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Volume 28 Issue 12
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GENERAL
Conservation Laws and Self-Consistent Sources for a Super-Classical-Boussinesq Hierarchy
YU Fa-Jun
Chin. Phys. Lett. 2011, 28 (12): 120201 .   DOI: 10.1088/0256-307X/28/12/120201
Abstract   PDF(pc) (391KB) ( 653 )
The super-classical-Boussinesq hierarchy with self-consistent sources is considered. Then, infinitely many conservation laws for the integrable super-classical-Boussinesq hierarchy are established.
Poisson Theory and Inverse Problem in a Controllable Mechanical System
XIA Li-Li
Chin. Phys. Lett. 2011, 28 (12): 120202 .   DOI: 10.1088/0256-307X/28/12/120202
Abstract   PDF(pc) (386KB) ( 388 )
The Poisson theory and inverse problem are studied in a controllable mechanical system. Equations of motion of the controllable mechanical system in phase space are given. Poisson's integral theory of the system is established. The potential force field is constructed by solving the inverse problem in a controllable mechanical system. Finally, an example is given to illustrate the application of the results.
Quantum Entanglement Channel based on Excited States in a Spin Chain
ZHANG Shao-Liang, DU Liang-Hui, GUO Guang-Can, ZHOU Xing-Xiang**, ZHOU Zheng-Wei**
Chin. Phys. Lett. 2011, 28 (12): 120301 .   DOI: 10.1088/0256-307X/28/12/120301
Abstract   PDF(pc) (484KB) ( 438 )
We study the possibility of using a spin chain to construct a quantum entanglement channel that can be used for quantum state transmission in a solid state system. We analyze the spin chain's states under various z-directional magnetic field and spin interactions to determine the entanglement between Alice and Bob's spins. We derive the conditions under which this entanglement can be distilled, and find that a spin chain of arbitrary length can be used as a quantum channel for quantum state transmission when the number of spin flips in the chain is large.
Non-Markovian Dynamics of Quantum and Classical Correlations in the Presence of System-Bath Coherence
LI Chuan-Feng**, WANG Hao-Tian, YUAN Hong-Yuan, GE Rong-Chun, GUO Guang-Can
Chin. Phys. Lett. 2011, 28 (12): 120302 .   DOI: 10.1088/0256-307X/28/12/120302
Abstract   PDF(pc) (634KB) ( 498 )
We present a detailed study on the dynamics of two-qubit correlations in non-Markovian environments, applying the hierarchy equations approach. This treatment is free from the limitation of perturbative, Markovian or rotating wave approximations. It is shown that crossovers and sudden changes in the classical and quantum correlations can appear when the strength of the interaction between qubits is gradually reduced. For some special initial states, there are even sudden transitions between the classical and quantum correlations.
An Effective Heisenberg Spin Chain in a Fiber-Cavity System
ZHONG Zhi-Rong**, ZHANG Bin, LIN Xiu, SU Wan-Jun
Chin. Phys. Lett. 2011, 28 (12): 120303 .   DOI: 10.1088/0256-307X/28/12/120303
Abstract   PDF(pc) (494KB) ( 422 )
We propose a scheme to realize the Heisenberg spin chain in a one-dimensional array of cavities connected by optical fibers. The proposed scheme is based on the off-resonant Raman transitions between two ground states of atoms, and is induced by the cavity modes and external fields. Under the interactions between the nearest neighbors (NNs) and the next NNs, the result shows that the atoms, via the exchange of virtual photons, can be effectively equal to a spin-1/2 Heisenberg model under certain conditions. The parameters of the effective Hamiltonian can be controlled by tuning the laser fields.
Manipulating Quantum State in Superconducting Dressed-State Systems
ZHANG Feng-Yang, PEI Pei, LI Chong**, SONG He-Shan**
Chin. Phys. Lett. 2011, 28 (12): 120304 .   DOI: 10.1088/0256-307X/28/12/120304
Abstract   PDF(pc) (514KB) ( 326 )
We construct a novel Λ-type system via the dressed states formed by the coupling between a superconducting qubit and a transmission line resonator (TLR). Compared with the conventional three-level structure, our model averts the decay of excited states. We choose the two lowest energy dressed states as the logical states. The single qubit quantum gate can be realized by the adiabatic passage and three-step operation method, respectively. Based on realistic parameters, the feasibility of the adiabatic passage method is discussed. Also, we calculate the fidelity (0.9996) of realizing the single qubit gate with the three-step operation method.
New Aspects of Field Entropy Squeezing as an Indicator for Mixed State Entanglement in an Effective Two-Level System with Stark Shift
S. Abdel-Khalek, **, M. M. A. Ahmed, A-S F. Obada
Chin. Phys. Lett. 2011, 28 (12): 120305 .   DOI: 10.1088/0256-307X/28/12/120305
Abstract   PDF(pc) (1564KB) ( 468 )
We present an effective two-level system in interaction through two-photon processes with a single mode quantized electromagnetic field, initially prepared in a coherent state. Field entropy squeezing as an indicator of the entanglement in a mixed state system is suggested. The temporal evolution of the negativity, Wehrl entropy, Wehrl phase distribution and field entropy squeezing are investigated. The results highlight the important roles played by both the Stark shift parameters and the mixed state setting in the dynamics of the Wehrl entropy, Wehrl phase distribution and field entropy squeezing.
Quantum Key Distribution Based on a Weak-Coupling Cavity QED Regime
LI Chun-Yan, , LI Yan-Song, **
Chin. Phys. Lett. 2011, 28 (12): 120306 .   DOI: 10.1088/0256-307X/28/12/120306
Abstract   PDF(pc) (402KB) ( 482 )
We present a quantum key distribution scheme using a weak-coupling cavity QED regime based on quantum dense coding. Hybrid entanglement statesof photons and electrons are used to distribute information. We just need to transmit photons without storing them in the scheme. The electron confined in a quantum dot, which is embedded in a microcavity, is held by one of the legitimate users throughout the whole communication process. Only the polarization of a single photon and spin of electron measurements are applied in this protocol, which are easier to perform than collective-Bell state measurements. Linear optical apparatus, such as a special polarizing beam splitter in a circular basis and single photon operations, make it more flexible to realize under current technology. Its efficiency will approach 100% in the ideal case. The security of the scheme is also discussed.
Quantum Memory via Wigner Crystals of Polar Molecules
XUE Peng
Chin. Phys. Lett. 2011, 28 (12): 120307 .   DOI: 10.1088/0256-307X/28/12/120307
Abstract   PDF(pc) (363KB) ( 378 )
Collective excitations of rotational and spin states of an ensemble of polar molecules as a candidate for a high-fidelity quantum memory are studied. The dipolar crystals are formed in the high-density limit of cold clouds of polar molecules under one-dimensional trapping conditions. The lifetime of quantum memory is calculated by identifying the dominant decoherence mechanisms, and we estimate their effects on gate operations, when a molecular ensemble qubit is transferred to a superconducting microwave cavity.
Arbitrary and Fast Quantum Gate with Semiconductor Double-Dot Molecules on a Chip
ZOU Wei-Ping, ZHANG Gang, XUE Zheng-Yuan**
Chin. Phys. Lett. 2011, 28 (12): 120308 .   DOI: 10.1088/0256-307X/28/12/120308
Abstract   PDF(pc) (446KB) ( 386 )
We propose a scheme to achieve a kind of nontrivial two-qubit operation using controllable electrons in double-dot molecules coupled to a transmission line resonator. The implemented operation is geometrical in nature and insensitive to the state of the transmission line resonator. In particular, we are able to avoid conventional dispersive coupling so that a high speed gate operation can be achieved, which is important in view of decoherence. Meanwhile, we are able to further generalize the operation to an arbitrary phase case by dynamic decoupling with two sequences.
Gödel-Type Universes in f(R) Gravity with an Arbitrary Coupling between Matter and Geometry
ZHANG Tao, WU Pu-Xun, YU Hong-Wei, **
Chin. Phys. Lett. 2011, 28 (12): 120401 .   DOI: 10.1088/0256-307X/28/12/120401
Abstract   PDF(pc) (442KB) ( 336 )
By studying the Gödel-type solution, the causality in f(R) gravity with an arbitrary coupling between matter and geometry is discussed. Assuming that the matter source is a perfect fluid and a scalar field, respectively, we find that for the perfect fluid case, noncausal Gödel−type solutions exist and there is a critical radius rc beyond which the causality is violated. For the scalar field case, the violation of causality is forbidden.
Scattering Behavior of Waveguide Channels of a New Coupled Integrable Dispersionless System
Abbagari Souleymanou, **, Victor K. Kuetche, Thomas B. Bouetou, , Timoleon C. Kofane
Chin. Phys. Lett. 2011, 28 (12): 120501 .   DOI: 10.1088/0256-307X/28/12/120501
Abstract   PDF(pc) (848KB) ( 345 )
Based upon the powerful Hirota method for unearthing soliton solutions to nonlinear partial differential evolution equations, we investigate the scattering properties of a new coupled integrable dispersionless system while surveying the interactions between its self-confined travelling wave solutions. As a result, we ascertain three types of scattering features depending strongly upon a characteristic parameter. Using such findings to depict soliton solutions with nonzero angular momenta, we derive an extended form of the dispersionless system, which is valuable for further physical applications.
Frequency Effect of Harmonic Noise on the FitzHugh–Nagumo Neuron Model
SONG Yan-Li
Chin. Phys. Lett. 2011, 28 (12): 120502 .   DOI: 10.1088/0256-307X/28/12/120502
Abstract   PDF(pc) (608KB) ( 402 )
Using harmonic noise, the frequency effect of noise on the FitzHugh–Nagumo neuron model is investigated. The results show that the neuron has a resonance characteristic and responds strongly to the noise with a certain frequency at fixed power. Driven by the noise with this frequency, the train is most regular and the coefficient of variation R has a minimum. The imperfect synchronization takes place, which, however, is optimal only for noise with an appropriate frequency. It is shown that there exists coherence resonance related to frequency.
Projective Synchronization of Complex Dynamical Networks with Time-Varying Coupling Strength via Hybrid Feedback Control
GUO Xiao-Yong, *, LI Jun-Min
Chin. Phys. Lett. 2011, 28 (12): 120503 .   DOI: 10.1088/0256-307X/28/12/120503
Abstract   PDF(pc) (609KB) ( 596 )
We introduce a hybrid feedback control scheme to design a controller for the projective synchronization of complex dynamical networks with unknown periodically time-varying parameters. A differential-difference mixed parametric learning law and an adaptive learning control law are constructed to ensure the asymptotic convergence of the error in the sense of square error norm. Moreover, numerical simulation results are used to verify the effectiveness of the proposed method.
Projective Synchronization in Modulated Time-Delayed Chaotic Systems Using an Active Control Approach
FENG Cun-Fang**, WANG Ying-Hai
Chin. Phys. Lett. 2011, 28 (12): 120504 .   DOI: 10.1088/0256-307X/28/12/120504
Abstract   PDF(pc) (527KB) ( 420 )
Projective synchronization in modulated time-delayed systems is studied by applying an active control method. Based on the Lyapunov asymptotical stability theorem, the controller and sufficient condition for projective synchronization are calculated analytically. We give a general method with which we can achieve projective synchronization in modulated time-delayed chaotic systems. This method allows us to adjust the desired scaling factor arbitrarily. The effectiveness of our method is confirmed by using the famous delay-differential equations related to optical bistable or hybrid optical bistable devices. Numerical simulations fully support the analytical approach.
Hurst's Exponent Determination for Radial Distribution Functions of In, Sn and In-40 wt%Sn Melt
ZHOU Yong-Zhi, LI Mei, GENG Hao-Ran**, YANG Zhong-Xi, SUN Chun-Jing
Chin. Phys. Lett. 2011, 28 (12): 120505 .   DOI: 10.1088/0256-307X/28/12/120505
Abstract   PDF(pc) (906KB) ( 387 )
Hurst's exponent of radial distribution functions (RDFs) within the short-range scope of In, Sn and In-40 wt%Sn melts are determined by the rescaled range analysis method. Hurst's exponents H are between 0.94 and 0.97, which display long−range dependence. Within short-range scope, the number of particles from a reference particle belongs to fractional Brownian motion. After RDF serials are randomly scrambled, Hurst's exponents all dramatically dropped, which proves long-range dependence. H irregularly varies as the temperature rises, but the change tendency is not consistent with the correlation radius rc.
Exact Solution of the Gyration Radius of an Individual's Trajectory for a Simplified Human Regular Mobility Model
YAN Xiao-Yong, HAN Xiao-Pu, ZHOU Tao, WANG Bing-Hong**
Chin. Phys. Lett. 2011, 28 (12): 120506 .   DOI: 10.1088/0256-307X/28/12/120506
Abstract   PDF(pc) (474KB) ( 655 )
We propose a simplified human regular mobility model to simulate an individual's daily travel with three sequential activities: commuting to workplace, going to do leisure activities and returning home. With the assumption that the individual has a constant travel speed and inferior limit of time at home and in work, we prove that the daily moving area of an individual is an ellipse, and finally obtain an exact solution of the gyration radius. The analytical solution captures the empirical observation well.
Fractal Analysis of Transport Properties in a Sinai Billiard
JIANG Guo-Hui, ZHANG Yan-Hui**, BIAN Hong-Tao, XU Xue-You
Chin. Phys. Lett. 2011, 28 (12): 120507 .   DOI: 10.1088/0256-307X/28/12/120507
Abstract   PDF(pc) (615KB) ( 543 )
Research contacting chaos with fractals is carried out. First, we employ the theoretical quarter Sinai billiard model to study its chaos by using the stationary expansion method. When the billiard is chaotic, the singular point shows self-similarity. We further utilize the method of simplified box counting to calculate the fractal dimension. The result evidently proves the self-similarity of the singular point before escaping from a potential well.
Backstepping-Based Synchronization Control of Cross-Strict Feedback Hyper-Chaotic Systems
LI Hai-Yan**, HU Yun-An
Chin. Phys. Lett. 2011, 28 (12): 120508 .   DOI: 10.1088/0256-307X/28/12/120508
Abstract   PDF(pc) (477KB) ( 465 )
A certain backstepping control is proposed for synchronization of a class of hyper-chaotic systems. Only two control inputs are used to realize synchronization between hyper-chaotic systems, and the control avoids the possible singularity in the virtual control design. In addition, the adaptive backstepping control is proposed for the synchronization when the system parameters are unknown. The proposed methods can be applied to a variety of chaos systems which can be described by the so-called cross-strict feedback form. Numerical simulations are given to demonstrate the efficiency of the proposed control schemes.
Fast Nondestructive Identification of Endothelium Corneum Gigeriae Galli Using Visible/Near-Infrared Spectroscopy
ZHANG Xiao-Yan, MENG Yao-Yong, **, ZHANG Hao, OU Wen-Juan, LIU Song-Hao
Chin. Phys. Lett. 2011, 28 (12): 120701 .   DOI: 10.1088/0256-307X/28/12/120701
Abstract   PDF(pc) (697KB) ( 467 )
Vis/NIR spectroscopy, in combination with partial least square (PLS) analysis and a back-propagation neural network, is investigated to identify endothelium corneum gigeriae galli (ECGG). The spectral features of ECGGs and their counterfeits are reasonably differentiated in vis/NIR region, which provides enough qualitative information to establish the relationship between the spectra and samples for identification. After pretreatment of the spectral data, cross validation is implemented for extracting the best number of principal components. Then the calibration and validation set are performed well. The PLS and back propagation neural network (BPNN) model gives the BPNN to be 0.9941 and the root mean square residual (RMSR) to be 0.0775 for the calibration set, and the multiple correlation coefficient (MCC) to 0.9874 and the RMSE to 0.1134 for the validation set. Thus the PLS and BPNN model is reliable and practicable. Through testing, a recognition accuracy of 100% is achieved. The present study could offer a new approach for fast and nondestructive discrimination of ECGG and its counterfeit.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Virial Relation for Compact Q-Balls in the Complex Signum-Gordon Model
WANG Hua-Wen, CHENG Hong-Bo*
Chin. Phys. Lett. 2011, 28 (12): 121101 .   DOI: 10.1088/0256-307X/28/12/121101
Abstract   PDF(pc) (476KB) ( 335 )
The properties of Q-balls in the complex signum-Gordon model in d spatial dimensions is studied. We obtain a general virial relation for this kind of Q-ball in higher-dimensional spacetime. We compute the energy and radii of a Q-ball with a V-shaped field potential as a function of spatial dimensionality and a parameter defining the model potential energy density to show that this kind of Q-ball can also survive stably in high-dimensional spacetime.
Semi-Leptonic and Non-Leptonic B Meson Decays to Charmed Mesons
FU Hui-Feng, WANG Guo-Li**, WANG Zhi-Hui, CHEN Xiang-Jun
Chin. Phys. Lett. 2011, 28 (12): 121301 .   DOI: 10.1088/0256-307X/28/12/121301
Abstract   PDF(pc) (540KB) ( 354 )
We study the semi-leptonic and non-leptonic B weak decays that are governed by the B→D(*) transitions. The branching ratios, CP asymmetries (CPAs) and polarization fractions of non−leptonic decays are investigated in the factorization approximation (FA). The B→D(*) form factors are estimated in the Salpeter method. Our estimation on branching ratios is in general agreement with existing experimental data. For CPAs and polarizations, comparisons among the FA results, the perturbative QCD predictions and experimental data are presented.
Flavor State of the Neutrino: Conditions for a Consistent Definition
RONG Shu-Jun**, LIU Qiu-Yu
Chin. Phys. Lett. 2011, 28 (12): 121401 .   DOI: 10.1088/0256-307X/28/12/121401
Abstract   PDF(pc) (461KB) ( 327 )
Similar to Blasone et al. [Phys. Rev. D 72 (2005) 013003] by examining the expectation value of the flavor charge under the normalized flavor state of the neutrino, we demonstrate that the introduction of the flavor state is consistent with the flavor charge only when the conditions, i.e. (A) |p|=0 (the low energy case), or |p|/mi≫1 (the relativistic case) and (B) the flavor state should be defined of the Pontecorvo form |νe〉=cosθ|ν1〉+sinθ|ν2〉 or equivalently except a global phase, are satisfied. The root of the issue lies in the structure of the flavor charge operator. The diagonalization of the flavor charge operator with the integer eigenvalue can be realized through the Bogoliubov–Valatin transformation when condition A is satisfied. The eigenstate of the diagonalized flavor charge is of the Pontecorvo form under condition B.
NUCLEAR PHYSICS
Chiral Doublet Bands with νh11/2νd5/2−1 Configuration in the Particle Rotor Model
QI Bin**, WANG Shou-Yu, ZHANG Shuang-Quan
Chin. Phys. Lett. 2011, 28 (12): 122101 .   DOI: 10.1088/0256-307X/28/12/122101
Abstract   PDF(pc) (784KB) ( 465 )
Doublet bands with νh11/2νd5/2−1 configuration are studied for the first time via the triaxial particle rotor model. The main properties of the doublet bands, including the energy spectra and the electromagnetic transitions, are presented for different triaxiality parameter γ. The aplanar rotation and chiral geometry are discussed based on the analysis of angular momentum components.
Nuclear Dynamical Quadrupole Deformations in Heavy-Ion Reactions
DOU Liang, WANG Nan**, ZHAO En-Guang
Chin. Phys. Lett. 2011, 28 (12): 122401 .   DOI: 10.1088/0256-307X/28/12/122401
Abstract   PDF(pc) (577KB) ( 474 )
Within the quantum molecular dynamics model, the evolution of heavy-ion quadrupole deformations as a function of the central distance between nuclei in the approaching process of fusion reactions near the barrier is studied. The dependences of the maximum prolate deformations for the projectile and the target on the incident energy and the impact parameter are also investigated. The ratios of the quadrupole deformation energies for the projectile to those for the target during the approaching process are also calculated and the results are compared with the assumption [Phys. Rev. C 65 (2001) 014607] by Zagrebaev et al.
Two-Pion Interferometry for the Granular Sources in Ultrarelativistic Heavy Ion Collisions at the RHIC and the LHC
ZHANG Wei-Ning, **, YIN Hong-Jie, REN Yan-Yu
Chin. Phys. Lett. 2011, 28 (12): 122501 .   DOI: 10.1088/0256-307X/28/12/122501
Abstract   PDF(pc) (1300KB) ( 383 )
We investigate the two-pion interferometry in ultrarelativistic heavy ion collisions in the granular source model of quark-gluon plasma droplets. The pion transverse momentum spectra and HBT radii of the granular sources agree well with the experimental data of the most central Au-Au collisions at (sNN)1/2=200 GeV at the RHIC and Pb−Pb collisions at (sNN)1/2=2.76 TeV at the LHC. In the granular source model the larger initial system breakup time for the LHC collisions as compared to the RHIC collisions may lead to the larger HBT radii Rout, Rside and Rlong. However, the large droplet transverse expansion and limited average relative emitting time of particles in the granular source lead to slightly smaller ratios of the transverse Hanbury–Brown–Twiss radii Rout/Rside.
Hadronic Transport Effects on Elliptic Flow
LI Na, SHI Shu-Su, **
Chin. Phys. Lett. 2011, 28 (12): 122502 .   DOI: 10.1088/0256-307X/28/12/122502
Abstract   PDF(pc) (495KB) ( 350 )
Elliptic flow v2 is considered as a probe to study partonic collectivity, and the measurement v2 can be used to describe the hydro behavior of the colliding system. We study the the effect of the hadronic process on the momentum anisotropy parameter v2 in a multiphase transport model. It is found that hadronic rescattering will depress the v2 signal built up at the partonic phase. A similar mass hierarchy is observed in the model as in the experiment at RHIC. We find that different particle species will approach the same ideal hydro limit if the hadronic process is excluded.
Fragmentation Functions for Heavy Baryons in the Recombination Model
PENG Ru
Chin. Phys. Lett. 2011, 28 (12): 122503 .   DOI: 10.1088/0256-307X/28/12/122503
Abstract   PDF(pc) (457KB) ( 312 )
Using the shower parton distributions determined by the recombination model, we predict the fragmentation functions for heavy baryons. Then we obtain the completed fragmentation functions of heavy quarks (c and b) splitting into their hadrons (mesons and baryons containing one heavy valence quark). The calculated process shows that the fragmentation functions for mesons and baryons are not independent if the hadronization of the shower partons is taken into account.
ATOMIC AND MOLECULAR PHYSICS
Calculation of Ion Equilibrium Temperature in Ultracold Neutral Plasmas
LI Jin-Xing, CAO Ming-Tao, HAN Liang, QI Yue-Rong, ZHANG Shou-Gang, GAO Hong**, LI Fu-Li, T. C. Killian
Chin. Phys. Lett. 2011, 28 (12): 123201 .   DOI: 10.1088/0256-307X/28/12/123201
Abstract   PDF(pc) (541KB) ( 433 )
We provide a fast iteration method to calculate the ion equilibrium temperature in an ultracold neutral plasma (UNP). The temperature as functions of electron initial temperature and ion density is obtained and compared with the recent UNP experimental data. The theoretical predictions agree with the experimental results very well. The calculated ion equilibrium temperature by this method can be applied to study the UNP expansion process more effectively.
Elastic Scattering Properties of Ultracold Strontium Atoms
ZHANG Ji-Cai**, ZHU Zun-Lue, LIU Yu-Fang, SUN Jin-Feng,
Chin. Phys. Lett. 2011, 28 (12): 123401 .   DOI: 10.1088/0256-307X/28/12/123401
Abstract   PDF(pc) (474KB) ( 398 )
We investigate the elastic scattering properties of strontium atoms at ultracold temperatures. The scattering parameters, such as s-wave scattering lengths, effective ranges and p-wave scattering lengths, are calculated for all stable isotope combinations of Sr atoms by the quantal method and semiclassical method, respectively. Good agreements are obtained. The scattering parameters are very sensitive to small changes of the reduced mass. Due to the repulsive interisotope and intraisotope s-wave scattering length and large elastic cross sections, 84Sr–86Sr mixture is a good candidate to realize Bose–Bose quantum degenerate atomic gases.
Lattice-Inversion Embedded-Atom-Method Interatomic Potentials for Group-VA Transition Metals
YUAN Xiao-Jian, **, CHEN Nan-Xian, SHEN Jiang
Chin. Phys. Lett. 2011, 28 (12): 123402 .   DOI: 10.1088/0256-307X/28/12/123402
Abstract   PDF(pc) (635KB) ( 457 )
The lattice-inversion embedded-atom-method (LI-EAM) interatomic potential we developed previously [J. Phys.: Condens. Matter 22 (2010) 375503] is extended to group-VA transition metals (V, Nb and Ta). It is found that considering interatomic interactions up to appropriate-distance-neighbor atoms is crucial to constructing accurate EAM potentials, especially for the prediction of surface energy. The LI-EAM interatomic potentials for group-VA transition metals are successfully built by considering interatomic interactions up to the fifth neighbor atoms. These angular-independent potentials drastically promote the accuracy of the predicted surface energies, which match the experimental results well.
Positronium Formation in Positron-Lithium Scattering
CHENG Yong-Jun, ZHOU Ya-Jun**, LIU Fang
Chin. Phys. Lett. 2011, 28 (12): 123403 .   DOI: 10.1088/0256-307X/28/12/123403
Abstract   PDF(pc) (651KB) ( 386 )
The positronium formation process in positron scattering with atomic lithium is investigated using the coupled-channel optical method. The cross sections of positronium formation into the n=1 and n=2 levels from 2 to 60 eV are reported. The present results show reasonable agreement with the available experimental measurements and theoretical calculations.
Reverse Polarization of a High-Energy Exciton in Conjugated Polymers
LI Xiao-Xue, DONG Xian-Feng, GAO Kun, XIE Shi-Jie**
Chin. Phys. Lett. 2011, 28 (12): 123601 .   DOI: 10.1088/0256-307X/28/12/123601
Abstract   PDF(pc) (542KB) ( 382 )
Polarization of a high-energy exciton in conjugated polymers is investigated theoretically by using an extended one-dimensional tight-binding Su–Schrieffer–Heeger (SSH) model. Under an external electric field, the reverse polarization of a high-energy exciton is obtained and the corresponding physical mechanism is analyzed. A critical field Ec is obtained, over which the polarization of the high-energy exciton will switch from negative to positive. In addition, by taking into account the effect of the non-degenerate confinement, we find that it is possible to realize reverse polarization through high energy photoexcitation in non-degenerate polymers.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Characterizing the Temporal Structure of a Relativistic Electron Bunch
DENG Hai-Xiao**, FENG Chao, LIU Bo, WANG Dong, WANG Xing-Tao, ZHANG Meng
Chin. Phys. Lett. 2011, 28 (12): 124101 .   DOI: 10.1088/0256-307X/28/12/124101
Abstract   PDF(pc) (783KB) ( 399 )
Using proper beam energy chirp and the undulator detuning effect, we propose a modified optical replica synthesizer scheme to characterize the temporal structure of a relativistic electron bunch, which predicts a 100-fs temporal resolution in numerical simulation. The proof of principle experiment demonstrates a peak current of 9 A and a slice energy spread of about 0.5 keV for the uncompressed electron beam of the Shanghai Deep UV Free Electron Laser Facility.
Transmission Characteristics of a Generalized Parallel Plate Dielectric Waveguide at THz Frequencies
YE Long-Fang, **, XU Rui-Min, ZHANG Yong, LIN Wei-Gan
Chin. Phys. Lett. 2011, 28 (12): 124102 .   DOI: 10.1088/0256-307X/28/12/124102
Abstract   PDF(pc) (584KB) ( 1598 )
A generalized parallel-plate dielectric waveguide (G-PPDW) is proposed as a new guiding medium for terahertz wave. A theoretical analysis of the transmission characteristics for the TE modes of this generalized structure is performed. Equations are presented for the field components, dispersion, power ratio, transmission loss and characteristic impedance as functions of the operating frequencies, dimensions and material constants. In the case of the lowest-order mode TE10, design curves covering frequencies and dimensions for the given material constants in the THz region are presented. The theoretical results of transmission characteristics obtained from these equations are verified by the finite-element method with a good agreement. The investigation results show that by selecting proper dimensions and dielectric materials, G-PPDW can be used to guide THz waves efficiently with high power confinement and low attenuation. These outstanding properties may open up a way to many important applications for THz integrated circuits and systems.
Peculiar Transmission Characteristics of the Large Gap Semi-Insulating GaAs Photoconductive Switch
SHI Wei**, MA Xiang-Rong,
Chin. Phys. Lett. 2011, 28 (12): 124201 .   DOI: 10.1088/0256-307X/28/12/124201
Abstract   PDF(pc) (688KB) ( 322 )
Unique experimental phenomena are discovered in a large gap semiinsulating (SI) GaAs photoconductive semiconductor switch (PCSS) and the peculiar transmission characteristics are exhibited in the experiment. The transmission characteristics for the large gap SI-GaAs PCSS are entirely different from the commonly designed PCSS. By analyzing the differences of the transmission characteristics between the common and the large gap SI-GaAs PCSS, a detailed statistical analysis and theoretical explanations are expounded. The large gap SI-GaAs PCSS works in the overvoltage relaxation limit space charge accumulation (LSA) mode when the conditions of 5×104 s⋅cm−3 ≤ n0/f ≤ 3×105 s⋅cm−3 and n0 L ≥ 1013 cm−2 must be met in the switch, with n0 being carrier concentration and f the frequency. The large gap SI-GaAs PCSS we developed has not shown the nonlinear (lock-in) behavior at high bias voltage, so the withstand voltage and service life for PCSS are improved.
Nonparaxial Propagation of a Radially Polarized Beam Diffracted by an Annular Aperture
CHEN Jian-Nong
Chin. Phys. Lett. 2011, 28 (12): 124202 .   DOI: 10.1088/0256-307X/28/12/124202
Abstract   PDF(pc) (591KB) ( 481 )
Based on the vectorial Rayleigh diffraction integral, the integral formulae of three electromagnetic field components for radially polarized Laguerre–Gaussian beams after diffraction by an annular aperture and the propagation distance in nonparaxial regimes are presented. The diffraction by a circular aperture or a circular disk or propagation in free space can be treated as the special cases of this general result. The numerical simulation shows that the electric field intensity distributions closely depend on both the inner truncation parameters and the outer truncation parameters of the annular aperture, as well as on the ratio of the waist of the incident Laguerre–Gaussian beam to the wavelength.
Spontaneous Emission Spectrum of a Λ-Typed Atom in a Coherent Photonic Reservoir
HUANG Xian-Shan, LIU Hai-Lian**
Chin. Phys. Lett. 2011, 28 (12): 124203 .   DOI: 10.1088/0256-307X/28/12/124203
Abstract   PDF(pc) (578KB) ( 296 )
The spontaneous emission of a three-level Λ−typed atom embedded in anisotropic photonic crystals with two coherent bands is investigated. The relative position of the atom is described by a position-dependent parameter θ(r0), in regard as the coherence of the two bands. The spectrum of the transition in free space vacuum is discussed. The spectral center can be manipulated by the coherent parameter θ(r0), and the spectral intensity can be adjusted via the atomic transition in the coherent photonic reservoir.
Nanosecond Square Pulse Fiber Laser based on the Nonlinear Amplifying Loop Mirror
CHEN Guo-Liang, GU Chun, XU Li-Xin**, WANG An-Ting, MING Hai
Chin. Phys. Lett. 2011, 28 (12): 124204 .   DOI: 10.1088/0256-307X/28/12/124204
Abstract   PDF(pc) (370KB) ( 707 )
We propose and demonstrate a nanosecond square pulse ytterbium doped fiber laser in the 1060 nm band. The laser is based on the figure-8 structure and has a tunable pulse bandwidth from 3 ns to beyond 100 ns, showing excellent temporal tuning ability. The experimental results show that a steady square pulse can be generated when the parameters of the cavity are chosen appropriately.
Tunable Single-Frequency Intracavity Frequency-Doubled Ti:Sapphire Laser around 461 nm
LI Feng-Qin**, SHI Zhu, LI Yong-Min, PENG Kun-Chi
Chin. Phys. Lett. 2011, 28 (12): 124205 .   DOI: 10.1088/0256-307X/28/12/124205
Abstract   PDF(pc) (716KB) ( 569 )
We demonstrate a tunable continuous-wave single frequency intracavity frequency-doubled Ti:sapphire laser. The highest output power of 280 mW at 461.62 nm is obtained by employing a type-I phase-matched BIBO crystal and the peak-to-peak fluctuation of the power is less than ±1% within three hours. The frequency stability is better than ±2.22 MHz over 10 min when the laser is locked to a confocal Fabry–Perot cavity. A three-plate birefringent filter allows for the tunable range from 457 nm to 467 nm, which covers the absorption line of the strontium atoms (460.86 nm).
Compact and Highly Efficient Passively Q−Switched Intracavity KTA-OPO at 1.53 and 3.47 µm
MIAO Jie-Guang**, PAN Yu-Zhai, QU Shi-Liang
Chin. Phys. Lett. 2011, 28 (12): 124206 .   DOI: 10.1088/0256-307X/28/12/124206
Abstract   PDF(pc) (671KB) ( 458 )
Both the signal (1.53 µm ) and idler (3.47 µm ) performances of a KTA−based optical parametric oscillator (OPO) are presented. The KTA-OPO is intracavity driven by a diode-pumped Nd:YVO4/Cr:YAG passively Q−switched laser with a quite compact configuration. The signal and idler average output powers up to 941 and 583 mW, respectively, have been achieved, corresponding to an improved diode-to-idler conversion efficiency of 6.5% and a diode-to-OPO (signal+idler) conversion efficiency of 16.9%. At different pump levels, the signal pulse duration and repetition rate are detected to be in the range of 1.8–3.2 ns and 13–112 kHz, respectively. Moreover, near diffraction limited and Gaussian type beam profiles at 1.53 and 3.47 µm are also observed.
Ghost Imaging Using Orbital Angular Momentum
ZHAO Sheng-Mei**, DING Jian, DONG Xiao-Liang, ZHENG Bao-Yu
Chin. Phys. Lett. 2011, 28 (12): 124207 .   DOI: 10.1088/0256-307X/28/12/124207
Abstract   PDF(pc) (559KB) ( 865 )
We present a novel encoding scheme in a ghost-imaging system using orbital angular momentum. In the signal arm, object spatial information is encoded as a phase matrix. For an N−grey-scale object, different phase matrices, varying from 0 to π with increment π/N, are used for different greyscales, and then they are modulated to a signal beam by a spatial light modulator. According to the conservation of the orbital angular momentum in the ghost imaging system, these changes will give different coincidence rates in measurement, and hence the object information can be extracted in the idler arm. By simulations and experiments, the results show that our scheme can improve the resolution of the image effectively. Compared with another encoding method using orbital angular momentum, our scheme has a better performance for both characters and the image object.
Influence of Ultrasonic Vibrations on the Static Friction Characteristics of a Rubber/Aluminum Couple
CHENG Ting-Hai**, GAO Han, BAO Gang
Chin. Phys. Lett. 2011, 28 (12): 124301 .   DOI: 10.1088/0256-307X/28/12/124301
Abstract   PDF(pc) (1636KB) ( 720 )
A novel ultrasonic vibration approach is introduced into a chloroprene rubber/aluminum friction couple for improving the static friction properties between rubber and metal. Compared to the test results without vibrations, the static friction force of a chloroprene rubber/aluminum couple decreases observably, leading to the ultimate displacement of rubber. The values of the static friction force and ultimate displacement can be ultimately reduced to 23.1% and 50% of those without ultrasonic vibrations, respectively.
Thermal Rectification in Graded Nonlinear Transmission Lines
XU Wen, CHEN Wei-Zhong**, TAO Feng,
Chin. Phys. Lett. 2011, 28 (12): 124401 .   DOI: 10.1088/0256-307X/28/12/124401
Abstract   PDF(pc) (500KB) ( 319 )
We consider heat conduction in a nonlinear inductance-capacitance (LC) transmission line with an inductance gradient by adding white-noise signals. It is found that the heat flux in the direction of inductance decrease is larger than that in the direction of inductance increase. When the low-inductance end is at higher temperature, the phonon density decreases due to conversion to high-frequency phonons, which can not move to the high-inductance end due to its lower cutoff frequency. However, when the high-inductance end is at higher temperature, the loss of phonon density can be compensated for because some high-frequency phonons can move to the low-inductance end dur to its higher cutoff frequency. This leads to the asymmetry of energy transfer. Discussion shows that this asymmetry exists in a particular range of temperatures, and increases with the increase of the difference between heat baths and the inductance gradient.
In-depth Study on Cylinder Wake Controlled by Lorentz Force
ZHANG Hui, FAN Bao-Chun**, CHEN Zhi-Hua
Chin. Phys. Lett. 2011, 28 (12): 124701 .   DOI: 10.1088/0256-307X/28/12/124701
Abstract   PDF(pc) (460KB) ( 312 )
The underlying mechanisms of the electromagnetic control of cylinder wake are investigated and discussed. The effects of Lorentz force are found to be composed of two parts, one is its direct action on the cylinder (the wall Lorentz force) and the other is applied to the fluid (called the field Lorentz force) near the cylinder surface. Our results show that the wall Lorentz force can generate thrust and reduce the drag; the field Lorentz force increases the drag. However, the cylinder drag is dominated by the wall Lorentz force. In addition, the field Lorentz force above the upper surface decreases the lift, while the upper wall Lorentz force increases it. The total lift is dominated by the upper wall Lorentz force.
Renormalization Group Analysis of Weakly Rotating Turbulent Flows
WANG Xiao-Hong**, ZHOU Quan
Chin. Phys. Lett. 2011, 28 (12): 124702 .   DOI: 10.1088/0256-307X/28/12/124702
Abstract   PDF(pc) (491KB) ( 308 )
Dynamic renormalization group (RNG) analysis is applied to the investigation of the behavior of the infrared limits of weakly rotating turbulence. For turbulent flow subject to weak rotation, the anisotropic part in the renormalized propagation is considered to be a perturbation of the isotropic part. Then, with a low-order approximation, the coarsening procedure of RNG transformation is performed. After implementing the coarsening and rescaling procedures, the RNG analysis suggests that the spherically averaged energy spectrum has the scaling behavior E(k)k−11/5 for weakly rotating turbulence. It is also shown that the Coriolis force will disturb the stability of the Kolmogorov −5/3 energy spectrum and will change the scaling behavior even in the case of weak rotation.
Mini-Jet Controlled Turbulent Round Air Jet
DU Cheng, MI Jian-Chun**, ZHOU Yu, ZHAN Jie
Chin. Phys. Lett. 2011, 28 (12): 124703 .   DOI: 10.1088/0256-307X/28/12/124703
Abstract   PDF(pc) (516KB) ( 386 )
We report an investigation of the active control of a round air jet by multiple radial blowing mini-jets. The Reynolds number based on the jet exit velocity and diameter is 8000. It is found that once the continuous mini-jets are replaced with pulsed ones, the centerline velocity decay rate K can be greatly increased as the pulsing frequency of mini−jets approaches the natural vortex frequency of the main jet. For example, the K value is amplified by more than 50% with two (or four) pulsed mini-jets blowing, compared with the continuous mini-jets at the same ratio of the mass flow rate of the mini-jets to that of the main jet.
Wake Oscillator Model Proposed for the Stream-Wise Vortex-Induced Vibration of a Circular Cylinder in the Second Excitation Region
XU Wan-Hai**, DU Jie, YU Jian-Xing, LI Jing-Cheng
Chin. Phys. Lett. 2011, 28 (12): 124704 .   DOI: 10.1088/0256-307X/28/12/124704
Abstract   PDF(pc) (545KB) ( 676 )
A wake oscillator model is presented for the stream-wise vortex-induced vibration of a circular cylinder in the second excitation region. The near wake dynamics related to the fluctuating nature of alternate vortex shedding is modeled based on the classical van der Pol equation. An appropriate approach used in cross-flow VIV is developed to estimate the model empirical parameters. The comparison between our calculations and experiments is carried out to validate the proposed model. It is found that the present model results agree fairly well with the experimental data.
Three-Dimensional Simulation of Detonation Propagation in a Rectangular Duct by an Improved CE/SE Scheme
SHEN Hua, LIU Kai-Xin, **, ZHANG De-Liang
Chin. Phys. Lett. 2011, 28 (12): 124705 .   DOI: 10.1088/0256-307X/28/12/124705
Abstract   PDF(pc) (3213KB) ( 354 )
A genuinely three-dimensional spacetime conservation element and solution element (CE/SE) scheme is built as simple, consistent and straightforward extensions of an improved high resolution 2D CE/SE scheme. It is applied to examine the mechanism of three-dimensional detonation process in rectangular ducts. The simulations clearly show detailed three-dimensional detonation modes, namely a rectangular mode and a diagonal mode. Furthermore, the formation of unreacted pockets with high density and low temperature behind the detonation is observed for the two modes.
Heat Transfer in a Moving Fluid over a Moving Non-Isothermal Flat Surface
Swati Mukhopadhyay
Chin. Phys. Lett. 2011, 28 (12): 124706 .   DOI: 10.1088/0256-307X/28/12/124706
Abstract   PDF(pc) (409KB) ( 494 )
Boundary layer forced convective flow and heat transfer passing a moving flat surface parallel to a moving stream are presented. The power-law surface temperature of the second degree at the boundary is described. The similarity solutions for the problem are obtained and the reduced ordinary differential equations are solved numerically. The numerical results are compared with the known results from the literature for some special cases of the present study to support their validity. It is found that dual solutions exist when the surface and the fluid move in opposite directions.
Unsteady Viscous Flow over an Expanding Stretching Cylinder
FANG Tie-Gang*, ZHANG Ji, ZHONG Yong-Fang, TAO Hua
Chin. Phys. Lett. 2011, 28 (12): 124707 .   DOI: 10.1088/0256-307X/28/12/124707
Abstract   PDF(pc) (478KB) ( 860 )
We study the viscous flow over an expanding stretching cylinder. The solution is exact to the Navier–Stokes equations. The stretching velocity of the cylinder is proportional to the axial distance from the origin and decreases with time. There exists a unique solution for the flow with all the studied values of Reynolds number and the unsteadiness parameter. Reversal flows exist for an expanding stretching cylinder. The velocity decays faster for a larger Reynolds number and a more rapidly expanding cylinder.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Sheath Criterion for a Collisional Electronegative Plasma Sheath in an Applied Magnetic Field
ZOU Xiu**, LIU Hui-Ping, QIU Ming-Hui, SUN Xiao-Hang
Chin. Phys. Lett. 2011, 28 (12): 125201 .   DOI: 10.1088/0256-307X/28/12/125201
Abstract   PDF(pc) (552KB) ( 935 )
The sheath criterion for a collisional electronegative plasma sheath in an applied magnetic field is investigated. It is assumed that the system consists of hot electrons, hot negative ions and cold positive ions. The effect of an applied magnetic field on the sheath criterion is discussed. The results reveal that the magnetic field has effects on both the upper and lower limits, which cause the range of the ion Mach number to increase. In addition, the numerical calculations of the electronegative plasma sheath are carried out to demonstrate the effects of sheath criterion on the characteristics of the sheath.
Methods of Generation and Detailed Characterization of Millimeter-Scale Plasmas Using a Gasbag Target
LI Zhi-Chao, **, ZHENG Jian, JIANG Xiao-Hua, WANG Zhe-Bin, YANG Dong, ZHANG Huan, LI San-Wei, WANG Feng, PENG Xiao-Shi, YIN Qiang, ZHU Fang-Hua, GUO Liang, YUAN Peng, LIU Shen-Ye, DING Yong-Kun
Chin. Phys. Lett. 2011, 28 (12): 125202 .   DOI: 10.1088/0256-307X/28/12/125202
Abstract   PDF(pc) (1148KB) ( 374 )
Gasbag targets are useful for the research of laser-plasma interactions in inertial confinement fusion, especially in the laser overlapping regime. We report that on the Shengguang-II laser facility, millimeter−scale plasmas are successfully generated by four 0.35 µm laser beams using a gasbag target. Multiple diagnostics are applied to characterize the millimeter−scale plasmas in detail. The images from the x-ray pinhole cameras confirm that millimeter-scale plasmas are indeed created. An optical Thomson scattering system diagnoses the electron temperature of the CH filling plasmas by probing the thermal ion-acoustic fluctuations, which indicates that the electron temperature has a 600 eV flat roof in 0.7–1.3 ns. Another key parameter, i.e. the electron density of the millimeter-scale plasmas, is inferred by the spectrum of the back stimulated Raman scattering of an additional 0.53 µm laser beam. The inferred electron density keeps stable at 0.1nc in early time consistent with the controlled filling pressure and splits into a higher density in late time, which is attributed to the blast wave entering into the SRS interaction region.
Korteweg de Vries Description of One-Dimensional Superfluid Fermi Gases
XU Yan-Xia, DUAN Wen-Shan**
Chin. Phys. Lett. 2011, 28 (12): 125203 .   DOI: 10.1088/0256-307X/28/12/125203
Abstract   PDF(pc) (517KB) ( 331 )
We study one-dimensional matter-wave pulses in cigar-shaped superfluid Fermi gases, including the linear and nonlinear waves of the system. A Korteweg de Vries (KdV) solitary wave is obtained for the superfluid Fermi gases in the limited case of a BEC regime, a BCS regime and unitarity. The dependences of the propagation velocity, amplitude and the width of the solitary wave on the dimensionless interaction parameter y=1/(kF asc) are given for the limited cases of BEC and unitarity.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Structural and Electronic Properties, and Pressure-Induced Phase Transition of Layered C5N: a First-Principles Investigation
HU Qian-Ku, **, WANG Hai-Yan, WU Qing-Hua, HE Ju-Long, ZHANG Guang-Lei
Chin. Phys. Lett. 2011, 28 (12): 126101 .   DOI: 10.1088/0256-307X/28/12/126101
Abstract   PDF(pc) (1002KB) ( 499 )
Seven layered C5N configurations constructed from hexagonal BN and graphite structures are studied using an ab initio pseudopotential density functional method. The structural and electronic properties, and pressure−induced phase transition are investigated by calculating the total energy, structural parameter, formation energy, elastic constant, band structure and electron density of state. The results show that the three C5N configurations constructed from the h−BN structure are more stable energetically than those four configurations from graphite structure. The C5N−I configuration with the highest symmetry and the AA stacking sequence along the c−axis is the most stable. This structure is stable mechanically and its phase separation is difficult. The C5N phase is expected to have a metallic character. A critical pressure of about 20 GPa is predicted for the synthesis of a monoclinic C5N phase from the layered C5N phase.
First-Principles Study of Fe-Doped ZnO Nanowires
ZHANG Fu-Chun**, ZHANG Wei-Hu, DONG Jun-Tang, ZHANG Zhi-Yong
Chin. Phys. Lett. 2011, 28 (12): 126102 .   DOI: 10.1088/0256-307X/28/12/126102
Abstract   PDF(pc) (844KB) ( 760 )
Using first-principles theory, we predict magnetic, electronic and optical properties in Fe-doped ZnO nanowires. The results show that ferromagnetic (FM) coupling of configuration V is the most stable, and the strong hybridization effect between Fe 3d and O 2p states is found near the Fermi level, and it is obvious that the ferromagnetic system is electron−spin polarization of 100% and half-metallic. Given antiferromagnetic (AFM) coupling, the system generates small spin polarization near the Fermi level, indicating metallicity. The magnetic moments mainly arise from Fe 3d orbitals. In addition, the results of optical properties show that the Fe-doped ZnO nanowires have apparent absorption peaks in the ultraviolet band and that there is a small red shift and a strong blue shift in the near and far ultraviolet band, indicating that Fe-doped ZnO nanowires are a type of magneto-optical materials with great promise.
In situ High-Pressure Synchrotron X-Ray Diffraction Study of Clinozoisite
FAN Da-Wei**, MA Mai-Ning, YANG Jun-Jie, WEI Shu-Yi, CHEN Zhi-Qiang, XIE Hong-Sen
Chin. Phys. Lett. 2011, 28 (12): 126103 .   DOI: 10.1088/0256-307X/28/12/126103
Abstract   PDF(pc) (684KB) ( 349 )
We investigate the elastic behavior of a natural clinozoisite under about 20.4 GPa at 300 K using in situ angle-dispersive x-ray diffraction and a diamond anvil cell at the National Synchrotron Light Source, Brookhaven National Laboratory. Over this pressure range, no phase change or disproportionation has been observed. The isothermal equation of state is determined. The values of V0 and K0 refined by the Murnaghan equation of state are V0=460.0±0.2 Å3, K0=138±3 GPa. Consequently, it can be concluded that the compressibility of clinozoisite under high pressures is accurately constrained.
Production and Mechanical Behaviour of Biomedical CoCrMo Alloy
O. Sahin**, A. R�, za Tuncdemir, H. Ali Cetinkara, H. Salih Guder, E. Sahin
Chin. Phys. Lett. 2011, 28 (12): 126201 .   DOI: 10.1088/0256-307X/28/12/126201
Abstract   PDF(pc) (711KB) ( 1299 )
Cobalt-based alloy (Co-30Cr-5.5Mo) is produced by the investment casting process. This alloy complies with the ASTM F75 standard and is widely used in the manufacturing of orthopedic implants because of its high strength, good corrosion resistance and excellent biocompatibility properties. SEM, XRD and microhardness tests are used to examine the mechanical properties of the material. The examined material exhibits the behaviour of indentation size effect (ISE). Our results reveal that Vickers and Knoop microhardness are dependent on indentation test load. The traditional Meyer's law, the proportional specimen resistance (PSR) model and the Hays-Kendall model (HK) are used to analyze the load dependence of the hardness. As a result, the Hays-Kendall model is found to be the most effective to determine the load-independent hardness HLI of CoCrMo alloy.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Vacancy and H Interactions in Nb
RAO Jian-Ping, OUYANG Chu-Ying**, LEI Min-Sheng, JIANG Feng-Yi
Chin. Phys. Lett. 2011, 28 (12): 127101 .   DOI: 10.1088/0256-307X/28/12/127101
Abstract   PDF(pc) (540KB) ( 329 )
The vacancy and H interactions in bcc Nb are important due to their implication in understanding of the H induced damage of Nb metallic membrane used in H2 separation and purification application. Using density functional theory, the vacancy formation energy and vacancy (Vac)−H interaction energies are calculated. The results show that vacancies have a strong trapping effect on H atoms, which lowers the formation energy of Vac-nH clusters substantially. The concentration of Vac−nH clusters is evaluated using a statistical model and the dependence of the concentration on the H−to-M ratio is obtained. It is shown that the concentration of the Vac-nH clusters can be as high as 10−3 at 573 K, i.e. one Vac-nH cluster per 1000 atoms, in good agreement with the experimental observations.
First-Principles Study of the Local Magnetic Moment on a N-Doped Cu2O (111) Surface
WANG Zhi
Chin. Phys. Lett. 2011, 28 (12): 127102 .   DOI: 10.1088/0256-307X/28/12/127102
Abstract   PDF(pc) (775KB) ( 558 )
First-principles calculations based on density functional theory within the generalized gradient approximation are used to study on magnetism in N-doped Cu2O. It is interesting that nitrogen does not induce magnetism in bulk Cu2O, while shows a total magnetism moment of 1.0µB at the Cu2O (111) surface, which is mainly localized on the doped N atoms. The local magnetic moment at the N−doped Cu2O (111) surface can be explained in terms of the surface state.
Magnetism of a Nitrogen-Implanted TiO2 Single Crystal
LIU Chun-Ming**, XIANG Xia, ZHANG Yan, JIANG Yong, ZU Xiao-Tao
Chin. Phys. Lett. 2011, 28 (12): 127201 .   DOI: 10.1088/0256-307X/28/12/127201
Abstract   PDF(pc) (630KB) ( 368 )
Single rutile crystal TiO2 was implanted using nitrogen ions with energy of 60 keV. The microstructure, ultraviolet−visible light absorption spectra, conductivity and magnetism are investigated. Except for the nitrogen dopant, no impurity can be detected by x-ray diffraction and x-ray photoelectron spectra. The absorption in the visible light region is enhanced with nitrogen implantation dose increasing. By measuring the temperature dependence of resistance, it is found that the sample implanted with 1×1018 ions/cm2 is changes from insulating to semiconducting, and the variable range hopping is the main conducting mechanism. Room-temperature ferromagnetism is also obtained in this sample. The magnetism as a function of temperature can be well fitted using the three-dimensional spin wave model plus the Curie–Weiss model, indicating that there is a mixed phase of ferromagnetism and paramagnetism.
Wafer-Scale Gigahertz Graphene Field Effect Transistors on SiC Substrates
PAN Hong-Liang, JIN Zhi**, MA Peng, GUO Jian-Nan, LIU Xin-Yu, YE Tian-Chun, LI Jia, DUN Shao-Bo, FENG Zhi-Hong
Chin. Phys. Lett. 2011, 28 (12): 127202 .   DOI: 10.1088/0256-307X/28/12/127202
Abstract   PDF(pc) (651KB) ( 378 )
Wafer-scale graphene field-effect transistors are fabricated using benzocyclobutene and atomic layer deposition Al2O3 as the top−gate dielectric. The epitaxial-graphene layer is formed by graphitization of a 2-inch-diameter Si-face semi-insulating 6H-SiC substrate. The graphene on the silicon carbide substrate is heavily n-doped and current saturation is not found. For the intrinsic characteristic of this particular channel material, the devices cannot be switched off. The cut-off frequencies of these graphene field-effect transistors, which have a gate length of 1 µm , are larger than 800 MHz. The largest one can reach 1.24 GHz. There are greater than 95% active devices that can be successfully applied. We thus succeed in fabricating wafer-scale gigahertz graphene field-effect transistors, which paves the way for high-performance graphene devices and circuits.
Improved Performance of Pentacene Organic Field-Effect Transistors by Inserting a V2O5 Metal Oxide Layer
ZHAO Geng, CHENG Xiao-Man, **, TIAN Hai-Jun, DU Bo-Qun, LIANG Xiao-Yu
Chin. Phys. Lett. 2011, 28 (12): 127203 .   DOI: 10.1088/0256-307X/28/12/127203
Abstract   PDF(pc) (668KB) ( 484 )
We fabricate pentacene-based organic field effect transistors (OFETs), inserting a transition metal oxide (V2O5) layer between the pentacene and Al source−drain (S/D) electrodes. The performance of the devices with V2O5/Al S/D electrodes is considerably improved compared to the pentacene−based OFET with only Al S/D electrodes. After the 10-nm V2O5 layer modification, the effective field-effect mobility of the devices increases from 2.7×10−3 cm2/V⋅s to 8.93×10−1 cm2/V⋅s. Owing to the change of the injection property, the effective threshold voltage (Vth) is changed from −7.5 V to −5 V and the on/off ratio shifts from 102 to 104. Moreover, the dispersion of sub−threshold current in the devices disappears. These performance improvements are ascribed to the low carrier injection barrier and the reduction of contact resistance. It is indicated that V2O5 layer modification is an effective approach to improve pentacene-based OFET performance.
Photoresponse Properties of an n-ZnS/p-Si Heterojunction
HUANG Jian**, WANG Lin-Jun, TANG Ke, XU Run, ZHANG Ji-Jun, LU Xiong-Gang, XIA Yi-Ben
Chin. Phys. Lett. 2011, 28 (12): 127301 .   DOI: 10.1088/0256-307X/28/12/127301
Abstract   PDF(pc) (580KB) ( 1182 )
An n-ZnS/p-Si heterojunction was fabricated by using the rf magnetron sputtering method. The band gap of the ZnS film is about 3.63 eV. Current-voltage (IV) characteristics of the ZnS/Si heterojunction are examined and the results show the distinct rectifying characteristics with a turn-on voltage of about 1.8 V. The UV (330 nm) and visible (450 nm) photoresponse properties of the heterojunction are also investigated, which demonstrates the potential of such an n-ZnS/p-Si heterojunction for detecting both UV and visible light.
Negative Photoconductivity Induced by Surface Plasmon Polaritons in the Kretschmann Configuration
ZHENG Jing-Gao, SUN Jia-Lin**, XUE Ping**
Chin. Phys. Lett. 2011, 28 (12): 127302 .   DOI: 10.1088/0256-307X/28/12/127302
Abstract   PDF(pc) (528KB) ( 403 )
Prism coupling in the Kretschmann configuration is a well-known method for the excitation of surface plasmon polaritons (SPPs) in thin films bounded from one side by a prism and from the other side by air. Based on the Kretschmann configuration, we experimentally study the transport properties of a silver thin film with a thickness of 55 nm and a width of 500 µm undergoing total internal reflection. We observe considerable negative photoconductivity in the film induced by the SPPs excited in this configuration and find that both SPP-electron interactions and SPP-induced heating have contributions to the negative photoconductivity. We believe that the new phenomena, which result from the combination of photonics and electronics, will be useful in relative technical applications and scientific research.
Surface Potential Equation for Metal-Oxide-Semiconductor Capacitors Considering the Degenerate Effect
ZHANG Da, SUN Jiu-Xun**, PU Jin-Rong
Chin. Phys. Lett. 2011, 28 (12): 127303 .   DOI: 10.1088/0256-307X/28/12/127303
Abstract   PDF(pc) (477KB) ( 340 )
A surface potential equation (SPE) considering the degenerate effect is derived. To make the degenerate SPE analysis, an empirical approximation for the Fermi integral is applied in the derivation. Dependences of surface potential and square of electric field on gate voltage calculated from the degenerate and non-degenerate models are compared with great discrepancy. Further, theoretical CV relationships are compared with the experimental data for two structures and it is shown that the degenerate SPE−based CgVg matches with the experimental data much better than the non-degenerate one, which confirms that the degenerate effect is inevitable for surface potential-based metal-oxide-semiconductor device modeling.
Single-Walled Carbon Nanotube Networked Field-Effect Transistors Functionalized with Thiolated Heme for NO2 Sensing
WEI Ang, LI Wei-Wei, WANG Jing-Xia, LONG Qing, WANG Zhao, XIONG Li, DONG Xiao-Chen**, HUANG Wei**
Chin. Phys. Lett. 2011, 28 (12): 127304 .   DOI: 10.1088/0256-307X/28/12/127304
Abstract   PDF(pc) (706KB) ( 346 )
The gas sensing properties of the single-walled carbon nanotube networked field-effect transistors for NO2 are investigated. After the modification of the gold contact electrodes of the carbon nanotube transistors with the thiolated heme, the NO2 sensing results indicate that the sensing sensitivity of the modified transistors is enhanced greatly and the sensing limit can reach below 100 ppb. It is also proposed that the mechanism of the sensitivity enhancement for NO2 detection mainly results from the modulation of the Schottky energy barrier at the Au/CNTs junction upon thiolated heme facilitated NO2 adsorption.
Photovoltaic Behaviors in an Isotype n-TiO2/n-Si Heterojunction
FAN Hui-Jie, ZHANG Hui-Qiang, WU Jing-Jing, WEN Zheng-Fang, MA Feng-Ying**
Chin. Phys. Lett. 2011, 28 (12): 127305 .   DOI: 10.1088/0256-307X/28/12/127305
Abstract   PDF(pc) (532KB) ( 768 )
An n-TiO2/n−Si isotype heterojunction is fabricated by depositing TiO2 thin films onto n−Si substrates. Obvious photovoltaic behaviors are observed in this isotype heterojunction. The open circuit voltage and short circuit current of the heterojunction can reach 123 mV and 20 µA/cm2, respectively. The mechanism for the photovoltaic behaviors can be understood in terms of the band alignment of the heterojunction. The results reported may provide a feasible route to easily available and low-cost isotyped photovoltaic devices.
Transparent Conductive Al-Doped ZnO/Cu Bilayer Films Grown on Polymer Substrates at Room Temperature
HUANG Ji-Jie, WANG Yu-Ping, LU Jian-Guo**, GONG Li, YE Zhi-Zhen
Chin. Phys. Lett. 2011, 28 (12): 127306 .   DOI: 10.1088/0256-307X/28/12/127306
Abstract   PDF(pc) (896KB) ( 562 )
Al-doped ZnO (AZO)/Cu bi-layer films are deposited by dc magnetron sputtering on polycarbonate substrates at room temperature. The structural, electrical and optical properties of the films are investigated at various sputtering powers of the Cu layer. The AZO/Cu bi-layer film deposited at a moderate sputtering power of 180 W for the Cu layer displayed the highest figure of merit of 3.47×10−3 Ω-1, with a low sheet resistance of 12.38 Ω/sq, an acceptable visible transmittance of 73%, and a high near-infrared reflectance of about 50%.
The Evidence for Ferroelectricity on Magnetite Ceramics below the Verwey Transition
WU Yu-Qiang, WU Hong-Ying**, ZHAO Jie, LU Cui-Min, ZHANG Bao-Long, LIU Qing-Suo, MA Yong-Chang,
Chin. Phys. Lett. 2011, 28 (12): 127701 .   DOI: 10.1088/0256-307X/28/12/127701
Abstract   PDF(pc) (791KB) ( 472 )
We report the temperature- and frequency-dependent dielectric spectrum of magnetite ceramic single phase samples at 77.4–300 K and 200 Hz–1 MHz. In temperature-dependent dc resistivity, the sharp transition expected in single crystals is much suppressed. At higher temperatures, the grain boundaries contribute to the relaxation process. Below 120 K, the temperature-dependent dielectric constant reveals a weak broadened peak as cooling, from our analysis this behavior may be intrinsically correlated with the charge ordering of Fe3+ and Fe2+. Under a relatively low dc bias at 77.4 K, the polarization of the magnetite ceramic decreases, while under a much stronger electrical field, the dielectric spectrum in the lower frequency region is suppressed remarkably for the excitation of carriers bounded by grain boundaries.
Temperature and Composition Dependence of GaNxAs1−x(0 < x ≤ 0.05) before and after Annealing
ZHAO Chuan-Zhen**, LI Na-Na, WEI Tong, TANG Chun-Xiao
Chin. Phys. Lett. 2011, 28 (12): 127801 .   DOI: 10.1088/0256-307X/28/12/127801
Abstract   PDF(pc) (661KB) ( 380 )
The parameters in the band-anticrossing model for GaNxAs1−x (0 < x ≤ 0.05) are obtained considering the effect of temperature and composition. It is found that the effect of composition on the N levels in the band-anticrossing model is weak. The temperature dependence of the N levels and the temperature dependence of the band gap energy of GaNAs are weaker than that of GaAs. In addition, the reason for a spectral blueshift and the effect of annealing on the parameters in the band-anticrossing model are also discussed.
Enhancement of Er3+ Emission from an Er−Si Codoped Al2O3 Film by Stacking Si−Doped Al2O3 Sublayers
WANG Xiao, JIANG Zui-Min, XU Fei, **, MA Zhong-Quan, XU Run, YU Bin, LI Ming-Zhu, ZHENG Ling-Ling, FAN Yong-Liang, HUANG Jian, LU Fang
Chin. Phys. Lett. 2011, 28 (12): 127802 .   DOI: 10.1088/0256-307X/28/12/127802
Abstract   PDF(pc) (825KB) ( 305 )
A multilayer film (multi-film), consisting of alternate Er-Si-codoped Al2O3 (ESA) and Si−doped Al2O3 (SA) sublayers, is synthesized by co−sputtering from separated Er, Si, and Al2O3 targets. The dependence of Er3+ related photoluminescence (PL) properties on annealing temperatures over 700–1100°C is studied. The maximum intensity of Er3+ photoluminance (PL), about 10 times higher than that of the monolayer film, is obtained from the multi−film annealed at 950°C. The enhancement of Er3+ PL intensity is attributed to the energy transfer from the silicon nanocrystals (Si−NCs) to the neighboring Er3+ ions. The effective characteristic interaction distance (or the critical ET length) between Er and carriers (Si−NCs) is 3 nm. The PL intensity exhibits a nonmonotonic temperature dependence. Meanwhile, the PL integrated intensity at room temperature is about 30% higher than that at 14 K.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Density Increase of Upper Quantum Dots in Dual InGaN Quantum-Dot Layers
LV Wen-Bin, WANG Lai**, WANG Jia-Xing, HAO Zhi-Biao, LUO Yi
Chin. Phys. Lett. 2011, 28 (12): 128101 .   DOI: 10.1088/0256-307X/28/12/128101
Abstract   PDF(pc) (1355KB) ( 346 )
Single and dual layers of InGaN quantum dots (QDs) are grown by metal organic chemical vapor deposition. In the former, the density, average height and diameter of QDs are 1.3×109 cm−2, 0.93 nm and 65.1 nm, respectively. The latter is grown under the same conditions and possesses a 20 nm low-temperature grown GaN barrier between two layers. The density, average height and diameter of QDs in the upper layer are 2.6×1010 cm−2, 4.6 nm and 81.3 nm, respectively. Two reasons are proposed to explain the QD density increase in the upper layer. First, the strain accumulation in the upper layer is higher, leading to a stronger three-dimensional growth. Second, the GaN barrier beneath the upper layer is so rough it induces growth QDs.
Spectroscopy of a Gamma Irradiated Poly(Acrylic Acid)-Clotrimazole System
M. Todica**, C. V. Pop, Luciana Udrescu, Traian Stefan
Chin. Phys. Lett. 2011, 28 (12): 128201 .   DOI: 10.1088/0256-307X/28/12/128201
Abstract   PDF(pc) (557KB) ( 494 )
A poly(acrylic acid)-clotrimazole system, gamma irradiated at different doses, is investigated by Raman spectroscopy. Modifications of the spectrum of the polymeric matrix appear for doses of radiation greater than 333 Gy, whereas the spectrum of clotrimazole remains unaffected at these doses of radiation. These changes correlate with modification of the vibration modes of COOH and CH2 groups of a polymeric matrix after irradiation.
An X-Ray Diffraction and Thermogravimetric Study of Layered Perovskite Y1−xBixBaCo4O7
ZHANG Ya-Mei**, HAN Ru-Qu, WU Xiao-Shan, WANG Zhi-He
Chin. Phys. Lett. 2011, 28 (12): 128202 .   DOI: 10.1088/0256-307X/28/12/128202
Abstract   PDF(pc) (845KB) ( 548 )
Layer-structured oxides Y1−xBixBaCo4O7(0.00 ≤ x ≤ 0.05) were successfully synthesized and their structural and oxygen absorption properties were investigated by x−ray diffraction and thermogravimetry. Though Bi solubility was limited to about 5%, corresponding to Y0.95Bi0.05BaCo4O7, it is found that the structure and oxygen absorption properties of Y1−xBixBaCo4O7 are affected significantly as the Bi content x increases. Rietveld refinement results show that Y1−xBixBaCo4O7(x ≤ 0.05) is single phase with a hexagonal crystal structure (space group P63mc). Unit cell parameters and volume are changed and CoO4 tetrahedra are distorted along the c−axis in Bi doped YBaCo4O7. The TG results show that Y1−xBixBaCo4O7 undergoes two oxygen absorption processes in oxygen from room temperature to 1000°C and the maximum mass increase of the doped samples is less than that of YBaCo4O7. Bi doping effects on the structure and oxygen absorption properties are discussed on the basis of average radius and disorder of the Y site, the valence of Bi and the oxygen activation energy.
Herding Effect in Coupled Pedestrian-Pedestrian Interacting Dynamics
DING Jian-Xun**, LING Xiang, HUANG Hai-Jun, TAKASHI Imamura
Chin. Phys. Lett. 2011, 28 (12): 128301 .   DOI: 10.1088/0256-307X/28/12/128301
Abstract   PDF(pc) (420KB) ( 334 )
A simple particle hopping model is proposed to investigate the interaction of two groups of pedestrians, namely straight walking pedestrians and cross-pedestrians. In the model, the straight walking pedestrians have greater priority walking on a main road, while other pedestrians arrive at the roadside and check to cross. Herding behavior, by which cross-pedestrians communicate with each other and self-organize to compete for common space with their straight walking counterparts, are newly introduced to reflect realistic crossing behavior in a crowed street. The results demonstrate that herding behavior brings adverse consequences to both types of pedestrians as a whole, although the pedestrians adopting prompt herding behavior can benefit. Furthermore, an increased number of crossing points to avoid the inefficiency of the coupled system is also investigated.
Highly Efficient PCDTBT:PC71 BM Based Photovoltaic Devices without Thermal Annealing Treatment
YANG Shao-Peng**, KONG Wei-Guang, LIU Bo-Ya, ZHENG Wen-Yao, LI Bao-Min, LIU Xian-Hao, FU Guang-Sheng
Chin. Phys. Lett. 2011, 28 (12): 128401 .   DOI: 10.1088/0256-307X/28/12/128401
Abstract   PDF(pc) (978KB) ( 1563 )
We propose an effective method to fabricate highly efficient organic photovoltaic cells based on poly [N−9"-hepta-decanyl-2, 7-carbazole-alt-5,5-(4'7'-di-2-thienyl-2'1'3'-b-enzothiadiazole):[6,6]-phenyl C71−butyric acid methyl ester (PCDTBT:PC71BM). A power conversion efficiency of as high as 5.6% and a fill factor of 53.7% are achieved from the optimized cells. The influence of surface morphology of the active layer on the performance of the cells is also investigated.
A Dielectric Multilayer Filter for Combining Photovoltaics with a Stirling Engine for Improvement of the Efficiency of Solar Electricity Generation
SHOU Chun-Hui, LUO Zhong-Yang**, WANG Tao, SHEN Wei-Dong, ROSENGARTEN Gary, WANG Cheng, NI Ming-Jiang, CEN Ke-Fa
Chin. Phys. Lett. 2011, 28 (12): 128402 .   DOI: 10.1088/0256-307X/28/12/128402
Abstract   PDF(pc) (914KB) ( 544 )
In this Letter we outline a dielectric multilayer spectrally selective filter designed for solar energy applications. The optical performance of this 78-layer interference filter constructed by TiOx and SiO2 is presented. A hybrid system combining photovoltaic cells with a solar-powered Stirling engine using the designed filter is analyzed. The calculated results show the advantages of this spectrally selective method for solar power generation.
Comparison of GaN-Based Light-Emitting Diodes by Using the AlGaN Electron-Blocking Layer and InAlN Electron-Blocking Layer
CHEN Jun, FAN Guang-Han**, PANG-Wei, ZHENG Shu-Wen
Chin. Phys. Lett. 2011, 28 (12): 128501 .   DOI: 10.1088/0256-307X/28/12/128501
Abstract   PDF(pc) (545KB) ( 515 )
Optical properties of GaN-based light-emitting diodes (LEDs) are studied numerically by using AlGaN and InAlN electron-blocking layers (EBLs). Through the simulations of emission spectra, carrier concentration distribution, energy band, electrostatic field, internal quantum efficiency and output power, the results show that the LEDs with design of the InAlN EBL structure have a better performance over the original LEDs using an AlGaN EBL. The spectrum intensity and output power are enhanced significantly, and the efficiency droop of internal quantum efficiency is improved effectively with this design of InAlN EBL structure. It is proved that the strengths of carrier confinement and electron leakage current play a critical role in the performance of luminescence in LEDs.
Characteristics and Time-Dependent Instability of Ga-Doped ZnO Thin Film Transistor Fabricated by Radio Frequency Magnetron Sputtering
HUANG Hai-Qin, SUN Jian, LIU Feng-Juan, ZHAO Jian-Wei, HU Zuo-Fu, LI Zhen-Jun, ZHANG Xi-Qing**, WANG Yong-Sheng
Chin. Phys. Lett. 2011, 28 (12): 128502 .   DOI: 10.1088/0256-307X/28/12/128502
Abstract   PDF(pc) (614KB) ( 746 )
We report on the fabrication and electrical characteristics of Ga-doped ZnO thin film transistors (TFTs). Low Ga-doped (0.7wt%) ZnO thin films were deposited on SiO2/p−Si substrates by rf magnetron sputtering. The GZO TFTs show a mobility of 1.76 cm2/V⋅s, an on/off ratio of 1.0×106, and a threshold voltage of 35 V. The time−dependent instability of the TFT is studied. The VTH shifts negatively. In addition, the device shows a decrease of the on/off ratio, mainly due to the increase of the off-current. The mechanisms of instability are discussed.
Design of a 1200-V Thin-Silicon-Layer p-Channel SOI LDMOS Device
HU Sheng-Dong, **, ZHANG Ling, LUO Xiao-Rong, ZHANG Bo, LI Zhao-Ji, WU Li-Juan
Chin. Phys. Lett. 2011, 28 (12): 128503 .   DOI: 10.1088/0256-307X/28/12/128503
Abstract   PDF(pc) (651KB) ( 583 )
A 1200-V thin-silicon-layer p-channel silicon-on-insulator (SOI) lateral double-diffused metal-oxide-semiconductor (LDMOS) transistor is designed. The device named INI SOI p-LDMOS is characterized by a series of equidistant high concentration n+ islands inserted at the interface of a top silicon layer and a buried oxide layer. Accumulation−mode holes, caused by the electric potential dispersion between the device surface and the substrate, are located in the spacing between two neighboring n+ islands, and greatly enhance the electric field of the buried oxide layer and therefore, effectively increase the device breakdown voltage. Based on a 2−µm −thick buried oxide layer and a 1.5-µm −thick top silicon layer, a breakdown voltage of 1224 V is obtained, resulting in the high electric field (608 V/µm ) of the buried oxide layer.
Unique Properties of Heat Generation in Nanoscale Systems
ZHOU Li-Ling
Chin. Phys. Lett. 2011, 28 (12): 128504 .   DOI: 10.1088/0256-307X/28/12/128504
Abstract   PDF(pc) (663KB) ( 291 )
We study the unique properties of current-induced heat generation Q in nanostructures and its absence in macroscopic bulks. A lead−quantum dot-lead system is taken into consideration and it is found that its unique properties stem from energy quantization of the system and arise only under conditions of low temperature and weak dot-lead coupling. The relation of QI (I is the system current) fails in nanosystems, while the Q peaks align with peaks of phonon−assisted current under small bias. As a result, one can expect a large current accompanied by relatively small Q when the elastic current peak does not coincide with the phonon-assisted one, the ideal working condition for a nanostructure.
Original Articles
Shallow Decay Phase of the Early X-Ray Afterglow from External Shock in a Wind Environment
LEI Hai-Dong, WANG Jiu-Zhou, LÜ, Jing, ZOU Yuan-Chuan**
Chin. Phys. Lett. 2011, 28 (12): 129801 .   DOI: 10.1088/0256-307X/28/12/129801
Abstract   PDF(pc) (409KB) ( 325 )
We investigate the shallow decay phase of an early x-ray afterglow in gamma-ray bursts discovered by Swift, and suggest that both the shallow decay phase and the normal phase are from external shock in a wind environment, while the transferring time is the deceleration time. We apply this model to GRBs 050319 and 081008, and find that they can be explained by choosing a proper set of parameters.
Gravitational Instability in Neutrino Dominated Accretion Disks
LIU Tong**, XUE Li
Chin. Phys. Lett. 2011, 28 (12): 129802 .   DOI: 10.1088/0256-307X/28/12/129802
Abstract   PDF(pc) (446KB) ( 331 )
We revisit the vertical structure of neutrino-dominated accretion flows (NDAFs) in spherical coordinates under a boundary condition based on a mechanical equilibrium. The solutions show that the NDAF is significantly geometrically thick. The Toomre parameter is determined by the mass accretion rate and the viscosity parameter, which is defined as Q=cS Ω/πGΣ, where cS , Ω and Σ are the sound speed, angular velocity and surface density, respectively. According to the distribution of the Toomre parameter, the possible fragments of the disk may appear near the disk surface in the outer region. These possible outflows originating from the gravitational instability of the disk may account for the late-time flares in gamma-ray bursts.
COMMENTS AND ERRATA
Withdrawal of Chinese Physics Letters 28 (2011) 107301 "High-Efficiency Graphene Photo Sensor Using a Transparent Electrode" by LIU Tao and HUANG Zheng
LIU Tao*, HUANG Zheng
Chin. Phys. Lett. 2011, 28 (12): 129901 .   DOI: 10.1088/0256-307X/28/12/129901
Abstract   PDF(pc) (182KB) ( 310 )
Erratum: 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 (12): 129902 .   DOI: 10.1088/0256-307X/28/12/129902
Abstract   PDF(pc) (189KB) ( 299 )
86 articles