Showing papers by "Beihang University published in 2004"
TL;DR: In this article, a room-temperature ionic liquid, 1-allyl-3-methylimidazolium chloride, was used for cellulose acetate synthesis.
633 citations
TL;DR: Wang et al. as discussed by the authors examined the relevance of seven technological innovation capabilities (TICs) to building and sustaining the competitiveness of Chinese firms and found that a strong R&D capability could safeguard innovation rate and product competitiveness in large and medium sized firms, whereas a resources allocation capability would enhance the sales growth in small firms.
516 citations
TL;DR: This paper examines the multi-criteria or the cost-versus-time network equilibrium and system optimum problem in a network with a discrete set of VOTs for several user classes.
Abstract: It is well known that in the standard traffic network equilibrium model with a single value of time (VOT) for all users, a so-called marginal-cost toll can drive a user equilibrium flow pattern to a system optimum. This result holds when either cost (money) or time units are used in expressing the objective function of the system optimum and the criterion for user equilibrium. This paper examines the multi-criteria or the cost-versus-time network equilibrium and system optimum problem in a network with a discrete set of VOTs for several user classes. Specifically, the following questions are investigated: Are the user-optimal flows dependent upon the unit (time or money) used in measuring the travel disutility in the presence of road pricing? Are there any uniform link tolls across all individuals (link tolls that are identical for all user classes) that can support a multi-class user equilibrium flow pattern as a system optimum when the system objective function is measured by either money or time units? What are the general properties of the valid toll set?
420 citations
Journal Article•
TL;DR: A projection operator is introduced, which leads to better sample error estimates especially for small complexity kernels, and the choice of the regularization parameter plays an important role in the analysis.
Abstract: The purpose of this paper is to provide a PAC error analysis for the q-norm soft margin classifier, a support vector machine classification algorithm. It consists of two parts: regularization error and sample error. While many techniques are available for treating the sample error, much less is known for the regularization error and the corresponding approximation error for reproducing kernel Hilbert spaces. We are mainly concerned about the regularization error. It is estimated for general distributions by a K-functional in weighted Lq spaces. For weakly separable distributions (i.e., the margin may be zero) satisfactory convergence rates are provided by means of separating functions. A projection operator is introduced, which leads to better sample error estimates especially for small complexity kernels. The misclassification error is bounded by the V-risk associated with a general class of loss functions V. The difficulty of bounding the offset is overcome. Polynomial kernels and Gaussian kernels are used to demonstrate the main results. The choice of the regularization parameter plays an important role in our analysis.
235 citations
TL;DR: In this paper, the effects of annealing on the structure, surface morphology, optical and electrical properties of indium tin oxide (ITO) films were studied and the results showed that the increase of the heating temperature improves the crystallinity of the ITO films, increases the surface roughness, and improves the optical properties.
226 citations
TL;DR: Fuzzy Petri Nets (FPN) is used as a modeling tool to build fault diagnosis models aimed to accurately diagnose faults when some incomplete and uncertain alarm information of protective relays and circuit breakers is detected.
Abstract: In this paper, Fuzzy Petri Nets (FPN) is used as a modeling tool to build fault diagnosis models aimed to accurately diagnose faults when some incomplete and uncertain alarm information of protective relays and circuit breakers is detected. In order to understand the significance of fault diagnosis models more conveniently, the definition and structure of FPNs are necessarily introduced at first. Then, models of fault diagnosis based on FPN are built, and their corresponding logical testifications are carried out. Finally, the validity and feasibility of this method is illustrated by simulation examples. It is shown from seven cases that the faulted system elements can be diagnosed correctly by use of these models, and a satisfying result can also be achieved even in the situation with large amount of incomplete and uncertain alarm information.
208 citations
TL;DR: The Mn-rich Ni50Mn25+xGa25−x (x=0-5) alloys were developed to investigate the structural transitions and magnetic properties.
187 citations
TL;DR: In this article, five different carbon/carbon composites (C/C) have been prepared and their thermophysical properties studied and the results show that the X -Y direction thermal expansion coefficient (CTE) is negative in the range 0 -100 °C with values ranging from −0.29 to −0.85 −10 −6 /K. The microstructure of the PyC has no obvious effect on the CTE for composites with the same preform architecture.
168 citations
TL;DR: In this paper, a survey was conducted recently in Hong Kong manufacturing industries to examine the importance and the extent to which the Hong Kong manufacturers practiced the strategies based on identified success factors.
Abstract: This paper presents the results of a study that examines the success factors in developing and implementing supply chain management strategies for Hong Kong manufacturers. A survey was conducted recently in Hong Kong manufacturing industries to examine the importance and the extent to which the Hong Kong manufacturers practiced the strategies based on these identified success factors. The results will help further in providing greater understanding of the success factors that lead to successful implementation of SCM strategies to reduce supply chain wide costs and to improve customer service levels.
127 citations
TL;DR: Based on the test data of frictional materials and previous research achievements in this field, a generalized nonlinear strength theory (GNST) is proposed in this article, which describes non-linear strength properties on the π-plane and the meridian plane using a unified formula.
Abstract: Based on the test data of frictional materials and previous research achievements in this field, a generalized non-linear strength theory (GNST) is proposed. It describes non-linear strength properties on the π-plane and the meridian plane using a unified formula, and it includes almost all the present non-linear strength theories, which can be used in just one material. The shape of failure function of the GNST is a smooth curve between the SMP criterion and the Mises criterion on the π-plane, and an exponential curve on the meridian plane. Through the transformed stress space based on the GNST, the combination of the GNST and various constitutive models using p and q as stress parameters can be realized simply and rationally in three-dimensional stress state.
116 citations
TL;DR: In this article, the ab initio tensile test has been applied to an Al-Sigma 9 grain boundary by using the Ab initio pseudopotential method, and the theoretical tensile strength is 9.50 GPa at the strain 21%.
Abstract: The ab initio tensile test has been applied to an Al \ensuremath{\Sigma}9 grain boundary by using the ab initio pseudopotential method. The theoretical tensile strength is 9.50 GPa at the strain 21%. As compared with the theoretical tensile strength in the direction [001] or [111] of an Al single crystal, the boundary is still strong due to the interface reconstruction. The interface extends at almost the same rate with the bulk interlayer until the strain of 19% in spite of the reduced number of interfacial bonds, which indicates the special strength of the reconstructed bonds. This feature can be regarded as a typical property of Al that strong local bonds are formed for less-coordinated atoms at defects.
TL;DR: Ni nanochains are synthesized with diameters of 150-250 nm and lengths of 0.5-2 microm by assembly of small nanoparticles, which exhibit a magnetic coercivity over two orders of magnitude larger than that of bulk Ni.
TL;DR: In this article, the authors investigated the mechanism structure of the magic ball by decomposing the mechanism into kinematic loops and chains and subsequently into basic sub-chains, leading to the analysis of the mobility of the ball mechanism.
TL;DR: In this paper, a well-aligned zinc oxide whiskers with high density were successfully prepared on amorphous substrate by atmospheric metal-organic chemical vapor deposition (MOCVD) and X-ray diffraction measurements indicated that the ZnO whiskers were wurtzite crystal structure, and grew non-epitaxially on glass substrate along a [0, 0, 0, 0, 1] direction.
TL;DR: Findings of scale-free characteristics are reported on the network constructed from the real urban transit system data in Beijing, it is shown that the connectivity distribution of the transit network decays as a power-law, and the exponent λ is about equal to 2.24 from the simulation graph.
Abstract: Many systems can be represented by networks as a set of nodes joined together by links indicating interaction. Recently studies have suggested that a lot of real networks are scale-free, such as the WWW, social networks, etc. In this paper, discoveries of scale-free characteristics are reported on the network constructed from the real urban transit system data in Beijing. It is shown that the connectivity distribution of the transit network decays as a power-law, and the exponent λ is about equal to 2.24 from the simulation graph. Based on the scale-free network topology structure of the transit network, if only transit "hub nodes" are controlled well, the transit network can resist random failures (such as traffic congestion, traffic accidents, etc.) successfully.
TL;DR: China, as well as other less developed countries in science, can earn relative competitive advantages in some new emerging or younger disciplines such as computer science by properly using catch-up strategy.
Abstract: The paper compares the research performance in computer science of four major Western countries, India and China, based on the data abstracted from INSPEC database during the period 1993–2002. A total of 9,632 computer science papers recorded in INSPEC database were used for the comparison. The findings indicate that, on the one hand, the number of papers produced in China has considerably increased in the past few years. Particularly, in recent years, China occupies a remarkable high position in terms of counts of papers indexed by the INSPEC database. On the other hand, Chinese scientists preferred to publish in domestic journals and proceedings and shares of SCI-papers to the total journal papers for China have still remained the lowest. This indicates that the research activities of Chinese scientists in computer science are still rather “local” and suffer from a low international visibility. Various scientometric indicators, such as Normalized Impact Factor, ratio of papers in high quality journals are further adopted to analyze research performance and diverse finding are obtained. Nevertheless, for these surrogate indicators, China has optimistically achieved great progress, characterized with “low level of beginning and high speed of developing”. The policy implication of the findings lies in that China, as well as other less developed countries in science, can earn relative competitive advantages in some new emerging or younger disciplines such as computer science by properly using catch-up strategy.
TL;DR: In this paper, an elastoplastic model for sands is presented, which can describe stress-strain behavior dependent on mean effective stress level and void ratio, and another new state parameter is used to determine the peak strength and describe the critical state behaviour of sands during shearing.
Abstract: An elastoplastic model for sands is presented in this paper, which can describe stress–strain behaviour dependent on mean effective stress level and void ratio. The main features of the proposed model are: (a) a new state parameter, which is dependent on the initial void ratio and initial mean stress, is proposed and applied to the yield function in order to predict the plastic deformation for very loose sands; and (b) another new state parameter, which is used to determine the peak strength and describe the critical state behaviour of sands during shearing, is proposed in order to predict simply negative/positive dilatancy and the hardening/softening behaviour of medium or dense sands. In addition, the proposed model can also predict the stress–strain behaviour of sands under three-dimensional stress conditions by using a transformed stress tensor instead of ordinary stress tensor. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, an accurate nonlinear mathematical model of an electro hydraulic force/torque servo control system was built up and a thorough theoretical analysis on the feedforward compensation for extraneous forces/torques was provided.
TL;DR: In this article, a microstructure consisting of ternary metal silicide Ti 2 Ni 3 Si primary dendrites and interdendritic Ti 2Ni 3 Si/NiTi eutectic was fabricated on a substrate of a titanium alloy BT9 by the laser cladding process.
TL;DR: In this article, the nanostructured thermal barrier coatings exhibited excellent thermal cyclic resistance and low thermal diffusivity, with a lifetime of about 600 h for 1-h cycles at 1050 °C.
TL;DR: In this paper, it was shown that the mechanical and shape memory characteristics of polycrystalline Ni 54 Mn 25 Ga 21 high temperature shape memory alloys can be improved by grain refinement.
TL;DR: In this article, a finite element simulation of the Berkovich, Vickers, Knoop, and cone indenters was carried out for the indentation of elastic-plastic material.
Abstract: Finite element simulation of the Berkovich, Vickers, Knoop, and cone indenters was carried out for the indentation of elastic–plastic material. To fix the semiapex angle of the cone, several rules of equivalence were used and examined. Despite the asymmetry and differences in the stress and strain fields, it was established that for the Berkovich and Vickers indenters, the load–displacement relation can closely be simulated by a single cone indenter having a semiapex angle equal to 70.3° in accordance with the rule of the volume equivalence. On the other hand, none of the rules is applicable to the Knoop indenter owing to its great asymmetry. The finite element method developed here is also applicable to layered or gradient materials with slight modifications.
01 Aug 2004
TL;DR: An improved linear matrix inequality (LMI) method for the design of reliable LQ fuzzy controllers is investigated, which reduces the conservatism of using a single Lyapunov function.
Abstract: This paper deals with the reliable linear quadratic (LQ) fuzzy control problem for continuous-time nonlinear systems with actuator faults. The Takagi-Sugeno (T-S) fuzzy model is employed to represent a nonlinear system. By using multiple Lyapunov functions, an improved linear matrix inequality (LMI) method for the design of reliable LQ fuzzy controllers is investigated, which reduces the conservatism of using a single Lyapunov function. The different upper bounds on the LQ performance cost function for the normal and different actuator fault cases are provided. A suboptimal reliable LQ fuzzy controller is given by means of an LMI optimization procedure, which can not only guarantee the stability of the closed-loop overall fuzzy system for all cases, but also provide an optimized upper bound on a weighted average LQ performance cost function. Finally, numerical simulations on the chaotic Lorenz system are given to illustrate the application of the proposed design method.
TL;DR: In this article, Li/ionomer/LiCoO2 cells were characterized by FT-IR spectroscopy, AC impedance, and cyclic voltammetry, and the discharge capacity of the first cycle was 126mAhg−1.
Abstract: Lithiated Nafion 112 ionomer was characterized by FT-IR spectroscopy, AC impedance, and cyclic voltammetry. The ionomer swollen with mixed solvents of propylene carbonate (PC) and ethylene carbonate shows ionic conductivity of 8.18×10−5Scm−1 at 25°C and good electrochemical stability to allow operation in Li/ionomer/LiCoO2 cells. The discharge capacity of the first cycle is 126mAhg−1. Significant capacity loss occurs during cycling due to the presence of PC. AC impedance shows that the passive layer formed at the Li/ionomer interface dominates the cycling performance of the cell.
01 Apr 2004
TL;DR: Based on the traditional economic order quantity (EOQ) formula, a modified EOQ model is set up and an algorithm for the model is presented and computational results verify the proposed model as well as the efficiency of the algorithm.
Abstract: In this paper, we address the problem of deciding the optimal ordering quantity and frequency for a supplier-retailer logistic system in which the transportation cost as well as the multiple uses of the vehicles are considered. Based on the traditional economic order quantity (EOQ) formula, a modified EOQ model is set up and an algorithm for the model is presented. Computational results verify the proposed model as well as the efficiency of the algorithm.
TL;DR: In this paper, high silicon-iron strips (near to 6.5%Si) were produced by the direct powder rolling (DPR) technique, where continuous strips could be compacted by rolling from silicon and iron powders and sintered by the following heat treatments.
TL;DR: Mo 2 Ni 3 Si/NiSi wear-resistant metal silicide composite coatings were fabricated on substrate of an austenitic stainless steel AISI321 by laser cladding using Ni-Mo-Si elemental powder blends as discussed by the authors.
TL;DR: The suboptimal H2 GC fuzzy controllers are given by means of the LMI optimization procedures, which cannot only guarantee that the closed-loop overall fuzzy systems are globally asymptotically stable, but also provide an optimized upper bound on the quadratic performance cost.
TL;DR: The laser pyrolysis technique seems to be a good alternative to the coprecipitation method for producing MRI contrast agents, with the advantage of being a continuous synthesis method that leads to very uniform particles capable of being dispersed and therefore transformed in a biocompatible magnetic liquid.
Abstract: Biocompatible magnetic dispersions have been prepared from γ-Fe2O3 nanoparticles (5 nm) synthesized by continuous laser pyrolysis of Fe(CO)5 vapours. The feasibility of using these dispersions as magnetic resonance imaging (MRI) contrast agents has been analysed in terms of chemical structure, magnetic properties, 1H NMR relaxation times and biokinetics. The magnetic nanoparticles were dispersed in a strong alkaline solution in the presence of dextran, yielding stable colloids in a single step. The dispersions consist of particle-aggregates 25 nm in diameter measured using transmission electron microscope and a hydrodynamic diameter of 42 nm measured using photon correlation spectroscopy. The magnetic and relaxometric properties of the dispersions were of the same order of magnitude as those of commercial contrast agents produced using coprecipitation. However, these dispersions, when injected intravenously in rats at standard doses showed a mono-exponential blood clearance instead of a biexponential one, with a blood half-life of 7 ± 1 min. Furthermore, an important enhancement of the image contrast was observed after the injection, mainly located at the liver and the spleen of the rat. In conclusion, the laser pyrolysis technique seems to be a good alternative to the coprecipitation method for producing MRI contrast agents, with the advantage of being a continuous synthesis method that leads to very uniform particles capable of being dispersed and therefore transformed in a biocompatible magnetic liquid.
01 Apr 2004
TL;DR: The fuzzy controller directly obtained from the LMI solutions can guarantee the stability of the closed-loop overall fuzzy system, while provide a guaranteed cost on the quadratic cost function of the system in the normal and actuator fault cases.
Abstract: This paper studies the reliable linear quadratic (LQ) fuzzy regulator problem for nonlinear discrete-time systems with actuator faults. The Takagi-Sugeno fuzzy model is employed to represent a nonlinear system. A sufficient condition expressed in linear matrix inequality (LMI) terms for the existence of reliable guaranteed cost (GC) fuzzy controllers is obtained. The fuzzy controller directly obtained from the LMI solutions can guarantee the stability of the closed-loop overall fuzzy system, while providing a guaranteed cost on the quadratic cost function of the system in the normal and actuator fault cases. Furthermore, an optimal reliable GC fuzzy controller in the sense of minimizing a bound on the worst or nominal case guaranteed cost is also given by means of an LMI optimization procedure. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed method.