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These are natural or artificial bodies revolving around a planet under its gravitational attraction.

Saturation Vapor Pressure

The maximum amount of humidity which air can hold, at a particular temperature is defined by so called saturation water vapor pressure.

Sawtooth Wave

A sawtooth wave, however, has ramps that drop or begin sharply, becoming similar to the teeth of a saw. It can be found in some music and graphics applications.

Scalar Product

 See Dot product.


 Physical quantity having only magnitude.

Scanning Electron Microscopy

It is a technique in which surface of a specimen to be examined is scanned with an electron beam and the reflected (or back scattered) beam of electrons is collected, and then displayed at same scanning rate on a cathode ray tube. The image on the screen, which may be photographed, represents the surface features of specimen. The surface may or may not be polished and etched, but it must be electrically conductive. A very thin metallic surface coating must be applied to non-conductive materials. Magnification ranging from 10X to in excess of 50,000X is possible.  

Scanning Probe Microscope

It is an instrument which generates a topographical map, on an atomic scale, that is representation of surface features and characteristics of specimen being examined. Scanning probe microscopes employ a tiny probe with a very sharp tip that is brought into very close proximity (i.e. within an order of a nano meter) of specimen surface. This probe is then raster scanned across the plane of the surface. During scanning, the probe experiences deflections perpendicular to this plane, in response to electronic or other interactions between the probe and specimen surface. The in – surface – plane and out of plane motions of probe are controlled by piezoelectric ceramic components that have nanometer resolutions. The probe movements are monitored electronically, and transferred to and stored in a computer, which then generates 3D surface image.   

Schottky Defect

The absence of cation or anion from the position which it is expected to occupy in the periodic arrangement of ions is known as Schottky defect.   


The formation of vacancies in ionic crystals for charge neutrally is called Schottky defect.

Schottky Effect (Thermionic Emission)

 An accelerating electric field when applied to the thermionic emitter, the ejected electrons gets accelerated towards collector, where they constitute thermionic current. The electric field also lowers the height of potential barrier at the surface and hence increases the emission. This increase of emission and its dependence on electrical field is called as schottky effect.

Scintillation Detector

The scintillation counter is a solid state radiation detector which uses a scintillation crystal (phosphor) to detect radiation and produce light pulses. As radiation interacts in the scintillation crystal, energy is transferred to bound electrons of the crystal’s atoms. If the energy that is transferred is greater than the ionization energy, the electron enters the conduction band and is free from the binding forces of the parent atom. This leaves a vacancy in the valence band and is termed a hole. If the energy transferred is less than the binding energy, the electron remains attached, but exists in an excited energy state. Once again, a hole is created in the valence band. By adding impurities during the growth of the scintillation crystal, the manufacturer is able to produce activator centers with energy levels located within the forbidden energy gap. The activator center can trap a mobile electron, which raises the activator center from its ground state, G, to an excited state, E. When the center de-excites, a photon is emitted. The activator centers in a scintillation crystal are referred to as luminescence centers. The emitted photons are in the visible region of the electromagnetic spectrum.

Scintillation Efficiency

It is a term used to characterize the efficiency by which energy lost by incident particle is converted into scintillation photons. Generally it is described as ratio of total energy of scintillation photons and total energy deposited by incident radiation.


Solid state crystal which converts ionizing radiation into scintillations i.e. photons, a phenomenon of luminescence. 

Screw Dislocation

 A linear crystalline defect associated with the lattice dislocation created when normally parallel planes are joined together to form a helical ramp.

Screw Gauge

A screw gauge is a device used to measure the thickness of thin plates and the diameter of a thin wire. 


It is a straight line drawn from the center of a circle through one end of a circular arc to a tangent drawn from the other end of the arc.


A trigonometric function, that in a right-angled triangle is the ratio of the length of the hypotenuse to that of the adjacent side.

Second Sound

Phenomenon in which normal fluid and super fluid oscillate out of phase giving rise to thermal waves for smoothing out temperature difference is called second sound.


The second is the duration of 9192631770 periods of the radiation corresponding to transition between two hyperfine levels of ground state of cesium 133 atom.

Secondary Bonds

Inter atomic and inter molecular bonds that are relatively weak and for which bonding energies are relatively small. Normally atomic or molecular dipoles are involved.

Secular Equilibrium

If the activity of parent becomes equal to that of the daughter, the two nuclides are said to be in secular equilibrium. This happens if the half life of parent is much greater than that of the daughter.

Siderial Day

sidereal day is the time it takes for the Earth to rotate about its axis so that the distant stars appear in the same position in the sky. A measurement of the sidereal day is made by noting the time at which a particular star passes the celestial meridian (i.e. directly overhead) on two successive nights. On Earth, a sidereal day lasts for 23 hours 56 minutes 4.091 seconds.