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Volume 29 Issue 5
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A New Class of Scaling Correction Methods
MEI Li-Jie,WU Xin**,LIU Fu-Yao
Chin. Phys. Lett. 2012, 29 (5): 050201 .   DOI: 10.1088/0256-307X/29/5/050201
Abstract   PDF(pc) (882KB) ( 916 )

When conventional integrators like Runge–Kutta-type algorithms are used, numerical errors can make an orbit deviate from a hypersurface determined by many constraints, which leads to unreliable numerical solutions. Scaling correction methods are a powerful tool to avoid this. We focus on their applications, and also develop a family of new velocity multiple scaling correction methods where scale factors only act on the related components of the integrated momenta. They can preserve exactly some first integrals of motion in discrete or continuous dynamical systems, so that rapid growth of roundoff or truncation errors is suppressed significantly.

Lax Pairs for Discrete Integrable Equations via Darboux Transformations
CAO Ce-Wen**,ZHANG Guang-Yao
Chin. Phys. Lett. 2012, 29 (5): 050202 .   DOI: 10.1088/0256-307X/29/5/050202
Abstract   PDF(pc) (362KB) ( 1341 )

A method is developed to construct discrete Lax pairs using Darboux transformations. More kinds of Lax pairs are found for some newly appeared discrete integrable equations, including the H1, the special H3 and the Q1 models in the Adler–Bobenko–Suris list and the closely related discrete and semi-discrete pKdV, pMKdV, SG and Liouville equations.

Stability and Hopf Bifurcation Analysis on a Numerical Discretization of the Distributed Delay Equation
WU Jie,ZHAN Xi-Sheng**,ZHANG Xian-He,GAO Hong-Liang
Chin. Phys. Lett. 2012, 29 (5): 050203 .   DOI: 10.1088/0256-307X/29/5/050203
Abstract   PDF(pc) (762KB) ( 1048 )

A kind of discrete logistic model with distributed delays obtained by the Euler method is investigated, where the discrete delay τ is regarded as a parameter. By analyzing the associated characteristic equation, it is found that the stability of the positive equilibrium and Hopf occurs when τ crosses some critical value. Then the explicit formulae which determine the stability, direction and other properties of the bifurcating periodic solution are derived by using the theory of normal form and center manifold. Finally, numerical simulations are performed to verify and illustrate the analytical results.

Quasicrystalline Phase with Eighteen-Fold Diffraction Symmetry in Molecular Dynamics Simulations
CHEN Zhi-Wei,FU Xiu-Jun**
Chin. Phys. Lett. 2012, 29 (5): 050204 .   DOI: 10.1088/0256-307X/29/5/050204
Abstract   PDF(pc) (720KB) ( 502 )

Using molecular dynamics simulations, we investigate two-dimensional systems, which are composed of one type of particle, with mutual interactions of Lennard-Jones-Gauss potentials. Under certain conditions, the model system tends to organize itself into quasiperiodic lattices with a certain rotational symmetry. Diffraction patterns with eighteen-fold symmetry are observed.

The Statistical Properties of a New Type of Photon-Subtracted Squeezed Coherent State
Chin. Phys. Lett. 2012, 29 (5): 050301 .   DOI: 10.1088/0256-307X/29/5/050301
Abstract   PDF(pc) (569KB) ( 650 )

We construct a new type of photon-subtracted squeezed coherent state (PSSCS) based on a squeezed coherent state (SCS) [Phys. Lett. A 220 (1996) 81]. Some of the statistical properties of the PSSCS, such as Mandel's Q parameter and photon-number distribution, are investigated and the corresponding non-classicality is discussed.

The Dynamics of a Bright–Bright Vector Soliton in Bose–Einstein Condensation
YAN Jia-Ren**,ZHOU Jie,AO Sheng-Mei
Chin. Phys. Lett. 2012, 29 (5): 050302 .   DOI: 10.1088/0256-307X/29/5/050302
Abstract   PDF(pc) (445KB) ( 476 )
The dynamics of a bright–bright vector soliton in cigar-shaped Bose–Einstein condensate trapping in a harmonic potential is studied. The interaction between bright solitons in different species with small separation is derived. Unlike the interaction between solitons of the same species, it is independent of the phase difference between the solitons, and may be of attraction or repulsion. In the former case, each soliton will oscillate about and pass through each other around the mass center of the system, which will also oscillate harmonically due to harmonic trapping potential.
A Quantum Network System of QSS-QDC Using χ-Type Entangled States
Chang Ho Hong,Jin O Heo,Jong in Lim,Hyung jin Yang,**
Chin. Phys. Lett. 2012, 29 (5): 050303 .   DOI: 10.1088/0256-307X/29/5/050303
Abstract   PDF(pc) (406KB) ( 535 )

A multiuser quantum direct communication network system for N users utilizing χ−type entangled states is proposed. The network system is composed of a communication center, N users, and N quantum lines linking the center and the N users. There is no quantum line among users, and therefore only N quantum lines are necessary for communication between users. Using one χ-type entangled state, in this protocol we are able to send two bits of information through direct communication and, at the same time, share two bits of quantum keys. The security of the protocol is then analyzed.

Protection of Two-Qubit Entanglement by the Quantum Erasing Effect
XIANG Shao-Hua**,DENG Xiao-Peng,SONG Ke-Hui
Chin. Phys. Lett. 2012, 29 (5): 050304 .   DOI: 10.1088/0256-307X/29/5/050304
Abstract   PDF(pc) (549KB) ( 500 )
We present a scheme to save the entanglement of two spatially separated atoms, each located in a leaky cavity, through the quantum erasing method. It is shown that no matter whether the two atoms are in the pure or mixed state, one can robustly save their initial entanglement even if the number of erasing events is finite. We also briefly discuss the challenging aspect of implementing such a scheme.
The Interference Effect of a Bose–Einstein Condensate in a Ring-Shaped Trap
CAO Li-Juan,LIU Shu-Juan**,LÜ Bao-Long
Chin. Phys. Lett. 2012, 29 (5): 050305 .   DOI: 10.1088/0256-307X/29/5/050305
Abstract   PDF(pc) (1420KB) ( 596 )

We have studied the interference effect of a Bose–Einstein condensate expanding in a ring-shaped trap. The dynamic process of the condensate is analyzed based on the Gross–Pitaevskii equation. Our numerical results show that a petal-like interference pattern is formed during expansion within the ring-shaped trap. The petal number depends on the evolution time, which can be well explained by the interference of two flows of the condensate.

Scale-Covariant Theory of Gravitation Through Self-Similarity
José Antonio Belinchón*
Chin. Phys. Lett. 2012, 29 (5): 050401 .   DOI: 10.1088/0256-307X/29/5/050401
Abstract   PDF(pc) (438KB) ( 516 )
We study the scale-covariant theory of gravitation proposed by Canuto under the self-similar hypothesis. By considering the matter collineation approach, we deduce the form of the main quantities and obtain some restrictions on the behavior of the gauge function, φ(t). We apply the obtained results to study the Bianchi I, VII0, IX and Kantowsky Sachs models, and arrive at the conclusion that instead of considering a varying G theory, the solution is only valid for a particular value of the parameter of the equation of state, γ,. This leads us to obtain φ(t) = const, and by taking into account the external condition, 2 = const, we may arrive at the conclusion that G = const. Therefore, all the obtained solutions are the same as the ones obtained in the framework of general relativity.
Spherically Symmetric Solutions on a Non-Trivial Frame in f(T) Theories of Gravity
Gamal G. L. Nashed*
Chin. Phys. Lett. 2012, 29 (5): 050402 .   DOI: 10.1088/0256-307X/29/5/050402
Abstract   PDF(pc) (502KB) ( 438 )
A new solution with constant torsion is derived using the field equations of f(T). Asymptotic forms of energy density, radial and transversal pressures are shown to meet the standard energy conditions, i.e., weak and null energy conditions according to some restrictions on T0, f(T0) and fT(T0). Other solutions are obtained for vanishing radial pressure and for specific choices of f(T). The physics relevant to the resulting models is discussed.
Shearfree Spherically Symmetric Fluid Models
M. Sharif*,Z. Yousaf
Chin. Phys. Lett. 2012, 29 (5): 050403 .   DOI: 10.1088/0256-307X/29/5/050403
Abstract   PDF(pc) (382KB) ( 1065 )
We attempt to discover some exact analytical models of the spherically symmetric spacetime of collapsing fluid under shearfree conditions. Two types of solution are considered: one is to impose a condition on the mass function, while the other is to restrict the pressure. We obtain five exact models in total, and some of them satisfy the Darmois conditions.
Zero-Lag Synchronization in Spatiotemporal Chaotic Systems with Long Range Delay Couplings
LI Jian-Ping,YU Lian-Chun,YU Mei-Chen,CHEN Yong**
Chin. Phys. Lett. 2012, 29 (5): 050501 .   DOI: 10.1088/0256-307X/29/5/050501
Abstract   PDF(pc) (981KB) ( 512 )
We study the synchronization of spatiotemporal chaos patterns between two delay-coupled excitable layers. It is found that zero-lag synchronization (ZLS) can be achieved by dynamical relay via a third mediating layer. Based on simulations with large parameter ranges, we investigate the influences of time delay and coupling strength on transition time. ZLS with a stronger coupling strength and shorter time delay appears to have a shorter transition time. This phenomenon has possible implications in network communication.
A Control Method for Congested Traffic in the Car-Following Model
GE Hong-Xia,YU Jian,LO Siu-Ming**
Chin. Phys. Lett. 2012, 29 (5): 050502 .   DOI: 10.1088/0256-307X/29/5/050502
Abstract   PDF(pc) (505KB) ( 603 )
A simple control method to suppress traffic congestion is proposed for the car-following model. The stability conditions are derived by using the control method, and the feedback signals, which act on our traffic system, are extended to the car-following model. The control signals will play an effect only if the traffic is congested. The corresponding numerical simulation results agree well with our theoretical analysis, and our control method can successfully suppress traffic jams.
An Effective Numerical Procedure to Determine Saddle-Type Unstable Invariant Limit Sets in Nonlinear Systems
Chin. Phys. Lett. 2012, 29 (5): 050503 .   DOI: 10.1088/0256-307X/29/5/050503
Abstract   PDF(pc) (1338KB) ( 414 )
A new technique that can efficiently approximate the attracting set of a nonlinear dynamical system is proposed under the framework of point mapping with the cell reference method. With the aid of the approximated attracting set, the difficulties encountered by the PIM-triple method and bisection procedure in finding trajectories on the stable manifolds of chaotic saddles in basins of attraction and on basin boundaries can be overcome well. On the basis of this development, an effective method to determine saddle-type invariant limit sets of nonlinear dynamical systems can be devised. Examples are presented for the purposes of illustration and to demonstrate the capabilities of the proposed method.
Theoretical Analysis on the Vibrational Resonance in Two Coupled Overdamped Anharmonic Oscillators
FANG Ci-Jun,LIU Xian-Bin**
Chin. Phys. Lett. 2012, 29 (5): 050504 .   DOI: 10.1088/0256-307X/29/5/050504
Abstract   PDF(pc) (452KB) ( 582 )
Under both low- and high-frequency signals, the phenomenon of vibrational resonance in two coupled overdamped anharmonic oscillators with time delay feedback is investigated. By separating the slow and fast motions, the approximate solution of the response amplitude of the coupled oscillators is obtained, and the analytical results are in good agreement with the numerical ones. In the delay-free systems, the traditional vibrational resonance is presented, and in the delayed systems, the delay-induced periodic pattern of the vibrational resonance profile with respect to the delay parameter is revealed.
The Slow Dynamics of the Zero-Range Process in the Framework of the Traps Model
QI Kai,TANG Ming**,CUI Ai-Xiang,FU Yan
Chin. Phys. Lett. 2012, 29 (5): 050505 .   DOI: 10.1088/0256-307X/29/5/050505
Abstract   PDF(pc) (1333KB) ( 433 )
The relaxation dynamics of the zero-range process (ZRP) has been an interesting problem. In this study, we set up the relationship between the ZRP and a model of traps, and investigate the slow dynamics of the ZRP in the framework of the trap model. Through statistical quantities such as the average rest time, the particle distribution, the two-time correlation function and the average escape time, we find that the particle interaction, especially the resulting condensation, can significantly influence the dynamics. In the stationary state, both the average rest time and the average escape time caused by the attraction among particles are obtained analytically. In the transient state, a hierarchical nature of the aging dynamics is revealed by both simulations and scaling analysis. Moreover, by comparing the particle diffusion in both the transient state and the stationary state, we find that the closer the ZRP systems approach the stationary state, the more slowly the particles diffuse.
Stochastic Resonance-Like and Resonance Suppression-Like Phenomena in a Bistable System with Time Delay and Additive Noise
SHU Chang-Zheng,NIE Lin-Ru**,ZHOU Zhong-Rao
Chin. Phys. Lett. 2012, 29 (5): 050506 .   DOI: 10.1088/0256-307X/29/5/050506
Abstract   PDF(pc) (547KB) ( 586 )
Stochastic resonance (SR)-like and resonance suppression (RS)-like phenomena in a time-delayed bistable system driven by additive white noise are investigated by means of stochastic simulations of the power spectrum, the quality factor of the power spectrum, and the mean first-passage time (MFPT) of the system. The calculative results indicate that: (i) as the system is driven by a small periodic signal, the quality factor as a function delay time exhibits a maximal value at smaller noise intensities, i.e., an SR-like phenomenon. With the increment in additive noise intensity, the extremum gradually disappears and the quality factor decreases monotonously with delay time. (ii) As the additive noise intensity is smaller, the curve of the MFPT with respect to delay time displays a peak, i.e., an RS-like phenomenon. At higher levels of noise, however, the non-monotonic behavior is lost.
A Terahertz Wavemeter Based on a Fabry–Perot Interferometer Composed of Two Identical Ge Etalons
MIAO Liang**,ZUO Du-Luo,CHENG Zu-Hai
Chin. Phys. Lett. 2012, 29 (5): 050701 .   DOI: 10.1088/0256-307X/29/5/050701
Abstract   PDF(pc) (573KB) ( 659 )
A simple and convenient terahertz wavemeter based on a Fabry–Perot interferometer (FPI) is presented. The interferometer is composed of two identical Ge etalons, which act as high-reflectance mirrors for terahertz waves. The transmission characteristics of the Ge FPI are analyzed using multiple-beam interference theory. The theoretical finesse of the FPI, defined as a ratio of 2π to the phase halfwidth of the transmission fringes, is larger than 12.5. Here, the wavemeter is used to measure the wavelengths of an optically pumped NH3 terahertz laser. The experimental results indicate that the measuring uncertainties are within ±1%. Higher accuracy can be expected if the power or pulse energy of the terahertz source is more stable.
The Observation of Martensite and Magnetic Domain Structures in Ni53Mn24Ga23 Shape Memory Alloys by Scanning Electron Acoustic Microscopy and Scanning Thermal Microscopy
ZHAO Kun-Yu,ZENG Hua-Rong**,SONG Hong-Zhang,HUI Sen-Xing,LI Guo-Rong,YIN Qing-Rui
Chin. Phys. Lett. 2012, 29 (5): 050702 .   DOI: 10.1088/0256-307X/29/5/050702
Abstract   PDF(pc) (1083KB) ( 568 )
We present observations of martensite variants and ferromagnetic domain structures of Ni53Mn24Ga23 ferromagnetic shape memory alloys with a pure tetragonal martensitic phase by using scanning electron acoustic microscopy (SEAM) and scanning thermal microscopy (SThM). Electron acoustic images show a polycrystalline morphology with martensite variants. Direct coincidence between crystallographic martensitic twin variants and magnetic domains is found. A domain-like structure, obtained by SThM, is firstly reported, and then confirmed by magnetic force microscopy (MFM). The experimental results will be helpful for investigating the local thermal properties of ferromagnets and understanding the relationship between martensite variants and magnetic domains.
The Microstructure and Thermal Conductivity of Aluminum Nitride Ceramics Sintered at High Pressure with CaC2
LI Xiao-Lei**,WANG Li-Ying
Chin. Phys. Lett. 2012, 29 (5): 050703 .   DOI: 10.1088/0256-307X/29/5/050703
Abstract   PDF(pc) (1344KB) ( 1711 )
Aluminum nitride (AlN) ceramics are sintered by high-pressure technology at 5 GPa/30 min/1500–1800°C, using aluminum nitride powder produced by direct nitriding methods and CaC2(3wt%) powder as the starting material and sintering additive, respectively. The sample sintered at 1800°C shows relatively high density (99.09%) and thermal conductivity (113.7 W/(m⋅K). XRD patterns indicate that there are no obvious impurity phases in the sintered AlN sample. Observation of the microstructure by SEM shows that the AlN powder grows into full crystal grains with uniform size, the crystal particles are in a regular hexagonal structure, and the grain boundary phases are clean without gas phase. The results suggest that AlN ceramics sintered with CaC2 can achieve the desired microstructure and high thermal conductivity.
High-Spin States in Transuranium Nuclei 242,244Pu
ZHAO Yue,KANG Xu-Zhong,SHEN Shui-Fa,**,YAN Yu-Peng,HE Chuang-Ye,YAN Shi-Wei
Chin. Phys. Lett. 2012, 29 (5): 052101 .   DOI: 10.1088/0256-307X/29/5/052101
Abstract   PDF(pc) (643KB) ( 468 )
We investigate the structure of yrast bands in the transuranium nuclei 242Pu and 244Pu in the framework of the projected shell model, which is a fully quantum mechanical and microscopic approach. It is found that an appropriate modification of the standard Nilsson spin−orbital parameters in the N=6 proton shell is necessary to correctly describe the high−spin backbending phenomenon in nucleus 244Pu. In order to test whether this modification is correct, the same modified parameters are used to calculate the yrast band of its neighboring isotope 242Pu. It is found that without this modification, a backbending will occur at spin I=20, which is not supported by the experimental data.
Effects of Symmetry Energy in the Reaction 40Ca+124Sn at 140 MeV/Nucleon
ZHANG Fang,HU Bi-Tao,YONG Gao-Chan,ZUO Wei
Chin. Phys. Lett. 2012, 29 (5): 052501 .   DOI: 10.1088/0256-307X/29/5/052501
Abstract   PDF(pc) (661KB) ( 317 )
Density-dependent symmetry energy is a hot topic in nuclear physics. Many laboratories across the world are planning to perform related experiments to probe symmetry energy. Based on the semiclassical Boltzmann–Uehling–Uhlenbeck (BUU) transport model, we study the effects of nuclear symmetry energy in the central reaction 40Ca+124Sn at 140 MeV/nucleon in the laboratory system. It is found that the rapidity distribution of the free nucleon's neutron-to-proton ratio is sensitive to the symmetry energy, especially at large rapidities. Free neutron-to-proton ratios at small or large rapidities may reflect high or low density behavior of nuclear symmetry energy. To probe the density dependence of nuclear symmetry energy, it is better to give the kinetic distribution and the rapidity distribution of emitted nucleons at the same time.
Probing Nuclear Symmetry Energy with the Sub-threshold Pion Production
ZHANG Fang**,LIU Yang,YONG Gao-Chan,ZUO Wei
Chin. Phys. Lett. 2012, 29 (5): 052502 .   DOI: 10.1088/0256-307X/29/5/052502
Abstract   PDF(pc) (627KB) ( 465 )
Within the framework of the semiclassical Boltzmann–Uehling–Uhlenbeck transport model, we investigate the effects of symmetry energy on the sub-threshold pion using the isospin MDI interaction with the stiff and soft symmetry energies in the central collision of 48Ca+48Ca at the incident beam energies of 100, 150, 200, 250 and 300 MeV/nucleon. We find that the ratio of π+ of sub-threshold charged pion production is greatly sensitive to the symmetry energy, particularly around 100 MeV/nucleon energies. Large sensitivity of sub-threshold charged pion production to nuclear symmetry energy may reduce uncertainties of probing nuclear symmetry energy via heavy-ion collision.
Photodetachment of Di-atomic Negative Ion H2 near a Surface
Muhammad Haneef*,Saleh Mohammad,Suneela Arif,Jehan Akbar,Nasrullah Shah,Imran Ullah
Chin. Phys. Lett. 2012, 29 (5): 053201 .   DOI: 10.1088/0256-307X/29/5/053201
Abstract   PDF(pc) (474KB) ( 479 )
We describe the effects of plane surface on the photo-detached electron spectra from H2. A z−polarized laser is used for the detachment of electrons. The detached electron flux and photodetachment cross section are derived. There exists strong dependence on the distance of the H2- from the surface and also on the separation of atomic centers of H2. The results show strong oscillations for smaller values of distances, whereas for larger values the oscillating structure disappears.
Resonances in Positron Hydrogen Scattering above the H (n=2) Threshold
YU Rong-Mei,CHENG Yong-Jun,JIAO Li-Guang,ZHOU Ya-Jun**
Chin. Phys. Lett. 2012, 29 (5): 053401 .   DOI: 10.1088/0256-307X/29/5/053401
Abstract   PDF(pc) (578KB) ( 397 )
We investigate high partial wave resonances in positron-hydrogen scattering using the momentum-space coupled-channels optical method above the H (n=2) threshold. Resonances with angular momenta of L=0–6 are reported. Ionization continuum and positronium formation channels are included via a complex equivalent local potential. Comparisons with the existing theoretical results are presented.
A Multistage Optical Stark Decelerator for use with a Pulsed Molecular Beam with an Electrostatic Storage Ring
XIA Yong,YIN Ya-Ling,JI Xiang,YIN Jian-Ping**
Chin. Phys. Lett. 2012, 29 (5): 053701 .   DOI: 10.1088/0256-307X/29/5/053701
Abstract   PDF(pc) (532KB) ( 524 )
We propose a promising scheme to repeatedly decelerate a pulsed molecular beam using a red-detuned quasi-cw semi-Gaussian laser beam (SGB) and an electrostatic storage ring. Using the Monte-Carlo simulation method, we demonstrate that this promising optical Stark decelerator can be used to efficiently slow a pulsed ND3 molecular beam extracted from a Stark decelerator or a cryogenic reservoir by using a single SGB. The deceleration effect of this scheme on the intensity of the SGB is discussed in detail.
Optical Bistability in Ag/Dielectric Multilayers
LI Heng,SHENG Chuan-Xiang**,CHEN Qian
Chin. Phys. Lett. 2012, 29 (5): 054201 .   DOI: 10.1088/0256-307X/29/5/054201
Abstract   PDF(pc) (627KB) ( 433 )
We numerically study the optical bistability (OBIS) in periodic multilayers of Ag/SiO2. The calculated dependence of the output on the input intensity shows two possible OBIS states at the test wavelength. One is due to the field localization effects in silver layers with nonlinear refractive index modifying resonant tunneling of electromagnetic waves; the other, with about a three times lower threshold input intensity, is attributed to the intensity dependence change of the Ag/SiO2 composite's effective dielectric constant from metallic−like (negative) to dielectric-like (positive). With appropriate design engineering the Ag/SiO2 multilayers could find broad applications in all-optical information processes.
Single- and Dual-Channel DPSK Signal Amplitude Regeneration Based on a Single Semiconductor Optical Amplifier
HUANG Xi,QIN Cui,YU Yu,ZHANG Zheng,ZHANG Xin-Liang**
Chin. Phys. Lett. 2012, 29 (5): 054202 .   DOI: 10.1088/0256-307X/29/5/054202
Abstract   PDF(pc) (699KB) ( 387 )
We experimentally demonstrate that, based on operational condition optimization, a common quantum well (QW) semiconductor optical amplifier (SOA) has the ability of amplitude regeneration for return-to-zero (RZ) differential phase shift keying (DPSK) signals. For a single-channel RZ-DPSK regeneration scheme, a significant eye-opening enhancement and a negative power penalty of about 1.0 dB are obtained. For dual-channel RZ-DPSK regeneration, it can also be found that the eye-opening improvement and power penalty decrease in each channel. In addition, the DPSK regeneration scheme based on a single QW SOA is quite simple and stable.
Wave Optics in Discrete Excitable Media
GU Guo-Feng,WEI Hai-Ming,TANG Guo-Ning**
Chin. Phys. Lett. 2012, 29 (5): 054203 .   DOI: 10.1088/0256-307X/29/5/054203
Abstract   PDF(pc) (2626KB) ( 420 )
Refraction and reflection of planar waves in a discrete excitable medium is numerically investigated by using the Greenberg–Hasting model. It is found that the medium is anisotropic because the speed of the planar wave depends on the excitability of the medium and the direction of wave propagation. The reflection, diffraction, refraction, double refraction and delayed refraction are observed by using the correct choice of model parameters. When the incident angle is larger than the critical angle, the reflection, which is a back refraction, takes place. The reflection angle changes with the incident angle. The refraction in certain situations obeys Snell's law. Also, our results demonstrate that the incident, refracted and reflected waves can have different periods. The reflected and refracted waves can disappear.
Absolute Angular Displacement Determination Based on Laser-Frequency Splitting Technology
REN Cheng**,YANG Xing-Tuan,ZHANG Shu-Lian
Chin. Phys. Lett. 2012, 29 (5): 054204 .   DOI: 10.1088/0256-307X/29/5/054204
Abstract   PDF(pc) (707KB) ( 440 )
We introduce an angle measurement system based on laser-frequency splitting technology, which is capable of absolute angular displacement determination. The core part is a dual-frequency microchip Nd:YAG laser which has two quarter-wave plates in the laser resonator and outputs two orthogonally linearly polarized lights with variable intermode frequency. A rotation of one of the wave plates shifts the frequency difference between modes. This angular displacement can thus be examined by detecting the shift of the frequency difference. The principle of the dual-frequency laser is demonstrated. A setup developed to accomplish angular displacement determinations and the experimental results of using this setup are then presented.
A Stable 22-W Low-Noise Continuous-Wave Single-Frequency Nd:YVO4 Laser at 1.06 µm Directly Pumped by a Laser Diode
LIU Qin,LIU Jian-Li,JIAO Yue-Chun,FENG Jin-Xia,ZHANG Kuan-Shou**
Chin. Phys. Lett. 2012, 29 (5): 054205 .   DOI: 10.1088/0256-307X/29/5/054205
Abstract   PDF(pc) (645KB) ( 565 )
We report a low-noise continous-wave single-frequency Nd:YVO4 laser at 1.06 µm directly pumped by an 880−nm laser diode. A maximum output power of 22 W is achieved with an optical-to-optical conversion efficiency of 46.3%. The stability of the output is better than ±0.7% in the given four hours. The output beam is almost diffraction−limited with a measured beam quality of Mx2=1.05 and My2=1.02. The intensity noise and the phase noise of the laser reach the shot-noise limit at an analysis frequency of 5 MHz.
Alkali-Responsive Absorption Spectra and Third-Order Optical Nonlinearities of Imino Squaramides
LI Zhong-Yu,**,XU Song,ZHOU Xin-Yu,ZHANG Fu-Shi
Chin. Phys. Lett. 2012, 29 (5): 054206 .   DOI: 10.1088/0256-307X/29/5/054206
Abstract   PDF(pc) (496KB) ( 347 )
Third-order optical nonlinearities and dynamic responses of two imino squaramides under neutral and base conditions were studied using the femtosecond degenerate four-wave mixing technique at 800 nm. Ultrafast optical responses have been observed and the magnitude of the second-order hyperpolarizabilities of the squaramides has been measured to be as large as 10−31 esu. The absorption spectra, color of solution, and third-order optical nonlinearities of two imino squaramides change with the addition of sodium hydroxide. The γ value under the base condition for each dye is approximately 1.25 times larger than that under neutral conditions.
Gain and Absorption of a Probe Light in an Open Tripod Atomic System
HU Zheng-Feng**,LIN Jin-Da,DENG Jian-Liao,HE Hui-Juan,WANG Yu-Zhu
Chin. Phys. Lett. 2012, 29 (5): 054207 .   DOI: 10.1088/0256-307X/29/5/054207
Abstract   PDF(pc) (815KB) ( 345 )
We theoretically investigate an open four-level atomic system interacting with control, probe and microwave fields. When there is no repumping light and a microwave field is applied, the probe light can be absorbed or amplified, which has different features than those of a system whose populations are pumped into only one ground state. In this system the microwave field and the population distributions of the ground states can be used as switches to control the propagation of the probe light.
Flat Supercontinuum Generation within the Telecommunication Wave Bands in a Photonic Crystal Fiber with Central Holes
HAN Ying,**,HOU Lan-Tian,ZHOU Gui-Yao,YUAN Jin-Hui,XIA Chang-Ming,WANG Wei,WANG Chao,HOU Zhi-Yun,
Chin. Phys. Lett. 2012, 29 (5): 054208 .   DOI: 10.1088/0256-307X/29/5/054208
Abstract   PDF(pc) (506KB) ( 499 )
Flat supercontinuum in the telecommunication wave bands of E+S+C is generated by coupling a train of femtosecond pulses generated by a mode-locked Ti:sapphire laser into the fundamental mode of a photonic crystal fiber with central holes fabricated in our lab. The pulse experiences the anomalous dispersion regime, and the soliton dynamic effect plays an important role in supercontinuum generation. The output spectrum in the wavelength range of 1360–1565 nm does not include significant ripples due to higher pump peak power, and the normalized intensity shows less fluctuation.
Luminescence and Thermal Properties of Er:GSGG and Yb,Er:GSGG Laser Crystals
SUN Dun-Lu**,LUO Jian-Qiao,XIAO Jing-Zhong,ZHANG Qing-Li,CHEN Jia-Kang,LIU Wen-Peng,KANG Hong-Xiang,YIN Shao-Tang
Chin. Phys. Lett. 2012, 29 (5): 054209 .   DOI: 10.1088/0256-307X/29/5/054209
Abstract   PDF(pc) (1011KB) ( 606 )
Er3+−doped and Yb3+/Er3+ co−doped Gd3Sc2Ga3O12 (abbreviated as Er:GSGG and Yb,Er:GSGG, respectively) laser crystals are investigated by using a combination of spectroscopic measurements and thermal characterizations. An absorption peak of Yb,Er:GSGG crystal shifts to 970 nm and its absorption band broadens obviously, which makes the crystal suitable for pumping by a 970 nm laser diode (LD). This crystal also exhibits a shorter lifetime of a lower laser level, a larger emission cross section and higher thermal conductivity than those of Er:GSGG. All these factors suggest that Yb3+/Er3+ co−doping has a positive effect on improving the spectroscopic and thermal performances in GSGG based laser crystals, and imply that double-doped Yb,Er:GSGG crystal is a potential candidate as an excellent LD pumped 2.79 µm laser material.
Phase Locking of Laser Diode Array by Using an Off-Axis External Talbot Cavity
SU Zhou-Ping**,JI Zhi-Cheng,ZHU Zhuo-Wei,QUE Li-Zhi,ZHU Yun
Chin. Phys. Lett. 2012, 29 (5): 054210 .   DOI: 10.1088/0256-307X/29/5/054210
Abstract   PDF(pc) (500KB) ( 595 )
Phase locking of a laser diode array is demonstrated experimentally by using an off-axis external Talbot cavity with a feedback plane mirror. Due to good spatial mode discrimination, the cavity does not need a spatial filter. By employing the cavity, a clear and stable far-field interference pattern can be observed when the driver current is less than 14 A. In addition, the spectral line width can be reduced to 0.8 nm. The slope efficiency of the phase-locked laser diode array is about 0.62 W/A.
Transmission Characteristics in a Coupled-Resonator Waveguide Interacting with a Two-Mode Nanocavity Containing a Three-Level Emitter
CHENG Mu-Tian,SONG Yan-Yan,YU Long-Bao**
Chin. Phys. Lett. 2012, 29 (5): 054211 .   DOI: 10.1088/0256-307X/29/5/054211
Abstract   PDF(pc) (592KB) ( 396 )

The photon transport in a coupled-resonator waveguide coupled to a two-mode nanocavity embedded with a three-level emitter is investigated. The transmission and reflection amplitudes are obtained by using the discrete coordinates approach. We show that the coherent transport properties of a single photon can be well controlled by detuning the coupling strength between the two-mode nanocavity and the emitter, and the coupling strength between the nanocavity and the coupled-resonator waveguide. These results may be useful for the design of photonic devices such as optical filters.

Pulsed Chemical Oxygen Iodine Lasers Excited by Pulse Gas Discharge with the Assistance of Surface Sliding Discharge Pre-ionization
LI Guo-Fu,**,YU Hai-Jun,DUO Li-Ping,JIN Yu-Qi,WANG Jian,SANG Feng-Ting,WANG De-Zhen
Chin. Phys. Lett. 2012, 29 (5): 054212 .   DOI: 10.1088/0256-307X/29/5/054212
Abstract   PDF(pc) (762KB) ( 508 )
Continuous-wave chemical oxygen-iodine lasers (COILs) can be operated in a pulsed operation mode to obtain a higher peak power. The key point is to obtain a uniform and stable glow discharge in the mixture of singlet delta oxygen and iodide. We propose using an electrode system with the assistance of surface sliding pre-ionization to solve the problem of the stable glow discharge with a large aperture. The pre-ionization unit is symmetrically fixed on the plane of the cathode surface. A uniform and stable glow discharge is obtained in a mixture of iodide (such as CH3I) and nitrogen at the specific deposition energy of 4.5 J/L, pressure of 1.99–3.32 kPa, aperture size of 11 cm×10 cm. The electrode system is applied in a pulsed COIL. Laser energy up to 4.4 J is obtained and the specific energy output is 2 J/L.
Tomographic Imaging and Three-Dimensional Reconstruction Based on a High-Gain Optical Parametric Amplifier
YANG Jing,DU Shi-Feng,ZHANG Jing-Yuan,*,CAO Dong,CUI Da-Fu,PENG Qin-Jun,XU Zu-Yan*
Chin. Phys. Lett. 2012, 29 (5): 054213 .   DOI: 10.1088/0256-307X/29/5/054213
Abstract   PDF(pc) (1037KB) ( 451 )
Tomographic imaging and three-dimensional reconstruction based on a high-gain picosecond optical parametric amplifier (OPA) is demonstrated. More than 40 dB intensity amplification of the image is achieved from the high-gain OPA. The images of various longitudinal positions of the target are extracted by the gated nature of the OPA, then a three-dimensional (3-D) surface topography of the target is reconstructed. The gated and high-gain property of the OPA allows tomographic optical imaging together with 3-D profile reconstruction of the target in turbid media.
Self-Q-Switched and Mode-Locked Cr,Nd:YAG Laser under Direct 885 nm Diode Laser Pumping
JIANG Man,ZHANG Qiu-Lin,ZHOU Wen-Jia,ZHANG Jing,ZHANG Dong-Xiang,FENG Bao-Hua**
Chin. Phys. Lett. 2012, 29 (5): 054214 .   DOI: 10.1088/0256-307X/29/5/054214
Abstract   PDF(pc) (1102KB) ( 529 )
A simultaneous self-Q-switched and mode-locked laser in a direct 885 nm diode-pumped Cr,Nd:YAG crystal is demonstrated. An improvement of the slope efficiency (38.1%) in the absorbed pump power is obtained under direct pumping. Under the maximum output power of 3.36 W, the repetition rate of the Q-switched envelopes is 95 kHz and the corresponding pulse width is 400 ns. Almost 100% mode-locked modulation depth is observed at the output power of 75 mW. The repetition rate of mode-locked pulses within a Q-switched envelope is 130 MHz, and the mode-locked pulse width stays within the scale of 500 ps.
High-Quality Fiber-Based Heralded Single-Photon Source at 1.5 µm
WANG Peng-Xiang,ZHOU Qiang,ZHANG Wei**,HUANG Yi-Dong,PENG Jiang-De
Chin. Phys. Lett. 2012, 29 (5): 054215 .   DOI: 10.1088/0256-307X/29/5/054215
Abstract   PDF(pc) (583KB) ( 816 )
A high-quality heralded single-photon source (HSPS) at 1.5 µm is experimentally demonstrated based on spontaneous four wave−mixing in a piece of dispersion-shifted fiber cooled by liquid nitrogen. To improve the up-limit of the preparation efficiency of the HSPS, commercial dense wavelength-division multiplexing components are used to reduce the loss of the filtering and splitting system between the fiber and the single-photon detectors. As a result, a preparation efficiency of 80% is realized under a g(0)(2) of 0.06 in our HSPS experimental system, which is the best performance for the fiber−based HSPS at 1.5 µm reported so far.
Performance Comparison of Mode-Locked Erbium-Doped Fiber Laser with Nonlinear Polarization Rotation and Saturable Absorber Approaches
M. A. Ismail,S. J. Tan,N. S. Shahabuddin,S. W. Harun,**,H. Arof,H. Ahmad
Chin. Phys. Lett. 2012, 29 (5): 054216 .   DOI: 10.1088/0256-307X/29/5/054216
Abstract   PDF(pc) (400KB) ( 945 )
A mode-locked erbium-doped fiber laser (EDFL) is demonstrated using a highly concentrated erbium-doped fiber (EDF) as the gain medium in a ring configuration with and without a saturable absorber (SA). Without the SA, the proposed laser generates soliton pulses with a repetition rate of 12 MHz, pulse width of 1.11 ps and energy pulse of 1.6 pJ. By incorporating SA in the ring cavity, the optical output of the laser changes from soliton to stretched pulses due to the slight change in the group velocity dispersion. With the SA, a cleaner pulse is obtained with a repetition rate of 11.3 MHz, a pulse width of 0.58 ps and a pulse energy of 2.3 pJ.
Effect of Coagulation and Diffusion on Nanoparticle Distribution in a Fully Developed Turbulent Boundary Layer
LIN Jian-Zhong,**,CHEN Zhong-Li
Chin. Phys. Lett. 2012, 29 (5): 054701 .   DOI: 10.1088/0256-307X/29/5/054701
Abstract   PDF(pc) (540KB) ( 567 )
Nanoparticle distributions in a fully developed turbulent boundary layer are simulated numerically using the moment method. The effects of Schmidt number and Damköhler number on the nanoparticle distribution are studied. It is found that the particle number concentration and total particle mass increase from the wall to the outside. The difference of particle number concentration and total particle mass near the wall and near the outside becomes smaller with the increasing Schmidt number Sc. The particle diameter and geometric standard deviation increase from the wall to the outside at a fixed Damköhler number Da, and grow with the increase of Da at the same lateral position.
Correlation between Temperature and Velocity Fluctuations in the Near-Wall Region of Rotating Turbulent Channel Flow
YANG Zi-Xuan,CUI Gui-Xiang**,XU Chun-Xiao,ZHANG Zhao-Shun,SHAO Liang
Chin. Phys. Lett. 2012, 29 (5): 054702 .   DOI: 10.1088/0256-307X/29/5/054702
Abstract   PDF(pc) (384KB) ( 876 )
The correlation between the temperature and streamwise velocity fluctuations in rotating turbulent channel flow is investigated. Unlike the previously found analogous property between the statistics of the temperature and streamwise velocity fluctuations, the correlation can more appropriately reveal the similarity between two random processes. The analysis of the correlation coefficient obtained from the database of direct numerical simulation indicates that the rotation weakens the correlation in most regions of the flow, especially on the suction side. Nevertheless, the correlation is slightly enhanced by the rotation in some regions of the rotating channel, which challenges the general understanding that rotation undoubtedly weakens the correlation. To discuss the mechanism of the rotating effect on the correlation, the transport equations of the variance of temperature and streamwise velocity fluctuations are considered. The Coriolis force is found to have an indirect effect on the correlation.
Heat Transfer Analysis of the Unsteady Flow of a Maxwell Fluid over a Stretching Surface in the Presence of a Heat Source/Sink
Swati Mukhopadhyay*
Chin. Phys. Lett. 2012, 29 (5): 054703 .   DOI: 10.1088/0256-307X/29/5/054703
Abstract   PDF(pc) (485KB) ( 1815 )
The unsteady two-dimensional flow of a MHD non-Newtonian Maxwell fluid over a stretching surface with a prescribed surface temperature in the presence of a heat source/sink is investigated. Similarity solutions for the governing equations are obtained. The transformed boundary layer equations are then solved numerically by using the shooting method. Fluid velocity initially decreases with the increasing unsteadiness parameter, and temperature decreases significantly due to unsteadiness. It is also found that the fluid velocity decreases with the increasing magnetic parameter. Increasing the Maxwell parameter values has the effect of suppressing the velocity field and increasing the temperature.
Collective Interaction of Vortices in Two-Dimensional Shear Layers
YANG Wu-Bing*,SHEN Qing,WANG Qiang
Chin. Phys. Lett. 2012, 29 (5): 054704 .   DOI: 10.1088/0256-307X/29/5/054704
Abstract   PDF(pc) (1130KB) ( 444 )
A phenomenological diagram is presented to explain the interaction between a fundamental wave and its subharmonic wave in 2D shear layers based on linear stability theory. These diagrams indicate that there are only four classes of subharmonic interactions, which are symmetric collective interaction, the first class of asymmetric collective interaction, the second class of collective interaction and tearing. Each of them can be determined uniquely by a couple of parameters m and p, where m is the ratio of wavenumber and p is a parameter of phase difference between the fundamental wave and its subharmonic wave. For each class of subharmonic interactions, a couple of parameters m and p have been deduced from the phenomenological diagram. We think that they are significant for accurate flow control of shear layers.
Evaluation of Presumed Probability-Density-Function Models in Non-Premixed Flames by using Large Eddy Simulation
CAO Hong-Jun,ZHANG Hui-Qiang**,LIN Wen-Yi
Chin. Phys. Lett. 2012, 29 (5): 054705 .   DOI: 10.1088/0256-307X/29/5/054705
Abstract   PDF(pc) (1286KB) ( 871 )
Four kinds of presumed probability-density-function (PDF) models for non-premixed turbulent combustion are evaluated in flames with various stoichiometric mixture fractions by using large eddy simulation (LES). The LES code is validated by the experimental data of a classical turbulent jet flame (Sandia flame D). The mean and rms temperatures obtained by the presumed PDF models are compared with the LES results. The β−function model achieves a good prediction for different flames. The predicted rms temperature by using the double-δ function model is very small and unphysical in the vicinity of the maximum mean temperature. The clip−Gaussian model and the multi-δ function model make a worse prediction of the extremely fuel-rich or fuel-lean side due to the clip at the boundary of the mixture fraction space. The results also show that the overall prediction performance of presumed PDF models is better at mediate stoichiometric mixture fractions than that at very small or very large ones.
Optical Emission Analysis of Molecular Nitrogen by Using a Self-Resonating Dielectric Barrier Plasma Reactor
A. M. A. Amry*,V. J. Law,I. W. Boyd
Chin. Phys. Lett. 2012, 29 (5): 055201 .   DOI: 10.1088/0256-307X/29/5/055201
Abstract   PDF(pc) (491KB) ( 2094 )
We present a spectroscopic investigation of molecular nitrogen using a self-resonating co-axial dielectric barrier plasma reactor. The properties of the nitrogen plasma generated were recorded as functions of radio frequency (27.12 MHz), power (20–50 W) and gas pressure (0.1–60 mbar). The intensity distribution of the transitional structure of the electronic bands C3Πu →B 3Πg, B 2Σu+→X 2Σg+ and D 2Πg→A 2Πu was measured as a function of gas pressure. Relative energy efficiency (total emitted intensity from the plasma It divided by total electric power to the discharge P), as high as 14% can be obtained at a dissipated electrical power level of 20 W and a pressure of 10 mbar.
Pressure and Discharge-Voltage Dependence of Self-Sustaining Pulses in Air-Glow Discharge
A. A. Azooz,Y. A. Al-Jawaady,Z. T. Ali
Chin. Phys. Lett. 2012, 29 (5): 055202 .   DOI: 10.1088/0256-307X/29/5/055202
Abstract   PDF(pc) (533KB) ( 928 )

The details of formation of micro discharges in air-glow discharge plasma are experimentally studied. The number of micro discharges formed per second is strongly related to both pressure and discharge voltage. This number tends to show reflections of the Patchen curve as far as its pressure dependence is concerned. The discharge-voltage dependence indicates that the transition from normal to abnormal glow discharge is not a sudden one, but has its roots during the normal glow stage and is initiated by the micro discharges which can be regarded as the early stage of abnormal glow.

Effect of Annealing Temperature on the Structural and Electrical Properties of a−Axis-Oriented SrTiO3 Films
WANG Xiao-Fei,**,HU Qiu-Bo,LI Li-Ben,CHEN Qing-Dong,WANG Hui-Xian,
Chin. Phys. Lett. 2012, 29 (5): 056101 .   DOI: 10.1088/0256-307X/29/5/056101.
Abstract   PDF(pc) (666KB) ( 854 )

Strontium titanate films with high a−axis-orientation [a(100)=94.1%] were deposited on (111) Pt/Ti/SiO2/Si substrates by the metal organic deposition process. X−ray diffraction shows that the degree of a-axis orientation increases with increasing annealing temperature. It is found that the dielectric properties are improved by a higher annealing temperature, while the leakage currents are also enhanced, and the possible causes of temperature dependence are discussed.

Role of Surface Hydrogen Bonds in Determining the Friction Behaviors of Hydrogenated Diamond-like Carbon Films
WANG Cheng-Bing**,SHI Jing,GENG Zhong-Rong,ZHANG Jun-Yan
Chin. Phys. Lett. 2012, 29 (5): 056201 .   DOI: 10.1088/0256-307X/29/5/056201
Abstract   PDF(pc) (1472KB) ( 950 )
Friction behaviors of hydrogenated diamond-like carbon (H-DLC) films are investigated on a ball-on-disk type tribometer in dry N2 and dry vacuum. The result shows that the friction behaviors of the H−DLC films are very sensitive to the testing environment, the H-DLC films exhibit a very low friction coefficient of 0.016 in dry N2, and similarly in an inert gas the friction coefficient increases to about 0.063 in dry vacuum. Combining the testing conditions, friction results, SEM and XPS investigation, it is concluded that the friction behaviors of the hydrogenated DLC films are associated with surface hydrogen of the H-DLC films and are dictated by whether or not hydrogen bonds are formed between the transfer films/H-DLC films at the sliding interface. A hydrogen-induced hydrogen bond model is proposed to interpret the friction behaviors of hydrogenated DLC films in different environments.
Chemisorption-Induced Resonance Frequency Shift of a Microcantilever
ZHANG Ji-Qiao**,FENG Xi-Qiao,HUANG Gan-Yun,YU Shou-Wen
Chin. Phys. Lett. 2012, 29 (5): 056801 .   DOI: 10.1088/0256-307X/29/5/056801
Abstract   PDF(pc) (524KB) ( 1002 )
The autonomy and property of atoms/molecules adsorbed on the surface of a microcantilever can be probed by measuring its resonance frequency shift due to adsorption. The resonance frequency change of a cantilever induced by chemisorption is theoretically studied. Oxygen chemisorbed on the Si(100) surface is taken as a representative example. We demonstrate that the resonant response of the cantilever is mainly determined by the chemisorption-induced bending stiffness variation, which depends on the bond configurations formed by the adsorbed atoms and substrate atoms. This study is helpful for optimal design of microcantilever-based sensors for various applications.
Exact Results for Intrinsic Electronic Transport in Graphene
HU Shi-Jie,DU Wei,ZHANG Gui-Ping,GAO Miao,LU Zhong-Yi,WANG Xiao-Qun**
Chin. Phys. Lett. 2012, 29 (5): 057201 .   DOI: 10.1088/0256-307X/29/5/057201
Abstract   PDF(pc) (629KB) ( 920 )
We present exact results for the electronic transport properties of graphene sheets connected to two metallic electrodes. Our results obtained by transfer-matrix methods are valid for all sheet widths and lengths. In the limit of the large width-to-length ratio relevant to recent experiments, we find a Dirac-point conductivity of 2e2/(√3 h) and a sub−Poissonian Fano factor of 2-3√3/π≃0.346 for armchair graphene; for the zigzag geometry they are respectively 0 and 1. Our results reflect essential effects from both the topology of graphene and the electronic structure of the leads, giving a complete microscopic understanding of the unique intrinsic transport in graphene.
In-Situ SRPES Study on the Band Alignment of (0001)CdS/CdTe Heterojunction
GAO Jun-Ning,JIE Wan-Qi**,YUAN Yan-Yan,ZHA Gang-Qiang,XU Ling-Yan,WU Heng,WANG Ya-Bin,YU Hui,ZHU Jun-Fa
Chin. Phys. Lett. 2012, 29 (5): 057301 .   DOI: 10.1088/0256-307X/29/5/057301
Abstract   PDF(pc) (630KB) ( 629 )
The band alignment of a (0001)CdS/CdTe heterojunction is in situ studied by synchrotron radiation photoemission spectroscopy (SRPES). The heterojunction is formed through stepwise deposition of a CdTe film on a wurtzite (0001)CdS single crystalline substrate via molecular beam epitaxy. CdS shows an upward band bending of 0.55 eV, the valence band offset ΔEV is calculated to be 0.65 eV and the conduction band offset ΔEC is 0.31 eV. The interfacial band alignment is sketched to display type-I band alignment.
Chemical Vapour Deposition Graphene Radio-Frequency Field-Effect Transistors
MA Peng,JIN Zhi**,GUO Jian-Nan,PAN Hong-Liang,LIU Xin-Yu,YE Tian-Chun,WANG Hong,WANG Guan-Zhong
Chin. Phys. Lett. 2012, 29 (5): 057302 .   DOI: 10.1088/0256-307X/29/5/057302
Abstract   PDF(pc) (908KB) ( 605 )
We report the dc and rf performance of graphene rf field-effect transistors, where the graphene films are grown on copper by using the chemical vapour deposition (CVD) method and transferred to SiO2/Si substrates. Composite materials, benzocyclobutene and atomic layer deposition Al2O3 are used as the gate dielectrics. The observation of n− and p-type transitions verifies the ambipolar characteristics in the graphene layers. While the intrinsic carrier mobility of CVD graphene is extracted to be 1200 cm2/V⋅s, the parasitic series resistances are demonstrated to have a serious impact on device performance. With a gate length of 1 µm and an extrinsic transconductance of 72 mS/mm, a cutoff frequency of 6.6 GHz and a maximum oscillation frequency of 8.8 GHz are measured for the transistors, illustrating the potential of the CVD graphene for rf applications.
Influence of Fermion Velocity Renormalization on Dynamical Mass Generation in QED3
CHANG Hao-Ran**,WANG Jing-Rong,WANG Jing
Chin. Phys. Lett. 2012, 29 (5): 057401 .   DOI: 10.1088/0256-307X/29/5/057401
Abstract   PDF(pc) (4232KB) ( 396 )

We study dynamical fermion mass generation in (2+1)-dimensional quantum electrodynamics with a gauge field coupling to massless Dirac fermions and non-relativistic scalar bosons. We calculate the fermion velocity renormalization and then examine its influence on dynamical mass generation by using the Dyson–Schwinger equation. It is found that dynamical mass generation takes place even after including the scalar bosons as long as the bosonic compressibility parameter ξ is sufficiently small. In addition, the fermion velocity renormalization enhances the dynamically generated mass.

Processing YCo5 Permanent Magnetic Submicron Flakes by Surfactant-Assisted High-Energy Ball Milling
ZHANG Jing-Jing,GAO Hong-Mei,YAN Yu,BAI Xue,WANG Wen-Quan,SU Feng,DU Xiao-Bo**
Chin. Phys. Lett. 2012, 29 (5): 057501 .   DOI: 10.1088/0256-307X/29/5/057501
Abstract   PDF(pc) (1395KB) ( 552 )
YCo5 alloy is processed by surfactant−assisted high-energy ball milling. Oleic acid is used as the surfactant and is 20% of the starting powder. The resultant particles are flakes of several microns in length and width, and 20–200 nm in thickness. The flakes have significant crystallographic anisotropy and the c-axis (also easy magnetization axes) is perpendicular to the flake's surface. Maximum coercivity of 192 kA/m is obtained in the sample milled for 100 min. Excess milling results in the appearance of Fe and deteriorates the permanent magnetic properties seriously.
Chromium Substitution Effect on the Magnetic Structure of Iron Oxides
Osman Murat Ozkendir**
Chin. Phys. Lett. 2012, 29 (5): 057502 .   DOI: 10.1088/0256-307X/29/5/057502
Abstract   PDF(pc) (594KB) ( 878 )
The local magnetic and electronic structures of chromium substituted iron oxide polycrystalline samples are investigated via Fe L-edge x-ray absorption near-edge structural and magnetic circular dichroism measurements. A strong dependence of atomic magnetic levels on the applied external magnetic field is observed. The magnetic behavior of Cr-doped iron oxides are determined to be dominantly governed by the dd hybridization between Fe and Cr valence levels. In addition, the formation of CrO2 and Cr2O3 chromium oxide clusters in the sample are observed to determine the magnetic ordering, i.e. anti-ferromagnetic or ferromagnetic with the changing external magnetic fields. The results highly agree with the previous studies.
Validity of Nonlinear Thermodynamic Models in Ferroelectric-Paraelectric Bilayers and Superlattices
LIU Yang**,PENG Xing-Ping
Chin. Phys. Lett. 2012, 29 (5): 057701 .   DOI: 10.1088/0256-307X/29/5/057701
Abstract   PDF(pc) (596KB) ( 448 )
We examine the validity of nonlinear thermodynamic models which incorporate the contribution of electrostatic coupling and interfacial space charge in ferroelectric-paraelectric bilayers. Inconsistency of the directions between build-in polarization and field is found. Evolution of ferroelectricity does not follow the variation in coupling strength between different layers. In addition, we observe that the field-induced polarization in the paraelectric layer deviates from the polarization derived by thermodynamic theory. These findings indicate that the current versions of thermodynamic models need to be modified.
A Substitution for the High-k Dielectric in an AlGaN/GaN Metal-insulator-Semiconductor Heterostructure
KONG Yue-Chan**,XUE Fang-Shi,ZHOU Jian-Jun,LI Liang,CHEN Chen,JIANG Wen-Hai
Chin. Phys. Lett. 2012, 29 (5): 057702 .   DOI: 10.1088/0256-307X/29/5/057702
Abstract   PDF(pc) (671KB) ( 519 )

Paraelectric state ferroelectric material is proposed as a novel substitution for the conventional high-k dielectric used in AlGaN/GaN metal−insulator-semiconductor (MIS) field-effect transistors. Its superior potential for improving device transconductance is due to its unique switchable polar nature. By self-consistent calculation involving the switchable polarization of the paraelectric, the 2DEG properties and CV characteristics are investigated and compared for the novel AlGaN/GaN metal−paraelectric-semiconductor (MPS) structure and an equivalent conventional MIS structure. It is shown that owing to the paraelectric polarization, the gate control of the 2DEG density is remarkably enhanced in the MPS structure and the gate capacitance is significantly improved with a smaller threshold voltage. The self-consistent polarization of the paraelectric in the MPS structure is non-linearly dependent on the saturated polarization, which implies an optimum saturated polarization of 5–10 µC/cm2 for the paraelectric.

Effect of Residual Stress on the Magnetoelectric Properties of Terfenol-D/PZT/Terfenol-D Laminates
PEI Yong-Mao***,XU Kui-Xue,ZENG An-Min,AI Shi-Gang
Chin. Phys. Lett. 2012, 29 (5): 057801 .   DOI: 10.1088/0256-307X/29/5/057801
Abstract   PDF(pc) (652KB) ( 722 )
The effect of residual stress on the magnetoelectric properties of terfenol-D/PZT/terfenol-D laminates is studied. The sandwich structure composites with two longitudinally magnetized terfenol-D plates and one transversely polarized Pb(Zr0.52Ti0.48)O3 plate are manufactured under different uniform and constant magnetic fields. The magnetic plates will deform before adhesion. Therefore, residual stress is induced by the mismatched strain between laminates when the magnetic field disappears. The experimental results show that magnetoelectric coefficient is improved about 130% for sandwich structure composites with residual stress. It can be explained that the proposed method can improve the interface mechanical coupling effect. Therefore, the magnetic energy can be transferred effectively to electric energy through the mechanical deformation. At the same time the strain derivative /dH is enhanced by residual stress. Thus, the electric polarization response is increased under a same disturbed magnetic field.
Electrical Properties of Lead Zirconate Titanate Thick Film Containing Micro- and Nano-Crystalline Particles
LU Ran,JIANG Gen-Shan,LI Bin,ZHAO Quan-Liang,ZHANG De-Qing,YUAN Jie,CAO Mao-Sheng**
Chin. Phys. Lett. 2012, 29 (5): 058101 .   DOI: 10.1088/0256-307X/29/5/058101
Abstract   PDF(pc) (1017KB) ( 1105 )
We report the ferroelectric, dielectric and piezoelectric properties of a dense and crack-free lead zirconate titanate (Pb(Zr0.52Ti0.48)O3, PZT) thick film containing micro− and nano-crystalline particles. The results show that these electrical properties are dependent strongly on the annealing temperature and film thickness. For the different-annealing-temperature and different-thickness films, the higher-annealing-temperature thicker ones show the larger remnant polarization and smaller coercive field. The dielectric results show that relative dielectric constant achieves the largest value at annealing temperature of 700°C, and increases with the increasing film thickness. For the piezoelectric properties, the longitudinal piezoelectric coefficient increases linearly with the film thickness increasing and the 4−µm -thick PZT film shows the largest value of about 200.65 pC/N. Therefore, the PZT thick films present good electric properties and enlarged potential in MEMS applications.
The Leakage Current Improvement of a Ni-Silicided SiGe/Si Junction Using a Si Cap Layer and the PAI Technique
CHANG Jian-Guang,WU Chun-Bo,JI Xiao-Li**,MA Hao-Wen,YAN Feng,SHI Yi,ZHANG Rong
Chin. Phys. Lett. 2012, 29 (5): 058501 .   DOI: 10.1088/0256-307X/29/5/058501
Abstract   PDF(pc) (682KB) ( 1971 )
We investigate the leakage current of ultra-shallow Ni-silicided SiGe/Si junctions for 45 nm CMOS technology using a Si cap layer and the pre-amorphization implantation (PAI) process. It is found that with the conventional Ni silicide method, the leakage current of a p+(SiGe)–n(Si) junction is large and attributed to band-to-band tunneling and the generation-recombination process. The two leakage contributors can be suppressed quite effectively when a Si cap layer is added in the Ni silicide method. The leakage reduction is about one order of magnitude and could be associated with the suppression of the agglomeration of the Ni germano-silicide film. In addition, the PAI process after the application of a Si cap layer has little effect on improving the junction leakage but reduces the sheet resistance of the silicide film. As a result, the novel Ni silicide method using a Si cap combined with PAI is a promising choice for SiGe junctions in advanced technology.
Imaging and Characteristics of a Bimaterial Microcantilever FPA Fabricated using Bulk Silicon Processes
ZHAO An-Di,ZHENG Yong-Jun,YU Xiao-Mei**
Chin. Phys. Lett. 2012, 29 (5): 058502 .   DOI: 10.1088/0256-307X/29/5/058502
Abstract   PDF(pc) (672KB) ( 446 )
For a focal plane array (FPA) fabricated with a surface sacrificial layer process, the IR flux must transmit through the silicon substrate and the air gap before it reaches the cantilever pixels. Part of the IR radiation energy is therefore lost owing to the reflection and absorption caused by the silicon substrate. We fabricate an infrared FPA consisting of 128×128 microcantilever pixels by using a novel bulk micro−electro-mechanical-system process. Thermal images of persons at room temperature are captured to demonstrate the IR imaging capability of the FPA. For the proposed device, the thermal response is calculated to be 4.03×10-3, the thermo−mechanical sensitivity is measured to be 0.273 µm /K, the noise equivalent temperature difference is measured to be 200 mK by a gray level change method and the time constant is calculated to be 15 ms under a 10 mTorr pressure.
Conductance and DNA Translocation Current Blockage of Solid-State Nanopores
LU Bo,JIN Wei-Liang,ZHAO Qing**,YU Da-Peng**
Chin. Phys. Lett. 2012, 29 (5): 058701 .   DOI: 10.1088/0256-307X/29/5/058701
Abstract   PDF(pc) (478KB) ( 604 )
The current blockage during DNA molecule translocation through a solid-state nanopore is very important in DNA analysis techniques based on nanopores. We use Poisson–Nernst–Planck descriptions of electrolyte behavior in a nanopore with and without the presence of DNA molecules to simulate the nanopore conductance and current blockage of DNA molecules. Actual experimental parameters, such as pore size, length of nanopores, DNA drift velocity, and the charge issue of nanopores and DNA, are applied to evaluate the precise current blockage amplitude, which is found to agree very well with the experimental results.
Statistical Physics of Economic Systems: a Survey for Open Economies
TAO Yong*,CHEN Xun
Chin. Phys. Lett. 2012, 29 (5): 058901 .   DOI: 10.1088/0256-307X/29/5/058901
Abstract   PDF(pc) (382KB) ( 519 )
We extend the theoretical framework of an independent economy developed by Tao [Phys. Rev. E 82 (2010) 036118] so as to include multiple economies. Since the starting point of our framework is on the basis of the theory of the competitive markets of traditional economics, this framework shall be suitable for any free market. Our study shows that integration of world economies can decrease trade friction among economic systems, but may also cause a global economic crisis whenever economy disequilibrium occurs in any one of these economic systems.
Influence of σ* and φ Mesons on Λ Hyperon 1S0 Superfluidity in Neutron Star Matter
XU Yan**,LIU Guang-Zhou,WANG Hong-Yan,DING Wen-Bo,ZHAO En-Guang
Chin. Phys. Lett. 2012, 29 (5): 059701 .   DOI: 10.1088/0256-307X/29/5/059701
Abstract   PDF(pc) (695KB) ( 474 )
Within the framework of the relativistic mean field theory, we investigate the 1S0 superfluidity (SF) of Λ hyperons in neutron star (NS) matter including σ* and φ mesons. The energy gap of Λ hyperons is calculated with the Nijmegen one−boson-exchange potentials for a ΛΛ pair. The parameter set we use is in line with the recent experimental data ΔBΛΛ1.01±0.20+0.18−0.11 MeV. It is found that with σ* and φ mesons the pairing energy gap ΔF of Λ hyperons and the corresponding SF critical temperature T are suppressed. In addition the NS mass range of Λ hyperon SF is enlarged obviously.
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