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place-value notation nemâdgân-e jâ-arezeši Fr.: notation positionnelle A mathematical notation system in which the → numerals get different values depending on their position relative to the other numerals. Same as → positional notation and → positional number system. |
plage plâž (#) Fr.: plage A bright cloud-like feature that appears in the vicinity of a sunspot. Plages represent regions of higher temperature and density within the chromosphere. They are particularly visible when photographed through filters passing the spectral light of hydrogen or calcium. From Fr., from It. piaggia, from L.L. plagia "shore;" noun use of the feminine of plagius "horizontal;" frpm Gk. plagios "slanting, sideways" from plag(os) "side" + -ios adj. suffix. Plâž, loan from Fr., as above. |
plain dašt (#) Fr.: plaine An extent of flat land not noticeably diversified with mountains, hills, or valleys. M.E. from O.Fr. plain, from L. planum "level ground, plain." Dašt, from Mid.Pers. dašt "plain, open ground." |
plan- taxt- (#) Fr.: plan- Variant of → plano-. → plano-. |
Planck Planck Fr.: Planck Short for Max Planck (1858-1947), German physicist, great authority on thermodynamics and creator of the quantum theory. |
Planck curve xam-e Planck Fr.: courbe de Planck Same as → blackbody curve. |
Planck density cagâli-ye Planck Fr.: densité de Planck The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρ_{P} = c^{5}/(ħG^{2}) ≅ 5.16 x 10^{93} g cm^{-3}, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant. |
Planck distribution vâbâžeš-e Planck Fr.: distribution de Planck The distribution of radiation with wavelength for a blackbody, given by → Planck's radiation law. → Planck; → distribution. |
Planck energy kâruž-e Planck Fr.: énergie de Planck The unit of energy in the system of Planck units. E_{P} = √ (ħ c^{5}/G) ≅ 1.22 x 10^{19} GeV. It can also be defined as E_{P} = ħ / t_{P}, where t_{P} is the Planck time. This is an extraordinarily large amount of energy on the subatomic scale and particle accelerators have yet to produce a particle with this magnitude of energy. Understanding the properties of a subatomic particle that contains the Planck Energy is helpful in developing a Unified Field Theory which encompasses the realms of Quantum Theory and Relativity, although this too has evaded complete scientific understanding. |
Planck era dowrân-e Planck Fr.: ère de Planck The first 10^{-43} seconds of the Universe's existence, when the size of the Universe was roughly the Planck length and during which quantum effects of gravity were significant. Also called Planck epoch. Our understanding of the Planck era is poor because theory which encompasses both quantum mechanics and general relativity is needed to be developed. |
Planck function karyâ-ye Planck Fr.: fonction de Planck Same as → Planck's blackbody formula. |
Planck length derâzâ-ye Planck (#) Fr.: longueur de Planck The size limit, l_{P} = √ (ħ G/ c^{3}), about 10^{-33} cm, at which Einstein's notions of space-time are supposed to break down, and space is predicted to become "foam like." |
Planck mass jerm-e Planck Fr.: masse de Planck The unit of mass in Planck's system of physical units, m_{P} = √ (ħ c/ G) = 2.176 x 10^{-8} kg. It is also the mass of a black hole whose Compton wavelength is comparable to its Schwarzschild radius. |
Planck postulate farâvas-e Planck Fr.: postulat de Planck The postulate that the energy of oscillators in a blackbody is quantized by E = nhν, where n = 1, 2, 3, ..., h is Planck's constant, and ν the frequency. |
Planck Satellite mâhvâre-ye Planck Fr.: Satellite Planck A European Space Agency (ESA) mission to map the full sky in the 30 GHz to 1 THz range and to measure the → anisotropies of the → cosmic microwave background (CMB) with a sensitivity set by fundamental limits, i.e. photon noise and contamination by foregrounds. It was launched on 14 May 2009, together with the → Herschel Satellite. Its observing position is a halo orbit around the L2 → Lagrangian point, some 1.5 million km from Earth. Its → Gregorian-like off-axis telescope has an effective aperture of 1.5 m and images the sky on two sets of feed-horns. The Low Frequency Instrument (LFI, at frequencies 30, 44, 70 GHz) amplifies with High Electron Mobility Transistors cooled at 20 K the radiation collected by 13 horns. The High Frequency Instrument (HFI, at 100, 143, 217, 353, 545, 857 GHz) detects the shorter waves with 52 bolometers cooled at only 0.1 degree above the → absolute zero. Both instruments can detect both the total intensity and polarization of photons. The Planck mission is intended to provide maps with a sensitivity of a few micro-Kelvin and an angular resolution down to 5 arcmin, which is considered as a major improvement with respect to the Wilkinson Microwave Anisotropy Probe (→ WMAP) launched by the NASA in 2002. Planck will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early Universe and the origin of cosmic structure. It will also provide to astronomers 9 complete maps of the full sky at wavelengths from 0.3 mm to 1 cm, that complement the 4 maps taken by the → IRAS satellite in the 2.5 to 100 micrometer range. |
Planck scale marple-e Planck Fr.: échelle de Plancck 1) A general term for anything roughly the size of the → Planck length. |
Planck spectrum binâb-e Planck Fr.: spectrum de Planck Same as → blackbody spectrum. |
Planck time zamân-e Planck Fr.: temps de Planck The time representing the → Planck length divided by the → speed of light. It is expressed by: t_{P} = (Għ/c^{5})^{1/2}≅ 5.4 x 10^{-44} s, where G is the → gravitational constant, ħ is the → reduced Planck's constant, and c is the → speed of light. At the Planck time, the mass density of the Universe is thought to approach the → Planck density. |
Planck units yekâhâ-ye Planck (#) Fr.: unités de Planck A set of → natural units in which the normalized units are: the gravitational constant, Planck's constant, the speed of light, the Coulomb constant, and Boltzmann's constant. |
Planck's blackbody formula disul-e siyah jesm-e Planck Fr.: formule du corps noir de Planck A formula that determines the distribution of intensity of radiation that prevails under conditions of thermal equilibrium at a temperature T: B_{v} = (2hν^{3} / c^{2})[exp(hν / kT) - 1]^{-1} where h is Planck's constant and ν is the frequency. |
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