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  • Trigger and control entanglement by atoms with different interaction times

    Ren Jie, Hao Xiang, Zhu Shi-Qun
    Chin. Phys. B 2007, 16 (3): 630-634
    The generation of the entanglement between two two-level atoms interacting with the third atom driven by white noise is investigated when the coupling between atoms is modulated by a pulse function. This paper finds that the initial triggering time and the width of the pulse can generate a peak in t...

Chin. Phys. B  
  Chin. Phys. B--2007, Vol.16, No.3
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Multifractal analysis of the Yellow River flows

Zang Bao-Jiang, Shang Peng-Jian
Chin. Phys., 2007, 16 (3): 565-569 doi: 10.1088/1009-1963/16/3/001
Full Text: [PDF 152 KB] (Downloads:956)
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This paper deals with time series of the Yellow River daily flows at Tongguan hydrological station, from the year 2000 to 2005. Power spectrum analysis and statistical moment scaling function on a range of scales revealed scaling qualities of the data. The partition function, which displayed a convex curvature, and the generalized dimension function showed that multifractality is presented. The singularity spectrum, which is single-humped, has shown strong multifractality degree.

Discrete variational principle and first integrals for Lagrange--Maxwell mechanico-electrical systems

Fu Jing-Li, Dai Gui-Dong, Salvador Jiménez, Tang Yi-Fa
Chin. Phys., 2007, 16 (3): 570-577 doi: 10.1088/1009-1963/16/3/002
Full Text: [PDF 162 KB] (Downloads:743)
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This paper presents a discrete variational principle and a method to build first-integrals for finite dimensional Lagrange--Maxwell mechanico-electrical systems with nonconservative forces and a dissipation function. The discrete variational principle and the corresponding Euler--Lagrange equations are derived from a discrete action associated to these systems. The first-integrals are obtained by introducing the infinitesimal transformation with respect to the generalized coordinates and electric quantities of the systems. This work also extends discrete Noether symmetries to mechanico-electrical dynamical systems. A practical example is presented to illustrate the results.

Asymptotic solution of a sea--air oscillator for ENSO mechanism

Mo Jia-Qi, Lin Wan-Tao, Wang Hui
Chin. Phys., 2007, 16 (3): 578-581 doi: 10.1088/1009-1963/16/3/003
Full Text: [PDF 95 KB] (Downloads:645)
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The EI Ni\~{n}o/La Ni\~{n}a--Southern Oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific ocean--atmosphere interactions. In this paper, a class of coupled system of the ENSO mechanism is considered. Based on a class of oscillator of ENSO model, the asymptotic solution of a corresponding problem is studied by employing the approximate method. It is proved from the results that the perturbation method can be used for analysing the sea surface temperature anomaly in the equatorial eastern Pacific and the thermocline depth anomaly of the atmosphere--ocean oscillation for the ENSO model.

The discrete variational principle and the first integrals of Birkhoff systems

Zhang Hong-Bin, Chen Li-Qun, Gu Shu-Long, Liu Chuan-Zhang
Chin. Phys., 2007, 16 (3): 582-587 doi: 10.1088/1009-1963/16/3/004
Full Text: [PDF 117 KB] (Downloads:633)
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This paper shows that first integrals of discrete equation of motion for Birkhoff systems can be determined explicitly by investigating the invariance properties of the discrete Pfaffian. The result obtained is a discrete analogue of theorem of Noether in the calculus of variations. An example is given to illustrate the application of the results.

Two types of loop algebras and their expanding Lax integrable models

Yue Chao, Zhang Yu-Feng, Wei Yuan
Chin. Phys., 2007, 16 (3): 588-594 doi: 10.1088/1009-1963/16/3/005
Full Text: [PDF 116 KB] (Downloads:478)
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Though various integrable hierarchies of evolution equations were obtained by choosing proper U in zero-curvature equation Ut-Vx+[U,V]=0, but in this paper, a new integrable hierarchy possessing bi-Hamiltonian structure is worked out by selecting V with spectral potentials. Then its expanding Lax integrable model of the hierarchy possessing a simple Hamiltonian operator \widetilde{J} is presented by constructing a subalgebra \widetilde{G } of the loop algebra \widetilde A2. As linear expansions of the above-mentioned integrable hierarchy and its expanding Lax integrable model with respect to their dimensional numbers, their (2+1)-dimensional forms are derived from a (2+1)-dimensional zero-curvature equation.

The Liouville integrable coupling system of the m-AKNS hierarchy and its Hamiltonian structure

Yue Chao, Yang Geng-Wen, Xu Yue-Cai
Chin. Phys., 2007, 16 (3): 595-598 doi: 10.1088/1009-1963/16/3/006
Full Text: [PDF 93 KB] (Downloads:470)
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In this paper a type of 9-dimensional vector loop algebra \tilde{F} is constructed, which is devoted to establish an isospectral problem. It follows that a Liouville integrable coupling system of the m-AKNS hierarchy is obtained by employing the Tu scheme, whose Hamiltonian structure is worked out by making use of constructed quadratic identity. The method given in the paper can be used to obtain many other integrable couplings and their Hamiltonian structures.

A series of non-Noether conservative quantities and Mei symmetries of nonconservative systems

Liu Hong-Ji, Fu Jing-Li, Tang Yi-Fa
Chin. Phys., 2007, 16 (3): 599-604 doi: 10.1088/1009-1963/16/3/007
Full Text: [PDF 119 KB] (Downloads:618)
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In this paper Mei symmetry is introduced for a nonconservative system. The necessary and sufficient condition for a Mei symmetry to be also a Lie symmetry is derived. It is proved that the Mei symmetry leads to a non-Noether conservative quantity via a Lie symmetry, and deduces a Lutzky conservative quantity via a Lie point symmetry.

Multi-component Dirac equation hierarchy and its multi-component integrable couplings system

Xia Tie-Cheng, You Fu-Cai
Chin. Phys., 2007, 16 (3): 605-610 doi: 10.1088/1009-1963/16/3/008
Full Text: [PDF 116 KB] (Downloads:829)
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A general scheme for generating a multi-component integrable equation hierarchy is proposed. A simple 3M-dimensional loop algebra \tilde{X} is produced. By taking advantage of \tilde{X}, a new isospectral problem is established and then by making use of the Tu scheme the multi-component Dirac equation hierarchy is obtained. Finally, an expanding loop algebra \tilde{F}M of the loop algebra \tilde{X} is presented. Based on the \tilde{F}M, the multi-component integrable coupling system of the multi-component Dirac equation hierarchy is investigated. The method in this paper can be applied to other nonlinear evolution equation hierarchies.

The extended trace identity and its application

Yao Yu-Qin, Chen Deng-Yuan
Chin. Phys., 2007, 16 (3): 611-620 doi: 10.1088/1009-1963/16/3/009
Full Text: [PDF 144 KB] (Downloads:528)
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The trace identity is extended to the general loop algebra. The Hamiltonian structures of the integrable systems concerning vector spectral problems and the multi-component integrable hierarchy can be worked out by using the extended trace identity. As its application, we have obtained the Hamiltonian structures of the Yang hierarchy, the Korteweg-de--Vries (KdV) hierarchy, the multi-component Ablowitz--Kaup--Newell--Segur (M-AKNS) hierarchy, the multi-component Ablowitz--Kaup--Newell--Segur Kaup--Newell (M-AKNS--KN) hierarchy and a new multi-component integrable hierarchy separately.

Quantum secure direct communication protocol with blind polarization bases and particles' transmitting order

Song Jie, Zhu Ai-Dong, Zhang Shou
Chin. Phys., 2007, 16 (3): 621-623 doi: 10.1088/1009-1963/16/3/010
Full Text: [PDF 82 KB] (Downloads:568)
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This paper presents a modified secure direct communication protocol by using the blind polarization bases and particles' random transmitting order. In our protocol, a sender (Alice) encodes secret messages by rotating a random polarization angle of particle and then the receiver (Bob) sends back these particles as a random sequence. This ensures the security of communication.

Probabilistic teleportation of an unknown N-atom state using a two-atom nonmaximally entangled state in cavity QED

Lin Xiu, Li Hong-Cai, Yang Rong-Can
Chin. Phys., 2007, 16 (3): 624-629 doi: 10.1088/1009-1963/16/3/011
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We present a scheme for realizing probabilistic teleportation of an unknown $N$-atom state via cavity QED. This scheme requires only a nonmaximally entangled pair to be used as a quantum channel, so the requirement of entanglement is reduced. In addition, our scheme does not involve the Bell-state measurement and is insensitive to the cavity decay, which is important from the experimental point of view. If the quantum channel is a two-atom maximally entangled state, teleportation of an unknown $N$-atom state can be realized by a simpler scheme via cavity QED.

Trigger and control entanglement by atoms with different interaction times Hot!

Ren Jie, Hao Xiang, Zhu Shi-Qun
Chin. Phys., 2007, 16 (3): 630-634 doi: 10.1088/1009-1963/16/3/012
Full Text: [PDF 208 KB] (Downloads:545)
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The generation of the entanglement between two two-level atoms interacting with the third atom driven by white noise is investigated when the coupling between atoms is modulated by a pulse function. This paper finds that the initial triggering time and the width of the pulse can generate a peak in the entanglement. There is an optimal width of the pulse for which the entanglement can reach a maximum. The asymmetry of the coupling between atoms can generate different entanglement in the system. The multiple triggers can generate multiple peaks in the entanglement. The separation between two peaks is increased as the width of the pulse is increased.

Remarks on interpretations of the E?tv?s experiment and misinterpretation of E=mc2

C. Y. Lo (Lu Zhong-Xian)
Chin. Phys., 2007, 16 (3): 635-639 doi: 10.1088/1009-1963/16/3/013
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The E\"{o}tv\"{o}s experiment on the verification of equivalence between inertial mass and gravitational mass of a body is famous for its accuracy. A question is, however, can these experimental results be applied to the case of a physical space in general relativity, where the space coordinates could be arbitrary? It is pointed out that it can be validly applied because it has been proven that Einstein's equivalence principle for a physical space must have a frame of reference with the Euclidean-like structure. Will claimed further that such an overall accuracy can be translated into an accuracy of the equivalence between inertial mass and each type of energy. It is shown that, according to general relativity, such a claim is incorrect. The root of this problem is due to an inadequate understanding of special relativity that produced the famous equation $E=mc^2$, which must be understood in terms of energy conservation. Concurrently, it is pointed out that this error is a problem in Will's book, `Theory and Experiment in Gravitational Physics'.

Scheme for entanglement concentration of unknown W class states via linear optics

Zhang Li-Hua, Dong Ping, Cao Zhuo-Liang
Chin. Phys., 2007, 16 (3): 640-643 doi: 10.1088/1009-1963/16/3/014
Full Text: [PDF 241 KB] (Downloads:649)
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This paper proposes a scheme for entanglement concentration of unknown triparticle $W$ class states with a certain probability. This protocol is mainly based on the coincidences of single-photon detectors and requires single-photon detectors and linear optical elements. The scheme is feasible within current technology.

The solution of the time-dependent Fokker--Planck equation of non-degenerate optical parametric amplification and its application to the optimum realization of EPR paradox

Zhao Chao-Ying, Tan Wei-Han
Chin. Phys., 2007, 16 (3): 644-649 doi: 10.1088/1009-1963/16/3/015
Full Text: [PDF 143 KB] (Downloads:496)
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In this paper, the solution of the time-dependent Fokker--Planck equation of non-degenerate optical parametric amplification is used to deduce the condition demonstrating the Einstein--Podolsky--Rosen (EPR) paradox. The analytics and numerical calculation show the influence of pump depletion on the error in the measurement of continuous variables. The optimum realization of EPR paradox can be achieved by adjusting the parameter of squeezing. This result is of practical importance when the realistic experimental conditions are taken into consideration.

Atomic population oscillations between two coupled Bose--Einstein condensates with time-dependent nonlinear interaction

Li Fei, Shu Wei-Xing, Luo Hai-Lu, Ren Zhong-Zhou
Chin. Phys., 2007, 16 (3): 650-659 doi: 10.1088/1009-1963/16/3/016
Full Text: [PDF 1058 KB] (Downloads:538)
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The atomic population oscillations between two Bose--Einstein condensates with time-dependent nonlinear interaction in a double-well potential are studied. We first analyse the stabilities of the system's steady-state solutions. And then in the perturbative regime, the Melnikov chaotic oscillation of atomic population imbalance is investigated and the Melnikov chaotic criterion is obtained. When the system is out of the perturbative regime, numerical calculations reveal that regulating the nonlinear parameter can lead the system to step into chaos via period doubling bifurcations. It is also numerically found that adjusting the nonlinear parameter and asymmetric trap potential can result in the running-phase macroscopic quantum self-trapping (MQST). In the presence of a weak asymmetric trap potential, there exists the parametric resonance in the system.

Chaos synchronization between two different 4D hyperchaotic Chen systems

Liu Yang-Zheng, Jiang Chang-Sheng, Lin Chang-Sheng, Jiang Yao-Mei
Chin. Phys., 2007, 16 (3): 660-665 doi: 10.1088/1009-1963/16/3/017
Full Text: [PDF 310 KB] (Downloads:988)
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This paper presents chaos synchronization between two different four-dimensional (4D) hyperchaotic Chen systems by nonlinear feedback control laws. A modified 4D hyperchaotic Chen system is obtained by changing the nonlinear function of the 4D hyperchaotic Chen system, furthermore, an electronic circuit to realize two different 4D hyperchaotic Chen systems is designed. With nonlinear feedback control method, chaos synchronization between two different 4D hyperchaotic Chen systems is achieved. Based on the stability theory, the functions of the nonlinear feedback control for synchronization of two different 4D hyperchaotic Chen systems is derived, the range of feedback gains is determined. Numerical simulations are shown to verify the theoretical results.

Adaptive synchronization of hyperchaotic Lü system with uncertainty

Gao Bing-Jian, Lu Jun-An
Chin. Phys., 2007, 16 (3): 666-670 doi: 10.1088/1009-1963/16/3/018
Full Text: [PDF 470 KB] (Downloads:697)
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This paper presents a novel adaptive control scheme for synchronization of the latest hyperchaotic Lü system. Based on the Lyapunov stability theory, a feedback controller and a parameter update law are designed for the synchronization of hyperchaotic L\"{u} systems with uncertainty. Numerical simulations are given to demonstrate the validity of the synchronization technique.

Electrostatic surface guiding of cold polar molecules with a single charged wire

Deng Lian-Zhong, Xia Yong, Yin Jian-Ping
Chin. Phys., 2007, 16 (3): 707-717 doi: 10.1088/1009-1963/16/3/025
Full Text: [PDF 1390 KB] (Downloads:605)
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This paper proposes a scheme to guide cold polar molecules by using a single charged wire half embanked in an insulating substrate and a homogeneous bias electric field, which is generated by a plate capacitor composed of two infinite parallel metal plates. The spatial distributions of the electrostatic field produced by the combination of the charged wire and the plate capacitor and the corresponding Stark potentials (including dipole forces) for metastable CO molecules are calculated, the relationships between the electric field and the parameters of our charged-wire layout are analysed. It also studies the influences of the insulator on the electric field distribution and the discharge effect. This study shows that the proposed scheme can be used to guide cold polar molecules in the weak-field -- seeking states, and to form various molecule-optical elements, such as molecular funnel, molecular beam-splitters and molecule interferometer, even to construct a variety of integrated molecule-optical elements and their molecule chips.

Phase control in an open Λ-type system with spontaneously generated coherence

Cui Ni, Fan Xi-Jun, Li Ai-Yun, Liu Cheng-Pu, Gong Shang-Qing, Xu Zhi-Zhan
Chin. Phys., 2007, 16 (3): 718-724 doi: 10.1088/1009-1963/16/3/026
Full Text: [PDF 192 KB] (Downloads:533)
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This paper investigates the control role of the relative phase between the probe and driving fields on the gain, dispersion and populations in an open \Lambda system with spontaneously generated coherence (SGC). It shows that by adjusting the value of the relative phase, a change from lasing with inversion to lasing without inversion can be realized; the values and frequency spectrum regions of the inversionless gain and dispersion can be obviously varied; high refractive index with zero absorption and electromagnetically induced transparency can be achieved. It is also found that when the driving field is resonant, the shapes of the dispersion and the gain curves versus the probe detuning are very similar if the relative phase of the dispersion lags \pi/2 than that of the gain, however for the off-resonant driving field the similarity will disappear; the gain, dispersion and populations are periodical functions of the relative phase, the modulation period is always 2\pi; the contribution of SGC to the inversionless gain and dispersion is much larger than that of the dynamically induced coherence.

Low-dimensional structures formed by irradiation of laser

Huang Wei-Qi, Liu Shi-Rong, Xu Li, Wu Ke-Yue, Qin Cao-Jian, Cai Sao-Hong
Chin. Phys., 2007, 16 (3): 725-729 doi: 10.1088/1009-1963/16/3/027
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Some kinds of low-dimensional nanostructures can be formed by irradiation of laser on the pure silicon sample and the SiGe alloy sample. This paper has studied the photoluminescence (PL) of the hole-net structure of silicon and the porous structure of SiGe where the PL intensity at 706nm and 725nm wavelength increases obviously. The effect of intensity-enhancing in the PL peaks cannot be explained within the quantum confinement alone. A mechanism for increasing PL emission in the above structures is proposed, in which the trap states of the interface between SiO2 and nanocrystal play an important role.

Significant improvement of OLED efficiency and stability by doping both HTL and ETL with different dopant in heterojunction of polymer/small-molecules

Nie Hai, Zhang Bo, Tang Xian-Zhong
Chin. Phys., 2007, 16 (3): 730-734 doi: 10.1088/1009-1963/16/3/028
Full Text: [PDF 158 KB] (Downloads:2499)
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This paper reports that the polymer/organic heterojunction doped light-emitting diodes using a novel poly-TPD as hole transport material and doping both hole transport layer and emitter layer with the highly fluorescent rubrene and DCJTB has been successfully fabricated. The basic structure of the heterostructure is PTPD/Alq3. When hole transport layer and electron transport layer are doped simultaneously with different dopant, the electroluminescence quantum efficiencies are about 3 times greater than that of the undoped device. Compared with undoped device and conventional TPD/Alq3 diode, the stability of the doping device is significantly improved. The process of emission for doped device may include carrier trapping as well as F\"{o}rster energy transfer.

Phenomena of optic-bound effect on fibre optic gyro

Song Ning-Fang, Zhang Chun-Xi, Jin Jing
Chin. Phys., 2007, 16 (3): 735-739 doi: 10.1088/1009-1963/16/3/029
Full Text: [PDF 173 KB] (Downloads:666)
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The optic-bound effect on fibre optic gyro (FOG) precision is analysed theoretically, and formulas describing the change of FOG light power under the action of optic-bound effect are given. It is confirmed that optic-bound effect is a main instantaneous non-reciprocity effect of FOG in addition to the Sagnac effect and can lead to a dynamic error of FOG in practical environments. An approach to suppressing or eliminating the error due to the optic-bound effect is presented and verified experimentally. The result shows that the approach is valid and the precision of FOG is improved observably.

Steering light into logic patterns with two-dimensional cascaded multimode waveguide

Zhou Hai-Feng, Yang Jian-Yi, Wang Ming-Hua, Jiang Xiao-Qing
Chin. Phys., 2007, 16 (3): 740-745 doi: 10.1088/1009-1963/16/3/030
Full Text: [PDF 571 KB] (Downloads:667)
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Steering light into logic patterns with two-dimensional cascaded multimode waveguide is demonstrated. By employing the imaging properties of 2D multimode interference (MMI) and partial phase modulation method, the design ideas and the implementing methods of the 2(2×2) bits type spatial logic steering are discussed; therefore the structure of logical pattern is proposed. Numerical simulation is carried out to verify the design in detail by using the beam propagation method. It is expected to realize logic coders by using the integrated optical methods and exploit their potential applications in the field of optical logic.

Acousto-electric well logging by eccentric source and extraction of shear wave

Cui Zhi-Wen, Wang Ke-Xie, Hu Heng-Shan, Sun Jian-Guo
Chin. Phys., 2007, 16 (3): 746-752 doi: 10.1088/1009-1963/16/3/031
Full Text: [PDF 204 KB] (Downloads:667)
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The nonaxisymmetric acousto-electric field excited by an eccentric acoustic source in the borehole based on Pride seismoelectric theory is considered. It is shown that the acoustic field inside the borehole, converted electric and magnetic fields and coupled fields outside the borehole are composed of an infinitude of multipole fields with different orders. The numerical results show that both the electromagnetic waves and the seismoelectric field in the borehole, and the three components of both electric field and magnetic field can be detected. Measurements on the borehole axis will be of advantage to determining shear velocity information. The components of the symmetric and nonsymmetric acoustic and electromagnetic fields can be strengthened or weakened by adding or subtracting the two full waveforms logged in some azimuths. It may be a new method of directly measuring the shear wave velocity by using the borehole seismoelectric effect.

Photodetachment cross section of S- in electric and magnetic fields

Wang De-Hua, Ding Shi-Liang
Chin. Phys., 2007, 16 (3): 671-674 doi: 10.1088/1009-1963/16/3/019
Full Text: [PDF 148 KB] (Downloads:553)
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In this paper, the quantum-mechanical photodetachment cross section of S- in uniform electric and magnetic fields at arbitrary angles is presented. It compares the quantum-mechanical cross section with the quantum source formalism cross section. The results show that at large angle, the two results have good agreements, however, with the decrease of the angles, they deviate obviously from each other. The reasons for this discrepancy are also discussed.

High-order harmonic generation spectrum of an excited one-dimensional Coulomb atom in an intense laser field

Zhou Zhao-Yan, Yuan Jian-Min
Chin. Phys., 2007, 16 (3): 675-679 doi: 10.1088/1009-1963/16/3/020
Full Text: [PDF 641 KB] (Downloads:714)
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Response of the wave packet of a one-dimensional Coulomb atom to an intense laser field is calculated using the symmetrized split operator fast Fourier method. The high-order harmonic generation (HHG) of the initial state separately being the ground and excited states is presented. When the hardness parameter \alpha in the soft Coulomb potential V(x)=-1/\sqrt{x^2+\alpha} is chosen to be small enough, the so-called hard Coulomb potential V(x)=-1/|x| can be obtained. It is well known that the hard one-dimensional Coulomb atom has an unstable ground state with an energy eigenvalue of $\sim0.5$ and it has no states corresponding to physical states in the true atoms, and has the first and second excited states being degenerate. The parity effects on the HHG can be seen from the first and second excited states of the hard one-dimensional Coulomb atom. The HHG spectra of the excited states from both the soft and hard Coulomb atom models are shown to have more complex structures and to be much stronger than the corresponding HHG spectrum of the ground state of the soft Coulomb model with $\alpha=2$ in the same laser field. Laser-induced non-resonant one-photon emission is also observed.

Ab initio calculations on the spectroscopic constants, vibrational levels and classical turning points for the 21u state of dimer 7Li2

Liu Yu-Fang, Sun Jin-Feng, Ma Heng, Zhu Zun-Lue
Chin. Phys., 2007, 16 (3): 680-685 doi: 10.1088/1009-1963/16/3/021
Full Text: [PDF 210 KB] (Downloads:584)
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The accurate dissociation energy and harmonic frequency for the highly excited 21\Piustate of dimer 7Li2 have been calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space. The calculated results are in excellent agreement with experimental measurements. The potential energy curves at numerous basis sets for this state are obtained over a wide internuclear separation range from about 2.4a0 to 37.0a0. And the conclusion is gained that the basis set 6-311++G(d,p) is a most suitable one. The calculated spectroscopic constants De, Re, {\omega }e, {\omega }e{\chi }e, {\alpha }e and Be at 6-311++G(d,p) are 0.9670~eV, 0.3125~{nm}, 238.6~{cm}-1, 1.3705~{cm}-1, 0.0039~{cm}-1 and 0.4921~{cm}-1, respectively. The vibrational levels are calculated by solving the radial Schr\"{o}dinger equation of nuclear motion. A total of 53 vibrational levels are found and reported for the first time. The classical turning points have been computed. Comparing with the measurements, in which only the first nine vibrational levels have been obtained so far, the present calculations are very encouraging. A careful comparison of the present results of the parameters De and {\omega }e with those obtained from previous theories clearly shows that the present calculations are much closer to the measurements than previous theoretical results, thus representing an improvement on the accuracy of the {\it ab initio} calculations of the potentials for this state.

Spin polarization effect for Mn2 molecule

Yan Shi-Ying, Xu Guo-Liang
Chin. Phys., 2007, 16 (3): 686-691 doi: 10.1088/1009-1963/16/3/022
Full Text: [PDF 367 KB] (Downloads:634)
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The density functional theory method (DFT) (b3p86) of Gaussian 03 has been used to optimize the structure of the Mn2 molecule. The result shows that the ground state of the Mn2 molecule is an 11-multiple state, indicating a spin polarization effect in the Mn2 molecule, a transition metal element molecule. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher-energy states. So the ground state for Mn2 molecule being of an 11-multiple state is the indicative of spin polarization effect of the Mn2 molecule among those in the transition metal elements: that is, there are 10 parallel spin electrons in a Mn2 molecule. The number of non-conjugated electrons is the greatest. These electrons occupy different spacious orbitals so that the energy of the Mn2 molecule is minimized. It can be concluded that the effect of parallel spin in the Mn2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state and other states of the Mn2 molecule are derived. The dissociation energy De for the ground state of the Mn2 molecule is 1.4477eV, equilibrium bond length Re is 0.2506nm, vibration frequency \omegae is 211.51cm-1. Its force constants f2, f3, and f4 are 0.7240aJ\cdotnm-2, -3.35574aJ\cdotnm-3, 11.4813aJ\cdotnm-4 respectively. The other spectroscopic data for the ground state of the Mn2 molecule \omega e\chie, Be, \alphae are 1.5301~cm-1, 0.0978~cm-1, 7.7825\times 10-4cm-1 respectively.

The closed-orbit and the photoabsorption spectra of the Rydberg hydrogen atom between two parallel metallic surfaces

Wang De-Hua
Chin. Phys., 2007, 16 (3): 692-699 doi: 10.1088/1009-1963/16/3/023
Full Text: [PDF 293 KB] (Downloads:606)
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Using the closed orbit theory, we study the classical motion and calculate the photoabsorption spectra of Rydberg hydrogen atom between two parallel metallic surfaces. The results show that the metallic surfaces have a significant effect on the photoabsorption process. When the distances between the hydrogen atom and the two metallic surfaces are close to a critical value dc, the number of the closed orbits is the greatest. When the distance larger or smaller than dc, the number of the closed orbits decreases and the absorption spectra are shown to exhibit a damping oscillation. This work is an interesting new application of closed-orbit theory and is of potential experimental interest.

Ab initio calculations for the absorption spectra and polarizabilities of small sulfur clusters

Bai Yu-Lin, Chen Xiang-Rong, Cheng Xiao-Hong, Yang Xiang-Dong
Chin. Phys., 2007, 16 (3): 700-706 doi: 10.1088/1009-1963/16/3/024
Full Text: [PDF 180 KB] (Downloads:776)
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Absorption spectra for S2 clusters (n=2\ldots8) are calculated using an adiabatic time-dependent density functional formalism within the local density approximation (LDA). We compare the calculated spectra with those computed using a simple LDA approach. The time-dependent LDA (TDLDA) spectra display a significant blue shift with respect to the LDA spectra. The calculated spectra present a variety of features that can be used for comparison with future experimental investigations. We also obtain a significant threshold absorption, which can distinguish between different ground states of the sulfur clusters. In addition, the polarizabilities of the clusters are calculated by using the higher-order finite-difference pseudopotential density functional method in real space. We find that the polarizabilities of the clusters considered are higher than the value estimated from the `hard sphere' model using the bulk static dielectric constant. The computed polarizabilities per atom tend to decrease with increasing cluster size. The polarizabilities are closely related to the HOMO--LUMO gaps and the geometrical configurations.

Characterization of doped hydrogenated nanocrystalline silicon films prepared by plasma enhanced chemical vapour deposition

Wang Jin-Liang, Wu Er-Xing
Chin. Phys., 2007, 16 (3): 848-853 doi: 10.1088/1009-1963/16/3/049
Full Text: [PDF 378 KB] (Downloads:545)
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The B- and P-doped hydrogenated nanocrystalline silicon films (nc-Si\jz{0.2ex}{:}H) are prepared by plasma-enhanced chemical vapour deposition (PECVD). The microstructures of doped nc-Si\jz{0.2ex}{:}H films are carefully and systematically characterized by using high resolution electron microscopy (HREM), Raman scattering, x-ray diffraction (XRD), Auger electron spectroscopy (AES), and resonant nucleus reaction (RNR). The results show that as the doping concentration of PH3 increases, the average grain size (d) tends to decrease and the crystalline volume percentage (Xc) increases simultaneously. For the B-doped samples, as the doping concentration of B2H\xj{6} increases, no obvious change in the value of d is observed, but the value of Xc is found to decrease. This is especially apparent in the case of heavy B2H2 doped samples, where the films change from nanocrystalline to amorphous.

Dynamic scaling behaviour of late-stage phase separation in Ni75AlxV25-x alloys

Li Yong-Sheng, Chen Zheng, Lu Yan-Li, Xu Guo-Dong
Chin. Phys., 2007, 16 (3): 854-861 doi: 10.1088/1009-1963/16/3/050
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The dynamic scaling behaviour of late-stage phase separation and coarsening mechanisms of L12 and D022 in Ni75AlxV25-x (3 \le x \le 10$, at.%) alloys are studied using the microscopic phase-field dynamic model. The microelasticity field is incorporated into the diffusion dynamic model. The results show the morphology and coarsening dynamics being greatly changed by the elastic interactions among different precipitates, the particles aligning along the dominant directions, the average domain size (ADS) of L12 and D022 deviating from the exponent of temporal power-law, and the growth slowing down due to the increasing of elastic interactions. The dynamic scaling regime of late-stage coarsening of the precipitates is attained. Thus the scaling behaviour of structure function is also applicable for elastic interaction systems. It is also found that the variations of ADS and scaling function depend on the volume fraction of precipitates.

Direct current hopping conductance along DNA chain

Ma Song-Shan, Xu Hui, Liu Xiao-Liang, Li Ming-Jun
Chin. Phys., 2007, 16 (3): 862-867 doi: 10.1088/1009-1963/16/3/051
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This paper proposes a model of direct current (DC) electron hopping transport in DNA, in which DNA is considered as a binary one-dimensional disordered system. To quantitatively study the DC conductivity in DNA, it numerically calculates the DC conductivity of DNA chains with different parameter values. The result shows that the DC conductivity of DNA chain increases with the increase of temperature. And the conductivity of DNA chain is depended on the probability p, which represents the degree of compositional disorder in a DNA sequence to some extent. For p<0.5, the conductivity of DNA chain decreases with the increase of p, while for p\geq0.5, the conductivity increases with the increase of p. The DC conductivity in DNA chain also varies with the change of the electric field, it presents non-Ohm's law conductivity characteristics.

The preferences of orientations between the pairs of amino acids

Chen Ying, Wang Jun, Wang Wei
Chin. Phys., 2007, 16 (3): 868-875 doi: 10.1088/1009-1963/16/3/052
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In this work, we make an investigation on the preferences of orientations between amino acids using the orientation defined based on the local geometry of the amino acids concerned. It is found that there are common preferences of orientations (70°, 30°}, 140°) and (110°, 340^{\circ}, 100°) for various pairs of amino acids. Different side chains may strengthen or weaken the common preferences, which is related to the effect of packing. Some amino acids having specific local flexibility may possess some preferences of orientations besides the common ones, such as (10°, 280°, 210°). Another analysis on the pairs of the amino acids with different secondary-structure preferences shows that the directional interaction may affect the distribution of orientation more effectively than the packing or local flexibility. All these results provide us some insight of the organization of amino acids in protein, and their relation with some related interactions.

Statistical analysis of aggregation in freeway traffic

Li Jun-Wei, Lin Bo-Liang, Huang Yong-Chang
Chin. Phys., 2007, 16 (3): 753-757 doi: 10.1088/1009-1963/16/3/032
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We restudy the master-equation approach to aggregation in freeway traffic based on the theory of birth--death process, in which the clustering behaviour in one-lane freeway traffic model is investigated. The transition probabilities for the jump processes are reconstructed by using Greenshields' model, and the equation of the mean size of the cluster at any time t is derived from the birth--death equation. Numerical experiments show the clustering behaviours varying with time very well.

Review of relaxation oscillations in plasma processing discharges

Zhou Zhu-Wen, M. A. Lieberman, Sungjin Kim
Chin. Phys., 2007, 16 (3): 758-765 doi: 10.1088/1009-1963/16/3/033
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Relaxation oscillations due to plasma instabilities at frequencies ranging from a few Hz to tens of kHz have been observed in various types of plasma processing discharges. Relaxation oscillations have been observed in electropositive capacitive discharges between a powered anode and a metallic chamber whose periphery is grounded through a slot with dielectric spacers. The oscillations of time-varying optical emission from the main discharge chamber show, for example, a high-frequency (\sim 40~kHz) relaxation oscillation at 13.33Pa, with an absorbed power being nearly the peripheral breakdown power, and a low-frequency ( \sim 3 Hz) oscillation, with an even higher absorbed power. The high-frequency oscillation is found to ignite plasma in the slot, but usually not in the peripheral chamber. The kilohertz oscillations are modelled using an electromagnetic model of the slot impedance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations, and indicate a variety of behaviours dependent on the matching conditions. In low-pressure inductive discharges, oscillations appear in the transition between low-density capacitively driven and high-density inductively driven discharges when attaching gases such as SF6 and Ar/SF6 mixtures are used. Oscillations of charged particles, plasma potential, and light, at frequencies ranging from a few Hz to tens of kHz, are seen for gas pressures between 0.133 Pa and 13.33 Pa and discharge powers in a range of 75--1200 W. The region of instability increases as the plasma becomes more electronegative, and the frequency of plasma oscillation increases as the power, pressure, and gas flow rate increase. A volume-averaged (global) model of the kilohertz instability has been developed; the results obtained from the model agree well with the experimental observations.

Theoretical analysis of a relativistic travelling wave tube filled with plasma

Xie Hong-Quan, Liu Pu-Kun
Chin. Phys., 2007, 16 (3): 766-771 doi: 10.1088/1009-1963/16/3/034
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A cold and uniform plasma-filled travelling wave tube with sinusoidally corrugated slow wave structure is driven by a finite thick annular intense relativistic electron beam with the entire system immersed in a strong longitudinal magnetic field. By means of the linear field theory, the dispersion relation for the relativistic travelling wave tube (RTWT) is derived. By numerical computation, the dispersion characteristics of the RTWT are analysed in different cases of various geometric parameters of the slow wave structure and plasma densities. Also the gain versus frequency for three different plasma densities and the peak gain of the tube versus plasma density are analysed. Some useful results are obtained on the basis of the discussion.

Experimental study on imploding characteristics of wire-array Z pinches on Qiangguang-1 facility

Wang Zhen, Xu Rong-Kun, Yang Jian-Lun, Hua Xin-Sheng, Li Lin-Bo, Xu Ze-Ping, Ning Jia-Min, Song Feng-Jun
Chin. Phys., 2007, 16 (3): 772-777 doi: 10.1088/1009-1963/16/3/035
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To investigate the imploding characteristics of cylindrical wire array, experiments with load current varying from 1.5\,MA to 1.7\,MA were carried out on the Qiangguang-1 facility. The complicated temporal-spatial distribution of x-ray radiation was measured by the one-dimensional (1D) x-ray imaging system. Other diagnostic equipments including the x-ray power meter (XRPM) and the time-integrated pinhole camera were used to record time-resolved x-ray power pulse and pinhole x-ray images. Analysis shows that the fast leading edge of the local x-ray radiation pulse is of primary importance in sharpening x-ray power pulse rather than the temporal synchrony and the spatial uniformity of implosion. Experimental results indicated that the better axial imploding synchrony, the faster the increase of x-ray power for an array consisting of 32 tungsten wires of 5\mum diameter than for the others, and the higher the x-ray radiation power with maximal convergence ratio (r_0/r_1) of 10.5. A `zipper-like' effect of x-ray radiation extending from the anode to the cathode was also observed.

Experimental study of polarity dependence in repetitive nanosecond-pulse breakdown

Shao Tao, Sun Guang-Sheng, Yan Ping, Wang Jue, Yuan Wei-Qun, Zhang Shi-Chang
Chin. Phys., 2007, 16 (3): 778-783 doi: 10.1088/1009-1963/16/3/036
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Pulsed breakdown of dry air at ambient pressure has been investigated in the point-plane geometry, using repetitive nanosecond pulses with 10 ns risetime, 20--30 ns duration, and up to 100 kV amplitude. A major concern in this paper is to study the dependence of breakdown strength on the point-electrode polarity. Applied voltage, breakdown current and repetitive stressing time are measured under the experimental conditions of some variables including pulse voltage peak, gap spacing and repetition rate. The results show that increasing the E-field strength can decrease breakdown time lag, repetitive stressing time and the number of applied pulses as expected. However, compared with the traditional polarity dependence it is weakened and not significant in the repetitive nanosecond-pulse breakdown. The ambiguous polarity dependence in the experimental study is involved with an accumulation effect of residual charges and metastable states. Moreover, it is suggested that the reactions associated with the detachment of negative ions and impact deactivation of metastable species could provide a source of primary initiating electrons for breakdown.

Determination of the sites of Fe atoms in Fe-substituted Mn12

Cao Hui-Bo, Chen Dong-Liang, He Lun-Hua, Zhang Jun-Rong, Wang Fang-Wei, Wu Zi-Yu, Yan Qi-Wei
Chin. Phys., 2007, 16 (3): 784-787 doi: 10.1088/1009-1963/16/3/037
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In this paper neutron diffraction experiments were performed for Fe-substituted Mn12 in order to determine the sites of Fe atoms. The results of structure refinements for the sample with our accessed highest Fe content showed that all Fe atoms occupied Mn(3) sites in the Mn12 skeleton. The x-ray absorption fine structure experiments as well as multiple scattering simulations gave the same result. Thus we concluded that Fe atoms only occupied Mn(3) sites. This conclusion also means that Fe-substituted Mn12 series only includes the four single-molecule magnets of [Mn12-xFexO12(CH3COO)16(H2O)4]\cdot 2CH3COOH\cdot 4H2O (x = 1, 2, 3, and 4), denoted by Mn11Fe1, Mn10Fe2, Mn9Fe3, and Mn8Fe4, respectively.

Composition-induced structural modifications in the quaternary CuIn1-xGaxSe2 thin films:bond properties versus Ga content

Xu Chuan-Ming, Sun Yun, Li Feng-Yan, Zhang Li, Xue Yu-Ming, He Qing, Liu Hong-Tu
Chin. Phys., 2007, 16 (3): 788-794 doi: 10.1088/1009-1963/16/3/038
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In this paper the dependence of structural properties of the quaternary CuIn1-xGaxSe2 films with tetragonal structure on the Ga content has been systematically investigated by Raman scattering and x-ray diffraction spectra. The shift of the dominant Ax mode, unlike the lattice constants, does not follow the linear Vegard law with increasing Ga content x, whereas exhibits approximately polynomial change from 174\,cm-1 for CuInSe2 to 185cm-1 for CuGaSe2. Such behaviour should be indicative of presence of the asymmetric distribution of Ga and In on a microscopic scale in the films, due to Ga addition. The changes in the tetragonal distortion \eta lead to a significant variation in the anion displacement parameter U, which should be responsible for the evolution of bond parameters and resultant Raman bands with x.

Charge storage characteristics of hydrogenated nanocrystalline silicon film prepared by rapid thermal annealing

Li Zhi-Gang, Long Shi-Bing, Liu Ming, Wang Cong-Shun, Jia Rui, Lv Jin, Shi Yi
Chin. Phys., 2007, 16 (3): 795-798 doi: 10.1088/1009-1963/16/3/039
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The early stages of hydrogenated nanocrystalline silicon (nc-Si:H) films deposited by plasma-enhanced chemical vapour deposition were characterized by atomic force microscopy. To increase the density of nanocrystals in the nc-Si:H films, the films were annealed by rapid thermal annealing (RTA) at different temperatures and then analysed by Raman spectroscopy. It was found that the recrystallization process of the film was optimal at around 1000℃. The effects of different RTA conditions on charge storage were characterized by capacitance--voltage measurement. Experimental results show that nc-Si:H films obtained by RTA have good charge storage characteristics for nonvolatile memory.

The microwave response of MgB2/Al2O3 superconducting thin films

Shi Li-Bin, Wang Yun-Fei, Ke Yu-Yang, Zhang Guo-Hua, Luo Sheng, Zhang Xue-Qiang, Li Chun-Guang, Li Hong, He Yu-Sheng, Yu Zeng-Qiang, Wang Fu-Ren
Chin. Phys., 2007, 16 (3): 799-804 doi: 10.1088/1009-1963/16/3/040
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Microwave characteristics of MgB2/2O3 superconducting thin films were investigated by coplanar resonator technique. The thin films studied have different grain sizes resulting from different growth techniques. The experimental results can be described very well by a grain-size model which combines coplanar resonator theory and Josephson junction network model. It was found that the penetration depth and surface resistance of thin films with smaller grain sizes are larger than those of thin films with larger grain sizes.

Investigation on stability of directionally solidified CBr4--C2Cl6 lamellar eutectic by using multiphase field simulation

Zhu Yao-Chan, Wang Jin-Cheng, Yang Gen-Cang, Zhao Da-Wen
Chin. Phys., 2007, 16 (3): 805-811 doi: 10.1088/1009-1963/16/3/041
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With the multiphase field method, the stability of lamellar basic state is investigated during the directional solidification of eutectic alloy CBr4--C2Cl6. A great number of lamellar patterns observed in experiments are simulated, and a stability diagram for lamellar pattern selections is presented. The simulated growth behaviours of these patterns are found to be qualitatively consistent with Karma \textit{et al}'s numerical calculations and experimental results. The formation of the primary instability is attributed to the destabilization of solute boundary layer.

Corner effects in double-gate/gate-all-around MOSFETs

Hou Xiao-Yu, Zhou Fa-Long, Huang Ru, Zhang Xing
Chin. Phys., 2007, 16 (3): 812-816 doi: 10.1088/1009-1963/16/3/042
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Two kinds of corner effects existing in double-gate (DG) and gate-all-around (GAA) MOSFETs have been investigated by three-dimensional (3D) and two-dimensional (2D) simulations. It is found that the corner effect caused by conterminous gates, which is usually deemed to deteriorate the transistor performance, does not always play a negative role in GAA transistors. It can suppress the leakage current of transistors with low channel doping, though it will enhance the leakage current at high channel doping. The study of another kind of corner effect, which exists in the corner at the bottom of the silicon pillar of DG/GAA vertical MOSFETs, indicates that the D-top structure with drain on the top of the device pillar of vertical transistor shows great advantage due to lower leakage current and better DIBL (drain induced barrier lowering) effect immunity than the S-top structure with source on the top of the device pillar. Therefore the D-top structure is more suitable when the requirement in leakage current and short channel character is critical.

Comparison of two kinds of active layers for high-power narrow-stripe distributed feedback laser diodes

Fu Sheng-Hui, Song Guo-Feng, Chen Liang-Hui
Chin. Phys., 2007, 16 (3): 817-820 doi: 10.1088/1009-1963/16/3/043
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Usually GaAs/AlGaAs is utilized as an active layer material in laser diodes operating in the spectral range of 800--850 nm. In this work, in addition to a traditional unstrained GaAs/AlGaAs distributed feedback (DFB) laser diode, a compressively strained InGaAlAs/AlGaAs DFB laser diode is numerically investigated in characteristic. The simulation results show that the compressively strained DFB laser diode has a lower transparency carrier density, higher gain, lower Auger recombination rate, and higher stimulated recombination rate, which lead to better a device performance, than the traditional unstrained GaAs/AlGaAs DFB laser diode.

Hot-carrier degradation for 90nm gate length LDD-NMOSFET with ultra-thin gate oxide under low gate voltage stress

Chen Hai-Feng, Hao Yue, Ma Xiao-Hua, Li Kang, Ni Jin-Yu
Chin. Phys., 2007, 16 (3): 821-825 doi: 10.1088/1009-1963/16/3/044
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The hot-carrier degradation for 90~nm gate length lightly-doped drain (LDD) NMOSFET with ultra-thin (1.4~nm) gate oxide under the low gate voltage (LGV) (at Vg=Vth, where Vth is the threshold voltage) stress has been investigated. It is found that the drain current decreases and the threshold voltage increases after the LGV (Vg=Vth stress. The results are opposite to the degradation phenomena of conventional NMOSFET for the case of this stress. By analysing the gate-induced drain leakage (GIDL) current before and after stresses, it is confirmed that under the LGV stress in ultra-short gate LDD-NMOSFET with ultra-thin gate oxide, the hot holes are trapped at interface in the LDD region and cannot shorten the channel to mask the influence of interface states as those in conventional NMOSFET do, which leads to the different degradation phenomena from those of the conventional NMOS devices. This paper also discusses the degradation in the 90~nm gate length LDD-NMOSFET with 1.4~nm gate oxide under the LGV stress at Vg=Vth with various drain biases. Experimental results show that the degradation slopes (n) range from 0.21 to 0.41. The value of n is less than that of conventional MOSFET (0.5-0.6) and also that of the long gate length LDD MOSFET (\sim0.8).

The upper critical field in two-band layered superconductors

Liu Min-Xia, Gan Zi-Zhao
Chin. Phys., 2007, 16 (3): 826-833 doi: 10.1088/1009-1963/16/3/045
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The upper critical field of clean MgB2 is investigated using the two-band layered Ginzburg--Landau (GL) theory. The calculated results are fitted to the experimental data of clean MgB2 crystal very well in a broad temperature range. Based on the GL theory for clean superconductors, a phenomenological theory for dirty superconductor is proposed. Selecting appropriate parameters, two-band layered GL theory is successfully applied to the crystal of Mg(B1-xCx)2 and the neutron irradiation samples of MgB2.

Energy spectrum and entanglement of two tunnel- coupled Bose--Einstein condensates

Cheng Rong, Liang Jiu-Qing
Chin. Phys., 2007, 16 (3): 834-839 doi: 10.1088/1009-1963/16/3/046
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This paper obtains the energy-spectrum and eigenstate corrections of two-mode Bose--Einstein condensates (BECs) coupled by quantum tunnelling by perturbation method in both strong and weak tunnelling regions. The population imbalance between two BECs are then studied in terms of the low-lying eigenstates which also characterize the intrinsic entanglement between the two-mode BECs. The strong parity effect in the weak tunnelling region is also investigated.

Reversal transient laser-induced voltages in La2/3Ca1/3MnO3 films

Zhao Kun, He Meng, Lü Hui-Bin
Chin. Phys., 2007, 16 (3): 840-842 doi: 10.1088/1009-1963/16/3/047
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This paper reports that the transient laser-induced voltages have been observed in La2/3Ca1/3MnO3 thin films on MgO (001) in the absence of an applied current. A peak voltage of \sim 0.15 V was detected in response to 0.015 J pulse of 308 nm laser. It is demonstrated that the signal polarity is reversed when the films are irradiated through the substrate rather than at the air/film interface. Off-diagonal thermoelectricity may support the inversion of the signal when the irradiation direction is reversed.

Electron emission degradation of nano-structured sp2-bonded amorphous carbon films

Lu Zhan-Ling, Wang Chang-Qing, Jia Yu, Zhang Bing-Lin, Yao Ning
Chin. Phys., 2007, 16 (3): 843-847 doi: 10.1088/1009-1963/16/3/048
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The initial field electron emission degradation behaviour of original nano-structured sp2-bonded amorphous carbon films has been observed, which can be attributed to the increase of the work function of the film in the field emission process analysed using a Fowler--Nordheim plot. The possible reason for the change of work function is suggested to be the desorption of hydrogen from the original hydrogen termination film surface due to field emission current-induced local heating.For the explanation of the emission degradation behaviour of the nano-structured sp2-bonded amorphous carbon film, a cluster model with a series of graphite (0001) basal surfaces has been presented, and the theoretical calculations have been performed to investigate work functions of graphite (0001) surfaces with different hydrogen atom and ion chemisorption sites by using first principles method based on density functional theory-local density approximation.

The parameters of binary black hole system in PKS 1510-089

Li Juan, Fan Jun-Hui, Yuan Yu-Hai
Chin. Phys., 2007, 16 (3): 876-880 doi: 10.1088/1009-1963/16/3/053
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Observations of PKS 1510-089 indicate the existence of a deep flux minimum with a timescale of \sim 35 min and an interval of about 336±14 d. A binary black hole system is proposed to be at the nucleus of this object. The secondary black hole orbits around the primary black hole. The minimum is caused by the periodic eclipse of the primary black hole by the secondary black hole. Based on the observations of PKS 1510-089, we estimate the parameters of the binary black hole system. The masses for the primary and secondary black holes are 1. 37×109M_{\odot} (M_{\odot} is the solar mass) and 1. 37 \times 107M_{\odot} , and the major axis for this pair being about 0.1 parsec(pc).
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