Table of Content

20 May 2007, Volume 16 Issue 5 Previous Issue    Next Issue

GENERAL

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Discrete integrable couplings associated with modified Korteweg--de Vries lattice and two hierarchies of discrete soliton equations Dong Huan-He 2007, 16 (5):  1177-1181.  doi: 10.1088/1009-1963/16/5/001 Abstract ( 0 )   PDF (97KB) ([an error occurred while processing this directive])   A direct way to construct integrable couplings for discrete systems is presented by use of two semi-direct sum Lie algebras. As their applications, the discrete integrable couplings associated with modified Korteweg--de Vries (m-KdV) lattice and two hierarchies of discrete soliton equations are developed. It is also indicated that the study of integrable couplings using semi-direct sums of Lie algebras is an important step towards the complete classification of integrable couplings.

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The construction of conserved quantities for linearly coupled oscillators and study of symmetries about the conserved quantities Lou Zhi-Mei 2007, 16 (5):  1182-1185.  doi: 10.1088/1009-1963/16/5/002 Abstract ( 0 )   PDF (83KB) ([an error occurred while processing this directive])   In this paper, the conserved quantities are constructed using two methods. The first method is by making an ansatz of the conserved quantity and then using the definition of Poisson bracket to obtain the coefficients in the ansatz. The main procedure for the second method is given as follows. Firstly, the coupled terms in Lagrangian are eliminated by changing the coordinate scales and rotating the coordinate axes, secondly, the conserved quantities are obtain in new coordinate directly, and at last, the conserved quantities are expressed in the original coordinates by using the inverse transform of the coordinates. The Noether symmetry and Lie symmetry of the infinitesimal transformations about the conserved quantities are also studied in this paper.

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Mathematical concepts and their physical foundation in the nonstandard analysis theory of turbulence Wu Feng 2007, 16 (5):  1186-1196.  doi: 10.1088/1009-1963/16/5/003 Abstract ( 0 )   PDF (348KB) ([an error occurred while processing this directive])   Main mathematical concepts and their physical foundation in the nonstandard analysis theory of turbulence are presented and discussed. The underlying fact is that there does not exist the absolute zero fluid-volume. Therefore, the physical object corresponding to the absolute point is just the uniform fluid-particle. The fluid-particle, in general, corresponds to the monad. The uniform fluid-particle corresponds to the uniform monad, while the nonuniform fluid-particle to the nonuniform monad. There are two kinds of the differentiations, one is based on the absolute point, and the other based on the monad. The former is adopted in the Navier--Stokes equations, and the latter in the fundamental equations presented in this paper for the nonstandard analysis theory of turbulence. The continuity of fluid is elucidated by virtue of the concepts of the fluid-particle and fluid-particle at a lower level. Furthermore, the characters of the continuity in two cases, i.e. in the standard and nonstandard analyses, are presented in this paper. And the difference in discretization between the Navier--Stokes equations and the fundamental equations given herein is also pointed out.

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Quantum secure direct communication via partially entangled states Man Zhong-Xiao, Xia Yun-Jie 2007, 16 (5):  1197-1200.  doi: 10.1088/1009-1963/16/5/004 Abstract ( 0 )   PDF (102KB) ([an error occurred while processing this directive])   We present in this paper a quantum secure direct communication (QSDC) protocol by using partially entangled states. In the scheme a third party (Trent) is introduced to authenticate the participants. After authentication, Alice can directly, deterministically and successfully send a secret message to Bob. The security of the scheme is also discussed and confirmed.

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Exotic interactions between solitons of the (2+1)-dimensional asymmetric Nizhnik--Novikov--Veselov system Dai Chao-Qing, Zhou Guo-Quan 2007, 16 (5):  1201-1208.  doi: 10.1088/1009-1963/16/5/005 Abstract ( 0 )   PDF (2243KB) ([an error occurred while processing this directive])   Starting from the extended tanh-function method (ETM) based on the mapping method, the variable separation solutions of the (2+1)-dimensional asymmetric Nizhnik--Novikov--Veselov (ANNV) system are derived. By further study, we find that these variable separation solutions are seemingly independent of but actually dependent on each other. Based on the variable separation solution and by choosing appropriate functions, some novel and interesting interactions between special solitons, such as bell-like compacton, peakon-like compacton and compacton-like semi-foldon, are investigated.

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Remote preparation of a Greenberger--Horne--Zeilinger state via a two-particle entangled state Lin Xiu, Li Hong-Cai, Lin Xiu-Min, Li Xing-Hua, Yang Rong-Can 2007, 16 (5):  1209-1214.  doi: 10.1088/1009-1963/16/5/006 Abstract ( 0 )   PDF (134KB) ([an error occurred while processing this directive])   We present two schemes for realizing the remote preparation of a Greenberger--Horne--Zeilinger (GHZ) state. The first scheme is to remotely prepare a general N-particle GHZ state with two steps. One is to prepare a qubit state by using finite classical bits from sender to receiver via a two-particle entangled state, and the other is that the receiver introduces N - 1 additional particles and performs N - 1 controlled-not (C-Not) operations. The second scheme is to remotely prepare an N-atom GHZ state via a two-atom entangled state in cavity quantum electrodynamics (QED). The two schemes require only a two-particle entangled state used as a quantum channel, so we reduce the requirement for entanglement.

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One-step discrimination scheme on N-particle Greenberger--Horne--Zeilinger bases Wang Xin-Wen, Liu Xiang, Fang Mao-Fa 2007, 16 (5):  1215-1219.  doi: 10.1088/1009-1963/16/5/007 Abstract ( 0 )   PDF (116KB) ([an error occurred while processing this directive])   We present an experimentally feasible one-step discrimination scheme on Bell bases with trapped ions, and then generalize it to the case of N-ion Greenberger--Horne--Zeilinger (GHZ) bases. In the scheme, all the orthogonal and complete N-ion GHZ internal states can be exactly discriminated only by one step, and thus it takes very short time. Moreover, the scheme is insensitive to thermal motion and dose not require the individual addressing of the ions. The Bell-state and GHZ-state one-step discrimination scheme can be widely used in quantum information processing based on ion-trap set-up.

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Generation of multi-atom cluster states via an unconventional geometric phase shift in cavity QED Jin Xing-Ri, Zhang Ying-Qiao, Zhang Shou, Jin Dong-Ze 2007, 16 (5):  1220-1224.  doi: 10.1088/1009-1963/16/5/008 Abstract ( 0 )   PDF (118KB) ([an error occurred while processing this directive])   This paper proposes two schemes to generate the multi-atom cluster states. The first scheme is based on the interaction of atoms with a highly detuned cavity mode and a classical field, the second scheme is based on the interaction of atoms with a cavity mode, strongly driven by a resonant classical field.

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Entanglement concentration and teleportation of multipartite entangled states in an ion trap Pan Chang-Ning, Fang Mao-Fa 2007, 16 (5):  1225-1228.  doi: 10.1088/1009-1963/16/5/009 Abstract ( 0 )   PDF (100KB) ([an error occurred while processing this directive])   We propose an effective scheme for the entanglement concentration of a four-particle state via entanglement swapping in an ion trap. Taking the maximally entangled state after concentration as a quantum channel, we can faithfully and determinatively teleport quantum entangled states from Alice to Bob without the joint Bell-state measurement. In the process of constructing the quantum channel, we adopt entanglement swapping to avoid the decrease of entanglement during the distribution of particles. Thus our scheme provides a new prospect for quantum teleportation over a longer distance. Furthermore, the success probability of our scheme is 1.0.

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Secure deterministic communication in a quantum loss channel using quantum error correction code Wu Shuang, Liang Lin-Mei, Li Cheng-Zu 2007, 16 (5):  1229-1232.  doi: 10.1088/1009-1963/16/5/010 Abstract ( 0 )   PDF (101KB) ([an error occurred while processing this directive])   The loss of a quantum channel leads to an irretrievable particle loss as well as information. In this paper, the loss of quantum channel is analysed and a method is put forward to recover the particle and information loss effectively using universal quantum error correction. Then a secure direct communication scheme is proposed, such that in a loss channel the information that an eavesdropper can obtain would be limited to arbitrarily small when the code is properly chosen and the correction operation is properly arranged.

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Explicit solutions of Boussinesq--Burgers equation Wang Zheng-Yan, Chen Ai-Hua 2007, 16 (5):  1233-1238.  doi: 10.1088/1009-1963/16/5/011 Abstract ( 0 )   PDF (1341KB) ([an error occurred while processing this directive])   Darboux transformation with multi-parameters for the Boussinesq--Burgers (B--B) equation is derived. For an application, some important explicit solutions of the B--B equation are obtained, including 2N-soliton solution and periodic solution. Finally, some elegant and interesting figures are plotted.

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The classification and analysis of dynamic networks Guo Jin-Li 2007, 16 (5):  1239-1245.  doi: 10.1088/1009-1963/16/5/012 Abstract ( 0 )   PDF (138KB) ([an error occurred while processing this directive])   In this paper we, firstly, classify the complex networks in which the nodes are of the lifetime distribution. Secondly, in order to study complex networks in terms of queuing system and homogeneous Markov chain, we establish the relation between the complex networks and queuing system, providing a new way of studying complex networks. Thirdly, we prove that there exist stationary degree distributions of M--G--P network, and obtain the analytic expression of the distribution by means of Markov chain theory. We also obtain the average path length and clustering coefficient of the network. The results show that M--G--P network is not only scale-free but also of a small-world feature in proper conditions.

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Generalized projective synchronization of a class of chaotic (hyperchaotic) systems with uncertain parameters Jia Zhen, Lu Jun-An, Deng Guang-Ming, Zhang Qun-Jiao 2007, 16 (5):  1246-1251.  doi: 10.1088/1009-1963/16/5/013 Abstract ( 0 )   PDF (587KB) ([an error occurred while processing this directive])   In this paper is investigated the generalized projective synchronization of a class of chaotic (or hyperchaotic) systems, in which certain parameters can be separated from uncertain parameters. Based on the adaptive technique, the globally generalized projective synchronization of two identical chaotic (hyperchaotic) systems is achieved by designing a novel nonlinear controller. Furthermore, the parameter identification is realized simultaneously. A sufficient condition for the globally projective synchronization is obtained. Finally, by taking the hyperchaotic Lü system as example, some numerical simulations are provided to demonstrate the effectiveness and feasibility of the proposed technique.

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A new method of determining the optimal embedding dimension based on nonlinear prediction Meng Qing-Fang, Peng Yu-Hua, Xue Pei-Jun 2007, 16 (5):  1252-1257.  doi: 10.1088/1009-1963/16/5/014 Abstract ( 0 )   PDF (514KB) ([an error occurred while processing this directive])   A new method is proposed to determine the optimal embedding dimension from a scalar time series in this paper. This method determines the optimal embedding dimension by optimizing the nonlinear autoregressive prediction model parameterized by the embedding dimension and the nonlinear degree. Simulation results show the effectiveness of this method. And this method is applicable to a short time series, stable to noise, computationally efficient, and without any purposely introduced parameters.

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Chaotifying a stable linear controllable system by single input state feedback Wu Zheng-Mao, Lu Jun-Guo, Xie Jian-Ying 2007, 16 (5):  1258-1262.  doi: 10.1088/1009-1963/16/5/015 Abstract ( 0 )   PDF (628KB) ([an error occurred while processing this directive])   In this paper, an approach for chaotifying a stable controllable linear system via single input state-feedback is presented. The overflow function of the system states is designed as the feedback controller, which can make the fixed point of the closed-loop system to be a snap-back repeller, thereby yields chaotic dynamics. Based on the Marotto theorem, it proves theoretically that the closed-loop system is chaotic in the sense of Li and Yorke. Finally, the simulation results are used to illustrate the effectiveness of the proposed method.

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Chaotic synchronization for a class of fractional-order chaotic systems Zhou Ping 2007, 16 (5):  1263-1266.  doi: 10.1088/1009-1963/16/5/016 Abstract ( 0 )   PDF (264KB) ([an error occurred while processing this directive])   In this paper, a very simple synchronization method is presented for a class of fractional-order chaotic systems only via feedback control. The synchronization technique, based on the stability theory of fractional-order systems, is simple and theoretically rigorous.

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A cellular automata model with probability infection and spatial dispersion Jin Zhen, Liu Quan-Xing, Mainul Haque 2007, 16 (5):  1267-1275.  doi: 10.1088/1009-1963/16/5/017 Abstract ( 0 )   PDF (1373KB) ([an error occurred while processing this directive])   In this article, we have proposed an epidemic model based on the probability cellular automata theory. The essential mathematical features are analysed with the help of stability theory. We have given an alternative modelling approach for the spatiotemporal system which is more realistic from the practical point of view. A discrete and spatiotemporal approach is shown by using cellular automata theory. It is interesting to note that both the size of the endemic equilibrium and the density of the individuals increase with the increase of the neighbourhood size and infection rate, but the infections decrease with the increase of the recovery rate. The stability of the system around the positive interior equilibrium has been shown by using a suitable Lyapunov function. Finally, experimental data simulation for SARS disease in China in 2003 and a brief discussion are given.

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The simulation of temperature dependence of responsivity and response time for 6H-SiC UV photodetector Zhang Yi-Men, Zhou Yong-Hua, Zhang Yu-Ming 2007, 16 (5):  1276-1279.  doi: 10.1088/1009-1963/16/5/018 Abstract ( 0 )   PDF (417KB) ([an error occurred while processing this directive])   In this paper the temperature dependence of responsivity and response time for 6H-SiC ultraviolet (UV) photodetector is simulated based on numerical model in the range from 300K to 900K. The simulation results show that the responsivity and the response time of device are less sensitive to temperature and this kind of UV photodetector has excellent temperature stability. Also the effects of device structure and bias voltage on the responsivity and the response time are presented. The thicker the drift region is, the higher the responsivity and the longer the response time are. So the thickness of drift region has to be carefully designed to make trade-off between responsivity and response time.

NUCLEAR PHYSICS

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Lie algebraic analysis for the beam transport in the spherical electrostatic analyser Lü Jian-Qin, Zhang Zhuo 2007, 16 (5):  1280-1284.  doi: 10.1088/1009-1963/16/5/019 Abstract ( 0 )   PDF (116KB) ([an error occurred while processing this directive])   This paper uses the Lie algebraic method to analyse the charged particle trajectories in the spherical electrostatic analyser, and obtains the nonlinear solutions. The results show that the focusing abilities both in the x and y directions of the analyser are almost the same. Moreover, there exist dispersion effects in the x direction, and no dispersion effects in the y direction.

ATOMIC AND MOLECULAR PHYSICS

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Energy loss of low energy ion N+q grazing on the Al(111) surface Hu Bi-Tao, Chen Chun-Hua, Song Yu-Shou, Gu Jian-Gang 2007, 16 (5):  1285-1289.  doi: 10.1088/1009-1963/16/5/020 Abstract ( 0 )   PDF (339KB) ([an error occurred while processing this directive])   The total energy loss of N+q ions (for v< Bohr velocity) grazing on the Al(111) has been simulated without any `fit' parameter and compared with the experimental data. The energy loss due to the charge exchange, happening before the N+q hits the Al(111) surface, is studied. The present simulation shows that the energy loss strongly depends on the charge state of the projectile and the lattice orientation of Al(111) surface. The calculated total energy loss agrees with experimental data very well.

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The molecular structure and analytical potential energy function of HCO (X2A') Wu Dong-Lan, Cheng Xin-Lu, Yang Xiang-Dong, Xie An-Dong, Ruan Wen, Yu Xiao-Guang, Wan Hui-Jun 2007, 16 (5):  1290-1294.  doi: 10.1088/1009-1963/16/5/021 Abstract ( 0 )   PDF (343KB) ([an error occurred while processing this directive])   In this paper the equilibrium structure of HCO has been optimized by using density functional theory (DFT)/ B3P86 method and CC-PVTZ basis. It has a bent (Cs, X2A') ground state structure with an angle of 124.4095℃. The vibronic frequencies and force constants have also been calculated. Based on the principles of atomic and molecular reaction statics, the possible electronic states and reasonable dissociation limits for the ground state of HCO molecule have been determined. The analytic potential energy function of HCO ( X2A') molecule has been derived by using the many-body expansion theory. The contour lines are constructed, which show the static properties of HCO ( X2A'), such as the equilibrium structure, the lowest energies, etc. The potential energy surface of HCO ( X2A') is reasonable and very satisfactory.

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Generation of sub-half-wavelength micro-optical traps by dichroic evanescent standing waves Zhang Jing, Zhang Tian-Cai, Wang Jun-Min, Peng Kun-Chi 2007, 16 (5):  1295-1299.  doi: 10.1088/1009-1963/16/5/022 Abstract ( 0 )   PDF (1024KB) ([an error occurred while processing this directive])   The bi-dimensional optical lattices formed by several sets of laser evanescent standing waves propagating at the surface of a dielectric prism are investigated. The characteristics of the optical traps including their depths and the sizes are analysed. It is shown that the micro-optical lattice with a sub-half-wavelength size can be achieved by the interference of the selected evanescent waves. The scheme together with the recently developed atomic chip may be used for atomic quantum manipulation.

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Fluorescence spectrum characteristic of ethanol--water excimer and mechanism of resonance energy transfer Liu Ying, Song Chun-Yuan, Luo Xiao-Sen, Lu Jian, Ni Xiao-Wu 2007, 16 (5):  1300-1306.  doi: 10.1088/1009-1963/16/5/023 Abstract ( 0 )   PDF (209KB) ([an error occurred while processing this directive])   The steady-state fluorescence spectrum characteristic of ethanol--water excimer has been studied in this paper. By analysing the features of the sharp emission spectrum with fine structures in a shortwave band and the characteristics of the broad and featureless fluorescence peaks in the longwave band, one can conclude that the excimers are formed between the new ethanol--water cluster molecules in the excited state and the ground state through the interaction among different chromophores. The excitation spectra in the two fluorescence bands have been studied, and their emission mechanisms have been ascertained based on the energy transfer theory. Furthermore, the critical distance of the resonance energy transfer has been calculated.

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Photo-detachment cross section of H- near two parallel interfaces Wang De-Hua, Ma Xiao-Guang, Wang Mei-Shan, Yang Chuan-Lu 2007, 16 (5):  1307-1314.  doi: 10.1088/1009-1963/16/5/024 Abstract ( 0 )   PDF (211KB) ([an error occurred while processing this directive])   The photo-detachment cross section of H- near two parallel elastic interfaces is derived and calculated by using the closed orbit theory. The photo-detachment cross section of H- near two interfaces is shown to exhibit multi-periodic oscillations when the distance between the H- and the interface is varied. Each peak in the Fourier transformed photo-detachment cross section corresponds to the length of a closed orbit, which is quite similar to the case of atomic spontaneous emissions in a dielectric slab. This study provides a new understanding of the photo-detachment process of H- in the presence of interfaces.

CLASSICAL AREAS OF PHENOMENOLOGY

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Waveguide resonance of subwavelength metallic slits Chen Yue-Gang, Wang Yan-Hua, Zhang Yan, Liu Shu-Tian 2007, 16 (5):  1315-1319.  doi: 10.1088/1009-1963/16/5/025 Abstract ( 0 )   PDF (818KB) ([an error occurred while processing this directive])   The transmission characteristics of a metallic film with subwavelength periodic slits are investigated by using the two-dimensional finite-difference time-domain method (2D-FDTD). Two models are constructed to show the dependance of the transmission spectrum on the slit structure. A sandwiched structure is used to exhibit the contribution of the metallic wall inside slits to the extraordinary high transmission. And a filled slit structure is employed to reflect the relation between the average refractive index inside the slits and the transmission spectrum of the structure. The transmission characteristics of two structures can be explained well with the waveguide resonance theory.

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Off-axial elliptical cosine-Gaussian beams and their propagation properties Lü Zhang-De 2007, 16 (5):  1320-1326.  doi: 10.1088/1009-1963/16/5/026 Abstract ( 0 )   PDF (2706KB) ([an error occurred while processing this directive])   In this paper, a new kind of light beam called off-axial elliptical cosine-Gaussian beam (ECosGBs) is defined by using the tensor method. An analytical propagation expression for the ECosGBs passing through axially nonsymmetrical optical systems is derived by using vector integration. The intensity distributions of ECosGBs on the input plane, on the output plane with the equivalent Fresnel number being equal to 0.1 and on the focal plane are respectively illustrated for the propagation properties. The results indicate that an ECosGB is eventually transformed into an elliptical cosh-Gaussian beam. In other words, ECosGBs and cosh-Gaussian beams act in a reciprocal manner after propagation.

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Angle-of-arrival fluctuations in moderate to strong turbulence Ma Jing, Gao Chong, Tan Li-Ying 2007, 16 (5):  1327-1333.  doi: 10.1088/1009-1963/16/5/027 Abstract ( 0 )   PDF (279KB) ([an error occurred while processing this directive])   Based on the modified spectrum, the analytic expressions for the variance and normalized covariance of angle-of-arrival (AOA) fluctuations are presented, which are applicable to the weak and strong regimes. The experimental data of AOA fluctuations validate the new derived expressions in weak and strong regimes. The results show that the receiving aperture D, outer scale and cell scale larger than the scattering disc S contribute significantly to the AOA fluctuations, and contributions from the small-scale turbulence are negligible. For the case of 4S/D\ll 1, the receiving aperture dominates low-pass filtering effects and the new displacement variances are in good agreement with the results from the old weak-fluctuation theory. For the case of 4S/D\gg 1, the scattering disc dominates the low-pass filtering effects and the new displacement variances depart from the results from the old weak-fluctuation theory.

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Light beams with orbital angular momentum for free space optics Wu Jing-Zhi, Li Yang-Jun 2007, 16 (5):  1334-1338.  doi: 10.1088/1009-1963/16/5/028 Abstract ( 0 )   PDF (375KB) ([an error occurred while processing this directive])   The light's orbital angular momentum (OAM) is a consequence of the spiral flow of the electromagnetic energy. In this paper, an analysis of light beams with OAM used for free space optics (FSO) is conducted. The basic description and conception of light's OAM are reviewed. Both encoding information into OAM states of single light beam and encoding information into spatial structure of the mixed optical vortex with OAM are discussed, and feasibility to improve the FSO's performance of security and obstruction of line of sight is examined.

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Implementing entanglement teleportation via adiabatic passage Chen Zhi-Hua, Lin Xiu-Min, Chen Mei-Ying, Du Qian-Hua, Lin Gong-Wei 2007, 16 (5):  1339-1343.  doi: 10.1088/1009-1963/16/5/029 Abstract ( 0 )   PDF (294KB) ([an error occurred while processing this directive])   This paper proposes a scheme for implementing teleportation of an entangled state of two trapped atoms through adiabatic passage and photonic interference. The scheme is robust against certain noise such as atomic spontaneous emission and the detector inefficiency.

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Quantum entanglement in the system of a moving V-type three-level atom interacting with the SU(1,1)-related coherent fields Hu Yao-Hua, Fang Mao-Fa, Liao Xiang-Ping 2007, 16 (5):  1344-1350.  doi: 10.1088/1009-1963/16/5/030 Abstract ( 0 )   PDF (249KB) ([an error occurred while processing this directive])   In a system with a moving V-type three-level atom interacting with the SU(1,1)-related coherent fields, we investigate the entanglement between the moving three-level atom and the SU(1,1)-related coherent fields by using the quantum-reduced entropy, and that between the SU(1,1)-related coherent fields by using the quantum relative entropy of entanglement. It is shown that the two kinds of entanglement are dependent on the atomic motion and exhibit the periodic evolution with a period of 2π/p. The maximal atom--field qutrit entanglement state can be prepared, and the entanglement preservation of the SU(1,1)-related coherent fields can be realized in the interacting process via the appropriate selection of system parameters and interaction time.

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Amplitude-squared squeezing of the generalized odd--even coherent states of the anharmonic oscillator in a finite-dimensional Hilbert space Muhammad Ashfaq Ahmad, Lin Jie, Qian Yan, Ma Zhi-Min, Ma Ai-Qun, Liu Shu-Tian 2007, 16 (5):  1351-1356.  doi: 10.1088/1009-1963/16/5/031 Abstract ( 0 )   PDF (704KB) ([an error occurred while processing this directive])   This paper discusses the properties of amplitude-squared squeezing of the generalized odd--even coherent states of anharmonic oscillator in finite-dimensional Hilbert space. It demonstrates that the generalized odd coherent states do exhibit strong amplitude-squared squeezing effects in comparison with the generalized even coherent states.

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Stationary entanglement between two spatially separated atoms driven by a coherent laser field Liao Xiang-Ping, Fang Mao-Fa, Zheng Xiao-Juan, Cai Jian-Wu 2007, 16 (5):  1357-1363.  doi: 10.1088/1009-1963/16/5/032 Abstract ( 0 )   PDF (173KB) ([an error occurred while processing this directive])   This paper studies quantum entanglement between two spatially separated atoms driven by a coherent laser field in the dissipative process of spontaneous emission. It is shown that the entanglement strongly depends on the detuning of the laser frequency from atomic transition frequency, the interatomic separation and the Rabi frequency of the coherent laser field. A considerable amount of steady state entanglement can be obtained near Δ=-α (i.e., the dipole--dipole interaction and the detuning cancel out mutually) for small atomic separation and large Rabi frequency of the coherent laser field.

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Security analysis of continuous-variable quantum key distribution scheme Zhu Jun, He Guang-Qiang, Zeng Gui-Hua 2007, 16 (5):  1364-1369.  doi: 10.1088/1009-1963/16/5/033 Abstract ( 0 )   PDF (439KB) ([an error occurred while processing this directive])   In this paper security of the quantum key distribution scheme using correlations of continuous variable Einstein--Podolsky--Rosen (EPR) pairs is investigated. A new approach for calculating the secret information rate Δ I is proposed by using the Shannon information theory. Employing an available parameter F which is associated with the entanglement of the EPR pairs, one can detect easily the eavesdropping. Results show that the proposed scheme is secure against individual beam splitter attack strategy with a proper squeeze parameter.

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Theoretical study of Ni-like Ag 13.9nm TCE x-ray laser driven by two picosecond pulses Qiao Xiu-Mei, Zhang Guo-Ping 2007, 16 (5):  1370-1373.  doi: 10.1088/1009-1963/16/5/034 Abstract ( 0 )   PDF (192KB) ([an error occurred while processing this directive])   The Ni-like Ag 13.9nm x-ray laser has been previously demonstrated that the higher gain near critical surface contributes little to the amplification of the x-ray laser because of severe refraction. In this paper, the transient collision excitation (TCE) Ni-like Ag 13.9nm x-ray laser is simulated, driven by two 3ps short pulse preceded by a 330ps long prepulse, optimization of the peak to peak delay time of the two short pulses is made to get the best results. Simulation indicates that by producing lowly ionized preplasma with smoothly varying electron density, it is possible to decrease electron density gradient in higher density region, and thus higher gains near this region could be utilized, and if the main short pulse is delayed by 900ps, local gains where electron density larger than ～ 4×1020cm-3 could be utilized.

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Decreased vibrational susceptibility of Fabry--Perot cavities via designs of geometry and structural support Yang Tao, Li Wen-Bo, Zang Er-Jun, Chen Li-Sheng 2007, 16 (5):  1374-1384.  doi: 10.1088/1009-1963/16/5/035 Abstract ( 0 )   PDF (2115KB) ([an error occurred while processing this directive])   Ultra-stable optical cavities are widely used for laser frequency stabilization. In these experiments the laser performance relies on the length stability of the Fabry--Perot cavities. Vibration-induced deformation is one of the dominant factors that affect the stability of ultra-stable optical cavities. We have quantitatively analysed the elastic deformation of Fabry--Perot cavities with various shapes and mounting configurations. Our numerical result facilitates a novel approach for the design of ultra-stable cavities that are insensitive to vibrational perturbations. This approach can be applied to many experiments such as laser frequency stabilization, high-precision laser spectroscopy, and optical frequency standards.

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Investigation on improving characteristics of two-cell SBS system with CCl4/C2H5OH liquid mixture Hasi Wu-Li-Ji, Lü Zhi-Wei, Li Qiang, He Wei-Ming 2007, 16 (5):  1385-1390.  doi: 10.1088/1009-1963/16/5/036 Abstract ( 0 )   PDF (474KB) ([an error occurred while processing this directive])   In order to improve the performance of the two-cell stimulated Brillouin scattering (SBS) system, this paper proposes the methods of using mixtures, which require amplifier media to have small absorption rate, and generator media to have high optical breakdown threshold and Brillouin frequency shift equal to that of the amplification media. The characteristics of the two-cell SBS system are studied experimentally by using CCl4 as amplifier medium and CCl4, C2H5OH and CCl4/C2H5OH liquid mixture as generator medium pumped by Nd:YAG Q-switched laser. The obtained results show that liquid mixture in generator cell improves the power load ability, phase conjugation fidelity, energy reflectivity (ER) and ER stability.

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Diffusion-induced deflection and the effect of two-wave mixing gain on dissipative photovoltaic solitons 2007, 16 (5):  1391-1398.  doi: 10.1088/1009-1963/16/5/037 Abstract ( 0 )   PDF (659KB) ([an error occurred while processing this directive])   In an open-circuit dissipative photovoltaic (PV) crystal, by considering the diffusion effect, the deflection of bright dissipative photovoltaic (DPV) solitons has been investigated by employing numerical technique and perturbational procedure. The relevant results show that the centre of the optical beam moves along a parabolic trajectory, while the central spatial-frequency component shifts linearly with the propagation distance; furthermore, both the spatial deflection and the angular derivation are associated with the photovoltaic field. Such DPV solitons have a fixed deflection degree completely determined by the parameters of the dissipative system. The small bending cannot affect the formation of the DPV soliton via two-wave mixing.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Tokamak resistive magnetohydrodynamic ballooning instability in the negative shear regime Shi Bing-Ren, Lin Jian-Long, Li Ji-Quan 2007, 16 (5):  1399-1404.  doi: 10.1088/1009-1963/16/5/038 Abstract ( 0 )   PDF (527KB) ([an error occurred while processing this directive])   Improved confinement of tokamak plasma with central negative shear is checked against the resistive ballooning mode. In the negative shear regime, the plasma is always unstable for purely growing resistive ballooning mode. For a simplest tokamak equilibrium model, the s--α model, characteristics of this kind of instability are fully clarified by numerically solving the high n resistive magnetohydrodynamic ballooning eigen-equation. Dependences of the growth rate on the resistivity, the absolute shear value, the pressure gradient are scanned in detail. It is found that the growth rate is a monotonically increasing function of α while it is not sensitive to the changes of the shear s, the initial phase \ta0 and the resistivity parameter \vaR.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Synthesis of flower-shape clustering GaN nanorods by ammoniating Ga2O3 films Xue Shou-Bin, Zhuang Hui-Zhao, Xue Cheng-Shan, Hu Li-Jun, Li Bao-Li, Zhang Shi-Ying 2007, 16 (5):  1405-1409.  doi: 10.1088/1009-1963/16/5/039 Abstract ( 0 )   PDF (689KB) ([an error occurred while processing this directive])   Flower-shape clustering GaN nanorods are successfully synthesized on Si(111) substrates through ammoniating Ga2O3/ZnO films at 950℃. The as-grown products are characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), field-emission transmission electron microscope (FETEM), Fourier transform infrared spectrum (FTIR) and fluorescence spectrophotometer. The SEM images demonstrate that the products consist of flower-shape clustering GaN nanorods. The XRD indicates that the reflections of the samples can be indexed to the hexagonal GaN phase and HRTEM shows that the nanorods are of pure hexagonal GaN single crystal. The photoluminescence (PL) spectrum indicates that the GaN nanorods have a good emission property. The growth mechanism is also briefly discussed.

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Pseudo nanocrystal silicon induced luminescence enhancement in a-Si /SiO2 multilayers Han Pei-Gao, Ma Zhong-Yuan, Xia Zheng-Yue, Chen De-Yuan, Xu Jun, Qian Bo, Chen San, Li Wei, Huang Xin-Fan, Chen Kun-Ji, Feng Duan 2007, 16 (5):  1410-1416.  doi: 10.1088/1009-1963/16/5/040 Abstract ( 0 )   PDF (1435KB) ([an error occurred while processing this directive])   Enhanced photoluminescence (PL) at room temperature from thermally annealed a-Si\jz{.2mm}{:}H/SiO2 multilayers is observed through the step-by-step thermal post-treatment. The correlation between the PL and the crystallization process is studied using temperature-dependent PL, Raman, cross section high-resolution transmission electron microscopy (X-HRTEM) and x-ray diffraction (XRD) techniques. An intensified PL band around 820nm is discovered from the sample annealed near the crystallization onset temperature, which is composed of two peaks centred at 773nm and 863nm, respectively. It is found that the PL band centred at 863nm is related to the pseudo nanocrystal (p-nc-Si) silicon, and the PL band centred at 773nm is attributed to Si = O bonds stabilized in the p-nc-Si surface.

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Electrical and optical characteristics of vanadium in 4H-SiC Wang Chao, Zhang Yi-Men, Zhang Yu-Ming 2007, 16 (5):  1417-1421.  doi: 10.1088/1009-1963/16/5/041 Abstract ( 0 )   PDF (617KB) ([an error occurred while processing this directive])   A semi-insulating layer is obtained in n-type 4H-SiC by vanadium-ion implantation. A little higher resistivity is obtained by increasing the annealing temperature from 1450 to 1650℃. The resistivity at room temperature is as high as 7.6×106\Omega .cm. Significant redistribution of vanadium is not observed even after 1650℃ annealing. Temperature-dependent resistivity and optical absorption of V-implanted samples are measured. The activation energy of vanadium acceptor level is observed to be at about EC-1.1eV.

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

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Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3 Zhang Chao, Wang Chun-Lei, Li Ji-Chao, Yang Kun 2007, 16 (5):  1422-1428.  doi: 10.1088/1009-1963/16/5/042 Abstract ( 0 )   PDF (1748KB) ([an error occurred while processing this directive])   We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrTiO3, but the gap changes from \Gamma--R point to \Gamma--X point.

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First principles calculations of relationship between the Cu surface states and relaxations Xie Yao-Ping, Luo Ying, Liu Shao-Jun 2007, 16 (5):  1429-1433.  doi: 10.1088/1009-1963/16/5/043 Abstract ( 0 )   PDF (153KB) ([an error occurred while processing this directive])   In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu(100), Cu(110), and Cu(111) surfaces is obtained by first-principles calculations. The calculations indicate that relaxations mainly occur in the layers at which the surface states electrons are localized, and the magnitudes of the multilayer relaxations correspond to the difference of electron density of surface states between adjacent layers. The larger the interlayer relaxation is, the larger the difference of electron density of surface states between two layers is.

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Charge transfer and variation of potential distributions in the formation of 4, 4'-bipyridine molecular junction Li Zong-Liang, Zou Bin, Yan Xun-Wang, Wang Chuan-Kui 2007, 16 (5):  1434-1439.  doi: 10.1088/1009-1963/16/5/044 Abstract ( 0 )   PDF (491KB) ([an error occurred while processing this directive])   In this paper the charge transfer and variation of potential distribution upon formation of 4, 4'-bipyridine molecular junction have been investigated by applying hybrid density-functional theory (B3LYP) at ab initio level. The numerical results show that there exist charge-accumulation and charge-depletion regions located at respective inside and outside of interfaces. The variation of potential distribution is obvious at interfaces. When distance between electrodes is changed, the charge transfer and variation of potential distribution clearly have distance-dependent performance. It is demonstrated that the contact structure between the molecule and electrodes is another key factor for dominating the properties of molecular junction. The qualitative explanation for experimental results is suggested.

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Dependences of spin polarization on the control parameters in the spin-polarized injection through the magnetic p-n junction Zhang Lei, Deng Ning, Ren Min, Dong Hao, Chen Pei-Yi 2007, 16 (5):  1440-1444.  doi: 10.1088/1009-1963/16/5/045 Abstract ( 0 )   PDF (423KB) ([an error occurred while processing this directive])   Effective spin-polarized injection from magnetic semiconductor (MS) to nonmagnetic semiconductor (NMS) has been highlighted in recent years. In this paper we study theoretically the dependence of nonequilibrium spin polarization (NESP) in NMS during spin-polarized injection through the magnetic p-n junction. Based on the theory in semiconductor physics, a model is established and the boundary conditions are determined in the case of no external spin-polarized injection and low bias. The control parameters that may influence the NESP in NMS are indicated by calculating the distribution of spin polarization. They are the doping concentrations, the equilibrium spin polarization in MS and the bias. The effective spin-polarized injection can be realized more easily by optimizing the above parameters.

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Degradation characteristics and mechanism of PMOSFETs under NBT--PBT--NBT stress Liu Hong-Xia, Li Zhong-He, Hao Yue 2007, 16 (5):  1445-1449.  doi: 10.1088/1009-1963/16/5/046 Abstract ( 0 )   PDF (458KB) ([an error occurred while processing this directive])   Degradation characteristics of PMOSFETs under negative bias temperature--positive bias temperature--negative bias temperature (NBT--PBT--NBT) stress conditions are investigated in this paper. It is found that for all device parameters, the threshold voltage has the largest shift under the first NBT stress condition. When the polarity of gate voltage is changed to positive, the shift of device parameters can be greatly recovered. However, this recovery is unstable. The more severe degradation appears soon after reapplication of NBT stress condition. The second NBT stress causes in linear drain current to degrade greatly, which is different from that of the first NBT stress. This more severe parameter shift results from the wear out of silicon substrate and oxide interface during the first NBT and PBT stress due to carrier trapping/detrapping and hydrogen related species diffusion.

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Ground state of a superconducting π ring array under external magnetic fields Li Zhuang-Zhi, Feng Yun, Wang Fu-Ren, Dai Yuan-Dong 2007, 16 (5):  1450-1458.  doi: 10.1088/1009-1963/16/5/047 Abstract ( 0 )   PDF (227KB) ([an error occurred while processing this directive])   The ground state of a two-dimensional square superconducting π ring array has been investigated. The circulating currents of the π ring array will spontaneously magnetize to the `antiferromagnetic' arrangement with directions of the nearest-neighbouring currents circulating oppositely in the absence of an external magnetic field. It is found that the external magnetic field could destroy the anti-parallel configuration effectively. The external magnetic field needed to destroy the anti-parallel configuration is related to the superconducting \pi ring's inductance parameter β=2\pi L Ic/\phi0. For a small β the anti-parallel configuration, which is the lowest-energy ground state of the system, will be fully destroyed and changed to the configuration that the circulating currents have the same direction and parallel to the external magnetic field when the magnetic flux reaches \phi0/4 in each ring. Moreover, the magnetic field needed to destroy the anti-parallel configuration will be very small when β is large enough.

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Optical microwave generation using two parallel DFB lasers integrated with Y-branch waveguide coupler Xie Hong-Yun, Wang Lu, Zhao Ling-Juan, Zhu Hong-Liang, Wang Wei 2007, 16 (5):  1459-1463.  doi: 10.1088/1009-1963/16/5/048 Abstract ( 0 )   PDF (1145KB) ([an error occurred while processing this directive])   A new device of two parallel distributed feedback (DFB) lasers integrated monolithically with Y-branch waveguide coupler was fabricated by means of quantum well intermixing. Optical microwave signal was generated in the Y-branch waveguide coupler through frequency beating of the two laser modes coming from two DFB laser in parallel, which had a small difference in frequency. Continuous rapid tuning of optical microwave signal from 13 to 42GHz were realized by adjusting independently the driving currents injected into the two DFB lasers.

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Transient demonstration of exciton behaviours in solid state cathodoluminescence under different driving voltage Zhang Fu-Jun, Zhao Su-Ling, Xu Zheng, Huang Jin-Zhao, Xu Xu-Rong 2007, 16 (5):  1464-1466.  doi: 10.1088/1009-1963/16/5/049 Abstract ( 0 )   PDF (148KB) ([an error occurred while processing this directive])   In the solid state cathodoluminescence (SSCL), organic materials were excited by hot electrons accelerated in silicon oxide (SiO2) layer under alternating current (AC). In this paper exciton behaviours were analysed by using transient spectra under different driving voltages. The threshold voltages of SSCL and exciton ionization were obtained from the transient spectra. The recombination radiation occurred when the driving voltage went beyond the threshold voltage of exciton ionization. From the transient spectrum of two kinds of luminescence (exciton emission and recombination radiation), it was demonstrated that recombination radiation should benefit from the exciton ionization.

CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si(111) substrates Liu Zhe, Wang Xiao-Liang, Wang Jun-Xi, Hu Guo-Xin, Guo Lun-Chun, Li Jin-Min 2007, 16 (5):  1467-1471.  doi: 10.1088/1009-1963/16/5/050 Abstract ( 0 )   PDF (947KB) ([an error occurred while processing this directive])   AlN/GaN superlattice buffer is inserted between GaN epitaxial layer and Si substrate before epitaxial growth of GaN layer. High-quality and crack-free GaN epitaxial layers can be obtained by inserting AlN/GaN superlattice buffer layer. The influence of AlN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by using AlN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Effects of South China Sea/western North Pacific summer monsoon on tropospheric biennial oscillation (TBO) Zheng Bin, Gu De-Jun, Lin Ai-Lan, Li Chun-Hui 2007, 16 (5):  1472-1476.  doi: 10.1088/1009-1963/16/5/051 Abstract ( 0 )   PDF (191KB) ([an error occurred while processing this directive])   Several theories have been developed to explain tropical biennial oscillation (TBO), as an air--sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including air--sea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon (SCS/WNPSM), a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air--sea coupling coefficient α, SST-thermocline feedback coefficient γ and wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS/WNPSM.

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Small-scale ion flux and magnetic field fluctuations in solar wind, foreshock and magnetosheath N. N. Shevyrev, Du Jian, G. N. Zastenker, Wang Chi, P. E. Eiges 2007, 16 (5):  1477-1487.  doi: 10.1088/1009-1963/16/5/052 Abstract ( 0 )   PDF (2123KB) ([an error occurred while processing this directive])   We have continued investigation of waves in the regions of undisturbed solar wind, foreshock and magnetosheath. The analysis of ion flux and magnetic field variations with the time interval 1--240s was performed in the regions above. Very large variation in such a time interval can be considered the common feature of the foreshock and magnetosheath. The results of case and statistical studies showed that the level of relative variations of ion flux and magnetic field magnitude in foreshock is about 3 times larger than in undisturbed solar wind. Variations of these parameters in the magnetosheath topologically connected with the quasi-parallel bow shock are about two times larger than those behind the quasi-perpendicular. We also compared the results from Interball-1 data analysis with those from statistical analysis of cluster magnetic field measurements. The magnetic field variations obtained from the different satellite data coincide with each other very well not only in quality but also in quantity.