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An Analysis of the Invariance and Conservation Laws of Some Classes of Nonlinear Ostrovsky Equations and Related Systems
K. Fakhar**, A. H. Kara
Chin. Phys. Lett. 2011, 28 (1): 010201 .   DOI: 10.1088/0256-307X/28/1/010201
Abstract   PDF(pc) (349KB) ( 1441 )
A large class of partial differential equations in the modelling of ocean waves are due to Ostrovsky. We determine the invariance properties (through the Lie point symmetry generators) and construct classes of conservation laws for some of the models. In the latter case, the method involves finding the 'multipliers' associated with the conservation laws with a stronger emphasis on the 'higher-order' ones. The relationship between the symmetries and conservation laws is investigated by considering the invariance properties of the multipliers.
Numerical Modeling for Generating the Bound State Energy via a Semi Inverse Variational Method Combined with a B-Spline Type Basis
A. Zerarka**, O. Haif-Khaif, K. Libarir, A. Attaf
Chin. Phys. Lett. 2011, 28 (1): 010202 .   DOI: 10.1088/0256-307X/28/1/010202
Abstract   PDF(pc) (415KB) ( 966 )
This research concerns with the development of a linear three-dimensional numerical model in a quantum environment. We use the semi inverse variational method together with B-spline bases to extract the structures of bound states of the Schrödinger equation. The model performances are demonstrated for the Coulomb type problem. From realistic examples, some state configurations are presented to illustrate the effectiveness and the exactitude of the proposed method.
Numerical Study of a Three-Dimensional Hénon Map
Gabriela A. Casas**, Paulo C. Rech***
Chin. Phys. Lett. 2011, 28 (1): 010203 .   DOI: 10.1088/0256-307X/28/1/010203
Abstract   PDF(pc) (1084KB) ( 750 )
We consider a three-dimensional generalization of the two-dimensional Hénon map. We first investigate the emergence of quasiperiodic states, as a result of Naimark–Sacker bifurcations of period-1 and period-2 orbits. Secondly we investigate the disappearance of the resonance torus in the transition from quasiperiodicity to chaos.
Influence of the Stark Shift on Entanglement Sudden Death and Birth in Cavity QED
ZHANG Jian-Song**, CHEN Ai-Xi, WU Kun-Hua
Chin. Phys. Lett. 2011, 28 (1): 010301 .   DOI: 10.1088/0256-307X/28/1/010301
Abstract   PDF(pc) (681KB) ( 783 )
We investigate the entanglement dynamics of two two-level atoms interacting with two vacuum fields of two spatially separated cavities with the Stark effects by employing the concurrence. It is shown that the entanglement sudden death (ESD) and birth (ESB) could be controlled by adjusting the Stark-shift parameters. If the Stark-shift parameters are chosen appropriately, then ESD and ESB phenomena will appear. In addition, the appearance of ESD before or after ESB depends on the Stark-shift values.
Ground State Density Distribution of Bose-Fermi Mixture in a One-Dimensional Harmonic Trap
HAO Ya-Jiang
Chin. Phys. Lett. 2011, 28 (1): 010302 .   DOI: 10.1088/0256-307X/28/1/010302
Abstract   PDF(pc) (547KB) ( 585 )
By the density-functional calculation we investigate the ground-state properties of Bose-Fermi mixture confined in one-dimensional harmonic traps. The homogeneous mixture of bosons and polarized fermions with contact interaction can be exactly solved by the Bethe-ansatz method. After giving the exact formula of ground state energy density, we employ the local-density approximation to determine the density distribution of each component. It is shown that with the increase in interaction, the total density distribution evolves to Fermi-like distribution and the system exhibits phase separation between two components when the interaction is strong enough but finite. While in the infinite interaction limit both bosons and fermions display the completely same Fermi-like distributions and phase separation disappears.
Charged Scalars in Transient Stellar Electromagnetic Fields
Marina-Aura Dariescu**, Ciprian Dariescu, Ovidiu Buhucianu
Chin. Phys. Lett. 2011, 28 (1): 010303 .   DOI: 10.1088/0256-307X/28/1/010303
Abstract   PDF(pc) (420KB) ( 492 )
We consider a non-rotating strongly magnetized object, whose magnetic induction is of the form Bx = B0(t) sinκz. In the electromagnetic field generated by only one component of the four-vector potential, we solve the Klein–Gordon equation and discuss the sudden growth of the scalar wave functions for wavenumbers inside computable ranges. In the case of unexcited transversal kinetic degrees, we write down the recurrent differential system for the amplitude functions and compute the respective conserved currents.
Generating Entangled States of Multilevel Atoms through a Selective Atom-Field Interaction
CHEN Zhi-Hua**, LIN Xiu-Min
Chin. Phys. Lett. 2011, 28 (1): 010304 .   DOI: 10.1088/0256-307X/28/1/010304
Abstract   PDF(pc) (343KB) ( 525 )
We present a scheme to generate entangled state of two multilevel atoms in a high-Q optical cavity. In the protocol, the selective atom-field interaction is highly controlled, which can yield a resonant interaction inside one selected atom-field subspace and leave the others in a highly dispersive regime. The atomic spontaneous emission is efficiently suppressed via the large atom-field detuning. Simultaneously, the proposal only requires commonly addressing on atoms inside the cavity, which reduces the difficulties of experiment.
Interference Pattern of Density-Density Correlation for Incoherent Atoms with Vortices Released from an Optical Lattice
XU Zhi-Jun**, ZHANG Dong-Mei, LIU Xia-Yin
Chin. Phys. Lett. 2011, 28 (1): 010305 .   DOI: 10.1088/0256-307X/28/1/010305
Abstract   PDF(pc) (768KB) ( 525 )
For a series of incoherent condensate atomic clouds with vortices (an orbital angular momentum) released from an optical lattice, the density-density correlation function of this freely expanding ultracold gases is theoretically investigated. It is shown that the nonzero angular momentum of the atoms has an important effect on the fringe pattern of density-density correlation. Particularly, for a short expansion time, even the rotation direction of the atoms could have an observable effect on the fringe pattern. Observation of this specific fringe pattern would constitute experimental evidence for the presence of a vortex in an atomic condensate.
Why Can We Copy Classical Information?
SHEN Yao, HAO Liang, LONG Gui-Lu**
Chin. Phys. Lett. 2011, 28 (1): 010306 .   DOI: 10.1088/0256-307X/28/1/010306
Abstract   PDF(pc) (310KB) ( 612 )
It is pointed out that the noncloning theorem in quantum mechanics also holds for unknown state in linear classical physics. The apparent capability of copying of a classical state is essentially the capability of perfect measurement in classical physics. The difference in copying between quantum and classical physics is the difference in measurement between the two theories. A classical copying process is the combined action of measurement of an unknown state and the preparation of this state onto another system. Hence perfect measurability in classical physics enables the copying of a classical state.
Switched Synchronization with a Guaranteed Performance
Choon Ki Ahn
Chin. Phys. Lett. 2011, 28 (1): 010501 .   DOI: 10.1088/0256-307X/28/1/010501
Abstract   PDF(pc) (489KB) ( 470 )
A new synchronization method is proposed for switched systems. Based on the Lyapunov stability theory and linear matrix inequality (LMI) formulation, an existence condition of the synchronization controller for switched systems is proposed such that the resulting synchronization error system is asymptotically stable with a guaranteed performance. It is also shown that the design of the desired controller is achieved by solving a set of LMIs, which can be facilitated efficiently by resorting to standard numerical algorithms. A numerical example with simulation results is provided to illustrate the effectiveness and performance of the developed approach.
Control of Fractal Erosion of Safe Basins in a Holmes–Duffing System via Delayed Position Feedback
Chin. Phys. Lett. 2011, 28 (1): 010502 .   DOI: 10.1088/0256-307X/28/1/010502
Abstract   PDF(pc) (514KB) ( 449 )
A linear delayed position feedback control is applied to control the erosion of safe basins in a Holmes–Duffing system. The conditions of fractal erosion of the safe basin of the controlled system on the basis that the range of time delay leading to good control is obtained by the Melnikov method. It is found that the increasing time delay can reduce the basin erosion under a weak and positive feedback gain. Then the evolutions of safe basins with time delay are presented in detail by the fourth Runge-Kutta and Monte-Carlo methods, which shows that the safe basin of the controlled Holmes–Duffing system can be expanded, and its fractal can be reduced by the increasing time delay. These results suggest that delayed position feedbacks can be used as a good approach to control the erosion of safe basins.
Security Analysis of a Block Encryption Algorithm Based on Dynamic Sequences of Multiple Chaotic Systems
DU Mao-Kang**, HE Bo, WANG Yong
Chin. Phys. Lett. 2011, 28 (1): 010503 .   DOI: 10.1088/0256-307X/28/1/010503
Abstract   PDF(pc) (457KB) ( 496 )
Recently, the cryptosystem based on chaos has attracted much attention. Wang and Yu (Commun. Nonlin. Sci. Numer. Simulat. 14 (2009) 574) proposed a block encryption algorithm based on dynamic sequences of multiple chaotic systems. We analyze the potential flaws in the algorithm. Then, a chosen-plaintext attack is presented. Some remedial measures are suggested to avoid the flaws effectively. Furthermore, an improved encryption algorithm is proposed to resist the attacks and to keep all the merits of the original cryptosystem.
Synchronization of Coupled Neurons Controlled by a Pacemaker
LI Mei-Sheng**, ZHANG Hong-Hui, ZHAO Yong, SHI Xia
Chin. Phys. Lett. 2011, 28 (1): 010504 .   DOI: 10.1088/0256-307X/28/1/010504
Abstract   PDF(pc) (704KB) ( 482 )
We investigate synchronization of Hindmarsh–Rose neurons with gap junctions under the control of a pacemaker. In a ring Hindmarsh–Rose neuronal network, the coupled neurons with the pacemaker can occur in synchronization more easily than those without the pacemaker. Furthermore, the pacemaker can induce phase synchronization or nearly-complete synchronization of nonidentical neurons. This synchronization can occur more easily when time delay is considered. Theses results can be helpful to understand the activities of the real neuronal system.
Fabrication of Dry Electrode for Recording Bio-potentials
WANG Yu, GUO Kai, PEI Wei-Hua**, GUI Qiang, LI Xiao-Qian, CHEN Hong-Da, YANG Jian-Hong
Chin. Phys. Lett. 2011, 28 (1): 010701 .   DOI: 10.1088/0256-307X/28/1/010701
Abstract   PDF(pc) (721KB) ( 782 )
Development of minimally invasive dry electrodes for recording biopotentials is presented. The detailed fabrication process is outlined. A dry electrode is formed by a number of microneedles. The lengths of the microneedles are about 150 μm and the diameters are about 50 μm. The tips of the microneedles are sharp enough to penetrate into the skin. The silver/silver chloride is grown on microneedle arrays and demonstrates good character. The electrocardiogram shows that the dry electrode is suitable for recording biopotentials.
Terahertz Direct Detection Characteristics of a Superconducting NbN Bolometer
REN Yuan, MIAO Wei, YAO Qi-Jun, ZHANG Wen, SHI Sheng-Cai**
Chin. Phys. Lett. 2011, 28 (1): 010702 .   DOI: 10.1088/0256-307X/28/1/010702
Abstract   PDF(pc) (563KB) ( 732 )
We report the terahertz direct detection characteristics of a spiral antenna coupled NbN superconducting hot-electron bolometer (HEB) at a bath temperature of 4.2 K. Thermal conductance determined from resistance transition curves with different bias currents is found to be 3×10−7 W/K. The device shows a read-out circuit limited noise equivalent power (NEP) of 4.5×10−12 W/Hz1/2 at 4.2 K with a home-made transimpedance amplifier operating at room temperature.
Analysis on the DNA Fingerprinting of Aspergillus Oryzae Mutant Induced by High Hydrostatic Pressure
WANG Hua, ZHANG Jian, YANG Fan, WANG Kai, SHEN Si-Le**, LIU Bing-Bing, ZOU Bo**, ZOU Guang-Tian
Chin. Phys. Lett. 2011, 28 (1): 010703 .   DOI: 10.1088/0256-307X/28/1/010703
Abstract   PDF(pc) (782KB) ( 609 )
The mutant strains of aspergillus oryzae (HP300a) are screened under 300 MPa for 20 min. Compared with the control strains, the screened mutant strains have unique properties such as genetic stability, rapid growth, lots of spores, and high protease activity. Random amplified polymorphic DNA (RAPD) and inter simple sequence repeats (ISSR) are used to analyze the DNA fingerprinting of HP300a and the control strains. There are 67.9% and 51.3% polymorphic bands obtained by these two markers, respectively, indicating significant genetic variations between HP300a and the control strains. In addition, comparison of HP300a and the control strains, the genetic distances of random sequence and simple sequence repeat of DNA are 0.51 and 0.34, respectively.
Negative Pion Induced Fission with Heavy Target Nuclei
G. Sher**, Mukhtar A. Rana, S. Manzoor, M. I. Shahzad
Chin. Phys. Lett. 2011, 28 (1): 012501 .   DOI: 10.1088/0256-307X/28/1/012501
Abstract   PDF(pc) (537KB) ( 373 )
We investigate fission induced by negative pions in copper and bismuth targets using CR-39 dielectric track detectors. The target-detector assemblies in 4π-geometric configuration were exposed at the AGS facility of Brookhaven National Laboratory, USA. The exposed detectors were chemically etched under appropriate etching conditions and scanned to collect data in the form of fission fragments tracks produced as a result of interaction of pions with the target nuclei. Using the track counts, the experimental fission cross sections for copper and bismuth have been measured at energies of 500, 672, 1068 and 1665 MeV and compared with the calculation using the Cascade-Exciton Model code (CEM95). The values of fission probability based on experimental fission cross-sections have been compared with the theoretically calculated values of fission probabilities obtained using the CEM95 code. Good agreement is observed between the measured and computed results.
Factorial Correlators and Oscillatory Multiplicity Moments at the CERN SPS Energy for Ring-Like and Jet-Like Events
Prabir Kumar Haldar**, Sanjib Kumar Manna
Chin. Phys. Lett. 2011, 28 (1): 012502 .   DOI: 10.1088/0256-307X/28/1/012502
Abstract   PDF(pc) (614KB) ( 372 )
We present an analysis of ring-like and jet-like events in terms of factorial correlations and oscillatory multiplicity moments of 32S–Ag/Br interactions at 200 A GeV. The investigation reveals that the correlated moments increase with decrease in bin−bin separation D, following the power law, which suggests the presence of an intermittent nature of self−similar dynamical fluctuations pattern for ring-like and jet-like events. The analysis further shows that the strength of the non-statistical fluctuations is larger for jet-like events than those of ring-like events and total events. However, ring-like and jet-like events are not to be consistent with the total events of the α model of intermittency. To go beyond the lower order correlation, the oscillatory multiplicity moments are used to study the higher order correlation. The ratios Hq (cumulant over factorial moments, Kq/Fq) are determined for ring-like, jet-like and the total events. The presence of few-particle short range correlation is established. It is extremely interesting to observe that the oscillations of ring-like events are different from the jet-like events and the total events. However, in almost all the cases, the simulated interactions fail to replicate the experimental results.
Computerized Control and Operation of Rutherford Backscattering/Channeling for an in situ Ion Beam System and Its Application for Measurement of Si(001) and ZnO(001)
HE Jun, J. C. LEE, LI Ming, WANG Ze-Song, LIU Chuan-Sheng, FU De-Jun**
Chin. Phys. Lett. 2011, 28 (1): 012901 .   DOI: 10.1088/0256-307X/28/1/012901
Abstract   PDF(pc) (673KB) ( 602 )
A computer-automated Rutherford backscattering/channeling (RBS/C) system is developed to provide in situ ion beam analysis of the accelerator-TEM system in Wuhan University. The basic system components are a PC equipped with a multichannel analyzer data acquisition board, motion control hardware including the Panmure stepping motor controller and integrated circuit modules, and a Labview programmed operating system with associated electronics. Single crystalline Si(001) and ZnO(001) implanted with Mn ions were characterized with this computerized setup. The crystalline quality χmin and channeling half angle of Si(001) were measured to be 4.65% and 0.52°, respectively, which are comparable to theoretical values 4.2% and 0.32°. The ion implantation induced damage depth profile derived from channeling and random spectrum is in reasonable agreement with the result calculated by the SRIM Monte-Carlo simulation code.
Collision Energies Effect on Stereodynamics for Ne+H2+→NeH++H Reaction
XIAO Jing, YANG Chuan-Lu**, WANG Mei-Shan, MA Xiao-Guang
Chin. Phys. Lett. 2011, 28 (1): 013101 .   DOI: 10.1088/0256-307X/28/1/013101
Abstract   PDF(pc) (766KB) ( 507 )
Vector correlation between reagents and products for the reaction Ne+H2+→NeH++H is studied using quasi−classical trajectory method at different collision energies on a new surface constructed by Lv et al.[J. Chem. Phys.132 (2010) 014303] The results of angular distributions P(θr) and P(φr) show that the product rotational angular momentum is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The four polarization−dependent generalized differential cross sections show that the scatting direction of product NeH+ is significantly affected by the collision energy.
Frequency Measurement of the Electric Quadrupole Transition in a Single Laser-Cooled 40Ca+
LIU Qu, , HUANG Yao, , CAO Jian, , OU Bao-Quan, , GUO Bin, **, GUAN Hua, HUANG Xue-Ren, ***, GAO Ke-Lin, ***
Chin. Phys. Lett. 2011, 28 (1): 013201 .   DOI: 10.1088/0256-307X/28/1/013201
Abstract   PDF(pc) (601KB) ( 527 )
The optical frequency of the 4s2S1/2–3d2D5/2 transition in a single trapped and laser−cooled 40Ca+ ion is measured with an optical frequency comb system referenced to a hydrogen maser. A 729−nm laser can be locked to the clock transition about ten hours and the Allan deviation is better than 2×10-14/1000s.
Measurement of Local Gravity via a Cold Atom Interferometer
ZHOU Lin, , XIONG Zong-Yuan, , YANG Wei, , TANG Biao, , PENG Wen-Cui, , WANG Yi-Bo, , XU Peng, , WANG Jin, ZHAN Ming-Sheng, **
Chin. Phys. Lett. 2011, 28 (1): 013701 .   DOI: 10.1088/0256-307X/28/1/013701
Abstract   PDF(pc) (1001KB) ( 1289 )
We demonstrate a precision measurement of local gravity acceleration g in Wuhan by a compact cold atom interferometer. The atom interferometer is in vertical Mach–Zehnder configuration realized using a π/2−π-π/2 Raman pulse sequence. Cold atoms were prepared in a magneto-optical trap, launched upward to form an atom fountain, and then coherently manipulated to interfere by stimulated Raman transition. Population signal vs Raman laser phase was recorded as interference fringes, and the local gravity was deduced from the interference signal. We have obtained a resolution of 7×10−9 g after an integration time of 236 s under the best vibrational environment conditions. The absolute g value was derived from the chirp rate with a difference of 1.5×10−7 g compared to the gravity reference value. The tidal phenomenon was observed by continuously monitoring the local gravity over 123 h.
An Inverse Electromagnetic Scattering Method for One-Dimensional Inhomogeneous Media
LIN Zhi-Wei**, XU Xin, ZHANG Xiao-Juan, FANG Guang-You
Chin. Phys. Lett. 2011, 28 (1): 014101 .   DOI: 10.1088/0256-307X/28/1/014101
Abstract   PDF(pc) (515KB) ( 546 )
A frequency-domain inversion scheme for reconstructing the permittivity profile of one-dimensional inhomogeneous media is proposed. The generalized reflection coefficients and the generalized transmission coefficients of the inhomogeneous media are used as the input data of the inverse model. A Newton-like iterative algorithm known as the generalized pulse-spectrum technique with the Tikhonov regularization is applied to solve the inverse problem. Novel boundary conditions are proposed for the inverse problem and therefore the permittivity at the boundary of the inhomogeneous media is not required as prior knowledge. The choice of frequency points of the frequency-domain method is also investigated. Numerical examples are carried out to validate the inversion technique. Good agreements between the reconstructed profiles and the true profiles are shown.
Electromagnetic Scattering and Inverse Scattering of Layered Media with a Slightly Rough Surface
LIN Zhi-Wei**, XU Xin, ZHANG Xiao-Juan, FANG Guang-You
Chin. Phys. Lett. 2011, 28 (1): 014102 .   DOI: 10.1088/0256-307X/28/1/014102
Abstract   PDF(pc) (920KB) ( 598 )
An electromagnetic (EM) scattering model for layered media covered by a 3D infinite rough surface and the corresponding inversion technique are investigated. The work aims at remote sensing the surface roughness and dielectric constant for different depths of bear soil through radar measurement data. The forward problem is carried out by the wave decomposition method. The small perturbation method (SPM) and EM boundary conditions are employed to solve the integral equations introduced by the wave decomposition method. The second-order SPM solution of the scattering field is involved in the computation of the forward problem for the first time. The backscattering coefficients of multiple frequencies, multiple angles and multiple polarizations are employed to create a nonlinear optimization problem. A genetic algorithm is introduced to help the inversion procedure approach to the global minimum of the cost function. Examples are carried out to validate the inversion technique. The inversion results show good agreement with the forward problem with given parameters and pose good tolerance to the input data with the additive white Gaussian noise.
Dual-Band Terahertz Left-Handed Metamaterial with Fishnet Structure
DU Qiu-Jiao, LIU Jin-Song**, WANG Ke-Jia, YI Xu-Nong, YANG Hong-Wu
Chin. Phys. Lett. 2011, 28 (1): 014201 .   DOI: 10.1088/0256-307X/28/1/014201
Abstract   PDF(pc) (700KB) ( 781 )
We present the design of a dual-band left-handed metamaterial with fishnet structure in the terahertz regime. Its left-handed properties are described by the retrieved effective electromagnetic parameters. We introduce an equivalent circuit which offers a theoretical explanation for the left-handed behavior of the dual-band fishnet metamaterial, and investigate its losses receiving higher figure of merit. The design is beneficial to the development of frequency agile and broadband THz materials and devices. The dual-band fishnet metamaterial can be extended to infrared and optical frequency ranges by regulating the structural parameters.
Relaxation Time for an Optical Bistable System Subjected to Color Noises
WANG Bing**, WU Xiu-Qing, CHENG Dong-Chao
Chin. Phys. Lett. 2011, 28 (1): 014202 .   DOI: 10.1088/0256-307X/28/1/014202
Abstract   PDF(pc) (441KB) ( 371 )
The relaxation time T of an optical bistable system with cross–correlated color noises and small time delay is investigated. Using the Novikov theorem and Fox approach, the steady probability distribution is obtained. The expression of T is derived using the Stratonovich decoupling ansatz formalism. It is found that the relaxation time T increases with the increasing cross–correlation time τ0 between the two noises or the self–correlation time τ1 of the multiplicative noise, but decreases with the increasing self–correlation time τ2 of the additive noise. T decreases with the increasing correlation intensity λ or the multiplicative noise intensity Q, but increases with the increasing additive noise intensity D. There exists a peak in the curve of T versus delay time τ.
Time-Delay Signature of Chaotic Vertical-Cavity Surface-Emitting Lasers with Polarization-Rotated Optical Feedback
XIANG Shui-Ying**, PAN Wei, YAN Lian-Shan, LUO Bin, ZOU Xi-Hua, JIANG Ning, WEN Kun-Hua
Chin. Phys. Lett. 2011, 28 (1): 014203 .   DOI: 10.1088/0256-307X/28/1/014203
Abstract   PDF(pc) (762KB) ( 573 )
To quantitatively evaluate the time-delay (TD) signatures of chaotic signals generated by vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated optical feedback (PROF), we propose four cases of resolution coefficients R based on correlation functions. The resolution coefficient characteristics for the x–polarization (XP) mode, y–polarization (YP) mode and the total output are considered. The dependences of R on the feedback strength and feedback delay are discussed and compared carefully. The two–dimensional maps of R show that the TD signatures for the single polarization mode (i.e., XP or YP mode) are much more difficult to retrieve than those for the total output in the entire parameter space. Thus, by using single polarization mode as a chaotic carrier, the TD signatures are extremely difficult to be identified, which contributes a lot in the security-enhanced VCSELs-based chaotic optical communication systems.
Design of Waveguide Integrated Ge-Quantum-Well Electro-Absorption Modulators
ZHAO Hong-Wei**, HU Wei-Xuan, XUE Chun-Lai, CHENG Bu-Wen, WANG Qi-Ming
Chin. Phys. Lett. 2011, 28 (1): 014204 .   DOI: 10.1088/0256-307X/28/1/014204
Abstract   PDF(pc) (863KB) ( 438 )
We present two designs for a waveguide Ge-quantum-well electro-absorption modulator. In our designs, the strip SOI waveguides are butt-coupled and evanescent-coupled to the modulator, respectively. The proposed Ge-quantum-well electro-absorption modulator is based on quantum-confined Stark effect (QCSE), having a 3-dB bandwidth above 50 GHz, as well as a low switching power (around 60 fJ/bit at 1435 nm). In the butt-coupled design, the optimized extinction ratio is up to 11.4 dB, while the insertion loss is only 6.74 dB. For the second one, which utilizes evanescent coupling, the extinction ratio and insertion loss are 9.18 dB and 6.72 dB, respectively.
Flashover in Back-Triggered Photoconductive Semiconductor Switch
SHI Wei, **, JIA Ji-Qiang, JI Wei-Li, GUI Huai-Meng
Chin. Phys. Lett. 2011, 28 (1): 014205 .   DOI: 10.1088/0256-307X/28/1/014205
Abstract   PDF(pc) (597KB) ( 417 )
Design of a new type of photoconductive semiconductor switches (PCSSs) is presented, and the withstand voltage is improved. The flashover voltage of the back-triggered PCSS is found to be higher than that of the front-triggered one. By analyzing the differences of the flashover voltage between the back-triggered PCSS and the front-triggered PCSS, a detailed statistics analysis and theoretical explanation are expounded. The experiments also prove that the PCSS we developed could resist a voltage as high as 20 kV under the repetition frequency of 30 Hz.
Simulation of Light Intensification Induced by Defects of Polished Fused Silica
WANG Feng-Rui, LIU Hong-Jie, HUANG Jin, ZHOU Xin-Da, JIANG Xiao-Dong**, WU Wei-Dong, ZHENG Wan-Guo, JU Xin
Chin. Phys. Lett. 2011, 28 (1): 014206 .   DOI: 10.1088/0256-307X/28/1/014206
Abstract   PDF(pc) (521KB) ( 424 )
Light intensity distribution in the vicinity of inclusions and etched cracks in polished fused silica at wavelength scale are simulated by using the finite-difference time-domain algorithm. Light intensity enhancement factor as functions of diameter and refractive index of inclusions are investigated, more than 10 times that of incident beam is obtained in the simulation. We model the etched crack in close proximity to a real structure, which is characterized by AFM. We find that the peak light intensity of the crack is a function of its cross sectional breadth depth ratio, providing good hints for the effective processing of fused silica samples to improve the damage threshold.
A Simple Birefringent Terahertz Waveguide Based on Polymer Elliptical Tube
WANG Jing-Li, **, YAO Jian-Quan, CHEN He-Ming, LI Zhong-Yang
Chin. Phys. Lett. 2011, 28 (1): 014207 .   DOI: 10.1088/0256-307X/28/1/014207
Abstract   PDF(pc) (514KB) ( 436 )
We propose a simple birefringent terahertz (THz) waveguide which is a polymer elliptical tube with a cross section of elliptical ring structure. It can be achieved by stretching a normal circular-tube in one direction. Simulations based on the full-vector finite element method (FEM) show that this kind of waveguides exhibits high birefringence on a level of 10−2 over a wide THz frequency range. Moreover, as a majority of modal power is trapped in the air core inside the polymer elliptical tube, the THz waveguide guiding loss caused by material absorption can be reduced effectively.
Correlation of Photosensitization and Binding Mode of Methylene Blue and DNA
LIU Tao, ZHANG Feng, CHEN Ping, TANG Guo-Qing, LIN Lie**
Chin. Phys. Lett. 2011, 28 (1): 014208 .   DOI: 10.1088/0256-307X/28/1/014208
Abstract   PDF(pc) (676KB) ( 666 )
Binding of methylene blue (MB) and DNA, photosensitization of MB in DNA, and correlation of photosensitization and binding mode are studied at different concentration ratios of DNA and MB. The absorption spectra indicate that the electrostatic binding is the main mode at low γ ratios (γ≤2), while at high γ ratios (γ>2) the intercalative binding is dominated. Studies on dynamics of photosensitization formation of singlet oxygen (1O2) for MB in DNA are carried out by using time−resolved technology. There are no obvious changes of the singlet oxygen lifetime and the triplet state MB molecule (MB3+∗) lifetime at low ratios, they are about 4 μs and 1 µs, respectively. However, we could not obtain the 1O2 lifetime and MB3+∗ lifetime due to the great decrease of 1O2 phosphorescence signals at high ratios. These results show that the photosensitization and binding mode of MB in DNA possess high correlation. When MB binds with DNA by electrostatic interaction, type−II photosensitization of MB plays a major role in photodynamic effect, the damage of DNA probably could be ascribed to 1O2. However, at high ratios, binding mode between MB and DNA turns to intercalative binding, which greatly weakens the type−II photosensitization process. Charge transfer between MB and DNA possibly becomes the main damage mechanism.
Preparation and Photoluminescence Properties of Eu2+−Doped Oxyapatite-Type SrxLa10−x (SiO4)6O3−x/2
CUI Zhao-Feng, YUAN Shuang-Long, **, YANG Yun-Xia, Franç, ois CHEVIRE **, Franck TESSIER, CHEN Guo-Rong
Chin. Phys. Lett. 2011, 28 (1): 014209 .   DOI: 10.1088/0256-307X/28/1/014209
Abstract   PDF(pc) (707KB) ( 691 )
Eu2+−doped oxyapatite SrxLa10−x(SiO4)6O3−x/2 phosphors are prepared by solid-state reaction at high temperatures under reducing atmosphere. Their crystal structures and photoluminescence are investigated by x-ray diffraction (XRD) and fluorescence spectroscopy, respectively. The XRD results indicate that the samples are pure oxyapatite phase (P63/m space group). The fluorescence spectra show two peaks corresponding to two sites (4f and 6h sites) for Eu2+ in the host lattice. As the Eu2+ content influences the intensity ratio of the two observed emission peaks, the photoluminescence mechanism is discussed.
Transmission Properties of an Air Waveguide with Left-Handed Holographic Photonic Crystal Cladding
DONG Guo-Yan**, YANG Xiu-Lun, CAI Lu-Zhong
Chin. Phys. Lett. 2011, 28 (1): 014210 .   DOI: 10.1088/0256-307X/28/1/014210
Abstract   PDF(pc) (666KB) ( 441 )
An air waveguide of left-handed photonic crystal (PhC) formed by holographic lithography is proposed. The symmetry mismatch between the incident wave and the Bloch modes of the holographic PhC is used to guide light efficiently. By properly designing the waveguide, backscattering loss can be significantly reduced. Due to the unique advantages of holographic photonic crystals, the serious problems of material loss and fabrication difficulty in left-handed material waveguides are also avoided. Furthermore it is shown that high transmission efficiency is easily achieved in the frequency region with effective refraction index near zero. These features may extend the possible guiding ability of holographic photonic crystal waveguide and its promising potential in the application of photonic integrated circuits.
Can Heavier Liquid Float on Top of a Lighter One?
A. H. Ayyad**, F. Takrori
Chin. Phys. Lett. 2011, 28 (1): 014701 .   DOI: 10.1088/0256-307X/28/1/014701
Abstract   PDF(pc) (512KB) ( 429 )
We report on a first observation of a floating spherical Hg (density 13 g/cm3) drop on top of a glycerin (density 1.26 g/cm3) drop, the latter is hemispherical and about four times larger in volume. This observation is clearly against nature's gravity law and has never been reported before. Here we present spectacular high resolution photos that clearly demonstrate this remarkable floating phenomenon. Using milli-Q water, the Hg drop would stay down adhered at the triple line. Instead, the coincidental use of tap water displays the same phenomenon. Increasing the volume of the supporting liquid to a certain value causes the Hg drop to sink. A 5-M NaCl aqueous solution is found enough to show the same floating phenomenon. This floating mercury as a phenomenon is puzzling. On this length scale it seems that surface tension and curvature dominate over gravity.
Properties of the Collision Efficiency of Nanoparticles in Brownian Coagulation
WANG Yu-Ming, LIN Jian-Zhong, **, CHEN Zhong-Li
Chin. Phys. Lett. 2011, 28 (1): 014702 .   DOI: 10.1088/0256-307X/28/1/014702
Abstract   PDF(pc) (538KB) ( 583 )
The collision efficiency of nanoparticles with diameters from 100 nm to 750 nm in the Brownian coagulation is studied by building and solving numerically the equations of particle collision in the presence of the van der Waals force, the elastic deformation force, the Stokes resistance, the lubrication force and the electrostatic force. The results show that the collision efficiency decreases overall with the increasing particle diameter. It is found that there exists an abrupt increase in the collision efficiency when the particle diameter equals 550 nm. Finally a new expression for the collision efficiency is presented.
MHD Control of Oblique Detonation Waves
SUN Xiao-Hui, CHEN Zhi-Hua**, ZHANG Huan-Hao
Chin. Phys. Lett. 2011, 28 (1): 014703 .   DOI: 10.1088/0256-307X/28/1/014703
Abstract   PDF(pc) (988KB) ( 427 )
Based on the Euler equation, the hybrid Roe/HLL scheme is employed to simulate the oblique detonation waves (ODWs). Furthermore, magnetohydrodynamic (MHD) control of both stable and unstable ODWs is investigated. It is shown that the stable ODW wave front can be controlled to the desired position under different inflow Mach numbers. However, for an unstable ODW, it is difficult for the MHD control to return the ODW front, but the unstable ODW turns to be stable with the Lorentz force applied in proper direction.
An Analysis of Peristaltic Flow of a Micropolar Fluid in a Curved Channel
N. Ali**, M. Sajid, T. Javed, Z. Abbas
Chin. Phys. Lett. 2011, 28 (1): 014704 .   DOI: 10.1088/0256-307X/28/1/014704
Abstract   PDF(pc) (455KB) ( 985 )
We analyze the two-dimensional peristaltic flow of a micropolar fluid in a curved channel. Long wavelength and low Reynolds number assumptions are used in deriving the governing equations. A shooting method with fourth-order Runge-Kutta algorithm is employed to solve the equations. The influence of dimensionless curvature radius on pumping and trapping phenomena is discussed with the help of graphical results. It is seen that the pressure rise per wavelength in the pumping region increases with an increase in the curvature of the channel. Moreover the symmetry of the trapped bolus destroys in going from straight to curved channel.
A Large Gap of Atmospheric Pressure RF-DBD Glow Discharges in Ar and Mixed Gases
LI Bin, CHEN Qiang**, LIU Zhong-Wei, WANG Zheng-Duo
Chin. Phys. Lett. 2011, 28 (1): 015201 .   DOI: 10.1088/0256-307X/28/1/015201
Abstract   PDF(pc) (460KB) ( 698 )
A large gap (up to 5.5 mm) between electrodes is acquired at Ar atmospheric pressure glow discharge (APGD) in radio frequency dielectric barrier discharge (RF-DBD). The characteristics of IV in single barrier Ar RF–DBD mixed with different ratios of O2 (0–100%) is studied in detail.
Analysis of Modified Williamson-Hall Plots on GaN Layers
LIU Jian-Qi, , QIU Yong-Xin, WANG Jian-Feng, XU Ke**, YANG Hui
Chin. Phys. Lett. 2011, 28 (1): 016101 .   DOI: 10.1088/0256-307X/28/1/016101
Abstract   PDF(pc) (546KB) ( 3274 )
Williamson–Hall (W-H) analysis is often used to separate the lateral coherence length (LCL) broadening and dislocation broadening on the ω−scan with a Lorentzian distribution. However, besides the LCL broadening and dislocation broadening, curvature also can broaden the ω−scan peak. Usually, the ω−scan can be described by a Pseudo-Voigt (P-V) function more precisely than a Lorentzian function. Based on the P-V fit peak profile, we modify the W-H plots. Both LCL broadening and curvature broadening can be eliminated from (00l) ω-scans plots simultaneously, and a reliable tilt can be obtained. This method is a good complementary for the existing method, but is more convenient. Although we focuse on GaN layers, the results are applicable to a wide range of other materials having mosaic structures.
Ion-implanted Mechanism of the Deposition Process for Diamond-Like Carbon Films
WANG Xue-Min, WU Wei-Dong**, WANG Yu-Ying, WANG Hai-Ping, GE Fang-Fang, TANG Yong-Jian, JU Xin
Chin. Phys. Lett. 2011, 28 (1): 016102 .   DOI: 10.1088/0256-307X/28/1/016102
Abstract   PDF(pc) (1354KB) ( 467 )
Due to the local densification, high-energy C and doped ions can greatly affect the bonding configurations of diamond-like carbon films. We investigate the corresponding affection of different incident ions with energy from 10 eV to 600 eV by Monte Carlo methods. The ion-implanted mechanism called the subplantation (for C, N, O, W, Y, etc.) is confirmed. Obvious thermal effect could be induced by the subplantation of the incident ions. Further, the subplantation of C ions is proved by in situ reflection high energy electron diffraction (RHEED). The observation from an atomic force microscope (AFM) indicates that the initial implantation of C ions might result in the final primitive-cell-like morphology of the smooth film (in an area of 1.2mm×0.9mm, rms roughness smaller than 20 nm by Wyko).
Microscopic Characteristics of Damage Evolution in Ultrapure Aluminum under Tensile Loading
QI Mei-Lan, **, ZHONG Sheng, FAN Duan, LUO Chao, HE Hong-Liang
Chin. Phys. Lett. 2011, 28 (1): 016103 .   DOI: 10.1088/0256-307X/28/1/016103
Abstract   PDF(pc) (879KB) ( 383 )
A series of plate-experiments are carried out to acquire ultrapure aluminum (purity, 99.999%) samples with damage. Based on the metallographic of all "soft-recovered" samples, the characteristics of damage evolution and spallation damage mechanism in ultrapure aluminum are analyzed in detail. Results show that the damage will increase regularly with increasing loading strength. Most of voids appear in the grain boundary and grow alone under tensile loading before they coalesce each other to form big irregular voids. These analysis results are helpful to understand the evolution process of ductile metal dynamic fracture and establish the damage evolution model.
A Novel Impact Tension Testing for OFHC Copper Bars under Local Strain Controlled
MA Dong-Fang, HOU Yan-Jun, CHEN Da-Nian**, WU Shan-Xing, WANG Huan-Ran
Chin. Phys. Lett. 2011, 28 (1): 016201 .   DOI: 10.1088/0256-307X/28/1/016201
Abstract   PDF(pc) (718KB) ( 512 )
A novel high-speed tensile facility (HSTF) with special fixture is applied to research the dynamic failure characteristics of oxygen-free high-conductivity (OFHC) copper bars at different levels of strain. The experimental tests are numerically simulated involving void evolution. It is indicated that the localized strains at necking region computed with the adjusted Johnson–Cook model and the Zerilli–Armstrong model are consistent with the experimental results.
Bubble Behavior and Heat Transfer of Nucleate Pool Boiling on Micro-Pin-Finned Surface in Microgravity
WEI Jin-Jia**, XUE Yan-Fang, ZHAO Jian-Fu, LI Jing
Chin. Phys. Lett. 2011, 28 (1): 016401 .   DOI: 10.1088/0256-307X/28/1/016401
Abstract   PDF(pc) (657KB) ( 653 )
Nucleate pool boiling on micro-pin-finned surface structure is proposed for efficiently cooling electronic components with high heat flux in microgravity, and was verified by experiments performed utilizing the drop tower Beijing. Micro-pin-fins with the dimensions of 50×60μm2 (thickness × height) and the space of 50 μm were fabricated on the chip surface by the dry etching technique. FC-72 was used as the working fluid. Nucleate pool boiling of FC-72 on a smooth surface was also tested for comparison. Unlike much obvious deterioration of heat transfer of nucleate pool boiling on the smooth surface in microgravity, constant heater surface temperature of nucleate pool boiling for the micro-pin-finned surface was observed, even though a large coalesced bubble completely covered the surface under microgravity condition. The performance of high efficient heat transfer on micro-pin-finned surface is independent of the gravity, which stems from the sufficient supply of fresh liquid to the heater surface due to the capillary forces.
Thermal Properties of Poly(vinyl chloride-co-vinyl acetate-co-2-hydroxypropyl acrylate) (PVVH) Polymer and Its Application in ZnO Based Nanogenerators
ZHANG Lei, YANG Jun-He**, WANG Xian-Ying**, HE Xing, ZHAO Bin, TANG Zhi-Hong, YANG Guang-Zhi, QIU Han-Xun
Chin. Phys. Lett. 2011, 28 (1): 016501 .   DOI: 10.1088/0256-307X/28/1/016501
Abstract   PDF(pc) (620KB) ( 431 )
A novel piezoelectricity based nano energy conversion device using vertically aligned ZnO nanowires/PVVH matrix as the working unit is proposed. Thermal energy is converted to electricity via the interaction of the PVVH polymer and ZnO nanowires. The thermal properties of PVVH are studied using Raman spectroscopy under different temperatures. The results show that the structure of PVVH is sensitive to fluctuations of the environmental temperatures. With the increasing temperature, PVVH tends to be crystallized and stress can be developed inside the polymer. The stress is responsible for the deformation and voltage generation of the ZnO nanowires.
Optical and Electrical Properties of ZnO/CdO Composite Thin Films Prepared by Pulse Laser Deposition
ZHENG Bi-Ju, LIAN Jian-She**, ZHAO Lei, JIANG Qing
Chin. Phys. Lett. 2011, 28 (1): 016801 .   DOI: 10.1088/0256-307X/28/1/016801
Abstract   PDF(pc) (1101KB) ( 2755 )
ZnO/CdO composite films with different CdO contents are obtained by pulse laser deposition technique. The structural, optical and electrical properties of the composite films are investigated by x-ray diffraction, photoluminescence and electrical resistivity measurements, respectively. The results show that the UV emission is at a constant peak position in the photoluminescence spectra. Meanwhile, their electrical resistivity decreases to very low level approaching to the value of the CdO film, which can be explained by the Matthiessen composite rule for resistivity. The peculiarity of low resistivity and high transmittance in the visible region enables these films suitable for optoelectronic device fabrication.
Channel Temperature Measurement of AlGaN/GaN HEMTs by Forward Schottky Characteristics2010-
ZHANG Guang-Chen, FENG Shi-Wei**, HU Pei-Feng, ZHAO Yan, GUO Chun-Sheng, XU Yang, CHEN Tang-Sheng, JIANG Yi-Jian
Chin. Phys. Lett. 2011, 28 (1): 017201 .   DOI: 10.1088/0256-307X/28/1/017201
Abstract   PDF(pc) (922KB) ( 1164 )
Channel temperature measurements of multi-finger AlGaN/GaN HEMTs by forward Schottky characteristics are presented. The temperature dependence of the forward gate-source Schottky junction voltage is investigated and it is used as the temperature sensitive parameter (TSP) by pulsed switching technique. The channel-to-mounting thermal resistance of the tested AlGaN/GaN HEMT sample is 19.6°C/W. Compared with both the measured results by micro-Raman method and simulated results of a three-dimensional heat conduction model, the physical meaning of the channel temperature for AlGaN/GaN HEMT tested by pulsed switching electrical TSP method is investigated quantitatively for the first time.
Negative Bias Temperature Instability
CAO Yan-Rong**, MA Xiao-Hua, HAO Yue, ZHU Min-Bo, TIAN Wen-Chao, ZHANG Yue
Chin. Phys. Lett. 2011, 28 (1): 017301 .   DOI: 10.1088/0256-307X/28/1/017301
Abstract   PDF(pc) (1277KB) ( 426 )
Different phenomena are observed under negative gate voltage stress which is smaller than the previous degradation stress in PMOSFETs with different oxide thicknesses. We adopt the real time method to make a point of the drain current to study the degradation and recovery of negative bias temperature instability (NBTI). For the device with thin oxide, recovery phenomenon appears when smaller negative voltage stress was applied, due to the more influencing oxide charges detrapping effects than the interface states. For the device with thick oxide, not recovery but degradation phenomenon comes forth. As many charges are trapped in the deeper position and higher energy level in the oxide, these charges can not be detrapped. Therefore, the effect of the charge detrapping is smaller than that of the interface states in the thick oxide. The degradation presents itself during the 'recovery' time.
Electrical Characteristics of High-Performance ZnO Field-Effect Transistors Prepared by Ultrasonic Spray Pyrolysis Technique
YI Ming-Dong, **, XIE Ling-Hai, LIU Yu-Yu, DAI Yan-Feng, HUANG Jin-Ying
Chin. Phys. Lett. 2011, 28 (1): 017302 .   DOI: 10.1088/0256-307X/28/1/017302
Abstract   PDF(pc) (571KB) ( 510 )
We have fabricated ZnO-based thin-film transistors (TFTs) by low-cost ultrasonic spray pyrolysis. The devices exhibit high saturation mobility of about 0.6 cm2/Vs and on−off current ratio of 105. The electrical characteristics of ZnO-based TFTs show that ultrasonic spray pyrolysis technique can be used as a promising approach to attain high-performance electronic devices. Furthermore, the deposition techniques make the operating process attractive for flexible electronics.
A 1100+V AlGaN/GaN-Based Planar Schottky Barrier Diode without Edge Termination
CAO Dong-Sheng, LU Hai, **, CHEN Dun-Jun, HAN Ping, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2011, 28 (1): 017303 .   DOI: 10.1088/0256-307X/28/1/017303
Abstract   PDF(pc) (603KB) ( 1516 )
AlGaN/GaN-based planar Schottky barrier diodes with various spacings between ohmic and Schottky contacts are fabricated without any edge termination. The reverse leakage current of the devices quickly saturates at low reverse bias when the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface is fully depleted. The corresponding breakdown voltage is found to follow a linear dependence on contact spacing and exceeds 1100 V at a contact spacing of 20 μm, yielding a high VBR2/RON value of >280 MWcm−2. The observations are tentatively explained by a "natural super-junction" theory, in which ionized surface states at front surface of the AlGaN barrier have to be neutralized by reverse surface leakage current from the Schottky electrode.
Thermal Shot Noise through Boundary Roughness of Carbon Nanotube Quantum Dots
Attia A. Awadalla, Adel H. Phillips**
Chin. Phys. Lett. 2011, 28 (1): 017304 .   DOI: 10.1088/0256-307X/28/1/017304
Abstract   PDF(pc) (446KB) ( 376 )
Thermal shot noise, thermal voltage and thermo power are studied through a carbon nanotube quantum dot coupled to two leads with random roughness of amplitude on each of the two boundaries, under the effect of microwave field, and magnetic field. The expressions for the thermal shot noise and thermal energy are deduced when the barrier strength and contact area are taken into consideration. A model for such mesoscopic devices is proposed as a carbon nanotube quantum dot coupled to two leads with random roughness of amplitude on each of the two boundaries. The results show oscillatory behaviors of the dependence of the thermal shot noise on the studied parameters. The thermopower oscillates with the variation of the contact area, and the peak heights decrease linearly with the contact area and increases with temperature. This trend of behavior is due to the interplay of the induced microwave photons and the tunneling rate through the side bands. This research is important for using a model as a high-frequency shot noise detector and the thermopower is sensitive to the energy dependence of the conductance.
Luminescence and Site Occupancy of Eu2+ in Ba2 Ca(BO3)2
LI Pan-Lai**, WANG Zhi-Jun, YANG Zhi-Ping, GUO Qing-Lin
Chin. Phys. Lett. 2011, 28 (1): 017801 .   DOI: 10.1088/0256-307X/28/1/017801
Abstract   PDF(pc) (567KB) ( 806 )
A green phosphor Ba2Ca(BO3)2:Eu2+ was synthesized by a high temperature solid–state reaction method under a reductive atmosphere. The luminescence and site occupancy of Eu2+ in Ba2Ca(BO3)2 are investigated. Ba2Ca(BO3)2:Eu2+ shows one green band (537 nm) under 400 nm near ultraviolet excitation which is suitable for UV LED. Ca2+ and Ba2+ ions in Ba2Ca(BO3)2 are replaced by Eu2+ ions, the Ba2Ca(BO3)2:Eu2+ shows a dissymmetrical emission band. The influence of Eu2+ doping concentrations on the emission intensity of Ba2Ca(BO3)2:Eu2+ is studied. It is found that the emission intensity is influenced by the Eu2+ concentration and reaches the maximum value at 2% Eu2+. According to the Dexter theory, the concentration quenching mechanisms of Eu2+ in Ba2Ca(BO3)2 are the ddinteraction.
Chemical Quenching of Positronium in CuO/Al2O3 Catalysts
ZHANG Hong-Jun, LIU Zhe-Wen, CHEN Zhi-Quan**, WANG Shao-Jie**
Chin. Phys. Lett. 2011, 28 (1): 017802 .   DOI: 10.1088/0256-307X/28/1/017802
Abstract   PDF(pc) (648KB) ( 535 )
CuO/Al2O3 catalysts were prepared by mixing CuO and γ−Al2O3 nanopowders. Microstructure and chemical environment of the catalysts are characterized by positron annihilation spectroscopy. The positron annihilation lifetime measurements reveal two long lifetime components τ3 and τ4, which correspond to ortho−positronium (o-Ps) annihilating in microvoids and large pores, respectively. With increasing CuO content from 0 to 40 wt%, both τ4 and its intensity I4 show significant decrease, which indicates quenching effect of o−Ps. The para-positronium (p-Ps) intensities derived from multi-Gaussian fitting of the coincidence Doppler broadening spectra also decrease gradually with increasing CuO content. This excludes the possibility of spin-conversion of positronium. Therefore, the chemical quenching by CuO is probably responsible for the decrease of o-Ps lifetime. Variation in the o-Ps annihilation rate λ4 (14) as a function of CuO content can be well fitted by a straight line, and the slope of the fitting line is (1.83±0.05)×107 s−1.
Trimeric Hydrogen Bond in Geometrically Frustrated Hydroxyl Cobalt Halogenides
LIU Xiao-Dong, **, Hagihala Masato, ZHENG Xu-Guang, **, TAO Wan-Jun, MENG Dong-Dong, ZHANG Sen-Lin, GUO Qi-Xin
Chin. Phys. Lett. 2011, 28 (1): 017803 .   DOI: 10.1088/0256-307X/28/1/017803
Abstract   PDF(pc) (568KB) ( 394 )
The mid-infrared absorption spectra of geometrically frustrated hydroxyl cobalt halogenides Co2(OH)3Cl and Co2(OH)3Br are measured by FTIR spectrometers, and the stretching vibrational modes of hydroxyl groups are found to be 3549 cm−1 and 3524 cm−1 respectively. Through finding their true terminal O–H group stretching vibration frequencies, we obtain 107 cm−1 and 99 cm−1 red shift caused by the corresponding O–H⋅⋅⋅Cl and O–H⋅⋅⋅Br hydrogen bonds. Rarely reported trimeric hydrogen bonds (Co3O–H)3⋅⋅⋅Cl/Br are pointed out to demonstrate the relative weakness of this kind of hydrogen bond which may have a critical effect on the lattice symmetry and magnetic structures.
Self-Trapped Exciton Photoluminescence from Polycrystalline K2AgI3 Obtained by Solid-State Reaction Method
DAI Peng, XU Zou-Ming, WANG Yu-Xia**
Chin. Phys. Lett. 2011, 28 (1): 017804 .   DOI: 10.1088/0256-307X/28/1/017804
Abstract   PDF(pc) (565KB) ( 541 )
Polycrystalline K2AgI3 is synthesized by solid-state reaction at 403 K using AgI and KI as starting materials. X-ray diffraction, photoluminescence (PL) spectra, photoluminescence excitation (PLE) spectra, electron paramagnetic resonance (EPR) and absorption spectra are employed to investigate the structure and photo-physical properties of such material. A broad luminescence band centered at about 608 nm at 180 K with large Stokes shift is found. When the temperature rises to about 300 K, an obvious PL blue-shift, PL intensity weakening, and an emission band broadening are observed. It is suggested that the emission at about 608 nm may originate from the recombination of self-trapped excitons.
Simulation of Interference Nanolithography of Second-Exciting Surface-Plasmon Polartions for Metal Nanograting Fabrication
LIANG Hui-Min**, WANG Jing-Quan
Chin. Phys. Lett. 2011, 28 (1): 018101 .   DOI: 10.1088/0256-307X/28/1/018101
Abstract   PDF(pc) (505KB) ( 406 )
Second-exciting surface-polasmon-polariton (SPP) interference lithography (SE-SPPIL) designed by an improving attenuated total reflection (ATR) mode is suggested for fabricating metal nanograting. A metal film coated under a prism excites SPP first, and then the SPP energy transmits into another metal film and launches SPP again. An interlayer between two metal films is a thin resist coated on the second metal film. An interference nanopattern is formed in the resist when two SPP waves are launched symmetrically. After development, chemical or physical etching, the nanopattern is transferred into the metal film. A random thickness metal grating can be achieved as the thickness of the second metal film does not influence the interference pattern intensity. This scheme is promising for fabricating metal nanograting at low cost.
Computational Investigation of InxGa1−xN/InN Quantum-Dot Intermediate-Band Solar Cell
DENG Qing-Wen**, WANG Xiao-Liang, , YANG Cui-Bai, XIAO Hong-Ling, WANG Cui-Mei, YIN Hai-Bo, HOU Qi-Feng, BI Yang, LI Jin-Min, WANG Zhan-Guo, HOU Xun
Chin. Phys. Lett. 2011, 28 (1): 018401 .   DOI: 10.1088/0256-307X/28/1/018401
Abstract   PDF(pc) (990KB) ( 929 )
An InxGa1−xN/InN quantum-dot intermediate-band solar cell is calculated by means of solving the Schrödinger equation according to the Kronig–Penney model. Based on particular assumptions, the power conversion efficiency is worked out. The results reveal that the InxGa1−xN/InN quantum-dot intermediate-band solar cell manifests much larger power conversion efficiency than that of p-n junction solar cells, and the power conversion efficiency strongly depends on the size of the quantum dot and the interdot distance.
A Compact Spice Model with Verilog-A for Phase Change Memory
CAI Dao-Lin**, SONG Zhi-Tang, LI Xi, CHEN Hou-Peng, CHEN Xiao-Gang
Chin. Phys. Lett. 2011, 28 (1): 018501 .   DOI: 10.1088/0256-307X/28/1/018501
Abstract   PDF(pc) (518KB) ( 1130 )
A compact spice model of the phase change memory with the crystalline fraction as the switching by Verilog-A language is proposed and demonstrated. The model can simulate not only the resistance change by the different electrical pulse, but also the temperature profile and crystalline fraction during programming operation. The simulated resistance as a function of the amplitude of programming voltage pulses is in good agreement with the experimental data.
Frequency-Locking in a Spatially Extended Predator-Prey Model
YU Cun-Juan**, TAN Ying-Xin
Chin. Phys. Lett. 2011, 28 (1): 018701 .   DOI: 10.1088/0256-307X/28/1/018701
Abstract   PDF(pc) (681KB) ( 471 )
The study is concerned with the effect of variable dispersal rates on Turing instability of a spatial Holling–Tanner system. A series of numerical simulations show that the oscillatory Turing pattern can emerge due to period diffusion coefficient. Moreover, we find that when the amplitude is above a threshold, 1:1 frequency-locking oscillation can be obtained. The results show that period diffusion coefficient plays an important role on the pattern formation in the predator-prey system.
Hidden Tree Structure is a Key to the Emergence of Scaling in the World Wide Web
ZHENG Bo-Jin, **, WANG Jian-Min, CHEN Gui-Sheng, JIANG Jian, SHEN Xian-Jun
Chin. Phys. Lett. 2011, 28 (1): 018901 .   DOI: 10.1088/0256-307X/28/1/018901
Abstract   PDF(pc) (547KB) ( 354 )
Preferential attachment is the most popular explanation for the emergence of scaling behavior in the World Wide Web, but this explanation has been challenged by the global information hypothesis, the existence of linear preference and the emergence of new big internet companies in the real world. We notice that most websites have an obvious feature that their pages are organized as a tree (namely hidden tree) and hence propose a new model that introduces a hidden tree structure into the Erdös–Rényi model by adding a new rule: when one node connects to another, it should also connect to all nodes in the path between these two nodes in the hidden tree. The experimental results show that the degree distribution of the generated graphs would obey power law distributions and have variable high clustering coefficients and variable small average lengths of shortest paths. The proposed model provides an alternative explanation to the emergence of scaling in the World Wide Web without the above-mentioned difficulties, and also explains the "preferential attachment" phenomenon.
A Simple Model of Interaction between Journals, Authors and Editorial Board Members
ZOU Sheng-Rong, XU Ying-Ying, XU Xiu-Lian, WANG Jian, HE Da-Ren**
Chin. Phys. Lett. 2011, 28 (1): 018902 .   DOI: 10.1088/0256-307X/28/1/018902
Abstract   PDF(pc) (510KB) ( 417 )
Recently, quantitative study on complex systems has become an attractive research area for physicists. Human scientific activity, including scientific paper publication, is an important complex system and therefore deserves an investigation. We present a simple model to describe the interaction between journals, authors and editorial board members. In the model the probabilities, with which a journal accepts papers from an author or invites him as an editorial board member, obey normal distributions. However, the most probable value of the latter distribution shifts such that the journal can have higher level authors being its editorial board members. The analytic derivation by the model is in rather good agreement with the empirical observation from the selected fifteen worldwide journals with different impact factors.
Radioactivity Levels and Gamma-Ray Dose Rate in Soil Samples from Kohistan (Pakistan) Using Gamma-Ray Spectrometry
Hasan M. Khan*, M. Ismail, K. Khan, P. Akhter
Chin. Phys. Lett. 2011, 28 (1): 019301 .   DOI: 10.1088/0256-307X/28/1/019301
Abstract   PDF(pc) (364KB) ( 1078 )
The analysis of naturally occurring radionuclides (226Ra, 232Th and 40K) and an anthropogenic radionuclide 137Cs is carried out in some soil samples collected from Kohistan district of N.W.F.P. (Pakistan), using gamma−ray spectrometry. The gamma spectrometry is operated using a high purity Germanium (HPGe) detector coupled with a computer based high resolution multi channel analyzer. The specific activity in soil ranges from 24.72 to 78.48 Bqkg−1 for 226Ra, 21.73 to 75.28 Bqkg−1 for 232Th, 7.06 to 14.9 Bqkg−1 for 137Cs and 298.46 to 570.77 Bqkg−1 for 40K with the mean values of 42.11, 43.27, 9.5 and 418.27 Bqkg−1, respectively. The radium equivalent activity in all the soil samples is lower than the safe limit set in the OECD report (370 Bqkg−1). Man-made radionuclide 137Cs is also present in detectable amount in all soil samples. Presence of 137Cs indicates that the samples in this remote area also receive some fallout from nuclear accident in Chernobyl power plant in 1986. The internal and external hazard indices have the mean values of 0.48 and 0.37 respectively. Absorbed dose rates and effective dose equivalents are also determined for the samples. The concentration of radionuclides found in the soil samples during the present study is nominal and does not pose any potential health hazard to the general public.
Particle Emission-Dependent Timing Noise of Pulsars
LIU Xiong-Wei**, NA Xue-Sen, XU Ren-Xin, QIAO Guo-Jun
Chin. Phys. Lett. 2011, 28 (1): 019701 .   DOI: 10.1088/0256-307X/28/1/019701
Abstract   PDF(pc) (678KB) ( 416 )
Though pulsars spin regularly, the differences between the observed and predicted ToA (time of arrival), known as "timing noise", can still reach a few milliseconds or more. We try to understand the noise in this study. As proposed by Xu and Qiao in 2001, both dipole radiation and particle emission would result in pulsar braking. Accordingly, possible fluctuation of particle current flow is suggested here to contribute significant ToA variation of pulsars. We find that the particle emission fluctuation could lead to timing noise which cannot be eliminated in timing process and that a longer period fluctuation would arouse a stronger noise. The simulated timing noise profile and amplitude are in agreement with the observed timing behaviors on the timescale of years.
63 articles