Econstudentlog

Wikipedia articles of interest

i. Scattered disc (featured).

“The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units (4.5×109 km; 2.8×109 mi). These extreme orbits are believed to be the result of gravitational “scattering” by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune. While the nearest distance to the Sun approached by scattered objects is about 30–35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects “among the most distant and cold objects in the Solar System”.[1] The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt,[2] but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the belt proper.[a]

Because of its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets observed in the Solar System, with the centaurs, a population of icy bodies between Jupiter and Neptune, being the intermediate stage in an object’s migration from the disc to the inner Solar System.[4] Eventually, perturbations from the giant planets send such objects towards the Sun, transforming them into periodic comets. Many Oort-cloud objects are also believed to have originated in the scattered disc. […]

The Kuiper belt is a relatively thick torus (or “doughnut”) of space, extending from about 30 to 50 AU[18] comprising two main populations of Kuiper belt objects (KBOs): the classical Kuiper-belt objects (or “cubewanos”), which lie in orbits untouched by Neptune, and the resonant Kuiper-belt objects; those which Neptune has locked into a precise orbital ratio such as 3:2 (the object goes around twice for every three Neptune orbits) and 2:1 (the object goes around once for every two Neptune orbits). These ratios, called orbital resonances, allow KBOs to persist in regions which Neptune’s gravitational influence would otherwise have cleared out over the age of the Solar System, since the objects are never close enough to Neptune to be scattered by its gravity. Those in 3:2 resonances are known as “plutinos“, because Pluto is the largest member of their group, whereas those in 2:1 resonances are known as “twotinos“.

In contrast to the Kuiper belt, the scattered-disc population can be disturbed by Neptune.[19] […] The MPC […] makes a clear distinction between the Kuiper belt and the scattered disc; separating those objects in stable orbits (the Kuiper belt) from those in scattered orbits (the scattered disc and the centaurs).[10] However, the difference between the Kuiper belt and the scattered disc is not clearcut, and many astronomers see the scattered disc not as a separate population but as an outward region of the Kuiper belt.”

ii. Bobcat (featured).

791px-Bobcat2

“The bobcat (Lynx rufus) is a North American mammal of the cat family Felidae, appearing during the Irvingtonian stage of around 1.8 million years ago (AEO).[3] With 12 recognized subspecies, it ranges from southern Canada to northern Mexico, including most of the continental United States. The bobcat is an adaptable predator that inhabits wooded areas, as well as semidesert, urban edge, forest edges, and swampland environments. It persists in much of its original range, and populations are healthy.

With a gray to brown coat, whiskered face, and black-tufted ears, the bobcat resembles the other species of the mid-sized Lynx genus. It is smaller on average than the Canada lynx, with which it shares parts of its range, but is about twice as large as the domestic cat. It has distinctive black bars on its forelegs and a black-tipped, stubby tail, from which it derives its name.

Though the bobcat prefers rabbits and hares, it will hunt anything from insects, chickens, and small rodents to deer. Prey selection depends on location and habitat, season, and abundance. Like most cats, the bobcat is territorial and largely solitary […]

The bobcat is believed to have evolved from the Eurasian lynx, which crossed into North America by way of the Bering Land Bridge during the Pleistocene, with progenitors arriving as early as 2.6 mya.[5] The first wave moved into the southern portion of North America, which was soon cut off from the north by glaciers. This population evolved into modern bobcats around 20,000 years ago. A second population arrived from Asia and settled in the north, developing into the modern Canada lynx.[4] Hybridization between the bobcat and the Canada lynx may sometimes occur […]

The bobcat has long been valued both for fur and sport; it has been hunted and trapped by humans, but has maintained a high population, even in the southern United States, where it is extensively hunted. Indirectly, kittens are most vulnerable to hunting given their dependence on an adult female for the first few months of life. […] The IUCN lists it as a species of “least concern“, noting it is relatively widespread and abundant”

iii. Luis Walter Alvarez (good article). A remarkable man who lived a remarkable life:

Luis W. Alvarez (June 13, 1911 – September 1, 1988) was an American experimental physicist and inventor, who was awarded the Nobel Prize in Physics in 1968. […]

After receiving his PhD from the University of Chicago in 1936, Alvarez went to work for Ernest Lawrence at the Radiation Laboratory at the University of California, Berkeley. Alvarez devised a set of experiments to observe K-electron capture in radioactive nuclei, predicted by the beta decay theory but never observed. He produced 3H using the cyclotron and measured its lifetime. In collaboration with Felix Bloch, he measured the magnetic moment of the neutron.

In 1940 Alvarez joined the MIT Radiation Laboratory, where he contributed to a number of World War II radar projects […] Alvarez spent a few months at the University of Chicago working on nuclear reactors for Enrico Fermi before coming to Los Alamos to work for Robert Oppenheimer on the Manhattan project. Alvarez worked on the design of explosive lenses, and the development of exploding-bridgewire detonators. As a member of Project Alberta, he observed the Trinity nuclear test from a B-29 Superfortress, and later the bombing of Hiroshima from the B-29 The Great Artiste. […]

After the war Alvarez was involved in the design of a liquid hydrogen bubble chamber that allowed his team to take millions of photographs of particle interactions, develop complex computer systems to measure and analyze these interactions, and discover entire families of new particles and resonance states. This work resulted in his being awarded the Nobel Prize in 1968. He was involved in a project to x-ray the Egyptian pyramids to search for unknown chambers. He analyzed film footage of the Kennedy assassination, and with his son, geologist Walter Alvarez, developed the Alvarez hypothesis which proposes that the extinction event that wiped out the dinosaurs was the result of an asteroid impact. […]

As a result of his radar work and the few months spent with Fermi, Alvarez arrived at Los Alamos in the spring of 1944, later than many of his contemporaries. The work on the “Little Boy” (a uranium bomb) was far along so Alvarez became involved in the design of the “Fat Man” (a plutonium bomb). The technique used for uranium, that of forcing the two sub-critical masses together using a type of gun, would not work with plutonium because the high level of background spontaneous neutrons would cause fissions as soon as the two parts approached each other, so heat and expansion would force the system apart before much energy has been released. It was decided to use a nearly critical sphere of plutonium and compress it quickly by explosives into a much smaller and denser core, a technical challenge at the time.[27]

To create the symmetrical implosion required to compress the plutonium core to the required density, thirty two explosive charges were to be simultaneously detonated around the spherical core. Using conventional explosive techniques with blasting caps, progress towards achieving simultaneity to within a small fraction of a microsecond was discouraging. Alvarez directed his graduate student, Lawrence H. Johnston, to use a large capacitor to deliver a high voltage charge directly to each explosive lens, replacing blasting caps with exploding-bridgewire detonators. The exploding wire detonated the thirty two charges to within a few tenths of a microsecond. The invention was critical to the success of the implosion-type nuclear weapon.”

iv. Nuclear binding energy. The ‘main article’ about binding energy is less detailed, but if you’re interested in this stuff you may want to check that one out too. It’s clearly still ‘a work in progress’, but there’s some good stuff here. From the article:

Nuclear binding energy is the energy required to split a nucleus of an atom into its component parts. The component parts are neutrons and protons, which are collectively called nucleons. The binding energy of nuclei is always a positive number, since all nuclei require net energy to separate them into individual protons and neutrons. Thus, the mass of an atom’s nucleus is always less than the sum of the individual masses of the constituent protons and neutrons when separated. This notable difference is a measure of the nuclear binding energy, which is a result of forces that hold the nucleus together. Because these forces result in the removal of energy when the nucleus is formed, and this energy has mass, mass is removed from the total mass of the original particles, and the mass is missing in the resulting nucleus. This missing mass is known as the mass defect, and represents the energy released when the nucleus is formed.

The term nuclear binding energy may also refer to the energy balance in processes in which the nucleus splits into fragments composed of more than one nucleon, and in this case the binding energies for the fragments, as compared to the whole, may be either positive or negative, depending on where the parent nucleus and the daughter fragments fall on the nuclear binding energy curve. If new binding energy is available when light nuclei fuse, or when heavy nuclei split, either of these processes result in releases of the binding energy. This energy, available as nuclear energy, can be used to produce electricity (nuclear power) or as a nuclear weapon. When a large nucleus splits into pieces, excess energy is emitted as photons (gamma rays) and as kinetic energy of a number of different ejected particles (nuclear fission products).

Total mass is conserved throughout all such processes, so long as the system is isolated. During each nuclear transmutation, the “mass defect” mass is relocated to, or carried away by, other particles that are no longer a part of the original nucleus.

The nuclear binding energies and forces are on the order of a million times greater than the electron binding energies of light atoms like hydrogen.[1]

The mass defect of a nucleus represents the mass of the energy of binding of the nucleus, and is the difference between the mass of a nucleus and the sum of the masses of the nucleons of which it is composed. […]

Small nuclei that are larger than hydrogen can combine into bigger ones and release energy, but in combining such nuclei, the amount of energy released is much smaller compared to hydrogen fusion. The reason is that while the overall process releases energy from letting the nuclear attraction do its work, energy must first be injected to force together positively charged protons, which also repel each other with their electric charge.[5]

For elements that weigh more than iron (a nucleus with 26 protons), the fusion process no longer releases energy. In even heavier nuclei energy is consumed, not released, by combining similar sized nuclei. With such large nuclei, overcoming the electric repulsion (which affects all protons in the nucleus) requires more energy than what is released by the nuclear attraction (which is effective mainly between close neighbors). […]

Nuclei heavier than uranium spontaneously break up too quickly to appear in nature, though they can be produced artificially. Generally, the heavier the nuclei are, the faster they spontaneously decay.[5]

Iron nuclei are the most stable nuclei (in particular iron-56), and the best sources of energy are therefore nuclei whose weights are as far removed from iron as possible. One can combine the lightest ones—nuclei of hydrogen (protons)—to form nuclei of helium, and that is how the Sun generates its energy. Or else one can break up the heaviest ones—nuclei of uranium—into smaller fragments, and that is what nuclear power reactors do.[5]

Binding_energy_curve_-_common_isotopes.svg

v. Surrender of Japan (featured). Lots of good stuff here I did not know.

vi. Spinal cord injury.

“A spinal cord injury (SCI) refers to any injury to the spinal cord that is caused by trauma instead of disease.[1] Depending on where the spinal cord and nerve roots are damaged, the symptoms can vary widely, from pain to paralysis to incontinence.[2][3] Spinal cord injuries are described at various levels of “incomplete”, which can vary from having no effect on the patient to a “complete” injury which means a total loss of function.

Treatment of spinal cord injuries starts with restraining the spine and controlling inflammation to prevent further damage. The actual treatment can vary widely depending on the location and extent of the injury. In many cases, spinal cord injuries require substantial physical therapy and rehabilitation, especially if the patient’s injury interferes with activities of daily life.

Spinal cord injuries have many causes, but are typically associated with major trauma from motor vehicle accidents, falls, sports injuries, and violence. Research into treatments for spinal cord injuries includes controlled hypothermia and stem cells, though many treatments have not been studied thoroughly and very little new research has been implemented in standard care. […]

In a “complete” spinal injury, all function below the injured area are lost. In an “incomplete” injury, some or all of the functions below the injured area may be unaffected. If the patient has the ability to contract the anal sphincter voluntarily or to feel a pinprick or touch around the anus, the injury is considered to be incomplete. The nerves in this area are connected to the very lowest region of the spine, the sacral region, and retaining sensation and function in these parts of the body indicates that the spinal cord is only partially damaged. An incomplete spinal cord injury involves preservation of motor or sensory function below the level of injury in the spinal cord.[8] […]

Spinal cord injuries frequently result in at least some incurable impairment even with the best possible treatment. In general, patients with complete injuries recover very little lost function and patients with incomplete injuries have more hope of recovery. Some patients that are initially assessed as having complete injuries are later reclassified as having incomplete injuries.

The place of the injury determines which parts of the body are affected. The severity of the injury determines how much the body will be affected. Consequently, a person with a mild, incomplete injury at the T5 vertebrae will have a much better chance of using his or her legs than a person with a severe, complete injury at exactly the same place in the spine.

Recovery is typically quickest during the first six months, with very few patients experiencing any substantial recovery more than nine months after the injury.[43] […]

In the United States, the incidence of spinal cord injury has been estimated to be about 40 cases (per 1 million people) per year or around 12,000 cases per year.[44][45] The most common causes of spinal cord injury are motor vehicle accidents, falls, violence and sports injuries.[45] The average age at the time of injury has slowly increased from a reported 29 years of age in the mid-1970s to a current average of around 40. Over 80% of the spinal injuries reported to a major national database occurred in males.[46] In the United States there are around 250,000 individuals living with spinal cord injuries.[25][47]

vii. Rhabdomyolysis (featured).

Rhabdomyolysis /ˌræbdɵmˈɒlɨsɪs/ is a condition in which damaged skeletal muscle tissue (Greek: ῥαβδω rhabdo- striped μυς myo- muscle) breaks down (Greek: λύσις –lysis) rapidly. Breakdown products of damaged muscle cells are released into the bloodstream; some of these, such as the protein myoglobin, are harmful to the kidneys and may lead to kidney failure. The severity of the symptoms, which may include muscle pains, vomiting and confusion, depends on the extent of muscle damage and whether kidney failure develops. The muscle damage may be caused by physical factors (e.g. crush injury, strenuous exercise), medications, drug abuse, and infections. Some people have a hereditary muscle condition that increases the risk of rhabdomyolysis. The diagnosis is usually made with blood tests and urinalysis. The mainstay of treatment is generous quantities of intravenous fluids, but may include dialysis or hemofiltration in more severe cases.[1][2]

Rhabdomyolysis and its complications are significant problems for those injured in disasters such as earthquakes and bombings. […]

Damage to skeletal muscle may take various forms. Crush injuries and other physical causes damage muscle cells directly or interfere with their blood supply, while non-physical causes interfere with muscle cell metabolism. When damaged, muscle tissue rapidly fills with fluid from the bloodstream, including sodium ions. The swelling itself may lead to destruction of muscle cells, but those cells that survive are subject to various disruptions that lead to rise in intracellular calcium ions; the accumulation of calcium in the sarcoplasmic reticulum leads to continuous muscle contraction and depletion of ATP, the main carrier of energy in the cell.[3][7] ATP depletion can itself lead to uncontrolled calcium influx.[2] The persistent contraction of the muscle cell leads to breakdown of intracellular proteins and disintegration of the cell.[2]

Neutrophil granulocytes—the most abundant type of white blood cell—enter the muscle tissue, producing an inflammatory reaction and releasing reactive oxygen species,[3] particularly after crush injury.[2] Crush syndrome may also cause reperfusion injury when blood flow to decompressed muscle is suddenly restored.[2]

The swollen, inflamed muscle may directly compress structures in the same fascial compartment, causing compartment syndrome. The swelling may also further compromise blood supply into the area. Finally, destroyed muscle cells release potassium ions, phosphate ions, the heme-containing protein myoglobin, the enzyme creatine kinase and uric acid (a breakdown product of purines from DNA) into the blood. Activation of the coagulation system may precipitate disseminated intravascular coagulation.[3] High potassium levels may lead to potentially fatal disruptions in heart rhythm. Phosphate binds to calcium from the circulation, leading to low calcium levels in the blood.[3]

Rhabdomyolysis may cause renal failure by several mechanisms. The most important problem is the accumulation of myoglobin in the kidney tubules.[2][3][7] […]

The prognosis depends on the underlying cause and whether any complications occur. Rhabdomyolysis complicated by acute kidney impairment in patients with traumatic injury may have a mortality rate of 20%.[1] Admission to the intensive care unit is associated with a mortality of 22% in the absence of acute kidney injury, and 59% if renal impairment occurs.[2] Most people who have sustained renal impairment due to rhabdomyolysis fully recover their renal function.[2] […]

Up to 85% of people with major traumatic injuries will experience some degree of rhabdomyolysis.[1] Of those with rhabdomyolysis, 10–50% develop acute kidney injury.[1][2] […] Rhabdomyolysis accounts for 7–10% of all cases of acute kidney injury in the U.S.[2][7]

September 11, 2013 - Posted by | astronomy, biology, history, medicine, wikipedia

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