高速磁浮线路道岔钢梁移位过程及其数值分析

高速磁浮线路道岔主体结构为一连续箱形截面钢梁。采用端部刚接和铰接两种支座条件、梁单元和壳单元两种计算模型,从结构受力角度对道岔切换方案进行了数值计算,并对计算结果进行了比较分析。在进行计算时,如果不要求得到截面上的细部结果,可用梁模型进行计算;如果要得到截面上的细部结果,就必须采用壳模型进行计算,获取相应的数据。

用有限元法研究桡骨远端伸直型骨折的机理

用有限元法定量计算桡骨远端骨折时儿童与成人桡骨各点的应力分布,得出最大应力点及断裂点。依据生物力学原理分析比较了儿童与成人桡骨远端伸直型骨折的裂纹走向及移位过程的区别,为临床整复及压垫固定提供依据。

Atomistic simulations of interactions between screw dislocation and twin boundaries in zirconium

Molecular statics was employed to simulate interaction between screw dislocation and twin boundaries（TB） in hexagonal close-packed zirconium. In the moving TB model, the interaction of a moving {10ˉ12} TB with a static 1/311ˉ20{10ˉ10} screw dislocation was investigated. Twinning dislocation（TD） nucleation and movement play an important role in the interaction. The screw dislocation passes through the moving TB and changes to a basal one with a wide core. In the moving dislocation model, a moving 1/31120{1010} dislocation passes through the TB, converting into a basal one containing two partial dislocations and an extremely short stacking fault. If the TB changes to the {1011} one, the moving1/31120{1010} prismatic screw dislocation can be absorbed by the static TB and dissociated into two TDs on the TB. Along with the stress-strain relationship, results reveal the complicated mechanisms of interactions between the dislocation and TBs.

Study on high and steep slope stability of surface mine based on RFPA-SRM

The instability and failure mechanism of high and steep slopes in surface mines, and the basis for some reasonable landslide prevention measures were provided using the RFPA-SRM. Based on the actual progress of the Pingzhuang Western Surface Mine and based on strength reduction method, the dynamic instability processes of the top high and steep slope was simulated. Also, the landslide mode was determined, the characteristics of the displacement distribution, the deformation, failure, and the stress distribution in the slope were demonstrated, and the stability was calculated. Conclusions can be drawn as follows： the landslide or failure of high and steep slopes on a surface mine is a gradual process, in which the slope undergoes the generation, expansion, and connection of the fractures and the displacement increases until landslide occurs; a small portion of the upper rocks fail due to the tension and the lower rocks fail due to the shear; the potential sliding surface is combined and the essential cause of the landslide is the shear stress concentration.

Fabricating high-loading Fe-N4 single-atom catalysts for oxygen reduction reaction by carbon-assisted pyrolysis of metal complexes

Iron-based single-atom catalysts with nitrogen-doped carbon as support(Fe-SA/NPC)are considered effective alternatives to replace Pt-group metals for scalable application in fuel cells.However,synthesizing high-loading Fe-SA catalysts by a simple procedure remains challenging.Herein,we report a high-loading(7.5 wt%)Fe-SA/NPC catalyst prepared by carbon-assisted pyrolysis of metal complexes.Both the nitrogen-doped porous carbon(NPC)support with high specific surface area and ο-phenylenediamine(o-PD)play key roles role in the preparation of high-loading Fe-SA/NPC catalysts.The results of X-ray photoelectron spectroscopy,high-angle annular dark-field scanning transmission electron microscopy,and X-ray absorption fine structure spectroscopy experiments show that the Fe atoms are anchored on the carbon carriers in a single-atom site configuration and coordinated with four of the doped nitrogen atoms of the carbon substrates(Fe-N_(4)).The activities of the Fe-SA/NPC catalysts in the oxygen reduction reaction increased with increasing iron loading.The optimized 250Fe-SA/NPC-800 catalyst exhibited an onset potential 0.97 V of and a half-wave potential of 0.85 V.Our study provides a simple approach for the large-scale synthesis of high-loading single-atom catalysts.

The Topic of Contact Zone Problems in the Shaft and Hole Joint, Taking into Account Component Form Errors

In assemblies constructed from components manufactured with radial deviations, cross-section deviations and deviations being combination of both, there occur variable values of local stresses and displacements. Both the types of shape deviations and their values need to be taken into account in the designing process and play an important role during machine operation. They have a crucial effect on the value and scatter of maximum reduced von Mises stresses and contact stresses. Axisymmetric joints were examined, in which shafts in selected shape variants and in variable angular positions were associated with a non-deformable hole. The aspects of contact zone problems are presented using the example of numerical simulation of contact between an elliptical saddle-shaped shaft placed in a rigid, non-deformable hole in different angular positions. Occurrence of both variable relative stresses and contact stresses as well as shaft＇s axial shift and rotary movement resistance were demonstrated.

评N.Chomsky的《语障》

本评论的译者曾简要地介绍过Chomsky《语障》(Barriers)一书的主要内容(吴道平“乔姆斯基新著《语障》”,《国外语言学》,1987,3)。《语障》一书,打算统一转换生成语法的两个分支理论—管辖(government)与界限(bounding)理论。但生成学派内部一些语言学家认为,语障理论并未达到这个月的。此处摘译的评论文章,载于美国《语言》(Language)64卷第2期。译者介绍这篇评论,除了想让大家对语障理论有较深的认识以外,也想让读者们借此而了解美国语言学家进行理论论战的一般状况:理论语言学之争,也和其他实证科学的论争一样,必须建立在对语言事实的详细分析的基础之上,决不是空泛地讲一些形而上的道理所能了事。原评论较长。因有部分内容国内语言学界尚不熟悉,而译者以前的介绍又未曾涉及,故只译出了一半左右。有些部分采用译述方式。文中涉及有关管辖与约束理论、语障理论一系列的概念,请参阅徐烈炯(“管辖与约束理论”,《国外语言学》,1984,2)、吴道平(1987),此处不重作介绍。凡上述两文解释过的术语,本文也不再解释或加注。关于术语的译名,吴道平(1987)发表时,编辑部作了些改动,本文现仍用译者原来的译名并附上编辑部的译名,以便读者查考。

Condensed form of complementarity formulation for discontinuous deformation analysis

While the classical discontinuous deformation analysis(DDA) is applied to the analysis of a given block system, one must preset stiffness parameters for artificial springs to be fixed during the open-close iteration. To a great degree, success or failure in applying DDA to a practical problem is dependent on the spring stiffness parameters, which is believed to be the biggest obstacle to more extensive applications of DDA. In order to evade the introduction of the artificial springs, this study reformulates DDA as a mixed linear complementarity problem(MLCP) in the primal form. Then, from the fact that the block displacement vector of each block can be expressed in terms of the contact forces acting on the block, the condensed form of MLCP is derived, which is more efficient than the primal form. Some typical examples including those designed by the DDA inventor are reanalyzed, proving that the procedure is feasible.

Memory Based Scheme to Monitor Non-Random Small Shift Patterns in Manufacturing Process

Consistent high-quality and defect-free production is the demand of the day. The product recall not only increases engineering and manufacturing cost but also affects the quality and the reliability of the product in the eye of users. The monitoring and improvement of a manufacturing process are the strength of statistical process control. In this article we propose a process monitoring memory-based scheme for continuous data under the assumption of normality to detect small non-random shift patterns in any manufacturing or service process.The control limits for the proposed scheme are constructed. The in-control and out-of-control average run length(AVL) expressions have been derived for the performance evaluation of the proposed scheme. Robustness to non-normality has been tested after simulation study of the run length distribution of the proposed scheme, and the comparisons with Shewhart and exponentially weighted moving average(EWMA) schemes are presented for various gamma and t-distributions. The proposed scheme is effective and attractive as it has one design parameter which differentiates it from the traditional schemes. Finally, some suggestions and recommendations are made for the future work.

Trans-Gulf of Mexico loop migration of tree swallows revealed by solar geolocation

One of the greatest feats of avian migration is the non-stop crossing of extensive areas of inhospitable habitat such as deserts and seas. Differences in spring and autumn migration routes have been reported in species that cross such barriers, and are thought to have evolved in response to seasonal variation in prevailing wind direction. We tested the hypothesis that migration routes vary seasonally with respect to the Gulf of Mexico in the tree swallow Tachycineta bicolor using solar geolocators attached and retrieved at 4 breeding sites in central North America. We found that 100 % of birds （n = 10） made a trans-Gulf flight of 〉850 km from Louisiana south to their wintering grounds in the Yucatan Peninsula in 12-36 hours, achieving minimum ground speeds as high as 32 m/s. Although most days during autumn migration were characterized by unfavorable headwinds blowing to the northwest, migration over the Gulf mostly occurred on days with strong winds blowing to the south. In contrast, in 8 of 9 （88 %） birds on spring migration returned from the wintering grounds towards Louisiana following a clockwise loop pat- tern flying over land to the west around the Gulf. During this spring period there were few days with prevailing winds from the south to assist northward migration. Results suggest that, despite being up to three times further （ca. 2,700 kin）, a coastal circum-Gulf spring migration represents the less risky route when wind conditions are not favorable. These findings also help to resolve a long-standing dispute in the literature concerning migration patterns between the US Gulf coast and Mexico, and provide insight into the factors shaping migration strategies of small songbirds migrating across large bodies of water [Current Zoology 60（5）： 653-559, 2014].

Tensile behaviors of filaments with misfit of chirality

Slender chiral filaments are ubiquitous in both artificial and biological materials.Due to their chiral microstructures,chiral filaments usually exhibit favorable properties such as superior elasticity and unusual stretch-twist coupling deformation.However,how these chiral microstructures affect the elastic behavior of filaments remains unclear.In this paper,a refined Cosserat rod model with misfit or mismatching of chirality induced by inhomogeneous arrangement of chiral microstructures incorporated is developed.Using the refined rod model,the force-displacement relationships and variation of structural chirality during the tensile processes of two typical helical structures,i.e.,single-strand helix and double-strand helix,are investigated.The results show that the misfit of chirality can lead to a bend-twist deformation with a high coupling degree,which makes the rod much“soft”when stretched.The chiral filaments undergo an unusual twist when stretched,corresponding to an obviously nonlinear variation of structural chirality.The work suggests that the misfit of chirality can be used to tune the elastic behavior of chiral filaments,which is helpful in guiding the design of flexible actuators and soft devices.