等离子体色散函数的计算方法

本文推出了复宗量ξ=x+iy的误差函数的级数表达式。在这一基础上,对0≤y≤1,|x|≤10宗量区,给出了较高精度的等离子体色散函数Z及其微商Z'的计算方法。进而,对复平面ξ的各个区域,系统地研完了等离子体色散函数和相应的计算方法;在VAX—11/750计算机上得到了满意的结果,文章对这些结果,所用方法及其精度作了讨论;分别对y≥0和y<0,描述了Z和Z'的基本行为。     

关于PCG迭代矩阵特征值近似计算

对于预处理共轭梯度法,本文给出其迭代矩阵AM^-1与三对角阵B_s之间的关系,并对B_s的特征值分布作了分析,进而得到关于AM^-1特征值的一些性质。通过算例对两者的特征值及条件数进行了探讨。     

波动方程辛算法的迭代求解

对(∂²)/(∂x²)利用中心差商算子,对expt作对角Padé逼近,由波动偏微分方程可得到两类具有O(Δx²+Δt^2l)和O(Δx⁴+Δt^2l)精度的辛格式.对由此类辛格式产生的线性方程组构造了两种迭代解法,并对l=1,2,3,4给出了它们的收敛条件.并进行了数值实验.     

插层化合物钨青铜单晶的生长

本工作对插层化合物钨青铜单晶生长过程中的一些现象进行了仔细的观察.对电流、温度、时间对单晶生长的影响进行了摸索,找到了单晶生长的最佳条件.利用熔盐电解法成功地生长出K_xWO₃,Na_yWO₃和K_xNa_yWO₃. 关键词：     

钴镍铁基金属玻璃结构弛豫的X射线研究

本工作在测定了Co_50.7Ni_19.5Fe_7.8Si₆B₁₆和Co_42.9Ni_27.3Fe_7.8Si₈B₁₄两种金属玻璃结构的基础上,进一步研究了不同保温时间的等温退火和不同温度下的等时退火对它们结构的影响,并测定了各退火态样品的小角度X射线散射强度,对其变化作了比较,分析了它们的结构弛豫现象。实验结果表明:结构弛豫可分为两种不同的类型,即拓扑短程序(TSRO)和化学短程序(CSRO)弛豫过程。本工作特别对后一种过程提供了直接的证据。最后还对这两种弛豫的原子过程作了初步的分析,强调了它们的并存和相关性。 关键词：     

Zn1-xMnxSe的低温磁化率和自旋玻璃现象

用超导量子干涉器(SQUID)磁强计对稀释磁性半导体Zn_1-xMn_xSe(0.1≤x≤0.50)的低温低场直流磁化率作了测量,测量温度从4.2K到30K,测量磁场为15Oe。当x≥0.30时,从磁化率-温度曲线的浑圆峰值,观察到了自旋玻璃的转变。自旋玻璃的转变温度T_f,对x=0.30,0.40,0.50,分别为10.5K,16K,19.5K。给出了顺磁相和自旋玻璃相的相图。比较了Zn_1-xMn_xSe和Cd_1-xMn_xSe的自旋玻璃转变温度,发现对同样的Mn离子浓度,Zn_1-xMn_xSe的T_f高于Cd_1-xMn_xSe的T_f,用交换作用的理论作了讨论。 关键词：     

车载大功率DC/DC电源变换器半实物仿真验证测试方法

介绍了一种车载大功率DC/DC电源变换器(以下简称DC/DC)的测试方法,运用V模式理念并结合半实物仿真验证测试方法对DC/DC的技术方案进行了全数字仿真验证测试、对DC/DC的控制电路部分进行了快速控制原型仿真验证测试、对DC/DC的功率电路部分进行了硬件在环仿真验证测试、对集成功率及控制电路的DC/DC进行了功率硬件在环验证测试,并根据测试结果又进行了迭代验证测试。通过半实物验证测试,对DC/DC各项设计参数的正确性及性能指标符合性进行验证测试,保证DC/DC技术方案的合理可行。     

用肖特基电容电压特性数值模拟法确定调制掺杂AlxGa1-xN/GaN异质结中的极化电荷

研究发展了用肖特基电容电压特性数值模拟确定调制掺杂Al_xGa_1-xN/GaN异质结中极化电荷的方法.在调制掺杂的Al_0.22Ga_0.78N/GaN异质结上制备了Pt肖特基接触,并对其进行了C-V测量.采用三维费米模型对调制掺杂的Al_0.22Ga_0.78N/GaN异质结上肖特基接触的C-V特性进行了数值模拟,分析了改变样品参数对C-V特性的影响.利用改变极化电荷、n-AlGaN 关键词： xGa_1-xN/GaN异质结')" href="#">Al_xGa_1-xN/GaN异质结 极化电荷 电容电压特性 数值模拟     

O-(α-氰基-间-苯氧基苄基)硫代磷酸酯和磷酰胺的NMR研究

本文合成了20个题示的化合物,研究了它们的¹H和³¹P谱,找出了δ_P与取代基关系的一些规律,观察到了手性中心对δ_H的影响、及一个手性中心对另一个手性中心R、S体不等价的诱导位移,并观察了产物中R、S体的不同含量比例。     

莰烯衍生物的1H、13C-NMR及UV研究

本文用¹H、¹³C NMR及UV对六个莰烯衍生物进行了研究,给出了全部¹³C谱线和部分¹H谱线的归属。对¹³C、¹H化学位移进行了关联,获得了近乎直线的¹³C-¹H相关图。结果表明,¹³C化学位移与UV λ_max无必然联系,而与电荷密度密切相关。本文对此进行了讨论。     

Saturated Solution of PbSO4 as Standard Stock Solution and Its Applications in Analytical Spectroscopy: Screening Analysis of Lead in Natural Water and Usnea longissima

A saturated PbSO₄ aqueous solution, which was prepared by dissolving commercially available solid PbSO₄ in doubly distilled water, was employed as a standard stock solution of lead for the visual colorimetric determination of lead in water and atomic fluorescence spectrometric determination of lead in whole Usnea longissima (i.e., Methuselah's beard lichen). The concentration of lead in this saturated solution is theoretically calculated to 27.8 mg/L by using the solubility product constant of PbSO₄ at 25°C. The standard solution series is by further dilution of the saturated solution. A validation experiment proved the feasibility of using the saturated solution as the standard stock solution of lead. The experimental conditions, mainly the temperature, that affect the equilibrium of precipitation–dissolution in the saturated solution were investigated. The saturated PbSO₄ solution was proved to be accurate enough for the purpose of screening analysis of lead in these samples.     

Selective wet etching of Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> phase-change thin films in thermal lithography with tetramethylammonium

In this paper, we study Ge₂Sb₂Te₅ phase-change film as a promising inorganic photoresist using organic alkaline: tetramethylammonium hydroxide (TMAH) solution, instead of inorganic alkali or acid as etchant. The basic etching properties are investigated by prior and posterior annealing Ge₂Sb₂Te₅ films. Selectivity is found to be dependent on concentration of TMAH. There is a good selectivity in the 25% TMAH solution, in which the amorphous state is etched away, whereas the crystalline state remains. The etching rate decreases when the concentration of TMAH is diluted; and an opposite selectivity, compared with 25% TMAH solution, is observed in the 0.125% TMAH solution. Selective etching with laser crystallization in different power levels is also studied, and an excellent wet selectivity in the 25% TMAH solution is obtained. The remaining crystalline lines are observed by atomic force microscopy. The surface roughness after etching is at a good level. The selective wet-etching mechanism is also discussed.     

Formation of fullerene clusters in carbon disulfide: Data on small-angle neutron scattering and molecular dynamics

Fullerene solutions in carbon disulfide are studied by small-angle neutron scattering (SANS). In addition to earlier experiments on the given system, the range of measured transmitted impulses is extended and the influence of solution preparation methods on C₆₀ cluster formation in these solutions is studied. It is shown that the formation of large C₆₀ clusters (with a size of about 10 nm) is due to nonequilibrium methods of solution preparation. For nonequilibrium dissolution, there is a 10% excess of the observed fullerene size in the solution over the calculated value. It has been established by simulation of the C₆₀/CS₂ interface by molecular dymanics methods that inclusion of how solvent molecules are organized on the C₆₀ surface leads to a decrease in the fullerene size in the solution, observed by using SANS. In this paper, the effect of excess R _g is explained by the presence of small clusters in the solution (approximately 10% of dissolved C₆₀ molecules). It is discovered that there is a time variation in the concentration of the saturated solution. The explanation of this effect using a model of formation and sedimentation of large clusters (with a size of 100 nm or more) is proposed.     

Inter- and intra-crystalline ion-exchange equilibria in the system FeCrAlO

The tie lines delineating ion-exchange equilibria between FeCr₂O₄FeAl₂O₄ spinel solid solution and Cr₂O₃Al₂O₃ solid solution with corundum structure have been determined at 1373 K by electron microprobe and EDAX point count analysis of oxide phases equilibrated with metallic iron. Activities in the spinel solid solution are derived from the tie lines and the thermodynamic data on Cr₂O₃Al₂O₃ solid solution available in the literature. The oxygen potentials corresponding to the tie-line composition of oxide phases in equilibrium with metallic iron were measured using solid oxide galvanic cells with CaOZrO₂ and Y₂O₃ThO₂ electrolytes. These electrochemical measurements also yield activities in the spinel solid solution, in good agreement with those obtained from tie lines. The activity-composition relationship in the spinel solid solution is analysed in terms of the intra-crystalline ion exchange between the tetrahedral and octahedral sites of the spinel structures. The ion exchange is governed by site-preference energies of the cations and the entropy of cations mixing on each site.     

Measurement on CO<Subscript>2</Subscript> solution density by optical technology

The optical technology based on Mach-Zehnder interferometry was successfully applied to a high-pressure liquid CO₂ and water system to measure CO₂ solution density. Experiments were carried out at a pressure range of from 5.0 to 12.5 MPa, temperatures from 273.25 to 284.15 K, and CO₂ mass fraction in solution up to 0.061. CO₂ solution density data were obtained from two sets of experiments. These data were calculated through the fringe shifts induced by density changes inside of the high-pressure vessel, which were directly recorded during the experiments, and a modified version of Lorentz-Lorenz formulation. The experimental results indicated that the density ratio of CO₂ solution to that of pure water at the same pressure and temperature is monotonically linear with the CO₂ concentration in the solution. The slope of this linear function, calculated by the experimental data fitting, is 0.275.     

The evolution of the cluster size distribution in a coagulation system

The coagulation equation with kernelK _ij =A+B(i+j)+C _ij and arbitrary initial conditions is studied analytically and a simple expression for the solution is found. For monodisperse initial conditions, we recover the known size distribution expressed in terms of a degeneracy factorN _k, which is determined by a recursion relation. For polydisperse initial conditions, a similar solution form is found, which includes a degeneracy factorN _kl, also determined by a recursion relation. The physical meaning ofN _kl and the recursion relation is given. A method to get explicit expressions forN _k andN _kl is illustrated. Finally, the pre-gel solution is given explicitly and a general method to get the post-gel solution is proposed.     

Glassy behavior and jamming of a random walk process for sequentially satisfying a constraint satisfaction formula

Random K-satisfiability (K-SAT) is a model system for studying typical-case complexity of combinatorial optimization. Recent theoretical and simulation work revealed that the solution space of a random K-SAT formula has very rich structures, including the emergence of solution communities within single solution clusters. In this paper we investigate the influence of the solution space landscape to a simple stochastic local search process SEQSAT, which satisfies a K-SAT formula in a sequential manner. Before satisfying each newly added clause, SEQSAT walk randomly by single-spin flips in a solution cluster of the old subformula. This search process is efficient when the constraint density α of the satisfied subformula is less than certain value α_cm; however it slows down considerably as α> α_cm and finally reaches a jammed state at α≈α_j. The glassy dynamical behavior of SEQSAT for α≥α_cm probably is due to the entropic trapping of various communities in the solution cluster of the satisfied subformula. For random 3-SAT, the jamming transition point α_j is larger than the solution space clustering transition point α_d, and its value can be predicted by a long-range frustration mean-field theory. For random K-SAT with K ≥ 4, however, our simulation results indicate that α_j = α_d. The relevance of this work for understanding the dynamic properties of glassy systems is also discussed.     

External-field-controlled laser wet etching of polycrystalline Al2O3TiC

Laser-induced etching of polycrystalline Al₂O₃TiC material by tightly focused CW Ar ion laser has been investigated in both H₃PO₄ and KOH solutions with influence of an external electric field. It is found that a weak external electric field will change the ions distribution in chemical solutions and cause obvious change in etching behavior. The laser etching in a H₃PO₄ solution can be enhanced by both positive and negative biases of the substrate. While etching in a KOH solution, a positive bias can enhance the etching reaction, whereas a negative bias can suppress the etching process. It is also found that the external electric field can always enhance the mass transfer between reaction products and fresh etchant in a H₃PO₄ solution. It is revealed that the supply of H⁺ ions contributes to the etching process in a H₃PO₄ solution, while the supply of OH^– ions contributes to the etching process in a KOH solution. The electric field can be used to control the etching process to achieve fast tuning and higher accuracy.     

Transient time in homogeneous nucleation

The problem of the transient time in nucleation is studied. The size-dependent transient time at a constant temperature is defined and the approximate analytical solution is found and compared with the exact numerical solution for the model Li₂O.2 SiO₂ melt. It is shown that the analytical solution for the size-dependent transient time is in agreement with the numerical result.     

液芯光纤中溶液吸收和荧光的性质对CS2受激拉曼散射阈值的影响

利用液芯光纤技术研究了不同浓度的β-Carotene的CS₂溶液的吸收与荧光的特性对CS₂的一、二阶Stokes谱线阈值的影响.实验发现随溶液浓度(10^-8—10^-6 mol/L)增加，CS₂的一阶Stokes谱线的激发阈值相对变高；并且与纯CS₂芯液的受激拉曼散射相比较，在低抽运能量激发下，就观察到CS₂的二阶Stokes谱线.这主要是由于在CS₂的受激拉曼谱线产生的过程中，β-Carotene的CS₂溶液的吸收和荧光共同影响了CS₂的一、二阶Stokes谱线的阈值.我们进行了理论上的拟合与分析，其结果与实验符合很好. 关键词： 2受激拉曼散射阈值')" href="#">CS₂受激拉曼散射阈值 液芯光纤 吸收与荧光