一种获得剪切模量压强二阶偏导数G″P的方法

从晶格材料的电子结构理论出发 ,推导了一个计算剪切模量G的压强二阶偏导数G″P 的方法 .针对 93钨合金材料计算得到G″P=- 0 .0 33GPa-1,把这一结果用于Birch Murnaghan有限应变理论的计算 ,并与G″P=0的计算结果进行了比较 .结果表明 ,G″P=0的计算结果明显高于G″P≠ 0的计算结果 ,在压强较高时 ,二者结果相差较大 .因此 ,在高压下 ,必须考虑G″P 带来的影响 .     

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     

一种计算剪切模量温度系数的方法

采用理论计算与动高压实验相结合的方法，提出了一个计算剪切模量温度系数G′T的新方法.首先用理论方法计算一个中间数据G(PS)，然后再与动高压实验数据G(PH)结合在一起计算出G′T,并针对93钨合金材料进行了计算.计算结果表明剪切模量温度系数G′T开始是随温度和压力变化的，但在高温高压下，它趋近于一常数.对于93钨合金，这个常数约为-004GPa／℃.同时，这也是对Steinberg本构模型中的剪切模量温度系数为常数的一个证明.并且，当把这一常数代入剪切模量温度系数的计算式中，将重新计算出的剪切模量与实验测得的剪切模量结果进行了比较，结果表明二者符合得很好，从而证明了本计算的剪切模量温度系数的正确性. 关键词： 有限应变物态方程 剪切模量温度系数 Steinberg本构模型 动高压实验     

铀的结构相变及力学性能的第一性原理计算

基于密度泛函理论, 分别计算了α, γ铀的晶格常数、平衡态体积、体弹模量及其导数等, 与实验和其他第一性原理计算结果符合较好; 并根据焓-压强曲线得到了两相的相变压强～111GPa. 通过体心立方结构理想拉伸强度的计算, 分析其在极端加载条件下的结构行为. 另外, 计算了小应变情况下U-Nb (6.25at.%) 的能量-应变关系, 发现对应于剪切模量c’的应变会使得该结构的能量降低, 揭示了该结构的力学不稳定性. 关键词： 铀 相变 理想强度 结构稳定性     

冲击加载下铝的剪切模量

分别用Steinberg-Cochran-Guinan (SCG)模型、修正的SCG模型和有限应变理论对材料的剪切模量做了数值计算，并与一维平面应变加载下铝的实验结果进行了比较.结果表明，修正的SCG模型与实验结果较为符合.在10—80GPa的压力范围下，剪切模量随冲击压力的增加而逐渐增大，这是由于压力的影响占主要地位，发生了加工硬化.在80—125GPa的压力范围下，剪切模量随冲击压力的增大快速减小，这是因为温度的影响比较严重，发生了高温软化现象.剪切模量最终在冲击压力为125GPa处趋于零，这是由于在该压力点冲击熔化发生，剪切强度消失. 关键词： 剪切模量 Steinberg-Cochran-Guinan模型 有限应变理论 铝     

Al、Cu、Ta高压熔化曲线的理论计算

由位错熔化理论和不同的静高压实验数据优化的体模量(B0)、剪切模量(G0)及它们对压力的一阶偏导数(B′0、G′0)值计算了Al、Cu、Ta的高压熔化曲线.理论计算的Al、Cu高压熔化曲线与静、动高压实验值较为吻合,Ta的理论高压熔化曲线与动高压实验结果一致,但与静高压实验结果相差较大.     

金红石结构TiO2结构和热力学性质的第一性原理研究

利用基于密度泛函理论的第一性原理计算方法以及准谐德拜模型研究了金红石TiO₂的结构和热力学性质.常温常压下所计算的晶格常数、体弹模量及其对压强的一阶导数与实验值和其他理论计算结果相符的较好.另外,我们还计算了体弹模量、热膨胀系数、热容与温度和压强的关系.     

ZrV2结构、弹性和热力学性质的第一性原理计算

采用基于密度泛函理论的第一性原理平面波赝势方法研究ZrV₂的晶体结构和弹性,利用准谐Debye模型计算在不同温度(T=0~1200 K)和不同压强(P=0~20 GPa)下ZrV₂的热力学性质,包括弹性模量与压强,热熔与温度,以及热膨胀系数与温度和压力的关系.结果表明:计算的ZrV₂晶格常数与实验值符合较好,晶体材料的弹性常数随着压力增加而增加;在一定温度下,相对体积、热熔随着压强的增加而减小,德拜温度、弹性模量随着压强的增加而增加,且高压下温度对ZrV₂热膨胀系数的影响小于压强的影响.     

高压下钨弹性和热力学性质的第一性原理研究

本文利用密度泛函理论研究了高压下bcc结构钨的弹性和热力学性质,计算得到钨的晶格常数、体弹模量以及其对压强的一阶偏导与实验值符合较好;在常压下弹性常数计算值与实验值符合较好的基础上,预测了其高压数据.针对钨的固相结构稳定性问题,根据力学稳定判断标准得到0~600 GPa范围内bcc结构是力学稳定的.此外,通过体模量和剪切模量的计算得到bcc结构钨在压力低于600 GPa时的力学性能表现为韧性.最后,基于准简谐德拜模型,成功预测了钨的热膨胀系数、等压热容、等容热容和熵随着压强和温度的变化关系,为钨及其合金的进一步设计及应用提供参考.     

高压下钨弹性和热力学性质的第一性原理研究

本文利用密度泛函理论研究了高压下bcc结构钨的弹性和热力学性质,计算得到钨的晶格常数、体弹模量以及其对压强的一阶偏导与实验值符合较好;在常压下弹性常数计算值与实验值符合较好的基础上,预测了其高压数据.针对钨的固相结构稳定性问题,根据力学稳定判断标准得到0~600 GPa范围内bcc结构是力学稳定的.此外,通过体模量和剪切模量的计算得到bcc结构钨在压力低于600 GPa时的力学性能表现为韧性.最后,基于准简谐德拜模型,成功预测了钨的热膨胀系数、等压热容、等容热容和熵随着压强和温度的变化关系,为钨及其合金的进一步设计及应用提供参考.     

Structural property of CsCl-type sodium chloride under pressure

The structure and equation of state of CsCl-type sodium chloride have been determined using high-pressure powder X-ray diffraction from 32 to 134 GPa. The CsCl-type phase remains stable over this entire pressure range. Pressure-volume data can be fitted with a Vinet equation of state with K_30 GPa=135.1 GPa, K′_30 GPa=3.9, and V_30 GPa=27.70 Å³. The nearest-neighbour distance between sodium and chlorine atoms decreased as pressure increased. Significant discrepancies of nearest-neighbour distance between previous theoretical predictions and this study were observed at pressures higher than 70 GPa.     

Rotational analysis of the B-X band system of the SbO molecule

Rotational analyses of the two 0-0 bands of theB ²ΣX ²Π_reg system of SbO were carried out for the first time from spectrograms taken in the second order of a 21 ft. concave grating spectrograph having a dispersion of 1·25 Å/mm. The rotational constants of the ν=0 vibrational levels of the upper and lower states, and of the coupling constant A₀ of the lower²Π_reg state were deduced. These values are summarised below. v₀₀=25 334·93 cm^?1 B′₀=0·3190 cm^?1 B″₀=0·3490 cm^?1 A ₀=2276 cm^?1 r′₀=1·933 Å r″₀=1·848 Å.     

一种计算金属剪切模量的本构模型：以Al为例

用两步法构建了一个与温度和压力相关的适用于金属材料的剪切模量本构模型,其中的第一步任务是求得沿0 K等温线上剪切模量随压力的变化规律,即求得G₁=G₁（P,0 K）的函数式.第二步是从0 K等温线上某一给定P的G值出发,求出沿等压线上剪切模量随温度T变化的规律,从而最终求得剪切模量本构模型G=G（P,T）的具体表达式.在这两个阶段的研究中都利用了超声波测量和第一性原理计算方法的研究结果.用铝为模型材料,对本模型的合理性进行了检验.结果表明,G的模型预测数据与试验测量及理论计算数据相比较,无论G的演化是沿冲击压缩轨迹、等熵压缩轨迹、等温压缩轨迹还是等压线轨迹,都能达到令人满意的程度,故可认为本模型具有良好的普适性和合理性. 关键词： 铝 本构模型 剪切模量 冲击波压缩     

Theoretical study of stereodynamics for the reaction O(3P) +D2 (v=0, j=0) to OD+D and isotope effect

Quasi-classical trajectory (QCT) calculations have been performed to study the product polarization behaviours in the reaction O(³P) + D₂ (v= 0, j= 0)→OD + D. By running trajectories on the ³A′ and ³A″ potential energy surfaces (PESs), vector correlations such as the distributions of the polarization-dependent differential cross sections (PDDCSs), the angular distributions of P(θ_r) and P(ø_r) are presented. Isotope effect is discussed in this work by a comprehensive comparison with the reaction O(³P) + H₂ (v= 0, j= 0) → H + H. Common characteristics as well as differences are discussed in product alignment and orientation for the two reactions. The isotope mass effect differs on the two potential energy surfaces: the isotope mass effect has stronger influence on P(θ_r) and PDDCSs of the ³A′ PES while the opposite on P(ø_r) of the ³A″ potential energy surface.     

A spectrum of rhenium oxide

The arc emission spectrum of the ReO molecule has been photographed in the region 590–860 nm and three bands of a single electronic transition have been rotationally analyzed. The separation of lines of the isotopic molecules ¹⁸⁵ReO and ¹⁸⁷ReO leads to the conclusion that the vibrational assignments for these bands are 1-0, 0-0, and 0–1. It is conceivable that an electronic isotope shift of ～0.08 cm^?1 exists. The following vibrational and rotational data (cm^?1) have been determined: ν₀(0-0) = 14 038.42, $\text{Δ}\text{G′(}\text{1}\text{2}\text{) = 867.85}$, $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 979.14}$; B′_e = 0.3889, α′_e = 0.0019, B″_e = 0.4257, α″_e = 0.0043. It is concluded that Λ′ ? Λ″ = +1 with Λ″ ≥ 2.     

Structure and magnetotransport properties of the new quasi-two-dimensional molecular metal β″-(BEDT-TTF)4H3O[Fe(C2O4)3] · C6H4Cl2

The β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G(A^I=NH ₄ ⁺ , H₃O⁺, K⁺, Rb⁺; M^III=Fe, Cr; G = “guest” solvent molecule) family of layered molecular conductors with magnetic metal oxalate anions exhibits a pronounced dependence of the conducting properties on the type of neutral solvent molecules introduced into the complex anion layer. A new organic dichlorobenzene (C₆H₄Cl₂)-containing conductor of this family, namely, β″-(BEDT-TTF)₄H₃O[Fe(C₂O₄)₃] · C₆H₄Cl₂, is synthesized. The structure of the synthesized single crystals studied by X-ray diffraction is characterized by the following parameters: a = 10.421(1) Å, b= 19.991(2) Å, c= 35.441(3) Å, β = 92.87(1)°, V= 7374(1) ų, space groupC2/c, and Z = 4. In the temperature range 0.5&;2-300 K, the conductivity of the crystals is metallic without changing into a superconducting state. The magnetotransport properties of the crystals are examined in magnetic fields up to 17 T at T = 0.5 K. In fields higher than 10 T, Shubnikov-de Haas oscillations are detected, and the Fourier spectrum of these oscillations contains two frequencies with maximum amplitudes of about 80 and 375 T. The experimental results are compared with the related data obtained for other phases of this family. The possible structural mechanisms of the effect of a guest solvent molecule on the transport properties of the β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G crystals are analyzed.     

Fluorescence studies of polycrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite constituents: piezo-spectroscopic calibration and applications

Optical fluorescence microscopy (OFM) was used to quantify the effect of applied stress or strain upon the position of the R fluorescence line of Al₂O₃ composite constituents (fibers and matrices) prior to composite processing. Polycrystalline Nextel^TM Nextel 720 fibers were tested under tension and compression by means of a cantilever beam technique, whereas the polycrystalline matrix was tested in compression. The position of the R fluorescence line was correlated to applied strain and stress in order to provide the piezo-spectroscopic calibration curve and the corresponding coefficients for both sensors, which form the basis for interpretation of frequency shifts from full, all-alumina, composites. The piezo-spectroscopic coefficients of the polycrystalline matrix were found to be 2.57 cm^-1GPa^-1 and 2.52 cm^-1GPa^-1 for the R1 and R2 lines respectively, whereas the coefficients for the polycrystalline Al₂O₃ Nextel 720 fibers were found to be 3.07 cm^-1GPa^-1 and 2.91 cm^-1GPa^-1 for the R1 and R2 lines, respectively. The effects of collection probe size, as well as penetration depth, are discussed. The established piezo-spectroscopic behavior is used inversely to quantify the residual stresses in the as-received fibers due to the presence of sizing, as well as in the thermally grown alumina layer of an industrial thermal barrier coating. PACS 87.64.Ni; 81.05.Je; 78.66.Sq     

High pressure investigation on double perovskite Ba2MgWO6

The results of high-pressure angle dispersive X-ray diffraction measurements up to 34.3 GPa on the double perovskite Ba₂MgWO₆ are presented. The ambient rock salt phase (SG: Fm-3m) is found to be stable up to the highest pressure of the present measurements. The third order Birch-Murnaghan equation of state when fitted to pressure-volume data, yielded a zero pressure bulk modulus (B₀),and its first and second pressure derivatives as 137.0(81) GPa, and 3.9(5) and −0.03 GPa⁻¹, respectively.     

一维元胞自动机随机交通流模型的理论分析与计算机实验

在一维局部作用元胞自动机(CA)交通流模型中，引入刹车噪声与产生、消失概率，得到一个完全随机的CA交通流模型．利用平衡自旋理论对该模型的研究表明，当P_in＝P_out≠0时，初始密度分布不影响系统的最终状态，求得ρ_ｔ＝0.5；当满足条件P_in＋P_b＝1与P_in＝P_out时，得到简单的“线性”模型，该模型在条件｜1－2P_in｜＝1下，表现出长程相关，导致严重交通“阻塞”的出现．理论结果与计算机实验一致． 关键词：