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Volume 28 Issue 3
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GENERAL
Approximate Symmetry Reduction for Initial-value Problems of the Extended KdV-Burgers Equations with Perturbation
LI Ji-Na, ZHANG Shun-Li, **
Chin. Phys. Lett. 2011, 28 (3): 030201 .   DOI: 10.1088/0256-307X/28/3/030201
Abstract   PDF(pc) (430KB) ( 548 )
Approximate generalized conditional symmetry is developed to study the approximate symmetry reduction for initial-value problems of the extended KdV-Burgers equations with perturbation. These equations can be reduced to initial-value problems for some systems of first-order perturbed ordinary differential equations in terms of a new approach. Complete classification theorems are obtained and an example is taken to show the main reduction procedure.
Traveling Wave Evolutions of a Cosh-Gaussian Laser Beam in Both Kerr and Cubic Quintic Nonlinear Media Based on Mathematica
WANG Jun-Min
Chin. Phys. Lett. 2011, 28 (3): 030202 .   DOI: 10.1088/0256-307X/28/3/030202
Abstract   PDF(pc) (520KB) ( 492 )
With the aid of Mathematica, three auxiliary equations, i.e. the Riccati equation, the Lenard equation and the Hyperbolic equation, are employed to investigate traveling wave solutions of a cosh-Gaussian laser beam in both Kerr and cubic quintic nonlinear media. As a result, many traveling wave solutions are obtained, including soliton-like solutions, hyperbolic function solutions and trigonometric function solutions.
Application of the CE/SE Method to a Two-Phase Detonation Model in Porous Media
DONG He-Fei, HONG Tao**, ZHANG De-Liang
Chin. Phys. Lett. 2011, 28 (3): 030203 .   DOI: 10.1088/0256-307X/28/3/030203
Abstract   PDF(pc) (545KB) ( 447 )
We extend the conservation-element and solution-element method to simulate a two-phase detonation model in porous media. The accuracy of the method is validated by calculating an inert compaction problem. The main characteristics of piston-driven detonation phenomena, including the compaction wave, the onset of combustion, and the transition to detonation, could be predicted successfully.
Nonlocality Sudden Birth and Transfer in System and Environment
QIU Liang
Chin. Phys. Lett. 2011, 28 (3): 030301 .   DOI: 10.1088/0256-307X/28/3/030301
Abstract   PDF(pc) (775KB) ( 450 )
Dynamics of the nonlocality measured by the violation of Svetlichny's Bell-type inequality is investigated in the non-Markovian model. The phenomenon of nonlocality sudden birth for the atoms and the reservoirs is obtained. The evolution of the nonlocality among the atoms or the reservoirs depends on the choice of the atom detuning from the cavity pseudomode, the cavity pseudomode decay and the rotation angles. For the small pseudomode decay in the near-resonance regime, the initial atomic nonlocality is completely transferred to the reservoirs ultimately.
Quantum Secure Direct Communication with Five-Qubit Entangled State
LIN Song, **, GAO Fei, LIU Xiao-Fen,
Chin. Phys. Lett. 2011, 28 (3): 030302 .   DOI: 10.1088/0256-307X/28/3/030302
Abstract   PDF(pc) (418KB) ( 575 )
Recently, a genuine five-qubit entangled state has been achieved by Brown et al. [J. Phys. A 38 (2005) 1119]. Later it was indicated that this state can be used for quantum teleportation and quantum state sharing. Here we build a quantum secure direct communication protocol with this state, and prove that it is secure in ideal conditions. In the protocol, the sender performs unitary transformations to encode a secret message on his/her particles and sends them to the receiver. The receiver then performs projective determinate measurement to decode the secret message directly. Furthermore, this protocol utilizes superdense coding to achieve a high intrinsic efficiency and source capacity.
Effect of the Inverse Volume Modification in Loop Quantum Cosmology
XIONG Hua-Hui**, ZHU Jian-Yang***
Chin. Phys. Lett. 2011, 28 (3): 030401 .   DOI: 10.1088/0256-307X/28/3/030401
Abstract   PDF(pc) (460KB) ( 368 )
After incorporating the inverse volume modifications both in the gravitational and matter part in the improved framework of LQC, we find that the inverse volume modification can decrease the bouncing energy scale, and the presence of nonsingular bounce is generic. For the backward evolution in the expanding branch, in terms of different initial states, the evolution trajectories classify into two classes. One class with larger initial energy density leads to the occurrence of bounce in the region a>ach where ach marks the different inverse volume modification region. The other class with smaller initial energy density evolves back into the region ach. In this region, both the energy density for the scalar field and the bouncing energy scale decrease with the backward evolution. The bounce is present when the bouncing energy scale decreases to be equal to the energy density of the scalar field.
Exotic Homoclinic Surface of a Saddle-Node Limit Cycle in a Leech Neuron Model
YOOER Chi-Feng, **, WEI Fang, XU Jian-Xue, ZHANG Xin-Hua
Chin. Phys. Lett. 2011, 28 (3): 030501 .   DOI: 10.1088/0256-307X/28/3/030501
Abstract   PDF(pc) (889KB) ( 442 )
We carry out numerical and theoretical investigations on the global unstable invariant set (manifold) of a saddle-node limit cycle in a leech heart interneuron model. The corresponding global bifurcation is accompanied by an explosion of secondary bifurcations of limit cycles and the emergence of loop-shaped bifurcation structures. The dynamical behaviors of the trajectories of the invariant set are very complicated and can only be partially explained by existing theories.
Existence of Stick-Slip Periodic Solutions in a Dry Friction Oscillator
LI Qun-Hong**, CHEN Yu-Ming, QIN Zhi-Ying
Chin. Phys. Lett. 2011, 28 (3): 030502 .   DOI: 10.1088/0256-307X/28/3/030502
Abstract   PDF(pc) (492KB) ( 573 )
The stick-slip behavior in friction oscillators is very complicated due to the non-smoothness of the dry friction, which is the basic form of motion of dynamical systems with friction. In this paper, the stick-slip periodic solution in a single-degree-of-freedom oscillator with dry friction is investigated in detail. Under the assumption of kinetic friction being the Coulomb friction, the existence of the stick-slip periodic solution is considered to give out an analytic criterion in a class of friction systems. A two-parameter unfolding diagram is also described. Moreover, the time and states of motion on the boundary of the stick and slip motions are semi-analytically obtained in a single stick-slip period.
Resonance and Rectification in a Two-Dimensional Frenkel–Kontorova Model with Triangular Symmetry
YANG Yang, WANG Cang-Long, DUAN Wen-Shan**, CHEN Jian-Min
Chin. Phys. Lett. 2011, 28 (3): 030503 .   DOI: 10.1088/0256-307X/28/3/030503
Abstract   PDF(pc) (576KB) ( 523 )
The mode-locking phenomena in the dc- and ac-driven overdamped two-dimensional Frenkel–Kontorova model with triangular symmetric structures are studied. The obtained results show that the transverse velocity <vx> increases in a series of quantized steps x (n=0, 1, 2, 3 ⋅⋅⋅). Moreover, the positive or negative rectification of longitudinal velocity <vy> can occur when n is an odd number. It is also found in our simulations that the critical depinning force oscillates with the amplitude of ac-driven force, i.e., the system is dominated by the ac-driven force. The oscillatory behavior is strongly determined by the initial phase of ac force.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Flat Currents of Green–Schwarz Superstring in AdS3×S3 under Symmetry Transformations
WANG Zhan-Yun, **, KE San-Min, HAO Kun, SHI Kang-Jie
Chin. Phys. Lett. 2011, 28 (3): 031101 .   DOI: 10.1088/0256-307X/28/3/031101
Abstract   PDF(pc) (449KB) ( 326 )
We show that for Green–Schwarz superstring in AdS3×S3, the one-parameter family of flat currents retains a zero-curvature condition and keeps the variation relations under κ-symmetry, diffeomorphism, local Lorentz SO(1,2)×SO(3) and global PSU(1,1|2)2 symmetry transformations respectively. This indicates that the flat currents exist in all the κ-symmetry gauge fixed cases. As a result, we find that the infinite conserved quantities are invariant under these transformations and independent of the gauge choice of the system.
Nucleon-Nucleon Interaction in Constituent Quark Models
XU Pu, HUANG Hong-Xia, PING Jia-Lun**, WANG Fan
Chin. Phys. Lett. 2011, 28 (3): 031301 .   DOI: 10.1088/0256-307X/28/3/031301
Abstract   PDF(pc) (702KB) ( 352 )
By using the chiral quark model and the quark delocalization colour screening model, the phase shifts of nucleon-nucleon scattering for high partial waves are studied. The results of both the models are almost equivalent. None of the quark models used have found any resonance-like structure in 3F2, 3F3, 3F4 and 3H4 partial waves.
NUCLEAR PHYSICS
Benford's Law in Nuclear Structure Physics
JIANG Hui, SHEN Jia-Jie, ZHAO Yu-Min, **
Chin. Phys. Lett. 2011, 28 (3): 032101 .   DOI: 10.1088/0256-307X/28/3/032101
Abstract   PDF(pc) (728KB) ( 403 )
We investigate Benford's law based on the 2003 version of atomic mass evaluation. It is demonstrated that the first non-zero digit distribution functions for a number of experimental quantities are in reasonable agreement with those predicted by Benford's law. The data that we investigate here include 3001 sets of Sp, 3060 sets of Sn, 2943 sets of two-neutron separation energies S2n, 2826 sets of two-proton separation energies S2p, 1643 sets of β+-decay energies Q(β+), 1243 sets of β--decay energies Q(β), 2595 sets of double β-decay energies Q(ββ), and 2711 sets of energies in electron-capture proton processes Q(ϵp). The first non-zero digits of these data favor the smaller ones in a logarithmic pattern.
ATOMIC AND MOLECULAR PHYSICS
Fine Structures of Atomic Excited States: Precision Atomic Spectroscopy and Electron-Ion Collision Process
GAO Xiang**, CHENG Cheng, LI Jia-Ming,
Chin. Phys. Lett. 2011, 28 (3): 033101 .   DOI: 10.1088/0256-307X/28/3/033101
Abstract   PDF(pc) (392KB) ( 455 )
Scientific research fields for future energies such as inertial confinement fusion researches and astrophysics studies especially with satellite observatories advance into stages of precision physics. The relevant atomic data are not only enormous but also of accuracy according to requirements, especially for both energy levels and the collision data. The fine structure of high excited states of atoms and ions can be measured by precision spectroscopy. Such precision measurements can provide not only knowledge about detailed dynamics of electron-ion interactions but also a bench mark examination of the accuracy of electron-ion collision data, especially incorporating theoretical computations. We illustrate that by using theoretical calculation methods which can treat the bound states and the adjacent continua on equal footing. The precision spectroscopic measurements of excited fine structures can be served as stringent tests of electron-ion collision data.
Magneto-Optical Trapping of 88Sr atoms with 689nm Laser
WANG Qiang**, LIN Bai-Ke, ZHAO Yang, LI Ye, WANG Shao-Kai, WANG Min-Ming, ZANG Er-Jun, LI Tian-Chu, FANG Zhan-Jun
Chin. Phys. Lett. 2011, 28 (3): 033201 .   DOI: 10.1088/0256-307X/28/3/033201
Abstract   PDF(pc) (651KB) ( 614 )
We report the experimental realization of strontium magneto-optical trap (MOT) operating on the intercombination transition 1S03P1 at 689 nm, namely red MOT. A 689 nm laser used for cooling and trapping is injection locked to a master laser, whose linewidth is narrowed to 150 Hz by locking to a high finesse optical reference cavity. 88Sr atoms pre-cooled and trapped by the broad 1S01P1 transition at 461 nm are transferred to the red MOT with the help of a time sequence controller. The transfer ratio is about 20% and the red MOT's temperature is estimated to be less than 20 µK by the time-of-flight (TOF) image analysis.
Modulation Transfer Spectroscopy of Ytterbium Atoms in a Hollow Cathode Lamp
WANG Wen-Li, XU Xin-Ye**
Chin. Phys. Lett. 2011, 28 (3): 033202 .   DOI: 10.1088/0256-307X/28/3/033202
Abstract   PDF(pc) (474KB) ( 635 )
We present the experimental study of modulation transfer spectroscopy of ytterbium atoms in a hollow cathode lamp. The dependences of its linewidth, slope and magnitude on the various experimental parameters are measured and fitted by the well-known theoretical expressions. The experimental results are in good agreement with the theoretical prediction. We have observed the Dicke narrowing effect by increasing the current of the hollow cathode lamp. It is also found that there are the optimal current and laser power to generate the better modulation transfer spectroscopy signal, which can be employed for locking the laser frequency to the atomic transition.
Ultrafast Photodissociation Dynamics of the F State of Sulfur Dioxide by Femtosecond Time-Resolved Pump-Probe Method
ZHANG Dong-Dong, NI Qiang, LUO Si-Zuo, ZHANG Jing, LIU Hang, XU Hai-Feng**, JIN Ming-Xing, DING Da-Jun
Chin. Phys. Lett. 2011, 28 (3): 033301 .   DOI: 10.1088/0256-307X/28/3/033301
Abstract   PDF(pc) (534KB) ( 423 )
A femtosecond pump-probe method is employed to study the dissociation dynamics of sulfur dioxide. SO2 molecules are excited to the F state by absorbing two photons of 267 nm femtosecond laser pulses, and ionized by 400 nm laser pulses at different delay times between the two lasers. Transients of both parent ions (SO2+) and the fragment ions (SO+, S+ and O+) are observed. The SO2+ transient can be well fitted to a biexponential decay comprising a fast and a slow component of 280 fs and 2.97 ps lifetimes, respectively. The SO+ transient consists of two growth components of 270 fs and 2.50 ps. The results clearly show that the F state of SO2 dissociates along an S−O bond. The transients of S+ and O+, however, have different behavior, which consist of a fast growth and a long decay component. A possible mechanism of the fragment formation is discussed to understand the dissociation dynamics of the F state of SO2.
Radiative Decay of Proton Colliding with Rb at Low Energies
ZHOU Yu, QU Yi-Zhi**, LIU Chun-Hua, LIU Xiao-Ju,
Chin. Phys. Lett. 2011, 28 (3): 033401 .   DOI: 10.1088/0256-307X/28/3/033401
Abstract   PDF(pc) (639KB) ( 324 )
The radiative decay and radiative charge transfer cross sections for H++Rb(5s) collisions are calculated by using the optical potential approach, the semiclassical and the fully quantum-mechanical methods, respectively, for the energy range 10-6–10 eV. The radiative association cross sections are obtained by the cross section differences between the radiative decay and radiative charge transfer processes. The relevant molecular data are calculated from the multi-reference single- and double-excitation configuration interaction approach. The emission spectra at resonant and non-resonant energies are analyzed, then the isolated sharp and broad resonances can be identified by their rotational and vibration quantum numbers.
Diffusion and Interface Reaction of Cu/Si (100) Films Prepared by Cluster Beam Deposition
GAO Xing-Xin, JIA Yan-Hui, LI Gong-Ping**, CHO Seong-Jin, KIM Hee
Chin. Phys. Lett. 2011, 28 (3): 033601 .   DOI: 10.1088/0256-307X/28/3/033601
Abstract   PDF(pc) (1688KB) ( 388 )
Cu thin films are deposited on Si (100) substrates by neutral cluster beams and ionized cluster beams. The atomic diffusion and interface reaction between the Cu films and the Si substrates of as-deposited and annealed at different temperatures (230°C, 450°C, 500°C and 600°C) are investigated by Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Some significant results are obtained on the following aspects: (1) For the Cu/Si(100) samples prepared by neutral cluster beams and ionized cluster beams at Va=0 kV, atomic diffusion phenomena are observed clearly in the as-deposited samples. With the increase of annealing temperature, the interdiffusion becomes more apparent. However, the diffusion intensities of the RBS spectra of the Cu/Si(100) films using neutral cluster beams are always higher than that of the Cu/Si(100) films using ionized cluster beams at Va=0 kV in the as-deposited and samples annealed at the same temperature. The compound of Cu3Si is observed in the as-deposited samples. (2) For the Cu/Si(100) samples prepared by ionized cluster beams at Va=1, 3, 5 kV, atomic diffusion phenomena are observed in the as-deposited samples at Va=1, 5 kV. For the samples prepared at Va=3 kV, the interdiffusion phenomenon is observed until 500°C annealing temperature. The reason for the difference is discussed.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Electromagnetic Scattering from Rough Sea Surface with PM Spectrum Covered by an Organic Film
WANG Rui**, GUO Li-Xin, WANG An-Qi, WU Zhen-Sen
Chin. Phys. Lett. 2011, 28 (3): 034101 .   DOI: 10.1088/0256-307X/28/3/034101
Abstract   PDF(pc) (771KB) ( 496 )
The rough sea surface covered by an organic film will cause attenuation of capillarity waves, which implies that the organic films play an important role in rough sea surface processes. We focus on a one-dimensional (1D) rough sea surface with the Pierson–Moskowitz (PM) spectrum distributed to the homogeneous insoluble organic slicks. First, the impact of the organic film on the PM surface spectrum is presented, as well as that of the correlation length, the rms height and slope of the rough sea surface. The damping effect of the organic film changes the physical parameters of the rough sea surface. For example, the organic film will reduce the rms height and slopee of the rough sea surface, which results in the attenuation of the high-frequency components of the PM spectrum leading to modification of the surface PM spectrum. Then, the influence of the organic film on the electromagnetic (EM) scattering coefficients from PM rough sea surface covered by the organic film is investigated and discussed in detail, compared with the clean PM rough sea surface through the method of moments.
Terahertz Generation in Nonlinear Crystals with Mid-Infrared CO2 Laser
LU Yan-Zhao, WANG Xin-Bing**, MIAO Liang, ZUO Du-Luo, CHENG Zu-Hai
Chin. Phys. Lett. 2011, 28 (3): 034201 .   DOI: 10.1088/0256-307X/28/3/034201
Abstract   PDF(pc) (812KB) ( 867 )
The terahertz (THz) generation based on difference frequency generation in nonlinear optical crystals pumped by mid-infrared CO2 laser has been investigated. We present a comprehensive study of the phase-matching conditions in the GaSe, ZnGeP2 and GaAs crystals. A comparison of the characteristics of these crystals as the THz frequency generator is also presented. The investigation of the conversion efficiency shows that GaSe and GaAs are the most promising nonlinear crystals for the efficient and widely tunable THz generation.
Optimization of Supercontinuum Sources for Ultra-Broadband T-CARS Spectroscopy
LIU Xing, LIU Wei, YIN Jun, QU Jun-Le, LIN Zi-Yang, NIU Han-Ben**
Chin. Phys. Lett. 2011, 28 (3): 034202 .   DOI: 10.1088/0256-307X/28/3/034202
Abstract   PDF(pc) (559KB) ( 486 )
For a typical photonic crystal fiber with two zero-dispersion wavelengths, we theoretically demonstrate a new way to generate supercontinuum using an input pulse of 30 fs duration and 10 kW peak power for providing a compact and cost effective light source to the ultra-broadband time-resolved coherent anti-Stokes Raman scattering spectroscopy.
Magneto-optic Crystal Polarization Controller Assisted Mode-Locked Fiber Laser
ZHAO Guang-Zhen, GUI Li-Li, XIAO Xiao-Sheng, YANG Chang-Xi**
Chin. Phys. Lett. 2011, 28 (3): 034203 .   DOI: 10.1088/0256-307X/28/3/034203
Abstract   PDF(pc) (662KB) ( 511 )
We report a passively mode-locked erbium-doped fiber laser based on a compact magneto-optic crystal polarization controller. The length of the polarization controller consisting of four magneto-optic crystal rotators and two quarter wave-plates is only 10 cm. Adjusting the polarization controller, central wavelength around 1559 nm and repetition rate 21.10 MHz mode-locked pulse are obtained. Pulse duration and 3 dB spectrum width are 598.4 fs and 6.24 nm respectively. Single pulse energy is about 151.7 pJ. Because of its small size, low insertion loss, good controllability and negligible dispersion, the magneto-optic crystal polarization controller could be an ideal polarization controller in fiber lasers.
Extending the Bandwidth of Electric Ring Resonator Metamaterial Absorber
LUO Hao, WANG Tao, GONG Rong-Zhou**, NIE Yan, WANG Xian
Chin. Phys. Lett. 2011, 28 (3): 034204 .   DOI: 10.1088/0256-307X/28/3/034204
Abstract   PDF(pc) (656KB) ( 947 )
An efficient method is proposed to extend the bandwidth of a metamaterial absorber with multi-resonance structure. The basic unit cell of a metamaterial absorber consists of the electric ring resonator, dielectric substrate (FR-4) and split-wire. By assembling five sandwiched structures with different geometric dimensions into a unit cell, we obtain the superposition of five different absorption peaks. Finally, the bandwidth of metamaterial absorption is extended and the full width at half maximum is up to 1.3 GHz. The simulated and experimental results are consistent.
Impact of Spectral Filter on Phase Modulation Pulse in Fiber Front End System
LI Jing, WANG Jian-Jun, XU Dang-Peng, LIN Hong-Huan, GENG Yuan-Chao, LI Ming-Zhong, DENG Ying, ZHU Na, ZHANG Rui, JING Feng**
Chin. Phys. Lett. 2011, 28 (3): 034205 .   DOI: 10.1088/0256-307X/28/3/034205
Abstract   PDF(pc) (746KB) ( 493 )
The transmission characteristics of phase modulation pulse transmitted through the filter in the power amplifier are investigated theoretically and experimentally. The narrow bandpass filter can induce large temporal modulation depth for the phase modulation pulse and induce double amplitude modulation (AM) if the frequency shift is lower than half bandwidth of the signal spectrum. We should choose a wider bandwidth filter to minimize the impact of the filter on the output pulse and suppress the amplified spontaneous emission (ASE) for the power fiber amplifier. These results are of benefit to the design of the fiber front end system.
Modified Raman Response Model and Supercontinuum Generation in Flat Dispersion Photonic Crystal Fiber with Two-Zero Dispersion Wavelengths
WANG He-Lin, YANG Ai-Jun**, LENG Yu-Xin, WANG Cheng
Chin. Phys. Lett. 2011, 28 (3): 034206 .   DOI: 10.1088/0256-307X/28/3/034206
Abstract   PDF(pc) (933KB) ( 617 )
The generation mechanisms of supercontinuum (SC) and the effect of the modified Raman model on SC are further analyzed in a flat dispersion photonic crystal fiber (PCF) with two-zero dispersion wavelengths (TZDWs) by introducing an accurate Raman response function in the scalar nonlinear Schrödinger equation. The results show that the introduction of Boson peak in the modified Raman gain model not only results in much rapider broadening of SC but also promotes more pump pulse energy transferred to the short wavelength region, which is related to stimulated Raman scattering. Moreover, SC generated from the PCF splits into two spectral bands, and their spectral peaks rapidly separate and broaden with the increase of incident power. Double-band central wavelengths are finally located at about 850 nm and 1220 nm. The pumping energy depletion phenomenon occurs. The simulated results from the modified Raman model are in better agreement with the experimental results than that from the single-Lorentzian model.
Cooperative Quantum Cutting in Er3+/Yb3+ Codoped Oxyfluoride Glass Ceramics
LUO Shi-Qiang, ZHAO Li-Juan**, HU Nan, ZHANG Ming, ZHANG Pan, WANG Ya-Zhou, YU Hua**
Chin. Phys. Lett. 2011, 28 (3): 034207 .   DOI: 10.1088/0256-307X/28/3/034207
Abstract   PDF(pc) (598KB) ( 447 )
Oxyfluoride glass ceramics doped with Er3+/Yb3+ was synthesized. Rare earth ions are doped into fluoride nanocrystals according to x-ray diffractive patterns. The enhanced red emission of Er3+/Yb3+ in the fluoride nanocrystals, excited by xenon lamp at 449 nm, is investigated and analyzed by cooperative quantum cutting mode. The cross relaxation appears from 4F5/24F9/2 to 4I15/24I13/2 because of the nearer distance of rare earth ions and the larger absorption section of 4I15/24I13/2 in the quantum cutting. It results in two emissions of 4F9/24I15/2 and 4I13/24I15/2. This implies that a 449 nm photon could dissolve into two photons with wavelength 665 nm and 1530 nm. This could be an effective way to obtain 1530 nm emission for optical communication.
Enhancing the Robustness of the Microcavity Coupling System
YAN Ying-Zhan, JI Zhe, YAN Shu-Bin**, LIU Jun, XUE Chen-Yang, ZHANG Wen-Dong, XIONG Ji-Jun**
Chin. Phys. Lett. 2011, 28 (3): 034208 .   DOI: 10.1088/0256-307X/28/3/034208
Abstract   PDF(pc) (632KB) ( 424 )
A novel method to enhance the robustness of the microcavity coupling system (MCS) is presented by encapsulating and solidifying the MCS with a low refractive index (RI) curable UV polymer. The encapsulating process is illustrated in detail for a typical microsphere with a radius of R about 240 µm. Three differences of the resonant characteristics before and after the package are observed and analyzed. The first two differences refer to the enhancement of the coupling strength and the shift of the resonant spectrum to the longer wavelength, which are both mainly because of the microsphere surrounding RI variation. Another difference is the quality factor (Q-factor) which decreases from 7.8×107 to 8.7×106 after the package due to the polymer absorption. Moreover, rotation testing experiments have been carried out to verify the robustness of the package MCS. Experimental results demonstrate that the packaged MCR has much better robust performance than the un-package sample. The enhancement of the robustness greatly promotes the microcavity research from fundamental investigations to application fields.
Improved Plane-Wave Expansion Method for Band Structure Calculation of Metal Photonic Crystal
JIANG Bin, ZHOU Wen-Jun, CHEN Wei, LIU An-Jin, ZHENG Wan-Hua, **
Chin. Phys. Lett. 2011, 28 (3): 034209 .   DOI: 10.1088/0256-307X/28/3/034209
Abstract   PDF(pc) (645KB) ( 1477 )
We combine Cartesian coordinates and polar coordinates wave number eigenvalue equations based on the plane-wave expansion (PWE) method to calculate and optimize the band structures of the two-dimensional (2D) metal photonic crystals (PhCs). Compared with the traditional PWE methods for metal PhCs, the band structures can be calculated directly in our method and no further procedures are needed to handle the folded band structures. With this method, we optimize the large gap-midgap ratio of the 2D square lattice of square metal rods and circular metal rods. The TM gap-midgap ratio of the 2D square lattice of square metal rods reaches 7.6246% with the side length L=0.71a with a being the lattice constant. The TM gap-midgap ratio of the 2D square lattice of circular metal rods reaches 16.3934% with radius R= 0.45a. Our method can be easily used in both square lattice and triangular lattice directly.
An Adaptive Objective Function for Evaporation Duct Estimations from Radar Sea Echo
ZHANG Jin-Peng, WU Zhen-Sen**, WANG Bo
Chin. Phys. Lett. 2011, 28 (3): 034301 .   DOI: 10.1088/0256-307X/28/3/034301
Abstract   PDF(pc) (529KB) ( 458 )
In the process of atmospheric refractivity estimation from radar sea echo, the objective function that calculates the match between the predicted and observed field plays an important role. To reduce the effect of noises from long ranges on the objective function, we present a selection method of final ranges for inversion. An adaptive objective function is introduced with a linear distance weight added to the least squares error function (LSEF). Through an evaporation duct height (EDH) retrieving process, the performance of the adaptive objective function is evaluated. The result illustrates that the present method performs better than the LSEF in EDH inversions from clutters with different clutter-to-noise ratios.
Experiment Observation on Acoustic Forward Scattering for Underwater Moving Object Detection
LEI Bo**, MA Yuan-Liang, YANG Kun-De
Chin. Phys. Lett. 2011, 28 (3): 034302 .   DOI: 10.1088/0256-307X/28/3/034302
Abstract   PDF(pc) (745KB) ( 481 )
The problem of detecting an object in shallow water by observing changes in the acoustic field as the object passes between an acoustic source and receiver is addressed. A signal processing scheme based on forward scattering is proposed to detect the perturbed field in the presence of the moving object. The periodic LFM wideband signal is transmitted and a sudden change of field is acquired using a normalized median filter. The experimental results on the lake show that the proposed scheme is successful for the detection of a slowly moving object in the bistatic blind zone.
Applications of Waveguide Invariant Theory to the Analysis of Interference Phenomena in Deep Water
LI Qian-Qian, **, LI Zheng-Lin, ZHANG Ren-He
Chin. Phys. Lett. 2011, 28 (3): 034303 .   DOI: 10.1088/0256-307X/28/3/034303
Abstract   PDF(pc) (1221KB) ( 512 )
The waveguide invariant, denoted as β, can be used to describe the slope of the intensity of a broadband acoustic signal. In deep water, the interference patterns of the areas with dominant waterborne modes and only with bottom bounce modes are greatly different. This phenomenon is illustrated by simulation and explained by the distribution of β. The theory shows that in the convergence zone, β approaches infinity, which leads to the larger slope of sound intensity; on the contrary, in the shadow zone, β is close to 1, leading to smaller slopes.
Tortuosity of Flow Paths through a Sierpinski Carpet
LI Jian-Hua, YU Bo-Ming**
Chin. Phys. Lett. 2011, 28 (3): 034701 .   DOI: 10.1088/0256-307X/28/3/034701
Abstract   PDF(pc) (428KB) ( 587 )
Sierpinski carpet is an exactly self-similar fractal, which is often used to simulate fractal porous media. A simple recursive model for the tortuosity of flow path in Sierpinski carpet is derived based on the self-similarity of the carpet. The proposed model is related to the stage of the carpet, and there is no empirical constant in this model. The model predictions are compared with those from available correlations by both numerical and experimental methods as well as analysis. Good agreement is found between the present model predictions and those from the available correlations. The present model may have the potential in analysis of transport properties in self-similar fractals.
A Mathematical Model for Studying the Slip Effect on Peristaltic Motion with Heat and Mass Transfer
Tasawar Hayat, **, Najma Saleem, Awatif A. Hendi
Chin. Phys. Lett. 2011, 28 (3): 034702 .   DOI: 10.1088/0256-307X/28/3/034702
Abstract   PDF(pc) (438KB) ( 356 )
A mathematical model is presented with an interest to examine the peristaltic motion in an asymmetric channel by taking into account the slip, heat and mass transfer. Constitutive relationships for a micropolar fluid are used. The solution procedure for nonlinear analysis is given under long wavelength and low Reynolds number approximations. The effects of sundry parameters entering into the expressions of axial velocity, temperature and concentration are explored. Pumping and trapping phenomena are discussed.
Statistical Analysis of Coherent Vortical Structures in a Supersonic Turbulent Boundary Layer
WANG Li, LU Xi-Yun**
Chin. Phys. Lett. 2011, 28 (3): 034703 .   DOI: 10.1088/0256-307X/28/3/034703
Abstract   PDF(pc) (565KB) ( 477 )
coherent vortical structures in a compressible turbulent boundary layer are statistically analyzed by means of direct numerical simulation of the compressible Navier–Stokes equations for Mach number M=2 and Reynolds number Reθ1000 based on the inlet momentum thickness. It is found that a large variety of hairpin-like and cane-like vortical structures exist in the boundary layer and the most popular structure is the cane-like one. The injection and sweep events contribute a major proportion of the total Reynolds stress. This study indicates structural similarities with the incompressible case. Moreover, the length scales of coherent structures in the streamwise and spanwise directions increase with the distance from the wall. The inclination angle of coherent vortical structures with respect to the streamwise direction increases from the sublayer to the buffer layer and then decreases from the buffer layer to the wake region.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Effects of Laser Parameters on Fast Electron Generation in a Multihole Array Target
JI Yan-Ling, DUAN Tao, JIANG Gang, WU Wei-Dong, TANG Yong-Jian**
Chin. Phys. Lett. 2011, 28 (3): 035201 .   DOI: 10.1088/0256-307X/28/3/035201
Abstract   PDF(pc) (659KB) ( 329 )
The effects of laser parameters on the production of fast electrons from laser-multihole array target interaction are investigated theoretically via two-dimensional particle-in-cell simulations. The results show that the fast electron temperature is scaled by I1/2λ2 with I and λ being the laser intensity and wavelength. When the laser intensity reaches 2.14×1020 W⋅cm−2, a typical bi-Maxwellian energy distribution is observed. The slope temperature of the low-energy component fits the linear scaling Th∼I1/2 well. The high-energy component has an increased slope temperature comparable to ponderomotive potential scaling law. In addition, the electron temperature rises linearly with the pulse duration, Th∼Δt. The divergence angle of the fast electrons increases with laser intensity and pulse duration, but is independent of laser wavelength.
Self-Assembled Wire Arrays and ITO Contacts for Silicon Nanowire Solar Cell Applications
YANG Cheng, ZHANG Gang, LEE Dae-Young, LI Hua-Min, LIM Young-Dae, YOO Won Jong**, PARK Young-Jun, KIM Jong-Min
Chin. Phys. Lett. 2011, 28 (3): 035202 .   DOI: 10.1088/0256-307X/28/3/035202
Abstract   PDF(pc) (784KB) ( 634 )
Self-assembly of silicon nanowire (SiNW) arrays is studied using SF6/O2 plasma treatment. The self-assembly method can be applied to single- and poly-crystalline Si substrates. Plasma conditions can control the length and diameter of the SiNW arrays. Lower reflectance of the wire arrays over the wavelength range 200–1100 nm is obtained. The conducting transparent indium-tin-oxide (ITO) electrode can be fully coated on the self-assembled SiNW arrays by sputtering. The ITO-coated SiNW solar cells show the same low surface light reflectance and a higher carrier collection efficiency than SiNW solar cells without ITO coating. An efficiency enhancement of around 3 times for ITO coated SiNW solar cells is demonstrated via experiments.
Time-Resolved Radiography using Chirp-Pulse Proton Beams
TENG Jian, ZHAO Zong-Qing, ZHU Bin, HONG Wei, CAO Lei-Feng, ZHOU Wei-Min, SHAN Lian-Qiang, GU Yu-Qiu**
Chin. Phys. Lett. 2011, 28 (3): 035203 .   DOI: 10.1088/0256-307X/28/3/035203
Abstract   PDF(pc) (1603KB) ( 438 )
Protons accelerated by the target normal sheath acceleration (TNSA) mechanism have a wide energy spectrum and are called chirp-pulse protons. The numerical simulation of chirp-pulse proton radiography in an implosion process with single shot is carried out using the Monte Carlo method. Two different methods are proposed. The first method, proton framing radiography, uses a stack of radiochromic film layers as the detector. Each layer deposits protons with energy corresponding to the Bragg peak, which can record the transient state of the implosion process. The second method, proton streak radiography, uses an external magnetic field to deflect protons. Different energies correspond to different times. By using a slit before the magnetic field, one-dimensional spatial resolution and temporal resolution can be obtained. This method is more suitable for the diagnosis of the implosion process.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Growth of Zinc Blende GaAs/AlGaAs Radial Heterostructure Nanowires by a Two-Temperature Process
GUO Jing-Wei**, HUANG Hui, REN Xiao-Min, YAN Xin, CAI Shi-Wei, GUO Xin, HUANG Yong-Qing, WANG Qi, ZHANG Xia, WANG Wei
Chin. Phys. Lett. 2011, 28 (3): 036101 .   DOI: 10.1088/0256-307X/28/3/036101
Abstract   PDF(pc) (799KB) ( 481 )
Zinc blende structure GaAs/AlGaAs core-multishell nanowires (NWs) are grown on a GaAs(111) B substrate by a two-temperature process using an Au-catalyzed vapor-liquid-solid mechanism and metal organic chemical vapor deposition, respectively. Defect-free radial heterostructure NWs are formed. It can be concluded that the NWs are grown with the main contributions from the direct impingement of the precursors onto the alloy droplets and little from adatom diffusion. The results indicate that the droplet acts as a catalyst rather than an adatom collector. The photoluminescence spectra reveal that the grown NWs have much higher optical efficiency than bare GaAs NWs.
Wetting of Liquid Iron in Carbon Nanotubes and on Graphene Sheets: A Molecular Dynamics Study
GAO Yu-Feng, YANG Yang, SUN De-Yan**
Chin. Phys. Lett. 2011, 28 (3): 036102 .   DOI: 10.1088/0256-307X/28/3/036102
Abstract   PDF(pc) (669KB) ( 564 )
Using molecular dynamics simulations, we study the wetting of liquid iron in a carbon nanotube and on a graphene sheet. It is found that the contact angle of a droplet in a carbon nanotube increases linearly with the increase of wall curvature but is independent of the length of the filled liquid. The contact angle for a droplet on a graphene sheet decreases with the increasing droplet size. The line tension of a droplet on a graphene sheet is also obtained. Detailed studies show that liquid iron near the carbon walls exhibits the ordering tendencies in both the normal and tangential directions.
Formation and Compression Behavior of Two-Phase Bulk Metallic Glasses with a Minor Addition of Aluminum
ZONG Hai-Tao, MA Ming-Zhen, ZHANG Xin-Yu, QI Li, LI Gong, JING Qin, LIU Ri-Ping**
Chin. Phys. Lett. 2011, 28 (3): 036103 .   DOI: 10.1088/0256-307X/28/3/036103
Abstract   PDF(pc) (1022KB) ( 502 )
A remarkable enhancement in room-temperature compressive deformability is realized by the minor-addition of 1.5 at.% Al in ZrTi-based bulk metallic glass. Two amorphous phases are observed by transmission electron microscopy in the Al-containing alloys and this explains the improvement of compression deformability. The studies suggest that phase separation might occur in glass forming alloys with a negative enthalpy of mixing.
Denuded Zone Formation in Germanium Codoped Heavily Phosphorus-Doped Czochralski Silicon
LIN Li-Xia, CHEN Jia-He, WU Peng, ZENG Yu-Heng, MA Xiang-Yang, YANG De-Ren**
Chin. Phys. Lett. 2011, 28 (3): 036104 .   DOI: 10.1088/0256-307X/28/3/036104
Abstract   PDF(pc) (1534KB) ( 710 )
The formation of a denuded zone (DZ) by conventional furnace annealing (CFA) and rapid thermal annealing (RTA) based denudation processing is investigated and the gettering of copper (Cu) atoms in germanium co-doped heavily phosphorus-doped Czochralski (GHPCZ) silicon wafers is evaluated. It is suggested that both a good quality defect-free DZ with a suitable width in the sub-surface area and a high density bulk micro-defect (BMD) region could be formed in heavily phosphorus-doped Czochralski (HPCZ) silicon and GHPCZ silicon wafers. This is ascribed to the formation of phosphorus-vacancy (P-V) related complexes and germanium-vacancy (Ge-V) related complexes. Compared with HPCZ silicon, the DZ width is wider in the GHPCZ silicon sample with CFA-based denudation processing but narrower in the one with two-step RTA pretreatments. These phenomena are ascribed to the enhancing effect of germanium on oxygen out-diffusion movement and oxygen precipitate nucleation, respectively. Furthermore, fairly clean DZs near the surface remain in both the HPCZ and GHPCZ silicon wafers after Cu in-diffusion, except for the HPCZ silicon wafer which underwent denudation processing with a CFA pretreatment, suggesting that germanium doping could improve the gettering of Cu contamination.
Influence of Oxygen in Sputtering and Annealing Processes on Properties of ZnO:Ag Films Deposited by rf Sputtering
DUAN Li**, GAO Wei
Chin. Phys. Lett. 2011, 28 (3): 036105 .   DOI: 10.1088/0256-307X/28/3/036105
Abstract   PDF(pc) (521KB) ( 553 )
ZnO:Ag films were prepared by rf sputtering on Si substrates. A detailed study on as-grown and annealed films was carried out using x-ray diffraction (XRD). The results indicate that the film crystalline quality and the Ag doping efficiency were both influenced by oxygen in the sputtering and annealing atmosphere. The optimum conditions are found. Ultraviolet and green emissions of annealed ZnO:Ag films were observed at room temperature. Photoluminescence results show that oxygen in annealing atmosphere reduces the deep-level defects in ZnO:Ag and increases the film quality.
Computer Simulation of the Electronic Structures and Absorption Spectra for a KMgF3 Crystal Containing a Potassium Vacancy
CHENG Fang, LIU Ting-Yu**, ZHANG Qi-Ren, QIAO Hai-Ling, ZHOU Xiu-Wen
Chin. Phys. Lett. 2011, 28 (3): 036106 .   DOI: 10.1088/0256-307X/28/3/036106
Abstract   PDF(pc) (739KB) ( 495 )
CASTEP code, based on the density functional theory (DFT) Electronic structures and absorption spectra for a perfect KMgF3 crystal and a KMgF3 crystal containing a potassium vacancy VK are optimized using the CASTEP density functional theory code. The calculated results indicate that the perfect KMgF3 crystal has no absorption in the visible energy region, however, a KMgF3 crystal containing VK has an additional absorption band peaking at 565 nm, fitting well with the experimental result that KMgF3 irradiated by an electron has an additional absorption peak at 565 nm. It is reasonably predicted that the 565 nm absorption band is related to the existence of VK in the KMgF3 crystal created by the electron irradiation.
First Principles Study of Dopant Site Selectivity in Ordered Perovskite CaCu3Ti4O12
XU Li-Chun, WANG Ru-Zhi**, DENG Yang, YAN Hui
Chin. Phys. Lett. 2011, 28 (3): 036107 .   DOI: 10.1088/0256-307X/28/3/036107
Abstract   PDF(pc) (556KB) ( 531 )
We investigate the dopant site selectivity of CaCu3Ti4O12 (CCTO) using the first principles calculations. Our results show that, for four cases of possible occupancy by La atom, lattice expansions and formation enthalpies with different dopant quantities indicate that doped La cations are preferentially substituted for Ca sites in CaCu3Ti4O12, which is excellent in agreement with the experimental observation (Choi et al. Adv. Mater. 21 (2009) 885). Furthermore, more interesting information of doping is also explored by the analysis of density of states and it is found that La substituting for Cu may advance the electron conduction in CCTO. It supplies a potential solution for limitations of CCTO devices by exploring the effect when La substitutes for Cu sites in the CCTO crystal.
Deep Energy Levels Formed by Se Implantation in Si
GAO Li-Peng, HAN Pei-De**, MAO Xue, FAN Yu-Jie, HU Shao-Xu, ZHAO Chun-Hua, MI Yan-Hong
Chin. Phys. Lett. 2011, 28 (3): 036108 .   DOI: 10.1088/0256-307X/28/3/036108
Abstract   PDF(pc) (634KB) ( 509 )
To transfer a photon with a 1.55 μm wavelength into an electron in an integrated optoelectronic silicon waveguide detector, selenium-doped silicon with deep energy levels is used. The deep levels in the silicon with implanted selenium are studied. Three levels are observed and their captured cross sections, concentrations and in-depth profiles are measured.
Critical Free Volume Concentration of Shear Banding Instability in Metallic Glasses
LIU Long-Fei**, CAI Zhi-Peng, LI Hui-Qiang, ZHANG Guang-Ye, GUO Shi-Bo
Chin. Phys. Lett. 2011, 28 (3): 036201 .   DOI: 10.1088/0256-307X/28/3/036201
Abstract   PDF(pc) (605KB) ( 486 )
We present a model which predicts the critical free volume concentration of shear banding instability in metallic glasses (MGs). From the stability map, this model demonstrates that the prediction of shear band thickness is valid only for a short time after shear instability, and the diffusion of defects should be included in the mature shear band in MGs. The results agree well with the experimental observations and simulations.
Isotropic Thermal Expansivity and Anisotropic Compressibility of ReB2
LIU Xi**, LIU Wei, HE Qiang, DENG Li-Wei, WANG He-Jin, HE Duan-Wei, LI Bao-Sheng
Chin. Phys. Lett. 2011, 28 (3): 036401 .   DOI: 10.1088/0256-307X/28/3/036401
Abstract   PDF(pc) (644KB) ( 536 )
We experimentally investigated some of the mechanical properties of ReB2 under high temperature/pressure (T/P) conditions. High-T experiments (up to 600°C at 1 atm) were carried out in a high-T oven attached to a conventional x-ray diffractometer and high-P experiments (up to about 42 GPa at 25°C) were conducted in a diamond-anvil cell using synchrotron x-ray radiation. The high-T data for ReB2 suggests a highly isotropic thermal expansivity, whereas the high-P data suggests a highly anisotropic compressibility.
Epitaxial Growth of Si(111)/Er2O3 (111) Structure on Si(111) by Molecular Beam Epitaxy
XU Run**, TANG Min-Yan, ZHU Yan-Yan, WANG Lin-Jun
Chin. Phys. Lett. 2011, 28 (3): 036801 .   DOI: 10.1088/0256-307X/28/3/036801
Abstract   PDF(pc) (2284KB) ( 908 )
The Si overlayers are grown by molecular beam epitaxy on atomically smooth Er2O3(111) films prepared on Si(111) substrates. Single crystalline Si overlayers are achieved and are evident due to the spot-like reflective high energy electron diffraction (RHEED) patterns and x-ray diffraction patterns. The epitaxial relationship of the Si overlayer along the surface with respect to the orientation of Er2O3 and the Si substrate is as follows: overgrown Si(111)//Er2O3(111)//Si(111). The rough surface of Si overlayers, as identified by both RHEED patterns and atomic force microscopy images, indicates a three-dimensional growth mode. The reason for this is based on the interfacial energy argument. Further growth of Er2O3 films on this rough Si overlayer leads to the polycrystalline nature of the topmost Er2O3 layer.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Electronic Structure and Optical Properties of Layered Ternary Carbide Ti3AlC2
JIANG Jiu-Xing, **, JIN Shan, WANG Zhen-Hua, TAN Chang-Long
Chin. Phys. Lett. 2011, 28 (3): 037101 .   DOI: 10.1088/0256-307X/28/3/037101
Abstract   PDF(pc) (591KB) ( 561 )
The electronic structure and optical properties of the layered ternary compound Ti3AlC2 are studied by the plane-wave psedudopotential method within the generalized gradient approximation. The results show that Ti3AlC2 is an electronic conductor. The total density of states at the Fermi level mainly originates from Ti d states. Moreover, it is found that the reflectivity is nonselective in the visible region. In particular, the reflectivity is high in the ultraviolet region, indicating that Ti3AlC2 can be a promising candidate for use as an anti-ultraviolet ray coating material. Furthermore, the mechanism of the optical properties is investigated on the basis of the electronic structure.
Cathodoluminescence of Yellow and Blue Luminescence in Undoped Semi-insulating GaN and n-GaN
HOU Qi-Feng**, WANG Xiao-Liang, XIAO Hong-Ling, WANG Cui-Mei, YANG Cui-Bai, YIN Hai-Bo, LI Jin-Min, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (3): 037102 .   DOI: 10.1088/0256-307X/28/3/037102
Abstract   PDF(pc) (707KB) ( 741 )
Yellow and blue luminescence in undoped GaN layers with different resistivities are studied by cathodoluminescence. Intense yellow and blue luminescence bands are observed in semi-insulating GaN, while in n-GaN the yellow luminescence and blue luminescence bands are very weak. The stronger yellow and blue luminescences in semi-insulating GaN are correlated to the higher edge-type dislocation density. The scanning cathodoluminescence image reveals strong defect-related luminescence at the grain boundaries where the dislocations accumulate. It is found that the relative intensity of the blue luminescence band to the yellow luminescence band increases with the cathodoluminescence beam energies and is larger in n-GaN with a lower density of edge-type dislocations. An approximately 3.35 eV shoulder next to the near-band-edge peak is observed in n-GaN but not in semi-insulating GaN. A redshift of the near-band-edge peak with cathodoluminescence beam energy is observed in both samples and is explained by internal absorption.
Exchange Enhancement of Spin-Splitting in AlxGa1−xN/GaN Heterostructures in Tilted Magnetic Fields
TANG Ning**, HAN Kui, LU Fang-Chao, DUAN Jun-Xi, XU Fu-Jun, SHEN Bo
Chin. Phys. Lett. 2011, 28 (3): 037103 .   DOI: 10.1088/0256-307X/28/3/037103
Abstract   PDF(pc) (527KB) ( 295 )
AlxGa1−xN/GaN heterostructures are investigated by magnetotransport experiments in tilted magnetic fields at low temperatures. The spin-split peaks of the Shubnikov-de Haas (SdH) oscillations are observed at high magnetic fields, which are attributed to the Zeeman spin-splitting of the two-dimensional electron gas at the heterointerface. The exchange enhanced g* of the spin-splitting is investigated by measuring the positions of the pairs of spin-split SdH maxima. Moreover, it is found that g* becomes smaller with the increasing tilt angle, which suggests the anisotropy of g* is due to the strong polarization-induced electric field at the AlxGa1−xN/GaN heterointerface.
Simultaneous Enhancement of Electrical Conductivity and Seebeck Coefficient of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Films Treated with Urea
KONG Fang-Fang, LIU Cong-Cong, XU Jing-Kun**, JIANG Feng-Xing, LU Bao-Yang, YUE Rui-Rui, LIU Guo-Dong, WANG Jian-Min
Chin. Phys. Lett. 2011, 28 (3): 037201 .   DOI: 10.1088/0256-307X/28/3/037201
Abstract   PDF(pc) (1008KB) ( 980 )
The thermoelectric performance of free-standing poly(3,4-ethylenedioythiophene): poly(styrenesulfonate) (PEDOT:PSS) thin films deposited from aqueous dispersion treated by different concentrations of urea are investigated in detail. The electrical conductivity, Seebeck coefficient and power factor of PEDOT:PSS films versus temperature are determined, respectively. It is found that both the electrical conductivity and Seebeck coefficient of PEDOT:PSS films are enhanced after treatment with urea. Conductivity could be enhanced from 8.16 to 63.13 S⋅cm−1, the Seebeck coefficient is increased from 14.47 to 20.7 µV⋅K−1 and the power factor is rises to 2.7 µW⋅m−1K−2 at 300 K.
Coupling of a Tl2Ba2CaCu2O8 Thin Film Intrinsic Josephson Junction and a Fabry–Perot Resonator
FAN Bin, WANG Zheng, YUE Hong-Wei, YAN Shao-Lin**, JI Lu, HE Ming, SONG Feng-Bin, FANG Lan, ZHAO Xin-Jie
Chin. Phys. Lett. 2011, 28 (3): 037401 .   DOI: 10.1088/0256-307X/28/3/037401
Abstract   PDF(pc) (1145KB) ( 385 )
We study the electromagnetic coupling mechanism of a Tl2Ba2CaCu2O8 (Tl-2212) thin film intrinsic Josephson junction to a hemispherical Fabry–Perot resonator. An effective model to analyze coupling mechanism is put forward. The dielectric substrate is used as a dielectric resonator antenna and the Josephson junction, and a superconducting film is used as the feed line to excite a resonance mode inside the dielectric resonator antenna. To confirm this method, two Josephson junction samples with different dimensions of substrate and shapes of superconducting film are fabricated and tested under microwave irradiations. At the same time, numerical simulations of the antenna characteristics and the field distribution of these samples are performed by numerical simulation. The different coupling intensities of the two samples with the Fabry–Perot resonator fit well with the numerical simulation results. The proposed model is important for Josephson junctions used in the microwave field.
Noncollinear Magnetism Calculation of Iron Clusters with Spin-Orbit Coupling
CHENG Zhi-Da, ZHU Jing, **, TANG Zheng
Chin. Phys. Lett. 2011, 28 (3): 037501 .   DOI: 10.1088/0256-307X/28/3/037501
Abstract   PDF(pc) (614KB) ( 714 )
We study iron clusters containing 2∼13 atoms by ab initio calculations with both collinear and noncollinear magnetic methods. Spin-orbit coupling is only available in the noncollinear method. After full structural relaxations, it is found that atom positions derived from the noncollinear method have better stability in all clusters, including those having coparallel spin arrangements. Binding energies of clusters calculated by the noncollinear method are also 17.3∼19.8 meV/atom lower, which are too large to ignore. By comparing the magnetic properties and electronic structures from the two methods, we believe that the difference has resulted from spin-orbit coupling. We recommend reconsidering the importance of the noncollinear magnetic method with spin-orbit coupling in magnetic systems. Especially in transition metal clusters when atom positions and energy values are important for determining the crucial properties.
Electron Paramagnetic Resonance and Optical Absorption of VO2+ Doped Ammonium Selenate Single Crystals
Ram Kripal**, Ashutosh Kumar Shukla
Chin. Phys. Lett. 2011, 28 (3): 037601 .   DOI: 10.1088/0256-307X/28/3/037601
Abstract   PDF(pc) (511KB) ( 359 )
An electron paramagnetic resonance study of vanadyl ions doped in ammonium selenate single crystals is carried out at room temperature. It is found that the VO2+ ion takes up an interstitial site. The spin Hamiltonian parameters obtained from the crystal rotations are g|| =1.9576 ±0.0002, g=1.9889±0.0002, A||=203±2 G, A=78± 2 G. An optical absorption study is also carried out to evaluate various bonding parameters. On the basis of these parameters the nature of bonding in the complex is discussed.
Microwave Absorption Properties of Ni-Foped SiC Powders in the 2–18GHz Frequency Range
JIN Hai-Bo**, LI Dan, CAO Mao-Sheng, DOU Yan-Kun, CHEN Tao, WEN Bo, Simeon Agathopoulos
Chin. Phys. Lett. 2011, 28 (3): 037701 .   DOI: 10.1088/0256-307X/28/3/037701
Abstract   PDF(pc) (616KB) ( 633 )
Ni-doped SiC powder with improved dielectric and microwave absorption properties was prepared by self-propagating high-temperature synthesis (SHS). The XRD analysis of the as-synthesized powders suggests that Ni is accommodated in the sites of Si in the lattice of SiC, which shrinks in the presence of Ni. The experimental results show an improvement in the dielectric properties of the Ni-doped SiC powder in the frequency range of 2–18 GHz. The bandwidth of the reflection loss below −10 dB is broadened from 3.04 (for pure SiC) to 4.56 GHz (for Ni-doped SiC), as well as the maximum reflection loss of produced powders from 13.34 to 22.57 dB, indicating that Ni-doped SiC could be used as an effective microwave absorption material.
Enhanced Ferromagnetism and Microwave Dielectric Properties of Bi0.95Y0.05FeO3 Nanocrystals
HOU Zhi-Ling**, ZHOU Hai-Feng, YUAN Jie, KANG Yu-Qing, YANG Hui-Jing, JIN Hai-Bo, CAO Mao-Sheng**
Chin. Phys. Lett. 2011, 28 (3): 037702 .   DOI: 10.1088/0256-307X/28/3/037702
Abstract   PDF(pc) (729KB) ( 901 )
Bi0.95Y0.05FeO3 nanocrystals are synthesized by a hydrothermal method, and are crystallized in a rhombohedrally distorted perovskite BiFeO3 structure in the R3c space, with compressive lattice distortion induced by the Y substitution at Bi sites from XRD study. Compared with BiFeO3 gained under similar conditions, the magnetic properties are greatly enhanced, with saturate magnetization of 2.3 emu/g at room temperature. Microwave dielectric properties of Bi0.95Y0.05FeO3 nanocrystals are investigated in the range of 2–18 GHz. The Y substitution results in the increase of permeability and decrease of permittivity, which are attributed to the enhanced spin relaxation of domain wall motion and the weakened electron-relaxation caused by decreasing Fe2+, respectively. The changes for microwave dielectric response could lead to the excellent microwave absorption due to the improvement of the impedance match between BiFeO3 and air.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Fabrication of a Polymer Micro Needle Array by Mask-Dragging X-Ray Lithography and Alignment X-Ray Lithography
LI Yi-Gui**, YANG Chun-Sheng, LIU Jing-Quan, SUGIYAMA Susumu
Chin. Phys. Lett. 2011, 28 (3): 038101 .   DOI: 10.1088/0256-307X/28/3/038101
Abstract   PDF(pc) (711KB) ( 762 )
Polymer materials such as transparent thermoplastic poly(methyl methacrylate) (PMMA) have been of great interest in the research and development of integrated circuits and micro-electromechanical systems due to their relatively low cost and easy process. We fabricated PMMA-based polymer hollow microneedle arrays by mask-dragging and aligning x-ray lithography. Techniques for 3D micromachining by direct lithography using x-rays are developed. These techniques are based on using image projection in which the x-ray is used to illuminate an appropriate gold pattern on a polyimide film mask. The mask is imaged onto the PMMA sample. A pattern with an area of up to 100 ×100 mm2 can be fabricated with sub-micron resolution and a highly accurate order of a few microns by using a dragging mask. The fabrication technology has several advantages, such as forming complex 3D micro structures, high throughput and low cost.
Intermediate-Band Solar Cells Based on InAs/GaAs Quantum Dots
YANG Xiao-Guang, YANG Tao**, WANG Ke-Fan, GU Yong-Xian, JI Hai-Ming, XU Peng-Fei, NI Hai-Qiao, NIU Zhi-Chuan, WANG Xiao-Dong, CHEN Yan-Ling, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (3): 038401 .   DOI: 10.1088/0256-307X/28/3/038401
Abstract   PDF(pc) (536KB) ( 485 )
We report the fabrication of intermediate-band solar cells (IBSCs) based on quantum dots (QDs), which consists of a standard P-I-N structure with multilayer stacks of InAs/GaAs QDs in the I-layer. Compared with conventional GaAs single-junction solar cells, the IBSCs based on InAs/GaAs QDs show a broader photo-response spectrum (> 1330 nm), a higher short-circle current (about 53% increase) and a stronger radiation hardness. The results have important applications for realizing high efficiency solar cells with stronger radiation hardness.
A Room-Temperature Pre-calibration Procedure for Gradiometer Sifting
ZHANG Shu-Lin, LIU Yang-Bo, LIU Ming, WANG Yong-Liang, KONG Xiang-Yan, XIE Xiao-Ming**
Chin. Phys. Lett. 2011, 28 (3): 038501 .   DOI: 10.1088/0256-307X/28/3/038501
Abstract   PDF(pc) (490KB) ( 416 )
In order to detect extremely weak magnetic signals, superconducting quantum interference device (SQUID) gradiometers are widely used to suppress environmental noise. A hardware SQUID gradiometer consists of a niobium gradio-antenna and an SQUID, which are coupled via an input coil. Here gradiometer imbalance may greatly reduce its noise suppression performance. The gradiometer balance depends on the geometrical forms of the antenna wound by niobium wire. We describe a simple method based on Faraday's law for the pre-calibration of the gradiometer balance at room temperature, before the gradiometer is set up. The pre-calibrating results are compared with the measured balance of an SQUID gradiometer system. This method may be used for sifting hardware gradiometers for multi-channel systems.
Hierarchical Porous Carbon Counter Electrode for Dye-Sensitized Solar Cells
WANG Gui-Qiang**, HUANG Cong-Cong, XING Wei, ZHUO Shu-Ping
Chin. Phys. Lett. 2011, 28 (3): 038801 .   DOI: 10.1088/0256-307X/28/3/038801
Abstract   PDF(pc) (506KB) ( 496 )
Hierarchical porous carbon is prepared by a combination of self-organization and chemical activation and explored as counter electrode for dye-sensitized solar cells. Pore structure analysis shows that micropores generated within the mesopore wall and the pristine mesopore structure of mesoporous carbon are preserved during KOH activation. Electrochemical impedance spectroscopy studies demonstrate a relatively high electrocatalytic activity of hierarchical porous carbon electrode for triiodide reduction, as compared with a pristine mesoporous carbon electrode. This enhanced electrocatalytic activity is beneficial for improving the photovoltaic performance of dye-sensitized solar cells. The overall conversion efficiency of dye-sensitized solar cells with the hierarchical porous carbon electrode increased by 11.5% compared with that of the cell with a pristine mesoporous carbon electrode.
Size Dependency of Income Distribution and Its Implications
ZHANG Jiang**, WANG You-Gui
Chin. Phys. Lett. 2011, 28 (3): 038901 .   DOI: 10.1088/0256-307X/28/3/038901
Abstract   PDF(pc) (502KB) ( 306 )
We systematically study the size dependency of income distributions, i.e. income distribution versus the population of a country. Using the generalized Lotka–Volterra model to fit the empirical income data for 1996–2007 in the U.S.A., we find an important parameter λ that can scale with a β power of the size (population) of the U.S.A. in that year. We point out that the size dependency of income distributions, which is a very important property but seldom addressed in previous studies, has two non-trivial implications: (1) the allometric growth pattern, i.e. the power-law relationship between population and GDP in different years, can be mathematically derived from the size-dependent income distributions and also supported by the empirical data; (2) the connection with the anomalous scaling for the probability density function in critical phenomena, since the re-scaled form of the income distributions has asymptotically exactly the same mathematical expression for the limit distribution of the sum of many correlated random variables.
A New Car-Following Model with Consideration of Driving Resistance
LI Chuan-Yao, TANG Tie-Qiao, **, HUANG Hai-Jun, SHANG Hua-Yan
Chin. Phys. Lett. 2011, 28 (3): 038902 .   DOI: 10.1088/0256-307X/28/3/038902
Abstract   PDF(pc) (549KB) ( 603 )
Based on the effects of driving resistance on car movement, we develop a new car-following model. The simulation results show that our model can describe the kinetic property of each car during the processes of starting and braking, however the braking process will be postponed and a prominent wavefront will appear during the braking process. With the increase in driving resistance, a car's movement will become more stable during the whole process, the headway of each car will increase and the wavefront will become more prominent. In addition, our model can reproduce the evolution of a small perturbation.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Diffusion Simulation of Outer Radiation Belt Electron Dynamics Induced by Superluminous L-O Mode Waves
XIAO Fu-Liang, **, HE Zhao-Guo ZHANG Sai, SU Zhen-Peng, CHEN Liang-Xu,
Chin. Phys. Lett. 2011, 28 (3): 039401 .   DOI: 10.1088/0256-307X/28/3/039401
Abstract   PDF(pc) (627KB) ( 395 )
Temporal evolution of outer radiation belt electron dynamics resulting from superluminous L-O mode waves is simulated at L=6.5. Diffusion rates are evaluated and then used as inputs to solve a 2D momentum-pitch-angle diffusion equation, particularly with and without cross diffusion terms. Simulated results demonstrate that phase space density (PSD) of energetic electrons due to L-O mode waves can enhance significantly within 24 h, covering a broader pitch-angle range in the absence of cross terms than that in the presence of cross terms. PSD evolution is also determined by the peak wave frequency, particularly at high kinetic energies. This result indicates that superluminous waves can be a potential candidate responsible for outer radiation belt electron dynamics.
Numerical Validation and Comparison of Three Solar Wind Heating Methods by the SIP-CESE MHD Model
YANG Li-Ping, **, FENG Xue-Shang, XIANG Chang-Qing, JIANG Chao-Wei,
Chin. Phys. Lett. 2011, 28 (3): 039601 .   DOI: 10.1088/0256-307X/28/3/039601
Abstract   PDF(pc) (697KB) ( 358 )
We conduct simulations using the three-dimensional (3D) solar-interplanetary conservation element/solution element (SIP-CESE) magnetohydrodynamic (MHD) model and magnetogram data from a Carrington rotation (CR) 1897 to compare the three commonly used heating methods, i.e. the Wentzel–Kramers–Brillouin (WKB) Alfvén wave heating method, the turbulence heating method and the volumetric heating method. Our results show that all three heating models can basically reproduce the bimodal structure of the solar wind observed near the solar minimum. The results also demonstrate that the major acceleration interval terminates about 4RS for the turbulence heating method and 10RS for both the WKB Alfvén wave heating method and the volumetric heating method. The turbulence heating and the volumetric heating methods can capture the observed changing trends by the WIND satellite, while the WKB Alfvén wave heating method does not.
A Constraint of Black Hole Mass and the Inner Edge Radius of Relativistic Accretion Disc
HE Liang, HUANG Chang-Yin, WANG Ding-Xiong**
Chin. Phys. Lett. 2011, 28 (3): 039701 .   DOI: 10.1088/0256-307X/28/3/039701
Abstract   PDF(pc) (449KB) ( 363 )
A constraint to black hole (BH) accretion has previously been derived for the inner edge fixed at the innermost stable circular orbit (ISCO) and the innermost bound circular orbit (IBCO). This constraint is referred to as the mass-radius (MR) relation in this study, and the validity of the MR relation is discussed for different cases. It is shown that the product of the BH mass and the inner edge radius decreases monotonically in the accretion process for the inner edge located between IBCO and ISCO. In addition, we discuss the validity of the MR relation by considering the magnetic coupling (MC) effects of a Kerr BH with its surrounding disc. Although theoretically the product of the BH mass and the radius of ISCO increases (decreases) with time for a BH spin greater (less) than some critical value in the MC process, this relation is approximately valid for an Eddington accretion rate persisting for a rather long time, such as more than 106 years. Finally, we discuss the possible application of the MR relation to astrophysics.
Original Articles
An Interacting Two-Fluid Scenario for Dark Energy in an FRW Universe
Hassan Amirhashchi, Anirudh Pradhan, **, Bijan Saha
Chin. Phys. Lett. 2011, 28 (3): 039801 .   DOI: 10.1088/0256-307X/28/3/039801
Abstract   PDF(pc) (473KB) ( 800 )
We study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic Friedmann–Robertson–Walker (FRW) model filled with barotropic fluid and dark energy. To obtain the deterministic solution we choose the scale factor a(t) =√tet, which yields a time-dependent deceleration parameter (DP). In doing so, we consider the case minimally coupled with dark energy to the perfect fluid as well as direct interaction with it.
67 articles