anticorrelation pâdhambâzâneš Fr.: anticorrelation Statistics: The correlation coefficient of two random variables X and Y is in general defined as the ratio of the Cov(X,Y) to the two standard deviations of X and Y. It varies between 1 and -1 corresponding to complete correlation or anticorrelation. Anticorrelation, from → anti- + → correlation. Pâdhambâzâneš, from pâd-, → anti-, + hambâzâneš, → correlation. |
autocorrelation xod-hambâzâneš Fr.: autocorrélation 1) In radio astronomy, a process performed by an → autocorrelator. Autocorrelation, from → auto- "self" + → correlation. Xod-hambâzâneš, from xod- "self" + hambâzâneš, → correlation. |
autocorrelation function karyâ-ye xod-hambâzâneš Fr.: fonction d'autocorrélation A mathematical function that describes the correlation between two values of the same variable at different points in time. → autocorrelation; → function. |
Boltzmann's relation bâzâneš-e Boltzmann Fr.: relation de Boltzmann A relation between the → entropy of a given → state of a → thermodynamic system and the → probability of the state: S = k . ln Ω where S is the entropy of the system, k is → Boltzmann's constant, and Ω the thermodynamic probability of the state. Boltzmann's relation connects → statistical mechanics and → thermodynamics. Ω is the number of possible → microstates of the system, and it represents the → randomness of the system. The relation also describes the statistical meaning of the → second law of thermodynamics. This expression has been carved above Boltzmann's name on his tombstone in Zentralfreihof in Vienna. Same as → Boltzmann's entropy formula. → Boltzmann's constant; → relation. |
canonical correlation hambâzânš-e hanjârvâr Fr.: correlation canonique The highest correlation between linear functions of two data sets when specific restrictions are imposed upon them. → canonical; → correlation. |
correlation hambâzâneš Fr.: corrélation General:
The degree to which two or more attributes or measurements on the
same group of elements show a tendency to vary together;
the state or relation of being correlated. From M.Fr. corrélation, from cor- "together," → com- + → relation. |
correlation coefficient hamgar-e hambâzâneš Fr.: coefficient de corrélation A number between -1 and 1 which measures the degree to which two variables are linearly related. → correlation; → coefficient. |
cross correlation hamvbâzâneš-e calipâyi, ~ xâji Fr.: corrélation croisée In radio astronomy, the process performed by a → cross correlator or the result of the process. → cross; → correlation. |
direct correlation hambâzâneš-e sarrâst Fr.: corrélation directe A correlation between two variables such that as one variable becomes large, the other also becomes large, and vice versa. The correlation coefficient is between 0 and +1. Also called positive correlation. → direct; → correlation. |
dispersion relation bâzâneš-e pâšeš Fr.: relation de dispersion An equation that describes how the → angular frequency, ω, of a wave depends on its → wave number, k. For the simplest of waves, where the speed of propagation, c, is a constant, ω(k) = ck. If the → phase velocity depends on k, that is for a dispersive medium, the function ω(k) is nonlinear. → dispersion; → relation. |
Faber-Jackson relation bâzâneš-e Faber-Jackson Fr.: relation Faber-Jackson An empirical power-law correlation between the luminosity (L) and the velocity dispersion of stars (σ) in the center of a elliptical galaxies. The original relation can be expressed mathematically as: L ∝ σ^{γ}, where the index γ is observed to be approximately equal to 4, but depends on the range of galaxy luminosities that is fitted. → Tully-Fisher relation. After the astronomers Sandra M. Faber and Robert Earl Jackson, who first noted this relation in 1976 (ApJ 204, 668); → relation. |
Larson relation bâzâneš-e Larson Fr.: relation de Larson An → empirical relationship between the internal → velocity dispersion of → molecular clouds and their size. The velocity dispersions are derived from molecular → linewidths, in particular those of → carbon monoxide. It was first established on star forming regions and found to be: σ (km s^{-1}) = 1.10 L (pc)^{0.38}, where σ is the velocity dispersion and L the size. The relation holds for 0.1 ≤ L ≤ 100 pc. More recent set of cloud data yield: σ (km s^{-1}) = L (pc)^{0.5}. This relation indicates that larger molecular clouds have larger internal velocity dispersions. It is usually interpreted as evidence for → turbulence in molecular clouds. Possible sources of interstellar turbulence include the following processes operating at various scales: galactic-scale (→ differential rotation, → infall of extragalactic gas on the galaxy), intermediate-scale (expansion of → supernova remnants, → shocks, → stellar winds from → massive stars), and smaller-scale processes (→ outflows from → young stellar objects). First derived by Richard B. Larson, American astrophysicist working at Yale University (Larson, 1981, MNRAS 194, 809). See Falgarone et al. (2009, A&A 507, 355) for a recent study; → relation. |
linear correlation hambâzâneš-e xatti Fr.: corrélation linéaire A measure of how well data points fit a straight line. When all the points fall on the line it is called a perfect correlation. When the points are scattered all over the graph there is no correlation. → linear; → correlation. |
mass-energy relation bâzâneš-e jerm-kâruž Fr.: relation masse-énergie The famous equation proposed by Einstein as a consequence of his special theory of relativity describing the equivalence of mass and energy: E = mc^{2}, where E is energy, m is the equivalent amount of mass, and c is the velocity of light. |
mass-luminosity relation bâzâneš-e jerm-tâbandegi Fr.: relation masse-luminosité A relationship between luminosity and mass for stars that are on the main sequence, specifying how bright a star of a given mass will be. Averaged over the whole main sequence, it has been found that L = M^{3.5}, where both L and M are in solar units. This means, for example, that if the mass is doubled, the luminosity increases more than 10-fold. → mass; → luminosity; → relation. |
morphology-density relation bâzâneš-e rixt-cagâli Fr.: relation morphologie-densité An observationally determined relationship between the → morphological classification of galaxies and the → environments in which they are located. Specifically, the morphology-density relation indicates that early-type galaxies (→ ETG) are preferentially located in high density environments, whereas late-type galaxies (→ LTG) are preferentially found in low density environments. Hence, spiral galaxies are rare in the high densities of clusters and are common in the lower density group environments. Early-type galaxies, on the other hand, are common in clusters and are rarely found in isolation. → morphology; → density; → relation. |
negative correlation hambâzâneš-e nâyidâr Fr.: corrélation négative A correlation between two variables such that as one variable's values tend to increase, the other variable's values tend to decrease. → negative; → correlation. |
Orion correlation theory negare-ye hambâzâneš-e Oryon Fr.: théorie de la corrélation d'Orion A controversial proposition according to which a coincidence would exist between the mutual positions of the three stars of → Orion's Belt and those of the main Giza pyramids. More specifically, Khufu, Khafre, and Menkaure would be the monumental representation of → Alnitak, → Alnilam, and → Mintaka, respectively. → Orion; → correlation; → theory. |
period-luminosity relation bâzâneš-e dowré-tâbandegi Fr.: relation période-luminosité A → correlation between the periods and luminosities of → Cepheid variable stars: Cepheids with longer periods are intrinsically more luminous than those with shorter periods. The relation was discovered by Henrietta Leavitt in 1912 when studying Cepheids in the → Small Magellanic Cloud. Once the period of a Cepheid variable is determined from observations, the period-luminosity relation can be used to derive its luminosity. Since luminosity is a function of → distance, the distance can then be calculated with the luminosity. The period-luminosity relation is an invaluable tool for the measurements of distances out to the nearest galaxies and thus for studying the structure of our own Galaxy and of the Universe. → period; → luminosity; → relation. |
period-mean density relation bâzâneš-e dowré-cagâli-ye miyângin Fr.: relation période-densité moyenne A relation that gives a rough estimate of the oscillation period of a → pulsating star as a function of its mean density. This relation is obtained by considering how long it would take a sound wave to travel across the diameter of a model star: Π ≅ (3π/2γGρ)^{1/2}, where ρ is the mean density, γ the ratio of → specific heats (C_{p}/C_{v}), and G the → gravitational constant. This relation shows that the pulsation period of a star is inversely proportional to the square root of its mean density. And this is the reason why the pulsation periods decrease along the → instability strip from the luminous, very tenuous → supergiants to the faint, very dense → white dwarfs. |