maximum density of water
cagâli-ye bišine-ye âb
Fr.: densité maximale de l'eau
The density of pure water occurring at 3.98 °C, which is 1.0000 g cm-3, or 1000 kg m-3. Water when cooled down contracts normally until the temperature is 3.98 °C, after which it expands. Because the maximum density of water occurs at about 4 °C, water becomes increasingly lighter at 3 °C, 2 °C, 1 °C, and 0 °C (→ freezing point). The density of liquid water at 0 °C is greater than the density of frozen water at the same temperature. Thus water is heavier as a liquid than as a solid, and this is why ice floats on water. When a mass of water cools below 4 °C, the density decreases and allows water to rise to the surface, where freezing occurs. The layer of ice formed on the surface does not sink and it acts as a thermal isolator, thus protecting the biological environment beneath it. This property of water liquid is very unusual; molecules pack more closely than in the crystal structure of ice. The reason is that → hydrogen bonds between liquid water are not stable, they are continuously broken and new bonds are created. In the crystal structure of ice molecules have a fixed pattern creating empty space between molecules.
maximum entropy method (MEM)
raveš-e dargâšt-e bišiné
Fr.: méthode d'entropie maximum
A deconvolution algorithm which functions by minimizing a smoothness function in an image. The MEM seeks to extract as much information from a measurement as is justified by the data's signal-to-noise ratio.
Fr.: maximum de lumière
Fr.: maximum de vraisemblance
A statistical procedure based on choosing the value of the unknown parameter under which the probability of obtaining an observed sample is highest.
After James Clerk Maxwell (1831-1879), British outstanding physicist, who made fundamental contributions to electromagnetic theory and the kinetic theory of gases.
Fr.: pont de Maxwell
Fr.: division de Maxwell
A division in Saturn's ring in the outer part of the C ring. It is about 87500 km from Saturn's center and is 500 km wide. The gap was discovered in 1980 by Voyager 1.
Fr.: démon de Maxwell
A → thought experiment meant to raise questions about the possibility of violating the → second law of thermodynamics. A wall separates two compartments filled with gas. A little "demon" sits by a tiny trap door in the wall. He is able to sort hot (faster) molecules from cold molecules without expending energy, thus bringing about a general decrease in → entropy and violating the second law of thermodynamics. The → paradox is explained by the fact that such a demon would still need to use energy to observe and sort the molecules. Thus the total entropy of the system still increases.
Fr.: équations de Maxwell
A set of four fundamental equations that describe the electric and
magnetic fields arising from varying electric charges and magnetic fields,
electric currents, charge distributions,
and how those fields change in time. In their vector differential form,
these equations are:
→ maxwell. It should be emphasized that the equations originally published by James Clerk Maxwell in 1873 (in A Treatise on Electricity and Magnetism) were 20 in number, had 20 variables, and were in scalar form. The German physicist Heinrich Rudolf Hertz (1857-1894) reduced them to 12 scalar equations (1884). It was the English mathematician/physicist Oliver Heaviside (1850-1925) who expressed Maxwell's equations in vector form using the notations of → gradient, → divergence, and → curl of a vector, thus simplifying them to the present 4 equations (1886). Before Einstein these equations were known as Maxwell-Heaviside-Hertz equations, Einstein (1940) popularized the name "Maxwell's Equations;" → equation.
Fr.: règle de Maxwell
Every part of a deformable electric circuit tends to move in such a direction as to enclose the maximum magnetic flux.
Fr.: distribution de Maxwell-Boltzmann
The distribution law for kinetic energies (or, equivalently, speeds) of molecules of an ideal gas in equilibrium at a given temperature.
Fr.: calendrier Maya
A complex calendar created by the ancient central American Mayas which uses three different dating systems in parallel: Long Count, Tzolkin, and Haab. Only Haab has a direct relationship with the length of the year. It is a solar → vague year consisting of 18 months of 20 days each, and an additional period of 5 → epagomenal days. Tzolkin is a calendar of 13 x 20 = 260 days running within Haab and is used for ritual purposes. A date is usually described by specifying its position in both the Tzolkin and Haab calendars. The least common multiple of the two calendars, called the Calendar Round, has 18,980 days, representing a cycle of 73 sacred years, or 52 vague years. The Long Count is the number of days since the start of the Maya era. There is disagreement about the beginning date of the Long Count. Most authorities agree, however, that the Long Count started in 3114 B.C., with several possible dates.
Maya, proper name; → calendar.
Fr.: ruban de Möbius
A surface with only one side, made by putting a simple twist in a long, rectangular strip of paper, then pasting the ends together.
After the German astronomer and geometer August Ferdinand Möbius (1790-1868); → band.
Fr.: effet Mössbauer
The resonant and recoil-free emission and absorption of gamma rays by atoms bound in a solid form.
Named after Rudolf Mößbauer (1929-), a German physicist who studied gamma rays from nuclear transitions, and discovered this phenomenon in 1957; → effect.
1) miyângin (#); 2) cemârdan
Fr.: 1) moyenne; 2) signifier, vouloir dire
1a) General: A quantity having a value intermediate between the values of other
quantities; an average.
Fr.: anomalie moyenne
The angle between the periapsis of an orbit and the position of a hypothetical body that orbits in the same period as the real one but at a constant mean angular velocity.
mean catalog place
jâ-ye miyângin-e kâtâlogi
Fr.: position catalogue moyenne
mean daily motion
jenbeš-e ruzâne-ye miyângin (#)
Fr.: mouvement diurne moyen
The average movement of a body along its orbit in one day, usually expressed in degrees.
Fr.: élément moyen
An element of an adopted reference orbit that approximates the actual, perturbed orbit. Mean elements may serve as the basis for calculating perturbations.
Fr.: équateur moyen
The orientation the Earth's equator would have if the nutation was subtracted.