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Chin. Phys. B  
  Chin. Phys. B--2005, Vol.14, No.4
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An exponential distribution network

Liu Jing-Zhou, Tang Yi-Fa
Chin. Phys., 2005, 14 (4): 643-645 doi: 10.1088/1009-1963/14/4/001
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A complex network with an exponential distribution p(k)\propto\e{-\frac{k}{k_{c}}}with k c =3.50±0.02 is introduced and found to have assortative correlation k i nn =B+qk i (q>0) from numerical simulation.

The scale-transformation of electromagnetic theory and its applications

Li Ying-Le, Huang Ji-Ying
Chin. Phys., 2005, 14 (4): 646-655 doi: 10.1088/1009-1963/14/4/003
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The scale-transformation of electromagnetic theory is investigated in detail based on the form of Maxwell equations in scale-transformation being unchanged in different coordinate systems. The relations of electromagnetic parameters in a rectangular coordinate system and in a spherical coordinate system are presented respectively. The scale-transformation invariants for electromagnetic field are derived and their physical meaning is also presented. It is indicated by simulation that the electromagnetic waves located in medium can be considered to be isotropic due to the fact that the size of propagating vector affected by the scale factors and observing azimuth is on a size of 10 -9, which provides a new approach for investigating the electromagnetic characteristics of ellipsoidal targets.

A new non-Noether conserved quantity of the relativistic holonomic nonconservative systems in general Lie transformations

Luo Shao-Kai, Cai Jian-Le, Jia Li-Qun
Chin. Phys., 2005, 14 (4): 656-659 doi: 10.1088/1009-1963/14/4/004
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For the relativistic holonomic nonconservative system, a new Lie symmetrical non-Noether conserved quantity is given under general infinitesimal transformations of groups in which time is variable. On the basis of the theory of invariance of differential equations of motion under infinitesimal transformations for $t$ and q s , we construct the relativistic Lie symmetrical determining equations and obtain directly a new relativistic Lie symmetrical non-Noether conserved quantity of the system, which only depend on the variables $t$, q s and q s . An example is given to illustrate the application of the results.

The parametric orbits and the form invariance of three-body in one-dimension

Lou Zhi-Mei
Chin. Phys., 2005, 14 (4): 660-662 doi: 10.1088/1009-1963/14/4/005
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In this paper, the differential equations of motion of a three-body interacting pairwise by inverse cubic forces (``centrifugal potential'') in addition to linear forces (``harmonical potential'') are expressed in Ermakov formalism in two-dimension polar coordinates, and the Ermakov invariant is obtained. By rescaling of the time variable and the space coordinates, the parametric orbits of the three bodies are expressed in terms of relative energy H11 and Ermakov invariant. The form invariance of the transformations of two conserved quantities are also studied.

Exact invariants and adiabatic invariants of holonomic system in terms of quasi-coordinates

Chen Xiang-Wei, Li Yan-Min
Chin. Phys., 2005, 14 (4): 663-668 doi: 10.1088/1009-1963/14/4/006
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Based on the theory of Lie symmetries and conserved quantities, the exact invariants and adiabatic invariants of holonomic system are studied in terms of quasi-coordinates. The perturbation to symmetries for the holonomic system in terms of quasi-coordinates under small excitation is discussed. The concept of high-order adiabatic invariant is presented, and the form of exact invariants and adiabatic invariants as well as the conditions for their existence are given. Then the corresponding inverse problem is studied.

New exact excitations and soliton fission and fusion for the (2+1)-dimensional Broer--Kaup--Kupershmidt system

Fang Jian-Ping, Zheng Chun-Long
Chin. Phys., 2005, 14 (4): 669-675 doi: 10.1088/1009-1963/14/4/007
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With the help of an extended mapping approach, a series of new types of exact excitations with two arbitrary functions of the (2+1)-dimensional Broer--Kaup--Kupershmidt (BKK) system is derived. Based on the derived solitary wave excitation, some specific soliton fission and fusion solutions of the higher-dimensional BKK system are also obtained.

Localized excitations with and without propagating properties in (2+1)-dimensions obtained by a mapping approach

Zheng Chun-Long, Fang Jian-Ping, Chen Li-Qun
Chin. Phys., 2005, 14 (4): 676-682 doi: 10.1088/1009-1963/14/4/008
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By means of an extended mapping approach, a new type of variable-separation excitation is derived with two arbitrary functions in a (2+1)-dimensional modified dispersive water-wave system. Based on the derived variable-separation excitation, abundant nonpropagating and propagating solitons such as dromions, rings, peakons and compactons are revealed by selecting appropriate functions in this paper.

Gravitational quasinormal modes of the Reissner--Nordstr?m de Sitter black hole

Jing Ji-Liang, Chen Song-Bai
Chin. Phys., 2005, 14 (4): 683-689 doi: 10.1088/1009-1963/14/4/009
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By using the P\"oschl--Teller potential approximation, the quasinormal modes of the Reissner--Nordstr\"om de Sitter black hole for the axial and polar gravitational perturbations are investigated. It is shown that the magnitude of imaginary part decreases as the cosmological constant increases, but it increases as the charge, or the overtone number or the orbital angular momentum increases. The imaginary part is almost linearly related to the real part as cosmological constant changes for a fixed charge. It is also found that the gravitational quasinormal modes are the same for both the axial and polar perturbations, which proves that the quasinormal modes are determined only by the parameters of the black hole and are independent of the initial perturbations.

Evolution of spin-dependent atomic wave packets in a harmonic potential

Wen Ling-Hua, Liu Min, Kong Ling-Bo, Chen Ai-Xi, Zhan Ming-Sheng
Chin. Phys., 2005, 14 (4): 690-696 doi: 10.1088/1009-1963/14/4/010
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We have investigated theoretically the evolution of spin-dependent atomic wave packets in a harmonic magnetic trapping potential. For a Bose-condensed gas, which undergoes a Mott insulator transition and a spin-dependent transport, the atomic wavefunction can be described by an entangled single-atom state. Due to the confinement of the harmonic potential, the density distributions exhibit periodic decay and revival, which is different from the case of free expansion after switching off the combined harmonic and optical lattice potential.

Chaotic coupling synchronization of hyperchaotic oscillators

Zou Yan-Li, Zhu Jie, Chen Guan-Rang
Chin. Phys., 2005, 14 (4): 697-702 doi: 10.1088/1009-1963/14/4/011
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In this paper, two kinds of chaotic coupling synchronization schemes are presented. The synchronizability of the coupled hyperchaotic oscillators is proved mathematically and the numerical simulation is also carried out. The numerical calculation of the largest conditional Lyapunov exponent shows that in a given range of coupling strengths, chaotic-coupling synchronization is quicker than the typical continuous-coupling synchronization.

Decentralized state-feedback chaotification method of discrete Takagi--Sugeno fuzzy systems

Lu Jun-Guo
Chin. Phys., 2005, 14 (4): 703-708 doi: 10.1088/1009-1963/14/4/012
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A new chaotification method is proposed for making an arbitrarily given discrete Takagi--Sugeno (TS) fuzzy system chaotic. Based on a given discrete TS fuzzy system, the new chaotification method uses the decentralized state-feedback control and the continuous sawtooth function, instead of the modulo operation, to construct a chaotic nonlinear system, which can generate discrete chaos with the arbitrarily desired amplitude bound. We apply the improved Marotto theorem to mathematically prove that the controlled system is chaotic in the sense of Li and Yorke. In particular, an explicit formula for the computation of chaotification parameters is obtained. A numerical example is used to illustrate the theoretical results.

Theoretical analysis of cavity saturation spectroscopy of weak molecular absorbance

Ma Wei-Guang, Dong Lei, Yin Wang-Bao, Jia Suo-Tang
Chin. Phys., 2005, 14 (4): 709-713 doi: 10.1088/1009-1963/14/4/013
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A theoretical analysis of sub-Doppler molecular saturation spectroscopy by use of a confocal Fabry--Perot (CFP) cavity is presented. The effects of gas pressure, cavity length and mirror reflectivity on the saturation dip amplitude are analysed. Such a treatment can provide the optimum conditions and a guidance for the experiment of saturating the weak molecular absorption lines.

Brewster-oriented passive Q-switch intracavity optical parametric oscillator

Wan Yong, Zhu Da-Yong, Zeng Qin-Yong, Zhang Zhi-Yong, Zhang Jing, Han Kai
Chin. Phys., 2005, 14 (4): 714-719 doi: 10.1088/1009-1963/14/4/014
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The behaviour of passively Q-switched solid-state lasers containing intracavity optical parametric oscillators (OPOs) is described, and a model to optimize this system's performance is developed. Meanwhile, an Nd:YAG laser-pumped KTiOPO4 (KTP) intracavity OPO for eye safe laser output is studied experimentally. A Brewster-oriented bis-(4-dimethylaminodithiobenzil)-nickel (BDN) dye film is employed in laser cavity, which plays the double role of a passive Q-switch and a Brewster plate, to Q-switch the light to increase its intensity and polarize the light so that the polarization plane of fundamental irradiation is perpendicular to the $Z$-axis of KTP serving as the OPO nonlinear crystal, thereby providing type II phase matching conditions to generate 1.572$\mu$m eye-safe signal laser. Eye-safe signal radiations of 6.6mJ per pulse at 1.572$\mu$m wavelength and pulse width as narrow as 6.0ns (FWHM) were obtained. Peak power was up to 1.1MW.

Frequency conversion of probe wave produced by 2D interaction with relativistic ionization front

Yan Li-Xin, Zhang Yong-Sheng, Liu Jing-Ru, Lü Min
Chin. Phys., 2005, 14 (4): 753-757 doi: 10.1088/1009-1963/14/4/020
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Frequency conversion of probe electromagnetic wave induced by relativistic ionization front is theoretically analysed based on ray-tracing equations in different regimes. Downshifting as well as upshifting in frequency produced by the front is predicted. The reflected and transmitted angles can be also dramatically changed in certain cases.

Raman scattering in a four-level atomic system with hyperfine structure

Li Jia-Hua, Yang Wen-Xing, Peng Ju-Cun
Chin. Phys., 2005, 14 (4): 758-763 doi: 10.1088/1009-1963/14/4/021
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We propose and analyse an efficient Raman scheme for suppressing the absorption of a weak probe beam in a typical four-level atomic system with a nearly hyperfine doublet structure of two higher-lying excited levels for the two cases of transient regime and steady-state process. For the transient process, using the numerical calculations by a nice MATHEMATICA code, we find that the magnitude of the probe absorption at line centre of the probe transition is small compared to the standard three-level atomic system based on electromagnetically induced transparency (EIT). In particular, our results show that the probe absorption can be completely eliminated under the condition of Raman resonance, i.e. we only require that two-photon detuning is zero within the range of the hyperfine two-level frequency gap for the case of the steady state. In contrast to the standard three-level EIT scheme, one of the key advantages of our four-level Raman scheme is that under the Raman resonance condition we can observe one transparency window without the need of exact vanishing of one- and two-photon detuning. As a consequence, the atomic hyperfine structure cannot be a hindrance for obtaining EIT.

Intensity correlation time of a single-mode laser driven by two coloured noises with coloured cross-correlation with direct signal modulation

Chen Li-Mei, Cao Li, Wu Da-Jin, Wang Zhong-Long
Chin. Phys., 2005, 14 (4): 764-770 doi: 10.1088/1009-1963/14/4/022
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In this paper, the intensity correlation time T is studied for the gain-noise model of a single-mode laser driven by coloured pump noise and coloured quantum noise with coloured cross-correlation with a direct signal modulation. By using the linear approximation method, it is found that when the pump noise is modulated directly by a signal, the effects of the cross-correlation between the pump noise and the quantum noise will disappear. In addition, there exists a maximum (i.e. resonance) in the curve of the intensity correlation time $T$ versus the pump noise self-correlation time \tau1. Furthermore, when \tau1\le\tau2, the intensity correlation time T increases monotonically with the increase of $D$ and decreases monotonically with the increase of Q, but when \tau1>\tau2, the intensity correlation time T increases monotonically with the increase of Q and decreases monotonically with the increase of D.

1.15kW continuous-wave generation by diode-side-pumped two-rod Nd:YAG laser

Bo Yong, Geng Ai-Cong, Bi Yong, Sun Zhi-Pei, Yang Xiao-Dong, Peng Qin-Jun, Li Hui-Qing, Li Rui-Ning, Cui Da-Fu, Xu Zu-Yan
Chin. Phys., 2005, 14 (4): 771-773 doi: 10.1088/1009-1963/14/4/023
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A high power and high efficiency laser head with five dual-line diode arrays for the side-pumped Nd:YAG rod is developed. By mounting two laser heads of this kind and a quartz 90$^\circ$ rotator into a thermally-near-unstable symmetrical flat--flat resonator, a continuous-wave power output of 1157W at 1064nm is obtained with a beam quality factor M2 of $\sim$39. To the authors' knowledge, this is the highest power output at 1064 nm for the diode-side-pumped two-rod Nd:YAG laser.

All-optical logic-gates based on bacteriorhodopsin film

Chen Gui-Ying, Zhang Chun-Ping, Guo Zong-Xia, Tian Jian-Guo, Zhang Guang-Yin, Song Qi-Wang
Chin. Phys., 2005, 14 (4): 774-778 doi: 10.1088/1009-1963/14/4/024
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Based on self-diffraction in bacteriorhodopsin (bR) film, we propose all-optical NOT, XOR, half adder and XNOR logic operations. Using the relation between diffraction light and the polarization states of recording beams, we demonstrate NOT and XNOR logic operations. Studying the relation of polarization states among the diffracting, recording and reading beams,we implement XOR logic and half adder operations with three inputs. The methods are simple and practicable.

Switchable and spacing-tunable dual-wavelength erbium-doped fibre lasers

Feng Xin-Huan, Liu Yan-Ge, Sun Lei, Yuan Shu-Zhong, Kai Gui-Yun, Dong Xiao-Yi
Chin. Phys., 2005, 14 (4): 779-784 doi: 10.1088/1009-1963/14/4/025
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Two switchable and spacing-tunable dual-wavelength linear cavity erbium-doped fibre lasers are demonstrated experimentally. One of them utilizes a Bragg grating in polarization-maintained PANDA fibre and the other uses a Bragg grating in standard single mode fibre for wavelength selection. Both exploit the birefringence characteristics of the FBG induced by transverse strain. The proposed lasers can be made to operate in stable dual-wavelength or switch between two wavelengths at room temperature just by simple adjustment of a polarization controller. Transverse strain loading on the FBG allows the wavelength spacing to be controlled.

Coherent population transfer in Rydberg potassium atom via stimulated Raman adiabatic passage

Zhang Xian-Zhou, Han Hui-Li, Han Hong-Pei, Fan Xiao-Wei
Chin. Phys., 2005, 14 (4): 720-724 doi: 10.1088/1009-1963/14/4/015
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By using the time-dependent multilevel approach, the coherent population transfer among the quantum states of potassium atom driven by partially overlapped pulse is studied. The result shows that the complete population transfer is related to both the pulse duration and the overlap, and takes place when the pulse duration and overlap each reach an adequate value, and at the same time population trapping is also formed.

Observation of EIA in closed and open caesium atomic system

Zhao Jian-Ming, Zhao Yan-Ting, Huang Tao, Xiao Lian-Tuan, Jia Suo-Tang
Chin. Phys., 2005, 14 (4): 725-728 doi: 10.1088/1009-1963/14/4/016
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We present an experimental study on electromagnetically induced absorption (EIA) in the closed transition of a degenerate two-level Cs atomic system.The coupling and probe lasers coupled with the transition 6S1/2 F=4 to 6P3/2F'=5 of caesium atom. The signal of EIA was obtained and the frequency detuning and intensity effect of the pumping laser were experimentally investigated. The EIA signal in 6S1/2 F =4 to 6P3/2F'=4 and 6S1/2 F =4 to 6P3/2F'=3 open transitions was also obtained. As the repumping laser couples with the transition of 6S1/2 F =3 to 6P3/2F'=4, the EIA signal is increased due to the hyperfine optical pumping.

Oscillatory disturbance in force calibration of optical tweezers

Liu Chun-Xiang, Guo Hong-Lian, Jiang Yu-Qiang, Li Zhao-Lin, Cheng Bing-Ying, Zhang Dao-Zhong
Chin. Phys., 2005, 14 (4): 729-733 doi: 10.1088/1009-1963/14/4/017
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In the calibration of the optical trap stiffness, it is found that there appears an attenuating oscillation as an oscillatory disturbance added tothe trapped bead movement, when the scanner is driven by a triangular waveinput. An equivalent oscillator model is put forward to explain themechanism of the oscillatory disturbance. Both the measurements andcalculations show that the attenuating oscillation comes from theoscillation of the scanner and the triangular wave drive causes thisadditional oscillation of the scanner. Furthermore, the analysis indicatesthat the oscillatory disturbance will become stronger, when the stiffness ofthe trap increases or the natural frequency of the scanner decreases. Weadopt another driving way, i.e. a sinusoidal wave input is used instead ofthe triangular wave input. Our experiment has verified that in this case theoscillatory disturbance is eliminated completely.

Mechanism for unidirectional movement of kinesin

Xie Ping, Dou Shuo-Xing, Wang Peng-Ye
Chin. Phys., 2005, 14 (4): 734-743 doi: 10.1088/1009-1963/14/4/018
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Kinesin motors have been studied extensively both experimentally and theoretically. However, the microscopic mechanism of the processive movement of kinesin is still an open question. In this paper, we propose a hand-over-hand model for the processivity of kinesin, which is based on chemical, mechanical, and electrical couplings. In the model the ATPase rates of the two kinesin heads are regulated by forces, both from internal elasticity and external load, exerted on their necks. At a low external load, the ATPase rate of the trailing head is much higher than the leading head and the two heads are coordinated in their ATP hydrolysis and mechanical cycles. The motor walks processively with one ATP being hydrolyzed per step. At a higher forward external load, the ATPase rates of the two heads become comparable and thus the two heads are no longer well coordinated in their ATP hydrolysis and mechanical cycles. The model is consistent with the structural study of kinesin and the measured pathway of the kinesin ATPase. Using the model we have estimated the driving force to be $\sim$5.8pN, which is in agreement with the experimental results (5--7.5pN). The estimated time for moving one step ($\sim$10$\mu$s) is also consistent with the measured values of 0--50$\mu$s. The previous observation of substeps within the 8nm step is explained. The shapes of velocity versus load (both positive and negative) curves show close resemblance to previous experimental results.

Model for processive movement of myosin V and myosin VI

Xie Ping, Dou Shuo-Xing, Wang Peng-Ye
Chin. Phys., 2005, 14 (4): 744-752 doi: 10.1088/1009-1963/14/4/019
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Myosin V and myosin VI are two classes of two-headed molecular motors of the myosin superfamily that move processively along helical actin filaments in opposite directions. Here we present a hand-over-hand model for their processive movements. In the model, the moving direction of a dimeric molecular motor is automatically determined by the relative orientation between its two heads at free state and its head's binding orientation on track filament. This determines that myosin V moves toward the barbed end and myosin VI moves toward the pointed end of actin. During the moving period in one step, one head remains bound to actin for myosin V whereas two heads are detached for myosin VI: the moving manner is determined by the length of neck domain. This naturally explains the similar dynamic behaviours but opposite moving directions of myosin VI and mutant myosin V (the neck of which is truncated to only one-sixth of the native length). Because of different moving manners, myosin VI and mutant myosin V exhibit significantly broader step-size distribution than native myosin V. However,all the three motors give the same mean step size of $\sim $36nm (the pseudo-repeat of actin helix). All these theoretical results are in agreement with previous experimental ones.

Preparation of high-quality hydrogenated amorphous silicon film with a new microwave electron cyclotron resonance chemical vapour deposition system assisted with hot wire

Zhu Xiu-Hong, Chen Guang-Hua, Yin Sheng-Yi, Rong Yan-Dong, Zhang Wen-Li, Hu Yue-Hui
Chin. Phys., 2005, 14 (4): 834-837 doi: 10.1088/1009-1963/14/4/036
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The preparation of high-quality hydrogenated amorphous silicon (a-Si:H) film with a new microwave electron cyclotron resonance-chemical vapour deposition (MWECR-CVD) system assisted with hot wire is presented. In this system the hot wire plays an important role in perfecting the microstructure as well as improving the stability and the optoelectronic properties of the a-Si:H film. The experimental results indicate that in the microstructure of the a-Si:H film, the concentration of dihydride is decreased and a trace of microcrystalline occurs, which is useful to improve its stability, and that in the optoelectronic properties of the a-Si:H film, the deposition rate reaches above 2.0nm/s and the photosensitivity increases up to 4.71$\times $105.

Modelling the crystal growth in highly undercooled alloy melts by non-isothermal phase-field method

Li Mei-E, Yang Gen-Cang, Zhou Yao-He
Chin. Phys., 2005, 14 (4): 838-843 doi: 10.1088/1009-1963/14/4/037
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A non-isothermal phase-field model is used to simulate the rapid solidification of highly undercooled alloy melts. The influence of undercooling on the solidification process is studied. It is indicated that with the increase of undercooling, the dendrite morphology changes from poorly developed dendrite, via the well-developed dendrite containing secondary and ternary arms, to the compact diamond-shaped grain. With increasing undercooling, the tip radius changes in the following rule: decrease $\to$ increase $\to$ decrease while the growth velocity increases constantly,which is consistent with the results predicted by the Boettinger--Coriell--Trivedi model. The thermal, solutal and kinetic undercooling contributions under different initial undercooling are also determined. It is shown that when the undercooling is increased beyond a certain value, the thermal undercooling contribution exceeds the solutal contribution and the dendrite growth transits from solutal diffusion controlled to thermal diffusion controlled one.

A molecular level study of liquid water with a flexible water model

Liu Chang-Song, Liang Yun-Feng, Zhu Zhen-Gang, Li Guang-Xu
Chin. Phys., 2005, 14 (4): 785-790 doi: 10.1088/1009-1963/14/4/026
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The structural properties of water at different temperatures and pressures have been investigated by using a flexible water model and the inherent structure mechanism. The presence of 60$^\circ$ peak in the O--O--O angle distribution function and the behaviours of the hydrogen bonds in the first shell indicate that some water molecules in the second shell move toward the central molecules through the bending (not breaking) of hydrogen bonds and even become first-shell molecules of the central molecule on the basis of the O--O cutoff distance but not first-shell molecules by means of the hydrogen-bond criterion. The inherent-structure analysis of the O--O radial distribution functions at different pressures shows that the first peak is almost independent of the pressure; the position of second peak moves from 0.45 to 0.32nm as the pressure increases from $1\times 10^5$Pa to $1\times 10^9$Pa. This particularly evident pressure effect, i.e. the constant nearest-neighbours and the transformation of outer-neighbours on the basis of O--O distance, together with the results at different temperatures, gives a positive evidence for the two-state outer-neighbour mixture model: liquid water is a mixture of Ice-Ih-type-bonding and Ice-II-type bonding structures.

An improvement of the lattice theory of dislocation for a two-dimensional triangular crystal

Wang Shao-Feng
Chin. Phys., 2005, 14 (4): 791-795 doi: 10.1088/1009-1963/14/4/027
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The structure of dislocation in a two-dimensional triangular crystal has been studied theoretically on the basis of atomic interaction and lattice statics. The theory presented in this paper is an improvement to that published previously. Within a reasonable interaction approximation, a new dislocation equation is obtained, which remedies a fault existing in the lattice theory of dislocation. A better simplification of non-diagonal terms of the kernel is given. The solution of the new dislocation equation asymptotically becomes the same as that obtained in the elastic theory, and agrees with experimental data. It is found that the solution is formally identical with that proposed phenomenologically by Foreman {\em et al}, where the parameter can be chosen freely, but cannot uniquely determined from theory. Indeed, if the parameter in the expression of the solution is selected suitably, the expression can be well applied to describe the fine structure of the dislocation.

Near-field x-ray phase contrast imaging and phase retrieval algorithm

Zhu Hua-Feng, Xie Hong-Lan, Gao Hong-Yi, Chen Jian-Wen, Li Ru-Xin, Xu Zhi-Zhan
Chin. Phys., 2005, 14 (4): 796-801 doi: 10.1088/1009-1963/14/4/028
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Theoretical analyses of x-ray diffraction phase contrast imaging and near field phase retrieval method are presented. A new variant of the near field intensity distribution is derived with the optimal phase imaging distance and spatial frequency of object taken into account. Numerical examples of phase retrieval using simulated data are also given. On the above basis, the influence of detecting distance and polychroism of radiation on the phase contrast image and the retrieved phase distribution are discussed. The present results should be useful in the practical application of in-line phase contrast imaging.

Investigation of multicomponent chemical short-range order in NiZr2

Hou Huai-Yu, Chen Guo-Liang, Chen Guang
Chin. Phys., 2005, 14 (4): 802-807 doi: 10.1088/1009-1963/14/4/029
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The local atomic configuration of multicomponent chemical short-range order (MCSRO) in NiZr2 has been investigated by means of molecular dynamics simulation (MD) in a wide temperature range. The potential functions for the system based on the embedded atom method are constructed and the parameters are obtained by fitting the structure and properties of NiZr2 crystal. The static structures such as pair distribution functions and the distribution of coordination number have been calculated. The local atomic configurations of the MCSROs in the melt were demonstrated as distorted coordination polyhedron of the compound structure and/or the structure similar to cubooctahedron analogues. It is indicated by the results of MD simulation that above the melting point the atomic packing of long-range order disappears, but the chemical interaction of coordinated atoms still exists, which leads to the formation of various MCSROs with atomic configurations similar to the stable or metastable unit cell of NiZr2 compound. When the system is just melted, many icosahedral polyhedron configurations appear, which decrease as the over-heating temperature increases.

A percolation study of RTS noise in deep sub-micron MOSFET by Monte Carlo simulation

Ma Zhong-Fa, Zhuang Yi-Qi, Du Lei, Wei Shan
Chin. Phys., 2005, 14 (4): 808-811 doi: 10.1088/1009-1963/14/4/030
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Based on percolation theory and random telegraph signal (RTS) noise generation mechanism, a numerical model for RTS in deep submicron metal-oxide-semiconductor field-effect transistor (MOSFET) was presented,with which the dependence of ${\tau_{\rm c} }/ {\tau_\e }$ (where $\tau_{\rm c} $=capture time, $\tau_\e$=emission period ) on energy levels and trap depth with respect to the interface of traps can be simulated. Compared with experimental results, the simulated ones showed a good qualitative agreement.

Enhancement of absorptive optical nonlinearity of asymmetrically coupled quantum well structures

Hu Zhen-Hua, Huang De-Xiu
Chin. Phys., 2005, 14 (4): 812-817 doi: 10.1088/1009-1963/14/4/031
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The third-order nonlinear susceptibility $\chi ^{({3})}$ of asymmetrically coupled quantum well (ACQW) structure is calculated by employing a V-type three-level model. The efficiency of absorptive optical nonlinearity, which we define as the ratio of the third-order nonlinear susceptibility $\chi ^{({3})}$ to the linear absorptive coefficient $\alpha_0$, is analysed for different electronic coherence oscillation frequencies. We show that the efficiency is enhanced with the increase of the electronic coherence oscillation frequency between the two wells but is degenerated as that of a single quantum well when the electronic coherence oscillation frequency is zero. Compared with single quantum well, the ACQW designed has the property of nonlinear absorption and dispersion depending strongly on the external electric field along the growth direction. We predict that ACQW structures can provide both high efficiency limiters and controllable optical Kerr switch in future communication systems.

Spontaneous magnetostriction of Y2Fe16Al compound

Hao Yan-Ming, Zhao Miao, Zhou Yan
Chin. Phys., 2005, 14 (4): 818-820 doi: 10.1088/1009-1963/14/4/032
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The structure and magnetic properties of Y2Fe16Al compound have been investigated by means of x-ray diffraction and magnetization measurements. The Y2Fe Fe16Al compound has a hexagonal Th$_{2}$Ni$_{17}$-type structure. Negative thermal expansion was found in Y2Fe16Al compound in the temperature range from 332 to 438K by x-ray dilatometry. The coefficient of the average thermal expansion is \alpha =-3.4\times 10-5K-1. The spontaneous magnetostrictive deformations from 293 to 427K have been calculated based on the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation \textit{$\omega $}$_{\rm S}$ decreases from 5.4$\times $10-3to near zero with temperature increasing from 293 to 427K, the spontaneous linear magnetostrictive deformation \textit{$\lambda $}$_{\rm c}$ along the $c$ axis is much larger than the spontaneous linear magnetostrictive deformation \textit{$\lambda $}$_{\rm a}$ in basal-plane in the same temperature range except near 427K.

Critical behaviour of coupled organic ferromagnet chains

Guo Ji-Yong, Chen Yu-Guang, Chen Hong
Chin. Phys., 2005, 14 (4): 821-825 doi: 10.1088/1009-1963/14/4/033
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The interchain coupling in a model, which is most relevant to organic ferromagnets, is studied by a kind of mean field theory. A full phase diagram is given for this model. It is shown that the interchain coupling dramatically affects the ferromagnetic order in the ground state. When the interchain coupling reaches a critical value, the high-spin ground state disappears and the system may transit from ferromagnetic phase into Kondo-singlet phase.

Spectroscopic characteristic of conical bubble luminescence

Chen Qi-Dai, Fu Li-Min, Ai Xi-Cheng, Zhang Jian-Ping, Wang Long
Chin. Phys., 2005, 14 (4): 826-829 doi: 10.1088/1009-1963/14/4/034
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The conical bubble sonoluminescence (CBSL) from the collapse of the bubble was observed in an improved U-tube apparatus. The emitted light energy of a single CBSL flash was measured to be $\sim $ 1.4mJ. The pulse width was about 100$\mu$s. The spectra of luminescence were continuum superimposed with the spectral bands from the excited-state C2, CN and CH. The CBSL provides a link between the light emission of the single-bubble and the multi-bubble sonoluminescence (SBSL and MBSL).

Effect of annealing on photoluminescence and microstructures of InGaN/GaN multi-quantum well with Mg-doped p-type GaN

Li Zhong-Hui, Yu Tong-Jun, Yang Zhi-Jian, Feng Yu-Chun, Zhang Guo-Yi, Guo Bao-Ping, Niu Han-Ben
Chin. Phys., 2005, 14 (4): 830-833 doi: 10.1088/1009-1963/14/4/035
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InGaN/GaN multi-quantum well structure with Mg-doped p-type GaN was grown by low-pressure metalorganic vapour phase epitaxy. After rapid-thermal-annealing at 700 and 900${^\circ}$C, both the red-shift and the blue-shift of the photoluminescence (PL) peak, the decreased and the enhancement of the PL intensity were observed. The transmission electron microscopic images showed that InGaN multi-quantum-dots-like (MQD-like) structures with dimensions less than 5$\tm$10nm were formed in InGaN wells. The changes of PL spectra could be tentatively attributed to the competition between the red-shift mechanism of the quantum-confined Stark effect and the blue-shift mechanism of the quantum size effect due to MQD-like structures.

An improved south Asian summer monsoon index with Monte Carlo test

Shi Neng, Gu Jun-Qiang, Yi Yan-Ming, Lin Zhen-Min
Chin. Phys., 2005, 14 (4): 844-849 doi: 10.1088/1009-1963/14/4/038
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The Indian monsoon intensity index suggested by Webster and Yang (WY index) is optimized and improved in this paper. At first, the area (40$^{\circ}$E--110$^{\circ}$E, 0$^{\circ}$--20$^{\circ}$N) for calculating the zonal wind-shear between 850hPa and 200hPa in the WY index is optimized and adjusted according to the significance test of differences of wind fields. Then the regionally averaged zonal wind is computed over the optimized area. Finally, the optimal linear combination of the zonal winds at the two levels is performed using the regression method, thus defining a new broad-scale circulation index for the interannual variability of the south Asian summer monsoon, i.e. the improved south Asian summer monsoon index. Results indicate that the improved south Asian summer monsoon index has two advantages: its correlation with the All Indian Summer Monsoon Rainfall index is higher than that of WY index, and its computational domain of circulation is also larger than that of WY index. The computational results based on the 1948--98 NCAR/NCEP wind data indicate that the correlation of the improved SASM index with the All Indian Summer Monsoon Rainfall index is higher than that of WY index by 0.27.

Interdecadal change of atmospheric stationary waves and North China drought

Dai Xin-Gang, Fu Cong-Bin, Wang Ping
Chin. Phys., 2005, 14 (4): 850-858 doi: 10.1088/1009-1963/14/4/039
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The inderdecadal change of atmospheric stationary waves (ATW) has been investigated for the two periods 1956--77 and 1978--99. The trough of ATW in the middle and low layer of the troposphere over the Asian continent has experienced a significant weakening during the past two decades, which exerts a great influence on the North China climate. The ATW in 200\,hPa has also exhibited some changes since 1977, as a stationary ridge appeared over the northwestern China while a stationary trough appeared above North China. This leads to an increasing of the upward motion above northwestern China and a decreasing above North China. A west--east section of the stationary waves at 40$^\circ$N shows that the ATW above North China tilted westward for the period 1956--77, but was almost upright during 1978--99. The composite analysis confirms that the climate mean ATW pattern after 1977 is similar to the dry pattern for North China, while the rainy pattern is similar to that before 1977. In consequence, the North China drought is partly due to the interdecadal change of the ATW over boreal Asia in the recent two decades.

Gravitational effect of centre mass with electric charge and a large number of magnetic monopoles

Gong Tian-Xi, Li Ai-Gen, Wang Yong-Jiu
Chin. Phys., 2005, 14 (4): 859-862 doi: 10.1088/1009-1963/14/4/040
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In this paper, using an elegant mathematical method advanced by us, we calculate the orbital effect in the gravitational field of the centre mass with electric charge and a large number of magnetic monopoles. Generalizing the effect in the Schwarzschild field, we obtain interesting results by discussing the parameters of the celestial body that provide a feasible experimental verification of the general relativity.

Massive molecular cloud cores and activities of star formation

Zhou Wu-Fei, Wu Yue-Fang, Wei Yue, Ju Bing-Gang
Chin. Phys., 2005, 14 (4): 863-868 doi: 10.1088/1009-1963/14/4/041
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We have mapped 23 sources in the $J$=1--0 lines of 12CO, 13CO and C18O with the 13.7-m telescope at Qinghai station of Purple Mountain Observatory.The samples were chosen from the massive star formation regions whose single point lines have the broad-wing profile. The mapping shows that 12 clouds have cores and 5 outflows were identified with the 12CO CO $J$=1--0 lines. Among the 12 cores, systematic velocity shifts were found in 2 cores, and blue asymmetric double-peak profile of 12CO line was found in IRAS 19529+2704, indicating that it may be an infall candidate. Physical parameters of the cores and outflows were derived from the local thermodynamic equilibrium assumption.The masses range from $\sim 9.4\times 102M_{ \odot }$ to $\sim 2.2\times 105M_{ \odot }$. The hydrogen molecule densities range from $\sim 3.4\times 102{\rm cm}-3 to $\sim 1.2\times 104{\rm cm}-3. The molecular outflows have masses larger than 3.5$M_{ \odot }$, and kinetic energies greater than 0.9$\times 1038J. The outflows have significantly greater masses and kinetic energies than those from low-mass young stellar objects (YSOs). For the cores, 2MASS data are available, dozens of 2MASS sources with different colour indices and brightness are often found around IRAS source, among which the reddest 2MASS source is always within the IRAS error ellipse thus probably corresponds to the IRAS source.
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