Hooke's law

In mechanics, and physics, Hooke's law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit. Materials for which Hooke's law is a useful approximation are known as linear-elastic or "Hookean" materials.

Mathematically, Hooke's law states that

where

x is the displacement of the end of the spring from its equilibrium position;

F is the restoring force exerted by the material; and

k is the force constant (or spring constant).

Hooke's law is named after the 17th century British physicist Robert Hooke. He first stated this law in 1676 as a Latin anagram,^[1] whose solution he published in 1678 as Ut tensio, sic vis, meaning, "As the extension, so the force".When this holds, the behavior is said to be linear. If shown on a graph, the line should show a direct variation. There is a negative sign on the right hand side of the equation because the restoring force always acts in the opposite direction of the displacement (for example, when a spring is stretched to the left, it pulls back to the right).

Examples of scalars

Some examples of scalars include the mass, charge, or the temperature, or electric potential at a point inside a medium. The distance between two points in three-dimensional space is a scalar, but the direction from one of those points to the other is not, since describing a direction requires two physical quantities such as the angle on the horizontal plane and the angle away from that plane. Force cannot be described using a scalar, since force is composed of direction and magnitude, however, the magnitude of a force alone can be described with a scalar, for instance the gravitational force acting on a particle is not a scalar, but its magnitude is. The speed of an object is a scalar (e.g. 180 km/h), while its velocity is not (i.e. 180 km/h north).

Examples of scalar quantities in Newtonian mechanics:

• electric charge and charge density

FBR

The fast breeder or fast breeder reactor (FBR) is a fast neutron reactor designed to breed fuel by producing more fissile material than it consumes. The FBR is one possible type of breeder reactor.

The reactors are used in nuclear power plants to produce nuclear power and nuclear fuel.

As of 2006, all large-scale FBR power stations have been liquid metal fast reactors (LMFBR) cooled by liquid sodium. These have been of one of two designs:

• Loop type, in which the primary coolant is circulated through primary heat exchangers external to the reactor tank (but within the biological shield owing to the presence of radioactive sodium-24 in the primary coolant).
• Pool type, in which the primary heat exchangers and circulators are immersed in the reactor tank.

Raman scattering

Raman scattering or the Raman effect (pronounced /ˈrɑːmən/) is the inelastic scattering of a photon. Discovered by Sir Chandrasekhara Venkata Raman in liquids[1] and by Grigory Landsberg and Leonid Mandelstam in crystals

In 1922, Indian physicist C. V. Raman published his work on the "Molecular Diffraction of Light," the first of a series of investigations with his collaborators which ultimately led to his discovery (on 28 February 1928) of the radiation effect which bears his name. The Raman effect was first reported by C. V. Raman and K. S. Krishnan, and independently by Grigory Landsberg and Leonid Mandelstam, in 1928. Raman received theNobel Prize in 1930 for his work on the scattering of light. In 1998 the Raman Effect was designated an ACS National Historical Chemical Landmark in recognition of its significance as a tool for analyzing the composition of liquids, gases, and solids

Malaria

Malaria is a vector-borne infectious disease caused by a eukaryotic protist of the genus Plasmodium. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 350–500 million cases of malaria,^[1] killing between one and three million people, the majority of whom are young children in Sub-Saharan Africa.Ninety percent of malaria-related deaths occur in Sub-Saharan Africa. Malaria is commonly associated with poverty, but is also a cause of poverty and a major hindrance to economic development.

Malaria is one of the most common infectious diseases and an enormous public health problem. Five species of the plasmodium parasite can infect humans; the most serious forms of the disease are caused by Plasmodium falciparum. Malaria caused by Plasmodium vivax, Plasmodium ovale and Plasmodium malariae causes milder disease in humans that is not generally fatal. A fifth species, Plasmodium knowlesi, causes malaria in macaques but can also infect humans. This group of human-pathogenic Plasmodium species is usually referred to as malaria parasites.

Usually, people get malaria by being bitten by an infective female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria, and they must have been infected through a previous blood meal taken on an infected person. When a mosquito bites an infected person, a small amount of blood is taken, which contains microscopic malaria parasites. About one week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito's saliva and are injected into the person being bitten. The parasites multiply within red blood cells, causing symptoms that include symptoms of anemia (light-headedness, shortness of breath, tachycardia, etc.), as well as other general symptoms such as fever, chills, nausea, flu-like illness, and, in severe cases, coma, and death. Malaria transmission can be reduced by preventing mosquito bites with mosquito nets and insect repellents, or by mosquito control measures such as spraying insecticides inside houses and draining standing water where mosquitoes lay their eggs. Work has been done on malaria vaccines with limited success and more exotic controls, such as genetic manipulation of mosquitoes to make them resistant to the parasite have also been considered

Glaucoma

Glaucoma is a disease that affects the optic nerve and involves loss of retinal ganglion cells in a characteristic pattern.

There are many different sub-types of glaucoma but they can all be considered as a type of optic neuropathy. Raised intraocular pressure is a significant risk factor for developing glaucoma (above 22 mmHg or 2.9 kPa). One person may develop nerve damage at a relatively low pressure, while another person may have high eye pressure for years and yet never develop damage. Untreated glaucoma leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness.

Haemophilia

Haemophilia (also spelled hemophilia in North America, is a group of hereditary genetic disorders that impair the body's ability to control blood clotting or coagulation, which is used to stop bleeding when a blood vessel is broken.

Haemophilia A (clotting factor VIII deficiency) is the most common form of the disorder, occurring at about 1 in 5,000–10,000 male births.

Haemophilia B (factor IX deficiency) occurs at about 1 in about 20,000–34,000 male births.

Causes

• Haemophilia A is a recessive X-linked genetic disorder involving a lack of functional clotting Factor VIII and represents 90% of haemophilia cases.
• Haemophilia B is a recessive X-linked genetic disorder involving a lack of functional clotting Factor IX. It is similar to but less common than haemophilia A.
• Haemophilia C is an autosomal genetic disorder (ie not X-linked) involving a lack of functional clotting Factor XI. Haemophilia C is not completely recessive: heterozygous individuals also show increased bleeding

Similarly to most recessive sex-linked, X chromosome disorders, only males typically exhibit symptoms. This is due to the fact that females have two X chromosomes while males have only one, lacking a 'back up' copy for the defective gene the defective gene becomes manifest more easily in males. Because females have two X chromosomes and because haemophilia is rare, the chance of a female having two defective copies of the gene is very low, thus females are almost exclusivelyasymptomatic carriers of the disorder. Female carriers may inherit the defective gene from either their mother, father, or it may be a new mutation. Only under rare circumstances do females actually have haemophilia. Affected males typically inherit the defective gene from their mother, or it can be a new mutation.

Haemophilia has featured prominently in European royalty and thus is sometimes known as "the royal disease".