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Volume 28 Issue 9
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GENERAL
SubHopf/Fold-Cycle Bursting in the Hindmarsh–Rose Neuronal Model with Periodic Stimulation
JI Ying**, BI Qin-Sheng
Chin. Phys. Lett. 2011, 28 (9): 090201 .   DOI: 10.1088/0256-307X/28/9/090201
Abstract   PDF(pc) (762KB) ( 642 )
The dynamics of Hindmarsh–Rose neuronal systems with periodic external stimulation is investigated. The bursting phenomenon can be observed in numerical simulations when an order gap exists between the stimulation frequency and the natural frequency of the system. By treating the external stimulation as a control parameter that modulates the dynamics of the system, the bifurcation mechanism for the periodic bursting solution is discussed with the slow-fast analysis method.
Coupled Nonlinear Schrödinger Equations and the Miura Transformation
LOU Yan, ZHU Jun-Yi**
Chin. Phys. Lett. 2011, 28 (9): 090202 .   DOI: 10.1088/0256-307X/28/9/090202
Abstract   PDF(pc) (402KB) ( 460 )
A wide class of coupled nonlinear Schrödinger (NLS) equations are derived by virtue of the dressing method, and the associated parametric solutions are discussed. As an illustration, the explicit solution of the coupled NLS-type equation associated with σ1 is given. The Miura transformation for a AKNS-type hierarchy is established, from which a modified coupled NLS-type equation is shown to be equivalent to the Heisenberg spin equation.
Theta-function Solutions to the (2+1)-Dimensional Breaking Soliton Equation
WANG Jun-Min**, YANG Xiao
Chin. Phys. Lett. 2011, 28 (9): 090203 .   DOI: 10.1088/0256-307X/28/9/090203
Abstract   PDF(pc) (795KB) ( 517 )
A new periodic wave solution in terms of theta functions is presented for a kind of elliptic equation. Based on the results, with the help of Mathematica and the improved generalized F-expansion method, some periodic wave solutions in terms of theta functions are obtained for the (2+1)-dimensional breaking soliton equation. In addition, x-direction periodic wave solutions are derived, their properties and profiles are displayed in 3D figures. To our knowledge, these solutions are reported for the first time.
A Note on the Invariance Properties and Conservation Laws of the Kadomstev–Petviashvili Equation with Power Law Nonlinearity
A H Bokhari, F D Zaman, K Fakhar, *, A H Kara
Chin. Phys. Lett. 2011, 28 (9): 090204 .   DOI: 10.1088/0256-307X/28/9/090204
Abstract   PDF(pc) (331KB) ( 354 )
First, we studied the invariance properties of the Kadomstev–Petviashvili equation with power law nonlinearity. Then, we determined the complete class of conservation laws and stated the corresponding conserved densities which are useful in finding the conserved quantities of the equation. The point symmetry generators were also used to reduce the equation to an exact solution and to verify the invariance properties of the conserved flows.
Quantum Correlation Generation in a Damped Cavity
LI Jun-Gang, **, ZOU Jian, **, XU Bao-Ming, SHAO Bin,
Chin. Phys. Lett. 2011, 28 (9): 090301 .   DOI: 10.1088/0256-307X/28/9/090301
Abstract   PDF(pc) (739KB) ( 651 )
Dynamic evolutions of the quantum discord and entanglement between two charge qubits located inside a damped cavity are demonstrated analytically. It is found that with cavity dissipation, the dynamics of the quantum discord between two qubits is sensitive to the degree of mixing of the initial qubits' state. This is different from steady entanglement, which is independent of the degree of mixing of the initial state of the qubits.
Quantum Information Transfer in Circuit QED with Landau–Zener Tunneling
LI Jun-Wang, WU Chun-Wang, DAI Hong-Yi**
Chin. Phys. Lett. 2011, 28 (9): 090302 .   DOI: 10.1088/0256-307X/28/9/090302
Abstract   PDF(pc) (478KB) ( 438 )
We propose a scheme to implement quantum information transfer between Cooper-pair boxes (CPBs) in a circuit quantum electrodynamic (QED) system with Landau–Zener tunneling. The system consists of two CPB qubits and a one-dimensional transmission line resonator (TLR). By analytically solving the eigenequation and numerically calculating the transition probability, the results show the quantum state transfer from one qubit to another via a fast adiabatic passage. The coupling mechanism is robust against decoherence effects.
Evolution of the Interference of Bose Condensates Released from a Double-Well Potential
ZHU Bi-Hui, , LIU Shu-Juan, XIONG Hong-Wei, **
Chin. Phys. Lett. 2011, 28 (9): 090303 .   DOI: 10.1088/0256-307X/28/9/090303
Abstract   PDF(pc) (498KB) ( 398 )
The interference pattern of two Bose–Einstein condensates released from a double-well potential for different holding times is theoretically investigated using a decoupled two-mode Bose–Hubbard model. For two coherently separated condensates, the interference displays a periodic behavior, which is closely related to the atomic interaction. A remarkable parity effect is found in the interference patterns. For certain holding times, the even/odd total number of atoms would result in different interference fringes. The influences of different initial conditions on the evolution of interference and the observation of parity effects are discussed.
Generation of Enhanced Three-Mode Continuously Variable Entanglement
YU You-Bin**, WANG Huai-Jun, FENG Jin-Xia
Chin. Phys. Lett. 2011, 28 (9): 090304 .   DOI: 10.1088/0256-307X/28/9/090304
Abstract   PDF(pc) (593KB) ( 350 )
The generation of enhanced three-mode continuously variable (CV) entanglement via difference-frequency amplification in an optical cavity above the threshold is investigated. The quantum entanglement characteristics among the pump, signal, and idler beams are demonstrated by applying a sufficient inseparability criterion for CV entanglement proposed by van Loock and Furusawa. Bright three-mode CV entanglement with different frequencies can be generated in this simple system when the optical cavity operates above its threshold, and the best three-mode CV entanglement can be obtained when the pump threshold parameter is modulated at about σ=1.3.
Experimental Realization of Braunstein's Weight-Decision Algorithm
HOU Shi-Yao, CUI Jing-Xin, LI Jun-Lin**
Chin. Phys. Lett. 2011, 28 (9): 090305 .   DOI: 10.1088/0256-307X/28/9/090305
Abstract   PDF(pc) (437KB) ( 343 )
Braunstein proposed an algorithm to distinguish the Boolean functions of two different weights. Here we implement the algorithm in a two-qubit nuclear magnetic resonance quantum information processor. The experiment shows that the algorithm could distinguish the Boolean functions of two different weights efficiently.
Bianchi Type-I String Cosmological Model with Bulk Viscosity and Time-Dependent Λ term
R. K. Tiwari*, S. Sharma**
Chin. Phys. Lett. 2011, 28 (9): 090401 .   DOI: 10.1088/0256-307X/28/9/090401
Abstract   PDF(pc) (406KB) ( 454 )
Einstein field equations with the cosmological constant is considered in the presence of bulk viscosity in a Bianchi type-I universe. Solutions of the field equations are obtained by assuming the following conditions: the bulk viscosity is proportional to the expansion scalar ξ∝θ; the expansion scalar is proportional to shear scalar θ∝σ; and Λ is proportional to the Hubble parameter Λ∝H. The corresponding interpretations of the cosmological solutions are also discussed.
Phantom Accretion onto the Schwarzschild de-Sitter Black Hole
M Sharif**, G Abbas
Chin. Phys. Lett. 2011, 28 (9): 090402 .   DOI: 10.1088/0256-307X/28/9/090402
Abstract   PDF(pc) (429KB) ( 276 )
We deal with phantom energy accretion onto the Schwarzschild de-Sitter black hole. The energy flux conservation, relativistic Bernoulli equation and mass flux conservation equation are formulated to discuss the phantom accretion. We discuss the conditions for critical accretion. It is found that the mass of the black hole decreases due to phantom accretion. There exist two critical points which lie in the exterior of horizons (black hole and cosmological horizons). The results for the phantom energy accretion onto the Schwarzschild black hole can be recovered by taking Λ→0.
Theoretical Analysis of a Modified Continuum Model
GE Hong-Xia, WU Shu-Zhen, CHENG Rong-Jun, LO Siu-ming**
Chin. Phys. Lett. 2011, 28 (9): 090501 .   DOI: 10.1088/0256-307X/28/9/090501
Abstract   PDF(pc) (443KB) ( 526 )
Based on the optimal velocity (OV) model, a new car-following model for traffic flow with the consideration of the driver's forecast effect (DFE) was proposed by Tang et al., which can be used to describe some complex traffic phenomena better. Using an asymptotic approximation between the headway and density, we obtain a new macro continuum version of the car-following model with the DFE. The linear stability theory is applied to derive the neutral stability condition. The Korteweg–de Vries equation near the neutral stability line is given by nonlinear analysis and the corresponding solution for the traffic density wave is derived.
Assessment of Time Series Complexity Using Improved Approximate Entropy
KONG De-Ren, XIE Hong-Bo**
Chin. Phys. Lett. 2011, 28 (9): 090502 .   DOI: 10.1088/0256-307X/28/9/090502
Abstract   PDF(pc) (843KB) ( 671 )
Approximate entropy (ApEn), a measure quantifying complexity and/or regularity, is believed to be an effective method of analyzing diverse settings. However, the similarity definition of vectors based on Heaviside function may cause some problems in the validity and accuracy of ApEn. To overcome the problems, an improved approximate entropy (iApEn) based on the sigmoid function is proposed. The performance of iApEn is tested on the independent identically distributed (IID) Gaussian noise, the MIX stochastic model, the Rossler map, the logistic map, and the high-dimensional Mackey–Glass oscillator. The results show that iApEn is superior to ApEn in several aspects, including better relative consistency, freedom of parameter selection, robust to noise, and more independence on record length when characterizing time series with different complexities.
Generalized Synchronization of Diverse Structure Chaotic Systems
KADIR Abdurahman, WANG Xing-Yuan**, ZHAO Yu-Zhang
Chin. Phys. Lett. 2011, 28 (9): 090503 .   DOI: 10.1088/0256-307X/28/9/090503
Abstract   PDF(pc) (621KB) ( 356 )
Generalized synchronization between two diverse structures of chaotic systems possesses significance in the research of synchronization. We propose an approach based on the Lyapunov stability theory to study it. This method can be used widely. Numerical examples are given to demonstrate the effectiveness of this approach.
Vibrational Resonance in an Overdamped System with a Sextic Double-Well Potential
WANG Can-Jun**
Chin. Phys. Lett. 2011, 28 (9): 090504 .   DOI: 10.1088/0256-307X/28/9/090504
Abstract   PDF(pc) (593KB) ( 505 )
The phenomenon of vibrational resonance (VR) in an overdamped system with a sextic double-well potential under the excitation of two different periodic signals is investigated. The approximate analytical expression of the resonance amplitude Q at the low−frequency ω is obtained. The VR is observed, and the values of B (the amplitude of the high−frequency signal) and Ω (the frequency of the high−frequency signal) at which VR occurs are determined. Moreover, the relationship between B and Ω is revealed. The theoretical predictions are found to be in good agreement with the numerical results.
Stochastic Multi-Resonance in a Linear System Driven by Multiplicative Polynomial Dichotomous Noise
ZHANG Lu, ZHONG Su-Chuan, PENG Hao, LUO Mao-Kang**
Chin. Phys. Lett. 2011, 28 (9): 090505 .   DOI: 10.1088/0256-307X/28/9/090505
Abstract   PDF(pc) (478KB) ( 386 )
We investigate stochastic resonance in a linear system subjected to multiplicative noise that is a polynomial function of colored noise. Using the stochastic averaging method, the analytical expression of the output signal-to-noise ratio (SNR) is derived. Theoretical analysis and numerical results show that the output SNR is a non-monotonic function of both the noise intensity and the correlation rate. Moreover, the phenomoenon of stochastic multi-resonance (SMR) is found, which is not observed in conventional linear systems driven by multiplicative noise with only a linear term.
Velocity Distributions in Inelastic Granular Gases with Continuous Size Distributions
LI Rui**, ZHANG Duan-Ming, LI Zhi-Hao
Chin. Phys. Lett. 2011, 28 (9): 090506 .   DOI: 10.1088/0256-307X/28/9/090506
Abstract   PDF(pc) (935KB) ( 323 )
We study by numerical simulation the property of velocity distributions of granular gases with a power-law size distribution, driven by uniform heating and boundary heating. It is found that the form of velocity distribution is primarily controlled by the restitution coefficient η and q, the ratio between the average number of heatings and the average number of collisions in the system. Furthermore, we show that uniform and boundary heating can be understood as different limits of q, with q≫1 and q≤1, respectively.
Coherence-Resonance-Induced Neuronal Firing near a Saddle-Node and Homoclinic Bifurcation Corresponding to Type-I Excitability
JIA Bing, GU Hua-Guang, **, LI Yu-Ye
Chin. Phys. Lett. 2011, 28 (9): 090507 .   DOI: 10.1088/0256-307X/28/9/090507
Abstract   PDF(pc) (1296KB) ( 488 )
Excitability is an essential characteristic of excitable media such as nervous and cardiac systems. Different types of neuronal excitability are related to different bifurcation structures. We simulate the coherence resonance effect near a saddle-node and homoclinic bifurcation corresponding to type-I excitability in a theoretical neuron model, and recognize the obvious features of the corresponding firing pattern. Similar firing patterns are discovered in rat hippocampal CA1 pyramidal neurons. The results are not only helpful for understanding the dynamics of the saddle-node bifurcation and type-I excitability in a realistic nervous system, but also provide a practical indicator to identify types of excitability and bifurcation.
One-Dimensional w-Component Fermions and Bosons with Delta Function Interaction
WEI Bo-Bo*
Chin. Phys. Lett. 2011, 28 (9): 090508 .   DOI: 10.1088/0256-307X/28/9/090508
Abstract   PDF(pc) (451KB) ( 362 )
The ground state energy for 1D multicomponent fermions and bosons with repulsive or attractive delta function interparticle interaction is studied.
High-Performance Humidity Sensors Based on Double-Layer ZnO-TiO2 Nanofibers via Electrospinning
YUE Xue-Jun, HONG Tian-Sheng**, XU Xing, LI Zhen
Chin. Phys. Lett. 2011, 28 (9): 090701 .   DOI: 10.1088/0256-307X/28/9/090701
Abstract   PDF(pc) (774KB) ( 1320 )
ZnO and TiO2 nanofibers are synthesized via electrospinning methods and characterized by x−ray diffraction, scanning electron microscopy, and transmission electron microscopy. Humidity sensors with double-layer sensing films are fabricated by spinning the ZnO and TiO2 nanofibers on ceramic substrates sequentially. Compared with sensors loading only one type of nanofiber, the double-layer sensors exhibit much better sensing properties. The corresponding impedance changes more than four orders of magnitude within the whole humidity range from 11% to 95% relative humidity, and the response and recovery times are about 11 and 7 s, respectively. Maximum hysteresis is around 1.5% RH, and excellent stability is also observed after 180 days. The humidity sensing mechanism is discussed in terms of the sensor structure. The experimental results provide a possible route for the design and fabrication of high performance humidity sensors based on one-dimensional nanomaterials.
Experiments on Broadband EMP Radiation with an Axial Mode Helix Antenna
SUN Qi-Zhi, FANG Dong-Fan**, LIU Wei, LIU Zheng-Fen, CHI Yuan, DAI Wen-Feng, HAN Wen-Hui
Chin. Phys. Lett. 2011, 28 (9): 090702 .   DOI: 10.1088/0256-307X/28/9/090702
Abstract   PDF(pc) (733KB) ( 892 )
To produce broadband electromagnetic pulse (EMP) radiation, we design and test a sub-ns pulse system which is utilized to drive an axial mode helix antenna. This sub-ns pulse system consists of a 10-stage Marx generator, an intermediate storage capacitor, an impedance transforming line, and can generate a high voltage of 570 kV with a rise time of 1–1.5 ns on a 300-Ω-resistance load. The diameter, pitch and turns of the helix antenna are 29 cm, 19.5 cm and 5, respectively, with a design frequency of 300 MHz. When the charging voltage of the Marx generator is 30 kV, the electric field of radiated EMP measured 3m from the source is 35 kV/m with a central frequency of 250 MHz. The relatively spectral bandwidth is 25%. The radiated EMP results are reproducible and the system will work in repetition mode if the available dc power is utilized.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Generalized Uncertainty Principle in the Presence of Extra Dimensions
MU Ben-Rong, WU Hou-Wen**, YANG Hai-Tang
Chin. Phys. Lett. 2011, 28 (9): 091101 .   DOI: 10.1088/0256-307X/28/9/091101
Abstract   PDF(pc) (473KB) ( 343 )
We argue that in the generalized uncertainty principle (GUP) model, the parameter β0 whose square root, multiplied by Planck length p, approximates the minimum measurable distance, varies with energy scales. Since the minimal measurable length and extra dimensions are both suggested by quantum gravity theories, we investigate the models based on the GUP and one extra dimension, compactified with radius ρ. We obtain an inspiring relation √β0p/ρ∼ O(1). This relation is also consistent with the predictions at Planck scale and the usual quantum mechanics scale. We also estimate the application range of the GUP model. It turns out that the minimum measurable length is exactly the compactification radius of the extra dimension.
NUCLEAR PHYSICS
Tensor Coupling Effects on Spin Symmetry in the Anti-Lambda Spectrum of Hypernuclei
SONG Chun-Yan, YAO Jiang-Ming, MENG Jie, **
Chin. Phys. Lett. 2011, 28 (9): 092101 .   DOI: 10.1088/0256-307X/28/9/092101
Abstract   PDF(pc) (622KB) ( 354 )
Effects of ΛΛ ω−tensor coupling on the spin symmetry of Λ spectra in Λ−nucleus systems are studied using relativistic mean-field theory. Taking 12C+Λ as an example, it is found that the tensor coupling enlarges the spin−orbit splittings of Λ by a factor of 5 but has a negligible effect on the wave functions of Λ. Similar conclusions are observed in other Λ−nuclei, including 16O+Λ, 40Ca+Λ and 208Pb+Λ. It is indicated that the spin symmetry in anti-lambda-nucleus systems is still a good approximation irrespective of the tensor coupling.
The Plateau of Moment of Inertia and the Energy Gap in 161−168Yb
HUANG Li-Xun, QI Yan-Jun, LI Tao, LIU Shu-Xin**
Chin. Phys. Lett. 2011, 28 (9): 092102 .   DOI: 10.1088/0256-307X/28/9/092102
Abstract   PDF(pc) (698KB) ( 312 )
The influence of the gap at Z=70 on the alignment in 161168Yb is studied using the particle number conserving method. If there is a gap at the Fermi surface, the occupation probability of the [523]7/2 proton orbital does not change as much as when there is no gap. The formation of the plateau of moment of inertia is sensitive to the relative position of the orbital π[404]7/2, π[411]1/2 and π[523]7/2. A third backbending caused by π[541]1/2 is predicted.
Fission of Weakly Prolate 119Sn and Weakly Oblate 209Bi Nuclei Induced by 500 and 672 MeV Negative Pions
Mukhtar Ahmed Rana*, Gul Sher, Shahid Manzoor, M. I. Shahzad
Chin. Phys. Lett. 2011, 28 (9): 092501 .   DOI: 10.1088/0256-307X/28/9/092501
Abstract   PDF(pc) (608KB) ( 313 )
Fission cross-sections of 119Sn and 209Bi induced by negative pions of two energies 500 and 672 MeV were measured using a CR−39 nuclear track detector. Target-detector stacks were exposed to pion beams at the Brookhaven National Laboratory (USA). Measurement results are compared with the corresponding calculations using the computer code CEM95. Agreement between measurements and calculations is fairly good for the 209Bi target nuclei whereas it is poor for 119Sn at both investigated energies of 500 and 672 MeV. Fission cross−section results of 119Sn and 209Bi are explained using the equilibrium properties of these nuclides including nuclear electric quadrupole moments which determine the shapes of nuclei. A logarithmic dependence of fission cross−section on Z2/A is observed for the above−mentioned reactions and a critical limit of Z2/A is identified with the value of 30 which divides the curve of σf versus Z2/A into two regimes, one with weak dependence and the other with strong dependence.
Collective Flow of Λ Hyperons within Covariant Kaon Dynamics
XING Yong-Zhong, **, ZHU Yu-Lan, WANG Yan-Yan, ZHENG Yu-Ming,
Chin. Phys. Lett. 2011, 28 (9): 092502 .   DOI: 10.1088/0256-307X/28/9/092502
Abstract   PDF(pc) (611KB) ( 304 )
The collective flow of Λ hyperons produced in association with positively charged kaon mesons in nuclear reactions at SIS energies is studied using the quantum molecular dynamics (QMD) model within covariant kaon dynamics. Our calculation indicates that both the directed and differential directed flows of Λs are almost in agreement with the experimental data. This suggest that the covariant kaon dynamics based on the chiral mean field approximation can not only explain the collective flow of kaon mesons, but also give reasonable results for the collective flow of Λ hyperons at SIS energies. The final−state interaction of Λ hyperons with dense nuclear matter enhances their directed flow and improves the agreement of their differential directed flow with the experimental data. The influence of the interaction on the Λ collective flow is more appreciable at large rapidity or transverse momentum region.
Centrality in Relativistic Nuclear Collisions and the Random Matrix Approach
Z. Wazir**
Chin. Phys. Lett. 2011, 28 (9): 092503 .   DOI: 10.1088/0256-307X/28/9/092503
Abstract   PDF(pc) (454KB) ( 341 )
Using the random matrix approach, results for nearest-neighbor distributions obtained from experimental data on 12C+12C collisions at 4.2 A GeV/c and simulations produced with the aid of an ultra-relativistic quantum molecular dynamics model are studied. Comparison reveals that the observed changes in the nearest-neighbor distributions for different multiplicities can be associated with the onset of a region of central collisions.
ATOMIC AND MOLECULAR PHYSICS
Effect of Collision Energy on the Reactivity O++T2OT++T by the Quasiclassical Trajectory Method
CHEN Jia-Wu, LIU Xin-Guo**, SUN Hai-Zhu, ZHANG Qing-Gang
Chin. Phys. Lett. 2011, 28 (9): 093101 .   DOI: 10.1088/0256-307X/28/9/093101
Abstract   PDF(pc) (718KB) ( 396 )
The reactivity O++T2→OT++T is studied by the quasiclassical trajectory method on the RODRIGO potential energy surface at the collision energies of 1.0, 1.3, 1.6 and 1.9 eV, respectively. The four polarization−dependent generalized differential cross sections (PDDCSs) (2π/σ)(dσ00 /t ), (2π/σ)(dσ20 /t ), (2π/σ)(dσ22+/t ) and (2π/σ)(dσ21− /t ) are calculated in the center-of-mass frame. Furthermore, the P(θr ) distribution describing the kj correlation, the distribution of dihedral angle P(φr ) and the distribution of P(θrr ), which describes the angular distribution of product rotational vectors in the form of polar plots in θr and φr are also investigated. The results demonstrate that the stereo-dynamical properties of the title reactivity are sensitive to collision energies.
Electronic Transport Properties of a Naphthopyran-Based Optical Molecular Switch: an ab initio Study
XIA Cai-Juan**, LIU De-Sheng, ZHANG Ying-Tang
Chin. Phys. Lett. 2011, 28 (9): 093102 .   DOI: 10.1088/0256-307X/28/9/093102
Abstract   PDF(pc) (710KB) ( 423 )
The electronic transport properties of a naphthopyran-based molecular optical switch are investigated by using the nonequilibrium Green's function formalism combined with first-principles density functional theory. The molecule that comprises the switch can convert between its open and closed forms upon photoexcitation. Theoretical results show that the current through the open form is significantly larger than that through the closed form, which is different from other optical switches based on ring-opening reactions of the molecular bridge. The maximum on-off ratio (about 90) can be obtained at 1.4 V. The physical origin of the switching behavior is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap. Our result shows that the naphthopyran-based molecule is a good candidate for optical molecular switches and will be useful in the near future.
Micromotion Compensation and Photoionization of Ions in a Linear Trap
XIE Yi, ZHOU Fei, CHEN Liang, WAN Wei, FENG Mang**
Chin. Phys. Lett. 2011, 28 (9): 093201 .   DOI: 10.1088/0256-307X/28/9/093201
Abstract   PDF(pc) (651KB) ( 422 )
The stable confinement of ions in an electromagnetic trap is a prerequisite of sideband cooling and quantum information processing. For a string of ions in a linear ion trap, we report our recent efforts of compensating for micromotion of the ions by three methods, which yields narrower fluorescence spectra and lower temperature. We also achieve a photoionization scheme that loads the ions deterministically into the linear trap from an atomic beam.
Collisional Energy Transfer between Highly Vibrationally Excited CsH(X1Σ+, v=15–22) and H2
ZHU Dong-Hui, ZHANG Bin, SHEN Yi-Fan**, DAI Kang
Chin. Phys. Lett. 2011, 28 (9): 093401 .   DOI: 10.1088/0256-307X/28/9/093401
Abstract   PDF(pc) (694KB) ( 437 )
The Cs atoms are prepared in the 6D state by two−photon absorption. CsH(X1 Σ+,v"=0) is generated from the Cs(6D)+H2 reaction. By overtone excitation with a pulsed dye laser, highly vibrational states v"≥15 of CsH in its ground electronic state are obtained. A diode laser is used to probe either the prepared vibrational state or the collisionally populated states. The decay signal of the time−resolved fluorescence from the A1 Σ+(v')→X1 Σ+(v") transition is monitored. Based on the Stern–Volmer equation, the total rate coefficients for v"=15–22 are yielded. The time evolution and relative intensities of three related states, v", v"−1 and v"−2, made by the initially prepared v" state of CsH are measured. Rate coefficients of single− and double-quantum relaxation are obtained. These results show that single-quantum relaxation accounts for 50% of the total relaxation out of states v"=17–20. Multiquantum relaxation (Δv≥2) makes major contribution (62%) to the vibrational relaxation at v"=21 and 22. A simple explanation is given.
Positron Impact Transitions of Atomic Sodium
CHENG Yong-Jun**, ZHOU Ya-Jun**
Chin. Phys. Lett. 2011, 28 (9): 093402 .   DOI: 10.1088/0256-307X/28/9/093402
Abstract   PDF(pc) (604KB) ( 324 )
We present a new investigation of elastic and inelastic positron-sodium scattering by using the coupled-channel optical method (CCO) at an incident energy region of 2–100 eV. The ionization continuum and positronium formation channels have been included via a complex equivalent-local optical potential. The present calculations are compared with available theoretical data and our investigation indicates that the inclusion of ionization and Ps-formation channels in the present calculations has a significant effect on the cross sections of elastic and inelastic positron-sodium scattering at lower energies.
Influence of Isotope Effects on the Stereodynamics of the N(4S)+H2 → NH+H Reactive System: a QCT Study
ZHANG Juan, CHU Tian-Shu**, DONG Shun-Le**, YUAN Shu-Ping, FU Ai-Ping, DUAN Yun-Bo
Chin. Phys. Lett. 2011, 28 (9): 093403 .   DOI: 10.1088/0256-307X/28/9/093403
Abstract   PDF(pc) (738KB) ( 469 )
To investigate the isotopic effects and their influence on the stereodynamical properties of the N(4S)+H2 reaction system, quasi−classical trajectory (QCT) calculations are carried out on the 4A" double many−body expansion (DMBE) potential energy surface (PES) [Phys. Chem. Chem. Phys. 7 (2005) 2867] at a collision energy of 40 kcal/mol. The generalized polarization-dependent differential cross sections (PDDCSs) and the three angular distributions of P(θr), P(φr) and P(θrr) are presented and discussed for the title reaction and its isotope variants. It is revealed that both intermolecular and intramolecular isotope effects can exert a substantial influence on the product polarizations.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Simultaneous PMD Mitigation for Two Polarization Tributaries of a PDM Signal using only One All-Optical Regenerator
CHEN Zhi-Yu, YAN Lian-Shan**, YI An-Lin, PAN Wei, LUO Bin
Chin. Phys. Lett. 2011, 28 (9): 094201 .   DOI: 10.1088/0256-307X/28/9/094201
Abstract   PDF(pc) (800KB) ( 379 )
A scheme of polarization-mode-dispersion (PMD) mitigation in a polarization-division-multiplexing (PDM) system is proposed and demonstrated with 2 ×10 Gb/s return−to-zero on-off-keying (RZ-OOK) transmission. Simultaneous mitigation for two polarization tributaries of the PDM signal is achieved based on the self-phase-modulation (SPM) effect and offset filtering in a polarization nonlinear loop configuration. The improvement of eye-diagram-based signal-to-noise ratio (SNR) is 3.5 dB in the presence of a 7.2-ps differential-group delay (DGD) when the pulsewidth of the PDM signal is 16.6 ps.
Characteristics of Soliton Evolution in the Wave-Breaking-Free Regime in a Passively Mode-Locked Yb-Doped Fiber Laser
WU Ge, TIAN Xiao-Jian, GAO Bo**, SHAN Jiang-Dong, RU Yu-Xing
Chin. Phys. Lett. 2011, 28 (9): 094202 .   DOI: 10.1088/0256-307X/28/9/094202
Abstract   PDF(pc) (652KB) ( 413 )
We focus on several aspects concerning the numerical simulation of a passively mode-locked Yb-doped fiber laser by a non-distributed model. The characteristics of soliton evolution in a wave-breaking-free regime are numerically investigated with the split-step Fourier method. Based on the model, a parabolic-shaped soliton with a nearly linear chirp and bound soliton pairs are obtained by controlling the intra-cavity average dispersion of the fiber laser. A phenomenon is observed that by keeping the system parameters unchanged, linearly chirped parabolic soliton and bound soliton pairs are attainable under different initial conditions in the transient region between these two kinds of solitons.
Lensless Ghost Diffraction with Partially Coherent Sources: Effects of the Source Size, Transverse Coherence, Detector Size and Defocusing Length
LIN Jie, **, CHENG Jing
Chin. Phys. Lett. 2011, 28 (9): 094203 .   DOI: 10.1088/0256-307X/28/9/094203
Abstract   PDF(pc) (511KB) ( 476 )
Lensless ghost diffraction with partially coherent sources is investigated theoretically and numerically. Based on the classical optical coherent theory and the Gauss–Shell model of the partially coherent sources, we derive an analytical imaging formula of lensless ghost diffraction (LGD). Using this formula, we can see the effects of the transverse size and coherence of the sources, the detector size and defocusing length on the quality of LGD. Numerical results are presented to show that for different detector sizes and defocusing lengths, high quality LGD can be realized by using sources with appropriate transverse sizes and coherent widths. These findings can be used to choose the optimal parameters in the design of a realistic LGD system.
Frequency Stabilization Using Polarization Spectroscopy and Cr-He Hollow Cathode Discharge
YIN Cong**, QIAN Jin, ZHANG Xiao-Ping, SHI Chun-Ying, WANG Han-Ping, HUANG Sheng-Ye
Chin. Phys. Lett. 2011, 28 (9): 094204 .   DOI: 10.1088/0256-307X/28/9/094204
Abstract   PDF(pc) (468KB) ( 403 )
Polarization spectroscopy is used to lock a frequency-doubled Ti:Sapphire laser to the 425.5 nm 7S37P40 transition of 52Cr. A Cr−He hollow cathode discharge cell is designed and fabricated to produce Cr atom vapor instead of a high temperature cell. Without any modulation devices or lock-in amplifiers, a high signal-to-background level polarization spectroscopy signal is obtained. Moreover, a frequency fluctuation of ±295 kHz for more than one hour is achieved.
High Power Widely Tunable Narrow Linewidth All-Solid-State Pulsed Titanium-Doped Sapphire Laser
DING Xin, LI Xue, SHENG Quan, **, SHI Chun-Peng, YIN Su-Jia, LI Bin, YU Xuan-Yi, WEN Wu-Qi, YAO Jian-Quan,
Chin. Phys. Lett. 2011, 28 (9): 094205 .   DOI: 10.1088/0256-307X/28/9/094205
Abstract   PDF(pc) (593KB) ( 407 )
We report a widely tunable, narrow linewidth, pulsed Ti:sapphire laser pumped by an all-solid-state Q-switched intra-cavity frequency-doubled Nd:YAG laser. By using four dense flint glass prisms as intra-cavity dispersive elements, the output wavelength can be continuously tuned over 675–970 nm and the spectral linewidth is shortened to 0.5 nm. The maximum output power of 6.65 W at 780 nm is obtained under 23.4 W pump power with repetition rate of 5.5 kHz; corresponding to an conversion efficiency of 28.4%. Due to the gain-switching characteristics of the Ti:sapphire laser, the output pulse duration is as short as 17.6 ns.
Optical Nonlinearity of Subwavelength Metal-dielectric Gratings: Effects of Strong Anisotropy
KANG Xiu-Bao, TIAN Tai-He, WANG Zhi-Guo**
Chin. Phys. Lett. 2011, 28 (9): 094206 .   DOI: 10.1088/0256-307X/28/9/094206
Abstract   PDF(pc) (1633KB) ( 444 )
The optical nonlinear properties of an effective anisotropic slab made of metal-dielectric lamellar gratings with a small grating-period-to-wavelength ratio Λ/λ→0 is studied. It is shown that when a transverse magnetic electromagnetic wave obliquely illuminates such a slab, whose effective normal permittivity is much smaller than its tangential one, the normal wave vector inside the effective medium is extremely sensitive to the fluctuation of the tangential effective permittivity. Based on this characteristic, obvious nonlinear modifications of the phase delay and step−like transmission are obtained by a moderate input intensity even if the thickness of the slab structure is only less than λ/6.
Improvement of Response Performance of Liquid Crystal Optical Devices by using a Low Viscosity Component
PENG Zeng-Hui, LIU Yong-Gang, YAO Li-Shuang, CAO Zhao-Liang, MU Quan-Quan, HU Li-Fa, LU Xing-Hai, XUAN Li**, ZHANG Zhi-Yong
Chin. Phys. Lett. 2011, 28 (9): 094207 .   DOI: 10.1088/0256-307X/28/9/094207
Abstract   PDF(pc) (536KB) ( 459 )
Difluorooxymethylene-bridged (CF2O) liquid crystal (LC) with low viscosity is prepared and used as a fast response LC material. When the material is mixed with isothiocyanato LCs with high birefringence, the visco−elastic coefficient of the mixture decreases evidently and, accordingly, the response performance increases. While the concentration of CF2O LCs is about 7%, the LC mixture approximately maintains high birefringence and exhibits a fastest response performance that is 14% higher than that of pure isothiocyanato LCs. Therefore, the LC material and mixing method could find useful applications in optical devices.
A 526 W Diode-Pumped Nd:YAG Ceramic Slab Laser
CHEN Yan-Zhong, LIU Wen-Bin, BO Yong**, JIANG Ben-Xue, XU Jian, KOU Hua-Min, XU Yi-Ting, PAN Yu-Bai, XU Jia-Lin, GUO Ya-Ding, YANG Feng-Tu, PENG Qin-Jun, CUI Da-Fu, JIANG Dong-Liang, XU Zu-Yan
Chin. Phys. Lett. 2011, 28 (9): 094208 .   DOI: 10.1088/0256-307X/28/9/094208
Abstract   PDF(pc) (519KB) ( 1200 )
A diode-side-pumped Nd:YAG ceramic slab laser with a high power output is presented. An average power of 526 W is achieved at 1064 nm with a repetition rate of 120 Hz and a pulse width of 180 µs from a 93mm×52mm×8mm ceramic slab at a pump power of 1928 W, corresponding to an optical-to-optical efficiency of 27.3%.
Influence Factors of an All-Optical Recovered Clock from Two-Section DFB Lasers
KONG Duan-Hua, ZHU Hong-Liang, LIANG Song, WANG Bao-Jun, BIAN Jing, MA Li, YU Wen-Ke, LOU Cai-Yun
Chin. Phys. Lett. 2011, 28 (9): 094209 .   DOI: 10.1088/0256-307X/28/9/094209
Abstract   PDF(pc) (555KB) ( 347 )
All-optical clock recovery by a two-section DFB laser with different injection wavelengths is demonstrated experimentally at 38.5 GHz. An optical clock with a root-mean-square timing jitter of 250 fs and an extinction ratio of 12.1 dB is obtained with 1551 nm injection. The timing jitter of the recovered clock is further investigated for various intensity ratios of the two DFB emission modes.
Coherent Beam Combining of Two Slab Laser Amplifiers and Second-Harmonic Phase Locking Based on a Multi-Dithering Technique
LI Xiao**, XIAO Hu, DONG Xiao-Lin, MA Yan-Xing, XU Xiao-Jun**
Chin. Phys. Lett. 2011, 28 (9): 094210 .   DOI: 10.1088/0256-307X/28/9/094210
Abstract   PDF(pc) (782KB) ( 598 )
Coherent beam combining (CBC) is an efficient way to scale the brightness of laser arrays. We demonstrate the active phase locking CBC of two slab laser amplifiers based on the multi-dithering technique. The experimental investigation on the 102 W coherent beam combining of two slab amplifiers shows that the whole system in a closed loop performs well over a long time observation. The contrast of the coherent combined beam profile is about 87% and the combining efficiency is nearly 85%. In addition, the CBC of two green lasers is realized based on the second-harmonic generation of the phase locking pump lasers. To the best of our knowledge, this is the first report about second-harmonic active phase locking, which indicates further potential applications of CBC.
Efficient High Power Ho,Tm:GdVO4 Laser
WANG Yue-Zhu, ZHU Guo-Li**, JU You-Lun, YAO Bao-Quan
Chin. Phys. Lett. 2011, 28 (9): 094211 .   DOI: 10.1088/0256-307X/28/9/094211
Abstract   PDF(pc) (484KB) ( 360 )
We report a 22.3 W cw diode-pumped cryogenic Ho(0.5at.%),Tm(at.5%):GdVO4 laser at a wavelength of 2.05 µm. It is pumped by two fiber−coupled laser diodes with a fiber core diameter of 0.4 mm, both of which provide 42 W pump power near 802 nm. A cw output power of 22.3 W was obtained at the pump power of 51.0 W, corresponding to an optical-to-optical conversion efficiency of 43.7% when the ratio of the pump beam to oscillating laser beam in the crystal was 1.33:1. The M2 factor was found to be 2.0 under an output power of 16.5 W.
A New Distributed Measurement of Birefringence Vectors by P-OTDR Assisted by a High Speed Polarization Analyzer
SHANG Chao, WU Chong-Qing**, LI Zheng-Yong, YANG Shuang-Shou**
Chin. Phys. Lett. 2011, 28 (9): 094212 .   DOI: 10.1088/0256-307X/28/9/094212
Abstract   PDF(pc) (1055KB) ( 385 )
A new polarimetric optical time domain reflectometry (P-OTDR) measurement device assisted by a high speed polarization analyzer is designed and a new algorithm, which can be used to accurately measure the birefringence vector, is proposed. In this method, only one measurement is required and the result is insensitive to the input state of polarization. An 1-km single mode fiber (SMF) is measured and the distribution of the local birefringence vector along the SMF is obtained with a resolution of 2 cm.
Locally Resonant Gaps of Phononic Beams Induced by Periodic Arrays of Resonant Shunts
CHEN Sheng-Bing**, WEN Ji-Hong, WANG Gang, HAN Xiao-Yun, WEN Xi-Sen
Chin. Phys. Lett. 2011, 28 (9): 094301 .   DOI: 10.1088/0256-307X/28/9/094301
Abstract   PDF(pc) (543KB) ( 403 )
Periodic arrays of shunted piezoelectric patches are employed to control the propagation of elastic waves in phononic beams. Each piezo-patch is connected to a single resistance-inductance-capacitance shunting circuit. Therefore, the resonances of the shunting circuits will produce locally resonant gaps in the phononic beam. However, the existence of locally resonant gaps induced by resonant shunts has not been clearly proved by experiment so far. In this work, the locally resonant gap in a piezo-shunted phononic beam is investigated theoretically and verified by experiment. The results prove that resonances of shunting circuits can produce locally resonant gaps in phononic beams.
Landau–Stanyukovich Rule and the Similarity Parameter of Converging Shock Waves in Magnetogasdynamics
Mithilesh Singh**, L. P. Singh, Akmal Husain
Chin. Phys. Lett. 2011, 28 (9): 094701 .   DOI: 10.1088/0256-307X/28/9/094701
Abstract   PDF(pc) (551KB) ( 548 )
Second-kind self-similar solutions to a problem of converging cylindrical shock waves in magnetogasdynamics are investigated. Two trial functions suggested by Chisnell and the shooting method of Landau–Stanyukovich are used to determine the similarity exponent for different values of specific heat ratio γ and the parameter k, where kın (0, 1]. Detailed analyses of flow patterns for different values of adiabatic heat exponent and magnetic field strength are carried out. It is observed that the general behavior of the velocity and density profiles is not affected in a magnetogasdynamics regime whereas there is an increase in the absolute value of the flow parameters with an increase in the magnetic field strength. However, the pressure profiles are greatly affected by the magnetic field interaction.
Slip Effects on an Unsteady Boundary Layer Stagnation-Point Flow and Heat Transfer towards a Stretching Sheet
Krishnendu Bhattacharyya**, Swati Mukhopadhyay, G. C. Layek
Chin. Phys. Lett. 2011, 28 (9): 094702 .   DOI: 10.1088/0256-307X/28/9/094702
Abstract   PDF(pc) (552KB) ( 733 )
An analysis is presented for an unsteady boundary layer stagnation-point flow of a Newtonian fluid and the heat transfer towards a stretching sheet taking non-conventional partial slip conditions at the sheet. The self-similar equations are obtained using similarity transformations and solved numerically by the shooting method. Effects of the parameters involved in the equations, especially velocity slip and thermal slip parameters on the velocity and temperature profiles, are analyzed extensively. It is revealed that due to the velocity and thermal slip parameters, the rate of heat transfer from the sheet and the wall skin friction change significantly.
Direct Force Control of a Rudder with the Action of a Coplanar Waveguide Product Microwave
LIU Zong-Kai, ZHOU Ben-Mou**, LIU Hui-Xing, LIU Zhi-Gang, JI Yan-Liang
Chin. Phys. Lett. 2011, 28 (9): 094703 .   DOI: 10.1088/0256-307X/28/9/094703
Abstract   PDF(pc) (573KB) ( 307 )
We investigate the distribution of electromagnetic body force in a fluid boundary layer produced by a coplanar waveguide (CPW) and focus on the fluid dynamic control effects of a rudder. The electromagnetic body force along the CPW direction can be created by the mutual coupling of landscape orientated electric and magnetic fields. With CPWs arranged on the rudder's surface, a direct-force-control rudder can be realized by adjusting the microwave sources. It is also found that a streamwise microwave electromagnetic body force can markedly enhance lift force and suppress rudder vibration, thus improving response time lag significantly. Furthermore, navigation stall caused by a large angle of attack can be avoided.
Thrust Vectoring of a Continuous Rotating Detonation Engine by Changing the Local Injection Pressure
LIU Shi-Jie**, LIN Zhi-Yong, SUN Ming-Bo, LIU Wei-Dong
Chin. Phys. Lett. 2011, 28 (9): 094704 .   DOI: 10.1088/0256-307X/28/9/094704
Abstract   PDF(pc) (1072KB) ( 612 )
The thrust vectoring ability of a continuous rotating detonation engine is numerically investigated, which is realized via increasing local injection stagnation pressure of half of the simulation domain compared to the other half. Under the homogeneous injection condition, both the flow-field structure and the detonation wave propagation process are analyzed. Due to the same injection condition along the inlet boundary, the outlines of fresh gas zones at different moments are similar to each other. The main flow-field features under thrust vectoring cases are similar to that under the baseline condition. However, due to the heterogeneous injection system, both the height of the fresh gas zone and the pressure value of the fresh gas in the high injection pressure zone are larger than that in the low injection pressure zone. Thus the average pressure in half of the engine is larger than that in the other half and the thrust vectoring adjustment is realized.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Dust Particle Density and Charges in Radio-Frequency Mixture Discharge Plasma
WU Jing, **, ZHANG Peng-Yun, SUN Ji-Zhong, YAO Lie-Ming, DUAN Xu-Ru
Chin. Phys. Lett. 2011, 28 (9): 095201 .   DOI: 10.1088/0256-307X/28/9/095201
Abstract   PDF(pc) (496KB) ( 544 )
We develop a method for measuring the density and charges of dust particles in a capacitive coupled cylinder discharge chamber in mixtures of gases SiH4/C2H4/Ar. Dust particles are created in situ using these reactive mixtures in rf discharge. A Langmuir probe is employed for the measurement of important plasma parameters, such as electron density, electron temperature and ion density. The density and charges of dust particles is then calculated based on the data of the measurement of these parameters and a known dust plasma sheath model. The curves of dust particle density versus rf power and gas pressure are presented, respectively, under various experimental conditions. The dust charges versus different experimental conditions are also evaluated and presented.
Locking of Tearing Modes by the Error Field
XU Tao**, HU Qi-Ming, HU Xi-Wei, YU Qing-Quan
Chin. Phys. Lett. 2011, 28 (9): 095202 .   DOI: 10.1088/0256-307X/28/9/095202
Abstract   PDF(pc) (548KB) ( 353 )
The locking of tearing modes by the error field is studied by nonlinear numerical modeling. The threshold of mode locking for J-TEXT tokamak plasmas is found.
Development of a Real-Time Ion Spectrometer with a Scintillator for Laser-Driven Ion Acceleration Experiments
XU Miao-Hua**, LI Hong-Wei, LIU Bi-Cheng, LIU Feng, SU Lu-Ning, DU Fei, ZHANG Lu, ZHENG Yi, MA Jing-Long, David Neely, Paul McKenna, WANG Zhao-Hua, WEI Zhi-Yi, YAN Xue-Qing, LI Yu-Tong**, LI Ying-Jun, ZHANG Jie,
Chin. Phys. Lett. 2011, 28 (9): 095203 .   DOI: 10.1088/0256-307X/28/9/095203
Abstract   PDF(pc) (920KB) ( 372 )
A real-time ion spectrometer mainly based on a high-resolution Thomson parabola and a plastic scintillator is designed and developed. The spectrometer is calibrated by protons from an electrostatic accelerator. The feasibility and reliability of the diagnostics are demonstrated in laser-driven ion acceleration experiments performed on the XL-II laser facility. The proton spectrum extrapolated from the scintillator data is in excellent agreement with the CR39 spectrum in terms of beam temperature and the cutoff energy. This real-time spectrometer allows an online measurement of the ion spectra in single shot, which enables efficient and statistical studies and applications in high-repetition-rate laser acceleration experiments.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Photorefractive Effect of a Liquid Crystal Cell with a ZnO Nanorod Doped in Only One PVA Layer
GUO Yu-Bing, CHEN Yong-Hai**, XIANG Ying, QU Sheng-Chun, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (9): 096101 .   DOI: 10.1088/0256-307X/28/9/096101
Abstract   PDF(pc) (578KB) ( 327 )
We observe obviously different diffraction efficiencies with forward and reverse dc voltages in a forced-light-scattering (FLS) experiment for a cell with ZnO nanorod doped in only one poly (vinyl alcohol) (PVA) layer. When a dc voltage with a positive pole on the ZnO nanorod doped side is applied, the excited charge carriers primarily move along the transverse direction, which results in a higher diffraction efficiency. Conversely, when the dc voltage with a negative pole on the ZnO nanorod doped side is applied, the excited charge carriers primarily move along the longitudinal direction, which leads to a lower diffraction efficiency. A largest diffraction efficiency of about 9% is achieved in the ZnO nanorod doped liquid crystal cell.
Light Emission and Dynamic Failure Mechanism of Hypervelocity Impact on Zr-Ti-Ni-Cu-Be Bulk Metallic Glass
SUN Bao-Ru, ZHAN Zai-Ji**, LIANG Bo, ZHANG Rui-Jun, WANG Wen-Kui
Chin. Phys. Lett. 2011, 28 (9): 096102 .   DOI: 10.1088/0256-307X/28/9/096102
Abstract   PDF(pc) (1654KB) ( 397 )
Hypervelocity impact on rectangular plate-shaped Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) is performed by a two−stage light gas gun. The targets used in the experiment are BMG plates with a thickness of 5 mm. The projectile, spherical aluminum (3.1 mm in diameter), is accelerated up to various velocities; the light is detected with a radiometer. The emission lasts from 200 µs up to 1500 µs and the intensity increases from 44 to 900 W/(Sr⋅µm). The duration and intensity of a light emission seem to depend on the impact velocity and the extent of target destruction through the formation of impact craters or penetration.
Accurately Predicting the Density and Hydrostatic Compression of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine from First Principles
SONG Hua-Jie, HUANG Feng-Lei**
Chin. Phys. Lett. 2011, 28 (9): 096103 .   DOI: 10.1088/0256-307X/28/9/096103
Abstract   PDF(pc) (532KB) ( 352 )
We predict the densities of crystalline hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by introducing a factor of (1+1.5 × 10−4 T) into the wavefunction-based potential of RDX constructed from first principles using the symmetry-adapted perturbation theory and the Williams–Stone–Misquitta method. The predicted values are within an accuracy of 1% of the density from 0 to 430 K and closely reproduced the RDX densities under hydrostatic compression. This work heralds a promising approach to predicting accurately the densities of high explosives at temperatures and pressures to which they are often subjected, which is a long-standing issue in the field of energetic materials.
Magnetic Resonance Imaging Study on the Miscibility of a CO2/n-Decane System
SONG Yong-Chen, ZHU Ning-Jun, LIU Yu**, ZHAO Jia-Fei, LIU Wei-Guo, ZHANG Yi, ZHAO Yue-Chao, JIANG Lan-Lan
Chin. Phys. Lett. 2011, 28 (9): 096401 .   DOI: 10.1088/0256-307X/28/9/096401
Abstract   PDF(pc) (579KB) ( 555 )
We provide a feasible method to estimate the minimum miscibility pressure (MMP) of a CO2/n−decane system by using high spatial resolution magnetic resonance imaging (MRI). During the measurement, the signal intensity of n-decane with CO2 dissolved is measured. The MRI images show that the signal intensity of n−decane decreases to zero and the interface disappears at the MMP. A good exponential growth relation is found between the signal intensity and the pressure of the CO2/n−decane system. The relationship between the MMP and the temperature is established quantitatively, which is in close agreement with previous studies. Moreover it could be used to predict the MMP of the CO2/n-decane system.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Preparation and Properties of Diluted Magnetic Semiconductors GaMnAs by Low-Temperature Molecular Epitaxy
JI Chang-Jian**, ZHANG Cheng-Qiang, ZHAO Gang, WANG Wen-Jing, SUN Gang, YUAN Hui-Min, HAN Qi-Feng
Chin. Phys. Lett. 2011, 28 (9): 097101 .   DOI: 10.1088/0256-307X/28/9/097101
Abstract   PDF(pc) (737KB) ( 352 )
GaMnAs films are prepared by low-temperature molecular beam epitaxy. Based on the experimental results, the influence of growth and annealing conditions on the physical properties and defect configurations is discussed. In particular, the major compensating defects, such as As antisite (AsGa) and Mn interstitials (MnI), are studied in detail. Thereby, the relationship between structure and magnetic properties is given. It is indicated that a higher annealing temperature can remove MnI out of the GaMnAs lattices so as to raise the Curie temperature TC. Meticulous optimization of growth techniques (TS=230°C, As2:Ga=5:1 and Ta=250°C) leads to reproducible physical properties and ferromagnetic transition temperatures well above 148 K.
Unconventional Bose–Einstein Condensations from Spin-Orbit Coupling
WU Cong-Jun**, Ian Mondragon-Shem, , ZHOU Xiang-Fa
Chin. Phys. Lett. 2011, 28 (9): 097102 .   DOI: 10.1088/0256-307X/28/9/097102
Abstract   PDF(pc) (523KB) ( 717 )
According to the "no-node" theorem, the many-body ground state wavefunctions of conventional Bose–Einstein condensations (BEC) are positive-definite, thus time-reversal symmetry cannot be spontaneously broken. We find that multi-component bosons with spin-orbit coupling provide an unconventional type of BECs beyond this paradigm. We focus on a subtle case of isotropic Rashba spin-orbit coupling and the spin-independent interaction. In the limit of the weak confining potential, the condensate wavefunctions are frustrated at the Hartree–Fock level due to the degeneracy of the Rashba ring. Quantum zero-point energy selects the spin-spiral type condensate through the "order-from-disorder" mechanism. In a strong harmonic confining trap, the condensate spontaneously generates a half-quantum vortex combined with the skyrmion type of spin texture. In both cases, time-reversal symmetry is spontaneously broken. These phenomena can be realized in both cold atom systems with artificial spin-orbit couplings generated from atom-laser interactions and exciton condensates in semi-conductor systems.
Dynamical Process of Dissociation of Excitons in Polymer Chains with Impurities
ZHAO Hong-Xia, ZHAO Hui**, CHEN Yu-Guang
Chin. Phys. Lett. 2011, 28 (9): 097201 .   DOI: 10.1088/0256-307X/28/9/097201
Abstract   PDF(pc) (1137KB) ( 371 )
Within an extended Su–Schrieffer–Heeger model including impurity interactions, the dynamical process of exciton dissociation in the presence of an external electric field is investigated by using a non-adiabatic evolution method. Under the action of impurities, the stability as well as the effective mass of the exciton is reduced. Our results show that the field required to dissociate the excitons depends sensitively on the strength of the impurity potential. As the impurity potential strength increases, the dissociation field decreases effectively. The theoretical results are expected to provide useful predictions concerning which polymers with properly impurity-assisted interactions are likely to be more suitable for use in organic solar cells.
Quantum Hall Effect and Different Zero-Energy Modes of Graphene
M. R. Setare, *, D. Jahani, **
Chin. Phys. Lett. 2011, 28 (9): 097302 .   DOI: 10.1088/0256-307X/28/9/097302
Abstract   PDF(pc) (425KB) ( 359 )
The effect of an inhomogeneous magnetic field, which varies inversely with distance on the ground state energy level of graphene, is studied. We analytically show that graphene under the influence of a magnetic field arising from a straight long current-carrying wire (proportional to the magnetic field from carbon nanotubes and nanowires) exhibits zero-energy solutions and find that contrary to the case of a uniform magnetic field for which the zero-energy modes show the localization of electrons entirely on just one sublattice corresponding to a single valley Hamiltonian, zero-energy solutions in this case reveal that the probabilities for the electrons to be on both sublattices, say A and B, are the same.
Frustrated Ferromagnetic Spin Chain near the Transition Point
ZHU Ren-Gui**
Chin. Phys. Lett. 2011, 28 (9): 097501 .   DOI: 10.1088/0256-307X/28/9/097501
Abstract   PDF(pc) (436KB) ( 339 )
The one-dimensional quantum spin-1/2 model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is considered. The Hamiltonian is firstly rewritten in a form with rotated spin operators, then bosonized by using the linear spin wave approximation and then treated by using the Green function approach. An integral expression of the quantum correction to the classical ground state energy is derived. The critical behavior of the ground state energy in the vicinity of the transition point from the ferromagnetic to the singlet ground state is analyzed by numerical calculation and the result is 8γ2.
Ground-State Behavior of the Quantum Compass Model in an External Field
SUN Ke-Wei**, CHEN Qing-Hu
Chin. Phys. Lett. 2011, 28 (9): 097502 .   DOI: 10.1088/0256-307X/28/9/097502
Abstract   PDF(pc) (641KB) ( 310 )
Ground-state (GS) properties of the two-dimensional (2D) quantum compass model in an external field on a square 5×5 lattice are investigated by using the exact diagonalization (ED) method. We obtain the GS energy and evaluate quantities such as its correlation functions, nearest-neighbor entanglement and local order parameter. As the external field is presented, the first-order quantum phase point is absent and the system exhibits the behaviors of the second-order phase transition.
Mechanism of the Pyroelectric Response under Direct-Current Bias in La-Modified Lead Zirconate Titanate Stannate Ceramics
ZHANG Hong-Ling, WANG Gen-Shui, CHEN Xue-Feng, CAO Fei, DONG Xian-Lin**, GU Yan, HE Hong-Liang, LIU Yu-Sheng
Chin. Phys. Lett. 2011, 28 (9): 097701 .   DOI: 10.1088/0256-307X/28/9/097701
Abstract   PDF(pc) (773KB) ( 438 )
Dielectric and pyroelectric properties of Pb0.97La0.02(Zr0.42Sn0.40Ti0.18)O3 ceramics are investigated as functions of temperature and dc bias field. Induced and intrinsic pyroelectric coefficients pind and p0 are calculated and analyzed. It is found that the sign, value and variation of the net pyroelectric coefficient p with increasing dc bias all are dominated by p0 under applied biases. Polarization and depolarization processes under dc biases are analyzed. Besides the contribution of pind, the diffuse and decreased pyroelectric response under dc bias compared with that of an identical field poled sample without dc bias is mainly attributed to the depolarization process under dc bias.
Dielectric Function of Silicon Nanoclusters: Role of Hydrogen
SIB KRISHNA Ghoshal**, M. R. Sahar, M. S. Rohani
Chin. Phys. Lett. 2011, 28 (9): 097801 .   DOI: 10.1088/0256-307X/28/9/097801
Abstract   PDF(pc) (569KB) ( 377 )
Electronic and optical properties of small silicon quantum dots having 3 to 44 atoms per dot with and without surface passivation are investigated by computer simulation using the pseudo-potential approach. An empirical pseudo-potential Hamiltonian, a plane-wave basis expansion and a basic tetrahedral structure with undistorted local bonding configurations are used. The structures of the quantum dots are relaxed and optimized before and after hydrogen passivation. It is found that the gap increases more for a hydrogenated surface than the unpassivated one. Thus, both quantum confinement and surface passivation determine the optical and electronic properties of Si quantum dots. Visible luminescence is probably due to the radiative recombination of electrons and holes in the quantum-confined nanostructures. The effect of passivation of the surface dangling bonds by hydrogen atoms and the role of surface states on the gap energy is also examined. The results for the density of states, the dielectric function, the frequency dependent optical absorption cross section, the extinction coefficient and the static dielectric constants of the size are presented. The importance of the confinement and the role of surface passivation on the optical effects are discussed.
Charge Transfer Channels in Formation of Exciplex in Polymer Blends
DOU Fei, ZHANG Xin-Ping**
Chin. Phys. Lett. 2011, 28 (9): 097802 .   DOI: 10.1088/0256-307X/28/9/097802
Abstract   PDF(pc) (715KB) ( 471 )
The strong dependence of photoluminescence of charge transfer excited states or exciplex in a blend film of poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-l,4– phenylenediamine) (PFB) on the excitation wavelengths and morphology is investigated. The experimental results reveal that electron transfer in the LUMOs from PFB to F8BT is more efficient than hole transfer in the HOMOs from PFB to F8BT for the formation of exciplex at the interfacial junctions between these two types of molecules in the blend film. Furthermore, energy transfer from the blue-emitting PFB to the green-emitting F8BT at the interfaces introduces an additional two-step channel and thus enhances the formation of an exciplex. This is important for understanding of charge generation and separation in organic bulk heterojunctions and for design of optoelectronic devices.
Measurement of the Optical Constants of Thin Metal Films by THz Differential Time Domain Spectroscopy
MA Feng-Ying, SU Jian-Po**, GONG Qiao-Xia, YANG Jing, DU Yan-Li, GUO Mao-Tian, YUAN Bin
Chin. Phys. Lett. 2011, 28 (9): 097803 .   DOI: 10.1088/0256-307X/28/9/097803
Abstract   PDF(pc) (624KB) ( 926 )
Three kinds of nanometer-scale metal films (Cr, Ni and Ti) with different thicknesses are fabricated. The complex refractive indices of the three metal films are quantitatively measured by using THz differential time-domain spectroscopy (THz-DTDS). The orders of the complex refractive indices of the thin metal films are equal to those of the reported values. Our results validated that THz-DTDS can be used to study the features of the ultra-thin metal films.
A Universal Formula for the Secondary Electron Yield of Metals at an Incident Angle of θ
XIE Ai-Gen**, ZHANG Jian, WANG Tie-Bang
Chin. Phys. Lett. 2011, 28 (9): 097901 .   DOI: 10.1088/0256-307X/28/9/097901
Abstract   PDF(pc) (679KB) ( 2037 )
Based on the main physical processes, we deduce the relationships among the incident energy Wp0 of the primary electron, the number of released secondary electrons (i.e. δPEθ) per primary electron entering the metal at incident angle θ and the angle θ itself. In addition, the relationship of δ PEθ at θ = 0°, i.e. δPE0, with Wp0 is determined. From the experimental results, the relationship of the ratio at θ = 0°, i.e. β0 which is the ratio of the average number of released secondary electrons generated by a single primary electron backscattered at the metal surface to that generated by a single primary electron entering the metal, with Wp0 is determined. Moreover, the relationships among the ratio βθ , Wp0 and θ are obtained. Based on the relationships among the secondary electron yield at θ (i.e. δθ), the yield at θ = 0° (i.e. δ0), the backscattering coefficient at θ (i.e. ηθ), the coefficient at θ = 0° (i.e. η0), δPEθ and δPE0, we deduce the universal formula for δθ0, ηθ, η0, and Wp0 for the primary electrons at an incident energy of 2–10 keV. The secondary electron yields calculated from the universal formula and the experimental yields of some metals are compared, and the results suggest that the proposed formula is universal for estimation of secondary electron yields at θ=0°−80°.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Epitaxial Growth of 4H-SiC on 4° Off-Axis Substrate for Power Devices
LI Zhe-Yang, **, HAN Ping, LI Yun, NI Wei-Jiang, BAO Hui-Qiang, LI Yu-Zhu
Chin. Phys. Lett. 2011, 28 (9): 098101 .   DOI: 10.1088/0256-307X/28/9/098101
Abstract   PDF(pc) (956KB) ( 593 )
Homo-epitaxial layers are successfully grown on Si-face 4° off−axis 4H-SiC substrates using the horizontal hot-wall chemical vapor deposition system. The smooth surface without morphological defects is obtained by the optimized in situ etching process and growth temperature. Schottky diodes fabricated on the epilayer present a typical IV characteristic. This is the first report of Schottky diodes fabricated on 4° off-axis 4H-SiC substrates made in China.
Anomalous Increase of Apparent Mass in a Silo due to Percolation
Ram Chand, Abdul Qadir, SHI Qing-Fan**, ZHENG Ning, SUN Gang**
Chin. Phys. Lett. 2011, 28 (9): 098301 .   DOI: 10.1088/0256-307X/28/9/098301
Abstract   PDF(pc) (660KB) ( 364 )
The apparent mass at the bottom of a granular pile confined in a vertical tube decreases for denser granular packing. We report that the denser granular packing comprising two different diameters of granules augments the apparent mass instead. This anomalous behavior occurs when small granules are stacked on the large ones. In the case of anomalous increase, a percolation effect is found and correlated with the augment of apparent mass at the bottom of the granular column. Finally, the results are qualitatively explained by using the Janssen model.
Influence of Size of ZnO Nanorods on Light Extraction Enhancement of GaN-Based Light-Emitting Diodes
DAI Ke-Hui, **, WANG Lian-Shan**, HUANG De-Xiu, SOH Chew-Beng, CHUA Soo-Jin,
Chin. Phys. Lett. 2011, 28 (9): 098501 .   DOI: 10.1088/0256-307X/28/9/098501
Abstract   PDF(pc) (2494KB) ( 512 )
We investigate the influence of size of ZnO nanorods on the light extraction efficiency (LEE) enhancement of GaN-based light-emitting diodes (GaN-LEDs). ZnO nanorods with different sizes are hydrothermally grown on patterned indium-doped tin oxide (ITO) electrodes of the GaN-LEDs in zinc acetate aqueous solutions of different concentrations. Measurements are conducted for the LEE enhancement of the LEDs with ZnO nanorods, compared to these without ZnO nanorods. The results suggest that the LEE of the LEDs with ZnO nanorods increases with the increasing size of ZnO nanorods. However, a saturation trend for the LEE improvement is also observed, which is attributed to the maximum limitation of light coupled into ZnO nanorods from GaN-based LEDs, and the reflection is increased by the increasing top surface of the ZnO nanorods.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Field-Aligned Currents at the PSBL on 17 August 2001 Storm: Relationships with solar Wind Conditions
CHENG Zheng-Wei**, SHI Jian-Kui, ZHANG Tie-Long, WANG Sheng-Guo, LIU Zhen-Xing
Chin. Phys. Lett. 2011, 28 (9): 099401 .   DOI: 10.1088/0256-307X/28/9/099401
Abstract   PDF(pc) (489KB) ( 388 )
Using magnetic field and plasma data acquired with Cluster spacecrafts, we investigate the relationship between the field-aligned currents (FACs) at the plasma sheet boundary layer (PSBL) and solar wind dynamic pressure, as well as the interplanetary magnetic field (IMF) By on 17 August 2001 storm. Our studies reveal that FAC density at the PSBL in the magnetotail in the storm time is controlled mainly by the solar wind dynamic pressure rather than IMF By. The FACs at the PSBL are associated with the low−altitude region-1 current and have the same polarity as region-1 current in the dawn sector. In the polar region, the footprints of the FACs at the PSBL expand equatorward. The data analysis also shows that a very strong FAC with a density over 40 nAm−2 appeared in this storm time when a substorm just occurred.
Original Articles
Evolution of the Brans–Dicke Parameter in Generalized Chameleon Cosmology
Mubasher Jamil*, D. Momeni**
Chin. Phys. Lett. 2011, 28 (9): 099801 .   DOI: 10.1088/0256-307X/28/9/099801
Abstract   PDF(pc) (412KB) ( 478 )
Motivated by an earlier study of Sahoo and Singh [Mod. Phys. Lett. A 17 (2002) 2409], we investigate the time dependence of the Brans–Dicke parameter ω(t) for an expanding Universe in the generalized Brans–Dicke Chameleon cosmology, and obtain an explicit dependence of ω(t) in different expansion phases of the Universe. Also, we discuss how the observed accelerated expansion of the observable Universe can be accommodated in the present formalism.
73 articles