Monday, December 28, 2009


Holography (from the Greek, ὅλος-hólos whole + γραφή-grafē writing, drawing) is a technique that allows the light scattered from an object to be recorded and later reconstructed so that it appears as if the object is in the same position relative to the recording medium as it was when recorded. The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the recorded image (hologram) appear three dimensional.
The technique of holography can also be used to optically store, retrieve, and process information. While holography is commonly used to display static 3-D pictures, it is not yet possible to generate arbitrary scenes by a holographic volumetric display.

Viewing the hologram
The holographic recording is the random variation in intensity which is an objective speckle pattern, and not the regular lines which are likely to be due to interference arising from multiple reflections in the glass plate on which the photographic emulsion is mounted. It is no more possible to discern the subject of the hologram from this than it is to identify the music on an audio CD by looking at the structure of the CD surface. When this hologram is illuminated by a divergent laser beam, the viewer will see the object used to make it (in this case, a toy van) because the light is diffracted by the hologram to reconstruct the light which was scattered from the object.
When one looks at a scene, each eye captures a portion of the light scattered from the scene, and the lens of the eye forms an image of the scene on the retina, in which light from each angular position is focused to a specific angular position in the image plane. Since the hologram reconstructs the whole of the scattered light field that was incident on the hologram, the viewer sees the same image whether it is derived from the light field scattered from the object, or the reconstructed light field produced by the hologram, and is unable to tell whether he or she is looking at the real or the virtual object. If the viewer moves about, the object will appear to move in exactly the same way whether he or she is looking at the original light field or the reconstructed light field. If there are several objects in the scene, they will exhibit parallax. If the viewer is using both eyes (stereoscopic vision), he or she will get depth information when viewing the hologram in exactly the same way as when he or she is viewing the real scene.
It should be clear from this why a hologram is not a 3D photograph. A photograph records an image of the recorded scene from a single viewpoint, which is defined by the position of the camera lens. The hologram is not an image, but an encoding system which enables the scattered light field to be reconstructed. Images can then be formed from any point in the reconstructed beam either with a camera or by eye. It was very common in the early days of holography to use a chess board as the object, and then take photographs at several different angles using the reconstructed light to show how the relative positions of the chess-pieces appeared to change.
Since each point in the hologram contains light from the whole of the original scene, the whole scene can, in principle, be reconstructed from an arbitrarily small part of the hologram. To demonstrate this concept, the hologram can be broken into small pieces and the entire object can still be seen from each small piece. If one envisions the hologram as a "window" on the object, then each small piece of hologram is just a part of the window from which it can still be viewed, even if the rest of the window is blocked off.

Viewing and authoring
The object and the reference beams must be able to produce an interference pattern that is stable during the time in which the holographic recording is made. To do this, they must have the same frequency and the same relative phase during this time, that is, they must be mutually coherent. Many laser beams satisfy this condition, and lasers have been used to make holograms since their invention, though it should be noted that the first holograms by Gabor used 'quasi-chromatic' light sources. In principle, two separate light sources could be used if the coherence condition could be satisfied, but in practice a single laser is always used.
In addition, the medium used to record the fringe pattern must be able to resolve the fringe patterns and some of the more common media used are listed below. The spacing of the fringes depends on the angle between object and reference beam. For example, if this angle is 45°, and the wavelength of the light is 0.5μm, the fringe spacing is about 0.7μm or 1300 lines/mm. A working hologram can be obtained even if all the fringes are not resolved, but the resolution of the image is reduced as the resolution of the recording medium reduces.
Mechanical stability is also very important when making a hologram. Any relative phase change between the object and reference beams due to vibration or air movement will cause the fringes on the recording medium to move, and if the phase changes is greater than π, the fringe pattern is averaged out, and no holographic recording is obtained. Recording time can be several seconds or more, and given that a phase change of π is equivalent to a movement of λ/2 this is quite a stringent stability requirement.
A good holography laser will typically have a coherence length of several meters, ample for a deep hologram. Certain pen laser pointers have been used to make small holograms. The size of these holograms is not restricted by the coherence length of the laser pointers (which can exceed several meters), but by their low power of below 5 mW.
The objects that form the scene must, in general, have optically rough surfaces so that they scatter light over a wide range of angles. A specularly reflecting (or shiny) surface reflects the light in only one direction at each point on its surface, so in general, most of the light will not be incident on the recording medium. It should be noted that the light scattered from objects with a rough surface forms an objective speckle pattern that has random amplitude and phase.
The reference beam is not normally a plane wavefront; it is usually a divergent wavefront that is formed by placing a convex lens in the path of the laser beam.
To reconstruct the object exactly from a transmission hologram, the reference beam must have the same wavelength and curvature, and must illuminate the hologram at the same angle as the original reference beam (i.e. only the phase can be changed). Departure from any of these conditions will give a distorted reconstruction. While nearly all holograms are recorded using lasers, a narrow-band lamp or even sunlight is enough to recognize the reconstructed image.
The reconstructed hologram is enlarged if the light used to reconstruct the hologram has a higher wavelength. This initially generated some interest since it seemed to be possible to use X-rays to make holograms of molecules and view them using visible light. However X-ray holograms have not been created to date. This effect can be demonstrated using a light source which emits several different frequencies.
Exact reconstruction is achieved in holographic interferometry where the holographically reconstructed wavefront interferes with the live wavefront, to map out any displacement of the live object, and gives a null fringe if the object has not moved.

Monday, December 21, 2009

Mount Kinabalu

Mount Kinabalu (Malay: Gunung Kinabalu) is a prominent mountain in Southeast Asia. It is located in Kinabalu National Park (a World Heritage Site) in the east Malaysian state of Sabah, which is on the island of Borneo in the tropics. It is the 4th tallest mountain in the Malay Archipelago after Indonesian Papua's Puncak Jaya, Puncak Trikora and Puncak Mandala.
In 1997, a re-survey using satellite technology established its summit (known as Low’s Peak) height at 4,095 metres (13,435 ft) above sea level, which is some 6 metres (20 ft) less than the previously thought and hitherto published figure of 4,101 metres (13,455 ft).
The mountain and its surroundings are among the most important biological sites in the world, with over 600 species of ferns, 326 species of birds, and 100 mammalian species identified. Among them are the gigantic Rafflesia plants and the orangutan. Mount Kinabalu has been accorded UNESCO World Heritage status.
The main peak of the mountain (Low's Peak) can be climbed easily by a person in good physical condition, and requires no mountaineering equipment. Other peaks along the massif, however, require rock climbing skills.

Significantly, Mount Kinabalu is well-known worldwide for its tremendous botanical and biological species biodiversity, with high levels of endemism (i.e. species which are found only within Kinabalu Park and are not found anywhere else in the world). As examples, it has one of the world’s richest orchid flora with over 800 species, over 600 species of ferns (more than the whole of Africa’s 500 species) of which 50 are found no where else, and is the richest place in the world for the Nepenthes insectivorous pitcher plants (five of the thirteen are found nowhere else on earth) which reach spectacular proportions (the largest in the world being the endemic Nepenthes rajah).
The parasitic Rafflesia plant, which has the largest single flower in the world, is also found in Kinabalu (particularly the Rafflesia keithii whose flower grows to 94 centimetres or 37 inches in diameter), though it should be noted that blooms of the flower are rare and difficult to find. A recent botanical survey of the mountain estimated a staggering 5,000 to 6,000 plant species (excluding mosses and liverworts but including ferns), which is more than all of Europe and North America (excluding tropical regions of Mexico) combined. It is therefore one of the world's most important biological sites.
Its incredible biodiversity in plant life is due to a combination of several unique factors: its setting in one of the richest plant regions of the world (the tropical biogeographical region known as western Malesia which comprises the island of Sumatra, the Malay Peninsula, and the island of Borneo), the fact that the mountain covers a wide climatic range from near sea level to freezing ground conditions near the summit, the jagged terrain and diversity of rocks and soils, the high levels of rainfall (averaging about 2700 mm a year at park HQ), and the climatic instability caused by periods of glaciation and catastrophic droughts which result in speciation. This diversity is greatest in the lowland regions (consisting of lowland dipterocarp forests, so called because the tree family Dipterocarpaceae are dominant). However, most of Kinabalu’s endemic species are found in the mountain forests, particularly on ultramafic soils (i.e soils which are low in phosphates and high in iron and metals poisonous to many plants; this high toxic content gave rise to the development of distinctive plant species found nowhere else).
Endemic annelids number less than a dozen known species but include the Kinabalu giant red leech that preys on various earthworms, including the Kinabalu giant earthworm.
There are some 326 species of birds in Kinabalu Park (including the spectacular Rhinoceros Hornbill); and some 100 mammalian species, including one of the four great apes, the orangutan (though sightings of these are uncommon; estimates of its numbers in the park range from 25 to 120).

Mount Kinabalu is essentially a massive granodiorite which is intrusive into sedimentary and ultrabasic rocks, and forms the central part, or core, of the Kinabalu massif. The granodiorite is intrusive into strongly folded strata, probably of Eocene to Miocene age, and associated ultrabasic and basic igneous rocks. It was pushed up from the earth’s crust as molten rock millions of years ago. In geological terms, it is a very young mountain as the granodiorite cooled and hardened only about 10 million years ago. The present landform is considered to be a mid-Pliocene peneplain, arched and deeply dissected, through which the Kinabalu granodiorite body has risen in isostatic adjustment. It is still pushing up at the rate of 5 mm per annum. During the Pleistocene Period of about 100,000 years ago, the massive mountain was covered by huge sheets of ice and glaciers which flowed down its slopes, scouring its surface in the process and creating the 1800 m deep Low's Gully ( named after Hugh Low) on its North side. Its granite composition and the glacial formative processes are readily apparent when viewing its craggy rocky peaks.

Climbing route
Climbers must be accompanied by accredited guides at all times. There are two main starting points for the climb: the Timpohon Gate (near the national park headquarters, at about Template:Unit), and the Mesilau Nature Resort. The latter starting point is slightly higher in elevation, but crosses a ridge, adding about two kilometres to the ascent and making the total elevation gain slightly higher. The two trails meet about two kilometres below Laban Rata.
Accommodation is available inside the park or outside near the headquarters. From there, climbers proceed to the Timpohon gate at 1866 m (6,122 ft), either by minibus or by walking, and then walk to the Laban Rata Resthouse at 3,270 m (10,728 ft). Most people accomplish this part of the climb in 3 to 6 hours. Since there are no roads, the supplies for the Laban Rata Resthouse are carried by porters, who bring up to 30 kilograms of supplies on their backs. Hot food and beverages, hot showers and heated rooms are available at Laban Rata. The last 2 km (2600 ft), from the Laban Rata Resthouse at 3,270 m to Low's Peak (summit) at 4,095.2 m, takes between 2 and 4 hours. The last part of the climb is on naked granite rock.
Given the high altitude, some people may suffer from altitude sickness and should return immediately to the bottom of the mountain, as breathing and any further movement becomes increasingly difficult.

Thursday, December 17, 2009


Geber is the Latinized form of "Jabir", with the full name of Abu Musa Jābir ibn Hayyān al azdi (Arabic: جابر بن حيان) (born c. 721 in Tus–died c. 815 in Kufa), a prominent polymath: a chemist and alchemist, astronomer and astrologer, engineer, geologist, philosopher, physicist, and pharmacist and physician. He is considered by many to be the "father of chemistry." His ethnic background is not clear; although some sources state that he was an Arab, other sources introduce him as Persian. Geber or Jabir is held to be the first practical alchemist. As early as the tenth century, the identity of Geber appears to have been disputed. Some scholars and historians have maintained that Jabir is the pen name of a group of Ismaili writers in the ninth and tenth centuries, and that he died—if indeed he ever lived—a century before the writings attributed to him were composed.

Jabir is mostly renowned for his contributions to chemistry. He emphasised systematic experimentation, and did much to free alchemy from superstition and turn it into a science.
He is credited with the invention of over twenty types of now-basic chemical laboratory equipment, such as the alembic and retort, and with the discovery and description of many now-commonplace chemical substances and processes – such as the hydrochloric and nitric acids, distillation, and crystallisation – that have become the foundation of today's chemistry and chemical engineering.
He also paved the way for most of the later Islamic alchemists, including al-Kindi, al-Razi and al-Iraqi, who lived in the 9th-13th centuries. His books strongly influenced the medieval European alchemists and justified their search for the philosopher's stone.
He clearly recognized and proclaimed the importance of experimentation. "The first essential in chemistry", he declared, "is that you should perform practical work and conduct experiments, for he who performs not practical work nor makes experiments will never attain the least degree of mastery."
Jabir is also credited with the invention and development of a number of chemical substances and instruments that are still used today. He discovered sulfuric acid, and by distilling it together with various salts, Jabir discovered hydrochloric acid (from salt) and nitric acid (from saltpeter). By combining the two, he invented aqua regia, one of the few substances that can dissolve gold. Besides its obvious applications to gold extraction and purification, this discovery would fuel the dreams and despair of alchemists for the next thousand years. He is also credited with the discovery of citric acid (the sour component of lemons and other unripe fruits), acetic acid (from vinegar), and tartaric acid (from wine-making residues). Jabir also discovered and isolated several chemical elements, such as arsenic, antimony and bismuth.
He was also the first to classify sulfur (‘the stone which burns’ that characterized the principle of combustibility) and mercury (which contained the idealized principle of metallic properties) as 'elements'. He was also the first to purify and isolate sulfur and mercury as pure elements.
Jabir applied his chemical knowledge to the improvement of many manufacturing processes, such as making steel and other metals, preventing rust, engraving gold, dyeing and waterproofing cloth, tanning leather, and the chemical analysis of pigments and other substances. He developed the use of manganese dioxide in glassmaking, to counteract the green tinge produced by iron — a process that is still used today. He noted that boiling wine released a flammable vapor, thus paving the way for the discovery of ethanol (alcohol) by Al-Kindi and Al-Razi. According to Ismail al-Faruqi and Lois Lamya al-Faruqi, "In response to Jafar al-Sadik's wishes, [Jabir ibn Hayyan] invented a kind of paper that resisted fire, and an ink that could be read at night. He invented an additive which, when applied to an iron surface, inhibited rust and when applied to a textile, would make it water repellent."
The seeds of the modern classification of elements into metals and non-metals could be seen in his chemical nomenclature. He proposed three categories:

1. "Spirits" which vaporise on heating, like arsenic (realgar, orpiment), camphor, mercury, sulfur, sal ammoniac, and ammonium chloride.
2. "Metals", like gold, silver, lead, tin, copper, iron, and khar-sini;
3. Non-malleable substances, that can be converted into powders, such as stones.
The origins of the idea of chemical equivalents can also be traced back to Jabir, who was the first to recognize that "a certain quantity of acid is necessary in order to neutralize a given amount of base." According to Jabir, the metals differ because of "different proportions of sulfur and mercury in them."
In the Middle Ages, Jabir's treatises on alchemy were translated into Latin and became standard texts for European alchemists. These include the Kitab al-Kimya (titled Book of the Composition of Alchemy in Europe), translated by Robert of Chester (1144); and the Kitab al-Sab'een by Gerard of Cremona (before 1187). Marcelin Berthelot translated some of his books under the fanciful titles Book of the Kingdom, Book of the Balances, and Book of Eastern Mercury. Several technical Arabic terms introduced by Jabir, such as alkali, have found their way into various European languages and have become part of scientific vocabulary.

Max Meyerhoff states the following on Jabir ibn Hayyan: "His influence may be traced throughout the whole historic course of European alchemy and chemistry."
The historian of chemistry Erick John Holmyard gives credit to Geber for developing alchemy into an experimental science and he writes that Geber's importance to the history of chemistry is equal to that of Robert Boyle and Antoine Lavoisier.
The historian Paul Kraus, who had studied most of Geber's extant works in Arabic and Latin, summarized the importance of Geber to the history of chemistry by comparing his experimental and systematic works in chemistry with that of the allegorical and unintelligible works of the ancient Greek alchemists.
The word gibberish is theorized to be derived from Geber's name, in reference to the incomprehensible technical jargon often used by alchemists, the most famous of whom was Geber. Other sources such as the Oxford English Dictionary suggest the term stems from gibber; however, the first known recorded use of the term "gibberish" was before the first known recorded use of the word "gibber".

Monday, December 14, 2009


The Jedi are fictional characters in the Star Wars universe, and the series' main protagonists. They use a quasi-telekinetic power known as "The Force" and swords that emit a laser known as a "lightsaber" to protect their galaxy and the Republic they serve from conflict and help to stabilize the government. They sometimes moderate peace talks between planets, and, if necessary, use their formidable fighting skills to quickly end a conflict.

The Jedi are first introduced in Star Wars Episode IV: A New Hope as an order of warrior monks who serve as "the guardians of peace and justice in the galaxy" and embrace the mystical Force. Obi-Wan Kenobi (Alec Guinness) explains that the Galactic Empire had all but exterminated the Jedi some 20 years before the events of the film, and seeks to train Luke Skywalker (Mark Hamill) to be the Order's last hope. Darth Vader (David Prowse/James Earl Jones) is also established as the Jedi's main enemy. By the end of the film, Luke is on the path to becoming a Jedi. In the sequel, Star Wars Episode V: The Empire Strikes Back, Luke receives extensive Jedi training from the elderly Jedi Master Yoda (Frank Oz), even as he learns that Vader is in fact his father, former Jedi Anakin Skywalker. The third film in the original trilogy, Star Wars Episode VI: Return of the Jedi, ends with Luke redeeming Vader and helping to destroy the Empire, thus fulfilling his destiny as a Jedi.
The prequel films depict the Jedi as troubled by the resurgence of the dark side of the Force and determined to fight their mortal enemies, the Sith. In Star Wars Episode I: The Phantom Menace, Jedi Master Qui-Gon Jinn (Liam Neeson) discovers the young Anakin Skywalker (Jake Lloyd), whom he believes to be the "Chosen One" of Jedi prophecy who is destined to bring balance to the Force; the boy is eventually paired with Qui-Gon's apprentice, the young Obi-Wan Kenobi (Ewan McGregor), who promises to train him. The sequel, Star Wars Episode II: Attack of the Clones, establishes that the Jedi forswear all emotional attachments, including romantic love, which proves problematic when the now-adult Anakin (Hayden Christensen) falls in love with Padmé Amidala (Natalie Portman). In Star Wars Episode III: Revenge of the Sith, Palpatine (Ian McDiarmid) – who is secretly the Sith Lord Darth Sidious – manipulates Anakin's love for Padmé in order to turn him to the dark side and become his apprentice, Darth Vader. Once corrupted, Vader helps Palpatine hunt down and destroy nearly all of the Jedi.
The Jedi's history before and after the time-line of the films is established within several novels, comic books and video games in the Expanded Universe of Star Wars media.

Members of the order progress through four to six tiers of rank, at times referred to as levels.

1. Jedi Youngling/Initiate : A Jedi Youngling is a Jedi learning to control the force and how to wield a lightsaber. The title of Jedi Youngling is the first part of a Jedi training. Younglings were seen training with Jedi Grand Master Yoda in a scene from Star Wars Episode II: Attack of the Clones.

2. Jedi Padawan/Apprentice: A Youngling that successfully completes their respective level of training undergoes Padawan apprentice training under the tutelage of a Jedi Knight or Jedi Master. As a rite of passage and the final test before the trials to knighthood, Padawans must build their own lightsabers. In the Old Republic, padawans with hair on their heads usually wore a braid on the right side of their head in their hair that were removed upon attaining knighthood.

3. Jedi Knight: Disciplined, experienced Jedi may become full-fledged Jedi Knights once they have completed "the trials" that test candidates' skills, knowledge, and dedication. The three tests are usually known as The Trial of Skill, The Trial of Spirit, and the Trial of Knowledge. In Return Of The Jedi, Master Yoda gives his apprentice Luke Skywalker the trial of confronting Darth Vader for a second time so he might become a full-fledged Knight. Occasionally, performing an extraordinary (usually heroic) act can earn a Padawan learner Jedi Knight status, such as when Obi-Wan Kenobi defeats the Sith Lord Darth Maul. Or in the case of Anakin Skywalker who defeats Sith Apprentice Asajj Ventress.

4. Jedi Master: A Jedi Knight may become a Jedi Master after successfully training a Padawan learner to Knight status. Though this is the most common manner, it is not always the case. If the council sees that a Jedi Knight has become more powerful and has gained more knowledge and discipline in the Force, then they can be nominated by one or more council members to take the trials again.

5. Jedi Council Member: When a Jedi Council Member vacates its seat, the council looks for an exemplary Jedi Master to fill the empty position. Presiding Council Members elect prospective candidates when openings become available. According to the Dorling Kindersley guide to Star Wars Episode I: The Phantom Menace, some members were permanent members (like Yoda and Mace Windu), while the rest served limited terms, after which they stepped down and another member would be elected to the Jedi Council. With the exceptions of Anakin Skywalker and Ki-Adi Mundi, who was the only Knight on the Council for a short period of time before becoming a Jedi Master, all council members require the status of Jedi Master prior to entering the council.

6. Jedi Grand Master: Formally "Grand Master of the Jedi Order," only the highest-ranking Jedi Masters take the title. The title of Grand Master/Supreme Master is merely a theoretical title given by Jedi Masters to a certain Master who has been most wise among other masters in the council, as with Master Yoda. The Jedi Grand Master does not enjoy any greater privilege than any council members because the council members also have a vote in any issues presented by the council. The Grand Master was apparently the "first among equals" of the Jedi High Council, or the later Masters' Council. It may also be implied that the Grand Master of the Jedi Order has a strong connection to Jedi who have pledged themselves to the Order (Yoda sensing the deaths of Jedi across the galaxy as Order 66 is being executed in Revenge of the Sith). Yoda and Luke Skywalker (in the expanded universe) are Grand Masters.

Thursday, December 10, 2009


Demining is the process of removing land mines or naval mines from an area. Minesweeping is the detection of such mines. There are two distinct types of mine detection and removal: military and humanitarian.

Mine clearance
In the combat zone, the process is referred to as mine clearance. The priority is to breach the minefield quickly to create a safe path for troops or ships. Speed is vital, both for tactical reasons and because units attempting to breach the minefield may be under enemy fire. In this situation, it is accepted that mine clearance will be imperfect and there may be casualties from undiscovered mines. Correspondingly, in these mine clearance operations, the methods that are applied for detection and removal are quicker, but not exact. These methods include those that detect and remove in a single action, such as mechanical demining, carpet bombing, burning of the land or the use of Bangalore torpedoes or mine-clearing line charges. According to the doctrine of the U.S. and other armies, mine clearance and demining is carried out by combat engineers.

Humanitarian demining
In times of relative peace, the process of mine removal is referred to as demining. This is a thorough, time-intensive process that seeks to locate all mines so that the land or sea area may be safely returned to normal use. It is vital that this process be exhaustive. Even if only a small handful of mines remain undiscovered, then demining can actually lead to an increase in civilian mine casualties as local people re-occupy an area they previously avoided in the belief that it has been made safe. In this context demining is one of the tools of mine action. Coordinated by Mine Action Coordination Centers run by the United Nations or a host government, civilian mine clearance agencies are tasked with the demining. In post-conflict areas, minefields are often contaminated with a mixture of explosive remnants of war (ERW) that includes unexploded ordnance as well as landmines. In that context, the humanitarian clearance effort is often referred to as battle area clearance.
In some situations, clearing landmines is a necessary condition before other humanitarian programs can be implemented. A large-scale international effort has been made to test and evaluate existing and new technologies for humanitarian demining, notably by the EU, US, Canadian and Japanese governments and by the Mine Action Centres of affected countries.

Current humanitarian demining methods
The main methods used for humanitarian demining on land are: manual detection using metal detectors and prodders, detection by specially trained mine detection dogs, and mechanical clearance using armored vehicles fitted with flails, tiller or similar devices. There is an organization, APOPO, that is training African rats to detect landmines much as dogs do, offering a local solution to countries in Africa. In many circumstances, the only method that meets the United Nations' requirements for effective humanitarian demining, the International Mine Action Standards (IMAS), is manual detection and disarmament. The process is typically slow, expensive and dangerous, although demining can be safer than construction work if procedures are followed rigorously. New technologies may provide effective alternatives.

Manual detection with a metal detector
Metal detectors were first used, after their invention by the Polish officer Józef Kosacki. His invention known as Polish mine detector Allies used to clear the German mine fields during the Second Battle of El Alamein when 500 units were shipped to Field Marshal Montgomery.
The first step in manual demining is to scan the area with metal detectors, which are sensitive enough to pick up most mines but which also yield about one thousand false positives for every mine. Some mines, referred to as minimum metal mines, are constructed with as little metal as possible - as little as 1 gram (0.035 oz) - to make them difficult to detect. Mines with no metal at all have been produced, but are rare. Areas where metal is detected are carefully probed to determine if a mine is present; the probing must continue until the object that set off the metal detector is found.

Well-trained dogs can sniff out explosive chemicals like TNT in landmines, and are used in several countries.

Like dogs, Giant pouched rats are being trained to sniff out chemicals like TNT in landmines. These rats are currently working in minefields in Mozambique and are trained in Tanzania by APOPO. The rats are called HeroRATS.
These animals also have the advantage of being far lower mass than the typical human. They are less likely to set off small mines intended to injure or kill people, if the bomb-sniffing animal crosses directly over the top of a buried mine.

Mechanical clearance
Special machines effectively combine mine detection and removal into one operation. In the past, these machines were applied in both mine clearance and demining but are now generally used only for demining. They can be used to verify land that is not expected to be contaminated or as an extra layer of security after an area has been cleared by another method, such as dogs.
The machines consist of a special vehicle that is driven through the minefield, deliberately detonating the mines it drives over. These vehicles are designed to withstand the explosions with little damage. Some are operated directly with armour to protect the driver; some are operated under remote control.

a) Mine rollers and mine flails. The roller method originated during World War I and the flail method during World War II but both are still used. Neither system is completely reliable and both will leave undetonated mines, requiring the minefield to be rechecked by another method. Mine flail effectiveness can approach 100% in ideal conditions, but clearance rates as low as 50%-60% have been reported. This is well below the 99.6% standard set by the United Nations for humanitarian demining.

b) Mine plow - a device in front of a tank that excavates the ground, exposing any mines or turning them upside down, which significantly lessens their effects if they explode.

c) Modified long-armed demining bulldozers are being used in a number of countries. It has the capability to remove vegetation before demining and can withstand antipersonnel and antitank landmines. Its long arms give it the benefit of reducing damage to the main body, especially to the operator's cab. Three inch (9 cm) thick bulletproof glass protects the operator from directional mines.

Sunday, December 6, 2009

Ocean current

An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon the water, such as the wind, Coriolis force, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun. Depth contours, shoreline configurations and interaction with other currents influence a current's direction and strength.
Ocean currents can flow for thousands of kilometers, and together they create the great flow of the global conveyor belt which plays a dominant part in determining the climate of many of the Earth’s regions. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any other region at the same latitude. Another example is the Hawaiian Islands, where the climate is cooler (sub-tropical) than the tropical latitudes in which they are located, because of the effect of the California Current.

The tides' influence on current flow is much more difficult to analyse, and data is much more difficult to collect. A tidal height is a simple number which applies to a wide region simultaneously. A flow has both a magnitude and a direction, both of which can vary substantially with depth and over short distances due to local bathymetry. Also, although a water channel's center is the most useful measuring site, mariners object when current-measuring equipment obstructs waterways. A flow proceeding up a curved channel is the same flow, even though its direction varies continuously along the channel. Surprisingly, flood and ebb flows are often not in opposite directions. Flow direction is determined by the upstream channel's shape, not the downstream channel's shape. Likewise, eddies may form in only one flow direction.
Nevertheless, current analysis is similar to tidal analysis: in the simple case, at a given location the flood flow is in mostly one direction, and the ebb flow in another direction. Flood velocities are given positive sign, and ebb velocities negative sign. Analysis proceeds as though these are tide heights.
In more complex situations, the main ebb and flood flows do not dominate. Instead, the flow direction and magnitude trace an ellipse over a tidal cycle (on a polar plot) instead of along the ebb and flood lines. In this case, analysis might proceed along pairs of directions, with the primary and secondary directions at right angles. An alternative is to treat the tidal flows as complex numbers, as each value has both a magnitude and a direction.
Tide flow information is most commonly seen on nautical charts, presented as a table of flow speeds and bearings at hourly intervals, with separate tables for spring and neap tides. The timing is relative to high water at some harbour where the tidal behaviour is similar in pattern, though it may be far away.

Surface ocean currents are generally wind driven and develop their typical clockwise spirals in the northern hemisphere and counter-clockwise rotation in the southern hemisphere because of the imposed wind stresses. In wind driven currents, the Ekman spiral effect results in the currents flowing at an angle to the driving winds. The areas of surface ocean currents move somewhat with the seasons; this is most notable in equatorial currents.
Ocean basins generally have a non-symmetric surface current, in that the eastern equatorward-flowing branch is broad and diffuse whereas the western poleward-flowing branch is very narrow. These western boundary currents (of which the gulf stream is an example) are a consequence of basic fluid dynamics.
Deep ocean currents are driven by density and temperature gradients. Thermohaline circulation, also known as the ocean's conveyor belt, refers to the deep ocean density-driven ocean basin currents. These currents, which flow under the surface of the ocean and are thus hidden from immediate detection, are called submarine rivers. These are currently being researched by a fleet of underwater robots called Argo. Upwelling and downwelling areas in the oceans are areas where significant vertical movement of ocean water is observed.
Surface currents make up about 10% of all the water in the ocean. Surface currents are generally restricted to the upper 400 meters of the ocean. The movement of deep water in the ocean basins is by density driven forces and gravity. The density difference is a function of different temperatures and salinity. Deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.
Ocean currents are measured in Sverdrup with the symbol Sv, where 1 Sv is equivalent to a volume flow rate of 106 cubic meters per second.

Significance to people and sea life
Knowledge of surface ocean currents is essential in reducing costs of shipping, since they reduce fuel costs. In the sail-ship era knowledge was even more essential. A good example of this is the Agulhas current, which long prevented Portuguese sailors from reaching India. Even today, the round-the-world sailing competitors employ surface currents to their benefit.
Ocean currents are also very important in the dispersal of many life forms. A example is the life-cycle of the eel.
Ocean currents are important in the study of marine debris, and vice versa.
These currents also affect temperatures throughout the world. For example, the current that brings warm water up the north Atlantic to northwest Europe stops ice from forming by the shores, which would block ships from entering and exiting ports.

East Australian Current
The East Australian Current (EAC) is an ocean current that moves warm water in a counter clock-wise fashion down the east coast of Australia. It is the largest ocean current close to the shores of Australia. Its source is the tropical Coral Sea off the north-east coast of Australia. It can reach speeds of up to 7 knots in some of the shallower waters along the Australian continental shelf, but is generally measured at 2 or 3 knots. The EAC results in a current vortex in the Tasman Sea between Australia and New Zealand. The EAC also acts to transport tropical marine fauna to habitats in sub-tropical regions along the south east Australian coast.

Tuesday, December 1, 2009

Asphalt concrete

Asphalt concrete, normally known simply as asphalt or AC (in North America), is a composite material commonly used for construction of pavement, highways and parking lots. It consists of asphalt binder and mineral aggregate mixed together then laid down in layers and compacted.

Mixture formulations
Mixing of asphalt and aggregate is accomplished in one of several ways:
a) Hot mix asphalt concrete (commonly abbreviated as HMAC or HMA) is produced by heating the asphalt binder to decrease its viscosity, and drying the aggregate to remove moisture from it prior to mixing. Mixing is generally performed with the aggregate at about 300 °F (roughly 150 °C) for virgin asphalt and 330 °F (166 °C) for polymer modified asphalt, and the asphalt cement at 200 °F (95 °C). Paving and compaction must be performed while the asphalt is sufficiently hot. In many countries paving is restricted to summer months because in winter the compacted base will cool the asphalt too much before it is packed to the optimal air content. HMAC is the form of asphalt concrete most commonly used on highly trafficked pavements such as those on major highways, racetracks and airfields.

b) Warm mix asphalt concrete (commonly abbreviated as WMA or WAM) is produced by adding either zeolites, waxes, or asphalt emulsions to the mix. This allows significantly lower mixing and laying temperatures and results in lower consumption of fossil fuels, thus releasing less carbon dioxide, aerosols and vapours. Not only are working conditions improved, but the lower laying-temperature also leads to more rapid availability of the surface for use, which is important for construction sites with critical time schedules. The usage of these additives in hot mixed asphalt (above) may afford easier compaction and allow cold weather paving or longer hauls.

c) Cold mix asphalt concrete is produced by emulsifying the asphalt in water with (essentially) soap prior to mixing with the aggregate. While in its emulsified state the asphalt is less viscous and the mixture is easy to work and compact. The emulsion will break after enough water evaporates and the cold mix will, ideally, take on the properties of cold HMAC. Cold mix is commonly used as a patching material and on lesser trafficked service roads.

d) Cut-back asphalt concrete is produced by dissolving the binder in kerosene or another lighter fraction of petroleum prior to mixing with the aggregate. While in its dissolved state the asphalt is less viscous and the mix is easy to work and compact. After the mix is laid down the lighter fraction evaporates.

e) Mastic asphalt concrete or sheet asphalt is produced by heating hard grade blown bitumen (oxidation) in a green cooker (mixer) until it has become a viscous liquid after which the aggregate mix is then added.

The bitumen aggregate mixture is cooked (matured) for around 6-8 hours and once it is ready the mastic asphalt mixer is transported to the work site where experienced layers empty the mixer and either machine or hand lay the mastic asphalt contents on to the road. Mastic asphalt concrete is generally laid to a thickness of around 3⁄4–1 3⁄16 inches (20-30 mm) for footpath and road applications and around 3⁄8 of an inch (10 mm) for flooring or roof applications.
In addition to the asphalt and aggregate, additives, such as
polymers, and antistripping agents may be added to improve the properties of the final product.

f) Natural asphalt concrete can be found in some parts of the world where rock near the surface has been impregnated with upwelling asphalt.

The terms asphalt concrete, bituminous asphalt concrete, etc., are typically used only in engineering jargon. Asphalt pavements are often called just asphalt by laypersons who tend to associate the term concrete with Portland cement concrete only. The engineering definition of concrete is any composite material composed of mineral aggregate glued together with a binder, whether that binder is Portland cement, asphalt or even epoxy. Informally, asphalt concrete is also referred to as blacktop.
Asphalt concrete is often touted as being 100% recyclable. Several in-place recycling techniques have been developed to rejuvenate oxidized binders and remove cracking, although the recycled material is generally not very water-tight or smooth and should be overlaid with a new layer of asphalt concrete. Asphalt concrete that is removed from a pavement is usually stockpiled for later use as a base course material. This reclaimed material, commonly known by the acronym 'RAP' for recycled or reclaimed asphalt pavement, is crushed to a consistent gradation and added to the HMA mixing process. Very little asphalt concrete is actually disposed of in landfills. Sometimes waste materials, such as rubber from old tires, are added to asphalt concrete as is the case with rubberized asphalt, but there is a concern that the hybrid material may not be recyclable.

Asphalt deterioration can include alligator cracks, potholes, upheaval, raveling, rutting, shoving, stripping, and grade depressions.

Asphalt concrete pavements—especially those at airfields—are sometimes called tarmac for historical reasons, although they do not contain tar and are not constructed using the macadam process.

Performance characteristics
Asphalt concrete has different performance characteristics in terms of surface durability, tire wear, braking efficiency and roadway noise. The appropriate asphalt performance characteristic is obtained by the traffic level amount in categories A,B,C,D,E, and friction coarse (FC-5). Asphalt concrete generates less roadway noise than Portland cement concrete surfacing, and is typically less noisy than chip seal surfaces. Tire noise effects are amplified at higher operating speeds. The sound energy is generated through rolling friction converting kinetic energy to sound waves. The idea that highway design could be influenced by acoustical engineering considerations including selection of surface paving types arose in the very early 1970s.
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