemicals is not necessary for recrystallization to occur.

Metamorphic rock textures
The five basic metamorphic textures with typical rock types are:
1. Slaty: slate and phyllite; the foliation is called 'slaty cleavage'
2. Schistose: schist; the foliation is called 'schistosity'
3. Gneissose: gneiss; the foliation is called 'gneissosity'
4. Granoblastic: granulite, some marbles and quartzite
5. Hornfelsic: hornfels and skarn

Malacca

2010-01-26T22:07:00.000+08:00

Malacca (Malay: Melaka, dubbed The Historical State or Negeri Bersejarah amongst locals) is the third smallest Malaysian state, after Perlis and Penang. It is located in the southern region of the Malay Peninsula, on the Straits of Mal acca. It borders Negeri Sembilan to the north and the state of Johor to the south. The capital is Malacca Town. This historical city centre has been listed as a UNESCO World Heritage Site since 7 July 2008.
Although one of the oldest Malay sultanates, the Yang di-Pertua Negeri or Governor, rather than a Sultan, acts as the head of state.

History

Sultanate of Malacca

Before the arrival of the first Sultan, Malacca was a simple fishing village inhabited by local Malays. Malacca was founded by Parameswara, a Srivijayan prince of Palembang who fled Sumatra following a Majapahit attack in 1377. He found his way to Malacca c. 1400 where he found a good port accessible in all seasons and on the strategically located narrowest point of the Malacca Straits.
According to a popular legend, Parameswara was resting under a gray tree near a river while hunting, when one of his dogs cornered a mouse deer. In self-defence, the mouse deer pushed the dog into the river. Impressed by the courage of the deer, and taking it as a propitious omen of the weak overcoming the powerful, Parameswara decided on the spot to found an empire on the very place that he was sitting. He named it 'Melaka' after the tree under which he had taken shelter. Another version of the story says that Parameswara chose the name 'Malacca' from the Tamil word 'mallakka' which means upside down or on ones back. Old illustrations of the scene where the mousedeer kicks the dog shows the dog falling on its back into the river, hence the inspiration. Parameswara converted to Islam in 1414 and changed his name to 'Raja Iskandar Shah'. In collaboration with allies from the sea-people (orang laut) the wandering proto-Malay privateers of the Straits, he established Malacca as major international port by compelling passing ships to call there, and establishing fair and reliable facilities for warehousing and trade. Mass settlement of Chinese, mostly from the imperial and merchant fleet occurred during the reign of Parameswara, occurred in the vicinity of the Bukit China ("Chinese Hill") area, which was perceived as having excellent Feng Shui (geomancy) in Malacca then. Sultan Iskandar Shah died in 1424, and was succeeded by his son, Sri Maharaja also called Sultan Muhammad Shah.

The prosperity of Malacca attracted the invasion of the Siamese. Attempts in 1446 and 1456, however, were warded off by Tun Perak, the then Bendahara (a position similar to Prime Minister). The development of relations between Malacca and China was then a strategic decision to ward off further Siamese attacks.
Because of its strategic location, Malacca was an important stopping point for Zheng He's fleet. To enhance relations, Hang Li Po, allegedly a princess of the Ming Emperor of China, arrived in Malacca, accompanied by 500 attendants, to marry Sultan Manshur Shah who reigned from 1456 until 1477. Her attendants married the locals and settled mostly in Bukit China (Bukit Cina).(See Zheng He in Malacca). Scholars have disputed Hang Li Po's status in China as because she was never recorded as a princess in the Chinese court of the Ming Dynasty in the Ming Chronicles. At the time of the arrival of the Sultan's envoy, the reigning Ming Emperor was Jingtai Emperor. Records of his reign was expunged following the ascension of Tianshun in 1457. It is likely that if she were a princess in the Ming court, records of her might not exist. In many historical text, she was said to have been a princess in the court of the Yongle Emperor(1402-1424).
A cultural result of the vibrant trade was the expansion of the Peranakan people, who spread to other major settlements in the region.
During its prime, Malacca was a powerful Sultanate which extended its rule over the southern Malay Peninsula and much of Sumatra. Its rise helped to hold off the Thai's southwards encroachment and arguably hasten the decline of the rival Majapahit Empire of Java which was in decline as Malacca was rising. Malacca was also central in the spread of Islam in the Malay Archipelago.

European colonization

In April 1511, Afonso de Albuquerque set sail from Goa to Malacca with a force of some 1200 men and seventeen or eighteen ships. They conquered the city on August 24, 1511. It became a strategic base for Portuguese expansion in the East Indies. Sultan Mahmud Shah, the last Sultan of Malacca took refuge in the hinterland, and made intermittent raids both by land and sea, causing considerable hardship for the Portuguese. In the meantime the Portuguese built the fort named A Famosa to defend Malacca (its gate is all that remains of the ruins at present). "In order to appease the King of Ayudhya" (Siam, whom had always intended in invading Malacca if not due to the latter's good relationship with the Ming Emperor, China) "the Portuguese sent up an ambassador, Duarte Fernandes, who was well received by Ramathibodi." in 1511.Finally in 1526, a large force of Portuguese ships, under the command of Pedro Mascarenhas, was sent to destroy Bintan, where Sultan Mahmud was based. Sultan Mahmud fled with his family across the Straits to Kampar in Sumatra, where he died two years later.

It soon became clear that Portuguese control of Malacca did not mean they now controlled Asian trade that centred around it. Their Malaccan rule was severely hampered by administrative and economic difficulties. Rather than achieving their ambition of dominating Asian trade, the Portuguese had fundamentally disrupted the organisation of the network. The centralised port of exchange of Asian wealth exchange had now gone, as was a Malay state to police the Straits of Malacca that made it safe for commercial traffic. Trade was now scattered over a number of ports amongst bitter warfare in the Straits.

The Jesuit missionary Francis Xavier spent several months in Malacca in 1545, 1546 and 1549. In 1641 the Dutch defeated the Portuguese to capture Malacca with the help of the Sultan of Johore. The Dutch ruled Malacca from 1641 to 1795 but they were not interested in developing it as a trading centre, placing greater importance to Batavia (Jakarta) in Indonesia as their administrative centre. However they still built their landmark better known as the Stadthuys or Red Building.
Malacca was ceded to the British in the Anglo-Dutch Treaty of 1824 in exchange for Bencoolen on Sumatra. From 1826 to 1946 Malacca was governed, first by the British East India Company and then as a Crown Colony. It formed part of the Straits Settlements, together with Singapore and Penang. After the dissolution of this crown colony, Malacca and Penang became part of the Malayan Union, which later became Malaysia.

Al-Khwārizmī

2010-01-22T23:25:00.000+08:00

Al-Khwārizmī (c. 780, Khwārizm – c. 850) was a Persian mathematician, astronomer and geographer, a scholar in the House of Wisdom in Baghdad.
His Kitab al-Jabr wa-l-Muqabala presented the first systematic solution of linear and quadratic equations. He is considered the founder of algebra, a credit he shares with Diop hantus. In the twelfth century, Latin translations of his work on the Indian numerals, introduced the decimal positional number system to the Western world. He revised Ptolemy's Geography and wrote on astronomy and astrology.
His contributions had a great impact on language. "Algebra" is derived from al-jabr, one of the two operations he used to solve quadratic equations. Algorism and algorithm stem from Algoritmi, the Latin form of his name. His name is the origin of (Spanish) guarismo and of (Portuguese) algarismo, both meaning digit.

Contributions

Al-Khwārizmī's contributions to mathematics, geography, astronomy, and cartography established the basis for innovation in algebra and trigonometry. His systematic approach to solving linear and quadratic equations led to algebra, a word derived from the title of his 830 book on the subject, "The Compendious Book on Calculation by Completion and Balancing" (al-Kitab al-mukhtasar fi hisab al-jabr wa'l-muqabalaالكتاب المختصر في حساب الجبر والمقابلة).
On the Calculation with Hindu Numerals written about 825, was principally responsible for spreading the Indian system of numeration throughout the Middle East and Europe. It was translated into Latin as Algoritmi de numero Indorum. Al-Khwārizmī, rendered as (Latin) Algoritmi, led to the term "algorithm".
Some of his work was based on Persian and Babylonian astronomy, Indian numbers, and Greek mathematics.
Al-Khwārizmī systematized and corrected Ptolemy's data for Africa and the Middle east. Another major book was Kitab surat al-ard ("The Image of the Earth"; translated as Geography), presenting the coordinates of places based on those in the Geography of Ptolemy but with improved values for the Mediterranean Sea, Asia, and Africa.
He also wrote on mechanical devices like the astrolabe and sundial.
He assisted a project to determine the circumference of the Earth and in making a world map for al-Ma'mun, the caliph, overseeing 70 geographers.
When, in the 12th century, his works spread to Europe through Latin translations, it had a profound impact on the advance of mathematics in Europe. He introduced Arabic numerals into the Latin West, based on a place-value decimal system developed from Indian sources.

Algebra

Al-Kitāb al-mukhtasar fī isāb al-jabr wa-l-muqābala (Arabic: الكتاب المختصر في حساب الجبر والمقابلة “The Compendious Book on Calculation by Completion and Balancing”) is a mathematical book written approximately 830 CE. The book was written with the encouragement of the Caliph Al-Ma'mun as a popular work on calculation and is replete with examples and applications to a wide range of problems in trade, surveying and legal inheritance. The term algebra is derived from the name of one of the basic operations with equations (al-jabr) described in this book. The book was translated in Latin as Liber algebrae et almucabala by Robert of Chester (Segovia, 1145) hence "algebra", and also by Gerard of Cremona. A unique Arabic copy is kept at Oxford and was translated in 1831 by F. Rosen. A Latin translation is kept in Cambridge.
The al-jabr is considered the foundational text of modern algebra. It provided an exhaustive account of solving polynomial equations up to the second degree, and introduced the fundamental methods of "reduction" and "balancing", referring to the transposition of subtracted terms to the other side of an equation, that is, the cancellation of like terms on opposite sides of the equation.

Arithmetic

Al-Khwārizmī's second major work was on the subject of arithmetic, which survived in a Latin translation but was lost in the original Arabic. The translation was most likely done in the twelfth century by Adelard of Bath, who had also translated the astronomical tables in 1126.
The Latin manuscripts are untitled, but are commonly referred to by the first two words with which they start: Dixit algorizmi ("So said al-Khwārizmī"), or Algoritmi de numero Indorum ("al-Khwārizmī on the Hindu Art of Reckoning"), a name given to the work by Baldassarre Boncompagni in 1857. The original Arabic title was possibly Kitāb al-Jam' wa-l-tafrīq bi-hisāb al-Hind ("The Book of Addition and Subtraction According to the Hindu Calculation")
Al-Khwarizmi's work on arithmetic was responsible for introducing the Arabic numerals, based on the Hindu-Arabic numeral system developed in Indian mathematics, to the Western world. The term "algorithm" is derived from the algorism, the technique of performing arithmetic with Hindu-Arabic numerals developed by al-Khwarizmi. Both "algorithm" and "algorism" are derived from the Latinized forms of al-Khwarizmi's name, Algoritmi and Algorismi, respectively.

Astronomy

Al-Khwārizmī's Zīj al-Sindhind (Arabic: زيج "astronomical tables of Sind and Hind") is a work consisting of approximately 37 chapters on calendrical and astronomical calculations and 116 tables with calendrical, astronomical and astrological data, as well as a table of si ne values. This is the first of many Arabic Zijes based on the Indian astronomical methods known as the sindhind. The work contains tables for the movements of the sun, the moon and the five planets known at the time. This work marked the turning point in Islamic astronomy. Hitherto, Muslim astronomers had adopted a primarily research approach to the field, translating works of others and learning already discovered knowledge. Al-Khwarizmi's work marked the beginning of non-traditional methods of study and calculations.

Quicksand

2010-01-17T12:25:00.000+08:00

Quicksand is a colloid hydrogel consisting of fine granular matter (such as sand or silt), clay, and salt water. In the name, as in that of quicksilver (mercury), "quick" does not mean "fast," but "living" (cf. the expression the quick and the dead).
Water ci rculation underground can focus in an area with the optimal mixture of fine sands and other materials such as clay. The water moves up and then down slowly in a convection-like manner throughout a column of sand, and the sand remains a generally solid mass. This lubricates the sand particles and renders them unable to support significant weight, since they move with little friction, behaving more like a liquid when exposed to stress. Since water does not usually go up to the surface of the sand, the sand on top appears solid, and can support leaves and other small debris, making quicksand difficult to distinguish from the surrounding environment.

Properties

Quicksand is a non-Newtonian fluid: when undisturbed it often appears to be solid ("gel" form), but a minor (less than 1%) change in the stress on the quicksand will cause a sudden decrease in its viscosity ("sol" form). After an initial disturbance—such as a person attempting to walk on it—the water and sand in the quicksand separate and dense regions of sand sediment form; it is because of the formation of these high volume fraction regions that the viscosity of the quicksand seems to increase suddenly. Someone stepping on it will start to sink. To move within the quicksand, a person or object must apply sufficient pre ssure on the compacted sand to re-introduce enough water to liquefy it. The forces required to do this are quite large: to remove a foot from quicksand at a speed of .01 m/s would require the same amount of force as "that needed to lift a medium-sized car."
Because of the higher density of the quicksand, it would be impossible for a human or animal to completely sink in the quicksand, though natural hazards present around the quicksand would lead people to believe that quicksand is dangerous. In actuality the quicksand itself is harmless on its own, but because it greatly impedes human locomotion, the quicksand would allow harsher elements like solar radiation, dehydration, or tides to harm a trapped person.

Prevalence

Quicksand may be found inland (on riverbanks, near lakes, or in marsh es), or near the coast.
One region notorious for its quicksands is Morecambe Bay, England. As the bay is very broad and shallow, a person trapped by the quicksand would be exposed to the danger of the returning tide, which can come in rapidly.

Dry quicksand

Dry quicksand is loose sand whose bulk density is reduced by blowing air through it and which yields easily to weight or pressure. It acts similarly to normal quicksand, but it does not contain any water and does not operate on the same principle. Dry quicksand is an example of a granular material.
Until recently, the existence of dry quicksand was doubted, and the reports of humans and complete caravans being lost in dry quicksand were considered to be folklore.

Scientific research

Writing in Nature, physicist Detlef Lohse and coworkers of University of Twente in Enschede, Netherlands allowed air to flow through very fine sand (typical grain diameter was about 40 micrometers) in a container with a perforated base. They then turned the air stream off before the start of the experiment and allowed the sand to settle: the packing fraction of this sand was only 41% (compared to 55–60% for untreated sand).
Lohse found that a weighted table tennis ball (radius 2 cm, mass 133 g), when released from just above the surface of the sand, would sink to about five diameters. Lohse also observed a "straight jet of sand [shooting] violently into the air after about 100 ms". Objects are known to make a splash when they hit sand, but this type of jet has never been described before.

Lohse concluded that
In nature, dry quicksands may evolve from the sedimentation of very fine sand after it has been blown into the air and, if large enough, might be a threat to humans. Indeed, reports that travellers and whole vehicles have been swallowed instantly may even turn out to be credible in the light of our results.

During the planning of the Project Apollo moon missions, dry quicksand on the moon was considered as a potential danger to the missions. The successful landings of the unmanned Surveyor probes a few years earlier and their observations of a solid, rocky surface largely discounted this possibility, however. The large plates at the end of legs of the Apollo Lunar Module were designed to reduce this danger, but the astronauts did not encounter dry quicksand.

Housefly

2010-01-11T18:08:00.000+08:00

The housefly (also house fly, house-fly or common housefly), Musca domestica, is a Diptera of the Brachycera suborder. It is the most common of all domestic flies, accounting for about 90% of all flies in human habitations, and indeed one of the most widely distributed insects, found all over the world; it is considered a pest that can carry serious diseases.

Physical description

The adults are 8–12 mm long. Their thorax is gray, with four longitudinal dark lines on the back. The underside of their abdomen is yellow, and their whole body is covered with hair-like projections. The females are slightly larger than the males, and have a much larger space between their red compound eyes. The mass of pupae can range from about 8 to 20 mg under different conditions.
Like other Diptera (meaning "two-winged"), houseflies have only one pair of wings; the hind pair is reduced to small halteres that aid in flight stability. caterpillars (M1+2 or fourth long vein of the wing) shows a sharp upward bend.
Species that appear similar to the housefly include:
a) The lesser house fly, Fannia canicularis, is somewhat smaller, more slender, and the media vein is straight.
b) The stable fly, Stomoxys calcitrans, has piercing mouthparts and the media vein is only slightly curved.

Life cycle

Each female fly can lay approximately 500 eggs in several batches of about 75 to 150. The eggs are white and are about 1.2 mm in length. Within a day, larvae (maggots) hatch from the eggs; they live and feed in (usually dead and decaying) organic material, such as garbage or feces. They are pale-whitish, 3–9 mm long, thinner at the mouth end, and have no legs. They live at least one week. At the end of their third instar, the maggots crawl to a dry cool place and transform into pupae, colored reddish or brown and about 8 mm long. The adult flies then emerge from the pupae. (This whole cycle is known as complete metamorphosis.) The adults live from two weeks to a month in the wild, or longer in benign laboratory conditions. After having emerged from the pupae, the flies cease to grow; small flies are not young flies, but are indeed the result of getting insufficient food during the larval stage.

Some 36 hours after having emerged from the pupa, the female is receptive for mating. The male mounts her from behind to inject sperm. Copulation takes between a few seconds to a couple of minutes. Normally the female mates only once, storing the sperm to use it repeatedly for laying several sets of eggs. Males are territorial: they will defend a certain territory against other males and will attempt to mount any females that enter that territory.

The flies depend on warm temperatures; generally, the warmer the temperature the faster the flies will develop. In winter, most of them survive in the larval or the pupa stage in some protected warm location.

Maggots

Some types of maggots found on corpses have been found to be of great use to forensic scientists; specifically Forensic Entomology. By their stage of development, these maggots (and other insects) can be used to give an indication of the time elapsed since death, as well as the place the organism died. The lack of maggot presence is also telling in an investigation.
Maggot species can be identified using their DNA. The size of the house fly maggot is 10–20 mm (⅜–¾ in). At the height of the summer season, a generation of flies (egg to adult) may be produced in 12–14 days. Some other families of Insecta, such as Histeridae, feed on maggots. Thus, the lack of maggots would increase the estimated time of death.
Other types of maggots are bred commercially, as a popular bait in angling, and a food for carnivorous pets such as reptiles or birds.
Maggots have been used in medicine to clean out necrotic wounds and in food production, particularly of cheeses designed to rot as part of their 'aging' process. (casu marzu).

Diet

Houseflies feed on feces, open sores, sputum, and moist decaying organic matter such as spoiled food, eggs and flesh. Houseflies can take in only liquid foods. They spit out saliva on solid foods to predigest it, and then suck it back in. They also regurgitate partly digested matter and pass it again to the abdomen.

Housefly as a vector of disease
Mechanical transmission of organisms on its hairs, mouthparts, vomitus and feces:
a) parasitic diseases: cysts of protozoa e.g. Entamoeba histolytica, Giardia lamblia and eggs of helminths e.g.: Ascaris lumbricoides, Trichuros trichura, Haemenolypes nana, Enterobius vermicularis.
b) bacterial diseases: typhoid, cholera, dysentery, pyogenic cocci...etc. House flies have been demonstrated to be vectors of Campylobacter and E. coli O157:H7 using PCR. House flies can be monitored for bacterial pathogens using filter paper spot cards and PCR
c) Viruses: enteroviruses: poliomyelitis, infective hepatitis (A & E)..etc

House flies feed on liquid or semi-liquid substances beside solid material which has been softened by saliva or vomit. Because of their high intake of food, they deposit feces constantly, one of the factors that makes the insect a dangerous carrier of pathogens. Although they are domestic flies, usually confined to the human habitations, they can fly for several miles from the breeding place. They are active only in daytime and rest at night e.g. at the corners of rooms, ceiling hangings, etc.

True polar wander

2010-01-07T21:44:00.000+08:00

True polar wander is a phenomenon in which a planet or moon undergoes a solid-body rotation with respect to its spin axis. As this occurs, the geographic locations of the North and South Poles change, or "wander". This can happen when the two larger moments of inertia are near equal.

Description in the context of Earth

The Earth is not a true sphere, and therefore has three orthogonal axes of inertia. The axis around which the moment of inertia is greatest is closely aligned with the rotation axis (the axis going through the North and South Poles). The other two axes are near the equator. This is similar to a brick rotating around an axis going through its shortest dimension (a vertical axis when the brick is lying flat). But if the moment of inertia around one of the two axes close to the equator becomes nearly equal to that around the polar axis, then the constraint on the orientation of the object (the Earth) is relaxed.
This situation is like an American football (or a Rugby ball) spinning around an axis running through its "equator". (Note that the "equator" of the ball does not correspond to the equator of the Earth.) Small perturbations can move the football so that it spins around another axis through this same "equator". In the same way, when the conditions are right, the Earth (both the crust and the mantle) can slowly reorient so that a new geographic point moves to the North Pole, while keeping the axis of low moment of inertia quite near the equator.
Such a reorientation changes the latitudes of most points on the Earth, by amounts that depend on how far they are from the axis near the equator that does not move.

Claimed examples

Cases of true polar wander have occurred several times in the course of the Earth's history.

The speed of rotation (around the axis of lowest inertia) is limited to about 1° per million years. Mars, Europa, and Enceladus are also believed to have undergone true pole wander, in the case of Europa by 80°, flipping over almost completely. The crust of Titan has also shifted, though pole wander has not been detected.

Distinctions and delimitations

Polar wander should not be confused with precession, which is where the axis of rotation moves, in other words the North Pole points toward a different star. Precession is caused by the gravitational attraction of the Moon and Sun, and occurs all the time and at a much faster rate than polar wander. It does not result in changes of latitude.
True polar wander has to be distinguished from continental drift, which is where different parts of the Earth's crust move in different directions because of circulation in the mantle.

Geomagnetic reversal

A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged. These events often involve an extended decline in field strength followed by a rapid recovery after the new orientation has been established. These events occur on a scale of tens of thousands of years or longer.
More generally, the term may refer to a reversal of the polarity of any magnetosphere.

Scientific opinion is divided on what causes geomagnetic reversals. One theory holds that they are due to events internal to the system that generates the Earth's magnetic field. The other holds that they are due to external events.

Internal events

Many scientists believe that reversals are an inherent aspect of the dynamo theory of how the geomagnetic field is generated. In computer simulations, it is observed that magnetic field lines can sometimes become tangled and disorganized through the ch aotic motions of liquid metal in the Earth's core.
In some simulations, this leads to an instability in which the magnetic field spontaneously flips over into the opposite orientation. This scenario is supported by observations of the solar magnetic field, which undergoes spontaneous reversals every 7–15 years. However, with the sun it is observed that the solar magnetic intensity greatly increases during a reversal, whereas all reversals on Earth seem to occur during periods of low field strength.
Present computational methods have used very strong simplifications in order to produce models that run to acceptable time scales for research programs.

External events
Others, such as Richard A. Muller, believe that geomagnetic reversals are not spontaneous processes but rather are triggered by external events which directly disrupt the flow in the Earth's core. Such processes may include the arrival of continental slabs carried down into the mantle by the action of plate tectonics at subduction zones, the initiation of new mantle plumes from the core-mantle boundary, and possibly mantle-core shear forces resulting from very large impact events. Supporters of this theory hold that any of these events could lead to a large scale disruption of the dynamo, effectively turning off the geomagnetic field. Because the magnetic field is stable in either the present North-South orientation or a reversed orientation, they propose that when the field recovers from such a disruption it spontaneously chooses one state or the other, such that a recovery is seen as a reversal in about half of all cases.
Brief disruptions which do not result in reversal are also known and are called geomagnetic excursions.

Jellyfish

2010-01-03T18:53:00.000+08:00

Jellyfish (also jellies or sea jellies) are free-swimming members of the phylum Cnidaria. Jellyfish have several different morphologies that represent several different cnidarian classes including the Scyphozoa (over 200 species), Staurozoa (about 50 species), Cubozoa (about 20 species), and Hydrozoa (about 1000-1500 species that make jellyfish and many more that do not). The jellyfish in these groups are also called, respectively, scyphomedusae, stauromedusae, cubomedusae, and hydromedusae; medusa is another word for jellyfish, but it also refers specifically to the adult stage of the life cycle.
Jellyfish are found in every ocean, from the surface to the deep sea. Some hydrozoan jellyfish, or hydromedusae, are also found in fresh water and are less than half an inch in size. They are partially white and clear and do not sting. Many of the best-known jellyfish, such as Aurelia, are scyphomedusae. These are the large, often colorful, jellyfish that are common in coastal zones worldwide.
In its broadest sense, the term jellyfish also generally refers to members of the phylum Ctenophora. Although not closely related to cnidarian jellyfish, ctenophores are also free-swimming planktonic carnivores, are generally transparent or translucent, and exist in shallow to deep portions of all the world's oceans.

Life cycle

Most jellyfish undergo two distinct life history stages (body forms) during their life cycle. The first is the polypoid stage, when the animal takes the form of a small stalk with feeding tentacles; this polyp may be sessile, living on the bottom or on similar substrata such as floats or boat-bottoms, or it may be free-floating or attached to tiny bits of free-living plankton or rarely, fish. Polyps generally have a mouth surrounded by upward-facing tentacles like miniatures of the closely-related anthozoan polyps (sea anemones and corals), also of the phylum Cnidaria. Polyps may be solitary or colonial, and some bud asexually by various means, making more polyps. Most are very small, measured in millimeters.
In the second stage, the tiny polyps asexually produce jellyfish, each of which is also known as a medusa. Tiny jellyfish (usually only a millimeter or two across) swim away from the polyp and then grow and feed in the plankton. Medusae have a radially symmetric, umbrella-shaped body called a bell, which is usually supplied with marginal tentacles - fringe-like protrusions from the bell's border that capture prey. A few species of jellyfish do not have the polyp portion of the life cycle, but go from jellyfish to the next generation of jellyfish through direct development of fertilized eggs.
Jellyfish are dioecious; that is, they are either male or female. In most cases, both release sperm and eggs into the surrounding water, where the (unprotected) eggs are fertilized and mature into new organisms. In a few species, the sperm swim into the female's mouth fertilizing the eggs within the female's body. In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber.
After fertilization and initial growth, a larval form, called the planula, develops. The planula is a small larva covered with cilia. It settles onto a firm surface and develops into a polyp. The polyp is cup-shaped with tentacles surrounding a single orifice, resembling a tiny sea anemone.

After a growth interval, the polyp begins reproducing asexually by budding and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma. New scyphistomae may be produced by budding or new, immature jellies called ephyrae may be formed. A few jellyfish species can produce new medusae by budding directly from the medusan stage. Budding sites vary by species; from the tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae. A few of species of hydromedusae reproduce by fission (splitting in half.)
Other species of jellyfish are among the most common and important jellyfish predators, some of which specialize in jellies. Other predators include tuna, shark, swordfish, sea turtles and at least one species of Pacific salmon. Sea birds sometimes pick symbiotic crustaceans from the jellyfish bells near the sea's surface, inevitably feeding also on the jellyfish hosts of these amphipods or young crabs and shrimp.
Jellyfish lifespans typically range from a few hours (in the case of some very small hydromedusae) to several months. Life span and maximum size varies by species. One unusual species is reported to live as long as 30 years. Another species, Turritopsis dohrnii as T. nutricula, may be effectively immortal because of its ability to transform between medusa and polyp, thereby escaping death. Most large coastal jellyfish live 2 to 6 months, during which they grow from a millimeter or two to many centimeters in diameter. They feed continuously and grow to adult size fairly rapidly. After reaching adult size, jellyfish spawn daily if there is enough food. In most species, spawning is controlled by light, so the entire population spawns at about the same time of day, often at either dusk or dawn.

Toxicity to humans

Scyphozoan jellyfish stings are not generally deadly, though some species of the completely separate class Cubozoa (box jellyfish), such as the famous and especially toxic Irukandji, can be.
Jellyfish sting using microscopic cells called nematocysts, which are capsules full of poison expelled through a microscopic lance. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom.
Jellyfish sting prey and threatening humans using their nematocysts, but only some jellyfish species harm humans. Even beached and dying jellyfish can still sting when touched. Sting effects range from no effect to extreme pain to death.
Stings may cause anaphylaxis, which may result in death. Hence, victims should immediately get out of the water. Medical care may include administration of an antivenom.
The three goals of first aid for uncomplicated jellyfish stings are: prevent injury to rescuers, inactivate the nematocysts, and remove tentacles attached to the patient. Rescuers should wear barrier clothing, such as panty hose, wet suits or full-body sting-proof suits. Inactivating the nematocysts, or stinging cells, prevents further injection of venom.