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Volume 28 Issue 11
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Inertial Lévy Flight with Nonlinear Friction
LÜ, Yan**, BAO Jing-Dong
Chin. Phys. Lett. 2011, 28 (11): 110201 .   DOI: 10.1088/0256-307X/28/11/110201
Abstract   PDF(pc) (631KB) ( 501 )
Lévy flight with nonlinear friction is studied. Due to the occurrence of extremely long jumps Lévy flights often possess infinite variance and are physically problematic if describing the dynamics of a particle of finite mass. However, by introducing nonlinear friction, we show that the stochastic process subject to Lévy noise exhibits finite variance, leading to a well-defined kinetic energy. In the force-free field, normal diffusion behavior is observed and the diffusion coefficient decreases with Lévy index μ. Furthermore, we find a kinetic resonance of the particle in the harmonic potential to the external oscillating field in the generally underdamped region and the value of the linear friction γ0 determines whether resonance occurs or not.
Rogue Wave, Breathers and Bright-Dark-Rogue Solutions for the Coupled Schrödinger Equations
GUO Bo-Ling, LING Li-Ming, **
Chin. Phys. Lett. 2011, 28 (11): 110202 .   DOI: 10.1088/0256-307X/28/11/110202
Abstract   PDF(pc) (529KB) ( 2863 )
We construct explicit rogue wave solutions, breather solitons, and rogue-bright-dark solutions for the coupled non-linear Schrödinger equations by the Darboux transformation.
Conformal Invariance of Higher-Order Lagrange Systems by Lie Point Transformation
HUANG Wei-Li, CAI Jian-Le**
Chin. Phys. Lett. 2011, 28 (11): 110203 .   DOI: 10.1088/0256-307X/28/11/110203
Abstract   PDF(pc) (434KB) ( 394 )
Conformal invariance and conserved quantities for a higher-order Lagrange system by Lie point transformation of groups are studied. The differential equation of motion for the higher-order Lagrange system is introduced. The definition of conformal invariance for the system together with its determining equations and conformal factor are provided. The necessary and sufficient condition that the system's conformal invariance would be Lie symmetry by the infinitesimal one-parameter point transformation group is deduced. The conserved quantity of the system is derived using the structural equation satisfied by the gauge function. An example of a higher-order mechanical system is offered to illustrate the application of the result.
Analysis and Control of Two-Layer Frenkel–Kontorova Model
TANG Wen-Yan**, QU Zhi-Hua, GUO Yi
Chin. Phys. Lett. 2011, 28 (11): 110204 .   DOI: 10.1088/0256-307X/28/11/110204
Abstract   PDF(pc) (526KB) ( 437 )
A one-dimensional two-layer Frenkel–Kontorova model is studied. Firstly, a feedback tracking control law is given. Then, the boundedness result for the error states of single particles of the model is derived using the Lyapunov Method. Especially, the motion of single particles can be approximated analytically for the case of sufficiently large targeted velocity. Simulations illustrate the accuracy of the derived results.
Novel Approach for a van der Pol Oscillator in the Continuous Time Domain
Junaid Ali Khan**, Muhammad Asif Zahoor Raja**, Ijaz Mansoor Qureshi
Chin. Phys. Lett. 2011, 28 (11): 110205 .   DOI: 10.1088/0256-307X/28/11/110205
Abstract   PDF(pc) (426KB) ( 723 )
We investigate the continuous time domain numerical treatment of a van der Pol oscillator, applying the trial solution as an artificial feed-forward neural network model containing unknown adjustable parameters. The optimization of the network is performed by simulated annealing in an unsupervised method. The proposed scheme is tested successfully by its application in both non-stiff and stiff conditions. Its reliability and effectiveness is validated through comprehensive statistical analyses. The obtained results are in good agreement with the classical RK45 method.
Dynamics of Nonclassical Correlation in Interacting Qubits under Correlated Dissipative Environments
QIU Liang
Chin. Phys. Lett. 2011, 28 (11): 110301 .   DOI: 10.1088/0256-307X/28/11/110301
Abstract   PDF(pc) (772KB) ( 405 )
The dynamical evolution of nonclassical correlation in interacting qubits is investigated under the correlated dissipative environments for two classes of initial states. If the correlated decay rate equals the independent decay rate, there will be stationary nonclassical correlation between the qubits prepared initially in some separable states. When the correlated decay rate is different from the independent decay rate, the nonclassical correlation between the qubits eventually decays to zero for a certain class of initial states.
Unification of General Relativity with Quantum Field Theory
NI Jun
Chin. Phys. Lett. 2011, 28 (11): 110401 .   DOI: 10.1088/0256-307X/28/11/110401
Abstract   PDF(pc) (334KB) ( 483 )
In the frame of quantum field theory, instead of using the action principle, we deduce the Einstein equation from purely the general covariant principle and the homogeneity of spacetime. The Einstein equation is shown to be the gauge equation to guarantee the local symmetry of spacetime translation. Gravity is an apparent force due to the curvature of spacetime resulted from the conservation of energy-momentum. In the action of quantum field theory, only electroweak-strong interactions should be considered with the curved spacetime metric determined by the Einstein equation.
Random Long-Range Interaction Induced Synchronization in Coupled Networks of Inertial Ratchets
WEI Du-Qu**, LUO Xiao-Shu, CHEN Hong-Bin, ZHANG Bo
Chin. Phys. Lett. 2011, 28 (11): 110501 .   DOI: 10.1088/0256-307X/28/11/110501
Abstract   PDF(pc) (2137KB) ( 370 )
We investigate how the random long-range interactions affect the synchronization features in networks of inertial ratchets, where each ratchet is driven by a periodic time-dependent external force, under the influence of an asymmetric periodic potential. It is found that for a given coupling strength C, the synchronization of the coupled ratchets is induced as the fraction of random long−range interactions p increases and the ratchet networks reach full synchronization for a larger p. It is also found that the system reaches synchronization more effectively for a stronger coupling strength.
Effect of Interface Structure on Thermal Boundary Conductance by using First-principles Density Functional Perturbation Theory
GAO Xue, ZHANG Yue**, SHANG Jia-Xiang
Chin. Phys. Lett. 2011, 28 (11): 110502 .   DOI: 10.1088/0256-307X/28/11/110502
Abstract   PDF(pc) (633KB) ( 523 )
We choose a Si/Ge interface as a research object to investigate the influence of interface disorder on thermal boundary conductance. In the calculations, the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials, while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory. The results show that interface disorder limits thermal transport. The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance. This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.
Fractal Erosion of the Safe Basin in a Helmholtz Oscillator and Its Control by Linear Delayed Velocity Feedback
SHANG Hui-Lin**, WEN Yong-Peng
Chin. Phys. Lett. 2011, 28 (11): 110503 .   DOI: 10.1088/0256-307X/28/11/110503
Abstract   PDF(pc) (522KB) ( 381 )
Fractal erosion of the safe basin in a Helmholtz oscillator system is studied. A linear delayed velocity feedback is employed to suppress the fractal erosion. The necessary basin erosion condition of the delayed feedback controlled system is obtained. The evolution of the boundary and area of the safe basin over time delay is also presented. It follows that the delayed velocity feedback can be used as an effective strategy to control fractal erosion of a safe basin.
Predicting Natural and Chaotic Time Series with a Swarm-Optimized Neural Network
Juan A. Lazzús**
Chin. Phys. Lett. 2011, 28 (11): 110504 .   DOI: 10.1088/0256-307X/28/11/110504
Abstract   PDF(pc) (563KB) ( 520 )
Natural and chaotic time series are predicted using an artificial neural network (ANN) based on particle swarm optimization (PSO). Firstly, the hybrid ANN+PSO algorithm is applied on Mackey–Glass series in the short-term prediction x(t+6), using the current value x(t) and the past values: x(t−6), x(t−12), x(t−18). Then, this method is applied on solar radiation data using the values of the past years: x(t−1), ..., x(t−4). The results show that the ANN+PSO method is a very powerful tool for making predictions of natural and chaotic time series.
Vibrational and Stochastic Resonance in the FitzHugh–Nagumo Neural Model with Multiplicative and Additive Noise
HE Zheng-You, ZHOU Yu-Rong**
Chin. Phys. Lett. 2011, 28 (11): 110505 .   DOI: 10.1088/0256-307X/28/11/110505
Abstract   PDF(pc) (484KB) ( 529 )
The vibrational resonance and stochastic resonance phenomena in the FitzHugh–Nagumo (FHN) neural model, driven by a high-frequency (HF) signal and a low-frequency (LF) signal and by coupled multiplicative and additive noises, is investigated. For the case that the frequency of the HF signal is much higher than that of the LF signal, under the adiabatic approximation condition, the expression of the signal-to-noise ratio (SNR) with respect to the LF signal is obtained. It is shown that the SNR is a non-monotonous function of the amplitude and frequency of the HF signal. In addition, the SNR varies non-monotonically with the increasing intensities of the multiplicative and additive noise as well as with the increasing system parameters of the FHN model. The influence of the coupling strength between the multiplicative and additive noises on the SNR is discussed.
Chaos Suppression in a Sine Square Map through Nonlinear Coupling
Eduardo L. Brugnago**, Paulo C. Rech
Chin. Phys. Lett. 2011, 28 (11): 110506 .   DOI: 10.1088/0256-307X/28/11/110506
Abstract   PDF(pc) (1867KB) ( 440 )
We study a pair of nonlinearly coupled identical chaotic sine square maps. More specifically, we investigate the chaos suppression associated with the variation of two parameters. Two-dimensional parameter-space regions where the chaotic dynamics of the individual chaotic sine square map is driven towards regular dynamics are delimited. Additionally, the dynamics of the coupled system is numerically characterized as the parameters are changed.
Adaptive Increasing-Order Synchronization and Anti-Synchronization of Chaotic Systems with Uncertain Parameters
M. Mossa Al-sawalha, M. S. M. Noorani
Chin. Phys. Lett. 2011, 28 (11): 110507 .   DOI: 10.1088/0256-307X/28/11/110507
Abstract   PDF(pc) (428KB) ( 453 )
We elaborate the concept of increasing-order synchronization and anti-synchronization of chaotic systems via an adaptive control scheme and modulation parameters. It is shown that the dynamical evolution of a third-order chaotic system can be synchronized and anti-synchronized with a fourth-order chaotic system even though their parameters are unknown. Theoretical analysis and numerical simulations are carried out to verify the results.
Temporal Parameter Optimization in Four-Dimensional Flash Trajectory Imaging
WANG Xin-Wei**, ZHOU Yan, FAN Song-Tao, LIU Yu-Liang
Chin. Phys. Lett. 2011, 28 (11): 110601 .   DOI: 10.1088/0256-307X/28/11/110601
Abstract   PDF(pc) (1330KB) ( 373 )
In four-dimensional flash trajectory imaging, temporal parameters include time delay, laser pulse width, gate time, pulse pair repetition frequency and the frame rate of CCD, which directly impact on the acquisition of target trajectories over time. We propose a method of optimizing the temporal parameters of flash trajectory imaging. All the temporal parameters can be estimated by the spatial parameters of the volumes of interest, target scale and velocity, and target sample number. The formulae for optimizing temporal parameters are derived, and the method is demonstrated in an experiment with a ball oscillating as a pendulum.
Highly Sensitive Rayleigh Wave Hydrogen Sensors with WO3 Sensing Layers at Room Temperature
WANG Cheng, FAN Li, ZHANG Shu-Yi**, YANG Yue-Tao, ZHOU Ding-Mao, SHUI Xiu-Ji
Chin. Phys. Lett. 2011, 28 (11): 110701 .   DOI: 10.1088/0256-307X/28/11/110701
Abstract   PDF(pc) (718KB) ( 441 )
Rayleigh wave hydrogen sensors based on 128° YX−LiNbO3 substrates with WO3 sensing layers operating at room temperature are studied. The experimental results indicate that the WO3 layers obtained by a sol−gel method have much higher sensitivities because the sensing layers produced by the sol-gel method have small grains and high roughness and porosity. It is also confirmed that in the sol-gel method, keeping WO3 solutions at low temperature and/or decreasing the viscosity of the solutions can decrease the grain sizes and increase the hydrogen-absorbability of the sensing layer. Under the optimized preparation conditions, the high sensitivity of the hydrogen sensors at room temperature is obtained, in which 1% hydrogen in natural air induces the frequency shift of 72 kHz at the operating frequency of 124.2 MHz.
Pressure-induced Phase Transition in Oleic Acid Studied by Raman Spectroscopy
FAN Ya, ZHOU Jing, LI Shuang, GUAN Fu-Ying, XU Da-Peng**
Chin. Phys. Lett. 2011, 28 (11): 110702 .   DOI: 10.1088/0256-307X/28/11/110702
Abstract   PDF(pc) (565KB) ( 583 )
High-pressure Raman studies up to 0.84 GPa are performed on oleic acid. Spectral analysis indicates that oleic acid undergoes a pressure-induced phase transition in the 0.29–0.36 GPa range. Only one high-pressure phase below 0.84 GPa is present, in which the polymethylene chains take the ordered all-trans conformation, with the methyl end of the chains exhibiting the ordered tt chain−end conformation and the olefin group taking the skew-cis−skew' conformation. The conformational characters of the oleic acid molecule show that the high-pressure phase is the same as the low-temperature crystalline γ phase. The pressure-induced phase transition is typical of first-order transitions and the transition path during compression is different from that during cooling.
Fermion Mass Hierarchies in Singlet-Extended Minimal-Supersymmetric-Standard-Model Quivers
Salah Eddine Ennadifi**, Adil Belhaj, El Hassan Saidi,
Chin. Phys. Lett. 2011, 28 (11): 111201 .   DOI: 10.1088/0256-307X/28/11/111201
Abstract   PDF(pc) (415KB) ( 290 )
In the context of type-IIA orientifold compactifications, we discuss the fermion masses in a two−singlet-extended minimal-supersymmetric-standard-model four-stack quiver with U(3)×Sp(1)×U(1)×U(1) gauge symmetry. The corresponding effective superpotential exhibits hierarchical coupling term scales giving a partial solution to the fermion masses problem. Using the known data with upper bound neutrino masses mντ≲ 2 eV, we estimate the relevant scales for the model.
A Simple Singlet Fermionic Dark-Matter Model Revisited
QIN Hong-Yi**, WANG Wen-Yu, XIONG Zhao-Hua
Chin. Phys. Lett. 2011, 28 (11): 111202 .   DOI: 10.1088/0256-307X/28/11/111202
Abstract   PDF(pc) (1898KB) ( 342 )
We evaluate the spin-independent elastic dark matter-nucleon scattering cross section in the framework of the simple singlet fermionic dark matter extension of the standard model and constrain the model parameter space with the following considerations: (i) new dark matter measurement, in which, apart from WMAP and CDMS, the results from the XENON experiment are also used in constraining the model; (ii) new fitted value of the quark fractions in nucleons, in which the updated value of fTs from the recent lattice simulation is much smaller than the previous one and may reduce the scattering rate significantly; (iii) new dark matter annihilation channels, in which the scenario where top quark and Higgs pairs produced by dark matter annihilation was not included in the previous works. We find that unlike in the minimal supersymmetric standard model, the cross section is just reduced by a factor of about 1/4 and dark matter lighter than 100 GeV is not favored by the WMAP, CDMS and XENON experiments.
Single Production of a Heavy T-Quark in the Left-Right Twin Higgs Model at LHeC
SHEN Jie-Fen**, CUI Xiao-Min, LI Yu-Qi, GAO Yin-Hao
Chin. Phys. Lett. 2011, 28 (11): 111203 .   DOI: 10.1088/0256-307X/28/11/111203
Abstract   PDF(pc) (679KB) ( 295 )
In the context of the left-right twin Higgs model, we study single production of a T−quark at the Large Hadron electron Collider based ep and γp colliders, which proceed via the processes e+b→νeT and γb→WT. For the main decay mode T→φ+b→tbb, these two processes mainly transfer to the final states of 3b+ l (e or μ) + missing ET and 3b + 2l + missing ET, respectively. With the electron energy Ee=500 GeV and photon energy Ep=7 TeV, we find that the production rates can reach tens fb when the heavy T−quark mass mT<600 GeV. A simple phenomenological analysis is also given for the decay mode T→W+b. Our numerical results show that the SM background can be reduced by applying a cut on the transverse momentum of the final b−quark and the invariant mass of Wb. However, such a channel is only useful for a tiny parameter space.
Next-to-Leading Order QCD Corrections to t
DUAN Peng-Fei, ZHANG Ren-You, MA Wen-Gan, HAN Liang, GUO Lei, WANG Shao-Ming
Chin. Phys. Lett. 2011, 28 (11): 111401 .   DOI: 10.1088/0256-307X/28/11/111401
Abstract   PDF(pc) (643KB) ( 316 )
We present theoretical predictions including the complete next-to-leading order (NLO) QCD corrections to the top quark pair production in association with a photon at the LHC with the center-of-mass system energy of 7 TeV. The uncertainties of the leading order (LO) and NLO QCD corrected cross sections due to the renormalization/factorization scale, and the distributions of the transverse momenta of the final top quark and the photon are studied. Moreover, we provide the numerical results of the LO, NLO QCD corrected cross sections and the corresponding K−factors with different photon transverse momentum cuts. We also discuss the impact of QCD corrections to the pp →ttγ+X in the case that there exists an exotic top quark with an electric charge of −4e/3 at the 7 TeV LHC.
Shape Evolution in Rotating 178Os
HAO Xin**, ZHU Li-Hua, WU Xiao-Guang, HE Chuang-Ye, ZHENG Yun, LI Li-Hua, SUN Hui-Bin, LI Guang-Sheng
Chin. Phys. Lett. 2011, 28 (11): 112101 .   DOI: 10.1088/0256-307X/28/11/112101
Abstract   PDF(pc) (474KB) ( 374 )
In order to investigate the evolution of X(5) in rotating 178Os, an experiment populating 178Os via the fusion evaporation reaction 154Sm(29Si,5n)178Os was performed at the HI−13 tandem accelerator at the China Institute of Atomic Energy (CIAE). Lifetimes of excited states above 8+ in the yrast band in 178Os have been measured using the Doppler shift attenuation method. Lifetimes above 12+ states were measured for the first time. The deduced transitional quadruple moments (Qt), together with the previous data using the recoil distance Doppler shift (RDDS) method are compared with theoretical calculations based on the X(5) model and the interaction Boson model (IBM). Above the 10+ states, the Qt values fit well with the X(5) predictions. The present result suggests that the shape of a nucleus 178Os keeps X(5) critical point symmetry as spin increases to at least 14+. The shape change of 178Os with spin increasing is similar to that of 176Os.
Symmetry Energy Effects in a Statistical Multifragmentation Model
ZHANG Lei**, GAO Yuan, , ZHANG Hong-Fei, CHEN Xi-Meng, Yu Mei-Ling, LI Jun-Qing
Chin. Phys. Lett. 2011, 28 (11): 112102 .   DOI: 10.1088/0256-307X/28/11/112102
Abstract   PDF(pc) (562KB) ( 516 )
The symmetry energy effects on the nuclear disintegration mechanisms of the neutron-rich system (A0=200, Z0=78) are studied in the framework of the statistical multifragmentation model (SMM) within its micro-canonical ensemble. A modified symmetry energy term with consideration of the volume and surface asymmetry is adopted instead of the original invariable value in the standard SMM model. The results indicate that as the volume and surface asymmetries are considered, the neutron-rich system translates to a fission-like process from evaporation earlier than the original standard SMM model at lower excitation energies, and its mass distribution has larger probabilities in the medium-heavy nuclei range so that the system breaks up more averagely. When the excitation energy becomes higher, the volume and surface asymmetry lead to a smaller average multiplicity.
Inclusive Proton Energy Spectra of the Deuteron Induced Reaction
WANG Jia, YE Tao, SUN Wei-Li**, Yukinobu Watanabe, Kazuyuki Ogata
Chin. Phys. Lett. 2011, 28 (11): 112401 .   DOI: 10.1088/0256-307X/28/11/112401
Abstract   PDF(pc) (599KB) ( 392 )
The continuum-discritized coupled channel method and the glauber model are applied for the description of deuteron elastic breakup and the stripping processes, respectively. Combined with the conventional two-component exciton model for pre-equilibrium processes and the Hauser-Feshbach theory for compound process, an approach based on models is proposed to analyze the inclusive proton energy spectra of a deuteron-induced reaction. The contributions from each process to the energy spectra of the 58Ni(d,xp) reaction are quantitatively given. The results show that this approach is able to reasonably reproduce the experimental data of the double differential cross sections, energy spectra and cross sections, although further improvements are needed.
Development of Vertical Buffered Electropolishing for Its Post-Treatment Technology on 1.5 GHz Niobium SRF Cavities
JIN Song, A. T. Wu**, LU Xiang-Yang, R. A. Rimmer, LIN Lin, ZHAO Kui
Chin. Phys. Lett. 2011, 28 (11): 112901 .   DOI: 10.1088/0256-307X/28/11/112901
Abstract   PDF(pc) (551KB) ( 442 )
We report the latest research development of vertical buffered electropolishing on its post-treatment procedure as well as the effects of several major post-treatment techniques for buffered electropolishing (BEP) processed 1.5 GHz niobium (Nb) superconducting radio frequency (SRF) cavities. With the established post-treatment procedure, an accelerating gradient of 28.4 MV/m is obtained on a single cell cavity of the cebaf shape. This is the best result in the history of BEP development. The cavity is limited by quench with a high quality factor over 1.2×1010 at the quench point. Analyses from optical inspection and temperature-mapping show that the quench should be originated from the pits that were already present on the cavity before this BEP treatment. All of these factors indicate that this procedure will have a great potential to produce better results if cavities without intrinsic performance limiting imperfections are used.
Reagent Vibration Effect on the Stereodynamics for the C+CDC2+D Reaction*
XIE Ting-Xian, SHI Ying**
Chin. Phys. Lett. 2011, 28 (11): 113101 .   DOI: 10.1088/0256-307X/28/11/113101
Abstract   PDF(pc) (939KB) ( 391 )
We study the effect of the reagent vibration of the CD on the stereodynamics of the C+CD→C2 +D reaction by using the quasi−classical trajectory method at a collision energy of 2.306 kcal/mol on the potential energy surface of the 12A' state [Boggio−Pasqua et al. Mol. Phys. 98 (2000) 1925]. The vector correlation distributions p(θr) and the dihedral−angle distribution p(φr) as well as p(θrr) are calculated. In addition, two polarization-dependent generalized differential cross sections of the product are presented and discussed within a center-of-mass framework. The results show that the effect of reagent vibration can cause obviously different effects on the stereodynamics of the title reaction.
Density Functional Theory and Grand Canonical Monte Carlo Simulations of the Hydrogen Storage Properties of Partially Truncated and Open Cage C60 Fullerenes
LI Xiao-Dong, TANG Yong-Jian, CHENG Xin-Lu, ZHANG Hong**
Chin. Phys. Lett. 2011, 28 (11): 113102 .   DOI: 31.15.E-, 81.05.Ug, 02.70.Lq
Abstract   PDF(pc) (630KB) ( 367 )
The potential energies of H2 molecules with partially truncated and open cage C60 fullerenes, including C58, C55, C54(I), C54(II) and C46, are investigated by means of the density functional theory method. The energy barrier for one H2 molecule (with two postures) entering into the nanocage decreases from 435.59 (513.45) kcal/mol to 3.64 (2.06) kcal/mol with the increase of the truncated pore. The grand canonical Monte Carlo simulations reveal that each nanocage can accommodate only one H2 molecule inside its cavity at both 77 K and 298 K. All the other H2 molecules are adsorbed round the truncated pores outside the nanocages. Exceptionally, the truncated C46 can store 2.28wt% H2 molecules at 77 K. Therefore, the truncating part of the C60 molecule may be a novel idea to explore C60 fullerene as a hydrogen storage material.
Output Enhancement of a THz Wave Based on a Surface-Emitted THz-Wave Parametric Oscillator
LI Zhong-Yang**, YAO Jian-Quan, XU De-Gang, BING Pi-Bin, ZHONG Kai
Chin. Phys. Lett. 2011, 28 (11): 114201 .   DOI: 10.1088/0256-307X/28/11/114201
Abstract   PDF(pc) (563KB) ( 300 )
High-power nanosecond pulsed THz-wave radiation is achieved via a surface-emitted THz-wave parametric oscillator. One MgO:LiNbO3 crystal with large volume is used as the gain medium. THz−wave radiation from 1.084 THz to 2.654 THz is obtained. The maximum THz-wave average power is 5.8 µW at 1.93 THz when the pump energy is 84 mJ, corresponding to a energy conversion efficiency of 6.9×10−6. The polarization characteristics of THz wave are analyzed. During the experiments the radiations of the first-order and the second-order Stokes wave are observed.
A [111]-Cut Si Hemisphere Two-Photon Response Photodetector
LIU Xiu-Huan, CHEN Zhan-Guo**, JIA Gang, WANG Hai-Yan, GAO Yan-Jun, LI Yi
Chin. Phys. Lett. 2011, 28 (11): 114202 .   DOI: 10.1088/0256-307X/28/11/114202
Abstract   PDF(pc) (590KB) ( 691 )
Properties of two-photon response in a [111]-cut nearly-intrinsic Si hemisphere photodetector are studied. The measured photocurrent of the photodetector responding to the 1.32 µm continuous wave laser shows a quadratic dependence on the coupled optical power and is saturated with the bias voltage. Also, the photocurrent is independent of polarization. Such properties are in good agreement with the theory of two−photon absorption. The isotropic photocurrent generated from the [111]-cut Si hemisphere is compared to the anisotropic one induced in the [110]-cut Si sample and the ratio of χxxxx /χxxyy for silicon performing at 1.32 µm is calculated to be 2.4 via the fitted function of the anisotropic photocurrent from the [110]-cut sample.
Passively Mode-Locked Fiber Laser with a Sub-Megahertz Repetition Rate
CHEN Jiong, JIA Dong-Fang**, WU Yong-Chao, WANG Chang-Le, WANG Zhao-Ying, YANG Tian-Xin
Chin. Phys. Lett. 2011, 28 (11): 114203 .   DOI: 10.1088/0256-307X/28/11/114203
Abstract   PDF(pc) (783KB) ( 651 )
We demonstrate an ultra-long cavity by which an all-fiber erbium-doped fiber laser is passively mode-locked by nonlinear polarization rotation. The length of the resonant cavity amounts to 466 m, which can be achieved by incorporating a 420 m highly nonlinear fiber. The laser generates stable mode-locked pulses with a 444 kHz fundamental repetition rate. A near transform-limited subpicosecond pulse is obtained without any dispersion compensation. The maximum average power of the output pulses is 5.16 mW, which corresponds to a per-pulse energy of 11.62 nJ.
Bandgaps of the Chalcogenide Glass Hollow-Core Photonic Crystal Fiber
LI Shu-Guang**, ZHOU Hong-Song, YIN Guo-Bing
Chin. Phys. Lett. 2011, 28 (11): 114204 .   DOI: 10.1088/0256-307X/28/11/114204
Abstract   PDF(pc) (718KB) ( 449 )
Bandgaps of chalcogenide glass hollow-core photonic crystal fibers (GLS HC-PCFs) are analyzed by using the plane-wave expansion method. A mid-infrared laser can propagate in these low confinement loss fibers when the wavelength falls into the bandgaps. For enlarging the bandgap width, an improved GLS HC-PCF is put forward, the normalized frequency of the improved fiber is from 7.2 to 8.5 in its first bandgap. The improved GLS HC−PCF with pitch of 4.2 µm can transmit the lights with wavelengths ranging from 3.1 µm to 3.7 µm .
Helium-Implanted Optical Planar Waveguides in Nd3+-Doped Phosphate Glass
LIU Chun-Xiao, , LIU Tao, LIU Xiu-Hong, WEI Wei**, PENG Bo**
Chin. Phys. Lett. 2011, 28 (11): 114205 .   DOI: 10.1088/0256-307X/28/11/114205
Abstract   PDF(pc) (595KB) ( 379 )
We report the fabrication of planar waveguides in Nd3+-doped phosphate glass by helium ion implantation. The guiding properties of the waveguide are evaluated by a prism coupler and end-face coupling methods. The refractive index profile of the waveguide is reconstructed by using the intensity calculation method. Absorption and fluorescence investigations reveal that helium ion implantation causes only slight changes in the optical properties, suggesting the possible application of the fabricated structures as waveguide lasers.
Compact All-Fiber 102 W Picosecond MOPA Laser with a Narrow Spectral Linewidth
WU Wen-Di, REN Ting-Qi**, ZHOU Jun**, DU Song-Tao, GU Xi-Jia, LOU Qi-Hong
Chin. Phys. Lett. 2011, 28 (11): 114206 .   DOI: 10.1088/0256-307X/28/11/114206
Abstract   PDF(pc) (458KB) ( 1119 )
We report an all-fiber-based master oscillator power amplifier picosecond ytterbium-doped fiber laser with an average power of 102 W and a spectral line width of 0.1 nm. The seed source is a compact single mode passively mode-locked fiber laser with an average power of 2.48 W. Finally, the laser maximum average output power of 102 W picosecond pulses is realized by a direct all-fiber amplifier structure in one stage. The experiment enables the optical-to-optical conversion efficiency to reach 61.4%, with the central wavelength of 1063.7nm. A significant feature of this experiment is the spectral line width of 0.1 nm. The spectrum has no broadening or nonlinear effects when the pump is strengthened.
An InP-Based Dual-Depletion-Region Electroabsorption Modulator with Low Capacitance and Predicted High Bandwidth
SHAO Yong-Bo**, ZHAO Ling-Juan, YU Hong-Yan, QIU Ji-Fang, QIU Ying-Ping, PAN Jiao-Qing, WANG Bao-Jun, ZHU Hong-Liang, WANG Wei
Chin. Phys. Lett. 2011, 28 (11): 114207 .   DOI: 10.1088/0256-307X/28/11/114207
Abstract   PDF(pc) (570KB) ( 510 )
A novel dual-depletion-region electroabsorption modulator (DDR-EAM) based on InP at 1550 nm is fabricated. The measured capacitance and extinction ratio of the DDR-EAM reveal that the dual depletion region structure can reduce the device capacitance significantly without any degradation of extinction ratio. Moreover, the bandwidth of the DDR-EAM predicted by using an equivalent circuit model is larger than twice the bandwidth of the conventional lumped-electrode EAM (L-EAM).
Diode Laser Optically Injected by Resonance of a Monolithic Cavity
PENG Yu, **, ZHAO Yang, LI Ye, YANG Tao, CAO Jian-Ping, FANG Zhan-Jun, ZANG Er-Jun
Chin. Phys. Lett. 2011, 28 (11): 114208 .   DOI: 10.1088/0256-307X/28/11/114208
Abstract   PDF(pc) (673KB) ( 14542 )
We demonstrate a self-injection locking extended cavity diode laser (ECDL) using resonant optical feedback from the p-polarization of a monolithic folded Fabry–Perot parallel cavity (MFC). The full width at half maximum of the MFC resonance is 31 MHz. With the help of a narrow-linewidth reference laser, the linewidth of the ECDL is measured to be about 7 kHz. The frequency of the laser could be tuned at 160 MHz with an amplitude of 40 V by a PZT mounted on the monolithic cavity and the voltage tuning coefficient is about 4 MHz/V.
Automatic Compensation of Total Phase Aberrations in Digital Holographic Biological Imaging
ZHANG Yi-Zhuo, WANG Da-Yong, **, WANG Yun-Xin, TAO Shi-Quan
Chin. Phys. Lett. 2011, 28 (11): 114209 .   DOI: 10.1088/0256-307X/28/11/114209
Abstract   PDF(pc) (2464KB) ( 362 )
Digital holographic microscopy has been a powerful metrological technique for phase-contrast imaging. However inherent phase aberrations always exist and degrade the quality of the phase-contrast images. A surface fitting method based on an improved mathematic model is proposed, which can be used to remove the phase aberrations without any pre-knowledge of the setup or manual operation. The improved mathematic model includes not only the usual terms but also the cross terms and the high order terms to describe the phase aberrations with high accuracy. Meanwhile, a non-iterative algorithm is used to solve the parametersand thus less computational load is imposed. The proposed method is applied to the live imaging of cells. The experimental results verify its validity.
Novel Propagation Properties of Total Internal Reflection Photonic Crystal Fibres with Rhombic Air Holes
YAN Hai-Feng**, YU Zhong-Yuan, LIU Yu-Min, TIAN Hong-Da, HAN Li-Hong
Chin. Phys. Lett. 2011, 28 (11): 114210 .   DOI: 10.1088/0256-307X/28/11/114210
Abstract   PDF(pc) (444KB) ( 563 )
We investigate the propagation properties of a multi-layer photonic crystal fiber with novel rhombic air holes using the finite element method, and calculate the dependence of the propagation properties on the wavelength in the fiber with different geometrical structural parameters, including the internal angle and the external arrangement of the rhombic air holes. Optimizing these parameters, we design a photonic crystal which exhibits both a small dispersion value and low loss near the wavelength of 1.55 µm .
Single and Multicasting Inverted-Wavelength Conversion at 80 Gb/s Based on a Single Semiconductor Optical Amplifier
HUANG Xi, QIN Cui, YU Yu, ZHANG Xin-Liang**
Chin. Phys. Lett. 2011, 28 (11): 114211 .   DOI: 10.1088/0256-307X/28/11/114211
Abstract   PDF(pc) (549KB) ( 353 )
We experimentally demonstrate single and multicasting inverted wavelength conversion at 80 Gb/s by using the cross-gain modulation and cross-phase modulation in a single semiconductor optical amplifier (SOA). In all the cases, converted signals with a high extinction ratio (ER) and large eye opening are obtained. For single-channel wavelength conversion, the ER of the output signal is as high as 30.10 dB. For three-channel wavelength multicasting, high quality converted signals could also be observed. The ERs with three channels are 21.54 dB, 18.58 dB and 17.72 dB, respectively. Thus, one- and three-channel wavelength conversion with high performance can be achieved by using a single quantum-well SOA.
Multicolor InAs/InP(100) Quantum Dot Laser
LI Shi-Guo**, GONG Qian, CAO Chun-Fang, WANG Xin-Zhong, WANG Rui-Chun, YUE Li, LIU Qing-Bo, WANG Hai-Long
Chin. Phys. Lett. 2011, 28 (11): 114212 .   DOI: 10.1088/0256-307X/28/11/114212
Abstract   PDF(pc) (611KB) ( 505 )
We report on a three-colour InAs/InP(100) quantum dot laser under continuous wave mode at an operation temperature of 20 °C. Three lasing peaks are observed simultaneously, the high-energy peak undergoes continuous blueshift, while the splitting energy gap between the low-energy peaks is somewhat fixed as the injection current increases. The maximum output power from one facet without coating is more than 34 mW with a slope efficiency of 102 mW/A just above the threshold current. Three peaks of differential efficiency of output power are observed, just corresponding to each peak in lasing spectra, respectively. At the same time, the far-field distribution shows only a single transverse mode over the full range of injection current.
Resonance Effects of Bilayered Piezoelectric Films Used for Bulk Acoustic Wave Sensors
Chin. Phys. Lett. 2011, 28 (11): 114301 .   DOI: 10.1088/0256-307X/28/11/114301
Abstract   PDF(pc) (551KB) ( 452 )
The resonance vibrations of acoustic sensors with two layers of (1120) textured hexagonal piezoelectric films are studied. When the acoustic and electric fields satisfy a special match condition, i.e. the phase variation of thickness shear mode (TSM) at each film equals π, both piezoelectric layers with opposite polarization directions reduce the first TSM and generate the second TSM with higher frequency and a higher quality factor. The excited second TSM can increase the product of the operating frequency and the quality factor, which is useful for improving the mass sensitivity and resolution of acoustic sensors. Additionally, both of the piezoelectric films have larger thickness and decrease the risk of mechanical damage in device production processes.
Data-Derived Estimation of Source Depth Using Vertical Line Array Data in Shallow Water
WANG Hao-Zhong, WANG Ning, GAO Da-Zhi
Chin. Phys. Lett. 2011, 28 (11): 114302 .   DOI: 10.1088/0256-307X/28/11/114302
Abstract   PDF(pc) (593KB) ( 373 )
Following the closure relation of normal mode theory, the source depth can be estimated approximately provided that the eigenfunction and the excited amplitude with correct polarity of each effective mode are given. Both the eigenfunction and the excited amplitude of each effective mode can be extracted using the data-derived method, which does not require a priori knowledge about ocean environment and source range but the sound pressure data observed by vertical line array. The polarities, undetermined by data-derived method, can be estimated using a cost function. Then, the source depth is determined by locating the peak of the object function defined by the closure relation with the correct polarities. Numerical simulation and experiment are carried out to illustrate the performance of this method.
Analytical Solution of the Blast Wave Problem in a Non-Ideal Gas
L. P. Singh, S. D. Ram**, D. B. Singh
Chin. Phys. Lett. 2011, 28 (11): 114303 .   DOI: 10.1088/0256-307X/28/11/114303
Abstract   PDF(pc) (383KB) ( 726 )
An analytical approach is used to construct the exact solution of the blast wave problem with generalized geometries in a non-ideal medium. It is assumed that the density ahead of the shock front varies according to a power of distance from the source of the blast wave. Also, an analytical expression for the total energy in a non-ideal medium is derived.
Effects of a Premixed Layer on the Richtmyer–Meshkov Instability
TIAN Bao-Lin, ZHANG Xin-Ting, QI Jin**, WANG Shuang-Hu
Chin. Phys. Lett. 2011, 28 (11): 114701 .   DOI: 10.1088/0256-307X/28/11/114701
Abstract   PDF(pc) (528KB) ( 374 )
The effects of a premixed layer on the Richmyer–Meshkov instability (RMI) are studied by setting a density gradient for the first shocked fluid in the RMI problems. The RMI with initial density gradients are simulated by using a high resolution arbitrary Lagrangian–Eulerian method. The effects of density gradient and gradient width are analyzed on the basis of the simulation results for the shock from a light fluid to a heavy fluid and for the shock from a heavy fluid to a light fluid. Overall, the premixed layer can suppress the perturbation growth, and the detailed effects are different depending on the detailed premixed configuration. The width of the premixed layer has a very light influence on the perturbation, while the density gradient has quite a significant effect on two kinds of RMIs.
Viscous Swirling Flow over a Stretching Cylinder
Tiegang FANG**, Shanshan YAO
Chin. Phys. Lett. 2011, 28 (11): 114702 .   DOI: 10.1088/0256-307X/28/11/114702
Abstract   PDF(pc) (493KB) ( 858 )
We investigate a viscous flow over a cylinder with stretching and torsional motion. There is an exact solution to the Navier–Stokes equations and there exists a unique solution for all the given values of the flow Reynolds number. The results show that velocity decays faster for a higher Reynolds number and the flow penetrates shallower into the ambient fluid. All the velocity profiles decay algebraically to the ambient zero velocity.
Observation of Hot Electrons in Surface-Wave Plasmas Excited by Surface Plasmon Polaritons
HU Ye-Lin, CHEN Zhao-Quan, **, LIU Ming-Hai**, HONG Ling-Li, LI Ping, ZHENG Xiao-Liang, XIA Guang-Qing**, HU Xi-Wei
Chin. Phys. Lett. 2011, 28 (11): 115201 .   DOI: 10.1088/0256-307X/28/11/115201
Abstract   PDF(pc) (654KB) ( 461 )
The electron energy distribution functions (EEDFs) are studied in the planar-type surface-wave plasma (SWP) caused by resonant excitation of surface plasmon polaritons (SPPs) using a single cylindrical probe. Sustained plasma characteristics can be considered as a bi-Maxwellian EEDF, which correspond to a superposition of the bulk low-temperature electron and the high-energy electron beam-like part. The beam component energy is pronounced at about 10 eV but the bulk part is lower than 3.5 eV. The hot electrons included in the proposed plasmas play a significant role in plasma heating and further affect the discharge chemistry.
Electric Discharge in Pin-Plate Audio Frequency Plasma
A. A. Azooz*, S. K. Talal
Chin. Phys. Lett. 2011, 28 (11): 115202 .   DOI: 10.1088/0256-307X/28/11/115202
Abstract   PDF(pc) (4770KB) ( 369 )
Experimental results on some properties of electric discharge initiated by audio frequency voltages in the range of 50–10000 Hz are presented. These results indicate that there are at least two modes of plasma ionic oscillations. A resonance-type behavior is seen when the driving field frequency becomes equal to the plasma ionic frequency. The results for plasma density and plasma temperature for both modes are presented.
Optical Limiting Properties of Ag-Cu Metal Alloy Nanoparticles Analysis by using MATLAB
WANG Yu-Hua**, LI Hui-Qing, LU Jian-Duo, WANG Ru-Wu
Chin. Phys. Lett. 2011, 28 (11): 116101 .   DOI: 10.1088/0256-307X/28/11/116101
Abstract   PDF(pc) (504KB) ( 785 )
Ag-Cu alloy nanoparticles were formed by sequential ion implantation (Ag and Cu) in silica using a metal vapor vacuum arc (MEVVA) ion source. Third-order nonlinear optical properties of the nanoparticles were measured at 1064 nm excitations using the Z-scan technique. Curve fitting analysis, based on the MATLAB features for Ag-Cu alloy nanoparticle optical limiting experiments, is used. The results show that Ag-Cu alloy nanoparticles display a refractive optical limiting effect at 1064 nm.
Formation Mechanism of Micropores on the Surface of Pure Aluminum Induced by High-Current Pulsed Electron Beam Irradiation
ZOU Yang, CAI Jie, WAN Ming-Zhen, LV Peng, GUAN Qing-Feng**
Chin. Phys. Lett. 2011, 28 (11): 116102 .   DOI: 10.1088/0256-307X/28/11/116102
Abstract   PDF(pc) (622KB) ( 386 )
The mechanism of micropores formed on the surface of polycrystalline pure aluminum under high-current pulsed electron beam (HCPEB) irradiation is explained. It is discovered that dispersed micropores with sizes of 0.1–1 µm on the irradiated surface of pure aluminum can be successfully fabricated after HCPEB irradiation. The dominant formation mechanism of the surface micropores should be attributed to the formation of supersaturation vacancies within the near surface during the HCPEB irradiation and the migration of vacancies along grain boundaries and/or dislocations towards the irradiated surface. It is expected that the HCPEB technique will become a new method for the rapid synthesis of surface porous materials.
Structural and Magnetic Studies of Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O
Murtaza Saleem**, Saadat A. Siddiqi, Shahid Atiq, M. Sabieh Anwar
Chin. Phys. Lett. 2011, 28 (11): 116103 .   DOI: 10.1088/0256-307X/28/11/116103
Abstract   PDF(pc) (593KB) ( 490 )
Single-phase Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O samples were prepared by a novel combustion method. X-ray diffraction studies exhibit the pure phase wurtzite structure of doped ZnO. Energy dispersive x-ray analysis confirms the incorporation of dopants into the host material. Scanning electron microscopy shows the ordered morphology in both of the samples. Temperature-dependent resistivity analysis describes the expected semiconducting behavior that is similar to the parent ZnO materials. Room-temperature magnetic measurements reveal the absence of ferromagnetism in Co-doped ZnO, while the Co and Al co-doped sample displays apparent room-temperature ferromagnetic behavior. The decrease of resistivity and presence of ferromagnetic behavior in Al-doped ZnCoO system corroborate the significant role of free carriers.
Effects of the Cooling Rate on the Plasticity of Pd40.5Ni40.5P19 Bulk Metallic Glasses
LI Yang, QIU Sheng-Bao, SHAO Yang, YAO Ke-Fu**
Chin. Phys. Lett. 2011, 28 (11): 116104 .   DOI: 10.1088/0256-307X/28/11/116104
Abstract   PDF(pc) (1188KB) ( 435 )
We prepare Pd40.5Ni40.5P19 glassy samples with purified ingots by copper mold casting at a high cooling rate and by water quenching at a low cooling rate. Both of them exhibit different supercooled liquid regions and multiple glass transition characteristics in their differential scanning calorimetric curves. The plasticity of the glassy sample prepared by copper mold casting is about 5% while that prepared by water quenching is almost zero (0.2%), indicating that cooling rate has influenced the plasticity of glassy alloys. By using high resolution TEM image analysis, it is revealed that there exist characteristic regions with different contrasts in the full glassy samples. The characteristic size is about 20–40 nm for the glassy sample prepared by water quenching and 2–4 nm for the one prepared by copper mold casting. The large difference in the plasticity of the glassy samples prepared by different cooling rates is believed to be related to the difference in the size of the characteristic nanoscale structures. The results indicate that adjusting cooling rate in preparation of glassy samples could modify the thermal and mechanical properties of the glassy alloys.
Stiction of a Nano-Beam with Surface Effect
LIU Jian-Lin**, XIA Re, ZHOU Yue-Ting
Chin. Phys. Lett. 2011, 28 (11): 116201 .   DOI: 10.1088/0256-307X/28/11/116201
Abstract   PDF(pc) (506KB) ( 466 )
Nanowire stiction is a crucial bottleneck for the development of M/NEMS devices. We present a model of a nano-beam stuck to the substrate in consideration of both surface elasticity and residual surface stress. The critical detachment length can be derived from the transversality condition using the variational method. The effects of the surface parameters on the adhesion of the nano-beam are discussed in detail. These analyses provide some suggestions for engineers in the design and fabrication of more accurate M/NEMS instruments.
Hydrogen Storage Materials Based on Single-Layer Aluminum Nitride Nanostructures
WANG Yu-Sheng, YUAN Peng-Fei, LI Meng, SUN Qiang, JIA Yu**
Chin. Phys. Lett. 2011, 28 (11): 116801 .   DOI: 10.1088/0256-307X/28/11/116801
Abstract   PDF(pc) (948KB) ( 732 )
Using the first-principles method based on density functional theory, we study the hydrogen storage properties of Li-doped single-layer aluminum nitride nanostructures (AlN). For the pristine AlN sheet, each Al atom adsorbs one H2 with an average binding energy of 0.14 eV/H2. The hydrogen binding energies and storage capacities can be markedly increased by doping Li atoms onto the AlN sheet. The charge analysis shows that there are charges transferring from the Li atoms to the AlN sheet, thus the charged Li atoms can polarize hydrogen molecules and enhance the interaction between hydrogen molecules and the AlN sheet. In the fully loaded cases, the Li−doped AlN sheet can contain up to 8.25wt% of molecular hydrogen with an average binding energy of 0.20 eV/H2.
Effect of Interface Bond Type on the Structure of InAs/GaSb Superlattices Grown by Metalorganic Chemical Vapor Deposition
LI Li-Gong, LIU Shu-Man**, LUO Shuai, YANG Tao, WANG Li-Jun, LIU Feng-Qi, YE Xiao-Ling, XU Bo, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (11): 116802 .   DOI: 10.1088/0256-307X/28/11/116802
Abstract   PDF(pc) (760KB) ( 569 )
InAs/GaSb type-II superlattices were grown on (100) GaSb substrates by metalorganic chemical vapor deposition. Raman scattering spectroscopy reveals that it is possible to grow superlattices with almost pure GaAs-like and mixed-like (plane of mixed As and Sb atoms that connect the GaSb and InAs layers) interfaces. Introducing the InSb-like interface results in nanopipes and As contamination of the GaSb layers. X-ray diffraction and atomic force microscopy demonstrate that the superlattices with a mixed-like interface have better morphology and crystalline quality.
Simulation and Suppression of the Gas Phase Pre-reaction in Metal-Organic Chemical Vapor Deposition of ZnO
ZHU Guang-Yao, GU Shu-Lin**, ZHU Shun-Ming, TANG Kun, YE Jian-Dong, ZHANG Rong, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2011, 28 (11): 116803 .   DOI: 10.1088/0256-307X/28/11/116803
Abstract   PDF(pc) (661KB) ( 448 )
The reaction mechanism and simulations of the metal-organic chemical vapor deposition reactor for ZnO film growth are presented, indicating the temperature of the reaction species. The gas phase pre-reaction can be modulated by several factors or conditions. Simulations verify the relationships between temperature and pyrolysis of precursors, and further reveal that the substrate temperature and flow rate of cooling water have great impacts on the temperature distribution. The experimental results agree with the simulations.
Geometric and Electronic Structures at the Interface between Iron Phthalocyanine and Si (110)
JIN Dan, Ateeq ur Rehman, QIAN Hui-Qin, JIANG Li-Zhen, ZHANG Han-Jie, LI Hai-Yang, HE Pi-Mo, BAO Shi-Ning
Chin. Phys. Lett. 2011, 28 (11): 116804 .   DOI: 10.1088/0256-307X/28/11/116804
Abstract   PDF(pc) (889KB) ( 594 )
The geometric and electronic structures at the interface between iron phthalocyanine (FePc) and Si(110) surface are studied by ultraviolet photoelectron spectroscopy and density functional theory (DFT) calculation. After FePc is deposited on Si(110), the emission features are located at 2.56, 4.90, 7.90, 10.88 eV below the Fermi level for monolayer and 2.73, 4.90, 7.74, 10.52 eV below the Fermi level for multilayer. At the coverage of 1 ML, FePc molecules are adsorbed on the bridge site in a flat-lying geometry with a 2.17 Å separation between the molecule and the substrate. The molecular plane is bent due to the interaction between the adsorbate and the substrate.
Optical and Electronic Properties of Wurtzite Structure Zn1−xMgxO Alloys
BAI Li-Na, LIAN Jian-She**, JIANG Qing
Chin. Phys. Lett. 2011, 28 (11): 117101 .   DOI: 10.1088/0256-307X/28/11/117101
Abstract   PDF(pc) (727KB) ( 671 )
Optical and electronic properties of Zn1−xMgxO ternary alloys of wurtzite structure are calculated by using first−principles based on the framework of generalized gradient approximation to density functional theory with the introduction of the on-site Coulomb interaction. The use of the U parameter on Zn−3d and O−2p orbits is obviously crucial, which can improve the GGA to predict the electronic properties and bandgap of the Zn1−xMgxO (0≤x≤0.25) system reasonably. It is further demonstrated that the bandgap widens with an increasing Mg concentration from 3.217 eV of ZnO to 3.877 eV of Zn0.75Mg0.25O. Therefore, the theoretical results show that Zn1−xMgxO ternary alloys are potential candidates for optoelectronic materials, especially for UV photon emitters and detectors.
Temperature-Dependent Optical Properties of InAs/GaAs Self-Assembled Quantum Dots: Spectroscopic Measurements and an Eight-Band Study
ZHOU Xiao-Hao**, CHEN Ping-Ping, CHEN Xiao-Shuang, LU Wei
Chin. Phys. Lett. 2011, 28 (11): 117301 .   DOI: 10.1088/0256-307X/28/11/117301
Abstract   PDF(pc) (736KB) ( 520 )
The temperature-dependent optical properties of InAs/GaAs self-assembled quantum dots are studied by spectroscopic measurements along with the corresponding theoretical calculations. We observe the redshift of photoluminescence peak energy with increasing temperature and the thermally activated quenching of each state, which result from the efficient redistribution of carriers in quantum dots. Meanwhile, the electronic structures of the InAs/GaAs quantum dots are investigated by a detailed theoretical study in terms of an eight-band k⋅p model, taking strain effects into account. The calculated transition energies of the excitons are in reasonable agreement with the results of the photoluminescence spectra. According to the spatial distribution of carriers, it is found that the evolution of photogenerated excitons in quantum dots with temperature mainly relies on the electrons rather than the holes.
The Tunable Bandgap of AB-Stacked Bilayer Graphene on SiO2 with H2O Molecule Adsorption
WANG Tao, GUO Qing**, AO Zhi-Min**, LIU Yan, WANG Wen-Bo, SHENG Kuang, YU Bin,
Chin. Phys. Lett. 2011, 28 (11): 117302 .   DOI: 10.1088/0256-307X/28/11/117302
Abstract   PDF(pc) (1684KB) ( 656 )
The atomic and electronic structures of AB-stacking bilayer graphene (BLG) in the presence of H2O molecules are investigated by density functional theory calculations. For free−standing BLG, the bandgap is opened to 0.101 eV with a single H2O molecule adsorbed on its surface. The perfectly suspended BLG is sensitive to H2O adsorbates, which break the BLG lattice symmetry and open an energy gap. While a single H2O molecule is adsorbed on the BLG surface with a SiO2 substrate, the bandgap widens to 0.363 eV. Both the H2O molecule adsorption and the oxide substrate contribute to the BLG bandgap opening. The phenomenon is interpreted with the charge transfer process in 2D carbon nanostructures.
Low-Frequency Dependence of Conductivity and Dielectric Properties of Polyaniline/ZnFe2O4 Nanocomposites
G. D. Prasanna, H. S. Jayanna*, Ashok R Lamani, M. L. Dinesha, C. S. Naveen, G. J. Shankaramurthy
Chin. Phys. Lett. 2011, 28 (11): 117701 .   DOI: 10.1088/0256-307X/28/11/117701
Abstract   PDF(pc) (769KB) ( 1557 )
Conducting polyaniline/ZnFe2O4 nanocomposites are synthesized by using a simple and inexpensive one−step in-situ polymerization method in the presence of ZnFe2O4 nanoparticles. The structural, morphological and electrical properties of the samples are characterized by x−ray diffraction, Fourier transform infrared spectra and scanning electron microscopy. These results reveal the formation of polyaniline/ZnFe2O4 nanocomposites. The morphology of these samples is studied by scanning electron microscopy. Further, the ac conductivity (σac ) of these composites is investigated in the frequency range of 1 kHz–10 MHz. The presence of polarons and bipolarons are responsible for the frequency dependence of ac conductivity in these nanocomposites. The ac conductivity is found to be constant up to 1 MHz and thereafter it increases steeply. The ac conductivity of 0.695 S⋅cm−1 at room temperature is observed as the maxima for the polyaniline with 40wt% of the ZnFe2O4 nanocomposite.
Numerical Simulations of Nonlinear Dynamics of Electron Cyclotron Maser with a Straight Beam
KONG Ling-Bao**, HOU Zhi-Ling
Chin. Phys. Lett. 2011, 28 (11): 117702 .   DOI: 10.1088/0256-307X/28/11/117702
Abstract   PDF(pc) (444KB) ( 386 )
An electron cyclotron maser based on anomalous Doppler effect (ADECM) with an initially axial beam velocity is considered, and the nonlinear equation of beam-wave interaction is presented. With the numerical methods, the nonlinear dynamics of the ADECM is investigated. It is shown that the saturated interaction efficiency of the ADECM approaches 90% and the interaction length for the saturated efficiency spans about 5–20 cm. The results may be of importance for designing a compact device in applications in microwave generations or microwave heating of ceramic laminates.
Influence of Rapid Thermal Annealing on Carrier Dynamics in GaInNAs/GaAs Multiple Quantum Wells
ZHOU Wei**, YANG Jie, XIA Su-Jing, LI Xiang, TANG Wu
Chin. Phys. Lett. 2011, 28 (11): 117801 .   DOI: 10.1088/0256-307X/28/11/117801
Abstract   PDF(pc) (745KB) ( 341 )
The excitation intensity and time-resolved photoluminescence spectroscopy are used to investigate the impact of annealing on the carrier dynamics in the Ga0.66In0.34N0.013As0.987/GaAs multiple quantum well structure grown by metalorganic chemical vapor deposition. The measurement of excitation intensity photoluminescence (PL), performed for as-grown and annealed samples at different temperatures, indicates that the localized potential has come down slightly after annealing but does not alter the fact that PL emission at low temperature is dominated by localized exciton recombination. In contrast, free carrier recombination is magnified by post-grown annealing at room temperature. Our results show that the decay times are 0.587 and 0.327 ns at 10 K for the as-grown and annealed samples, and radiative decay times also shorten significantly after annealing at all temperatures. Hence the improvement of luminescence efficiency after annealing is caused by the reduction of localization and enhancement of radiative recombination rate. The reduction of the density of nonradiative centers is demonstrated indirectly after annealing.
Ultrafast Dynamics of Polythiophene with Phenyl Vinylene Branches Studied by Femtosecond Fluorescence Spectroscopy in Solution
CHU Sai-Sai, GAO Chao, WANG Shu-Feng**, GONG Qi-Huang**
Chin. Phys. Lett. 2011, 28 (11): 117802 .   DOI: 10.1088/0256-307X/28/11/117802
Abstract   PDF(pc) (597KB) ( 422 )
Two polythiophene based polymers, poly[(3-[2-[4-(2-ethyl-hexyloxy)-phenyl]-vinyl]-thiophene)-co-thiophene] (PT1) and poly(3-[2-[4-(2-ethyl-hexyloxy)-phenyl]-vinyl]-thiophene) (PT2), are synthesized and investigated by static, picosecond fluorescence spectroscopies and the femtosecond up-conversion technique in solution. Compared with pristine poly(3-hexylthiophene) (P3HT), PT1 and PT2, in which the main chains are decorated with phenyl vinylene present a 'camel back' structure in the absorption spectra. Phenyl vinylene side chains induce a new process of charge transfer, chain twisting motion and defect-induced fluorescence quenching at time scales of 1 ps, 10 ps and 150 ps, respectively.
Structural and Optoelectronic Properties of Cubic CsPbF3 for Novel Applications
G. Murtaza, Iftikhar Ahmad, **, M. Maqbool, H. A. Rahnamaye Aliabad, A. Afaq
Chin. Phys. Lett. 2011, 28 (11): 117803 .   DOI: 10.1088/0256-307X/28/11/117803
Abstract   PDF(pc) (921KB) ( 784 )
Chemical bonding as well as structural, electronic and optical properties of CsPbF3 are calculated using the highly accurate full potential linearized augmented plane−wave method within the framework of density functional theory (DFT). The calculated lattice constant is found to be in good agreement with the experimental results. The electron density plots reveal strong ionic bonding in Cs-F and strong covalent bonding in Pb-F. The calculations show that the material is a direct and wide bandgap semiconductor with a fundamental gap at the R-symmetry point. Optical properties such as the real and imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, optical conductivity and absorption coefficient are also calculated. Based on the calculated wide and direct bandgap, as well as other optical properties of the compound, it is predicted that CsPbF3 is suitable for optoelectronic devices and anti-reflecting coatings.
Growth of Few-Layer Graphene on Sapphire Substrates by Directly Depositing Carbon Atoms
KANG Chao-Yang, TANG Jun, LIU Zhong-Liang, LI Li-Min, YAN Wen-Sheng, WEI Shi-Qiang, XU Peng-Shou**
Chin. Phys. Lett. 2011, 28 (11): 118101 .   DOI: 10.1088/0256-307X/28/11/118101
Abstract   PDF(pc) (517KB) ( 530 )
Few-layer graphene (FLG) is successfully grown on sapphire substrates by directly depositing carbon atoms at the substrate temperature of 1300 °C in a molecular beam epitaxy chamber. The reflection high energy diffraction, Raman spectroscopy and near−edge x-ray absorption fine structure are used to characterize the sample, which confirm the formation of graphene layers. The mean domain size of FLG is around 29.2 nm and the layer number is about 2–3. The results demonstrate that the grown FLG displays a turbostratic stacking structure similar to that of the FLG produced by annealing C-terminated α-SiC surface.
Annealing Effect of Pulsed Laser Deposited Transparent Conductive Ta-Doped Titanium Oxide Films
WU Bin-Bin, PAN Feng-Ming**, YANG Yu-E
Chin. Phys. Lett. 2011, 28 (11): 118102 .   DOI: 10.1088/0256-307X/28/11/118102
Abstract   PDF(pc) (747KB) ( 997 )
Tantalum-doped TiO2 films were deposited on glass at 300°C by pulsed laser deposition (PLD). After post−annealing in vacuum (∼10−4 Pa) at temperatures ranging from 450°C to 650°C, these films were crystallized into an anatase TiO2 structure and presented good conductive features. With increasing annealing temperature up to 550°C, the resistivity of the films was measured to be around 8.7×10−4 Ω⋅cm. Such films exhibit high transparency of over 80% in the visible light region. These results indicate that tantalum-doped anatase TiO2 films have a great potential as transparent conducting oxides.
Mechanical Performances of Carbonitriding Films on Cast Iron by Plasma Electrolytic Carbonitriding
PANG Hua**, ZHANG Gu-Ling, WANG Xing-Quan, LV Guo-Hua, CHEN Huan, YANG Si-Ze,
Chin. Phys. Lett. 2011, 28 (11): 118103 .   DOI: 10.1088/0256-307X/28/11/118103
Abstract   PDF(pc) (1201KB) ( 831 )
The plasma electrolytic carbonitriding (PEC/N) process is applied to cast iron using an aqueous solution of acetamide and glycerin as the electrolyte. Mechanical properties of the carbonitriding layers on cast iron are investigated. After the PEC/N treatment, the microhardness and wear resistance of cast iron are improved significantly compared to the untreated substrate. When the substrate is processed at 350 V for 60 s, the coating presents the highest microhardness and it is about 554.14HK0.02, and the coating with the highest hardness has the best wear resistance.
Preparation and Luminescence Properties of the Na2W2O7 Crystal
WEI Qin-Hua, SHI Hong-Sheng**, CHAI Wen-Xiang, QIN Lai-Shun, SHU Kang-Ying
Chin. Phys. Lett. 2011, 28 (11): 118104 .   DOI: 10.1088/0256-307X/28/11/118104
Abstract   PDF(pc) (1042KB) ( 636 )
We discuss the synthesis of Na2W2O7 polycrystalline materials based on the TG−DSC experiment. The luminescence properties of the Na2W2O7 crystal are investigated using the Nd:YAG laser as the excitation source. It is found that the maximum emission peak of the Na2W2O7 crystal is at 525 nm. The 525−nm luminescence decay has two components. One has decay time 1.8 µs and the other 49.1 µs. By comparing this results with that of the Na2W4O13 crystal, it is assumed that the 525−nm luminescence emission of the Na2W2O7 crystal originates from the WO66− octahedral group.
Efficiency Droop Effect Mechanism in an InGaN/GaN Blue MQW LED
WANG Jia-Xing, WANG Lai**, HAO Zhi-Biao, LUO Yi
Chin. Phys. Lett. 2011, 28 (11): 118105 .   DOI: 10.1088/0256-307X/28/11/118105
Abstract   PDF(pc) (617KB) ( 2274 )
In order to clarify the origin of the efficiency droop effect in InGaN based blue multiple-quantum-well (MQW) light emitting diodes (LEDs), a reasonable model is set up, taking all the possible factor (carrier delocalization, carrier leakage and Auger recombination) into account. By fitting the external quantum efficiency-injection current (ηI) measurements of two LED samples, the validity of the model is demonstrated. The fit results show that the main origin of efficiency droop at a high injection current is carrier leakage. Furthermore it is also indicated that carrier delocalization plays an important role in the efficiency droop effect in those LEDs of large localization degree.
Bifurcation of a Swelling Gel with a Mechanical Load and Geometric Constraint
XUE Feng, YONG Hua-Dong, ZHOU You-He**
Chin. Phys. Lett. 2011, 28 (11): 118301 .   DOI: 10.1088/0256-307X/28/11/118301
Abstract   PDF(pc) (425KB) ( 401 )
We present an analysis of the bifurcation phenomenon of a gel in contact with a solvent. When a Mooney–Rivlin form-free energy function is introduced, an asymmetric swelling may appear for a gel swelling under uniaxial constraint or subjected to equal dead loads, which results in an interesting pitchfork bifurcation phenomenon. We present an analytical investigation of this problem based on the classical theory of continuum mechanics. The bifurcation points are obtained for different values of the chemical potential of the solvent molecules. The results demonstrate that the free swelling of the gel under uniaxial constraint will not result in the bifurcation unless further mechanical loads are applied.
Partially Loaded Cavity Analysis by Using the 2-D FDTD Method
YAO Bin, ZHENG Qin-Hong, **, PENG Jin-Hui, ZHONG Ru-Neng, XIANG Tai, XU Wan-Song
Chin. Phys. Lett. 2011, 28 (11): 118401 .   DOI: 10.1088/0256-307X/28/11/118401
Abstract   PDF(pc) (500KB) ( 392 )
A compact two-dimensional (2-D) finite-difference time-domain (FDTD) method is proposed to calculate the resonant frequencies and quality factors of a partially loaded cavity that is uniform in the z−direction and has an arbitrary cross section in the xy plane. With the description of z dependence by kz , the three-dimensional (3-D) problem can be transformed into a 2-D problem. Therefore, less memory and CPU time are required as compared to the conventional 3-D FDTD method. Three representative examples, a half-loaded rectangular cavity, an inhomogeneous cylindrical cavity and a cubic cavity loaded with dielectric post, are presented to validate the utility and efficiency of the proposed method.
Improved Performance of Fluorinated Copper Phthalocyanine Thin Film Transistors Using Para-hexaphenyl as the Inducing Layer
MA Feng, WANG Shi-Rong**, LI Xiang-Gao, YAN Dong-Hang
Chin. Phys. Lett. 2011, 28 (11): 118501 .   DOI: 10.1088/0256-307X/28/11/118501
Abstract   PDF(pc) (676KB) ( 394 )
We demonstrate n-type organic thin film transistors (OTFTs) employing copper hexadecafluorophthalocyanine (CuPcF16) as the active layer and para−hexaphenyl (p−6p) as the inducing layer. Compared with the CuPcF16−based OTFTs without the p−6p inducing layer, the performance of the CuPcF16/p−6p OTFTs is greatly improved. The charge carrier field-effect mobility μ, on−off current ratio Ion/Ioff and threshold voltage VT of the CuPcF16/p−6p OTFTs are 0.07 cm2/V⋅s, 1.61×105 and 6.28 V, respectively, approaching the level of a single crystal device. The improved performance is attributed to the introduction of p−6p to form a highly oriented and continuous film of CuPcF16 with the molecular ππ stack direction parallel to the substrate.
High Performance Polymer Field-Effect Transistors Based on Thermally Crosslinked Poly(3-hexylthiophene)
JIANG Chun-Xia, YANG Xiao-Yan, ZHAO Kai, WU Xiao-Ming, YANG Li-Ying, CHENG Xiao-Man, WEI Jun, YIN Shou-Gen, **
Chin. Phys. Lett. 2011, 28 (11): 118502 .   DOI: 10.1088/0256-307X/28/11/118502
Abstract   PDF(pc) (1044KB) ( 383 )
The performance of polymer field-effect transistors is improved by thermal crosslinking of poly(3-hexylthiophene), using ditert butyl peroxide as the crosslinker. The device performance depends on the crosslinker concentration significantly. We obtain an optimal on/off ratio of 105 and the saturate field−effect mobility of 0.34 cm2V−1s−1, by using a suitable ratios of ditert butyl peroxide, 0.5 wt% of poly(3-hexylthiophene). The microstructure images show that the crosslinked poly(3-hexylthiophene) active layers simultaneously possess appropriate crystallinity and smooth morphology. Moreover, crosslinking of poly(3-hexylthiophene) prevents the transistors from large threshold voltage shifts under ambient bias-stressing, showing an advantage in encouraging device environmental and operating stability.
Depth Determination of an Abnormal Heat Source in Biological Tissues
WANG Qing-Hua**, LI Zhen-Hua, LAI Jian-Cheng, HE An-Zhi
Chin. Phys. Lett. 2011, 28 (11): 118701 .   DOI: 10.1088/0256-307X/28/11/118701
Abstract   PDF(pc) (536KB) ( 381 )
We deduce the surface temperature distribution generated by the inner point heat source in biological tissues and propose a graphic method to retrieve the depth of the point heat source. The practical surface temperature distribution can be regarded as the convolution of the temperature distribution of the inner point heat source with the heat source shape function. The depth of an abnormal heat source in biological tissues can be retrieved by using the graphic method combined with the blind deconvolution scheme.
Effects of Labeling Thiophilic FRET Dyes on the Stability and Dimerization Process of β-Lactoglobulin
PAN Hai, XIE Jin-Bing, CAO Yi**, QIN Meng**, WANG Wei
Chin. Phys. Lett. 2011, 28 (11): 118702 .   DOI: 10.1088/0256-307X/28/11/118702
Abstract   PDF(pc) (721KB) ( 413 )
The stability and dimeric state of β−lactoglobulin (β−lg) can be dramatically affected by labeling the thiophilic agent to Cys121, whereas the underlining mechanism of such an effect is still unclear. We label a fluorescence-resonance-energy-transfer (FRET) pair of donor (1,5-IAEDANS) and acceptor (5-IAF) dyes to Cys121 of β−lg monomers to investigate the effect of bulky thiophilic modification on the structure and stability of β−lg. It is found that the modification dramatically destroys the native structure of β−lg and results in an obvious increase of the α−helical content, coincident with the accumulation of non-native α−helical intermediates during its folding process. Importantly, the dimeric state of β-lg can still be reached whereas its dimerization rate decreases dramatically, allowing us to characterize the dimerization process using the FRET method based on a stopped-flow apparatus. Our results reveal that the dimerization process occurs before the completely folding of individual monomers, providing direct evidence on the cooperativity of folding and binding processes.
Self-Organized Criticality in Small-World Networks Based on the Social Balance Dynamics
MENG Qing-Kuan
Chin. Phys. Lett. 2011, 28 (11): 118901 .   DOI: 10.1088/0256-307X/28/11/118901
Abstract   PDF(pc) (644KB) ( 378 )
A node model is proposed to study the self-organized criticality in the small-world networks which represent the social networks. Based on the node model and the social balance dynamics, the social networks are mapped to the thermodynamic systems and the phenomena are studied with physical methods. It is found that the avalanche in the small-world networks at the critical state satisfies the power-law distribution spatially and temporally.
Percolation of Mobile Individuals on Weighted Scale-Free Networks
WU An-Cai
Chin. Phys. Lett. 2011, 28 (11): 118902 .   DOI: 10.1088/0256-307X/28/11/118902
Abstract   PDF(pc) (535KB) ( 481 )
The percolation-like phase transition of mobile individuals is studied on weighted scale-free (WSF) networks, in which the maximum occupancy at each node is one individual (i.e. hard core interaction) and individuals can move to neighbor void node. Especially, the condition for the existence of a spanning cluster of individuals (a connected cluster of neighbor nodes occupied by individuals that span the entire systems) is investigated and it is found that there exists a critical value of weight coupling parameter βc, above which the density threshold of individuals is zero and below which the density threshold is larger than zero for WSF networks in the thermodynamic limit N→∞. Furthermore, the finite size scaling analysis show that for certain value β, the percolation transition of mobile individuals on a WSF network belongs to the same universality class of regular random graph percolation.
Interactions between Intersecting Pedestrian and Vehicle Flows on Roads
GUO Ren-Yong**, GUO Xi
Chin. Phys. Lett. 2011, 28 (11): 118903 .   DOI: 10.1088/0256-307X/28/11/118903
Abstract   PDF(pc) (661KB) ( 429 )
The crossing of vehicle flow by pedestrians at either signalized crosswalks or locations away from crosswalks is studied using a car-following model. The model process is constructed, and two safe criterions deciding whether pedestrians begin to cross a road and a rule stopping vehicles at a signal intersection are proposed. Numerical results indicate that the relations of both vehicles' and pedestrians' delays to the width of pedestrian arrival interval are nonlinear; careful pedestrians unnecessarily spend more time to cross a road than aggressive ones; pedestrians crossing near a traffic signal have more influence on their and vehicles' delays. When pedestrians are permitted to cross a road using the gaps between slow vehicles, their delay may increase.
Model of the Crustal Magnetic Field in the Martian Aurora Zone
TONG Dong-Sheng, CHEN Chu-Xin**
Chin. Phys. Lett. 2011, 28 (11): 119601 .   DOI: 10.1088/0256-307X/28/11/119601
Abstract   PDF(pc) (568KB) ( 379 )
It is well known that aurorae are prominent on planets with a global magnetic field and occur where open magnetic field lines converge. The UV spectrometer used for investigating the characteristics of the atmosphere of Mars (SPICAM) on board the Mars Express made the first observation of auroral-type emission in the cusp region of the strong crustal magnetic field on Mars and found that the arc of the Martian aurora zone is very narrow in width, which obviously differs from that of other planets. Based on the observation, we put forward a model of a crustal magnetic field on the Martian aurora zone through the morphology of Martian aurorae. In the model, equivalent currents are proposed; the topology and magnitude of the magnetic field generated by these equivalent currents are consistent with that of the crustal magnetic field in the Martian aurora zone. The morphology of the Martian aurora zone generated through the model matches well with the observations made by the Mars Express orbiter.
Original Articles
Modified Chaplygin Gas with Variable G and Λ
Ujjal Debnath
Chin. Phys. Lett. 2011, 28 (11): 119801 .   DOI: 10.1088/0256-307X/28/11/119801
Abstract   PDF(pc) (469KB) ( 404 )
We consider a modified Chaplygin gas with the gravitational constant G and the cosmological constant Λ. The trivial solution describes decelerating phase to accelerating phase of the universe. The non−static with constant equation of state describes the inflationary solution. For static universe, G and Λ must be formed arbitrarily, and for static universe with constant equation of state, G and Λ should be constant.
79 articles