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Chin. Phys. B  
  Chin. Phys. B--2007, Vol.16, No.4
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Topological aspect of Chern--Simons p-branes

Duan Yi-Shi, Zhao Li, Liu Yu-Xiao, Ren Ji-Rong
Chin. Phys., 2007, 16 (4): 881-886 doi: 10.1088/1009-1963/16/4/001
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By generalizing the topological current of Abelian Chern--Simons (CS) vortices, we present a topological tensor current of CS p-branes based on the \phi -mapping topological current theory. It is revealed that CS p-branes are located at the isolated zeros of the vector field \phi(x), and the topological structure of CS p-branes is characterized by the winding number of the \phi-mappings. Furthermore, the Nambu--Goto action and the equation of motion for multi CS p-branes are obtained.

A new type of conserved quantity of Mei symmetry for Lagrange system

Fang Jian-Hui, Ding Ning, Wang Peng
Chin. Phys., 2007, 16 (4): 887-890 doi: 10.1088/1009-1963/16/4/002
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This paper studies a new type of conserved quantity which is directly induced by Mei symmetry of the Lagrange system. Firstly, the definition and criterion of Mei symmetry for the Lagrange system are given. Secondly, a coordination function is introduced, and the conditions of existence of the new conserved quantity as well as its forms are proposed. Lastly, an illustrated example is given. The result indicates that the coordination function can be selected properly according to the demand for finding the gauge function, and thereby the gauge function can be found more easily. Furthermore, since the choice of the coordination function has multiformity, many more conserved quantities of Mei symmetry for the Lagrange system can be obtained.

Stability and vibration of a helical rod with circular cross section in a viscous medium

Liu Yan-Zhu, Sheng Li-Wei
Chin. Phys., 2007, 16 (4): 891-896 doi: 10.1088/1009-1963/16/4/003
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The stability and vibration of a thin elastic helical rod with circular cross section in a viscous medium are discussed. The dynamical equations of the rod in the viscous medium are established in the Frenet coordinates of the centreline with the Euler angles describing the attitudes of the cross section as variables. We have proved that the Lyapunov and Euler conditions of stability of a helical rod in the space domain are the necessary conditions for the asymptotic stability of the rod in the time domain. The free frequencies and damping coefficients of torsional and flexural vibrations of the helical rod in the viscous medium are calculated.

Exact solution to the one-dimensional Dirac equation of linear potential

Long Chao-Yun, Qin Shui -Jie
Chin. Phys., 2007, 16 (4): 897-900 doi: 10.1088/1009-1963/16/4/004
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In this paper the one-dimensional Dirac equation with linear potential has been solved by the method of canonical transformation. The bound-state wavefunctions and the corresponding energy spectrum have been obtained for all bound states.

Enhancing the capability of controlling quantum systems via ancillary systems

Zhang Ming, Gao Da-Yuan, Dai Hong-Yi, Xie Hong-Wei, Hu De-Wen
Chin. Phys., 2007, 16 (4): 901-905 doi: 10.1088/1009-1963/16/4/005
Full Text: [PDF 117 KB] (Downloads:504)
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This paper explores the potential of controlling quantum systems by introducing ancillary systems and then performing unitary operation on the resulting composite systems. It generalizes the concept of pure state controllability for quantum systems and establishes the link between the operator controllability of the composite system and the generalized pure state controllability of its subsystem. It is constructively demonstrated that if a composite quantum system can be transferred between any pair of orthonormal pure vectors, then its subsystem is generalized pure-state controllable. Furthermore, the unitary operation and the coherent control can be concretely given to transfer the system from an initial state to the target state. Therefore, these properties may be potentially applied in quantum information, such as manipulating multiple quantum bits and creating entangled pure states. A concrete example has been given to illustrate that a maximally entangled pure state of a quantum system can be generated by introducing an ancillary system and performing open-loop coherent control on the resulting composite system.

Fast scheme for generating quantum-interference states and GHZ state of N trapped ions

Zheng Xiao-Juan, Fang Mao-Fa, Liao Xiang-Ping, Cai Jian-Wu, Cao Shuai
Chin. Phys., 2007, 16 (4): 906-909 doi: 10.1088/1009-1963/16/4/006
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We propose a fast scheme to generate the quantum-interference states of N trapped ions. In the scheme the ions are driven by a standing-wave laser beam whose carrier frequency is tuned such that the ion transition can take place. We also propose a simple and fast scheme to produce the GHZ state of N hot trapped ions and this scheme is insensitive to the heating of vibrational motion, which is important from the viewpoint of decoherence.

An efficient two-step quantum key distribution protocol with orthogonal product states

Yang Yu-Guang, Wen Qiao-Yan, Zhu Fu-Chen
Chin. Phys., 2007, 16 (4): 910-914 doi: 10.1088/1009-1963/16/4/007
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An efficient two-step quantum key distribution (QKD) protocol with orthogonal product states in the n\otimes n(n\geq3) Hilbert space is presented. In this protocol, the particles in the orthogonal product states form two particle sequences. The sender, Alice, first sends one sequence to the receiver, Bob. After Bob receives the first particle sequence, Alice and Bob check eavesdropping by measuring a fraction of particles randomly chosen. After ensuring the security of the quantum channel, Alice sends the other particle sequence to Bob. By making an orthogonal measurement on the two particle sequences, Bob can obtain the information of the orthogonal product states sent by Alice. This protocol has many distinct features such as great capacity, high efficiency in that it uses all orthogonal product states in distributing the key except those chosen for checking eavesdroppers.

The effect of quantum noise on multiplayer quantum game

Cao Shuai, Fang Mao-Fa, Zheng Xiao-Juan
Chin. Phys., 2007, 16 (4): 915-918 doi: 10.1088/1009-1963/16/4/008
Full Text: [PDF 236 KB] (Downloads:524)
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It has recently been realized that quantum strategies have a great advantage over classical ones in quantum games. However, quantum states are easily affected by the quantum noise, resulting in decoherence. In this paper, we investigate the effect of quantum noise on a multiplayer quantum game with a certain strategic space, with all players affected by the same quantum noise at the same time. Our results show that in a maximally entangled state, a special Nash equilibrium appears in the range of 0\leq p\leq0.622 (p is the quantum noise parameter), and then disappears in the range of 0.622

Entanglement swapping without joint measurement via a Λ-type atom interacting with bimodal cavity field

Lin Xiu, Li Hong-Cai, Yang Rong-Can, Huang Zhi-Ping
Chin. Phys., 2007, 16 (4): 919-922 doi: 10.1088/1009-1963/16/4/009
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This paper proposes a scheme for realizing entanglement swapping in cavity QED. The scheme is based on the resonant interaction of a two-mode cavity field with a {\Lambda}-type three-level atom. In contrast with the previously proposed schemes, the present scheme is ascendant, since the fidelity is 1.0 and the joint measurement isn't needed. And the scheme is experimentally feasible based on the current cavity QED technique.

Massive particles' tunnelling radiation from the black hole with a mass-quadruple moment

Han Yi-Wen
Chin. Phys., 2007, 16 (4): 923-927 doi: 10.1088/1009-1963/16/4/010
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In this paper, we extend Zhang and Zhao's recent work to the black hole with a mass-quadruple moment. The behaviour of the tunnelling massive particles is investigated, and the emission rate at which massive particles tunnel across the event horizon of the black hole is calculated. The result is consistent with an underlying unitary theory, and takes the same functional form as that of a massless particle.

Mean first-passage time of an asymmetric bistable system driven by colour-correlated noise

Zhang Xiao-Yan, Xu Wei
Chin. Phys., 2007, 16 (4): 928-932 doi: 10.1088/1009-1963/16/4/011
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In this paper, the effect of every parameter (including p, q, r, \la, \tau) on the mean first-passage time (MFPT) is investigated in an asymmetric bistable system driven by colour-correlated noise. The expression of MFPT has been obtained by applying the steepest-descent approximation. Numerical results show that (1) the intensity of multiplicative noise p and the intensity of additive noise q play different roles in the MFPT of the system, (2) suppression appears on the curve of the MFPT with small \la (e.g. \la<0.5) but there is a peak on the curve of the MFPT when \la is big (e.g. \la >0.5), and (3) with different values of r (e.g. r=0.1, 0.5, 1.5), the effort of \tau on the MFPT is diverse.

Study on bifurcation and stability of the closed-loop current-programmed boost converters

Zhao Yi- Bo, Zhang Dao-Yang, Zhang Chi-Jian
Chin. Phys., 2007, 16 (4): 933-936 doi: 10.1088/1009-1963/16/4/012
Full Text: [PDF 126 KB] (Downloads:838)
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In order to predict bifurcation point of the closed-loop current-programmed boost converter and enable this converter to operate at stable parameter space, this paper firstly establishes stroboscopic maps for this converter in the continuous conduction mode according to operating characteristics and topple of this converter. Parameter space at the steady state and bifurcation types are analysed together with stability theory of nonlinear equation. In the solving course, the duty cycle is avoided because of inversive solution, and accuracy is increased. Finally, correction is proved by numerical calculation.

Chaotic synchronization via linear controller

Chen Feng-Xiang, Zhang Wei-Dong
Chin. Phys., 2007, 16 (4): 937-941 doi: 10.1088/1009-1963/16/4/013
Full Text: [PDF 114 KB] (Downloads:650)
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A technical framework of constructing a linear controller for chaotic synchronization by utilizing the stability theory of cascade-connected system is presented. Based on the method developed in the paper, two simple and linear feedback controllers, as examples, are derived for the synchronization of Liu chaotic system and Duffing oscillator, respectively. This method is quite flexible in constructing a control law. Its effectiveness is also illustrated by the simulation results.

A new multi-scroll chaotic generator

Wang Fa-Qiang, Liu Chong-Xin
Chin. Phys., 2007, 16 (4): 942-945 doi: 10.1088/1009-1963/16/4/014
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In this paper a new simple multi-scroll chaotic generator is studied. The characteristic of this new multi-scroll chaotic generator is that it is easy to generate different number of scroll chaotic attractors through modifying the nature number n after fixing the suitable system parameters and it does not need complex mathematical derivation. Various number of scroll chaotic attractors are illustrated not only by computer simulation but also by the realization of an electronic circuit experiment on Electronic Workbench (EWB).

Passive control of a 4-scroll chaotic system

Wang Fa-Qiang, Liu Chong-Xin
Chin. Phys., 2007, 16 (4): 946-950 doi: 10.1088/1009-1963/16/4/015
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This paper studies the control of a new chaotic system which can generate 4-scroll attractors. Based on the properties of a passive system, it derives the essential conditions under which this new chaotic system could be equivalent to a passive system and globally asymptotically stabilize at a zero equilibrium point via smooth state feedback. Simulation results and circuit experiment show that the proposed chaos control method is effective.

Variational iteration method for solving perturbed mechanism of western boundary undercurrents in the Pacific Hot!

Mo Jia-Qi, Lin Wan-Tao, Wang Hui
Chin. Phys., 2007, 16 (4): 951-954 doi: 10.1088/1009-1963/16/4/016
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A class of perturbed mechanisms for the western boundary undercurrents in the Pacific is considered. The model of generalized governing equations is studied. Employing the method of variational iteration, an approximate solution of corresponding model is obtained. It is proved from the results that the solution for the variational iteration method can be used for analysing operation of the perturbed mechanism of western boundary undercurrents in the Pacific.

Suppression of spiral waves using intermittent local electric shock

Ma Jun, Ying He-Ping, Li Yan-Long
Chin. Phys., 2007, 16 (4): 955-961 doi: 10.1088/1009-1963/16/4/017
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In this paper, an intermittent local electric shock scheme is proposed to suppress stable spiral waves in the Barkley model by a weak electric shock (about 0.4 to 0.7) imposed on a random selected n×n grids (n=1-5, compared with the original 256×256 lattice) and monitored synchronically the evolutions of the activator on the grids as the sampled signal of the activator steps out a given threshold (i.e., the electric shock works on the n×n grids if the activator u\leq0.4 or u \geq 0.8). The numerical simulations show that a breakup of spiral is observed in the media state evolution to finally obtain homogeneous states if the electric shock with appropriate intensity is imposed.

Quantum study of Foldy--Wouthuysen--Tani theory on lattice

Liu Da-Qing
Chin. Phys., 2007, 16 (4): 962-974 doi: 10.1088/1009-1963/16/4/018
Full Text: [PDF 198 KB] (Downloads:440)
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We study here a quantum version of Foldy--Wouthuysen--Tani (FWT) transformation and compare the similarities and differences between the quantum and the classic FWT theories. Then the improvement of action on lattice is discussed. The result shows that it is not necessary to improve the covariant difference along the time direction on lattice. Finally we discuss briefly the structure of physical vacuum and give a model independent of field condensate.

Description of dynamics of stock prices by a Langevin approach

Huang Zi-Gang, Chen Yong, Zhang Yong, Wang Ying-Hai
Chin. Phys., 2007, 16 (4): 975-983 doi: 10.1088/1009-1963/16/4/019
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We have studied the Langevin description of stochastic dynamics of financial time series. A sliding-window algorithm is used for our analysis. We find that the fluctuation of stock prices can be understood from the view of a time-dependent drift force corresponding to the drift parameter in Langevin equation. It is revealed that the statistical results of the drift force estimated from financial time series can be approximately considered as a linear restoring force. We investigate the significance of this linear restoring force to the prices evolution from its two coefficients, the equilibrium position and the slope coefficient. The daily log-returns of S&P 500 index from 1950 to 1999 are especially analysed. The new simple form of the restoring force obtained both from mathematical and numerical analyses suggests that the Langevin approach can effectively present not only the macroscopical but also the detailed properties of the price evolution.

Focusing high-energy x-rays by a PMMA compound x-ray lens on Beijing synchrotron radiation facility

Le Zi-Chun, Liang Jing-Qiu, Dong Wen, Zhu Pei-Ping, Peng Liang-Qiang, Wang Wei-Biao, Huang Wan-Xia, Yuan Qing-Xi, Wang Jun-Yue
Chin. Phys., 2007, 16 (4): 984-988 doi: 10.1088/1009-1963/16/4/020
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The x-ray compound lens is a novel refractive x-ray optical device. This paper reports the authors' recent research on a polymethyl methacrylate (PMMA) compound x-ray lens. Firstly the designing and LIGA fabrication process for the PMMA compound x-ray lens are briefly described. Then, a method for theoretical analysis, as well as the experimental system for measurement is also introduced. Finally, the focusing spots for 8keV monochromatic x-rays by the PMMA compound x-ray lens are measured and analysed. According to the experimental results, it is concluded that the PMMA compound x-ray lens promises a good focusing performance under the high-energy x-rays.

106,110Pd (p,nγ)106,110Ag reactions at Ep=6.0-7.7MeV

Hu Bi-Tao, P.P. Zarubin, U.U. Juravlev
Chin. Phys., 2007, 16 (4): 989-993 doi: 10.1088/1009-1963/16/4/021
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This paper reports that the experimental excitation functions of reaction (p,n) are measured for 106,110Pd and ^{110}Pd at proton energy Ep=6.1-7.5MeV and Ep=6.0-7.7MeV respectively. The off-resonance excitation functions were compared with calculation values of the statistical model. A new formula used to estimate the peak cross section of isobaric analogue resonance was tested and it was found that calculation values agree reasonably well with the present data within experimental error, which confirms that the excitation strength of isobaric analogue state in (p,n) reaction not only depends on its spin, but also proportionally increases with the projectile proton spatial transmission Tp and the spectroscopic factor S for reaction (d,p) on the same target.

Intensity modulation in single-mode microchip Nd:YAG lasers with asymmetric external cavity

Tan Yi-Dong, Zhang Shu-Lian, Liu Wei-Xin, Mao Wei
Chin. Phys., 2007, 16 (4): 1020-1026 doi: 10.1088/1009-1963/16/4/026
Full Text: [PDF 253 KB] (Downloads:502)
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Intensity modulation induced by the asymmetric external cavity in single-mode microchip Nd:YAG lasers is presented. Two kinds of experimental results are discussed based on multiple feedback effects. In one case, the intensity modulation curve is a normal sine wave, whose fringe frequency is four times higher than that of a conventional optical feedback system, caused by multiple feedback effects. In the other case, the intensity modulation curve is the overlapping of the above quadruple-frequency signal and conventional optical feedback signal, which is determined by the additional phase difference induced by the asymmetric external cavity. The theoretical analyses are in good agreement with the experimental results. The quadruple-frequency modulation of the laser output intensity can greatly increase the resolution of displacement measurement of an optical feedback system.

Entanglement swapping between atom and cavity and generation of entangled state of cavity fields

Chen Ai-Xi, Deng Li
Chin. Phys., 2007, 16 (4): 1027-1030 doi: 10.1088/1009-1963/16/4/027
Full Text: [PDF 95 KB] (Downloads:574)
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This paper proposes a scheme where entanglement swapping between atom and cavity can be realized. \Lambda -type three-level atoms interacting resonantly with cavity field are considered. By detecting atom and cavity field, it realizes entanglement swapping between atom and cavity. It uses the technique of entanglement swapping to generate an entangled state of two cavity fields by measuring on atoms. It discusses the experimental feasibility of the proposed scheme and application of entangled state of cavity fields.

Analysis of the far spatial coherent suppressed single peak field distribution of a rectangular wave-guide laser

Wu Xing-Fei, Yang Jing, Xin Jian-Guo
Chin. Phys., 2007, 16 (4): 1031-1037 doi: 10.1088/1009-1963/16/4/028
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A theory of the far spatial coherent-suppressed single-peak field distribution of a rectangular wave-guide CO2 laser is presented. The theoretical analysis shows that a rectangular wave-guide laser can have an output intensity distribution in far field similar to that produced from a wave-guide array laser, which is in agreement with the experimental result. A single-peak mode output is obtained within 5 metres. The experimental far-field spread angle in the bigger-Fresnel number direction is 0.63 mrad, compared to the calculated one, 0.6 mrad, and when the length of the laser resonator is changed, a double-peak or multi-peak in far-field distribution of the laser is obtained.

Generation of 207-femtosecond pulses from a ytterbium figure-of-eight fibre laser

Zhao Wei, Zhang Wei, Ma Hai-Quan, Liu Chang, Chen Guo-Fu, Lu Ke-Qing
Chin. Phys., 2007, 16 (4): 1038-1041 doi: 10.1088/1009-1963/16/4/029
Full Text: [PDF 246 KB] (Downloads:583)
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We report the generation of 207-fs pulses with 1.2mW average power at 1036nm directly from a passively mode-locked Yb-doped fibre laser with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. These results imply a 4-fold reduction in pulse duration over previously reported figure-of-eight cavity passively mode-locked Yb-doped fibre lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0MHz. On the other hand, this laser offers a cleaner spectrum and greater stability and is completely self-starting.

Atomic coherence in nondegenerate four-wave mixing

Zuo Zhan-Chun, Sun Jiang, Liu Xia, Mi Xin, Yu Zu-He, Jiang Qian, Fu Pan-Ming, Wu Ling-An
Chin. Phys., 2007, 16 (4): 1042-1046 doi: 10.1088/1009-1963/16/4/030
Full Text: [PDF 238 KB] (Downloads:494)
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Two-photon resonant nondegenerate four-wave mixing (NFWM) with the addition of a coupling field in Ba atomic vapour has been studied. We find that coherence of the atomic level transitions leads to suppression of the NFWM signal, giving rise to a dip with a linewidth that is linearly proportional to the intensity of the coupling field.

All-optical switching and nonlinear optical properties of HBT in ethanol solution

Zheng Jia-Jin, Zhang Gui-Lan, Guo Yang-Xue, Li Xiang-Ping, Chen Wen-Ju
Chin. Phys., 2007, 16 (4): 1047-1051 doi: 10.1088/1009-1963/16/4/031
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This paper demonstrates an all-optical switching model system comprising a single pulsed pump beam at 355 nm and a CW He--Ne signal beam at 632.8 nm with 2-(2^\prime -hydroxyphenyl)benzothiazole (HBT) in ethanol solution. The origins of the optical switching effect were discussed. By the study of nonlinear optical properties for HBT in ethanol solvent, this paper verified that the excited-state intramolecular proton transfer (ESIPT) effect of HBT and the thermal effect of solvent worked on quite different time scales and together induced the change of the refractive index of HBT solution, leading to the signal beam deflection. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitive optical switching devices.

Internal mode of incoherent photovoltaic vector solitons

Zhang Bing-Zhi, Wang Hong-Cheng, She Wei-Long
Chin. Phys., 2007, 16 (4): 1052-1056 doi: 10.1088/1009-1963/16/4/032
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The internal modes of incoherent vector solitons (IVSs) in photovoltaic photorefractive materials are investigated in the framework of coupled nonlinear Schr\"{o}dinger equations. It is found that there is a pair of internal modes corresponding to a bright--bright IVS. The propagation dynamics of the bright-bright IVS perturbed by the internal modes is simulated by numerical method.

Existing conditions of full bandgaps and absolute negative refraction in metallic-dielectric photonic crystal

Dong Jian-Wen, Hu Xin-Hua, Wang He-Zhou
Chin. Phys., 2007, 16 (4): 1057-1061 doi: 10.1088/1009-1963/16/4/033
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This paper has theoretically studied the characteristic frequencies of band structures in two-dimensional metallic-dielectric photonic crystals. It is demonstrated that a large filling fraction benefits the existence of absolute photonic band gap, while a smaller filling fraction benefits an absolute negative refraction band. In addition, it also finds that the relation between the cut-off frequency of E-polarized wave and the filling fraction exceeding 10{\%} is content with a linear increasing function, whose coefficients are exponential to the normalized lattice constant. These investigations have significant implications for tuning the operational frequencies to desired applications and manufacturing photonic crystals.

Mechanism of the excitation of single pure mode L(0, 2) and its interaction with the defect in a hollow cylinder

Tang Li-Guo, Cheng Jian-Chun, Xu Xiao-Mei
Chin. Phys., 2007, 16 (4): 1062-1071 doi: 10.1088/1009-1963/16/4/034
Full Text: [PDF 604 KB] (Downloads:483)
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Guided elastic waves have a great potential in pipe inspection as an efficient and low-cost nondestructive evaluation (NDE) technique, among which the wave of mode L(0,2) receives a lot of attention because this mode is the fastest mode in a weakly dispersive region of frequency to minimize dispersion effects over a long distance and sensitive to the defects distributed circumferentially. Though many experimental and numerical researches have already been carried out about the excitation of L(0,2) and its interaction with the defect in a hollow cylinder, its excitation mechanism has not been clarified yet. In this paper based on the transient response solution of the hollow cylinder, derived by the method of eigenfunction expansion, the theory about the exciting mechanism of mode L(0,2) is advanced and the effects of the spatial distribution, vibration frequency and direction of the external force on the excitation are discussed. And the pure mode L(0,2) is excited successfully under the parameters obtained through theoretical analysis. Furthermore, its interactions with some kinds of defects in hollow cylinders are simulated with the method of finite element analysis (FEA) and the results agree well with those obtained by other researchers.

Analysis of a kind of Duffing oscillator system used to detect weak signals

Li Yue, Yang Bao-Jun, Yuan Ye, Liu Xiao-Hua
Chin. Phys., 2007, 16 (4): 1072-1076 doi: 10.1088/1009-1963/16/4/035
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The stability of the periodic solution of the Duffing oscillator system in the periodic phase state is proved by using the Yoshizaw theorem, which establishes a theoretical basis for using this kind of chaotic oscillator system to detect weak signals. The restoring force term of the system affects the weak-signal detection ability of the system directly, the quantitative relationship between the coefficients of the linear and nonlinear items of the restoring force of the Duffing oscillator system and the SNR in the detection of weak signals is obtained through a large number of simulation experiments, then a new restoring force function with better detection results is established.

Open loop control of vortex-induced vibration of a circular cylinder

Chen Zhi-Hua, Fan Bao-Chun, Zhou Ben-Mou, Li Hong-Zhi
Chin. Phys., 2007, 16 (4): 1077-1083 doi: 10.1088/1009-1963/16/4/036
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In this paper both numerical and experimental investigations have been carried out to suppress the vortex-induced vibration (VIV) of a circular cylinder in an electrically low-conducting fluid. The electromagnetic forces (Lorentz forces) in the azimuthal direction were generated through the mounted electrodes and magnets locally on the surface of the cylinder, which have been proved having an accelerating effect to the fluid on the surface of the cylinder. Results of computations are presented for synchronous vibration phenomenon of a cylinder at Re=200, which are in good agreement with previous computational results. With the Lorentz forces loaded, the VIV of the cylinder has been suppressed successfully. Experimental results have also shown the same tendency and are in reasonable agreement with the numerical results.

Coherent spectroscopy of the 87RbFg=1→ Fe=0 closed transition

Wang Yi, Zhan Ming-Sheng, Wang Yu-Zhu
Chin. Phys., 2007, 16 (4): 994-997 doi: 10.1088/1009-1963/16/4/022
Full Text: [PDF 154 KB] (Downloads:466)
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This paper has observed linewidth narrowing of dark states in rubidium cell by using the Hanle configuration. The reduction of the coherent resonance width under the transition of 87Rb Fg=1\rightarrow Fe=0 is observed and the qualitative explanation about its mechanism is presented. Multiple subnatural width dips are obtained with a linearly polarized laser beam for the transitions of 87Rb Fg=1\rightarrow Fe=0, 1, 2. The feature of negative and positive slope, namely dispersionlike feature, is observed in the transmitted light.

Optical pumping and population transfer of nuclear-spin states of caesium atoms in high magnetic fields

Luo Jun, Sun Xian-Ping, Zeng Xi-Zhi, Zhan Ming-Sheng
Chin. Phys., 2007, 16 (4): 998-1007 doi: 10.1088/1009-1963/16/4/023
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Nuclear-spin states of gaseous-state Cs atoms in the ground state are optically manipulated using a Ti:sapphire laser in a magnetic field of 1.516T, in which optical coupling of the nuclear-spin states is achieved through hyperfine interactions between electrons and nuclei. The steady-state population distribution in the hyperfine Zeeman sublevels of the ground state is detected by using a tunable diode laser. Furthermore, the state population transfer among the hyperfine Zeeman sublevels, which results from the collision-induced modification \delta a(\bm S \cdot \bm I) of the hyperfine interaction of Cs in the ground state due to stochastic collisions between Cs atoms and buffer-gas molecules, is studied at different buffer-gas pressures. The experimental results show that high-field optical pumping and the small change \delta a(\bm S \cdot \bm I) of the hyperfine interaction can strongly cause the state population transfer and spin-state interchange among the hyperfine Zeeman sublevels. The calculated results maybe explain the steady-state population in hyperfine Zeeman sublevels in terms of rates of optical-pumping, electron-spin flip, nuclear spin flip, and electron-nuclear spin flip-flop transitions among the hyperfine Zeeman sublevels of the ground state of Cs atoms. This method may be applied to the nuclear-spin-based solid-state quantum computation.

Calculation of photon angular distribution and polarization for radiative recombination for high-charged hydrogen-like ions

Shen Tian-Ming, Chen Chong-Yang, Wang Yan-Sen
Chin. Phys., 2007, 16 (4): 1008-1013 doi: 10.1088/1009-1963/16/4/024
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In this paper a systematic study is carried out on the angular distribution and polarization of photons emitted following radiative recombination of H-like ions by a non-relativistic dipole approximation. In order to incorporate the screening effect due to inner-shell electrons, a distorted wave approach is used. The dependences of the calculated angular distribution and polarization on the reduced energy and nuclear charge are fitted by the corresponding empirical formulas respectively.

Structure and stability of neutral and cationic AlnO clusters

Yang Peng, Ge Jian-Hua, Jiang Zhen-Yi
Chin. Phys., 2007, 16 (4): 1014-1019 doi: 10.1088/1009-1963/16/4/025
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In this paper various structural possibilities for AlnO neutral and cationic isomers were investigated by using the B3LYP/6-311G(3df) method. Calculations of this paper predicted the existence of a number of previously unknown isomers. The stabilities of the AlnO (n=2-7) clusters with even n are greater than those with odd n, however the stabilities of cationic ions have the opposite odd--even alternation. The mass spectra observations of Al17O+ and Al19O+ ions support our theoretical predictions on their stabilities.

Breakup of spiral wave under different boundary conditions

Zhao Ying-Kui, Wang Guang-Rui, Chen Shi-Gang
Chin. Phys., 2007, 16 (4): 1159-1166 doi: 10.1088/1009-1963/16/4/051
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In this paper, we investigate the breakup of spiral wave under no-flux, periodic and Dirichlet boundary conditions respectively. When the parameter \varepsilon is close to a critical value for Doppler-induced wave breakup, the instability of the system caused by the boundary effect occurs in the last two cases, resulting in the breakup of spiral wave near the boundary. With our defined average order measure of spiral wave (AOMSW), we quantify the degree of order of the system when the boundary-induced breakup of spiral wave happens. By analysing the AOMSW and outer diameter R of the spiral tip orbit, it is easy to find that this boundary effect is correlated with large values of R, especially under the Dirichlet boundary condition. This correlation is nonlinear, so the AOMSW sometimes oscillates with the variation of \varepsilon.

Measurement and analyses of the mean effective ion charge in the centre of tokamak discharges

Zheng Yong-Zhen, Ding Xuan-Tong, Zhuo Yan
Chin. Phys., 2007, 16 (4): 1084-1088 doi: 10.1088/1009-1963/16/4/037
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There are two different definitions for specifying the mean effective ion charge Zeff in plasmas: a) from the Spizer electrical resistivity of the plasma and b) from bremsstrahlung radiation losses of the plasma. In this paper Zeff in the centre of tokamak ohmic discharges has been determined from information on sawtooth-relaxations of the steady state plasma, based on the analysis for the power balance of the plasma electrons in the plasma centre during the period of recovery after the sawtooth crashes. This method is found to supply reliable results for tokamak parameters. While its application requires some efforts in data analysis, it can provide a reliable determination of Zeff, independent of the information from bremsstrahlung radiation losses of the plasma.

Numerical studies of atmospheric pressure glow discharge controlled by a dielectric barrier between two coaxial electrodes

Zhang Hong-Yan, Wang De-Zhen, Wang Xiao-Gang
Chin. Phys., 2007, 16 (4): 1089-1096 doi: 10.1088/1009-1963/16/4/038
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The glow discharge in pure helium at atmospheric pressure, controlled by a dielectric barrier between coaxial electrodes, is investigated based on a one-dimensional self-consistent fluid model. By solving the continuity equations for electrons, ions, and excited atoms, with the current conservation equation and the electric field profile, the time evolution of the discharge current, gas voltage and the surface density of charged particles on the dielectric barrier are calculated. The simulation results show that the peak values of the discharge current, gas voltage and electric field in the first half period are asymmetric to the second half. When the current reaches its positive or negative maximum, the electric field profile, and the electron and ion densities represent similar properties to the typical glow discharge at low pressures. Obviously there exist a cathode fall, a negative glow region, and a positive column. Effects of the barrier position in between the two coaxial electrodes and the discharge gap width on discharge current characteristics are also analysed. The result indicates that, in the case when the dielectric covering the outer electrode only, the gas is punctured earlier during the former half period and later during the latter half period than other cases, also the current peak value is higher, and the difference of pulse width between the two half periods is more obvious. On reducing the gap width, the multiple current pulse discharge happens.

A CAD oriented quasi-analytical large-signal drain current model for 4H-SiC MESFETs

Cao Quan-Jun, Zhang Yi-Men, Zhang Yu-Ming, Lü Hong-Liana, Wang Yue-Hu, Chang Yuan-Cheng, Tang Xiao-Yan
Chin. Phys., 2007, 16 (4): 1097-1100 doi: 10.1088/1009-1963/16/4/039
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This paper reports that a 4H-SiC MESFET (Metal Semiconductor Field Effect Transistor) large signal drain current model based on physical expressions has been developed to be used in CAD tools. The form of drain current model is based on semi-empirical MESFET model, and all parameters in this model are determined by physical parameters of 4H-SiC MESFET. The verification of the present model embedded in CAD tools is made, which shows a good agreement with measured data of large signal DC I-V characteristics, PAE (power added efficiency), output power and gain.

Deposition of SiOx barrier films by O2/TMDSO RF-PECVD

Zhou Mei-Li, Fu Ya-Bo, Chen Qiang, Ge Yuan-Jing
Chin. Phys., 2007, 16 (4): 1101-1104 doi: 10.1088/1009-1963/16/4/040
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This paper reports that the SiOx barrier films are deposited on polyethylene terephthalate substrate by plasma-enhanced chemical vapour deposition (PECVD) for the application of transparent barrier packaging. The variations of O2/ Tetramethyldisiloxane (TMDSO) ratio and input power in radio frequency (RF) plasma are carried out to optimize barrier properties of the SiOx coated film. The properties of the coatings are characterized by Fourier transform infrared, water vapour transmission rate (WVTR), oxygen transmission rate (OTR), and atomic force microscopy analysers. It is found that the O2/TMDSO ratio exceeding 2:1 and the input power over 200~W yield SiOx films with low carbon contents which can be good to the barrier (WVTR and OTR) properties of the SiOx coatings. Also, the film properties not only depend on oxygen concentration of the inlet gas mixtures and input power, but also relate to the surface morphology of the coating.

Nanocomposite TiC/a-C:H film prepared on titanium aluminium alloy substrates by PSII assistant MW-ECRCVD

Ma Guo-Jia, Liu Xi-Liang, Zhang Hua-Fang, Wu Hong-Chen, Peng Li-Ping
Chin. Phys., 2007, 16 (4): 1105-1110 doi: 10.1088/1009-1963/16/4/041
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Thin films of titanium carbide and amorphous hydrogenated carbon have been synthesized on titanium aluminium alloy substrates by PSII assisted MW-ECRCVD with a mirror field. The microstructure, chemical composition and mechanical property were investigated. Using XPS and TEM, the films were identified to be a-C:H film containing TiC nanometre grains (namely, the so-called nanocomposite structure). The size of TiC grains of nanocomposite TiC/DLC film is about 5 nm. The nanocomposite structure has obvious improvement in the mechanical properties of DLC film. The hardness of a-C:H film with Ti is enhanced to 34 G Pa, while that of a-C:H film without Ti is about 12 G Pa, and the coherent strength is also obviously enhanced at the critical load of about 35N.

Elastic analysis of a mode II crack in an icosahedral quasicrystal

Zhu Ai-Yu, Fan Tian-You
Chin. Phys., 2007, 16 (4): 1111-1118 doi: 10.1088/1009-1963/16/4/042
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Based on the displacement potential functions, the elastic analysis of a mode II crack in an icosahedral quasicrystal is performed by using the Fourier transform and dual integral equation theory. By the solution, the analytic expressions for the displacement field and stress field are obtained. The asymptotic behaviours of the phonon and phason stress fields around the crack tip indicate that the stresses near the crack tip exhibit a square root singularity. The most important physical quantities of fracture theory, crack stress intensity factor and energy release rate, are evaluated in an explicit version.

Effects of high-dose Ge ion implantation and post-implantation annealing on ZnO thin films

Xue Shu-Wen, Zu Xiao-Tao, Su Hai-Qiao, Zheng Wan-Guo, Xiang Xia, Deng Hong, Yang Chun-Rong
Chin. Phys., 2007, 16 (4): 1119-1124 doi: 10.1088/1009-1963/16/4/043
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This paper reports that ion implantation to a dose of 1×1017 ions/cm2 was performed on c-axis-orientated ZnO thin films deposited on (0001) sapphire substrates by the sol-gel technique. After ion implantation, the as-implanted ZnO films were annealed in argon ambient at different temperatures from 600-900℃. The effects of ion implantation and post-implantation annealing on the structural and optical properties of the ZnO films were investigated by x-ray diffraction (XRD), photoluminescence (PL). It was found that the intensities of (002) peak and near band edge (NBE) exitonic ultraviolet emission increased with increasing annealing temperature from 600-900℃. The defect related deep level emission (DLE) firstly increased with increasing annealing temperature from 600- 750℃, and then decreased quickly with increasing annealing temperature. The recovery of the intensities of NBE and DLE occurs at \sim 850℃ and \sim 750℃ respectively. The relative PL intensity ratio of NBE to DLE showed that the quality of ZnO films increased continuously with increasing annealing temperature from 600 - 900℃.

Light induced microstructure transformation in a-Si:H films

Liu Guo-Han, Ding Yi, Zhang Wen-Li, Chen Guang-Hua, He De-Yan, Deng Jin-Xiang
Chin. Phys., 2007, 16 (4): 1125-1128 doi: 10.1088/1009-1963/16/4/044
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A series of a-Si:H films are deposited by hot wire assisted microwave electron cyclotron resonant chemical vapour deposition (HW-MWECR-CVD), subsequently exposed under simulated illumination for three hours. This paper studies the microstructure change during illumination by Fourier Transformation Infrared (FTIR) spectra. There are two typical transformation tendencies of microstructure after illumination. It proposes a model of light induced structural change based on the experimental results. It is found that all samples follow the same mechanism during illumination, and intrinsic structure of samples affect the total H content.

Optical processes in the formation of stimulated emission from ZnO nanowires

Liu Rui-Bin, Pan An-Lian, Wang Fei-Fei, Zou Bing-Suo
Chin. Phys., 2007, 16 (4): 1129-1134 doi: 10.1088/1009-1963/16/4/045
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This paper studies power dependent photoluminescence spectra, the stimulated emission occurring at ultraviolet (UV) band instead of the green emission band of ZnO nanowires, which are prepared with a chemical reduction method. The dynamics of the UV emission and green emission is given to demonstrate the reason of stimulated emission occurring at UV band but not the green emission band under high excitation, which indicates that the slow decay rate of trap state makes it easy to be fully filled and saturated, while the fast decay rate of near-band-edge exciton state makes the UV emission dominate the radiative recombination under high excitation. The UV emission, as well as the corresponding stimulated emission, occurs in competition with the green deep-trap emission. In addition, when pump fluence further increases, the multiple lasing modes appear. The dependence of these lasing modes on the pump fluence is first discussed. This diagram should be helpful to understand and design the optical nanodevices of ZnO nanowires.

High power and high reliability GaN/InGaN flip-chip light-emitting diodes

Zhang Jian-Ming, Zou De-Shu, Xu Chen, Zhu Yan-Xu, Liang Ting, Da Xiao-Li, Shen Guang-Di
Chin. Phys., 2007, 16 (4): 1135-1139 doi: 10.1088/1009-1963/16/4/046
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High-power and high-reliability GaN/InGaN flip-chip light-emitting diodes (FCLEDs) have been demonstrated by employing a flip-chip design, and its fabrication process is developed. FCLED is composed of a LED die and a submount which is integrated with circuits to protect the LED from electrostatic discharge (ESD) damage. The LED die is flip-chip soldered to the submount, and light is extracted through the transparent sapphire substrate instead of an absorbing Ni/Au contact layer as in conventional GaN/InGaN LED epitaxial designs. The optical and electrical characteristics of the FCLED are presented. According to ESD IEC61000-4-2 standard (human body model), the FCLEDs tolerated at least 10\,kV ESD shock have ten times more capacity than conventional GaN/InGaN LEDs. It is shown that the light output from the FCLEDs at forward current 350mA with a forward voltage of 3.3\,V is 144.68\,mW, and 236.59\,mW at 1.0\,A of forward current. With employing an optimized contact scheme the FCLEDs can easily operate up to 1.0\,A without significant power degradation or failure. The life test of FCLEDs is performed at forward current of 200\,mA at room temperature. The degradation of the light output power is no more than 9\% after 1010.75\,h of life test, indicating the excellent reliability. FCLEDs can be used in practice where high power and high reliability are necessary, and allow designs with a reduced number of LEDs.

Study on the recovery of NBTI of ultra-deep sub-micro MOSFETs

Cao Yan-Rong, Ma Xiao-Hua, Hao Yue, Zhang Yue, Yu Lei, Zhu Zhi-Wei, Chen Hai-Feng
Chin. Phys., 2007, 16 (4): 1140-1144 doi: 10.1088/1009-1963/16/4/047
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Taking the actual operating condition of complementary metal oxide semiconductor (CMOS) circuit into account, conventional direct current (DC) stress study on negative bias temperature instability (NBTI) neglects the detrapping of oxide positive charges and the recovery of interface states under the `low' state of p-channel metal oxide semiconductor field effect transistors (MOSFETs) inverter operation. In this paper we have studied the degradation and recovery of NBTI under alternating stress, and presented a possible recovery mechanism. The three stages of recovery mechanism under positive bias are fast recovery, slow recovery and recovery saturation.

Polymer thin-film transistor based on a high dielectric constant gate insulator

Lü Wen, Peng Jun-Biao, Yang Kai-Xia, Lan Lin-Feng, Niu Qiao-Li, Cao Yong
Chin. Phys., 2007, 16 (4): 1145-1149 doi: 10.1088/1009-1963/16/4/048
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In this paper full polymer thin-film transistors (PTFTs) based on Poly (acrylonitrile) (PAN) as the gate dielectric and poly (2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) as the semiconductor layer were investigated by using different channel width/length ratios. Relatively high dielectric constant of the polymer dielectric layer (6.27) can remarkably reduce the threshold voltage of the transistors to below -3V. Hole field-effect mobility of MEH-PPV of the PTFTs was about 4.8×10-4cm2/Vs, and on/off current ratio was larger than 102, which was comparable with that of transistors with widely used Poly (4-vinyl phenol) (PVP) or SiO2 as gate dielectrics.

Pressure effects in AlAs/InxGa1-xAs/GaAs resonant tunnelling diodes for application in micromachined sensors

Wang Jian, Zhang Wen-Dong, Xue Chen-Yang, Xiong Ji-Jun, Liu Jun, Xie Bin
Chin. Phys., 2007, 16 (4): 1150-1154 doi: 10.1088/1009-1963/16/4/049
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This paper reports the current--voltage characteristics of [001]-oriented AlAs/InxGa1-xAs/GaAs resonant tunnelling diodes (RTDs) as a function of uniaxial external stress applied parallel to the [110] and the [1\bar{1}0] orientations, and the output characteristics of the GaAs pressure sensor based on the pressure effect on the RTDs. Under [110] stress, the resonance peak voltages of the RTDs shift to more positive voltages. For [1\bar{1}0] stress, the peaks shift toward more negative voltages. The resonance peak voltage is linearly dependent on the [110] and [1\bar{1}0] stresses and the linear sensitivities are up to 0.69mV/MPa, -0.69mV/MPa respectively. For the pressure sensor, the linear sensitivity is up to 0.37mV/kPa.

Laser-diode excited intense upconversion luminescence of Er3+ in bismuth--lead--germanate glasses

Li Tao, Zhang Qin-Yuan, Jiang Zhong-Hong
Chin. Phys., 2007, 16 (4): 1155-1158 doi: 10.1088/1009-1963/16/4/050
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We have investigated infrared-to-visible upconversion luminescence of Er3+ in bismuth--lead--germanate glasses. The UV cutoff wavelength is shortened while its lifetime is increased almost linearly, with PbF2 substituting for PbO in the bismuth--lead--germanate glasses. Three emissions centred at around 529, 545 and 657nm are clearly observed, which are identified as originating from the 2H11/2\rightarrow ^4{\rm I15/2, 4S3/2\rightarrow 4I15/2 and 4 F9/2\rightarrow 4I15/2 transitions, respectively. It is noted that all the upconversion emission intensities increase with PbF2 concentration increasing. The ratio between the intensities of red and green emissions increases with the increasing of PbF2 content. Energy transfer processes and nonradiative phonon-assisted decays account for the populations of the 2H11/2,4 S3/2 and 4F9/2 levels. The quadratic dependence of fluorescence on excitation laser power confirms a two-photon process to contribute to the upconversion emissions.

Density functional approximation for van der Waals fluids: based on hard sphere density functional approximation

Zhou Shi-Qi
Chin. Phys., 2007, 16 (4): 1167-1175 doi: 10.1088/1009-1963/16/4/052
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A universal theoretical approach is proposed which enables all hard sphere density functional approximations (DFAs) applicable to van der Waals fluids. The resultant DFA obtained by combining the universal theoretical approach with any hard sphere DFAs only needs as input a second-order direct correlation function (DCF) of a coexistence bulk fluid, and is applicable in both supercritical and subcritical temperature regions. The associated effective hard sphere density can be specified by a hard wall sum rule. It is indicated that the value of the effective hard sphere density so determined can be universal, i.e. can be applied to any external potentials different from the single hard wall. As an illustrating example, the universal theoretical approach is combined with a hard sphere bridge DFA to predict the density profile of a hard core attractive Yukawa model fluid influenced by diverse external fields; agreement between the present formalism's predictions and the corresponding simulation data is good or at least comparable to several previous DFT approaches. The primary advantage of the present theoretical approach combined with other hard sphere DFAs is discussed.
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