On the dimension of Goppa codes

A lower bound for the dimension of geometric BCH codes (i.e. subfield subcodes of Goppa codes) has been given by M. Wirtz [7]. We prove that this bound is actually exact for small enough divisorG.     

On the shape and dimension of the Lorenz attractor

It is shown how the global attractor of the Lorenz equations is contained in a volume bounded by a sphere, a cylinder, the volume between two parabolic sheets, an ellipsoid and a cone. The first four are absorbing volumes while the interior of the cone is expelling. By a numerical search over these volumes, it is found that the origin is the most unstable point on the attractor and that an upper bound for the attractor's Lyapunov dimension is 2.401 when b = 8/3, r = 28 and a = 10.     

A multiscale strategy for structural optimization

This paper presents a multiscale strategy dedicated to structural optimization. The applications concern the study of geometric details (such as holes, surface profiles, etc) within the structures with frictional contacts. The first characteristic of the method is that it uses a micro–macro approach. This approach is based on a domain decomposition into substructures and interfaces, which involves the resolution of independent ‘micro’ problems in each substructure and transfers ‘macro’ information only through the interfaces. The second characteristic is the use of a multiresolution strategy in order to reduce the computation cost for problems with evolving design parameters. The last characteristic is the capability to model the geometry of details without remeshing thanks to two features: the use of a local enrichment method , and the use of level set functions to easily modify the boundary of the detail during the optimization process. Copyright © 2008 John Wiley & Sons, Ltd.     

On the shape and dimension of the Lorenz attractor

It is shown how the global attractor of the Lorenz equations is contained in a volume bounded by a sphere, a cylinder, the volume between two parabolic sheets, an ellipsoid and a cone. The first four are absorbing volumes while the interior of the cone is expelling. By a numerical search over these volumes, it is found that the origin is the most unstable point on the attractor and that an upper bound for the attractor's Lyapunov dimension is 2.401 when b = 8/3, r = 28 and a = 10.     

On the fractal dimension of fracture surfaces of concrete elements

The problem of the relation between the fractal dimension of a fractured surface and the fracture toughness expressed by the stress intensity factor is investigated. The theoretical conditions for such assumptions are discussed. Collected experimental results and new tests performed onconcrete specimens subjected to Mode II fracture seem to confirm that relation within the scope of materials tested and with certain necessary restrictions.     

Fractal dimension of structural inhomogeneities in granular YBCO superconductor in magnetic field

The influence of a fractal character of the structure of an YBCO type high-temperature superconductor on its current-voltage characteristic in a magnetic field has been studied. The fractal dimension and connectivity index of vortex transport channels are determined as functions of the magnetic field strength. It is established that the glassy state index corresponds to that of a vortex glass.     

基于产业价值链的我国制造业竞争战略研究

在跨国公司主导的产业价值链体系中,以寻求比较优势为目标的传统竞争战略对我国制造业竞争力产生了严重的削弱作用。研究表明,为获得可持续竞争力,我国制造业竞争战略的重点应聚焦如何建立在产业价值链中的主导和控制地位。     

On the dynamic fracture of structural metals

Some fundamental aspects of dynamic crack growth in structural steels are presented and discussed. The discussion takes the form of a direct comparison of experimental results to elastic-plastic analyses, and attempts to clarify the role of material inertia and plasticity in the dynamic crack growth process. In addition the relation of crack growth criteria to micromechanical void growth models is considered.Potential problems in the analysis of data obtained by either direct optical measurements or numerical simulations of crack growth are presented. It is demonstrated that large errors in the velocity records caused by stress wave effects are a main source of uncertainty in the interpretation of experimental results.

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Résumé On présente et on discute certains aspects fondamentaux de la croissance dynamique d'une fissure dans des aciers de construction. La discussion prend la forme d'une comparaison directe des résultats expérimentaux à l'analyse élasto-plastique et tente de clarifier le rôle de l'inertie et de la plasticité du matériau dans le processus de croissance dynamique d'une fissure. On considère en outre la relation qui les critères de la croissance d'une fissure aux modèles micro-mécaniques de croissance des lacunes.On présente les problèmes potentiels que peuvent surgir dans l'analyse des données obtenues par des mesures directes optiques ou par des simulations numériques de la croissance d'une fissure. On démontre que des erreurs importantes dans les enregistrements de vitesse causées par des effets d'onde de contrainte sont la source principale d'incertitudes dans l'interprétation des résultats expérimentaux.

     

一种基于组合降维的图像识别方法

为克服图像识别中传统方法需要进行高维矩阵奇异值分解的困难，提出了先局部降维再总体降维的组合变换方法．ORL人脸图像数据库的实验表明，这一方法不仅减少了运算量，而且能较好地解决人脸这样一类复杂的图像识别问题；总体来说优于传统的基于KL变换的识别方法．     

论第三代结构设计理论

该文采用新点估计法和简化四阶矩法对丁发兴提出的钢管混凝土轴压承载力公式进行可靠度分析,该公式考虑了不同截面钢管形状约束系数,且探讨了不同截面形状、混凝土等级、钢材强度等级、两种荷载组合以及不同荷载比对可靠指标的影响。分析结果表明,不同截面形状的钢管混凝土轴压承载力公式的可靠指标均高于3.7,满足目标可靠指标3.2的要求;当办公室活恒载比为1.0时,混凝土强度越高时,可靠指标越大。     

A move limit strategy for level set based structural optimization

A move limit strategy is proposed for level set based structural optimization, which offers a tool to restrict the allowable change of the free boundary of a structure in each iterative step of optimization. To realize the move limit strategy, a function for modifying the extended design velocity is proposed. Application of the move limit strategy is demonstrated by several numerical examples of 2D structures. The results show that the move limit strategy is helpful to improve the stability and convergence rate of level set based structural optimization.     

Qualitative reasoning inference strategy and its application to structural engineering

The space-centered framework is a reasoning methodology for obtaining qualitative solutions to boundary value problems. The inference strategy uses backward-and-forward propagation. The backward propagation assumes a component or connection qualitative state consistent with available knowledge about the component or connection. The forward propagation uses the topology of the structure and derives values without ambiguity consistent with the new information assumed by the backward propagation. The forward propagation considerably improves the inference efficiency. A computer program named Agrippa implements the famework. The framework is applied to the evaluation of the load transfer characteristics of two conceptual structural designs.     

体育设施标准化战略研究

一、概述体育设施指的是用于开展体育竞赛、训练、教学和群众性体育活动的建筑物、场地和固定附属设备。随着体育运动项目的进一步发展,体育设施功能要求的不断提高,体育设施产品的不断丰富,施工作业技术的日趋复杂,国内外对体育设施标准的要求越来越高,也越来越全面。但在新形势下,体育设施在建设、使用、管理等方面均出现了新的矛盾和问题,设施建设缺少技术标准,服务管理缺少管理标准,建成使用没有检测、验评机构,生产企业没有产品标准,产品标准技术过时或与国际标准不兼容,标准化技术协会的力量薄弱。从标准化工作的角度看,这是体育设施…     

论我国技术标准战略实施

简述了技术标准的重要性及其在国内外的发展概况,介绍了我国开展技术标准研究的最新进展,指出了大力开展综合标准化的研究对我国实施技术标准战略的重要性及未来发展前景.     

On the variability of the creep coefficient of structural concrete

Experimental data from many creep test series are compared with predictions from various formulas in international codes. A mathematical simple creep formula is proposed and its accuracy is determined from comparison with the experimental data. Based hereon, a probabilistic model for the creep coefficient is proposed and the different sources of uncertainty are quantified. The proposed model is well suited for hand calculations.     

On stability sampling strategy at the slope scale

Snow slope stability evaluation is often based on a single test location within a slope. However, we know that snow cover properties and stability may vary at the slope scale. Reliably estimating the slope-scale variability requires many samples, ideally more than 100. As this is unpractical, it has been proposed to perform at least two tests — about 10 m apart — on a given slope. In addition, if small column stability tests are used (such as the compression test), it seems reasonable to perform two tests at each of the two locations. Differences between the two tests at one location allow one to assess the small (or pit-) scale variability (and/or the test uncertainty), whereas differences between the pairs at different locations may hint at the slope-scale variability. We analyzed 22 small slopes each with four pairs of stability tests. In 61-75% of the cases the two stability tests at a specific location provided consistent results, depending whether we focused on the CT score or the fracture character (which was less variable). Comparing the different sampling locations on a given slope (∼ 10-15 m apart) showed that at the slope-scale the differences between sampling locations (59-75%) were similar to the differences found at the pit-scale. Rather stable slopes tended to have more pit-scale variation than rather unstable slopes. Based on our analysis, we suggest an interpretation scheme and an adjusted sampling procedure. In particular, a second pit on a slope seems only necessary if the first pit does not indicate instability. In all other cases, a second pit can reduce the number of false-stable predictions.     

一维,二维和三维Si基纳米线的制备

在Ar气氛中，SiC粉末分别在Fe、Co、Fe：Co(1：1)的催化下，经一步反应制备了一维、二维和三维si基纳米线。SEM、HRTEM、EDX分析表明一维线状和二维网状Si基纳米线由C、Si、O组成，存在两类纳米线，一类是SiO，包裹的Si纳米线；另一类是SiO，包裹的SiC纳米线。三维Si基纳米线组成象花一样的结构，仅由SiOx组成。SiOx和Si是无定形结构，SiC是β-SiC单晶。     

On structural reliability of parallel systems

The distribution of strength of a bundle of perfectly brittle components in parallel with equal load sharing is studied. An early asymptotic result for stochastically independent components which is due to Daniels is generalized for components whose bearing capacities depend on a second uncertain variable in a multiplicative manner. In particular, if the componental strengths are log-normally distributed and equicorrelated it is shown that system strength is asymptotically ormal. Some applications and their validity to structural design are discussed.