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Volume 28 Issue 5
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Construction of Lyapunov Function for Dissipative Gyroscopic System
XU Wei, YUAN Bo, AO Ping, **
Chin. Phys. Lett. 2011, 28 (5): 050201 .   DOI: 10.1088/0256-307X/28/5/050201
Abstract   PDF(pc) (409KB) ( 860 )
We introduce a force decomposition to construct a potential function in deterministic dynamics described by ordinary differential equations in the context of dissipative gyroscopic systems. Such a potential function serves as the corresponding Lyapunov function for the dynamics, hence it gives both quantitative and qualitative descriptions for stability of motion. As an example we apply our force decomposition to a four-dimensional dissipative gyroscopic system. We explicitly obtain the potential function for all parameter regimes in the linear limit, including those regimes where the Lyapunov function was previously believed not to exist.
Hamiltonian Structures and Integrability for a Discrete Coupled KdV-Type Equation Hierarchy
ZHAO Hai-Qiong, ZHU Zuo-Nong**, ZHANG Jing-Li
Chin. Phys. Lett. 2011, 28 (5): 050202 .   DOI: 10.1088/0256-307X/28/5/050202
Abstract   PDF(pc) (450KB) ( 438 )
Coupled Korteweg-de Vries (KdV) systems have many important physical applications. By considering a 4×4 spectral problem, we derive a discrete coupled KdV-type equation hierarchy. Our hierarchy includes the coupled Volterra system proposed by Lou et al.(e-print arXiv:0711.0420) as the first member which is a discrete version of the coupled KdV equation. We also investigate the integrability in the Liouville sense and the multi-Hamiltonian structures for the obtained hierarchy.
Analytical Solution of Fick's Law of the TRISO-Coated Fuel Particles and Fuel Elements in Pebble-Bed High Temperature Gas-Cooled Reactors
CAO Jian-Zhu, FANG Chao**, SUN Li-Feng
Chin. Phys. Lett. 2011, 28 (5): 050203 .   DOI: 10.1088/0256-307X/28/5/050203
Abstract   PDF(pc) (776KB) ( 1028 )
Two kinds of approaches are built to solve the fission products diffusion models (Fick's equation) based on sphere fuel particles and sphere fuel elements exactly. Two models for homogenous TRISO-coated fuel particles and fuel elements used in pebble-bed high temperature gas-cooled reactors are presented, respectively. The analytical solution of Fick's equation for fission products diffusion in fuel particles is derived by variables separation. In the fuel element system, a modification of the diffusion coefficient from D to D/r is made to characterize the difference of diffusion rates in distinct areas and it is shown that the Laplace and Hankel transformations are effective as the diffusion coefficient in Fick's equation is dependant on the radius of the fuel element. Both the solutions are useful for the prediction of the fission product behaviors and could be programmed in the corresponding engineering calculations.
Nonlocal Symmetries and Geometric Integrability of Multi-Component Camassa–Holm and Hunter–Saxton Systems
YAN Lu, SONG Jun-Feng, QU Chang-Zheng**
Chin. Phys. Lett. 2011, 28 (5): 050204 .   DOI: 10.1088/0256-307X/28/5/050204
Abstract   PDF(pc) (448KB) ( 6552 )
We present the multi-component Hunter–Saxton and μ−Camassa–Holm systems. It is shown that the multi-component Camassa–Holm, Hunter–Saxton and μ-Camassa–Holm systems are geometrically integrable, namely they describe pseudo-spherical surfaces. As a consequence, their infinite number of conservation laws can be directly constructed. For the three-component Camassa–Holm and Hunter–Saxton systems, their nonlocal symmetries depending on the pseudo-potentials are obtained.
Eliminating Next-Nearest-Neighbor Interactions in the Preparation of Cluster State
ZHANG Ji-Ying, ZHOU Zheng-Wei**, GUO Guang-Can
Chin. Phys. Lett. 2011, 28 (5): 050301 .   DOI: 10.1088/0256-307X/28/5/050301
Abstract   PDF(pc) (538KB) ( 527 )
By analyzing recent schemes for preparing the chain cluster state, we find that the existence of long-range couplings between qubits will induce a quick decay of the fidelity of the cluster state. We propose some schemes for eliminating the effect of the next-nearest-neighbor interactions in the XY and Ising models by dynamical decoupling method. In our approach, the undesired next-nearest-neighbor interactions are effectively suppressed and the fidelity of the generated cluster state is greatly improved by the pulse operations.
Controlled Phase Gate Based on an Electron Floating on Helium
SHI Yan-Li, MEI Feng, YU Ya-Fei, ZHANG Zhi-Ming**
Chin. Phys. Lett. 2011, 28 (5): 050302 .   DOI: 10.1088/0256-307X/28/5/050302
Abstract   PDF(pc) (429KB) ( 552 )
We propose a scheme to generate the controlled phase gate by using an electron floating on liquid helium. The electron is also driven by a classical laser beam and by an oscillating magnetic field. In the process, the vibration of the electron is used as the qubus to couple the energy level qubit (1D Stark-shifted hydrogen) and spin qubit. Ultimately, the controlled phase gate can be generated.
A Novel Multiparty Quantum Secret Sharing Scheme of Secure Direct Communication Based on Bell States and Bell Measurements
SHI Run-Hua, **, HUANG Liu-Sheng, YANG Wei, ZHONG Hong
Chin. Phys. Lett. 2011, 28 (5): 050303 .   DOI: 10.1088/0256-307X/28/5/050303
Abstract   PDF(pc) (416KB) ( 676 )
We present a novel quantum secret sharing scheme of secure direct communication and analyze its security. This scheme takes Einstein–Podolsky–Rosen (EPR) pairs in Bell states as quantum resources. In order to obtain the direct communication message, all agents only need to perform Bell measurements, not to perform any local unitary operation. The total efficiency in this scheme approaches 100% as the classical information exchanged is unnecessary except for the eavesdropping checks.
Analytical Approximation to the -Wave Solutions of the Hulthén Potential in Tridiagonal Representation
ZHANG Min-Cang**, HUANG-FU Guo-Qing
Chin. Phys. Lett. 2011, 28 (5): 050304 .   DOI: 10.1088/0256-307X/28/5/050304
Abstract   PDF(pc) (435KB) ( 450 )
The Schrödinger equation with the Hulthén potential is studied by working in a complete square integrable basis that carries a tridiagonal matrix representation of the wave operator. The arbitrary -wave solutions are obtained by using an approximation of the centrifugal term. The resulting three-term recursion relation for the expansion coefficients of the wavefunction is presented and the wavefunctions are expressed in terms of the Jacobi polynomial. The discrete spectrum of the bound states is obtained by the diagonalization of the recursion relation.
Controlling of Fusion of Two Solitons in a Two-Component Condensate by an Anharmonic External Potential
ZHANG Zhi-Qiang, WANG Deng-Long**, LUO Xiao-Qing, HE Zhang-Ming, DING Jian-Wen
Chin. Phys. Lett. 2011, 28 (5): 050305 .   DOI: 10.1088/0256-307X/28/5/050305
Abstract   PDF(pc) (571KB) ( 434 )
By using the multiple-scale method, we analytically study dynamical properties of two-component Bose-Einstein condensates trapped in a harmonic plus quartic anharmonic potential. It is shown that the anharmonic potential has an important effect on the dark solitons of the condensates. In particular, when the strength of the anharmonic external potential increases, the fusion of the two solitons becomes faster. This implies that the fusion of the two solitons can be controlled by an anharmonic potential.
Quantum Effects of Uniform Bose Atomic Gases with Weak Attraction
Chin. Phys. Lett. 2011, 28 (5): 050306 .   DOI: 10.1088/0256-307X/28/5/050306
Abstract   PDF(pc) (469KB) ( 429 )
We find that uniform Bose atomic gases with weak attraction can undergo a Bardeen–Cooper–Schrieffer (BCS) condensation below a critical temperature. In the BCS condensation state, bare atoms with opposite wave vectors are bound into pairs, and unpaired bare atoms are transformed into a new kind of quasi-particles, i.e. the dressed atoms. The atom-pair system is a condensate or a superfluid and the dressed-atom system is a normal fluid. The critical temperature and the effective mass of dressed atoms are derived analytically. The transition from the BCS condensation state to the normal state is a first-order phase transition.
Entangling Gate of Dipolar Molecules Coupled to a Photonic Crystal
XUE Peng**
Chin. Phys. Lett. 2011, 28 (5): 050307 .   DOI: 10.1088/0256-307X/28/5/050307
Abstract   PDF(pc) (464KB) ( 375 )
A hybrid entangling gate is proposed by using the coherent interaction between dipolar molecules and a photonic crystal microcavity, which is effected by virtual electric dipole transitions. Noise is included in the present model and high feasibility of the scheme with current experimental conditions is shown.
Entanglement of Two-Superconducting-Qubit System Coupled with a Fixed Capacitor
TIAN Li-Jun, **, QIN Li-Guo, ZHANG Hong-Biao
Chin. Phys. Lett. 2011, 28 (5): 050308 .   DOI: 10.1088/0256-307X/28/5/050308
Abstract   PDF(pc) (830KB) ( 448 )
We study thermal entanglement in a two-superconducting-qubit system in two cases, either identical or distinct. By calculating the concurrence of system, we find that the entangled degree of the system is greatly enhanced in the case of very low temperature and Josephson energies for the identical superconducting qubits and our result is in a good agreement with the experimental data.
Entanglement Enhancement in an XY Spin Chain
SU Xiao-Qiang**
Chin. Phys. Lett. 2011, 28 (5): 050309 .   DOI: 10.1088/0256-307X/28/5/050309
Abstract   PDF(pc) (1773KB) ( 596 )
We study evolution of entanglement in an XY-type spin channel and find that the entanglement can be enhanced by the spin channel. The parameter regions of the initial states for different numbers of sites are obtained. Furthermore, we consider a common spin environment coupling to the spin chains and find that the entanglement enhancement can also be implemented only for the chains with the odd numbers of sites.
Quantum Nonlocally Correlated Observables for Non-Gaussian States
LI Hong-Rong**, LI Fu-Li, ZHU Shi-Yao
Chin. Phys. Lett. 2011, 28 (5): 050310 .   DOI: 10.1088/0256-307X/28/5/050310
Abstract   PDF(pc) (598KB) ( 485 )
Quantum nonlocally correlated observables of the squeezed Bell-like states are investigated. We find that the higher amount of the entanglement does not always mean the stronger correlation of positions and momentums in the non-Gaussian states such as the photon-added states and the squeezed number states. Quantum nonlocal correlations of the amplitude-squared operators signal the entanglement existence of all the squeezed Bell-like states.
Foliation and the First Law of Black Hole Thermodynamics
Azad A. Siddiqui**, Syed Muhammad Jawwad Riaz, M. Akbar
Chin. Phys. Lett. 2011, 28 (5): 050401 .   DOI: 10.1088/0256-307X/28/5/050401
Abstract   PDF(pc) (377KB) ( 501 )
There has been lots of interest in exploring the thermodynamic properties at the horizon of a black hole spacetime. It has been shown earlier that for different spacetimes, the Einstein field equations at the horizon can be expressed as the first law of black hole thermodynamics. Using the idea of foliation, we develop a simpler procedure to obtain such results. We consider r= constant slices, for the Schwarzschild and Reissner–Nordstrom black hole spacetimes. The Einstein field equations for the induced 3−dimensional metrics of the hypersurfaces are expressed in thermodynamic quantities under the virtual displacements of the hypersurfaces. As expected, it is found that the field equations of the induced metric corresponding to the horizon can be written as a first law of black hole thermodynamics. It is to be mentioned here that our procedure is much easier, to obtain such results, as here one has to essentially deal with (n-1)−dimensional induced metric for an n-dimensional spacetime.
A New Wronskian Condition for a (3+1)-Dimensional Nonlinear Evolution Equation
WU Jian-Ping**
Chin. Phys. Lett. 2011, 28 (5): 050501 .   DOI: 10.1088/0256-307X/28/5/050501
Abstract   PDF(pc) (344KB) ( 482 )
A new Wronskian condition is set for a (3+1)-dimensional nonlinear evolution equation. With the aid of the Hirota bilinear transformation, a novel Wronskian determinant solution is presented for the equation.
Chaotic Synchronization of Two Electrical Coupled Neurons with Unknown Parameters Based on Adaptive Control
WANG Xing-Yuan**, REN Xiao-Li
Chin. Phys. Lett. 2011, 28 (5): 050502 .   DOI: 10.1088/0256-307X/28/5/050502
Abstract   PDF(pc) (719KB) ( 507 )
Chaotic synchronization of two electrical coupled FitzHugh–Nagumo (FHN) neurons with unknown parameters via adaptive control is investigated. Based on the Lyapunov stability theory, an adaptive controller and a parameter update law are designed, which can achieve the synchronization of the two gap junction coupled FHN neurons when the individual neuron is chaotic, without considering the coupling strength. Moreover, the unknown parameters are identified successfully and the controller is robust to the random noise. The numerical simulation results confirm the effectiveness of the designed controller.
On Group Phase Quantization and Its Physical Characteristics
DU Bao-Qiang, ZHOU Wei, YU Jian-Guo, DONG Shao-Feng
Chin. Phys. Lett. 2011, 28 (5): 050601 .   DOI: 10.1088/0256-307X/28/5/050601
Abstract   PDF(pc) (457KB) ( 397 )
The physical characteristics of phase quantum are further revealed, based on the proposition of concepts of the greatest common factor frequency, the least common multiple period, quantized phase shift resolution and equivalent phase comparison frequency. Then the problem of phase comparison between different frequency signals is certified in detail. Using the basic principle of phase comparison between different frequencies and the variation law of group phase difference, a point of view on group phase quantization is presented. Group phase quantum is not only an indivisible individual of group phase, but also a basic unit composing group phase difference. It is equal to the equivalent phase comparison period of phase comparison between different frequencies in size. Experimental results show not only a high measurement resolution of 10−12/s in frequency measurement based on group phase quantum, but also a super-high locked phase precision of 10−13/s in active H atomic clock.
An Alternative Interacting Boson Model Description of The N =90 Nuclei
DAI Lian-Rong**, TENG Wei-Xin, PAN Feng, WANG Sheng-Hua
Chin. Phys. Lett. 2011, 28 (5): 052101 .   DOI: 10.1088/0256-307X/28/5/052101
Abstract   PDF(pc) (517KB) ( 374 )
The SU(3) quadrupole−quadrupole interaction is replaced by the SO(6) cubic [Q(0)×Q(0)×Q(0)]0 interaction in fitting energy levels, some energy ratios and B(E2) ratios. It is shown that the alternative scheme can indeed be used to describe properties of the X(5) nuclei, for example, 150Nd, 152Sm, 154Gd. The results of the new scheme are compared with the corresponding experimental data and with those of the traditional U(5)−SU(3) transitional description. It is clearly shown that the results are better than those obtained from the traditional U(5)− SU(3) transitional description.
Astrophysical Rates for the 6He(p, γ)7Li Reaction
LI Er-Tao, LI Zhi-Hong**, SU Jun, GUO Bing, LI Yun-Ju, YAN Sheng-Quan, BAI Xi-Xiang, WANG You-Bao, WANG Bao-Xiang, LIAN Gang, ZENG Sheng, FANG Xiao, ZHAO Wei-Juan, LIU Wei-Ping
Chin. Phys. Lett. 2011, 28 (5): 052102 .   DOI: 10.1088/0256-307X/28/5/052102
Abstract   PDF(pc) (703KB) ( 377 )
Angular distribution of the 6He(d,n)7Li reaction at Ec.m.=9.1 MeV is measured in inverse kinematics for the first time. The proton spectroscopic factors for the ground and first excited states of 7Li are derived by using the distorted wave Born approximation analysis. The astrophysical rates of 6He(p,γ)7Li reaction are then deduced and fitted with an expression of REACLIB.
Description of the Chiral Doublet Bands in 135Nd and 136Nd
ZHANG Da-Li**, DING Bin-Gang
Chin. Phys. Lett. 2011, 28 (5): 052103 .   DOI: 10.1088/0256-307X/28/5/052103
Abstract   PDF(pc) (503KB) ( 387 )
The chiral doublet bands in 135Nd and 136Nd are investigated systematically within the supersymmetry scheme including many-body interactions and possessing the SO(5)(or SU(5)) symmetry on the rotational symmetry. Quantitatively good results of the energy spectra, the energy staggering parameter as a function of the spin and the spin assignment are obtained. The calculation shows that the stronger competition between the pairing and anti-pairing effects exists in these chiral doublet bands and the SU(3) symmetry breaking more seriously exists in the stable chiral structure.
A Phenomenological Model for Decay Process of Long-Persistent Phosphorescence
CHEN Bin, HAO Hong-Chen, ZHU Jiang, LU Ming**
Chin. Phys. Lett. 2011, 28 (5): 053201 .   DOI: 10.1088/0256-307X/28/5/053201
Abstract   PDF(pc) (611KB) ( 561 )
A sum of two or more exponential decay functions is empirically adopted nowadays to analyze the decay curve of long-persistent phosphor. However, the fitting parameters of this empirical model lack well-defined physical meanings, especially when the number of exponential decay function is greater than two. We propose a phenomenological model to describe the decay curve of long-persistent phosphor based on an analysis of the relationship between carrier concentration and light-emitting intensity. This model has a few fitting parameters with well-defined physical meanings as compared to the current empirical one. With this model, we quantitatively analyze the decay processes of typical long-persistent phosphors of SrAl2O4:Eu,Dy and obtain reasonable fitting results.
Simulation of Hydrogen Emission Spectrum in Debye Plasmas
DING Qi-Yong, **, ZHANG Song-Bin, WANG Jian-Guo
Chin. Phys. Lett. 2011, 28 (5): 053202 .   DOI: 10.1088/0256-307X/28/5/053202
Abstract   PDF(pc) (802KB) ( 796 )
We investigate the screening effects on the spectrum of spontaneous radiation and radiative recombination to the 1s, 2s and 2p states of hydrogen with total atom density N=1.7×1019 cm−3 and electron temperatures 1 eV, 2 eV and 5 eV under the local thermodynamic equilibrium (LTE) model. The needed atomic energy levels, the radiative transition probabilities and radiative recombination cross sections are calculated by solving the Schrödinger equation numerically incorporating the Debye–Hückel model in plasmas. The plasma emission spectrum is simulated for the first time by using the screened atomic parameters. The red shift and the cutoff of Rydberg spectra are observed and it is also found that the 2 eV electron temperature case has the strongest screening effects and the emission spectra to the 2s and 2p states are more likely affected by screening effects than that of the 1s state.
Relationship between Fermi Resonance and Solvent Effects
JIANG Xiu-Lan, LI Dong-Fei, SUN Cheng-Lin, LI Zhan-Long, YANG Guang, ZHOU Mi, LI Zuo-Wei, **, GAO Shu-Qin
Chin. Phys. Lett. 2011, 28 (5): 053301 .   DOI: 10.1088/0256-307X/28/5/053301
Abstract   PDF(pc) (638KB) ( 681 )
We theoretically and experimentally study the relationship between Fermi resonance and solvent effects and investigate the Fermi resonance of p-benzoquinone and cyclopentanone in different solvents and the Fermi resonance of CS2 in C6H6 at different concentrations. Also, we investigate the Fermi resonance of C6H6 and CCl4 in their solution at different pressures. It is found that solvent effects can be utilized to search Fermi resonance parameters such as coupling coefficient and spectral intensity ratio, etc., on the other hand, the mechanism of solvent effects can be revealed according to Fermi resonance at high pressure.
Inner-Shell Excitations of 2p Electrons of Argon Investigated by Fast Electron Impact with High Resolution
REN Lin-Mao, WANG You-Yan, LI Dong-Dong, YUAN Zhen-Sheng, ZHU Lin-Fan**
Chin. Phys. Lett. 2011, 28 (5): 053401 .   DOI: 10.1088/0256-307X/28/5/053401
Abstract   PDF(pc) (539KB) ( 400 )
Electron energy loss spectra of inner-shell excitations of 2p electrons of argon are measured at an incident electron energy of 2500 eV and scattering angles of 0° and 4°. The dipole−forbidden transitions of 2p3/2-14p and 2p3/2-15p are observed in the measured spectra and assigned based on the calculations of the Cowan code. The positions and line widths for the excitations of 2p3/2-1nl and 2p1/2-1 nl(n≤5) of argon are determined. The present results show that the line widths of the electric quadrupole transitions of 2p3/2-14p[5/2+3/2]2 and the electric monopole one of 2p3/2-14p[1/2]0 are less than those of the dipole-allowed transitions.
Potential and Kinetic Electron Emissions from HOPG Surface Irradiated by Highly Charged Xenon and Neon Ions
WANG Yu-Yu, **, ZHAO Yong-Tao, SUN Jian-Rong, LI De-Hui, QAYYUM Abdul , LI Jin-Yu, WANG Ping-Zhi, XIAO Guo-Qing
Chin. Phys. Lett. 2011, 28 (5): 053402 .   DOI: 10.1088/0256-307X/28/5/053402
Abstract   PDF(pc) (865KB) ( 537 )
Highly charged 129Xeq+ (q=10–30) and 40Neq+ (q=4–8) ion−induced secondary electron emissions on the surface of highly oriented pyrolytic graphite (HOPG) are reported. The total secondary electron yield is measured as a function of the potential energy of incident ions. The experimental data are used to separate contributions of kinetic and potential electron yields. Our results show that about 4.5% and 13.2% of ion's potential energies are consumed in potential electron emission due to different Xeq+−HOPG and Neq+-HOPG combinations. A simple formula is introduced to estimate the fraction of ion's potential energy for potential electron emission.
Diffusion of Six-Atom Cu Islands on Cu(111) and Ag(111)
Sardar Sikandar Hayat**, I. Ahmad, M. Arshad Choudhry
Chin. Phys. Lett. 2011, 28 (5): 053601 .   DOI: 10.1088/0256-307X/28/5/053601
Abstract   PDF(pc) (988KB) ( 529 )
Diffusion of Cu hexamer islands on Cu(111) and Ag(111) is studied using a molecular dynamics simulation technique with many-body potentials obtained from the embedded atom method. Simulations are carried out at temperatures 300, 500 and 700 K, showing that shape-changing multiple-atom processes are more helpful for the diffusion rather than concerted motion of islands. Arrhenius plots of the diffusion coefficients provide effective energy barrier values of 161.29±5 meV for Cu(111) and 179.34±5 meV for Ag(111) surfaces. At 700 K, one pop-up atom among island atoms is observed with correlative changes in the position and shape of the lower-layer adatoms.
A Simplified Cold Atom Source for 3-D MOT Loading
WANG Xiao-Long, CHENG Bing, WU Bin, WANG Zhao-Ying, LIN Qiang**
Chin. Phys. Lett. 2011, 28 (5): 053701 .   DOI: 10.1088/0256-307X/28/5/053701
Abstract   PDF(pc) (656KB) ( 373 )
A simplified two-dimensional (2-D) magneto-optical trap (MOT) for loading atoms into a 3-D MOT is realized. Instead of utilizing multiple wave plates and beam splitters to cover a large cooling region, we deploy cooling beams with elliptical cross-section profiles to achieve a comparable cooling volume. This simplification reduces the cost and difficulty of alignment. The 3-D MOT achieves a loading rate of 2×108 atoms per second via this simplified 2-D MOT. Correlation between the loading rate and parameters of optical system is also determined.
Repulsive and Restoring Casimir Forces Based on Magneto-Optical Effect
ZENG Ran**, YANG Ya-Ping,
Chin. Phys. Lett. 2011, 28 (5): 054201 .   DOI: 10.1088/0256-307X/28/5/054201
Abstract   PDF(pc) (613KB) ( 363 )
The Casimir force direction tuned by the external magnetic field due to the magneto-optical Voigt effect is investigated. The magneto-optical effect gives rise to the modified frequency-dependent electric permittivity and thus the electromagnetic properties of the materials can be adjusted to satisfy the condition of the formation of repulsive Casimir force. It is found that between the ordinary dielectric slab and magneto-optical material slab, a repulsive force may exist by adjusting the applied magnetic field. The restoring Casimir force can also be obtained if suitable parameter values are taken. For realistic materials, the repulsive and the restoring force is shown to possibly take place at typical distances in microelectromechanical systems.
Compact Continuous-Wave Nd:YVO4 Laser with Self-Raman Conversion and Sum Frequency Generation
ZHU Hai-Yong**, ZHANG Ge, DUAN Yan-Min, HUANG Cheng-Hui, WEI Yong
Chin. Phys. Lett. 2011, 28 (5): 054202 .   DOI: 10.1088/0256-307X/28/5/054202
Abstract   PDF(pc) (552KB) ( 1324 )
Low threshold and compact cw Nd:YVO4 self−Raman lasers at 1176 nm and sum-frequency mixing of fundamental and first-Stokes wavelengths are demonstrated. A 20-mm Nd:YVO4 crystal is adopted in a compact plane-concave resonator. The results show that the cw Raman conversion is sensitive to cavity length. At an incident pump power of 22.5 W, output power of 1.53 W at 1175.6 nm is achieved, corresponding to the threshold of only 0.8 W and the slop efficiency of 8.1%. Intra-cavity sum-frequency generation is realized in a type-II phase-matching cut KTP crystal, 480 mW at 558.6 nm is obtained at incident pump power of 12 W.
All-Optical Format Conversion from RZ-DPSK to NRZ-DPSK at 40Gbit/s
ZHANG Zheng, PAN Di, YU Yu**, ZHANG Xin-Liang
Chin. Phys. Lett. 2011, 28 (5): 054203 .   DOI: 10.1088/0256-307X/28/5/054203
Abstract   PDF(pc) (556KB) ( 540 )
All-optical format conversion from return-to-zero differential phase shift keying (RZ-DPSK) to non-return-to-zero DPSK (NRZ-DPSK) is demonstrated by using a delay interferometer and a 1-nm-bandwidth filter at 40 Gbit/s. The operation principle is theoretically analyzed and numerically simulated with the help of VPI Transmission Maker 8.5. The simulated results are in agreement well with the experimental results. The conversion can be achieved with power penalty of 0.7 dB.
Propagation of Coherent Gaussian Schell-Model Beam Array in a Misaligned Optical System
ZHOU Pu**, WANG Xiao-Lin, MA Yan-Xing, MA Hao-Tong, XU Xiao-Jun, LIU Ze-Jin
Chin. Phys. Lett. 2011, 28 (5): 054204 .   DOI: 10.1088/0256-307X/28/5/054204
Abstract   PDF(pc) (499KB) ( 752 )
Based on a generalized Collins formula, the analytical formula for the propagation property of coherent Gaussian Schell-model (GSM) beam array through a misaligned optical system is derived. As numerical examples, the propagation of a coherent GSM beam array in a typical misaligned optical system with a thin lens is evaluated. The influence of different misalignment parameters is calculated and the normalized-intensity distribution is graphically illustrated.
High-Resolution Plasmonic Refractive-Index Sensor Based on a Metal-Insulator-Metal Structure
ZHU Jia-Hu, HUANG Xu-Guang**, MEI Xian
Chin. Phys. Lett. 2011, 28 (5): 054205 .   DOI: 10.1088/0256-307X/28/5/054205
Abstract   PDF(pc) (690KB) ( 768 )
A high-resolution plasmonic refractive-index sensor based on a metal-insulator-metal structure consisting of a straight bus waveguide and a resonator waveguide is proposed and numerically simulated by using the finite difference time domain method under a perfectly matched layer absorbing boundary condition. Both analytic and simulated results show that the resonant wavelengths of the sensor have a linear relationship with the refractive index of material under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of one of the resonant wavelengths. The resolution of refractive index of the nanometeric plasmonic sensor can reach as high as 10−6, giving the wavelength resolution of 0.01 nm. It could be applied to highly-resolution biological sensing.
Luminance Effects on Neural Mechanism at Photopic Level
GE Jing-Jing**, WANG Zhao-Qi
Chin. Phys. Lett. 2011, 28 (5): 054206 .   DOI: 10.1088/0256-307X/28/5/054206
Abstract   PDF(pc) (1286KB) ( 303 )
In order to obtain the influence of the luminance at photopic level on the neural mechanism, a neural contrast sensitivity function (NCSF) measurement system is established. The contrast sensitivity function (CSF) of the visual system and the modulation transfer function (MTF) of the eye's optical system are first measured with correspondent instruments respectively. Then the NCSF is calculated as the ratio of CSF to MTF. Four individual eyes are involved in the cases of green light and white light. With increasing luminance, the tendency of the variation of the CSFs is similar to that of the NCSFs, while the gain is larger than that of the NCSFs, especially in the region of higher spatial frequency. It is the NCSF, rather than CSF, that reflects the luminance sensitivity in the retina-brain neural system, because the influence of the eye's optical system is excluded.
A New Type of Absorbance Sensors Based on Long-Period Fiber Gratings
LUO Tao, GU Zheng-Tian**
Chin. Phys. Lett. 2011, 28 (5): 054207 .   DOI: 10.1088/0256-307X/28/5/054207
Abstract   PDF(pc) (458KB) ( 353 )
A new absorbance sensor based on long-period fiber gratings (LPFGs) is presented, The measurand is coated on the cladding of the LPFG. It is found that the depth of the stop band of the LPFG spectrum will be strongly affected by the absorbance of the measurand if an optimum coating thickness is selected. The analysis shows that within the optimal thickness range, the cladding modes could transform into the overlay modes and interact with the measurand more effectively. An absorbance sensitivity of 7×103 is available when the sensor structure is optimized.
Slow-Light Propagation in a Tapered Dielectric Periodic Waveguide over Broad Frequency Range
FANG Yi-Jiao, CHEN Zhuo**, WANG Zhen-Lin
Chin. Phys. Lett. 2011, 28 (5): 054208 .   DOI: 10.1088/0256-307X/28/5/054208
Abstract   PDF(pc) (761KB) ( 320 )
A tapered waveguide composed of a one-dimensional periodic arrangement of dielectric material is proposed for light trapping. The equifrequency contours (EFC) of silicon-air multilayer photonic crystals within the first band-gap region are first studied. A zero-group-velocity at the first Brillouin zone boundary along the grating vector is predicted. The propagation constants and eigenfrequencies of the first-order guiding modes are numerically investigated for photonic crystal waveguide structures with a finite thickness. Different frequency components of the guiding modes are found to slow and stop at different thicknesses inside such a tapered waveguide structure. In addition, the time-evolution of a femto-second pulse propagating in the tapered waveguide is also demonstrated.
Simulation of Far-Field Superresolution Fluorescence Imaging with Two-Color One-Photon Excitation of Reversible Photoactivatable Protein
WANG Chen**, QIAO Ling-Ling, MAO Zheng-Le
Chin. Phys. Lett. 2011, 28 (5): 054209 .   DOI: 10.1088/0256-307X/28/5/054209
Abstract   PDF(pc) (587KB) ( 358 )
We propose to achieve far-field super-resolution imaging by using offset two-color one-photon (2C1P) excitation of reversible photoactivatable fluorescence proteins. Due to the distinctive photoswitching performance of the proteins, such as dronpa, the fluorescence emission will only come from the overlapped region of activation beam and excitation beam. The analysis solution of rate equation shows that the resolution of offset 2C1P microscope is "engineered" by laser power of excitation and activation beams and the power ratio between them. Superior lateral and transverse resolution is theoretically demonstrated compared with conventional fluorescence scanning microscopy.
Efficient Tunable Mid-Wave Infrared Laser from 2µm Tm,Ho:YVO4 Pumped Gain−Switched Cr2+:ZnSe Laser
MENG Pei-Bei, YAO Bao-Quan**, LI Gang, JU You-Lun, WANG Yue-Zhu
Chin. Phys. Lett. 2011, 28 (5): 054210 .   DOI: 10.1088/0256-307X/28/5/054210
Abstract   PDF(pc) (577KB) ( 448 )
An efficient mid-wave infrared gain-switched Cr2+:ZnSe laser pumped by a 2.058 µm Tm,Ho:YVO4 laser is reported. As much as 3.86 W output is achieved with the pump power of 13.4 W at pulse repetition frequency of 15 kHz, corresponding to the slope efficiency of 30.9%. With a quartz birefringent filter inserted in the laser cavity and by rotating the external angle of the quartz birefringent filter, wavelength tuning range nearly from 2453 nm to 2508 nm with 5 nm linewidth (FWHM) is also obtained.
A Novel Method for Heightening Sensitivity of Prism Coupler-Based SPR Sensor
ZHANG Zhi-Wei, **, WEN Ting-Dun, WU Zhi-Fang
Chin. Phys. Lett. 2011, 28 (5): 054211 .   DOI: 10.1088/0256-307X/28/5/054211
Abstract   PDF(pc) (485KB) ( 620 )
We present a novel method for heightening the sensitivity of a prism coupler-based surface plasmon resonance (SPR) sensor. The method is based on the total reflection prism made of BK7 glass combined with the Kretschmann geometry of theattenuated total reflection (ATR) method. Compared to the conventional methods of prism coupler-based SPR, the novel method provides higher sensitivity to the measurement system. Theoretical simulations show that the detection sensitivity to the refractive index (RI) of the sensor based on the novel approach has a strong dependence on the thickness of the metal layer. The RI resolution of the sensor is predicted to be 8×10−7 refractive index units (RIU) under the condition of optimum metal film thickness. This novel method can leave out a precision angle rotation device in the angle modulation and it is unnecessary to adjust the acceptance angle of the light detector. The principal advantage of this method over other methods of light intensity modulation based on prism coupler-based SPR is high sensitivity, expediency to measure and application of long distances.
High Power Passive Phase Locking of Four Yb-Doped Fiber Amplifiers by an All-Optical Feedback Loop
XUE Yu-Hao, HE Bing**, ZHOU Jun***, LI Zhen, FAN Yuan-Yuan, QI Yun-Feng, LIU Chi, YUAN Zhi-Jun, ZHANG Hai-Bo, LOU Qi-Hong
Chin. Phys. Lett. 2011, 28 (5): 054212 .   DOI: 10.1088/0256-307X/28/5/054212
Abstract   PDF(pc) (826KB) ( 613 )
We report the passive phase locking of four high power Yb-doped fiber amplifiers with ring cavity. The interference patterns at different output power are observed and the Strehl ratios are measured. The maximum coherent output power of the fiber array is up to 1062 W by multi-stage amplification. The stable beam profiles of various phase relationships are observed by controlling the position of the feedback fiber, in good agreement with the calculated results. By using master oscillator power-amplifier (MOPA) architecture and broadband operation of passively phased systems, higher power scaling with high beam quality appears to be feasible.
Enhancement of Light Absorption in Thin Film Silicon Solar Cells with Metallic Grating and One-Dimensional Photonic Crystals
ZHENG Gai-Ge, XIAN Feng-Lin, LI Xiang-Yin**
Chin. Phys. Lett. 2011, 28 (5): 054213 .   DOI: 10.1088/0256-307X/28/5/054213
Abstract   PDF(pc) (617KB) ( 761 )
We design an effective light trapping scheme through engineering metallic gratings and one-dimensional dielectric photonic crystals (PhCs) to increase the optical path length of light within the solar cells. This incorporation can result in broadband optical absorption enhancement not only for transverse magnetic polarized light but also for transverse-electric polarization. Even when no plasmonic mode can be excited, due to the high reflection of the PhCs, the absorption in the active region can still be enhanced. Rigorous coupled wave analysis results demonstrate that such a hybrid structure boosts the overall cell performance by increasing the light trapping capabilities and is especially effective at the silicon band edge. This kind of design can be used to increase the optical absorption over a wide spectral range and is relatively independent of the angle of incidence.
Enhanced Visible Light Generation from 1µm Femtosecond Pulses within High-Δ Photonic Crystal Fibers
ZHANG Xin-Ben, ZHU Xian, CHEN Xiang, PENG Jing-Gang, DAI Neng-Li, LI Jin-Yan**
Chin. Phys. Lett. 2011, 28 (5): 054214 .   DOI: 10.1088/0256-307X/28/5/054214
Abstract   PDF(pc) (618KB) ( 358 )
We demonstrate the blue light generated in high-Δ photonic crystal fibers (PCFs). A femtosecond Yb−doped fiber laser, operating at 1039 nm, is used to pump a GeO2-doped PCF in the largely anomalous group velocity dispersion (GVD) region. The emitted radiation covers 418.6–544.6 nm with 5 dB flatness. The calculated result indicates that the cross phase module (XPM) effect induced by higher-mode soliton makes a contribution to the blue component generation.
Analysis of Optical Vortices in the Near Field of a Thin Metal Film
ZHANG Jin-Long, **
Chin. Phys. Lett. 2011, 28 (5): 054215 .   DOI: 10.1088/0256-307X/28/5/054215
Abstract   PDF(pc) (612KB) ( 358 )
Optical vortices are shown to be generated in the near-field of a slab lens with a realistic thin metal film due to the amplification of the evanescent wave by the metal film in the TM polarization. The vortices are connected to two saddle points near the output interface of the lens. By means of varying the position of the object with respect to the lens and the wavelength, the strength of circulation of the power flow, the position and the rotation of the vortices can be well controlled. The influence of the gain to the optical vortices is also illustrated.
Light Extraction Enhancement of GaN LED with a Two-Dimensional Photonic Crystal Slab
LIU Hong-Wei**, KAN Qiang, WANG Chun-Xia, HU Hai-Yang, XU Xing-Sheng, CHEN Hong-Da
Chin. Phys. Lett. 2011, 28 (5): 054216 .   DOI: 10.1088/0256-307X/28/5/054216
Abstract   PDF(pc) (643KB) ( 1542 )
Light extraction effects of a photonic crystal slab with a micrometer scale lattice constant are studied. A GaN light emitting diode (LED) with a photonic crystal slab is fabricated. The light extraction effects and the enhancement mechanism are investigated. From theoretical analysis, it is found that the characteristics of LED light emission are modulated by the photonic crystal slab. Experimental results show that the LED light emission intensity is enhanced by 38% due to guide mode extracting by the photonic crystal.
A Hemispherical-Involute Cavity Receiver for Stirling Engine Powered by a Xenon Arc Solar Simulator
LI Zhi-Gang**, TANG Da-Wei, LI Tie, DU Jing-Long,
Chin. Phys. Lett. 2011, 28 (5): 054401 .   DOI: 10.1088/0256-307X/28/5/054401
Abstract   PDF(pc) (1161KB) ( 992 )
We develop a solar simulator composed of multiple xenon arc lamps combined with a faceted paraboloidal dish concentrator to drive a Stirling engine in our laboratory for all-weather indoor testing. Experiments and numerical analysis are performed to determine the radiation flux and temperature distributions on the solar receiver surface. Based on the theoretical results, we present a receiver design for a solar Stirling engine with involute tubes closely conforming to the imaginary hemisphere to obtain a substantially uniform temperature field and a high solar-thermal efficiency of 67.1%.
Exact Solutions on MHD Flow Past an Accelerated Porous Plate in a Rotating Frame
T. Hayat, Liaqat Ali. Khan, R. Ellahi**, S. Obaidat
Chin. Phys. Lett. 2011, 28 (5): 054701 .   DOI: 10.1088/0256-307X/28/5/054701
Abstract   PDF(pc) (464KB) ( 556 )
We present an analysis of an electrically conducting viscous fluid over a porous plate in a rotating system. The plate starts impulsively from rest relative to the rotating fluid moving with uniform acceleration in its own plane. Exact solutions are developed for both large and small times. In addition, skin friction is computed. The variations of magnetic field and porosity are displayed and discussed. It is noted that steady state behavior is not achieved even under the simultaneous effects of suction, magnetic field and rotation.
TR PIV Experimental Investigation on Bypass Transition Induced by a Cylinder Wake
TANG Zhan-Qi, JIANG Nan, **
Chin. Phys. Lett. 2011, 28 (5): 054702 .   DOI: 10.1088/0256-307X/28/5/054702
Abstract   PDF(pc) (728KB) ( 561 )
The process of laminar to turbulent transition induced by a cylinder wake is studied by time-resolved (TR) particle image velocimetry (PIV) in a water channel. The combination of multi-scale local-averaged structure function analysis with criteria is used to identify the generation of secondary transverse vortex structure and to track its evolution along the streamwise. At the beginning of transition, with the decent of cylinder wake vortex, the secondary vortex structure is induced near the wall. As the secondary vortex moves downstream, it is induced to lift up by the wake vortex, meanwhile they are diffused and dissipated. According to the method of spatial conditional average, a low-speed hump is found in the near-wall region along the bypass transition zone, accompanied by a low-speed region in the free stream occupied by the wake vortex. With further downstream, the hump in the near-wall region becomes more and more obvious. At the later stage of transition zone, hairpin vortex can be seen by conditional-averaged low-pass filtered vorticity. The hairpin head is almost vertical to the wall with an inclination angle of about 90°, which is attributed to the additional lift-up behavior induced by wake vortex. It can be concluded that in the process of bypass transition, the wake vortex would not only induce the secondary vortex but also leaven its growth and evolution, resulting in the robust and rapidly growing hairpin vortex.
Transient Growth of Perturbation Energy in the Taylor–Couette Problem with Radial Flow
CHEN Cheng, GUO Zhi-Wei, WANG Bo-Fu, SUN De-Jun**
Chin. Phys. Lett. 2011, 28 (5): 054703 .   DOI: 10.1088/0256-307X/28/5/054703
Abstract   PDF(pc) (729KB) ( 441 )
Transient growth of perturbation energy in the Taylor–Couette problem with radial flow is investigated. The effects of radial flow on transient growth and structure of the optimal perturbation are mainly considered. For the wide gap case, strong radial flow, either inward or outward, shifts the peak of the amplitude of optimal perturbation towards the outer cylinder and the lift-up mechanism cannot be observed. However, for the narrow gap case, the optimal perturbation is almost unaffected by the radial flow and the lift-up mechanism still exists.
Lifetime Calculations on Collector Optics from Laser Plasma Extreme Ultraviolet Sources with Minimum Mass
WU Tao, WANG Xin-Bing**
Chin. Phys. Lett. 2011, 28 (5): 055201 .   DOI: 10.1088/0256-307X/28/5/055201
Abstract   PDF(pc) (525KB) ( 541 )
An ion flux and its kinetic energy spectrum are obtained using a self similar spherically symmetric fluid model of expansion of a collisionless plasma into vacuum. According to the ion flux and energy distribution, the collector optical lifetime is estimated by knowledge of the sputtering yield of conventional Mo/Si multilayer coatings for the CO2 and Nd:YAG pulsed−laser produced plasmas based on the minimum mass tin droplet target without debris mitigation. The results show that the longer wavelength of the CO2 laser produced plasma light source is more suitable for extreme ultraviolet lithography than Nd:YAG laser in respect of fast ion debris induced sputtering damage to the collector mirror.
Similar Rayleigh–Taylor Instability of Shock Fronts Perturbed by Corrugated Interfaces
HE Yong**, HU Xi-Wei, JIANG Zhong-He
Chin. Phys. Lett. 2011, 28 (5): 055202 .   DOI: 10.1088/0256-307X/28/5/055202
Abstract   PDF(pc) (408KB) ( 348 )
Instability of a planar shock front perturbed by a corrugated interface is analyzed, where the perturbation wavelength is along the shock front plane. The presented analysis involves the effects of the features on the shock front, which is different from a general method presented by D'yakov and Kontorovich, where the shock front is taken as an infinitely discontinuity. The growth rate of the instability of the perturbed shock front is obtained and compared with the growth rate of the Rayleigh–Taylor instability (RTI) of an interface, on which the density gradient and the initial conditions are similar to the perturbed shock front. The analysis and comparisons of the growth rate of the instability indicate that the features of the shock front should be considered seriously in the shock interface interactions.
A Transition Phase in the Transformation from α-;, β- and ϵ- to δ-Bismuth Oxide
DENG Hong-Yan, HAO Wei-Chang, XU Huai-Zhe**
Chin. Phys. Lett. 2011, 28 (5): 056101 .   DOI: 10.1088/0256-307X/28/5/056101
Abstract   PDF(pc) (774KB) ( 916 )
As an important functional material, Bi2O3 is found in seven polymorphs. We systematically analyze the transformation from α-, β- and ϵ- to δ-Bi2O3 by using crystallographic group theory and structural simulations. A transition phase is proved to exist in the transformation from the α-, β- and ϵ-Bi2O3 to δ-Bi2O3. The transition phase is supposed to be tetragonal phase Bi2O2.7 (Z=2) with the 139th I 4/m 2/m 2/m space group.
Superlubricity of a Mixed Aqueous Solution
MA Zhi-Zuo, ZHANG Chen-Hui**, LUO Jian-Bin, LU Xin-Chun, WEN Shi-Zhu
Chin. Phys. Lett. 2011, 28 (5): 056201 .   DOI: 10.1088/0256-307X/28/5/056201
Abstract   PDF(pc) (882KB) ( 1646 )
A super-low friction coefficient of 0.0028 is measured under a pressure of 300 MPa when the friction pair (the silicon nitride ball sliding on the silicate glass) is lubricated by the mixed aqueous solution of glycerol and boric acid. The morphorlogies of the hydroxylated glass plate are observed by an atomic force microscope (AFM) in deionized water, glycerol, boric acid and their mixed aqueous solution. Bonding peaks of the retained liquids adhered on the surface of the sliding track are detected by an infrared spectrum apparatus and a Raman spectrum apparatus. The mechanism of the superlubricity of the glycerol and boric acid mixed aqueous solution is discussed. It is deduced that the formation of the lubricant film has enough strength to support higher loads, the hydration effect offering the super lower shear resistance. Key words: superlubricity, water based lubricant, ultra-low friction
Preparation of Curled Microfibers by Electrospinning with Tip Collector
TANG Cheng-Chun, CHEN Jun-Chi, LONG Yun-Ze**, YIN Hong-Xing, SUN Bin, ZHANG Hong-Di
Chin. Phys. Lett. 2011, 28 (5): 056801 .   DOI: 10.1088/0256-307X/28/5/056801
Abstract   PDF(pc) (1110KB) ( 950 )
We report on curled polyvinylpyrrolidone (PVP) microfibers fabricated by a modified electrospinning with a small nail as the tip collector. PVP (45 wt%) ethanol solution is electrospun under different working voltages ranging from 10 to 15, 20, 30 and 40 kV. It is found that with the increase of working voltage, the proportion of the curled fibers increases and the uniformity of the curled fibers improves, as well as the repeat distance of the curled structures reducing. Particularly, some curled fibers develop into helical structures under relatively high voltages. Further analyses indicate that the formation mechanism for the curled polymer fibers can be ascribed to electrical driven bending instability and/or mechanical jet buckling when hitting the collector surface. This modified electrospinning technique may be a cost-effective approach for the mass production of curled microfibers.
Explosive Synchronization and Emergence of Assortativity on Adaptive Networks
JIANG Hui-Jun, WU Hao, HOU Zhong-Huai**
Chin. Phys. Lett. 2011, 28 (5): 056802 .   DOI: 10.1088/0256-307X/28/5/056802
Abstract   PDF(pc) (614KB) ( 440 )
We report an explosive transition from incoherence to synchronization of coupled phase oscillators on adaptive networks, following an Achlioptas process based on dynamic clustering information. During each adaptive step of the network topology, a portion of the links is randomly removed and the same amount of new links is generated following the so-called product rules (PRs) applied to the dynamic clusters. Particularly, two types of PRs are considered, namely, the min-PR and max-PR. We demonstrate that the synchronization transition becomes explosive in both cases. Interestingly, we find that the min-PR rule can lead to disassortativity of the network topology, while the max-PR rule leads to assortativity.
Prediction of a Low-Dense BC2N Phase
Chin. Phys. Lett. 2011, 28 (5): 057101 .   DOI: 10.1088/0256-307X/28/5/057101
Abstract   PDF(pc) (594KB) ( 354 )
We predict a low-dense phase of ternary boron-carbon-nitrogen compound with a cubic symmetry, named as ld−BC2N. Crystal and electronic structures are studied by the ab initio pseudopotential density functional method. Lattice constant, electronic band structure and density of state as well as the phonon spectrum of ld−BC2N are calculated. Our results show that ld−BC2N is an indirect gap semiconductor with a band gap of 3.6 eV, a theoretical Vickers hardness of 67.5 GPa and the bulk modulus of 280 GPa suggest that ld−BC2N is a superhard material which has low elastic moduli and high hardness compared with cubic BN.
Improved AlGaN/GaN HEMTs Grown on Si Substrates Using Stacked AlGaN/AlN Interlayer by MOCVD
WANG Yong, **, YU Nai-Sen, LI Ming, LAU Kei-May
Chin. Phys. Lett. 2011, 28 (5): 057102 .   DOI: 10.1088/0256-307X/28/5/057102
Abstract   PDF(pc) (647KB) ( 619 )
AlGaN/GaN high electron mobility transistors (HEMTs) are grown on 2-inch Si (111) substrates by MOCVD. The stacked AlGaN/AlN interlayer with different AlGaN thickness and indium surfactant doped is designed and optimized to relieve the tensile stress during GaN epitaxial growth. The top 1.0 µm GaN buffer layer grown on the optimized AlGaN/AlN interlayer shows a crack-free and shining surface. The XRD results show that GaN(002) FWHM is 480 arcsec and GaN(102) FWHM is 900 arcsec. The AGaN/GaN HEMTs with optimized and non-optimized AlGaN/AlN interlayer are grown and processed for comparison and the dc and rf characteristics are characterized. For the dc characteristics of the device with optimized AlGaN/AlN interlayer, maximum drain current density Idss of 737 mA/mm, peak transconductance Gm of 185 mS/mm, drain leakage current density Ids of 1.7 µA/mm, gate leakage current density Igs of 24.8 µA/mm and off−state breakdown voltage VBR of 67 V are achieved with Lg/Wg/Lgs/Lgd = 1/10/1/1 µm. For the small signal rf characteristics of the device with optimized AlGaN/AlN interlayer, current gain cutoff frequency fT of 8.3 GHz and power gain cutoff frequency fmax of 19.9 GHz are achieved with Lg/Wg/Lgs/Lgd=1/100/1/1 µm. Furthermore, the best rf performance with fT of 14.5 GHz and fmax of 37.3 GHz is achieved with a reduced gate length of 0.7 µm.
Frequency-Dependent Electrical Transport Properties of 4,4',4
LI Bi-Xin, CHEN Jiang-Shan, ZHAO Yong-Biao, MA Dong-Ge**
Chin. Phys. Lett. 2011, 28 (5): 057201 .   DOI: 10.1088/0256-307X/28/5/057201
Abstract   PDF(pc) (736KB) ( 760 )
Frequency-dependent electrical transport properties of 4,4',4"−tri(N−carbazolyl)-triphenylamine (TCTA) are analyzed by impedance spectroscopy (IS) as functions of bias and temperature. The Cole-Cole plot shows a single semicircle which indicates that the equivalent circuit can be designed as a single parallel resistor Rp and capacitor Cp network with a series resistance Rs. The bulk capacitance Cp remains unchanged while the resistance Rp decreases along with bias voltage. Conduction mechanism matches well with the space-charge-limited current (SCLC) model with exponential trap charge distributions. The temperature-dependent impedance studies reveal the activation energy of 0.246 eV with no phase change in the temperature range 220–320 K. These results indicate that the IS method is applicable for organic semiconductors having a wide band gap.
Photocatalysis of InGaN Nanodots Responsive to Visible Light
WANG Lai**, ZHAO Wei, HAO Zhi-Biao, LUO Yi
Chin. Phys. Lett. 2011, 28 (5): 057301 .   DOI: 10.1088/0256-307X/28/5/057301
Abstract   PDF(pc) (632KB) ( 558 )
Photocatalysis of InGaN nanodots grown on GaN/sapphire templates by metal organic vapor phase epitaxy is studied. Photodegradation of methylene orange by InGaN nanodots responsive to visible light is observed. Analysis through atomic force microscopy and time-resolved photoluminescence measurements show that wider bandgap of InGaN, larger specific surface area and more proportion of photocarriers diffusing to the surface before recombination are propitious to photodegradation.
Pure Electric and Pure Magnetic Resonances in Near-Infrared Metal Double-Triangle Metamaterial Arrays
CAO Zhi-Shen, PAN Jian, CHEN Zhuo, ZHAN Peng, MIN Nai-Ben, WANG Zhen-Lin**
Chin. Phys. Lett. 2011, 28 (5): 057302 .   DOI: 10.1088/0256-307X/28/5/057302
Abstract   PDF(pc) (907KB) ( 459 )
We experimentally and numerically investigate the optical properties of metamaterial arrays composed of double partially-overlapped metallic nanotriangles fabricated by an angle-resolved nanosphere lithography. We demonstrate that each double-triangle can be viewed as an artificial magnetic element analogous to the conventional metal split-ring-resonator. It is shown that under normal-incidence conditions, individual double-triangle can exhibit a strong local magnetic resonance, but the collective response of the metamaterial arrays is purely electric because magnetic resonances of the two double-triangles in a unit cell having opposite openings are out of phase. For oblique incidences the metamaterial arrays are shown to support a pure magnetic response at the same frequency band. Therefore, switchable electric and magnetic resonances are achieved in double-triangle arrays. Moreover, both the electric and magnetic resonances are shown to allow for a tunability over a large spectral range down to near-infrared.
A Trade-off between Propagation Length and Light Confinement in Cylindrical Metal-Dielectric Waveguides
SUN Bao-Qing, GU Ying**, HU Xiao-Yong, GONG Qi-Huang**
Chin. Phys. Lett. 2011, 28 (5): 057303 .   DOI: 10.1088/0256-307X/28/5/057303
Abstract   PDF(pc) (744KB) ( 563 )
We theoretically investigate the hybrid plasmonic modes of cylindrical nanocables with gold nanocore and two dielectric nanolayers (SiO2 and BN). By solving a complete set of Maxwell's equations, the propagation constants and effective radii depending on geometrical parameters are numerically calculated. By declining a trade−off between propagation length and light confinement, high quality hybrid modes which can travel a long range of 120–200λ with a subwavelength effective radius are obtained at the optical wavelength. These modes in one-dimensional cylindrical waveguides should have potential applications in nanoscale optical device designs.
Growth, Characterization and Fermi Surface of Heavy Fermion CeCoIn5 Superconductor
JIA Xiao-Wen, LIU Yan, YU Li, HE Jun-Feng, ZHAO Lin, ZHANG Wen-Tao, LIU Hai-Yun, LIU Guo-Dong, HE Shao-Long, ZHANG Jun, LU Wei, WU Yue, DONG Xiao-Li, SUN Li-Ling, WANG Gui-Ling, ZHU Yong, WANG Xiao-Yang, PENG Qin-Jun, WANG Zhi-Min, ZHANG Shen-Jin, YANG Feng, XU Zu-Yan, CHEN Chuang-Tian, ZHOU Xing-Jiang**
Chin. Phys. Lett. 2011, 28 (5): 057401 .   DOI: 10.1088/0256-307X/28/5/057401
Abstract   PDF(pc) (873KB) ( 487 )
High quality single crystals of heavy Fermion CeCoIn5 superconductor have been grown by flux method with a typical size of (12)×(1−2)×(∼0.1) mm3. The single crystals are characterized by structural analysis from x−ray diffraction and Laue diffraction, as well as compositional analysis. Magnetic and electrical measurements on the single crystals show a sharp superconducting transition with a transition temperature at Tc,onset∼2.3 K and a transition width of 0.15 K. The resistivity of the CeCoIn5 crystal exhibits a hump at 45 K, which is typical of a heavy Fermion system. High resolution angle−resolved photoemission spectroscopy (ARPES) measurements of CeCoIn5 reveal clear Fermi surface sheets that are consistent with the band structure calculations when assuming itinerant Ce 4f electrons at low temperature. This work provides important information on the electronic structure of heavy Fermion CeCoIn5 superconductor. It also lays a foundation for further studies on the physical properties and superconducting mechanism of the heavy Fermion superconductors.
Electronic Structure of KFe2Se2 from First-Principles Calculations
CAO Chao**, DAI Jian-Hui, **
Chin. Phys. Lett. 2011, 28 (5): 057402 .   DOI: 10.1088/0256-307X/28/5/057402
Abstract   PDF(pc) (552KB) ( 726 )
Electronic structures and magnetic properties for iron-selenide KFe2Se2 are studied by first−principles calculations. The ground state is collinear antiferromagnetic with calculated 2.26 μB magnetic moment on Fe atoms; and the J1 and J2 coupling strengths are calculated to be 0.038 eV and 0.029 eV. The states around EF are dominated by the Fe 3d orbitals which hybridize noticeably to the Se 4p orbitals. While the band structure of KFe2Se2 is similar to a heavily electron−doped BaFe2As2 or FeSe system, the Fermi surface of KFe2Se2 is much closer to the FeSe system since the electron sheets around M are symmetric with respect to xy exchange. These features, as well as the absence of Fermi surface nesting, suggest that the parent KFe2Se2 could be regarded as an electron doped FeSe system with possible local moment magnetism.
Magnetism and Substrate Effects of Mn3 Clusters on Cu(111), Pd(111) and Ne(111)
ZHONG Ke-Hua**, WENG Zhen-Zhen, FENG Qian, YANG Yan-Min, HUANG Zhi-Gao**
Chin. Phys. Lett. 2011, 28 (5): 057501 .   DOI: 10.1088/0256-307X/28/5/057501
Abstract   PDF(pc) (560KB) ( 307 )
The magnetic moments of Mn3 clusters on Cu(111), Pd(111) and Ne(111) non−magnetic substrates are investigated using first-principles methods based on density-functional theory. The calculated results reveal that the Mn magnetic moments are closely associated with the geometric structures of the clusters and the interparticle separation. Moreover, it is found that the magnetic moments of Mn3 clusters on three different Cu(111), Pd(111) and Ne(111) substrates are quite different. Meanwhile, the orbit annihilating induced from the crystalline field of the substrates and the electron transfer from the substrate atoms to Mn3 adatoms are used to explain the different changes of the average magnetic moments of Mn3.
Thermal Decay and Reversal of Exchange Bias Field of CoFe/PtMn Bilayer after Ga+ Irradiation
ZHOU Guang-Hong, **, ZHU Yu-Fu, LIN Yue-Bin
Chin. Phys. Lett. 2011, 28 (5): 057502 .   DOI: 10.1088/0256-307X/28/5/057502
Abstract   PDF(pc) (650KB) ( 415 )
An applied field is used to perform Ga+ ion irradiation on a CoFe/PtMn bilayer. Effects of the applied field and energy transfer between Ga+ ions and antiferromagnetic (AFM) atoms on the exchange bias field H ex are investigated. A partially reversed Hex is found in CoFe/PtMn specimens irradiated at a dose of 1×1014 ions/cm2 with an applied field anti−parallel to the original exchange bias direction. We believe that the rapid energy transfer and local temperature increase originating from the interaction between Ga+ ions and AFM atoms result in spin reversal and the formation of reversed AFM domains when specimens are irradiated with anti−parallel fields. The decrease in H ex when annealing the film in a negative saturation field indicates a thermal decay process. The AFM moments are reversed by thermal activation over an energy barrier distribution, which may change in some way as the temperature increases.
Nonresonant Metamaterials with an Ultra-High Permittivity
HE Xiao-Yang, CHEN Qi, LI Lin-Cui, YANG Chun**, LI Biao, ZHOU Bang-Hua, TANG Chuan-Xiang
Chin. Phys. Lett. 2011, 28 (5): 057701 .   DOI: 10.1088/0256-307X/28/5/057701
Abstract   PDF(pc) (522KB) ( 663 )
A nonresonant structure composed of metal cut-wires for realization of metamaterials is proposed. This kind of metamaterial works at an ultra broad bandwidth with uniform permittivity. Theoretical analysis and numerical simulations are carried out to study this inclusion and expression for the effective permittivity is given. Several methods are studied to enhance the permittivity and a nonresonant metamaterial with an ultra-high permittivity is obtained. A demonstration shows that the permittivity of this metamaterial can be as high as 145.
L-cystine-Assisted Growth and Mechanism of CuInS2 Nanocrystallines via Solvothermal Process
LIU Hai-Tao, ZHONG Jia-Song, LIU Bing-Feng, LIANG Xiao-Juan, YANG Xin-Yu, JIN Huai-Dong, YANG Fan, XIANG Wei-Dong, **
Chin. Phys. Lett. 2011, 28 (5): 057702 .   DOI: 10.1088/0256-307X/28/5/057702
Abstract   PDF(pc) (871KB) ( 549 )
L-cystine is successfully used as a kind of sulfur source to grow CuInS2 nanocrystallines at 200°C for 18 h in a mixed solution made of 20 mL ethylenediamine and 20 mL distilled water. The diameter of the CuInS2 nanocrystallines ranges from 300 to 500 nm. The structure of nanocrystallines is determined to be of the tetragonal phase of CuInS2. A reasonable possible mechanism for the growth of CuInS2 nanocrystallines is proposed. The as−obtained CuInS2 products are examined using diverse techniques including x-ray powder diffraction, x-ray photoelectron spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction and high-resolution transmission electron microscopy.
Ordered Gold Nanobowl Arrays as Substrates for Surface-Enhanced Raman Spectroscopy
CHEN Ling, LIU Fan-Xin, ZHAN Peng, PAN Jian, WANG Zhen-Lin**
Chin. Phys. Lett. 2011, 28 (5): 057801 .   DOI: 10.1088/0256-307X/28/5/057801
Abstract   PDF(pc) (754KB) ( 508 )
We demonstrate that an interlinked gold half-shell array fabricated by metal deposition on a sacrificial two-dimensional colloidal crystal template can show a large enhancement in surface-enhanced Raman spectroscopy at its main transmission resonance. It is further observed that Raman signal enhancement shows a noticeable difference when reversing the orientations of the Au nanobowls in relation to the underlying flat dielectric substrate. As the pump laser wavelength is tuned in the vicinity of the resonant plasmonic mode of the structure, the enhancement on an upward Au nanobowl array can be five-fold compared to that on a downward one. Numerical simulation confirms that for the upward nanobowls, a strong localized mode inside the Au nanobowls is formed at the resonant excitation wavelength, which helps to explain this observed extra enhancement in Raman scattering.
AlGaN/GaN Ultraviolet Detector with Dual Band Response
GAO Bo**, LIU Hong-Xia, WANG Shu-Long
Chin. Phys. Lett. 2011, 28 (5): 057802 .   DOI: 10.1088/0256-307X/28/5/057802
Abstract   PDF(pc) (527KB) ( 562 )
The AlGaN/GaN ultraviolet detector with dual band response is investigated by a self-consistent solution of the Poisson–Schrödinger equation. Because of the polarization effect, the AlGaN/GaN UV detector with dual band response can be realized by varying the external voltage. At a low external voltage, the detector is mainly sensitive to the short wavelength. When the increasing external voltage is larger than the critical voltage, the detector has an obvious dual band response characteristic and the critical voltage is calculated. This characteristic makes nitride-based UV detector a larger potential application to develop multi band response by adjusting the Aluminum mole fraction in the AlGaN layer or even by using the AlGaN/GaN/InGaN heterostructure.
Localized Surface Plasmons Enhanced Ultraviolet Emission of ZnO Films
LIU Yan-Song, LU Hai-Fei, XU Xiao-Liang**, GONG Mao-Gang, LIU Ling, YANG Zhou
Chin. Phys. Lett. 2011, 28 (5): 057803 .   DOI: 10.1088/0256-307X/28/5/057803
Abstract   PDF(pc) (653KB) ( 756 )
ZnO and ZnO/Ag films are grown on Si (111) substrates by rf magnetron sputtering at room temperature. After annealing, it is found that the ultraviolet (UV) emission of ZnO/Ag films strongly depends on the thickness of the initial internal Ag layer. During the annealing process, Ag nanoparticles are formed and diffused into the ZnO film. The resonant coupling between localized surface plasmons (LSPs) of Ag nanoparticles and ZnO enhances the UV emission. The largest UV enhancement over 12 times is found when the initial internal Ag layer is 10 nm. It is also observed that the diffusion of Ag nanoparticles destroys the ZnO crystal quality in different grades, depending on the sizes of the Ag nanoparticles. The poor crystal quality induces bad UV emission. It is concluded that the UV emission is the result of the competition between the LSP enhancement and the thermal diffusion destroying effect from Ag nanoparticles.
Gallium Nitride Nanowires Grown by Hydride Vapor Phase Epitaxy
LIU Zhan-Hui, XIU Xiang-Qian**, YAN Huai-Yue, ZHANG Rong, XIE Zi-Li, HAN Ping, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2011, 28 (5): 057804 .   DOI: 10.1088/0256-307X/28/5/057804
Abstract   PDF(pc) (908KB) ( 632 )
GaN nanowires are grown by hydride vapor phase epitaxy using nickel as a catalyst. The properties of the obtained GaN nanowires are characterized by scanning and transmission electron microscopy, electron diffraction, room-temperature photoluminescence and energy dispersive spectroscopy. The results show that the nanowires are wurtzite single crystals growing along the [0001] direction and a redshift in the photoluminescence is observed due to a superposition of several effects. The Raman spectra are close to those of the bulk GaN and the significantly broadening of those modes indicates the phonon confinement effects associated with the nanoscale dimensions of the system.
Linear and Nonlinear Optical Properties of Micrometer-Scale Gold Nanoplates
LIU Xiao-Lan, PENG Xiao-Niu, YANG Zhong-Jian, LI Min, ZHOU Li**
Chin. Phys. Lett. 2011, 28 (5): 057805 .   DOI: 10.1088/0256-307X/28/5/057805
Abstract   PDF(pc) (967KB) ( 491 )
Micrometer-scale gold nanoplates have been synthesized in high yield through a polyol process. The morphology, crystal structure and linear optical extinction of the gold nanoplates have been characterized. These gold nanoplates are single-crystalline with triangular, truncated triangular and hexagonal shapes, exhibiting strong surface plasmon resonance (SPR) extinction in the visible and near-infrared (NIR) region. The linear optical properties of gold nanoplates are also investigated by theoretical calculations. We further investigate the nonlinear optical properties of the gold nanoplates in solution by Z−scan technique. The nonlinear absorption (NLA) coefficient and nonlinear refraction (NLR) index are measured to be 1.18×102 cm/GW and 1.04×10−3 cm2/GW, respectively.
Measurement of Beta Particles Induced Electron-Hole Pairs Recombination in Depletion Region of GaAs PN Junction
CHEN Hai-Yang, JIANG Lan**, LI Da-Rang
Chin. Phys. Lett. 2011, 28 (5): 058101 .   DOI: 10.1088/0256-307X/28/5/058101
Abstract   PDF(pc) (412KB) ( 510 )
PN junctions and schottky diodes are widely employed as electron-hole pair collectors in electron beam induced current (EBIC) techniques and betavoltaic batteries, in which the recombination in depletion regions is ignored. We measured the beta particles induced electron-hole pairs recombination in the depletion region of a GaAs P+PN+ junction, based on comparisons between measured short currents and ideal values. The results show that only 20% electron-hole pairs in the depletion can be collected, causing the short current. This indicates an electron-hole pair diffusion length of 0.2 µm in the depletion region. Hence, it is necessary to evaluate the recombination in the EBIC techniques and betavoltaic design.
Interaction of a Spherical Colloid and a Porous Membrane in a Bulk Electrolyte
LIAN Zeng-Ju**
Chin. Phys. Lett. 2011, 28 (5): 058201 .   DOI: 10.1088/0256-307X/28/5/058201
Abstract   PDF(pc) (625KB) ( 309 )
A systemic computation of an electrostatic interaction between a charged spherical colloid and a charged porous membrane with a fixed potential is made under the linear Poisson–Boltzmann theory. The colloid moves along the symmetry axis of the membrane and they are both immersed in a bulk electrolyte. In the calculation, a significant attraction between the colloid and the membrane is found. The orifices on or around the centre of the membrane play a major role in the attraction. The effect of the reduced orifice sizes of the membrane on the interaction is taken into account. Furthermore, the electrostatic interaction energies are significantly changed by the variation of ionic strengths (concentration and valence relating the Dybe length).
Analysis of Imaging Contrast of Small Cracks in FNR Specimens
DOU Hai-Feng**, TANG Bin, WU Yang
Chin. Phys. Lett. 2011, 28 (5): 058901 .   DOI: 10.1088/0256-307X/28/5/058901
Abstract   PDF(pc) (518KB) ( 321 )
Scattering neutrons are one of the key factors which may affect the images of fast neutron radiography (FNR). We develop a math model of FNR physical process and deduce an image contrast formula that is further confirmed by comparing the results obtained by the formula with the results given by Monte Carlo simulation and experimental results. We provide a simple method to predict the image contrast in the FNR experiment.
Effect of Adaptive Delivery Capacity on Networked Traffic Dynamics
CAO Xian-Bin, DU Wen-Bo, **, CHEN Cai-Long, ZHANG Jun
Chin. Phys. Lett. 2011, 28 (5): 058902 .   DOI: 10.1088/0256-307X/28/5/058902
Abstract   PDF(pc) (1198KB) ( 511 )
We introduce an adaptive delivering capacity mechanism into the traffic dynamic model on scale-free networks under shortest path routing strategy and focus on its effect on the network capacity measured by the critical point (Rc) of phase transition from free flow to congestion. Under this mechanism, the total node's delivering capacity is fixed and the allocation of delivering capacity on node i is proportional to niφ, where ni is the queue length of node i and φ is the adjustable parameter. It is found that the network capacity monotonously increases with the increment of φ, but there exists an optimal value of parameter φ leading to the highest transportation efficiency measured by average travelling time (〈T 〉). Our work may be helpful for optimal design of networked traffic dynamics.
Effects of Variant Rates and Noise on Epidemic Spreading
LI Wei, **, GAO Zong-Mao, GU Jiao,
Chin. Phys. Lett. 2011, 28 (5): 058903 .   DOI: 10.1088/0256-307X/28/5/058903
Abstract   PDF(pc) (494KB) ( 369 )
We introduce variant rates, for both infection and recovery and noise into the susceptible-infected-removed (SIR) model for epidemic spreading. The changing rates are taken mainly due to the changing profiles of an epidemic during its evolution. However, the noise parameter which is taken from a given distribution, i.e. Gaussian can describe the fluctuations of the infection and recovery rates. The numerical simulations show that the SIR model with variant rates and noise and can improve the fitting with real SARS data in the near-stationary stage.
Attack Robustness of Scale-Free Networks Based on Grey Information
LI Jun, WU Jun**, LI Yong, DENG Hong-Zhong, TAN Yue-Jin**
Chin. Phys. Lett. 2011, 28 (5): 058904 .   DOI: 10.1088/0256-307X/28/5/058904
Abstract   PDF(pc) (481KB) ( 428 )
We introduce an attack robustness model of scale-free networks based on grey information, which means that one can obtain the information of all nodes, but the attack information may be imprecise. The known random failure and the intentional attack are two extreme cases of our investigation. Using the generating function method, we derive the analytical value of the critical removal fraction of nodes for the disintegration of networks, which agree with the simulation results well. We also investigate the effect of grey information on the attack robustness of scale-free networks and find that decreasing the precision of attack information can remarkably enhance the attack robustness of scale-free networks.
Electrical Properties of Hydrous Forsterite Derived from First-Principles Calculations
WANG Duo-Jun**, LIU Zai-Yang, YI Li, SHI Bao-Ping
Chin. Phys. Lett. 2011, 28 (5): 059101 .   DOI: 10.1088/0256-307X/28/5/059101
Abstract   PDF(pc) (597KB) ( 478 )
We investigate electrical properties of anhydrous and hydrous forsterite crystal with 3.2 wt% water by using first-principles calculations. The calculation results indicate that the pressure weakly affects the electrical properties of anhydrous forsterite. Two types of defect configurations involving the two hydrogen atoms in different positions are considered. Type 1 involves the entrapment of two hydrogen atoms in a Mg vacancy, which demonstrates little effect on the electronic density of states (DoS) of the forsterite crystal. Type 2 corresponds to the replacement of one hydrogen atom into the Mg vacancy with the other one located in different orientations (free proton model). It is this configuration that can significantly change the DoS of the forsterite crystal. The gap energy of the free proton model derived at different orientations is in the range of 0.693–1.007 eV.
A Three-Box Model of Thermohaline Circulation under the Energy Constraint
SHEN Yang, GUAN Yu-Ping**, LIANG Chu-Jin, CHEN Da-Ke
Chin. Phys. Lett. 2011, 28 (5): 059201 .   DOI: 10.1088/0256-307X/28/5/059201
Abstract   PDF(pc) (501KB) ( 595 )
The driving mechanism of thermohaline circulation is still a controversial topic in physical oceanography. Classic theory is based on Stommel's two-box model under buoyancy constraint. Recently, Guan and Huang proposed a new viewpoint in the framework of energy constraint with a two-box model. We extend it to a three-box model, including the effect of wind-driven circulation. Using this simple model, we further study how ocean mixing impacts on thermohaline circulation under the energy constraint.
Standing Shocks in the Inner Slow Solar Wind
LI Bo, **, CHEN Yan-Jun, LI Xing
Chin. Phys. Lett. 2011, 28 (5): 059601 .   DOI: 10.1088/0256-307X/28/5/059601
Abstract   PDF(pc) (505KB) ( 339 )
We examine whether the flow tube along the edge of a coronal streamer supports standing shocks in the inner slow wind by solving an isothermal wind model in terms of the Lambert W function. It is shown that solutions with standing shocks do exist and they exist in a broad area in the parameter space characterizing the wind temperature and flow tube. In particular, streamers with cusps located at a heliocentric distance ≳3.2 Rʘ can readily support discontinuous slow winds with temperatures barely higher than 1 MK.
80 articles