Showing papers by "Beijing University of Technology published in 2005"

On Automatic Differentiation

Abstract: Evaluation relevant to the partial derivatives of the multivariable functions is often done in scientific computation, usually by means of the symbolic differentiation or the divided difference. But for the middle and large scale problems, the computation cost by symbolic differentiation is very expensive. When the direction derivative is evaluated, the computation cost by divided difference can be reduced, but it is only one kind of aproximate computation. Moreover, it is very difficult to confirm the divided difference interval rightly. Automatic differentiation, by which the derivatives of the function can be evaluated both exactly and economically, is applied to the field of scientific and engineering computation extensively.

Dynamic Modeling of Compliant Mechanisms Based on the Pseudo-Rigid-Body Model

Abstract: Based on the principle of dynamic equivalence, a new dynamic model of compliant mechanisms is developed using the pseudo-rigid-body model. The dynamic equation of general planar compliant mechanisms is derived. The natural frequency of a compliant mechanism is obtained in the example of a planar compliant parallel-guiding mechanism. The numerical results show the effectiveness and advantage of the proposed method compared with the methods of FEA and flexible mechanisms.

Quasineutral Limit of Euler–Poisson System with and without Viscosity

Abstract: The quasineutral limit of Euler–Poisson system with and without viscosity in plasma physics in the torus 𝕋 d , d ≥ 1 is studied. That quasineutral regimes are the incompressible Euler or Navier–Stokes equations is proven. In the mean time, long-time existence for large amplitude smooth solutions of Euler–Poisson system in torus 𝕋 d , d ≥ 1, with or without viscosity as the Debye length λ → 0 is also obtained provided that the smooth solution of incompressible Euler or Navier–Stokes equations exists globally for nearby initial data. In particular, the existence of large amplitude smooth solutions of Euler–Poisson system in torus 𝕋2 with or without viscosity and with sufficiently small Debye length is obtained on any arbitrary time interval. The proof of these results is based on a straightforward extension of the classical energy method, the modulated energy method, the iteration techniques and the standard compactness argument.

Lanthanum and nitrogen co-doped SrTiO3 powders as visible light sensitive photocatalyst

Abstract: Lanthanum and nitrogen co-doped SrTiO 3 was prepared by a mechanochemical reaction method using SrTiO 3 , urea and La 2 O 3 as the raw materials Nitrogen-doped SrTiO 3 could be prepared by heating the mixture of SrTiO 3 and La 2 O 3 under flowing NH 3 gas at 600 °C The sample prepared with 02 mol% La 2 O 3, 22 mol% urea and 778 mol% SrTiO 3 which has nearly the same nitrogen and lanthanum doping atomic fractions could be obtained by a mechanochemical method and exhibited high photocatalytic activities Under the irradiation of light with wavelengths larger than 400 and 290 nm, the photocatalytic activity of nitrogen and lanthanum co-doped SrTiO 3 was 26 and two times greater than that of pure SrTiO 3 A new absorption edge, which was formed in the visible light region and higher visible light absorption after co-doping were the reason for the high visible light photocatalytic activity of this substance

Global Bifurcations and Chaotic Dynamics in Nonlinear Nonplanar Oscillations of a Parametrically Excited Cantilever Beam

Abstract: This paper presents the analysis of the global bifurcations and chaotic dynamics for the nonlinear nonplanar oscillations of a cantilever beam subjected to a harmonic axial excitation and transverse excitations at the free end. The governing nonlinear equations of nonplanar motion with parametric and external excitations are obtained. The Galerkin procedure is applied to the partial differential governing equation to obtain a two-degree-of-freedom nonlinear system with parametric and forcing excitations. The resonant case considered here is 2:1 internal resonance, principal parametric resonance-1/2 subharmonic resonance for the in-plane mode and fundamental parametric resonance–primary resonance for the out-of-plane mode. The parametrically and externally excited system is transformed to the averaged equations by using the method of multiple scales. From the averaged equation obtained here, the theory of normal form is applied to find the explicit formulas of normal forms associated with a double zero and a pair of pure imaginary eigenvalues. Based on the normal form obtained above, a global perturbation method is utilized to analyze the global bifurcations and chaotic dynamics in the nonlinear nonplanar oscillations of the cantilever beam. The global bifurcation analysis indicates that there exist the heteroclinic bifurcations and the Silnikov type single-pulse homoclinic orbit in the averaged equation for the nonlinear nonplanar oscillations of the cantilever beam. These results show that the chaotic motions can occur in the nonlinear nonplanar oscillations of the cantilever beam. Numerical simulations verify the analytical predictions.

Effect of rare earth element addition on the microstructure of Sn-Ag-Cu solder joint

Abstract: The effects of minimal rare earth (RE) element additions on the microstructure of Sn-Ag-Cu solder joint, especially the intermetallic compounds (IMCs), were investigated. The range of RE content in Sn-Ag-Cu alloys varied from 0 wt.% to 0.25 wt.%. Experimental results showed that IMCs could be dramatically repressed with the appropriate addition of RE, resulting in a fine microstructure. However, there existed an effective range for the RE addition. The best RE content was found to be 0.1 wt.% in the current study. In addition to the typical morphology of Ag3Sn and Cu6Sn5 IMCs, other types of IMCs that have irregular morphology and uncertain constituents were also observed. The IMCs with large plate shape mainly contained Ag and Sn, but the content of Ag was much lower than that of Ag3Sn. The cross sections of Cu6Sn5 IMCs whiskers showed various morphologies. Furthermore, some eutectic-like structures, including lamellar-, rod-, and needle-like phases, were observed. The morphology of eutectic-like structure was related to the RE content in solder alloys. When the content of RE is 0.1 wt.%, the needle-like phase was dominant, while the lamellar structure prevailed when the RE content was 0.05 wt.% or 0.25 wt.%. It is suggested that the morphology change of the eutectic-like structure directly affects the creep properties of the solder joint.

Periodic and Chaotic Motions of a Rotor-Active Magnetic Bearing with Quadratic and Cubic Terms and Time-Varying Stiffness

Abstract: In this paper, we use the asymptotic perturbation method to investigate nonlinear oscillations and chaotic dynamics in a rotor-active magnetic bearings (AMB) system with 8-pole legs and the time-varying stiffness. The stiffness in the AMB is considered as the time varying in a periodic form. Because of considering the weight of the rotor, the formulation on the electromagnetic force resultants includes the quadratic and cubic nonlinearities. The resulting dimensionless equations of motion for the rotor-AMB system with the time-varying stiffness in the horizontal and vertical directions are a two-degree-of-freedom nonlinear system with quadratic and cubic nonlinearities and parametric excitation. The asymptotic perturbation method is used to obtain the averaged equations in the case of primary parametric resonance and 1/2 subharmonic resonance. It is found that there exist period-3, period-4, period-6, period-7, period-8, quasiperiodic and chaotic modulated amplitude oscillations in the rotor-AMB system with the time-varying stiffness. It is seen from the numerical results that there are the phenomena of the multiple solutions and the soft-spring type and the hardening-spring type in nonlinear frequency-response curves for the rotor-AMB system. The parametric excitation, or the time-varying stiffness produced by the PD controller is considered to be a controlling force which can control the chaotic response in the rotor-AMB system to a period n motion.

China's Ownership Transformation: Process, Outcomes, Prospects

Abstract: China's emergence as a global economic player has been accompanied by a major internal transformation. Over the past decade, the economy has made the transition from complete reliance on state-owned and collective enterprise to a mixed economy where private enterprise also plays a strong role. Gaizhi, a Chinese term meaning transforming the system,"" has become a major phenomenon in most parts of the country; in many cases it has involved full privatization. China's Ownership Transformation applies descriptive and econometric analysis to survey, and official statistical data to examine, the progress of gaizhi over the years and across regions. It discusses the main players in the process, their motivation and incentives, and looks at the forms, scope, and timing of gaizhi. The authors also provide an assessment of the outcomes of gaizhi, focusing on employee issues, corporate governance issues and frm performance. The book concludes with discussion of the issues related to the fairness and efficiency of the gaizhi process, particularly concerning the role of management buy-outs and outside investors. These issues are at the center of a lively public debate in China, which is likely to influence future Chinese policies toward gaizhi. This title provides researchers, students, policymakers, and those interested in the emergence of China as a global manufacturing and economic powerhouse with in-depth information on the transformation of its state-owned sector.

Extending OWL by fuzzy description logic

Abstract: Technology about ontology plays an important role in all kinds of technologies about the semantic Web OWL, the standard Web ontology language is proposed by W3C Vocabularies in OWL only represent certain and complete concepts and roles In order to represent fuzzy knowledge, this paper extends existing OWL language by encoding fuzzy constructors, axioms and constraints and maps semantics of these new vocabularies to fuzzy description logic Extended OWL can represent fuzzy ontology and resolve some fuzzy entailment tasks by constraint propagation calculus of fuzzy description logic

Hopping conduction in single ZnO nanowires

Abstract: ZnO nanowires were synthesized by chemical vapour deposition (CVD). The dc electrical conductivity of a single ZnO nanowire was investigated over a wide temperature range from 300 to 6 K. It is found that the temperature dependence of conductivity follows the relation . The conductivity data suggest that the dominant conduction mechanism is Efros–Shklovskii variable-range hopping conduction. The strong electron–electron interaction in the nanowire is also proved by the I–V and d I/d V curves, on which there emerges a Coulomb gap-like structure at low temperatures.

Processing and creep properties of Sn-Cu composite solders with small amounts of nanosized Ag reinforcement additions

Abstract: In this research, nanosized Ag reinforcement particles were incorporated by mechanical means into a promising lead-free solder, Sn-0.7Cu, in an effort to improve the comprehensive property of the Sn-0.7Cu solder. Wettability, mechanical performance, and creep-rupture life tests were conducted to study the difference between Sn-0.7Cu solder and its composite solder with different Ag reinforcement volume fractions. Experimental results indicated that the composite solders and their joints showed better wettability and mechanical properties, as well as longer creep-rupture lives, than Sn-0.7Cu solder. The composite solder with 1vol.%Ag reinforcement addition exhibited the best comprehensive property as compared to the composite solders with other reinforcement volume fractions. Systematic creep-rupture life tests were conducted on the 1vol.%Ag-reinforced Sn-0.7Cu-based composite solder joints. Significant enhancement of the creep-rupture lives were found in the composite solder joints under different stress and temperature combinations as compared to the Sn-0.7Cu solder joint. Ductile rupture surfaces were exhibited in most of the broken solder joints.

Fabrication and properties of machinable 3Y–ZrO2/BN nanocomposites

Abstract: 3Y–ZrO 2 /BN ceramic composites with nano-sized BN dispersoids ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing turbostratic BN (t-BN) coating 3Y–ZrO 2 powders, which were prepared via in situ reaction between boric acid and urea on the surface of 3Y–ZrO 2 particles in nitrogen gas. XRD analysis and TEM observations revealed that the nano-sized turbostratic and hexagonal BN (t/h-BN) particulates were dominantly dispersed at ZrO 2 grain boundaries. Vickers hardness of materials decreased directly with an increase of BN content. The fracture strength and the fracture toughness were considerably improved, in comparison to corresponding 3Y–ZrO 2 /BN microcomposites. The nanocomposites with BN content more than 20 vol.% were ready for machining. The preliminary information on the relationship between microstructures and properties are provided.

The fracture and fatigue performance in flexure of carbon fiber reinforced concrete

Abstract: The fracture parameters and fatigue performances of carbon fiber reinforced concrete is investigated by three point bending tests. In comparison with the results of quasi-static tests where no pre-cyclic loading is applied, the influence of pre-cyclic loading history on fracture parameters was researched by using compliance calibration. The test results show that the fracture parameters of carbon fiber reinforced concrete and plain concrete will be reduced if the pre-cyclic loading stress levels are higher than a certain threshold, and this threshold value for carbon fiber reinforced concrete is higher than that of plain concrete. The critical effective crack length for carbon fiber reinforced concrete is significantly larger than that of plain concrete and independent of the pre-cyclic loading history and fatigue life. Carbon fiber reinforced concrete has a considerable beneficial effect on the behaviour of concrete subjected to flexure fatigue loading.

Characteristics of scandate-impregnated cathodes with sub-micron scandia-doped matrices

Abstract: We describe in this paper scandate-impregnated cathodes with sub-micron scandia-doped tungsten matrices having an improved uniformity of the Sc distribution. The scandia-doped tungsten powders were made by both liquid–solid doping and liquid–liquid doping methods on the basis of previous research. By improving pressing, sintering and impregnating procedures, we have obtained scandate-impregnated cathodes with a good uniformity of the Sc 2 O 3 - distribution. The porosity of the sub-micron structure matrix and content of impregnants inside the matrix are similar to those of conventionally impregnated cathodes. Space charge limited current densities of more than 30 A/cm 2 at 850 °C b have been obtained in a reproducible way. The current density continuously increases during the first 2000 h life test at 950 °C b with a dc load of 2 A/cm 2 and are stable for at least 3000 h.

Building a data‐mining grid for multiple human brain data analysis

Abstract: E-science is about global collaboration in key areas of science such as cognitive science and brain science, and the next generation of infrastructure such as the Wisdom Web and Knowledge Grids As a case study, we investigate human multiperception mechanism by cooperatively using various psychological experiments, physiological measurements, and data mining techniques for developing artificial systems which match human ability in specific aspects In particular, we observe fMRI (functional magnetic resonance imaging) and EEG (electroencephalogram) brain activations from the viewpoint of peculiarity oriented mining and propose a way of peculiarity oriented mining for knowledge discovery in multiple human brain data Based on such experience and needs, we concentrate on the architectural aspect of a brain-informatics portal from the perspective of the Wisdom Web and Knowledge Grids We describe how to build a data-mining grid on the Wisdom Web for multiaspect human brain data analysis The proposed methodology attempts to change the perspective of cognitive scientists from a single type of experimental data analysis toward a holistic view at a long-term, global field of vision

Simple fabrication of nano-sized NiO2 powder and its application to oxidation reactions

Abstract: A novel, facile, and environmentally-friendly process for fabrication of NiO2 was developed and used as both a stoichiometric oxidant and an effective catalyst for benzyl alcohol oxidation. That simultaneous stoichiometric and catalytic reactions might exist in many reactions is proposed.

A nonlinear adaptive fuzzy approximator technique with its application to prediction of non-stationary EEG dynamics and estimation of single-sweep evoked potentials

Abstract: In this paper, we apply a fast training paradigm to the optimization of fuzzy approximator and a nonlinear adaptive fuzzy approximator (NAFA) is constructed. Using TSK fuzzy rules, the structured knowledge along with numerical information are parameterized and utilized in the NAFA, which can be easily configured as a multi-layer network when its transparency is desired. We propose a fast training paradigm, which is actually a combination of Kalman filtering and LMS adaptation, to optimize the linear and nonlinear parameters of the NAFA separately. The NAFA is characterized by concise representation of structured knowledge, fast learning capability, as well as universal approximation property. The NAFA is applied to forecast the non-stationary EEG time-series and to estimate single-sweep evoked potentials (EPs). The corresponding simulation results are given. It is concluded that the NAFA technique can provide efficient nonlinear separation of single-sweep EPs, which allows for quantitative examination of the cross-trial variability of clinical EPs.