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Dipole and Quadrupole Phase Transitions in Spin-l Models
Get PDF[[abstract]]A spin-1 Hamiltonian with arbitrary bilinear and biquadratic pair interactions has been studied in the molecular-field approximation by using one- and two-sublattice models. Various types of orderings and transitions are found for the Hamiltonians with different symmetries. For a system described by a one-sublattice Hamiltonian with Ising, isotropic, or cubic symmetry, only one phase transition is found; either from the paramagnetic phase to a ferromagnetic or to a ferroquadrupolar phase. (Parallel alignment of quadrupoles is denoted ferroquadrupolar.) For the one-sublattice Hamiltonian with axial symmetry, we find two separate phase transitions; first from the paramagnetic phase to a ferroquadrupolar phase and then to a ferromagnetic phase. A two-sublattice system described by an Ising or isotropic Hamiltonian can have a transition either from the paramagnetic phase to a ferromagnetic phase, or to a ferriquadrupolar phase. Additional transitions are also found from the ferromagnetic to a ferrimagnetic phase and then back to the ferromagnetic phase. The system can have as many as three successive transitions. For a two-sublattice Hamiltonian with cubic symmetry, besides the transitions found in Ising systems, there are "reorientation" phase transitions; i.e., transitions from a quadrupole ordering along the cube edge to an ordering along the cube diagonal. This system can have more than three successive phase transitions.[[fileno]]2010111010011[[department]]物理
A Generalised Equivalent Neighbor Model I. Derivation of the High-Temperature Lattice Constants
Get PDF[[abstract]]A new equivalent-neighbour model is introduced in which the spins within a hypercube of volume (2R+1)d interact equally with the spin at the centre of the hypercube. The lattice dimensionality d and the range of the interaction R are variables. The concept of the coincidable occurrence factors is introduced. Connections between the coincidable occurrence factors and the high-temperature lattice constants are shown. A systematic way of deriving the high-temperature lattice constants through the use of the coincidable occurrence factors is developed. The high-temperature lattice constants are derived up to eighth order. The extension of d and R from integers to real values is discussed. The present model can also be extended to an anisotropic one in which the ranges of interactions are different in different lattice directions.[[fileno]]2010111010022[[department]]物理
Series Analysis of High-Temperature Susceptibility for the Four-Dimensional Ising Model
No full text[[abstract]]High-temperature susceptibility series for the spin-1/2 Ising model are obtained to the 8th order forseveral four-dimensional lattices: the simple hypercubic, the body-centered hypercubic, the hypertriangular,and the generalized equivalent nieghbor lattices. These series are analyzed by assuming a singularity of theform（方程式無法摘錄）. Several methods of analysis are considered. We find that it is difficult to deter-mine both T and independently. However, if is known, T and A can be determined easily. Adopt-ing the result of renormalization group approach, =1/3, we have determined the critical temperaturesT and the critical amplitudes A for various four-dimensional lattices.
本文求出若干四維晶格上自旋為1/2艾辛模型之高溫磁化率級數至第8階。這些四維晶格為簡單超立方晶格、體心超立方晶格、超三角晶格及廣義等鄰晶格。假設在臨界溫度附近這些級數的發散情形為（方程式無法摘錄），本文考慮了數種分析這些臨界參數的方法。我們發現T 及很難獨立求出。但是，如果知道了，T 及A可以很容易求得。採用了再歸元群法之結果=1/3，我們定出了前述四維晶格之臨界溫度為T 及臨界振幅A。[[fileno]]2010111010026[[department]]物理
Preservation of the Free Energy in a Migdal-Kadanoff Approximation for the Spin-l/2 Anisotropic Heisenberg Model
Get PDF[[abstract]]A modification of the Migdal-Kadanoff approximation is applied to study the spin-(1/2 anisotropic Heisenberg model. The approximate decimation introduced by Suzuki and Takano, and the method of preserving the free energy developed by Walker are adopted. Fixed points and critical lines are determined for cubic lattices. The dependence of fixed points on the number of terms used in the series expansion of the free energy is analyzed and discussed.[[fileno]]2010111010036[[department]]物理
Common Properties of Some Multiattribute File Systems
No full text[[abstract]]This paper results from an attempt to unify several different file system design theories. We define a term "partial match pattern" and show that in order to produce file systems optimal with respect to partial match patterns, both the multikey hashing (MKH) method [16] and the multidimensional directory (MDD) method [11] must be in such a form that the number of subdivisions is the same for all domains of keys. We show the conditions for the string homomorphism hashing (SHH) method [15], the MKH method, and the MDD method to be equivalent to one another. We define the so-called Cartesian product files and show that if all records are present, the records in a Cartesian product file form a shortest spanning path in which the Hamming distance between every pair of consecutive records is 1. Thus the SHH method, the MKH method, the MDD method, and the multikey sorting (MKS) method [10] are linked together. Finally, we show that for both partial and best match queries, the file systems exhibit a common characteristic: similar records are grouped together.[[fileno]]2030256010026[[department]]資訊工程學
A Parallel Algorithm to Solve the Stable Marriage Problem
No full text[[abstract]]In this paper a parallel algorithm to solve the stable marriage problem is given. The worst case performance of this algorithm is stated. A theoretical analysis shows that the probability of the occurrence of this worst case is extremely small. For instance, if there are sixteen men and sixteen women involved, then the probability that the worst case occurs is only 10–45. Possible future research is also discussed in this paper.[[fileno]]2030256010087[[department]]資訊工程學
Time scale of disk and planet formation
No full text[[abstract]]We review the current theories and observations of the formation of Sun-like stars and protoplanetary disks in distributed and clustered environments. The astrophysical estimates for the temporal durations of various phases of the process are calibrated by theoretical calculations of pre-main sequence contraction tracks for T Tauri stars, a task which is fairly firmly grounded at present.[[fileno]]2010118030011[[department]]物理
Protostellar cosmic rays and extinct radioactivities in meteorites
Get PDF[[abstract]]Calcium-aluminum-rich inclusions (CAIs) and chondrules of chondritic meteorites may originate with the melting of dustballs launched by a magnetically driven bipolar outflow from the inner edge of the primitive solar nebula. Bombardment by protostellar cosmic rays may make the rock precursors of CAIs and chondrules radioactive, producing radionuclides found in meteorites that are difficult to obtain with other mechanisms. Reasonable scalings from the observed hard X-rays for the cosmic-ray protons released by flares in young stellar objects yield the correct amounts of Ca-41, Mn-53, and La-138 inferred for meteorites, but proton- and alpha-induced transformations underproduce Al-26 by a factor of about 20. The missing Al-26 may be synthesized by He-3 nuclei accelerated in impulsive flares reacting primarily with Mg-24, an abundant isotope in the target precursor rocks. The mechanism allows a simple explanation for the very different ratios of Al-26/Al-27 inferred for normal CAIs, CAIs with fractionated and unidentified nuclear (FUN) anomalies, and chondrules. The overproduction of Ca-41 by analogous He-3 reactions and the case of Fe-60 inferred for eucritic meteorites require special interpretations in this picture.[[fileno]]2010118010045[[department]]物理
MAGNETOCENTRIFUGALLY DRIVEN FLOWS FROM YOUNG STARS AND DISKS .5. ASYMPTOTIC COLLIMATION INTO JETS
No full text[[abstract]]We consider the asymptotic behavior of magnetocentrifugally driven X-winds, taking into proper account the pressure balance across the interface between the open stellar field lines of the dead zone devoid of matter and the open field lines of the wind. At large distances from the source the outflow collimates into jets along the rotation axis. Being almost cylindrically symmetric even close to the source of the outflow, the density distribution appears more jetlike than the collection of streamlines, which always contains a few members that skim over the surface of the disk.[[fileno]]2010118010057[[department]]物理
戰後台灣社會研究的回顧
No full text[[abstract]]本文回顧過去四十年來，台灣學術界有關「台灣社會研究」重要論述的變遷，檢討不同的論述如何將「台灣社會」作為一個被研究的對象，賦與它何種的意義，以及這些論述在何種的歷史結構條件下形成和變遷。[[fileno]]204_JA05_1993_n1_p1