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Volume 29 Issue 6
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GENERAL
Exact Solutions of Nonlinear Evolution Equations in Mathematical Physics Using the Modified Simple Equation Method
E. M. E. Zayed, S. A. Hoda Ibrahim
Chin. Phys. Lett. 2012, 29 (6): 060201 .   DOI: 10.1088/0256-307X/29/6/060201
Abstract   PDF(pc) (378KB) ( 1953 )
The modified simple equation method is employed to construct the exact solutions involving parameters of nonlinear evolution equations via the (1+1)-dimensional modified KdV equation, and the (1+1)-dimensional reaction-diffusion equation. When these parameters are taken to be special values, the solitary wave solutions are derived from the exact solutions. It is shown that the proposed method provides a more powerful mathematical tool for solving nonlinear evolution equations in mathematical physics.
The Reduction of Chazy Classes and Other Third-Order Differential Equations Related to Boundary Layer Flow Models
K. Fakhar, A. H. Kara
Chin. Phys. Lett. 2012, 29 (6): 060202 .   DOI: 10.1088/0256-307X/29/6/060202
Abstract   PDF(pc) (381KB) ( 1049 )
We study the symmetries, conservation laws and reduction of third-order equations that evolve from a prior reduction of models that arise in fluid phenomena. These could be the ordinary differential equations (ODEs) that are reductions of partial differential equations (PDEs) or, alternatively, PDEs related to given ODEs. In this class, the analysis includes the well-known Blasius, Chazy, and other associated third-order ODEs.
Exact Solutions to a Toda-Like Lattice Equation in 2+1 Dimensions
WU Yong-Qi
Chin. Phys. Lett. 2012, 29 (6): 060203 .   DOI: 10.1088/0256-307X/29/6/060203
Abstract   PDF(pc) (425KB) ( 563 )

A completely integrable Toda-like lattice equation in 2+1 dimensions is studied. Four kinds of exact solutions to this equation are derived by virtue of variable separation and the Hirota bilinear approach. The relations between each two solutions are also presented.

Weak Signal Frequency Detection Based on a Fractional-Order Bistable System
HE Gui-Tian, LUO Mao-Kang
Chin. Phys. Lett. 2012, 29 (6): 060204 .   DOI: 10.1088/0256-307X/29/6/060204
Abstract   PDF(pc) (1040KB) ( 564 )

We apply spectral power amplification to quantifying and investigating the phenomenon of stochastic resonance in fractional-order systems. Moreover, the frequency of the weak mixed signal is detected by a stochastic resonance mechanism together with a power spectrum. The corresponding numerical results demonstrate the effectiveness of the proposed methods.

Quantum Cyclotron Orbits of a Neutral Atom Trapped in a Triple Well with a Synthetic Gauge Field
WANG Qiang, YE Chong, FU Li-Bin
Chin. Phys. Lett. 2012, 29 (6): 060301 .   DOI: 10.1088/0256-307X/29/6/060301
Abstract   PDF(pc) (1467KB) ( 573 )
The strong effective magnetic fields with flux to the order of one flux quantum per plaquette has been realized for ultracold atoms, and the quantum cyclotron orbit of a single atom in a single plaquette exposed to the magnetic field was directly revealed recently [Phys. Rev. Lett. 107 (2011) 255301]. We study the quantum cyclotron orbits of a bosonic atom in a triple well with a synthetic gauge field, and find that the dynamics of the atom in real space is similar to a classical dynamic billiard. It is interesting that the billiard-like motion is a signature of the quantum evolution of the three-level system, and its behaviors are determined by the ratio of the two energy gaps of the three energy levels.
Macroscopic Quantum States and Quantum Phase Transition in the Dicke Model
LIAN Jin-Ling, ZHANG Yuan-Wei, LIANG Jiu-Qing
Chin. Phys. Lett. 2012, 29 (6): 060302 .   DOI: 10.1088/0256-307X/29/6/060302
Abstract   PDF(pc) (550KB) ( 497 )
The energy spectrum of Dicke Hamiltonians with and without the rotating wave approximation for an arbitrary atom number is obtained analytically by means of the variational method, in which the effective pseudo-spin Hamiltonian resulting from the expectation value in the boson-field coherent state is diagonalized by the spin-coherent-state transformation. In addition to the ground-state energy, an excited macroscopic quantum-state is found corresponding to the south- and north-pole gauges of the spin-coherent states, respectively. Our results of ground-state energies in exact agreement with various approaches show that these models exhibit a zero-temperature quantum phase transition of the second order for any number of atoms, which was commonly considered as a phenomenon of the thermodynamic limit with the atom number tending to infinity. The critical behavior of the geometric phase is analyzed.
Quantum Teleportation between Two Distant Bose–Einstein Condensates
GUO Yu, LUO Xiao-Bing
Chin. Phys. Lett. 2012, 29 (6): 060303 .   DOI: 10.1088/0256-307X/29/6/060303
Abstract   PDF(pc) (507KB) ( 521 )

We propose protocols for quantum teleportation of superposed coherent states of atomic Bose–Einstein condensates. We use the photon entanglement states as the quantum channel, which makes it possible to realize the distant teleportation of atomic states. Two robust protocols are introduced: one is a single-photon scheme in which an entangled single-photon state serves as the quantum channel, and the other is a multi-photon scheme where an entangled coherent state of the probe lasers is used as the quantum channel.

Experimental Generation of Multimode Squeezing in an Optical Parametric Amplifier
LIU Kui, CUI Shu-Zhen, YANG Rong-Guo, ZHANG Jun-Xiang, GAO Jiang-Rui
Chin. Phys. Lett. 2012, 29 (6): 060304 .   DOI: 10.1088/0256-307X/29/6/060304
Abstract   PDF(pc) (775KB) ( 585 )

We experimentally demonstrate that HG01 (Hermit–Gauss) and HG10 squeezed states can be generated simultaneously in an optical parametric amplifier. The HG01 mode is a bright squeezed state and the HG10 mode is a vacuum squeezed state. The squeezing of the HG01 mode is -2.8 dB, and the squeezing of the HG10 mode is -1.6 dB. We also demonstrate that the output field is also continuous-variable entanglement with orbital angular momentum.

Quantum Discord and Entanglement in Heisenberg XXZ Spin Chain after Quenches
REN Jie, WU Yin-Zhong, ZHU Shi-Qun
Chin. Phys. Lett. 2012, 29 (6): 060305 .   DOI: 10.1088/0256-307X/29/6/060305
Abstract   PDF(pc) (714KB) ( 659 )
Using the adaptive time-dependent density-matrix renormalization group method, the dynamics of entanglement and quantum discord of an one-dimensional spin-1/2 XXZ chain is studied when anisotropic interaction quenches are applied at different temperatures. The dynamics of the quantum discord and pairwise entanglement between the nearest qubits shows that the entanglement and quantum discord will first oscillate and then approach to a constant value. The quantum discord can be used to predict the quantum phase transition, while the entanglement cannot.
Energy Spectra of the Coulomb Perturbed Potential in N-Dimensional Hilbert Space
Ramesh Kumar, Fakir Chand
Chin. Phys. Lett. 2012, 29 (6): 060306 .   DOI: 10.1088/0256-307X/29/6/060306
Abstract   PDF(pc) (398KB) ( 554 )

We deal with the solutions to the radial Schröinger equation for the Coulomb perturbed potential in N-dimensional Hilbert space by using two methods, i.e. the power series technique via a suitable ansatz to the wavefunction and the Virial theorem. Analytic expressions for eigenvalues and normalized eigenfunctions are derived. A recursion relation among series expansion coefficients, a condition for convergence of series and inter-dimensional degeneracies are also investigated. As special cases, the problem is solved in 3 and 4 dimensions with some specific parameter values. The obtained analytical and numerical results are in good agreement with the results of other studies.

Solutions to the Klein–Gordon Equation with Equal Scalar and Vector Modified Hylleraas Plus Exponential Rosen Morse Potentials
Akpan N. Ikot
Chin. Phys. Lett. 2012, 29 (6): 060307 .   DOI: 10.1088/0256-307X/29/6/060307
Abstract   PDF(pc) (380KB) ( 643 )

We present the bound-state solutions to the Klein–Gordon equation with equal scalar and vector modified Hylleraas plus exponential Rosen Morse potentials using the parametric Nikiforov–Uvarov method. We use the elegant approximation scheme to the centrifugal term. The bound state energy eigenvalues and the corresponding wave function are obtained. We also discuss the special cases.

Influence of the Earth's Rotation on Measurement of Newton's Constant by using the Angular Acceleration Method
LUO Jie, SHAO Cheng-Gang, WANG Dian-Hong, TIAN Yuan
Chin. Phys. Lett. 2012, 29 (6): 060401 .   DOI: 10.1088/0256-307X/29/6/060401
Abstract   PDF(pc) (446KB) ( 542 )

Using the relativistic Lagrangian expression, we develop a method to derive the equation of motion of the torsion balance in a non-inertial reference frame, which is used to analyze the gravitational experiment in measuring Newton's constant G with the angular acceleration method. Our calculation shows that the Earth's rotation couples with the vibration, which should be considered in the high?accuracy experiments of determining the gravitational constant G.

Bifurcation and Stability Analysis of the Hamiltonian–Casimir Model of Liquid Sloshing
Salman Ahmad, YUE Bao-Zeng
Chin. Phys. Lett. 2012, 29 (6): 060501 .   DOI: 10.1088/0256-307X/29/6/060501
Abstract   PDF(pc) (739KB) ( 570 )

Motion stability of a spacecraft is discussed. A canonical Hamiltonian model for liquid sloshing is presented for a moving rigid body. An equivalent mechanical pendulum model is used to represent the fuel slosh inside the container. In this model sloshing is represented by the moving mass, the rest of the mass of the spacecraft is assumed to be stationary. The spacecraft structure is considered to be an elliptical rigid shape and the steady rotation along the x-axis is taken as the major-axis rotation. Motion stability for the present model is analyzed using the Lyapunov theory with Casimir energy functions. Conditions for stability and instability are derived for a steady principal axis rotation of the rigid body. Simulation results are presented to distribute the region into stable and unstable regions. Besides this, the nonlinear behavior of the system is analyzed under the influence of an external force acting periodically. Chaos is observed through a bifurcation diagram. The time history map and phase portrait are also presented to analyze the nonlinear behavior of the system.

Modified Homotopy Perturbation Method for Certain Strongly Nonlinear Oscillators
NIU Yao-Bin, WANG Zhong-Wei, DONG Si-Wei
Chin. Phys. Lett. 2012, 29 (6): 060502 .   DOI: 10.1088/0256-307X/29/6/060502
Abstract   PDF(pc) (430KB) ( 547 )

A new modified homotopy perturbation method is presented for strongly non-linear oscillation by coupling the homotopy perturbation method and the modified Lindstedt–Poincaré method. The advantage of this method is that it does not need a small parameter in the physical system as in He's homotopy perturbation method, and the accuracy is greatly improved. Some examples are tested, and the obtained results show that the current method is very effective and convenient for solving strongly nonlinear oscillators.

Role of the Bath Spectrum in the Specific Heat Anomalies of a Damped Oscillator
BAI Zhan-Wu
Chin. Phys. Lett. 2012, 29 (6): 060503 .   DOI: 10.1088/0256-307X/29/6/060503
Abstract   PDF(pc) (462KB) ( 432 )

The specific heat anomalies are analytically studied in the system in which a harmonic oscillator couples to a heat bath with harmonic noise. The physical explanation leads to a general spectral dependence of the specific heat anomalies. The condition of a dip appearance and the behaviors of the dip can be given according to the shape of the bath's power spectrum by employing the minimal heat bath model.

Study on Congestion and Bursting in Small-World Networks with Time Delay from the Viewpoint of Nonlinear Dynamics
LIU Yan, LIU Li-Guang, WANG Hang
Chin. Phys. Lett. 2012, 29 (6): 060504 .   DOI: 10.1088/0256-307X/29/6/060504
Abstract   PDF(pc) (1215KB) ( 372 )
The small-world network model represented by a set of evolution equations with time delay is used to investigate the nonlinear dynamics of networks, and the nature of instability phenomena in traffic, namely, congestion and bursting in the networks, are studied and explained from bifurcation analysis. Then, the governing equation in the vector field is further reduced into a map, and the ensuing period-doubling bifurcation, sequence of period-doubling bifurcation and period-3 are studied intuitively. The existence of chaos is verified numerically. In particular, the influences of time delay on the nonlinear dynamics are presented. The results show that there are a rich variety of nonlinear dynamics related to the intermittency of the traffic flows in the system, and the results can gain a fundamental understanding of the instability in the networks, and the time delay can be used as a key parameter in the control of the systems.
Variational Approach for Fractional Diffusion-Wave Equations on Cantor Sets
WU Guo-Cheng, WU Kai-Teng
Chin. Phys. Lett. 2012, 29 (6): 060505 .   DOI: 10.1088/0256-307X/29/6/060505
Abstract   PDF(pc) (406KB) ( 543 )

The fractional variational iteration method is used to investigate the diffusion-wave problem on Cantor sets. The approximate solution is obtained in forms of fractional differentiable functions.

Dynamics in the Parameter Space of a Neuron Model
Paulo C. Rech
Chin. Phys. Lett. 2012, 29 (6): 060506 .   DOI: 10.1088/0256-307X/29/6/060506
Abstract   PDF(pc) (4580KB) ( 442 )
Some two-dimensional parameter-space diagrams are numerically obtained by considering the largest Lyapunov exponent for a four-dimensional thirteen-parameter Hindmarsh–Rose neuron model. Several different parameter planes are considered, and it is shown that depending on the combination of parameters, a typical scenario can be preserved: for some choice of two parameters, the parameter plane presents a comb-shaped chaotic region embedded in a large periodic region. It is also shown that there exist regions close to these comb-shaped chaotic regions, separated by the comb teeth, organizing themselves in period-adding bifurcation cascades.
Amplitude Oscillations of the Resonant Phenomena in a Frenkel–Kontorova Model with an Incommensurate Structure
YAN Yan-Zong, WANG Cang-Long, SHAO Zhi-Gang, YANG Lei
Chin. Phys. Lett. 2012, 29 (6): 060507 .   DOI: 10.1088/0256-307X/29/6/060507
Abstract   PDF(pc) (531KB) ( 431 )
Dynamical mode locking phenomena in incommensurate structures of the dc- and ac-driven overdamped Frenkel–Kontorova model are studied by molecular-dynamics simulations. It is found that the Shapiro steps exhibit significantly different amplitude and frequency dependences from the ones observed in the commensurate structures. The step widths still oscillate with the amplitude, but the form is no longer Bessel-like, i.e., the anomaly appears in our simulations. The same type of anomalies is also exhibited by the critical depinning force. The oscillatory behavior and the anomalies are also revealed in the (F,Fac) phase diagram where three phases are observed. These oscillations are directly correlated with the existence and the stability of interference phenomena in real systems.
New Wronskian Form of the N-Soliton Solution to a (2+1)-Dimensional Breaking Soliton Equation
CUI Kai
Chin. Phys. Lett. 2012, 29 (6): 060508 .   DOI: 10.1088/0256-307X/29/6/060508
Abstract   PDF(pc) (384KB) ( 546 )
Soliton phenomena exist in nonlinear science and the financial field. By using the Wronskian technique, a new Wronskian condition is proposed for a (2+1)-dimensional breaking soliton equation. Moreover, with the help of the bilinear transformation, a new Wronskian form of the N-soliton solution is obtained for the (2+1)-dimensional breaking soliton equation.
Non-Rational Rogue Waves Induced by Inhomogeneity
HE Jing-Song, WANG You-Ying, LI Lin-Jing
Chin. Phys. Lett. 2012, 29 (6): 060509 .   DOI: 10.1088/0256-307X/29/6/060509
Abstract   PDF(pc) (2109KB) ( 546 )
The variable Sine–Gordon (VSG) equation is often used to model several kinds of systems with inhomogeneity and it can be realized by the management of dispersion and nonlinearity in optics and Feschbach resonance in Bose-Einstein condensates. We derive four new kinds of non-rational rogue wave (RW) of the VSG by using an explicit transformation and the designable integrability. These RWs have novel profiles and interesting internal structures. It is shown that the RW is induced by the inhomogeneity of the system modeled by the VSG. The theoretical prediction of the corresponding relations between the RWs and some extreme events in DNA is discussed.
Influence of Passivation Layers for Metal Grating-Based Quantum Well Infrared Photodetectors
LIU Dong, FU Yong-Qi, YANG Le-Chen, ZHANG Bao-Shun, LI Hai-Jun, FU Kai, XIONG Min
Chin. Phys. Lett. 2012, 29 (6): 060701 .   DOI: 10.1088/0256-307X/29/6/060701
Abstract   PDF(pc) (1213KB) ( 545 )

To improve absorption of quantum well infrared photodetectors (QWIPs), a coupling layer with metallic grating is designed and fabricated above the quantum well. The metal grating is composed of 100 nm Au film on top, and a 20-nm Ti thin layer between the Au film and the sapphire substrate is coated as an adhesion/buffer layer. To protect the photodetector from oxidation and to decrease leakage, a SiO2 film is deposited by means of plasma-enhanced chemical vapor deposition. A value of about 800 nm is an optimized thickness for the SiO2 applied in the metallic grating?based mid-infrared QWIP. In addition, a QWIP passivation layer is studied experimentally. The results demonstrate that the contribution from the layer is positive for metal grating coupling with the quantum well. The closer the permittivity of the two dielectric layers (SiO2 and the passivation layers), and the closer the two transmission peaks, the greater the QWIP enhancement will be.

Fatigue-Induced Micro-damage Characterization of Austenitic Stainless Steel 316 Using Innovative Nonlinear Acoustics
Chung-Seok KIM, Kyung-Young JHANG
Chin. Phys. Lett. 2012, 29 (6): 060702 .   DOI: 10.1088/0256-307X/29/6/060702
Abstract   PDF(pc) (541KB) ( 578 )
We present innovative nonlinear acoustics for characterizing fatigue-induced micro-damage of austenitic stainless steel 316 subjected to high-cycle fatigue. Various fatigue-driven deformations are accumulated at several positions near the middle of hourglass-shaped specimens. A bell-shaped curve of acoustic nonlinearity as a function of position is observed, and the variation in acoustic nonlinearity is attributed to the evolution of a lattice defect (dislocation) and stress-induced martensite based on transmission electron microscopy (TEM) observations. An oblique incidence technique using a longitudinal waveform is a potentially viable method for characterizing the high-cycle fatigue deformation of austenitic stainless steel 316 alloys.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
An Improved Quasi-particle Model Framework for Quark-Gluon Plasma from the Path Integral Formalism
CAO Jing, ZHAO A-Meng, SUN Wei-Min, ZONG Hong-Shi
Chin. Phys. Lett. 2012, 29 (6): 061201 .   DOI: 10.1088/0256-307X/29/6/061201
Abstract   PDF(pc) (436KB) ( 448 )
An improved framework for the quasi-particle model is presented. Unlike the previous approach of establishing the quasi-particle model, we introduce a classical background field (it is allowed to depend on temperature) to deal with the infinity of thermal vacuum energy which exists in previous quasi-particle models. After taking into account the effect of this classical background field, the partition function of the quasi-particle system can be well defined. Based on this and following the standard ensemble theory, we construct a thermodynamically consistent quasi-particle model without the need to reformulate the statistical mechanics or the thermodynamic consistency relation. It is shown that our method is general and can be generalized to the case in which the effective mass depends not only on the temperature but also on the chemical potential.
NUCLEAR PHYSICS
The Symmetry Energy from the Neutron-Rich Nucleus Produced in the Intermediate-Energy 40,48Ca and 58,64Ni Projectile Fragmentation
MA Chun-Wang, PU Jie, WANG Shan-Shan, WEI Hui-Ling
Chin. Phys. Lett. 2012, 29 (6): 062101 .   DOI: 10.1088/0256-307X/29/6/062101
Abstract   PDF(pc) (543KB) ( 391 )
In the framework of a modified Fisher model, using the isobaric yield ratio method, we investigate the fragments produced in the 140 A MeV 40,48Ca+9Be and 58,64Ni+9Be projectile fragmentation reactions. Using different approximation methods, asym/T (the ratio of symmetry?energy coefficient to temperature) of symmetric and neutron-rich fragments are extracted. It is found that asym/T of fragments depend on the reference nucleus and the neutron excess of fragments. The asym/T of the isobar decreases when the neutron?excess of the isobar increases, while for a fragment with the same neutron-excess, asym/T increases as the mass of the fragment increases but saturate when the mass of the fragment becomes larger.
High Spin States of 113In
MA Ke-Yan, LU Jing-Bin, YANG Dong, LI Jian, WANG Hui-Dong, LIU Yun-Zuo, WU Xiao-Guang, ZHU Li-Hua, ZHENG Yun, HE Chuang-Ye
Chin. Phys. Lett. 2012, 29 (6): 062102 .   DOI: 10.1088/0256-307X/29/6/062102
Abstract   PDF(pc) (608KB) ( 457 )
Level structures of 113In are studied through the fusion-evaporation reaction 110Pd(7Li,4n)113In at a beam energy of 50 MeV. Two new bands are established for the first time. Here the ΔI = 2 band based on proton excitation is assigned to the πg9/2-2νh11/22d5/2 configuration. In addition, the backbending associated with the additional aligned h11/2 neutron pair is found in the negative parity yrast band. The experimental results are compared with self-consistent tilted axis cranking relativistic mean field calculations. Several decay paths of the πh11/2 intruder band are established, by which the level energies and spins of the πh11/2 intruder band are determined. The bandcrossing delay of the πh11/2 intruder bands around the Z=50 shell and the dynamic moment of inertia of the πg9/2-1νh11/22 bands in 113,115,117,119In are studied systematically.
High-Spin Structure in Odd-Odd 160Lu Nucleus
WANG Lie-Lin, LU Jing-Bin, YANG Dong, MA Ke-Yan, ZHOU Yin-Hang, YIN Li-Chang, WU Xiao-Guang, WEN Shu-Xian, LI Guang-Sheng, YANG Chun-Xiang
Chin. Phys. Lett. 2012, 29 (6): 062103 .   DOI: 10.1088/0256-307X/29/6/062103
Abstract   PDF(pc) (566KB) ( 365 )
The high-spin states of 160Lu are populated by the fusion-evaporation reaction 144Sm(19F,3n)160Lu at beam energies of 90 and 106 MeV. A new level scheme of 160Lu is established. A possible isomeric state based on the πh11/2νh9/2 configuration is observed. The new decoupled band with the configuration of πd3/2[411]1/2+νi13/2[660]1/2+ is established, and the configurations of these similar decoupled bands in the neighboring odd-odd 162-166Lu nuclei are suggested. A positive parity coupled band is assigned as the πd5/2 [402]5/2+νi13/2[660]1/2+ configuration.
Symmetry Potential and Effective Mass with Consistent Three-Body Force
LI Zeng-Hua, ZUO Wei
Chin. Phys. Lett. 2012, 29 (6): 062104 .   DOI: 10.1088/0256-307X/29/6/062104
Abstract   PDF(pc) (622KB) ( 435 )
The momentum and isospin dependence of symmetry potential and effective mass in isospin asymmetric nuclear matter is investigated in the framework of the Brueckner–Hartree–Fock approach by adopting the realistic Bonn B two-body interaction in combination with a consistent microscopic three-body force. It is demonstrated that symmetry potentials at the normal density for different asymmetry parameters are in good agreement with the empirical value constrained by the experimental data, and the neutron and proton effective masses show strong isospin splitting with mn*>mp* on the whole range of asymmetry parameters. In the end, the density dependence of the Landau mass is displayed.
Radio-Frequency Power Test of a Four-Rod RFQ Accelerator for PKUNIFTY
ZENG Hong-Jin, LIU Ge, LU Yuan-Rong, CHEN Wei, ZHOU Quan-Feng, ZHU Kun, XIA Wen-Long, SHI Ben-Liang, GAO Shu-Li, YAN Xue-Qing, GUO Zhi-Yu, CHEN Jia-Er
Chin. Phys. Lett. 2012, 29 (6): 062901 .   DOI: 10.1088/0256-307X/29/6/062901
Abstract   PDF(pc) (1960KB) ( 717 )
A four-rod radio frequency quadruple (RFQ) accelerator is designed, manufactured, installed and commissioned for the Peking University Neutron Imaging Facility (PKUNIFTY). This 2699.6-mm-long RFQ accelerator with the mean aperture radius of 3.88 mm is operating at 201.5 MHz in pulse mode. An inter-electrode voltage of 70 kV is needed to accelerate the injected 50 keV 40 mA D+ ions up to 2 MeV. We present the rf system, high rf power feeder design, lower rf measurements and higher rf power test. Especially, the rf commissioning was carried out with rf power up to ~280 kW and duty factor of 4%. The measured x-ray spectrum shows that the rf inter-electrode voltage reaches 70.7 kV. It is found that the specific shunt impedance of the RFQ cavity reaches 52.7 kΩ⋅m.
ATOMIC AND MOLECULAR PHYSICS
Relativistic Quadrupole Polarizability for the Ground State of Hydrogen-Like Ions
ZHANG Yong-Hui, TANG Li-Yan, ZHANG Xian-Zhou, SHI Ting-Yun, Jim Mitroy
Chin. Phys. Lett. 2012, 29 (6): 063101 .   DOI: 10.1088/0256-307X/29/6/063101
Abstract   PDF(pc) (540KB) ( 441 )
The static quadrupole polarizabilities for hydrogen-like ions from Z=1 to Z=100 in the 1S1/2 ground state are calculated to high precision by solving the Dirac equation using the B-spline Galerkin method. The results are consistent with the expression of Kaneko [J. Phys. B 10 (1977) 3347] at low Z. The quadrupole oscillator strength sum n fgn(2) is computed to be zero to a very high degree of precision.
Shake-up Processes in the 3d Photoionization of Sr I and the Subsequent Auger Decay
DING Xiao-Bin, DONG Chen-Zhong, Gerard O'Sullivan
Chin. Phys. Lett. 2012, 29 (6): 063201 .   DOI: 10.1088/0256-307X/29/6/063201
Abstract   PDF(pc) (516KB) ( 427 )
The shake-up processes accompanied by 3d photoionization and subsequent Auger decay are studied using multi-configuration Dirac–Fock methods. General agreement is obtained with the experimental results for both the photoelectron and Auger electron spectra. The energy and relative intensity of the 5s→6s shake-up accompanied by the 3d photoionization process are identified quantitatively.
Chaotic Dynamics of Triatomic Normal Mode Molecules
ZHAI Liang-Jun, ZHENG Yu-Jun, DING Shi-Liang
Chin. Phys. Lett. 2012, 29 (6): 063301 .   DOI: 10.1088/0256-307X/29/6/063301
Abstract   PDF(pc) (1070KB) ( 402 )
We investigate the chaotic dynamics of normal mode molecules from the classical point of view using the coupling Morse oscillators. New interesting phenomena of the fractured tori and the cross of tori on the Poincar-section, which go against our traditional understanding, are found and investigated. Also, we find that the phenomenon of tori cross is a signature of the single bond's energy beyond the total vibrational energy. Finally, a method to improve this scarcity is proposed.
The Rate Constant Calculations for the Reaction H(2S)+NH(X3Σ-) to N(4S)+H2 by using Quantum Mechanics Method
ZHAI Hong-Sheng, ZHOU Pan-Wang
Chin. Phys. Lett. 2012, 29 (6): 063401 .   DOI: 10.1088/0256-307X/29/6/063401
Abstract   PDF(pc) (550KB) ( 415 )
The quantum reactive scattering dynamics calculations are carried out over the collision energy range of 0–1.0 eV on the double many-body expansion (DMBE) potential energy surface reported by Poveda and Varandas [Phys. Chem. Chem. Phys. 7 (2005) 2867]. The reaction probabilities, integral cross-section and rate constants for the title reaction are calculated. The calculated rate constants are in agreement with the available experimental results at high temperature but lower than the experimental results at low temperature.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Electrostatic Levitation of Plant Seeds and Flower Buds
HU Liang, WANG Hai-Peng, LI Liu-Hui, WEI Bing-Bo
Chin. Phys. Lett. 2012, 29 (6): 064101 .   DOI: 10.1088/0256-307X/29/6/064101
Abstract   PDF(pc) (3419KB) ( 560 )
We report the electrostatic levitation of various kinds of seeds and flower buds. Coral berry and pepper near a spherical shape show a stable levitation state. The prolate ellipsoid soybean and flower buds are always "standing" in the free space with satisfactory levitation stability. For the irregular mushroom and wheat grain, the levitation state is characterized as a "top-heavy" posture. These special stable equilibrium states are proved by the analysis of surface charge distribution. The obtained saturation polarization charge of samples presents a good accordance with experimental data. The levitation ability is weighed by the factor m(εr+2)/(εrD2).
All-Fiber Gain-Switched Thulium-Doped Fiber Laser Pumped by 1.558μm Laser
ZHOU Ren-Lai, ZHAO Jie, YUANG-Chi, CHEN Zhao-Yu, JU You-Lun, WANG Yue-Zhu
Chin. Phys. Lett. 2012, 29 (6): 064201 .   DOI: 10.1088/0256-307X/29/6/064201
Abstract   PDF(pc) (738KB) ( 931 )
We present an all-fiber gain-switched thulium (Tm) doped fiber laser operating in the eye-safe region at 1940 nm. The fibre Bragg gratings (FBGs) inscribed by phase mask technology are used as cavity mirrors, and the transmission spectra of FBGs are also measured. The output characteristics are studied at pulse repetition frequencies of 10, 20 and 30 kHz, and the maximum output powers of 28.9, 67.0 and 71.0 mW are achieved under incident pump powers of 122, 247 and 250 mW. The narrowest pulse width of 29 ns and shortest pulse built-time of 140 ns are obtained at 10 kHz. The relation between pulse built-time and cavity length are discussed.
High-Stability Superfluorescent Fiber Source Based on an Er3+-Doped Photonic Crystal Fiber
LIU Cheng-Xiang, ZHANG Li, WU Xu, RUAN Shuang-Chen
Chin. Phys. Lett. 2012, 29 (6): 064202 .   DOI: 10.1088/0256-307X/29/6/064202
Abstract   PDF(pc) (716KB) ( 528 )
A superfluorescent fiber source (SFS) based on an Er3+-doped photonic crystal fiber (EDPCF) is reported. Owing to the temperature insensitivity of the EDPCF, we show that it is possible to improve the mean wavelength stability of an SFS. Using single-backward configuration, the EDPCF SFS mean wavelength variation at temperatures from -40°C to 60°C is less than 100 ppm, indicating that the thermal coefficient of the EDPCF is smaller than 1 ppm/°C and 3–6 times smaller than those of two conventional Er3+-doped fibers under the same experimental conditions. The best performance of the EDPCF-based SFS is obtained between 0°C and 60°C, at which the change in the mean wavelength is only 17.445 ppm.
Generation of Ultraviolet Radiation at 266 nm with RbBe2BO3F2 Crystal
WANG Li-Rong, WANG Gui-Ling, ZHANG Xin, LIU Li-Juan, WANG Xiao-Yang, ZHU Yong, CHEN Chuang-Tian
Chin. Phys. Lett. 2012, 29 (6): 064203 .   DOI: 10.1088/0256-307X/29/6/064203
Abstract   PDF(pc) (661KB) ( 851 )
High-average-power fourth-harmonic generation (4thHG) of an Nd:YAG laser is achieved with a RbBe2BO3F2 (RBBF) crystal. A maximum output power of 3 W at 266 nm is obtained. To our knowledge, this is the first time that efficient 4thHG is realized with RBBF. The angular bandwidth of 4thHG is also measured.
Characteristic Optimization of 1.3 μm High-Speed MQW InGaAsP-AlGaInAs Lasers
MAO Yi-Wei, WANG Yao, CHEN Yang-Hua, XUE Zheng-Qun, LIN Qi, DUAN Yan-Min, SU Hui
Chin. Phys. Lett. 2012, 29 (6): 064204 .   DOI: 10.1088/0256-307X/29/6/064204
Abstract   PDF(pc) (715KB) ( 1758 )
We investigate 1.3 μm multi quantum-well (MQW) lasers with InGaAsP (well) and InGaAlAs (barrier) on InP for high speed application, compared to the typical structures of InGaAsP (well)-InGaAsP (barrier)/InP and InGaAlAs (well)-InGaAlAs (barrier)/InP with the same quaternary in the well and barrier. We calculate the characteristics of band offset and gain of InGaAsP-AlGaInAs quantum wells (QWs). The advances of the new QW design are mainly rooted in the large ratio between conduction-band and valence-band offsets (ΔEcEv=7:1), higher than the typical value of 4:6 in InGaAsP-InGaAsP and 7:3 in InGaAlAs-InGaAlAs for 1.3 μm lasers. Due to the low confinement energy of holes, non-uniformity of carrier distribution over multi-InGaAsP-AlGaInAs QWs is significantly reduced. The enhancement of high-speed performance of InGaAsP-AlGaInAs MQW lasers is investigated in terms of turn-on oscillation.
Optical Torque Exerted on a Rotator under Illumination of a Vortex Beam
LI Dong-Hua, PU Ji-Xiong, WANG Xi-Qing
Chin. Phys. Lett. 2012, 29 (6): 064205 .   DOI: 10.1088/0256-307X/29/6/064205
Abstract   PDF(pc) (602KB) ( 384 )
We investigate the torque on a specially shaped rotator produced by a vortex beam. The formulas for the torque along x, y and z directions are derived, and numerical calculation is performed. It is found that for the specially shaped rotator, the torque brought by the Laguerre–Gauss (LG) vortex beam is dependent upon the angle of the facet for each part of the rotator, and the topological charge of the vortex beam. It is shown that torque is generated from both the light momentum and orbital angular momentum (OAM) of the incident vortex beam, indicating that we can control the rotation of the rotator by modulating the OAM of the incident light beam.
A Polarization-Adjustable Picosecond Deep-Ultraviolet Laser for Spin- and Angle-Resolved Photoemission Spectroscopy
ZHANG Feng-Feng, YANG Feng, ZHANG Shen-Jin, WANG Zhi-Min, XU Feng-Liang, PENG Qin-Jun, ZHANG Jing-Yuan, WANG Xiao-Yang, CHEN Chuang-Tian, XU Zu-Yan
Chin. Phys. Lett. 2012, 29 (6): 064206 .   DOI: 10.1088/0256-307X/29/6/064206
Abstract   PDF(pc) (484KB) ( 479 )
We report on a polarization-adjustable picosecond deep-ultraviolet (DUV) laser at 177.3 nm. The DUV laser was produced by second harmonic generation from a mode-locked laser at 355 nm in nonlinear optical crystal KBBF. The laser delivered a maximum average output power of 1.1 mW at 177.3 nm. The polarization of the 177.3 nm beam was adjusted with linear and circular polarization by means of λ/4 and λ/2 wave plates. To the best of our knowledge, the laser has been employed as the circularly polarized and linearly polarized DUV light source for a spin- and angle-resolved photoemission spectroscopy with high resolution for the first time.
A Tunable Ultrafast Source by Sum-Frequency Generation between Two Actively Synchronized Ultrafast Lasers
XUAN Hong-Wen, WANG Nan, ZHANG Yong-Dong, WANG Zhao-Hua, WEI Zhi-Yi
Chin. Phys. Lett. 2012, 29 (6): 064207 .   DOI: 10.1088/0256-307X/29/6/064207
Abstract   PDF(pc) (553KB) ( 486 )
We demonstrate an experimental setup of a tunable ultrafast laser source by sum-frequency generation (SFG) between a mode-locking Ti:sapphire laser and a Nd:YVO4 laser. The generated wavelength by SFG is tunable from 450 nm to 480 nm with timing jitter no more than 1 ps. The average output power is over 20 mW and the maximum is about 30 mW at 457 nm. This ultrafast laser is a simple and easy tuning source applied to some pump-probe spectroscopy and ultrafast dynamics experiments.
Beam Splitting in Induced Inhomogeneous Media
WANG Chun-Fang, BAI Yan-Feng, GUO Hong-Ju, CHENG Jing
Chin. Phys. Lett. 2012, 29 (6): 064208 .   DOI: 10.1088/0256-307X/29/6/064208
Abstract   PDF(pc) (540KB) ( 379 )
We study the spatial behavior of a deflected beam in a coherent Λ-type three-level atomic medium with an inhomogeneous control laser. When the Rabi coupling by the control laser is in a Gaussian profile, the spatial-dependent refraction index of the atomic medium will result in a beam splitting as well as the deflection of the slow probe light under electromagnetically induced transparency. In terms of the phase difference between the two splitting beams and the position of the splitting, the possible interpretation of the splitting is given in theory.
Experimental Study of Tunneling modes in Photonic Crystal Heterostructure Consisting of Single-Negative Materials
ZHANG Li-Wei, ZHANG Ye-Wen, HE Li, WANG You-Zhen
Chin. Phys. Lett. 2012, 29 (6): 064209 .   DOI: 10.1088/0256-307X/29/6/064209
Abstract   PDF(pc) (2924KB) ( 420 )
The pair structure and the photonic crystal heterostructure consisting of ε-negative and μ-negative materials are successfully fabricated by using the transmission line approach. We experimentally investigate the tunneling mode properties by simulating and measuring the scattering parameters and phase shifts. It is shown that the pair structure and the photonic crystal heterostructures possess tunneling modes when the general zero average permittivity and zero average permeability condition are satisfied. At the tunneling frequency, the field (voltage) mainly concentrates in the center of the constructed structures based on the amplification of the evanescent wave. Moreover, the tunneling mode of the photonic crystal heterostructure has zero phase delay. The characteristics have potential applications in design of zero phase delay filters.
Optical 90° Hybrid Based on an InP 4×4 Multimode Interference Coupler for Coherent Receiver Application
LIU Wei-Hua, ZHAO Yan-Li, XU Cheng-Zhi, ZHAO Jian-Yi, LIU Wen, XU Yuan-Zhong
Chin. Phys. Lett. 2012, 29 (6): 064210 .   DOI: 10.1088/0256-307X/29/6/064210
Abstract   PDF(pc) (761KB) ( 1228 )
An optical 90° hybrid based on an InP 4×4 multimode interference (MMI) coupler is designed and fabricated for the application in a coherent receiver. It reveals that the width of multimode waveguide is the most critical parameter for the devices, and the multimode waveguide width can be accurately controlled within 0.1 μm in our experiments. Across the entire C-band (1527–1561 nm), the maximum imbalance of the devices is less than 0.7 dB, and the common mode rejection ratios for in-phase channels and quadrature channels are better than -24 dB.
Self-Trapping of Three-Dimensional Spatiotemporal Solitary Waves in Self-Focusing Kerr Media
YANG Zheng-Ping, ZHONG Wei-Ping
Chin. Phys. Lett. 2012, 29 (6): 064211 .   DOI: 10.1088/0256-307X/29/6/064211
Abstract   PDF(pc) (1280KB) ( 486 )
We theoretically demonstrate that Kerr media under self-focusing nonlinearity support three-dimensional spatiotemporal solitary waves in various patterns, such as necklace-, disk-, and vortex-ring shapes. The structures of these solitons are defined by the set of radial, orbital, and azimuthal quantum numbers, (n,l,m), respectively.
The Laser Action of a Yb:CLNGG Crystal with an Efficiency Approaching Its Quantum Defect Imposed Limit
ZHOU Zhi-Chao, TIAN Xue-Ping, DAI Qi-Biao, HAN Wen-Juan, HUANG Jia-Yin, LIU Jun-Hai, ZHANG Huai-Jin
Chin. Phys. Lett. 2012, 29 (6): 064212 .   DOI: 10.1088/0256-307X/29/6/064212
Abstract   PDF(pc) (537KB) ( 451 )
Continuous-wave laser operation is demonstrated at room temperature with a new disordered Yb:CLNGG crystal. A maximum output power of 5.05 W is generated with 7.8 W of pump power absorbed in the crystal, resulting in an optical-to-optical efficiency of 65%, whereas the slope efficiency is determined to be 92%, approaching the limit imposed by the quantum defect in the laser emission process.
Self-Detection of Leaking Pipes by One-Dimensional Photonic Crystals
ZHOU Yan, YIN Li-Qun
Chin. Phys. Lett. 2012, 29 (6): 064213 .   DOI: 10.1088/0256-307X/29/6/064213
Abstract   PDF(pc) (423KB) ( 367 )
We report a new self-detection control system for leaking pipes by making use of the surface defects of 1D photonic crystals, where the key concept is analog to the Bragg fiber structure. The current low costs and coating techniques of SiO2 are beneficial to the applications, and its error is below the standard requirement. The problem of leaking pipes can be resolved by devising a remote pipeline control system which combines a long-distance pipeline and a signal transmission system.
A Surface Plasmon Polariton Electro-Optic Switch Based on a Metal-Insulator-Metal Structure with a Strip Waveguide and Two Side-Coupled Cavities
ZHU Yun-Jin, HUANG Xu-Guang, MEI Xian
Chin. Phys. Lett. 2012, 29 (6): 064214 .   DOI: 10.1088/0256-307X/29/6/064214
Abstract   PDF(pc) (455KB) ( 584 )
We propose and numerically simulate a nanoscale electro-optic (EO) switch based on a metal-insulator-metal structure composed of a strip waveguide and two side-coupled cavities filled with an EO material of 4-dimethyl-amino-N-methyl-4-stilbazolium tosylate, using the finite difference time domain method. It is found that the structure can be operated as an EO switch at a wavelength of 945 nm, with a modulation depth of 27 dB, a half-wave voltage of 5.3 V and a switching time of about 50 ps.
Flow-Noise Calculation Using the Mutual Coupling Between Vulcanized Rubber and the Flow Around in Water
LI Xue-Gang, YANG Kun-De, MA Yuan-Liang
Chin. Phys. Lett. 2012, 29 (6): 064301 .   DOI: 10.1088/0256-307X/29/6/064301
Abstract   PDF(pc) (2541KB) ( 519 )
A vulcanized rubber layer is usually used on the head of an axisymmetric body to keep it streamlined and watertight. The elastic boundary condition is considered when the flow noise of an axisymmetric body is calculated, and we employ the mutual coupling method between the vulcanized rubber layer and the flow around to solve the flow-noise field for an axisymmetric body in water. The results show that the deformation of the vulcanized rubber layer is reduced with the increase in Young's modulus. The Young's modulus of the rubber material should be large enough to keep it streamlined, and the noise power levels in the peak of the axisymmetric body are smaller than the other positions, which provides us with important theoretical support for laying acoustic arrays on the head of the body.
Broadband Attenuation in Phononic Beams Induced by Periodic Arrays of Feedback Shunted Piezoelectric Patches
WANG Jian-Wei, WANG Gang, CHEN Sheng-Bing, WEN Ji-Hong
Chin. Phys. Lett. 2012, 29 (6): 064302 .   DOI: 10.1088/0256-307X/29/6/064302
Abstract   PDF(pc) (903KB) ( 368 )
The effect of periodic arrays of feedback shunted piezoelectric patches in the flexural wave attenuation of phononic beams is analyzed theoretically and experimentally. A numerical model based on transfer matrix methodology is developed to predict the transmission of vibration and the frequency ranges of the band gaps. Broadband vibration attenuations are observed in or out of the band gaps. The proposed concept is validated on a suspended epoxy beam driven by a shaker, and the experimental results are presented in terms of the vibration transmissions recorded using two accelerometers placed on both sides of the beam.
Energy Measurement of Bubble Bursting Based on Vibration Signals
LIU Xiao-Bo, ZHANG Jian-Run, LI Pu, LE Van-Quynh
Chin. Phys. Lett. 2012, 29 (6): 064701 .   DOI: 10.1088/0256-307X/29/6/064701
Abstract   PDF(pc) (1678KB) ( 583 )
An experimental study of the energy of bubble bursting at the surface of a high-viscosity liquid on a cantilever beam is reported. The sudden bursting event of a bubble at the liquid surface can cause a vibration of the cantilever beam besides the acoustic wave and jet wave. The peaks of the vibration signal from the beam slightly lag the peaks of the acoustic signal, and the energy transferred to the vibration is larger than that transferred to the acoustic wave. The amplitude of the jet wave depends on the thickness of the liquid film and the size of the bubble. The results of the investigation can be used to understand the dynamic characteristics of bubble bursting.
A New Method of Simulating Fiber Suspensions and Applications to Channel Flows
YANG Wei, ZHOU Kun
Chin. Phys. Lett. 2012, 29 (6): 064702 .   DOI: 10.1088/0256-307X/29/6/064702
Abstract   PDF(pc) (464KB) ( 342 )
A successive iteration method is proposed to numerically simulate fiber suspensions. The computational field is discretized with the collocated finite volume method, and an ergodic hypothesis is adopted to greatly accelerate the solution to the Fokker–Planck equation. The method is employed in channel flows with different fiber volume fractions and aspect ratios, and its effectiveness is proved. The numerical results show that the existence of fibers significantly changes the pressure distribution, and the fiber aspect ratio has a greater effect on the velocity profile than on the volume faction. At the center of the channel, the velocity increases along the streamwise direction, while the velocity near the wall decreases slightly. The uncoupling and coupling solutions of the additional stress of the fiber suspensions are quite different.
A Computational Study of Cavitation Model Validity Using a New Quantitative Criterion
Hagar Alm El-Din, ZHANG Yu-Sheng, Medhat Elkelawy
Chin. Phys. Lett. 2012, 29 (6): 064703 .   DOI: 10.1088/0256-307X/29/6/064703
Abstract   PDF(pc) (558KB) ( 1152 )
The predictive capability of two different numerical cavitation models accounting for the onset and development of cavitation inside real-sized diesel nozzle holes is assessed on the basis of the referenced experimental data. The calculations performed indicate that for the same model assumptions, numerical implementation, discretization scheme, and turbulence grid resolution model, the predictions for differently applied physical cavitation sub-models are phenomenologically distinct from each other. We present a comparison by applying a new criterion for the quantitative comparison between the results obtained from both cavitation models.
Large-Eddy Simulation of Underexpanded Supersonic Swirling Jets
WANG Guo-Lei, LU Xi-Yun
Chin. Phys. Lett. 2012, 29 (6): 064704 .   DOI: 10.1088/0256-307X/29/6/064704
Abstract   PDF(pc) (725KB) ( 710 )
A large-eddy simulation of underexpanded supersonic swirling jets issuing into a quiescent environment was carried out for two typical swirl numbers. The corresponding nonswirling jet was also calculated for comparison and validation against the experimental data. The swirling effect on the various fundamental mechanisms that dictate the intricate flow phenomena, including flow features, shock cell structures, jet spreading characteristics and turbulence behaviors, was carefully analyzed, and it is found that the first shock cell length is reduced in the swirling jet in comparison with the nonswirling jet. A recirculation zone is formed in the high swirl number case, and the jet spreads quickly in the radial direction due to the swirling effect. Moreover, intensive turbulent fluctuations are generated along the jet shear layer and at the end of the jet potential core, which will be helpful in the mixing process. The obtained results provide a physical insight into understanding the mechanisms relevant to underexpanded supersonic swirling jets.
Reducing Spurious Velocities at the Interfaces of Two-Phase Flows for Lattice Boltzmann Simulations
WEI Yi-Kun, QIAN Yue-Hong
Chin. Phys. Lett. 2012, 29 (6): 064705 .   DOI: 10.1088/0256-307X/29/6/064705
Abstract   PDF(pc) (504KB) ( 820 )
Fractional propagation is used to reduce the spurious velocities for multiphase lattice Boltzmann models. The numerical results show that the maximum spurious velocity at the interfaces could be reduced effectively in comparison with some of the early models. Eight spurious eddies, which previously existed in the D2Q9 model at the interfaces of two-phase flows, are completely eliminated. Simulations are used to confirm these results using different parameters.
Fractal Analysis of Robertson-Stiff Fluid Flow in Porous Media
YUN Mei-Juan, ZHENG Wei
Chin. Phys. Lett. 2012, 29 (6): 064706 .   DOI: 10.1088/0256-307X/29/6/064706
Abstract   PDF(pc) (436KB) ( 466 )
The Robertson–Stiff (RS) fluid is the representative fluid which may be reduced to Bingham, power-law and Newtonian fluids under appropriate conditions. We present fractal models for the flow rate, velocity, starting pressure gradient and effective permeability for RS fluids in porous media based on the fractal characteristics of porous media and capillary models. The proposed models are expressed as functions of the fractal dimensions, porosity, maximum pore size and the representative length of the porous media. Every parameter in the proposed expressions has clear physical meaning, and the proposed models relate the flow characteristics of the RS fluids to the structural parameters of the porous media. The analytical expressions reveal the physical principles of RS fluid flow in porous media.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Electrostatic Dust Acoustic Solitons in Pair-Ion-Electron Plasmas
Hafeez Ur Rehman
Chin. Phys. Lett. 2012, 29 (6): 065201 .   DOI: 10.1088/0256-307X/29/6/065201
Abstract   PDF(pc) (467KB) ( 503 )
Using the reductive perturbation method, a Korteweg-de Vries (KdV) equation is derived to study the nonlinear properties of electrostatic collisionless dust acoustic solitons in pair-ion-electron (p-i-e) plasmas. The fluid model is chosen for positive ions, negative ions, and the fraction of electrons and charged (both positive and negative) dynamic dust particles. It is realized that electrostatic hump structures can be found when the dust particles are positively charged, and electrostatic dip structures can be detected for negatively charged dust particles. Numerical solutions for these dust acoustic solitons are plotted and their characteristics are discussed. It is found that the amplitude and width of the electrostatic dust acoustic solitons increase when the density of the dust particles and/or the temperature of the negative ions increases, and that the amplitude and width of these solitons decrease when the temperature of the positive ions increases. As pair-ion plasmas mimic electron-positron plasmas, our results might be helpful in understanding the nonlinear dust acoustic solitary waves in super dense astronomical bodies like neutron stars.
The Effect of Spectral Index Parameter κ on Obliquely Propagating Solitary Wave Structures in Magneto-Rotating Plasmas
S. Hussain
Chin. Phys. Lett. 2012, 29 (6): 065202 .   DOI: 10.1088/0256-307X/29/6/065202
Abstract   PDF(pc) (477KB) ( 529 )
Nonlinear ion-acoustic solitary wave structures in collisionless, non-relativistic, homogenous, magneto-rotating plasma, in which the electron species follow the kappa distribution function, are studied. The Korteweg-de Vries (KdV) equation is derived by using the reductive perturbation method, and the effects of different plasma parameters on the obliquely propagating nonlinear solitary wave structures in the magneto-rotating plasma are presented. It is noticed that the spectral index parameter κ significantly modifies the nonlinear wave structure.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Self Ordering of Nematic Liquid Crystal Molecules in HPDLC Bragg Gratings
CHENG Wen-Kai, GAO Bin, PU Hai-Hui, LIU Jian-Hua
Chin. Phys. Lett. 2012, 29 (6): 066101 .   DOI: 10.1088/0256-307X/29/6/066101
Abstract   PDF(pc) (734KB) ( 469 )
Using the simple treatments of back refilling and subsequent annealing above the clear point of the liquid crystal, the self ordering of liquid crystal molecules is observed in a holographic polymer dispersed liquid crystal (HPDLC) Bragg grating without orientational layers or mechanical rubbing. Transmittance curve fitted anisotropy of the liquid crystal (Δn) is in good agreement with its nominal value.
Laser-Induced Distortions and Disturbance Propagation of Delocalized Electronic States in Monatomic Carbon Chains
YANG Gong-Xian, GONG Xiu-Fang
Chin. Phys. Lett. 2012, 29 (6): 066102 .   DOI: 10.1088/0256-307X/29/6/066102
Abstract   PDF(pc) (613KB) ( 374 )
Tight-binding electron-ion dynamics of carbon chains pumped by intense laser pulses are performed to study the interactions between monatomic carbon chains and lasers. Laser-induced distortions of carbon chains, which are enhanced by a long wavelength laser, are investigated. The carbon chains with a strong laser beam focused on one terminal are simulated to study the disturbance of electronic states. By the superposition of delocalized π band states, the disturbance propagates from the illuminated area to the non-illuminated area in a velocity of about 106 m/s at 0 K, and this velocity is weakened at room temperature due to the localization effect of thermal fluctuation.
Cross-over of the Plasticity Mechanism in Nanocrystalline Cu
YUE Yong-Hai, WANG Li-Hua, ZHANG Ze, HAN Xiao-Dong
Chin. Phys. Lett. 2012, 29 (6): 066201 .   DOI: 10.1088/0256-307X/29/6/066201
Abstract   PDF(pc) (1222KB) ( 492 )
Via in situ uniaxial tensile tests in a high-resolution transmission electron microscope, we directly observed a cross-over of plastic deformation mechanisms in a nanocrystalline (nc) Cu thin film containing nano-twin lamellae. For a certain twin lamellae length, the twin lamellae with a larger thickness emit dislocations inclined (Schmidt-factor dislocations, i.e., S-dislocations) toward the twin boundaries. Upon decreasing the twin lamellae thickness to a critical value, such as approximately 15 nm, the plasticity switches toward emission of twinning partial dislocations (T-dislocations) parallel to the twin planes that cause migration of the twin boundaries. The critical twin thickness value also depends on the length of the twin. These results provide direct evidence for the strengthening and softening mechanisms in nano-twinning structured metals.
Theoretical Study of the Structural and Thermodynamic Properties of Amorphous SiO2 and Amorphous SiO2 with an Oxygen Defect Center
SU Wei, LOU Shu-Qin, YIN Guo-Lu
Chin. Phys. Lett. 2012, 29 (6): 066202 .   DOI: 10.1088/0256-307X/29/6/066202
Abstract   PDF(pc) (720KB) ( 726 )
Structural properties and thermodynamic properties of amorphous SiO2(a-SiO2) and amorphous SiO2 with an oxygen defect center (a-SiO2-ODC) are investigated by using interatomic pair potentials. Amorphous configurations of SiO2 glass are constructed by quenching using the molecular-dynamics method and subsequent relaxation using the first-principles method. The numerical result demonstrates that the calculated short-range structural parameters coincide well with the previous experimental and theoretical results reported. The thermodynamic properties including specific heat, Debye temperature, vibrational entropy, and so on are analyzed by calculating the phonon density. Furthermore, mechanical properties of both structures are obtained.
Nano-Metal Film Thermal Conductivity Measurement by using the Femtosecond Laser Pump and Probe Method
ZHU Li-Dan, SUN Fang-Yuan, ZHU Jie, TANG Da-Wei, LI Yu-Hua, GUO Chao-Hong
Chin. Phys. Lett. 2012, 29 (6): 066301 .   DOI: 10.1088/0256-307X/29/6/066301
Abstract   PDF(pc) (902KB) ( 1428 )
Heat management at nanoscale is a critical issue across many areas of science and engineering, where the size effect of thermal properties plays an important role. We measure the transient thermoreflectance signals of thin metal films with thicknesses from 50 to 200 nm by using the femtosecond laser pump and probe method, and the experimental data are combined with the parabolic two-step model to enable us to measure thermal conductivity of the thin metal films. The measurement results of Ni and Al films show that, in the thickness range from tens to hundreds of nanometer, the thermal conductivity increases with the increasing thicknesses of the films, which agrees well with the previous conclusions.
The Structural Modification of LiTaO3 Crystal Induced by 100-keV H-ion Implantation
PANG Li-Long, WANG Zhi-Guang, YAO Cun-Feng, ZANG Hang, LI Yuan-Fei, SUN Jian-Rong, SHEN Tie-Long, WEI Kong-Fang, ZHU Ya-Bin, SHENG Yan-Bin, CUI Ming-Huan, JIN Yun-Fan
Chin. Phys. Lett. 2012, 29 (6): 066801 .   DOI: 10.1088/0256-307X/29/6/066801
Abstract   PDF(pc) (662KB) ( 1258 )
The effects of 100 keV H-ion implantation on the structure of LiTaO3 crystal are investigated by Raman and UV/VIS/NIR spectroscopies. The implantation fluence is in the range from 1.0×1013 to 1.0×1017 H+/cm2. The experimental results show the dependence of the crystal structure on ion fluence. It is found that the structural modification of the LiTaO3 crystal is due to two processes. One is H?ions occupying lithium vacancies (VLi), which is predominant at a fluence less than 1.0×1014 H+/cm2. This process causes the reduction of negative charge centers in the crystal and relaxation of distortion in the local lattice structure. The other is the influence of defects created during implantation, which plays a dominant role gradually in the structural modification at a fluence larger than 1.0×1015 H+/cm2.
Modulation of Step Heights of Thin Pb Films by the Quantum Size Effect Observed by Non-Contact Atomic Force Microscopy
MAO Han-Qing, LI Na, CHEN Xi, XUE Qi-Kun
Chin. Phys. Lett. 2012, 29 (6): 066802 .   DOI: 10.1088/0256-307X/29/6/066802
Abstract   PDF(pc) (880KB) ( 408 )
Using a home-made Q-plus sensor, simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) measurements were performed on the wedge-shaped Pb islands grown on Si(111)-7-7. Atomic resolved AFM images were observed. The contrast of AFM topography shows no dependence on the sample bias (tip is grounded), while the simultaneously obtained tunneling current image exhibits strong bias dependence due to quantum well states (QWS). Furthermore, In the AFM mode, neighboring Pb films with one monolayer (ML) thickness difference within the same Pb island show the same apparent height, which means that the apparent step heights of Pb films oscillate with a bilayer periodicity, being consistent with previous observations by helium atom scattering, x-ray diffraction, and STM. The possible reasons underlying the oscillation of apparent step heights in AFM topography are discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Coupled Optical Tamm States in a Planar Dielectric Mirror Structure Containing a Thin Metal Film
ZHOU Hai-Chun, YANG Guang, WANG Kai, LONG Hua, LU Pei-Xiang
Chin. Phys. Lett. 2012, 29 (6): 067101 .   DOI: 10.1088/0256-307X/29/6/067101
Abstract   PDF(pc) (505KB) ( 580 )
The coupling between two optical Tamm states (OTSs) with the same eigenenergy is numerically investigated in a planar dielectric mirror structure containing a thin metal film. The reflectivity map in this structure at normal incidence is obtained by applying the transfer matrix method. Two splitting branches appear in the photonic bandgap region when both adjacent dielectric layers of metal film are properly set. The splitting energy of two branches strongly depends on the thickness of the metal film. According to the electric field distribution in this structure, it is found that the high-energy branch corresponds to the antisymmetric coupling between two OTSs, while the low-energy branch is associated with the symmetric coupling between two OTSs. Moreover, the optical difference frequency of two branches is located in a broad terahertz region.
Numerical Analysis of Efficiency Enhancement in Plasmonic Thin-Film Solar Cells by Using the SILVACO TCAD Simulator
KIM Un-Chol, JIANG Xiao-Qing
Chin. Phys. Lett. 2012, 29 (6): 067301 .   DOI: 10.1088/0256-307X/29/6/067301
Abstract   PDF(pc) (1105KB) ( 1638 )
A physical model for simulating plasmonic solar cells (SCs) using the SILVACO TCAD simulator is established and the effects of some factors on the efficiency enhancement of the amorphous silicon thin film SCs are simulated. Through this simulation, it is demonstrated that our method can successfully simulate the optical and electrical properties of plasmonic solar cells without the overestimation of the characteristics and without the neglect of parameter change in the device operation process. It is shown that not only the size and kind of metal nanoparticles but also other factors, such as the surrounding medium, the distance from the bottom of particles to the device surface, and the light incident angle, play important roles in the optical and electrical properties of plasmonic SCs.
Impact of Interfacial Trap Density of States on the Stability of Amorphous InGaZnO-Based Thin-Film Transistors
HUANG Xiao-Ming, WU Chen-Fei, LU Hai, XU Qing-Yu, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2012, 29 (6): 067302 .   DOI: 10.1088/0256-307X/29/6/067302
Abstract   PDF(pc) (615KB) ( 2513 )
The impact of interfacial trap states on the stability of amorphous indium-gallium-zinc oxide thin film transistors is studied under positive gate bias stress. With increasing stress time, the device exhibits a large positive drift of threshold voltage while maintaining a stable sub-threshold swing and a constant field-effect mobility of channel electrons. The threshold voltage drift is explained by charge trapping at the high-density trap states near the channel/dielectric interface, which is confirmed by photo-excited charge-collection spectroscopy measurement.
Effect of Cleaving Temperature on the Surface and Bulk Fermi Surface of Sr2RuO4 Investigated by High Resolution Angle-Resolved Photoemission
LIU Shan-Yu, ZHANG Wen-Tao, WENG Hong-Ming, ZHAO Lin, LIU Hai-Yun, JIA Xiao-Wen, LIU Guo-Dong, DONG Xiao-Li, ZHANG Jun, MAO Zhi-Qiang, CHEN Chuang-Tian, XU Zu-Yan, DAI Xi, FANG Zhong, ZHOU Xing-Jiang
Chin. Phys. Lett. 2012, 29 (6): 067401 .   DOI: 10.1088/0256-307X/29/6/067401
Abstract   PDF(pc) (743KB) ( 349 )
High resolution angle-resolved photoemission measurements are carried out to systematically investigate the effect of cleaving temperature on the electronic structures and Fermi surfaces of Sr2RuO4. Unlike previous reports, which found that a high cleaving temperature can suppress the surface Fermi surface, we find that the surface Fermi surface remains obvious and strong in Sr2RuO4 cleaved at high temperature, even at room temperature. This indicates that cleaving temperature is not a key effective factor in suppressing surface bands. On the other hand, the bulk bands can be enhanced in an aged surface of Sr2RuO4 that has been cleaved and held for a long time. We have also carried out laser ARPES measurements on Sr2RuO4 by using a vacuum ultra-violet laser (photon energy at 6.994 eV) and found an obvious enhancement of bulk bands even for samples cleaved at low temperature. This information is important for realizing an effective approach to manipulating and detecting the surface and bulk electronic structure of Sr2RuO4. In particular, the enhancement of bulk sensitivity, along with the super-high instrumental resolution of VUV laser ARPES, will be advantageous in investigating fine electronic structure and superconducting properties of Sr2RuO4 in the future.
NMR Study of Superconductivity and Spin Fluctuations in Hole-Doped Superconductor Ca1-xNaxFe2As2 (Tc=32 K)
MA Long, ZHANG Jin-Shan, WANG Du-Ming, HE Jun-Bao, XIA Tian-Long, CHEN Gen-Fu, YU Wei-Qiang
Chin. Phys. Lett. 2012, 29 (6): 067402 .   DOI: 10.1088/0256-307X/29/6/067402
Abstract   PDF(pc) (1035KB) ( 477 )
We report both 23Na and 75As nuclear magnetic resonance (NMR) studies on hole?doped Ca1-xNaxFe2As2 superconducting single crystals (x≈0.67) with the superconducting temperature Tc=32 K. Singlet superconductivity is suggested by a sharp drop of the Knight shift 75K below Tc. The spin-lattice relaxation rate 1/T1 does not show the Slichter–Hebel coherence peak, which suggests an unconventional pairing. The penetration depth is estimated to be 0.24 μm at temperature T=2 K. Here 1/75T1T shows an anisotropic behavior and a prominent low-temperature upturn , with 75T1 denoting the 75As spin-lattice relaxation time and T the temperature, which indicates strong low-energy antiferromagnetic spin fluctuations and supports a magnetic origin of superconductivity.
Effect of Carrier Differences on Magnetoresistance in Organic and Inorganic Spin Valves
YUAN Xiao-Bo, REN Jun-Feng, HU Gui-Chao
Chin. Phys. Lett. 2012, 29 (6): 067501 .   DOI: 10.1088/0256-307X/29/6/067501
Abstract   PDF(pc) (568KB) ( 433 )
Magnetoresistance in the structure of ferromagnetic/nonmagnetic/ferromagnetic spin valves are studied theoretically from the spin diffusion theory and Ohm's law. The nonmagnetic layer could be an organic or inorganic semiconductor. Carrier mobility and the spin-flip time in organic semiconductors are different from those in inorganic semiconductors, and effects of these differences on the magnetoresistance in organic and inorganic spin valves are discussed. From the calculation, it is found that the magnetoresistance in inorganic spin valves is higher than that in organic spin valves. Effects of the conductivity matching and spin-dependent interfacial resistances between ferromagnetic and nonmagnetic layers, thickness of the nonmagnetic layer, and the bulk spin polarization of the ferromagnetic layer on the magnetoresistance are also discussed.
Terahertz Emission of Ferromagnetic Ni-Fe Thin Films Excited by Ultrafast Laser Pulses
SHEN Jian, ZHANG Huai-Wu, LI Yuan-Xun
Chin. Phys. Lett. 2012, 29 (6): 067502 .   DOI: 10.1088/0256-307X/29/6/067502
Abstract   PDF(pc) (524KB) ( 458 )
It is believed that the ultrafast demagnetization process in ferromagnetic film is intrinsically a thermal effect, which is induced by ultrafast laser pulses. We present experimental evidence that such ultrafast demagnetization of the NiFe thin film can radiate electromagnetic waves in the terahertz range. We also demonstrate that the magnitude of the terahertz electromagnetic pulse emitted from ferromagnetic films after pulsed laser excitation can be tuned by the Gilbert damping factor α, which is conventionally used to describe damping of GHz precession motion of magnetization. Different damping factors are obtained by varying the normal metal film adjacent to the magnetic film via spin pumping. The measured radiated electric field in the far field is found to be proportional to the Gilbert damping factor.
Electric and Magnetic Properties of the (1-x)Ba0.6Sr0.4TiO3-xCoFe2O4 Multiferroic Composite Ceramics
WANG Ye-An, WANG Yun-Bo, RAO Wei, GAO Jun-Xiong, ZHOU Wen-Li, YU Jun
Chin. Phys. Lett. 2012, 29 (6): 067701 .   DOI: 10.1088/0256-307X/29/6/067701
Abstract   PDF(pc) (1876KB) ( 693 )
The (1-x)Ba0.6Sr0.4TiO3-xCoFe2O4 multiferroic composite ceramics (x=0.15–0.45) were fabricated by using the solid-state reaction method. X-ray diffraction shows that the composites are composed of the perovskite Ba0.6Sr0.4TiO3 phase and cubic spinel CoFe2O4 phase, without the other secondary phase. Scanning electron microscopy shows that the morphology of the composites is dense and comparatively homogenous. The variations of the dielectric constant and loss with frequency and temperature indicate that the composites behave as relaxor ferroelectrics. The composites display ferromagnetic and ferroelectric properties simultaneously. The saturated polarization of the composites decreases with increasing ferrite content, while the remnant polarization increases with the increasing ferrite content. The remnant polarization of the composite with x=0.45 is even larger than that of the pure Ba0.6Sr0.4TiO3 ceramic. The enhanced ferroelectricity of the composites may be attributed to the space charge effect in the composites.
The Influences of Temperature, Concentration and Pressure Uncertainties on the Measurement Results of Wavelength Modulation Spectroscopy
CHE Lu, DING Yan-Jun, PENG Zhi-Min
Chin. Phys. Lett. 2012, 29 (6): 067801 .   DOI: 10.1088/0256-307X/29/6/067801
Abstract   PDF(pc) (1664KB) ( 411 )
Gas temperature, species concentration, and pressure uncertainties inevitably affect the measurement results of wavelength modulation spectroscopy. We analyze and calculate the influences of these uncertainties on CO2 concentration and temperature measurement results. Calculation results show that uncertainties in the pressure and CO2 concentration have little influence on temperature measurement results. On the contrary, CO2 concentration measurement results are notably influenced by pressure uncertainty, and greatly influenced by temperature uncertainty. To solve these problems in the temperature, species concentration, and pressure uncertainties, we take the experimental data from the previous study and analyze them using the iteration method with the purpose of obtaining the optimal values of gas temperature and CO2 concentration.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Green Emission from a Strain-Modulated InGaN Active Layer
WANG Guo-Biao, XIONG Huan, LIN You-Xi, FANG Zhi-Lai, KANG Jun-Yong, DUAN Yu, SHEN Wen-Zhong
Chin. Phys. Lett. 2012, 29 (6): 068101 .   DOI: 10.1088/0256-307X/29/6/068101
Abstract   PDF(pc) (1045KB) ( 695 )
Strain-induced quantum dots (QDs) like island formations are demonstrated to effectively suppress pits/dislocation generation in high indium content (26.8%) InGaN active layers. In addition to the strain redistribution in the QD-like islands, strain modulation on the InGaN active layers by using the GaN island capping is employed to form an increased surface potential barrier around the dislocation cores, which inhibits the carrier transport to the surrounding dislocations. Cathodoluminescence shows distinct double-peak emissions at 503 nm and 444 nm, corresponding to the In-rich QD-like emission and the normal quantum well emission, respectively. The QD-like emission becomes dominated in photoluminescence due to the carrier localization effect of In-rich InGaN QDs at relatively low "carrier injection current". Accordingly, green emission may be enhanced by the following origins: (1) reduction in pits/dislocations density, (2) carrier localization and strain reduction in QDs, (3) strain modulation by GaN island capping, (4) enhanced light extraction with faceted GaN islands on the surface.
All-Optical Cesium Atomic Magnetometer with High Sensitivity
ZHANG Jun-Hai, LIU Qiang, ZENG Xian-Jin, LI Jiu-Xing, SUN Wei-Min
Chin. Phys. Lett. 2012, 29 (6): 068501 .   DOI: 10.1088/0256-307X/29/6/068501
Abstract   PDF(pc) (508KB) ( 1300 )
An all-optical cesium magnetometer with high sensitivity based on absorptive detection is reported. The experiment achieves a polarized rotational spectrum of the probe light which is induced by circular dichroism and a quarter wave plate together. The frequency response of the rotational spectrum is 1.8 mrad/Hz at Larmor precession resonance. Analyzing the signal-to-noise ratio from the experimentally observed spectrum, we predict that the magnetic measurement sensitivity of 0.3 pT/Hz1/2 would be obtained in the responsive range from 20 nT to 2000 nT.
Noise Suppression Effect of Composites Containing Glass-Covered Amorphous CoFeSiBCr Wires
ZHANG Jun-Feng, LI De-Ren, CHEN Zheng, LU Zhi-Chao, ZHOU Shao-Xiong
Chin. Phys. Lett. 2012, 29 (6): 068502 .   DOI: 10.1088/0256-307X/29/6/068502
Abstract   PDF(pc) (2237KB) ( 808 )
The noise suppression effect and its mechanism are investigated for a composite sheet and a composite film made of glass-covered amorphous CoFeSiBCr wires. Both samples show a significant noise suppression effect. The power loss ratio of the composite sheet is above 80% from 1.6 GHz to 8.5 GHz, and that of the composite film is above 70% from 3.2 GHz to 8.5 GHz even if its thickness is only 0.20 mm. The composite sheet demonstrates high real and imaginary permittivity above 30.7 and low real and imaginary permeability below 1.2. The surface resistivities of the two composite samples are as high as about 3×1012 Ω/square. The power loss of the composite containing glass-covered wires should be mainly contributed by dielectric loss derived from electronic polarization and relaxation.
Interaction between a Functionalized Single-Walled Carbon Nanotube and the YAP65WW Protein Domain: a Molecular Dynamics Simulation Study
DOU Quan-Tao, ZUO Guang-Hong, FANG Hai-Ping
Chin. Phys. Lett. 2012, 29 (6): 068701 .   DOI: 10.1088/0256-307X/29/6/068701
Abstract   PDF(pc) (1353KB) ( 658 )
The interaction between a functionalized single-walled carbon nanotube (f-SWCNT) and the YAP65WW protein domain is investigated by using molecular dynamics simulations. It is found that the f-SWCNT binds onto the active site of the YAP65WW domain and leads to a substantial conformational change of the protein domain, which may securely affect the original function of protein. Both the hydrophobic interaction and the long lifetime hydrogen bonds play important roles in the binding.
Calculation of Collective Variable-based PMF by Combining WHAM with Umbrella Sampling
XU Wei-Xin, LI Yang, ZHANG John Z. H.
Chin. Phys. Lett. 2012, 29 (6): 068702 .   DOI: 10.1088/0256-307X/29/6/068702
Abstract   PDF(pc) (646KB) ( 533 )
Potential of mean force (PMF) with respect to localized reaction coordinates (RCs) such as distance is often applied to evaluate the free energy profile along the reaction pathway for complex molecular systems. However, calculation of PMF as a function of global RCs is still a challenging and important problem in computational biology. We examine the combined use of the weighted histogram analysis method and the umbrella sampling method for the calculation of PMF as a function of a global RC from the coarse-grained Langevin dynamics simulations for a model protein. The method yields the folding free energy profile projected onto a global RC, which is in accord with benchmark results. With this method rare global events would be sufficiently sampled because the biased potential can be used for restricting the global conformation to specific regions during free energy calculations. The strategy presented can also be utilized in calculating the global intra- and intermolecular PMF at more detailed levels.
High Concentration InGaN/GaN Multi-Quantum Well Solar Cells with a Peak Open-Circuit Voltage of 2.45 V
ZHANG Dong-Yan, ZHENG Xin-He, LI Xue-Fei, WU Yuan-Yuan, WANG Jian-Feng, YANG Hui
Chin. Phys. Lett. 2012, 29 (6): 068801 .   DOI: 10.1088/0256-307X/29/6/068801
Abstract   PDF(pc) (690KB) ( 789 )
We report InGaN/GaN multi-quantum well (MQW) solar cells with a comparatively high open-circuit voltage and good concentration properties. The open circuit voltage (Voc) keeps increasing logarithmically with concentration ratio until 60 suns. The peak Voc of InGaN/GaN MQW solar cells, which has a predominant peak wavelength of 456 nm from electroluminescence measurements, is found to be 2.45 V when the concentration ratio reaches 333×. Furthermore, the dependence of conversion efficiency and fill factor on concentration ratio are analyzed.
Empirical Evidence for the Look-Ahead Behavior of Pedestrians in Bi-directional Flows
GUO Ren-Yong, WONG S. C., XIA Yin-Hua, HUANG Hai-Jun, LAM William H. K., CHOI Keechoo
Chin. Phys. Lett. 2012, 29 (6): 068901 .   DOI: 10.1088/0256-307X/29/6/068901
Abstract   PDF(pc) (880KB) ( 519 )
Using the sample data obtained from a group of pedestrian experiments, a function formulating the velocity-density relationship of pedestrians and linear regression is proposed to provide empirical evidence for the look-ahead behavior of pedestrians in bi-directional flows. We find that the velocity of pedestrians is negatively correlated with not only the densities of the opposite-direction and the identical-direction pedestrians around them but also the densities of the same-direction pedestrians ahead of them. Moreover, the movement of pedestrians is most affected by other pedestrians moving in the same direction about 1 m ahead.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Effects of the Recombination of Nucleons into α-Particles on the R-process in Proto-magnetar Wind
CHEN Yan-Jun, YUAN Ye-Fei
Chin. Phys. Lett. 2012, 29 (6): 069701 .   DOI: 10.1088/0256-307X/29/6/069701
Abstract   PDF(pc) (542KB) ( 369 )
We take the recombination of nucleons to α-particles into account in proto-magnetar winds and evaluate its effects on r-process nucleosynthesis. The proto-magnetar winds are described in the time-independent Newtonian magnetohydrodynamic wind scenario. It is found that stellar rotation and strong magnetic fields significantly affect the properties of the winds. Also, the fact that the recombination of nucleons can enhance the wind entropy by approximately twenty percent and somewhat reduce the expansion timescale indicates that the effects of this recombination on the r-process can not be ignored.
82 articles