An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 12 Search : Fermi
fermi (#)

Fr.: fermi   

A unit of length equal to 10-13 cm.

After Enrico Fermi (1901-1954), the Italian-born American physicist who was a key figure in the development of nuclear physics. He was awarded the 1938 Nobel Prize for Physics.

Fermi constant
  پایای ِ فرمی   
pâyâ-ye Fermi

Fr.: constante de Fermi   

The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. CF = 1.167 x 10-5 GeV-2.

Fermi; → constant.

Fermi energy
  کاروژ ِ فرمی   
kâruž-e Fermi

Fr.: énergie de Fermi   

The energy of the highest occupied quantum state in a system of fermions at absolute zero temperature. See also → Fermi sea.

fermi; → energy.

Fermi Gamma-ray Space Telescope
  دوربین ِ فضایی ِ پرتوهای ِ گاما فرمی   
Durbin-e fazâyi-ye partowhâ-ye gâmâ Fermi

Fr.: Télescope spatial à rayons gamma Fermi   

A space observatory, formerly named GLAST, devoted to the study of → gamma rays emitted from astrophysical objects. Developed by NASA in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States, Fermi was launched on June 11, 2008. The main instrument, the Large Area Telescope (LAT), is an imaging → camera covering the energy range from about 20 → MeV to more than 300 → GeV. Such gamma rays are emitted only in the most extreme conditions, by particles moving very nearly at the → speed of light. The LAT's → field of view covers about 20% of the sky at any time, and it scans continuously, covering the whole sky every three hours. Another instrument, the Gamma-ray Burst Monitor (GBM) has a field of view several times larger than the LAT and provides → spectral coverage of → gamma-ray burst that extends from the lower limit of the LAT down to 10 → keV.

Fermi; → gamma ray; → space; → telescope.

Fermi interaction
  اندرژیرش ِ فرمی   
andaržirš-e Fermi

Fr.: interaction de Fermi   

An old explanation, proposed by Enrico Fermi, of the → weak interaction.

fermi; → interaction.

Fermi level
  تراز ِ فرمی   
tarâz-e Fermi

Fr.: niveau de Fermi   

A measure of the → energy of the least tightly held → electrons within a → solid at a → non-zero → temperature. The value of the Fermi level at → absolute zero (-273.15 °C) is called the → Fermi energy and is a constant for each solid. In other words, the Fermi level is any → energy level having the probability that it is exactly half filled with electrons in the → Fermi-Dirac statistics. Levels of lower energy than the Fermi level tend to be entirely filled with electrons, whereas energy levels higher than the Fermi tend to be empty.

Fermi; → level.

Fermi paradox
  پارادخش ِ فرمی   
pârâdaxš-e Fermi

Fr.: paradoxe de Fermi   

The apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations.

fermi; → paradox.

Fermi pressure
  فشار ِ فرمی   
fešâr-e Fermi

Fr.: pression de Fermi   

Same as → degeneracy pressure.

fermi; → pressure.

Fermi sea
  دریای ِ فرمی   
daryâ-ye Fermi

Fr.: mer de Fermi   

A large aggregate of single-state → fermions of lowest energy. When the temperature is lowered to absolute zero, all electrons in solids attempt to get into the lowest available energy level. However, electrons cannot all occupy the lowest energy, or ground state, in virtue of the → Pauli exclusion principle. They stack up in the lowest energy states, with two fermions in each state, one spin up and one spin down. Such assemblage of filled states is called the Fermi "sea," and this state of matter is called → degenerate. All states with energy less than the Fermi energy are filled, and all states above the Fermi energy are empty.

fermi; → sea.

Fermi-Dirac statistics
  آمار ِ فرمی-دیراک   
âmâr-e Fermi-Dirac (#)

Fr.: distribution Fermi-Dirac   

The statistical distribution of → fermions over the energy states for a system in → thermodynamic equilibrium. In other words, the probability that a given energy level be occupied by a fermion.

fermi, → Dirac function; → statistics.

Fermi-Pasta-Ulam problem
  پراسه‌ی ِ فرمی-پستا-اولام   
parâse-ye Fermi-Pasta-Ulam

Fr.: expérience Fermi-Pasta-Ulam   

A computer experiment that was aimed to study the → thermalization process of a → solid. In other words, the goal was to see whether there is an approximate → equipartition of energy in the system, which would mean that the motion is → chaotic. Using computer simulation, Fermi-Pasta-Ulam studied the behavior of a chain of 64 mass particles connected by → nonlinear springs. In fact, they were looking for a theoretical physics problem suitable for an investigation with one of the very first computers, the he MANIAC (Mathematical Analyzer, Numerical Integrator and Computer). They decided to study how a → crystal evolves toward → thermal equilibrium by simulating a chain of particles, linked by a quadratic interaction potential, but also by a weak nonlinear interaction. Fermi-Pasta-Ulam assumed that if the interaction in the chain were nonlinear, then an exchange of energy among the normal modes would occur, and this would bring forth the equipartition of energy, i.e. the thermalization. Contrary to expectations, the energy revealed no tendency toward equipartition. The system had a simple quasi-periodic behavior, and no → chaoticity was observed. This result, known as the Fermi-Pasta-Ulam paradox, shows that → nonlinearity is not enough to guarantee the equipartition of energy (see, e.g., Dauxois et al., 2005, Eur. J. Phys., 26, S3).

E. Fermi, J. Pasta, S. Ulam, 1955, Los Alamos report LA-1940; → problem.

fermion (#)

Fr.: fermion   

An elementary particle, such as → electron, → proton, or → neutron, having a half integral value of → spin. Fermions obey the → Pauli exclusion principle.

From Fermi → fermi + → -on.