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排序方式: 共有627条查询结果,搜索用时 15 毫秒
71.
Dinh Tuan Hai 《Journal of Constructional Steel Research》2006,62(10):987-994
Currently, the deterioration of bridge conditions is causing many problems. Therefore, the work reported in this paper was carried out to survey the present condition of railway bridges in Vietnam, concentrating on steel deficiencies. Literature reviews were initiated to identify common defects with site inspections and personal interviews to ascertain their validity. Finding the defects draws an overall picture of Vietnamese railway bridges that are in poor physical condition, thus providing poor serviceability. Besides structural failure, local defects were already identified, consisting of corrosion, fatigue, functional obsolescence and aging. New problems that have been identified are human invasions and missing elements. It is widely considered that overload, collision impacts, adverse climate conditions and poor maintenance are the main causes. Additionally, this paper includes previous wars, improper data keeping, and elemental burglary as country-specific causes. It suggests that maintenance efforts should be prioritized to eliminate these deficiencies. Trained maintenance crews need to be established and further research should be carried out to create an adequate maintenance management system in Vietnam. 相似文献
72.
J.-P. Maneval Kh. Harrabi Vu Dinh Lam F. Boyer F.-R. Ladan 《Journal of Superconductivity》2002,15(5):417-419
By means of nanosecond pulse techniques, we have studied the current-induced dissipation in one-dimensional superconducting bridges, namely, metallic and high-T
c films. It is well known that narrow strips dissipate through phase-slip centers (PSC) close to T
c, or hot spots (HS) at low T, rather than by flux flow. When driven by step pulses of current, PSC give stable voltages, while HS produce a voltage linearly changing with time. By using two-step pulses of current, we have studied the decay of a HS into another HS, or a PSC, or into a zero-resistance state. It was thus found possible to reach the PSC state at arbitrary low temperatures. 相似文献
73.
Based on ab initio electronic structure calculations of Mn-doped III–V nitrides (AlN, GaN, InN), a co-doping method with size compensation to enhance the Curie temperature (TC) of Nitride-based DMS is proposed. Three cases are considered: (1) Single doping: cations are substituted randomly by Mn. (2) One-site co-doping: Cations or anions are substituted by co-dopants. (3) Two-site co-doping: co-dopants are introduced into both cation and anion sites. Be is chosen as co-dopant for (Al, Mn)N and (Ga, Mn)N, and Cd (or C) for (In, Mn)N. Concentrations of co-dopants are chosen as a function of Mn concentration so that the volume distortion caused by Mn doping is reduced. It is found that, by hole co-doping, the ferromagnetism is more stabilized than that in the single doping case. The anti-ferromagnetic super-exchange interaction, which remains dominant for high Mn concentrations in (Al, Mn)N and (Ga, Mn)N due to the small lattice constant, is reduced by co-doping Be into both kinds of sites, resulting in a strong enhancement of TC in the regime of high Mn-concentrations. Furthermore, as the 3d-partial density of states at the Fermi level gains its maxima, one can expect that TC reaches its highest value. 相似文献
74.
T. N. Dinh V. A. Bui R. R. Nourgaliev T. Okkonen B. R. Sehgal 《Nuclear Engineering and Design》1996,163(1-2)
The objective of this paper is to study the heat and mass trasnfer processes related to core melt discharge from a reactor vessel in a light water reactor severe accident. The phenomenology modelled includes the convection in, and heat transfer from, the melt pool in contact with the vessel lower head wall, the fluid dynamics and heat transfer of the melt flow in the growing discharge hole and multi-dimensional heat conduction in the ablating lower head wall. A research programme is underway at the Royal Institute of Technology (Kungliga Tekniska Högskolan, KTH) to (1) identify the dominant heat and mass transfer processes determining the characteristics of the lower head ablation process: (2) develop and validate efficient analytical/computational models for these processes; (3) apply models to assess the character of the melt discharge process in a reactor-scale situation; (4) determine the sensitivity of the melt discharge to structural differences and variations in the in-vessel melt progression scenarios. The paper also presents a comparison with recent results of vessel hole ablation experiments conducted at KTH with a melt simulant. 相似文献
75.
76.
R. Glowinski Q.V. Dinh J. Periaux 《Computer Methods in Applied Mechanics and Engineering》1983,40(1):27-109
The numerical solution of finite element approximations of complicated two- and three-dimensional nonlinear problems can be a most formidable task. In order to overcome this difficulty related to dimensionality, domain-splitting methods can be very effective, particularly in view of obtaining a fast and economical conjugate gradient solver, which can be used to precondition the solution of nonlinear problems by optimization methods via nonlinear least squares or weighted residual formulations. A new technique of this type will be introduced and analysed and its efficiency will be discussed from numerical experiments concerning the numerical simulation of transonic flows for compressible inviscid fluids and incompressible viscous flows modelled by the Navier-Stokes equations. 相似文献
77.
SJ McConnell T Dinh MH Le SJ Brown K Becherer K Blumeyer C Kautzer F Axelrod DG Spinella 《Canadian Metallurgical Quarterly》1998,379(10):1279-1286
Cyclic peptides capable of activating the erythropoietin receptor (EPOR) were isolated from phage display libraries by screening with a novel EPOR-IgG fusion protein reagent. A parental clone ERB1 (EPO Receptor Binder 1) was first isolated from a phage display library displaying 38 random amino acids as an N-terminal fusion with the M13 minor capsid protein, pill. An evolved library was then produced from the parental sequence using an oligonucleotide saturation mutagenesis strategy which yielded EPOR binding sequences with 20 times the relative affinity of ERB1. Two synthetic peptides were constructed from these sequences both of which bind the EPO receptor in specific ELISA, and act as full agonists in EPO dependent cell proliferation assays. These peptides are 18 amino acids in length, disulfide-bonded, and have a minimum consensus sequence of CXXGWVGXCXXW, where X represents positions tolerant of several amino acids. 相似文献
78.
Dang Dinh Ang 《International Journal of Fracture》1984,26(1):55-64
The paper presents a method of constructing, by successive approximation, stabilized approximate solutions of certain integral equations of first kind in contact problems of elasticity. In these equations, the unknown function is a surface stress under the stamp, which is allowed to have a square root singularity under the edges of the stamp, and is therefore not square integrable. The author shows that it is nevertheless possible to apply the theory of positive operators to the present problem by constructing an appropriate L2-space which includes functions with square root singularities.
Résumé On présente une méthode d'élaboration par approximations successives de solutions approchées stables de certaines équations intégrales du premier genre relatives à des problèmes de contact élastique. Dans ces équations, la fonction inconnue est une contrainte de surface sous le point de contact, qui peut présenter une singularité d'ordre 1/2 sous les bords du poin¢on, et qui dès lors n'est pas intégrable par voie quadratique.L'auteur montre qu'il est néanmoins possible d'appliquer la théorie des opérateurs positifs à un tel problème, en construisant un espace de Hilbert incluant des fonctions présentant des singularités d'ordre 1/2.相似文献
79.
Phung SL Bouzerdoum A Chai D 《IEEE transactions on pattern analysis and machine intelligence》2005,27(1):148-154
This work presents a study of three important issues of the color pixel classification approach to skin segmentation: color representation, color quantization, and classification algorithm. Our analysis of several representative color spaces using the Bayesian classifier with the histogram technique shows that skin segmentation based on color pixel classification is largely unaffected by the choice of the color space. However, segmentation performance degrades when only chrominance channels are used in classification. Furthermore, we find that color quantization can be as low as 64 bins per channel, although higher histogram sizes give better segmentation performance. The Bayesian classifier with the histogram technique and the multilayer perceptron classifier are found to perform better compared to other tested classifiers, including three piecewise linear classifiers, three unimodal Gaussian classifiers, and a Gaussian mixture classifier. 相似文献
80.