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Now showing items 81 - 96 of 1311

  • Analysis of the effects of compressive stresses on fatigue crack propagation rate

    J. Zhang   X.D. He    S.Y. Du  

    In this study, the effects of compressive stresses on the crack tip parameters and its implication on fatigue crack growth have been studied. Elastic–plastic finite element analysis has been used to analyse the change of crack tip parameters with the increase of the applied compressive stress level.The near crack tip opening displacements and the reverse plastic zone size around the crack tip have been obtained. The finite element analysis shows that when unloading from peak tensile applied stress to zero applied stress, the crack tip is still kept open and the crack tip opening displacement gradually decreases further with the applied compressive stress. It has been found that for a tension–compression stress cycle these crack tip parameters are determined mainly by two loading parameters, the maximum stress intensity Kmax in the tension part of the stress cycle and the maximum compressive stress σmaxcom in the compression part of the stress cycle.Based on the two parameters, Kmax, and σmaxcom, a fatigue crack propagation model for negative R ratios only has been developed to include the compressive stress effect on the fatigue crack propagation rate.Experimental fatigue crack propagation data sets were used for the verification of this model, good agreements have been obtained.
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  • Analysis of the effects of compressive stresses on fatigue crack propagation rate

    J. Zhang   X.D. He   S.Y. Du  

    In this study, the effects of compressive stresses on the crack tip parameters and its implication on fatigue crack growth have been studied. Elastic–plastic finite element analysis has been used to analyse the change of crack tip parameters with the increase of the applied compressive stress level.The near crack tip opening displacements and the reverse plastic zone size around the crack tip have been obtained. The finite element analysis shows that when unloading from peak tensile applied stress to zero applied stress, the crack tip is still kept open and the crack tip opening displacement gradually decreases further with the applied compressive stress. It has been found that for a tension–compression stress cycle these crack tip parameters are determined mainly by two loading parameters, the maximum stress intensity Kmax in the tension part of the stress cycle and the maximum compressive stress σmaxcom in the compression part of the stress cycle.Based on the two parameters, Kmax, and σmaxcom, a fatigue crack propagation model for negative R ratios only has been developed to include the compressive stress effect on the fatigue crack propagation rate.Experimental fatigue crack propagation data sets were used for the verification of this model, good agreements have been obtained.
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  • NdFeB alloy as a magnetic electrode material for lithium-ion batteries

    J. Zhang   J.L. Shui   S.L. Zhang   X. Wei   Y.J. Xiang   S. Xie   C.F. Zhu   C.H. Chen  

    The search for a reliable indicator of state of charge and even the remaining energy of a lithium-ion cell is of great importance for various applications. This study was an exploratory effort to use magnetic susceptibility as the indicator. In this work, for the first time the change of ac susceptibility of cells was in situ monitored during charge-discharge process. A strong permanent magnetic material, NdFeB alloy, was investigated as an anode material for rechargeable lithium batteries. Both original and partially oxidized NdFeB powders were made into electrodes. Structural characterization was performed on the NdFeB electrodes by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. An alloy (core)-oxide (shell) structure was found for those partially oxidized samples. The electrochemical cycling of cells made of the NdFeB electrodes against lithium was measured. The first lithium intercalation capacity of a treated NdFeB can be up to about 831mAh/g, while a rather reversible capacity of up to 352mAh/g can be obtained. With a specially designed cell, we were able to monitor in situ the change of relative ac susceptibility during charge and/or discharge steps. A clearly monotonous relationship is found between the ac susceptibility of a cell and its depth-of-discharge (DOD). A mechanism based on skin effect and eddy current change is proposed to explain this susceptibility versus DOD relationship. [All rights reserved Elsevier]
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  • Commercial carbon nanotubes as heterogeneous catalysts in energy related applications

    J. Zhang   D.S. Su   R. Schl?gl  

    Abstract We report the application of commercial carbon nanotubes (CNTs) in two important heterogeneously catalyzed reactions, i.e., NH3 decomposition and oxidative dehydrogenation of ethylbenzene (EB). For NH3 decomposition, CNTs were used as supports for Co–Mo nanoparticles. The structure of fresh and used catalysts was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and line-scan energy dispersive X-ray (EDX). Most of the nanoparticles are individually separated and the synergism mainly increases the long-term stability rather than the activity. For the oxidative dehydrogenation, the metal-free CNTs display a superior performance as compared to the Fe-doped CNTs. The outstanding results in both reactions predict an extremely promising future of commercial nanocarbons in modern catalysis.
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  • Modeling and Parametric Studies of External MHD Generators

    G. Chen   C. Lee   J. Zhang   and Z. Chen   National Lab. for Computational Fluid Dynamics   Beijing   China (prc)  

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  • Maternal immunization promotes the immune response of neonates towards hepatitis B vaccine

    W. Zhang   Z. Guo   L. Zhang   Z. Liu   J. Li   Z. Ji   R. Xu   N. Zhao   F. Li   X. Chen   Y. Yan   J. Zhang   Q. An   H. Yang   Z. Den and Z. Shao  

    Infants infected with hepatitis B virus (HBV) face the risk of developing severe complications. Unfortunately, in spite of universal vaccination programmes, 5% or more of vaccinated newborns still do not achieve protective levels of anti-hepatitis B virus surface antigen titres (anti-HBs). The aim of this study was to use animal experiments and population-based research to determine whether maternal vaccination against HBV affects the outcome of neonatal vaccination. Six sows and 53 newborn piglets were used for this study and randomly assigned to the vaccination group (three 20 μg doses of recombinant HBV vaccine). All the piglets were followed up to 10 weeks of age, and peripheral blood was withdrawn for measurement of anti-HBs. A cross-sectional study was also conducted on 449 mothers with infants. A structured questionnaire was used to collect demographic, medical and maternal data, and their peripheral blood was collected for measurement of anti-HBs. The results of animal experiments demonstrated that nonvaccinated piglets born to vaccinated sows and nonvaccinated piglets born to nonvaccinated sows were negative for anti-HBs. Repeated measures analysis of variance showed that the titres of anti-HBs in vaccinated piglets born to vaccinated sows were significantly higher than in vaccinated piglets born to nonvaccinated sows (P < 0.05). In a population-based study, a cumulative logistic regression analysis showed that the strongest influences on neonatal anti-HBs titres were delay of the first vaccination dose [OR = 3.02(95% CI: 1.72–5.30)] and maternal anti-HBs titres [OR = 2.48(95% CI: 2.03–3.04)]. In conclusion, high maternal anti-HBs titres can enhance the response to HBV vaccination in infants.
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  • Effect of Particle Size Ratio on the Drag Force of an Interactive Particle

    J. Zhang   J.P. Zhang   L.-S. Fan  

    The paper presents an experimental study on the drag forces of two interactive particles with unequal diameters. A circulating loop for the fluid flow is set up. The particles are arranged in a line parallel to the direction of the flow in the test section. Direct measurements of the drag force of the downstream trailing particle are performed by utilizing a micro-balance force measuring system. The tests are conducted under different conditions. The obtained results illustrate the effects of particle size ratio and Reynolds number on the drag force of the trailing particle. It is found that the drag force ratio of the trailing particle increases with the particle size ratio under both circumstances of the particle size ratio being larger than 1 and less than 1. The drag force ratio of the trailing particle tends to decrease with increasing particle Reynolds number for the present cases being studied
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  • Noise Resistant OFDM for Power-Line Communication Systems

    J. Zhang   J. Meng  

    In this paper, we present a new approach to noise suppression for power-line communications based on orthogonal frequency-division multiplexing (OFDM). Previous work for wireless systems has suggested that augmentation of OFDM using spreading codes prior to modulation offers some narrowband interference (NBI) resistant capabilities. We present a study of the performance of such a system for power-line networks-well known to be affected by such noise. Termed interference suppression OFDM (IS-OFDM) and its counterpart NBI avoidance (NBIA), we also present a further modification of these techniques in order to improve NBI suppression performance. The proposed algorithm, orthogonal narrowband interference avoidance (ONBIA), avoids narrowband interference on contaminated subcarriers while preserving the orthogonality of the spreading code. Both theoretical analysis and simulation results demonstrate the improvements of ONBIA over the standard IS-OFDM and NBIA methods across a wide range of interference-to-signal ratios (ISR).
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  • Adaptable End Effector for Atomic Force Microscopy Based Nanomanipulation

    J. Zhang   N. Xi   G. Li   H. Chan   U. C. Wejinya  

    Nanomanipulation using the atomic force microscope (AFM) has been extensively investigated for many years. But the efficiency and accuracy of AFM-based nanomanipulation are still major issues due to the nonlinearities and uncertainties in nanomanipulation operations. The deformation of the cantilever caused by manipulation force is one of the most major nonlinearities and uncertainties. It causes difficulties in accurately controlling the tip position, and results in missing the position of the object. The softness of the conventional cantilevers also causes the failure of manipulation of sticky nano-objects because the tip can easily slip over the nano-objects. In this paper, an active atomic force microscopy probe is used as an adaptable end effector to solve these problems by actively controlling the cantilever's flexibility or rigidity during nanomanipulation. A control voltage is applied to the piezo layer of the adaptable end effector to exert a reverse bending moment on the cantilever to balance the bending moment caused by the interaction force during manipulation. Thus, the adaptable end effector is controlled to maintain straight shape during manipulation. A detailed model of the adaptable end effector is presented in the paper. Control of the adaptable end effector employing an optimal LQR control law is derived and implemented. The experimental results verify the validity of the model and effectiveness of the controller. The nanomanipulation results also prove the increased efficiency of AFM-based nanomanipulation using the adaptable end effector
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  • System optimization and experimental research on air source heat pump water heater

    J. Zhang   R.Z. Wang   J.Y. Wu  

    This paper deals with the system optimization of air source heat pump water heater (ASHPWH), including calculating and testing. The ASHPWH system consists of a heat pump, a water tank and connecting pipes. Air energy is absorbed at the evaporator and pumped to storage tank via a Rankine cycle. The coil pipe/condenser releases condensing heat of the refrigerant to the water side. An ASHPWH using a rotary compressor heated the water from initial temperature to the set temperature (55degC). The capillary tube length, the filling quantity of refrigerant, the condenser coil tube length and system matching are discussed accordingly. From the testing results, it could be seen that the system performance COP could be improved obviously. [All rights reserved Elsevier].
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  • Factors affecting the membrane performance in submerged membrane bioreactors

    J. Zhang   H.C. Chua   J. Zhou and A.G. Fane  

    Submerged membrane bioreactors (SMBRs) operate at constant imposed flux usually with the membranes in direct contact with the mixed liquor. Membrane fouling is evident as a rise in the required transmembrane pressure (TMP). In this paper we describe the rise in TMP as a three stage process. Stage 1 occurs in a period of a few hours and involves abrupt TMP rise due to ‘conditioning’, presumably by pore blockage and closure. Stage 2 is a prolonged period of slow TMP rise, which we ascribe to accumulation of extracellular polymeric substances (EPS) and other products of bioactivity, either deposited from the bulk liquor or produced in biofilms on the membrane surface. Polysaccharides are predominant in the supernatant EPS, and appear to be major membrane foulants deposited by the filtration process. Stage 3 is a sudden rise in TMP, which rapidly leads to inoperability of the membranes. This stage could have several causes, which we summarize, and which are all driven by the self-accelerating nature of fouling under constant flux operation.In order to understand the complex nature of fouling in submerged MBRs we have developed the MBR ‘roadmap’ that shows the relationship between the many operational and design characteristics of the MBR and the generic ‘fouling factors’, i.e. the nature of the feed (to the membrane), the membrane properties, and the hydrodynamic environment. We also present a MBR ‘fouling mechanism map’ which depicts the three stages of fouling and the multiple fouling mechanisms that could occur. Experimental observations are provided in support of many of the proposed fouling mechanisms.
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  • Factors affecting the membrane performance in submerged membrane bioreactors

    J. Zhang   H.C. Chua   J. Zhou   A.G. Fane  

    Submerged membrane bioreactors (SMBRs) operate at constant imposed flux usually with the membranes in direct contact with the mixed liquor. Membrane fouling is evident as a rise in the required transmembrane pressure (TMP). In this paper we describe the rise in TMP as a three stage process. Stage 1 occurs in a period of a few hours and involves abrupt TMP rise due to ‘conditioning’, presumably by pore blockage and closure. Stage 2 is a prolonged period of slow TMP rise, which we ascribe to accumulation of extracellular polymeric substances (EPS) and other products of bioactivity, either deposited from the bulk liquor or produced in biofilms on the membrane surface. Polysaccharides are predominant in the supernatant EPS, and appear to be major membrane foulants deposited by the filtration process. Stage 3 is a sudden rise in TMP, which rapidly leads to inoperability of the membranes. This stage could have several causes, which we summarize, and which are all driven by the self-accelerating nature of fouling under constant flux operation.In order to understand the complex nature of fouling in submerged MBRs we have developed the MBR ‘roadmap’ that shows the relationship between the many operational and design characteristics of the MBR and the generic ‘fouling factors’, i.e. the nature of the feed (to the membrane), the membrane properties, and the hydrodynamic environment. We also present a MBR ‘fouling mechanism map’ which depicts the three stages of fouling and the multiple fouling mechanisms that could occur. Experimental observations are provided in support of many of the proposed fouling mechanisms.
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  • Numerical modeling of negative-corona discharge in oxygen under different pressures

    J. Zhang   K. Adamiak   G.S.P. Castle  

    This paper presents a numerical model of the negative-corona discharge in oxygen under different pressures at room temperature. The model assumes the presence of two charged species: electrons and ions. The boundary element and finite-element methods have been used to calculate the electric field and the method of characteristics has been employed for the densities of electrons and ions. The simulation has been performed for an axisymmetrical point-plane geometry with a hyperboloidal needle perpendicular to infinitely large conducting plate. The results of computations show the effect of pressure on the electron and negative-ion densities along the axial direction, electric field distribution along the axis of symmetry and current density on the ground plane.
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  • A multi-regional computation scheme in an AR-assisted in situ CNC simulation environment

    J. Zhang   S.K. Ong   A.Y.C. Nee  

    Computer numerical control (CNC) simulation systems based on 3D graphics have been well researched and developed for NC tool path verification and optimization. Although widely used in the manufacturing industries, these CNC simulation systems are usually software-centric rather than machine tool-centric. The user has to adjust himself from the 3D graphic environment to the real machining environment. Augmented reality (AR) is a technology that supplements a real world with virtual information, where virtual information is augmented on to real objects. This paper builds on previous works of integrating the AR technology with a CNC machining environment using tracking and registration methodologies, with an emphasis on in situ simulation. Specifically configured for a 3-axis CNC machine, a multi-regional computation scheme is proposed to render a cutting simulation between a real cutter and a virtual workpiece, which can be conducted in situ to provide the machinist with a familiar and comprehensive environment. A hybrid tracking method and an NC code-adaptive cutter registration method are proposed and validated with experimental results. The experiments conducted show that this in situ simulation system can enhance the operator's understanding and inspection of the machining process as the simulations are performed on real machines. The potential application of the proposed system is in training and machining simulation before performing actual machining operations. [All rights reserved Elsevier].
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  • Systematic review: applications and future of gastric electrical stimulation

    J. ZHANG   J. D. Z. CHEN  

    BACKGROUND: Over the past 20 years, gastric electrical stimulation has received increasing attention among researchers and clinicians.AIM: To give a systematic review on the effects, mechanisms and applications of gastric electrical stimulation.METHODS: Medline was used to identify the articles to be included in this review. Key words used for the search included gastric electrical stimulation, gastric pacing, electrical stimulation, stomach, gastrointestinal motility, central nervous system, gastroparesis, nausea and vomiting; obesity and weight loss. Combinational uses of these keywords were made to identify relevant articles. Most of the articles included in this review ranged from 1985 to 2006.RESULTS: Based on the general search, the review was structured as follows: (i) peripheral and central effects and mechanisms of gastric electrical stimulation; (ii) clinical applications of gastric electrical stimulation for gastroparesis and obesity and (iii) future development of gastric electrical stimulation.CONCLUSIONS: Great progress has been made during the past decades. Gastric electrical stimulation has been shown to be effective in normalizing gastric dysrhythmia, accelerating gastric emptying and improving nausea and vomiting. Implantable device has been made available for treating gastroparesis as well as obesity. However, development of a new device and controlled clinical studies are required to further prove clinical efficacy of gastric electrical stimulation.
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  • Soft ovarian stimulation IVF (Mini–IVF) vs conventional IVF: an economic perspective

    J. Zhang   A. Chavez-Badiola   W. Peng   L. Chang   L.A. Ruvalcaba-Castellon  

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