The
lowest temperature theoretically possible; the temperature at
which the thermal energy of random motion of the particles of a
system in thermal equilibrium is zero. 0 K = -273.15°C =
-459.69°F
A theory advanced in
1957 by three researchers, John Bardeen,
Leon Cooper, and J.R. Schrieffer, that explained how low-temperature
superconductors work.
Any product made from earth derived
materials such as clays,
silicates, or sand, usually requiring the application of high temperature in
a kiln or oven at some stage of the process.
The maximum value of electrical current per unit of
cross-sectional area that a superconductor can carry without resistance. For
practical applications, J values in excess of 1000 amperes per square
millimeter (A/mm), are desirable in both bulk conductors and thin film
superconductors.
Above this value of an
externally applied magnetic
field a superconductor becomes nonsuperconducting. When an external
magnetic field is applied to a Type I superconductor the transition from
superconducting to normal is sharp. Type II superconductors do not
possess perfect diamagnetism (flux penetration of the material is
possible). When an external magnetic field is applied to Type II
superconductors the transition to the normal state is over a much
broader region between a lower critical field, H, and an upper critical
field, H.
The highest temperature
at which superconductivity
occurs in a material. Below this transition temperature T the resistivity
of the material is equal to zero.
cryogenicsA branch of physics dealing
with the properties of matter at extremely low temperatures.
The rate of flow of electrons,
measured in amperes, in a conductor.
The conduction of current of 1 ampere is equal to the flow of about
10 electrons per second.
Circulating vortices of current and
flux contained in the vortices.
fluxTo "flow". Referring to the rate of
flow of radiation from a given source.
flux pinningSuperconducting material
properties are altered locally by the
presence of defects in the material. A fluxoid adjacent to such a defect
in the material has its energy altered and its free motion through the
superconductor is inhibited. Flux pining causes a field gradient in the
superconductor and gives rise to a net current in the material.
gaussThe CGS-electromagnetic unit of magnetic
flux
density. 1 G = 10 tesla.
Symbol: G
The element
helium, (Greek, meaning the sun) was
named so because it was first discovered in the sun by spectrographics in
1868. Helium gas does not become liquid until the temperature
reaches 4.2 K, about -269°C.
The
magnetic flux passing through unit area of a
magnetic field in a direction at right angles to the magnetic force. The
vector product of the magnetic flux density and the current in a
conductor gives the force per unit length of the conductor. It is
measured in teslas.
Acronym for
Magnetic Resonance Imaging. MRI is a diagnostic imaging
technique that produces cross-sectional images. Its primary use is for
organic materials and soft body tissue.
The regime of magnetic
fields between the lower critical field,
H, and the upper critical field, H. Diamagnetism is less
than perfect
because supercurrent vortices confine magnetic field within quantized
filaments of normal-state material that pass through the superconductor.
The SI unit of electrical resistance,
defined as the resistance between two
points on a conductor through which a current of one ampere flows as a
result of a potential difference of one volt applied between the points.
The electrical current in any
conductor is proportional to the
potential difference between its ends. Ohm's law is often expressed as
I=E/R, where I is the current, E is the potential difference, and
R the
resistance.
An
element or compound whose electrical properties are
midway between a conductor and insulator. A substance with relatively
high resistance and corresponding low conductivity.
Material with perfect electrical conductivity for direct
current that also possesses perfect diamagnetism. When an external
magnetic field is applied on this superconductor, the transition
temperature from superconducting to normal is sharp.
Material with perfect electrical conductivity for direct
current that possesses moderate diamagnetism at high field. When an
external magnetic field is increased, the transition from superconducting
to normal state occurs after going through a broad "mixed state" region.