Tuesday, September 29, 2009

Narcolepsy

Narcolepsy is chronic sleep disorder, or dyssomnia. The condition is characterized by excessive daytime sleepiness (EDS) in which a person experiences extreme fatigue and possibly falls asleep at inappropriate times, such as while at work or at school. A narcoleptic will most probably experience disturbed nocturnal sleep and also abnormal daytime sleep pattern, which is often confused with insomnia. When a person with narcolepsy falls asleep or goes to bed they will generally experience the REM stage of sleep (rapid eye movement/dreaming state), within 10 minutes; whereas for most people, this shouldn't occur until generally 30 minutes of slumber. Cataplexy, a sudden muscular weakness brought on by strong emotions (though many people experience cataplexy without having a emotional trigger, is known to be one of the other problems that some narcoleptics will experience. Often manifesting as muscular weaknesses ranging from a barely perceptible slackening of the facial muscles to the dropping of the jaw or head, weakness at the knees, or a total collapse. Usually only speech is slurred, vision is impaired (double vision, inability to focus), but hearing and awareness remain normal. In some rare cases, an individual's body becomes paralyzed and muscles will become stiff.
The term narcolepsy derives from the French word narcolepsie created by the French physician Jean-Baptiste-Édouard Gélineau by combining the Greek narke numbness, stupor and lepsis attack, seizure.

Causes
Although the cause of narcolepsy was not determined for many years after its discovery, scientists had discovered conditions that seemed to be associated with an increase in an individual's risk of having the disorder. Specifically, there appeared to be a strong link between narcoleptic individuals and certain genetic conditions. One factor that seemed to predispose an individual to narcolepsy involved an area of Chromosome 6 known as the HLA complex. There appeared to be a correlation between narcoleptic individuals and certain variations in HLA genes, although it was not required for the condition to occur. Certain variations in the HLA complex were thought to increase the risk of an auto-immune response to protein-producing neurons in the brain. The protein produced, called hypocretin or orexin, is responsible for controlling appetite and sleep patterns. Individuals with narcolepsy often have reduced numbers of these protein-producing neurons in their brains. In 2009 the autoimmune hypothesis was supported by research carried out at Stanford University School of Medicine.
The neural control of normal sleep states and the relationship to narcolepsy are only partially understood. In humans, narcoleptic sleep is characterized by a tendency to go abruptly from a waking state to REM sleep with little or no intervening non-REM sleep. The changes in the motor and proprioceptive systems during REM sleep have been studied in both human and animal models. During normal REM sleep, spinal and brainstem alpha motor neuron depolarization produces almost complete atonia of skeletal muscles via an inhibitory descending reticulospinal pathway. Acetylcholine may be one of the neurotransmitters involved in this pathway. In narcolepsy, the reflex inhibition of the motor system seen in cataplexy is believed identical to that seen in normal REM sleep.
In 2004 researchers in Australia induced narcolepsy-like symptoms in mice by injecting them with antibodies from narcoleptic humans. The research has been published in the Lancet providing strong evidence suggesting that some cases of narcolepsy might be caused by autoimmune disease. Narcolepsy is strongly associated with HLA-DQB1*0602 genotype. There is also an association with HLA-DR2 and HLA-DQ1. This may represent linkage disequilibrium. Despite the experimental evidence in human narcolepsy that there may be an inherited basis for at least some forms of narcolepsy, the mode of inheritance remains unknown. Some cases are associated with genetic diseases such as Niemann-Pick disease or Prader-Willi syndrome.
Diagnosis
Diagnosis is relatively easy when all the symptoms of narcolepsy are present, but if the sleep attacks are isolated and cataplexy is mild or absent, diagnosis is more difficult. It is also possible for cataplexy to occur in isolation. Two tests that are commonly used in diagnosing narcolepsy are the polysomnogram and the multiple sleep latency test (MSLT). These tests are usually performed by a sleep specialist. The polysomnogram involves continuous recording of sleep brain waves and a number of nerve and muscle functions during nighttime sleep. When tested, people with narcolepsy fall asleep rapidly, enter REM sleep early, and may awaken often during the night. The polysomnogram also helps to detect other possible sleep disorders that could cause daytime sleepiness.
For the multiple sleep latency test, a person is given a chance to sleep every 2 hours during normal wake times. Observations are made of the time taken to reach various stages of sleep (sleep onset latency). This test measures the degree of daytime sleepiness and also detects how soon REM sleep begins. Again, people with narcolepsy fall asleep rapidly and enter REM sleep early.

Treatment
Treatment is tailored to the individual, based on symptoms and therapeutic response. The time required to achieve optimal control of symptoms is highly variable, and may take several months or longer. Medication adjustments are also frequently necessary, and complete control of symptoms is seldom possible. While oral medications are the mainstay of formal narcolepsy treatment, lifestyle changes are also important.
The main treatment of excessive daytime sleepiness in narcolepsy is with a group of drugs called central nervous system stimulants such as methylphenidate, racemic - amphetamine, dextroamphetamine, and methamphetamine, or modafinil, a new stimulant with a different pharmacologic mechanism. In Fall 2007 an alert for severe adverse skin reactions to modafinil was issued by the FDA. Other medications used are codeine and selegiline. Another drug that is used is atomoxetine (Strattera), a non-stimulant and Norepinephrine reuptake inhibitor (NRI), that has little or no abuse potential. In many cases, planned regular short naps can reduce the need for pharmacological treatment of the EDS to a low or non-existent level.
Cataplexy and other REM-sleep symptoms are frequently treated with tricyclic antidepressants such as clomipramine, imipramine, or protriptyline, as well as other drugs that suppress REM sleep. Venlafaxine, a newer antidepressant which blocks the reuptake of serotonin and norepinephrine, has shown usefulness in managing symptoms of cataplexy. Gamma-hydroxybutyrate (GHB), a medication recently approved by the FDA, is the only medication specifically indicated for cataplexy. Gamma-hydroxybutyrate has also been shown to reduce symptoms of EDS associated with narcolepsy. While the exact mechanism of action is unknown, GHB is thought to improve the quality of nocturnal sleep.
In addition to drug therapy, an important part of treatment is scheduling short naps (10 to 15 minutes) two to three times per day to help control excessive daytime sleepiness and help the person stay as alert as possible. Daytime naps are not a replacement for nighttime sleep. Ongoing communication between the health care provider, patient, and the patient's family members is important for optimal management of narcolepsy. Finally, a recent study reported that transplantation of hypocretin neurons into the pontine reticular formation in rats is feasible, indicating the development of alternative therapeutic strategies in addition to pharmacological interventions.

Saturday, September 26, 2009

Fjord

Geologically, a fjord (pronounced /fjɔrd/ ( listen) or pronounced /fiːɔrd/) is a long, narrow inlet with steep sides, created in a valley carved by glacial activity.

Formation
Fjords are formed when a glacier cuts a U-shaped valley by abrasion of the surrounding bedrock. Many such valleys were formed during the recent ice age. Glacial melting is accompanied by rebound of Earth's crust as the ice load and eroded sediment is removed (also called isostasy or glacial rebound). In some cases this rebound is faster than sea level rise. Most fjords are deeper than the adjacent sea; Sognefjord, Norway, reaches as much as 1,300 m (4,265 ft) below sea level. Fjords generally have a sill or rise at their mouth caused by the previous glacier's terminal moraine, in many cases causing extreme currents and large saltwater rapids (see skookumchuck). Saltstraumen in Norway is often described as the worlds strongest tidal current. These characteristics distinguish fjords from rias (e.g. the Bay of Kotor), which are drowned valleys flooded by the rising sea.

Fjord features and variations
Coral reefs
As late as 2000, some of the world's largest coral reefs were discovered along the bottoms of the Norwegian fjords. These reefs were found in fjords from the north of Norway to the south. The marine life on the reefs is believed to be one of the most important reasons why the Norwegian coastline is such a generous fishing ground. Since this discovery is fairly new, little research has been done. The reefs are host to thousands of lifeforms such as plankton, coral, anemones, fish, several species of sharks, and many more. Most are specially adapted to life under the greater pressure of the water column above it, and the total darkness of the deep sea.
New Zealand's fjords are also host to deep sea corals, but a surface layer of dark fresh water allows these corals to grow in much shallower water than usual. An underwater observatory in Milford Sound allows tourists to view them without diving.

Skerries
In some places near the seaward margins of areas with fjords, the ice-scoured channels are so numerous and varied in direction that the rocky coast is divided into thousands of island blocks, some large and mountainous while others are merely rocky points or rock reefs, menacing navigation. These are called skerries. The term skerry is derived from the Old Norse sker, which means a rock in the sea.
Skerries are most commonly formed at the outlet of fjords where submerged glacially formed valleys perpendicular to the coast join with other cross valleys in a complex array. The island fringe of Norway is such a group of skerries (called a skjærgård); many of the cross fjords are so arranged that they parallel the coast and provide a protected channel behind an almost unbroken succession of mountainous islands and skerries. By this channel one can travel through a protected passage almost the entire 1,601 km (995 mi) route from Stavanger to North Cape, Norway. The Blindleia is a skerry-protected waterway that starts near Kristiansand in southern Norway, and continues past Lillesand. The Swedish coast along Bohuslän is likewise skerry guarded. The Inside Passage provides a similar route from Seattle, Washington and Vancouver, British Columbia to Skagway, Alaska. Yet another such skerry protected passage extends from the Straits of Magellan north for 800 km (500 mi).
Freshwater fjords
Some Norwegian freshwater lakes which have formed in long glacially carved valleys with terminal moraines blocking the outlet follow the Norwegian naming convention; they are named fjords. Outside of Norway, the three western arms of New Zealand's Lake Te Anau are named North Fiord, Middle Fiord and South Fiord. Another freshwater "fjord" in a larger lake is Baie Fine, located on the northeastern coast of Georgian Bay of Lake Huron in Ontario. Western Brook Pond, in Newfoundland's Gros Morne National Park, is also often described as a fjord, but is actually a freshwater lake cut off from the sea, so is not a fjord in the English sense of the term. Such lakes are sometimes called "fjord lakes". Okanagan Lake was the first North American lake to be so described, in 1962. The bedrock there has been eroded up to 650 m (2,133 ft) below sea level, which is 2,000 m (6,562 ft) below the surrounding regional topography. Fjord lakes are common on the inland lea of the Coast Mountains and Cascade Range; notable ones include Lake Chelan, Seton Lake, Chilko Lake, and Atlin Lake. Kootenay Lake, Slocan Lake and others in the basin of the Columbia River are also fjord-like in nature, and created by glaciation in the same way. Along the British Columbia Coast, a notable fjord-lake is Owikeno Lake, which is a freshwater extension of Rivers Inlet. Another area notable for fjord lakes is northern Italy and southern Switzerland - Lake Como and its neighbours.

Locations
The principal mountainous regions where fjords have formed are in the higher middle latitudes and the high latitudes reaching to 80°N (Svalbard, Greenland), where, during the glacial period, many valley glaciers descended to the then-lower sea level. The fjords develop best in mountain ranges against which the prevailing westerly marine winds are orographically lifted over the mountainous regions, resulting in abundant snowfall to feed the glaciers. Hence coasts having the most pronounced fjords include the west coast of Europe, the west coast of North America from Puget Sound to Alaska, the west coast of New Zealand, and the west coast of South America and to south-western Tasmania. In Tasmania there are many small Fjords with mountains surrounding reaching 1000 m in southern districts, though these are not glaciated they are often covered in snow, sometimes in summer. These fjords have formed by past glaciers ripping through to the sea.
Extreme fjords
The longest fjords in the world are:
Scoresby Sund in Greenland - 350 km (217 mi)
Sognefjord in Norway - 203 km (126 mi)
Limfjorden in Denmark - 180 km (112 mi)
Hardangerfjord in Norway - 179 km (111 mi)

Deep fjords include:
Skelton Inlet in Antarctica - 1,933 m (6,342 ft)
Sognefjord in Norway - 1,308 m (4,291 ft) (the mountains then rise to up to 1,000 m (3,281 ft))
Messier Channel in Chile - 1,288 m (4,226 ft)
Even deeper is the Vanderford Valley (2,287 m (7,503 ft)), carved by Antarctica's Vanderford Glacier. This undersea valley lies offshore, however, and so is not a fjord.

Sunday, September 13, 2009

Aircraft Ice protection system

Ice protection systems are designed to keep atmospheric ice from accumulating on aircraft flight surfaces while in flight. The effects of ice accretion on an aircraft can cause loss of control, resulting in a catastrophic flight event.

Types of ice protection systems
a) Pneumatic deicing boots

b) Thermal
i. Turbine engine bleed air
ii. Electrical heating elements

c) Electro-mechanical
i. Weeping Wing
ii. Electro-Mechanical Expulsion Deicing System (EMEDS)
iii. Hybrid Electro-Mechanical Expulsion Deicing System

The pneumatic boot is a rubber device attached to a wing's leading edge, invented by the Goodrich Corporation (previously known as B.F. Goodrich) in 1923. Portions of the boot are inflated to break ice off the boot, de-icing the wing. Rubber boots are used on jets and propeller driven aircraft.
A bleed air system is used by jet aircraft to keep flight surfaces above the freezing temperature required for ice to accumulate (called anti-icing). The hot air is "bled" off the jet engine into tubes routed through wings, tail surfaces, and engine inlets.
Electrical thermal systems use electricity to heat the protected surface. The electric heaters are usually flexible enough to use as anti-icers or de-icers. As a de-icer, the heater melts the ice, the ice no longer sticks to the surface due to aerodynamic forces. As an anti-icer, the heater keeps the surface to the point that the ice does not form.
Electro-mechanical Expulsion Deicing Systems use a mechanical force to knock the ice off the flight surface. Typically, actuators are installed underneath the skin of the structure. The actuator is moved to induce a shock wave in the protected surface to dislodge the ice.
Hybrid Electro-Mechanical Expulsion Deicing Systems combine an EMEDS de-icer with an electrical heating element anti-icer. The heater prevents ice accumulation on the leading edge of the airfoil and the actuators of the EMED system remove ice that accumulates aft of the heated portion of the airfoil.
A weeping wing system uses a liquid (such as ethylene glycol) to coat the surface and prevent ice from accumulating.

Airframe icing
Ice accumulates on the leading edge of wings, tailplanes, and vertical stabilizers as an aircraft flies through a cloud containing super-cooled water droplets. Super-cooled water is water that is below freezing, but still a liquid. Normally, this water would turn to ice at 32 F, but there are no "contaminants" (droplet nuclei) on which the drops can freeze. When the airplane flies through the super-cooled water droplets, the plane becomes the droplet nucleus, allowing the water to freeze on the surface. This process is known as accretion.
A popular misconception is that aircraft icing events result from the weight of accreted ice on the airframe. This is not the case. Rather, airframe icing causes problems by modifying the airflow over flight surfaces upon which the ice accretes. When ice accretes on aerodynamic lift surfaces, such as the wing and tailplane, the modification of airflow changes the aerodynamics of the surfaces by modifying both their shape and their surface roughness, typically increasing their drag and decreasing their lift. The particular effect of icing on the aerodynamics of a lift surface is a complicated function of the ice shape and location as well as of the amount of ice. These characteristics in turn depend in a complicated fashion on atmospheric conditions such as the amount, temperature, and droplet size of water in the air. The composite effect of this aerodynamic deterioration over all lift surfaces is a degradation of aircraft flight dynamics. In severe atmospheric conditions, dangerous levels of icing can be obtained in as little as 5 minutes. Small to moderate amounts of icing generally cause a reduction in aircraft performance in terms of climb rates, range, endurance, and maximum speed and acceleration. Icing effects of this type are known as performance events. As icing increases, separation of air flow from the flight surfaces can cause loss of pilot control and even wildly unstable behaviour. These more severe icing events, known as handling events, are often precipitated by a change in the aircraft configuration or an aircraft maneuver effected by a pilot unaware of the flight-dynamics degradation. This was the case with American Eagle Flight 4184 where the aircraft experienced an uncontrolled roll of 120 degrees in five seconds after the pilot initiated a flap retraction. Handling events generally can be classified into either tailplane stall, where the aircraft pitches forward, or asymmetric wing effects causing a roll upset (or roll snatch) as in the American Eagle Flight 4184 accident.

Rotary-surface icing
Ice can also accumulate on helicopter rotor blades and aircraft propellers. The accretion causes weight and aerodynamic imbalances that are amplified due to the rapid rotation of the propeller or rotor.

Engine-inlet icing
Ice accreting on the leading edge (lip) of engine inlets causes flow problems and can lead to ice ingestion. In turbofan engines, laminar airflow is required at the face of the fan. Because of this, most engine ice protection systems are anti-ice systems (prevent build up).

Thursday, September 10, 2009

JR–Maglev

JR-Maglev is a magnetic levitation train system developed by the Central Japan Railway Company and Railway Technical Research Institute (association of Japan Railways Group). JR-Maglev MLX01 (X means experimental) is one of the latest designs of a series of Maglev trains in development in Japan since the 1970s. It is composed of a maximum five cars to run on the Yamanashi Maglev Test Line. On December 2, 2003, a three-car train set attained a maximum speed of 581 km/h (361 mph) (world speed record for railed vehicles) in a manned vehicle run.

Fundamental technology elements
The term "maglev" refers not only to the vehicles, but to the railway system as well, specifically designed for magnetic levitation and propulsion. All operational implementations of maglev technology have had minimal overlap with wheeled train technology and have not been compatible with conventional rail tracks. Because they cannot share existing infrastructure, these maglev systems must be designed as complete transportation systems. The Applied Levitation SPM Maglev system is inter-operable with steel rail tracks and would permit maglev vehicles and conventional trains to operate at the same time on the same right of way.
There are three primary types of maglev technology:
1) For electromagnetic suspension (EMS), electromagnets in the train repel it away from a magnetically conductive (usually steel) track.
2) electrodynamic suspension (EDS) uses electromagnets on both track and train to push the train away from the rail.
3) stabilized permanent magnet suspension (SPM) uses opposing arrays of permanent magnets to levitate the train above the rail.

Another experimental technology, which was designed, proven mathematically, peer reviewed, and patented, but is yet to be built, is the magnetodynamic suspension (MDS), which uses the attractive magnetic force of a permanent magnet array near a steel track to lift the train and hold it in place.

Commercial operation
The first commercial Maglev "people-mover" was officially opened in 1984 in Birmingham, England. It operated on an elevated 600-metre (2,000 ft) section of monorail track between Birmingham International Airport and Birmingham International railway station. It ran at 42 km/h (26 mph) until the system was eventually closed in 1995 due to reliability and design problems.
The best-known high-speed maglev currently operating commercially is the IOS (initial operating segment) demonstration line of the German-built Transrapid train in Shanghai, China that transports people 30 km (18.6 miles) to the airport in just 7 minutes 20 seconds, achieving a top speed of 431 km/h (268 mph), averaging 250 km/h (150 mph).
Other commercially operating lines exist in Japan, such as the Linimo line. Maglev projects worldwide are being studied for feasibility. In Japan at the Yamanashi test track, current maglev train technology is mature, but costs and problems remain a barrier to development. Alternative technologies are being developed to address those issues.

Levitation
The JR-Maglev levitation train uses an Electro-dynamic Suspension (EDS) system. Moving magnetic fields create a reactive force in a conductor because of the magnetic field induction effect. This force holds up the train. The maglev-trains have superconducting magnetic coils, and the guide ways contain levitation coils.
When the trains run at high speed, levitation coils on the guide way produce reactive forces in response to the approach of the superconducting magnetic coils onboard the trains.
EDS has the advantage of larger gaps than EMS, but EDS needs support wheels which are employed in low speed running, because EDS can't produce a large levitation force at low(er) speeds (150km/h or less in JR-Maglev). However, once the train reaches a certain speed, the wheels will actually retract so that the train is floating.

Guide
Levitation coils which are located on the guide way generate guiding and stabilizing forces also.

Driving
JR-Maglev is driven by a Linear Synchronous Motor (LSM) System. This system is needed to supply power to the coils at the guide way.

Evacuated tubes
Some systems (notably the swissmetro system) propose the use of vactrains — evacuated (airless) tubes used in tandem with maglev technology to minimize air drag. This has the potential to increase speed and efficiency greatly, as most of the energy for conventional Maglev trains is lost in air drag.
One potential risk for passengers of trains operating in evacuated tubes is that they could be exposed to the risk of cabin depressurization and asphyxiation unless tunnel safety monitoring systems can repressurize the tube in the event of a train malfunction or accident.

Yamanashi Test Track
Yamanashi Experiment Lines are facilities that currently have a practical use. It includes about 18.4 km of track (including 16.0 km of tunnels).

JR-Maglev, Japan
Japan has a demonstration line in Yamanashi prefecture where test trains JR-Maglev MLX01 have reached 581 kilometres per hour (361 mph), slightly faster than any wheeled trains (the current TGV speed record is 574.8 kilometres per hour (357.2 mph)). A documentary video about the Japanese maglev can be viewed here.
These trains use superconducting magnets which allow for a larger gap, and repulsive-type electrodynamic suspension (EDS). In comparison Transrapid uses conventional electromagnets and attractive-type electromagnetic suspension (EMS). These "Superconducting Maglev Shinkansen", developed by the Central Japan Railway Company (JR Central) and Kawasaki Heavy Industries, are currently the fastest trains in the world, achieving a record speed of 581 kilometres per hour (361 mph) on December 2, 2003. Yamanashi Prefecture residents (and government officials) can sign up to ride this for free, and some 100,000 have done so already.

Friday, September 4, 2009

Islamic architecture

Islamic architecture encompasses a wide range of both secular and religious styles from the foundation of Islam to the present day, influencing the design and construction of buildings and structures in Islamic culture. the building show the wealth of the person that lives in it. The principal Islamic architectural types are: the Mosque, the Tomb, the Palace and the Fort. From these four types, the vocabulary of Islamic architecture is derived and used for buildings of lesser importance such as public baths, fountains and domestic architecture.

History
In 630C.E. the Islamic prophet Muhammad's army reconquered the city of Mecca from the Banu Quraish tribe. The Kaaba sanctuary was rebuilt and re-dedicated to Islam, the reconstruction being carried out before Muhammad's death in 632C.E. by a shipwrecked Abyssinian carpenter in his native style. This sanctuary was amongst the first major works of Islamic architecture. Later doctrines of Islam dating from the eighth century and originating from the Hadith, forbade the use of humans and animals in architectural design, in order to obey God's command (and thou shalt not make for thyself an image or idol of God) and also (thou shalt have no god before me) from the ten commandments and similar Islamic teachings. For Jews and Muslims veneration violates these commandments. They read these commandments as prohibiting the use of idols and images during worship in any way.
In the 7th century, Muslim armies conquered a huge expanse of land. Once the Muslims had taken control of a region, their first need was for somewhere to worship - a mosque. The simple layout provided elements that were to be incorporated into all mosques and the early Muslims put up simple buildings based on the model of Muhammad's house or adapted existing buildings for their own use.
Recent discoveries have shown that quasicrystal patterns were first employed in the girih tiles found in medieval Islamic architecture dating back over five centuries. In 1998, Professor Peter Lu of Harvard University and Professor Paul Steinhardt of Princeton University published a paper in the journal Science suggesting that girih tilings possessed properties consistent with self-similar fractal quasicrystalline tilings such as the Penrose tilings, predating them by five centuries.

Influences and styles
A specifically recognisable Islamic architectural style emerged soon after Muhammad's time, developing from localized adaptations of Egyptian, Byzantine, and Persian/Sassanid models. An early example may be identified as early as 691 AD with the completion of the Dome of the Rock (Qubbat al-Sakhrah) in Jerusalem. It featured interior vaulted spaces, a circular dome, and the use of stylized repeating decorative patterns (arabesque).
The Great Mosque of Samarra in Iraq, completed in 847 AD, combined the hypostyle architecture of rows of columns supporting a flat base above which a huge spiraling minaret was constructed.
The Hagia Sophia in Istanbul also influenced Islamic architecture. When the Ottomans captured the city from the Byzantines, they converted the basilica to a mosque (now a museum) and incorporated Byzantine architectural elements into their own work (e.g. domes). The Hagia Sophia also served as a model for many Ottoman mosques such as the Shehzade Mosque, the Suleiman Mosque, and the Rüstem Pasha Mosque.
Distinguishing motifs of Islamic architecture have always been ordered repetition, radiating structures, and rhythmic, metric patterns. In this respect, fractal geometry has been a key utility, especially for mosques and palaces. Other significant features employed as motifs include columns, piers and arches, organized and interwoven with alternating sequences of niches and colonnettes. The role of domes in Islamic architecture has been considerable. Its usage spans centuries, first appearing in 691 with the construction of the Dome of the Rock, and recurring even up until the 17th century with the Taj Mahal. As late as the 19th century, Islamic domes had been incorporated into Western architecture.

Elements of Islamic style
Islamic architecture may be identified with the following design elements, which were inherited from the first mosque built byr hall (originally a feature of the Masjid al-Nabawi).
1. Minarets or towers (these were originally used as torch-lit watchtowers, as seen in the Great Mosque of Damascus; hence the derivation of the word from the Arabic nur, meaning "light").
2. A four-iwan plan, with three subordinate halls and one principal one that faces toward Mecca
3. Mihrab or prayer niche on an inside wall indicating the direction to Mecca.
4. Domes and Cupolas.
5. Iwans to intermediate between different pavilions.
6. The use of geometric shapes and repetitive art (arabesque).
7. The use of muqarnas, a unique Arabic/Islamic space-enclosing system, for the decoration of domes, minarets and portals. Used at the Alhambra.(Compare mocárabe.) Modern muqarnas designs
8. The use of decorative Islamic calligraphy instead of pictures which were haram (forbidden) in mosque architecture.
9. Central fountains used for ablutions (once used as a wudu area for Muslims).
10. The use of bright color, if the style is Persian or Indian (Mughal); paler sandstone and grey stones are preferred among Arab buildings. Compare the Registan complex of Uzbekistan to the Al-Azhar University of Cairo.
11. Focus both on the interior space of a building and the exterior

Differences between Islamic architecture and Persian architecture
Like this of other nations that became part of the Islamic realm, Persian Architecture is not to be confused with Islamic Architecture and refers broadly to architectural styles across the Islamic world. Islamic architecture, therefore, does not directly include reference to Persian styles prior to the rise of Islam. Persian architecture, like other nations', predates Islamic architecture and can be correctly understood as an important influence on overall Islamic architecture as well as a branch of Islamic architecture since the introduction of Islam in Persia. Islamic architecture can be classified according to chronology, geography, and building typology.

Tuesday, September 1, 2009

Hypothermia

Hypothermia (from Greek ὑποθερμία) is a condition in which an organism's temperature drops below that required for normal metabolism and body functions. In warm-blooded animals, core body temperature is maintained near a constant level through biologic homeostasis. However, when the body is exposed to cold, its internal mechanisms may be unable to replenish the heat that is being lost to the organism's surroundings.
Hypothermia is the opposite of hyperthermia, the condition that causes heat exhaustion and heat stroke.

Symptoms
Normal body temperature in humans is 36.6–37.0 °C (97.9–98.6 °F). Hypothermia can be divided into three stages of severity.

Stage 1
Body temperature drops by 1–2 °C (1.8–3.6 °F) below normal temperature (35–37 °C or 95–98.6 °F. Mild to strong shivering occurs. The victim is unable to perform complex tasks with the hands; the hands become numb. Blood vessels in the outer extremities constrict, lessening heat loss to the outside air. Breathing becomes quick and shallow. Goose bumps form, raising body hair on end in an attempt to create an insulating layer of air around the body (which is of limited use in humans due to lack of sufficient hair, but useful in other species). Victim may feel sick to their stomach, and very tired. Often, a person will experience a warm sensation, as if they have recovered, but they are in fact heading into Stage 2. Another test to see if the person is entering stage 2 is if they are unable to touch their thumb with their little finger; this is the first stage of muscles not working. They might start to have trouble seeing.

Stage 2
Body temperature drops by 2–4 °C (3.8–7.6 °F) below normal temperature (33–35 °C or 91–94.8 °F). Shivering becomes more violent. Muscle mis-coordination becomes apparent. Movements are slow and labored, accompanied by a stumbling pace and mild confusion, although the victim may appear alert. Surface blood vessels contract further as the body focuses its remaining resources on keeping the vital organs warm. The victim becomes pale. Lips, ears, fingers and toes may become blue.

Stage 3
Body temperature drops below approximately 32 °C (89.6 °F). Shivering usually stops. Difficulty speaking, sluggish thinking, and amnesia start to appear; inability to use hands and stumbling is also usually present. Cellular metabolic processes shut down. Below 30 °C (86.0 °F), the exposed skin becomes blue and puffy, muscle coordination becomes very poor, walking becomes almost impossible, and the victim exhibits incoherent/irrational behavior including terminal burrowing or even a stupor. Pulse and respiration rates decrease significantly, but fast heart rates (ventricular tachycardia, atrial fibrillation) can occur. Major organs fail. Clinical death occurs. Because of decreased cellular activity in stage 3 hypothermia, the body will actually take longer to undergo brain death.

Immersion hypothermia
Hypothermia of both the extremities and body core continues to be a major limitation to diving in cold water. Cooling in the extremities is often the limitation to operations. The limitation of finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries.
For divers breathing heliox below 100 meters wearing hot water suits, the inspired gas must be heated, or the symptoms of hypothermia can set in without the divers realizing it.
Other predisposing factors leading to immersion hypothermia include dehydration, inadequate rewarming with repetitive operations, starting operations while wearing cold, wet dry suit undergarments, sweating with work, inadequate thermal insulation (for example, thin dry suit undergarment), lack of heated breathing gas with deep heliox diving, and poor physical conditioning.
Moderate and severe cases of hypothermia require immediate hospitalization. In a hospital, external treatments, such as heated blankets are used to warm patients with mild hypothermia, as well as internal treatments such as injected warm fluids. For severe cases of hypothermia, patients may undergo lavage (washing) of the bladder, stomach, chest and abdominal cavities with warmed fluids. These patients are at high risk for arrhythmias (irregular heartbeats), and care must be taken to minimize jostling and other disturbances until they have been sufficiently warmed, as these arrhythmias are very difficult to treat while the victim is still cold.
An important tenet of treatment is that a person cannot be considered dead until he/she has been adequately warmed. Remarkable accounts of recovery after prolonged cardiac arrest have been reported in patients with hypothermia, such as children who have been submerged in cold water for more than 15 minutes (called mini-hibernation). It is presumed that this is because the low temperature prevents some of the cellular damage that occurs when blood flow and oxygen are lost for an extended period of time.

Prevention
Appropriate clothing helps to prevent hypothermia. Wearing cotton in chilly weather is a particular hypothermia risk as it retains water, and water quickly conducts heat away from the body. Even in dry weather, cotton clothing can become damp from perspiration, and chilly after the wearer stops exercising. Synthetic and wool fabrics provide far better insulation when wet and dry more quickly. Some synthetic fabrics are even designed to wick perspiration away from the body, such as liner socks.
Heat loss on land is very difficult to predict due to multiple variables such as clothing type and quantity, amount of insulating fat on the victim, environmental humidity or personal dampness such as after exertion, the circumstances surrounding the hypothermic episode, and so on. Heat is lost much faster in water, hence the need for wetsuits or drysuits in cold-weather activities such as kayaking. Water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia very quickly. For example, a water temperature of 10 °C (50 °F) can be expected to lead to death in approximately 1 hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. On the other end of the scale, in water even a temperature as high as 26 °C (80 °F) may eventually (after many hours) lead to mild hypothermia.
Alcohol consumption prior to cold exposure may increase one's risk of becoming hypothermic. Alcohol acts as a vasodilator, increasing blood flow to the body's extremities, thereby increasing heat loss. Ironically, this may cause the victim to feel warm while rapidly losing heat to the surrounding environment.
The United States Coast Guard promotes using life vests as a method of protection against hypothermia through the 50/50/50 rule: If someone is in 50 °F water for 50 minutes, he/she has a 50 percent better chance of survival if wearing a life jacket.
 
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