Table of contents

20 November 2005, Volume 14 Issue 11 Previous issue    Next issue

GENERAL

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Multi-agent controlled teleportation of multi-qubit quantum information via two-step protocol Yang Jie (杨杰) Chinese Physics, 2005, 14 (11):  2149-2152.  DOI: 10.1088/1009-1963/14/11/001 Abstract ( 1506 )   PDF (174KB) ( 774 )   Utilizing both the general quantum teleportation and the two-step protocol, a new method is presented by which multi-qubit quantum information can be teleported in a much easier way from a sender Alice to a receiver Bob via the control of many agents in a network than by Yang et al's method. In this method, only all the agents collaborate with Bob can the unknown states in Alice's qubits be fully reconstructed in Bob's qubits. Comparisons between the method and Yang et al's method are made. Results show that, in this method,the preparation difficulty of initial states and the identification difficulty of entangled states are considerably reduced, new method is more feasible in technique, and Hadamard operations are not needed at all.

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Dynamic properties of epidemic spreading on finite size complex networks Li Ying (李旲), Liu Yang (刘旸), Shan Xiu-Ming (山秀明), Ren Yong (任勇), Jiao Jian (焦健), Qiu Ben (仇贲) Chinese Physics, 2005, 14 (11):  2153-2157.  DOI: 10.1088/1009-1963/14/11/002 Abstract ( 1841 )   PDF (235KB) ( 977 )   The Internet presents a complex topological structure, on which computer viruses can easily spread. By using theoretical analysis and computer simulation methods, the dynamic process of disease spreading on finite size networks with complex topological structure is investigated. On the finite size networks, the spreading process of SIS (susceptible--infected--susceptible) model is a finite Markov chain with an absorbing state. Two parameters, the survival probability and the conditional infecting probability, are introduced to describe the dynamic properties of disease spreading on finite size networks. Our results can help understanding computer virus epidemics and other spreading phenomena on communication and social networks. Also, knowledge about the dynamic character of virus spreading is helpful for adopting immunity policy.

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A method for constructing exact solutions and application to Benjamin Ono equation Wang Zhen (王振), Li De-Sheng (李德生), Lu Hui-Fang (鲁慧芳), Zhang Hong-Qing (张鸿庆) Chinese Physics, 2005, 14 (11):  2158-2163.  DOI: 10.1088/1009-1963/14/11/003 Abstract ( 1834 )   PDF (242KB) ( 1159 )   By using an improved projective Riccati equation method, this paper obtains several types of exact travelling wave solutions to the Benjamin Ono equation which include multiple soliton solutions, periodic soliton solutions and Weierstrass function solutions. Some of them are found for the first time. The method can be applied to other nonlinear evolution equations in mathematical physics.

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A realizable quantum encryption algorithm for qubits Zhou Nan-Run (周南润), Zeng Gui-Hua (曾贵华) Chinese Physics, 2005, 14 (11):  2164-2169.  DOI: 10.1088/1009-1963/14/11/004 Abstract ( 1800 )   PDF (235KB) ( 958 )   A realizable quantum encryption algorithm for qubits is presented by employing bit-wise quantum computation. System extension and bit-swapping are introduced into the encryption process, which makes the ciphertext space expanded greatly. The security of the proposed algorithm is analysed in detail and the schematic physical implementation is also provided. It is shown that the algorithm, which can prevent quantum attack strategy as well as classical attack strategy, is effective to protect qubits. Finally, we extend our algorithm to encrypt classical binary bits and quantum entanglements.

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Generalized path-integral solution and coherent states of the harmonic oscillator in D-dimensions Ma Yu-Quan (马余全), Zhang Jin (张晋), Chen Yong-Kang (陈永康), Dai Hong (戴宏) Chinese Physics, 2005, 14 (11):  2170-2175.  DOI: 10.1088/1009-1963/14/11/005 Abstract ( 1640 )   PDF (228KB) ( 847 )   We construct a general form of propagator in arbitrary dimensions and give an exact wavefunction of a time-dependent forced harmonic oscillator in D (D $\geq$ 1) dimensions. The coherent states, defined as the eigenstates of annihilation operator, of the D-dimensional harmonic oscillator are derived. These coherent states correspond to the minimum uncertainty states and the relation between them is investigated.

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Blind source separation of multichannel electroencephalogram based on wavelet transform and ICA You Rong-Yi (游荣义), Chen Zhong (陈忠) Chinese Physics, 2005, 14 (11):  2176-2180.  DOI: 10.1088/1009-1963/14/11/006 Abstract ( 1519 )   PDF (270KB) ( 926 )   Combination of the wavelet transform and independent component analysis (ICA) was employed for blind source separation (BSS) of multichannel electroencephalogram (EEG). After denoising the original signals by discrete wavelet transform, high frequency components of some noises and artifacts were removed from the original signals. The denoised signals were reconstructed again for the purpose of ICA, such that the drawback that ICA cannot distinguish noises from source signals can be overcome effectively. The practical processing results showed that this method is an effective way to BSS of multichannel EEG. The method is actually a combination of wavelet transform with adaptive neural network, so it is also useful for BBS of other complex signals.

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Neural Volterra filter for chaotic time series prediction Li Heng-Chao (李恒超), Zhang Jia-Shu (张家树), Xiao Xian-Ci (肖先赐) Chinese Physics, 2005, 14 (11):  2181-2188.  DOI: 10.1088/1009-1963/14/11/007 Abstract ( 1548 )   PDF (372KB) ( 791 )   A new second-order neural Volterra filter (SONVF) with conjugate gradient (CG) algorithm is proposed to predict chaotic time series based on phase space delay-coordinate reconstruction of chaotic dynamics system in this paper, where the neuron activation functions are introduced to constraint Volterra series terms for improving the nonlinear approximation of second-order Volterra filter (SOVF). The SONVF with CG algorithm improves the accuracy of prediction without increasing the computation complexity. Meanwhile, the difficulty of neuron number determination does not exist here. Experimental results show that the proposed filter can predict chaotic time series effectively, and one-step and multi-step prediction performances are obviously superior to those of SOVF, which demonstrate that the proposed SONVF is feasible and effective.

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Transition to complete synchronization via near-synchronization in two coupled chaotic neurons Wang Qing-Yun (王青云), Lu Qi-Shao (陆启韶), Wang Hai-Xia (王海侠) Chinese Physics, 2005, 14 (11):  2189-2195.  DOI: 10.1088/1009-1963/14/11/008 Abstract ( 1502 )   PDF (343KB) ( 1159 )   The synchronization transition in two coupled chaotic Morris--Lecar (ML) neurons with gap junction is studied with the coupling strength increasing. The conditional Lyapunov exponents,along with the synchronization errors are calculated to diagnose synchronization of two coupled chaotic ML neurons. As a result, it is shown that the increase in the coupling strength leads to incoherence, then induces a transition process consisting of three different synchronization states in succession, namely, burst synchronization, near-synchronization and embedded burst synchronization, and achieves complete synchronization of two coupled neurons finally.These sequential transitions to synchronization reveal a new transition route from incoherence to complete synchronization in coupled systems with multi-time scales.

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Digital communication of two-dimensional messages in a chaotic optical system Zhou Yun (周云), Wu Liang (吴亮), Zhu Shi-Qun (朱士群) Chinese Physics, 2005, 14 (11):  2196-2201.  DOI: 10.1088/1009-1963/14/11/009 Abstract ( 1398 )   PDF (911KB) ( 629 )   The digital communication of two-dimensional messages is investigated when two solid state multi-mode chaotic lasers are employed in a master-slave configuration. By introducing the time derivative of intensity difference between the receiver (carrier) and the transmittal (carrier plus signal), several signals can be encoded into a single pulse. If one signal contains several binary bits, two-dimensional messages in the form of a matrix can be encoded and transmitted on a single pulse. With these improvements in secure communications using chaotic multi-mode lasers, not only the transmission rate can be increased but also the privacy can be enhanced greatly.

ATOMIC AND MOLECULAR PHYSICS

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Solvent effects on optical properties of a newly synthesized two-photon polymerization initiator: BPYPA Guo Ya-Hui (郭雅慧), Sun Yuan-Hong (孙元红), Tao Li-Min (陶丽敏), Zhao Ke (赵珂), Wang Chuan-Kui (王传奎) Chinese Physics, 2005, 14 (11):  2202-2207.  DOI: 10.1088/1009-1963/14/11/010 Abstract ( 1440 )   PDF (286KB) ( 528 )   Time-dependent hybrid density functional theory in combination with polarized continuum model is applied to study the solvent effects on the geometrical and electronic structures as well as one- and two-photon absorption processes, of a newly synthesized asymmetrical charge-transfer organic molecule bis-(4-bromo-phenyl)-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine (BPYPA).There exist two charge-transfer states for the compound in visible region. The two-photon absorption cross section calculated by a three-state model and solvatochromic shift of the charge-transfer states are found to be solvent-dependent, where a nonmonotonic behaviour with respect to the polarity of the solvents is observed. The numerical results show that the organic molecule exhibits a rather large two-photon absorption cross section as compared with the compound 4-trans-[p-(N, N-Di-n-butylamino)-p-stilbenyl vinyl] pyridine (DBASVP) reported previously, and is predicted to be a good two-photon polymerization initiator. The hydrogen-bond effect is analysed. The computational results are in good agreement with the measurements.

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Total cross sections for electrons scattering from simple molecules containing the larger atom sulfur at 30--5000eV Shi De-Heng (施德恒), Liu Yu-Fang (刘玉芳), Sun Jin-Feng (孙金锋), Yang Xiang-Dong (杨向东), Zhu Zun-Lue (朱遵略) Chinese Physics, 2005, 14 (11):  2208-2213.  DOI: 10.1088/1009-1963/14/11/011 Abstract ( 1237 )   PDF (252KB) ( 423 )   A complex optical model potential modified by the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds, is employed to calculate the total cross sections for electrons scattering from simple molecules (SO2, H2S, OCS,CS2 and SO3) containing the larger atom, sulfur, at 30--5000eV by using the additivity rule model at Hartree--Fock level. The quantitative molecular total cross section results are compared with those obtained in experiments and other calculations wherever available, and good agreement is obtained. It is shown that the additivity rule model together with the complex optical model potential modified by the concept of bonded atom can give the results closer to the experiments than the one unmodified by it. So, the introduction of bonded-atom concept in complex optical model potential betters the accuracy of the total cross section calculations of electrons from the molecules containing the larger atom, sulfur.

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Numerical study of the coupling between F0 with varied numbers of c-subunits and F1 in an ATP synthase Qian Jun (钱钧), Xie Ping (谢平), Dou Shuo-Xing (窦硕星), Wang Peng-Ye (王鹏业) Chinese Physics, 2005, 14 (11):  2214-2221.  DOI: 10.1088/1009-1963/14/11/012 Abstract ( 1363 )   PDF (410KB) ( 408 )   ATP synthase is a rotary motor which is composed of two portions: the `rotor' F0, consisting of a c-ring, and the `stator' F1, consisting of an $\alpha$3$\beta$3 hexamer. In different species, the number of c-subunits which form the c-ring is varied from 10 to 14, whereas the $\alpha$3$\beta$3 hexamer is fixed to be 3-fold symmetrical. We have numerically studied the rotational coupling between F0 with varied number of c-subunits and F1. It is found that, for any number of c-subunits, the rotor F0 advances 3 steps per revolution on average, which is determined by the period of F1, whereas the exact angular pausing positions are determined by the period of F0. When the symmetry of the c-ring of F0 is matched with the 3-fold symmetry of F1, the three steps have equivalent sizes. If not matched, the three steps become nonequivalent: both the step size and average dwell time are different for these steps.

CLASSICAL AREAS OF PHENOMENOLOGY

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Grover search algorithm in an ion trap system Zheng Shi-Biao (郑仕标) Chinese Physics, 2005, 14 (11):  2222-2225.  DOI: 10.1088/1009-1963/14/11/013 Abstract ( 1826 )   PDF (203KB) ( 878 )   Two schemes for the implementation of the two-qubit Grover search algorithm in the ion trap system are proposed. These schemes might be experimentally realizable with presently available techniques. The experimental implementation of the schemes would be an important step toward more complex quantum computation in the ion trap system.

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Ultrafast third-order optical nonlinearity of several sandwich-type phthalocyaninato and porphyrinato europium complexes Huang Wen-Tao (黄文涛), Li Yan (李焱), Xiang Hong (向红), Yang Hong (杨宏), Gong Qi-Huang (龚旗煌), Huang Yan-Yi (黄岩谊), Huang Chun-Hui (黄春辉), Jiang Jian-Zhuang (姜建壮) Chinese Physics, 2005, 14 (11):  2226-2230.  DOI: 10.1088/1009-1963/14/11/014 Abstract ( 1424 )   PDF (267KB) ( 536 )   The third-order optical nonlinearity of two sandwich-type phthalocyaninato and porphyrinato europium complexes, including double- and triple-deckers Eu[Pc(OC5H11)8]2, Eu2(Pc)(TPP)2, Pc=phthalocyanine, TPP=5, 10, 15, 20- tetraphenylporphyrinate), was investigated by using the femtosecond time-resolved optical Kerr gate method at 830 nm wavelength. Their second-order hyperpolarizability is estimated to be 0.74×10-30esu and 3.0×10-30esu respectively. This exhibits an evident enhancement in comparison with 0.47×10-30esu for one-decker Eu(Pc)(acac) (acac=acetylacetonate), which is also measured under the same conditions. The enhancement is attributed to the introduction of lanthanide metal to the large \pi -conjugated system, intermacrocycle interaction and two-photon resonance etc.

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Light-induced acoustic effect in LiNbO3:Fe:Ce crystals Huang Wei (黄伟), Wu Zhong-Kang (吴仲康), Wang Chang-Qing (王长青) Chinese Physics, 2005, 14 (11):  2231-2234.  DOI: 10.1088/1009-1963/14/11/015 Abstract ( 1229 )   PDF (321KB) ( 497 )   The phenomena of acoustic emission in LiNbO3:Fe:Ce crystals have been observed in the process of light-induced quasi-breakdown. It is found that the ultra-high frequency acoustic signal introduced into the crystal is modulated by the low frequency acoustic waves. Its frequency increases with the increase of the intensity of incident light and its jump period of breakdown is the same as that of the photovoltaic current Ic, the change of light-induced refractive index $\Delta n$ and the diffracted light intensity L. This phenomenon has been analysed in this paper, which is caused by the inverse piezoelectric strain effect of the jump of space charge field during the quasi-breakdown.

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Effect of structure random disturbances on characterizations of microstructured optical fibres Lu Yang (陆洋), Zhang Ye-Jin (张冶金), Yang Si-Gang (杨四刚), Peng Xiao-Zhou (彭小舟), Chen Xiang-Fei (陈向飞), Xie Shi-Zhong (谢世钟) Chinese Physics, 2005, 14 (11):  2235-2240.  DOI: 10.1088/1009-1963/14/11/016 Abstract ( 1376 )   PDF (344KB) ( 552 )   A method is presented to analyse the effect of structure random disturbances on the confinement loss and the chromatic dispersion characterizations of microstructured optical fibres, which combines multipole methods with the random statistics process. Some useful results to the fabrication of microstructured optical fibres have been obtained.

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Characteristics of local photonic state density in an infinite two-dimensional photonic crystal Zhou Yun-Song (周云松), Wang Xue-Hua (王雪华), Gu Ben-Yuan (顾本源), Wang Fu-He (王福合) Chinese Physics, 2005, 14 (11):  2241-2245.  DOI: 10.1088/1009-1963/14/11/017 Abstract ( 1305 )   PDF (543KB) ( 1269 )   The local density of photonic states (LDPS) of an infinite two-dimensional (2D) photonic crystal (PC) composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion method in a combination with the point group theory. The calculation results show that the LDPS strongly depends on the spatial positions. The variations of the LDPS as functions of the radial coordinate and frequency exhibit ``mountain chain'' structures with sharp peaks. The LDPS with large value spans a finite area and falls abruptly down to small value at the position corresponding to the interfaces between two different refractive index materials. The larger/lower LDPS occurs inward the lower/larger dielectric-constant medium. This feature can be well interpreted by the continuity of electric-displacement vector at the interface. In the frequency range of the pseudo-PBG (photonic band gap), the LDPS keeps very low value over the whole Wiger--Seitz cell. It indicates that the spontaneous emission in 2D PCs cannot be prohibited completely, but it can be inhibited intensively when the resonate frequency falls into the pseudo-PBG.

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Host dependent thermal stability and frequency upconversion of Er3+-doped heavy metal xyfluoride germanate glasses Xu Shi-Qing (徐时清), Fang Da-Wei (方达伟), Zhang Zai-Xuan (张在宣), Zhao Shi-Long (赵士龙), Zhang Li-Yan (张丽艳), Wang Bao-Ling (王宝玲), Jiang Zhong-Hong (姜中宏) Chinese Physics, 2005, 14 (11):  2246-2250.  DOI: 10.1088/1009-1963/14/11/018 Abstract ( 1176 )   PDF (269KB) ( 720 )   The upconversion properties of Er3+-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green (551 and 529 nm) and relatively weak red (657 nm) emissions corresponding to the transitions 4S3/2 $\to$ 4I15/2,2H11/2 $\to$ 4I15/2 and 4F9/2 $\to$ 4I15/2, respectively, were simultaneously observed at room temperature. The content of PbF2 has an important influence on the upconversion luminescence emission. With increasing content of PbF2, the intensities of green (529 nm) and red (657 nm) emissions increase slightly, while the green emission (551 nm) increases markedly. These results suggest that PbF2 has an influence on the green (551 nm) emission more than on the green (529 nm) and red (657 nm) emissions.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Theoretical analysis of ion cyclotron range of frequency antenna array for HT-7U Zhang Xin-Jun (张新军), Qin Cheng-Ming (秦成明), Zhao Yan-Ping (赵燕平) Chinese Physics, 2005, 14 (11):  2251-2255.  DOI: 10.1088/1009-1963/14/11/019 Abstract ( 1128 )   PDF (1013KB) ( 523 )   This paper considers the coupling analysis of phased antenna array designed to excite fast wave in the ion cyclotron range of frequency. The coupling of the antenna is calculated in slab geometry. The coupling code based on the variational principle gives the self-consistent current flowing in the antenna, this method has been extended so that it can be applied to a phased antenna array. As an example, this paper analyses the coupling prosperities of a 2×2 phased antenna array. It gives the optimum geometry of antenna array. The fields excited at plasma surface are found to more or less correspond to the antenna current phasing.

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Calculation of ion energy distributions of argon excimer ions generated in helicon plasma Fang Tong-Zhen (房同珍), Jiang Nan (江南), Wang Long (王龙) Chinese Physics, 2005, 14 (11):  2256-2261.  DOI: 10.1088/1009-1963/14/11/020 Abstract ( 1343 )   PDF (279KB) ( 584 )   A program is developed to calculate the ion energy distributions (IEDs) of Ar2+ making use of a simplified kinetic model with a combination of Monte Carlo method. Several coefficients are used to realize good match between the calculated and measured results. Some important assumptions are confirmed: argon excimer ions have short lifetime, hence they are formed in a short range before the collecting electrode. The excimer ions that encounter collisions will be discarded because they turn to other ion species after they collide with argon atoms. From the calculated results some plasma parameters such as the cross section or neutral density in discharge could be evaluated.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Formation and spectroscopic characterization of mono-dispersed CdSe nanocrystals Miao Yan-Ming (苗雁鸣), Li Chao-Rong (李超荣), Cao Li (曹立), Liu Rui-Bin (刘瑞斌), He Yu-Ping (何玉平), Xie Si-Shen (解思深), Zou Bing-Suo (邹炳锁) Chinese Physics, 2005, 14 (11):  2262-2268.  DOI: 10.1088/1009-1963/14/11/021 Abstract ( 1258 )   PDF (2031KB) ( 712 )   In this article, mono-dispersed hexagonal structure CdSe nanocrystals with polyhedron shape were prepared by an open solvent thermal reaction. They show a discrete excitonic transition structure in the absorption spectra and the minimal photoluminescence (PL) peak full-width at half-maximum of 19 nm. The PL quantum yield is about 60%. Transmission electron micrographs,high-resolution transmission electron micrographs, x-ray powder diffraction patterns, UV-vis absorption spectra and PL spectra were obtained for the as-prepared CdSe nanocrystals. The size of the CdSe nanocrystals can be tuned by changing the reaction temperature or time. Due to the improved synthesis method, a different growth mechanism of the CdSe nanocrystals is discussed.

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Controlled growth of large-scale silver nanowires Xiao Cong-Wen (肖从文), Yang Hai-Tao (杨海涛), Shen Cheng-Min (申承民), Li Zi-An (李子安), Zhang Huai-Ruo (张怀若), Liu Fei (刘飞), Yang Tian-Zhong (杨天中), Chen Shu-Tang (陈书堂), Gao Hong-Jun (高鸿钧) Chinese Physics, 2005, 14 (11):  2269-2275.  DOI: 10.1088/1009-1963/14/11/022 Abstract ( 1122 )   PDF (4986KB) ( 513 )   Large-scale silver nanowires with controlled aspect ratio were synthesized via reducing silver nitrate with 1, 2-propanediol in the presence of poly (vinyl pyrrolidone) (PVP). Scanning electron microscopy, transmission electron microscopy and x-ray powder diffraction were employed to characterize these silver nanowires. The diameter of the silver nanowires can be readily controlled in the range of 100 to 400 nm by varying the experimental conditions. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results show that there exists no chemical bond between the silver and the nitrogen atoms. The interaction between PVP and silver nanowires is mainly through the oxygen atom in the carbonyl group.

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Relationship between width of pulses and Lorentz factor expected from the light curve of fireball sources Zhang Fu-Wen (张富文), Qin Yi-Ping (覃一平) Chinese Physics, 2005, 14 (11):  2276-2286.  DOI: 10.1088/1009-1963/14/11/023 Abstract ( 1569 )   PDF (402KB) ( 473 )   Time profiles of many gamma-ray bursts consist of distinct pulses, which provides a possibility of characterizing the temporal structure of these bursts. We employ a simple model of highly symmetric fireballs to analyse the effect of the expansion speed on the light curve arising from different forms of local pulses. The relationship between the ratio r of the FWHM width of the rising phase of the light curve to that of the decaying phase and the Lorentz factor is investigated. The analysis shows that, when the rest frame radiation form is ignored, temporal profiles of the light curve arising from pulses of fireballs will not be affected by the expansion speed (that is, r is almost a constant) as long as the fireball expands relativistically. When the rest frame radiation form is taken into account, there will be a break in the curves of r$-$log$\varGamma$. The location of the break depends mainly on the adopted value of the rest frame peak frequency $\nu _{\rm 0,p}$. One would reach almost the same result when a jet is considered. In addition, we utilize a sample of 48 individual GRB pulses to check the relationship between the ratio r and the expansion speed $\varGamma$. We find no significant correlation between them, and this is consistent with the theoretical analysis.

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First principles study on the charge density and the bulk modulus of the transition metals and their carbides and nitrides Li Cheng-Bin (李承斌), Li Ming-Kai (黎明锴), Yin Dong (尹东), Liu Fu-Qing (刘福庆), Fan Xiang-Jun (范湘军) Chinese Physics, 2005, 14 (11):  2287-2292.  DOI: 10.1088/1009-1963/14/11/024 Abstract ( 1916 )   PDF (330KB) ( 926 )   A first principles study of the electronic properties and bulk modulus (B0 of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.

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Rectifying barrier at GaN/SiC hetero-junction studied with positron annihilation spectroscopy Hu Yi-Fan (胡一帆), Beling C. D. Chinese Physics, 2005, 14 (11):  2293-2229.  DOI: 10.1088/1009-1963/14/11/025 Abstract ( 1246 )   PDF (321KB) ( 642 )   Positron annihilation spectroscopy on GaN films grown on SiC substrate with MBE are presented. It is shown that the GaN/SiC interface is rectifying towards positrons, such that positrons can only travel from SiC to GaN and not vice versa. Potential steps seen by the positron at the GaN/SiC interface are calculated from experimental values of electron and positron work function. This ``rectifying'' effect has been successfully mimicked by inserting a thin region of very high electric field in the Variable Energy Positron Fit (VEPF) analysis. The built-in electric field is attributed to different positron affinities, dislocation and/or interface defects at the GaN/SiC interface.

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

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Variational analysis of the disc-loaded waveguide slow-wave structures Li Jian-Qing (李建清), Mo Yuan-Long (莫元龙) Chinese Physics, 2005, 14 (11):  2300-2304.  DOI: 10.1088/1009-1963/14/11/026 Abstract ( 1456 )   PDF (251KB) ( 726 )   The variational method is applied to calculate the dispersion characteristics of disc-loaded waveguide slow-wave structures. The parameters describing the waveguide discontinuities in disc-loaded waveguide are calculated by the variational method. Then the dispersion characteristics of slow-wave structures are obtained using lossless microwave quadrupole theory. Good agreement was observed between results of the variational method and those of field matching method and high frequency structure simulator. In the case of broad band, results of the variational method are better than those of field matching method.

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Scattering characteristics of conducting cylinder coated with nonuniform magnetized ferrite Hu Bin-Jie (胡斌杰), Edward Yung Kai-Ning (容启宁), Zhang Jun (张军), Toutain Serge Chinese Physics, 2005, 14 (11):  2305-2313.  DOI: 10.1088/1009-1963/14/11/027 Abstract ( 1254 )   PDF (332KB) ( 587 )   An analytical technique, referred to as the scattering matrix method (SMM), is developed to analyse the scattering of a planar wave from a conducting cylinder coated with nonuniform magnetized ferrite. The SMM solution for the nonuniform ferrite coating can be reduced to the expressions for the scattering and penetrated coefficients in four particular cases: nonuniform magnetized ferrite cylinder, uniform magnetized ferrite-coated conducting cylinder, uniform ferrite cylinder as well as homogeneous dielectric-coated conducting cylinder. The resonant condition for the nonuniform ferrite coating is obtained. The distinctive differences in scattering between the nonuniform ferrite coating and the nonuniform dielectric coating are demonstrated. The effects of applied magnetic fields and wave frequencies on the scattering characteristics for two types of the linear profiles are revealed.

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On the binding energies of excitons in polar quantum well structures in a weak electric field Wu Yun-Feng (吴云峰), Liang Xi-Xia (梁希侠), K. K. Baja Chinese Physics, 2005, 14 (11):  2314-2319.  DOI: 10.1088/1009-1963/14/11/028 Abstract ( 1303 )   PDF (273KB) ( 887 )   The binding energies of excitons in quantum well structures subjected to an applied uniform electric field by taking into account the exciton longitudinal optical phonon interaction is calculated. The binding energies and corresponding Stark shifts for III--V and II--VI compound semiconductor quantum well structures have been numerically computed. The results for GaAs/AlGaAs and ZnCdSe/ZnSe quantum wells are given and discussed. Theoretical results show that the exciton--phonon coupling reduces both the exciton binding energies and the Stark shifts by screening the Coulomb interaction. This effect is observable experimentally and cannot be neglected.

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Effect of external noise on the dynamical localization of two coupling electrons in quantum dot array He An-Min (何安民), Duan Su-Qing (段素青), Zhao Xian-Geng (赵宪庚) Chinese Physics, 2005, 14 (11):  2320-2324.  DOI: 10.1088/1009-1963/14/11/029 Abstract ( 1133 )   PDF (257KB) ( 464 )   The effect of external noise, which is characterized by an Ornstein--Uhlenbeck process, on the dynamical localization of two coupling electrons in a quantum dot array under the action of an ac electric field is studied. A numerical solution of the stochastic equations is obtained by averaging over stochastic trajectories. The results show that the external noise may destroy the dynamical localization, but the anti-noise capacity of the system is stronger when the two electrons are localized at the ends of the quantum dot array.

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Bulk MgB2 superconductor with high critical current density synthesized by self-propagating high-temperature synthesis method Feng Wang-Jun (冯旺军), Xia Tian-Dong (夏天东), Liu Tian-Zuo (刘天佐), Zhao Wen-Jun (赵文军), Wei Zhi-Qiang (魏智强) Chinese Physics, 2005, 14 (11):  2325-2328.  DOI: 10.1088/1009-1963/14/11/030 Abstract ( 1504 )   PDF (793KB) ( 648 )   Pure MgB$_{2}$ bulk samples are successfully synthesized by self-propagating high-temperature synthesis (SHS) method. The experiments show that the best preheating temperature is 250℃, the highest Jc values of the prepared MgB2 reach 1.5×106A/cm2 (10K, 0.5T) and 1.7×106A/cm2 (20K, 0T), and the MgB2 particle sizes range from 2 to 5$\mu$m. The advantages of this method are that it is simple, economical and suitable for the manufacture of bulk MgB2 materials on industrial scale.

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Magnetoresistances and magnetic entropy changes associated with negative lattice expansions in NaZn13-type compounds LaFeCoSi Hu Feng-Xia (胡凤霞), Qian Xiao-Ling (钱小陵), Wang Guang-Jun (王光军), Sun Ji-Rong (孙继荣), Shen Bao-Gen (沈保根), Cheng Zhao-Hua (成昭华), Gao Ju (高炬) Chinese Physics, 2005, 14 (11):  2329-2334.  DOI: 10.1088/1009-1963/14/11/031 Abstract ( 1596 )   PDF (284KB) ( 630 )   Magnetoresistances and magnetic entropy changes in NaZn13-type compounds La(Fe1-xCox)11.9Si1.1(x=0.04, 0.06, and 0.08) with Curie temperatures of 243 K, 274 K, and 301 K, respectively, are studied. The ferromagnetic ordering is accompanied by a negative lattice expansion. Large magnetic entropy changes in a wide temperature range from ~230 K to ~320 K are achieved. Raising Co content increases the Curie temperature but weakens the gnetovolume effect, thereby causing a decrease in magnetic entropy change. These materials exhibit a metallic character below TC, whereas the electrical resistance decreases abruptly and then recovers the metal-like behaviour above TC. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase in magnetic field leads to an increase in electrical resistance at temperatures near but above TC, which is a consequence of the field-induced metamagnetic transition from a paramagnetic state to a ferromagnetic state.

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Extraction of optical constants and thickness of nanometre scale TiO2 film Yang Ying-Ge (杨莺歌), Liu Pi-Jun (刘丕均), Wang Ying (王英), Zhang Ya-Fei (张亚非) Chinese Physics, 2005, 14 (11):  2335-2337.  DOI: 10.1088/1009-1963/14/11/032 Abstract ( 1491 )   PDF (212KB) ( 1102 )   TiO$_{2}$ thin films were deposited on glass substrates by sputtering in a conventional rf magnetron sputtering system. X-ray diffraction pattern and transmission spectrum were measured. The curves of refraction index and extinction coefficient distributions as well as the thickness of films calculated from transmission spectrum were obtained. The optimization problem was also solved using a method based on a constrained nonlinear programming algorithm.

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Design and fabrication of triangular inner cladding double-clad ytterbium doped fibre for high power lasers Fu Yong-Jun (傅永军), Jian Wei (简伟), Zheng Kai (郑凯), Yan Feng-Ping (延凤平), Chang De-Yuan (常德远), Jian Shui-Sheng (简水生) Chinese Physics, 2005, 14 (11):  2338-2341.  DOI: 10.1088/1009-1963/14/11/033 Abstract ( 1424 )   PDF (1188KB) ( 794 )   To improve the performance of double clad high power fibre lasers, inner cladding design plays a significant role. A triangular inner cladding and silica structure second cladding with large air holes to acquire high inner cladding numerical aperture are designed. Single mode and high power output of the fibre lasers need the double clad Yb doped fibre with large core. A fibre with annular refractive index distribution core and low numerical aperture to acquire a large mode area fibre core is designed and fabricated. Furthermore co-doping with aluminium (Al) has been used to improve the solubility of ytterbium (Yb) into silicate network, and the core absorption coefficients of two Yb doped fibres are compared with different Al concentration experimentally.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Influence of the deposition parameters on the transition region of hydrogenated silicon films growth Lei Qing-Song (雷青松), Wu Zhi-Meng (吴志猛), Geng Xin-Hua (耿新华), Zhao Ying (赵颖), Xi Jian-Ping (奚建平) Chinese Physics, 2005, 14 (11):  2342-2347.  DOI: 10.1088/1009-1963/14/11/034 Abstract ( 801 )   PDF (291KB) ( 479 )   Hydrogenated microcrystalline and amorphous silicon thin films were prepared by very high frequency plasma-enhanced chemical vapour deposition (VHF PECVD) by using a mixture of silane and hydrogen as source gas. The influence of deposition parameters on the transition region of hydrogenated silicon films growth was investigated by varying the silane concentration (SC), plasma power (Pw), working pressure (P), and substrate temperature (Ts). Results suggest that SC and Ts are the most critical factors that affect the film structure transition from microcrystalline to amorphous phase. A narrow region in the range of SC and Ts, in which the rapid phase transition takes place, was identified. It was found that at lower P or higher Pw, the transition region is shifted to larger SC. In addition, the dark conductivity and photoconductivity decrease with SC and show sharp changes in the transition region. It proposed that the transition process and the transition region are determined by the competition between the etching effect of atomic hydrogen and the growth of amorphous phase.

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Study on stability of hydrogenated amorphous silicon films Zhu Xiu-Hong (朱秀红), Chen Guang-Hua (陈光华), Zhang Wen-Li (张文理), Ding Yi (丁毅), Ma Zhan-Jie (马占洁), Hu Yue-Hui (胡跃辉), He Bin (何斌), Rong Yan-Dong (荣延栋) Chinese Physics, 2005, 14 (11):  2348-2351.  DOI: 10.1088/1009-1963/14/11/035 Abstract ( 1060 )   PDF (231KB) ( 483 )   Hydrogenated amorphous silicon (a-Si:H) films with high and same order of magnitude photosensitivity (~$10^{5}$) but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content (CH) as well as H--Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature,hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si:H films. We used hydrogen elimination model to explain our experimental results.

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Structural and electrical properties of SrTiO3 thin films as insulator of metal--ferroelectric--insulator--semiconductor (MFIS) structures Ma Jian-Hua (马建华), Meng Xiang-Jian (孟祥建), Lin Tie (林铁), Liu Shi-Jian (刘世建), Zhang Xiao-Dong (张晓东), Sun Jing-Lan (孙璟兰), Chu Jun-Hao (褚君浩) Chinese Physics, 2005, 14 (11):  2352-2359.  DOI: 10.1088/1009-1963/14/11/036 Abstract ( 1145 )   PDF (328KB) ( 563 )   SrTiO3 (STO) thin films were deposited on p-Si(100) substrates at various substrate temperatures from 300℃ to 700℃ by radio frequency (RF) magnetron sputtering technique. Their structure and electrical properties were investigated. It was found that the transition from amorphous phase to polycrystalline phase occurred at the substrate temperatures 300--400℃. Their crystallinity became better when the substrate temperatures further increased. The dielectric and leakage current measurements were carried out by using the Si/STO/Pt metal--insulator--semiconductor (MIS) structures at room temperature. It was found that the fixed charge density decreased and both the interface trap density and the dielectric constant increased when the substrate temperatures were increased. The leakage current mechanisms for STO MIS structures with STO films prepared at 700℃ followed the space charge limited current (SCLC) under the low applied electric field and the Poole--Frenkel emission under the high one. In addition, the resistivity for films prepared at 700℃ was higher than 1011 $\Omega\cdot$cm under the voltage lower than 10V (corresponding to the electric field of $1.54\times$ 103kV$\cdot$cm-1). It suggested that the STO films prepared at 700℃ were suitable for acting as the insulator of metal--ferroelectric--insulator--semiconductor (MFIS) structures.

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Determination of aerosol extinction coefficient and mass extinction efficiency by DOAS with a flashlight source Si Fu-Qi (司福祺), Liu Jian-Guo (刘建国), Xie Pin-Hua (谢品华), Zhang Yu-Jun (张玉钧), Liu Wen-Qing (刘文清), Hiroaki Kuze, Liu Cheng (刘诚), Nofel Lagrosas, Nobuo Takeuchi Chinese Physics, 2005, 14 (11):  2360-2364.  DOI: 10.1088/1009-1963/14/11/037 Abstract ( 1226 )   PDF (248KB) ( 597 )   With the method of differential optical absorption spectroscopy (DOAS),average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter (SPM). Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency (MEE) to be possible in the lower troposphere. The average MEE value is about 7.6m2$\cdot$g-1, and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.

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Functional structures and folding dynamics of two peptides Sheng Yue-Biao (盛乐标), Li Jing (李菁), Ma Bao-Liang (马保亮), Wang Wei (王炜) Chinese Physics, 2005, 14 (11):  2365-2369.  DOI: 10.1088/1009-1963/14/11/038 Abstract ( 1102 )   PDF (1108KB) ( 422 )   The folding dynamics and structural characteristics of peptides RTKAWNRQLYPEW (P1) and RTKQLYPEW (P2) are investigated by using all-atomic simulation procedure CHARMM in this work. The results show that P1, a segment of an antigen, has a folding motif of $\alpha$-helix, whereas P2, which is derived by deleting four residues AWNR from peptide P1, prevents the formation of helix and presents a $\beta$-strand. And peptide P1 experiences a more rugged energy landscape than peptide P2. From our results, it is inferred that the antibody CD8 cytolytic T lymphocyte prefers an antigen with a $\beta$-folding structure to that with an α-helical one.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Nonlinear evolution characteristics of the climate system on the interdecadal-centennial timescale Gao Xin-Quan (高新全), Zhang Wen (张文) Chinese Physics, 2005, 14 (11):  2370-2378.  DOI: 10.1088/1009-1963/14/11/039 Abstract ( 1171 )   PDF (514KB) ( 515 )   To better understand the physical mechanism of the climate change on interdecadal-centennial timescale, this paper focuses on analysing and modelling the evolution characteristics of the climate change. The method of wavelet transform is used to pick out the interdecadal timescale oscillations from long-term instrumental observations, natural proxy records, and modelling series. The modelling series derived from the most simplified nonlinear climatic model are used to identify whether modifications are concerned with some forcings such as the solar radiation on the climate system. The results show that two major oscillations exist in various observations and model series, namely the 20--30a and the 60--70a timescale respectively, and these quasi-periodicities are modulated with time. Further, modelling results suggest that the originations of these oscillations are not directly linked with the periodic variation of solar radiations such as the 1-year cycle, the 11-year cycle, and others, but possibly induced by the internal nonlinear effects of the climate system. It seems that the future study on the genesis of the climate change with interdecadal-centennial timescale should focus on the internal nonlinear dynamics in the climate system.