Satellite
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.
Scalar
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.
or
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.
Scintillator
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.
Secant
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.
or
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.
Second
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
A 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.
