理想弹塑性固体Riemann问题的解结构与初值条件

针对理想弹塑性固体材料的一维Riemann问题，在不考虑真空的情况下，讨论其所有可能存在的解结构，给出每一种解结构下对应的初值条件且证明该系列初值条件的完备性，即任意给定的物理量初值均有且只有一种解结构与之对应.基于该理论，在设计精确或近似理想弹塑性Riemann问题求解器时，可以依据初值条件对任意物理量初值直接判断其对应的解结构，从而提高求解器的精度和效率.数值试验验证了该系列初值条件的正确性和有效性.     

超声共振法测定圆柱体材料弹性常数的影响因素分析

为明确超声共振频谱分析法(RUS)测定圆柱体试样弹性常数的影响因素, 由此针对各向同性圆柱体开展实验, 观察圆柱体试样测量结果的分散性和稳定性, 且主要研究横纵比和有效模态数量对测量结果的影响, 并与拉伸试验的结果进行比较. 以测量结果标准差、变异系数和95%置信度下均值的区间估计3个指标来衡量结果的稳定性和分散性, 且从模态简并角度对实验结果进行分析. 最终结果表明, 当超声共振频谱分析法的有效模态数量在17左右、试样横纵比接近1时, 测量结果的稳定性和分散性较小.     

Two-dimensional magneto-thermoelastic interactions in a micropolar functionally graded solid

Abstract

The present work is concerned with the 2D deformation in a nonhomogeneous, isotropic, micropolar, magneto-thermoelastic medium in the context of Lord-Shulman theory as a result of an inclined load. The inclined load is supposed to be a linear combination of normal load and tangential load. Material properties are assumed to be graded in x-direction. Normal mode technique is proposed to obtain the analytical expressions for the temperature field, displacement components, and stresses. These are also calculated numerically and depicted graphically to observe the variations of the considered physical variables.

Communicated by Seonho Cho.     

First-principles investigation on ideal strength of B2 NiAl and NiTi alloys

For B2 NiAl and NiTi intermetallic compounds, the ideal stress–strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along <001> crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant C(66). The shear failure under {110}{111} shear deformation occurring in process of tension may result in a small ideal tensile strength(~ 2 GPa) for NiTi. The unlikeness in the ideal strength of Ni Al and Ni Ti alloys is discussed based on the charge density difference.     

New measurements and reanalysis of 14N elastic scattering on 10B target

The angular distributions of elastic scattering of ¹⁴N ions on ¹⁰B targets have been measured at incident beam energies of 21.0 and 24.5 MeV. Angular distributions at higher energies 38–94.0 MeV (previously measured) were also included in the analysis. All data were analyzed within the framework of the optical model and the distorted waves Born approximation method. The observed rise in cross sections at large angles was interpreted as a possible contribution of the α-cluster exchange mechanism. Spectroscopic amplitudes SA₂ and SA₄ for the configuration ¹⁴N→ ¹⁰B +α were extracted. Their average values are 0.58±0.10 and 0.81±0.12 for SA₂ and SA₄, respectively, suggesting that the exchange mechanism is a major component of the elastic scattering for this system. The energy dependence of the depths for the real and imaginary potentials was found.     

Fluid‐structure coupling of linear elastic model with compressible flow models

Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure.     

元素分析仪测定土壤、沉积物样品碳氮含量的影响因素及数据校正

使用元素分析仪进行土壤、沉积物样品碳、氮含量检测时,样品前处理过程(烘干和酸化)、包样质量以及参考标准品等因素均会对检测结果造成影响.试验结果表明:酸化导致氮百分质量的测定结果降低2.6%~40.0%,碳百分质量的测定受包样质量的影响较大,使用的校正标准与被测样品越相似,校正结果越准确.     

龙门山地区水系沉积物中铀含量分布特征

铀元素是具有毒性和放射性的锕系元素之一,对区域环境和人体健康具有极大的危害,开展铀元素污染评价具有重要的现实意义。以龙门山地区主要水系为主要研究对象,采集了大量的水系沉积物样品,对该地区的铀元素分布特征进行了研究。研究表明,大渡河水系沉积物中铀平均质量分数为5.50 mg/kg,绵远河水系沉积物中的铀平均质量分数为3.07 mg/kg,其余河流水系沉积物中铀含量均较低。通过龙门山地区水系沉积物中铀元素分布特征与龙门山地区矿产分布对比发现,煤矿、磷矿开发区是水系主要铀元素来源。     

Determination of acid volatile sulphur in river sediments by ICP-OES coupled with purge and trap method

The developed and tested method is based on the acid volatile sulphur (AVS) releasing from a sample of sediment by acidification with hydrochloric acid and sequential absorption of released hydrogen sulphide into the absorption solution of sodium hydroxide. Total sulphur absorbed in the absorption solution is subsequently determined by inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The method was tested using both model and real samples of the river sediment. Obtained results were compared with the results of iodometric determination as the method routinely used for the AVS determination. In case of using ICP-OES with purge and trap, there is no spectral interference of calcium; therefore for the determination of sulphur, it is possible to use atomic emission line of sulphur S I 180.7 nm. The tested method provides the results comparable with the iodometric method within the range of tested concentrations. The detection limit (LOD) of this method is 0.09 mg· S^2? ? L^?1 in the absorption solution which corresponds to 0.23 mg S^2?·kg^?1 in a sediment. Value of LOD is comparable with the iodometric determination.     

Multicomponent Molecular Orbital–Climbing Image–Nudged Elastic Band Method to Analyze Chemical Reactions Including Nuclear Quantum Effect

To analyze the H/D isotope effects on hydrogen transfer reactions in XHCHCHCHY?XCHCHCHYH (X, Y=O, NH, or CH₂) including the nuclear quantum effect of proton and deuteron, we propose a multicomponent molecular orbital‐climbing image‐nudged elastic band (MC_MO–CI–NEB) method. We obtain not only transition state structures but also minimum‐energy paths (MEPs) on the MC_MO effective potential energy surface by using MC_MO–CI–NEB method. We find that nuclear quantum effect affects not only stationary‐point geometries but also MEPs and electronic structures in the reactions. We clearly demonstrate the importance of including nuclear quantum effects for H/D isotope effect on rate constants (k_H/k_D).