Table of contents

20 November 2007, Volume 16 Issue 11 Previous issue    Next issue

RAPID COMMUNICATION

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Formation of graphene on Ru(0001) surface Pan Yi(潘毅), Shi Dong-Xia(时东霞), and Gao Hong-Jun(高鸿钧) Chinese Physics, 2007, 16 (11):  3151-3153.  DOI: 10.1088/1009-1963/16/11/001 Abstract ( 2032 )   PDF (873KB) ( 975 )   We report on the formation of a graphene monolayer on a Ru(0001) surface by annealing the Ru(0001) crystal. The samples are characterized by scanning tunnelling microscopy (STM) and Auger electron spectroscopy (AES). STM images show that the Moiré pattern is caused by the graphene layer mismatched with the underlying Ru(0001) surface and has an $N\times N$ superlattice. It is further found that the graphene monolayer on a Ru(0001) surface is very stable at high temperatures. Our results provide a simple and convenient method to produce a graphene monolayer on the Ru(0001) surface, which is used as a template for fabricating functional nanostructures needed in future nano devices and catalysis.

GENERAL

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An algorithm and its application for obtaining some kind of infinite-dimensional Hamiltonian canonical formulation Ren Wen-Xiu(任文秀) and Alatancang(阿拉坦仓) Chinese Physics, 2007, 16 (11):  3154-3160.  DOI: 10.1088/1009-1963/16/11/002 Abstract ( 1683 )   PDF (129KB) ( 652 )   Using factorization viewpoint of differential operator, this paper discusses how to transform a nonlinear evolution equation to infinite-dimensional Hamiltonian linear canonical formulation. It proves a sufficient condition of canonical factorization of operator, and provides a kind of mechanical algebraic method to achieve canonical ` $\partial/\partial x$'-type expression, correspondingly. Then three examples are given, which show the application of the obtained algorithm. Thus a novel idea for inverse problem can be derived feasibly.

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Conserved quantities and symmetries related to stochastic Hamiltonian systems Shang Mei(尚玫) and Mei Feng-Xiang (梅凤翔) Chinese Physics, 2007, 16 (11):  3161-3167.  DOI: 10.1088/1009-1963/16/11/003 Abstract ( 1712 )   PDF (194KB) ( 692 )   In this paper symmetries and conservation laws for stochastic dynamical systems are discussed in detail. Determining equations for infinitesimal approximate symmetries of Ito and Stratonovich dynamical systems are derived. It shows how to derive conserved quantities for stochastic dynamical systems by using their symmetries without recourse to Noether's theorem.

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Hojman conserved quantity for nonholonomic systems of unilateral non-Chetaev type in the event space Jia Li-Qun(贾利群), Zhang Yao-Yu(张耀宇), and Luo Shao-Kai(罗绍凯) Chinese Physics, 2007, 16 (11):  3168-3175.  DOI: 10.1088/1009-1963/16/11/004 Abstract ( 1367 )   PDF (133KB) ( 513 )   Hojman conserved quantities deduced from the special Lie symmetry, the Noether symmetry and the form invariance for a nonholonomic system of the unilateral non-Chetaev type in the event space are investigated. The differential equations of motion of the system above are established. The criteria of the Lie symmetry, the Noether symmetry and the form invariance are given and the relations between them are obtained. The Hojman conserved quantities are gained by which the Hojman theorem is extended and applied to the nonholonomic system of the unilateral non-Chetaev type in the event space. An example is given to illustrate the application of the results.

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Lie symmetrical perturbation and adiabatic invariants of generalized Hojman type for Lagrange systems Luo Shao-Kai(罗绍凯), Chen Xiang-Wei(陈向炜), and Guo Yong-Xin(郭永新) Chinese Physics, 2007, 16 (11):  3176-3181.  DOI: 10.1088/1009-1963/16/11/005 Abstract ( 1561 )   PDF (118KB) ( 773 )   Based on the invariance of differential equations under infinitesimal transformations of group, Lie symmetries, exact invariants, perturbation to the symmetries and adiabatic invariants in form of non-Noether for a Lagrange system are presented. Firstly, the exact invariants of generalized Hojman type led directly by Lie symmetries for a Lagrange system without perturbations are given. Then, on the basis of the concepts of Lie symmetries and higher order adiabatic invariants of a mechanical system, the perturbation of Lie symmetries for the system with the action of small disturbance is investigated, the adiabatic invariants of generalized Hojman type for the system are directly obtained, the conditions for existence of the adiabatic invariants and their forms are proved. Finally an example is presented to illustrate these results.

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Noether symmetry and non-Noether conserved quantity of the relativistic holonomic nonconservative systems in general Lie transformations Luo Shao-Kai(罗绍凯) Chinese Physics, 2007, 16 (11):  3182-3186.  DOI: 10.1088/1009-1963/16/11/006 Abstract ( 1560 )   PDF (103KB) ( 565 )   For a relativistic holonomic nonconservative system, by using the Noether symmetry, a new non-Noether conserved quantity is given under general infinitesimal transformations of groups. On the basis of the theory of invariance of differential equations of motion under general infinitesimal transformations, we construct the relativistic Noether symmetry, Lie symmetry and the condition under which the Noether symmetry is a Lie symmetry under general infinitesimal transformations. By using the Noether symmetry, a new relativistic non-Noether conserved quantity is given which only depends on the variables $t$, $q_s $ and $\dot{q}_s $. An example is given to illustrate the application of the results.

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Exact periodic wave and soliton solutions in two-component Bose--Einstein condensates Li Hua-Mei (李画眉) Chinese Physics, 2007, 16 (11):  3187-3191.  DOI: 10.1088/1009-1963/16/11/007 Abstract ( 1492 )   PDF (97KB) ( 697 )   We present several families of exact solutions to a system of coupled nonlinear Schr?dinger equations. The model describes a binary mixture of two Bose--Einstein condensates in a magnetic trap potential. Using a mapping deformation method, we find exact periodic wave and soliton solutions, including bright and dark soliton pairs.

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Exact solutions for four coupled complex nonlinear differential equations Hu Jian-Lan(胡建兰) Chinese Physics, 2007, 16 (11):  3192-3196.  DOI: 10.1088/1009-1963/16/11/008 Abstract ( 1765 )   PDF (101KB) ( 565 )   In this paper, exact solutions are derived for four coupled complex nonlinear different equations by using simplified transformation method and algebraic equations.

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The stability of Bose--Einstein condensates in a two-dimensional shallow trap Zhou Xiao-Yan(周小燕), Mu Ai-Xia(穆爱霞), and Xue Ju-Kui(薛具奎) Chinese Physics, 2007, 16 (11):  3197-3203.  DOI: 10.1088/1009-1963/16/11/009 Abstract ( 1618 )   PDF (740KB) ( 2199 )   The stability of Bose--Einstein condensates (BECs) loaded into a two-dimensional shallow harmonic potential well is studied. By using the variational method, the ground state properties for interacting BECs in the shallow trap are discussed. It is shown that the possible stable bound state can exist. The depth of the shallow well plays an important role in stabilizing the BECs. The stability of BECs in the shallow trap with the periodic modulating of atom interaction by using the Feshbach resonance is also discussed. The results show that the collapse and diffusion of BECs in a shallow trap can be controlled by the temporal modulation of the scattering length.

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Remote interactions between two d -dimensional distributed quantum systems: nonlocal generalized quantum control-NOT gate and entanglement swapping Chen Li-Bing(陈立冰), Lu Hong(路洪), and Jin Rui-Bo(金瑞博) Chinese Physics, 2007, 16 (11):  3204-3211.  DOI: 10.1088/1009-1963/16/11/010 Abstract ( 1720 )   PDF (130KB) ( 569 )   We present a systematic simple method to implement a generalized quantum control-NOT (CNOT) gate on two $d$-dimensional distributed systems. First, we show how the nonlocal generalized quantum CNOT gate can be implemented with unity fidelity and unity probability by using a maximally entangled pair of qudits as a quantum channel. We also put forward a scheme for probabilistically implementing the nonlocal operation with unity fidelity by employing a partially entangled qudit pair as a quantum channel. Analysis of the scheme indicates that the use of partially entangled quantum channel for implementing the nonlocal generalized quantum CNOT gate leads to the problem of `the general optimal information extraction'. We also point out that the nonlocal generalized quantum CNOT gate can be used in the entanglement swapping between particles belonging to distant users in a communication network and distributed quantum computer.

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Gravitational frequency-shift and deflection of light by quintessence Chen Ju-Hua(陈菊华) and Wang Yong-Jiu(王永久) Chinese Physics, 2007, 16 (11):  3212-3215.  DOI: 10.1088/1009-1963/16/11/011 Abstract ( 1434 )   PDF (175KB) ( 561 )   In this paper we investigate the gravitational frequency-shift and deflection of light in the Schwarzschild black hole space-time surrounded by quintessence. With the analytical and numerical methods, we find that the gravitational frequency-shift of light in the Schwarzschild black hole space-time surrounded by the quintessence increases as the values of the normalization factor $c$ increases, but the gravitational frequency-shift of light decreases with the quintessential state parameter $ \omega_{\rm q}$ increasing. We also calculate the deflection of light by quintessence and find that the deflection rate decreases as the values of the quintessential parameters $c$ and $ \omega_{\rm q}$ increase.

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Density fluctuation of the 3He reaction--diffusion model in nonextensive statistical mechanics Wu Jun-Lin(吴俊林) and Huang Xin-Min(黄新民) Chinese Physics, 2007, 16 (11):  3216-3219.  DOI: 10.1088/1009-1963/16/11/012 Abstract ( 1493 )   PDF (103KB) ( 440 )   In this paper the time-space correlation of density fluctuation of the 3He reaction–diffusion model is investigated where the equilibrium distribution is described by the generalized Maxwell–Boltzmann distribution in the framework of Tsallis statistics. By using the density operator technique, the nonextensive pressure effect is introduced into the master equation and thus the generalized master equation is derived for the nonextensive system. This paper uses the 3He reaction–diffusion model to analyse the effect of nonextensive pressure on the fluctuation and finds that the nonextensive parameter q plays a very important role in determining the characteristics of the fluctuation waves.

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The improved local linear prediction of chaotic time series Meng Qing-Fang(孟庆芳), Peng Yu-Hua(彭玉华), and Sun Jia(孙佳) Chinese Physics, 2007, 16 (11):  3220-3225.  DOI: 10.1088/1009-1963/16/11/013 Abstract ( 1405 )   PDF (1718KB) ( 852 )   Based on the Bayesian information criterion, this paper proposes the improved local linear prediction method to predict chaotic time series. This method uses spatial correlation and temporal correlation simultaneously. Simulation results show that the improved local linear prediction method can effectively make multi-step and one-step prediction of chaotic time series and the multi-step prediction performance and one-step prediction accuracy of the improved local linear prediction method are superior to those of the traditional local linear prediction method.

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New scheme of anticipating synchronization for arbitrary anticipation time and its application to long-term prediction of chaotic states Sun Zhong-Kui(孙中奎), Xu Wei (徐伟), and Yang Xiao-Li(杨晓丽) Chinese Physics, 2007, 16 (11):  3226-3230.  DOI: 10.1088/1009-1963/16/11/014 Abstract ( 1996 )   PDF (351KB) ( 3557 )   How to predict the dynamics of nonlinear chaotic systems is still a challenging subject with important real-life applications. The present paper deals with this important yet difficult problem via a new scheme of anticipating synchronization. A global, robust, analytical and delay-independent sufficient condition is obtained to guarantee the existence of anticipating synchronization manifold theoretically in the framework of the Krasovskii– yapunov theory. Different from ‘traditional techniques (or regimes)’ proposed in the previous literature, the present scheme guarantees that the receiver system can synchronize with the future state of a transmitter system for an arbitrarily long anticipation time, which allows one to predict the dynamics of chaotic transmitter at any point of time if necessary. Also it is simple to implement in practice. A classical chaotic system is employed to demonstrate the application of the proposed scheme to the long-term prediction of chaotic states.

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Adaptive projective synchronization of unified chaotic systems and its application to secure communication Hu Man-Feng(胡满峰) and Xu Zhen-Yuan(徐振源 ) Chinese Physics, 2007, 16 (11):  3231-3237.  DOI: 10.1088/1009-1963/16/11/015 Abstract ( 1934 )   PDF (1018KB) ( 831 )   In this paper, a simple adaptive linear feedback control method is proposed for controlling the scaling factor between two coupled unified chaotic systems to a desired value, based on the invariance principle of differential equations. Under this control strategy, one can arbitrarily select the scaling factor. Numerical simulations are given to support the effectiveness of the proposed method and show the robustness against noise. Furthermore, a secure communication scheme based on the adaptive projective synchronization of unified chaotic systems is presented and numerical simulation shows its feasibility.

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A novel hyperchaos evolved from three dimensional modified Lorenz chaotic system Wang Fan-Zhen(王繁珍), Chen Zeng-Qiang(陈增强), Wu Wen-Juan(吴文娟), and Yuan Zhu-Zhi(袁著祉) Chinese Physics, 2007, 16 (11):  3238-3243.  DOI: 10.1088/1009-1963/16/11/016 Abstract ( 1853 )   PDF (2457KB) ( 1939 )   This paper reports a new four-dimensional continuous autonomous hyperchaos generated from the Lorenz chaotic system by introducing a nonlinear state feedback controller. Some basic properties of the system are investigated by means of Lyapunov exponent spectrum and bifurcation diagrams. By numerical simulating, this paper verifies that the four-dimensional system can evolve into periodic, quasi-periodic, chaotic and hyperchaotic behaviours. And the new dynamical system is hyperchaotic in a large region. In comparison with other known hyperchaos, the two positive Lyapunov exponents of the new system are relatively more larger. Thus it has more complex degree.

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Adaptive robust control of chaotic oscillations in power system with excitation limits Wei Du-Qu(韦笃取) and Luo Xiao-Shu(罗晓曙) Chinese Physics, 2007, 16 (11):  3244-3248.  DOI: 10.1088/1009-1963/16/11/017 Abstract ( 1719 )   PDF (474KB) ( 903 )   With system parameters falling into a certain area, power system with excitation limits experiences complicated chaotic oscillations which threaten the secure and stable operation of power system. In this paper, to control these unwanted chaotic oscillations, a straightforward adaptive chaos controller based on Lyapunov asymptotical stability theory is designed. Since the presented controller does not need to change the controlled system structure and not to use any information of system except the system state variables, the designed controller is simple and desirable. Simulation results show that the proposed control law is very effective. This work is helpful to maintain the power system’s security operation.

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Synchronization between two different noise-perturbed chaotic systems with unknown parameters Jia Fei-Lei (贾飞蕾), Xu Wei (徐伟), and Du Lin (都琳) Chinese Physics, 2007, 16 (11):  3249-3255.  DOI: 10.1088/1009-1963/16/11/018 Abstract ( 1832 )   PDF (578KB) ( 1413 )   In this paper, a general method of synchronizing noise-perturbed chaotic systems with unknown parameters is proposed. Based on the LaSalle-type invariance principle for stochastic differential equations and by employing a combination of feedback control and adaptive control, some sufficient conditions of chaos synchronization between these noise-perturbed systems with unknown parameters are established. The model used in the research is the chaotic system, but the method is also applicable to the hyperchaotic systems. Unified system and noise-perturbed R¨ossler system, hyperchaotic Chen system and noise-perturbed hyperchaotic R¨ossler system are taken for illustrative examples to demonstrate this technique.

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Notch filter feedback controlled chaos in buck converter Lu Wei-Guo(卢伟国), Zhou Luo-Wei(周雒维), and Luo Quan-Ming(罗全明) Chinese Physics, 2007, 16 (11):  3256-3261.  DOI: 10.1088/1009-1963/16/11/019 Abstract ( 1666 )   PDF (833KB) ( 1447 )   A method of controlling chaos in the voltage-mode buck converter is presented by using an improved notch filter feedback control in this paper. The proposed control part comprises a notch filter and a low-pass filter. The discrepancy between the outputs of the two filters is introduced into the control prototype of the power converter. In this way, the system period-1 solution is kept unchanged. The harmonic balance method is applied to analysing the variation law of the system bifurcation point, and then the stable range of the feedback gain is ascertained. The results of simulation and experiment are also given finally.

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Prediction of chaotic time series based on modified minimax probability machine regression Sun Jian-Cheng(孙建成) Chinese Physics, 2007, 16 (11):  3262-3270.  DOI: 10.1088/1009-1963/16/11/020 Abstract ( 1474 )   PDF (1850KB) ( 572 )   Long-term prediction of chaotic time series is very difficult, for the chaos restricts predictability. In this paper a new method is studied to model and predict chaotic time series based on minimax probability machine regression (MPMR). Since the positive global Lyapunov exponents lead the errors to increase exponentially in modelling the chaotic time series, a weighted term is introduced to compensate a cost function. Using mean square error (MSE) and absolute error (AE) as a criterion, simulation results show that the proposed method is more effective and accurate for multistep prediction. It can identify the system characteristics quite well and provide a new way to make long-term predictions of the chaotic time series.

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Study of dual-directional high rate secure communication systems using chaotic multiple-quantum-well lasers Yan Sen-Lin(颜森林) Chinese Physics, 2007, 16 (11):  3271-3278.  DOI: 10.1088/1009-1963/16/11/021 Abstract ( 1512 )   PDF (1583KB) ( 698 )   A scheme of synchronized injection multi-quantum-well (MQW) laser system using optical coupling-feedback is presented for performing chaotic dual-directional secure communication. The performance characterization of chaos masking is investigated theoretically, the equation of synchronization demodulation is deduced and its root is also given. Chaos masking encoding with a rate of 5 Gbit/s and a modulation frequency of 1 GHz, chaos modulation with a rate of 0.2 Gbit/s and a modulation frequency of 0.2 GHz and chaos shifting key with a rate of 0.2 Gbit/s are numerically simulated, separately. The ratio of the signal to the absolute synchronous error and the time for achieving synchronous demodulation are analysed in detail. The results illustrate that the system has stronger privacy and good performances so that it can be applied in chaotic dual-directional high rate secure communications.

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A new hyperchaotic dynamical system Liu Chong-Xin(刘崇新) Chinese Physics, 2007, 16 (11):  3279-3284.  DOI: 10.1088/1009-1963/16/11/022 Abstract ( 1653 )   PDF (2264KB) ( 1589 )   In this paper a new hyperchaotic system is reported. Some basic dynamical properties, such as continuous spectrum, Lyapunov exponents, fractal dimensions, strange attractor and Poincaré mapping of the new hyperchaotic system are studied. Dynamical behaviours of the new hyperchaotic system are proved by not only numerical simulation and brief theoretical analysis but also an electronic circuit experiment.

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Analysis of second-harmonic generation microscopy under refractive index mismatch Wang Xiang-Hui(王湘晖), Lin Lie(林列), and Zhang Yang(张杨) Chinese Physics, 2007, 16 (11):  3285-3289.  DOI: 10.1088/1009-1963/16/11/023 Abstract ( 1666 )   PDF (519KB) ( 539 )   On the basis of the vector diffraction theory and Green’s function method, this paper investigates the effects of refractive index mismatch on second-harmonic generation (SHG) microscopy. The polarization distribution and SHG intensity are calculated as functions of the sample radius and probe depth. The numerical results show that refractive index mismatch can result in peak intensity degradation, increase secondary lobes and extension of secondharmonic polarization distribution. Because of the attenuation of polarization intensity, the detected SHG intensity significantly decreases with increasing probe depth, which can limit the imaging depth of SHG microscopy inside thick samples. Forward SHG intensity decays slowly than backward SHG, due to the combination of extension secondharmonic polarization distribution and strong dependency of forward SHG on sample radius.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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Hyperon coupling dependence of hadron matter properties in relativistic mean field model Mi Ai-Jun(米爱军), Zuo Wei(左维), and Li Ang(李昂) Chinese Physics, 2007, 16 (11):  3290-3296.  DOI: 10.1088/1009-1963/16/11/024 Abstract ( 1708 )   PDF (1004KB) ( 546 )   The properties of hadronic matter at $\beta$ equilibrium in a wide range of densities are described by appropriate equations of state in the framework of the relativistic mean field model. Strange meson fields, namely the scalar meson field $\sigma$* (975) and the vector meson field $\phi$(1020), are included in the present work. We discuss and compare the results of the equation of state, nucleon effective mass, and strangeness fraction obtained by adopting the TM1, TMA, and GL parameter sets for nuclear sector and three different choices for the hyperon couplings. We find that the parameter set TM1 favours the onset of hyperons most, while at high densities the GL parameter set leads to the most hyperon-rich matter. For a certain parameter set (e.g. TM1), the most hyperon-rich matter is obtained for the hyperon potential model. The influence of the hyperon couplings on the effective mass of nucleon, is much weaker than that on the nucleon parameter set. The nonstrange mesons dominate essentially the global properties of dense hyperon matter. The hyperon potential model predicts the lowest value of the neutron star maximum mass of about 1.45 Msun to be 0.4-0.5 Msun lower than the prediction by using the other choices for hyperon couplings.

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The mass of the isodoublet of the 2 1S0 meson nonet revisited Feng Xue-Chao(冯学超) and Feng Jun-Lan(冯军兰) Chinese Physics, 2007, 16 (11):  3297-3299.  DOI: 10.1088/1009-1963/16/11/025 Abstract ( 1434 )   PDF (113KB) ( 499 )   In the $q\bar{q}$ quark model, the states $\pi$(1300), $\eta$(1295) and $\eta$(1475) are assigned as the 21S0 meson nonet. The mass of the isodoublet remains interesting and needs further confirmation in experiments. This paper employs the phenomenological trajectory on the (N, M2)-plot and meson–meson mixing methods to calculate the mass of this state, the calculated results are 1341 MeV and 1311.58 ± 59 MeV respectively. These predictions can be compared with experiments in the future.

NUCLEAR PHYSICS

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Resonance reaction rate of 21Na(p, $\gamma$)22Mg Liu Hong-Lin(刘宏林), Liu Men-Quan(刘门全), Liu Jing-Jing(刘晶晶), and Luo Zhi-Quan(罗志全) Chinese Physics, 2007, 16 (11):  3300-3304.  DOI: 10.1088/1009-1963/16/11/026 Abstract ( 1509 )   PDF (292KB) ( 544 )   By using the new Coulomb screening model and most recent experimental results, this paper calculates the resonance reaction rates of 21Na(p, $\gamma$)22Mg. The derived result shows that the effect of electron screening on resonant reaction is prominent in astrophysical interesting temperature range. In conjunction with the experimental results, the recommended rates of 21Na(p, $\gamma$)22Mg would increase at least 10%, which undoubtedly affect the nucleosynthesis of some heavier nuclei in a variety of astrophysical sites.

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Probing the medium effect and isospin dependence of the in-medium nucleon--nucleon cross section in heavy ion collisions Liu Jian-Ye(刘建业), Guo Wen-Jun(郭文军), and Xing Yong-Zhong(邢永忠) Chinese Physics, 2007, 16 (11):  3305-3311.  DOI: 10.1088/1009-1963/16/11/027 Abstract ( 1758 )   PDF (819KB) ( 425 )   Probing in-medium nucleon--nucleon (NN) cross section $\sigma^{1}_{\rm NN}(\alpha)$ in heavy ion collisions has been investigated by means of the isospin-dependent quantum molecular dynamics (IQMD) with the isospin- and momentum-dependent interaction (IMDI$(\tau)$). It is found that there are the very obvious medium effect and the sensitive isospin-dependence of nuclear stopping $R$ on the in-medium NN cross section $\sigma^{1}_{\rm NN}(\alpha)$ in the nuclear reactions induced by halo-neutron projectile and the same-mass stable projectile. However, $R$ induced by the neutron-halo projectile is obviously lower than that induced by the corresponding stable projectile. In particular, there is a very obvious dependence of $R$ on the medium effect of $\sigma^{1}_{\rm NN}(\alpha)$ in the whole beam energy region for the above two kinds of projectiles. Therefore, the comparison between the results of $R$'s in the reactions induced by the neutron-halo projectile and the corresponding same-mass stable projectile is a more favourable probe for extracting the information of $\sigma^{1}_{\rm NN}(\alpha)$ because of adding a new judgement.

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Effects of a liquid lithium curtain as the first wall in a fusion reactor plasma Li Cheng-Yue(李承跃), J. P. Allain, and Deng Bai-Quan(邓柏权) Chinese Physics, 2007, 16 (11):  3312-3318.  DOI: 10.1088/1009-1963/16/11/028 Abstract ( 1567 )   PDF (447KB) ( 478 )   This paper explores the effect of a liquid lithium curtain on fusion reactor plasma, such curtain is utilized as the first wall for the engineering outline design of the Fusion Experimental Breeder (FEB-E). The relationships between the surface temperature of a liquid lithium curtain and the effective plasma charge, fuel dilution and fusion power production have been derived. Results indicate that under normal operation, the evaporation of liquid lithium does not seriously affect the effective plasma charge, but effects on fuel dilution and fusion power are more sensitive. As an example, it has investigated the relationships between the liquid lithium curtain flow velocity and the rise of surface temperature based on operation scenario II of the FEB-E design with reversed shear configuration and high power density. Results show that even if the liquid lithium curtain flow velocity is as low as 0.5 m/s, the effects of evaporation from the liquid lithium curtain on plasma are negligible. In the present design, the sputtering of liquid lithium curtain and the particle removal effects of the divertor are not yet considered in detail. Further studies are in progress, and in this work implication of lithium erosion and divertor physics on fusion reactor operation are discussed.

ATOMIC AND MOLECULAR PHYSICS

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Collision-induced absorption in the v2 fundamental band of 12CH4 Yang Ze-Jin(杨则金), Cheng Xin-Lu(程新路), and Yang Xiang-Dong(杨向东) Chinese Physics, 2007, 16 (11):  3319-3322.  DOI: 10.1088/1009-1963/16/11/029 Abstract ( 1594 )   PDF (115KB) ( 430 )   The integrated intensities of the collision-induced absorption of the $\nu _{2}$ band of $^{12}$CH$_{4}$ perturbed by Ar have been calculated  theoretically using the ab initio calculations, and the value of the quadrupole transition moment we obtained is $\langle {0| Q |\nu _2 } \rangle  =5.226ea_0^2 $. The corresponding experimental value obtained from $^{12}$CH$_{4}$--Ar spectra is $| {\langle {0| Q |\nu _2 } \rangle } |=4.931ea_0^2 $. Ignoring vibration--rotation interaction and Coriolis interaction, and considering both the theoretical approximations and experimental uncertainties, the agreement can be regarded as good, thus confirming that the enhancement is due to the quadrupole collision-induced mechanism.

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Solvent effects on structure and optical properties of a D-$\pi$-A azobenzene dye Wang Chuan-Kui(王传奎), Xing Xiao-Juan(邢晓娟), Huang Xiao-Ming(黄晓明), and Gao Yun(高云) Chinese Physics, 2007, 16 (11):  3323-3327.  DOI: 10.1088/1009-1963/16/11/030 Abstract ( 1620 )   PDF (198KB) ( 616 )   Time-dependent hybrid density functional theory in combination with Onsager reaction field model and super-molecular model has been applied to study solvent effects on the geometrical and electronic structures, as well as one/two-photon absorption properties, of 4-(N-(2-hydroxyethyl)-N-methyl)-amino-4’-nitroazobenzene. It is found that the short-range interaction has a large effect on the electronic structure of the solute molecule, namely, large red-shift of the maximum one-photon absorption is induced by hydrogen bonding. The solute molecule has a large two-photon absorption cross section, which is enhanced by the solvent effect. The computational results are in good agreement with measurements.

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Phase transformation and nanograting structure on TiO2 rutile single crystal induced by infrared femtosecond laser Ma Hong-Liang(马洪良), Yang Jun-Yi(杨俊毅), Lu Bo(鲁波), and Ma Guo-Hong(马国宏) Chinese Physics, 2007, 16 (11):  3328-3331.  DOI: 10.1088/1009-1963/16/11/031 Abstract ( 1624 )   PDF (810KB) ( 665 )   In this paper, Titanium dioxide (TiO$_{2})$ rutile single crystal was irradiated by infrared femtosecond laser pulses with repetition rate of 250 kHz. For a P-polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was formed . The periodicity is much less than the laser wavelength. The direction of nanograting alignment depends on the polarization laser beam. Micro-Raman spectra show that the intensity of  Eg Raman vibrating mode of rutile phase increases and that of A1g Raman vibrating mode decreases apparently within the ablation crater. With the increase of irradiation time and laser average power, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO$_{2}$ single crystal is partly transformed into anatase phase.

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Raman spectroscopic study of G--A mismatches Liao Yu-Bo(廖昱博), Meng Yao-Yong(孟耀勇), Lei Hao-Dong(雷浩东), and Wang Ying(王英) Chinese Physics, 2007, 16 (11):  3332-3338.  DOI: 10.1088/1009-1963/16/11/032 Abstract ( 1629 )   PDF (620KB) ( 454 )   G--A mismatches are non-canonical base pairs that widely occur in native nucleic acids. They have been found to be functionally important in adopting unusual structures. In this paper, G--A mispairing was studied by Raman spectral characterization of Polyadenylic acid (PolyA), Polyguanylic acid (PolyG) and their equimolar mixture in solution of 0.08 mol/L Na$^{+}$, pH7.0. The experiment showed the following three results. (1) At the experimental conditions used in the present work, PolyA and G--A complexes existed as single-stranded and double-stranded helix of A form, respectively. And PolyG mainly occurred to be anti-parallel quadruplex conformers. (2) The formation of G--A complexes, on one hand strengthened parts of base stacking interactions especially for PolyG, leading to Raman hypochromism effect with some corresponding bands shifting, and on the other hand weakened other base stacking interactions especially for PolyA to a certain degree. During this process, the backbone of PolyG underwent a significant change, but PolyA still conserved its main chain conformation. (3) The formation of G--A complexes was stabilized by two interbase hydrogen-bond interactions (i.e. N6H$_{2 }$(A)---N3 (G) and N7 (A)---N2H$_{2 }$(G)) and a third hydrogen bond between O2' (G) and N6 (A). The third hydrogen bond was responsible for the remarkable changes of PolyG backbone conformation.

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Differential cross sections of elastic electron scattering from CH4, CF4 and SF6 in the energy range 100--700eV Ma Er-Jun(马二俊), Ma Yu-Gang(马余刚), Cai Xiang-Zhou(蔡翔舟), Fang De-Qing(方德清), Shen Wen-Qing(沈文庆), and Tian Wen-Dong(田文栋) Chinese Physics, 2007, 16 (11):  3339-3344.  DOI: 10.1088/1009-1963/16/11/033 Abstract ( 1662 )   PDF (799KB) ( 1851 )   We investigate the differential cross sections (DCS) of elastic electron scattering from CH$_{4}$, CF$_{4}$ and SF$_{6}$ at six impact energies in a range of 100--700 eV by employing the independent atom model (IAM) together with the relativistic partial waves. The atom is present in an optical potential which is complex, spherically symmetric, and energy dependent. The optical potential of the atom is the sum of the direct static, dynamic polarization, local exchange and modified absorption potentials. The results obtained by using a modified absorption potential show significant improvements on the unmodified absorption potential results. The present results are generally in good agreement with experimental data available. In addition, the present results indicate that the structure of molecule manifests the observable effects on electron--molecule scattering.

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The effect of the attractive well of the potential energy surface for Ne--HCl on rotationally inelastic partial wave cross sections Yu Chun-Ri(余春日), Shi Shou-Hua(史守华), Wang Rong-Kai(汪荣凯), and Yang Xiang-Dong(杨向东) Chinese Physics, 2007, 16 (11):  3345-3351.  DOI: 10.1088/1009-1963/16/11/034 Abstract ( 1699 )   PDF (459KB) ( 626 )   An interaction potential of the Ne--HCl van der Waals complex is obtained by utilizing the Huxley analytic potential function to fit the accurate interaction energy data, which have been computed at the coupled cluster singles and doubles including connected triple excitations level and with the augmented correlation consistent polarized valence quintuple zeta basis set extended with a set of 3s3p2d1f1g mid-bond functions [CCSD (T) /aug-cc-pV5Z-33211]. The close coupling calculation of state- o-state partial cross sections for collision of Ne with HCl is first performed by employing the fitted interaction potential. This calculation is performed at the incident energies: 40, 60, 75 and 100 meV, separately. The effects of the long-range attractive and the short-range anisotropic interactions on the inelastic state-to-state partial cross sections are discussed in detail. Two maxima are present in the rotationally inelastic partial cross sections and they originate from different mechanisms.

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Theoretical calculation of the partial cross section for first vibrational excitation in He--H2 (D2 ,T2) collisions Shen Guang-Xian(沈光先), Linghu Rong-Feng(令狐荣锋), Wang Rong-Kai(汪荣凯), and Yang Xiang-Dong(杨向东) Chinese Physics, 2007, 16 (11):  3352-3358.  DOI: 10.1088/1009-1963/16/11/035 Abstract ( 1864 )   PDF (530KB) ( 480 )   In this paper, close-coupling method was applied to the He--H$_{2}$(D$_{2}$,T$_{2})$ system, and the first vibrational excitation cross sections of `00--10, 00--12, 00--14, 00--16' at different incident energy have been calculated．By analyzing the differences of these partial wave cross sections, this paper have obtained the change rules of the partial wave cross sections with increases of quantum number, and with change of reduced mass of system. Based on the calculation,  influence on the partial wave cross sections brought by the variations in the reduced mass of systems and in the relative kinetic energy of incident atoms is discussed.

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First-principle studies of the geometries and electronic properties of Cum Sin (2≤m+n≤7)clusters Liu Xia(刘霞), Zhao Gao-Feng(赵高峰), Guo Ling-Ju(郭令举), Wang Xian-Wei(王献伟), Zhang Jun(张俊), Jing Qun(井群), and Luo You-Hua(罗有华) Chinese Physics, 2007, 16 (11):  3359-3369.  DOI: 10.1088/1009-1963/16/11/036 Abstract ( 1804 )   PDF (1578KB) ( 813 )   The equilibrium geometries and electronic properties of Cu$_{m}$Si$_{n}$ ($2 \le m+n \le 7$) clusters have been studied by using density functional theory at the B3LYP/6-311+G (d) level. Our results indicate that the structure of CuSi$_{n}$ ($n<$6) keeps the frame of the corresponding Si$_{n}$ cluster unchanged, while for Cu$_{n}$Si clusters, the rectangular pyramid structure of Cu$_{4}$Si is shown to be a building block in many structures of larger Cu$_{n}$Si clusters. The growth patterns of Cu$_{m}$Si$_{n}$ clusters become more complicated as the number of Cu atoms increases. Both the binding energies and the fragmentation energies indicate that the Si--Si bond is stronger than the Cu--Si bond, and the latter is stronger than the Cu--Cu bond. Combining the fragmentation energies in the process Cu$_{m}$Si$_{n} \to $Cu+Cu$_{m - 1}$Si$_{n}$ and the second- rder difference $\Delta_{2}E$($m)$ against the number of Cu atoms of Cu$_{m}$Si$_{n}$, we conclude that Cu$_{m}$Si$_{n}$ clusters with even number of Cu atoms have higher stabilities than those with odd $m$. According to frontier orbital analyses, there exists a mixed ionic and covalent bonding picture between Cu and Si atoms, and the Cu d orbitals contribute little to the Cu--Si bonding. For a certain cluster size ($m+n$ = 3, 4, 5, 6, 7), the energy gaps of the most stable Cu$_{m}$Si$_{n}$ clusters show odd--even oscillation with changing $m$, the clusters with odd $m$ exhibit stronger chemical reactivity than those with even $m$.

CLASSICAL AREAS OF PHENOMENOLOGY

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Modelling of passively Q-switched lasers with intracavity Raman conversion Su Fu-Fang(苏富芳), Zhang Xing-Yu(张行愚), Wang Qing-Pu(王青圃), Chang Jun(常军), Jia Peng(贾鹏), Li Shu-Tao(李述涛), Zhang Xiao-Lei(张晓磊), and Cong Zhen-Hua(丛振华) Chinese Physics, 2007, 16 (11):  3370-3376.  DOI: 10.1088/1009-1963/16/11/037 Abstract ( 1767 )   PDF (894KB) ( 798 )   We present a model of passively Q-switched Raman lasers by utilizing the rate equations. The intracavity fundamental photon density, Raman photon density and the initial population-inversion density of the gain medium are assumed to be of Gaussian spatial distributions. These rate equations are normalized by introducing some synthetic parameters and solved numerically, and a group of general curves are generated. From these curves we can understand the dependence of the Raman laser pulse characteristics on the parameters about the pumping, the gain medium, the Raman medium and the resonator. An illustrative calculation for a passively Q-switched Nd$^{3 + }$:GdVO$_{4}$ self-Raman laser is presented to demonstrate the usage of the curves and related formulas.

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Structural polarization properties of vector Gaussian beam in the far field Zhou Guo-Quan(周国泉), Ni Yong-Zhou(倪涌舟), and Chu Xiu-Xiang(储修祥) Chinese Physics, 2007, 16 (11):  3377-3381.  DOI: 10.1088/1009-1963/16/11/038 Abstract ( 2076 )   PDF (336KB) ( 655 )   Based on the vector angular spectrum representation of optical beam and the method of stationary phase, the analytical TE and TM terms of vector Gaussian beam have been presented in the far field. By using the local polarization matrix, the polarization properties of the TE and TM terms in the far field are investigated, and it is found that the degree of their polarization is only determined by the spatial location. When the source is completely polarized, the TE and TM terms are both completely polarized in the far field. When the source is completely unpolarized, the TE and TM terms in the far field are partially polarized. The whole beam is also partially polarized except on the propagating axis. Moreover, the degrees of polarization of TE and TM terms are both larger than that of the whole beam.

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A scheme for the implementation of unconventional geometric phase gates with trapped ions Xie Hong(谢鸿), Li Hong-Cai(李洪才), Yang Rong-Can(杨榕灿), Lin Xiu(林秀), and Huang Zhi-Ping(黄志平) Chinese Physics, 2007, 16 (11):  3382-3385.  DOI: 10.1088/1009-1963/16/11/039 Abstract ( 1560 )   PDF (103KB) ( 513 )   We propose a scheme for the realization of unconventional geometric two-qubit phase gates with two identical two-level ions. In the present scheme, the two ions are simultaneously illuminated by a standing-wave laser pulse with its pulse frequency being tuned to the ionic transition. The gate operation time can be much shorter, making the system robust against decoherence. In addition, we choose the appropriate experimental parameters to construct the geometric phase gate in one step, and thus avoid implementing the pure geometric single qubit operation.

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Ultra slow light propagation without any control light field Chen Ai-Xi(陈爱喜), Deng Li(邓黎), and Wu Qing-Ping(伍清萍) Chinese Physics, 2007, 16 (11):  3386-3390.  DOI: 10.1088/1009-1963/16/11/040 Abstract ( 1561 )   PDF (501KB) ( 527 )   Without need of another control light, this paper analyses in a time-dependent way a new scheme to achieve ultraslow propagation of the input probe field through a medium composed of two-level atoms where their upper level is split into two hyperfine sub-levels via some applied static field such as a DC magnetic or a DC electric field or whatever other static field.

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Faithfully probabilistic teleportation of an unknown atomic state and cavity field state with a single measurement Yang Zhen-Biao(杨贞标), Wu Huai-Zhi(吴怀志), Su Wan-Jun(苏万钧), Zhong Zhi-Rong(钟志荣), and Zheng Shi-Biao(郑仕标) Chinese Physics, 2007, 16 (11):  3391-3395.  DOI: 10.1088/1009-1963/16/11/041 Abstract ( 1764 )   PDF (1211KB) ( 648 )   This paper shows that, based on the single-photon JC model depicting the resonant interaction of a two-level atom with a single cavity mode, an unknown atomic state and cavity photon superposition state can be faithfully teleported with only a single measurement. The scheme is probabilistic, its success lies on the event that the sender atom (or the medi-atom, for teleportation of cavity field state) is detected in the higher state. The scheme is in contrast to the previous ones of using a maximally two- article entangled state as quantum channel.

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Entanglement between two atoms in the system of Schrödinger cat state interacting with two entangled atoms Liu Tang-Kun(刘堂昆) Chinese Physics, 2007, 16 (11):  3396-3401.  DOI: 10.1088/1009-1963/16/11/042 Abstract ( 1633 )   PDF (787KB) ( 642 )   By the negative eigenvalues of partial transposition of density matrix, this paper investigates the time evolution of entanglement of the two entangled atoms in the system of two atoms interacting with Schr?dinger cat state. The result shows that the two atoms are always in the entanglement state, and the degree of entanglement between the two atoms exhibits ordinary collapses and revivals at 0.2 degree of entanglement, when the light field is large enough. On the other hand, the reinforcement of three different light fields on the degree of entanglement between two atoms is not evident.

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Influence of multi-photon pulses on practical differential-phase-shift quantum key distribution Zhao Feng(赵峰), Fu Ming-Xing(傅明星), Lu Yi-Qun(路轶群), and Liu Song-Hao(刘颂豪) Chinese Physics, 2007, 16 (11):  3402-3406.  DOI: 10.1088/1009-1963/16/11/043 Abstract ( 1807 )   PDF (329KB) ( 746 )   The influence of multi-photon pulses on practical differential-phase-shift quantum key distribution (DPS-QKD) is analysed. We have estimated the information which Eve obtained by PNS (photon-number splitting) attack and BS (beam splitting) attack. The result indicates that the PNS attack and BS attack will not limit the transmission distance as long as we select an appropriate mean photon number. Also, the maximum mean photon number under BS attack in practical DPS-QKD system and the set of practical assumptions about Eve’s capabilities are presented.

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Six-wave mixing phase-dispersion by optical heterodyne detection in dressed reverse N-type four-level system Gan Chen-Li(甘琛利), Nie Zhi-Qiang (聂志强), Li Ling(李岭), Shen Lei-Jian(沈磊剑), Zhang Yan-Peng(张彦鹏), Song Jian-Ping(宋建平), Li Yuan-Yuan(李院院), Zhang Xiang-Chen(张相臣), and Lu Ke-Qing(卢克清) Chinese Physics, 2007, 16 (11):  3407-3415.  DOI: 10.1088/1009-1963/16/11/044 Abstract ( 1511 )   PDF (743KB) ( 537 )   We have investigated the dressed effects of non-degenerate four-wave mixing (NDFWM) and demonstrated a phase-sensitive method of studying the fifth-order nonlinear susceptibility due to atomic coherence in RN-type four-level system. In the presence of a strong coupling field, NDFWM spectrum exhibits Autler–Townes splitting, accompanied by either suppression or enhancement of the NDFWM signal, which is directly related to the competition between the absorption and dispersion contributions. The heterodyne-detected nonlinear absorption and dispersion of six-wave mixing signal in the RN-type system show that the hybrid radiation-matter detuning damping oscillation is in the THz range and can be controlled and modified through the colour-locked correlation of twin noisy fields.

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Optical feedback characteristics in a helium neon laser with a birefringent internal cavity Mao Wei(毛威), Zhang Shu-Lian(张书练), Xu Ting(徐亭), Wan Xin-Jun(万新军), and Liu Gang(刘刚) Chinese Physics, 2007, 16 (11):  3416-3422.  DOI: 10.1088/1009-1963/16/11/045 Abstract ( 1690 )   PDF (2591KB) ( 695 )   The output characteristics of optical feedback in a helium–neon laser with a birefringent internal cavity are studied systematically in five different regions of the gain curve for the two orthogonally polarized modes. When the laser operates in the two end regions of the laser gain curve, one of the two orthogonally polarized modes will be a leading one in optical feedback. Strong mode competition can be observed. However, when the laser operates in the middle region of the laser gain curve, the two modes can oscillate equally with optical feedback. Besides the intensity of the two polarized lights, the total light intensity is also studied at the same time. M-shaped optical feedback curves are found. Particularly, when the average intensities of the two lights are comparable, the intensity modulation curve of the total light is doubled, which can be used to improve the resolution of an optical feedback system.

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Grey screening-photovoltaic soliton-induced waveguides Lu Ke-Qing(卢克清), Yang Yan-Long(杨延龙), Zhao Wei(赵卫), Zhang Mei-Zhi(张美志), Yang Yang(杨阳), Zhang Lei(张磊), Liu Xue-Ming(刘雪明), and Zhang Yan-Peng(张彦鹏) Chinese Physics, 2007, 16 (11):  3423-3428.  DOI: 10.1088/1009-1963/16/11/046 Abstract ( 1723 )   PDF (482KB) ( 393 )   This paper shows that waveguides induced by grey screening-photovoltaic solitons are always single mode for all  intensity ratios, which are the ratio between the peak intensity of the soliton and the dark irradiance. It finds that the confined energy near the centre of the grey soliton and the propagation constant of the guided mode increase monotonically with increasing intensity ratio. On the other hand, when the soliton greyness increases, the confined energy near the centre of the grey soliton and the propagation constant of the guided mode reduce monotonically. When the bulk photovoltaic effect is neglected for short circuits, these waveguides become waveguides induced by grey screening solitons. When the external bias field is absent, these waveguides become waveguides induced by grey photovoltaic solitons.

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The study of numerical character for femtosecond pulse shaping Zou Hua(邹华), Zhu Wei-Hua(朱卫华), and Wang Guo-Dong(王国栋) Chinese Physics, 2007, 16 (11):  3429-3433.  DOI: 10.1088/1009-1963/16/11/047 Abstract ( 1481 )   PDF (815KB) ( 467 )   This paper describes the generation of shaped femtosecond multiple pulses by using the phase-only Dammann filters in 4f femtosecond shaper and gives the experimental result of femtosecond pulse characterization by the frequency-resolved optical gating (FROG) technique. With the theoretical simulation, it concludes that the quality of the generated output array is relevant to the number of pixels and the spacing between the components.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Modification to poloidal charge exchange recombination spectroscopy measurement in JT-60U tokamak Ding Bo-Jiang(丁伯江), Sakamoto Yoshiteru, and Miura Yukitoshi Chinese Physics, 2007, 16 (11):  3434-3442.  DOI: 10.1088/1009-1963/16/11/048 Abstract ( 1402 )   PDF (686KB) ( 491 )   With consideration of the effects of the atomic process and the sight line direction on the charge exchange recombination spectroscopy (CXRS), a code used to modify the poloidal CXRS measurement on Tokamak-60 Upgrade (JT-60U) in Japan Atomic Energy Research Institute is developed, offering an effective tool to modify the measurement and analyse experimental results further. The results show that the poloidal velocity of ion is overestimated but the ion temperature is underestimated by the poloidal CXRS measurement, and they also indicate that the effect of observation angle on rotation velocity is a dominant one in a core region ($r/a<0.65$), whereas in an edge region where the sight line is nearly normal to the neutral beam, the observation angle effect is very small. The difference between the modified velocity and the neoclassical velocity is not larger than the error in measurement. The difference inside the internal transport barrier (ITB) region is 2--3 times larger than that outside the ITB region, and it increases when the effect of excited components in neutral beam is taken into account. The radial electric field profile is affected greatly by the poloidal rotation term, which possibly indicates the correlation between the poloidal rotation and the transport barrier formation.

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The effect of toroidal field on the rotating magnetic field current drive in rotamak plasmas Zhong Fang-Chuan(钟方川), Huang Tian-Sen, and Petrov Yuri Chinese Physics, 2007, 16 (11):  3443-3450.  DOI: 10.1088/1009-1963/16/11/049 Abstract ( 1310 )   PDF (1007KB) ( 373 )   A rotamak is one kind of compact spherically shaped magnetic-confinement device. In a rotamak the plasma current is driven by means of rotating magnetic field (RMF). The driven current can reverse the original equilibrium field and generate a field- eversed-configuration. In a conventional rotamak, a toroidal field (TF) is not necessary for the RMF to drive plasma current, but it was found that the present of an additional TF can influence the RMF current drive. In this paper the effect of TF on the RMF current drive in a rotamak are investigated in some detail. The experimental results show that addition of TF increases the RMF driven current greatly and enhances the RMF penetration dramatically. Without TF, the RMF can only penetrate into plasma in the edge region. When a TF is added, the RMF can reach almost the whole plasma region. This is an optimal strength of toroidal magnetic field for getting maximum plasma current when $B_{\rm v}$ and radio frequency generator power are fixed. Besides driving current, the RMF generates high harmonic fields in rotamak plasma. The effect of TF on the harmonic field spectra are also reported.

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Preliminary analysis of impurity transport in HL-2A ohmic discharges Chen Wei(陈伟), Cui Zheng-Ying(崔正英), Sun Ping(孙平), Huang Yuan(黄渊), Zhang Peng(张鹏), Deng Wei(邓玮), Pan Yu-Dong(潘宇东), Shi Zhong-Bing(石中兵), Zhou Yan(周艳), Zheng Yong-Zhen(郑永真), and Yang Qing-Wei(杨青巍) Chinese Physics, 2007, 16 (11):  3451-3457.  DOI: 10.1088/1009-1963/16/11/050 Abstract ( 1703 )   PDF (1539KB) ( 510 )   This paper describes the behaviour of impurity transport in HL-2A ohmic discharges. In 2005, small quantities of metallic impurities (Al, Ni and Ti) were successfully injected into HL-2A plasmas by laser blow-off technique, and their progression was followed by the soft x-ray cameras with good spatial and temporal resolutions. The impurity confinement time is estimated from the characteristic decay time of the soft x-ray signal of the injected impurities, and it is about 30–60ms. The transport coefficients of impurities (including diffusion coefficient and convection velocity) in radial different region have been derived by using a one-dimensional impurity transport code, the results present that diffusion coefficient is much smaller in the central region of plasmas than the outside of it, and it is much larger than that of neoclassical theory predictions; namely, it is anomalous.

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Study of impurity behaviour in non-coronal equilibrium state Cheng Fa-Yin(程发银) and Shi Bing-Ren(石秉仁) Chinese Physics, 2007, 16 (11):  3458-3463.  DOI: 10.1088/1009-1963/16/11/051 Abstract ( 1627 )   PDF (584KB) ( 851 )   A physical model of analysing the behaviour of impurities out of coronal equilibrium in tokamak plasmas has been proposed. Through solving the time-dependent rate equations including the effects of atomic processes and the particle transport losses, the ionization state distribution is obtained for a range of low $Z$ impurities such as helium, carbon, oxygen and argon. By using  the ionization state distribution of these impurities, the radiation rate coefficients and the mean charge state changing with plasma temperature are calculated. The results show that the mean charge state $\langle { Z} \rangle $ is sensitively dependent on the parameter $n_{\rm e} \tau $, and this is the reason why the radiation power of impurities under non-coronal equilibrium conditions is several orders of magnitude higher than that  under coronal equilibrium condition.

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Effects of trapped electrons on off-axis lower hybrid current drive in tokamaks Jiao Yi-Ming(焦一鸣), Long Yong-Xing(龙永兴), Dong Jia-Qi(董家齐), Gao Qing-Di(高庆弟), Wang Ai-Ke(王爱科), and Liu Yong(刘永) Chinese Physics, 2007, 16 (11):  3464-3469.  DOI: 10.1088/1009-1963/16/11/052 Abstract ( 1855 )   PDF (356KB) ( 392 )   The effects of trapped electrons on off-axis lower hybrid current drive (LHCD) in tokamaks are studied, A computer code for solving the Fokker–Planck equation in a toroidal geometry is developed and employed. The code is suitable for various auxiliary heating and current drive schemes in tokamak plasmas. The influence of the resonance regime on the current drive efficiency as well as the influence of trapped particle fraction on the current drive efficiency are emphasized. It is shown that, as an electrostatic force, the lower hybrid wave causes some of the trapped electrons to be untrapped and lose their energy, which can cut the LHCD efficiency by about 30%. The ITER scaling law is also used to estimate the trapped electron effects.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Island-growth of SiCGe films on SiC Li Lian-Bi(李连碧), Chen Zhi-Ming(陈治明), Lin Tao(林涛), Pu Hong-Bin (蒲红斌), Li Qing-Min(李青民), and Li Jia(李佳) Chinese Physics, 2007, 16 (11):  3470-3474.  DOI: 10.1088/1009-1963/16/11/053 Abstract ( 1712 )   PDF (1755KB) ( 467 )   SiCGe ternary alloys have been grown on SiC by hot-wall low-pressure chemical vapour deposition. It has been found that the samples exhibit an island configuration, and the island growth of SiCGe epilayer depends on the processing parameters such as the growth temperature. When the growth temperature is comparatively low, the epilayer has two types of islands: one is spherical island; another is cascading triangular island. With the increase of the growth temperature, the islands change from spherical to cascading triangular mode. The size and density of the islands depend on the growth duration and GeH$_{4}$ flow- ate. A longer growth time and a larger GeH$_{4}$ flow-rate can increase the size and density of the island in the initial stage of the epitaxy. In our case, The optimal growth for a high density of uniform islands occurred at a growth temperature of 1100℃ for 1-minute growth, with 10 SCCM GeH$_{4}$, resulting in a narrow size distribution (about 30 nm diameter) and high density (about $3.5\times10^{10}$ dots/cm$^{2})$. The growth follows Stranski--Krastanov mode (2D to 3D mode), both of the islands and the 2D growth layer have face-centred cubic structure, and the critical thickness of the 2D growth layer is only 2.5 nm.

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Investigation of vapour--liquid nucleation properties for spherical and chain-like fluids by density functional theory Fu Dong(付东) and Liao Tao(廖涛) Chinese Physics, 2007, 16 (11):  3475-3482.  DOI: 10.1088/1009-1963/16/11/054 Abstract ( 1813 )   PDF (418KB) ( 391 )   The excess Helmholtz free energy functional for nonpolar chain-like molecules is formulated in terms of a weighted density approximation (WDA) for short-range interactions and a Weaks–Chandler–Andersen (WCA) approximation and a Barker– enderson (BH) theory for long-range attraction. Within the framework of density functional theory (DFT), vapour–liquid interfacial properties including density profile and surface tension, and vapour–liquid nucleation properties including density profile, work of formation and number of particles are investigated for spherical and chain- like molecules. The obtained vapour– iquid surface tension and the number of particles in critical nucleus for Lennard- Jones (LJ) fluids are consistent with the simulation results. The influences of supersaturation, temperature and chain length on vapour–liquid nucleation properties are discussed.

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Cluster-size dependent randomization traffic flow model Gao Kun (高坤), Wang Bing-Hong (汪秉宏), Fu Chuan-Ji (付传技), and Lu Yu-Feng (陆玉凤) Chinese Physics, 2007, 16 (11):  3483-3493.  DOI: 10.1088/1009-1963/16/11/055 Abstract ( 1778 )   PDF (6625KB) ( 788 )   In order to exhibit the meta-stable states, several slow-to-start rules have been investigated as modification to Nagel– chreckenberg (NS) model. These models can reproduce some realistic phenomena which are absent in the original NS model. But in these models, the size of cluster is still not considered as a useful parameter. In real traffic, the slow-to-start motion of a standing vehicle often depends on the degree of congestion which can be measured by the clusters’ size. According to this idea, we propose a cluster-size dependent slow-to-start model based on the speeddependent slow-to-start rule (VDR) model. It gives expected results through simulations. Comparing with the VDR model, our new model has a better traffic efficiency and shows richer complex characters.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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MMIC LNA based novel composite-channel Al0.3Ga0.7N/Al0.05Ga 0.95N/GaN HEMTs Cheng Zhi-Qun(程知群), Cai Yong(蔡勇), Liu Jie(刘杰), Zhou Yu-Gang(周玉刚), Lau Kei May, and Chen J. Kevin Chinese Physics, 2007, 16 (11):  3494-3497.  DOI: 10.1088/1009-1963/16/11/056 Abstract ( 1643 )   PDF (519KB) ( 872 )   A microwave monolithic integrated circuit (MMIC) C-band low noise amplifier (LNA) using 1 $\mu $m-gate composite-channel Al$_{0.3}$Ga$_{0.7}$N/Al$_{0.05}$Ga$_{0.95}$N/GaN  high electron mobility transistors (CC-HEMTs) has been designed, fabricated and characterized. The material structure and special channel of CC-HEMT were given and analysed. The MMIC LNA with CC-HEMT showed a noise figure of 2.4 dB, an associated gain of 12.3 dB, an input return loss of --6 dB and an output return loss of --16 dB at 6 GHz. The IIP3 of the LNA is 13 dBm at 6 GHz. The LNA with 1 $\mu $m $\times $ 100 $\mu $m device showed very high-dynamic range with decent gain and noise figure.

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AlGaInP thin-film LED with omni-directionally reflector and ITO transparent conducting n-type contact Zhang Jian-Ming(张剑铭), Zou De-Shu(邹德恕), Xu Chen(徐晨), Guo Wei-Ling(郭伟玲), Zhu Yan-Xu(朱彦旭), Liang Ting(梁庭), Da Xiao-Li(达小丽), Li Jian-Jun(李建军), and Shen Guang-Di(沈光地) Chinese Physics, 2007, 16 (11):  3498-3501.  DOI: 10.1088/1009-1963/16/11/057 Abstract ( 1800 )   PDF (1082KB) ( 1259 )   In this paper a novel AlGaInP thin-film light-emitting diode (LED) with omni-directionally reflector (ODR) and transparent conducting indium tin oxide (ITO) n-type contact structure is proposed, and fabrication process is developed. This reflector is realized with the combination of a low-refractive-index dielectric layer and a high reflectivity metal layer. This allows the light emitted or internally reflected downwardly towards the GaAs substrate at any angle of incidence to be reflected towards the top surface of the chip. ITO n-type contact is used for anti-reflection and current spreading layers on the ODR-LED with ITO. The sheet resistance of the ITO films (95 nm) deposited on n-ohmic contact of ODR-LED is of the order 23.5${\Omega}$/$\Box$ with up to 90% transmittance (above 92% for 590--770 nm) in the visible region of the spectrum. The optical and electrical characteristics of the ODR-LED with ITO are presented and compared to conventional AS-LED and ODR-LED without ITO. It is shown that the light output from the ODR-LED with ITO at forward current 20 mA exceeds that of AS-LED and ODR- ED without ITO by about a factor of 1.63 and 0.16, respectively. A favourable luminous intensity of 218.3 mcd from the ODR- ED with ITO (peak wavelength 620 nm) could be obtained under 20 mA injection, which is 2.63 times and 1.21 times higher than that of AS-LED and ODR-LED without ITO, respectively.

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Low voltage substrate current: a monitor for interface states generation in ultra-thin oxide n-OSFETs under constant voltage stresses Wang Yan-Gang(王彦刚), Xu Ming-Zhen(许铭真), and Tan Chang-Hua(谭长华) Chinese Physics, 2007, 16 (11):  3502-3506.  DOI: 10.1088/1009-1963/16/11/058 Abstract ( 1726 )   PDF (882KB) ( 569 )   The low voltage substrate current (Ib) has been studied based on generation kinetics and used as a monitor of interface states (Nit) generation for ultra-thin oxide n-MOSFETs under constant voltage stress. It is found that the low voltage Ib is formed by electrons tunnelling through interface states, and the variations of Ib($\Delta$Ib) are proportional to variations of Nit ($\Delta$Nit). The Nit energy distributions were determined by differentiating Nit(Vg). The results have been compared with that measured by using gate diode technique.

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Electronic transport through an open elliptic cavity Wang Zhe-Xian(王哲献), Ming Yi(明燚), and Ding Ze-Jun(丁泽军) Chinese Physics, 2007, 16 (11):  3507-3513.  DOI: 10.1088/1009-1963/16/11/059 Abstract ( 2262 )   PDF (1309KB) ( 3211 )   This paper computes the conductance of an open ellipse cavity and discusses the effect of finite leads on conductance. The lead introduces mode coupling with bound states in the cavity which contributes to Fano resonant line shapes in conductance. By examining the resonant states in the cavity, the effects of state mixing and annular probability distribution of wave function due to the presence of leads are found. The results have been compared with the transport properties of other systems. The finite leads result in two effects, i.e. the evanescent mode contribution and additional oscillations, to the conductance.

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Coherence effects in S/I/N/I/FS tunnel junctions Li Xiao-Wei(李晓薇) Chinese Physics, 2007, 16 (11):  3514-3519.  DOI: 10.1088/1009-1963/16/11/060 Abstract ( 1680 )   PDF (493KB) ( 464 )   The dc Josephson effect in superconductor / insulator / normal metal / insulator /ferromagnetic superconductor junctions has been studied. We calculate the dc Josephson current based on the Bogoliubov de Gennes equation. The Josephson current is derived as a function of exchange field in ferromagnetic superconductor, normal metal thickness and insulating barrier strength. It is found that there exists an oscillation relation between the critical Josephson current and the normal metal thickness. The oscillation amplitude decreases as the thickness of the normal metal increases or the exchange field augments.

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Origin of magnetization-induced anisotropy of magnetic films Jin Han-Min(金汉民), Chong-Oh Kim, Taek-Dong Lee, and Hyo-Jin Kim Chinese Physics, 2007, 16 (11):  3520-3535.  DOI: 10.1088/1009-1963/16/11/061 Abstract ( 1513 )   PDF (1504KB) ( 444 )   It is proposed that the magnetization-induced anisotropy of magnetic films of cubic crystal structure originates from the anisotropy of atomic pair ordering, shape anisotropy, and strain anisotropy resulting from the constraint of the magnetostriction strain imposed on the film by the substrate. Calculated are the three anisotropy constants and their sum $K $ vs temperature for Ni, Fe, and 55%Ni--Fe films; the room temperature (RT) constants vs the substrate temperature $T_{\rm t}$ during deposition or annealing  after deposition for Ni and 50%Ni--Co films; the RT constants vs composition fraction for Fe--Ni films with $T_{\rm t}=$ RT,  250$^\circ$C and 450$^\circ$C, Co--Ni films at $T_{\rm t} =$ RT, 100$^\circ$C  and 320$^\circ$C, and Fe--Co films with $T_{\rm t}=$ RT and 300$^\circ$C;  the spread of RT $K$ vs composition fraction for Fe--Ni films; and RT $\Delta K/K$ vs composition fraction for Fe--Ni and Co--Ni films, where $\Delta K$ denotes the variation of $K$ of the film that is detached from its substrate. The calculated curves well accord with the measurements. The irrelevancy of $K$ to the substrate material and the fast kinetics of the annealing in a field applied in the direction of the hard axis are explained reasonably.  The anisotropies of Fe and Ni films originate mainly from the shape anisotropy and the strain anisotropy, respectively. The major anisotropy component in many cases depends not only on composition fraction but also on $T_{\rm t}$ . For example, the RT anisotropy of 40$- $70%Ni--Fe films, when $T_{\rm t}$ is RT, mostly comes from the anisotropy of atomic pair ordering while it stems mostly from the shape anisotropy when $T_{\rm t}$  is 450$^\circ$C.  The most important cause of the spread in values of $K$ is the spread of the intrinsic anisotropic stresses superimposed on the intrinsic isotropic planar stress. It is suggested that the field cooling induced magnetic anisotropy originating from the induced crystal texture observed in the bulk alloys  is also a major origin for Co and Co-rich alloy films of hexagonal crystal structure.

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Reduced-temperature ordering of FePt nanoparticle assembled films by Fe30Pt70/Fe3O4 core/shell structure He Shu-Li(贺淑莉), Peng Yin(彭印), Liu Li-Li(刘丽丽), Jiang Hong-Wei(姜宏伟), Liu Li-Feng(刘丽峰), Zheng Wu(郑鹉), and Wang Ai-Ling(王艾玲) Chinese Physics, 2007, 16 (11):  3536-3540.  DOI: 10.1088/1009-1963/16/11/062 Abstract ( 1765 )   PDF (856KB) ( 397 )   In this paper, Fe$_{30}$Pt$_{70}$/Fe$_{3}$O$_{4}$ core/shell nanoparticles were synthesized by chemical routine and the layered polyethylenimine (PEI)-Fe$_{30}$Pt$_{70}$/Fe$_{3}$O$_{4 }$ structure was constructed by molecule-mediated self-assembly technique. The dimension of core/shell structured nanoparticles was that of 4nm core and 2 nm shell. After annealing under a flow of forming gas (50%Ar$_{2}$+30%H$_{2})$ for 1 h at or above 400℃, the iron oxide shell was reduced to Fe and diffused to Pt-rich core, which leaded to the formation of L1$_{0}$ phase FePt at low temperature. The x-ray diffraction results and magnetic properties measurement showed that the chemical ordering temperature of Fe$_{30}$Pt$_{70}$/Fe$_{3}$O$_{4}$ core/shell nanoparticles assembly can be reduced to as low as 400℃. The sample annealed at 400℃ showed the coercivity of 4 KOe with the applied field of 1.5T. The core/shell structure was suggested to be an effective way to reduce the ordering temperature obviously.

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Magnetization reversal of ultrathin Fe film grown on Si(111) using iron silicide template He Wei(何为), Zhan Qing-Feng(詹清峰), Wang De-Yong(王德勇), Chen Li-Jun(陈立军), Sun Young(孙阳), and Cheng Zhao-Hua(成昭华) Chinese Physics, 2007, 16 (11):  3541-3544.  DOI: 10.1088/1009-1963/16/11/063 Abstract ( 1385 )   PDF (809KB) ( 390 )   Ultrathin Fe films were epitaxially grown on Si(111) by using an ultrathin iron silicide film with $p(2\times2$) surface reconstruction as a template. The surface structure and magnetic properties were investigated in situ by low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), and surface magneto-optical effect (SMOKE). Polar SMOKE hysteresis loops demonstrate that the Fe ultrathin films with thickness $t<6$ ML (monolayers) exhibit perpendicular magnetic anisotropy. The characters of $M$--$H$ loops with the external magnetic field at difference angles and the angular dependence of coercivity suggest that the domain-wall pinning plays a dominant role in the magnetization reversal process.

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Electrodeposition of aligned ZnO sheet array on ITO substrate and their field emission characteristics Wang Chong(王翀), Wang Fei-Fei(王菲菲), Fu Xing-Qiu(付星球), and Wang Tai-Hong(王太宏) Chinese Physics, 2007, 16 (11):  3545-3548.  DOI: 10.1088/1009-1963/16/11/064 Abstract ( 1691 )   PDF (673KB) ( 1558 )   ZnO sheet array was fabricated by a simple electrodeposition method on the transparent ITO substrate at a temperature of about 60℃. The field emission properties of the ZnO sheet array were investigated. The fluctuation of the field emission current is less than 5% over several hours. The Fowler–Nordheim curves with a roughly linear characteristic were obtained by analysing the current density and the intensity of the electrical field. The results prove that such a simple electrochemical method can potentially meet the demands on the production of cold cathodes for field emission display.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Fast preparation and thermal transport property of TiCoSb-based half-Heusler compounds Xie Wen-Jie(谢文杰), Tang Xin-Feng(唐新峰), and Zhang Qing-Jie(张清杰) Chinese Physics, 2007, 16 (11):  3549-3552.  DOI: 10.1088/1009-1963/16/11/065 Abstract ( 1171 )   PDF (805KB) ( 565 )   TiCoSb-based half-Heusler compounds with the substitution of Zr for Ti  have been prepared quickly by combining high- nergy ball milling method with spark plasma sintering technique,  and their  thermal transport properties have been investigated. With the increase of the  concentration of Zr, the thermal conductivity of Ti$_{1 - x}$Zr$_{x}$CoSb compounds decreases significantly. Compared with the thermal conductivity of TiCoSb compound, that of Ti$_{0.5}$Zr$_{0.5}$CoSb decreases by 107% at 1000 K.