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Moment of truth
More than 25 million people died in Europe from the bubonic plague (the black death) in five years, from 1347 to 1352.

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saccharides Chem.
Derive from Greek, meaning sugar. See carbohydrates.

salivary amylase Biol.
See ptyalin.

Sars Med.
Abbreviation for the Severe Acute Respiratory Syndrome, of which the first known case was discovered in Guangdong province, China in November 2002. The illness was caused by a new virus member of the Corona family not known before and is called Sars-CoV. Known symptoms are similar to those of flu, including high fever, headache, sore throat, cough and shortness of breath. Mortality rate is estimated around 10-15%.

scalar Math.
A mathematical quantity that is entirely defined by a numerical magnitude in appropriate units whereby the quantity specify is unrelated to any direction in space. For example, the mass of an object specify in unit kg. Another example is the speed of an object which defines how fast it is moving, but not the direction it is heading. It is also called a scalar product. See also vector.

scalar product Math.
See dot product.

scanning tunneling microscope (STM) Phys.
A probe microscope by making use of quantum tunneling effect to obtain topographic image of a surface material. The instrument consists of a probe tip (usually made of tungsten, with only a single atom on the tip) that is attached to a piezodrive which position the tip within a few angstrom to the surface sample. A small bias voltage is applied and the current flows as a result of electron tunneling between the sample and the tip. The current is kept constant by the motion of the tip according to the surface contour: The tip will move away from the sample if current increases, and move nearer if the current decreases. The vertical motion is then translated into a three-dimensional image plot. The plot is in fact the electron density profile of the surface and, strictly speaking, do not always indicate the position of atoms.

Schottky defect Chem., Phys.
A defect or disorder in the crystal lattice whereby an atom or ion is removed from its lattice site, creating a vacancy. Usually, the defect is created in pairs in order to preserve the overall charge neutrality of the system. For example, both sodium cation and chloride anion are missing from the lattice site:

Schottky defect

Schrödinger equation Phys.
The fundamental postulate of dealing with behavior of the atomic world, quantum mechanics. It was developed by the Austrian physicist Erwin Schrödinger in 1925. Basically, the equation contains all possible states of a quantum mechanical system, and any state at any time is described by a state vector that contains the probability distributions of all possible measurements (observables) that applied to the system. It is written mathematically as

Schrodinger equation

where H is the Hamiltonian operator which contains the potential and kinetic energy terms; ħ = h/2p where h = Planck constant and t is the time. The symbol Y is the wavefunction that contains the probability distribution of all observable of a system.

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