Sunday, February 21, 2010

Solid-fuel rocket

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 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

Thursday, February 18, 2010

Langkawi Geopark

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.

Sunday, February 14, 2010

Abu Rayhan Biruni

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 geographer and traveler, a geodesist and geologist, a mathematician, a pharmacist 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.

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 exact 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."

Sunday, February 7, 2010

Stockholm syndrome

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.

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.

Monday, February 1, 2010

Metamorphic rock

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 recrystallization. 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.

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
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