Current Issue

Volume 26 Issue 7
Online Date:
Previous Issue    Next Issue
Topology Identification of General Dynamical Network with Distributed Time Delays
WU Zhao-Yan, FU Xin-Chu
Chin. Phys. Lett. 2009, 26 (7): 070201 .   DOI: 10.1088/0256-307X/26/7/070201
Abstract   PDF(pc) (336KB) ( 27428 )
General dynamical networks with distributed time delays are studied. The topology of the networks are viewed as unknown parameters, which need to be identified. Some auxiliary systems (also called the network estimators) are designed to achieve this goal. Both linear feedback control and adaptive strategy are applied in designing these network estimators. Based on linear matrix inequalities and the Lyapunov function method, the sufficient condition for the achievement of topology identification is obtained. This method can also better monitor the switching topology of dynamical networks. Illustrative examples are provided to show the effectiveness of this method.
Structural Equation and Mei Conserved Quantity of Mei Symmetry for Appell Equations with Redundant Coordinates
XIE Guang-Xi, CUI Jin-Chao, ZHANG Yao-Yu, JIA Li-Qun
Chin. Phys. Lett. 2009, 26 (7): 070202 .   DOI: 10.1088/0256-307X/26/7/070202
Abstract   PDF(pc) (250KB) ( 429 )
Structural equations and Mei conserved quantity of Mei symmetry for Appell equations in a holonomic system with redundant coordinates are studied. Some aspects, including the differential equations of motion, the definition and the criterion of Mei symmetry, the form of structural equations and Mei conserved quantity of Mei symmetry of Appell equations for a holonomic system with redundant coordinates, are also investigated. Finally, an example is given to illustrate the application of the results.
Perturbation to Mei Symmetry and Generalized Mei Adiabatic Invariants for Nonholonomic Systems in Terms of Quasi-Coordinates
PANG Ting, FANG Jian-Hui, ZHANG Ming-Jiang, LIN Peng, LU Kai
Chin. Phys. Lett. 2009, 26 (7): 070203 .   DOI: 10.1088/0256-307X/26/7/070203
Abstract   PDF(pc) (224KB) ( 359 )
By introducing the coordination function f, the generalized Mei conserved quantities for the nonholonomic systems in terms of quasi-coordinates are given. Then based on the concept of adiabatic invariant, the perturbation to Mei symmetry and the generalized Mei adiabatic invariants for nonholonomic systems in terms of quasi-coordinates are studied.
Entanglement Swapping of Pair Coherent States with Phase Decoherence
ZHANG Ye-Qi, XU Jing-Bo
Chin. Phys. Lett. 2009, 26 (7): 070301 .   DOI: 10.1088/0256-307X/26/7/070301
Abstract   PDF(pc) (557KB) ( 622 )
We investigate the entanglement swapping of continuous variable using the pair coherent state as the input state and the two-mode squeezed vacuum which is exposed in a phase decoherence environment as the quantum channel. By adopting the log-negativity as the measure of entanglement, we analyze how entanglement of the two initial states and the phase decoherence environment affect the entanglement swapping quality.
Experimental Non-Local Generation of Entanglement from Independent Sources
JIN Xian-Min, RÖ, CH Jügen, YIN Juan, YANG Tao
Chin. Phys. Lett. 2009, 26 (7): 070302 .   DOI: 10.1088/0256-307X/26/7/070302
Abstract   PDF(pc) (334KB) ( 606 )
We experimentally demonstrate a non-local generation of entanglement from two independent photonic sources in an ancilla-free process. Two bosons (photons) are entangled in polarization space by steering into a novel interferometer setup, in which they have never met each other. The entangled photons are delivered to polarization analyzers in different sites, respectively, and a non-local interaction is observed. Entanglement is further verified by the way of the measured violation of a CHSH type Bell's inequality with S-values of 2.54 and 27 standard deviations. Our results will shine a new light onto the understanding of how quantum mechanics works, have possible philosophic consequences on the one hand and provide an essential element for quantum information processing on the other hand. Potential applications of our results are briefly discussed.
Stability Diagrams of a Bose-Einstein Condensate in a Periodic Array of Quantum Wells
XUE Rui, LIANG Zhao-Xin, LI Wei-Dong
Chin. Phys. Lett. 2009, 26 (7): 070303 .   DOI: 10.1088/0256-307X/26/7/070303
Abstract   PDF(pc) (302KB) ( 547 )
With the help of a set of exact closed-form solutions to the stationary Gross-Pitaevskii equation, we comprehensively investigate Landau and dynamical instabilities of a Bose-Einstein condensate in a periodic array of quantum wells. In the tight-binding limit, the analytical expressions for both Landau and dynamical instabilities are obtained in terms of the compressibility and effective mass of the BEC system. Then the stability phase diagrams are shown to be similar to the one in the case of the sinusoidal optical lattice.
First and Second Sound Modes in a Uniform Fermi Gas
HUANG Bei-Bing, WAN Shao-Long
Chin. Phys. Lett. 2009, 26 (7): 070304 .   DOI: 10.1088/0256-307X/26/7/070304
Abstract   PDF(pc) (297KB) ( 481 )
First and second sound modes in a uniform fermionic atom gas with Feshbach resonance are investigated in the frame of a two-fluid model at finite temperature. All thermodynamic quantities are calculated for a given thermodynamic potential. The analytical results for thermodynamic quantities and sound velocities in BCS and BEC limits are obtained. The numerical results show that there exists a continuous interpolation for sound velocities of the first and second sound modes at fixed T/Tc between BCS and BEC limits. The existence of the second sound mode indicates the existence of superfluidity.
Proof of Kochen-Specker Theorem: Conversion of Product Rule to Sum Rule
S.P.Toh, Hishamuddin Zainuddin
Chin. Phys. Lett. 2009, 26 (7): 070305 .   DOI: 10.1088/0256-307X/26/7/070305
Abstract   PDF(pc) (156KB) ( 480 )
Valuation functions of observables in quantum mechanics are often expected to obey two constraints called the sum rule and product rule. However, the Kochen-Specker (KS) theorem shows that for a Hilbert space of quantum mechanics of dimension d≥3, these constraints contradict individually with the assumption of value definiteness. The two rules are not irrelated and Peres [Found. Phys. 26(1996)807] has conceived a method of converting the product rule into a sum rule for the case of two qubits. Here we apply this method to a proof provided by Mermin based on the product rule for a three-qubit system involving nine operators. We provide the conversion of this proof to one based on sum rule involving ten operators.
Probabilistic Controlled Teleportation of a Triplet W State with Combined Channel of Non-Maximally Entangled Einstein-Podolsky-Rosen and Greenberger-Horne-Zeilinger States
DONG Jian, TENG Jian-Fu
Chin. Phys. Lett. 2009, 26 (7): 070306 .   DOI: 10.1088/0256-307X/26/7/070306
Abstract   PDF(pc) (192KB) ( 523 )
A scheme for probabilistic controlled teleportation of a triplet W state using combined non-maximally entangled channel of two Einstein-Podolsky-Rosen (EPR) states and one Greenberger-Horne-Zeilinger (GHZ) state is proposed. In this scheme, an (m+2)-qubit GHZ state serves not only as the control parameter but also as the quantum channel. The m control qubits are shared by m supervisors. With the aid of local operations and individual measurements, including Bell-state measurement, Von Neumann measurement, and mutual classical communication etc., Bob can faithfully reconstruct the original state by performing relevant unitary transformations. The total probability of successful teleportation is only dependent on channel coefficients of EPR states and GHZ, independent of the number of supervisor m. This protocol can also be extended to probabilistic controlled teleportation of an arbitrary N-qubit state using combined non-maximally entangled channel of N-1 EPR states and one (m+2)-qubit GHZ.
Generalized Coherent States of a Particle in a Time-Dependent Linear Potential
L. Krache, M. Maamache, Y. Saadi, A. Beniaiche
Chin. Phys. Lett. 2009, 26 (7): 070307 .   DOI: 10.1088/0256-307X/26/7/070307
Abstract   PDF(pc) (192KB) ( 820 )
We derive, with an invariant operator method and unitary transformation approach, that the Schrödinger equation with a time-dependent linear potential possesses an infinite string of shape-preseving wave-packet states |φα,λ>(t)> having classical motion. The qualitative properties of the invariant eigenvalue spectrum (discrete or continuous) are described separately for the different values of the frequency ω of a harmonic oscillator. It is also shown that, for a discrete eigenvalue spectrum, the states |φα,n>(t)> could be obtained from the coherent state |φα,0>(t).
Hawking radiation as tunneling and the unified first law of thermodynamics at the apparent horizon of the FRW universe
JIANG Ke-Xia, KE San-Min, PENG Dan-Tao, FENG Jun
Chin. Phys. Lett. 2009, 26 (7): 070401 .   DOI: 10.1088/0256-307X/26/7/070401
Abstract   PDF(pc) (218KB) ( 490 )
Relations between the tunneling rate and the unified first law of thermodynamics at the apparent horizon of the FRW universe are investigated. The tunneling rate arises as a consequence of the unified first law of thermodynamics in such a dynamical system. Analysis shows how the tunneling is intimately connected with the unified first law of thermodynamics through the principle of conservation of energy.
The character of an anisotropic and spherically symmetric star in the presence of a cosmological constant
CHEN Xia, WANG Yong-Jiu
Chin. Phys. Lett. 2009, 26 (7): 070402 .   DOI: 10.1088/0256-307X/26/7/070402
Abstract   PDF(pc) (181KB) ( 406 )
From the gravitational structure equations of an anisotropic and spherically symmetric star in the presence of a cosmological constant, we derive the inequality which limits the mass-radius ratio, imposing energy conditions on the matter. From this inequality, we display how the cosmological constant modifies the Buchdahl limit, and express the bounds on both the mass-radius ratio and surface redshift in terms of the ratio between the cosmological constant and mean energy density of the star.
Two-dimensional discrete gap breathers in a two-dimensional discrete diatomic Klein-Gordon lattice
XU Quan, QIANG Tian
Chin. Phys. Lett. 2009, 26 (7): 070501 .   DOI: 10.1088/0256-307X/26/7/070501
Abstract   PDF(pc) (1009KB) ( 495 )
We study the existence and stability of two-dimensional discrete breathers in a two-dimensional discrete diatomic Klein-Gordon lattice consisting of alternating light and heavy atoms, with nearest-neighbor harmonic coupling. Localized solutions to the corresponding nonlinear differential equations with frequencies inside the gap of the linear wave spectrum, i.e. two-dimensional gap breathers, are investigated numerically. The numerical results of the corresponding algebraic equations demonstrate the possibility of the existence of two-dimensional gap breathers with three types of symmetries, i.e., symmetric, twin-antisymmetric and single-antisymmetric. Their stability depends on the nonlinear on-site potential (soft or hard), the interaction potential (attractive or repulsive) and the center of the two-dimensional gap breathers (on a light or a heavy atom).
Coalescence in coupled Duffing oscillators
YANG Jun-Zhong
Chin. Phys. Lett. 2009, 26 (7): 070502 .   DOI: 10.1088/0256-307X/26/7/070502
Abstract   PDF(pc) (667KB) ( 460 )
The forced Duffing oscillator has a pair of symmetrical attractors in a proper parameter regime. When a lot of Duffing oscillators are coupled linearly, the system tends to form clusters in which the neighboring oscillators fall onto the same attractor. When the coupling strength is strong, all of the oscillators fall onto one attractor. In this work, we investigate coalescence in the coupled forced Duffing oscillators. Some phenomena are found and explanations are presented.
The chaotification of discrete Hopfield neural networks via impulsive control
LIU Na, GUAN Zhi-Hong
Chin. Phys. Lett. 2009, 26 (7): 070503 .   DOI: 10.1088/0256-307X/26/7/070503
Abstract   PDF(pc) (232KB) ( 568 )
The chaotification of discrete Hopfield neural networks is studied with impulsive control techniques. No matter whether the original systems are stable or not, chaotification theorems for discrete Hopfield neural networks are derived, respectively. Finally, the effectiveness of the theoretical results is illustrated by some numerical examples.
New Canards Bursting and Canards Periodic-Chaotic Sequence
YOOER Chi-Feng, XU Jian-Xue, ZHANG Xin-Hua
Chin. Phys. Lett. 2009, 26 (7): 070504 .   DOI: 10.1088/0256-307X/26/7/070504
Abstract   PDF(pc) (290KB) ( 500 )
A trajectory following the repelling branch of an equilibrium or a periodic orbit is called a canards solution. Using a continuation method, we find a new type of canards bursting which manifests itself in an alternation between the oscillation phase following attracting the limit cycle branch and resting phase following a repelling fixed point branch in a reduced leech neuron model. Via periodic-chaotic alternating of infinite times, the number of windings within a canards bursting can approach infinity at a Gavrilov-Shilnikov homoclinic tangency bifurcation of a simple saddle limit cycle
Femtosecond Laser-Written Waveguides in a Bismuth Germanate Single Crystal
QIAN Bin, LIAO Yang, DONG Guo-Ping, LUO Fang-Fang, SU Liang-Bi, SUN Sheng-Zhi, QIU Jian-Rong
Chin. Phys. Lett. 2009, 26 (7): 070601 .   DOI: 10.1088/0256-307X/26/7/070601
Abstract   PDF(pc) (476KB) ( 496 )
We demonstrate the fabrication of symmetric waveguides in a bismuth germanate (BGO) single crystal using a double line approach by an 800nm femtosecond laser. The optical attenuation of the single mode waveguide is measured to be 4.2dB/cm at 633nm. The influence of pulse energy and focal depth on the end facet of the irradiated region is also studied. This technique is promising to fabricate buried BGO waveguide arrays used in positron emission tomography systems.
A Group-Period Phase Comparison Method Based on Equivalent Phase Comparison Frequency
DU Bao-Qiang, ZHOU Wei, DONG Shao-Feng, ZHOU Hai-Niu
Chin. Phys. Lett. 2009, 26 (7): 070602 .   DOI: 10.1088/0256-307X/26/7/070602
Abstract   PDF(pc) (304KB) ( 522 )
Based on the principle of equivalent phase comparison frequency, we propose a group-period phase comparison method. This method can be used to reveal the inherent relations between periodic signals and the change laws of the phase difference. If these laws are applied in the processing of the mutual relations between frequency signals, phase comparison can be accomplished without frequency normalization. Experimental results show that the method can enhance the measurement resolution to 10-13/s in the time domain.
Phase Transition in CCl4 under Pressure: a Raman Spectroscopic Study
LIU Tie-Cheng, ZHOU Mi, GAO Shu-Qin, LI Zuo-Wei, LI Zhan-Long, ZHANGPeng, LI Liang, LV Tian-Quan, XU Da-Peng
Chin. Phys. Lett. 2009, 26 (7): 070701 .   DOI: 10.1088/0256-307X/26/7/070701
Abstract   PDF(pc) (431KB) ( 598 )
High-pressure Raman studies at room temperature are performed on CCl4 up to 13GPa. The Raman bands of the internal modes (v2, v4 and v1) show entirely positive pressure dependence. The slopes dω/dP of the internal modes exhibit two sudden changes at 0.73GPa and 7.13GPa, respectively. A new lower frequency mode (225cm-1) appears at 3.03GPa, and the splitting of v2, ν3 and v4 occurs at about 7.13GPa. Moreover, Raman spectra of Fermi
resonance show that the relative position of the v1 + v4 combination and the ν3 fundamental firstly interchanges corresponding to that at ambient pressure, then the v1 +v4 combination disappears in the gradual process of compression. It is indicated that the pressure-induced phase transition from CCl4 II to CCl4 III occurs at 0.73GPa, and CCl4 III undergoes a transition to CCl4 IV below 3.03GPa. Further CCl4 IV transforms in a new high-pressure phase at about 7.13GPa, and the symmetry of the new high-pressure phase is lower than that of CCl4 IV. All the transitions are reversible during decompression.
An Electromagnetic Form Factor of a Charged Scalar Meson with Schwinger-Dyson and Bethe-Salpeter Equations
XIE Chuan-Mei, LI Heng-Mei, WAN Shao-Long
Chin. Phys. Lett. 2009, 26 (7): 071401 .   DOI: 10.1088/0256-307X/26/7/071401
Abstract   PDF(pc) (302KB) ( 361 )
The wave functions and electromagnetic form factor of charged scalar mesons are studied with a modified vector-vector flat-bottom potential model under the framework of the Schwinger-Dyson and Bethe-Salpeter equations. The obtained results agree well with other theories.
A systematic study on the binding energy of Λ hypernuclei
LAN Mi-Xiang, LI Lei, NING Ping-Zhi
Chin. Phys. Lett. 2009, 26 (7): 072101 .   DOI: 10.1088/0256-307X/26/7/072101
Abstract   PDF(pc) (302KB) ( 474 )
We calculate the binding energy per baryon of the Λ hypernuclei systematically, using the relativistic mean field theory (RMF) in a static frame. Some similar properties are found for most of the Λ hypernuclei confirmed by experiments. The data show that a Λ hypernucleus will be more stable if it is made by adding a Λ hyperon to a stable normal nuclear core, or by replacing a neutron by a Λ hyperon to a stable normal nuclear core. According to our calculations, the existence of some new Λ hypernuclei are predicted under the frame of RMF.
Theoretical Analysis and New Formulae for Half-Lives of Proton Emission
ZHANG Hong-Fei, DONG Jian-Min, WANG Yan-Zhao, SU Xin-Ning, WANG Yong-Jia, CAI Ling-Zhi, ZHU Tian-Bao, HU Bi-Tao, ZUO Wei, LI Jun-Qing,
Chin. Phys. Lett. 2009, 26 (7): 072301 .   DOI: 10.1088/0256-307X/26/7/072301
Abstract   PDF(pc) (351KB) ( 427 )
The proton radioactivity half-lives of spherical proton emitters are calculated by the cluster model with the contribution of a centrifugal potential barrier considered separately. The results are compared with the experimental data and other theoretical data, and good agreement is found for most nuclei. In addition, two formulae are proposed for the proton decay half-life of spherical proton emitters through the least squares fit to the experimental data available, and could reproduce the experimental half-lives successfully.
Angular Distribution of the 12C(6He, 7Li)11B Reaction
LI Er-Tao, LI Zhi-Hong, LI Yun-Ju, YAN Sheng-Quan, BAI Xi-Xiang, GUOBing, SU Jun, WANG You-Bao, WANG Bao-Xiang, LIAN Gang, ZENGSheng, FANG Xiao, ZHAO Wei-Juan, LIU Wei-Ping
Chin. Phys. Lett. 2009, 26 (7): 072401 .   DOI: 10.1088/0256-307X/26/7/072401
Abstract   PDF(pc) (523KB) ( 425 )
Angular distribution of the 12C(6He,7Li)11B transfer reaction is measured with a secondary 6He beam of 36.4MeV for the first time. The experimental angular distribution is well reproduced by the distorted-wave Born approximation (DWBA) calculation. The success of the present experiment shows that it is feasible to measure one-nucleon transfer reaction on a light nucleus target with the secondary beam facility of the HI-13 tandem accelerator at China Institute of Atomic Energy (CIAE), Beijing.
A Non-Zero Hadronic Elliptic Flow with a Vanished Partonic Elliptic Flow in a Coalescence Scenario
LIU Jian-Li, SHAN Lian-Qiang, FENG Qi-Chun, WU Feng-Juan, ZHANG Jing-Bo, TANG Gui-Xin, HUO Lei
Chin. Phys. Lett. 2009, 26 (7): 072501 .   DOI: 10.1088/0256-307X/26/7/072501
Abstract   PDF(pc) (301KB) ( 390 )
The elliptic flow of a hadron is calculated using a quark coalescence model based on the quark phase space distribution produced by a free streaming locally thermalized quark in a two-dimensional transverse plane at initial time. Without assuming the quark's elliptic flow, it is shown that the hadron obtains a non-zero elliptic flow in this model. The elliptic flow of the hadron is shown to be sensitive to both space momentum correlation and the hadron's internal structure. Quark number scaling is obtained only for some special cases.
The influence of Isospin Dependence of In-Medium NN Cross Sections on the Ratio of Emitted Neutrons to Protons in HICs
JIA Yi-Jian, ZHANG Ying-Xun, LI Zhu-Xia, LU Xiao-Hua, LIU Fu-Hu
Chin. Phys. Lett. 2009, 26 (7): 072502 .   DOI: 10.1088/0256-307X/26/7/072502
Abstract   PDF(pc) (415KB) ( 410 )
The influence of isospin dependence of in-medium nucleon-nucleon cross sections on the n/p ratios for emitted nucleons in reactions 96Zr+96Zr and 96Ru+96Ru at Eb=400AMeV is investigated by means of an improved quantum molecular dynamics model. Our results show that the high energy part of the spectra of the n/p ratios for emitted nucleons is sensitive to the isospin dependence of in-medium nucleon-nucleon cross sections for neutron-rich reaction systems. Therefore, we propose that the n/p ratio of emitted high energy nucleons in a very neutron-rich reaction system at several hundreds of AMeV can be taken as sensitive observables to constrain the isospindependence of in-medium nucleon-nucleon cross sections.
Microtubule as a Transmission Line for Ionic Currents
Chin. Phys. Lett. 2009, 26 (7): 073101 .   DOI: 10.1088/0256-307X/26/7/073101
Abstract   PDF(pc) (386KB) ( 584 )
We establish a new model for ionic waves along microtubules based on polyelectrolyte features of cylindrical biopolymers. The nonlinear transmission line described by a nonlinear differential equation is obtained with stable kink solution pertinent to the shape of the front of accompanying potential. The localized ionic wave could be used to explain the behavior of microtubules as biomolecular transistors capable of amplifying electrical information in neurons.
Simulation of Chromium Atom Deposition Pattern in a Gaussain Laser Standing Wave with Different Laser Power
ZHANG Wen-Tao, ZHU Bao-Hua
Chin. Phys. Lett. 2009, 26 (7): 073201 .   DOI: 10.1088/0256-307X/26/7/073201
Abstract   PDF(pc) (404KB) ( 458 )
One-dimensional deposition of a neutral chromium atomic beam focused by a near-resonant Gaussian standing-laser field is discussed by using a fourth-order Runge-Kutta type algorithm. The deposition pattern of neutral chromium atoms in a laser standing wave with different laser power is discussed and the simulation result shows that the full width at half maximum (FWHM) of a nanometer stripe is 115nm and the contrast is 2.5:1 with laser power 3.93mW; the FWHM is 0.8nm and the contrast is 27:1 with laser power 16mW, the optimal laser power; but with laser power increasing to 50mW, the nanometer structure forms multi-crests and the quality worsens quickly with increasing laser power.
Collision-Induced Coherence Effect on Coherent Population Transfer
YANG Xi-Hua, ZHANG Jun, ZHANG Hui-Fang, YAN Xiao-Na
Chin. Phys. Lett. 2009, 26 (7): 073202 .   DOI: 10.1088/0256-307X/26/7/073202
Abstract   PDF(pc) (340KB) ( 482 )
We investigate the effect of collision-induced coherence on coherent population transfer with the stimulated Raman adiabatic passage technique in a double Λ-type four-level system with a widely separated excited doublet. It is shown that when the two pulsed lasers with Rabi frequencies nearly comparable to the energy separation of the doublet are tuned to the particular frequency where the condition for quantum interference is satisfied, the very low transfer efficiency due to the nonadiabatic coupling between the two degenerate adiabatic states could be enhanced significantly with the increase of the collisional decay rates in a moderate range. The enhanced transfer efficiency results from the weakening of the nonadiabatic coupling between the two degenerate adiabatic states realized through collision-induced destructive quantum interference.
Theoretical Investigation of Femtosecond-Resolved Photoelectron Spectra of the Li2 Molecule
LIU Yu-Fang, LIU Rui-Qiong, DING Jun-Xia
Chin. Phys. Lett. 2009, 26 (7): 073301 .   DOI: 10.1088/0256-307X/26/7/073301
Abstract   PDF(pc) (345KB) ( 387 )
The time-dependent quantum wave packet method is used to investigate the dynamics for the Li2 molecule, and the time-resolved photoelectron spectra (TRPES) of the Li2 molecule are calculated. At the short delay time, the particular phenomenon of TRPES with four peaks is qualitatively interpreted in a dressed state picture by analyzing wave packet motion on light-induced potential (LIP). The significant difference in the electronic structure of E1g+ between the inner and outer turning points has an impact on the TRPES. The control for the first excited state A1u+ of the initial wave packet is discussed.
A Time-Dependent Wavepacket Method for Photodissociation Dynamics of Triatomic Molecule
Mohammad Noh Daud, Gabriel G. Balint-Kurti
Chin. Phys. Lett. 2009, 26 (7): 073302 .   DOI: 10.1088/0256-307X/26/7/073302
Abstract   PDF(pc) (236KB) ( 467 )
We report a time-dependent quantum wavepacket theory employed to interpret the photoabsorption spectrum of the N2O molecule in terms of the nuclear motion on the upper 21A' and 11A'' potential energy surfaces. The N2-O bond breaks upon excitation leading to dissociation. The total angular momentum is treated correctly taking into account the vector property of the electric field of the exciting radiation.
Magnetic Field Structure and Induced Electric Current Distribution on a Cylindrical Model: Application to Magnetic Nerve Stimulation
Taishi Okita, Toshiyuki Takagi
Chin. Phys. Lett. 2009, 26 (7): 074101 .   DOI: 10.1088/0256-307X/26/7/074101
Abstract   PDF(pc) (278KB) ( 594 )
We study the relation between the magnetic field structure and the induced electric-current distribution based on a cylindrical model composed of a uniform electrically conductive medium. When the time-varying magnetic fields are axisymmetrically applied in the axial direction of the model, the electric fields are induced around the central axis in accordance with Faraday's law. We examine the eddy-current distributions generated by loop-coils with various geometries carrying an alternating electric current. It is shown that the radial structure of the induced fields can significantly be controlled by the loop coil geometry, which will be suitable for practical use especially in magnetic nerve stimulation on bioelectromagnetics, if we appropriately place the exciting coil with optimum geometry.
In-Situ Characterization of Three-Dimensional Optical Matters by Light Diffraction
JIANG Lai-Dong, DAI Qiao-Feng, FENG Tian-Hua, LIU Jin, WU Li-Jun, LAN Sheng, A. V. Gopal, V. A. Trofimov
Chin. Phys. Lett. 2009, 26 (7): 074201 .   DOI: 10.1088/0256-307X/26/7/074201
Abstract   PDF(pc) (573KB) ( 330 )
Three-dimensional optical matters are created by combining the single beam optical trapping with the conventional Z-scan technique. Dynamic light diffraction is employed to evaluate the structure and quality of the optical matter formed at the optimum trapping power. The lattice constant of the optical matter is extracted based on the Bragg and Snell laws, showing that polystyrene spheres are nearly close-packed in the optical matter, confirmed by comparing the diffraction pattern of the optical matter with that of a colloidal photonic crystal fabricated by the self-assembled technique. The relatively broad diffraction peaks observed in the optical matter indicate that the density of disorders in it is higher than that in the photonic crystal. It is suggested that the optical matter possesses a random close-packed structure rather than a face centered cubic one.
Conical Double Frequency Emission by Femtosecond Laser Pulses from DKDP
ZHANG Xi-Peng, JIANG Hong-Bing, TANG Shan-Chun, GONG Qi-Huang
Chin. Phys. Lett. 2009, 26 (7): 074202 .   DOI: 10.1088/0256-307X/26/7/074202
Abstract   PDF(pc) (269KB) ( 357 )
Conical double frequency emission is investigated by femtosecond laser pulses at a wavelength of 800nm in a DKDP crystal. It is demonstrated that the sum frequency of incident wave and its scattering wave accounts for the conical double frequency emission. The gaps on the conical rings are observed and they are very sensitive to the propagation direction, and thus could be used to detect the small angle deviation of surface direction.
Effect of Vacuum on the Laser-Induced Damage of Anti-Reflection Coatings
LING Xiu-Lan, ZHAO Yuan-An, LI Da-Wei, ZHOU Ming, SHAO Jian-Da, FANZheng-Xiu
Chin. Phys. Lett. 2009, 26 (7): 074203 .   DOI: 10.1088/0256-307X/26/7/074203
Abstract   PDF(pc) (676KB) ( 455 )
In the comparison of damage modifications, absorption measurement and energy dispersive x-ray analysis, the effect of vacuum on the laser-induced damage of anti-reflection coatings is analyzed. It is found that vacuum decreases the laser-induced damage threshold of the films. The low laser-induced damage threshold in vacuum environments as opposed to air environments is attributed to water absorption and the formation of the O/Si, O/Zr sub-stoichiometry in the course of laser irradiation.
End-Pumped Tm:YAG Ceramic Slab Lasers
CHENG Xiao-Jin, XU Jian-Qiu, ZHANG Wen-Xin, JIANG Ben-Xue, PAN Yu-Bai
Chin. Phys. Lett. 2009, 26 (7): 074204 .   DOI: 10.1088/0256-307X/26/7/074204
Abstract   PDF(pc) (293KB) ( 665 )
Lasers from a Tm:YAG ceramic aare reported for the first time to our best knowledge. The Tm:YAG ceramic slab is end-pumped by a laser diode with central wavelength 792nm. At room temperature, the maximum continuous-wave output power is 4.5W, and the sloping efficiency is obtained to be 20.5%. The laser spectrum of the Tm:YAG ceramic is centered at 2015nm.
Experimental Study on Coherence Time of a Light Field with Single Photon Counting
LI Yuan, ZHANG Yu-Chi, ZHANG Peng-Fei, GUO Yan-Qiang, LI Gang, WANGJun-Min, ZHANG Tian-Cai
Chin. Phys. Lett. 2009, 26 (7): 074205 .   DOI: 10.1088/0256-307X/26/7/074205
Abstract   PDF(pc) (387KB) ( 848 )
The second-order degree of coherence of pseudo-thermal light and coherence time are experimentally studied via the Hanbruy-Brown-Twiss (HBT) scheme. The system consists of two non-photon-number-resolving single-photon-counting modules (SPCMs) operating in the Geiger mode. We investigate the coherence time of the incident beam for different spot sizes on a ground glass and speeds of a rotating ground glass. The corresponding coherence time can be obtained from Gaussian fitting for the measured second-order degree of coherence. The results show that the coherence time of measured pseudo-thermal light depends on the spot sizes and the rotating speeds of the ground glass. The maximum value of the second-order degree of coherence is reduced as the rotating speed decreases. This result can be well explained by the model of mixed thermal and coherent fields with different ratios.
Damage Performance of Multilayer Films under Simultaneous Exposure to Multi-Wavelength Pulses
Chin. Phys. Lett. 2009, 26 (7): 074206 .   DOI: 10.1088/0256-307X/26/7/074206
Abstract   PDF(pc) (382KB) ( 389 )
Laser damage performance of multilayer films with combined irradiation of 1ω and 2ω is studied to probe the damage mechanisms during wavelength division. The laser induced damage thresholds (LIDTs) of the samples are obtained and tested with only 2ω with various energy densities of 1ω. Different 1ω polarization directions combined with the 2ω case are also investigated. The result suggests that 1ω can raise the damage probability of multilayer mirrors when two light wavelengths are present simultaneously; the increasing number of sensitive defects for 2ω can be related to the decline of the LIDTs of the multilayer mirrors.
Spectral Analysis using Linearly Chirped Gaussian Pulse Stacking
ZHENG Huan, WANG An-Ting, XU Li-Xin, MING Hai
Chin. Phys. Lett. 2009, 26 (7): 074207 .   DOI: 10.1088/0256-307X/26/7/074207
Abstract   PDF(pc) (321KB) ( 401 )
We analyze the spectrum of a stacked pulse with the technique of linearly chirped Gaussian pulse stacking. Our results show that there are modulation structures in the spectrum of the stacked pulse. The modulation frequencies are discussed in detail. By applying spectral analysis, we find that the intensity fluctuation cannot be smoothed by introducing an optical amplitude filter.
A Tunable Acousto-Optic Fiber Filter Based on Two Simultaneous Mode Coupling Processes
MIAO Ren, ZHANG Wei, FENG Xue, ZHAO Jian-Hui, LIU Xiao-Ming
Chin. Phys. Lett. 2009, 26 (7): 074208 .   DOI: 10.1088/0256-307X/26/7/074208
Abstract   PDF(pc) (461KB) ( 478 )
A dynamically tunable fiber filter realizing complex spectra of phase-shifted long period fiber gratings (LPFGs) is proposed and demonstrated experimentally. The principle of the filter is based on two acousto-optic coupling processes occurring simultaneously. The first coupling process acts as a normal LPFG, while the second makes the coupling direction of the first process change continuously, leading to a similar transmission spectrum with the phase-shifted LPFGs, in which the changing of coupling direction is realized by the discrete phase shifts of the index modulation. By adjusting the acoustic drive signals, its transmission spectrum can be dynamically tuned to realize the phase-shifted LPFGs' spectra under different phase shift numbers and locations.
Design and Fabrication of an Er-Doped Silica Optical Fiber with Six Photosensitive Subcores
LI Jian, , WANG Jing, LIU Peng, , LU Shao-Hua, MAO Xiang-Qiao, JIANG Wei-Wei, NING Ti-Gang, JIAN Shui-Sheng,
Chin. Phys. Lett. 2009, 26 (7): 074209 .   DOI: 10.1088/0256-307X/26/7/074209
Abstract   PDF(pc) (507KB) ( 571 )
A type of multi-core Er-doped photosensitive silica optical fiber (MC-EDPF) is proposed and fabricated, in which a high consistency Er-doped core is surrounded by six high consistency Ge-doped cores. The multi-core design can overcome the difficulties encountered in the design and fabrication of single-core EDPFs through a modified chemical vapor deposition method combined with solution doping technology, and there is a conflict between high consistency Er doping and high consistency Ge doping. The absorption of MC-EDPFs achieved 15.876dB/m at 1550nm and 10dB/m at 980nm. The reflectivity of the fiber Bragg gratings (FBGs) written directly on the MC-EDPFs is as much as 96.84%.
A Kilowatt Radio-Frequency Excited Diffusively Cooled All-Metal Slab Waveguide CO2 Laser
SHA Peng-Fei, Xin Jian-Guo
Chin. Phys. Lett. 2009, 26 (7): 074210 .   DOI: 10.1088/0256-307X/26/7/074210
Abstract   PDF(pc) (213KB) ( 605 )
A new type of rf excited diffusively cooled all-metal slab waveguide CO2 laser is presented, in which the waveguide channel is constructed by two copper side walls and two copper electrodes, and the discharge is confined in the slab waveguide channel in terms of the voltage division structure. From this type of structure, over 1kW laser power is obtained with an efficiency of more than 13%.
A Simple Loop for Simultaneous OTDM Demultiplexing and Clock Recovery
CHEN Ming, LU Dan, GONG Tao-Rong, LV Bo, WANG Mu-Guang, LI Tang-Jun, JIAN Shui-Sheng
Chin. Phys. Lett. 2009, 26 (7): 074211 .   DOI: 10.1088/0256-307X/26/7/074211
Abstract   PDF(pc) (624KB) ( 517 )
A simple and stable loop consisting of a pair of concatenated electroabsorption modulators (EAMs) and 10 GHz clock recovery module is presented and demonstrated experimentally for simultaneous demultiplexing and clock recovery for OTDM networks. The 10Gb/s demultiplexed signal and 10GHz recovered clock are successfully implemented from 80Gbit/s and 160Gbit/s OTDM signals utilizing the loop. The loop based on EAM-PLL can provide excellent tolerance range (>5dB) of the OSCR of the source laser, and the recovered clock signal exhibits low rms jitter over a dynamic input optical power range of 15dB.
Numerical Study of Low-Loss Cross Left-Handed Metamaterials at Visible Frequency
ZHU Wei-Ren, ZHAO Xiao-Peng
Chin. Phys. Lett. 2009, 26 (7): 074212 .   DOI: 10.1088/0256-307X/26/7/074212
Abstract   PDF(pc) (368KB) ( 494 )
We present a numerical study of left-handed metamaterials (LHMs) composed of double cross pairs at visible frequency. The S-parameter retrieval method is adopted to confirm the negative refractive characteristic of this design. Compared with fishnet LHMs, the proposed cross LHMs have a much lower loss, which will greatly facilitate practical applications. It is also found that, with the same size of resonant cells, the cross LHMs have a higher frequency than fishnet LHMs, which is explained using a simple effective LC circuit model.
Analysis and Simulation of Adiabatic Bend Transitions in Optical Fibers
YAO Lei, LOU Shu-Qin, JIAN Shui-Sheng
Chin. Phys. Lett. 2009, 26 (7): 074213 .   DOI: 10.1088/0256-307X/26/7/074213
Abstract   PDF(pc) (236KB) ( 863 )
A low-loss criterion for bend transitions in optical fibers is proposed. An optical fiber can be tightly bent with low loss to be adiabatic for the fundamental mode, provided that an approximate upper bound on the rate of change of bend curvature for a given bend curvature is satisfied. Two typical adiabatic bend transition paths, the optimum profile and linear profile, are analyzed and studied numerically. A realizable adiabatic transition with an Archimedean spiral profile is introduced for low bend loss in tightly bent optical fibers. Design of the transitions is based on modeling of the propagation and coupling characteristics of the core and cladding modes, which clearly illustrate the physical processes involved.
A Wavelength-Tunable Fiber-Coupled Narrow-Band Twin-Photon Source
HUANG Jian-Fa, LIU Bi-Heng, FANG Bin, HUANG Yun-Feng, GUO Guang-Can
Chin. Phys. Lett. 2009, 26 (7): 074214 .   DOI: 10.1088/0256-307X/26/7/074214
Abstract   PDF(pc) (298KB) ( 650 )
We present a wavelength-tunable narrow-band fiber-coupled source to generate correlated photon pairs at 539nm and 1550nm. Using a 10-mm PPLN crystal, we obtain more than 50mm tunable range near 1550nm. This source, given its spectral property and tunable property, is well suited for tasks in fiber-optic quantum communication and cryptography networks.
Spatial Soliton Solutions in a Harmonic Potential
XU Si-Liu, LIANG Jian-Chu, YI Lin
Chin. Phys. Lett. 2009, 26 (7): 074215 .   DOI: 10.1088/0256-307X/26/7/074215
Abstract   PDF(pc) (410KB) ( 580 )
The F-expansion technique and the homogeneous nonlinear balance principle have been applied for solving a general (1+1)-dimensional nonlinear Schrödinger equation (NLSE) with varying coefficients and a harmonic potential. A family of (1+1)D spatial solitons has been obtained. The evolution features of exact solutions have been investigated.
Slow Light by Two-Dimensional Photonic Crystal Waveguides
ZHANG Chao, HUANG Yan, MAO Xiao-Yu, CUI Kai-Yu, HUANG Yi-Dong, ZHANG Wei, PENG Jiang-De
Chin. Phys. Lett. 2009, 26 (7): 074216 .   DOI: 10.1088/0256-307X/26/7/074216
Abstract   PDF(pc) (376KB) ( 426 )
A simple and effective way to measure the group velocity of photonic crystal waveguides (PCWGs) is developed by using a fiber Mach-Zehnder interferometer. A PCWG with perfect air-bridge structure is fabricated and slow light with group velocity slower than c/80 is demonstrated.
Green-Beam Generation of 40W by Use of an Intracavity Frequency-Doubled Diode Side-Pumped Nd:YAG Laser
ZHANG Yu-Ping, ZHANG Hui-Yun, GENG You-Fu, TAN Xiao-Ling, ZHONG Kai, LI Xi-Fu, WANG Peng, YAO Jian-Quan
Chin. Phys. Lett. 2009, 26 (7): 074217 .   DOI: 10.1088/0256-307X/26/7/074217
Abstract   PDF(pc) (399KB) ( 491 )
A cw diode side-pumped Nd:YAG laser is frequency doubled to 532nm with an intracavity KTP crystal in a V-shaped arrangement, achieving an output power of 40W corresponding to an optical-optical conversion efficiency of 9.7%. The instabilities and the M2-parameters of the laser are measured at different output powers after the beam is filtered.
Optimal Design of an Achromatic Angle-Insensitive Phase Retarder Used in MWIR Imaging Polarimetry
KANG Guo-Guo, TAN Qiao-Feng, JIN Guo-Fan
Chin. Phys. Lett. 2009, 26 (7): 074218 .   DOI: 10.1088/0256-307X/26/7/074218
Abstract   PDF(pc) (228KB) ( 521 )
Dielectric gratings with period in the range from λ/10 to λ/4 with λ being the illumination wavelength not only exclude higher order diffractions but also exhibit strong dispersion of effective indices which are proportional to the wavelength. Moreover, they are insensitive to the incident angle of the illumination wave. With these features, we can design a true zero-order achromatic and angle-insensitive phase retarder which can be used as the polarization state analyzer in middle wave infrared (MWIR) imaging polarimetry. A design method using effective medium theory is described, and the performance of the designed phase retarder is evaluated by rigorous coupled wave analysis theory. The calculation results demonstrate that the retardance deviates from 45° by<±1.6° within a field of view ±pm 10° over the MWIR bandwidth (3-5μm).
An Encryption-Decryption Method Using XOR Gate Based on the XPM between O-Band and C-Band Light Waves
WANG Ya-Ping, WU Chong-Qing, WANG Zhi, WANG Yong-Jun, YANG Shuang-Shou, SHENG Xin-Zhi
Chin. Phys. Lett. 2009, 26 (7): 074219 .   DOI: 10.1088/0256-307X/26/7/074219
Abstract   PDF(pc) (781KB) ( 899 )
An all-optical encryption-decryption method using an exclusive-or gate based on the cross-phase modulation between O-band and C-band light waves is proposed. The feasibility of the encryption-decryption technique is verified by handling binary signals at 2.5Gbps, with less than 3dB penalty of extinction ratio and 1dB polarization dependent loss.
Effects of Turbulent Aberrations on Probability Distribution of Orbital Angular Momentum for Optical Communication
Chin. Phys. Lett. 2009, 26 (7): 074220 .   DOI: 10.1088/0256-307X/26/7/074220
Abstract   PDF(pc) (228KB) ( 641 )
Effects of atmospheric turbulence tilt, defocus, astigmatism and coma aberrations on the orbital angular momentum measurement probability of photons propagating in weak turbulent regime are modeled with Rytov approximation. By considering the resulting wave as a superposition of angular momentum eigenstates, the orbital angular momentum measurement probabilities of the transmitted digit are presented. Our results show that the effect of turbulent tilt aberration on the orbital angular momentum measurement probabilities of photons is the maximum among these four kinds of aberrations. As the aberration order increases, the effects of turbulence aberrations on the measurement probabilities of orbital angular momentum generally decrease, whereas the effect of turbulence defocus can be ignored. For tilt aberration, as the difference between the measured orbital angular momentum and the original orbital angular momentum increases, the orbital angular momentum measurement probability decreases.
Ultrasound Attenuation in Biological Tissue Predicted by the Modified Doublet Mechanics Model
JIANG Xin, LIU Xiao-Zhou, WU Jun-Ru
Chin. Phys. Lett. 2009, 26 (7): 074301 .   DOI: 10.1088/0256-307X/26/7/074301
Abstract   PDF(pc) (343KB) ( 484 )
Experimental results have shown that in the megahertz frequency range the relationship between the acoustic attenuation coefficient in soft tissues and frequency is nearly linear. The classical continuum mechanics (CCM), which assumes that the material is uniform and continuous, fails to explain this relationship particularly in the high megahertz range. Doublet mechanics (DM) is a new elastic theory which takes the discrete nature of material into account. The current DM theory however does not consider the loss. We revise the doublet mechanics (DM) theory by including the loss term, and calculate the attenuation of a soft tissue as a function of frequency using the modified the DM theory (MDM). The MDM can now well explain the nearly linear relationship between the acoustic attenuation coefficient in soft tissues and frequency.
Asymmetric Heat Conduction in One-Dimensional Hard-Point Model with Mass Gradient
LI Hai-Bin, NIE Qing-Miao, XIN Xiao-Tian
Chin. Phys. Lett. 2009, 26 (7): 074401 .   DOI: 10.1088/0256-307X/26/7/074401
Abstract   PDF(pc) (286KB) ( 413 )
The heat conduction in a one-dimensional (1D) hard-point model with mass gradient is studied. Using numerical simulation, we find an asymmetric heat conduction in this model with greater heat current in the direction of mass increase. The increase of temperature gradient, mass gradient and system size are found to enhance the asymmetric heat conduction. Based on the collision dynamic of a hard-point particle, we give a qualitative explanation for the underlying mechanism of asymmetric effect.
Jourdain Principle of a Super-Thin Elastic Rod Dynamics
XUE Yun, SHANG Hui-Lin
Chin. Phys. Lett. 2009, 26 (7): 074501 .   DOI: 10.1088/0256-307X/26/7/074501
Abstract   PDF(pc) (194KB) ( 394 )
A super thin elastic rod is modeled with a background of DNA super coiling structure, and its dynamics is discussed based on the Jourdain variation. The cross section of the rod is taken as the object of this study and two velocity spaces about arc coordinate and the time are obtained respectively. Virtual displacements of the section on the two velocity spaces are defined and can be expressed in terms of Jourdain variation. Jourdain principles of a super thin elastic rod dynamics on arc coordinate and the time velocity space are established, respectively, which show that there are two ways to realize the constraint conditions. If the constitutive relation of the rod is linear, the Jourdain principle takes the Euler-Lagrange form with generalized oordinates. The Kirchhoff equation, Lagrange equation and Appell equation can be derived from the present Jourdain principle. While the rod subjected to a surface constraint, Lagrange equation with undetermined multipliers may be derived.
Numerical Simulation of Vapor Bubble Growth and Heat Transfer in a Thin Liquid Film
TAO Yu-Jia, HUAI Xiu-Lan, LI Zhi-Gang
Chin. Phys. Lett. 2009, 26 (7): 074701 .   DOI: 10.1088/0256-307X/26/7/074701
Abstract   PDF(pc) (485KB) ( 674 )
A mathematical model is developed to investigate the dynamics of vapor bubble growth in a thin liquid film, movement of the interface between two fluids and the surface heat transfer characteristics. The model takes into account the effects of phase change between the vapor and liquid, gravity, surface tension and viscosity. The details of the multiphase flow and heat transfer are discussed for two cases: (1) when a water micro-droplet impacts a thin liquid film with a vapor bubble growing and (2) when the vapor bubble grows and merges with the vapor layer above the liquid film without the droplet impacting. The development trend of the interface between the vapor and liquid is coincident qualitatively with the available literature, mostly at the first stage. We also provide an important method to better understand the mechanism of nucleate spray cooling.
The Blood Flow at Arterial Bifurcations Simulated by the Lattice Boltzmann Method
JI Yu-Pin, KANG Xiu-Ying, LIU Da-He
Chin. Phys. Lett. 2009, 26 (7): 074702 .   DOI: 10.1088/0256-307X/26/7/074702
Abstract   PDF(pc) (545KB) ( 837 )
The Programmed model of non-Newtonian blood flow (the Casson model) at arterial bifurcations is established by the lattice Boltzmann method. The blood flow field under different Reynolds numbers is simulated, and distribution of dynamic factors such as flow velocity, shear stress, pressure and shear rate are presented. The existence of the fluid separation zone is analyzed. This provides a basis for further studies of the relationship between hemodynamic factors and pathogenesis, as well as a reference for a better understanding of the pathological changes and location of sediments, and the plague factor in arteries.
Vortex Turbulence due to the Interplay of Filament Tension and Rotational Anisotropy
Chin. Phys. Lett. 2009, 26 (7): 074703 .   DOI: 10.1088/0256-307X/26/7/074703
Abstract   PDF(pc) (273KB) ( 393 )
The mechanism of scroll wave turbulence is investigated in excitable media with rotational anisotropy. We adopt the Barkley model with heterogeneity in the diffusion constants. Through comparative numerical studies, we demonstrate the vortex turbulence results from the rotational anisotropy's cooperation with negative filament tension or competition with positive filament tension. The presence of rotational anisotropy can enlarge the parameter region leading to negative-tension induced wave turbulence in isotropic media.
A Weakly Nonlinear Model for Kelvin-Helmholtz Instability in Incompressible Fluids
WANG Li-Feng, YE Wen-Hua, , FAN Zheng-Feng, XUE Chuang, LI Ying-Jun
Chin. Phys. Lett. 2009, 26 (7): 074704 .   DOI: 10.1088/0256-307X/26/7/074704
Abstract   PDF(pc) (393KB) ( 462 )
A weakly nonlinear model is proposed for the Kelvin-Helmholtz instability in two-dimensional incompressible fluids by expanding the perturbation velocity potential to third order. The third-order harmonic generation effects of single-mode perturbation are analyzed, as well as the nonlinear correction to the exponential growth of the fundamental modulation. The weakly nonlinear results are supported by numerical simulations. Density and resonance effects exist in the development of mode coupling.
The Phase Transition of Eu2O3 under High Pressures
JIANG Sheng, BAI Li-Gang, LIU Jing, XIAO Wan-Sheng, LI Xiao-Dong, LI Yan-Chun, TANG Ling-Yun, ZHANG Yu-Feng, ZHANG De-Chun, ZHENG Li-Rong
Chin. Phys. Lett. 2009, 26 (7): 076101 .   DOI: 10.1088/0256-307X/26/7/076101
Abstract   PDF(pc) (716KB) ( 725 )
Pressure-induced phase transition of cubic Eu2O3 is studied by angle-dispersive x-ray diffraction (ADXD) up to 42.3GPa at room temperature. A structural transformation from a cubic phase to a hexagonal phase is observed, which starts at 5.0GPa and finishes at about 13.1GPa. The phase transition leads to a volume collapse of 9.0% at 8.6GPa. The hexagonal phase of Eu2O3 maintains stable up to the highest experiment pressure. After release of pressure, the high-pressure phase transforms to a monoclinic phase. The pressure-volume data are fitted with the Birch-Murnaghan equation of state. The bulk moduli obtained upon compression from the fitting are 145(2)GPa and 151(6)GPa for the cubic and hexagonal phases, respectively, when their first pressure derivatives are fixed at 4.
Curvature and Hybridization Effects on the Persistent Current of a Carbon Nanotorus
XU Ning, DING Jian-Wen, CHEN Hong-Bo, MA Ming-Ming
Chin. Phys. Lett. 2009, 26 (7): 076102 .   DOI: 10.1088/0256-307X/26/7/076102
Abstract   PDF(pc) (451KB) ( 477 )
To accurately describe the persistent current for various toroidal carbon nanotubes (TCNs), a semiempirical sp3 tight-binding model is presented, in which the intrinsic curvature and hybridization have been fully taken into account. The calculations show that the curvature and hybridization can induce dramatic changes in the energy spectra of TCNs such as the Fermi energy EF shifting up, an energy gap opening at EF, and the energy spectrum symmetry about EF destroyed, which leads to a decrease of persistent current and changes in the shape of the flux-dependent current. In the presence of curvature and hybridization, the persistent current in non-armchair TCNs is nearly an order of magnitude lower than that obtained by using the Brillouin-zone folding approach, while it is of the same order of magnitude in armchair TCNs.
The Effect of Orientation Relaxation on Polymer Melt Crystallization Studied by Monte Carlo Simulations
WANG Mao-Xiang
Chin. Phys. Lett. 2009, 26 (7): 076103 .   DOI: 10.1088/0256-307X/26/7/076103
Abstract   PDF(pc) (268KB) ( 1133 )
We use dynamic Monte Carlo simulations to study the athermal relaxation of bulk extended chains and the isothermal crystallization in intermediately relaxed melts. It is found that the memory of chain orientations in the melt can significantly enhance the crystallization rates. The crystal orientation and lamellar thickness essentially depend on the orientational relaxation. Moreover, there is a transition of the nucleation mechanism during the isothermal crystallization from the intermediately relaxed melts. These results explain the mechanism of the self-nucleation by orientation and suggest that in flow-induced polymer crystallization, the orientational relaxation of chains decides the crystal orientation.
Curvature Correction of FWHM in the X-Ray Rocking Curve of Bent Heteroepitaxial Films
WANG Liang-Ji, ZHANG Shu-Ming, WANG Yu-Tian, JIANG De-Sheng, ZHU Jian-Jun, ZHAO De-Gang, LIU Zong-Shun, WANG Hui, SHI Yong-Sheng, WANG Hai, LIU Su-Ying, YANG Hui,
Chin. Phys. Lett. 2009, 26 (7): 076104 .   DOI: 10.1088/0256-307X/26/7/076104
Abstract   PDF(pc) (369KB) ( 1518 )
A method for accurate determination of the curvature radius of semiconductor thin films is proposed. The curvature-induced broadening of the x-ray rocking curve (XRC) of a heteroepitaxially grown layer can be determined if the dependence of the full width at half maximum (FWHM) of XRC is measured as a function of the width of incident x-ray beam. It is found that the curvature radii of two GaN films grown on a sapphire wafer are different when they are grown under similar MOCVD conditions but have different values of layer thickness. At the same time, the dislocation-induced broadening of XRC and thus the dislocation density of the epitaxial film can be well calculated after the curvature correction.
Crystal Structure and High Hardness Mechanism of Orthorhomic Si2N2O
XIONG Lan-Tian, CAO Mao-Sheng, HOU Zhi-Ling
Chin. Phys. Lett. 2009, 26 (7): 076201 .   DOI: 10.1088/0256-307X/26/7/076201
Abstract   PDF(pc) (418KB) ( 655 )
A quasi-single-phase orthorombic Si2N2O compound is obtained by hot-pressing sintering using homogeneous precursors as raw materials under nitrogen atmosphere. The bulk hardness of orthorombic Si2N2O (o-Si2N2O) is investigated by a nanoindenter experiment; the results show that o-Si2N2O with maximal value about 19GPa has a high hardness covalent crystal besides β-Si3N4. It is discovered that the high hardness is mainly attributed to the unique crystal structure. The bridging O atoms in the o-Si2N2O are responsible for decreasing hardness. It is found that the Si-O bonds in the open tetrahedral crystal structure are more easily broken and tilted than other bonds.
Orientation and Rate Dependence of Wave Propagation in Shocked Beta-SiC from Atomistic Simulations
CHENG Qin, WU Heng-An, WANG Yu, WANG Xiu-Xi
Chin. Phys. Lett. 2009, 26 (7): 076202 .   DOI: 10.1088/0256-307X/26/7/076202
Abstract   PDF(pc) (407KB) ( 498 )
The orientation dependence of planar wave propagation in beta-SiC is studied via the molecular dynamics (MD) method. Simulations are implemented under impact loadings in four main crystal directions, i.e., <100>, <110>, <111>, and <112>. The dispersion of stress states in different directions increases with rising impact velocity, which implies the anisotropic characteristic of shock wave propagation for beta-SiC materials. We also obtain the Hugoniot relations between the shock wave velocity and the impact velocity, and find that the shock velocity falls into a plateau above a threshold of impact velocity. The shock velocity of the plateaux is dependent on the shock directions, while <111> and <112> can be regarded as equivalent directions as they almost reach the same plateau. A comparison between the atomic stress from MD and the stress from Rankine-Hugoniot jump conditions is also made, and it is found that they agree with each other very well.
A Method to Design Synthetic Cell-Cycle Networks
Chin. Phys. Lett. 2009, 26 (7): 076401 .   DOI: 10.1088/0256-307X/26/7/076401
Abstract   PDF(pc) (393KB) ( 385 )
The interactions among proteins, DNA and RNA in an organism form elaborate cell-cycle networks which govern cell growth and proliferation. Understanding the common structure of cell-cycle networks will be of great benefit to science research. Here, inspired by the importance of the cell-cycle regulatory network of yeast which has been studied intensively, we focus on small networks with 11 nodes, equivalent to that of the cell-cycle regulatory network used by Li et al. [Proc. Natl. Acad. Sci. USA 101(2004)4781] Using a Boolean model, we study the correlation between structure and function, and a possible common structure. It is found that cascade-like networks with a great number of interactions between nodes are stable. Based on these findings, we are able to construct synthetic networks that have the same functions as the cell-cycle regulatory network.
Preparation and Thermal Characterization of Diamond-Like Carbon Films
BAI Su-Yuan, TANG Zhen-An, HUANG Zheng-Xing, Yu Jun, WANG Jing, LIU Gui-Chang
Chin. Phys. Lett. 2009, 26 (7): 076601 .   DOI: 10.1088/0256-307X/26/7/076601
Abstract   PDF(pc) (410KB) ( 664 )
Diamond-like carbon (DLC) films are prepared on silicon substrates by microwave electron cyclotron resonance plasma enhanced chemical vapor deposition. Raman spectroscopy indicates that the films have an amorphous structure and typical characteristics. The topographies of the films are presented by AFM images. Effective thermal conductivities of the films are measured using a nanosecond pulsed photothermal reflectance method. The results show that thermal conductivity is dominated by the microstructure of the films.
Low-Energy Collective Excitation of Bose-Einstein Condensates in an Anisotropic Magnetic Trap
YANG Lu, WANG Xiao-Rui, LI Ke, TAN Xin-Zhou, XIONG Hong-Wei, LU Bao-Long
Chin. Phys. Lett. 2009, 26 (7): 076701 .   DOI: 10.1088/0256-307X/26/7/076701
Abstract   PDF(pc) (343KB) ( 602 )
We experimentally investigate the collective excitation of 87Rb Bose-Einstein condensates confined in a cigar-shaped magnetic trap (QUIC trap). Using a method of magnetic perturbation, the center-of-mass oscillation of the condensate is excited, so that the radial trapping frequency of the QUIC trap can be precisely determined. A high-order excitation, characterized by a fast shape oscillation, also occurs simultaneously, with a noticeable damping in the oscillation amplitude compared with the oscillation of the center of mass. The measured oscillation frequencies, associated with these two low-energy excitation modes, agree well with theoretical predictions based on the Gross-Pitaevskii equation.
Density Functional Calculation of the 0.5ML-Terminated Allyl Mercaptan/Si(100)-(2×1) Surface
TANG Chun-Mei, DENG Kai-Ming, CHEN Xuan, XIAO Chuan-Yun, LIU Yu-Zhen, LI Qun-Xiang
Chin. Phys. Lett. 2009, 26 (7): 076801 .   DOI: 10.1088/0256-307X/26/7/076801
Abstract   PDF(pc) (424KB) ( 429 )
The structural and electronic properties of the 0.5ML-terminated allyl mercaptan (ALM)/Si(100)-(2×1) surface are studied using the density functional method. The calculated absorption energy of the ALM molecule on the 0.5ML-terminated ALM/Si(100)-(2×1) surface is 3.36eV, implying that adsorption is strongly favorable. The electronic structure calculations show that the ALM/Si(100)-(2×1), the clean Si(100)-(2×1), and the fully-terminated H/Si(100)-(2×1) surfaces have the nature of an indirect band gap semiconductor. The highest occupied molecular orbital is dominated by the ALM, confirming the mechanism proposed by Hossain for its chain reaction.
Halopentacenes: Promising Candidates for Organic Semiconductors
DU Gong-He, REN Zhao-Yu, GUO Ping, ZHENG Ji-Ming
Chin. Phys. Lett. 2009, 26 (7): 077101 .   DOI: 10.1088/0256-307X/26/7/077101
Abstract   PDF(pc) (469KB) ( 495 )
We introduce polar substituents such as F, Cl, Br into pentacene to enhance the dissolubility in common organic solvents while retaining the high charge-carrier mobilities of pentacene. Geometric structures, dipole moments, frontier molecule orbits, ionization potentials and electron affinities, as well as reorganization energies of those molecules, and of pentacene for comparison, are successively calculated by density functional theory. The results indicate that halopentacenes have rather small reorganization energies (<0.2eV), and when the substituents are in position 2 or positions 2 and 9, they are polarity molecules. Thus we conjecture that they can easily be dissolved in common organic solvents, and are promising candidates for organic semiconductors.
Bulk Modulus and Electronic Band Structure of ZnGa2X4(X=S,Se): a First-Principles Study
JIANG Xiao-Shu, MI Shu, SUN Peng-Jun, LU Yuan, LIANG Jiu-Qing
Chin. Phys. Lett. 2009, 26 (7): 077102 .   DOI: 10.1088/0256-307X/26/7/077102
Abstract   PDF(pc) (286KB) ( 661 )
First-principles local density functional calculations are presented for the compounds ZnGa2X4 (X=S,Se). We investigate the bulk moduli and electronic band structures in a defect chalcopyrite structure. The lattice constants and internal parameters are optimized. The electronic structures are analysed with the help of total and partial density of states. The relation between the cohesive energy and the unit cell volume is obtained by fully relaxed structures. We derive the bulk modulus of ZnGa2X4 by fitting the Birch-Murnaghan's equation of state. The extended Cohen's empirical formula agrees well with our ab initio results.
First-Principles Study of Structural Stabilities, Electronic and Optical Properties of SrF2 under High Pressure
HAO Ai-Min, YANG Xiao-Cui, LI Jie, XIN Wei, ZHANG Su-Hong, ZHANG Xin-Yu, LIU Ri-Ping
Chin. Phys. Lett. 2009, 26 (7): 077103 .   DOI: 10.1088/0256-307X/26/7/077103
Abstract   PDF(pc) (467KB) ( 724 )
An investigation of structural stabilities, electronic and optical properties of SrF2 under high pressure is conducted using a first-principles calculation based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. Our results predict that the second high-pressure phase of SrF2 is of a Ni2In-type structure, and demonstrate that the sequence of the pressure-induced phase transition of SrF2 is the fluorite structure (Fm3m) to the PbCl2-type structure (Pnma), and to the Ni2In-type phase (P63/mmc). The first and second phase transition pressures are 5.77 and 45.58GPa, respectively. The energy gap increases initially with pressure in the Fm3m, and begins to decrease in the Pnma phases at 30GPa. The band gap overlap metallization does not occur up to 210GPa. The pressure effect on the optical properties is discussed.
Electric Field Control of Interface Related Spin Splitting in Step Quantum Wells
HAO Ya-Fei, CHEN Yong-Hai, HAO Guo-Dong, WANG Zhan-Guo
Chin. Phys. Lett. 2009, 26 (7): 077104 .   DOI: 10.1088/0256-307X/26/7/077104
Abstract   PDF(pc) (300KB) ( 505 )
Spin splitting of the AlyGa1-yAs/GaAs/AlxGa1-xAs/AlyGa1-yAs (x≠y) step quantum wells (QWs) has been theoretically investigated with a model that includes both the interface and the external electric field contribution. The overall spin splitting is mainly determined by the interface contribution, which can be well manipulated by the external electric field. In the absence of the electric field, the Rashba effect exists due to the internal structure inversion asymmetry (SIA). The electric field can strengthen or suppress the internal SIA, resulting in an increase or decrease of the spin splitting. The step QW, which results in large spin splitting, has advantages in applications to spintronic devices compared with symmetrical and asymmetrical QWs. Due to the special structure design, the spin splitting does not change with the external electric field.
Effects of Different Plasma Energy Treatments on n-Type Al0.4Ga0.6N Material
YANG Ling, HAO Yue, ZHOU Xiao-Wei, MA Xiao-Hua
Chin. Phys. Lett. 2009, 26 (7): 077105 .   DOI: 10.1088/0256-307X/26/7/077105
Abstract   PDF(pc) (425KB) ( 667 )
Electronic properties, surface chemistry and surface morphology of plasma-treated n-Al0.4Ga0.6N material are studied by electrical contact measurements, atomic force microscopy and x-ray photoemission spectroscopy. Although excessive etching can cause the surface roughness to significantly increase, the nitrogen vacancies VN produced by the excessive etching can be compensated for by the negative effects of the rougher surface. Thus, VN produced by excessive etching plays a key role in Ohmic contact of high-Al content AlGaN and it can reduce Ohmic contact resistance. The effect of rapid thermal annealing on the performance of n-Al0.4Ga0.6N can significantly reduce the etching damage caused by excessive etching.
First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2
HOU Xing-Gang, LIU An-Dong, HUANG Mei-Dong, LIAO Bin, WU Xiao-Ling
Chin. Phys. Lett. 2009, 26 (7): 077106 .   DOI: 10.1088/0256-307X/26/7/077106
Abstract   PDF(pc) (424KB) ( 895 )
The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density functional theory with the full-potential linearized-augmented-plane-wave method. New occupied bands are found between the band gaps of both Ag-doped rutile and anatase TiO2. The formation of these new bands can be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption.
Effect of Tunneling Current on Schottky Barrier Height in ZnO Varistors at Low Temperature
LI Sheng-Tao, YANG Yan, ZHANG Le, CHENG Peng-Fei, LI Jian-Ying
Chin. Phys. Lett. 2009, 26 (7): 077201 .   DOI: 10.1088/0256-307X/26/7/077201
Abstract   PDF(pc) (384KB) ( 1019 )
On the basis of the Schottky barrier and thermionic emission models, the temperature dependence of barrier height in ZnO varistors is investigated by the I-V characteristics in a wide temperature range from 93K to 373K. The obtained barrier height decreases with reducing temperature, which is ascribed to the contribution of tunneling current in measured current. From the proposed equivalent circuit, it is suggested that two current components coexist. One is thermionic emission current, which reflects the thermionic emission barrier height. The other is tunneling current, which appears even at low voltage, especially in low temperature ranges, and thus makes the barrier height obtained from measured current vary with temperature.
Field-Effect Transistor Based on Si with LaAlO3-δ as the Source and Drain
YANG Fang, JIN Kui-Juan, LU Hui-Bin, HE Meng, YANG Guo-Zhen
Chin. Phys. Lett. 2009, 26 (7): 077301 .   DOI: 10.1088/0256-307X/26/7/077301
Abstract   PDF(pc) (288KB) ( 347 )
N-type LaAlO3-δ thin films are epitaxially grown on p-type Si substrates. An enhancement mode field-effect transistor is constructed with oxygen deficient LaAlO3-δ as the source and drain, p-type Si as the semiconducting channel, and SiO2 as the gate insulator, respectively. The typical current-voltage behavior with field-effect transistor characteristic is observed. The ON/OFF ratio reaches 14at a gate voltage of 10V, the field-effect mobility is 10cm2/V&#12539;s at a gate voltage of 2V, and the transconductance is 5×10-6 A/V at a drain-source voltage of 0.8V at room temperature. The present field-effect transistor device demonstrates the possibility of realizing the integration of multifunctional perovskite oxides and the conventional Si semiconductor.
A Physics-Based Charge-Control Model for InP DHBT Including Current-Blocking Effect
GE Ji, JIN Zhi, SU Yong-Bo, CHENG Wei, WANG Xian-Tai, CHEN Gao-Peng, LIU Xin-Yu
Chin. Phys. Lett. 2009, 26 (7): 077302 .   DOI: 10.1088/0256-307X/26/7/077302
Abstract   PDF(pc) (388KB) ( 512 )
We develop a physics-based charge-control InP double heterojunction bipolar transistor model including three important effects: current blocking, mobile-charge modulation of the base-collector capacitance and velocity-field modulation in the transit time. The bias-dependent base-collector depletion charge is obtained analytically, which takes into account the mobile-charge modulation. Then, a measurement based voltage-dependent transit time formulation is implemented. As aresult, over a wide range of biases, the developed model shows good agreement between the modeled and measured S-parameters and cutoff frequency. Also, the model considering current blocking effect demonstrates more accurate prediction of the output characteristics than conventional vertical bipolar inter company results.
Bipolar Resistance Switching Characteristics of ZnO/Nb-Doped SrTiO3 Heterojunctions
ZHANG Hong-Jian, ZHANG Xiao-Ping, ZHAO Yong-Gang
Chin. Phys. Lett. 2009, 26 (7): 077303 .   DOI: 10.1088/0256-307X/26/7/077303
Abstract   PDF(pc) (483KB) ( 603 )
An electrical pulse induced resistance switching effect in ZnO/Nb-doped SrTiO3 heterojunctions is reported. The current-voltage curves of these junctions show hysteresis. Multi-resistance states are realized by applying voltage pulses with different amplitudes, and the resistance switching effect is more remarkable at low temperatures. The junction capacitance decreases dramatically with increasing frequency. Analysis of the results suggests that the trapping-detrapping process plays an important role in the resistance switching effect.
Phase Locking and Chaos in a Josephson Junction Array Shunted by a Common Resistance
ZHOU Tie-Ge, MAO Jing, LIU Ting-Shu, LAI Yue, YAN Shao-Lin
Chin. Phys. Lett. 2009, 26 (7): 077401 .   DOI: 10.1088/0256-307X/26/7/077401
Abstract   PDF(pc) (593KB) ( 459 )
The dynamics of a Josephson junction array shunted by a common resistance are investigated by using numerical methods. Coexistence of phase locking and chaos is observed in the system when the resistively and capacitively shunted junction model is adopted. The corresponding parameter ranges for phase locking and chaos are presented. When there are three resistively shunted junctions in the array, chaos is found for the first time and the parameter range for chaos is also presented. According to the theory of Chernikov and Schmidt, when there are four or more junctions in the array, the system exhibits chaotic behavior. Our results indicate that the theory of Chernikov and Schmidt is not exactly appropriate.
Phase-Transition and Magnetic Moment of the Gd3+ Ion in the Gd2Fe17 Compound
HAO Yan-Ming, FU Bin, ZHOU Yan, ZHAO Miao
Chin. Phys. Lett. 2009, 26 (7): 077501 .   DOI: 10.1088/0256-307X/26/7/077501
Abstract   PDF(pc) (463KB) ( 569 )
The structure and magnetic phase transitions of the Gd2Fe17 compound are investigated by using a differential thermal/thermogravimetric analyzer, x-ray diffraction, and magnetization measurements. The result shows that there are two phase structures for the Gd2Fe17 compound: the hexagonal Th2Ni17-type structure at high temperatures (above 1243°C), and the rhombohedral Th2Zn17-type structure, respectively. A method to measure the magnetic moments of the Gd-sublattice and the Fe-sublattice in the Gd2Fe17 compound is presented. The moments of the Gd-sublattice and the Fe-sublattice in the Gd2Fe17 compound from 77 to 500K are measured in this way with a vibrating sample magnetometer. A detailed discussion is presented.
Structural and Magnetic Properties of Sm Implanted GaN
JIANG Li-Juan, WANG Xiao-Liang, XIAO Hong-Ling, WANG Zhan-Guo, FENG Chun, ZHANG Ming-Lan, TANG Jian
Chin. Phys. Lett. 2009, 26 (7): 077502 .   DOI: 10.1088/0256-307X/26/7/077502
Abstract   PDF(pc) (404KB) ( 509 )
The structural and magnetic properties of Sm ion-implanted GaN with different Sm concentrations are investigated. XRD results do not show any peaks associated with second phase formation. Magnetic investigations performed by superconducting quantum interference device reveal ferromagnetic behavior with an ordering temperature above room temperature in all the implanted samples, while the effective magnetic moment per Sm obtained from saturation magnetization gives a much higher value than the atomic moment of Sm. These results could be explained by the phenomenological model proposed by Dhar et al. [Phys. Rev. Lett. 94(2005)037205, Phys. Rev. B 72(2005)245203] in terms of a long-range spin polarization of the GaN matrix by the Sm atoms.
Magnetization Reversal Mechanism for CoFeB Ferromagnetic Nanotube Arrays
LIU Hai-Rui, S. Shamaila, CHEN Jun-Yang, R. Sharif, LU Qing-Feng, HAN Xiu-Feng
Chin. Phys. Lett. 2009, 26 (7): 077503 .   DOI: 10.1088/0256-307X/26/7/077503
Abstract   PDF(pc) (564KB) ( 591 )
CoFeB nanotube arrays are fabricated in anodic aluminum oxide (AAO) membranes and track etched polycarbonate (PCTE) membranes by using an electrochemical method, and their magnetic properties are investigated by vibrating sample magnetometry. The coercivity Hc and remanent squareness SQ of these CoFeB nanotube arrays are derived from hysteresis loops as a function of angle between the field and tube axis. The Hc(θ) curves for CoFeB nanotube arrays in AAO and PCTE membranes show M-type variation, while they change shape from M to mountain-type as the tube length increases. However, the overall easy axis perpendicular to tube axis does not change with tube length. The different angular dependences are attributed to different magnetization reversal mechanisms.
Magnetic Relaxation Study on Single Crystals of Ni4 Single-Molecule Magnets
LI Yan-Rong, LIU Hai-Qing, LIU Ying, SU Shao-Kui, WANG Yun-Ping
Chin. Phys. Lett. 2009, 26 (7): 077504 .   DOI: 10.1088/0256-307X/26/7/077504
Abstract   PDF(pc) (375KB) ( 476 )
The ac susceptibility of single crystals of Ni4 single-molecule magnets is measured by a compensation measurement setup. The magnetic relaxation time calculated from the peak of the out-phase component of the susceptibility fits the Arrhenius law well and gives an effective spin-flipping energy barrier of Ueff=7.2K. This value is far below the classical activation energy barrier of U=14K, whereas it is close to the energy gap between the Sz=±4 and Sz=±3 doublets, which indicates that quantum tunneling between the Sz=3 and Sz=-3 states plays a key role in the magnetic relaxation. Therefore the relaxation process combines thermal activation and quantum tunneling. Also we deduce that the blocking temperature of Ni4 single-molecule magnets is lower than 0.3K by extrapolating the relaxation time plot, which ensures that this single-molecule magnet material enters a long-range magnetic ordered state instead of a spin glass state at 0.91K.
Transition of Magnetoresistance in Co/Alq3 Granular Film on Silicon Substrate
SHU Qi, ZHAO Xiao-Meng, ZHANG Yan, SHENG Peng, TANG Zhen-Yao, NI Gang,
Chin. Phys. Lett. 2009, 26 (7): 077505 .   DOI: 10.1088/0256-307X/26/7/077505
Abstract   PDF(pc) (488KB) ( 470 )
A Co0.38(Alq3)0.62 granular film is prepared using a co-evaporating technique on a silicon substrate with a native oxide layer. A crossover of magnetoresistance (MR) from positive to negative is observed. The positive MR ratio reaches 17.5% at room temperature (H=50 kOe), and the negative MR ratio reaches -1.35% at 15K (H=10 kOe). Furthermore, a metal-insulator transition is also observed. The transition of resistance and MR results from the channel switching of electron transport between the upper Co-Alq3
granular film and the inversion layer underneath. The negative MR originates from the tunneling magnetoresistance effect due to the tunneling conducting between adjacent Co granules, and the positive MR may be attributed to the transport of high mobility carriers in the SiO2/Si inversion layer.
Influence of Concentration of Vanadium in Zinc Oxide on Structural and Optical Properties with Lower Concentration
WANG Li-Wei, , XU Zheng, MENG Li-Jian, Vasco Teixeira, SONG Shi-Geng, XU Xu-Rong
Chin. Phys. Lett. 2009, 26 (7): 077801 .   DOI: 10.1088/0256-307X/26/7/077801
Abstract   PDF(pc) (702KB) ( 681 )
ZnO films doped with different vanadium concentrations are deposited onto glass substrates by dc reactive magnetron sputtering using a zinc target doped with vanadium. The vanadium concentrations are examined by energy dispersive spectroscopy (EDS) and the charge state of vanadium in ZnO thin films is characterized by x-ray photoelectron spectroscopy. The results of x-ray diffraction (XRD) show that all the films have a wurtzite structure and grow mainly in the c-axis orientation. The grain size and residual stress in the deposited films are estimated by fitting the XRD results. The optical properties of the films are studied by measuring the transmittance. The optical constants (refractive index and extinction coefficient) and the film thickness are obtained by fitting the transmittance. All the results are discussed in relation with the doping of the vanadium.
Manipulative Properties of Asymmetric Double Quantum Dots via Laser and Gate Voltage
ZHAO Shun-Cai, LIU Zheng-Dong
Chin. Phys. Lett. 2009, 26 (7): 077802 .   DOI: 10.1088/0256-307X/26/7/077802
Abstract   PDF(pc) (247KB) ( 424 )
We present a density matrix approach for the theoretical description of an asymmetric double quantum dot (QD) system. The results show that the properties of gain, absorption and dispersion of the double QD system, the population of the state with one hole in one dot and an electron in another dot transferred by tunneling can be manipulated by a laser pulse or gate voltage. Our scheme may demonstrate the possibility of electro-optical manipulation of quantum systems.
Optical Characterization of rf-Magnetron Sputtered Nanostructured SnO2 Thin Films
Abdul Faheem Khan, Mazhar Mehmood, A. M. Rana, M. T. Bhatti, A. Mahmood
Chin. Phys. Lett. 2009, 26 (7): 077803 .   DOI: 10.1088/0256-307X/26/7/077803
Abstract   PDF(pc) (864KB) ( 1395 )
Tin oxide (SnO2) thin films are deposited by rf-magnetron sputtering and annealed at various temperatures in the range of 100-500°C for 15min. Raman spectra of the annealed films depict the formation of a small amount of SnO phase in the tetragonal SnO2 matrix, which is verified by x-ray diffraction. The average particle size is found to be about 20-30nm, as calculated from x-ray peak broadening and SEM images. Various optical parameters such as optical band gap energy, refractive index, optical conductivity, carrier mobility, carrier concentration etc. are determined from the optical transmittance and reflectance data recorded in the wavelength range 250-2500nm. The results are analyzed and compared with the data in the literature.
Nondoped Electrophosphorescent Organic Light-Emitting Diodes Based on Platinum Complexes
YANG Gang, ZHANG Di, WANG Jun, JIANG Quan, ZHONG Jian, YUJun-Sheng, ZHU Feng-Zhi, LUO Kai-Jun, XIE Yun, XU Ling-Ling
Chin. Phys. Lett. 2009, 26 (7): 077804 .   DOI: 10.1088/0256-307X/26/7/077804
Abstract   PDF(pc) (433KB) ( 501 )
An undoped electrophosphorescent organic light-emitting diode is fabricated using a pure platinum(II) (2-phenylpyridinato-N, C2) (3-benzoyl-camphor) [(ppy)pt(bcam)] phosphorescent layer acting as the emitting layer. A maximum power efficiency ηp of 6.62lm/W and current efficiency of 14.78cd/A at 745cd/m2 are obtained from the device. The roll-off percentage of ηp of the pure phosphorescent phosphor layer device is reduced to 5% at a current density of 20mA/cm2, which is about 11% for conventional phosphorescent devices. The low roll-off efficiency is attributed to the phosphorescent material, which has the molecular structure of a strong steric hindrance effect.
Photoluminescence of a ZnO/GaN Heterostructure Interface
LIU Shu-Jian, YU Qing-Xuan, WANG Jian, LIAO Yuan, LI Xiao-Guang
Chin. Phys. Lett. 2009, 26 (7): 077805 .   DOI: 10.1088/0256-307X/26/7/077805
Abstract   PDF(pc) (834KB) ( 737 )
Growth of a ZnO/GaN heterostructure is carried out using pulsed laser deposition. By etching the ZnO layer from the ZnO/GaN structure, the photoluminescence (PL) of the associated GaN layer shows that the donor-acceptor luminescence of GaN shifts to about 3.27eV, which is consistent with the electroluminescence (EL) of n-ZnO/p-GaN already reported. XPS shows that oxygen diffuses into the GaN crystal lattice from the surface to 20nm depth. The PL spectra at different temperatures and excitation densities show that oxygen plays the role of potential fluctuation. The associated PL results of the interface in these LEDs could be helpful to understand the mechanism of EL spectra for ZnO/GaN p-n junctions.
Dynamics of Förster Energy Transfer in Pyridium Salt-Doped Thin Films
XU Deng, ZHUANG Xiao-Hong
Chin. Phys. Lett. 2009, 26 (7): 077806 .   DOI: 10.1088/0256-307X/26/7/077806
Abstract   PDF(pc) (339KB) ( 502 )
Properties of photoluminescence and Förster energy transfer dynamics based on an organic pyridium salt trans-4-[p-(N-Hydroxyethyl-N-methylamino)Styryl]-N-methylpyridinium iodide (ASPI) and organic small molecule Alq3 in PMMA polymeric thin films are investigated by steady-state and time-resolved fluorescent spectra as well as theoretical calculation. The observation of reduced emission intensity and the fluorescent lifetime of Alq3 is demonstrated, while the ASPI emission gradually increases and is finally dominant in the PL spectra with increasing ASPI doping concentration. Such results show that there exists an efficient Förster energy transfer (FET) from Alq3 to ASPI due to the large spectral overlap between ASPI absorption and Alq3 emission. The difference between the theoretical FET efficiency and the experimental data is caused by the lower mobility of the Alq3 exciton in the MMA matrix.
Optical Dispersion Behavior and Band Gap Energy of Relaxor Ferroelectric 0.92Pb(Mg1/3Nb2/3)O3-0.08PbTiO3 Single Crystal
LIN Yan-Ting, REN Bo, ZHAO Xiang-Yong, WANG Fei-Fei, WANG Yao-Jin, XU Hai-Qing, LIN Di, LUO Hao-Su
Chin. Phys. Lett. 2009, 26 (7): 077807 .   DOI: 10.1088/0256-307X/26/7/077807
Abstract   PDF(pc) (422KB) ( 560 )
Refractive indices and extinction coefficients of 0.92Pb(Mg1/3Nb2/3)O3-0.08PbTiO3(PMN-0.08PT) single crystal are investigated by variable angle spectroscopic ellipsometry (VASE) at different wavelengths. The parameters relative to the energy band structure are obtained by fitting to the single-oscillator dispersion equation, and the band gap energy is also deduced from the Tauc equation. Similar to most oxygen-octahedra ferroelectrics, PMN-0.08PT has the same dispersion behavior described by the refractive-index dispersion parameters.
Structural and Photoluminescence Properties for Highly Strain-Compensated InGaAs/InAlAs Superlattice
GU Yi, ZHANG Yong-Gang, LI Ai-Zhen, WANG Kai, LI Cheng, LIYao-Yao
Chin. Phys. Lett. 2009, 26 (7): 077808 .   DOI: 10.1088/0256-307X/26/7/077808
Abstract   PDF(pc) (395KB) ( 586 )
The effects of strain compensation are investigated by using twenty periods of highly strain-compensated InGaAs/InAlAs superlattice. The lattice mismatches of individual layers are as high as about 1%, and the thicknesses are close to critical thicknesses. X-ray diffraction measurements show that lattice imperfectness is not serious but still present, though the structural parameters are within the range of theoretical design criteria for structural stability. Rough interfaces and composition fluctuations are the primary causes for lattice imperfectness. Photoluminescence measurements show the large thermally activated nonradiative recombination in the sample. In addition, the recombination process gradually evolves from excitonic recombination at lower temperatures to band-to-band recombination at higher temperatures, which should be considered in device applications.
Silver-Doping Induced Lattice Distortion in TiO2 Nanoparticles
WU Xue-Wei, WU Da-Jian, LIU Xiao-Jun
Chin. Phys. Lett. 2009, 26 (7): 077809 .   DOI: 10.1088/0256-307X/26/7/077809
Abstract   PDF(pc) (422KB) ( 2085 )
The Ag-doping effects on TiO2 nanoparticles are investigated by means of x-ray diffraction (XRD) and Raman scattering spectroscopy. XRD and Raman results indicate that Ag-doping stabilizes the rutile phase in TiO2. We find an Ag-doping induced lattice expansion in both anatase and rutile phases. The Ag-doping has different influences on the lattice distortion for anatase and rutile phases, that is, the c/a-value for the anatase phase decreases with 0.5% Ag-doping and then increases with 1% Ag-doping while that for the rutile phase shows a gradual increase with increasing Ag-doping. We have ascribed the different variations of lattice distortion due to Ag-doping to the change of interfacial interaction between the anatase and rutile phases induced by different Ag concentrations.
Steady State and Time-Resolved Fluorescence Dynamics of Triphenylamine Based Oligomers with Phenylene/Thiophene/Furan in Solvents
ZENG Qi, LIU Ying-Liang, MENG Kang, ZHAO Xiang-Jie, WANG Shu-Feng, GONG Qi-Huang
Chin. Phys. Lett. 2009, 26 (7): 077810 .   DOI: 10.1088/0256-307X/26/7/077810
Abstract   PDF(pc) (342KB) ( 481 )
We investigate the photo-physical properties of a series of triphenylamine-based oligomers by steady-state and picosecond transient fluorescence measurements in solvents. The oligomers are composed alternatively with triphenylamine and phenylene/thiophene/furan group, bridged by vinyl group (PNB/PNT/PNF). Their fluorescence spectra show bathochromic phenomenon with solvent polarity and viscosity increasing. The fluorescence decays are bi-exponential for PNB and PNT, and tri-exponential for PNF in THF and aniline. The strong viscosity dependence suggests conformational relaxation along the PNF chain after photo excitation.
Efficient White Light Emission Using a Single Copolymer with Red and Green Chromophores on a Conjugated Polyfluorene Backbone Hybridized with InGaN-Based Light-Emitting Diodes
ZHANG Yong, HOU Qiong, NIU Qiao-Li, ZHENG Shu-Wen, LI Shu-Ti, HE Miao, FAN Guang-Han
Chin. Phys. Lett. 2009, 26 (7): 077811 .   DOI: 10.1088/0256-307X/26/7/077811
Abstract   PDF(pc) (428KB) ( 398 )
We report an efficient white-light emission based on a single copolymer/InGaN hybrid light-emitting diode. The single copolymer consists of a conjugated polyfluorene backbone by incorporating 2,1,3-benzothiadiazole (BT) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (DBT) as green and red light-emitting units, respectively. For the single copolymer/InGaN hybrid device, the Commission Internationale de l'Eclairage (CIE) coordinates, color temperature Tc and color rendering index Ra at 20mA are (0.323,0.329), 5960K and 86, respectively. In comparison with the performance of red copolymer PFO-DBT15 (DOF:DBT=85:15 with DOF being 9'9-dioctylfluorene) and green copolymer PFO-BT35 (DOF:BT=65:35) blend/InGaN hybrid white devices, it is concluded that the chemically doped copolymer hybridized device shows a higher emission intensity and spectral stability at a high driving current than the polymer blend.
Monodisperse Silver Nanoparticles Synthesized by a Microwave-Assisted Method
ZHU Shao-Peng, TANG Shao-Chun, MENG Xiang-Kang
Chin. Phys. Lett. 2009, 26 (7): 078101 .   DOI: 10.1088/0256-307X/26/7/078101
Abstract   PDF(pc) (514KB) ( 667 )
Silver nanoparticles with an average size of about 20nm are synthesized in a colloidal solution with the aid of microwave irradiation. Neither additional reductant nor stabilizer is required in this microwave-assisted method. The color of the colloidal solution is found to be dark green, different from the characteristic yellow of silver colloidal solutions. The silver nanoparticles in the colloidal solution have a narrow size distribution and large yield quantity. UV-visible absorption spectroscopy analysis reveals that the as-synthesized monodisperse silver nanoparticles have exceptional optical properties. Raman spectroscopy measurements demonstrate that these silver nanoparticles exhibit a notable surface-enhanced Raman scattering ability.
Effects of Raw Material Content on Efficiency of TiN Synthesized by Reactive Ball Milling Ti and Urea
SUN Jin-Feng, LI Xiao-Pu, LIANG Bao-Yan, ZHAO Yu-Cheng, WANG Ming-Zhi
Chin. Phys. Lett. 2009, 26 (7): 078102 .   DOI: 10.1088/0256-307X/26/7/078102
Abstract   PDF(pc) (582KB) ( 479 )
Ti and urea mixed according to the molar ratios of 2:1, 3:1 and 4:1 are milled under the same condition. The structures of the as-synthesized powders are analyzed by an x-ray diffractometer (XRD). The decomposed temperature of the urea and the products decomposed are characterized by differential scanning calorimetry (DSC) and thermogravimetry analysis-Fourier transform infrared (TG-FTIR) spectrometry. The results show that the reaction progress is a diffusion reaction. The efficiency of TiN synthesized by reactive ball milling can be increased by increasing the content of Ti. The reactive ball milling time decreases from more than 90h to 40h corresponding to the content ratio between Ti and urea increasing from 2:1 to 4:1. Ammonia gas (NH3) and cyanic acid (HNCO), the decomposed products of urea, react with the refined Ti to form TiN. The grain refinement of Ti has a significant effect on the efficiency of reactive ball milling.
Silicon Purification by a New Type of Solar Furnace
CHEN Ying-Tian, LIM Chern-Sing, HO Tso-Hsiu, LIM Boon-Han, WANG Yi-Nan
Chin. Phys. Lett. 2009, 26 (7): 078103 .   DOI: 10.1088/0256-307X/26/7/078103
Abstract   PDF(pc) (428KB) ( 699 )
We propose a new method to reveal a direct transformation from solar energy to solar electricity. Instead of using electricity in the process, we use concentrated solar rays with a crucibleless process to upgrade metallurgical silicon into solar-grade silicon feedstock.
Analysis of Rheological Behavior of Some Aqueous PEO Gels under Thermal Treatment
M. Todica
Chin. Phys. Lett. 2009, 26 (7): 078201 .   DOI: 10.1088/0256-307X/26/7/078201
Abstract   PDF(pc) (243KB) ( 402 )
Evolution of viscosity of some aqueous poly (ethylene oxide) gels is observed as functions of polymeric concentration and temperature for samples subjected to thermal shock. The experimental data are analyzed following an appropriate algorithm, and reveal the transient effect from Newtonian to non-Newtonian flow as a function of the polymeric concentration.
A Novel Method for the Initial-Condition Estimation of a Tent Map
CHEN Xi, GAO Yong, YANG Yuan
Chin. Phys. Lett. 2009, 26 (7): 078202 .   DOI: 10.1088/0256-307X/26/7/078202
Abstract   PDF(pc) (178KB) ( 630 )
Based on the connection between the tent map and the saw tooth map or Bernoulli map, a novel method for the initial-condition estimation of the tent map is presented. In the method, firstly the symbolic sequence generated from the tent map is converted to the forms obtained from the saw tooth map and Bernoulli map, and then the relationship between the symbolic sequence and the initial condition of the tent map can be obtained from the initial-condition estimation equations, which can be easily obtained, hence the estimation of the tent map can be achieved finally. The method is computationally simple and the error of the estimator is less than 1/2N. The method is verified by software simulation.
Growth Related Carrier Mobility Enhancement of Pentacene Thin-Film Transistors with High-k Oxide Gate Dielectric
YU Ai-Fang, QI Qiong, JIANG Peng, JIANG Chao
Chin. Phys. Lett. 2009, 26 (7): 078501 .   DOI: 10.1088/0256-307X/26/7/078501
Abstract   PDF(pc) (714KB) ( 411 )
Carrier mobility enhancement from 0.09 to 0.59cm2/Vs is achieved for pentacene-based thin-film transistors (TFTs) by modifying the HfO2 gate dielectric with a polystyrene (PS) thin film. The improvement of the transistor's performance is found to be strongly related to the initial film morphologies of pentacene on the dielectrics. In contrast to the three-dimensional island-like growth mode on the HfO2 surface, the Stranski-Krastanov growth mode on the smooth and nonpolar PS/HfO2 surface is believed to be the origin of the excellent carrier mobility of the TFTs. A large well-connected first monolayer with fewer boundaries is formed via the Stranski-Krastanov growth mode, which facilitates a charge transport parallel to the substrate and promotes higher carrier mobility.
Wavelength Red-Shift of Long Wavelength InGaN/GaN Multi-Quantum Well by Using an InGaN Underlying Layer
HUANG Li-Rong, WEN Feng, TONG Liang-Zhu, HUANG De-Xiu
Chin. Phys. Lett. 2009, 26 (7): 078502 .   DOI: 10.1088/0256-307X/26/7/078502
Abstract   PDF(pc) (347KB) ( 701 )
Long-wavelength GaN based light-emitting diodes are of importance in full color displays, monolithic white light-emitting diodes and solid-state lighting, etc. However, their epitaxial growth faces great challenges because high indium (In) compositions of InGaN are difficult to grow. In order to enhance In incorporation and lengthen the emission wavelength of a InGaN/GaN multi-quantum well (MQW), we insert an InGaN underlying layer underneath the MQW. InGaN/GaN MQWs with various InGaN underlying layers, such as graded InyGa1-yN material with linearly increasing In content, or InyGa1-yN with fixed In content but different thicknesses, are grown by metal-organic chemical vapor deposition. Experimental results demonstrate the enhancement of In incorporation and the emission wavelength redshift by the insertion of an InGaN underlying layer.
Water in the Neck-Zipper Region of Kinesin
HUANG Yan-Bin, PAN Zhang, ZHANG Hui, AN Li, KONG De-Xin, JI Qing
Chin. Phys. Lett. 2009, 26 (7): 078701 .   DOI: 10.1088/0256-307X/26/7/078701
Abstract   PDF(pc) (670KB) ( 392 )
Neck linker (NL) is one of the most important mechanical elements of kinesin motors. The zipping up process of the neck-zipper (NZ) formed by NL and the related secondary structure elements is one of the major parts of kinesin's power stroke. All the weak interactions that are responsible for the formation of NZ are sensitive to or dependent on water. To investigate the role of water in the NZ region, a molecular dynamics (MD) model is set up with a crystal structure of kinesin 2KIN surrounded by a 10Å, water layer, and minimization is performed to determine the positions of hydrogen atoms and other atoms. It is revealed that water molecules can assist the docking process of NL by forming hydrogen bonds at those positions where direct hydrogen bonding between the two sides of NZ is hindered and then acts as a constructive component of NZ at the docked state of NL. This result may improve the understanding of the mechanism for the docking of NL of kinesin wherein the function of water has not been comprehended sufficiently.
Small-World Connections to Induce Firing Activity and Phase Synchronization in Neural Networks
QIN Ying-Hua, LUO Xiao-Shu
Chin. Phys. Lett. 2009, 26 (7): 078901 .   DOI: 10.1088/0256-307X/26/7/078901
Abstract   PDF(pc) (1840KB) ( 492 )
We investigate how the firing activity and the subsequent phase synchronization of neural networks with small-world topological connections depend on the probability p of adding-links. Network elements are described by two-dimensional map neurons (2DMNs) in a quiescent original state. Neurons burst for a given coupling strength when the topological randomness p increases, which is absent in a regular-lattice neural network. The bursting activity becomes frequent and synchronization of neurons emerges as topological randomness further increases. The maximal firing frequency and phase synchronization appear at a particular value of p. However, if the randomness p further increases, the firing frequency decreases and synchronization is apparently destroyed.
An Investigation into Node Strength Connectivity Correlation
SHI Jian-Jun, WANG Yong-Li, HE Da-Ren
Chin. Phys. Lett. 2009, 26 (7): 078902 .   DOI: 10.1088/0256-307X/26/7/078902
Abstract   PDF(pc) (319KB) ( 628 )
We propose investigating the node strength connectivity correlation by a resource-allocation method and the traditional multiple edge method, respectively. A rough analysis suggests that the resource-allocation node strength connectivity correlation is always negative, which is different from the connectivity correlation of the traditional multiple edge node strength (it can show either positive, negative or no correlation). As examples, empirical investigation results for two real world cooperation-competition networks (the 2004 Athens Olympic Games network and the mixed drink network) are presented. We believe that the resource-allocation node strength connectivity correlation can serve as a description of the relative crackajack distribution, which is a complementarity of the traditional multiple edge one.
Information Feedback Strategies in a Signal Controlled Network with Overlapped Routes
TIAN Li-Jun, HUANG Hai-Jun, LIU Tian-Liang
Chin. Phys. Lett. 2009, 26 (7): 078903 .   DOI: 10.1088/0256-307X/26/7/078903
Abstract   PDF(pc) (1493KB) ( 451 )
We investigate the effects of four different information feedback strategies on the dynamics of traffic, travelers' route choice and the resultant system performance in a signal controlled network with overlapped routes. Simulation results given by the cellular automaton model show that the system purpose-based mean velocity feedback strategy and the congestion coefficient feedback strategy have more advantages in improving network utilization efficiency and reducing travelers' travel times. The travel time feedback strategy and the individual purposed-based mean velocity feedback strategy behave slightly better to ensure userequity
Topological Aspects in an Interacting Mixture of a Charged and a Neutral Superfluid in Neutron Stars
REN Ji-Rong, GUO Heng, ZHANG Xin-Hui, LI Ran
Chin. Phys. Lett. 2009, 26 (7): 079701 .   DOI: 10.1088/0256-307X/26/7/079701
Abstract   PDF(pc) (265KB) ( 412 )

By making use of the decomposition of U(1) gauge potential theory and the Φ-mapping method we discuss a mixture of interacting neutral and charged Bose condensates, which is supposed to be realized in the interior of neutron stars in the form of a coexistent neutron superfluid and protonic superconductor. We propose that this system possesses vortex line knotted solitons and the topological charges of vortex lines are characterized by the winding numbers of the Φ-mapping. Furthermore the spatial bifurcation of vortices is also discussed.

Withdrawal of Chinese Physics Letters 26 (2009) 016104 "In Situ Tests of Multiwalled Carbon Nanotubes with Strength Close to Theoretical Predictions"by Peng Bei et al.
Chin. Phys. Lett. 2009, 26 (7): 079901 .   DOI: 10.1088/0256-307X/26/7/079901
Abstract   PDF(pc) (48KB) ( 320 )

This paper has been retracted, as requested by Chinese Physics Letters, because of its substantial replication of an earlier paper, 'Measurements of near-ultimate strength for multiwalled carbon nanotubes and irradiation-induced crosslinking improvements' by Peng B et al., which appeared in Nature Nanotechnology 3(2008)626.I alone, as the first author of the paper, was responsible for this misconduct. Therefore, I would like to express my deepest apology to Professor Horacio Espinosa whose name was included in the above referenced paper without his knowledge, and to both journals, Chinese Physics Letters and Nature Nanotechnology.

108 articles