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 Chin. Phys. B
 Chin. Phys. B--2010, Vol.19, No.1
GENERAL
Ma Li-Min, Wu Zong-Min
Chin. Phys. B 2010, 19 (1): 010201;  doi: 10.1088/1674-1056/19/1/010201
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In this paper, we use a kind of univariate multiquadric quasi-interpolation to solve a parabolic equation with overspecified data, which has arisen in many physical phenomena. We obtain the numerical scheme by using the derivative of the quasi-interpolation to approximate the spatial derivative of the dependent variable and a simple forward difference to approximate the temporal derivative of the dependent variable. The advantage of the presented scheme is that the algorithm is very simple so it is very easy to implement. The results of the numerical experiment are presented and are compared with the exact solution to confirm the good accuracy of the presented scheme.
Wang Xin-Zeng, Dong Huan-He
Chin. Phys. B 2010, 19 (1): 010202;  doi: 10.1088/1674-1056/19/1/010202
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A new eight-dimensional Lie superalgebra is constructed and two isospectral problems with six potentials are designed. Corresponding hierarchies of nonlinear evolution equations, as well as super-AKNS and super-Levi, are derived. Their super-Hamiltonian structures are established by making use of the supertrace identity, and they are integrable in the sense of Liouville.
Mo Jia-Qi
Chin. Phys. B 2010, 19 (1): 010203;  doi: 10.1088/1674-1056/19/1/010203
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A class of singularly perturbed initial boundary value problems of reaction diffusion equations for the nonlinear boundary condition with two parameters is considered. Under suitable conditions, by using the theory of differential inequalities, the existence and the asymptotic behaviour of the solution for the initial boundary value problem are studied. The obtained solution indicates that there are initial and boundary layers and the thickness of the boundary layer is less than the thickness of the initial layer.
Du Wen-Bo, Cao Xian-Bin, Yang Han-Xin, Hu Mao-Bin
Chin. Phys. B 2010, 19 (1): 010204;  doi: 10.1088/1674-1056/19/1/010204
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In this paper, we introduce an asymmetric payoff distribution mechanism into the evolutionary prisoner's dilemma game (PDG) on Newman--Watts social networks, and study its effects on the evolution of cooperation. The asymmetric payoff distribution mechanism can be adjusted by the parameter α: if α>0, the rich will exploit the poor to get richer; if α<0, the rich are forced to offer part of their income to the poor. Numerical results show that the cooperator frequency monotonously increases with α and is remarkably promoted when α>0. The effects of updating order and self-interaction are also investigated. The co-action of random updating and self-interaction can induce the highest cooperation level. Moreover, we employ the Gini coefficient to investigate the effect of asymmetric payoff distribution on the the system's wealth distribution. This work may be helpful for understanding cooperative behaviour and wealth inequality in society.
Han Jia-Jing, Fu Wei-Juan
Chin. Phys. B 2010, 19 (1): 010205;  doi: 10.1088/1674-1056/19/1/010205
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Chaos game representation (CGR) is proposed as a scale-independent representation for DNA sequences and provides information about the statistical distribution of oligonucleotides in a DNA sequence. CGR images of DNA sequences represent some kinds of fractal patterns, but the common multifractal analysis based on the box counting method cannot deal with CGR images perfectly. Here, the wavelet transform modulus maxima (WTMM) method is applied to the multifractal analysis of CGR images. The results show that the scale-invariance range of CGR edge images can be extended to three orders of magnitude, and complete singularity spectra can be calculated. Spectrum parameters such as the singularity spectrum span are extracted to describe the statistical character of DNA sequences. Compared with the singularity spectrum span, exon sequences with a minimal spectrum span have the most uniform fractal structure. Also, the singularity spectrum parameters are related to oligonucleotide length, sequence component and species, thereby providing a method of studying the length polymorphism of repeat oligonucleotides.
Zhao Li, Fu Jing-Li, Chen Ben-Yong
Chin. Phys. B 2010, 19 (1): 010301;  doi: 10.1088/1674-1056/19/1/010301
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The Lie symmetries and conserved quantities of a two-dimensional nonlinear diffusion equation of concentration are considered. Based on the invariance of the two-dimensional nonlinear diffusion equation of concentration under the infinitesimal transformation with respect to the generalized coordinates and time, the determining equations of Lie symmetries are presented. The Lie groups of transformation and infinitesimal generators of this equation are obtained. The conserved quantities associated with the nonlinear diffusion equation of concentration are derived by integrating the characteristic equations. Also, the solutions of the two-dimensional nonlinear diffusion equation of concentration can be obtained.
Lin Qiong-Gui
Chin. Phys. B 2010, 19 (1): 010302;  doi: 10.1088/1674-1056/19/1/010302
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Cylindrical waveguides without end surfaces can serve as two-dimensional resonant cavities. In such cavities the electromagnetic oscillations corresponding to an eigenfrequency can always be taken as TM or TE modes even when the walls have a finite conductivity and the medium is absorptive. This paper obtains analytic solutions to the field equations when the cylinder has a circular cross section. Some nonperturbative conclusions are drawn from the eigenvalue equation. Approximate analytic results for the resonant frequencies are obtained when the absorption of the medium is small and the walls are good conductors. Stability of the eigen modes is discussed. Similar results for the coaxial line are presented.
Chen Xiu-Bo, Wen Qiao-Yan, Sun Zhong-Xu, Shangguan Li-Ying, Yang Yi-Xian
Chin. Phys. B 2010, 19 (1): 010303;  doi: 10.1088/1674-1056/19/1/010303
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Utilizing a three-particle W state, we come up with a protocol for the teleportation of an unknown two-particle entangled state. It is shown that the teleportation can be deterministically and exactly realized. Moreover, two-particle entanglement teleportation is generalized to a system consisting of many particles via a three-particle W state and a multi-particle W state, respectively. All unitary transformations performed by the receiver are given in a concise formula.
Zhou Zheng, Yu Hui-You, Yan Jia-Ren
Chin. Phys. B 2010, 19 (1): 010304;  doi: 10.1088/1674-1056/19/1/010304
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We present two kinds of exact vector-soliton solutions for coupled nonlinear Schr?dinger equations with time-varying interactions and time-varying harmonic potential. Using the variational approach, we investigate the dynamics of the vector solitons. It is found that the two bright solitons oscillate about slightly and pass through each other around the equilibration state which means that they are stable under our model. At the same time, we obtain the opposite situation for dark--dark solitons.
Li Zhi-Jian, Cheng Lu, Wen Jiao-Jin
Chin. Phys. B 2010, 19 (1): 010305;  doi: 10.1088/1674-1056/19/1/010305
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We consider a two-qubit system described by the Heisenberg XY model with Dzyaloshinski--Moriya (DM) anisotropic interaction in a perpendicular magnetic field to investigate the relation between entanglement, geometric phase and quantum phase transition (QPT). It is shown that the DM interaction has an effect on the critical boundary. The combination of entanglement and geometric phase may characterize QPT completely. Their jumps mean that the occurrence of QPT and inversely the QPT at the critical point at least corresponds to a jump of one of them.
Choi Jeong-Ryeol
Chin. Phys. B 2010, 19 (1): 010306;  doi: 10.1088/1674-1056/19/1/010306
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After the birth of quantum mechanics, the notion in physics that the frequency of light is the only factor that determines the energy of a single photon has played a fundamental role. However, under the assumption that the theory of Lewis--Riesenfeld invariants is applicable in quantum optics, it is shown in the present work that this widely accepted notion is valid only for light described by a time-independent Hamiltonian, i.e., for light in media satisfying the conditions,ε(t)=ε(0), μ(t)=μ(0), and σ(t)=0 simultaneously. The use of the Lewis--Riesenfeld invariant operator method in quantum optics leads to a marvelous result:the energy of a single photon propagating through time-varying linear media exhibits nontrivial time dependence without a change of frequency.
Li Yan-Ling, Fang Mao-Fa, Zeng Ke
Chin. Phys. B 2010, 19 (1): 010307;  doi: 10.1088/1674-1056/19/1/010307
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A scheme, based on the two two-level atoms resonantly driven by the classical field separately trapped in two cavities coupled by an optical fibre, for the implementation of remote two-qubit gates is investigated. It is found that the quantum controlled-phase and swap gates can be achieved with the assistance of the classical field when there are detunings of the coupling quantum fields. Moreover, the influence of the dissipation of the cavities and the optical fibre is analysed while the spontaneous emission of the atoms can be effectively suppressed by introducing Λ-type atoms.
Li Chi-Sheng, Luo Han-Wen
Chin. Phys. B 2010, 19 (1): 010308;  doi: 10.1088/1674-1056/19/1/010308
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Using the intermediate coordinate--momentum representation |x>s,r, we introduce a new Hadamard transform. It is found that the operator U corresponding to this transform can be considered as a combination of the Fresnel operator F(r,s) and the Fourier transform operator F by decomposing U. We also find that the matrix element s,r< x| U|f> just corresponds to an optical scaled Fresnel--Fourier transform.
Zheng Xiao-Juan, Xu Hui, Fang Mao-Fa, Zhu Kai-Cheng
Chin. Phys. B 2010, 19 (1): 010309;  doi: 10.1088/1674-1056/19/1/010309
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An experimentally feasible scheme for implementing four-atom quantum dense coding of an atom--cavity system is proposed. The cavity is only virtually excited and no quantum information will be transferred from the atoms to the cavity. Thus the scheme is insensitive to cavity decay and the thermal field. In the scheme, Alice can send faithfully 4 bits of classical information to Bob by sending two qubits. Generalized Bell states can be exactly distinguished by detecting the atomic state, and quantum dense coding can be realized in a simple way.
Guo Jin-Liang, Xia Yan, Song He-Shan
Chin. Phys. B 2010, 19 (1): 010310;  doi: 10.1088/1674-1056/19/1/010310
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Based on the concept of concurrence, we have investigated the entanglement dynamics of two two-level atoms coupled to a single-mode cavity field with inhomogeneous couplings. We find that, for some initial states, the inhomogeneous couplings not only induce but also enhance the entanglement in the process of its evolution. In addition, considering the intrinsic decoherence proposed by Milburn, we also find that a proper value of inhomogeneous couplings can enhance the stationary entanglement, and as a result, the destructive effect of intrinsic decoherence on entanglement can be moderated by the inhomogeneous couplings.
Ji Ying-Hua, Cai Shi-Hua, Le Jian-Xin, Wang Zi-Sheng
Chin. Phys. B 2010, 19 (1): 010311;  doi: 10.1088/1674-1056/19/1/010311
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A scheme to perfectly preserve an initial qubit state in geometric quantum computation is proposed for a single-qubit geometric quantum gate in a nuclear magnetic resonance system. At first, by adjusting some magnetic field parameters, one can let the dynamic phase be proportional to the geometric phase. Then, by controlling the azimuthal angle in the initial state, we may realize a geometric quantum gate whose fidelity is equal to one under cyclic evolution. This means that the quantum information is no distortion in the process of geometric quantum computation.
Liu Yu, Zhang Bin-Bin
Chin. Phys. B 2010, 19 (1): 010312;  doi: 10.1088/1674-1056/19/1/010312
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In this paper, we propose a classical secret broadcasting and splitting joint protocol in a quantum scenario. With those genuinely entangled states, the boss can always broadcast some of his secrets and split some others to multi-receivers at the same time. The efficiency of the joint protocol is also compared with that of two separate ones which realise classical secret broadcasting and classical secret splitting respectively, and based on the comparison we can see the promising advantage of our joint protocol is that it can realise the two tasks more efficiently and more conveniently.
Wu Chun-Wang, Han Yang, Deng Zhi-Jiao, Liang Lin-Mei, Li Cheng-Zu
Chin. Phys. B 2010, 19 (1): 010313;  doi: 10.1088/1674-1056/19/1/010313
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A simple scheme is proposed to generate the W state of N Λ-type neutral atoms trapped in an optical cavity via Raman transition. Conditional on no photon leakage from the cavity, the N-qubit W state can be prepared perfectly by turning on a classical coupling field for an appropriate time. Compared with the previous ones, our scheme requires neither individual laser addressing of the atoms, nor demand for controlling N atoms to go through an optical cavity simultaneously with a constant velocity. We investigate the influence of cavity decay using the quantum jump approach and show that the preparation time decreases and the success probability increases with atom number because of a collective enhancement of the coupling.
Li Hong-Juan, Sun Jia-Kui, Xiao Jing-Lin
Chin. Phys. B 2010, 19 (1): 010314;  doi: 10.1088/1674-1056/19/1/010314
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We study the eigenenergies and eigenfunctions of the ground and first-excited states of an electron which is strongly coupled to an LO-phonon in a quantum dot with a triangular bound potential and Coulomb bound potential by using the Pekar variational method. This system may be used as a two-level qubit. Phonon spontaneous emission causes the decoherence of the qubit. Numerical calculations are performed on the decoherence rate as a function of the polar angle, the Coulomb binding parameter, the coupling strength, the confinement length of the quantum dot and the dispersion coefficient.
Liang Bao-Long, Wang Ji-Suo, Meng Xiang-Guo, Su Jie
Chin. Phys. B 2010, 19 (1): 010315;  doi: 10.1088/1674-1056/19/1/010315
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The macroscopic quantum entanglement in capacitively coupled SQUID (superconducting quantum interference device)-based charge qubits is investigated theoretically. The entanglement characteristic is discussed by employing the quantum Rabi oscillations and the concurrence. An interesting conclusion is obtained, i.e., the magnetic fluxes Фx1 and Фx2 through the superconducting loops can adjust the entanglement degree between the qubits.
Huang Jia-Hui, Sheng Zheng-Mao
Chin. Phys. B 2010, 19 (1): 010316;  doi: 10.1088/1674-1056/19/1/010316
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This paper uses the background field method to calculate one-loop divergent corrections to the gauge field propagators in noncommutative U(1) gauge theory with scalar fields. It shows that for a massless scalar field, the gauge field propagators are renormalizable to θ2-order, but for a massive scalar field they are renormalizable only to θ-order.
Chen Ju-Hua, Wang Yong-Jiu
Chin. Phys. B 2010, 19 (1): 010401;  doi: 10.1088/1674-1056/19/1/010401
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In this paper we investigate the evolution of the cosmology model with dark energy interacting with massive neutrinos and dark matter. Using the numerical method to investigate the dynamical system, we find that the stronger the interaction between dark energy and dark matter, the lower the ratio of dark matter in the universe is; also, the stronger the interaction between dark energy and massive neutrinos, the lower the ratio of massive neutrinos in the universe is. On the other hand, the interaction between dark energy and dark matter or massive neutrinos has an effect on disturbing the universe's acceleration; we also find that our universe is still accelerating.
Zhao Ren, Zhang Li-Chun, Wu Yue-Qin, Li Huai-Fan
Chin. Phys. B 2010, 19 (1): 010402;  doi: 10.1088/1674-1056/19/1/010402
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After considering the generalized uncertainty principle, we discuss the quantum tunneling radiation of a five-dimensional Schwarzschild anti de Sitter black hole. The radiation spectrum and the correction value of the Bekenstein--Hawking entropy are derived. In a five-dimensional black hole the one order correction term in the Bekenstein--Hawking entropy correction term is proportional to the third power of the area, and the logarithmic correction term is a two-order small quantity. The correction term is related to the dimension constant introduced in the generalized uncertainty principle. Because the black hole entropy is not divergent, the lowest value of the five-dimensional Schwarzschild anti de Sitter black hole horizon radius is obtained. After considering the generalized uncertainty principle, the radiation spectrum is still consistent with normalization theory.
Zhou Shi-Wei, Liu Bo, Huang Ji-Li, Liu Wen-Biao
Chin. Phys. B 2010, 19 (1): 010403;  doi: 10.1088/1674-1056/19/1/010403
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Taking a black hole as a black body system, using general black body radiation theory, a Schwarzschild black hole and a Kerr--Newman black hole are investigated respectively. It is concluded that a black hole can be regarded as an ideal general black body system exactly for the changing process only. However, a stationary global black hole cannot be smoothly regarded as a general black body system. A black hole has some special characteristics which different from a general thermodynamics system. This conclusion means that a black hole should be inherently dynamical, at least when it is taken as a black body system.
Xiang You-Lin, Mei Dong-Cheng
Chin. Phys. B 2010, 19 (1): 010501;  doi: 10.1088/1674-1056/19/1/010501
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This paper investigates the two-time intensity correlation function of a two-mode ring laser system subjected to both pump and quantum noises by stochastic simulation. It finds that the decay rate of the intensity correlation function of one mode gets faster with decreasing values of relevant parameters, i.e., the coupling constant ξ, the cross-correlation coefficient λ , the difference of the pump parameters Δa and the pump parameter a1; however, its variations get complex in the other mode when relevant parameters are changed. The investigating results also show that the effects of the mode competition on intensity correlation function are obvious.
Dong Xiao-Juan
Chin. Phys. B 2010, 19 (1): 010502;  doi: 10.1088/1674-1056/19/1/010502
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This paper investigates the correlation between stochastic resonance (SR) and the average phase-synchronization time which is between the input signal and the output signal in a bistable system driven by colour-correlated noises. The results show that the output signal-to-noise ratio can reach a maximum with the increase of the average phase-synchronization time, which may be helpful for understanding the principle of SR from the point of synchronization; however, SR and the maximum of the average phase-synchronization time appear at different optimal noise level, moreover, the effects on them of additive and multiplicative noise are different.
Yung Kai-Leung, Lei You-Ming, Xu Yan
Chin. Phys. B 2010, 19 (1): 010503;  doi: 10.1088/1674-1056/19/1/010503
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We investigate stochastic resonance (SR) in the FitzHugh--Nagumo system under combined bounded noise and weak harmonic excitation. Taking a spectral amplification factor as a signal-to-noise ratio, we show numerically that bounded noise can induce SR by adjusting either the intensity of bounded noise or its colour. Moreover, the increase of noise colour can enhance the SR and make the peak of the SR shift toward lower noise intensities, which is more feasible in practice. Since bounded noise is flexible to model random excitation, these findings may have some potential applications in engineering, neuroscience and biology.
Chen Lin-Jie, Ma Chang-Feng
Chin. Phys. B 2010, 19 (1): 010504;  doi: 10.1088/1674-1056/19/1/010504
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This paper proposes a lattice Boltzmann model with an amending function for one-dimensional nonlinear partial differential equations (NPDEs) in the form u_t+α uusub>x+β unusub>x+γ usub>xx+δ usub>xxx+ζ usub>xxxx=0. This model is different from existing models because it lets the time step be equivalent to the square of the space step and derives higher accuracy and nonlinear terms in NPDEs. With the Chapman--Enskog expansion, the governing evolution equation is recovered correctly from the continuous Boltzmann equation. The numerical results agree well with the analytical solutions.
Zheng Yu, Zhang Xiao-Dan
Chin. Phys. B 2010, 19 (1): 010505;  doi: 10.1088/1674-1056/19/1/010505
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A chaotic system is bounded, and its trajectory is confined to a certain region which is called the chaotic attractor. No matter how unstable the interior of the system is, the trajectory never exceeds the chaotic attractor. In the present paper, the sphere bound of the generalized Lorenz system is given, based on the Lyapunov function and the Lagrange multiplier method. Furthermore, we show the actual parameters and perform numerical simulations.
Li Dong, Wang Shi-Long, Zhang Xiao-Hong, Yang Dan
Chin. Phys. B 2010, 19 (1): 010506;  doi: 10.1088/1674-1056/19/1/010506
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A permanent magnet synchronous motor (PMSM) may have chaotic behaviours under certain working conditions, especially for uncertain values of parameters, which threatens the security and stability of motor-driven operation. Hence, it is important to study methods of controlling or suppressing chaos in PMSMs. In this paper, the stability of a PMSM with parameter uncertainties is investigated. After uncertain matrices which represent the variable system parameters are formulated through matrix analysis, a novel asymptotical stability criterion is established by employing the method of Lyapunov functions and linear matrix inequality technology. An example is also given to illustrate the effectiveness of our results.
Zhang Li-Ping, Jiang Hai-Bo, Bi Qin-Sheng
Chin. Phys. B 2010, 19 (1): 010507;  doi: 10.1088/1674-1056/19/1/010507
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The problem of reliable impulsive synchronization for a class of nonlinear chaotic systems has been investigated in this paper. Firstly a reliable impulsive controller is designed by using the impulsive control theory. Then by the uniform asymptotic stability criteria of systems with impulsive effects, some sufficient conditions for reliable impulsive synchronization between the drive system and the response system are obtained. Numerical simulations are given to show the effectiveness of the proposed method.
Li Rui-Hong, Chen Wei-Sheng, Li Shuang
Chin. Phys. B 2010, 19 (1): 010508;  doi: 10.1088/1674-1056/19/1/010508
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In this paper, a novel adaptive control approach is presented to simultaneously achieve synchronization and anti-synchronization in partially linear chaotic systems. Through appropriately separating state vectors of such systems, synchronization and anti-synchronization could be simultaneously realized in different subspaces, which may be strictly proven theoretically. Simulation results for a Lorenz chaotic system and a new hyper-chaotic system are provided to illustrate the effectiveness of the proposed method. Finally, a new secure communication scheme based on such a synchronization phenomenon of the hyper-chaotic system is demonstrated. Numerical results show success in transmitting a periodic signal with high security.
Fang Chao, Wu Guo-Zhen
Chin. Phys. B 2010, 19 (1): 010509;  doi: 10.1088/1674-1056/19/1/010509
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The vibrational dynamics of HOCl and HOBr between bending and OCl/OBr stretching coordinates with anharmonicity and Fermi coupling is studied with the classical dynamical potential approach. The quantal vibrational dynamics is mostly mapped out by the classical nonlinear variables such as fixed points, except for the state energies, which are quantized. This approach is global in the sense that the focus is on a set of levels instead of individual ones. The dynamics of HOBr is demonstrated to be less complicated. The localized modes along the OCl/OBr stretching coordinates are also shown to have O--Br bonds more prone to dissociation.
Ni Fei, Xu Wei, Fang Tong, Yue Xiao-Le
Chin. Phys. B 2010, 19 (1): 010510;  doi: 10.1088/1674-1056/19/1/010510
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This paper aims to study the stochastic period-doubling bifurcation of the three-dimensional R?ssler system with an arch-like bounded random parameter. First, we transform the stochastic R?ssler system into its equivalent deterministic one in the sense of minimal residual error by the Chebyshev polynomial approximation method. Then, we explore the dynamical behaviour of the stochastic R?ssler system through its equivalent deterministic system by numerical simulations. The numerical results show that some stochastic period-doubling bifurcation, akin to the conventional one in the deterministic case, may also appear in the stochastic R?ssler system. In addition, we also examine the influence of the random parameter intensity on bifurcation phenomena in the stochastic R?ssler system.
Tian Jun-Fang, Jia Bin, Li Xing-Gang, Gao Zi-You
Chin. Phys. B 2010, 19 (1): 010511;  doi: 10.1088/1674-1056/19/1/010511
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The full velocity difference model proposed by Jiang et al. [2001 Phys. Rev. E 64 017101] has been improved by introducing velocity anticipation. Velocity anticipation means the follower estimates the future velocity of the leader. The stability condition of the new model is obtained by using the linear stability theory. Theoretical results show that the stability region increases when we increase the anticipation time interval. The mKdV equation is derived to describe the kink--antikink soliton wave and obtain the coexisting stability line. The delay time of car motion and kinematic wave speed at jam density are obtained in this model. Numerical simulations exhibit that when we increase the anticipation time interval enough, the new model could avoid accidents under urgent braking cases. Also, the traffic jam could be suppressed by considering the anticipation velocity. All results demonstrate that this model is an improvement on the full velocity difference model.
Gao Li-Feng, Shi Jian-Jun, Guan Shan
Chin. Phys. B 2010, 19 (1): 010512;  doi: 10.1088/1674-1056/19/1/010512
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In this paper, we attempt to understand complex network evolution from the underlying evolutionary relationship between biological organisms. Firstly, we construct a Pfam domain interaction network for each of the 470 completely sequenced organisms, and therefore each organism is correlated with a specific Pfam domain interaction network; secondly, we infer the evolutionary relationship of these organisms with the nearest neighbour joining method; thirdly, we use the evolutionary relationship between organisms constructed in the second step as the evolutionary course of the Pfam domain interaction network constructed in the first step. This analysis of the evolutionary course shows: (i) there is a conserved sub-network structure in network evolution; in this sub-network, nodes with lower degree prefer to maintain their connectivity invariant, and hubs tend to maintain their role as a hub is attached preferentially to new added nodes; (ii) few nodes are conserved as hubs; most of the other nodes are conserved as one with very low degree; (iii) in the course of network evolution, new nodes are added to the network either individually in most cases or as clusters with relative high clustering coefficients in a very few cases.
Qi Jian-Xun, Jiang Fan
Chin. Phys. B 2010, 19 (1): 010601;  doi: 10.1088/1674-1056/19/1/010601
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Based on a recent loopless mounting method, a simplified loopless and bufferless crystal mounting method is developed for macromolecular crystallography. This simplified crystal mounting system is composed of the following components: a home-made glass capillary, a brass seat for holding the glass capillary, a flow regulator, and a vacuum pump for evacuation. Compared with the currently prevalent loop mounting method, this simplified method has almost the same mounting procedure and thus is compatible with the current automated crystal mounting system. The advantages of this method include higher signal-to-noise ratio, more accurate measurement, more rapid flash cooling, less x-ray absorption and thus less radiation damage to the crystal. This method can be extended to the flash-freeing of a crystal without or with soaking it in a lower concentration of cryoprotectant, thus it may be the best option for data collection in the absence of suitable cryoprotectant. Therefore, it is suggested that this mounting method should be further improved and extensively applied to cryocrystallographic experiments.
Cheng Teng, Zhang Qing-Chuan, Chen Da-Peng, Shi Hai-Tao, Gao Jie, Qian Jian, Wu Xiao-Ping
Chin. Phys. B 2010, 19 (1): 010701;  doi: 10.1088/1674-1056/19/1/010701
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We propose a substrate-free focal plane array (FPA) in this paper. The solid substrate is completely removed, and the microcantilevers extend from a supporting frame. Using finite element analysis, the thermal and mechanical characterizations of the substrate-free FPA are presented. Because of the large decrease in thermal conductance, the supporting frame is temperature dependent, which brings out a unique feature: the lower the thermal conductance of the supporting frame is, the higher the energy conversion efficiency in the substrate-free FPA will be. The results from the finite element analyses are consistent with our measurements: two types of substrate-free FPAs with pixel sizes of 200× 200 and 60× 60~μ m2 are implemented in the proposed infrared detector. The noise equivalent temperature difference (NETD) values are experimentally measured to be 520 and 300~mK respectively. Further refinements are considered in various aspects, and the substrate-free FPA with a pixel size of 30× 30~μ m2 has a potential of achieving an NETD value of 10~mK.
Yue Jin-Ying, Liu Hua, Lu Zhen-Wu, Xu Wen-Bin, Zhang Hu, Zhang Hong-Xin, Liu Ying
Chin. Phys. B 2010, 19 (1): 010702;  doi: 10.1088/1674-1056/19/1/010702
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The compound diffractive telescope is a novel space optical system which combines the structure of compound eyes with diffractive optics and so it has a lighter weight, a wider field of view (FOV), a lower cost as well as looser fabrication tolerance. In this paper, the design of a compound diffractive telescope composed of one primary lens and twenty-one eyepieces is introduced. Then the influence of diffraction orders on the performance of the system is analysed. A modified phase function model of diffractive optics is proposed to analyse the modulation transfer function (MTF) curves for 0℃ FOV, which provides a more accurate prediction of the performance of the system. In addition, an optimized mechanism is also proposed to suppress stray light. The star image and resolution tests show that the system can achieve diffraction limit imaging within ± 2℃ of FOV and ±4~mm of eccentricity. Finally, a series of pictures of an object are taken from different channels, and the splicing of pictures from adjacent FOVs is demonstrated. In summary, the designed system has been proved to have great potential applications.
Tan Xin-Jian, Ouyang Xiao-Ping, Wang Qun-Shu, Song Zhao-Hui, Kang Ke-Jun, Xia Liang-Bin
Chin. Phys. B 2010, 19 (1): 010703;  doi: 10.1088/1674-1056/19/1/010703
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The accelerator-generating 6.13~MeV pulsed Gamma by 19F(p, αγ )160 reaction usually synchronizes with an intense bremsstrahlung x-ray which has a maximum energy of 1~MeV. This paper proposes a new method, named the scattering and absorbing method, to diagnose the 6.13~MeV Gamma. This method includes two parts: the detector and a scatterer placed in front of the detector. The detector converts the Gamma to electrons and then collects the electrons by a scintillator. In order to restrain the interference of the low-energy background, the scintillator collects the electrons at a small angle. The scintillator is wrapped with electro-absorbing material to absorb the low-energy electrons generated by background x-rays. The theoretical sensitivity ratio of 6.13~MeV Gamma to 1~MeV x-rays is greater than 150. The scatterer is a pretreatment tool to scatter some background x-rays away from the radial beam before they enter the detector. By varying the length, the scatterer can reduce the background x-rays to an acceptable level for the detector.
NUCLEAR PHYSICS
M. Shafiq, M. Hassan, K. Shahzad, A. Qayyum, S. Ahmad, R. S. Rawat, M.Zakaullah
Chin. Phys. B 2010, 19 (1): 012801;  doi: 10.1088/1674-1056/19/1/012801
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The carburizing of titanium (Ti) is accomplished by utilizing energetic ion pulses of a 1.5 kJ Mather type dense plasma focus (DPF) device operated in methane discharge. X-ray diffraction (XRD) analysis confirms the deposition of polycrystalline titanium carbide (TiC). The samples carburized at lower axial and angular positions show an improved texture for a typical (200)TiC plane. The Williamson--Hall method is employed to estimate average crystallite size and microstrains in the carburized Ti surface. Crystallite size is found to vary from ～ 50 to 100~nm, depending on the deposition parameters. Microstrains vary with the sample position and hence ion flux, and are converted from tensile to compressive by increasing the flux. The carburizing of Ti is confirmed by two major doublets extending from 300 to 390~cm-1 and from 560 to 620~cm-1 corresponding to acoustic and optical active modes in Raman spectra, respectively. Analyses by scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) have provided qualitative and quantitative profiles of the carburized surface. The Vickers microhardness of Ti is significantly improved after carburizing.
ATOMIC AND MOLECULAR PHYSICS
Huang Gui-Yang, Wang Chong-Yu, Wang Jian-Tao
Chin. Phys. B 2010, 19 (1): 013101;  doi: 10.1088/1674-1056/19/1/013101
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A detailed first-principles study of the diffusion behaviour of point defects in the O-terminated (0001) surface in wurtzite ZnO was performed. The O vacancy and interstitial are found to diffuse much more easily in surface than in bulk. The Zn vacancy has a similar migration barrier for both bulk and surface, but has much smaller barrier for the diffuse-in process. The Zn interstitial is difficult to diffuse in the surface directly, but it can diffuse into the bulk relatively easily. Specific values of corresponding migration barriers are obtained.
Liu Wei-Long, Wang De-Min, Zheng Zhi-Ren, Li Ai-Hua, Su Wen-Hui
Chin. Phys. B 2010, 19 (1): 013102;  doi: 10.1088/1674-1056/19/1/013102
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Absorption spectra of β -carotene in 31 solvents are measured in ambient conditions. Solvent effects on the 0--0 band energy, the bandwidth, and the transition moment of the S0 → S2 transition are analysed. The discrepancies between published results of the solvent effects on the 0--0 band energy are explained by taking into account microscopic solute-solvent interactions. The contributions of polarity and polarizability of solvents to 0--0 band energy and bandwidth are quantitatively distinguished. The 0--0 transition energy of the S2 state at the gas phase is predicted to locate between 23000 and 23600~cm-1.
Zhang Xiao-Niu, Shi De-Heng, Sun Jin-Feng, Zhu Zun-Lue
Chin. Phys. B 2010, 19 (1): 013501;  doi: 10.1088/1674-1056/19/1/013501
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An interaction potential for an N2(X1σg+) molecule is constructed by using the highly accurate valence internally contracted multireference configuration interaction method and the largest basis set, aug-cc-pV6Z, in the valence range. The potential is used to investigate the elastic scattering of two N atoms at energies from 1.0× 10-11 to 1.0× 10-4 a.u. The derived total elastic cross sections are very large and almost constant at ultralow temperatures, and the shape of total elastic cross section curve is mainly dominated by the s-partial wave at very low collision energies. Three shape resonances are found in the total elastic cross sections. Concretely, the first one is very sharp and strong. It results from the g-partial-wave contribution and the resonant energy is 3.645× 10-6 a.u. The second one is contributed by the h-partial wave and the resonant energy is 1.752× 10-5 a.u. This resonance is broadened by those from the d- and f-partial waves. The third one comes from the l = 6 partial wave contribution and the resonant energy is 3.522× 10-5 a.u. This resonance is broadened by those from the g- and h-partial waves. The N2(X1σg+) molecular parameters, which are determined at the current theoretical level, achieve very high accuracy due to the employment of the largest correlation-consistent basis set in the valence range.
Dong Xi-Jie, Hu Yi-Fan, Wu Yu-Ying
Chin. Phys. B 2010, 19 (1): 013601;  doi: 10.1088/1674-1056/19/1/013601
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Depth profiled positronium (Ps) annihilation lifetime spectroscopy (PALS) is an extremely useful probe of the pore characteristics in nanoporous low-dielectric (low-k) constant thin films. PALS has also been considered as a potential probe to investigate diffusion barrier integrity and the structural changes of porous low-k films during their integration with Cu. Hence, it is essential to understand the diffusion behaviour of positronium/Cu atoms in the films. In this work, based on the fact that porous materials possess characteristics of statistical self-similarity, a fractal model, the Menger sponge model, has been applied to simulate the structure of a promising dielectric, porous methylsilsesquioxane (MSQ) films. The diffusion behaviour of Ps out of the fractal model and into the surrounding vacuum is studied by means of the diffusion equation and traditional advective--diffusive theory. Predictive results from our model show good agreement with measurement data.
CLASSICAL AREAS OF PHENOMENOLOGY
Chin. Phys. B 2010, 19 (1): 014201;  doi: 10.1088/1674-1056/19/1/014201
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This paper stuides numerically the model equation in a one dimensional defective photonic lattice by modifying the potential function to a periodic function. It is found that defect modes (DMs) can be regarded as Bloch modes which are excited from the extended photonic band-gap structure at Bloch wave-numbers with kx = 0. The DMs for both positive and negative defects are considered in this method.
Zhou Pu, Ma Yan-Xing, Wang Xiao-Lin, Ma Hao-Tong, Xu Xiao-Jun, Liu Ze-Jin
Chin. Phys. B 2010, 19 (1): 014202;  doi: 10.1088/1674-1056/19/1/014202
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We demonstrate coherent beam combining of two tiled-aperture single-frequency fibre amplifiers with a total output power of 29.65~W by using the multi-dithering technique. The two laser beams are packaged closely by using free-space mirrors side by side into a tiled-aperture with a near-field fill factor of 62\%. Active phase control of the amplifier is performed on commercially available digital lock-in amplifiers. Experimental results show that the power contained in the main-lobe in closed-loop is 1.72 times greater than that in open-loop, which is 86\% for the ideal case. The fringe contrast of the far-field fringe pattern is as high as 80\% when the system is in closed-loop. The beam quality of the combined beam is computed to be BQ = 1.48. The whole system in closed-loop performs well in a long-time observation.
Xu Guan-Lei, Wang Xiao-Tong, Xu Xiao-Gang
Chin. Phys. B 2010, 19 (1): 014203;  doi: 10.1088/1674-1056/19/1/014203
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In this paper the relations between two spreads, between two group delays, and between one spread and one group delay in fractional Fourier transform (FRFT) domains, are presented and three theorems on the uncertainty principle in FRFT domains are also developed. Theorem 1 gives the bounds of two spreads in two FRFT domains. Theorem 2 shows the uncertainty relation between two group delays in two FRFT domains. Theorem 3 presents the crossed uncertainty relation between one group delay and one spread in two FRFT domains. The novelty of their results lies in connecting the products of different physical measures and giving their physical interpretations. The existing uncertainty principle in the FRFT domain is only a special case of theorem 1, and the conventional uncertainty principle in time-frequency domains is a special case of their results. Therefore, three theorems develop the relations of two spreads in time-frequency domains into the relations between two spreads, between two group delays, and between one spread and one group delay in FRFT domains.
Chen Ke, Cheng Jian-Qun, Wang Yan, Huang Ming-Ju
Chin. Phys. B 2010, 19 (1): 014204;  doi: 10.1088/1674-1056/19/1/014204
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A dynamic theoretical model of photochemistry and hologram formation in holographic photopolymer is established, and the dynamic development process of holographic gratings in the photopolymer is discussed with the model. A novel multi-wavelength visible light sensitive photopolymer for holographic storage is prepared. The influence of exposure wavelength on holographic storage characteristics is analysed. By fitting the experimental data of transmittance and diffraction efficiency to a function of time with different exposure intensities and wavelengths, the variations of dynamic parameters of photochemistry and photopolymerization diffusion are presented.
Tan Hua-Tang
Chin. Phys. B 2010, 19 (1): 014205;  doi: 10.1088/1674-1056/19/1/014205
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In this paper, we investigate the effects of the spatial variation of driving-laser phase in a collective two-atom system on the intensity--intensity correlations of the resonant fluorescence. It is shown that the intensity--intensity correlations exhibit quite different characteristics for the different values of the spatial phase of the laser at the position of the two atoms in both cases of the weak and strong driving lasers. Our results suggest that the intensity--intensity correlations can serve as a probe of the spatial interference effect arising from the spatial variation of the laser phase.
Kang Dong-Peng, Liao Qing-Hong, Ahamd Muhammad Ashfaq, Wang Yue-Yuan, Liu Shu-Tian
Chin. Phys. B 2010, 19 (1): 014206;  doi: 10.1088/1674-1056/19/1/014206
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The entropy squeezing of an atom with a k-photon in the Jaynes--Cummings model is investigated. For comparison, we also study the corresponding variance squeezing and atomic inversion. Analytical results show that entropy squeezing is preferable to variance squeezing for zero atomic inversion. Moreover, for initial conditions of the system the relation between squeezing and photon transition number is also discussed. This provides a theoretical approach to finding out the optimal entropy squeezing.
Wang Ji-Suo, MengXiang-Guo, Liang Bao-Long
Chin. Phys. B 2010, 19 (1): 014207;  doi: 10.1088/1674-1056/19/1/014207
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Based on the Einstein, Podolsky, and Rosen (EPR) entangled state representation, this paper introduces the wave function for the squeezed atomic coherent state (SACS), which turns out to be just proportional to a single-variable ordinary Hermite polynomial of order 2j. As important applications of the wave function, the Wigner function of the SACS and its marginal distribution are obtained and the eigenproblems of some Hamiltonians for the generalized angular momentum system are solved.
Wang Shuai, Jiang Ji-Jian, Xu Shi-Min, Li Hong-Qi
Chin. Phys. B 2010, 19 (1): 014208;  doi: 10.1088/1674-1056/19/1/014208
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Based on the rotation transformation in phase space and the technique of integration within an ordered product of operators, the coherent state representation of the multimode phase shifting operator and one of its new applications in quantum mechanics are given. It is proved that the coherent state is a natural language for describing the phase shifting operator or multimode phase shifting operator. The multimode phase shifting operator is also a useful tool to solve the dynamic problems of the multimode coordinate--momentum coupled harmonic oscillators. The exact energy spectra and eigenstates of such multimode coupled harmonic oscillators can be easily obtained by using the multimode phase shifting operator.
Wang Hai-Jun, Gao Yun-Feng
Chin. Phys. B 2010, 19 (1): 014209;  doi: 10.1088/1674-1056/19/1/014209
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The emission spectrum of a two-level atom interacting dispersively with a single mode radiation field in the dissipative cavity is investigated. A general expression for the emission spectrum is derived. The numerical results for the initial field in coherent state are calculated. It is found that the spectrum structure is influenced significantly by the cavity damping constant \kappa , and the spectrum structure is dependent on the interaction time T when the cavity dissipation is present. Only one peak located at Ωa appears in the atomic spectra for larger T.
Xu Xun-Wei, Liu Nian-Hua
Chin. Phys. B 2010, 19 (1): 014210;  doi: 10.1088/1674-1056/19/1/014210
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The effects of an applied low frequency field on the dynamics of a two-level atom interacting with a single-mode field are investigated. It is shown that the time evolution of the atomic population is mainly controlled by the coupling constants and the frequency of the low frequency field, which leads to a low frequency modulation function for the time evolution of the upper state population. The amplitude of the modulation function becomes larger as the coupling constants increase. The frequency of the modulation function is proportional to the frequency of the low frequency field, and decreases with increasing coupling constant.
Zhao Shun-Cai, Liu Zheng-Dong, Wu Qi-Xuan
Chin. Phys. B 2010, 19 (1): 014211;  doi: 10.1088/1674-1056/19/1/014211
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In this paper we have investigated three external fields interacting with the four-level Y-type atomic system described by the density-matrix approach. The results show that left-handedness with zero absorption is achieved. The zero absorption property displays the possibility of manipulation by varying the phase and the intensity of the coupling field. Also, the zero absorption property may be used to amplify the evanescent waves that have been lost in imaging by traditional lenses. We propose an approach to obtain a negative refractive medium with zero absorption and the possibility of enhanceingthe imaging resolution in realizing superlenses'.
Zhang Yu-Ying, Zhang Chi, Hu Ming-Lie, Wang Si-Jia, Song You-Jian, Chai Lu, Wang Qing-Yue
Chin. Phys. B 2010, 19 (1): 014212;  doi: 10.1088/1674-1056/19/1/014212
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The filtering mechanism of a free output coupler mode-locked laser based on large-mode-area photonic-crystal fibre is analysed. A filtering-soliton mode-locked laser with 495~fs pulse width and 21 nJ pulse energy is achieved. Another novel cavity configuration is established to eliminate the filtering effect. Pulses, each 457~fs in width and 16.5 nJ in energy, are obtained in a soliton-like regime. Pulses, each 387~fs in width and 15.8 nJ in energy, are also generated in a stretched pulse regime and could be dechirped to 119~fs externally to the cavity.
Wu Jian, H. D. Summers
Chin. Phys. B 2010, 19 (1): 014213;  doi: 10.1088/1674-1056/19/1/014213
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It is important to determine quantitatively the internal carrier loss arising from heating and barrier height variation in a vertical-cavity surface-emitting quantum well laser (VCSEL). However, it is generally difficult to realize this goal using purely theoretical formulas due to difficulty in deriving the parameters relating to the quantum well structure. In this paper, we describe an efficient approach to characterizing and calculating the carrier loss due to the heating and the barrier height change in the VCSEL. In the method, the thermal carrier loss mechanism is combined with gain measurement and calculation. The carrier loss is re-characterized in a calculable form by constructing the threshold current and gain detuning-related loss current using the measured gain data and then substituting them for the quantum well-related parameters in the formula. The result can be expressed as a product of an exponential weight factor linked to the barrier height change and the difference between the threshold current and gain detuning-related loss current. The gain variation at cavity frequency due to thermal carrier loss and gain detuning processes is measured by using an AlInGaAs--AlGaAs VCSEL structure. This work provides a useful approach to analysing threshold and loss properties of the VCSEL, particularly, gain offset design for high temperature operation of VCSELs.
H. Mehdian, S. Saviz
Chin. Phys. B 2010, 19 (1): 014214;  doi: 10.1088/1674-1056/19/1/014214
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A theory of a two-stream free-electron laser in a combined electromagnetic wiggler (EMW) is developed, in which we use an axial-guide magnetic field and take into account the effects of the self-fields. The electron trajectories and the small signal gain are derived. The stability of the trajectories, the characteristics of the linear-gain, and the normalised maximum gain are studied numerically. The results show that there are nine stable groups of orbits in the presence of self-fields instead of seven groups reported in the absence of the self-field. It is also shown that the normalised gains of four groups of the orbits are decreasing and those for the rest of them are increasing with growing \barΩ0. Furthermore, it is found that the two-stream laser with self-field enhances the maximum gain in comparison with the single stream case.
Liu Hua-Gang, Hu Ming-Lie, Song You-Jian, Li Yan-Feng, Chai Lu, Wang Ching-Yue
Chin. Phys. B 2010, 19 (1): 014215;  doi: 10.1088/1674-1056/19/1/014215
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A Kerr-lens mode-locked Ti:sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti:sapphire laser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37~ps to 2.11~ps, and 36~fs pulses are achieved after extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr?dinger equation, and the simulation results are in good agreement with the experimental results.
Wang Nan, Zhang Yun-Dong, Wang Hao, Tian He, Qiu Wei, Wang Jin-Fang, Yuan Ping
Chin. Phys. B 2010, 19 (1): 014216;  doi: 10.1088/1674-1056/19/1/014216
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A novel relative rotation sensor based on slow light is proposed and analysed. A theoretical analysis shows that the high sensitivity of the proposed rotation sensor is achieved through an electromagnetically-induced-transparency medium. Unlike the tradition detection method, the idea of rotation sensing is to detect group delay between counterpropagating wave packets. It can be used to realize an ultra-precise rotation sensor.
Jin Xiao, Wang Yu-Xiao, Shui Min, Li Chang-Wei, Yang Jun-Yi, Zhang Xue-Ru, Yang Kun, Song Ying-Lin
Chin. Phys. B 2010, 19 (1): 014217;  doi: 10.1088/1674-1056/19/1/014217
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Nonsymmetrical transition from reverse-saturable absorption (RSA) to saturable absorption (SA) caused by excited state absorption induced mass transport of the CuPcTs dissolved in dimethyl sulfoxide is observed in an open aperture Z-scan experiment with a 21-ps laser pulse. The nonsymmetrical transition from RSA to SA is ascribed neither to saturation of excited state absorption nor to thermal induced mass transport, the so-called Soret effect. In our consideration, strong nonlinear absorption causes the rapid accumulation of the non-uniform kinetic energy of the solute molecules. The non-uniform kinetic field in turn causes the migration of the solute molecules. Additionally, an energy-gradient-induced mass transport theory is presented to interpret the experimental results, and the theoretical calculations are also taken to fit our experimental results.
Zhu Teng-Fei, Tan Bing-Hui, Pan Xue-Feng, Tao Wei-Dong
Chin. Phys. B 2010, 19 (1): 014218;  doi: 10.1088/1674-1056/19/1/014218
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2D and 3D submicron periodic structures are first fabricated by red-induced photopolymerization using a common 635~nm semiconductor laser and specially developed red-sensitive polymer material. The principle of this new photo-polymer material fabrication is explained and the absorption spectra of the material are measured. This fabrication technique allows a deeper penetration into volume and larger interference irradiation area which is more than 1~cm2. The optical design, theoretical calculations and experimental results including diffraction patterns verifying the formation of periodic structures are presented. Compared with other fabrication technologies using high-power lasers, this approach has greatly reduced the demand for laser apparatus. Therefore, it is much more accessible to most laboratories and potentially usable in holographic fabrication of photonic crystals and devices in micro electro-mechanical systems (MEMS).
Zhu Yu, Xu Xue-Jun, Li Zhi-Yong, Zhou Liang, Han Wei-Hua, Fan Zhong-Chao, Yu Yu-De, Yu Jin-Zhong
Chin. Phys. B 2010, 19 (1): 014219;  doi: 10.1088/1674-1056/19/1/014219
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A high efficiency and broad bandwidth grating coupler between a silicon-on-insulator (SOI) nanophotonic waveguide and fibre is designed and fabricated. Coupling efficiencies of 46\% and 25\% at a wavelength of 1.55~μ m are achieved by simulation and experiment, respectively. An optical 3~dB bandwidth of 45~nm from 1530~nm to 1575~nm is also obtained in experiment. Numerical calculation shows that a tolerance to fabrication error of 10~nm in etch depth is achievable. The measurement results indicate that the alignment error of ±2~μ m results in less than 1~dB additional coupling loss.
Xu Hong-Hua, Liu Xiao-Yan, He Yu-Hui, Fan Chun, Du Gang, Sun Ai-Dong, Han Ru-Qi, Kang Jin-Feng
Chin. Phys. B 2010, 19 (1): 014601;  doi: 10.1088/1674-1056/19/1/014601
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In this work, we investigate strain effects induced by the deposition of gate dielectrics on the valence band structures in Si (110) nanowire via the simulation of strain distribution and the calculation of a generalized 6× 6k.p strained valence band. The nanowire is surrounded by the gate dielectric. Our simulation indicates that the strain of the amorphous SiO2 insulator is negligible without considering temperature factors. On the other hand, the thermal residual strain in a nanowire with amorphous SiO2 insulator which has negligible lattice misfit strain pushes the valence subbands upwards by chemical vapour deposition and downwards by thermal oxidation treatment. In contrast with the strain of the amorphous SiO2 insulator, the strain of the HfO2 gate insulator in Si (110) nanowire pushes the valence subbands upwards remarkably. The thermal residual strain by HfO2 insulator contributes to the up-shifting tendency. Our simulation results for valence band shifting and warping in Si nanowires can provide useful guidance for further nanowire device design.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Xu Ning, Ding Jian-Wen, Ma Ming-Ming, Tang Xian
Chin. Phys. B 2010, 19 (1): 016101;  doi: 10.1088/1674-1056/19/1/016101
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Taking into account both the intrinsic curvature and Zeeman effects, persistent currents in a multi-walled carbon nanotorus are explored by using a supercell method, within the tight-binding formalism. It is shown that in the absence of the Zeeman effect, the intrinsic curvature induces some dramatic changes in energy spectra and thus changes in the shape of the flux-dependent current. A paramagnetism--diamagnetism transition is observed. With consideration of the Zeeman splitting energy, the period of persistent current is destroyed, and a diamagnetism--paramagnetism transition is obtained at high magnetic field. In addition, we further explore the effect of external electric field energy (Eef) on persistent current, indicating that it changes unmonotonously with Eef.
Fang Qi-Hong, Song Hao-Peng, Liu You-Wen
Chin. Phys. B 2010, 19 (1): 016102;  doi: 10.1088/1674-1056/19/1/016102
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The interaction between an edge dislocation and a crack emanating from a semi-elliptic hole is dealt with. Utilizing the complex variable method, closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the edge dislocation are also calculated. The influence of the morphology of the blunt crack and the position of the edge dislocation on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases acutely when the dislocation approaches the tip of the crack. The effect of the morphology of the blunt crack on the stress intensity factor of the crack and the image force is very significant.
Cheng Xiu-Wei, Guan Qing-Feng, Fan Xian-Hong, Chen Bo
Chin. Phys. B 2010, 19 (1): 016103;  doi: 10.1088/1674-1056/19/1/016103
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We investigate the microstructures of the pure aluminium foil and filter used on the space solar telescope, irradiated by photons with different doses. The vacancy defect clusters induced by proton irradiation in both samples are characterized by transmission electron microscopy, and the density and the size distribution of vacancy defect clusters are determined. Their transmittances are measured before and after irradiating the samples by protons with energy E=100~keV and dose φ =6× 1011/mm2. Our experimental results show that the density and the size of vacancy defect clusters increase with the increase of irradiation doses in the irradiated pure aluminium foils. As irradiation dose increases, vacancies incline to form larger defect clusters. In the irradiated filter, a large number of banded void defects are observed at the agglomerate boundary, which results in the degradation of the optical and mechanical performances of the filter after proton irradiation.
Zhao Wen-Jie, Xu Hong-Bin, Wang Yuan-Xu
Chin. Phys. B 2010, 19 (1): 016201;  doi: 10.1088/1674-1056/19/1/016201
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Using first-principles calculations, this paper systematically investigates the structural, elastic, and electronic properties of ReN4. The calculated positive eigenvalues of the elastic constant matrix show that the orthorhombic Pbca structure of ReN4 is elastically stable. The calculated band structure indicates that ReN4 is metallic. Compared with the synthesized superhard material WB4, it finds that ReN4 exhibits larger bulk and shear moduli as well as a smaller Poisson's ratio. In addition, the elastic constant c_44 of ReN4 is larger than all the known 5d transition metal nitrides and borides. This combination of properties makes it an ideal candidate for a superhard material.
Miao Ling, Liu Hui-Jun, Hu Yi, Zhou Xiang, Hu Cheng-Zheng, Shi Jing
Chin. Phys. B 2010, 19 (1): 016301;  doi: 10.1088/1674-1056/19/1/016301
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The phonon dispersion relations of three kinds of 4~? carbon nanotubes are calculated by using the density functional perturbation theory. It is found that the frequencies of some phonon modes are very sensitive to the smearing width used in the calculations, and eventually become negative at low electronic temperature. Moreover, two kinds of soft modes are identified for the (5,0) tube which are quite different from those reported previously. Our results suggest that the (5,0) tube remains metallic at very low temperature, instead of the metallic-semiconducting transition claimed before.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
D. Bloor, A. Graham, P. J.Laughlin, D. Lussey
Chin. Phys. B 2010, 19 (1): 017001;  doi: 10.1088/1674-1056/19/1/017001
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This paper describes the accepted meaning of the termnegative resistance' and its use in the literature, and discusses the features in the previously published data on QTCTM (market name of a metal--polymer composite) that show that the non-linear, hysteretic current voltage characteristics are not caused by Joule heating. The benefit of the high metal filler loading in QTCTM and other unique features of this composite are reviewed.
Yun Jiang-Ni, Zhang Zhi-Yong, Yan Jun-Feng, Deng Zhou-Hu
Chin. Phys. B 2010, 19 (1): 017101;  doi: 10.1088/1674-1056/19/1/017101
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The effects of La and Sb doping on the electronic structure and optical properties of SrTiO3 are investigated by first-principles calculation of the plane wave ultra-soft pseudo-potential based on density functional theory. The calculated results reveal that corner-shared TiO6 octahedra dominate the main electronic properties of SrTiO3, and its structural stability can be improved by La doping. The La3+ ion fully acts as an electron donor in Sr0.875La0.125TiO3 and the Fermi level shifts into the conduction bands (CBs) after La doping. As for SrSb0.125Ti0.875O3, there is a distortion near the bottom of the CBs for SrSb0.125Ti0.875O3 after Sb doping and an incipient localization of some of the doped electrons trapped in the Ti site, making it impossible to describe the evolution of the density of states (DOS) within the rigid band model. At the same time, the DOSs of the two electron-doped systems shift towards low energies and the optical band gaps are broadened by about 0.4 and 0.6 eV for Sr_0.875La_0.125TiO3 and SrSb0.125Ti0.875O3, respectively. Moreover, the transmittance of SrSb0.125Ti0.875O3 is as high as 95\% in most of the visible region, which is higher than that of Sr0.875La0.125TiO_3 (85\%). The wide band gap, the small transition probability and the weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the significant optical transparency of SrSb_0.125Ti_0.875O3.
Liu Hui-Mei, Lu Cheng-Liang, WangKe-Feng, Liu Jun-Ming, Wang Qing, Dong Chuang
Chin. Phys. B 2010, 19 (1): 017102;  doi: 10.1088/1674-1056/19/1/017102
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The low temperature specific heat of Sm-Al-Co ternary metallic glasses is investigated and a clear anomaly associated with the Boson peak is identified. While this anomaly depends slightly on the chemical composition, it has no dependence on external magnetic field. To figure out the mechanism of the Boson peak, we interpret the data within various model frameworks. Unlike earlier work, our study shows that this Boson peak is mainly ascribed to an additional T2 term of the specific heat, which may originate from the quasi-two-dimensional and short-range ordered structure units possibly existing in the metallic glasses.
Li Gui-Qin
Chin. Phys. B 2010, 19 (1): 017201;  doi: 10.1088/1674-1056/19/1/017201
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Conductances of different geometric conformations of boron ribbon devices are calculated by the ab initio method. The I--V characteristics of three devices are rather different due to the difference in structure. The current of the hexagonal boron device is the largest and increases nonlinearly. The current of the hybrid hexagon-triangle boron device displays a large low-bias current and saturates at a value of about 5.2~μ A. The current of the flat triangular boron flake exhibits a voltage gap at low bias and rises sharply with increasing voltage. The flat triangular boron device can be either conducting or insulating, depending on the field.
Yang Hang-Sheng, Nie An-Min, Qiu Fa-Min
Chin. Phys. B 2010, 19 (1): 017202;  doi: 10.1088/1674-1056/19/1/017202
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Cubic boron nitride thin films were deposited on silicon substrates by low-pressure inductively coupled plasma-enhanced chemical vapour deposition. It was found that the introduction of O2 into the deposition system suppresses both nucleation and growth of cubic boron nitride. At a B2H6 concentration of 2.5\% during film deposition, the critical O2 concentration allowed for the nucleation of cubic boron nitride was found to be less than 1.4\%, while that for the growth of cubic boron nitride was higher than 2.1\%. Moreover, the infrared absorption peak observed at around 1230--1280~cm-1, frequently detected for cubic boron nitride films prepared using non-ultrahigh vacuum systems, appears to be due to the absorption of boron oxide, a contaminant formed as a result of the oxygen impurity. Therefore, the existence of trace oxygen contamination in boron nitride films can be evaluated qualitatively by this infrared absorption peak.
Wang Shou-Guo, Zhang Yan, Zhang Yi-Men, Zhang Yu-Ming
Chin. Phys. B 2010, 19 (1): 017203;  doi: 10.1088/1674-1056/19/1/017203
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Ion-implantation layers are fabricated by multiple nitrogen ion-implantations (3 times for sample A and 4 times for sample B) into a p-type 4H-SiC epitaxial layer. The implantation depth profiles are calculated by using the Monte Carlo simulator TRIM. The fabrication process and the I--V and C--V characteristics of the lateral Ti/4H-SiC Schottky barrier diodes (SBDs) fabricated on these multiple box-like ion-implantation layers are presented in detail. Measurements of the reverse I--V characteristics demonstrate a low reverse current, which is good enough for many SiC-based devices such as SiC metal--semiconductor field-effect transistors (MESFETs), and SiC static induction transistors (SITs). The parameters of the diodes are extracted from the forward I--V and C--V characteristics. The values of ideality factor n of SBDs for samples A and B are 3.0 and 3.5 respectively, and the values of series resistance R_\rm s are 11.9 and 1.0~kΩ respectively. The values of barrier height φ _\rm B of Ti/4H-SiC are 0.95 and 0.72 eV obtained by the I--V method and 1.14 and 0.93 eV obtained by the C--V method for samples A and B respectively. The activation rates for the implanted nitrogen ions of samples A and B are 2\% and 4\% respectively extracted from C--V testing results.
Wang Shou-Guo, Zhang Yan, Zhang Yi-Men, Zhang Yu-Ming
Chin. Phys. B 2010, 19 (1): 017204;  doi: 10.1088/1674-1056/19/1/017204
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The ohmic contacts of 4H-SiC are fabricated on nitrogen ion implanted layers made by performing box-like-profile implantation three and four times. Implantation parameters such as the standard deviation σ and the projection range Rp are calculated by the Monte Carlo simulator TRIM. Ni/Cr ohmic contacts on Si-face 4H-SiC implantation layers are measured by transfer length methods (TLMs). The results show that the values of sheet resistance Rsh are 30~kΩ /□ and 4.9~kΩ/□ and the values of specific contact resistance ρc of ohmic contacts are 7.1× 10-4Ω.cm2 and 9.5× 10-5Ω.cm2 for the implanted layers with implantation performed three and four times respectively.
Deng Yong-He
Chin. Phys. B 2010, 19 (1): 017301;  doi: 10.1088/1674-1056/19/1/017301
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The interaction of Ag atoms with a defective MgO(001) surface is systematically studied based on density functional theory. The Ag clusters are deposited on neutral and charged oxygen vacancies of the MgO(001) surface. The structures of Ag clusters take the shape of simple models of two- or three-dimensional (2D and 3D) metal particles deposited on the MgO surface. When the nucleation of the metal clusters occurs in the Fs (missing neutral O) centre, the interaction with the substrate is considerably stronger than that in the Fs+ (missing O- ) centre. The results show that the adsorption of Ag atoms on the MgO surface with oxygen vacancy is stronger than on a clear MgO surface, thereby attracting more Ag atoms to cluster together, and forming atomic islands.
Xue Wen-Rui, Guo Ya-Nan, Zhang Wen-Mei
Chin. Phys. B 2010, 19 (1): 017302;  doi: 10.1088/1674-1056/19/1/017302
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In this paper, two kinds of modified surface plasmonic waveguides formed by nanometric parallel lines are proposed. The finite-difference frequency-domain method is used to study propagation properties of the fundamental mode supported by these surface plasmonic waveguide structures. Results show that the transverse magnetic field of the fundamental mode is mainly distributed in the face to face region formed by two rods. With the same geometrical parameters and the same working wavelength of 632.8~nm, in the case of rods with a triangular cross-section, the degree of localization of field is strong, i.e. the mode area is small, but the fraction of the modal power in the metal increases, so the effective index increases and the propagation length of the mode decreases. With the same geometrical parameters, relative to the case of a working wavelength of 632.8~nm, when working wavelength is large, the mode area of transverse magnetic field distribution is large, i.e. the degree of localization of field is weak, and the interaction of field and silver is weak too, then the effective index decreases, so the propagation length increases. The rounded radii of rods have a great influence on the performance of the surface plasmonic waveguides with rounded triangular cross-sections, but have little influence on the performance of surface plasmonic waveguides with rounded square cross-sections. Since the distribution of transverse magnetic field, effective index, propagation length and the mode area can be adjusted by the geometrical parameters, this kind of modified surface plasmonic waveguide can be applied to the field of photonic device integration and sensors.
Wang Li-Chun, Deng Li, Cui Ni, Niu Yue-Ping, Gong Shang-Qing
Chin. Phys. B 2010, 19 (1): 017303;  doi: 10.1088/1674-1056/19/1/017303
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We investigate the transmission properties of a normally incident TM plane wave through metal films with periodic parabolic-shaped grooves on single and double surfaces using the finite-difference-time-domain method. Nearly zero transmission efficiency is found at wavelengths corresponding to surface plasmon excitation on a flat surface in the case where the single surface is grooved. Meanwhile, resonant excitation of surface plasmon polariton (SPP) Bloch modes leads to a strong transmission peak at slightly larger wavelengths. When the grating is grooved on double surfaces, the transmission enhancement can be dramatically improved due to the resonant tunnelling between SPP Bloch modes.
Yun Da-Qin, Feng Wei, Wu Hong-Cai, Liu Xiao-Zeng, Qiang Jun-Feng
Chin. Phys. B 2010, 19 (1): 017304;  doi: 10.1088/1674-1056/19/1/017304
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Nanocomposites of poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene]-zinc selenide (MOPPV-ZnSe) are synthesized by mixing the polymerization of 1,4-bis (chloromethyl)-2-methoxy-5-octoxy-benzene in the presence of ZnSe quantum dots. The resulting MOPPV-ZnSe nanocomposites possess a well-defined interfacial contact, thus significantly promoting the dispersion of ZnSe within the MOPPV matrix and facilitating the electronic interaction between these two components. Raman and UV--visible absorption spectra are influenced by the incorporation of ZnSe nanocrystals. High-resolution transmission electron microscopic and tapping-mode atomic force microscopic results show clearly the evidence for phase-segregated networks of ZnSe nanocrystals, which provide a large area of interface for charge separation to occur. Steady-state spectra of MOPPV-ZnSe nanocomposites are markedly quenched by the introduction of intimate polymer/ZnSe junctions. Time-resolved photoluminescence measurements show that the lifetime decays quickly, which further confirms the occurrence of charge transfer in MOPPV-ZnSe nanocomposites.
Wang Zhi-Jun, Wang Jin-Cheng, Yang Gen-Cang
Chin. Phys. B 2010, 19 (1): 017305;  doi: 10.1088/1674-1056/19/1/017305
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Phase field investigation reveals that the stability of the planar interface is related to the anisotropic intensity of surface tension and the misorientation of preferred crystallographic orientation with respect to the heat flow direction. The large anisotropic intensity may compete to determine the stability of the planar interface. The destabilizing effect or the stabilizing effect depends on the misorientation. Moreover, the interface morphology of initial instability is also affected by the surface tension anisotropy.
Ren Fan, Hao Zhi-Biao, Wang Lei, Wang Lai, Li Hong-Tao, Luo Yi
Chin. Phys. B 2010, 19 (1): 017306;  doi: 10.1088/1674-1056/19/1/017306
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SiN_x is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors (HEMTs). In this paper, the effects of SiN_x passivation film on both two-dimensional electron gas characteristics and current collapse of AlGaN/GaN HEMTs are investigated. The SiN_x films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results.
Wang Liang-Ji, Zhang Shu-Ming, Zhu Ji-Hong, ZhuJian-Jun, Zhao De-Gang, Liu Zong-Shun, Jiang De-Sheng, WangYu-Tian, Yang Hui
Chin. Phys. B 2010, 19 (1): 017307;  doi: 10.1088/1674-1056/19/1/017307
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To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5~nm/5~nm) film deposition. The surface morphology of wafers and the current--voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.
Kang Yu-Qing, CaoMao-Sheng, Yuan Jie, Fang Xiao-Yong
Chin. Phys. B 2010, 19 (1): 017701;  doi: 10.1088/1674-1056/19/1/017701
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The influence of orientation on electromagnetic properties of basalt fibre/nickel core--shell heterostructures prepared by a simple electroless plating method is investigated. For comparison, the same investigation is also performed on naked basalt fibres. For electromagnetic measurement, the directions of basalt fibre/nickel and naked basalt fibres are parallel, random and perpendicular to the direction of external electric field, termed E_\vert\vert sample, random sample and E sample, respectively. Electromagnetic anisotropy can be clearly observed in the basalt fibre/nickel core--shell heterostructures, while electromagnetic properties of naked basalt fibres are unrelated to the orientation. The E basalt fibre/nickel shows the highest dielectric loss but the lowest magnetic loss, and E|| basalt fibre/nickel exhibits the highest magnetic loss but the lowest dielectric loss. The dielectric loss of E basalt fibre/nickel is several times as large as that of E|| basalt fibre/nickel, which could be attributed to the increase of polarization relaxation time as a consequence of the nanosize-confinement effect. The magnetic loss of E|| basalt fibre/nickel is even one order of magnitude higher than that of E basalt fibre/nickel, which originates mainly from the natural magnetic resonance of basalt fibre/nickel core--shell heterostructures.
HouZhi-Ling, Cao Mao-Sheng, Yuan Jie, Song Wei-Li
Chin. Phys. B 2010, 19 (1): 017702;  doi: 10.1088/1674-1056/19/1/017702
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This paper reports that single-phase γ -Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ -Y2Si2O7 as a function of the temperature and frequency. The γ -Y2Si2O7 exhibits low dielectric loss and non-Debye relaxation behaviour from 25 to 1400~℃C in the range of 7.3--18~GHz. The mechanism for polarization relaxation of the as-prepared γ -Y2Si2O7 differing from that of SiO2 is explained. Such particular dielectric properties could potentially make specific attraction for extensive practical applications.
Wang Zhi-Jun, Li Pan-Lai, Yang Zhi-Ping, Guo Qing-Lin, Li Xu
Chin. Phys. B 2010, 19 (1): 017801;  doi: 10.1088/1674-1056/19/1/017801
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This paper reports that a novel yellow phosphor, LiSrBO3:Eusup>2+, was synthesized by the solid-state reaction. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (360 and 400~nm) and blue (425 and 460~nm) light, and exhibits a satisfactory yellow performance (565~nm). The role of concentration of Eusup>2+ on the emission intensity in LiSrBO3 is studied, and it is found that the critical concentration is 3 mol\%, and the concentration self-quenching mechanism is the dipole--dipole interaction according to the Dexter theory. White light emitting diodes were generated by using an InGaN chip (460~nm or 400~nm) with LiSrBO3:Eusup>2+ phosphor, the CIE chromaticity is (x=0.341, y=0.321) and (x=0.324, y=0.318), respectively. Therefore, LiSrBO3:Eusup>2+ is a promising yellow phosphor for white light emitting diodes.
8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Wang Xiao-Wei, Cai Guo-Biao, Jin Ping
Chin. Phys. B 2010, 19 (1): 019401;  doi: 10.1088/1674-1056/19/1/019401
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The scaling of the flowfield in a gas--gas combustion chamber is investigated theoretically, numerically and experimentally. To obtain the scaling criterion of the gas--gas combustion flowfield, formulation analysis of the three-dimensional (3D) Navier--Stokes equations for a gaseous multi-component mixing reaction flow is conducted and dimensional analysis on the gas--gas combustion phenomena is also carried out. The criterion implies that the size and the pressure of the gas--gas combustion chamber can be changed. Based on the criterion, multi-element injector chambers with different geometric sizes and at different chamber pressures ranging from 3~MPa to 20~MPa are numerically simulated. A multi-element injector chamber is designed and hot-fire tested at five chamber pressures from 1.64~MPa to 3.68~MPa. Wall temperature measurements are used to understand the similarity of combustion flowfields in the tests. The results have verified the similarities between combustion flowfields under different chamber pressures and geometries, with the criterion applied.
Zou Pu, Li Ru-Xin, Zeng Zhi-Nan, Xiong Hui, Liu Peng, Leng Yu-Xin, Fan Pin-Zhong, Xu Zhi-Zhan
Chin. Phys. B 2010, 19 (1): 019501;  doi: 10.1088/1674-1056/19/1/019501
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We propose a scheme to generate isolated attosecond pulses in the water-window spectral region. Based on the numerical solutions of the single active electron model, we investigate high-order harmonic generation in helium atoms driven by a multi-cycle two-colour optical field synthesized by an intense 2000 nm, 20 fs pulse and its frequency-doubled pulse. When the latter is slightly detuned and properly phase shifted with respect to the fundamental laser pulse, an ultra-broad extreme ultraviolet supercontinuum with a spectral width of 130~eV can be generated in the 270--400~eV spectral regions. A supercontinuum from 280--340~eV in the water window can be selected to yield an isolated 67 attosecond pulse without employing any phase compensation. This water window coherent x-ray pulse with less than 100 attosecond duration is a potential tool for studying the ultrafast electronic dynamics of biological samples in water.
Wang Yu-Ting, Xu Li-Xin, Lü Jian-Bo, Gui Yuan-Xing
Chin. Phys. B 2010, 19 (1): 019801;  doi: 10.1088/1674-1056/19/1/019801
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In this paper, the properties of dark energy are investigated according to the parameterized deceleration parameter q(z), which is used to describe the extent of the accelerating expansion of the universe. The potential of dark energy V(φ) and the cosmological parameters, such as the dimensionless energy density \varOmega_φ, \varOmega_m, and the state parameter w_φ, are connected to it. Concretely, by giving two kinds of parameterized deceleration parameters q(z)=a+bz/(1+z) and q(z)=1/2+(az+b)/(1+z)^2, the evolution of these parameters and the reconstructed potentials V(φ) are plotted and analysed. It is found that the potentials run away with the evolution of universe.
Cui Jing-Lei, Zhang Li, Zhang Jing-Fei, Zhang Xin
Chin. Phys. B 2010, 19 (1): 019802;  doi: 10.1088/1674-1056/19/1/019802
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Combining the general relativity and the uncertainty relation in quantum mechanics, the energy density of quantum fluctuations of space-time can be viewed as dark energy. The so-called agegraphic dark energy model is just based on this viewpoint, in which the age of the universe is introduced as the length measure. Recently, the new agegraphic dark energy model was proposed, where the dynamical dark energy is measured by the conformal age of the universe. On the other hand, scalar-field dark energy models like tachyons are often regarded as an effective description of some underlying theory of dark energy. In this paper, we show that the new agegraphic dark energy can be described completely by a tachyon scalar-field. We thus reconstruct the potential and the dynamics of the tachyon scalar-field, according to the evolution of the new agegraphic dark energy.
Qin Yi-Ping
Chin. Phys. B 2010, 19 (1): 019803;  doi: 10.1088/1674-1056/19/1/019803
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According to recent investigations of states of quantum fields, we postulate that there exist negative energy photons in the universe. With this assumption, we find a solution of Einstein's equation without introducing the cosmological constant. A new and sizable type Ia supernovae sample is employed to perform a fit with our model and the conventional model. Both models can well account for the current type Ia supernovae observation and they are not distinguishable. With the new model, the cause of the accelerated expansion of the universe and the mechanism of the negative pressure existing in outer space can be explained in ordinary physical terms.
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