2015年, 第64卷, 第02期　
刊出日期：2015-08-01

  

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  Symmetry Reduction of the (2+1)-Dimensional Modified Dispersive Water-Wave System

  马正义, 费金喜, 杜晓阳

  理论物理通讯. 2015, 64(02): 127-132.

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  Using the standard truncated Painlevé expansion, the residual symmetry of the (2+1)-dimensional modified dispersive water-wave system is localized in the properly prolonged system with the Lie point symmetry vector. Some different transformation invariances are derived by utilizing the obtained symmetries. The symmetries of the system are also derived through the Clarkson-Kruskal direct method, and several types of explicit reduction solutions relate to the trigonometric or the hyperbolic functions are obtained. Finally, some special solitons are depicted from one of the solutions.
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  Stationary States and Modulational Instability of Coupled Two-Component Bose-Einstein Condensates in a Ring Trap

  邓海明, 钟宏华, 黄嘉豪, 代慧, 姚敏, 黄小益

  理论物理通讯. 2015, 64(02): 133-138.

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  We investigate modulational instability (MI) of a coupled two-component Bose-Einstein condensates in a rotating ring trap. The excitation spectrum and the MI condition of the system are presented analytically. We find that the coupling between the two components strongly modifies the MI condition, and the MI condition is phase-dependent. Furthermore, we discuss the effect of MI on both density excitation and spin excitation. If the inter- and intra-component interaction strengths are all equal, the MI causes density excitation but not spin excitation, and if the inter- and intra-component interaction strengths are different, the MI causes both density excitation and spin excitation. Our results provide a promising approach for controlling the stability and excitation of a rotating two-component Bose-Einstein condensates by modulating its coupling strength and interaction strength.
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  Evolution of Dissipative Anisotropic Expansion-Free Axial Fluids

  M. Sharif, Zunaira Nasir

  理论物理通讯. 2015, 64(02): 139-144.

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  A general study of non-static restricted class of axial system with anisotropic dissipative expansion-free fluid under geodesic condition is carried out. It is found that expansion-free model must be dissipative under geodesic condition to preserve axial symmetry. We also investigate this system without geodesic condition. Finally, the role of dissipation is explored via transport equation.
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  New Agegraphic Pilgrim Dark Energy in f(T, TG) Gravity

  Abdul Jawad, Ujjal Debnath

  理论物理通讯. 2015, 64(02): 145-150.

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  In this work, we briefly discuss a novel class of modified gravity like f(T, T_G) gravity. In this background, we assume the new agegraphic version of pilgrim dark energy and reconstruct f(T, T_G) models for two specific values of s. We also discuss the equation of state parameter, squared speed of sound and w_DE-w'_DE plane for these reconstructed f(T, T_G) models. The equation of state parameter provides phantom-like behavior of the universe. The w_DE-w'_DE plane also corresponds to CDM limit, thawing and freezing regions for both models.
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  Colored Noises-Induced Regime Shifts in a Vegetation Ecological System

  韩清林, 曾嘉葵, 杨涛, 张春, 龙飞, 伏云昌, 曾春华

  理论物理通讯. 2015, 64(02): 151-158.

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  In this paper, we investigate the stationary probability distribution and mean first passage time in a vegetation ecological system, which is driven by cross-correlation between intrinsic and extrinsic colored noises as well as the nonzero cross-correlation in between. The impacts of the self-correlation time τ₁ and τ₂, the cross-correlation time τ₃ and intensity k on the stationary probability distribution and mean first passage time are discussed, respectively. Our main results show that: (#em/em#) the self-correlation time τ₁ can induce regime shifts from the desert state to the sustainable vegetation state, while the self-correlation time τ₂, cross-correlation time τ₃ and intensity k can induce regime shifts from the sustainable vegetation state to the desert state; and (ii) the self-correlation time τ₁ or τ₂ can enhance the stability of the sustainable vegetation biomass, while the cross-correlation time τ₃ or strength k weakens the stability of the sustainable vegetation biomass.
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  The Effect of Spin-Orbit Coupling and Spin-Spin Coupling of Compact Binaries on Chaos

  王洪, 黄国庆

  理论物理通讯. 2015, 64(02): 159-165.

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  There are spin-orbit interaction and spin-spin interaction in a generic post-Newtonian Lagrangian formu-lation of comparable mass spinning compact binaries. The spin-orbit coupling or the spin-spin coupling plays a quite important role in changing the evolution of the system and may sometime cause chaotic behavior. How do the two types of couplings exert together any influences on chaos in this formulation? To answer it, we simply take the Lagrangian formulation of a special binary system, including the Newtonian term and the leading-order spin-orbit and spin-spin couplings. The key to this question can be found from a Hamiltonian formulation that is completely identical to the Lagrangian formulation. If the Lagrangian does not include the spin-spin coupling, its equivalent Hamiltonian has an additional term (i.e. the next-order spin-spin coupling) as well as those terms of the Lagrangian. The spin-spin coupling rather than the spin-orbit coupling makes the Hamiltonian typically nonintegrable and probably chaotic when two objects spin. When the leading-order spin-spin coupling is also added to the Lagrangian, it still appears in the Hamiltonian. In this sense, the total Hamiltonian contains the leading-order spin-spin coupling and the next-order spin-spin coupling, which have different signs. Therefore, the chaos resulting from the spin-spin interaction in the Legrangian formulations is somewhat weakened by the spin-orbit coupling.
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  SUSY-QCD Effects in Top Quark Pair Production in Association with a Gluon at the ILC

  张延明, 刘宁

  理论物理通讯. 2015, 64(02): 166-170.

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  Given the null results of searches for new physics at the LHC, we investigate the one-loop effects SUSY QCD in the process e⁺e^-→ttg at the ILC in Minimal Supersymmetric Standard Model (MSSM). We find that the relative SUSY-QCD corrections to the cross section of e⁺e^-→ttg can maximally reach 6.5%(3.2%) at the ILC with √s=1000 GeV when m=313:4 GeV and m=500(1500) GeV.
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  Perturbation to Mei Symmetry and Adiabatic Invariants for Disturbed El-Nabulsi's Fractional Birkhoff System

  宋传静, 张毅

  理论物理通讯. 2015, 64(02): 171-176.

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  For El-Nabulsi's fractional Birkhoff system, Mei symmetry perturbation, the corresponding Mei-type adiabatic invariants and Noether-type adiabatic invariants are investigated in this paper. Firstly, based on El-Nabulsi-Birkhoff fractional equations, Mei symmetry and the corresponding Mei conserved quantity, Noether conserved quantity deduced indirectly by Mei symmetry are studied. Secondly, Mei-type exact invariants and Noether-type exact invariants are given on the basis of the definition of adiabatic invatiant. Thirdly, Mei symmetry perturbation, Mei-type adiabatic invariants and Noether-type adiabatic invariants for the disturbed El-Nabulsi's fractional Birkhoff system are studied. Finally, two examples, Hojman-Urrutia problem for Mei-type adiabatic invariants and another for the Noether-type adiabatic invariants, are given to illustrate the application of the results.
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  The Analytical Parametrization of Fusion Barrier by Using the Skyrme Energy-Density Function Model

  V. Zanganeh, M. Mirzaei, N. Wang

  理论物理通讯. 2015, 64(02): 177-184.

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  Using the skyrme energy density formalism, a pocket formula is introduced for barrier heights and positions of 95 fusion reactions (48 ≤ Z_PZ_T ≤ 1520) with respect to the charge and mass numbers of the interacting nuclei. It is shown that the parameterized values of RB and VB are able to reproduce the corresponding experimental data with good accuracy. Moreover, the absolute errors of our formulas are less than those obtained using the analytical parametrization forms of the fusion barrier based on the proximity versions. The ability of the parameterized forms of the barrier heights and its positions to reproduce the experimental data of the fusion cross section have been analyzed using the Wong model.
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  Role of Surface Energy Coefficients and Temperature in the Fusion Reactions Induced by Weakly Bound Projectiles

  R. Gharaei, O.N. Ghodsi

  理论物理通讯. 2015, 64(02): 185-196.

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  A systematic study is provided to analyze the behaviors of the interaction potential and complete fusion cross section which are influenced by the effects of the surface energy coefficients fl and temperature T. Our framework is restricted to the proximity formalism for fusion reactions induced by weakly bound projectiles ⁶Li, ⁷Li and ⁹Be. The different surface energy coefficients (γ-MN76, γ-MN95, γ-MS00 and fl-PD03) are used to study the role of the parameter fl in the proximity potentials AW 95 and BW 91. Comparison of the theoretical and the experimental values of the barrier characteristics (barrier heights and its positions) indicates that the modified versions AW 95 (γ-MS00) and BW 91 (γ-MS00) give the least deviations for fusion barrier heights. Moreover, it is shown that the temperature-dependence improves the calculated barrier heights based on the potentials AW 95 and BW 91. In the present study, the analysis of the mentioned effects on the complete fusion cross sections has been also discussed for the systems of interest. The obtained results reveal that the above-modified versions provide a more accurate description for behavior of the complete fusion cross sections than the original potentials at above-barrier energies. It is demonstrated that the increase of the temperature T enhances the complete fusion suppression at this energy range.
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  Hopf Bifurcation in a New Four-Dimensional Hyperchaotic System

  李昕, 闫振亚

  理论物理通讯. 2015, 64(02): 197-202.

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  In this paper, the Hopf bifurcation in a new hyperchaotic system is studied. Based on the first Lya-punov coefficient theory and symbolic computation, the conditions of supercritical and subcritical bifurcation in the new hyperchaotic system are obtained. Numerical simulations are used to illustrate some main results.
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  Numerical Simulation of Antennas with Improved Integral Equation Method

  马骥, 方广有, 卢伟

  理论物理通讯. 2015, 64(02): 203-207.

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  Simulating antennas around a conducting object is a challenge task in computational electromagnetism, which is concerned with the behaviour of electromagnetic fields. To analyze this model efficiently, an improved integral equation-fast Fourier transform (IE-FFT) algorithm is presented in this paper. The proposed scheme employs two Cartesian grids with different size and location to enclose the antenna and the other object, respectively. On the one hand, IE-FFT technique is used to store matrix in a sparse form and accelerate the matrix-vector multiplication for each sub-domain independently. On the other hand, the mutual interaction between sub-domains is taken as the additional exciting voltage in each matrix equation. By updating integral equations several times, the whole electromagnetic system can achieve a stable status. Finally, the validity of the presented method is verified through the analysis of typical antennas in the presence of a conducting object.
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  Roles of Superthermal Electrons and Adiabatic Heavy Ions on Heavy-Ion-Acoustic Solitary and Shock Waves in a Multi-Component Plasma

  M.G. Shah, M.M. Rahman, M.R. Hossen, A.A. Mamun

  理论物理通讯. 2015, 64(02): 208-214.

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  Heavy-ion-acoustic (HIA) waves in an unmagnetized collisionless plasma system comprising superthermal electrons, Boltzmann distributed light ions, and adiabatic positively charged inertial heavy ions have been investigated both numerically and analytically. The well-known reductive perturbation method has been used to derive the Korteweg-de Vries (K-dV) and Burgers (BG) equations. The parametric regimes for the existence of both the positive and negative solitary and shock waves have been obtained. The effects of adiabaticity of heavy ions and superthermality of electrons, which are found to notably modify the fundamental features (viz. polarity, amplitude, phase speed, etc.) of HIA solitary and shock waves, are precisely studied. The results of our theoretical investigation can be applicable to understand the characteristics and basic nonlinear structures of HIA waves both in space and laboratory plasma situations.
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  A Comprehensive Numerical Investigation on the Mechanical Properties of Hetero-Junction Carbon Nanotubes

  Ali Ghavamian, Andreas Öchsner

  理论物理通讯. 2015, 64(02): 215-230.

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  A set of forty-three hetero-junction CNTs, made of forty-four homogeneous carbon nanotubes of different chiralities and configurations with all possible hetero-connection types, were numerically simulated, based on the finite element method in a commercial finite element software and their Young's and shear moduli, and critical buckling loads were obtained and evaluated under the tensile, torsional and buckling loads with an assumption of linear elastic deformation and also compared with each other. The comparison of the linear elastic behavior of hetero-junction CNTs and their corresponding fundamental tubes revealed that the size, type of the connection, and the bending angle in the structure of hetero-junction CNTs considerably influences the mechanical properties of these hetero-structures. It was also discovered that the Stone-Wales defect leads to lower elastic and torsional strength of hetero-junction CNTs when compared to homogeneous CNTs. However, the buckling strength of the hetero-junction CNTs was found to lie in the range of the buckling strength of their corresponding fundamental tubes. It was also determined that the shear modulus of hetero-junction carbon nanotubes generally tends to be closer to the shear modulus of their wider fundamental tubes while critical buckling loads of these heterostructures seem to be closer to critical buckling loads of their thinner fundamental tubes. The evaluation of the elastic properties of hetero-junction carbon nanotubes showed that among the hetero-junction models, those with armchair-armchair and zigzag-zigzag kinks have the highest elastic modulus while the models with armchair-zigzag connections show the lowest elastic stiffness. The results from torsion tests also revealed the fact that zigzag-zigzag and armchair-zigzag hetero-junction carbon nanotubes have the highest and the lowest shear modulus, respectively. Finally, it was observed that the highest critical buckling loads belong to armchair-armchair hetero-junction carbon nanotubes and the lowest buckling strength was found with the hetero-junction models with armchair-zigzag connection.
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  Critical Behaviors and Universality Classes of Percolation Phase Transitions on Two-Dimensional Square Lattice

  朱勇, 杨子清, 张欣, 陈晓松

  理论物理通讯. 2015, 64(02): 231-236.

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  We have investigated both site and bond percolation on two-dimensional lattice under the random rule and the product rule respectively. With the random rule, sites or bonds are added randomly into the lattice. From two candidates picked randomly, the site or bond with the smaller size product of two connected clusters is added when the product rule is taken. Not only the size of the largest cluster but also its size jump are studied to characterize the universality class of percolation. The finite-size scaling forms of giant cluster size and size jump are proposed and used to determine the critical exponents of percolation from Monte Carlo data. It is found that the critical exponents of both size and size jump in random site percolation are equal to that in random bond percolation. With the random rule, site and bond percolation belong to the same universality class. We obtain the critical exponents of the site percolation under the product rule, which are different from that of both random percolation and the bond percolation under the product rule. The universality class of site percolation differs different from that of bond percolation when the product rule is used.
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  Structural, Elastic, and Electronic Properties of a New Phase of Carbon

  邢孟江, 李彬华, 余正涛, 陈颀

  理论物理通讯. 2015, 64(02): 237-243.

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  Based on density function theory with the ultrasoft pseudopotential scheme in the frame of the local density approximation and the generalized gradient approximation, the structural, elastic, and electronic properties of carbon with P222₁ phase have been systematically studied in this paper. The calculated results show that the P222₁ phase of carbon is mechanically stable and dynamically stable at ambient pressure. The anisotropy studies of Young's modulus, Poisson's ratio, shear anisotropic factor, the percentage of elastic anisotropy for bulk modulus, the percentage of elastic anisotropy for shear modulus and the universal anisotropic index show that P222₁ phase of carbon exhibits anisotropy. In addition, P222₁ phase is an indirect semiconductor with bandgap of 3.423 eV. But, the band gap of P222₁ phase for carbon increase with increasing pressure.
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  Structural and Optical Properties of Point Defects in α-SiO₂ Cluster

  刘猛, 芦鹏飞, 杨阳, 伍利源, 苏锐, 陈军

  理论物理通讯. 2015, 64(02): 244-248.

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  First-principles methods based on the density functional theory (DFT) are used in order to calculate the structural and optical properties of α-SiO₂ cluster with the non-bridging oxygen hole centers (NBOHC) and NBOHC-E' defects. We clarify the stable structure of the NBOHC-E' point defects for the first time using the functional B3LYP, which is also tested to investigate the influence of electronic properties. The calculation is carried out for cluster configurations extracted from supercell. The results of optical absorption peak for Si₂O₇H₆ and Si₅O₁₆H₁₂ with NBOHC-E' defects are found at 2.66 eV, which is higher than the often observed OA peak at 2.0 eV for the NBOHC defect in α-SiO₂. The overall absorption spectra are in qualitative agreement with the experiment.
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  Influences of the Structure of Lipids on Thermal Stability of Lipid Membranes

  海楠楠, 周昕, 黎明

  理论物理通讯. 2015, 64(02): 249-258.

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  The binding free energy (BFE) of lipid to lipid bilayer is a critical factor to determine the thermal or mechanical stability of the bilayer. Although the molecular structure of lipids has significant impacts on BFE of the lipid, there lacks a systematic study on this issue. In this paper we use coarse-grained molecular dynamics simulation to investigate this problem for several typical phospholipids. We find that both the tail length and tail unsaturation can significantly affect the BFE of lipids but in opposite way, namely, BFE decreases linearly with increasing length, but increases linearly with addition of unsaturated bonds. Inspired by the specific structure of cholesterol which is a crucial component of biomembrane, we also find that introduction of carbo-ring-like structures to the lipid tail or to the bilayer may greatly enhance the stability of the bilayer. Our simulation also shows that temperature can influence the bilayer stability and this effect can be significant when the bilayer undergoes phase transition. These results may be helpful to the design of liposome or other self-assembled lipid systems.