Hyperscaling Inequalities for the Contact Process and Oriented Percolation

The contact process and oriented percolation are expected to exhibit the same critical behavior in any dimension. Above their upper critical dimension d _c, they exhibit the same critical behavior as the branching process. Assuming existence of the critical exponents, we prove a pair of hyperscaling inequalities which, together with the results of refs. 16 and 18, implies d _c=4.     

Study of the three-dimensional Ising model on film geometry with the cluster Monte Carlo method

Topological properties of clusters are used to extract critical parameters. This method is tested for the bulk properties ofd=2 percolation and thed=2, 3 Ising model. For the latter we obtain an accurate value of the critical temperatureJ/k _B T _c=0.221617(18). In the case of thed=3 Ising model with film geometry the critical value of the surface coupling at the special transitions is determined as J_1c/J=1.5004(20) together with the critical exponents ₁ ^m =0.237(5) and=0.461(15).     

Magnetic field dependence ofT c and temperature dependence ofH c2 in layered superconductors with open normal state Fermi surface

A theoretical framework for treating the effects of magnetic fieldH on the pairing theory of superconductivity is considered, where the field is taken in an arbitrary direction with respect to crystal axes. This is applicable to closed, as well as open normal state Fermi surface (FS), including simple layered metals. The orbital effects of the magnetic field are treated semiclassically while retaining the full anisotropic paramagnetic contribution. Explicit calculations are presented in the limits |H| → |H _c2(T)|,T ∼ 0 andT →T _c(|H|), |H| ∼ 0. Effects of weak nonmagnetic impurity scattering, without vertex corrections, have also been taken into account in a phenomenological way. The final results for the case of open FS and layered materials are found to differ considerably from those of the closed FS. For example, an important parameter,h(T=0)=|H_c2(0)|/[-Tδ|H _c2 T|δT]_T{s0} for the case of a FS open ink _z-direction with thek _z-bandwidth, 4t ₃, very small compared to the Fermi energy,E _F, is close to 0.5906, compared to 0.7273 for the closed FS, in the clean limit. Analytical results are given for the magnetic field dependence ofT _c and the temperature dependence of H _c2 for a model of layered superconductors with widely open FS. For a set of band structure parameters for YBa₂Cu₃O₇ used elsewhere, we find reasonable values for the upper critical fieldH _c2(0), the slope (dH _c2/dT)_{T c0}, anisotropic coherence lengths ζ_i(T=0),i=x, y, z, and (dT _c/d|H|)_{|H| → 0}.     

A note on differentiability of the cluster density for independent percolation in high dimensions

The cluster density function of independent percolation in ad-dimensional lattice is considered. For eachn, it is shown that(p) has finitenth leftderivative at critical probabilityp _c ifd is sufficiently large. This result agrees with the Bethe lattice approximation, where thenth one-sided derivative of(p) is bounded atp _c for alln.     

On the phase transition to sheet percolation in random Cantor sets

Thed-dimensional random Cantor set is a generalization of the classical middle-thirds Cantor set. Starting with the unit cube [0, 1] ^d , at every stage of the construction we divide each cube remaining intoM ^d equal subcubes, and select each of these at random with probabilityp. The resulting limit set is a random fractal, which may be crossed by paths or (d–1)-dimensional sheets. We examine the critical probabilityp _s(M, d) marking the existence of these sheet crossings, and show that p_s(M,d)1–p_c(M ^d) asM, where p_c(M ^d) is the critical probability of site percolation on the lattice (M ^d) obtained by adding the diagonal edges to the hypercubic lattice ^d. This result is then used to show that, at least for sufficiently large values ofM, the phases corresponding to the existence of path and sheet crossings are distinct.     

Response of Makrofol polycarbonate plastic track detector to 1.1 MeV/N 54 132 Xe-ion

Makrofol polycarbonate plastic track detectors have been exposed to ₅₄ ¹³² Xe -ions of energy 1.1 MeV/N from the cyclotron beam. The bulk etch rate and track etch rate are measured for different temperatures and the activation energies are calculated. The maximum etched track length is compared with the theoretically computed range. The critical energy loss is (dE/dx) _c =5 MeV cm² mg⁻¹ for this detector material.     

Critical behavior of electrical resistivity in amorphous Fe-Zr alloys

Electrical resistivity (ρ) of the amorphous (a-)Fe_100−c Zr _c (c=8.5, 9.5 and 10) alloys has been measured in the temperature range 77 to 300 K, which embraces the second-order magnetic phase transition at the Curie temperature point T _c. Analysis of the resistivity data particularly in the critical region reveals that these systems have a much wider range of critical region compared to other crystalline ferromagnetic materials. The value of T _c and specific heat critical exponent, α has the same values as those determined from our earlier magnetic measurements. The value of α for all the present investigated alloys are in close agreement with the values predicted for three-dimensional (3D) Heisenberg ferromagnet systems, which gives contradiction to the earlier results on similar alloys. It is observed from the analysis that the presence of quenched disorder does not have any influence on critical behavior.     

阴极电压脉冲占空比对钛合金微弧氧化膜特性的影响

利用自制多功能微弧氧化电源,在保持双极性电压脉冲幅度不变的条件下,研究了阴极电压脉冲占空比（d_c）对钛合金微弧氧化膜特性的影响.结果表明：阴、阳极的峰值电流随处理时间的变化分为几个不同阶段,各阶段的开始和结束时间与d_c密切相关.氧化膜主要由金红石和锐钛矿相TiO₂组成,金红石相TiO₂的相对含量在d_c=50%附近随d_c的 关键词： 微弧氧化 钛合金 占空比     

Onset of local ordering in some copper-based alloys: critical solute concentration vis-a-vis various solutionhardening parameters

The mode of planar distribution of solute atoms in Cu single crystals alloyed with 0.5 to 8.0 at.%Ge has been investigated via the temperature dependence of the critical resolved shear stress of these alloys. It is found that there exists a critical solute concentration c _m ≈ 5 at.%Ge below which the distribution of solute atoms in the crystal is random, and above which some local ordering occurs. This together with such data available in the literature for Cu-Zn, Cu-Al and Cu-Mn alloys, i.e. c _m ≈7 at. %Zn, 7 at.%Al and 1 at.%Mn, when examined as a function of the size-misfit factor δ = (1/b)(db/dc)of a given binary alloy system, shows that the value of c _m strongly depends on δ; the smaller the magnitude of δ, the greater the value of c _m and vice versa. Also, the value of c _m is found to correlate well with the electron-to-atom ratio (e/a)of the Cu-Zn, Cu-Al, Cu-Ge and Cu-Mn alloys with the solute concentration c = c _m . However, no systematic correlation exists between the critical solute concentration c _m for the onset of local ordering and the modulus-mismatch parameter η = (1/G)(dG/dc).      

High-temperature series analysis of the p-state Potts glass model on d-dimensional hypercubic lattices

We analyze recently extended high-temperature series expansions for the “Edwards-Anderson” spin-glass susceptibility of the p-state Potts glass model on d-dimensional hypercubic lattices for the case of a symmetric bimodal distribution of ferro- and antiferromagnetic nearest-neighbor couplings . In these star-graph expansions up to order 22 in the inverse temperature , the number of Potts states p and the dimension d are kept as free parameters which can take any value. By applying several series analysis techniques to the new series expansions, this enabled us to determine the critical coupling K_c and the critical exponent of the spin-glass susceptibility in a large region of the two-dimensional (p,d)-parameter space. We discuss the thus obtained information with emphasis on the lower and upper critical dimensions of the model and present a careful comparison with previous estimates for special values of p and d. Received: 25 May 1998 / Revised and Accepted: 11 August 1998     

阶梯化对快离子导体LixTiS2的结构与能量性质的影响

根据密度波理论建立了stage-2有序Li_xTiS₂(x=1/8,1/6,1/4,1/3,3/8,1/2)系统的晶胞模型.采用平面波赝势方法,对stage-2有序系统和stage-1有序Li_xTiS₂(x=0,1/4,1/3,1/2,2/3,3/4,1)系统进行了几何结构优化和总能量计算,并进行了对比研究.发现stage-2晶胞的参量c(d关键词： xTiS₂')" href="#">Li_xTiS₂ 阶梯结构 有序—无序相变 第一性原理计算     

Effects of neutron irradiation on superconducting properties of orthorhombic Y–Ba–Cu oxides

Abstract

We have studied the effects of fast neutron (E>0.1 MeV) irradiation at reactor (～ 360 K) and low (～ 20 K) temperatures on the superconducting properties of polycrystalline orthorhombic YBa₂Cu₃O_7?y . Measurements were made on the superconducting critical temperature T_c , critical current J_c , Meissner effect and magnetic field dependence of J_c . The T_c drops by an irradiation at reactor temperature and J_c increases with increasing fluence. On the other hand with the irradiation at low temperature, T_c rises and J_c increases. Results of observation of Meissner effect and the magnetic field dependence of J_c are consistent with the behavior of T_c and J_c .     

Self-interstitial solute interaction in aluminium base alloys: Problems of data interpretation

The interpretation of electrical resistivity measurement results of Al base alloys is critically discussed. Correct numerical data evaluation with respect to the atomistic properties r_c/r_p, r_t and Pf^t/Pf is yet impossible for Al and its alloys because of the overlapping of Ic and Id recovery for those electron irradiations for which damage rate measurements exist and because of the unexplained scatter of initial damage rate data.     

Finite-size scaling in systems with long-range interaction

The finite-size critical properties of the (n) vector ϕ⁴ model, with long-range interaction decaying algebraically with the interparticle distance r like r ^{-d - σ}, are investigated. The system is confined to a finite geometry subject to periodic boundary condition. Special attention is paid to the finite-size correction to the bulk susceptibility above the critical temperature T _c. We show that this correction has a power-law nature in the case of pure long-range interaction i.e. 0 < σ < 2 and it turns out to be exponential in case of short-range interaction i.e.σ = 2. The results are valid for arbitrary dimension d, between the lower ( d _< = σ) and the upper ( d _> = 2σ) critical dimensions. Received 2 July 2001 and Received in final form 4 Septembre 2001     

Series and Monte Carlo study of high-dimensional Ising models

Ising models in high dimensions are used to compare high-temperature series expansions with Monte Carlo simulations. Simulations of the magnetization on four-, six-, and seven-dimensional hypercubic lattices give consistent values of the critical temperature from both equilibrium and nonequilibrium data ford=6 and 7. We tabulate 15 terms of series expansions for the susceptibility for generald and giveJ/k _B T _c =0.092295 (3) and 0.077706 (2) ford=6 and 7. In contrast to five dimensions, where earlier series found nonanalytic scaling corrections, for d=6 and 7 the leading scaling correction may be analytic inT-T _c . In most cases these expansions gave more accurate results than these simulations.     

二维颗粒流从稀疏态到密集态的临界转变

研究了斜槽中的二维颗粒流由稀疏到密集转变的临界现象.在二维颗粒槽的入口流量Q₀和出口尺寸d固定的条件下，记录并统计了稀疏流转变为密集流所经历的时间.研究发现，在统计时间内转变不发生的概率C(t)随时间指数衰减，其衰减的特征时间尺度α^-1(d)可以很好地由幂律函数a(d_c-d)^-γ来拟合，其中d_c为临界开口尺寸.此临界尺寸的存在确定了稀疏流到密集流转变的临界现象. 关键词： 颗粒物质 颗粒流 非平衡态相变 几何相变     

Effect of pressure on the superconducting transition in Bi-Sr-Ca-Cu-O system

Abstract

The effect of pressure on T_c was studied on 110 K class Bi-Sr-Ca-Cu-O (1:1:1:2) compounds. T_c was varied with current in I^3/2 , and defined at the value extrapolated to zero current. dT_c /dP = + 0.18 K/kbar was obtained up to 10.9 kbars.     

Electronic structure and glass forming ability in early and late transition metal alloys

A correlation between the change in magnetic susceptibility (Δχ_exp) upon crystallisation of Cu–Zr and Hf metallic glasses (MG) with their glass forming ability (GFA) observed recently, is found to apply to Cu–Ti and Zr–Ni alloys, too. In particular, small Δχ_exp, which reflects similar electronic structures, ES, of glassy and corresponding crystalline alloys, corresponds to high GFA. Here, we studied Δχ_exp for five Cu–Ti and four Cu–Zr and Ni–Zr MGs. The fully crystalline final state of all alloys was verified from X-ray diffraction patterns. The variation of GFA with composition in Cu–Ti, Cu–Zr and Cu–Hf MGs was established from the variation of the corresponding critical casting thickness, d_c. Due to the absence of data for d_c in Ni–Zr MGs their GFA was described using empirical criteria, such as the reduced glass transition temperature. A very good correlation between Δχ_exp and d_c (and/or other criteria for GFA) was observed for all alloys studied. The correlation between the ES and GFA showed up best for Cu–Zr and NiZr₂ alloys where direct data for the change in ES (ΔES) upon crystallisation are available. The applicability of the Δχ_exp (ΔES) criterion for high GFA (which provides a simple way to select the compositions with high GFA) to other metal-metal MGs (including ternary and multicomponent bulk MGs) is briefly discussed.