Nano
Materials
Materials whose
dimensions are less than 100 nm.
Natural
Frequency
Frequency of system when set in free
vibration.
Natural
Logarithm
A logarithm to the base ‘e’ which is
irrational and whose value is equal to 2.71829. It is represented as log eX..
It is also called as Napier logarithm.
Nebula
A visible, thinly spread cloud of
interstellar gas and dust. Some nebulae are remnants of supernova explosion
others are gravity induced condensations of gases in interstellar medium which
in certain cases may become a site for formation of new stars. The term was
formerly used of any hazy , seemingly cloud like object, including what are now
recognized as other galaxies beyond milky way, it is restricted now to actual
clouds of gas and dust within our own galaxy.
Negative
Feedback
When feedback
energy is out of phase with input signal and opposite to it, then it is called
negative effect.
Negatron
Term used for
electron when it is necessary to distinguish between electrons and positrons.
Neptunium
Series
It is a radioactive
series that does not now occur in nature and that begins with Plutonium of mass
number-241 and continues to Americium to the longer lived member of series i.e.
Neptunium of mass number 237, and eventually to stable end product Bismuth.
Neutrino
An elementary
particle introduced by Pauli in 1952. It was introduced in weak interactions
involving beta decay to avoid violation of law of conservation of energy and
angular momentum. It has solved mystery of variable energy of beta particles in
beta decays.
Neutron
Diffraction
It is a non destructive technique that is
used to probe the structure of materials at the atomic level. The sample is
placed within a neutron beam and the angles at which the neutrons are deflected
or scattered by material are recorded to generate a “diffraction pattern” from which structural
information can be extracted. Diffraction occurs when the neutrons encounter
atomic nuclei or magnetic diploes within the sample. With an effective
wavelength of 0.1-20 nm, thermal neutrons are ideally suited for probing atomic
scale structures with high resolution. As neutrons do not possess an electric
charge, they readily pass through matter regardless of local charge
distribution. In consequence, a neutron beam is capable of penetrating well
beyond surface of a sample, to a depth of few centimeters in most condensed
phases. The technique is widely used in engineering for stress mapping and to
examine mechanical behavior of materials and engineering components.
Neutron
Flux
The neutron flux (φ) measures the intensity
of neutrons passing through a cubic centimeter of material. It is given by: φ=
nv; where n is the density of neutrons (the number of neutrons per cm3) and v
is the speed of the neutrons. The unit for neutron flux is neutrons.cm-2.sec-1.
In physical
terms, the quantity ‘φ’ is the total distance traveled in one second by all the
neutrons in the one cm3 volume, since it is obtained by multiplying
the number of neutrons in that cm3 by the speed each is travelling.
This is equivalent to the total length of all the neutron tracks laid down in
one cm3 in one second. The expression for neutron flux applies to
any neutron energy. When applied to thermal neutrons the product is known as
the thermal neutron flux.
Newton
It
is SI unit of force. It is force required
to accelerate a mass of one kilogram one meter per second per second.
Newton’s
First Law
Everybody
continues in its state of rest or of uniform motion in a straight line unless
it is compelled by an external force to change that state.
Newton’s
Law of Cooling
The rate of loss
of heat of a hot body (or rate of cooling of body) is directly proportional to
mean excess of temperature of hot body over that of its surroundings.
Newton’s
Second Law
The rate of
change of momentum of a body is directly proportional to external force acting
on it and takes place in the direction of force.
Newton’s
Third Law
For every action,
there is equal and opposite reaction.
