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Lei Z.X.,City University of Hong Kong | Lei Z.X.,University of Science and Technology of China | Lei Z.X.,Cityint Advanced Research Center | Liew K.M.,City University of Hong Kong | And 3 more authors.
Computer Methods in Applied Mechanics and Engineering | Year: 2013

A nonlinear analysis is presented for functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates using the element-free kp-Ritz method. The nonlinear governing equations are developed to investigate problems related to small strains and moderate rotations, based on the first-order shear deformation plate theory and von Kármán strains. Two-dimensional displacement fields of the plates are approximated by a set of mesh-free kernel particle functions. Single-walled carbon nanotubes (SWCNTs) are selected as reinforcement and effective material properties of FG-CNTRC plates are assumed to be graded through the thickness direction and are estimated through an equivalent continuum model based on the Eshelby-Mori-Tanaka approach. For eliminating shear locking for a very thin plate, a stabilized conforming nodal integration scheme is employed to evaluate the system bending stiffness, and the membrane as well as shear terms are calculated by the direct nodal integration method. Numerical simulations are carried out to investigate effects of various parameters on nonlinear behaviors of FG-CNTRC plates and results for uniformly distributed (UD) CNTRC plates are provided for comparison. Numerical results indicate that carbon nanotube content by volume, plate width-to-thickness ratio, plate aspect ratio and boundary condition have pronounced effects on the nonlinear response of CNTRC plates. © 2012 Elsevier B.V.


Yan J.W.,City University of Hong Kong | Yan J.W.,Hefei University of Technology | Yan J.W.,Cityint Advanced Research Center | Liew K.M.,City University of Hong Kong | And 3 more authors.
Computer Methods in Applied Mechanics and Engineering | Year: 2012

The higher-order Cauchy-Born rule is applied to predict the mechanical response of single-walled carbon nanotubes (SWCNTs). As second-order deformation gradients can describe the bending effect of C-C bond vectors involved in the theoretical scheme of the higher-order gradient continuum, the established constitutive model accords extremely well with physical behavior. From the constitutive relationship constructed, a novel computational method is proposed for numerical simulation of buckling behaviors of SWCNTs. In this study, a new mesh-free method developed from the moving Kriging (MK) interpolation is employed to implement numerical simulation of mechanical properties of SWCNTs under axis-symmetrical loadings. As the mesh-free shape function constructed using the MK interpolation has the delta function property, the shape functions satisfy the essential boundary conditions automatically. Therefore, the essential boundary conditions can be easily implemented. Several numerical examples of buckling behaviors of SWCNTs are presented to test the effectiveness and efficiency of this method. The numerical results are also compared with those obtained from the full atomistic simulation method, and are found to be in agreement. Moreover, this computational method can largely reduce the degrees of freedom of the system, and thus save a large amount of computational resources. As a result, this is a very attractive approach, which has great potential in the engineering field. This mesh-free method is further applied to the study of post-buckling of SWCNTs. The results are compared with those obtained from full atomistic simulation, and demonstrate that this method is truly effective and efficient. © 2012 Elsevier B.V.


Lei Z.X.,City University of Hong Kong | Lei Z.X.,University of Science and Technology of China | Lei Z.X.,Cityint Advanced Research Center | Liew K.M.,City University of Hong Kong | And 3 more authors.
Composite Structures | Year: 2013

This paper presents the buckling analysis of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates under various in-plane mechanical loads, using the element-free kp-Ritz method. The first-order shear deformation plate theory is applied and a set of mesh-free kernel particle functions are used to approximate two-dimensional displacement fields. Effective properties of materials of the plates reinforced by single-walled carbon nanotubes (SWCNTs) are estimated through a micromechanical model based on either the Eshelby-Mori-Tanaka approach or the extended rule of mixture. Comparison study and numerical simulations with various parameters are conducted to assess efficacy and accuracy of the present method for analysis of buckling of SWCNT-reinforced composite plates. Results demonstrate that the change of carbon nanotube volume fraction, plate width-to-thickness ratio, plate aspect ratio, loading condition and temperature have pronounced effects on buckling strength of CNTRC plates as well as the boundary condition. © 2012 Elsevier Ltd.


Shi W.X.,Hefei University of Technology | Shi W.X.,City University of Hong Kong | Shi W.X.,Cityint Advanced Research Center | Ji J.,Hefei University of Technology | And 6 more authors.
Applied Energy | Year: 2014

Safety and energy efficiency of high rise buildings have attracted public attention in recent decades. In this paper, a set of experiments was conducted in a scaled building model with 12 floors to study the influence of the staircase ventilation state on the flow and heat transfer of the heated room on the middle floor. The airflow, room temperature and fuel burning rate were investigated. It is found that when the window above the heated room is opened, the vents state below the heated room has a significant effect on the airflow and heat transfer in the heated room. When the vents below the heated room are closed, the single-directional air flows into the heated room owing to the stronger stack effect. And the flame tilt angle is larger and the upper hot smoke temperature in the heated room is low. However, when the windows above the heated room are closed, the vents state below the heated room has little influence on the airflow and heat transfer in the heated room. And, there is two-directional air flowing through the door of the heated room The burning rate of heat source is also affected by the staircase ventilation state, and the variation trend varies with the opened window position and pool size. © 2014 Elsevier Ltd.


Zhu P.,City University of Hong Kong | Lei Z.X.,City University of Hong Kong | Lei Z.X.,Cityint Advanced Research Center | Lei Z.X.,University of Science and Technology of China | And 2 more authors.
Composite Structures | Year: 2012

This paper mainly presents bending and free vibration analyses of thin-to-moderately thick composite plates reinforced by single-walled carbon nanotubes using the finite element method based on the first order shear deformation plate theory. Four types of distributions of the uniaxially aligned reinforcement material are considered, that is, uniform and three kinds of functionally graded distributions of carbon nanotubes along the thickness direction of plates. The effective material properties of the nanocomposite plates are estimated according to the rule of mixture. Detailed parametric studies have been carried out to reveal the influences of the volume fractions of carbon nanotubes and the edge-to-thickness ratios on the bending responses, natural frequencies and mode shapes of the plates. In addition, the effects of different boundary conditions are also examined. Numerical examples are computed by an in-house finite element code and the results show good agreement with the solutions obtained by the FE commercial package ANSYS. © 2011 Elsevier Ltd.


Yu L.,Cityint Advanced Research Center | Yu L.,City University of Hong Kong | Li W.-W.,Cityint Advanced Research Center | Li W.-W.,Hefei University of Technology | And 2 more authors.
Applied Microbiology and Biotechnology | Year: 2011

Adsorption and decolorization kinetics of methyl orange (MO) by anaerobic sludge in anaerobic sequencing batch reactors were investigated. The anaerobic sludge was found to have a saturated adsorption capacity of 36±1 mg g MLSS-1 to MO. UV/visible spectrophotometer and high-performance liquid chromatography analytical results indicated that the MO adsorption and decolorization occurred simultaneously in this system. This process at various substrate concentrations could be well simulated using a modified two-stage model with apparent pseudo first-order kinetics. Furthermore, a noncompetitive inhibition kinetic model was also developed to describe the MO decolorization process at high NaCl concentrations, and an inhibition constant of 3.67 g NaCl l-1 was estimated. This study offers an insight into the adsorption and decolorization processes of azo dyes by anaerobic sludge and provides a better understanding of the anaerobic dye decolorization mechanisms. © 2011 Springer-Verlag.


Wang C.,City University of Hong Kong | Wang C.,Cityint Advanced Research Center | Wang C.,Hefei University of Technology | Li S.,City University of Hong Kong | And 3 more authors.
Nanoscale | Year: 2012

We investigated the adsorption of three aromatic amino acids - phenylalanine, tyrosine, and tryptophan - on the sidewalls of a number of representative single-walled carbon nanotubes (SWNTs) using density-functional tight-binding calculations, complemented by an empirical dispersion correction. The armchair (n, n) SWNTs (n = 3-12) and zigzag (n, 0) SWNTs (n = 4-12) were thoroughly examined. We found that the most stable amino acid/SWNT complexes for different SWNTs have similar local structures, and that the distance between the amino acid and SWNT is about 3 Å. Owing to the π-π and H-π stacking interactions, the benzene and indole rings are not exactly parallel to the SWNTs but instead lie at a small angle. We also investigated the diameter and chirality dependences of binding energies and found that SWNT (5, 0) has an especially large binding energy that can be used for SWNT identification or selection. © 2012 The Royal Society of Chemistry.


Li J.,Hefei University of Technology | Li J.,Cityint Advanced Research Center | Xue C.J.,City University of Hong Kong | Xu Y.,Hefei University of Technology
2011 IEEE/IFIP 19th International Conference on VLSI and System-on-Chip, VLSI-SoC 2011 | Year: 2011

Modern high performance Chip Multiprocessor (CMP) systems rely on large on-chip cache hierarchy. As technology scales down, the leakage power of present SRAM based cache gradually dominates the on-chip power consumption, which can severely jeopardize system performance. The emerging nonvolatile Spin Transfer Torque RAM (STT-RAM) is a promising candidate for large on-chip cache because of the ultra low leakage power. However, the write operations on STT-RAM suffer from considerably higher energy as well as longer latency compared with SRAM which will make STT-RAM in trouble for write-intensive workloads. In this paper, we propose to integrate SRAM with STT-RAM to construct a novel hybrid cache architecture for CMPs. We also propose dedicated microarchitectural mechanisms to make the hybrid cache robust to workloads with different write patterns. Extensive simulation results demonstrate that the proposed hybrid scheme is adaptive to variations of workloads. Overall power consumption is reduced by 37.1% and performance is improved by 23.6% on average compared with SRAM based static NUCA under the same area configuration. © 2011 IEEE.


Lim C.W.,City University of Hong Kong | Lim C.W.,Cityint Advanced Research Center | Li C.,City University of Hong Kong | Li C.,Anhui University of Science and Technology | And 3 more authors.
Journal of Sound and Vibration | Year: 2012

A new elastic nonlocal stress model and analytical solutions are developed for torsional dynamic behaviors of circular nanorods/nanotubes. Unlike the previous approaches which directly substitute the nonlocal stress into the equations of motion, this new model begins with the derivation of strain energy using the nonlocal stress and by considering the nonlinear history of straining. The variational principle is applied to derive an infinite-order differential nonlocal equation of motion and the corresponding higher-order boundary conditions which contain a nonlocal nanoscale parameter. Subsequently, free torsional vibration of nanorods/nanotubes and axially moving nanorods/nanotubes are investigated in detail. Unlike the previous conclusions of reduced vibration frequency, the solutions indicate that natural frequency for free torsional vibration increases with increasing nonlocal nanoscale. Furthermore, the critical speed for torsional vibration of axially moving nanorods/nanotubes is derived and it is concluded that this critical speed is significantly influenced by the nonlocal nanoscale. © 2012 Elsevier Ltd. All rights reserved.


Wu Y.,City University of Hong Kong | Wu Y.,Cityint Advanced Research Center | Wu Y.,Hefei University of Technology | Sun D.,City University of Hong Kong | And 3 more authors.
Journal of Biomechanics | Year: 2011

Laser trapping with optical tweezers is a noninvasive manipulation technique and has received increasing attentions in biological applications. Understanding forces exerted on live cells is essential to cell biomechanical characterizations. Traditional numerical or experimental force measurement assumes live cells as ideal objects, ignoring their complicated inner structures and rough membranes. In this paper, we propose a new experimental method to calibrate the trapping and drag forces acted on live cells. Binding a micro polystyrene sphere to a live cell and moving the mixture with optical tweezers, we can obtain the drag force on the cell by subtracting the drag force on the sphere from the total drag force on the mixture, under the condition of extremely low Reynolds number. The trapping force on the cell is then obtained from the drag force when the cell is in force equilibrium state. Experiments on numerous live cells demonstrate the effectiveness of the proposed force calibration approach. © 2010 Elsevier Ltd.

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