Gruhn-Hess两体势修正模型向列相液晶微滴的Monte Carlo模拟

基于Gruhn-Hess两体势修正模型,用Monte Carlo方法模拟向列相液晶微滴.Gruhn-Hess两体势是空间各向异性的,修正模型的势参数依赖于液晶的弹性常数K₁₁、K₂₂、K₃₃及表面弹性常数K₁₃.假设向列相液晶微滴具有自由表面,在低温下计算分子二阶序参数和切向内禀强度在微滴内不同区域的变化,并与Gruhn-Hess两体势模型一作对比分析.结果表明:附加K₁₃项的修正模型在微滴表面产生内禀锚定,其大小决定了内禀易取向方向及内禀锚定强度的大小,且内禀强度的大小与K₃₃/K₁₁值有关;空间不完整的向列相液晶微滴由内层到外层有序度逐渐降低.     

全漏光导波技术确定液晶材料的挠曲电系数

利用全漏光导波技术,测量负性向列相液晶材料MS-N01300-000的展曲和弯曲挠曲电系数之和.根据液晶弹性和多层光学理论得到同一电压下不同挠曲电系数的反射率随内角(入射到液晶层角度)的理论变化曲线.实验中,将液晶材料灌注到混合排列向列相液晶盒中,在液晶盒上分别加交流电和直流电,采用全漏光导波技术得到反映液晶指向矢分布的液晶波导反射率随内角变化曲线.实验发现,由于液晶挠曲电作用,同一电压值下反射率随内角变化曲线发生微小移动.对比理论与实验曲线,由曲线移动距离得到MS-N01300-000液晶材料展曲和弯曲挠曲电系数之和为2.5×10-11 C/m.     

压力及杂质氢对金属锂弹性特性的影响

针对六角密堆金属锂16个原子超晶胞(supercell)、填隙一个氢原子的周期单元，采用基于密度泛函理论的平面波-赝势方法，研究了零温条件下压力及填隙氢掺杂对体系弹性性质的影响.结果表明氢掺杂导致体系的体模量增加.常压下掺杂体系的弹性常数C₁₁，C₃₃，C₆₆和C₁₂高于单质体系，剪切模量C₄₄有所下降，而C₁₃则与单质体系持平.压力作用下C₁₁，C₃₃和C₆₆一直大于单质体系，但C₁₂的值低于单质体系.在2GPa—4GPa压力区间内，弹性常数C₁₃呈反常变化，小于单质体系；在高压区掺杂体系的C₄₄和C₁₃则高于单质体系的相应量值，压力导致掺杂体系和单质体系之间剪切模的偏离加剧.掺杂体系在压力作用下依然保持压缩模的各向同性，具有和单质体系相似的特性. 关键词： 第一性原理 压力效应 弹性常数 金属锂     

{Cu3}单分子磁体在磁场中的热纠缠

本文研究单分子磁体Na₉[Cu₃Na₃(H₂O)₉ (α-AsW₉O₃₃)₂]·26H₂O中三角自旋 环在磁场作用下的热纠缠性质, 利用数值计算求出任意两个Cu²⁺离子量子比特之间的配对纠缠度, 分别记为C₁₂, C₂₃和C₁₃. 研究结果表明, 磁场的方向和大小以及温度对配对纠缠度具有重要影响, 而且参数的变化对C₁₂, C₂₃和C₁₃的影响也是各不相同. 给出外加三个不同方向的磁场时, 配对纠缠度C₁₂, C₂₃和C₁₃各自对应的临界温度T_c随磁场强度的变化图, 由此可以得到单分子磁体三角自旋环中存在纠缠态的参数范围. 通过选择适当的磁场方向和大小以及温度等实验参数, 可以有效地调节和提高单分子磁体中的配对纠缠度. 关键词： 配对纠缠 单分子磁体 三角自旋环     

基于液晶动态响应的挠曲电系数测量EI北大核心CSCD

基于自组装的液晶动态响应实验装置,研究了液晶挠曲电效应对强锚泊混合排列向列相(HAN)液晶动态响应过程的影响。实验中HAN液晶盒施加脉宽为250 ms、幅度可调的正负单脉冲电压信号,结果发现:幅度相同的正负脉冲电压信号作用下液晶的动态响应不同,幅度不同的正脉冲或负脉冲电压信号作用下液晶的动态响应也不同。通过幅度不同的正脉冲电压信号(3、4、5、6 V)作用下液晶动态响应实验曲线与考虑挠曲电效应情形下液晶动态响应理论曲线之间的比较,得到了液晶材料E7的挠曲电系数为e11+e33=4.0×10-11C/m,与文献中报道的实验测量值基本一致。     

基于液晶动态响应的挠曲电系数测量

基于自组装的液晶动态响应实验装置,研究了液晶挠曲电效应对强锚泊混合排列向列相(HAN)液晶动态响应过程的影响。实验中HAN液晶盒施加脉宽为250 ms、幅度可调的正负单脉冲电压信号,结果发现:幅度相同的正负脉冲电压信号作用下液晶的动态响应不同,幅度不同的正脉冲或负脉冲电压信号作用下液晶的动态响应也不同。通过幅度不同的正脉冲电压信号(3、4、5、6 V)作用下液晶动态响应实验曲线与考虑挠曲电效应情形下液晶动态响应理论曲线之间的比较,得到了液晶材料E7的挠曲电系数为e11+e33=4.0×10-11C/m,与文献中报道的实验测量值基本一致。     

基于p1-p2与a1+a2共同本征态的相干纠缠态表象的构建及性质

利用有序算符乘积内的积分技术（IWOP）,建立了一种称之为相干纠缠态的两粒子体系的新表象,研究了这种新表象的性质,从理论上探讨了这种相干纠缠态的产生方法.结果表明：本文建立的这种p₁-p₂与a₁+a₂的共同本征态|p,β〉,既具有相干态的特性,又体现了纠缠态的特征,具有超完备性,完全可以作为一个表象使用. 物理上可以用光分束器来实现|< 关键词： IWOP技术 相干纠缠态表象 分束器     

Er3+-Yb3+共掺碲酸盐玻璃上转换绿光激发过程的研究

根据Er³⁺-Yb³⁺共掺碲酸盐玻璃绿光上转换发光的能级结构和相关跃迁建立的速率方程模型,分析了Er³⁺的⁴S_3/2能级上升特性与⁴I_11/2能级和Yb³⁺的²F_5/2能级的关系.通过模型对实验观测的上升和衰减曲线的拟合,确定速率方程模型的相关参数,计算⁴S_3/2能级粒子数布居趋于稳定时能量传递粒子数与激发态吸收粒子数之比.进一步分析了Er³⁺-Yb³⁺共掺绿光上转换发光的动力学过程. 关键词： 速率方程模型 上转换 3+-Yb³⁺')" href="#">Er³⁺-Yb³⁺ 方波激发     

方波激发下Er3+上转换绿光发光动力学过程的研究

用方波电源驱动808 nm,980 nm激光二极管（LD）激发Er³⁺掺杂的亚碲酸盐氟氧化物玻璃,测量²H_11/2,⁴S_3/2能级上转换发光的上升和衰减,不同波长激发下的上升时间常数不同,说明808 nm LD和980 nm LD激发下²H_11/2,⁴S_3/2能级上转换激发途径不同.通过建立速率方程模型分析了⁴S_3/2能级的上升特性与中间能级寿命的关系,从而确定了两种波长激发下上转换绿光的激发机理. 关键词： 上转换 激发过程 3+')" href="#">Er³⁺ 方波激发     

Monte Carlo模拟空间各向异性势向列相液晶微滴

基于分子两体势,用Monte Carlo方法计算向列相液晶微滴.两体势基于格点模型,是空间各向异性的且依赖于液晶的弹性常数.假定向列相液晶微滴具有自由表面,引入切向内禀强度定量描写表面引发的分子内禀易取向的强弱.通过各向异性势的两种方案,在低温下计算切向内禀强度和二阶序参数在微滴内不同区域的变化,与Lebwohl-Lasher模型作对比分析.结果表明:只有一种方案在微滴表面产生内禀易取向,且内禀强度值的大小与K₃₃/K₁₁值有关;空间不完整的向列相液晶使得微滴由内层到外层有序度越来越低.     

Investigation of scattering of elastic waves by cylinders in 1-3 piezocomposites

The scattering behavior of P-waves in piezoelectric composites with 1–3 connectivity is studied. The method of wave function expansion is adopted for the theoretical derivations. Analytical expressions are obtained for the distributions of mechanical displacement in z-direction along the circumferences of piezoelectric cylinders. These solutions are used to study the influence of each element of the stiffness matrix and the piezoelectric matrix on the various resonant modes of vibration. Numerical results obtained indicate that perturbations of the elements c₄₄ and e₁₅ significantly affect resonant frequencies and amplitudes, perturbations of c₁₁ and c₁₂ have pronounced effects on resonant modes of high frequencies also. However, the resonant modes are not so sensitive to the perturbations of c₁₃, e₃₁ and e₃₃. The dynamic characteristics of 1–3 connectivity piezoelectric composites exposed here are meaningful for the design and manufacture of sensor/actuator elements by this kind of composites as well as the on-line health monitoring of the mechanical properties variations of the composites itself.     

Measurement and analysis of the infrared reflection spectrum of semiconducting SnS

The infrared reflection spectrum of p-type SnS single crystals was measured between 2 and 25μ. The observed dispersion was ascribed to the combined effects of lattice vibrations and free holes. An analysis gave for the index of refraction n₀ = 3.6 ± 0.1, the dielectric constant = 19.5 ± 2, and the effective charge on the atoms e^* = 0.7e₀.

The effective mass of holes is isotropic in the plane perpendicular to the c-axis, with m^* = 0.20m₀; the effective mass parallel to the c-axis is much larger: m^* m₀.     

Elastic scattering of polarized deuterons from Al, Si and Ni between 7 and 11 MeV

Polarization parameters have been determined for deuteron elastic scattering from ²⁷Al, Si and ⁶⁰Ni at energies between 7 and 11 MeV and laboratory scattering angles from 30° to 135°. The vector polarization, iT₁₁, and two tensor parameters T₂₀ and T₂₂, were measured by scattering polarized and unpolarized deuterons which were obtained from a tandem accelerator. The largest polarization was |iT₁₁| ≈ 0.3 and |T₂₀| ≈ 0.2 for ²⁷Al at 11 MeV. For ⁶⁰Ni, the observed polarizations were substantially smaller. Angular distributions of the unpolarized cross section were also measured for ²⁷Al and Si. An optical-model analysis of the polarization and cross-section data was performed. The vector polarization was reproduced reasonably well by a vector spin-orbit coupling of similar strength as found for nucleon scattering. A tensor interaction appears to be needed to account for the observed tensor polarizations.     

Pseudo-billiards

A new class of Hamiltonian dynamical systems with two degrees of freedom and kinetic energy of the form T = c₁|p₁| + c₂|p₂| (called “pseudo-billiards”) is studied. For any kind of interaction, the canonical equations can always be integrated on sequential time intervals; i.e. in principle all the trajectories can be found explicitly.

Depending on the potential, a dynamical system of this class can either be completely integrable or behave just as a usual non-integrable Hamiltonian system with two degrees of freedom: in its phase space there exist invariant tori, stochastic layers, domains of global chaos, etc. Pseudo-billiard models of both the types are considered.

If a potential of a pseudo-billiard system has critical points (equilibria), then trajectories close to these points (“loops”) can exist; they can be treated as images of self-localized objects with finite duration. Such a model (with quartic potential) is also studied.     

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。     

A piecewise linear model for the zones of instability of an area-preserving map

In this note we study the global behavior of the piecewise linear area-preserving transformation x₁ = 1 − y₀ + |x₀|, y₁ = x₀, of the plane. We show that there are infinitely many invariant polygons surrounding an elliptic fixed point. The regions between these invariant polygons serve as models for the “zones of instability” in the corresponding smooth case. For our model we show that some of these annular zones contain only finitely many elliptic islands. The map is hyperbolic on the complement of these islands and hence exhibits stochastic behavior in this region. Unstable periodic points are dense in this region.     

MRI of hepatic lymphoma

Thirteen patients with biopsy proven hepatic lymphoma (2 Hodgkin, 11 Non-Hodgkin) and a control group of 15 patients with hepatic metastases were analyzed quantitatively and qualitatively by MRI. Focal hepatic lymphoma was most reliably detected (eight of eight patients) and appeared hypointense relative to liver on T₁ weighted (CNR − 7.4 ± 2.3) and hyperintense on T₂ weighted (CNR + 8.4 ± 2.9) images. The mean T₁ and T₂ relaxation times of focal hepatic lymphoma (T₁ = 832 ± 234 msec, T₂ = 84 ± 16 ms) differed significantly from adjacent non-tumorous liver (T₁ = 420 ± 121 ms, T₂ = 51 ± 9 ms; p < 0.05), however CNR values and relaxation times were similar to those of hepatic metastases. Diffuse hepatic lymphoma (microscopic periportal infiltration) was undetectable by MRI in three patients by either morphologic features or quantitative criteria. A mixed pattern of hepatic lymphoma (focal lesions and diffuse infiltration) showed focal areas of slightly decreased signal intensity on T₁ weighted images (CNR = −1.7 ± 0.4) while T₂ weighted images revealed multiple regions of focal hyperintensity (CNR = +13.3 ± 8.4) superimposed on a diffusely hyperintense liver. Our experience demonstrates that either T₁ or T₂ weighted techniques are useful in detecting focal and that T₂ weighted techniques are useful in detecting mixed hepatic lymphoma. Conventional image derived relaxation time measurements and quantitative parameters were of no additional diagnostic value.     

Current-induced step bunching at vicinal surfaces during crystal sublimation

The limits of the applicability of the generalized BCF model of electromigration-affected sublimation are discussed in detail. Only in surface-diffusion limited sublimation are the steps boundaries, effectively separating the transport processes at neighbouring terraces. In the opposite case of high surface mobility and slow exchange between the 2D gas of mobile adatoms and the crystal, many atoms simply cross the steps, spending some time in an intermediate state of adsorption at the step edge, but never becoming “crystal atoms”. In this regime of sublimation the steps are no longer boundaries. Therefore, one cannot analyze diffusion and desorption on one separate terrace (as in the generalized BCF model) since the coupling between the adatom concentration fields on neighbouring terraces cannot be neglected. A relevant model for this regime of electromigration-affected sublimation is proposed in this paper. This model manifests step buching at the step-up direction of the adatom electromigration. The central result of the mathematical treatment is the formula (x₂−x₁)^{n + 2}=(4kT/F) l^{n + 1}₀, relating the interstep distance x₂−x₁ in a stable pair of steps with the electromigration inducing force F. Here n and l₀ determine the form and the magnitude of the step-step interaction. The formula obtained for x₂−x₁ provides a gound to evaluate n and l₀ from a set of experimental data on sublimation by combined DC and radiative heating.     

Solid-state electrochemical CO2 sensor by coupling lithium ion conductor (Li2CO3-Li3PO4-Asl2O3) with oxide ion-electron mixed conductor (La0.9Sr0.1MnO3)

A solid-state electrochemical cell of the type O₂(air), PtLa_0.9Sr_0.1MnO₃/Li₂CO₃(+5 mol% Li₃PO₄ + 6 mol% Al₂O₃)/Au, CO₂, O₂ was composed to determine CO₂ concentration, where Li₂CO₃, a lithium ion conductor, was used as an electrolyte, and the perovskite-type oxide (La_0.9Sr_0.1MnO₃)/O₂-electrode as a reference electrode. The electromotive force (EMF) of the cell was found to be proportional to the logarithm of CO/₂ partial pressure in CO₂/O₂/N₂ gas mixtures at temperatures between 300 and 400 °C. The EMF responded to changes of CO₂ partial pressure within 1 min at 400 °C. The sensitivity to CO₂ of this cell was not affected by coexistence of O₂, and the EMF remained constant after the first 15 days. The mechanism for sensing CO₂ is discussed.