Chin. Phys. Lett.

Volume 27 Issue 3

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GENERAL

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Modulational Instability and Variable Separation Solution for a Generalized (2+1)-Dimensional Hirota Equation

LIANG Zu-Feng, TANG Xiao-Yan

Chin. Phys. Lett. 2010, 27 (3): 030201 . DOI: 10.1088/0256-307X/27/3/030201

Abstract

PDF(pc) (535KB) ( 1272 )

It is demonstrated by the linear modulational instability analysis that a generalized (2+1)-dimensional Hirota equation is modulationally stable. Then, a Bäcklund transformation (BT) is obtained by means of the truncated Painlevé approach. Using the BT, the model is transformed to a system of equations, which finally leads to a special variable separation solution with arbitrary functions.

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Integrable Curve Motions in n-Dimensional Centro-Affine Geometries

LI Yan-Yan

Chin. Phys. Lett. 2010, 27 (3): 030202 . DOI: 10.1088/0256-307X/27/3/030202

Abstract

PDF(pc) (292KB) ( 636 )

Motions of curves in n-dimensional (n ≥ 4) centro-affine geometries are studied. It is shown that the 1+1-dimensional KdV equations and their hierarchy satisfied by the curvatures of curves under inextensible motions arise from such motions.

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Robustness of Cooperation on Highly Clustered Scale-Free Networks

CONG Rui, QIU Yuan-Ying, CHEN Xiao-Jie, WANG Long,

Chin. Phys. Lett. 2010, 27 (3): 030203 . DOI: 10.1088/0256-307X/27/3/030203

Abstract

PDF(pc) (610KB) ( 700 )

We study the effect of mutation on the evolutionary prisoner's dilemma in highly clustered scale-free networks. It is found that cooperation is more sensitive and vulnerable to strategy mutation in more highly clustered networks. For small mutation rates, high clustering coefficient promotes cooperation. For medium mutation rates, high clustering coefficient inhibits the emergence of cooperation. For large mutation rates, cooperation is insensitive to clustering property. We provide explanations for the effects of clustering on cooperation with varied mutation rates.

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Entanglement Purification for Mixed Entangled Quantum Dot States via Superconducing Transmission Line Resonators

DONG Ping, ZHANG Gang, CAO Zhuo-Liang

Chin. Phys. Lett. 2010, 27 (3): 030301 . DOI: 10.1088/0256-307X/27/3/030301

Abstract

PDF(pc) (329KB) ( 820 )

An entanglement purification protocol for mixed entangled states is presented via double quantum dot molecules inside a superconducing transmission line resonator (TLR). In the current scenario, coupling for arbitrary double quantum dot molecules can be tuned via the TLR in the large detuning region by controlling the qubit level splitting. The TLR is always empty and only virtually excited, so the interaction is insensitive to both the TLR decay and thermal field. Discussion about the feasibility of our scheme shows that the entanglement purification can be implemented with high fidelity and successful probability.

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Implementing a Multi-Qubit Quantum Phase Gate Encoded by Photonic Qubit

LU Pei-Min, SONG Jie, XIA Yan

Chin. Phys. Lett. 2010, 27 (3): 030302 . DOI: 10.1088/0256-307X/27/3/030302

Abstract

PDF(pc) (387KB) ( 633 )

A protocol is proposed to implement a three-qubit phase gate for photonic qubits in a three-mode cavity. The idea can be extended to directly implement a N-qubit phase gate. We also show that the interaction time remains unchanged with the increasing number of qubits. In addition, the influence of cavity decay and atomic spontaneous emission on the gate fidelity and photon loss probability is also discussed by numerical calculation.

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Adiabatic Fidelity of Coherent Atom-Heteronuclear Molecule Conversion

GENG Zhen-Duo, JIA Ning, ZHAO Xu, XIA Tian-Yu, JING Hui

Chin. Phys. Lett. 2010, 27 (3): 030303 . DOI: 10.1088/0256-307X/27/3/030303

Abstract

PDF(pc) (501KB) ( 692 )

We study the adiabatic dark-state evolutions in coherent creations of heteronuclear diatomic or triatomic molecules from an ultracold two-species atomic condensate. We find that, for different nonlinear systems, the relations between the adiabatic fidelities and the adiabatic parameters are in a universal power law but with quite different parameters.

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Bose--Einstein Condensates with Two- and Three-Body Interactions in an Anharmonic Trap at Finite Temperature

LI Hao-Cai, CHEN Hai-Jun, XUE Ju-Kui

Chin. Phys. Lett. 2010, 27 (3): 030304 . DOI: 10.1088/0256-307X/27/3/030304

Abstract

PDF(pc) (494KB) ( 782 )

The transition temperature, the depletion of the condensate atoms and the collective excitations of a Bose-Einstein condensation (BEC) with two- and three-body interactions in an anharmonic trap at finite temperature are studied in detail. By using the Popov version of the Hartree-Fock-Bogoliubov (HFB) approximation, an extended self-consistent model describing BEC with both two- and three-body interactions in a distorted harmonic potential at finite temperature is obtained and solved numerically. The results show that the transition temperature, the condensed atom number and the collective excitations are modified dramatically by the atomic three-body interactions and the distortion of the harmonic trap.

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Bell Operator Method to Classify Local Realistic Theories

Koji Nagata

Chin. Phys. Lett. 2010, 27 (3): 030305 . DOI: 10.1088/0256-307X/27/3/030305

Abstract

PDF(pc) (284KB) ( 517 )

We review the historical fact of multipartite Bell inequalities with an arbitrary number of settings. An explicit local realistic model for the values of a correlation function, given in a two-setting Bell experiment (two-setting model), works only for the specific set of settings in the given experiment, but cannot construct a local realistic model for the values of a correlation function, given in a continuous-infinite settings Bell experiment (infinite-setting model), even though there exist two-setting models for all directions in space. Hence, the two-setting model does not have the property that the infinite-setting model has. Here, we show that an explicit two-setting model cannot construct a local realistic model for the values of a correlation function, given in an M-setting Bell experiment (M-setting model), even though there exist two-setting models for the M measurement directions chosen in the given M-setting experiment. Hence, the two-setting model does not have the property that the M-setting model has.

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The n-Qubit W State of Ground-State Atoms Using Cavity QED and Single Photon Detection

PAN Chang-Ning, ZHANG Jun-Xiang, ZHAO Xue-Hui

Chin. Phys. Lett. 2010, 27 (3): 030306 . DOI: 10.1088/0256-307X/27/3/030306

Abstract

PDF(pc) (397KB) ( 494 )

We present a simple scheme for the probabilistic generation of the $n$-qubit W state of three-level systems in cavity quantum electrodynamics. Once the W state is prepared, it will be insensitive to the spontaneous emission of atoms due to the fact that only the two degenerate ground states of the three-level atoms are involved. With time evolution of the system, the success probability and the experimental feasibility are also discussed.

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Another Conserved Quantity by Mei Symmetry of Tzénoff Equation for Non-Holonomic Systems

ZHENG Shi-Wang, XIE Jia-Fang, WANG Jian-Bo, CHEN Xiang-Wei

Chin. Phys. Lett. 2010, 27 (3): 030307 . DOI: 10.1088/0256-307X/27/3/030307

Abstract

PDF(pc) (301KB) ( 529 )

As a direct result of Mei symmetry of the Ténoff equation for non-holonomic mechanical systems, another conserved quantity is studied. The expression and the determining equations of the above conserved quantity are also presented. Using this method, it is easier to find out conserved quantity than ever. In the last, an example is presented to illustrate applications of the new results.

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A New Method to Solve the Spheroidal Wave Equations

TIAN Gui-Hua

Chin. Phys. Lett. 2010, 27 (3): 030308 . DOI: 10.1088/0256-307X/27/3/030308

Abstract

PDF(pc) (278KB) ( 530 )

The perturbation method in supersymmetric quantum mechanics is used to study the spheroidal wave functions' eigenvalue problem. The super-potential are solved in series of the parameter α, and the general form of all its terms is obtained. This means that the spheroidal problem is solved completely in the way for the ground eigen-value problem. The shape invariance property is proved retained for the super-potential and subsequently all the excited eigen-value problem could be solved. The results show that the spheroidal wave equations are integrable.

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Bifurcation Control of Current-Mode Buck Converter via TDFC

LU Wei-Guo, XU Ping-Ye, ZHOU Luo-Wei, LUO Quan-Ming

Chin. Phys. Lett. 2010, 27 (3): 030501 . DOI: 10.1088/0256-307X/27/3/030501

Abstract

PDF(pc) (564KB) ( 867 )

Considering the TDFC controlled current-mode Buck converter featuring periodicity we propose a Fourier-decomposition based method for the bifurcation analysis of this system, hence the theoretical range of control gain of TDFC is determined. In addition, the power-stage experiment circuit is built and the control part is realized in a digital controller. The experimental results show that either bifurcation or chaos in the current-mode Buck converter can be controlled into the expectant period-1 orbit rapidly.

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Effect of Time Delay on Stochastic Tumor Growth

TIAN Jing, CHEN Yong

Chin. Phys. Lett. 2010, 27 (3): 030502 . DOI: 10.1088/0256-307X/27/3/030502

Abstract

PDF(pc) (466KB) ( 1160 )

We study the dynamics of tumor cell growth with time-delayed feedback driven by multiplicative noise in an asymmetrical bistable potential well. For a small delay time, the analytical solutions of the probability distribution and the first passage time show that, with the increasing delay time, the peak of the probability distribution in a lower population state would increase, but in a higher population state it decreases. It is shown that the multiplicative noise and the time delay play opposite roles in the tumor cell growth.

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Level Statistics for the Nilsson Single-Particle Levels

CHEN Fang-Qi, ZHOU Xian-Rong, GU Jian-Zhong

Chin. Phys. Lett. 2010, 27 (3): 030503 . DOI: 10.1088/0256-307X/27/3/030503

Abstract

PDF(pc) (450KB) ( 585 )

We perform level statistics of the Nilsson single-particle levels. The effects of the l² and l ・ s; s terms are discussed as well as their interplay with the deformations. The results show that when the l² term is added to the harmonic oscillator potential, chaotic motion occurs. The strength ranges of the l² term in which chaotic motion exists are related to the deformation of the harmonic oscillator potential. The calculations of the localization length in different bases demonstrate that it is the spherical or axial symmetries that govern the chaotic motion. The degree of chaoticity increases significantly with the l ・ s; s term included.

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Synchronization of Coupled Nonidentical Dynamical Systems

ZHANG Gang, ZHANG Wei, LIU Zeng-Rong

Chin. Phys. Lett. 2010, 27 (3): 030504 . DOI: 10.1088/0256-307X/27/3/030504

Abstract

PDF(pc) (612KB) ( 1043 )

Synchronization behavior of coupled dynamical systems is discussed. An equivalence relation is found between the diffeomorphic generalized synchronization and the complete synchronization of coupled nonidentical systems. Employing the method of the complete synchronization, the problem of the generalized synchronization can be unraveled. By constructing an appropriate coupling term, a sufficient condition is obtained for determining the complete synchronization of coupled nonidentical systems. Numerical simulations are also given to show the effectiveness of the proposed schemes.

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Adaptive Synchronization of an Array of Time-Varying Coupled Delayed Neural Networks

WANG Jian-An, LIU He-Ping

Chin. Phys. Lett. 2010, 27 (3): 030505 . DOI: 10.1088/0256-307X/27/3/030505

Abstract

PDF(pc) (355KB) ( 549 )

Synchronization in an array of time-varying coupled delayed neural networks is investigated. We assume that the entries of time-varying coupling configuration matrix and inner-coupling matrix of the model are all bounded. By combining linear feedback with an adaptive control approach, some simple controllers are proposed to ensure the states of such coupled networks globally asymptotically synchronize to a desired synchronous solution. Simulation results are provided to demonstrate the effectiveness of the proposed approach.

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Adaptive H_∞Chaos Anti-synchronization

Choon Ki Ahn

Chin. Phys. Lett. 2010, 27 (3): 030506 . DOI: 10.1088/0256-307X/27/3/030506

Abstract

PDF(pc) (537KB) ( 696 )

A new adaptive H_∞ anti-synchronization (AHAS) method is proposed for chaotic systems in the presence of unknown parameters and external disturbances. Based on the Lyapunov theory and linear matrix inequality formulation, the AHAS controller with adaptive laws of unknown parameters is derived to not only guarantee adaptive anti-synchronization but also reduce the effect of external disturbances to an H_∞ norm constraint. As an application of the proposed AHAS method, the H_∞anti-synchronization problem for Genesio-Tesi chaotic systems is investigated.

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Structure Identification of Nonlinearly Coupled Complex Networks with Non-Delayed and Delayed Coupling

GUO Wan-Li, Francis Austin, CHEN Shi-Hua

Chin. Phys. Lett. 2010, 27 (3): 030507 . DOI: 10.1088/0256-307X/27/3/030507

Abstract

PDF(pc) (537KB) ( 527 )

Topology identification is an important problem for complex networks because much information about networks in practice such as the topological structure is uncertain. We propose an adaptive control method for identifying the topology of general nonlinearly-coupled complex network models that are either non-delayed or delayed coupled. Simulation results are also presented to illustrate the effectiveness of the method.

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Chaos Control and Synchronization of Cellular Neural Network with Delays Based on OPNCL Control

TANG Qian, WANG Xing-Yuan

Chin. Phys. Lett. 2010, 27 (3): 030508 . DOI: 10.1088/0256-307X/27/3/030508

Abstract

PDF(pc) (367KB) ( 595 )

The problem of chaos control and complete synchronization of cellular neural network with delays is studied. Based on the open plus nonlinear closed loop (OPNCL) method, the control scheme and synchronization scheme are designed. Both the schemes can achieve the chaos control and complete synchronization of chaotic neural network respectively, and their validity is further verified by numerical simulation experiments.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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The Casimir Force between Parallel Plates in Randall--Sundrum I Model

CHENG Hong-Bo

Chin. Phys. Lett. 2010, 27 (3): 031101 . DOI: 10.1088/0256-307X/27/3/031101

Abstract

PDF(pc) (356KB) ( 529 )

The Casimir effect for parallel plates within the frame of the five-dimensional Randall-Sundrum model with two branes is re-examined. We argue that the nature of Casimir force is repulsive if the distance between the plates is not extremely tiny, which is not consistent with the experimental phenomena, meaning that the Randall-Sundrum I model can not be acceptable. We also point out that the estimation of the separation between the two branes, by means of Casimir effect for two-parallel-plate system, is not feasible, in contrast to another recent study.

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Calculation of Quark-Number Susceptibility at Finite Chemical Potential and Temperature

CAO Jing, ZHAO A-Meng, LUO Liu-Jun, SUN Wei-Min, ZONG Hong-Shi,

Chin. Phys. Lett. 2010, 27 (3): 031201 . DOI: 10.1088/0256-307X/27/3/031201

Abstract

PDF(pc) (399KB) ( 672 )

We use the direct method proposed by He et al. [Phys. Lett. B 680 (2009) 432) to calculate the quark-number susceptibility (QNS) at finite temperature and the chemical potential in the quasi-particle model. In our approach the QNS is given by a formula solely involving the dressed quark propagator at finite chemical potential μ and temperature Τ. The QNS at finite μ and Τ is calculated in the quasi-particle model. It is found that at high temperatures the QNS tends to the ideal quark gas result. At very small temperatures the QNS vanishes. This vanishing behavior in the low-temperature region is consistent with the lattice results. For μ∈ [0,180] MeV, our results show that there exists a rapid increase of QNS near some temperatures. The temperature at which the rapid increase occurs shifts to smaller values with the increasing quark chemical potential. This rapid increase could be regarded as a signal of a crossover.

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Probe R-Parity Violating Supersymmetry in Forward--Backward Asymmetry

GUO Lei, HAN Liang, MA Wen-Gan, XI Yun-Feng, YANG Si-Qi, ZHANG Ren-You

Chin. Phys. Lett. 2010, 27 (3): 031301 . DOI: 10.1088/0256-307X/27/3/031301

Abstract

PDF(pc) (399KB) ( 496 )

We investigate the possibility of probing R-parity violating interactions in forward-backward asymmetries, and conclude that the Tevatron collider is the best place to measure new interactions involving the first generation of quarks. With additional down type squark ^~d_k contributions, the charge asymmetry in e⁺e^—events around Z-pole mass region at the Tevatron will be sensitive to R-parity violating couplings λ’_11k, which was inaccessible to the LEP Q_fb ^hadinclusive measurement. Assuming no apparent deviation from SM prediction is observed, λ’_11k< 0.19 at 95% C.L. with squark mass M^~d_k=100 GeV can be derived.

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Flavor-Changing Neutral-Current Production of t^-c in Association with a Neutral Top-Higgs at LHC in the Topcolor-Assisted Technicolor Model

LU Gong-Ru, WU Lei

Chin. Phys. Lett. 2010, 27 (3): 031401 . DOI: 10.1088/0256-307X/27/3/031401

Abstract

PDF(pc) (409KB) ( 540 )

In the framework of the topcolor-assisted technicolor (TC2) model we investigate the flavor-changing neutral-current production pp→ t^-ch_to at the Large Hadron Collider (LHC), which proceeds through the parton-level processes gg→ t^-ch_to , uu→ t^-ch_to and d^-d → t^-ch_to . We calculate the production rate and present the distributions of the transverse momenta and the invarient mass of the neutral top-higgs. It is found that the cross section of pp→ t^-ch_to can reach a few hundreds of fb in a large part of the allowed parameter space. Considering the main decay mode of top-higgs for m_ht<2m_t, we find that such a production may provide copious events. In the case of unobservation, the LHC can set meaningful constraints on the TC2 model.

NUCLEAR PHYSICS

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De-excitation Energy of Superdeformed Secondary Minima of Odd-Odd Au Isotopes and Its Sensitivity to the Density Dependence of Symmetry Energy

JIANG Wei-Zhou, CHEN Yun-Peng, LU Xing

Chin. Phys. Lett. 2010, 27 (3): 032101 . DOI: 10.1088/0256-307X/27/3/032101

Abstract

PDF(pc) (378KB) ( 485 )

The de-excitation energy of superdeformed secondary minima of odd-odd Au isotopes is investigated using the relativistic mean field model with the inclusion of the isoscalar-isovector coupling. It is shown that the de-excitation energies of superdeformed secondary minima relative to the ground states can serve as a significant probe to the density dependence of the symmetry energy.

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De-excitation Energy of Superdeformed Secondary Minima of Odd-Odd Au Isotopes and Its Sensitivity to the Density Dependence of Symmetry Energy

JIANG Wei-Zhou, CHEN Yun-Peng, LU Xing

Chin. Phys. Lett. 2010, 27 (3): 032101 . DOI: 10.1088/0256-307X/27/3/032101

Abstract

PDF(pc) (378KB) ( 462 )

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Excited States in ¹⁸Ne Studied via ¹⁷F+p *

JIN Sun-Jun, , WANG You-Bao, WANG Bao-Xiang, BAI Xi-Xiang, FANG Xiao, GUO Bing, LI Er-Tao, LI Yun-Ju, LI Zhi-Hong, LIAN Gang, SU Jun, YAN Sheng-Quan, ZENG Sheng, YAO Ze-En, LIU Wei-Ping

Chin. Phys. Lett. 2010, 27 (3): 032102 . DOI: 10.1088/0256-307X/27/3/032102

Abstract

PDF(pc) (1471KB) ( 593 )

The elastic resonance scattering of ¹⁷F+p is studied in inverse kinematics via a thick-target method. The excitation function for ¹⁷F+p elastic scattering is obtained within the energy interval of E_{c.m ^≈}0.4-1.7 MeV. The experimental excitation function is analyzed with a multilevel R-matrix code MULTI7, and the proton widths are deduced. The α decay from 6.15 MeV 1^-state in ¹⁸Ne is observed, which is critical to the ¹⁴O(α, p)¹⁷F reaction as the main breakout route from CNO cycle to rp-process in supernovae and x-ray bursts.

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Experimental Study on the Exotic Structure of 12N in RIBLL

LI Jia-Xing, LIU Ping-Ping, WANG Jian-Song, HU Zheng-Guo, MAO Rui-Shi, LI Chen, CHEN Ruo-Fu, SUN Zhi-Yu, XU Hu-Shan, XIAO Guo-Qing, GUO Zhong-Yan

Chin. Phys. Lett. 2010, 27 (3): 032501 . DOI: 10.1088/0256-307X/27/3/032501

Abstract

PDF(pc) (538KB) ( 749 )

We measured the total reaction cross sections of ¹²N in Si at 36.2 MeV/u using Radioactive Ion Beam Line in Lanzhou (RIBLL) with a new method. The reaction target was installed at the intermediate focusing point T1 at RIBLL. This scheme allows us to identify particles before and after the reaction target unambiguously. The total reaction cross section (1760±78 mb) of ¹²N in Si is obtained. Assuming that ¹²N consists of a core ¹¹C plus one halo proton, the excitation function of ¹²N on the Si and C targets is calculated with the Glauber model and the Fermi-Fermi density distributions. It can fit the experimental data very well. A large diffusion of the protons density distribution supports the halo structure for ¹²N.

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Intermediate Energy Coulomb Excitation of Neutron-Rich Nuclei

Rajiv Kumar, Rajesh Kharab, H. C. Sharma

Chin. Phys. Lett. 2010, 27 (3): 032502 . DOI: 10.1088/0256-307X/27/3/032502

Abstract

PDF(pc) (406KB) ( 701 )

We reinvestigate the collective effects of the retardation as well as the bending on the Coulomb excitation cross sections and also on the B(E2) strengths of some neutron-rich isotopes using the intermediate energy Coulomb excitation theory. It is found that the B(E2) strengths extracted from the experimental Coulomb excitation cross section data get suppressed approximately by 6%. Furthermore, the obtained B(E2) strengths in the energy range 30-100 MeV/A are found to be in better agreement with the corresponding values known from other sources, than those obtained by using the recoil-corrected relativistic Coulomb excitation theory.

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Pseudorapidity Distributions of Charged Particles and Contributions of Leading Nucleons in Cu-Cu Collisions at High Energies

SUN Jian-Xin, LIU Fu-Hu, WANG Er-Qin

Chin. Phys. Lett. 2010, 27 (3): 032503 . DOI: 10.1088/0256-307X/27/3/032503

Abstract

PDF(pc) (558KB) ( 656 )

The pseudorapidity distributions of charged particles produced in Cu-Cu collisions over an energy range from 22.4 GeV to 200 GeV are investigated by using a multi-source ideal gas model which contains systematically the contributions of leading nucleons. It is shown that the calculated results are in agreement with the experimental data and the model is successful in the description of the pseudorapidity distribution of charged particles. The contributions of leading nucleons increase with the increasing impact parameter. The cylinder length (the longitudinal shift of the interacting system) in rapidity space increases with the increasing energy and does not depend on centrality at a given energy.

ATOMIC AND MOLECULAR PHYSICS

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Theoretical Study of Interesting Fine-Structure Splittings Based on a Scenario for Precise Calculations

ZHANG Xiao-Le, CHENG Cheng, GAO Xiang, LI Jia-Ming,

Chin. Phys. Lett. 2010, 27 (3): 033101 . DOI: 10.1088/0256-307X/27/3/033101

Abstract

PDF(pc) (331KB) ( 682 )

Based on the multi-configuration Dirac-Fock self-consistent field method, a scenario has been presented to calculate the fine-structure energy levels of C²⁺ and Si²⁺ excited states (3¹D₂ and 3₃D_1,2,3). The Breit interactions and quantum electrodynamics corrections are added as perturbations. The present calculation results are found to be in excellent agreement with the experimental data. By means of the precise calculation procedure, we elucidate that four competitive mechanisms influence the interesting fine-structure splittings in C²⁺ and Si²⁺, such as spin-orbit interactions, relativistic corrections of exchange interactions, the Breit interactions and electron correlation effects. Furthermore, the mechanism of relativistic correction of exchange interactions has been studied clearly. We elucidate that the inner shell 2p_1/2,3/2 orbitals are essential to relativistic corrections of exchange interactions which are crucial for the final anomalous fine-structure splittings.

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Quasi-classical Trajectory Study of Reaction O (³P)+HCl (v =2; j=1,6,9) →OH+Cl

ZHU Tong, HU Guo-Dong, ZHANG Qing-Gang

Chin. Phys. Lett. 2010, 27 (3): 033102 . DOI: 10.1088/0256-307X/27/3/033102

Abstract

PDF(pc) (496KB) ( 482 )

The reaction O(³P)+HCl (v=2; j= 1,6,9) → OH+Cl is theoretically studied with a quasi-classical trajectory method (QCT) on the benchmark potential energy surface of the ground 3A'' state [J. Chem. Phys. 119(2003)9550]. The QCT-calculated state-resolved rotational distributions are in good agreement with the experimental results. The rotational polarization of the product OH molecule becomes weaker as the initial HCl rotation is excited. The calculated results can be explained from the large mass factor cos²β of the title reaction, the van der Waals well in the potential energy surface and the secondary encounters in the exit channel.

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Destructive and Constructive Interference of High-Order Harmonic Generation in Mixture of He and Ne Gases

JIN Cheng, ZHOU Xiao-Xin, ZHAO Song-Feng

Chin. Phys. Lett. 2010, 27 (3): 033301 . DOI: 10.1088/0256-307X/27/3/033301

Abstract

PDF(pc) (433KB) ( 1030 )

Using the single-atom induced dipole moment under strong field approximation as a source, we suggest a model to simulate the macroscopic high-order harmonic generation (HHG) from the mixed gases (He and Ne) interacting with intense infrared laser by solving the three-dimensional Maxwell's equation of the harmonic field. Regular destructive interference (DI) and constructive interference (CI) are observed in the macroscopic HHG spectra when the gas jet is put at a good phase-matching position. A semiclassical model of short and long electron trajectories is applied to interpret the DI and CI of HHG qualitatively.

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A Monte Carlo Study of Low-Energy Electron Transport in Liquid Water: Influence of the Rutherford Formula and the Mott Model

JIANG Ding-Ju, TAN Zhen-Yu

Chin. Phys. Lett. 2010, 27 (3): 033401 . DOI: 10.1088/0256-307X/27/3/033401

Abstract

PDF(pc) (478KB) ( 1088 )

Influence of the Rutherford formula and the Mott model on the Monte Carlo simulation of low-energy electron (<10 keV) transport in liquid water is investigated. One of the features of the constructed Monte Carlo code is the implementation of the new optical-data model from Emfietzoglou et al. in inelastic cross section based on the dielectric response theory. In addition, a novel mean elastic cross section by means of the Mott model is proposed to calculate the electron elastic scattering for high simulation efficiency. The systematical calculations of both the distribution of energy depositions and penetration parameter for low-energy electrons in liquid water are performed by using the Rutherford formula and the Mott model, respectively, for the elastic collisions in the simulations. The calculated results show that the effect of the two models is evident at energies below about 1 keV.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

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Three-Dimensional Analytical Formula for Oblique and Off-Axis Gaussian Beams Propagating through a Cat-Eye Optical Lens

ZHAO Yan-Zhong, SUN Hua-Yan, YU Xia-Qiong, FAN Meng-Shan

Chin. Phys. Lett. 2010, 27 (3): 034101 . DOI: 10.1088/0256-307X/27/3/034101

Abstract

PDF(pc) (1863KB) ( 682 )

Based on the Collins formula in a cylindrical coordinate system and the method of introducing a hard aperture function into a finite sum of complex Gaussian functions, an approximate three-dimensional analytical formula for oblique and off-axis Gaussian beams propagating through a cat-eye optical lens is derived. Numerical results show that a reasonable choice of the obliquity factor would result in a better focus beam with a higher central intensity at the return place than that without obliquity, whereas the previous conclusion based on geometry optics is that the highest central intensity could be obtained when there is no obliquity.

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An Improved Method of Designing Isotropic Multilayered Spherical Cloak for Electromagnetic Invisibility

CHEN Ming-Ji, PEI Yong-Mao, FANG Dai-Ning,

Chin. Phys. Lett. 2010, 27 (3): 034102 . DOI: 10.1088/0256-307X/27/3/034102

Abstract

PDF(pc) (467KB) ( 847 )

The classic anisotropic spherical cloak can be mimicked by many alternating thin layers of isotropic metamaterials [Qiu et al. Phys. Rev. E 79 (2009) 047602]. We propose an improved method of designing permittivity and permeability in each isotropic layer, which eliminates the jumping of the refractive index at the interface. Multilayered spherical cloaks designed by the present method perform much better than those by Qiu et al., especially for forward scattering. It is found that the ratio of layer thickness to the operating wavelength plays an important role in achieving invisibility. The presented cloak should be discretized to at least 40 layers to meet the thickness threshold corresponding to 10% scattering.

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Dual-Band Negative-Index Materials with Sandwich Configuration

WANG Xu-Dong, YE Yong-Hong, ZHENG Chao

Chin. Phys. Lett. 2010, 27 (3): 034103 . DOI: 10.1088/0256-307X/27/3/034103

Abstract

PDF(pc) (585KB) ( 638 )

Dual-band negative-index properties of the silver-SU-8-silver sandwich configuration, perforated with a square array of cross dipole apertures, are simulated and analyzed in the midinfrared region. The first and the second negative-index bands correspond to the (1,0) and (1,1) internal surface plasmon polariton (SPP) modes, respectively. The internal and external SPP modes acquired by the SPP dispersion relation of the metal/dielectric/metal model match well with the simulated transmission peaks. The effective parameters for the two negative-index bands are retrieved using simulated S parameters. The coupling effect between the (1,1) internal SPP mode and the localized resonance mode can be tuned by the arm length of cross dipole, which can weaken or destroy the negative electromagnetic response of the second negative-index band. The electric quadrupole mode of the second negative-index band accounts for its strong dependence on the dielectric loss of the interlayer.

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Experimental Verification of Left-Handed Metamaterials Composed of Coplanar Electric and Magnetic Resonators

WANG Jia-Fu, QU Shao-Bo, XU Zhuo, XIA Song, MA Hua, WANG Qian, YANG Yi-Ming, WU Xiang

Chin. Phys. Lett. 2010, 27 (3): 034104 . DOI: 10.1088/0256-307X/27/3/034104

Abstract

PDF(pc) (620KB) ( 547 )

We verified experimentally left-handed metamaterials (LHM) composed of coplanar electric and magnetic resonators. A typical LHM sample composed of coplanar resonator unit cells was fabricated, investigated and tested. The experimental results show that the tested sample has a left-handed band of width 1.4 GHz in the X band. The experimental results agree quite well with the simulation ones. Moreover, both the simulation and experimental results show that the LHM under study can automatically achieve good impedance-matching in the left-handed band.

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An Adaptive Fast Multipole Higher Order Boundary Element Method for Power Frequency Electric Field of Substation

ZHANG Zhan-Long, DENG Jun, XIAO Dong-Ping, HE Wei, TANG Ju

Chin. Phys. Lett. 2010, 27 (3): 034105 . DOI: 10.1088/0256-307X/27/3/034105

Abstract

PDF(pc) (472KB) ( 605 )

An adaptive fast multipole higher order boundary element method combining fast multipole (FM) with a higher order boundary element method is studied to solve the power frequency electric field (PFEF) of substations. In this new technique, the iterative equation solver GMRES is used in the FM, where matrix-vector multiplications are calculated using fast multipole expansions. The coefficients in the preconditioner for GMRES are stored and are used repeatedly in the direct evaluations of the near-field contributions. Then a 500kV outdoor substation is modeled and the PFEF of the substation is analyzed by the novel algorithm and other conventional methods. The results show that, in computational cost and the storages capability aspects, the algorithm proposed in this study has obvious advantages. It is suitable for the calculation of the large-scale PFEF in complex substations and the design of electromagnetic compatibility.

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Numerical Simulations of Backward-to-Forward Leaky-Wave Antenna with Composite Right/Left-Handed Coplanar Waveguide

SI Li-Ming, SUN Hou-Jun, LV Xin

Chin. Phys. Lett. 2010, 27 (3): 034106 . DOI: 10.1088/0256-307X/27/3/034106

Abstract

PDF(pc) (626KB) ( 1431 )

A composite right/left-handed (CRLH) coplanar waveguide (CPW) structure and its leaky-wave antenna (LWA) with continuous backward-to-forward scanning applications are proposed. The structure of the CRLH transmission line (TL) is composed of split-ring resonators (SRRs) for left-handed (LH) series capacitance and short-circuited stubs connected between the CPW central signal line and the ground for LH shunt inductance, while the unavoidable right-handed (RH) parasitic effects series inductance and shunt capacitance are generated by wave propagation through the host transmission line. The dispersion relations are calculated and compared with the equivalent circuit model method and 3D full-wave simulations, which can be used to determine the physical dimensions of the CRLH-CPW, such as in the balanced CRLH-TL case. As a main example, a CRLH-CPW-LWA operating from 1.67 GHz to 1.80 GHz with the dispersion characteristics of the balanced CRLH-TL case shows continuous leakage frequency band (fast wave region) from LH (phase constant β <0, .67<f<1.74 GHz) to RH (β>0, 1.74<f<1.80 GHz) state through the transition frequency point (β=0, f=1.74 GHz), whereas conventional LWAs operated in RH state only provide forward scanning capabilities (β>0).

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Diode Pumped Operation of Tm,Ho:YVO₄ Microchip Laser

LI Gang, YAO Bao-Quan, ZHANG Chao-Hui, WANG Qiang, WANG Yue-Zhu, JU You-Lun

Chin. Phys. Lett. 2010, 27 (3): 034201 . DOI: 10.1088/0256-307X/27/3/034201

Abstract

PDF(pc) (548KB) ( 835 )

A cryogenic and room-temperature diode pumped Tm,Ho:YVO₄ microchip laser with 0.5 mm crystal length lasing around 2μm is demonstrated for the first time to our knowledge. Under cryogenic temperature of 77 K, as much as 1.2 W output and slope efficiency of 35% with respect to absorbed pump power are obtained. At temperature of 5ºC the maximum output power of 48mW is obtained at an absorbed pump power of 503 mW, representing a 9.5% optical to optical conversion efficiency. In addition, as much as 8 mW single-frequency output lasing at 2052.6 nm is achieved at room temperature of 15ºC.

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Intensity Distribution and Phase Vortices of Speckle Fields Generated by Multi-Aperture Random Scattering Screens

LIU Man, SONG Hong-Sheng, CHEN Xiao-Yi, LIU Gui-Yuan, TENG Shu-Yun, CHENG Chuan-Fu

Chin. Phys. Lett. 2010, 27 (3): 034202 . DOI: 10.1088/0256-307X/27/3/034202

Abstract

PDF(pc) (1392KB) ( 1232 )

The intensity distribution and phase vortices of the speckle fields generated by multi-aperture random scattering screens are simulated, and it is found that the vortices exhibit layer-like structures and the dislocation phenomena occur in the local phase patterns produced by the two-pinhole aperture, whose phase distributions appear as striped structures. For three- or four-pinhole aperture, there are many circular bright spots appearing in the speckle grains, and there is one vortex between the neighboring circular bright spots. The positive and negative phase vortex lattices appear in the phase distributions, and the regions circled by the isothetic phase lines form irregular quadrilaterals or hexagons. Moreover, the relative positions of the vortices or bright spots can be adjusted by changing those of the pinhole apertures.

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Coherent Beam Combination of Eight Watt-Level Polarization-Maintained Fiber Amplifiers

ZHOU Pu, WANG Xiao-Lin, MA Yan-Xing, MA Hao-Tong, XU Xiao-Jun, LIU Ze-Jin

Chin. Phys. Lett. 2010, 27 (3): 034203 . DOI: 10.1088/0256-307X/27/3/034203

Abstract

PDF(pc) (439KB) ( 758 )

We demonstrate the coherent beam combination of eight Watt-level polarization-maintained fiber amplifiers. The phase control signal of each amplifier is generated by running a stochastic parallel gradient descent algorithm on a digital signal processor (DSP). The experimental result shows that the whole system in close-loop performs well for long-time observation. Energy encircled in the target pinhole is 6.68 times more than that in open-loop. The combination efficiency is as high as 84.5%.

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Transverse Inhomogeneous Carrier-Envelope Phase Distribution of Idler Generated through Difference-Frequency-Generation

QIU Ping, WANG Ke, ZHU He-Yuan, QIAN Lie-Jia

Chin. Phys. Lett. 2010, 27 (3): 034204 . DOI: 10.1088/0256-307X/27/3/034204

Abstract

PDF(pc) (457KB) ( 525 )

The transverse inhomogeneous carrier-envelope phase (CEP) distribution of idler generated through difference-frequency-generation (DFG) in quadratic nonlinear crystals is theoretically studied. In practical CEP stabilized DFG setups, the pump and the signal are usually Gaussian beams with non-uniform intensity distribution. Since the idler CEP is dependent on gain, this non-uniform intensity distribution leads to inhomogeneous gain across the aperture of the idler beam, resulting in a varying transverse idler CEP. Simulation results show that in practical settings, in the high-gain regime, transverse inhomogeneous CEP can be much smaller compared with π/2. However, when gain on the propagation axis reaches saturation, CEP difference can well exceed π/2.

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Improved Microfluidic Coupled-Cavity Waveguides for Slow Light Transmission

LÜ, Shu-Yuan, ZHAO Jian-Lin, ZHANG Dong

Chin. Phys. Lett. 2010, 27 (3): 034205 . DOI: 10.1088/0256-307X/27/3/034205

Abstract

PDF(pc) (362KB) ( 968 )

We present a method based on the selective liquid infiltration in air holes to produce slow light in a coupled-cavity waveguide structured by two-dimensional photonic crystal and analyze the slow light propagation in the coupled-cavity waveguide with triangular lattice. The group velocity profile of different coupled-cavity waveguides, obtained by the selective liquid infiltration in the holes between the cavities in waveguide and the increased radius of the first row of holes adjacent to the waveguide, is evaluated by using both the plane-wave expansion method and a tight binding model. We determine the optimal parameters to reduce the group velocity. Using a simpler coupled-cavity waveguide structure we obtain smaller group velocity compared to most investigations.

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Numerical Study on Light Localization in Impedance-Matched Meta-Material Random Systems

CHEN Hui-Ping, YAO Pei-Jun, LIANG Zi-Xian, JIANG Xun-Ya, HAN Wen-Da

Chin. Phys. Lett. 2010, 27 (3): 034206 . DOI: 10.1088/0256-307X/27/3/034206

Abstract

PDF(pc) (399KB) ( 477 )

We investigate the localization properties of light propagating in two-dimensional systems with impedance-matched meta-material scatterers which are randomly positioned. Numerically, the localization length ξ versus the index of meta-material is obtained first. We find that, unlike traditional random systems, the localization length of such meta-material random systems does not depend on the total scattering cross section of scatterers, but on the back-scattering cross-section of scatterers. Furthermore, our analysis shows that there are “back-scattering paths of single scattere” in such meta-material systems, which can cause a strong localization effect. Such back-scattering paths inside single scatterers can be thought of as the supplement to the traditional back-scattering paths of multiple scatterers.

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Efficient Phase Locking of Fiber Amplifiers Using a Low-Cost and High-Damage-Threshold Phase Control System

ZHOU Pu, MA Yan-Xing, WANG Xiao-Lin, MA Hao-Tong, XU Xiao-Jun, LIU Ze-Jin

Chin. Phys. Lett. 2010, 27 (3): 034207 . DOI: 10.1088/0256-307X/27/3/034207

Abstract

PDF(pc) (463KB) ( 588 )

We propose a low-cost and high-damage-threshold phase control system that employs a piezoelectric ceramic transducer modulator controlled by a stochastic parallel gradient descent algorithm. Efficient phase locking of two fiber amplifiers is demonstrated. Experimental results show that energy encircled in the target pinhole is increased by a factor of 1.76 and the visibility of the fringe pattern is as high as 90% when the system is in close-loop. The phase control system has potential in phase locking of large-number and high-power fiber laser endeavors.

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Compact Wavelength Division Multiplexer Based on Microstrip Resonator Containing Effective Zero-Index Media

LI Yun-Hui, CAI Zhe, SUN Yong, HE Li, JIANG Hai-Tao

Chin. Phys. Lett. 2010, 27 (3): 034208 . DOI: 10.1088/0256-307X/27/3/034208

Abstract

PDF(pc) (874KB) ( 501 )

A compact wavelength division multiplexer (WDM) based on a microstrip resonator containing effective zero-index media is proposed. Both numerical simulations and microwave experiments demonstrate the crosstalk suppression phenomenon in this WDM. By properly adjusting the values of lumped elements, it is convenient to achieve crosstalk suppression over 10dB. Therefore, this compact WDM is promising for applications in modern microwave communication systems for its compact device volume and unique capability to suppress the crosstalk between WDM channels.

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A 10Gb/s Directly-Modulated 1.3μm InAs/GaAs Quantum-Dot Laser

JI Hai-Ming, YANG Tao, CAO Yu-Lian, XU Peng-Fei, GU Yong-Xian, LIU Yu, XIE Liang, WANG Zhan-Guo

Chin. Phys. Lett. 2010, 27 (3): 034209 . DOI: 10.1088/0256-307X/27/3/034209

Abstract

PDF(pc) (516KB) ( 709 )

We demonstrate 10 Gb/s directly-modulated 1.3 μm InAs quantum-dot (QD) lasers grown on GaAs substrates by molecular beam epitaxy. The active region of the QD lasers consists of five-stacked InAs QD layers. Ridge-waveguide lasers with a ridge width of 4 μm and a cavity length of 600 μm are fabricated with standard lithography and wet etching techniques. It is found that the lasers emit at 1293 nm with a very low threshold current of 5 mA at room temperature. Furthermore, clear eye-opening patterns under 10 Gb/s modulation rate at temperatures of up to 50ºC are achieved by the QD lasers. The results presented here have important implications for realizing low-cost, low-power-consumption, and high-speed light sources for next-generation communication systems.

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Phase Noise Quenching in a Four-Level Laser

Javaid Anwar

Chin. Phys. Lett. 2010, 27 (3): 034210 . DOI: 10.1088/0256-307X/27/3/034210

Abstract

PDF(pc) (286KB) ( 512 )

In the presence of usual transmission losses, it is shown that phase noise in a four-level laser can be reduced below the Schawlow-Townes limit when lasing levels are coupled to a squeezed vacuum reservoir. The squeezed vacuum coupled to the lasing mode modifies the phase diffusion rate and dominates the contribution from transmission losses. It is predicted to obtain phase stability in the system and phase noise vanishes for larger squeezing. Gain of the laser remains positive under these conditions.

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Influence of Excitation Pulse Width on the Second-Order Correlation Functions of the Exciton-Biexciton Emissions

KIM Nam-Chol, LI Jian-Bo, LIU Shao-Ding, CHENG Mu-Tian, HAO Zhong-Hua

Chin. Phys. Lett. 2010, 27 (3): 034211 . DOI: 10.1088/0256-307X/27/3/034211

Abstract

PDF(pc) (535KB) ( 857 )

We investigate theoretically the population dynamics and the second-order correlation functions of photon emissions from the biexciton-exciton system of a single quantum dot with excitation from pulses to continuous wave. The dynamic equations of the correlation functions are deduced by applying quantum regression theorem to optical Bloch equations. The influences of excitation pulse width on the correlation function have been discussed in detail.

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A Quasi-One-Dimensional Model for a Chain of Water Molecules on the Nanometer Scale

WU Ke-Fei, WAN Rong-Zheng, WANG Chun-Lei, REN Xiu-Ping, FANG Hai-Ping,

Chin. Phys. Lett. 2010, 27 (3): 034501 . DOI: 10.1088/0256-307X/27/3/034501

Abstract

PDF(pc) (380KB) ( 538 )

Water confined into the interior channels of narrow carbon nanotubes or transmembrane proteins can form collectively oriented molecular chains held together by tight hydrogen bonds. We develop a quasi-one-dimensional model for a chain of water molecules which interact with each other via the Coulomb and power-like repulsive interactions. We explore the equilibrium property of the water chain and derive an exact analytical expression for the total interaction energy of the water chain, denoted by W^(0)_int. It is found that W^(0)_int is minimal when the distance between the two neighboring water molecules in a hydrogen-bonded chain is equal to 0.265 nm. The model is expected to be useful for studying analytically the properties of single-file water molecules inside water channels, such as the concerted motion of water molecules.

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Generalized Lorenz Equation Derived from Thermal Convection of Viscoelastic Fluids in a Loop

YANG Fan, ZHU Ke-Qin

Chin. Phys. Lett. 2010, 27 (3): 034601 . DOI: 10.1088/0256-307X/27/3/034601

Abstract

PDF(pc) (1108KB) ( 1313 )

A new generalized Lorenz system is presented based on the thermal convection of Oldroyd-B fluids in a circular loop. Two non-dimensional parameters De₁ (a measure of the fluid relaxation) and De₂ (a measure of the fluid retardation) appear in the equation. Then we study this generalized Lorenz equation numerically and find that the values of De₁ and De₂ can greatly influence the behavior of the solution. The fluid relaxation De₁is found to precipitate the onset of periodic solution (limit cycle) in the system and impedes the onset of chaos while the fluid retardation (De₂) tends to delay the onset of the periodic solution and precipitate the onset of chaos in the system.

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Statistical Analysis of the Random Convective Dispersion Models

WU Jing-Chun, QIN Sheng-Gao, LV Xiao-Ming

Chin. Phys. Lett. 2010, 27 (3): 034701 . DOI: 10.1088/0256-307X/27/3/034701

Abstract

PDF(pc) (482KB) ( 625 )

The convective dispersion models are derived by the material balance method in an infinitesimal volume. In comparison with the derivation process by the Markov method, they indicate statistical foundation of random particle movement. By numerical method, the mass transport laws are analyzed comparatively for the models.

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Mechanism Responsible for the Complete Suppression of Kármán Vortex in Flows Past a Wavy Square-Section Cylinder

LIN Li-Ming, LING Guo-Can, WU Ying-Xiang

Chin. Phys. Lett. 2010, 27 (3): 034702 . DOI: 10.1088/0256-307X/27/3/034702

Abstract

PDF(pc) (2895KB) ( 491 )

The Kármán vortex shedding is totally suppressed in flows past a wavy square-section cylinder at a Reynolds number of 100 and the wave steepness of 0.025. Such a phenomenon is illuminated by the numerical simulations. In the present study, the mechanism responsible for it is mainly attributed to the vertical vorticity. The geometric disturbance on the rear surface leads to the appearance of spanwise flow near the base. The specific vertical vorticity is generated on the rear surface and convecting into the near wake. The wake flow is recirculated with the appearance of the pair of recirculating cells. The interaction between the upper and lower shear layers is weakened by such cells, so that the vortex rolls could not be formed and the near wake flow becomes stable.

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Analysis of Hysteretic Strongly Nonlinearity for Quad Iced Bundle Conductors

LIU Fu-Hao, ZHANG Qi-Chang, WANG Wei

Chin. Phys. Lett. 2010, 27 (3): 034703 . DOI: 10.1088/0256-307X/27/3/034703

Abstract

PDF(pc) (398KB) ( 578 )

A new hysteretic nonlinear model of quad iced bundle conductors is constructed. The bifurcation equation is obtained by applying the undetermined fundamental frequency method of the complex normal form. The transition set and bifurcation diagrams for the singularity are presented. Then the corresponding relations between the unfolding parameters and the system parameters are given, and the sensitivity parameters and its range of values are obtained to analyze and to control the galloping of the quad iced bundle conductor.

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Thin Film Flow of a Second Grade Fluid over a Stretching/Shrinking Sheet with Variable Temperature-Dependent Viscosity

S. Nadeem, Naeem Faraz

Chin. Phys. Lett. 2010, 27 (3): 034704 . DOI: 10.1088/0256-307X/27/3/034704

Abstract

PDF(pc) (390KB) ( 851 )

Effects of variable viscosity on the flow and heat transfer in a thin film on a horizontal porous stretching sheet are analyzed. The steady boundary layer equations for momentum and thermal energy are simplified by using similarity transformations. The resulted and coupled nonlinear differential equations are solved by Homotopy analysis method. The results are presented graphically to interpret various physical parameters appearing in the problem.

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Change in Continuous Detonation Wave Propagation Mode from Rotating Detonation to Standing Detonation

SHAO Ye-Tao, WANG Jian-Ping

Chin. Phys. Lett. 2010, 27 (3): 034705 . DOI: 10.1088/0256-307X/27/3/034705

Abstract

PDF(pc) (816KB) ( 1148 )

We perform a three-dimensional numerical simulation based on a one-step chemical reaction model to investigate changes in the mode of H₂-Air detonation wave propagation from rotating detonation wave (RDW) mode to standing detonation wave mode. The physical characteristics of an RDW with injection velocity of 500 m/s are analyzed to investigate the physical mechanisms involved. We find that with increasing injection velocity, the detonation wave gradually changes from perpendicular to the head wall to parallel to the head wall. When the injection velocity exceeds the Chapman-Jouguet velocity V_CJ (about 1984 m/s), the detonation wave changes orientation to become perpendicular to the fuel injection direction, and the rotating mode changes accordingly to a standing mode. Finally, the plane detonation characteristic triple-wave structures can be found from the standing mode.

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Relaxation Oscillation of Thermal Convection in Rotating Cylindrical Annulus

TAO Jian-Jun, TAN Wen-Chang

Chin. Phys. Lett. 2010, 27 (3): 034706 . DOI: 10.1088/0256-307X/27/3/034706

Abstract

PDF(pc) (526KB) ( 533 )

Chaotic thermal convection in a rapidly rotating cylindrical annulus is investigated numerically and the relaxation oscillation state is obtained under the no-slip boundary condition. The dominant frequency of the oscillation is inherited directly from a vacillating mode, whose nonlinear interaction with another high-frequency vacillating mode leads to the chaotic state at high Rayleigh numbers through an RTN-type route. Furthermore, the effects of Coriolis parameter and Rayleigh number on the quasi-periodic burst of kinetic energy are discussed as well.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Enhancement of the Number of Fast Electrons Generated in a Laser Inverse Cone Interaction

JI Yan-Ling, JIANG Gang, WU Wei-Dong, ZHANG Ji-Cheng, TANG Yong-Jian

Chin. Phys. Lett. 2010, 27 (3): 035201 . DOI: 10.1088/0256-307X/27/3/035201

Abstract

PDF(pc) (712KB) ( 547 )

Enhancement of the energy-conversion efficiency from laser to target electrons is demonstrated by two-dimensional particle-in-cell simulations in a laser-inverse cone interaction. When an intense short-pulse laser illuminates the inverse cone target, the electrons at the cone end are accelerated by the ponderomotive force. Then these electrons are guided and confined to transport along the inverse cone walls by the induced electromagnetic fields. A device consisting of inverse hollow-cone and multihole array plasma is proposed in order to increase the energy-conversion efficiency from laser to electrons. Particle-in-cell simulations present that the multiholes transpiercing the cone end help to enhance the number of fast electrons and the maximum electron energy significantly.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

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Tracing Nucleation and Growth on Atomic Level in Amorphous Sodium by Molecular Dynamics Simulation

HOU Zhao-Yang, LIU Li-Xia, LIU Rang-Su, TIAN Ze-An

Chin. Phys. Lett. 2010, 27 (3): 036101 . DOI: 10.1088/0256-307X/27/3/036101

Abstract

PDF(pc) (410KB) ( 844 )

Crystallization of amorphous Na is simulated by using the molecular dynamics method, and the evolutions of atomic clusters are traced by the cluster-type index method (CTIM) we proposed previously. It is demonstrated that the crystallization process exhibits three distinct stages of nucleation, subsequent growth of nuclei and coarsening of crystal grains. Both the size and the internal structure of a cluster play crucial roles in determining whether it is a nucleus. The cluster tracing analysis can identify different crystallization stages more clearly and accurately than other methods. Meanwhile, the simulation results can provide a reasonable explanation at an atomic level for the experimental phenomenon obtained previously.

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Strong-Superstrong Transition in Glass Transition of Metallic Glass

WANG Dan, PENG Hong-Yan, XU Xiao-Yu, CHEN Bao-Ling, WU Chun-Lei, SUN Min-Hua

Chin. Phys. Lett. 2010, 27 (3): 036401 . DOI: 10.1088/0256-307X/27/3/036401

Abstract

PDF(pc) (588KB) ( 761 )

Dynamic fragility of bulk metallic glass (BMG) of Zr₆₄Cu₁₆Ni₁₀Al₁₀ alloy is studied by three-point beam bending methods. The fragility parameter mfor Zr₆₄Cu₁₆Ni₁₀Al₁₀ BMG is calculated to be 24.5 at high temperature, which means that the liquid is a "strong" liquid, while to be 13.4 at low temperature which means that the liquid is a "super-strong" liquid. The dynamical behavior of Zr₆₄Cu₁₆Ni₁₀Al₁₀ BMG in the supercooled region undergoes a strong to super-strong transition. To our knowledge, it is the first time that a strong-to-superstrong transition is found in the metallic glass. Using small angle x-ray scattering experiments, we find that this transition is assumed to be related to a phase separation process in supercooled liquid.

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Phase Transition Behavior of LiCr _0.35 Mn_0.65O₂ under High Pressure by Electrical Conductivity Measurement

CUI Xiao-Yan, HU Ting-Jing, HAN Yong-Hao, GAO Chun-Xiao, PENG Gang, LIU Cai-Long, WU Bao-Jia, WANG Yue, LIU Bao, REN Wan-Bin, LI Yan, SU Ning-Ning, ZOU Guang-Tian, DU Fei, CHEN Gang

Chin. Phys. Lett. 2010, 27 (3): 036402 . DOI: 10.1088/0256-307X/27/3/036402

Abstract

PDF(pc) (458KB) ( 827 )

The electrical conductivity of powdered LiCr _0.35 Mn_0.65O₂ is measured under high pressure up to 26.22 GPa in the temperature range 300-413 K by using a diamond anvil cell. It is found that both conductivity and activation enthalpy change discontinuously at 5.36 GPa and 21.66 GPa. In the pressure range 1.10-5.36 GPa, pressure increases the activation enthalpy and reduces the carrier scattering, which finally leads to the conductivity increase. In the pressure ranges 6.32-21.66 GPa and 22.60-26.22 GPa, the activation enthalpy decreases with pressure increasing, which has a positive contribution to electrical conductivity increase. Two pressure-induced structural phase transitions are found by in-situ x-ray diffraction under high pressure, which results in the discontinuous changes of conductivity and activation enthalpy.

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Equation of State and Elastic Constants of Compressed fcc Cu

BAI Li-Gang, LIU Jing

Chin. Phys. Lett. 2010, 27 (3): 036403 . DOI: 10.1088/0256-307X/27/3/036403

Abstract

PDF(pc) (489KB) ( 1706 )

First-principles calculations of equation of state and single-crystal elastic constants of copper are carried out up to twofold compression. The Helmholtz free energies are calculated using the quasi-harmonic phonon approach based on density-functional theory within both the local density approximation and the generalized gradient approximation (GGA). We find that the results calculated within GGA agree better with the experimental measurements in overall. The equation of state and the zero-pressure single-crystal elastic constants are close to the experimental values.

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Molecular Dynamics Simulations of Thermal Properties of Solid Uranium Dioxide

LI Jiu-Kai, TIAN Xiao-Feng

Chin. Phys. Lett. 2010, 27 (3): 036501 . DOI: 10.1088/0256-307X/27/3/036501

Abstract

PDF(pc) (577KB) ( 819 )

Molecular dynamics simulations are performed with the recently developed empirical interaction potential by Morelon et al. Thermodynamics properties of solid UO₂that have been assessed include melt point, density, enthalpy, heat capacity, lattice parameter variation with temperature, mean-square-displacement and diffusion coefficients of oxygen ion. The results are compared with the data in literature and it is suggested that the rigid ionic potential provides perfect results below the superionic range. The data showing thermodynamics properties will become unacceptable when the temperature is higher than 2500 K. Compared with the previous empirical potentials, the empirical potential developed by Morelon et al. improves the agreement of these data with the recommend ones.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Thin-Thick Film Transitions on a Planar Solid Surface: A Density Functional Study

YU Yang-Xin, LI Ying-Feng, ZHENG Yuan-Xiang

Chin. Phys. Lett. 2010, 27 (3): 037101 . DOI: 10.1088/0256-307X/27/3/037101

Abstract

PDF(pc) (471KB) ( 660 )

A weighted density functional theory is proposed to predict the surface tension and thin-thick film transition of a Lennard-Jones fluid on a planar solid surface. The underlying density functional theory for the Lennard-Jones fluid at low temperature is based on a modified fundamental measure theory for the hard-core repulsion, a Taylor expansion around zero-bulk-density for attraction, and a correlation term evaluated by the weighted density approximation with a weight function of the Heaviside step function. The predicted surface tension and thin-thick film transition agree well with the results from the Monte Carlo simulations, better than those from alternative approaches. For the Ar/CO₂ system, the prewetting line has been calculated. The predicted reduced surface critical temperature is about 0.97, and the calculated wetting temperature is below the triple-point temperature. This is in agreement with the experimental observation.

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Effects of AlN and AlGaN Interlayer on Properties of InAlN/GaN Heterostructures

DONG Xun, LI Zhong-Hui, LI Zhe-Yang, ZHOU Jian-Jun, LI Liang, LI Yun, ZHANG Lan, XU Xiao-Jun, XU Xuan, HAN Chun-Lin

Chin. Phys. Lett. 2010, 27 (3): 037102 . DOI: 10.1088/0256-307X/27/3/037102

Abstract

PDF(pc) (478KB) ( 1038 )

InAlN/GaN heterojunction structures are grown on two-inch c-face(0001) sapphire substrates by metalorganic chemical vapour deposition. AlN and AlGaN interlayers are intentionally inserted into the structure to improve the electrical properties. The lowest sheet resistance of 359 Ω/sq and the highest room-temperature two-dimensional electron gas (2DEG) mobility of 1051 cm² V^-1s^-1is obtained in the structure with AlN thickness of 1.3 nm. The structure with AlN thickness of 2 nm exhibits the highest 2DEG concentration of 1.84×10¹³cm^-2. The sample with an AlGaN interlayer gives a smoother surface morphology compared to the one using an AlN interlayer, indicating potential applications of this technique in device fabrication.

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First-Principles Study of Electronic and Optical Properties of Y_1-xCa_xTiO₃ (x=0, 0.25, 0.5, 0.75)

GONG Sai, WANG Yue-Hua, ZHAO Na, DUAN Yi-Feng

Chin. Phys. Lett. 2010, 27 (3): 037103 . DOI: 10.1088/0256-307X/27/3/037103

Abstract

PDF(pc) (681KB) ( 764 )

The full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) is applied to study the electronic and optical properties of perovskite-type compounds Y_1-xCa_xTiO₃. The lattice parameters, magnetic moment, band structure, density of states and optical conductivity are obtained. The results show that the Ca ion plays an important role in the electronic properties and optical responses. Moreover, the optical properties including the dielectric function, absorption spectrum, extinction coefficient, energy-loss spectrum and refractive index are also discussed.

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Luminescence Properties of Sr₂SnO₄:Sm³⁺ Afterglow Phosphor

LEI Bing-Fu, YUE Song, ZHANG Yong-Zhe, LIU Ying-Liang

Chin. Phys. Lett. 2010, 27 (3): 037201 . DOI: 10.1088/0256-307X/27/3/037201

Abstract

PDF(pc) (548KB) ( 1271 )

A new long-lasting phosphorescence (LLP) phosphor, Sr₂SnO₄:Sm³⁺ which emits reddish-orange LLP upon UV-excitation, is prepared by a conventional high-temperature solid-state method. After irradiation under 247-nm UV light, Sr₂SnO₄:Sm³⁺ emits an intense reddish-orange emission afterglow from the ⁴G_5/2 to ⁶H_J (J = 5/2,7/2,9/2) transitions. The afterglow decay curve of the Sm³⁺-doped Sr₂SnO₄ phosphor contains a fast decay component and another slow decay one. Due to the presence of the slow decay component, the afterglow can be seen with the naked eye in the dark clearly for more than 1 h after removal of the excitation source.

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Effect of Channel Length and Width on NBTI in Ultra Deep Sub-Micron PMOSFETs

CAO Yan-Rong, MA Xiao-Hua, HAO Yue, TIAN Wen-Chao

Chin. Phys. Lett. 2010, 27 (3): 037301 . DOI: 10.1088/0256-307X/27/3/037301

Abstract

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Effect of Uniaxial Strain on Band Gap of Armchair-Edge Graphene Nanoribbons

HAN Mei, ZHANG Yong, ZHENG Hong-Bo

Chin. Phys. Lett. 2010, 27 (3): 037302 . DOI: 10.1088/0256-307X/27/3/037302

Abstract

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Based on the tight-binding approximation, analytical solutions of the energy dispersion and band gap of armchair-edge graphene nanoribbons (AGNRs) under uniaxial strains are derived. Subsequent numerical results on band gap are found to be consistent with the analytical solutions. It is shown that the energy gap of AGNRs is sensitive to the uniaxial strains and is predicted to change with a V shape as a function of the applied uniaxial strain. It is interesting to find that the uniaxial strain could induce metal-semiconductor transition for the AGNRs with a width of n=3m+2 ((3m + 2)-AGNRs) and semiconductor-metal-semiconductor phase transition for the (3m + 1)-AGNRs, but no phase transition is induced for the 3m-AGNRs.

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Enhanced Optical Absorption of Amorphous Silicon Films by Ag Nanostructures

ZHOU Bing, LI Dong-Sheng, XIANG Lue-Lue, YANG De-Ren

Chin. Phys. Lett. 2010, 27 (3): 037303 . DOI: 10.1088/0256-307X/27/3/037303

Abstract

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The optical absorption of amorphous silicon (α-Si) films is enhanced by silver (Ag) nanostructures deposited on the films. The reflection at the long wavelength side of localized plasmon polaritons (LPPs) resonance originated from Ag nanostructures is significantly decreased, i.e. the optical absorption is enhanced. The results show that the average reflection value of the amorphous silicon films in the wavelength range of 900-1200 nm could be decreased by 11.4%. Moreover, the reduction of the reflection is found to be mainly dependent on the size of the Ag nanostructures, which is related to the island sizes, i.e. the LPP's resonance peak position.

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AC Alternating-Current Loss Analyses of a Thin High-Temperature Superconducting Tube Carrying AC Transport Current in AC External Magnetic Field

PI Wei, WANG Yin-Shun, DONG Jin, CHEN Lei

Chin. Phys. Lett. 2010, 27 (3): 037401 . DOI: 10.1088/0256-307X/27/3/037401

Abstract

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Numerical simulations on the AC loss characteristics in a thin high-temperature superconducting (HTS) tube are presented. Geometry of the HTS conductor is modeled as a tube with negligible thickness, and assumed to carry a transport current with the same phase as an AC externally applied magnetic field perpendicular to the axis. Based on the classical theory of AC loss with the Bean critical current model, the distribution of critical current density j_c and AC loss Q are obtained by means of numerical analysis. The results are in very good agreement with experiments. A double-peak profile is observed in the curve of the critical current density distribution along the azimuth angle. This numerical simulation method is suitable for a thin HTS tube, which may be applicable on a thin tube configuration consisting of coated superconductors.

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Sizable Residual Quasiparticle Density of States Induced by Impurity Scattering Effect in Ba(Fe_1-xCo_x)₂As₂ Single Crystals

MU Gang, ZENG Bin, CHENG Peng, WANG Zhao-Sheng, FANG Lei, SHEN Bing, SHAN Lei, REN Cong, WEN Hai-Hu

Chin. Phys. Lett. 2010, 27 (3): 037402 . DOI: 10.1088/0256-307X/27/3/037402

Abstract

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Low-temperature specific heat C_p is measured on Ba(Fe_1-xCo_x)₂As₂single crystals in a wide doping region. A sizeable residual specific heat coefficient γo is observed in the low temperature limit of all samples. The specific heat jump near T_c, i.e. ΔC_p/T\_{T_c}, is also determined. It is found that -γo, ΔC_p/T\_{T_c} and T_c all share a similar evolution with doping. These can be well understood within the model of S^± pairing symmetry when accounting for the cobalt-dopants as unitary scattering centers in the FeAs planes. Our results reveal a non-trivial impact of impurity scattering in FeAs-based.

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Numerical Confirmation of Multi-Reflections of Light Inside a Subwavelength Metal Slit Structure

Chin. Phys. Lett. 2010, 27 (3): 037801 . DOI: 10.1088/0256-307X/27/3/037801

Abstract

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The propagation behavior of light passing through a subwavelength metal slit structure is usually modeled by a Fabry-Perot (FP) resonant cavity based on the feature of transmission spectra. However, this mechanism belongs to a conjecture and it should be proven. We present a direct evidence from the numerical simulations of the amplitude distribution of the magnetic field by employing the time-domain simulation method. The light propagation behavior clearly shows a multi-reflection process inside a subwavelength slit as soon as it enters the slit. An analytical formula for calculating the field distribution involving the multi-reflection process is presented, and the theoretical calculations agree with the numerically simulated results. Our results provide explicit evidence that the FP model is reasonable to the description of the propagation process of light inside a subwavelength slit structure.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Preparation of High-Density Nanocrystalline Bulk Selenium by Rapid Compressing of Melt

HU Yun, SU Lei, LIU Xiu-Ru, SUN Zhen-Ya, LV Shi-Jie, YUAN Chao-Sheng, JIA Ru, SHEN Ru, HONG Shi-Ming

Chin. Phys. Lett. 2010, 27 (3): 038101 . DOI: 10.1088/0256-307X/27/3/038101

Abstract

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The melt's solidification behavior of elemental selenium is investigated by a series of experiments including rapid compressing to 2.8 and 3.5 GPa within 20ms respectively, slow compressing to 2.8 GPa for 20 min and natural cooling at ambient pressure. Based on the x-ray diffraction, scanning electron microscope and transmission electron microscope results of the recovered samples, it is clearly shown that homogenous nanostructures are formed only by the rapid compression processes, and that the average crystal sizes are about 18.7 and 19.0 nm in the samples recovered from 2.8 and 3.5 GPa, respectively. The relative density of the nanocrystalline bulk reaches 98.17% of the theoretical value. It is suggested that rapid compression could induce pervasive nucleation and restrain grain growth during the solidification, which is related to fast supercooling, higher viscosity of the melt and lower diffusivity of atoms under high pressure.

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Fabrication of Mn-Doped GaN Nanobars

XUE Cheng-Shan, LIU Wen-Jun, SHI Feng, ZHUANG Hui-Zhao, GUO Yong-Fu, CAO Yu-Ping, SUN Hai-Bo

Chin. Phys. Lett. 2010, 27 (3): 038102 . DOI: 10.1088/0256-307X/27/3/038102

Abstract

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We report a new method for large-scale production of GaMnN nanobars, by ammoniating Ga₂O₃ films doped with Mn under flowing ammonia atmosphere at 1000ºC. The Mn-doped GaN sword-like nanobars are a single-crystal hexagonal structure, containing Mn up to 5.43 atom%. Thickness is about 100 nm and with a width of 200-400 nm. The nanobars are characterized by x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and photoluminescence. The GaN nanobars show two emission bands with a well-defined PL peak at 388 nm and 409 nm respectively. The large distinct redshift (409 nm) are comparable to pure GaN(370 nm) at room temperature. The red-shift photoluminescence is due to Mn doping. The growth mechanism of crystalline GaN nanobars is discussed briefly.

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Effects of AlGaN/AlN Stacked Interlayers on GaN Growth on Si (111)

WANG Hui, LIANG Hu, WANG Yong, NG Kar-Wei, DENG Dong-Mei, LAU Kei-May

Chin. Phys. Lett. 2010, 27 (3): 038103 . DOI: 10.1088/0256-307X/27/3/038103

Abstract

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We report the growth of high quality and crack-free GaN film on Si (111) substrate using Al_0.2Ga_0.8N/AlN stacked interlayers. Compared with the previously used single AlN interlayer, the AlGaN/AlN stacked interlayers can more effectively reduce the tensile stress inside the GaN layer. The cross-sectional TEM image reveals the bending and annihilation of threading dislocations (TDs) in the overgrown GaN film which leads to a decrease of TD density.

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Using Gamma-Radiation for Drug Releasing from MWNT Vehicle

LI Jun, SUN Hao, DAI Yao-Dong

Chin. Phys. Lett. 2010, 27 (3): 038104 . DOI: 10.1088/0256-307X/27/3/038104

Abstract

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A drug delivery system via multi-walled carbon nanotube (MWNT) vehicle was synthesized in aqueous solution. MWNTs were first noncovalently functionalized with chitosan oligomers (CS) with a molecule weight of 4000-6000, making MWNTs water-soluble, and then a cancer ancillary drug tea polyphenols (TP) was conjugated mainly via the hydrogen bond between CS and TP molecules, making MWNTs efficient vehicle for drug delivering. The release of drug molecules can be realized by pH variation and γ-radiation, leading to new methods for controlling drug release from carbon nanotubes carrier. Due to the high penetrability of γ-rays, γ-radiation shows up new opportunities in controlled drug release, possibly facilitating the future cancer treatment in vivo.

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Two-Photon Fluorescence Property and Ultrafast Dynamics of Two Dipolar Compounds with Dipicolinate as Electron Acceptor

WANG Yao-Chuan, ZHOU Hui, DING Jin-Liang, CHEN Qiang, XIAO Hai-Bo, TAO Xiao-Ming, QIAN Shi-Xiong

Chin. Phys. Lett. 2010, 27 (3): 038201 . DOI: 10.1088/0256-307X/27/3/038201

Abstract

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Linear and nonlinear photophysical properties of two novel dipolar compounds named as trans- dimethyl-4-[4'-(N,N-dimethylamino)-styry1]-pyridin-2,6-dicarboxylate (Xiao-1) and trans-dimethyl-4-[4'-(N,N-diphenylamino)-styry1]-pyridin-2,6-dicarboxylate (Xiao-2) are investigated by steady-state absorption and fluorescence spectroscopy, Z-scan and two-photon excited fluorescence measurements. Strong two-photon fluorescence emission and the pronounced positive solvatochromism are observed from two compounds. The two-photon absorption cross section of Xiao-2 is about 1.5 times larger than that of Xiao-1. One-color and two-color femtosecond pump-probe experiments are employed to investigate the excited state dynamics of two compounds. The relaxation lifetime of the intra-molecular charge transfer state is determined to be in the hundreds of picosecond domain for both the compounds in THF, and several tens of picosecond in DMSO solutions.

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A Study on Porosity Distribution in Nanoporous TiO_2 Photoelectrodes for Output Performance of Dye-Sensitized Solar Cells

XU Wei-Wei, HU Lin-Hua, DAI Song-Yuan, ZHANG Chang-Neng, LUO Xiang-Dong, JING Wei-Ping

Chin. Phys. Lett. 2010, 27 (3): 038202 . DOI: 10.1088/0256-307X/27/3/038202

Abstract

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Porosity as one of the crucial factors to film morphology affects the overall electrical current-voltage characteristics of dye-sensitized solar cell (DSC). We search for the short-circuit current density, the open-circuit voltage and the maximum power output as the main functional parameters of DSC closely related to porosity under different film thickness. The theoretical analyses show some exciting results. As porosity changes from 0.41 to 0.75, the short-circuit current density shows the optimal value when the film thickness is 8-10 μm. The open-circuit voltage presents different variation tendencies for the film thicknesses within 1-8 μm and within 10-30 μm. The porosity is near 0.41 and the film thickness is about 10 μm, DSC will have the maximum power output. The theoretical studies also illustrate that given a good porosity distribution, DSC can obtain an excellent short-circuit current characteristic, which agrees well with the experimental results reported in previous literature.

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Design and Application of a Near Field Microwave Antenna for the Spin Control of Nitrogen-Vacancy Centers

YANG Li-Li, LIU Gang-Qin, PAN Xin-Yu, CHEN Dong-Min

Chin. Phys. Lett. 2010, 27 (3): 038401 . DOI: 10.1088/0256-307X/27/3/038401

Abstract

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Controlled manipulation of the electron spin by means of a microwave field is investigated. The near magnetic field generated by a copper wire antenna is measured experimentally and simulated theoretically, and the optimum antenna length and position are obtained. By measuring the change in the fluorescence of nitrogen-vacancy (N-V) centers in diamond after excitation with a 532 nm continuous wave laser at room temperature, it is verified that the spin of the N-V center can be effectively controlled by the microwave field.

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Strain-Compensated InGaAs/InAlAs Quantum Cascade Detector of 4.5 μm Operating at Room Temperature

KONG Ning, LIU Jun-Qi, LI Lu, LIU Feng-Qi, WANG Li-Jun, WANG Zhan-Guo

Chin. Phys. Lett. 2010, 27 (3): 038501 . DOI: 10.1088/0256-307X/27/3/038501

Abstract

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We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8× 10^-4. A clear narrow band detection spectrum centered at 4.5 μm has been observed above room temperature for a device with 200\times 200 ×μm²square mesa.

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Three-Dimensional Finite Element Analysis of Phase Change Memory Cell with Thin TiO₂ Film

LIU Yan, SONG Zhi-Tang, LING Yun, FENG Song-Lin

Chin. Phys. Lett. 2010, 27 (3): 038502 . DOI: 10.1088/0256-307X/27/3/038502

Abstract

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A thin TiO₂ layer inserted in a phase change memory (PCM) cell to form a deep sub-micro bottom electrode (DBE) is proposed and its electro-thermal characteristics are investigated with the three-dimensional finite element analysis. Compared with the conventional PCM cell with a SiN stop layer, the reset threshold current of the PCM cell with the TiO₂ layer is reduced from 1.8 mA to 1.2 mA and the ratio of the amorphous resistance and crystalline resistive increases from 65 to 100. The optimum thickness of the TiO₂ layer and the optimum height of DBE are 10nm and 200nm, respectively. Therefore, the PCM cell with the TiO₂ layer can decrease the programming power consumption and increase heating efficiency. The TiO₂ film is a better candidate for the SiN film in the PCM cell structure to prepare DBE and to reduce programming power in the reset operation.

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Effect of Interface Nanotexture on Light Extraction of InGaN-Based Green Light Emitting Diodes

PAN Yao-Bo, HAO Mao-Sheng, QI Sheng-Li, FANG Hao, ZHANG Guo-Yi

Chin. Phys. Lett. 2010, 27 (3): 038503 . DOI: 10.1088/0256-307X/27/3/038503

Abstract

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We report the enhancement of the light extraction of InGaN-based green light emitting diodes (LEDs) via the interface nanotexturing. The texture consists of high-density nanocraters on the surface of a sapphire substrate with an in situ etching. The width of nanocraters is about 0.5 µm and the depth is around 0.1 µm. It is demonstrated that the LEDs with interface texture exhibit about a 27% improvement in luminance intensity, compared with standard LEDs. High power InGaN-based green LEDs are obtained by using the interface nanotexture. An optical ray-tracing simulation is performed to investigate the effect of interface nanotexture on light extraction.

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Metamorphic InGaAs p-i-n Photodetectors with 1.75 μm Cut-Off Wavelength Grown on GaAs

ZHU Bin, HAN Qin, YANG Xiao-Hong, NI Hai-Qiao, HE Ji-Fang, NIU Zhi-Chuan, WANG Xin, WANG Xiu-Ping, WANG Jie

Chin. Phys. Lett. 2010, 27 (3): 038504 . DOI: 10.1088/0256-307X/27/3/038504

Abstract

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Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 μm at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 × 10^-6 A/cm² at 0 V bias and 2.24 × 10^-4 A/cm² at a reverse bias of 5 V. At a wavelength of 1.55 μm, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 μm diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices.

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Monte Carlo Simulation on Growth of Antibody-Antigen Complexes: the Role of Unequal Reactivity

ZHANG Ping, WANG Hai-Jun,

Chin. Phys. Lett. 2010, 27 (3): 038701 . DOI: 10.1088/0256-307X/27/3/038701

Abstract

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Growth of Antibody-Antigen complexes in a multivalent Antibody-Antigen system is studied by the Monte Carlo simulation method. The validity of the algorithm is first demonstrated for the case of the equal reactivity, then the simulation is presented for the case of unequal reactivity. It is shown that the influence of the unequal reactivity on the critical point, size distribution and the weight-average binding degree is significant. Especially, the gelation regions for the cases of unequal reactivity are studied, which can provide some useful clues for the immunological experiments.

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Dissection of the Zipping-and-Assembly Mechanism for Folding of Model Proteins

SUN Li, WANG Jun, WANG Wei

Chin. Phys. Lett. 2010, 27 (3): 038702 . DOI: 10.1088/0256-307X/27/3/038702

Abstract

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Zipping-and-assembly mechanism (ZAM) is a new mechanism describing the kinetics of protein folding. To dissect the validity of this mechanism for various protein-like systems, a prediction test based on three-dimensional HP lattice models is carried out. It is found that only the native structures of a part of protein-like models could be predicted with a ZAM-based method. The detailed comparisons between the model proteins which are predicted or failed with the ZAM-based method suggest that the ZAM is likely to be applicable for the model proteins with the weak hydrophobicity, the low contact order for native conformations, and the large separation between the energies of native state and denatured states. These observations bring us more information about the protein-like systems for which the ZAM could be applied.

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Comparative Study on Polarization of DNA and CdSe Quantum Dots

ZHOU Xing-Fei, CUI Cheng-Yi, ZHANG Jin-Hai, LIU Jian-Hua, LIU Jing-Song

Chin. Phys. Lett. 2010, 27 (3): 038703 . DOI: 10.1088/0256-307X/27/3/038703

Abstract

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The polarizabilities of DNA in transverse direction and CdSe semiconductor quantum dots (QDs) deposited on mica surface are compared by means of electrostatic force microscopy (EFM). We observe clear EFM-phase shift over CdSe QDs, while no obvious signal on DNA is detected, suggesting that DNA molecules is an electrical insulator.

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Scale-free Networks with Self-Similarity Degree Exponents

Guo Jin-Li

Chin. Phys. Lett. 2010, 27 (3): 038901 . DOI: 10.1088/0256-307X/27/3/038901

Abstract

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Ravasz et al. structured a deterministic model of a geometrically growing network to describe metabolic networks. Inspired by the model of Ravasz et al., a random model of a geometrically growing network is proposed. It is a model of copying nodes continuously and can better describe metabolic networks than the model of Ravasz et al. Analysis shows that the analytic method based on uniform distributions (i.e., Barabási-Albert method) is not suitable for the analysis of the model and the simulation process is beyond computing power owing to its geometric growth mechanism. The model can be better analyzed by the Poisson process. Results show that the model is scale-free with a self-similarity degree exponent, which is dependent on the common ratio of the growth process and similar to that of fractal networks.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Assessment of Primordial Radionuclides in Pakistani Red Bricks and Associated Radiation Doses

K. Khan, A. Jabbar, P. Akhter, M. Tufail, H. M. Khan

Chin. Phys. Lett. 2010, 27 (3): 039301 . DOI: 10.1088/0256-307X/27/3/039301

Abstract

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Specific activity of primordial radionuclides and associated radiation hazards due to ⁴⁰K, ²²⁶Ra, and ²³²Th have been measured in backed red brick samples, collected from five highly populated areas of the North West Frontier Province of Pakistan. For the detection, analysis and data acquisition, a high purity germanium detector was used. Associated external doses were calculated using a Monte Carlo neutron photon transport code. A theoretical model to determine the gamma dose rate at 1 m height from the floor, made of bricks, was employed for the calculation of mass attenuation coefficient and self-absorption in the floor for the gamma energies of these radionuclides and their progeny. Monte Carlo simulation shows that in this study the floor, having more than an effective thickness of 15 cm, contributes very little to the external gamma dose rate. The values of the external dose rate and annual effective dose are found to be much lower than the world average as well as from other countries of the world.

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