36967 research outputs found
Sort by
Critical Temperatures of the Anisotropic Heisenberg Ferromagnets
No full text[[abstract]]High temperature series expansions for the fluctuation in the long range order Mx is obtained through order T-7 for a spin-1/2 anisotropic Heisenberg Hamiltonian. The critical temperatures at which the spontaneous magnetization occurs on the xy-plane are determined.[[fileno]]2010111010013[[department]]物理
Constant-Coupling Approximation of the Exchange-Interaction Model of Ferromagnetism
Get PDF[[abstract]]The ferromagnetic-exchange-interaction model is studied by the Oguchi method and the constant-coupling approximation (CCA). The polarization q(T), which describes the ordering of the model, is determined for various spins. The phase transition is first order for all spins S greater-than-or-equal-to 1. The transition temperature obtained with the CCA is kT(c)/J = 2/{lnS(2S - 1) - ln[(2S)(zeta) - S(2S + 1)]}, where zeta depends on the lattice coordination number z and is given by zeta = 2(z - 1 )/z. Both the CCA and the Oguchi method show that the discontinuity of q at T(c) is q(c) = (2S - 1)/2S, which is exactly the same as the mean-field result.[[fileno]]2010111010046[[department]]物理
A Triangulation Method for the Sequential Mapping of Points from N-Space to 2-Space
No full text[[abstract]]A method for the sequential mapping of points in a high-dimensional space onto a plane is presented. Whenever a new point is mapped, its distgnces to two points previously mapped are exactly preserved. On the resulting map, 2M -3 of the original distances can be exactly preserved. The mapping is based on the distances of a minimal spanning tree constructed from the points. All of the distances on the minimal spanning tree are exactly preserved.[[fileno]]2030256010012[[department]]資訊工程學
MEASUREMENT ACCURACY OF INTELLIGENT DIFFERENTIAL PRESSURE TRANSMITTERS
No full text[[fileno]]2010101010012[[department]]物理
RHENIUM-OSMIUM IN IRON-NICKEL, SULFIDE, AND PHOSPHIDE - THE POSSIBLE DETERMINATION OF INTERNAL ISOCHRONS FOR IRON-METEORITES
No full text[[fileno]]2010101010018[[department]]物理
THE FORMATION OF LOW MASS STARS - THEORY
No full text[[abstract]]Overview Bimodal Star Formation The Bipolar Outflow Phase: Observations Rotating, Magnetized, Molecular Cloud Cores Protostar Formation from Collapsing Cloud Cores Infrared Appearance of Rotating Protostellar Objects Protostar Formation By Disk Accretion Stellar Winds and Bipolar Flows: Theory Revealed T Tauri Stars The Disks Inferred for T Tauri Stars Binary Stars and Planetary Systems[[fileno]]2010118030018[[department]]物理
Relativistic self-similar disks
Get PDF[[abstract]]We formulate and solve by semianalytic means the axisymmetric equilibria of relativistic self-similar disks of infinitesimal vertical thickness. These disks are supported in the horizontal directions against their self-gravity by a combination of isothermal (two-dimensional) pressure and a flat rotation curve. The dragging of inertial frames restricts possible solutions to rotation speeds that are always less than 0.438 times the speed of light, a result first obtained by Lynden-Bell & Pineault in 1978 for a cold disk. We show that prograde circular orbits of massive test particles exist and are stable for all of our model disks but that retrograde circular orbits cannot be maintained with particle velocities less than the speed of light once the disk develops an ergoregion. We also compute photon trajectories, planar and non-planar, in the resulting spacetime for disks with and without ergoregions. We find that all photon orbits, except for a set of measure zero, tend to be focused by the gravity of the flattened mass-energy distribution toward the plane of the disk. This result suggests that strongly relativistic, rapidly rotating, compact objects may have difficulty ejecting collimated beams of matter or light along the rotation axes until the flows get well beyond the flattened parts of the relativistic mass distribution (which cannot happen in the self-similar models considered in this paper).[[fileno]]2010118010031[[department]]物理
THERMAL STRUCTURE OF NEUTRAL WINDS FROM YOUNG STELLAR OBJECTS
No full text[[abstract]]We discuss the physical processes that control the thermal structure of lightly ionized winds from cool protostars. We concentrate our attention on the hydrogen gas and examine the heating, cooling, and chemical processes that affect the neutral and ionic species of atomic and molecular hydrogen. Warm silicate dust may condense out of the cooling wind and may heat the gas through collisions. Singly ionized sodium atoms, which do not recombine for the mass-loss rates we consider, set a lower limit to the ionization fraction in the wind. Magnetic fields, which are presumed to accelerate the wind, couple directly to the ionic component of the gas and transfer momentum and energy to the neutral component through collisions. We find this process of ambipolar diffusion to be the dominant source of heat input to the gas. We also find that the rate of ambipolar diffusion heating is sensitive to the ionization fraction in the gas and that ambipolar diffusion can keep the gas temperature above 103 K within about 102 stellar radii. Stellar winds having larger mass-loss rates tend to have cooler temperatures. In most cases, the hydrogen in the wind remains atomic and little H2 is formed. The wind remains, however, a conducive environment for the formation of CO molecules.[[fileno]]2010118010074[[department]]物理
ON STATISTICAL MECHANICAL THEORIES OF VIOLENT RELAXATION
No full text[[abstract]]The criticisms of Madsen (1987) directed against the author's particulate description for the statistical mechanics of violent relaxation are answered. To Madsen's argument that the particulate approach violates Liouville's theorem, it is answered that the theorem is necessarily violated on a macroscopic level if the concept of violent relaxation is to have sensible meaning. The use of macrocells and microcells in the particulate approach to describe stars and elementary particles is discussed, and the argument against the particulate approach based on constraints on maximum phase-space density are considered.
--------------------------------------------------------------------------------[[fileno]]2010118010086[[department]]物理
GRAVITATIONAL COLLAPSE OF A UNIFORM SPHEROID
No full text[[abstract]]A uniform, non-rotating, pressure-free spheroid is supposed to collapse gravitationally from rest. It is shown that the initial eccentricity is steadily increased by the anisotropic gravitational field: an initially oblate spheroid tends toward a disk, and an initially prolate spheroid toward a spindle. Numerical results are computed for a series of initial eccentricities.[[fileno]]2010118010140[[department]]物理