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Search Results: 1 - 10 of 115821 matches for " CHEN Zhi-dong "
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Time-Dependent Transport in Nanoscale Devices

CHEN Zhi-Dong,ZHANG Jin-Yu,YU Zhi-Ping,

中国物理快报 , 2009,
Abstract: A method for simulating ballistic time-dependent device transport, which solves the time-dependent Schr dinger equation using the finite difference time domain (FDTD) method together with Poisson's equation, is described in detail. The effective mass Schr dinger equation is solved. The continuous energy spectrum of the system is discretized using adaptive mesh, resulting in energy levels that sample the density-of-states. By calculating time evolution of wavefunctions at sampled energies, time-dependent transport characteristics such as current and charge density distributions are obtained. Simulation results in a nanowire and a coaxially gated carbon nanotube field-effect transistor (CNTFET) are presented. Transient effects, e.g., finite rising time, are investigated in these devices.
Numerical Analysis of Alternating-Current Small-Signal Response in Graphene Nanoribbons

CHEN Zhi-Dong,ZHANG Jin-Yu,YU Zhi-Ping,

中国物理快报 , 2010,


物理学报 , 1988,
Abstract: A cell theory of nematic liquid crystals is presented, which provides a calculable theoretical model for investigation of molecular short-range correlations. Numerical calculations are made for PAA The theoretical values are improved in compared with the other theories'. The effects of molecular correlations on calculated results and relations between the cell theory and the other theories are discussed.


物理学报 , 1994,
Abstract: Some important physical effects appear due to molecular short range correlations in nematic liquid crystals. When the orientational pair potential including the higher order terms, recent theories are not yet able to give reliable calculations. This paper is devoted to developing a new numerical method to solve the equation for equili-brium state, based upon the cell theory. We do not use any empirical expansions for the orientational distribution function but obtain the accurate molecular orientational distrbutions. Then we give the accurate numerical results of the order parameter at the phase transition, the entropy change etc., and obtain the correction for the Sene-ralized mean field theory made by the short range correlations.
Conjectures on exact solution of three - dimensional (3D) simple orthorhombic Ising lattices
Zhi-dong Zhang
Physics , 2007, DOI: 10.1080/14786430701646325
Abstract: We report the conjectures on the three-dimensional (3D) Ising model on simple orthorhombic lattices, together with the details of calculations for a putative exact solution. Two conjectures, an additional rotation in the fourth curled-up dimension and the weight factors on the eigenvectors, are proposed to serve as a boundary condition to deal with the topologic problem of the 3D Ising model. The partition function of the 3D simple orthorhombic Ising model is evaluated by spinor analysis, by employing these conjectures. Based on the validity of the conjectures, the critical temperature of the simple orthorhombic Ising lattices could be determined by the relation of KK* = KK' + KK'' + K'K'' or sinh 2K sinh 2(K' + K'' + K'K''/K) = 1. For a simple cubic Ising lattice, the critical point is putatively determined to locate exactly at the golden ratio xc = exp(-2Kc) = (sq(5) - 1)/2, as derived from K* = 3K or sinh 2K sinh 6K = 1. If the conjectures would be true, the specific heat of the simple orthorhombic Ising system would show a logarithmic singularity at the critical point of the phase transition. The spontaneous magnetization and the spin correlation functions of the simple orthorhombic Ising ferromagnet are derived explicitly. The putative critical exponents derived explicitly for the simple orthorhombic Ising lattices are alpha = 0, beta = 3/8, gamma = 5/4, delta = 13/3, eta = 1/8 and nu = 2/3, showing the universality behavior and satisfying the scaling laws. The cooperative phenomena near the critical point are studied and the results obtained based on the conjectures are compared with those of the approximation methods and the experimental findings. The 3D to 2D crossover phenomenon differs with the 2D to 1D crossover phenomenon and there is a gradual crossover of the exponents from the 3D values to the 2D ones.
Mathematical structure of three - dimensional (3D) Ising model
Zhi-dong Zhang
Physics , 2013, DOI: 10.1088/1674-1056/22/3/030513
Abstract: An overview of the mathematical structure of the three-dimensional (3D) Ising model is given, from the viewpoints of topologic, algebraic and geometric aspects. By analyzing the relations among transfer matrices of the 3D Ising model, Reidemeister moves in the knot theory, Yang-Baxter and tetrahedron equations, the following facts are illustrated for the 3D Ising model: 1) The complexified quaternion basis constructed for the 3D Ising model represents naturally the rotation in a (3 + 1) - dimensional space-time, as a relativistic quantum statistical mechanics model, which is consistent with the 4-fold integrand of the partition function by taking the time average. 2) A unitary transformation with a matrix being a spin representation in 2^(nlo)-space corresponds to a rotation in 2nlo-space, which serves to smooth all the crossings in the transfer matrices and contributes as the non-trivial topologic part of the partition function of the 3D Ising model. 3) A tetrahedron relation would ensure the commutativity of the transfer matrices and the integrability of the 3D Ising model, and its existence is guaranteed also by the Jordan algebra and the Jordan-von Neumann-Wigner procedures. 4) The unitary transformation for smoothing the crossings in the transfer matrices changes the wave functions by complex phases {\Phi}x, {\Phi}y, and {\Phi}z. The relation with quantum field and gauge theories, physical significance of weight factors are discussed in details. The conjectured exact solution is compared with numerical results, and singularities at/near infinite temperature are inspected. The analyticity in {\beta} = 1/(kB T) of both the hard-core and Ising models has been proved for {\beta} > 0, not for {\beta} = 0. Thus the high-temperature series cannot serve as a standard for judging a putative exact solution of the 3D Ising model.
Derivative of Electron Density in Non-Equilibrium Green's Function Technique and Its Application to Boost Performance of Convergence

YUAN Ze,CHEN Zhi-Dong,ZHANG Jin-Yu,HE Yu,ZHANG Ming,YU Zhi-Ping,

中国物理快报 , 2009,
Abstract: The non-equilibrium Green's function (NEGF) technique provides a solid foundation for the development of quantum mechanical simulators. However, the convergence is always of great concern. We present a general analytical formalism to acquire the accurate derivative of electron density with respect to electrical potential in the framework of NEGF. This formalism not only provides physical insight on non-local quantum phenomena in devicesimulation, but also can be used to set up a new scheme in solving the Poisson equation to boost the performance of convergence when the NEGF and Poisson equations are solved self-consistently. This method is illustrated by a simple one-dimensional example of an N++N+N++ resistor. The total simulation time and iteration number are largely reduced.
Bias, Variance and Risk Analysis of Uniform Threshod Function in Wavelet Shrinkage

Zhao Zhi-dong,Pan Min,Chen Yu-quan,

电子与信息学报 , 2005,
Abstract: 该文建立了小波阈值消噪的统一阈值函数,推导了统一阈值函数的偏差、方差、风险的明确关系式。利 用这些公式研究了参数不同时(以u=1,2,∞为例)统一阈值函数估计的偏差、方差、风险与阈值以及小波系数的关 系,得到了小波统一阈值函数消噪估计的性能,对小波消噪在工程中应用有重要的理论指导意义。
Photochemical Degradation of Petroleum on Soil Surfaces Under Simulated Visible Light

LI Zhi-dong,ZHAO Ya-zhi,QUAN Xie,CHEN Shuo,

环境科学 , 2007,
Abstract: The factors influencing photochemical degradation of petroleum on soil surfaces under simulated visible light, such as the initial oil concentrations, soil types and pH, were investigated. The concentrations of petroleum in photolytic processes were analyzed by UV-Vis. GC-FID and FTIR were used for the characterization of petroleum hydrocarbons. Experimental results indicated that photochemical degradation of petroleum on soil surfaces followed pseudo first-order kinetics with the rate constant of 0.0026~0.0172 h-1and half-life of 40~267 h. GC-FID analysis showed that, after 50 h of irradiation, the content of saturated hydrocarbons with longer chain decreased, while the proportion of shorter chain ones increased slightly; in addition, most chromatogram peaks of aromatics weakened or disappeared. After 60 h of photolysis, the appearance of carbonyl compounds in FTIR spectra of the extract from soil demonstrated that petroleum was gradually oxidized in the photolytic process.
Significance of MD-2 and MD-2B expression in rat liver during acute cholangitis
Hui-Lai Miao, Zhi-Dong Qiu, Fu-Long Hao, Yong-Hui Bi, Ming-Yi Li, Ming Chen, Nian-Ping Chen, Fei Zhou
World Journal of Hepatology , 2010,
Abstract: AIM: To investigate the expression of myeloid differentiation protein-2 (MD-2), MD-2B (a splicing isoform of MD-2 that can block Toll-like receptor 4 (TLR4)/MD-2 LPS-mediated signal transduction) and TLR4 in the liver of acute cholangitis rats.METHODS: Male Sprague-Dawley rats (SPF level) were randomly divided into four groups: (A) sham-operated group; (B) simple common bile duct ligation group; (C) acute cholangitis group; and (D) acute cholangitis anti-TLR4 intervention group (n = 25 per group). Rat liver tissue samples were used to detect TLR4, MD-2 and MD-2B mRNA expression by fluorescence quantitative PCR in parallel with pathological changes.RESULTS: In acute cholangitis, liver TLR4 and MD-2 mRNA expression levels at 6, 12, 24, 48 and 72 h were gradually up-regulated but MD-2B mRNA expression gradually down-regulated (P < 0.05). After TLR4 antibody treatment, TLR4 and MD-2 mRNA expression were lower compared with the acute cholangitis group (P < 0.05). However, MD-2B mRNA expression was higher than in the acute cholangitis group (P < 0.05). MD-2 and TLR4 mRNA expressions were positively correlated (r = 0.94981, P < 0.05) and MD-2B mRNA expression was negatively correlated with MD-2 and TLR4 mRNA (r = -0.89031, -0.88997, P < 0.05).CONCLUSION: In acute cholangitis, MD-2 plays an important role in the process of TLR4- mediated inflammatory response to liver injury while MD-2B plays a negative regulatory role.
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