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Volume 28 Issue 2
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GENERAL
Symmetry Reduction, Exact Solutions and Conservation Laws of the Modified Kadomtzev–Patvishvili-II Equation
XIN Xiang-Peng, LIU Xi-Qiang, ZHANG Lin-Lin
Chin. Phys. Lett. 2011, 28 (2): 020201 .   DOI: 10.1088/0256-307X/28/2/020201
Abstract   PDF(pc) (407KB) ( 679 )
Employing the modified Clarkson–Kruskal direct method, we realize the symmetries of the nonlinear (2+1)-dimensional modified Kadomtzev–Patvishvili-II equation. Applying the given Lie symmetry, we obtain the similarity reduction and new exact solutions. We also obtain conservation laws of the equations with the corresponding Lie symmetry.
Numerical Simulation of Coupled Nonlinear Schrödinger Equations Using the Generalized Differential Quadrature Method
R. Mokhtari**, A. Samadi Toodar, N. G. Chegini
Chin. Phys. Lett. 2011, 28 (2): 020202 .   DOI: 10.1088/0256-307X/28/2/020202
Abstract   PDF(pc) (893KB) ( 748 )
We the extend application of the generalized differential quadrature method (GDQM) to solve some coupled nonlinear Schrödinger equations. The cosine-based GDQM is employed and the obtained system of ordinary differential equations is solved via the fourth order Runge–Kutta method. The numerical solutions coincide with the exact solutions in desired machine precision and invariant quantities are conserved sensibly. Some comparisons with the methods applied in the literature are carried out.
Strong Symmetries of Non-Isospectral Ablowitz–Ladik Equations
WU Hua, ZHANG Da-Jun**
Chin. Phys. Lett. 2011, 28 (2): 020203 .   DOI: 10.1088/0256-307X/28/2/020203
Abstract   PDF(pc) (377KB) ( 418 )
For each non-isospectral Ablowitz–Ladik equation a strong symmetry operator is given. The strong symmetry contains time variable explicitly and by means of it two sets of symmetries are generated. Functional derivative formulae between the strong symmetry and symmetries are derived, by which the obtained symmetries are shown to compose a centerless Kac–Moody–Virasoro algebra. Master symmetries for non-isospectral Ablowitz–Ladik equations are also discussed.
Prolongation Structure Analysis of a Coupled Dispersionless System
Souleymanou Abbagari, **, Bouetou Bouetou Thomas, Kuetche Kamgang Victor, Mouna Ferdinand, Timoleon Crepin Kofane
Chin. Phys. Lett. 2011, 28 (2): 020204 .   DOI: 10.1088/0256-307X/28/2/020204
Abstract   PDF(pc) (491KB) ( 594 )
We address the problem of integrability of a coupled dispersionless system recently introduced by Zhaqilao, Zhao and Li [Chin. Phys. B 18 (2009) 1780] which physically describes the propagation of electromagnetic fields within an optical nonlinear medium, but also arrives in the physical description of a charged object dynamics in an external magnetic field. Following the prolongation structure analysis developed by Wahlquist and Estabrook, we derive a more general form of Lax pairs of the previous coupled dispersionless system and its concrete non-Abelian Lie algebra resorting to a hidden symmetry. Also, we construct the Bäcklund transformation of the system using the Riccati form of the linear eigenvalue problem.
Non-Lie Symmetry Group and New Exact Solutions for the Two-Dimensional KdV-Burgers Equation
WANG Hong**, TIAN Ying-Hui, CHEN Han-Lin
Chin. Phys. Lett. 2011, 28 (2): 020205 .   DOI: 10.1088/0256-307X/28/2/020205
Abstract   PDF(pc) (393KB) ( 635 )
By using the modified Clarkson–Kruskal (CK) direct method, we obtain the non-Lie symmetry group of the two-dimensional KdV-Burgers equation. Under some constraint conditions, Lie point symmetry is also obtained. Through the symmetry group, some new exact solutions of the two-dimensional KdV-Burgers equation are found.
Stochastic Computational Approach for Complex Nonlinear Ordinary Differential Equations
Junaid Ali Khan*, Muhammad Asif Zahoor Raja**, Ijaz Mansoor Qureshi
Chin. Phys. Lett. 2011, 28 (2): 020206 .   DOI: 10.1088/0256-307X/28/2/020206
Abstract   PDF(pc) (440KB) ( 623 )
We present an evolutionary computational approach for the solution of nonlinear ordinary differential equations (NLODEs). The mathematical modeling is performed by a feed-forward artificial neural network that defines an unsupervised error. The training of these networks is achieved by a hybrid intelligent algorithm, a combination of global search with genetic algorithm and local search by pattern search technique. The applicability of this approach ranges from single order NLODEs, to systems of coupled differential equations. We illustrate the method by solving a variety of model problems and present comparisons with solutions obtained by exact methods and classical numerical methods. The solution is provided on a continuous finite time interval unlike the other numerical techniques with comparable accuracy. With the advent of neuroprocessors and digital signal processors the method becomes particularly interesting due to the expected essential gains in the execution speed.
Classification of Four-Qubit States by Means of a Stochastic Local Operation and the Classical Communication Invariant
ZHA Xin-Wei**, MA Gang-Long
Chin. Phys. Lett. 2011, 28 (2): 020301 .   DOI: 10.1088/0256-307X/28/2/020301
Abstract   PDF(pc) (345KB) ( 609 )
It is a recent observation that entanglement classification for qubits is closely related to stochastic local operations and classical communication (SLOCC) invariants. Verstraete et al.[Phys. Rev. A 65 (2002) 052112] showed that for pure states of four qubits there are nine different degenerate SLOCC entanglement classes. Li et al.[Phys. Rev. A 76 (2007) 052311] showed that there are at least 28 distinct true SLOCC entanglement classes for four qubits by means of the SLOCC invariant and semi-invariant. We give 16 different entanglement classes for four qubits by means of basic SLOCC invariants.
Local Unitary Equivalent Consistence for n−Party States and Their (n-1)-Party Reduced Density Matrices
WANG Zhen, WANG He-Ping, WANG Zhi-Xi**, FEI Shao-Ming
Chin. Phys. Lett. 2011, 28 (2): 020302 .   DOI: 10.1088/0256-307X/28/2/020302
Abstract   PDF(pc) (438KB) ( 435 )
We present that the local unitary equivalence of n−party pure states is consistent with that of their (n-1)-party reduced density matrices. As an application, we obtain the local invariants for a class of tripartite pure qudits.
Cryptanalysis of Quantum Secure Direct Communication and Authentication Scheme via Bell States
GAO Fei**, QIN Su-Juan, GUO Fen-Zhuo, WEN Qiao-Yan
Chin. Phys. Lett. 2011, 28 (2): 020303 .   DOI: 10.1088/0256-307X/28/2/020303
Abstract   PDF(pc) (392KB) ( 756 )
The security of the quantum secure direct communication (QSDC) and authentication protocol based on Bell states is analyzed. It is shown that an eavesdropper can invalidate the authentication function, and implement a successful man-in-the-middle attack, where he/she can obtain or even modify the transmitted secret without introducing any error. The particular attack strategy is demonstrated and an improved protocol is presented.
Fault-Tolerate Three-Party Quantum Secret Sharing over a Collective-Noise Channel
LI Chun-Yan, LI Yan-Song**
Chin. Phys. Lett. 2011, 28 (2): 020304 .   DOI: 10.1088/0256-307X/28/2/020304
Abstract   PDF(pc) (371KB) ( 456 )
We present a fault-tolerate three-party quantum secret sharing (QSS) scheme over a collective-noise channel. Decoherence-free subspaces are used to tolerate two noise modes, a collective-dephasing channel and a collective-rotating channel, respectively. In this scheme, the boss uses two physical qubits to construct a logical qubit which acts as a quantum channel to transmit one bit information to her two agents. The agents can get the information of the private key established by the boss only if they collaborate. The boss Alice encodes information with two unitary operations. Only single-photon measurements are required to rebuilt Alice's information and detect the security by the agents Bob and Charlie, not Bell-state measurements. Moreover, Almost all of the photons are used to distribute information, and its success efficiency approaches 100% in theory.
Loss of Exchange Symmetry in Multiqubit States under Ising Chain Evolution
Sudha, **, B. G. Divyamani, A. R. Usha Devi,
Chin. Phys. Lett. 2011, 28 (2): 020305 .   DOI: 10.1088/0256-307X/28/2/020305
Abstract   PDF(pc) (460KB) ( 327 )
Keeping in view of importance of exchange symmetry aspects in studies on spin squeezing of multiqubit states, we show that the one-dimensional Ising Hamiltonian with nearest neighbor interactions does not retain the exchange symmetry of initially symmetric multiqubit states. Specifically we show that among 4−qubit states obeying exchange symmetry, all states except W class (and their linear combination) lose their symmetry under time evolution with Ising Hamiltonian. Attributing the loss of symmetry of the initially symmetric states to rotational asymmetry of the one-dimensional Ising Hamiltonian with more than 3 qubits, we indicate that all N−qubit states (N≥5) obeying permutation symmetry lose their symmetry after time evolution with Ising Hamiltonian.
Thermal Entanglement in a Two-Qutrit Spin-1 Anisotropic Heisenberg Model
Erhan Albayrak
Chin. Phys. Lett. 2011, 28 (2): 020306 .   DOI: 10.1088/0256-307X/28/2/020306
Abstract   PDF(pc) (1541KB) ( 596 )
The negativity (N) as a measure of thermal entanglement (TE) is studied for a two−qutrit spin-1 anisotropic Heisenberg XXZ chain with Dzyaloshinskii–Moriya (DM) interaction in an inhomogeneous magnetic field in detail. The effects of the DM interaction parameter Dz on the thermal variation of the N for given values of the external magnetic field B, a parameter b which controls the inhomogeneity of B and the bilinear interaction parameters Jx=Jy≠Jz are obtained. It is found that N persists to higher values and to higher temperatures for the higher values of ±Dz and for the higher positive values of Jz, i.e. in the antiferromagnetic (AFM) case. When Jz<0, the ferromagnetic (FM) case, and Dz is small, and if Jz is strong enough to compete with Dz, N decreases. In addition, N declines with the increasing values of B and b.
Effects of Dzyaloshinskii–Moriya Interaction on Optimal Dense Coding Using a Two-Qubit Heisenberg XXZ Chain with and without External Magnetic Field
CAI Jiang-Tao, ABLIZ Ahmad**, BAI Yan-Kui, JIN Guang-Sheng
Chin. Phys. Lett. 2011, 28 (2): 020307 .   DOI: 10.1088/0256-307X/28/2/020307
Abstract   PDF(pc) (1022KB) ( 378 )
We investigate the effects of different components of the Dzyaloshinskii–Moriya (DM) anisotropic antisymmetric interaction on optimal dense coding with a two-qubit Heisenberg XXZ chain in the presence and in the absence of external magnetic fields. The anisotropic coupling parameter Δ, isotropic coupling parameter J, and the DM interaction parameters are found to be effective for optimal dense coding, while the magnetic field turns out to be destructive. Moreover, the results show that the case of antiferromagnetic (AFM) is more ideal for optimal dense coding than the case of ferromagnetic (FM) in general. In the case of AFM, by comparison of the two cases with the same fixed x− and z−component parameters of DM interaction (Dx and Dz), the appropriate model for optimal dense coding is indicated for the different value intervals of Δ. Comparison of the effects of Dz and Dx on optimal dense coding is made and their dominant regions are clarified.
Entanglement Dynamics of Arbitrary Two-Qubit Pure States under Amplitude and Phase Damping Channels
JIANG Feng-Jian, SHI Ming-Jun**, DU Jiang-Feng**
Chin. Phys. Lett. 2011, 28 (2): 020308 .   DOI: 10.1088/0256-307X/28/2/020308
Abstract   PDF(pc) (1394KB) ( 521 )
Analytic results are presented for the entanglement evolution for arbitrary two-qubit pure state under amplitude damping and particularly phase damping channel. The disentanglement time and the relationship between it and the form of initial state are given explicitly. The lower bounds of disentanglement time are obtained and shown to be the monotone functions of initial concurrence.
Non Existence of Shear in Bianchi Type-III String Cosmological Models with Bulk Viscosity and Time−Dependent Λ Term
R. K. Tiwari, Sonia Sharma**
Chin. Phys. Lett. 2011, 28 (2): 020401 .   DOI: 10.1088/0256-307X/28/2/020401
Abstract   PDF(pc) (398KB) ( 443 )
We study the non existence of shear in locally rotationally symmetric Bianchi type-III string cosmological models with bulk viscosity and variable cosmological term Λ. Exact solutions of the field equations are obtained by assuming the conditions: the bulk viscosity is proportional to the expansion scalar, ξ∝θ, expansion scalar is proportional to shear scalar, θ∝σ, and Λ is proportional to the Hubble parameter. The coefficient of bulk viscosity is assumed to be a power function of mass density. The corresponding physical interpretations of the cosmological solutions are also discussed.
Thermodynamics of Slowly Rotating Charged Black Holes in Anti-de Sitter Einstein–Gauss–Bonnet Gravity
ZOU De-Cheng, YANG Zhan-Ying**, YUE Rui-Hong**
Chin. Phys. Lett. 2011, 28 (2): 020402 .   DOI: 10.1088/0256-307X/28/2/020402
Abstract   PDF(pc) (430KB) ( 438 )
By using a new approach, we demonstrate the analytic expressions for slowly rotating Gauss–Bonnet charged black hole solutions with one non-vanishing angular momentum in higher-dimensional anti-de Sitter spaces. Up to linear order of the rotating parameter a, the mass, Hawking temperature and entropy of the charged black holes get no corrections from rotation.
Diffusion of Active Particles Subject both to Additive and Multiplicative Noises
WANG Shao-Hua, YANG Ming**, WU Da-Jin
Chin. Phys. Lett. 2011, 28 (2): 020501 .   DOI: 10.1088/0256-307X/28/2/020501
Abstract   PDF(pc) (517KB) ( 434 )
We consider a Langevin equation of active Brownian motion which contains a multiplicative as well as an additive noise term. We study the dependences of the effective diffusion coefficient Deff on both the additive and multiplicative noises. It is found that for fixed small additive noise intensity Deff varies non−monotonously with multiplicative noise intensity, with a minimum at a moderate value of multiplicative noise, and Deff increases monotonously, however, with the multiplicative noise intensity for relatively strong additive noise; for fixed multiplicative noise intensity Deff decreases with growing additive noise intensity until it approaches a constant. An explanation is also given of the different behavior of Deff as additive and multiplicative noises approach infinity, respectively.
A Denoising Algorithm for Noisy Chaotic Signals Based on the Higher Order Threshold Function in Wavelet-Packet
DENG Ke, ZHANG Lu, LUO Mao-Kang**
Chin. Phys. Lett. 2011, 28 (2): 020502 .   DOI: 10.1088/0256-307X/28/2/020502
Abstract   PDF(pc) (930KB) ( 484 )
Aiming at the shortage of conventional threshold function in wavelet noise reduction of chaotic signals, we propose a wavelet-packet noise reduction method of chaotic signals based on a new higher order threshold function. The method retains the useful high-frequency information, and the threshold function is continuous and derivable, therefore it is more consistent with the characteristics of the continuous signal. Contrast simulation experiment shows that the effect of noise reduction and the precision of noise reduction of chaotic signals both are improved.
One-Dimensional w-Component Fermions and Bosons with Repulsive Delta Function Interaction
C. N. YANG, **, YOU Yi-Zhuang
Chin. Phys. Lett. 2011, 28 (2): 020503 .   DOI: 10.1088/0256-307X/28/2/020503
Abstract   PDF(pc) (447KB) ( 880 )
We prove in theorems 2 and 3 that for 1D Bosons with repulsive delta function interaction with any number of components and any Young tableau, the energy per particle as N→∞ is the same as for spinless Bosons.
Spiral Wave Dynamics in a Response System Subjected to a Spiral Wave Forcing
LI Guang-Zhao, CHEN Yong-Qi, TANG Guo-Ning**, LIU Jun-Xian
Chin. Phys. Lett. 2011, 28 (2): 020504 .   DOI: 10.1088/0256-307X/28/2/020504
Abstract   PDF(pc) (1462KB) ( 407 )
Unidirectional linear error feedback coupling of two excitable medium systems displaying spiral waves is considered. The spiral wave in the response system is thus subjected to a spiral wave forcing. We find that the unidirectional feedback coupling can lead to richer behaviour than the mutual coupling. The spiral wave dynamics in the response system depends on the coupling strength and frequency mismatch. When the coupling strength is small, the feedback coupling induces the drift or meander of the forced spiral wave. When the coupling strength is large enough, the feedback coupling may lead to the transition from spiral wave to anti-target or target-like wave. The generation of anti-target wave in coupled excitable media is observed for the first time. Furthermore, when the coupling strength is strong, the synchronization between two subsystems can be established.
A Parameter Modulation Chaotic Secure Communication Scheme with Channel Noises
ZHANG Ying-Qian, WANG Xing-Yuan**
Chin. Phys. Lett. 2011, 28 (2): 020505 .   DOI: 10.1088/0256-307X/28/2/020505
Abstract   PDF(pc) (506KB) ( 774 )
We propose a new communication system which is able to separate noise successfully by using independent component analysis (ICA), and a parameter modulation method based on a Lorenz chaotic system is employed for recovery of the source signals. The results indicate that our proposed secure communication has robustness against noise.
ATOMIC AND MOLECULAR PHYSICS
QCT Calculations of Reactions of F+LiHLiF+H and F+LiDLiF+D: Product Polarization and Isotope Effects
WANG Tao, YUE Xian-Fang
Chin. Phys. Lett. 2011, 28 (2): 023101 .   DOI: 10.1088/0256-307X/28/2/023101
Abstract   PDF(pc) (946KB) ( 459 )
Using the quasi-classical trajectory (QCT) method, the product polarization at the collision energy of 46 kcal/mol is investigated for the reactions of F+LiH (v=0, j=0)LiF+H and F+LiD (v=0, j=0)LiF+D on the 2A' ground state potential energy surface (PES)[J. Chem. Phys. 106(1997)1013). The distribution of P(θr), which represents the K and J' correlation, the dihedral angle distribution of K−K'-J' P(φr), the angular distribution P(θrr) and the four PDDCSs[(2π/σ)(dσ00/t), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/t), (2π/σ)(dσ21−/t)] are presented and discussed. In addition, isotope effects are investigated. The results indicate that at the collision energy of 46 kcal/mol, with isotopic mass substitution, the orientation degree of LiF perpendicular to the scattering degree becomes stronger while the polarization degree of LiF perpendicular to K keeps almost changeless. In addition, the angular distribution of LiF strongly prefers forward scattering.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Efficient Spherical Wavefront Correction near the Focus for the 0.89PW/29.0fs Ti:Sapphire Laser Beam
REN Zhi-Jun, LIANG Xiao-Yan**, YU Liang-Hong, LU Xiao-Ming, LENG Yu-Xin, LI Ru-Xin**, XU Zhi-Zhan**
Chin. Phys. Lett. 2011, 28 (2): 024201 .   DOI: 10.1088/0256-307X/28/2/024201
Abstract   PDF(pc) (1259KB) ( 486 )
We demonstrate a new loop system of the spherical wavefront (SW) correction near the beam focus to effectively improve the focusability of 0.89 PW/29.0 fs Ti:sapphire chirped pulse amplification laser. After wavefront correction, the Strehl ratio is improved to reach 0.91, and the focal spot size using the f/4 off−axis parabola is reduced to 6.34×6.94 μm2 (corresponding to 1.63×1.78 times diffraction limitation). With full peak power of 0.89 PW, the peak intensity of 2.59×1021 W/cm2 is obtained. The experimental results show that the SW correction scheme near the beam focus is comparatively simple, economic and high-efficient.
A Full-Duplex Radio-over-Fiber System Based on Frequency Twelvefold
ZHU Jia-Hu, HUANG Xu-Guang**, TAO Jin, XIE Jin-Ling
Chin. Phys. Lett. 2011, 28 (2): 024202 .   DOI: 10.1088/0256-307X/28/2/024202
Abstract   PDF(pc) (797KB) ( 535 )
A full-duplex radio-over-fiber system using frequency-twelvefold optical millimeter-wave based on external modulation via a Mach–Zehnder modulator is proposed and analyzed theoretically. The simulation results show that the power penalties for both the downstream and upstream signals are less than 0.5 dB. In this scheme, the configuration of a base station is simplified without laser, while the frequency of local oscillator signal is largely reduced due to the frequency-twelvefold millimeter-wave technique. The cost of the new system is largely reduced.
Measurement of Ultra-Short Single-Photon Pulse Duration with Two-Photon Interference
LV Fan, SUN Fang-Wen**, ZOU Chang-Ling, HAN Zheng-Fu, GUO Guang-Can
Chin. Phys. Lett. 2011, 28 (2): 024203 .   DOI: 10.1088/0256-307X/28/2/024203
Abstract   PDF(pc) (447KB) ( 422 )
We proposed a protocol of measuring the duration of ultra-short single-photon pulse with two-photon interference. The pulse duration can be obtained from the width of the visibility of two-photon Hong-Ou-Mandel interference or the indistinguishability of the two photons. Moreover, the shape of a single-photon pulse can be measured with ultra-short single-photon pulses through the two-photon interference.
Phase Noise Monitor and Reduction by Parametric Saturation Approach in Phase Modulation Systems
XU Ming**, ZHOU Zhen, PU Xiao, JI Jian-Hua, YANG Shu-Wen
Chin. Phys. Lett. 2011, 28 (2): 024204 .   DOI: 10.1088/0256-307X/28/2/024204
Abstract   PDF(pc) (746KB) ( 379 )
Nonlinear phase noise (NLPN) is investigated theoretically and numerically to be mitigated by parametric saturation approach in DPSK systems. The nonlinear propagation equation that incorporates the phase of linear and nonlinear is analyzed with parametric saturation processing (PSP). The NLPN is picked and monitored with the power change factors in the DPSK system. This process can be realized by an optical PSP limiter and a novel apparatus with feedback MZI. The monitor range of phase noise is 0°–90°, which may be reduced to 0°–45° if the monitor factor is about the Stockes wave but not an anti-Stockes wave. It is shown that DPSK signal performance can be improved based on the parametric saturation approach.
Interplay of Coexisting Odd-Order Wave Mixings in a Five-Level Atomic System
SONG Yue, HUO Shu-Li, LI Pei-Ying, SANG Su-Ling, WANG Zhi-Guo**, ZHANG Yan-Peng**
Chin. Phys. Lett. 2011, 28 (2): 024205 .   DOI: 10.1088/0256-307X/28/2/024205
Abstract   PDF(pc) (602KB) ( 356 )
We experimentally investigate the interplay between two coexisting six-wave mixing (SWM) signals and the interference between coexisting four-wave mixing (FWM) and SWM signals in a five-level atomic system of 85Rb. When two electromagnetically induced transparency windows gradually overlap in frequency, the competition between these two SWM signals arises. Moreover, we report the experimental result which shows that the temporal interference with femtosecond time scales between FWM and SWM signals.
Measurement of Random Surface Parameters by Angle-Resolved In-plane Light Scattering with Constant Perpendicular Wave Vector
LI Hai-Xia, LIU Chun-Xiang, CHEN Xiao-Yi, ZHANG Mei-Na, CHENG Chuan-Fu**
Chin. Phys. Lett. 2011, 28 (2): 024206 .   DOI: 10.1088/0256-307X/28/2/024206
Abstract   PDF(pc) (762KB) ( 434 )
We report the experimental method of angle-resolved in-plane light scattering for random surface parameter extraction. In the measurement of the scattered intensity profile at a certain angle of incidence, the perpendicular component of wave vector remains constant, which is realized by controlling the movement of the detector along a specified circular arc segment. We use the central δ−peak and the half-width of the diffused intensity profiles and their variations to obtain the roughness w, the lateral correlation length ξ and roughness exponent α of the rough surface sample. The measurement copes strictly with the theoretical analysis, and the inherent problem in previous in-plane light scattering experiment is overcome so that the changes of the perpendicular component of wave vector affect the half width a diffused intensity profile and the measurement accuracy.
Experimental Observation of Dark Soliton Emitting with Spectral Sideband in an All-Fiber Ring Cavity Laser
WANG Hui-Yi, XU Wen-Cheng**, LUO Zhi-Chao, LUO Ai-Ping, CAO Wen-Jun, DONG Jiang-Li, WANG Lu-Yan
Chin. Phys. Lett. 2011, 28 (2): 024207 .   DOI: 10.1088/0256-307X/28/2/024207
Abstract   PDF(pc) (873KB) ( 470 )
The dark soliton pulse with spectral sideband is experimentally observed in a dispersion-managed all-fiber ring laser with net negative cavity group velocity dispersion. We find that, for single or multiple dark solitons, the spectral sidebands always appear and exhibit asymmetric characteristics which are similar to bright solitons. The experimental measurements of spectral sideband positions are carried out and the results are in good agreement with the calculated values. Our results show that spectral sideband effect is also an intrinsic feature of a dark soliton fiber laser.
Performance Investigation of All-Optical NRZ-to-Manchester Format Conversion with SOA-MZI Based XOR Logic Gate
CHEN Jian-Bo**, ZHOU Rui, ZHANG Qi, YU Chong-Xiu, XIN Xiang-Jun
Chin. Phys. Lett. 2011, 28 (2): 024208 .   DOI: 10.1088/0256-307X/28/2/024208
Abstract   PDF(pc) (820KB) ( 734 )
All-optical format conversion between non-return-to-zero (NRZ) and the Manchester code is implemented by using an optical exclusive-OR (XOR) logic gate based on a semiconductor optical amplifier Mach–Zehnder Interferometer (SOA-MZI). There is 10 Gbit/s all-optical NRZ-to-Manchester conversion implemented in our simulation system and BER performance of the format conversion is investigated. Transmission performances of the converted Manchester coded signal are discussed in terms of transmission length and received optical power.
Antireflective Characteristics of Sub-Wavelength Periodic Structure with Square Hole
XU Qi-Yuan**, LIU Zheng-Tang, LI Yang-Ping, WU Qian, ZHANG Shao-Feng
Chin. Phys. Lett. 2011, 28 (2): 024209 .   DOI: 10.1088/0256-307X/28/2/024209
Abstract   PDF(pc) (508KB) ( 441 )
In order to enhance transmittance in the long-wavelength infrared range, the major parameters of periodic sub-wavelength structures (SWS) with square holes on zinc sulfide (ZnS) substrates are designed and analyzed for applications in normal incidence by using rigorous coupled-wave analysis (RCWA) and thin film theory (TFT). Finally the optimal antireflective parameters are achieved. The structures on ZnS substrates are fabricated on the basis of the simulation results by photolithography technology and reactive ion etching technology. A substantial antireflection effect is observed over the wavelength band 8–12 μm by a factor greater than 4.5.
Diode-End-Pumped Tm:Ho:GdVO4 Microchip Laser at Room Temperature
YAO Bao-Quan**, CHEN Fang, WANG Qiang, WU Chun-Ting, LI Gang, ZHANG Chao-Hui, WANG Yue-Zhu, JU You-Lun
Chin. Phys. Lett. 2011, 28 (2): 024210 .   DOI: 10.1088/0256-307X/28/2/024210
Abstract   PDF(pc) (568KB) ( 476 )
Room-temperature Tm:Ho:GdVO4 microchip laser operated around 2 μm is demonstrated for the first time to our knowledge. At a heat sink temperature of 283 K, maximum output power of 29.7 mW is obtained by using a 0.25−mm-long crystal at an absorbed pump power of 912 mW, corresponding to a slope efficiency of 5.0%. At the temperature to 283 K, a single-longitudinal-mode laser as much as 8mW at 2048.5 nm is achieved. The M2 factor is measured to be 1.4.
Multi-Beam Interference Transmission Spectrum Observed from an Eccentric Core Single-Mode Fiber
FAN Lin-Yong**, JIANG Wei-Wei, ZHAO Rui-Feng, PEI Li, JIAN Shui-Sheng
Chin. Phys. Lett. 2011, 28 (2): 024211 .   DOI: 10.1088/0256-307X/28/2/024211
Abstract   PDF(pc) (754KB) ( 434 )
An eccentric core single-mode fiber, whose core is away from the axis of the fiber, is fabricated by using the fiber preform goniometric-groove method and the stack-and-draw method. An eccentric core single-mode fiber without coating is spliced between two single-mode fibers. Fundamental mode and cladding modes are excited at one splicing point between the eccentric core single-mode fiber and the single-mode fiber, and propagate in the eccentric core single-mode fiber, then interfere with each other at the other splicing point. Multi-beam interference transmission spectrum is observed. An in-line fiber interferometric strain sensor based on the eccentric core single-mode fiber is realized.
A Sampled Grating DBR Laser Monolithically Integrated by Using SOAs with 22mW Output Power and 51ITU 100GHz Channels over 43nm
LIU Yang, YE Nan, ZHOU Dai-Bing, WANG Bao-Jun, PAN Jiao-Qing, ZHAO Ling-Juan, WANG Wei
Chin. Phys. Lett. 2011, 28 (2): 024212 .   DOI: 10.1088/0256-307X/28/2/024212
Abstract   PDF(pc) (1019KB) ( 669 )
A sampled grating distributed Bragg reflector (SG-DBR) laser monolithically integrated with semiconductor optical amplifiers (SOAs), which has a tuning range over 43 nm from 1514.05 nm to 1557.4 nm covering 49 continuous and totally 51 ITU 100 GHz standard channels and an output power more than 22 mW for all output wavelengths, is successfully demonstrated.
Tunable Vertical-Cavity Surface-Emitting Lasers Integrated with Two Wafers
REN Xiu-Juan, GUAN Bao-Lu, GUO Shuai, LI Shuo, LI Chuan-Chuan, HAO Cong-Xia, ZHOU Hong-Yi, GUO Xia**
Chin. Phys. Lett. 2011, 28 (2): 024213 .   DOI: 10.1088/0256-307X/28/2/024213
Abstract   PDF(pc) (499KB) ( 495 )
A novel two-wafer concept for micro-electro-mechanically tunable vertical cavity surface emitting lasers (VCSELs) is presented. The VCSEL is composed by two wafers: one micro-electromechanical-system membrane wafer with four arms to adjust the cavity length through electrostatic actuation and a "half-VCSEL" wafer consisting of a fixed bottom mirror and an amplifying active region. The measurement results of the electricity pumped tunable VCSEL with more than 9 mW output power at room temperature over the tuning range prove the feasibility of the proposition.
Influence of Turbulent Atmosphere on Polarization Properties of Stochastic Electromagnetic Pulsed Beams
DING Chao-Liang**, ZHAO Zhi-Guo, LI Xiao-Feng, PAN Liu-Zhan***, YUAN Xiao
Chin. Phys. Lett. 2011, 28 (2): 024214 .   DOI: 10.1088/0256-307X/28/2/024214
Abstract   PDF(pc) (1416KB) ( 445 )
Using the coherence theory of non-stationary fields and the characterization of stochastic electromagnetic pulsed beams, the analytical expression for the spectral degree of polarization of stochastic electromagnetic Gaussian Schell-model pulsed (GSMP) beams in turbulent atmosphere is derived and is used to study the polarization properties of stochastic electromagnetic GSMP beams propagating through turbulent atmosphere. The results of numerical calculation are given to illustrate the dependence of spectral degree of polarization on the pulse frequency, refraction index structure constant and spatial correlation length. It is shown that, compared with free-space case, in turbulent atmosphere propagation there are two positions at which the on-axis spectral degree of polarization P is equal to zero. The position change depends on the pulse frequency, refraction index structure constant and spatial correlation length.
A Scaled Underwater Launch System Accomplished by Stress Wave Propagation Technique
WEI Yan-Peng**, WANG Yi-Wei, FANG Xin, HUANG Chen-Guang, DUAN Zhu-Ping
Chin. Phys. Lett. 2011, 28 (2): 024601 .   DOI: 10.1088/0256-307X/28/2/024601
Abstract   PDF(pc) (869KB) ( 450 )
A scaled underwater launch system based on the stress wave theory and the slip Hopkinson pressure bar (SHPB) technique is developed to study the phenomenon of cavitations and other hydrodynamic features of high-speed submerged bodies. The present system can achieve a transient acceleration in the water instead of long-time acceleration outside the water. The projectile can obtain a maximum speed of 30 m/s in about 200 μs by the SHPB launcher. The cavitation characteristics in the stage of acceleration and deceleration are captured by the high-speed camera. The processes of cavitation inception, development and collapse are also simulated with the business software FLUENT, and the results are in good agreement with experiment. There is about 20–30% energy loss during the launching processes, the mechanism of energy loss is also preliminary investigated by measuring the energy of the incident bar and the projectile.
MHD Boundary Layer Slip Flow and Heat Transfer over a Flat Plate
Krishnendu Bhattacharyya**, Swati Mukhopadhyay, G. C. Layek
Chin. Phys. Lett. 2011, 28 (2): 024701 .   DOI: 10.1088/0256-307X/28/2/024701
Abstract   PDF(pc) (471KB) ( 1934 )
An analysis of magnetohydrodynamic (MHD) boundary layer flow and heat transfer over a flat plate with slip condition at the boundary is presented. A complete self-similar set of equations are obtained from the governing equations using similarity transformations and are solved by a shooting method. In the boundary slip condition no local similarity occurs. Velocity and temperature distributions within the boundary layer are presented. Our analysis reveals that the increase of magnetic and slip parameters reduce the boundary layer thickness and also enhance the heat transfer from the plate.
Gravity-Driven Instability in a Liquid Film Overlying an Inhomogeneous Porous Layer
ZHAO Si-Cheng, LIU Qiu-Sheng**, NGUYEN-THI Henri, BILLIA Bernard
Chin. Phys. Lett. 2011, 28 (2): 024702 .   DOI: 10.1088/0256-307X/28/2/024702
Abstract   PDF(pc) (499KB) ( 335 )
A new model consisting of a liquid film overlying a saturated and inhomogeneous porous layer is investigated. We concentrate on effects of inhomogeneity on transition of instability modes. Influences of the averaged porosity and the gradient of porosity distribution on the instability behaviors of a liquid-porous layer system are emphasized. The average permeability of the porous layer is a key factor to determine the penetration of convection in the system.
Micro-acting Force in Boundary Layer in Low-Permeability Porous Media
FENG Yu-Liang, ZHANG Yuan, JI Bing-Yu, MU Wen-Zhi
Chin. Phys. Lett. 2011, 28 (2): 024703 .   DOI: 10.1088/0256-307X/28/2/024703
Abstract   PDF(pc) (497KB) ( 334 )
There are lots of reasons to restrict a low-permeability oil layer to enhance the recovery factor. Based on the research results of non-Darcy flow, microflow of water drive and micro-acting force in low permeability porous media are studied by establishing the expression of fluid viscosity factor. Numerical calculation shows that under the condition of L/S interaction, the radial velocity distribution near the solid wall changes obviously, and the curve form changes from convex to concave. The tinier the capillary radius is, the stronger the L/S interaction is. The larger the n value is, more obviously the flowing velocity decreases. The results will help people to deal with improving recovery factor of low permeability reservoir, and understanding the fluid flow behavior in blood capillary.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Electron Whistler Mode Waves Associated with Collisionless Magnetic Reconnection
GUO Jun, **, YU Bin, GUO Guang-Hai, ZHAO Bo
Chin. Phys. Lett. 2011, 28 (2): 025201 .   DOI: 10.1088/0256-307X/28/2/025201
Abstract   PDF(pc) (1268KB) ( 550 )
The results of particle-in-cell (PIC) simulations are presented on the evolution of the electron whistler waves during the collisionless magnetic reconnection. The simulation results show that the electron whistler waves with frequency higher than the lower hybrid frequency are found to occur in the electrons outflow region. Moreover, the present results indicate that these electron whistler waves with high-frequency in the region greater than an ion inertial scale of the x-line are irrelevant to the fast reconnection, but are generated as a result of the reconnection processes.
Identification of Low-Frequency Zonal Flow in a Linear Magnetic Plasma Device
CHEN Ran, XIE Jin-Lin**, YU Chang-Xuan, LIU A-Di, LAN Tao, ZHANG Shou-Biao, HU Guang-Hai, LI Hong, LIU Wan-Dong
Chin. Phys. Lett. 2011, 28 (2): 025202 .   DOI: 10.1088/0256-307X/28/2/025202
Abstract   PDF(pc) (643KB) ( 367 )
A low-frequency (f<2 kHz) potential structure (LFPS) is observed in a linear magnetic plasma device using Langmuir probe arrays. The center frequency of this structure is near zero. This structure has azimuthal and axial symmetries while with a finite radial wavenumber. The complete 3D spectra features of this structure have been identified to have the characteristics expected for zonal flows.
One-Step Preparation of N-Doped Nanowhisker TiO2 by Micro Arc Oxidation
SU Yu-Cheng, ZHANG Gu-Ling**, WANG Wen-Zhong, ZOU Bin, AO Le
Chin. Phys. Lett. 2011, 28 (2): 025203 .   DOI: 10.1088/0256-307X/28/2/025203
Abstract   PDF(pc) (813KB) ( 509 )
Flowers, trees and coral like TiO2 films are first produced by the micro−arc-oxidation method in electrolyte of phosphate. Nanowhiskers with high surface area grow at the tail ends of the coralloid film when the positive current density is set to be 17.14 A/dm2. With acetamide in electrolyte, N element is doped. The analysis results indicate that the ratio of anatase phase to rutile phases is about 2:1 in the micro−arc-oxidation produced N-TiO2 film. The optical absorption edge red shifts in the presence of N doping.
Clarification on Polarity of Bipolar Electric Field Solitary Structures in Space Plasmas with Satellite Observation
M. N. S. Qureshi, **, SHI Jian-Kui, Klaus Torkar, LIU Zhen-Xing
Chin. Phys. Lett. 2011, 28 (2): 025204 .   DOI: 10.1088/0256-307X/28/2/025204
Abstract   PDF(pc) (499KB) ( 328 )
The bipolar electric field solitary (EFS) structures observed frequently in space plasmas by satellites have two different polarities, first positive electric field peak then negative (i.e., positive/negative) and first negative then positive peak (i.e., negative/positive). We provide the physical explanation on the polarity of observed bipolar EFS structures with an electrostatic ion fluid model. The results show that if initial electric field E0>0, the polarity of the bipolar EFS structure will be positive/negative; and if E0 <0, the polarity of the bipolar EFS structure will be negative/positive. However, for a fixed polarity of the EFS, either positive/negative or negative/positive, if the satellite is located at the positive side of the EFS, the observed polarity should be positive/negative, if the satellite is located at the negative side of the EFS, the observed polarity should be negative/positive. Therefore, we provide a method to clarify the natural polarity of the EFS with observed polarity by satellites. Our results are significant to understand the physical process in space plasma with the satellite observation.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Curvature Dependence of Interfacial Properties for Associating Lennard–Jones Fluids: A Density Functional Study
SUN Zong-Li, KANG Yan-Shuang
Chin. Phys. Lett. 2011, 28 (2): 026101 .   DOI: 10.1088/0256-307X/28/2/026101
Abstract   PDF(pc) (624KB) ( 377 )
Classical density functional theory is used to study the associating Lennard–Jones fluids in contact with spherical hard wall of different curvature radii. The interfacial properties including contact density and fluid-solid interfacial tension are investigated. The influences of associating energy, curvature of hard wall and the bulk density of fluids on these properties are analyzed in detail. The results may provide helpful clues to understand the interfacial properties of other complex fluids.
Evaluation of a Filter-Based Model for Computations of Cavitating Flows
HUANG Biao, WANG Guo-Yu**
Chin. Phys. Lett. 2011, 28 (2): 026401 .   DOI: 10.1088/0256-307X/28/2/026401
Abstract   PDF(pc) (1077KB) ( 578 )
To identify ways to improve the predictive capability of the current RANS-based cavitating turbulent closure, a filter-based model (FBM) is introduced by considering sub-filter stresses. The sub-filter stress is constructed directly by using the filter size and the conventional turbulence closure. The model is evaluated in steady cavitating flow over a blunt body revolution and unsteady cavitating flow around a Clark-Y hydrofoil respectively. Compared with the experimental data, those results indicate that FBM can be used to improve the predictive capability considerably.
Effect of Pressure on Thermal Stability and Decomposition of KDP Crystal
DING Jian-Xu, WANG Tao, WANG Sheng-Lai**, CUI De-Liang**, MU Xiao-Ming, XU Xin-Guang
Chin. Phys. Lett. 2011, 28 (2): 026402 .   DOI: 10.1088/0256-307X/28/2/026402
Abstract   PDF(pc) (482KB) ( 482 )
Effect of pressure on thermal behavior of KDP crystals is investigated by using the in-situ infrared reflective spectra. Compared with that under normal atmosphere, the onset temperature of decomposition under pressure of 1 MPa is improved to from 210 °C to 213 °C, suggesting that the thermal stability of KDP is enhanced. Under pressure of 2 MPa, the thermal stability is deteriorated and KDP begins to decompose at 183 °C. Under normal atmosphere KDP decomposes in route of translating to K4P2O7 firstly, and then to KPO3. Under pressures of 1 MPa and 2 MPa, KDP translates to KPO3 directly without any other polymeric intermediates.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Polarization Mechanism of Oxygen Vacancy and Its Influence on Dielectric Properties in ZnO
WANG Li-Na, FANG Xiao-Yong**, HOU Zhi-Ling, LI Ya-Lin, WANG Kun, YUAN Jie, CAO Mao-Sheng**
Chin. Phys. Lett. 2011, 28 (2): 027101 .   DOI: 10.1088/0256-307X/28/2/027101
Abstract   PDF(pc) (1224KB) ( 671 )
We report on the mechanism of the dielectric properties of oxygen vacancy in ZnO, using ab initio numerical simulations of oxygen vacancy on the band structure and dielectric properties, to develop photoelectric material applications. It is revealed that the appearance of oxygen vacancies leads to wider energy band gap, obvious blue shift and increase in the peak of dielectric function as compared to the intrinsic ZnO simulation. We explain these unusual phenomena and analyze the dielectric changes with the mechanism of polarization in the semiconductors. It is shown that the main mechanism of influencing dielectric properties is the electron displacement polarization. The result may be helpful for development of photoelectric materials.
Properties of Si Doped Al0.4Ga0.6N Epilayers with Different AlGaN Window Layer Grown on High Quality AlN Buffer by MOCVD
YU Chen-Hui, LIU Cheng, HAN Xiang-Yun, KANG Wei, FANG Yan-Yan, DAI Jiang-Nan, WU Zhi-Hao, CHEN Chang-Qing**
Chin. Phys. Lett. 2011, 28 (2): 027301 .   DOI: 10.1088/0256-307X/28/2/027301
Abstract   PDF(pc) (949KB) ( 546 )
Si-doped Al0.4Ga0.6N (Si−Al0.4Ga0.6N) epilayers grown on an AlGaN window layer (WL) with different Al contents are prepared using a high−quality AlN buffer layer by metal-organic chemical vapor deposition. Surface morphology, crystalline quality and electric properties of these epilayers are investigated by using atomic force microscopy, x-ray diffraction, Raman scattering spectrum and Hall techniques. Results show that the surface morphology of these epilayers are mainly determined by the Si-doping level which, together with the effect of Al content of WL, also has an obvious impact on the electron concentrations. On the other hand, the insertion of AlGaN WL is helpful to the increase of Si doping level and conductivity of subsequently grown Si-Al0.4Ga0.6N epilayers. However, the insertion as well as the increase of Al content of WL result in increase of dislocation densities, compressive strain in Si−Al0.4Ga0.6N epilayers, and tilt of AlN subgrains at the top interface of the buffer layer. Further, the degradation of crystalline quality with the Al content of WL exerts a decisive influence on the conductivity of the Si−Al0.4Ga0.6N epilayers grown on WL with Al content of 0.6 through a dramatic decrease in electron mobility.
Electronic Non-Resonant Tunneling through Diaminoacenes: A First-Principles Investigation
ZHENG Ji-Ming, HUANG Yao-Qing**, REN Zhao-Yu, YANG Hui-Jing, CAO Mao-Sheng**
Chin. Phys. Lett. 2011, 28 (2): 027302 .   DOI: 10.1088/0256-307X/28/2/027302
Abstract   PDF(pc) (584KB) ( 359 )
The electron transport through diaminoacenes sandwiched between two Au electrodes is simulated by using a first-principles analysis. The nonlinear current-voltage characteristic is observed. Effects of the ring number and positions of amine groups on equilibrium transport properties are found. For 1,4 series, the greater the number of the rings, the stronger the transmission spectrum near the Fermi energy. For 2,6 series, the larger the number of the rings, the weaker the transmission spectrum near the Fermi energy. This is helpful for understanding the recently reported results on conductance measurements using amines.
Magnetic Properties of Orthorhombic Perovskite Ho1−xLaxMnO3
WANG Hong-Tao, ZHOU Tong, HONG Bo, TAO Qian, XU Zhu-An**
Chin. Phys. Lett. 2011, 28 (2): 027501 .   DOI: 10.1088/0256-307X/28/2/027501
Abstract   PDF(pc) (710KB) ( 452 )
Single phase orthorhombic perovskite Ho1−xLaxMnO3 (x=0.1, 0.15) compounds are successfully synthesized by using a sol−gel method. We find that the orthorhombic perovskite structure of HoMoO3 compound can be stabilized by partial substitution of smaller Ho ion by larger La ion. The magnetic properties of orthorhombic perovskite Ho1−xLaxMnO3 are investigated for the first time. For the x=0.15 sample, a ferromagnetic−like transition is found around T = 130 K, which should correspond to partial FM ordering of Mn3+ magnetic moments. The partial substitution of Ho by La causes a switch of magnetic state of Mn3+ moments from AFM order to FM-like order. Our study indicates that La doping has significant influence on the magnetic structures of Mn ions.
Anomalous Temperature Dependence of Photoluminescence in InAs/InAlGaAs/InP Quantum Wire and Dot Hybrid Nanostructures
YANG Xin-Rong**, XU Bo, WANG Hai-Fei, ZHAO Guo-Qing, SHI Shu-Hui, SHEN Xiao-Zhi, LI Jun-Feng, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (2): 027801 .   DOI: 10.1088/0256-307X/28/2/027801
Abstract   PDF(pc) (478KB) ( 461 )
Self-assembled InAs quantum wires (QWRs) are fabricated on an InP substrate by solid-source molecular beam epitaxy (SSMBE). Photoluminescence (PL) spectra are investigated in these nanostructures as a function of temperature. An anomalous enhancement of PL intensity and a temperature insensitive PL emission are observed from InAs nanostructures grown on InP substrates using InAlGaAs as the matrix layer and the origin of this phenomenon is discussed. We attribute the anomalous temperature dependence of photoluminescence to the formation of Al-rich and In-rich region in the InAlGaAs buffer layer and the cap layer.
Up-Conversion Photostimulated Luminescence of Mg2SnO4 for Optical Storage
ZHANG Jia-Chi**, QIN Qing-Song, YU Ming-Hui, SUN Jia-Yao, SHI Liu-Rong, MA Xin-Long
Chin. Phys. Lett. 2011, 28 (2): 027802 .   DOI: 10.1088/0256-307X/28/2/027802
Abstract   PDF(pc) (469KB) ( 576 )
We report the first observation of up-conversion photostimulated luminescence in non-doped Mg2SnO4. Stimulated by 980 nm infrared laser (reading) after ultraviolet irradiation (writing), the phosphor shows photostimulated emission band covering 470–550 nm, which is due to the recombination of F centers with holes. After ceasing ultraviolet irradiation, the storage intensity would rapidly decrease to 59% of its original storage intensity in 2.5 h and then would not degrade anymore. It is suggested that the Mg2SnO4 has potential applications for optical storage. Accordingly, the possible photostimulated luminescence mechanisms of Mg2SnO4 are proposed.
Photoluminescence of Nominally Undoped Heavy n-Type ZnO Nanowires
TANG Hai-Ping, HE Hai-Ping**, LIU Chao, KWON Bong-Jun, YE Zhi-Zhen, LEE Soonil, PARK Ji-Yong***
Chin. Phys. Lett. 2011, 28 (2): 027803 .   DOI: 10.1088/0256-307X/28/2/027803
Abstract   PDF(pc) (673KB) ( 544 )
We report the identification of a donor band and the correlation between n-type conductivity and the green emission in ZnO nanowires. Temperature-dependent photoluminescence is used to investigate nominally undoped ZnO nanowires with high n-type conductivity. Within the whole temperature range, a dominant free-to-bound transition with a donor band of about 150 meV below the conduction band minimum is observed. The nanowires show very strong green emission, which is quenched with activation energy of about 220 meV. The correlation between the high n-type conductivity and the strong green emission is discussed in detail, and we suggest that they may have different origins.
Nd-Doping Induced Lattice Distortion in TiO2 Nanoparticles
WANG Yue, WU Da-Jian, YANG Yue-Tao, LIU Xiao-Jun**
Chin. Phys. Lett. 2011, 28 (2): 027804 .   DOI: 10.1088/0256-307X/28/2/027804
Abstract   PDF(pc) (902KB) ( 915 )
Nd-doping effects are investigated in TiO2 nanoparticles with various annealing temperatures T from 70 °C to 1100 °C by means of x−ray diffraction (XRD) and Raman scattering spectroscopy. XRD results indicate that the sample shows a rutile phase at 1100 °C, which changes to anatase phase at 900 °C. With decreasing T down to 300 °C, a significant lattice shrink is found, that is, the lattice parameter c is significantly suppressed while the a value shows a gradual decrease. With further decrease of T, the c−value shows an unexpected increase while the a−value keeps a gradual decrease. Thus, a lattice distortion takes place with changing the annealing temperature. In Raman investigation, all the Raman modes for the anatase phase show hardening behaviors with decreasing T in the range 900–300 °C, and then the Eg and A1g modes show softening behaviors below 300 °C, suggesting the variation of the lattice distortion. The variation of the lattice distortion at different annealing temperatures is ascribed to different depositions of Nd ions on the surface of TiO2 nanoparticles.
Synthesis of Red Phosphor CaZrO3:Eu3+ for White Light-Emitting Diodes
LI Xu, GUAN Li**, AN Jia-Yi, JIN Li-Tao, YANG Zhi-Ping, YANG Yan-Min, LI Pan-Lai, FU Guang-Sheng
Chin. Phys. Lett. 2011, 28 (2): 027805 .   DOI: 10.1088/0256-307X/28/2/027805
Abstract   PDF(pc) (754KB) ( 857 )
A red-emitting CaZrO3:Eu3+ phosphor has been prepared by solid state reaction and its luminescent properties are studied. The crystal structure is investigated by the x−ray diffraction. Through energy transitions of 5D07FJ (J=0, 1, 2, 3) in Eu3+ ions, the emission spectrum of the phosphor shows a series of narrow bands under near−ultraviolet light and the strongest peak locates at 613 nm. The emission intensity of Ca1-xZrO3:xEu3+ phosphor will reach the maximum as the molar concentration of Eu3+ is 5 mol%.
Optical Characteristics of La-Doped ZnS Thin Films Prepared by Chemical Bath Deposition
XIE Hai-Qing, CHEN Yuan, HUANG Wei-Qing, HUANG Gui-Fang, PENG Ping, PENG Li, WANG Tai-Hong, ZENG Yun, **
Chin. Phys. Lett. 2011, 28 (2): 027806 .   DOI: 10.1088/0256-307X/28/2/027806
Abstract   PDF(pc) (601KB) ( 1072 )
Undoped and La-doped ZnS thin films are prepared by chemical bath deposition (CBD) process through the co-precipitation reaction of inorganic precursors zinc sulfate, thiosulfate ammonia and La2O3. Composition of the films is analyzed using an energy-dispersive x-ray spectroscopy (EDS). Absorption spectra and spectral transmittances of the films are measured using a double beam UV-VIS spectrophotometer (TU-1901). It is found that significant red shifts in absorption spectra and decrease in absorptivity are obtained with increasing lanthanum. Moreover, optical transmittance is increased as La is doped, with a transmittance of more than 80% for wavelength above 360 nm in La-doped ZnS thin films. Compared to pure ZnS, the band gap decreases and flat-band potential positively shifts to quasi-metal for the La-doped ZnS. These results indicate that La-doped ZnS thin films could be valuably adopted as transparent electrodes.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
A Novel Model of the H Radical in Hot-Filament Chemical Vapor Deposition
GUO Xiao-Song, BAO Zhong, ZHANG Shan-Shan, XIE Er-Qing**
Chin. Phys. Lett. 2011, 28 (2): 028101 .   DOI: 10.1088/0256-307X/28/2/028101
Abstract   PDF(pc) (869KB) ( 514 )
Amorphous hydrogenated and crystalline silicon thin films were prepared by hot-filament chemical vapor deposition. A structural transformation from amorphous phase to crystalline phase by increasing the filament temperature T fil from 1600 °C to 1650 °C was observed. This phenomenon may result from the associated abundance of H radicals participating in the growth of the films. A probability distribution model of the H radical is proposed to elucidate this phenomenon. According to this model, the phase transition is due to a distinct difference in the probability distribution of the H radicals, which seems to be dependent upon Tfil.
Influence of N2 Flux on InN Film Deposition on Sapphire (0001) Substrates by ECR-PEMOCVD
ZHOU Zhi-Feng, QIN Fu-Wen, **, ZANG Hai-Rong, ZHANG Dong, CHEN Wei-Ji, ZHI An-Bo, LIU Xing-Long, YU Bo, JIANG Xin,
Chin. Phys. Lett. 2011, 28 (2): 028102 .   DOI: 10.1088/0256-307X/28/2/028102
Abstract   PDF(pc) (637KB) ( 358 )
Highly preferred InN films are deposited on sapphire (0001) substrates by electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) without using a buffer layer. The structure, surface morphological and electrical characteristics of InN are investigated by in-situ reflection high energy electron diffraction, x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy and Hall effect measurement. The quality of the as-grown InN films is markedly improved at the optimized N2 flux of 100 sccm. The results show that the properties of the films are strongly dependent on N2 flux.
Effect of Substrate Temperature on the Structural, Electrical and Optical Properties of Nanocrystalline Silicon Films in Hot-Filament Chemical Vapor Deposition
GUO Xiao-Song, ZHANG Shan-Shan, BAO Zhong, ZHANG Hong-Liang, CHEN Chang-Cheng, LIU Li-Xin, LIU Yan-Xia, XIE Er-Qing**
Chin. Phys. Lett. 2011, 28 (2): 028103 .   DOI: 10.1088/0256-307X/28/2/028103
Abstract   PDF(pc) (1622KB) ( 386 )
Hydrogenated nanocrystalline silicon films are deposited onto glass substrates at different substrate temperatures (140–400 °C) by hot−filament chemical vapor deposition. The effect of substrate temperature on the structural properties are investigated. With an increasing substrate temperature, the Raman crystalline volume fraction increases, but decreases with a further increase. The maximum Raman crystalline volume fraction of the nanocrystalline silicon films is about 74% and also has the highest microstructural factor (R=0.89) at a substrate temperature of 250 °C. The deposition rate exhibits a contrary tendency to that of the crystalline volume fraction. The continuous transition of the film structures from columnar to agglomerated is observed at a substrate temperature of 300 °C. The optical band gaps of the grown thin films declines (from 1.89 to 1.53 eV) and dark electrical conductivity increases (from about 1010 to about 10−6 S/cm) with the increasing substrate temperature.
The Effect of Current Density on CNx Crystal Grain Growth in Electrochemical Deposition
YU Wei-Feng, CAO Rong-Gen, TIAN Yu, WANG Jian-Zhong, NING Xi-Jing, **
Chin. Phys. Lett. 2011, 28 (2): 028104 .   DOI: 10.1088/0256-307X/28/2/028104
Abstract   PDF(pc) (651KB) ( 370 )
The effect of charge current density on the growth of CNx films by electrolysis of a methanol−urea solution is investigated experimentally. It is seen that the c−C3N4 phase grains in the films are about 200–300 nm for a density of 55 mA/cm2 and dendrite growth takes place with grains as large as 7 μm formed when density is about 70 mA/cm2.
Synchronized Firings in Retinal Ganglion Cells in Response to Natural Stimulation
ZHANG Ying-Ying, XIAO Lei, LIU Wen-Zhong, GONG Hai-Qing, LIANG Pei-Ji**
Chin. Phys. Lett. 2011, 28 (2): 028701 .   DOI: 10.1088/0256-307X/28/2/028701
Abstract   PDF(pc) (451KB) ( 321 )
The response of synchronously firing groups of population retinal ganglion cells (RGCs) to natural movies (NMs) and pseudo-random white-noise checker-board flickering (CB, as control) are investigated using an information-theoretic algorithm. The main results are: (1) the population RGCs tend to fire in synchrony far more frequently than expected by chance during both NM and CB stimulation; (2) more synchronous groups could be formed and each group contains more neurons under NM than CB stimulation; (3) the individual neurons also participate in more groups and have more distinct partners in NM than CB stimulation. All these results suggest that the synchronized firings in RGCs are more extensive and diverse, which may account for more effective information processing in representing the natural visual environment.
Photo-Crosslinking Induced Geometric Restriction Controls the Self-Assembly of Diphenylalanine Based Peptides
TIE Zuo-Xiu, QIN Meng**, ZOU Da-Wei, CAO Yi**, WANG Wei
Chin. Phys. Lett. 2011, 28 (2): 028702 .   DOI: 10.1088/0256-307X/28/2/028702
Abstract   PDF(pc) (616KB) ( 493 )
The diphenylalanine (FF) motif has been widely used in the design of peptides that are capable of forming various ordered structures, such as nanotubes, nanospheres and hydrogels. In these assemblies, FF based peptides adopt an antiparallel structure and are stabilized by π−π stacking among the phenyl groups. Here we show that assembly of FF-based peptides can be controlled by their geometric restrictions. Using tripeptide FFY (L-Phe-L-Phe-L-Tyr) as an example, we demonstrate that photo-crosslinking of C-terminal tyrosine can impose a geometric restriction to the formation of an antiparallel structure, leading to a structural change of the assemblies from nanosphere to amorphous. This finding is confirmed using far-UV circular dichroism, Fourier transform infrared spectroscopy and atomic force microscopy. Based on such a mechanism, we are able to control the gel-sol transition of Fmoc-FFY using the geometric restriction induced by photo-crosslinking of C-terminal tyrosine groups. We believe that geometric restriction should be considered as an important factor in the design of peptide-based materials. It can also be implemented as a useful strategy for the construction of environment-responsive "smart" materials.
A New Method to Measure Trap Characteristics of Silicon Solar Cells
MA Xun, LIU Zu-Ming, QU Sheng, WANG Shu-Rong, HAO Rui-Ting, LIAO Hua
Chin. Phys. Lett. 2011, 28 (2): 028801 .   DOI: 10.1088/0256-307X/28/2/028801
Abstract   PDF(pc) (514KB) ( 531 )
A new method to measure trap characteristics in crystalline silicon solar cells is presented. Important parameters of traps including energy level, total concentration of trapping centers and capture cross-section ratio of hole to electron are deduced using the Shockley–Read–Hall theory of crystalline silicon solar cells in base region. Based on the as-deduced model, these important parameters of traps are determined by measuring open-circuit voltages of silicon solar cells under monochromatic illumination in the wavelength range 500–1050 nm with and without bias light. The effects of wavelength and intensity of bias light on the measurement results are also discussed. The measurement system used in our experiments is very similar to a quantum efficiency test system which is commercially available. Therefore, our method is very convenient and valuable for detecting deep level traps in crystalline silicon solar cells.
Competition Ability Dependence on Uniqueness in General Cooperation-Competition Systems
LIU Ai-Fen, XU Xiu-Lian, FU Chun-Hua, WANG Jian, HE Da-Ren**
Chin. Phys. Lett. 2011, 28 (2): 028901 .   DOI: 10.1088/0256-307X/28/2/028901
Abstract   PDF(pc) (1468KB) ( 371 )
We discuss the dependence of competition ability on uniqueness for the general cooperation-competition networks. An empirical investigation of the 15 real world systems is made. We find that the dependence varies with the change of systems. Although most of the systems show positive tendency, we find that a special system shows negative one. The relationship between the heterogeneity indexes for the distributions of competition ability and uniqueness is also discussed analytically and empirically.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Interference Phase of Mass Neutrino in Schwarzschild de Sitter Field
CAO Guang-Tao**, WANG Yong-Jiu
Chin. Phys. Lett. 2011, 28 (2): 029701 .   DOI: 10.1088/0256-307X/28/2/029701
Abstract   PDF(pc) (390KB) ( 388 )
We calculate the interference phase of the mass neutrinos in high energy limit propagating in radial and nonradial directions along the geodesic by solving Hamilton-Jacobi equation, and discuss the contributions of cosmological constant λ and angular momentum L to the phase shift in Schwarzschild de Sitter spacetime.
Original Articles
Evolution of Interacting Viscous Dark Energy Model in Einstein Cosmology
CHEN Ju-Hua, **, ZHOU Sheng, WANG Yong-Jiu,
Chin. Phys. Lett. 2011, 28 (2): 029801 .   DOI: 10.1088/0256-307X/28/2/029801
Abstract   PDF(pc) (481KB) ( 479 )
We investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model. By using the linearizing theory of the dynamical system, we find that, in our model, there exists a stable late time scaling solution which corresponds to the accelerating universe. We also find the unstable solution under some appropriate parameters. In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy with the dark matter. However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model. That is to say, both the non-perfect fluid model and the interacting the dark energy cosmic model can alleviate or soften the singularity of the universe.
Inflation and Singularity in Einstein–Cartan Theory
HUANG Zeng-Guang**, FANG Wei, LU Hui-Qing, **
Chin. Phys. Lett. 2011, 28 (2): 029802 .   DOI: 10.1088/0256-307X/28/2/029802
Abstract   PDF(pc) (503KB) ( 467 )
Within the framework of Einstein–Cartan theory, we obtain a general condition leading to singularity and inflation for all Bianchi cosmological models. If the spin energy is smaller than anisotropic energy density (i.e. S2−σ2≤0), the Universe can not avoid singularity. If S2−σ2>-ρv/2 (ρv is vacuum energy density), the Universe can undergo an inflation phase. Examples of Bianchi type−IX, I and V cosmological models are discussed.
Friedman–Robertson–Walker Models with Late-Time Acceleration
Abdussattar**, S. R. Prajapati**
Chin. Phys. Lett. 2011, 28 (2): 029803 .   DOI: 10.1088/0256-307X/28/2/029803
Abstract   PDF(pc) (375KB) ( 308 )
In order to account for the observed cosmic acceleration, a modification of the ansatz for the variation of density in Friedman–Robertson–Walker (FRW) FRW models given by Islam is proposed. The modified ansatz leads to an equation of state which corresponds to that of a variable Chaplygin gas, which in the course of evolution reduces to that of a modified generalized Chaplygin gas (MGCG) and a Chaplygin gas (CG), exhibiting late-time acceleration.
69 articles