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CN 11-5639/O4
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  • Measurement of anomalous nuclear reaction in deuterium-loaded metal

    Jiang Song-Sheng, Li Jing-Huai, Wang Jian-Qing, He Ming, Wu Shao-Yong, Zhang Hong-Tao, Yao Shun-He, Zhao Yong-Gang
    Chin. Phys. B 2009, 18 (4): 1428-1435
    This paper reports on an experiment for testing natural nuclear fusion at low temperature searching for evidence of the origin of 3He from natural nuclear fusion in deep Earth. The experiment was carried out using deuterium-loaded titanium foil samples and powder sample. Detection of charged particl...

     
Chin. Phys. B  
  Chin. Phys. B--2009, Vol.18, No.4
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GENERAL

Topological structure of Gauss--Bonnet--Chern theorem and p-branes

Tian Miao, Zhang Xin-Hui, Duan Yi-Shi
Chin. Phys. B, 2009, 18 (4): 1301-1305 doi: 10.1088/1674-1056/18/4/001
Full Text: [PDF 187 KB] (Downloads:881)
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By making use of the φ-mapping topological current theory, this paper shows that the Gauss--Bonnet--Chern density (the Euler--Poincaré characteristic χ(M) density) can be expressed in terms of a smooth vector field φ and take the form of δ(φ), which means that only the zeros of φ contribute to χ(M). This is the elementary fact of the Hopf theorem. Furthermore, it presents that a new topological tensor current of \tilde {p}-branes can be derived from the Gauss--Bonnet--Chern density. Using this topological current, it obtains the generalized Nambu action for multi \tilde p-branes.

Effect of incubation period on epidemic spreading in complex networks

Huang Wei, Jiang Rui, Hu Mao-Bin, Wu Qing-Song
Chin. Phys. B, 2009, 18 (4): 1306-1311 doi: 10.1088/1674-1056/18/4/002
Full Text: [PDF 462 KB] (Downloads:742)
Show Abstract
We study the effect of incubation period on epidemic spreading in the Barabasi--Albert scale-free network and the Watts--Strogatz small world network by using a Suspectable-Incubated-Infected-Suspectable model. Our analytical investigations show that the epidemic threshold is independent of incubation period in both networks, which is verified by our large-scale simulation results. We also investigate the effect of incubation period on the epidemic dynamics in a supercritical regime. It is found that with the increase of incubation period Ω , a damped oscillation evolution of ρT(the ratio of persons in incubated state) appears and the time needed to reach a saturation value increases. Moreover, the steady value of ρT increases and approaches to an asymptotic constant with the value of {\it\Omega} increasing. As a result, the infected ratio ρI decreases with the increase of Ω according to a power law.

A generalized Mei conserved quantity and Mei symmetry of Birkhoff system

Wang Peng, Fang Jian-Hui, Wang Xian-Ming
Chin. Phys. B, 2009, 18 (4): 1312-1315 doi: 10.1088/1674-1056/18/4/003
Full Text: [PDF 138 KB] (Downloads:781)
Show Abstract
This paper studies a new conserved quantity which can be called generalized Mei conserved quantity and directly deduced by Mei symmetry of Birkhoff system. The conditions under which the Mei symmetry can directly lead to generalized Mei conserved quantity and the form of generalized Mei conserved quantity are given. An example is given to illustrate the application of the results.

Coupled flexural-torsional vibration band gap in periodic beam including warping effect

Fang Jian-Yu, Yu Dian-Long, Han Xiao-Yun, Cai Li
Chin. Phys. B, 2009, 18 (4): 1316-1321 doi: 10.1088/1674-1056/18/4/004
Full Text: [PDF 1514 KB] (Downloads:980)
Show Abstract
The propagation of coupled flexural-torsional vibration in the periodic beam including warping effect is investigated with the transfer matrix theory. The band structures of the periodic beam, both including warping effect and ignoring warping effect, are obtained. The frequency response function of the finite periodic beams is simulated with finite element method, which shows large vibration attenuation in the frequency range of the gap as expected. The effect of warping stiffness on the band structure is studied and it is concluded that substantial error can be produced in high frequency range if the effect is ignored. The result including warping effect agrees quite well with the simulated result.

Lattice models of traffic flow considering drivers' delay in response

Zhu Hui-Bing
Chin. Phys. B, 2009, 18 (4): 1322-1327 doi: 10.1088/1674-1056/18/4/005
Full Text: [PDF 169 KB] (Downloads:830)
Show Abstract
This paper proposes two lattice traffic models by taking into account the drivers' delay in response. The lattice versions of the hydrodynamic model are described by the differential-difference equation and difference-difference equation, respectively. The stability conditions for the two models are obtained by using the linear stability theory. The modified KdV equation near the critical point is derived to describe the traffic jam by using the reductive perturbation method, and the kink--antikink soliton solutions related to the traffic density waves are obtained. The results show that the drivers' delay in sensing headway plays an important role in jamming transition.

Two-mode excited entangled coherent states and their entanglement properties

Zhou Dong-Lin, Kuang Le-Man
Chin. Phys. B, 2009, 18 (4): 1328-1332 doi: 10.1088/1674-1056/18/4/006
Full Text: [PDF 113 KB] (Downloads:731)
Show Abstract
This paper introduces two types of two-mode excited entangled coherent states (TMEECSs) |Ψ±(α,m,n)>, studies their entanglement characteristics, and investigates the influence of photon excitations on quantum entanglement. It shows that for the state |Ψ+(α,m,m)> the two-mode photon excitations affect seriously entanglement character while the state |Ψ-(α,m,m)> is always a maximally entangled state, and shows how such states can be produced by using cavity quantum electrodynamics and quantum measurements. It finds that the entanglement amount of the TMEECSs is larger than that of the single-mode excited entangled coherent states with the same photon excitation number.

Participant attack on quantum secret sharing based on entanglement swapping

Song Ting-Ting, Zhang Jie, Gao Fei, Wen Qiao-Yan, Zhu Fu-Chen
Chin. Phys. B, 2009, 18 (4): 1333-1337 doi: 10.1088/1674-1056/18/4/007
Full Text: [PDF 107 KB] (Downloads:814)
Show Abstract
The security of quantum secret sharing based on entanglement swapping is revisited and a participant attack is presented. In this attack two dishonest agents together can illegally recover the secret quantum state without the help of any other controller, and it will not be detected by any other users. Furthermore, by modifying the distribution process of particles and adding a detection step after each distribution process, we propose an improved protocol which can resist this kind of attack.

Bipartite entanglement of a two-qubit system with anisotropic couplings under nonuniform magnetic fields

Qin Meng, Tian Dong-Ping
Chin. Phys. B, 2009, 18 (4): 1338-1341 doi: 10.1088/1674-1056/18/4/008
Full Text: [PDF 166 KB] (Downloads:647)
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This paper investigates bipartite entanglement of a two-qubit system with anisotropic couplings under an inhomogeneous magnetic field. This work is mainly to investigate the characteristics of a Heisenberg XYZ chain and obtains some meaningful results. By the concept of negativity, it finds that the inhomogeneity of magnetic field may induce entanglement and the critical magnetic field is independent of Jz. The inhomogeneous magnetic field can increase the value of critical magnetic field Bc. It also finds that the magnetic field not only suppresses the entanglement but also can induce it to revival for some time.

Proof of the insecurity of quantum secret sharing based on the Smolin bound entangled states

Yu Ya-Fei, Zhang Zhi-Ming
Chin. Phys. B, 2009, 18 (4): 1342-1345 doi: 10.1088/1674-1056/18/4/009
Full Text: [PDF 102 KB] (Downloads:634)
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This paper reconsiders carefully the possibility of using the Smolin bound entangled states as the carrier for sharing quantum secret. It finds that the process of quantum secret sharing based on Smolin states has insecurity though the Smolin state was reported to violate maximally the two-setting Bell-inequality. The general proof is given.

Macroscopic inequivalent entanglement witness in Heisenberg spin chain

Zhang Ting, Chen Ping-Xing, Li Cheng-Zu
Chin. Phys. B, 2009, 18 (4): 1346-1351 doi: 10.1088/1674-1056/18/4/010
Full Text: [PDF 134 KB] (Downloads:570)
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Motivated by the wise idea of entanglement witness (EW), we present an inequivalent entanglement witness (IEEW) that can analogously classify certain eigenstates entangled in inequivalent ways under stochastic local operations and classical communication (SLOCC) in the Heisenberg spin chain. Since the IEEW is the absolute value of magnetization | M| that is a macroscopically measurable quantity, our conclusions provide a macroscopic method to detect inequivalent entanglement between microscopic spins, on the one hand, and clearly show that inequivalent entanglement can yield different macroscopic effects, on the other hand.

Quantum logic gates with two-level trapped ions beyond Lamb--Dicke limit

Zheng Xiao-Juan, Luo Yi-Min, Cai Jian-Wu
Chin. Phys. B, 2009, 18 (4): 1352-1356 doi: 10.1088/1674-1056/18/4/011
Full Text: [PDF 139 KB] (Downloads:554)
Show Abstract
In the system with two two-level ions confined in a linear trap, this paper presents a simple scheme to realize the quantum phase gate (QPG) and the swap gate beyond the Lamb--Dicke (LD) limit. These two-qubit quantum logic gates only involve the internal states of two trapped ions. The scheme does not use the vibrational mode as the data bus and only requires a single resonant interaction of the ions with the lasers. Neither the LD approximation nor the auxiliary atomic level is needed in the proposed scheme. Thus the scheme is simple and the interaction time is very short, which is important in view of decoherence. The experimental feasibility for achieving this scheme is also discussed.

Properties on the distant distribution of entanglement for arbitrary two-qubit pure states via noisy quantum channels

Wang Qiong, Li Ji-Xin, Zeng Hao-Sheng
Chin. Phys. B, 2009, 18 (4): 1357-1361 doi: 10.1088/1674-1056/18/4/012
Full Text: [PDF 97 KB] (Downloads:527)
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This paper investigates the change of entanglement for transmitting an arbitrarily entangled two-qubit pure state via one of three typical kinds of noisy quantum channels: amplitude damping quantum channel, phase damping quantum channel and depolarizing quantum channel. It finds, in all these three cases, that the output distant entanglement (measured by concurrence) reduces proportionately with respect to its initial amount, and the decaying ratio is determined only by the noisy characteristics of quantum channels and independent of the form of initial input state.

An exact inflationary solution in the chaotic model with non-minimal coupling

Liu Xiong-Wei, Yang Shu-Zheng, Chen Shi-Wu, Lin Kai
Chin. Phys. B, 2009, 18 (4): 1362-1366 doi: 10.1088/1674-1056/18/4/013
Full Text: [PDF 120 KB] (Downloads:525)
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This paper presents a new exact inflationary solution to the non-minimally coupled scalar field. The inflation is driven by the evolution of a scalar field with inflation potential V(φ ) = (λ/ 4)φ4+ b1 φ2+ b2 + b3 φ-2 + b4 φ-4. The spectral index of the scalar density fluctuations ns is consistent with the result of WMAP3 (Wilkinson Microwave Anisotropy Probe 3) for λCDM (Lambda-Cold Dark Matter). This model relaxes the constraint to the quartic coupling constant. And it can enter smoothly into a radiation-dominated stage when inflation ends.

Chirality-asymmetry force between ɑ-quartz and copper block

Hu Yong-Hong, Xu Qing, Liu Zhong-Zhu
Chin. Phys. B, 2009, 18 (4): 1367-1372 doi: 10.1088/1674-1056/18/4/014
Full Text: [PDF 341 KB] (Downloads:478)
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The chirality-asymmetry macroscopic force mediated by light pseudoscalar particles between α -quartz and some achiral matter is studied. If this force between achiral source mass and α -quartz with some chirality is attractive, it will become repulsive when the chirality of the α -quartz crystal is changed. According to the tested limits of the coupling constant gs gp /\hbar c< 1.5× 10-24 at the Compton wavelength λ = 10-3 m, the force (F) between a 0.08× 0.08× 0.002 m3 block of α -quartz and a 0.08× 0.08× 0.01 m3 copper block with a separation being 0.5× 10-3 \mbox{m} in between, is estimated from the published data at less than 4.64× 10-24 N, i.e. F < 4.64× 10-24 N.

Fluctuations and pseudo long range dependence in network flows: A non-stationary Poisson process model

Chen Yu-Dong, Li Li, Zhang Yi, Hu Jian-Ming
Chin. Phys. B, 2009, 18 (4): 1373-1379 doi: 10.1088/1674-1056/18/4/015
Full Text: [PDF 252 KB] (Downloads:487)
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In the study of complex networks (systems), the scaling phenomenon of flow fluctuations refers to a certain power-law between the mean flux (activity) < Fi> of the i-th node and its variance σi as Fi ∝ <Fiα. Such scaling laws are found to be prevalent both in natural and man-made network systems, but the understanding of their origins still remains limited. This paper proposes a non-stationary Poisson process model to give an analytical explanation of the non-universal scaling phenomenon: the exponent α varies between 1/2 and 1 depending on the size of sampling time window and the relative strength of the external/internal driven forces of the systems. The crossover behaviour and the relation of fluctuation scaling with pseudo long range dependence are also accounted for by the model. Numerical experiments show that the proposed model can recover the multi-scaling phenomenon.

Nonextensive and extensive thermostatistic properties of Fermi systems trapped in different external potentials

Huang Zhi-Fu, Ou Cong-Jie, Chen Jin-Can
Chin. Phys. B, 2009, 18 (4): 1380-1388 doi: 10.1088/1674-1056/18/4/016
Full Text: [PDF 417 KB] (Downloads:553)
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The thermostatistic properties of a q-generalized Fermi system trapped in a generic power-law potential are studied, based on the generalized statistic distribution derived from the Tsallis entropy. The total number of particles, the total energy, and the heat capacity at constant volume of the system are derived. The thermostatistic characteristics of the system are discussed in detail. It is found that the thermostatistic properties of such a system depend closely on parameter q, dimensional number of the space, kinetic characteristics of particles and shapes of the external potential, and the external potential has a great influence on the thermostatistic properties of the system. Moreover, it is shown that the results obtained here are very general and can be used to unify the description of the nonextensive and extensive thermostatistic properties of a class of Fermi systems trapped in different external potentials so that the important conclusions of many typical Fermi systems in the literature may be directly derived from the present paper.

Stochastic resonance in a single-mode laser driven by quadratic pump noise and amplitude-modulated signal

Zhang Li
Chin. Phys. B, 2009, 18 (4): 1389-1393 doi: 10.1088/1674-1056/18/4/017
Full Text: [PDF 176 KB] (Downloads:627)
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This paper investigates the phenomenon of stochastic resonance in a single-mode laser driven by quadratic pump noise and amplitude-modulated signal. A new linear approximation approach is advanced to calculate the signal-to-noise ratio. In the linear approximation only the drift term is linearized, the multiplicative noise term is unchangeable. It is found that there appears not only the standard form of stochastic resonance but also the broad sense of stochastic resonance, especially stochastic multiresonance appears in the curve of signal-to-noise ratio as a function of coupling strength λ between the real and imaginary parts of the pump noise.

A new hyperchaos system and its circuit simulation by EWB

Zhou Ping, Cao Yu-Xia, Cheng Xue-Feng
Chin. Phys. B, 2009, 18 (4): 1394-1398 doi: 10.1088/1674-1056/18/4/018
Full Text: [PDF 1351 KB] (Downloads:959)
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This paper reports a new hyperchaotic system evolved from the three-dimensional Lü chaotic system. The Lyapunov exponents spectrum and the bifurcation diagram of this new hyperchaotic system are obtained. Hyperchaotic attractor, periodic orbit and chaotic attractor are obtained by computer simulation. A circuit is designed to realize this new hyperchaotic system by electronic workbench.

Controlling chaos in permanent magnet synchronous motor based on finite-time stability theory

Wei Du-Qu, Zhang Bo
Chin. Phys. B, 2009, 18 (4): 1399-1403 doi: 10.1088/1674-1056/18/4/019
Full Text: [PDF 682 KB] (Downloads:1680)
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This paper reports that the performance of permanent magnet synchronous motor (PMSM) degrades due to chaos when its systemic parameters fall into a certain area. To control the undesirable chaos in PMSM, a nonlinear controller, which is simple and easy to be constructed, is presented to achieve finite-time chaos control based on the finite-time stability theory. Computer simulation results show that the proposed controller is very effective. The obtained results may help to maintain the industrial servo driven system's security operation.

Synchronization of time-delay chaotic systems on small-world networks with delayed coupling

Qi Wei, Wang Ying-Hai
Chin. Phys. B, 2009, 18 (4): 1404-1408 doi: 10.1088/1674-1056/18/4/020
Full Text: [PDF 603 KB] (Downloads:711)
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By using the well-known Ikeda model as the node dynamics, this paper studies synchronization of time-delay systems on small-world networks where the connections between units involve time delays. It shows that, in contrast with the undelayed case, networks with delays can actually synchronize more easily. Specifically, for randomly distributed delays, time-delayed mutual coupling suppresses the chaotic behaviour by stabilizing a fixed point that is unstable for the uncoupled dynamical system.

A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb

Yi Lin, Yuan Jie, Qi Xiang-Hui, Chen Wen-Lan, Zhou Da-Wei, Zhou Tong, Zhou Xiao-Ji, Chen Xu-Zong
Chin. Phys. B, 2009, 18 (4): 1409-1412 doi: 10.1088/1674-1056/18/4/021
Full Text: [PDF 545 KB] (Downloads:690)
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This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634 nm referencing on the hyperfine B-X transition R(80)8-4 of 127I2. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8×10^{-12} (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz.
NUCLEAR PHYSICS

Analysis of prompt fission neutron spectrum and multiplicity for 237Np(n, f) in the frame of multi-modal Los Alamos model

Zheng Na, Ding Yi, Zhong Chun-Lai, Chen Jin-Xiang, Fan Tie-Shuan
Chin. Phys. B, 2009, 18 (4): 1413-1420 doi: 10.1088/1674-1056/18/4/022
Full Text: [PDF 269 KB] (Downloads:562)
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The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons emitted from fragments for the three most dominant fission modes (standard I, standard II and superlong) are calculated separately and the total spectrum is synthesized. The multi-modal parameters contained in the spectrum model are determined on the basis of experimental data of fission fragment mass distributions. The calculated total prompt fission neutron spectrum and multiplicity are better agreement with the experimental data than those obtained from the conventional treatment of the Los Alamos model.

Determination of the stellar reaction rate for 12C(ɑ, γ)16O: using a new expression with the reaction mechanism

Xu Yi, Xu Wang, Ma Yu-Gang, Cai Xiang-Zhou, Chen Jin-Gen, Fan Gong-Tao, Fan Guang-Wei, Guo Wei, Luo Wen, Pan Qiang-Yan, Shen Wen-Qing, Yang Li-Feng
Chin. Phys. B, 2009, 18 (4): 1421-1427 doi: 10.1088/1674-1056/18/4/023
Full Text: [PDF 376 KB] (Downloads:538)
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The astrophysical reaction rate of 12C(α, γ)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9=0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(α,γ)16O reaction rates are calculated in the temperature range from T9=0.3 to 2 according to all the available cross section data. A new analytic expression of the 12C(α,γ)16O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3∑gma fit errors, are obtained from fit to our calculated reaction rate from T9=0.3 to 2. Using the fit results, the analytic expression of 12C(α,γ)16O reaction rate is extrapolated down to T9=0.05 based on the underlying physics. The 12C(α,γ)16O reaction rate at T9=0.2 is (8.78\pm1.52)×1015 cm3s-1mol-1. Some comparisons and discussions about our new 12C(α, γ)16O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9=2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(α,γ)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(α,γ)16O reaction rates.

Measurement of anomalous nuclear reaction in deuterium-loaded metal Hot!

Jiang Song-Sheng, Li Jing-Huai, Wang Jian-Qing, He Ming, Wu Shao-Yong, Zhang Hong-Tao, Yao Shun-He, Zhao Yong-Gang
Chin. Phys. B, 2009, 18 (4): 1428-1435 doi: 10.1088/1674-1056/18/4/024
Full Text: [PDF 242 KB] (Downloads:515)
Show Abstract
This paper reports on an experiment for testing natural nuclear fusion at low temperature searching for evidence of the origin of 3He from natural nuclear fusion in deep Earth. The experiment was carried out using deuterium-loaded titanium foil samples and powder sample. Detection of charged particle was carried out using a low-level charged particle spectrometer. An Al foil was used as an energy absorber for identification of charged particle. Although the counting rate is very low in the experiment, the emission of energetic particle from the sample is observed and the particle is identified as a proton having energy about 2.8 MeV after exiting the titanium sample. This work provides a positive result for the emission of charged particle in the deuterium-loaded titanium foil samples at low temperature, but a negative result for the deuterium-loaded titanium powder sample. The average reaction yield is deduced to be (0.46±0.08) protons/h for the foil samples. With the suggestion that the proton originates from d--d reaction, we calculate the reaction rate for d--d reaction, and the obtained result is 1.4× 10-24 fusion/d--d\cdot sec. The negative result of the deuterium-loaded titanium powder sample suggests that the reaction yield might be correlated with the density or microscopic variables of deuterium-loaded titanium materials. The negative result also indicates that d--d reaction catalysed by μ-meson from cosmic ray can be excluded in the samples in this experiment.
CLASSICAL AREAS OF PHENOMENOLOGY

Hybrid method for investigation of electromagnetic scattering from conducting target above the randomly rough surface

Wang Rui, Guo Li-Xin, Ma Jun, Wu Zhen-Sen
Chin. Phys. B, 2009, 18 (4): 1503-1511 doi: 10.1088/1674-1056/18/4/036
Full Text: [PDF 726 KB] (Downloads:771)
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A current based hybrid method (HM) is proposed which combines the method of moment (MOM) with the Kirchhoff approximation (KA) for the analysis of scattering interaction between a two-dimensional (2D) infinitely long conducting target with arbitrary cross section and a one-dimensional (1D) Gaussian rough surface. The electromagnetic scattering region in the HM is split into KA region and MOM region. The electric field integral equation (EFIE) in MOM region (target) is derived, the computational time of the HM depends mainly on the number of unknowns of the target. The bistatic scattering coefficient for the infinitely long cylinder above the rough surface with Gaussian roughness spectrum is calculated, and the numerical results are compared and verified with those obtained by the conventional MOM, which shows the high efficiency of the HM. Finally, the influence of the size, location of the target, the rms height and correlation length of the rough surface on the bistatic scattering coefficient with different polarizations is discussed in detail.

Single-mode photon number measurement for the squeezed two-mode number state

Xu Xue-Fen, Zhu Shi-Qun
Chin. Phys. B, 2009, 18 (4): 1512-1516 doi: 10.1088/1674-1056/18/4/037
Full Text: [PDF 106 KB] (Downloads:417)
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Based on the fact that a two-mode squeezed number state is a two-variable Hermite polynomial excitation of the two-mode squeezed vacuum state, the result of one-mode l-photon measurement for the two-mode squeezed number state S2| m,n> is discussed. It is found that a remaining field-mode simultaneously collapses into a number state | n-m+l> with the coefficient being a Jacobi polynomial of n,m and l, which manifestly exhibits the entanglement between the two modes, i.e. it depends on the number-difference between the two modes. The second mode collapses into an excited coherent state when the first mode is measured as a coherent state.

Entropy squeezing for a two-level atom in two-mode Raman coupled model with intrinsic decoherence

Zhang Jian, Shao Bin, Zou Jian
Chin. Phys. B, 2009, 18 (4): 1517-1527 doi: 10.1088/1674-1056/18/4/038
Full Text: [PDF 323 KB] (Downloads:560)
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In this paper, we investigate the entropy squeezing for a two-level atom interacting with two quantized fields through Raman coupling. We obtain the dynamical evolution of the total system under the influence of intrinsic decoherence when the two quantized fields are prepared in a two-mode squeezing vacuum state initially. The effects of the field squeezing factor, the two-level atomic transition frequency, the second field frequency and the intrinsic decoherence on the entropy squeezing are discussed. Without intrinsic decoherence, the increase of field squeezing factor can break the entropy squeezing. The two-level atomic transition frequency changes only the period of oscillation but not the strength of entropy squeezing. The influence of the second field frequency is complicated. With the intrinsic decoherence taken into consideration, the results show that the stronger the intrinsic decoherence is, the more quickly the entropy squeezing will disappear. The increase of the atomic transition frequency can hasten the disappearance of entropy squeezing.

Ultraslow optical solitons in tunnel-coupled double semiconductor quantum well

Chen Ai-Xi, Xu Yan-Qiu, Deng Li, Zhou Su-Yun
Chin. Phys. B, 2009, 18 (4): 1528-1533 doi: 10.1088/1674-1056/18/4/039
Full Text: [PDF 448 KB] (Downloads:482)
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This paper investigates the nonlinear evolution of the pulse probe field in an asymmetric coupled-quantum well driven coherently by a pulse probe field and two controlled fields. This study shows that, by choosing appropriate physical parameters, self-modulation can precisely balance group velocity dispersion in the investigated system, leading to the formation of ultraslow optical solitons of the probe field. The proposed scheme may lead to the development of the controlled technique of optical buffers and optical delay lines.

Normal ordering and antinormal ordering of the operator ( fQ+gP)n and some of their applications

Meng Xiang-Guo, Wang Ji-Suo, Liang Bao-Long
Chin. Phys. B, 2009, 18 (4): 1534-1541 doi: 10.1088/1674-1056/18/4/040
Full Text: [PDF 141 KB] (Downloads:410)
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In this paper by virtue of the technique of integration within an ordered product (IWOP) of operators and the intermediate coordinate-momentum representation in quantum optics, we derive the normal ordering and antinormal ordering products of the operator ( fQ+gP)n when n is an arbitrary integer. These products are very useful in calculating their matrix elements and expectation values and obtaining some useful mathematical formulae. Finally, the applications of some new identities are given.

Kinetic analysis of the factors limiting the output power of the Ne--CuBr UV laser

Mao Bang-Ning, Pan Bai-Liang, Chen Li, Wang Ya-Juan, Yao Zhi-Xin
Chin. Phys. B, 2009, 18 (4): 1542-1546 doi: 10.1088/1674-1056/18/4/041
Full Text: [PDF 500 KB] (Downloads:529)
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The parametric optimization of the Ne--CuBr UV laser excited by longitudinal pulsed discharge is analysed by using a self-consistent kinetic model. Consistent characteristics of the optimization process are obtained by comparing with the experimental results. Simulation results show that neon ions come into being along with considerable depletion of the ground-state copper atoms. And the optimization of the discharge tube diameter is the tradeoff between the specific output photon density and the total active volume. Both the optimal neon gas pressure and the optimal reservoir temperature result from the balance between the neon ion density and the ground-state copper atom density to arrive at a maximum of their product.

Theoretical analysis and experimental research on thermal focal length of a YVO4/Nd:YVO4 composite crystal

Zhou Cheng
Chin. Phys. B, 2009, 18 (4): 1547-1552 doi: 10.1088/1674-1056/18/4/042
Full Text: [PDF 579 KB] (Downloads:949)
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This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respectively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7 mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.

Analysis of thermal conductivity in tree-like branched networks

Kou Jian-Long, Lu Hang-Jun, Wu Feng-Min, Xu You-Sheng
Chin. Phys. B, 2009, 18 (4): 1553-1559 doi: 10.1088/1674-1056/18/4/043
Full Text: [PDF 880 KB] (Downloads:725)
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Asymmetric tree-like branched networks are explored by geometric algorithms. Based on the network, an analysis of the thermal conductivity is presented. The relationship between effective thermal conductivity and geometric structures is obtained by using the thermal-electrical analogy technique. In all studied cases, a clear behaviour is observed, where angle (δ ,θ ) among parent branching extended lines, branches and parameter of the geometric structures have stronger effects on the effective thermal conductivity. When the angle δ is fixed, the optical diameter ratio β* is dependent on angle θ . Moreover, γ and m are not related to β * . The longer the branch is, the smaller the effective thermal conductivity will be. It is also found that when the angle θ < δ / 2, the higher the iteration m is, the lower the thermal conductivity will be and it tends to zero, otherwise, it is bigger than zero. When the diameter ratio β 1< 0.707 and angle δ is bigger, the optimal k of the perfect ratio increases with the increase of the angle δ ; when β 1> 0.707, the optimal k decreases. In addition, the effective thermal conductivity is always less than that of single channel material. The present results also show that the effective thermal conductivity of the asymmetric tree-like branched networks does not obey Murray's law.
ATOMIC AND MOLECULAR PHYSICS

Structures, stabilities and magnetic moment of small copper-nickel clusters

Feng Cui-Ju, Xue Yong-Hong, Zhang Xiao-Yan, Zhang Xiao-Chun
Chin. Phys. B, 2009, 18 (4): 1436-1442 doi: 10.1088/1674-1056/18/4/025
Full Text: [PDF 1235 KB] (Downloads:822)
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This paper obtains the lowest-energy geometric structures and the electronic and magnetic properties of small CuNiN clusters by using all-electron density functional theory. The calculated results reveal that the Cu atom prefers to occupy the apical site when N ≤ 9 and for the clusters with N=10, the Cu atom starts to encapsulate in the cage. The CuNi7} and CuNi9 are magic clusters. The magnetism correlates closely with the symmetry of the clusters. For these clusters, the charge tends to transfer from the nickel atoms to the copper atoms. It finds that the doping of Cu atom decreases the stability of pure NiN clusters.

Studies of K-shell x-ray energy shifts induced by MeV/u heavy ions

Song Zhang-Yong, Yang Zhi-Hu, Shao Jian-Xiong, Cui Ying, Zhang Hong-Qiang, Ruan Fang-Fang, Du Juan, Gao Zhi-Min, Yu De-Yang, Chen Xi-Meng, Cai Xiao-Hong
Chin. Phys. B, 2009, 18 (4): 1443-1450 doi: 10.1088/1674-1056/18/4/026
Full Text: [PDF 197 KB] (Downloads:594)
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This paper reports that the K x-ray spectra of the thin target 47Ag, 48Cd, 49In and 50Sn were measured by an HPGe semi-conductor detector in collisions with 84.5~MeV 6C4+ ions. Our experiment revealed the Kα x-ray energy shifts were not obvious and the Kβ1 x-ray energy shifts were about 90~110~eV. The simple model of Burch \emph{et al} has been previously used to calculate the K x-ray energy shifts due to an additional vacancy in 2p orbit. The present work extends the model of Burch to calculate the x-ray energy shifts of multiple ionized atoms induced by heavy ions with kinetic energy of MeV/u. In addition to our experimental results, many other experimental results are compared with the calculated values by using the model.

Variation of photoabsorption cross section of atomic silver from isolated to condensed conditions

Ma Xiao-Guang, Gong Yu-Bing, Qu Zhao-Jun
Chin. Phys. B, 2009, 18 (4): 1451-1457 doi: 10.1088/1674-1056/18/4/027
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The influence of the local-field on the photoabsorption cross section of the atomic silver is studied in detail by using the Clausius--Mossotti (CM) model and the Onsager model separately. The variations of the photoabsorption cross section of atomic silver with number density and radius of the environmental interaction cavity are studied systematically by using more general expressions for the photoabsorption cross sections, proposed by Sun et al recently. It has proved to be reasonable to model the optical response properties of bulky material by coupling the property of isolated atom with the environmental effects in the present work.

Phase-dependent quantum interference between different pathways in bichromatic harmonic generation

Cai Jun, Wang Li-Ming, Qiao Hao-Xue
Chin. Phys. B, 2009, 18 (4): 1458-1462 doi: 10.1088/1674-1056/18/4/028
Full Text: [PDF 550 KB] (Downloads:600)
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This paper studies the harmonic generation of the hydrogen atom subjected to a collinear bichromatic laser field by numerically solving the time-dependent Schr?dinger equation using the split-operator pseudo-spectral method. By adding a frequency variation to the additional field, the contributions of different pathways to particular order harmonic generation can be isolated. The quantum interference pattern between harmonic pathways, which influences the harmonic intensity, is found to be either constructive or destructive with respect to different relative phase of the two field components. Detailed description of up to the 35th-order harmonics and the harmonic pathways for a wide range of field parameters is presented.

Ultrafast multiplex CARS investigation of vibrational characteristics in chloroform and PMMA

Wang Ying-Hui, Peng Ya-Jing, He Xing, Song Yun-Fei, Yang Yan-Qiang
Chin. Phys. B, 2009, 18 (4): 1463-1468 doi: 10.1088/1674-1056/18/4/029
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This paper demonstrates the femtosecond time-resolved coherent anti-Stokes Raman scattering by using folded BOXCARS geometry where an ultrashort broadband coherent white light continuum was used as Stokes pulse, and carries out the non-contact detection at long distance. The CARS signal is so easy to be detected that it can be seen even by nude eye. The C--H bonds of chloroform or PMMA were detected and the vibration modes belonging to the side chain and the main chain in PMMA were also compared. Their vibrational characteristics involved decay process and quantum beating were discussed. This modified CARS experimental technique could make up the deficiency of traditional CARS technique.

Tunable phase-stabilized infrared parametric laser source

Zhang Chun-Mei, Wang Jian-Liang, Wei Peng-Fei, Song Li-Wei, Li Chuang, Kim Cheol-Jung, Leng Yu-Xin
Chin. Phys. B, 2009, 18 (4): 1469-1472 doi: 10.1088/1674-1056/18/4/030
Full Text: [PDF 700 KB] (Downloads:702)
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This paper reports that the tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With an 800 nm pump source, the output idler pulses are tunable from 1.3 μm to 2.3 μm, and the maximum output energy of the idler pulses is higher than 1 mJ at 1.6 μm by using 6 mJ pump laser. A carrier-envelope phase fluctuation of ~ 0.15 rad (rms) for the idler pulses is measured for longer than one hour by using a home build f-to-2f interferometer.

Quantum-mechanical analysis of pulse reconstruction for a narrow bandwidth attosecond x-ray pulse

Ge Yu-Cheng
Chin. Phys. B, 2009, 18 (4): 1473-1478 doi: 10.1088/1674-1056/18/4/031
Full Text: [PDF 279 KB] (Downloads:528)
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The photoelectron energy spectra (PESs) excited by narrow bandwidth attosecond x-ray pulses in the presence of a few-cycle laser are quantum-mechanically calculated. Transfer equations are used to reconstruct the detailed temporal structure of an attosecond x-ray pulse directly from a measured PES. Theoretical analysis shows that the temporal uncertainties of the pulse reconstruction depend on the x-ray bandwidth. The procedure of pulse reconstruction is direct and simple without making any previous pulse assumption, data fitting analysis and time-resolved measurement of PESs. The temporal measurement range is half of a laser optical cycle.

Time-dependent theoretical approach to the influence of laser fields on the resonance enhanced multi-photon ionization of SH radical

Yue Da-Guang, Zheng Xiao-Yun, Liu Hao, Wang Chun-Xing, Meng Qing-Tian
Chin. Phys. B, 2009, 18 (4): 1479-1485 doi: 10.1088/1674-1056/18/4/032
Full Text: [PDF 238 KB] (Downloads:443)
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This paper reports that the (2+1) resonance enhanced multi-photon ionization spectra of SH radical in external fields are simulated using the split-operator scheme of time-dependent wave-packet method. Two ionic states, i.e.~a1Δ and b1+, are involved in the simulation. It gives the simulated photoelectron spectra, the population in each electronic state, as well as the projection of the wave-packet in each electronic state on different vibrational states. These results show that the so-called four-state model can represent the experimental results well.

Calculation of the elastic collision properties of Na and Li atoms at ultracold temperature

Zhang Ji-Cai, Zhang Ying, Du Bing-Ge, Sun Jin-Feng
Chin. Phys. B, 2009, 18 (4): 1486-1490 doi: 10.1088/1674-1056/18/4/033
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This paper firstly reports a theoretical study of elastic scattering properties in a mixture of 23Na and 7Li atoms at cold and ultracold temperatures in detail. Based on the new constructed accurate singlet X1g+ and the triplet a3u+ states interatomic potentials for 23Na7Li mixture, it calculates the scattering lengths and the effective ranges by three computational methods, and obtains good agreements. Using the mass scaling method, it also calculates 23Na6Li scattering lengths and s-wave and total elastic cross sections, whose rich resonance structures were found and interpreted in terms of quasibound diatomic levels trapped behind a centrifugal barrier.

An ab initio study of niobium (n = 2--11) clusters: structure, stability and magnetism

Ren Feng-Zhu, Wang uan-Xu, Zhang Guang-Biao, Wei Shu-Ke, Luo You-Hua
Chin. Phys. B, 2009, 18 (4): 1491-1497 doi: 10.1088/1674-1056/18/4/034
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The ground-state configurations of the Nbn (n= 2--11) clusters are studied through the first-principles calculations. It is found that niobium clusters (n= 2--11) tend to form compact structures with low symmetry. The clusters with 4, 8 and 10 atoms are found to be magic and have relatively large highest occupied--lowest unoccupied molecular orbital (HOMO-LUMO) gaps. The Nbn clusters possess low magnetic moments, which exhibit an odd-even oscillational character. The analyses of calculated electronic density and population of the lowest-energy niobium clusters for n= 2, 3, 5, 7, 9, 11 show that the total magnetic moments of Nbn originate mainly from a few Nb atoms with longer spacings between them in most cases, while they are located on two Nb atoms for n= 2, 3, 5. The total magnetic moments come mainly from the 4d local moments but with the exception of the Nb5 cluster.

Analysis of femtosecond laser ionization/dissociation of olyatomic molecule C6H10O from one-colour pump—probe measurement

Hu Fei-Fei, Zhou Sheng-Peng, Hu Zhan, Jin Ming-Xing, Zhang Dong-Dong, Wu Di, Cheng Xi-Hui, Jiang Dian-Wu, Ding Da-Jun
Chin. Phys. B, 2009, 18 (4): 1498-1502 doi: 10.1088/1674-1056/18/4/035
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This paper reports that a one-colour fs pump--probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone (C6H10O) in intense laser field. Two of the fragments from cyclohexanone, C2H3+ and C3}H3+, are studied under 800 nm laser pump--probe and the results obtained show similar time evolutions. It proposes a feasible model for analysing the experimental observations of the one-colour {fs} pump--probe measurement. The results demonstrate that as an intermediate product, the excited molecular parent ions play a very important role in photionization/photodissociation processes in intense laser field.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Monte Carlo simulations of biaxial structure in thin hybrid nematic film based upon spatially anisotropic pair potential

Zhang Zhi-Dong, Chang Chun-Rui, Ma Dong-Lai
Chin. Phys. B, 2009, 18 (4): 1560-1563 doi: 10.1088/1674-1056/18/4/044
Full Text: [PDF 142 KB] (Downloads:436)
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Hybrid nematic films have been studied by Monte Carlo simulations using a lattice spin model, in which the pair potential is spatially anisotropic and dependent on elastic constants of liquid crystals. We confirm in the thin hybrid nematic film the existence of a biaxially nonbent structure and the structure transition from the biaxial to the bent-director structure, which is similar to the result obtained using the Lebwohl--Lasher model. However, the step-like director's profile, characteristic for the biaxial structure, is spatially asymmetric in the film because the pair potential leads to K1 ≠ K3. We estimate the upper cell thickness to be 69 spin layers, in which the biaxial structure can be found.

Shielding effect and emission criterion of a screw dislocation near an interfacial blunt crack

Song Hao-Peng, Fang Qi-Hong, Liu You-Wen
Chin. Phys. B, 2009, 18 (4): 1564-1569 doi: 10.1088/1674-1056/18/4/045
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Shielding effect and emission criterion of a screw dislocation near an interfacial blunt crack are dealt with in this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentials and stress fields due to a screw dislocation located near the interfacial blunt crack. The stress intensity factor on the crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of the orientation of the dislocation and the morphology of the blunt crack as well as the material elastic dissimilarity on the shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations can reduce the stress intensity factor of the interfacial blunt crack tip (shielding effect). The shielding effect increases with the increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuth angle. The critical loads at infinity for dislocation emission increases with the increase of emission angle and curvature radius of blunt crack tip, and the most probable angle for screw dislocation emission is zero. The present solutions contain previous results as special cases.

Ultra-thin a-SiNx protective overcoats for hard disks and read/write heads

Ding Wan-Yu, Xu Jun, Lu Wen-Qi, Deng Xin-Lu, Dong Chuang
Chin. Phys. B, 2009, 18 (4): 1570-1573 doi: 10.1088/1674-1056/18/4/046
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This paper reports that amorphous silicon nitride (a-SiNx) overcoats were deposited at room temperature by microwave ECR plasma enhanced unbalanced magnetron sputtering. The 2 nm a-SiNx overcoat has better anti-corrosion properties than that of reference a-CNx overcoats (2--4.5 nm). The superior anti-corrosion performance is attributed to its stoichiometric bond structure, where 94.8% Si atoms form Si--N asymmetric stretching vibration bonds. The N/Si ratio is 1.33 as in the stoichiometry of Si3N4 and corresponds to the highest hardness of 25.0 GPa. The surface is atomically smooth with RMS <0.2 nm. The ultra-thin a-SiNx overcoats are promising for hard disks and read/write heads protective coatings.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Ab initio study on phase transition and magnetism of BiFeO3 under pressure

Feng Hong-Jian, Liu Fa-Min
Chin. Phys. B, 2009, 18 (4): 1574-1577 doi: 10.1088/1674-1056/18/4/047
Full Text: [PDF 140 KB] (Downloads:835)
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In this paper the first-principles calculations within local spin density approximation (LSDA)+U show that BiFeO3 experiences a mixed phase state with P4mm structure being the intermediate phase before the pressure of phase transition is reached. The critical pressure for the insulator--metal transition (IMT) is found to be about 50 GPa. A pressure induced crossover of high-spin states and low-spin states is observed close to the IMT pressure in R3c structure. The LSDA+U calculations account well for the mechanism of the IMT and crossover of spin states predicted in recent experiment (Ref.[1]).

Ground state energy of excitons in quantum dot treated variationally via Hylleraas-like wavefunction

Chin. Phys. B, 2009, 18 (4): 1578-1585 doi: 10.1088/1674-1056/18/4/048
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In this work, the effects of quantum confinement on the ground state energy of a correlated electron--hole pair in a spherical and in a disc-like quantum dot have been investigated as a function of quantum dot size. Under parabolic confinement potential and within effective mass approximation Ritz's variational method is applied to Hylleraas-like trial wavefunction. An efficient method for reducing the main effort of the calculation of terms like rehkexp{(-λ reh)} is introduced. The main contribution of the present work is the introduction of integral transforms which provide the calculation of expectation value of energy and the related matrix elements to be done analytically over single-particle coordinates instead of Hylleraas coordinates.

Investigations of the electron paramagnetic resonance parameters and the tetragonal local structure for (VCl6)4- coordination complex in MCl:V2+ (M=Na, K, Rb) systems

Qi Lin, Kuang Xiao-Yu, Chai Rui-Peng, Duan Mei-Ling, Zhang Cai-Xia
Chin. Phys. B, 2009, 18 (4): 1586-1593 doi: 10.1088/1674-1056/18/4/049
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By simulating the electron paramagnetic resonance (EPR) and optical spectra on the basis of the 120× 120 complete energy matrix, this paper determines the local lattice structure parameters R1 and R2 for MCl:V2+ (M=Na, K, Rb) systems at 77 K, 195 K and RT (room temperature 295 K or 302 K), respectively. The theoretical results indicate that there exists a compressed distortion in MCl:V2+ systems. Meanwhile, it finds that the structure parameters R1 , R2 and |Δ R |(= R1 - R2 ) increase with the rising temperature. Subsequently, from the analysis it concludes that the relation of EPR parameter D vs. Δ R is approximately linear. Finally, the effects of orbital reduction factor k on the g factors for the three systems have been discussed.

The research on suspended ZnO nanowire field-effect transistor

Li Ming, Zhang Hai-Ying, Guo Chang-Xin, Xu Jing-Bo, Fu Xiao-Jun
Chin. Phys. B, 2009, 18 (4): 1594-1597 doi: 10.1088/1674-1056/18/4/050
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This paper reports that a novel type of suspended ZnO nanowire field-effect transistors (FETs) were successfully fabricated using a photolithography process, and their electrical properties were characterized by I--V measurements. Single-crystalline ZnO nanowires were synthesized by a hydrothermal method, they were used as a suspended ZnO nanowire channel of back-gate field-effect transistors (FET). The fabricated suspended nanowire FETs showed a p-channel depletion mode, exhibited high on--off current ratio of ~105. When VDS=2.5 V, the peak transconductances of the suspended FETs were 0.396 μS, the oxide capacitance was found to be 1.547 fF, the pinch-off voltage VTH was about 0.6 V, the electron mobility was on average 50.17 cm2/Vs. The resistivity of the ZnO nanowire channel was estimated to be 0.96× 102Ω cm at VGS = 0 V. These characteristics revealed that the suspended nanowire FET fabricated by the photolithography process had excellent performance. Better contacts between the ZnO nanowire and metal electrodes could be improved through annealing and metal deposition using a focused ion beam.

Frequency selective surface structure optimized by genetic algorithm

Lu Jun, Wang Jian-Bo, Sun Guan-Cheng
Chin. Phys. B, 2009, 18 (4): 1598-1600 doi: 10.1088/1674-1056/18/4/051
Full Text: [PDF 389 KB] (Downloads:733)
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Frequency selective surface (FSS) is a two-dimensional periodic structure which has prominent characteristics of bandpass or bandblock when interacting with electromagnetic waves. In this paper, the thickness, the dielectric constant, the element graph and the arrangement periodicity of an FSS medium are investigated by Genetic Algorithm (GA) when an electromagnetic wave is incident on the FSS at a wide angle, and an optimized FSS structure and transmission characteristics are obtained. The results show that the optimized structure has better stability in relation to incident angle of electromagnetic wave and preserves the stability of centre frequency even at an incident angle as large as 80°, thereby laying the foundation for the application of FSS to curved surfaces at wide angles.

High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors

Gu Wen-Ping, Duan Huan-Tao, Ni Jin-Yu, Hao Yue, Zhang Jin-Cheng, Feng Qian, Ma Xiao-Hua
Chin. Phys. B, 2009, 18 (4): 1601-1608 doi: 10.1088/1674-1056/18/4/052
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AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current IDsat, maximal transconductance gm, and the positive shift of threshold voltage VTH at high drain-source voltage VDS. The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEG depletion a little during the high-electric-field stress. After the hot carrier stress with VDS=20 V and VGS=0 V applied to the device for 104 sec, the SiN passivation decreases the stress-induced degradation of IDsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of IDsat, which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted.

Localized states of flattened quantum elliptic rings and their optical properties

Situ Shu-Ping
Chin. Phys. B, 2009, 18 (4): 1609-1613 doi: 10.1088/1674-1056/18/4/053
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A flattened elliptic ring containing an electron is studied. The emphasis is placed on clarifying the effect of the flattening. The localized states are classified into four types according to their inherent nodes. When the ring becomes more flattened, the total probability of dipole absorption of each state is found to be reduced. Furthermore, each spectral line of absorption is found to shift towards red and may split into a few lines, and these lines as a whole become more diffusive.

The leakage current mechanisms in the Schottky diode with a thin Al layer insertion between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact

Liu Fang, Wang Tao, Shen Bo, Huang Sen, Lin Fang, Ma Nan, Xu Fu-Jun, Wang Peng, Yao Jian-Quan
Chin. Phys. B, 2009, 18 (4): 1614-1617 doi: 10.1088/1674-1056/18/4/054
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This paper investigates the behaviour of the reverse-bias leakage current of the Schottky diode with a thin Al inserting layer inserted between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25--350 °C. It compares with the Schottky diode without Aluminium inserting layer. The experimental results show that in the Schottky diode with Al layer the minimum point of I--V curve drifts to the minus voltage, and with the increase of temperature increasing, the minimum point of I--V curve returns the 0 point. The temperature dependence of gate-leakage currents in the novelty diode and the traditional diode are studied. The results show that the Al inserting layer introduces interface states between metal and Al0.245Ga0.755N. Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current. The reliability of the diode at the high temperature is improved by inserting a thin Al layer.

Thermal annealing behaviour of Al/Ni/Au multilayer on n-GaN Schottky contacts

Liu Fang, Wang Tao, Shen Bo, Huang Sen, Lin Fang, Ma Nan, Xu Fu-Jun, Wang Peng, Yao Jian-Quan
Chin. Phys. B, 2009, 18 (4): 1618-1621 doi: 10.1088/1674-1056/18/4/055
Full Text: [PDF 334 KB] (Downloads:691)
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Recently GaN-based high electron mobility transistors (HEMTs) have revealed the superior properties of a high breakdown field and high electron saturation velocity. Reduction of the gate leakage current is one of the key issues to be solved for their further improvement. This paper reports that an Al layer as thin as 3 nm was inserted between the conventional Ni/Au Schottky contact and n-GaN epilayers, and the Schottky behaviour of Al/Ni/Au contact was investigated under various annealing conditions by current--voltage (I--V) measurements. A non-linear fitting method was used to extract the contact parameters from the I--V characteristic curves. Experimental results indicate that reduction of the gate leakage current by as much as four orders of magnitude was successfully recorded by thermal annealing. And high quality Schottky contact with a barrier height of 0.875 eV and the lowest reverse-bias leakage current, respectively, can be obtained under 12 min annealing at 450°C in N2 ambience.

Conductance switching mechanism of Rose Bengal organic thin films in ambient conditions

Cai Li, Guo Hai-Ming, Zhu Xi, Du Shi-Xuan, Shi Dong-Xia, Gao Hong-Jun
Chin. Phys. B, 2009, 18 (4): 1622-1626 doi: 10.1088/1674-1056/18/4/056
Full Text: [PDF 460 KB] (Downloads:434)
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The molecular thin films of Rose Bengal (RB) embedded in polymethyl methacrylate matrix are fabricated by using the spin-coating technique. The macroscopic current--voltage (I--V) characterization of the film shows that the RB molecule has two conductance switching states with a high ON/OFF ratio in ambient conditions. The infrared spectra indicate that intermolecular hydrogen bonds can form in the RB thin films after their hydrolysis in air. With the first-principles calculations, we demonstrate that the hydrogen bonds will be destroyed in concomitance with the conformational change when the RB molecule switches to its high-conductance state after applying a voltage.

Numerical model of multilayer organic light-emitting devices

Hu Yue, Rao Hai-Bo
Chin. Phys. B, 2009, 18 (4): 1627-1630 doi: 10.1088/1674-1056/18/4/057
Full Text: [PDF 277 KB] (Downloads:1853)
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A numerical model of multilayer organic light-emitting devices is presented in this article. This model is based on the drift-diffusion equations which include charge injection, transport, space charge effects, trapping, heterojunction interface and recombination process. The device structure in the simulation is ITO/CuPc (20 nm)/NPD (40 nm)/Alq3 (60 nm)/LiF/Al. There are two heterojunctions which should be dealt with in the simulation. The I--V characteristics, carrier distribution and recombination rate of a device are calculated. The simulation results and measured data are in good agreement.

Study on reaction mechanism of YBa2Cu3O7-x film by TFA-MOD process

Ding Fa-Zhu, Lü Xu-Dong, Gu Hong-Wei, Li Tao, Cao Jiang-Li
Chin. Phys. B, 2009, 18 (4): 1631-1636 doi: 10.1088/1674-1056/18/4/058
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This paper systematically investigates the intermediate phases of YBa2Cu3O7-x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725 °C. The influence of water vapour pressure on the YBa2Cu3O7-x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40--140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture.

Raman scattering studies on manganese ion-implanted GaN

Xu Da-Qing, Zhang Yi-Men, Zhang Yu-Ming, Li Pei-Xian, Wang Chao
Chin. Phys. B, 2009, 18 (4): 1637-1642 doi: 10.1088/1674-1056/18/4/059
Full Text: [PDF 198 KB] (Downloads:552)
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This paper reports that the Raman spectra have been recorded on the metal-organic chemical vapour deposition epitaxially grown GaN before and after the Mn ions implanted. Several Raman defect modes have emerged from the implanted samples. The structures around 182 cm-1 modes are attributed to the disorder-activated Raman scattering, whereas the 361 cm-1 and 660 cm-1 peaks are assigned to nitrogen vacancy-related defect scattering. One additional peak at 280 cm-1 is attributed to the vibrational mode of gallium vacancy-related defects and/or to disorder activated Raman scattering. A Raman-scattering study of lattice recovery is also presented by rapid thermal annealing at different temperatures between 700 °C and 1050 °C on Mn implanted GaN epilayers. The behaviour of peak-shape change and full width at half maximum (FWHM) of the A1(LO) (733 cm-1) and EH2 (566 cm-1) Raman modes are explained on the basis of implantation-induced lattice damage in GaN epilayers.

Investigation of fabrication and hetero-epitaxy relationship of CoCrPt thin films grown on CrW underlayer

Li Song-Tian, Liu Xi, Shi Wen-Kui, Cao Jiang-Wei, Wei Fu-Lin, Wei Dan
Chin. Phys. B, 2009, 18 (4): 1643-1646 doi: 10.1088/1674-1056/18/4/060
Full Text: [PDF 140 KB] (Downloads:473)
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This paper reports that longitudinally oriented CoCrPt thin films with Cr85W15 underlayer and CoCr intermediate layer for use of giant magnetoresistance heads were fabricated by magnetron sputtering. Without CoCr intermediate layer, CoCrPt layer deposited directly on Cr85W15 underlayer which has a dominant (200) texture exhibits unexpected (10\bar {1}1) texture. After introducing CoCr intermediate layer, the CoCrPt layer shifts into (11\bar {2}0) texture. This article studies the crystallographic hetero-epitaxy relationship between magnetic layer and underlayer in order to understand the appearance of CoCrPt (10\bar {1}1) texture on (200) textured Cr underlayer and the influence of CoCr intermediate layer on the inducement of CoCrPt (11\bar {2}0) texture. The CoCr intermediate layer plays a crucial role in controlling the microstructure and consequently the magnetic properties of the overlying magnetic layer.

First principles study on the magnetocrystalline anisotropy of Fe--Ga magnetostrictive alloys

Zheng Lei, Jiang Cheng-Bao, Shang Jia-Xiang, Xu Hui-Bin
Chin. Phys. B, 2009, 18 (4): 1647-1652 doi: 10.1088/1674-1056/18/4/061
Full Text: [PDF 306 KB] (Downloads:824)
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This paper investigates the electronic structure and magnetocrystalline anisotropy of Fe--Ga magnetostrictive material by means of the full potential-linearized augmented plane-wave method within the generalized gradient approximation. The 3d-orbit splitting of Fe atoms in D03, B2-like and L12 crystalline structures of Fe--Ga is calculated with consideration of the crystal field as well as the spin--orbit coupling effect. Because of the frozen orbital angular momenta of the 3d-orbit for Fe atoms in Fe--Ga magnetostrictive alloys and the spin--orbit coupling, the distribution of the electron cloud is not isotropic, which leads to the anisotropy of exchange interaction between the different atoms. A method on estimating the magnetocrystalline anisotropy of Fe--Ga alloys by means of calculating orbit-projected density of states for Fe atoms is performed. The anisotropic distribution of the electron cloud of Fe atoms in these three crystalline structures of Fe--Ga is studied based on the above method showing the highest magnetic anisotropy for B2-like structure. This qualitative method comes closer to physical reality with a vivid physical view, which can evaluate the anisotropy of electron cloud for 3d transition atoms directly. The calculated results are in good agreement with both the previous theoretical computation and the tested value on the magnetic anisotropy constant, which confirms that the electron cloud anisotropy of Fe atoms could well characterize the magnetocrystalline anisotropy of Fe--Ga magnetostrictive material.

Microwave left-handed composite material made of slim ferrite rods and metallic wires

Xu Fang, Bai Yang, Qiao Li-Jie, Zhao Hong-Jie, Zhou Ji
Chin. Phys. B, 2009, 18 (4): 1653-1657 doi: 10.1088/1674-1056/18/4/062
Full Text: [PDF 888 KB] (Downloads:626)
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This paper reports on experimental study of the microwave properties of a composite material consisting of ferrite and copper wires. It finds that the slim ferrite rods can modify the magnetic field distribution through their anisotropy, so that the ferrite's negative influence on the copper wires' plasma will be reduced. Left-handed properties are observed even in the specimen with close stuck ferrite rods and copper wires.

Combined effect of the transition layer and interfacial coupling on the properties of ferroelectric bilayer film

Sun Pu-Nan, Cui Lian, Lü Tian-Quan
Chin. Phys. B, 2009, 18 (4): 1658-664 doi: 10.1088/1674-1056/18/4/063
Full Text: [PDF 989 KB] (Downloads:544)
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Within the framework of modified Ginzburg--Landau--Devonshire phenomenological theory, a ferroelectric bilayer film with a transition layer within each constituent film and an interfacial coupling between two materials has been studied. Properties including the Curie temperature and the spontaneous polarization of a bilayer film composed of two equally thick ferroelectric constituent films are discussed. The results show that the combined effect of the transition layer and the interfacial coupling plays an important role in explaining the interesting behaviour of ferroelectric multilayer structures consisting of two ferroelectric materials.

Potts-Ising model for simulation of polarization switching in polycrystalline ferroelectrics

Zhang Yan-Fei, Wang Chun-Lei, Zhao Ming-Lei, Li Ji-Chao, Zhang Rui-Zhi
Chin. Phys. B, 2009, 18 (4): 1665-1668 doi: 10.1088/1674-1056/18/4/064
Full Text: [PDF 435 KB] (Downloads:545)
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This paper proposes a scheme based on the Potts and Ising models for simulating polarization switching of polycrystalline ferroelectrics using the Monte Carlo method. The polycrystalline texture with different average grain size is produced from the Potts model. Then Ising model is implemented in the polycrystalline texture to produce the domain pattern and hysteresis loop. The domain patterns and hysteresis loops have been obtained for polycrystalline texture with different average grain size. From the results of domain pattern evolution process under an applied electric field using this scheme, an extended domain, which covers more than one grain with polarization aligned roughly in the same direction, has been observed during the polarization reversal. This scheme can well reproduce the basic properties of polycrystalline ferroelectrics and is a valuable tool for exploring the physical properties of polycrystalline ferroelectrics.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Interference phase of mass neutrino in CM space--time

Chen Xia, Wang Yong-Jiu
Chin. Phys. B, 2009, 18 (4): 1707-1710 doi: 10.1088/1674-1056/18/4/071
Full Text: [PDF 142 KB] (Downloads:430)
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In the gravitational field of central mass with electric and magnetic charges and magnetic moment (CM space-time), this paper calculates the interference phase of mass neutrino along geodesic in the radial direction, and discusses the contribution of the electric and magnetic charges and magnetic moment of the central mass to the phase.

Observational constraints on the accelerating universe in the framework of a 5D bounce cosmological model

Lü Jian-Bo, Xu Li-Xin, Liu Mo-Lin, Gui Yuan-Xing
Chin. Phys. B, 2009, 18 (4): 1711-1720 doi: 10.1088/1674-1056/18/4/072
Full Text: [PDF 475 KB] (Downloads:462)
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In the framework of a five-dimensional (5D) bounce cosmological model, a useful function f(z) is obtained by giving a concrete expression of deceleration parameter q(z)=q1+{q2}/{1+ln (1+ z)}. Then using the obtained Hubble parameter H(z) according to the function f(z), we constrain the accelerating universe from recent cosmic observations: the 192 ESSENCE SNe Ia and the 9 observational H(z) data. The best fitting values of transition redshift zT and current deceleration parameter q0 are given as zT= 0.65-0.120.25 and q0 = - 0.76-0.15+0.15 (1σ). Furthermore, in the 5D bounce model it can be seen that the evolution of equation of state (EOS) for dark energy wde can cross over -1 at about z=0.23 and the current value w0de= - 1.15<- 1. On the other hand, by giving a concrete expression of model-independent EOS of dark energy wde, in the 5D bounce model we obtain the best fitting values zT= 0.660.08+0.11 and q0 = - 0.690.10+0.10 (1σ) from the recently observed data: the 192 ESSENCE SNe Ia, the observational H(z) data, the 3-year Wilkinson Microwave Anisotropy Probe (WMAP), the Sloan Digital Sky Survey (SDSS) baryon acoustic peak and the x-ray gas mass fraction in clusters.
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