块体非晶合金的黏度与玻璃形成能力的关系

基于经典结晶理论讨论了非晶合金的晶化动力学因素和晶化热力学因素对玻璃形成能力（GFA）的影响.分析表明,合金的等温转变（TTT）曲线“鼻尖”温度T_n对应的黏度与晶化阻力因子成正比;重新加热时晶化开始温度T_x对应的黏度与晶化驱动力因子成反比.由此得到了新的GFA参数ω₀=（T_g-T₀）/（T_x-T₀）-（T_g-T₀）/（T_n-T₀）,其中T_g为玻璃转变温度,T₀为理想玻璃转变温度.统计结果显示,ω₀与临界冷却速率具有较高的相关性,R²高达09626.进一步分析表明：新提出的ω₀参数可以合理地解释过冷熔体的黏度、脆性、液相稳定性、热稳定性以及T_rg、ΔT_x、γ、γ_m、ΔT_rg、α、β、δ和φ等参数与GFA的关系. 关键词： 块体非晶合金 黏度 脆性 玻璃形成能力     

倾斜度及温度震荡频率对三维多孔介质方腔自然对流换热的影响

对三维多孔介质倾斜方腔内非稳态自然对流换热进行数值研究.腔体右壁面(X=1)保持恒温T₀,左壁面(X=0)基于温度T₀按正弦规律变化,其他所有壁面保持绝热.采用Brinkman扩展达西模型及SIMPLE算法模拟方腔内的流动.方腔沿y轴转动倾角α1的变化范围为0°~90°,沿x轴转动倾角α2的变化范围为0°~45°,无量纲温度震荡频率f的变化范围为5π~90π.详细研究倾角和温度震荡频率对三维方腔自然对流换热的影响.计算结果表明:当倾角α1=46°,α2=45°及温度震荡频率f=45π时,方腔内的换热最强.     

AlAs相变及热动力学性质的第一性原理研究

利用基于密度泛函理论的全势能线性糕模轨函法研究了闪锌矿（B3）,NiAs（B8）和岩盐（B1）结构的AlAs的相变、结构性质以及热动力学性质.对B3-B8和B3-B1结构的能量体积曲线做公切线,得到了B3→B8相变压力为5.44 GPa,并预测到B3→B1相变压力为6.46 GPa.同时计算了高压下B8相的结构性质,结果显示当V/V₀≈0.7—1.05时,c/a基本保持恒定（仅有约 0.2%的波动）;当V/V₀≈0.4—0.7,c/a随着V/V₀的减小而近似线性地增大.通过状态方程拟合,得到了AlAs的相对体积V/V₀与压强P的函数关系,B8相的状态方程与实验结果符合很好.最后利用准谐德拜模型得到了AlAs的体弹模量B随压力P的变化关系以及不同压强下热容C_V与温度T的关系. 关键词： 相变 热力学性质 第一性原理     

冲击压缩下铝、铜、钨的剪切模量和屈服强度与压力和温度的相关性

对铝、铜和钨在冲击压缩状态下的剪切模量和屈服强度的实验数据进行了综合分析，并与St einberg-Cochran-Guinan(SCG)模型的计算结果进行了比较，结果表明，铝在50 GPa、铜在1 00 GPa、钨在200 GPa冲击压力以内，三种材料的剪切模量和屈服强度随温度和压力的变化 趋势基本相似，即SCG模型的假设Y′_pY₀=G′_pG ₀,Y′_TY₀=G′_TG₀对这三种材料在上述冲击压力范围内近似成立，利用该模型可以较好地描述材料在冲击压缩 下的本构行为. 关键词： 剪切模量 屈服强度 压力 温度     

双色噪声驱动光学双稳系统的弛豫时间研究

研究乘性及加性噪声的自关联时间τ₁和τ₂,交叉关联时间τ对光学双稳系统的弛豫时间的影响.弛豫时间T由Mei等所采用的方法得到. 经数值计算, 结果表明: 两噪声间交叉关联时间τ及乘性噪声的自关联时间τ₁延缓系统涨落的消退(T随τ及τ₁的增大而增大);T随加性噪声的自关联时间τ 关键词： 关联噪声 弛豫时间 光学双稳系统     

水溶液中稀土离子与甘氨酸、丝氨酸、天冬氨酸作用的13C NMR研究

测定了酸性水溶液中甘氨酸、丝氨酸和天冬氨酸稀土络合物(Ln=La、Pr、Nd、Eu、Tb、Dy、Ho、Er、Tm和Yb)的¹³C诱导位移。对位移试剂的分析指出,三种氨基酸通过α-羧基以双齿形式配位于稀土,配位键长为0.23nm~0.25nm,天冬氨酸的γ-羧基也是配位基团。由本文与文献中已报道的各种氨基酸稀土络合物的¹³C诱导位移的系统分析表明,配体¹³C超精细偶合常数A值和结构因子G值有如下规律:(1)│A(C₀)│<│A(C_α)│;A(C₀)为正,A(C_α)为负;(2)│G(C₀)│>│G(C_α)│;配体碳核的G均为负值。     

激光极化129Xe核自旋弛豫率的测量

由弱磁场下光泵自旋交换、强磁场中核磁共振测量方法,获得激光极化低压同位素¹²⁹Xe气体的核自旋弛豫率1/T₁及其与N₂气压力、环境温度的关系.结果表明:在291K的室温下,对于0~11 333.05Pa的N₂气压力范围,1/T₁随着N₂气压力的增加而增大;N₂气压力为1 466.63Pa时,1/T₁随着样品温度从234K到292K增高而减小     

基于蒙特卡罗算法的低场核磁共振测量效率提高方法

核磁共振（NMR）的纵向弛豫时间（T₁）、横向弛豫时间（T₂）、自扩散系数（D₀）,以及T₂-T₁、T₂-D₀测量目前广泛应用于石油测井行业.在测量D₀的SGSE序列中,通过逐渐增大90°和180°脉冲之间的时间间隔（T_d）,可以对液体扩散行为产生的影响进行调节.然而T_d的"起点"、"步进数"和"终点"等参数必须设置得当才能准确测量T₁和D₀.目前参数的设置依赖多次的人工调整和测量人员的经验,耗时且使用门槛较高.本文用蒙特卡罗方法进行大量随机模拟,根据前面若干点的测量结果筛选出满足要求的随机值,预测下一个测量点的位置.该算法可以实时更新参数设置,实现自动化测量,达到降低测量门槛、缩短测量时间的目的.经验证,该算法可以适用于T₁、D₀的测量.     

交叉关联噪声对光学双稳系统平均首通时间的影响

研究了乘性色噪声和加性白噪声驱动的光学双稳系统中噪声对系统两个方向平均首通时间T₊（x_s1→x_s2）和T_-（x_s2→x_s1）的影响（平均首通时间是指从一稳态出发越过势垒到另一稳态所用时间的平均值）.通过Novikov定理和Fox近似方法得到相应的Fokker-Planck方程,利用最速下降法得到T₊（x_s1→x_s2）和T_-（x_s2→x_s1）的表达式.研究发现：乘性噪声强度Q和加性噪声强度D对T₊（x_s1→x_s2）的影响相同,对T_-（x_s2→x_s1）的影响不同;T₊（x_s1→x_s2）随乘性色噪声自关联时间τ的增大而增大,但随噪声间的交叉关联强度λ的增大而减小;T_-（x_s2→x_s1）随τ的增大而减小,随λ的增大而增大. 关键词： 平均首通时间 光学双稳系统 乘性色噪声 加性白噪声     

关于MgB2/Al2O3超导薄膜电阻转变和各向异性的研究

利用电子束蒸发方法将MgB₂超导薄膜沉积到Al₂O₃(001)衬底上.采用标准的四引线法研究了磁场平行和垂直超导薄膜ab平面下的电阻转变.一个激活能模型 U(T,H)=U₀(1-T/(T_c+δ))ⁿ(1-H/H 关键词： 2/Al₂O₃')" href="#">MgB₂/Al₂O₃ 超导体 电阻转变 各向异性     

Two equivalent criteria for modularity of the lattice of all physical decision effects

This paper answers the open question 1 of [3] in the affirmative and, conditionally, the open question 2 of [3], too. Assuming irreducibility of the orthomodular latticeG of all physical decision effectsE, we shall prove in the first section that modularity ofG implies symmetry of the physical probability function . In the second section, we shall consider the filter algebra (B) being assumed to possess an involution * such thatT*T=0 impliesT=0. Then this will be proved: If every atomic filterT _P is a fixpoint of * and * is, in a restricted manner, norm-preserving on the minimal left ideal _P :=(B)T _P , thenG is modular.     

Coupled temperature dependences of volume and compressibility

We present a new method for understanding the changes with temperature of the volume and compressibility of solids. These changes depend on five parameters: V ₀, B ₀, Θ, γ _G and δ _T. V ₀ and B ₀ are the atomic volume and bulk modulus at T?=?0?K, Θ is the Debye temperature, γ _G is the Grüneisen parameter, and δ _T is the Anderson–Grüneisen parameter. Equations for the temperature-dependent volume, bulk modulus and thermal expansion are given, and examples of the use of these equations are provided, with particular emphasis on the light actinides. For the elements, we examine the relationship between experimental values of γ _G and δ _T, and find no clear correlation. In particular, Swenson's rule, which states that the bulk modulus does not change with temperature if the volume is held constant, is a poor approximation to the data. We reveal a new useful approximate relationship between dB/dP and γ _G. We find that the thermodynamic quantity q, which describes the variation in γ _G with volume, distributes around 2, not around 1, as often assumed. We show that the thermal- expansion behavior of Si and Ge (including negative thermal expansion at low temperatures) are well described with the use of a two-level invar model.     

Ni-15%Mo合金熔体热物理性质的Monte Carlo模拟

采用EAM势对6×6×6的Ni-15%Mo合金熔体进行Monte Carlo模拟,通过对不同温度下获得的NVT系统的平衡态统计分析得出Ni-15%Mo合金熔体在过冷态和过热态时的热物理性质.通过构造系统生成新表面,表面张力做功使系统能量发生改变,从而得到液态表面张力的模拟结果.Ni-15%Mo合金熔体的表面张力在1500—2000 K的温度范围内,随温度的变化规律为σ=1.918-1.130×10^-3（T-T_m） N/m 关键词： Monte Carlo模拟 表面张力 比热 Ni-15%Mo合金     

Synthesis, structure and magnetic properties of the new double perovskite Ca2CrSbO6

The title double perovskite has been synthesized by solid-state reaction in air. The crystal structure has been studied from powder X-ray diffraction data. Rietveld fits to the pattern show that this compound has a monoclinic symmetry [a=5.4932(3) Å, b=5.4081(3) Å, c=7.6901(5) Å, β=90.0022(1)°, at 300 K] defined in the space group P2₁/n, where the Cr and Sb cations are almost completely ordered in the B-sublattice of the perovskite structure. Magnetic susceptibility and magnetization measurements show that this compound behaves as a Curie-Weiss paramagnet at high temperatures with μ_eff=3.53(1) μ_B and θ_P=8 K, and exhibits a robust ferromagnetic component below the ordering temperature of T_C=13 K, with a saturation magnetization of 2.36 μ_B/f.u. at 5 K. To our knowledge, this is the first example of a ferromagnetic double perovskite containing a non-magnetic element, such as Sb, occupying one half of the B positions of the perovskite structure.     

Temperature and pressure dependence of molar volume in solid phases of ammonia near the melting point

Temperature and pressure dependencies of the molar volume are studied here along the transition curve between solid I and solid II phases near the melting point in ammonia. The molar volumes are calculated in the temperature range of 217 to 224  K and in the pressure range of 3 to 8 kbar with respect to the triple point (T_t = 217.34 K, P_t = 3.070 kbar) where the melting curves of solid I and solid II coincide with the transition curve in ammonia.     

Photoconductivity derived from an exact modelling of the uncompensated one-donor model. II—computer simulation of the steady-state exact model

Abstract

Stationary photoconductivity is treated with the model of Part I, free from any of the usual simplifying approximations of the related equations. This simulation leads to set forth a new concept of characteristic temperature T ₀, at which the donor population is independent of the illumination intensity G. T ₀ separates two intervals of temperature over which G either partially empties (T< T ₀) or fills (T > T ₀) the level. Also T ₀ has, in particular, an influence on the ratio n/p of free electrons and holes. The effective isothermal behaviour of n(G) shows that n(G) ∞ G ^1/2 on the lower side of the G range, and n(G) ∞ G at higher G. Variations of n(T) at constant G also display original, T ₀ dependent, characteristics. Finally, a qualitative comparison is made of the 1D model with the two 1D_ai approximate models described in I, in order to distinguish their most prominent behaviour differences.     

Equation of state of liquid Fe–17 wt%Si to 12 GPa

Equation of state (EOS) of liquid Fe–17 wt%Si has been investigated at a temperature of 1773 K and pressures up to 12 GPa by the sink/float technique using composite spheres. The EOS of liquid Fe–17 wt%Si, in the form of the second order Birch–Murnaghan equation, produces K _0T=68±2 GPa when K′_0T=4.0. Considering the effect of temperature and pressure on K _0T, extrapolation of this EOS to Earth's outer core conditions reveals that the addition of Si to liquid Fe decreases its density ρ and increases its compressional wave velocity V _P , indicating that Si is a possible light element candidate in the outer core. The possible existence of Si in the cores of other planetary bodies is also discussed.     

Magnetic phases in UNi<Subscript>2</Subscript>Si<Subscript>2</Subscript>

The tetragonal compound UNi₂Si₂ exhibits in zero magnetic field three different antiferromagnetic phases belowT _N =124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q _z ). Two additional order-order magnetic phase transitions are observed below T _N , namely atT ₁=108 K and T ₂=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel to the c-axis. UNi₂Si₂ single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity, susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5 T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties of UNi₂Si₂.