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Volume 26 Issue 12
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GENERAL
Perturbation to Noether Symmetry and Noether Adiabatic Invariants of General Discrete Holonomic Systems
ZHANG Ming-Jiang, FANG Jian-Hui, LU Kai, ZHANG Ke-Jun
Chin. Phys. Lett. 2009, 26 (12): 120201 .   DOI: 10.1088/0256-307X/26/12/120201
Abstract   PDF(pc) (288KB) ( 759 )
The perturbation to Noether symmetry and Noether adiabatic invariants of general discrete holonomic systems are studied. First, the discrete Noether exact invariant induced directly from the Noether symmetry of the system without perturbation is given. Secondly, the concept of discrete high-order adiabatic invariant is presented, the criterion of the perturbation to Noether symmetry is established, and the discrete Noether adiabatic invariant induced directly from the perturbation to Noether symmetry is obtained. Lastly, an example is discussed to illustrate the application of the results.
New Discrete Element Models for Three-Dimensional Impact Problems
SHAN Li, CHENG Ming, LIU Kai-Xin, LIU Wei-Fu, CHEN Shi-Yang
Chin. Phys. Lett. 2009, 26 (12): 120202 .   DOI: 10.1088/0256-307X/26/12/120202
Abstract   PDF(pc) (841KB) ( 568 )
Two 3-D numerical models of the discrete element method (DEM) for impact problems are proposed. The models can calculate not only the impact problems of continuum and non-continuum, but also the transient process from continuum to non-continuum. The stress wave propagation in a concrete block and a dynamic splitting process of a marble disc under impact loading are numerically simulated with the proposed models. By comparing the numerical results with the corresponding results obtained by the finite element method (FEM) and the experiments, it is proved that the models are reliable for three-dimensional impact problems.
The Soliton Solutions of A (2+1)-Dimensional Integrable Equation of Classical Spin System
DENG Ming
Chin. Phys. Lett. 2009, 26 (12): 120203 .   DOI: 10.1088/0256-307X/26/12/120203
Abstract   PDF(pc) (1235KB) ( 475 )
We present the bilinear equivalence expression of a (2+1)-dimensional integrable equation of a classical spin system. Based on this, we construct its single-soliton solutions and two-soliton solutions by Hirota's bilinear method. Meanwhile we show the evolution and propagation manners of two-solitons of the spin system graphically.
Dynamics of Bright Solitons in Bose-Einstein Condensates with Complicated Potential
ZHAO Li-Chen, YANG Zhan-Ying, ZHANG Tao, SHI Kang-Jie
Chin. Phys. Lett. 2009, 26 (12): 120301 .   DOI: 10.1088/0256-307X/26/12/120301
Abstract   PDF(pc) (795KB) ( 555 )
We present analytical solutions of the one-dimensional nonlinear Schrodinger equations of Bose-Einstein condensates in an expulsive parabolic background with a complex potential and gravitational field, by performing the Darboux transformation from a trivial seed solution. It is shown that under a safe range of parameter, the shape of bright soliton can be controlled well by adjusting the experimental parameter of the ratio of axial oscillation to radial oscillation and feeding condensates from a thermal cloud. The gravitational field can change the contrail of the bright soliton trains without changing their peak and width.
Scheme for Generating Cluster States with Charge Qubits in a Cavity
SONG Ke-Hui
Chin. Phys. Lett. 2009, 26 (12): 120302 .   DOI: 10.1088/0256-307X/26/12/120302
Abstract   PDF(pc) (299KB) ( 470 )
Based on superconducting charge qubits (SCCQs) coupled to a single-mode microwave cavity, we propose a scheme for generating charge cluster states. For all SCCQs, the controlled gate voltages are all in their degeneracy points, the quantum information is encoded in two logic states of charge basis. The generation of the multi-qubit cluster state can be achieved step by step on a pair of nearest-neighbor qubits. Considering effective long-rang coupling, we provide an efficient way to one-step generating of a highly entangled cluster state, in which the qubit-qubit coupling is mediated by the cavity mode. Our quantum operations are insensitive to the initial state of the cavity mode by removing the influence of the cavity mode via the periodical evolution of the system. Thus, our operation may be against the decoherence from the cavity.
Transformation Operator and Criterion for Perfectly Teleporting Arbitrary Three-Qubit State with Six-Qubit Channel and Bell-State Measurement
ZHANG Zi-Yun, LIU Yi-Min, ZUO Xue-Qin, ZHANG Wen, ZHANG Zhan-Jun
Chin. Phys. Lett. 2009, 26 (12): 120303 .   DOI: 10.1088/0256-307X/26/12/120303
Abstract   PDF(pc) (331KB) ( 603 )
Using the method presented recently [Phys.Rev.A 77(2008)014306; Phys.Lett.A 369(2007)377], the transformation operator (TO) is explicitly given for teleporting an arbitrary three-qubit state with a six-qubit channel and Bell-state measurements. A criterion on whether such quantum teleportation can be perfectly realized is educed in terms of TO. Moreover, six instantiations on TO and criterion are concisely shown.
Improved Quantum Evolutionary Computation Based on Particle SwarmOptimization and Two-Crossovers
DUAN Hai-Bin, XING Zhi-Hui
Chin. Phys. Lett. 2009, 26 (12): 120304 .   DOI: 10.1088/0256-307X/26/12/120304
Abstract   PDF(pc) (328KB) ( 416 )
A quantum evolutionary computation (QEC) algorithm with particle swarm optimization (PSO) and two-crossovers is proposed to overcome identified limitations. PSO is adopted to update the Q-bit automatically, and two-crossovers are applied to improve the convergence quality in the basic QEC model. This hybrid strategy can effectively employ both the ability to jump out of the local minima and the capacity of searching the global optimum. The performance of the proposed approach is compared with basic QEC on the standard unconstrained scalable benchmark problem that numerous hard combinatorial optimization problems can be formulated. The experimental results show that the proposed method outperforms the basic QEC quite significantly.
Stability of Manifold of Equilibrium States for Nonholonomic Systems in Relative Motion
ZHANG Yi
Chin. Phys. Lett. 2009, 26 (12): 120305 .   DOI: 10.1088/0256-307X/26/12/120305
Abstract   PDF(pc) (299KB) ( 321 )
The stability of manifold of equilibrium states for a class of nonholonomic systems in relative motion is studied. The Voronets equations and their canonical forms for dynamics of relative motion of the nonholonomic systems are established. The equations of relative equilibrium for the systems are given, and some criteria of the stability for the manifold of relative equilibrium states are obtained. An example is given to illustrate the application of the results.
Effects of Dzyaloshinski-Moriya Interaction on Entanglement and Teleportation in a Two-Qubit Ising System with Intrinsic Cecoherence
QIAN Li, FANG Jian-Xing
Chin. Phys. Lett. 2009, 26 (12): 120306 .   DOI: 10.1088/0256-307X/26/12/120306
Abstract   PDF(pc) (394KB) ( 496 )
We study the effects of Dzyaloshinski-Moriya (DM) interaction on entanglement and teleportation in a two-qubit Ising system with intrinsic decoherence taken into account. It is found that for the unentangled state, DM interaction is a benefit for entanglement and teleportation.
Cryptanalysis and Improvement of Quantum Secret Sharing Protocol between Multiparty and Multiparty with Single Photons and Unitary Transformations
LIN Song, WEN Qiao-Yan, LIU Xiao-Fen
Chin. Phys. Lett. 2009, 26 (12): 120307 .   DOI: 10.1088/0256-307X/26/12/120307
Abstract   PDF(pc) (337KB) ( 842 )
In a recent paper [Yan F L et al. Chin.Phys.Lett. 25(2008)1187], a quantum secret sharing the protocol between multiparty and multiparty with single photons and unitary transformations was presented. We analyze the security of the protocol and find that a dishonest participant can eavesdrop the key by using a special attack. Finally, we give a description of this strategy and put forward an improved version of this protocol which can stand against this kind of attack.
Bright Soliton Solutions in Degenerate Femi Gas near Feshbach Resonance
LIU Hong, HE Dai-Hai, LOU Sen-Yue, HE Xian-Tu
Chin. Phys. Lett. 2009, 26 (12): 120308 .   DOI: 10.1088/0256-307X/26/12/120308
Abstract   PDF(pc) (934KB) ( 745 )
For molecular and standard Bose-Einstein condensates and Fermi gases near Feshbach resonances, the general polytropic equation of states is P∝n γ+1. According to the effective power γ≈0.5~1.3, we resolve the time-dependent nonlinear Schrodinger equation and find series bright solitons. The analysis could help in the search for matter-wave soliton trains in degenerate Femi gas.
Tortoise Coordinates and Hawking Radiation in a Dynamical Spherically Symmetric Spacetime
YANG Jian, ZHAO Zheng, TIAN Gui-Hua, LIU Wen-Biao
Chin. Phys. Lett. 2009, 26 (12): 120401 .   DOI: 10.1088/0256-307X/26/12/120401
Abstract   PDF(pc) (326KB) ( 668 )
Hawking effect from dynamical spherical Vaidya black hole, Vaidya-Bonner black hole, and Vaidya-de Sitter black hole is investigated using the improved Damour-Ruffini method. After the new tortoise coordinate transformation in which the position r of event horizon is an undetermined function and the temperature parameter κ is an undetermined constant, the Klein-Gordon equation can be written as the standard form at the event horizon, and both r and κ can be determined automatically. Then extending the outgoing wave from outside to inside of the horizon analytically, the Hawking temperature can also be obtained automatically.
A Hyperchaotic Attractor with Multiple Positive Lyapunov Exponents
HU Guo-Si
Chin. Phys. Lett. 2009, 26 (12): 120501 .   DOI: 10.1088/0256-307X/26/12/120501
Abstract   PDF(pc) (763KB) ( 648 )
There are many hyperchaotic systems, but few systems can generate hyperchaotic attractors with more than three PLEs (positive Lyapunov exponents). A new hyperchaotic system, constructed by adding an approximate time-delay state feedback to a five-dimensional hyperchaotic system, is presented. With the increasing number of phase-shift units used in this system, the number of PLEs also steadily increases. Hyperchaotic attractors with 25 PLEs can be generated by this system with 32 phase-shift units. The sum of the PLEs will reach the maximum value when 23 phase-shift units are used. A simple electronic circuit, consisting of 16 operational amplifiers and two analogy multipliers, is presented for confirming hyperchaos of order 5, i.e., with 5 PLEs.
Chaotic Control of Network Traffic
YANG Tan, CUI Yi-Dong, JIN Yue-Hui, CHENG Shi-Duan
Chin. Phys. Lett. 2009, 26 (12): 120502 .   DOI: 10.1088/0256-307X/26/12/120502
Abstract   PDF(pc) (670KB) ( 418 )
A method of chaotic control on network traffic is presented. By this method, the chaotic network traffic can be controlled to a pre-assigned equilibrium point according to chaotic prediction and the largest Lyapunov exponent of
the traffic on congested link is reduced, thereby the probability of traffic burst and network congestion can be reduced. Numerical examples show that this method is effective.
One Specific State Variable for a Class of Fractional-Order Chaotic Systems and Its Applications
ZHOU Ping, CHENG Yuan-Ming
Chin. Phys. Lett. 2009, 26 (12): 120503 .   DOI: 10.1088/0256-307X/26/12/120503
Abstract   PDF(pc) (419KB) ( 466 )
We present a specific state variable for a class of fractional-order chaotic systems. By using a specific state variable and its (q-order, 2q-order, ..., and (n-1) q-order) time derivatives, all the state variables can be obtained. Several fractional-order chaotic systems are used to demonstrate this idea. A hybrid projective synchronization scheme is presented to show its applications.
Ground State of Fermions in a 1D Trap with δ Function Interaction
C. N. Yang
Chin. Phys. Lett. 2009, 26 (12): 120504 .   DOI: 10.1088/0256-307X/26/12/120504
Abstract   PDF(pc) (315KB) ( 2541 )
The ground state of fermions in a 1D trap with δ function interaction is studied mathematically with group theory ideas.
Ground State Energy for Fermions in a 1D Harmonic Trap with Delta Function Interaction
MA Zhong-Qi, C. N. Yang,
Chin. Phys. Lett. 2009, 26 (12): 120505 .   DOI: 10.1088/0256-307X/26/12/120505
Abstract   PDF(pc) (356KB) ( 517 )
Conjectures are made for the ground state energy of a large spin 1/2 Fermion system trapped in a 1D harmonic trap with delta function interaction. States with different spin J are separately studied. The Thomas-Fermi method is used as an effective test for the conjecture.
Spinless Bosons in a 1D Harmonic Trap with Repulsive Delta Function Interparticle Interaction I: General Theory
MA Zhong-Qi, C. N. Yang,
Chin. Phys. Lett. 2009, 26 (12): 120506 .   DOI: 10.1088/0256-307X/26/12/120506
Abstract   PDF(pc) (313KB) ( 587 )
In these two papers, we solve the N body 1D harmonically trapped spinless Boson problem with repulsive δ function interaction in the limit N→∞. The general theory is given in paper I and the numerical solutions will be given in paper II.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Monte Carlo Study on Singly Tagged D Mesons at BES-III
ZHAO Ming-Gang, YU Chun-Xu, LI Xue-Qian
Chin. Phys. Lett. 2009, 26 (12): 121401 .   DOI: 10.1088/0256-307X/26/12/121401
Abstract   PDF(pc) (352KB) ( 388 )
We present Monte Carlo studies on the singly tagged D mesons, which are crucial in the absolute measurements of D meson decays, based on a full Monte Carlo simulation for the BES-III detector, with the BES-III Offline Software System. The expected detection efficiencies and mass resolutions of the tagged D mesons are well estimated.
NUCLEAR PHYSICS
Collective Transverse Flow in Intermediate Energy Heavy-Ion Collisions
ZHANG Fang, ZUO Wei, , HU Bi-Tao, YONG Gao-Chan, ZHOU Zhen-Xiao
Chin. Phys. Lett. 2009, 26 (12): 122101 .   DOI: 10.1088/0256-307X/26/12/122101
Abstract   PDF(pc) (439KB) ( 555 )
Within the hadronic transport model IBUU04, we study the density-dependent symmetry energy by using the neutron-proton differential flow from the 132Sn+124Sn reactions at beam energies of 200, 400, 600 and 800MeV per nucleon. The strong effect of the symmetry energy is shown at the incident beam energy of 400MeV/A. The small medium-effect of the neutron-proton differential flow is also found. We also study the neutron-proton differential flows with impact parameters of 3, 5, 7fm. It is found that in semi-central collisions the sensitivity of the neutron-proton differential flow to the symmetry energy is larger.
Spin Symmetry for Anti-Lambda Spectrum in Atomic Nucleus
SONG Chun-Yan, YAO Jiang-Ming, MENG Jie,
Chin. Phys. Lett. 2009, 26 (12): 122102 .   DOI: 10.1088/0256-307X/26/12/122102
Abstract   PDF(pc) (419KB) ( 512 )
The spin symmetry of the anti-Lambda spectrum in nucleus 16O is studied in the relativistic mean field theory. The spin-orbit splittings of spin doublets are found to be around 0.03-0.07MeV and the dominant components of the Dirac spinor for the anti-Lambda spin doublets are found to be near identical. It is indicated that there is an even better spin symmetry in the anti-Lambda spectrum than that in the anti-nucleon spectrum.
Nonplanar Ion Acoustic Solitary Waves in a Two-Electron Temperature Plasma
W. Masood, S. Hussain, S. Mahmood, Arshad M. Mirza
Chin. Phys. Lett. 2009, 26 (12): 122301 .   DOI: 10.1088/0256-307X/26/12/122301
Abstract   PDF(pc) (366KB) ( 543 )
Linear and non-linear properties of ion acoustic wave (IAW) propagating in a two-electron temperature plasma are investigated from both analytical and numerical perspectives by employing the fluid theory. A one-dimensional modified Korteweg de Vries equation is derived for the IAW using the reductive perturbative technique in a nonplanar geometry. It is observed that the ion acoustic soliton in a two-temperature plasma admits rarefactive (dip like) solitons. In the limit that the cold electron population goes to zero, it is observed that the ion acoustic soliton yields compressive (hump like) solitons. The variation of the ion acoustic soliton with different plasma parameters is also shown. The present investigation may be beneficial to explain some aspects of ion acoustic rarefactive solitary structures observed in space environments where two-electron temperature plasmas have been observed.
A Simple Model for Ignition of Magnetized Target Fusion
YANG Xian-Jun, DONG Zhi-Wei, SHI Ji-Rong
Chin. Phys. Lett. 2009, 26 (12): 122801 .   DOI: 10.1088/0256-307X/26/12/122801
Abstract   PDF(pc) (373KB) ( 469 )
A simple model for magnetized target fusion is proposed. Self-consistent equations are made as equivalent circuit is included. Ignition conditions and physical process are analyzed with practical parameters. It is shown that system temperature rises as external work is equal to or greater than the loss of Bremsstrahlung, and ignition of target happens as thermonuclear reaction energy is equal to or greater than the radiation loss from the target.
ATOMIC AND MOLECULAR PHYSICS
Progress of the 87Rb Fountain Clock
ZHOU Zi-Chao, WEI Rong, SHI Chun-Yan, LV De-Sheng, LI Tang, WANGYu-Zhu
Chin. Phys. Lett. 2009, 26 (12): 123201 .   DOI: 10.1088/0256-307X/26/12/123201
Abstract   PDF(pc) (465KB) ( 712 )
A fountain atomic clock based on cold 87Rb atoms has been in operation in our laboratory for several months. We therefore report the design of the rubidium fountain clock including its physical package, optical system and daily operation. Ramsey fringes have been attained with the signal to noise ratio of about 100.
Differential Cross Section and Polarization of Radiative Recombination
WU Ze-Qing, LI Yue-Ming, DUAN Bin, ZHANG Hong, YAN Jun
Chin. Phys. Lett. 2009, 26 (12): 123202 .   DOI: 10.1088/0256-307X/26/12/123202
Abstract   PDF(pc) (405KB) ( 424 )
The formulae of photon angular distribution and polarization degree for radiative recombination are presented to include the contribution of multipoles and their correlations. A fully relativistic code is then developed to calculate the photon angular distribution and polarization. The calculated polarization degree and differential cross-sections agree well with that of Scofild's results within 10%. The effects of multipoles on polarization and angular distribution are investigated. The polarization and the angular distribution become asymmetric when the multipoles are accounted as the electron energy increases.
Collapse and Revival of an Atomic Beam Interacting with a Coherent State Light Field
LI Ben, CHEN Jing-Biao
Chin. Phys. Lett. 2009, 26 (12): 123203 .   DOI: 10.1088/0256-307X/26/12/123203
Abstract   PDF(pc) (461KB) ( 457 )
We report on the phenomena of the periodic spontaneous collapse and revival in the dynamics of an atomic beam interacting with a single-mode and coherent-state light field. Conventional collapse and revival by Eberly et al. [Phys. Rev. Lett. 44(1980)1323 ] are presented in the case of the evolution with time of the population inversion. Here, we study the evolution with coupling strength of population inversion. We define the collapse and revival coupling strengths as characteristic parameters to describe the above collapse and revival. Furthermore, we present the analytic formulas for the population inversion, the collapse and revival coupling strengths.
Photoelectron Angular Distributions of Positronium in Intense Laser Field
WANG Yi, ZHANG Jing-Tao, REN Xiang-He, XU Zhi-Zhan, GUO Dong-Sheng
Chin. Phys. Lett. 2009, 26 (12): 123204 .   DOI: 10.1088/0256-307X/26/12/123204
Abstract   PDF(pc) (402KB) ( 453 )
When positronium is generated in super intense laser fields irradiated by an intense laser field, it breaks up into an electron and a positron. The momentum of the electron as well as that of the positron depends on the relative direction with respect to the laser propagation. Thus, the photoelectron angular distributions show inversion asymmetry. The inversion asymmetry becomes notable for higher kinetic energy of electrons.
Light-Induced Hofstadter's Butterfly Spectrum of Ultracold Atoms on the Two-Dimensional Kagomé Lattice
HOU Jing-Min
Chin. Phys. Lett. 2009, 26 (12): 123701 .   DOI: 10.1088/0256-307X/26/12/123701
Abstract   PDF(pc) (493KB) ( 510 )
We investigate the energy spectrum of ultracold atoms on the two-dimensional Kagomé optical lattice under an effective magnetic field, which can be realized with laser beams. We derive the generalized Harper's equations from the Schrödinger equation. The energy spectrum with a fractal band structure is obtained by numerically solving the generalized Harper's equations. We analyze the properties of the Hofstadter's butterfly spectrum and discuss its observability.
Polarization Gradient Cooling by Zeeman-Effect-Assisted Saturated Absorption
HAN Shun-Li, CHENG Bing, ZHANG Jing-Fang, XU Yun-Fei, WANG Zhao-Ying, LIN Qiang
Chin. Phys. Lett. 2009, 26 (12): 123702 .   DOI: 10.1088/0256-307X/26/12/123702
Abstract   PDF(pc) (808KB) ( 523 )
A novel and simple method to realize polarization gradient cooling (PGC) is reported. The stabilizing, shifting and rapid tuning of the frequency of the external cavity diode laser is realized by using the Zeeman-effect-assisted Doppler-free saturated absorption technique. Based on this convenient technique, 87Rb cold atoms are captured from room-temperature background vapor in the magneto-optical trap (MOT). Meanwhile, the steady-state number, the density and the lifetime of atoms in the MOT are measured. Subsequently, a frequency-fast-varying circuit is designed to realize PGC, which is demonstrated effectively and reliably in experiments. The temperature of the cold atom cloud is measured by two different methods, which coincide with each other.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Characterizing THz Coherent Synchrotron Radiation at Femtosecond Linear Accelerator
LIN Xu-Ling, ZHANG Jian-Bing, LU YU, LUO Feng, LU Shan-Liang, YU Tie-Min, DAI Zhi-Min,
Chin. Phys. Lett. 2009, 26 (12): 124101 .   DOI: 10.1088/0256-307X/26/12/124101
Abstract   PDF(pc) (708KB) ( 423 )
The generation and observation of coherent THz synchrotron radiation from femtosecond electron bunches in the Shanghai Institute of Applied Physics femtosecond accelerator device is reported. We describe the experiment setup and present the first result of THz radiation properties such as power and spectrum.
An Efficient Photon Conversion Efficiency Ammonia Terahertz Cavity Laser
QI Chun-Chao, ZUO Du-Luo, LU Yan-Zhao, TANG Jian, YANG Chen-Guang, KE Lin-Da, CHENG Zu-Hai,
Chin. Phys. Lett. 2009, 26 (12): 124201 .   DOI: 10.1088/0256-307X/26/12/124201
Abstract   PDF(pc) (421KB) ( 553 )
An efficient ammonia terahertz (THz) cavity laser is reported experimentally. Unlike the past design schemes such as hole couplers and freestanding mesh couplers, in our systems the input and output couplers are fabricated by depositing nickel capacitive metallic meshes on ZnSe and high-resistivity silicon substrates. Thus the couplers not only can be constructed as an F-P oscillator but also can be used as sealed windows that are easier to perform the adjustment of alignment with. To enhanceTHz laser output energy and photon conversion efficiency, the dominant factors such as pump intensity and gas pressure are investigated experimentally. Finally, a 1.35mJ terahertz radiation of ammonia laser with 90μm wavelength (3.33THz) operating at 1.09kPa pumped by a 402mJ TEA CO2 laser with 9R (16) line is generated, and photon conversion efficiencies of 6.5% are achieved.
Numerical Investigation and Optimization of SBS-Based Slow-Light Using Filtered Incoherent Pump
ZHENG Di, PAN Wei, YAN Lian-Shan, LUO Bin, ZOU Xi-Hua, WEN Kun-Hua, JIANG Ning
Chin. Phys. Lett. 2009, 26 (12): 124202 .   DOI: 10.1088/0256-307X/26/12/124202
Abstract   PDF(pc) (436KB) ( 676 )
The performance of stimulated Brillouin scattering (SBS)-based slow light using a novel spectrally-sliced broadband incoherent pump source is numerically studied. The profile of the pump-power spectrum is determined by the transmission spectra of the optical filter followed by the polarized broadband incoherent pump source. We also investigate the performance of Gaussian-type and super-Gaussian-type filtering under different spectrally-sliced
bandwidths and pump power levels for 2.5Gbit/s return-to-zero pulse (50% duty-cycle). The pulse broadening is characterized by the full width of half maximum (FWHM) and the rms pulse width, respectively. However,the results obtained by the two kinds of measurement methods deviate from each other with increasing pump power. Compared with the regular Gaussian-type filtering, the pulse broadening can be significantly reduced using super-Gaussian-type filtering at the cost of a small reduction in delay time. Furthermore, the maximum improvement in pulse broadening of ∆ BFWHM =28.4% and ∆ B RMS =10.4% is achieved by using a five-order super-Gaussian-type filter and a pump power of 500mW.
Wavefront Correction of Pettawat Laser System by a Deformable Mirror with 50mm Active Aperture
REN Zhi-Jun, LIANG Xiao-Yan, LIU Mei-Biao, XIA Chang-Quan, LU Xiao-Ming, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2009, 26 (12): 124203 .   DOI: 10.1088/0256-307X/26/12/124203
Abstract   PDF(pc) (542KB) ( 504 )
We firstly propose and demonstrate a new economical approach that can correct the wavefront of the petwatt Ti:sapphire laser system with a beam size of 150mm. By using a deformable mirror with 50mm active aperture in the end of the laser, the focal spot size is reduced effectively. The experimental results show that the new approach is simple, less-expensive and valid from a technical and economical point. This technique could be applied to correct the wavefront of a large optical beam with a smaller aperture deformable mirror.
Bending Efficiency of Bent Multiple-Slot Waveguides
Hamid Keivani, Alireza Kargar,
Chin. Phys. Lett. 2009, 26 (12): 124204 .   DOI: 10.1088/0256-307X/26/12/124204
Abstract   PDF(pc) (389KB) ( 528 )
The bending efficiency of three-dimensional bent multiple-slot waveguides is studied by applying a combined method of effective-index and modified transfer-matrix methods. The effects of asymmetric structure, asymmetric slots, and asymmetric middle strips on the bending efficiency are investigated. We show that the bending efficiency can be improved by the use of asymmetric structures and asymmetric middle strips. The bending efficiency of different slot waveguides (up to quintuple-slot structure) is compared. It is revealed that although the single-slot waveguide in general provides the lowest bending loss for the same waveguide parameters, it is possible that the multiple-slot waveguide can present a lower bending loss than the single-slot one.
Plasmonic Corrugated Horn Structure for Optical Transmission Enhancement
LI Guang-Yuan, CAI Lin, XIAO Feng, XU An-Shi
Chin. Phys. Lett. 2009, 26 (12): 124205 .   DOI: 10.1088/0256-307X/26/12/124205
Abstract   PDF(pc) (639KB) ( 917 )
We propose and theoretically analyze a plasmonic corrugated horn structure for enhanced optical transmission. It makes use of the enhancement of unidirectional propagating surface plasmon polaritons at oblique incidence. Geometric parameters such as the groove depth and width are optimized. Analysis shows that it presents a better performance than the bull's eye structure for a small number of grooves.
Analysis of Optical Readout Sensitivity for Uncooled Infrared Detector
CHENG Teng, ZHANG Qing-Chuan, JIAO Bin-Bin, CHEN Da-Peng, WU Xiao-Ping
Chin. Phys. Lett. 2009, 26 (12): 124206 .   DOI: 10.1088/0256-307X/26/12/124206
Abstract   PDF(pc) (653KB) ( 348 )
An optical readout uncooled infrared detector, employing a substrate-free focal plane array with pitch size 60μm, is established. The reflector deformation induced by the stress mismatching of the bi-layer structure is discussed and, in turn, a universal solution to determine both the optical readout sensitivity and the optimal filter position is found. By applying this solution, the optical readout sensitivity for the ideal plane reflector could theoretically increase by 80% as compared with the conventional operation, and the sensitivity loss caused by the reflector deformation can also be reduced to a reasonable level.
Generation of Carrier and Odd Sidebands Suppressed Optical MM-Wave with Signal Only on One Sideband Using an External Integrated Mach-Zehnder Modulator
XU Wei, XIN Xiang-Jun, ZHAO Tong-Gang, LING Jing, YU Chong-Xiu
Chin. Phys. Lett. 2009, 26 (12): 124207 .   DOI: 10.1088/0256-307X/26/12/124207
Abstract   PDF(pc) (1302KB) ( 1008 )
A novel scheme to generate millimeter (mm)-wave is proposed where the quadrupling of local radio frequency is formed by using an external integrated Mach-Zehnder modulator through intensity modulation or phase modulation. Generated optical mm-wave signal suffers from neither power periodical fading nor time shift of the sidebands as it is transmitted along the fiber. Receiver sensitivity of our 10Gbit/s radio-over-fiber system based on the proposed scheme is -28.3dBm under intensity modulation while -24dBm under phase modulation after 65km transmission, and bit error rate is at 10-4 level after 100km transmission. Optical carrier in uplink is provided by the central station to simplify the base station, which also reduces the cost of the base station.
Measurement of the Carrier Recovery Time in Semiconductor Optical Amplifier Based on Dual-Pump Four-Wave Mixing Technology
CHENG Cheng, ZHANG Xin-Liang, ZHANG Yu, ZHOU En-Bo, LIU Lei, ZHANGYin, HUANG De-Xiu
Chin. Phys. Lett. 2009, 26 (12): 124208 .   DOI: 10.1088/0256-307X/26/12/124208
Abstract   PDF(pc) (401KB) ( 548 )
A scheme of measuring the carrier recovery time in semiconductor optical amplifiers (SOAs) based on dual pump Four-wave mixing technology is presented. The carrier recovery times under 120mA, 180mA 240mA and 300mA injected currents are measured to be 111ps, 81ps, 71ps and 53ps, respectively. The carrier recovery time of the spacing between the two umps is also investigated. The experimental results show that the conversion efficiency keeps constant when the spacing of the two pumps varies within a small range.
Energy Transfer and Avalanche Upconversion of NdxY1-xVO4 Nanocrystals
XIAO Si, ZHOU Li, WANG Qu-Quan, DENG Hong, YANG Shi-He
Chin. Phys. Lett. 2009, 26 (12): 124209 .   DOI: 10.1088/0256-307X/26/12/124209
Abstract   PDF(pc) (998KB) ( 556 )
We explore Nd3+ concentration and excitation power dependences of the avalanche upconversion of NdxY1-xVO4 (x=0-1) nanocrystals with uniform size and shape. The avalanche threshold power caused by the near-resonant energy transfer between 4F5/24I13/2 and 4F5/22G9/2 significantly decreases as the Nd3+ concentration increases. The off-resonant energy transfer between 4F5/24I13/2 and 4F5/24G11/2 in the strong excitation regime leads to apparent broadening on the blue-side of the upconversion spectrum of NdVO4 nanocrystals.
Rayleigh Range of Hermite-Gaussian Array Beams
JI Xiao-Ling
Chin. Phys. Lett. 2009, 26 (12): 124210 .   DOI: 10.1088/0256-307X/26/12/124210
Abstract   PDF(pc) (366KB) ( 1056 )
An analytical expression for the Rayleigh range of Hermite-Gaussian (H-G) array beams is derived. It is shown that under the non-phase-locked case the Rayleigh range zR increases monotonously with the increasing beam number M, the beam separation distance xd and the beam waist widthw0, and with decreasing the beam order m. However, under the phase-locked case there exists oscillatory behavior of zR versus m and xd. For Gaussian array beams, under the phase-locked case, zR is always larger than that under the non-phase-locked case. However, it holds true only when xd is small enough or w0 is large enough for H-G array beams. In addition, zR of Gaussian array beams is always larger than that of H-G array beams.
Q-Switched Tm:YAG Laser Intracavity-Pumped by a 1064nm Laser
MA Qing-Lei, ZONG Nan, XIE Shi-Yong, YANG Feng, GUO Ya-Ding, XU Jia-Lin, BO Yong, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2009, 26 (12): 124211 .   DOI: 10.1088/0256-307X/26/12/124211
Abstract   PDF(pc) (435KB) ( 547 )
We report a Q-switched 2-μm Tm:YAG laser based on intracavity-pumped by a 1064-nm Nd:YAG laser operating at room temperature for the first time. An average output power of 5.1W is obtained with the repetition rate of 30kHz and a pulse width of 300ns. In addition, we demonstrate a 12.5-W continuous-wave 2-μm Tm:YAG laser, which is, to our best knowledge, the highest power for intracavity-pumping configuration.
The Second Order Guided Modes Based on Photonic Bandgap Effects in Air/Glass Photonic Crystal Fibers
YAO Lei, LOU Shu-Qin, JIAN Shui-Sheng
Chin. Phys. Lett. 2009, 26 (12): 124212 .   DOI: 10.1088/0256-307X/26/12/124212
Abstract   PDF(pc) (457KB) ( 445 )
We introduce a defect site in the periodic structure of a photonic bandgap fiber, to confine and guide the second order mode by photonic bandgap effects. Based on a high air-filling fraction photonic crystal cladding structure, a simplified model with an equivalent air cladding was proposed to explore and analyze the properties of this second order guided mode.
Low Threshold and High Conversion Efficiency Nanosecond Mid-Infrared KTA OPO
ZHONG Kai, LI Jian-Song, CUI Hai-Xia, XU Deng-Gang, WANG Yu-Ye, ZHOU Rui, WANG Jing-Li, WANG Peng, YAO Jian-Quan,
Chin. Phys. Lett. 2009, 26 (12): 124213 .   DOI: 10.1088/0256-307X/26/12/124213
Abstract   PDF(pc) (454KB) ( 1365 )
Based on a Type II non-critically phase-matched KTA crystal, a low-threshold and high conversion efficiency mid-infrared optical parametric oscillator (OPO) pumped by a diode-end-pumped Nd:YVO4 laser is demonstrated. The OPO threshold is only 0.825W. The maximum output power of 435mW at 3.47μm is achieved with the repetition rate of 30kHz, corresponding to an optical-to-optical conversion efficiency of 4.4%. The photon conversion efficiency is as high as about 64%. The pulse width is 3.5ns with a peak power of 4kW for the maximum output power.
Mid-IR Dual-Wavelength Difference Frequency Generation Using Fiber Lasers as Pump and Signal Light Sources
JIANG Jian, CHANG Jian-Hua, FENG Su-Juan, MAO Qing-He, LIU Wen-Qing
Chin. Phys. Lett. 2009, 26 (12): 124214 .   DOI: 10.1088/0256-307X/26/12/124214
Abstract   PDF(pc) (368KB) ( 746 )
A continuous-wave mid-IR difference frequency laser source, which respectively uses an ytterbium-doped fiber laser as the pump source and a multiwavelength erbium-doped fiber laser cascaded with an erbium-doped fiber amplifier as the signal source, is demonstrated. Our experimental results show that two stable mid-IR radiation lines with a spacing of about 5.4nm may be simultaneously emitted by a suitable setting the pump and signal polarization orientations. The number of the mid-IR radiation lines is limited by the quasi-phase-matching acceptance bandwidth. By changing the PPMgLN temperature the two mid-IR radiation lines may be synchronously tuned in the mid-IR range between 3295 and 3356.3nm.
Determination of Heat Transport Mechanism in Aqueous Nanofluids Using Regime Diagram
M. CHANDRASEKAR, S. SURESH
Chin. Phys. Lett. 2009, 26 (12): 124401 .   DOI: 10.1088/0256-307X/26/12/124401
Abstract   PDF(pc) (369KB) ( 685 )
We provide an approximate method to determine the dominant heat transport mechanism responsible for the anomalous enhancement of thermal conductivity in aqueous nanofluids. Due to a large degree of randomness and scatter observed in the published experimental data, limits to nanofluid thermal conductivity are fixed analytically by taking into account the contribution of particle Brownian motion and clustering, and a regime diagram is developed. Experimental data from a range of independent published sources is used for validation of the developed regime diagram.
Homotopy Analysis Approach to Periodic Solutions of a Nonlinear Jerk Equation
FENG Shao-Dong, CHEN Li-Qun,
Chin. Phys. Lett. 2009, 26 (12): 124501 .   DOI: 10.1088/0256-307X/26/12/124501
Abstract   PDF(pc) (628KB) ( 635 )
The homotopy analysis method is applied to seek periodic solutions of a nonlinear jerk equation involving the third-order time-derivative. The periodic solutions can be approximated via an analytical series. An auxiliary parameter is introduced to control the convergence region of the solution series. Two numerical examples are presented to demonstrate the effectiveness of the homotopy analysis approach. The examples indicate that, by choosing a proper value of the auxiliary parameter, the first few terms in the solution series yield excellent results.
An Extension of the Two-Dimensional JKR Theory to the Case with a Large Contact Width
CHEN Shao-Hua, PENG Zhi-Long
Chin. Phys. Lett. 2009, 26 (12): 124601 .   DOI: 10.1088/0256-307X/26/12/124601
Abstract   PDF(pc) (407KB) ( 694 )
In the Hertz and JKR theories, parabolic assumptions for the rounded profiles of the sphere or cylinder are adopted under the condition that the contact radius (width) should be very small compared to the radius of the sphere or
cylinder. However, a large contact radius (width) is often found in experiments even under a zero external loading. We aim at extending the plane strain JKR theory to the case with a large contact width. The relation between the external loading and the contact width is given. Solutions for the Hertz, JKR and rounded-profile cases are compared and analyzed. It is found that when the ratio of a/R is approximately larger than about 0.4, the parabolic assumptions in the Hertz and JKR theories are no longer valid and the exact rounded profile function should be used.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Effects of Anode Temperature on Working Characteristics and Performance of a Low Power Arcjet Thruster
PAN Wen-Xia, LI Teng, WU Cheng-Kang
Chin. Phys. Lett. 2009, 26 (12): 125201 .   DOI: 10.1088/0256-307X/26/12/125201
Abstract   PDF(pc) (410KB) ( 481 )
An arc-heated thruster of 130-800W input power is tested in a vacuum chamber at pressures lower than 20Pa with argon or H2-N2 gas mixture as propellant. The time-dependent arc voltage-current curve, outside-surface temperature of the anode nozzle and the produced thrust of the firing arcjet thruster are measured in situ simultaneously, in order to analyze and evaluate the dependence of thruster working characteristics and output properties, such as specific impulse and thrust efficiency, on nozzle temperature.
Simulation of Dual Frequency Capacitive Sheath over a Concave Electrode in Low Pressure
HAO Mei-Lan, DAI Zhong-Ling, WANG You-Nian
Chin. Phys. Lett. 2009, 26 (12): 125202 .   DOI: 10.1088/0256-307X/26/12/125202
Abstract   PDF(pc) (611KB) ( 456 )
A self-consistent two-dimensional (2D) collisionless fluid model is developed to simulate the characteristics of a dual frequency capacitive sheath over an electrode with a cylindrical hole. The model consists of 2D time-dependent fluid equations coupled with Poisson's equation, in which the low-frequency (LF) and high-frequency current sources are applied to an electrode. Thus, the so-called equivalent circuit model coupling with the fluid equations will be able to self-consistently determine the relationship between the instantaneous voltage on the powered electrode and the sheath thickness. The time-averaged potential, electric field, ion density in the sheath and ion energy distributions at the bottom of the hole are calculated and compared for different LF frequencies. The results show that the LF frequency is crucial for determining the sheath structure. The existence of the cylindrical hole on the electrode obviously affects the sheath profile in the parallel to the electrode and makes the sheath profile tend to adapt the contours of the electrode, which is the plasma molding effect.
Coulomb Explosion and Energy Loss of Energetic C20 Clusters in Dense Plasmas
WANG Gui-Qiu, LI Wen-Kun, WANG You-Nian
Chin. Phys. Lett. 2009, 26 (12): 125203 .   DOI: 10.1088/0256-307X/26/12/125203
Abstract   PDF(pc) (586KB) ( 441 )
The molecular dynamics (MD) method is used to simulate the interactions of energetic C20 clusters with the dense plasma targets within the framework of the linear Vlasov-Poisson theory. The influences of various clusters (H2, N2, C20 and C60 respectively) on stopping power are discussed. The simulation results show that the vicinage effects in the Coulomb explosion dynamics and the stopping power are strongly affected by the variations in the cluster speed and the plasma parameters. Coulomb explosions are found to proceed faster for higher speeds, lower plasma densities and higher electron temperatures. In addition, the cluster stopping power is strongly enhanced in the early stages of Coulomb explosions due to the vicinage effect, but this enhancement eventually diminishes, after the cluster constituent ions are sufficiently separated. For the large and heavy clusters, the stopping power ratio reaches much higher values in the early stage of Coulomb explosion owing to the constructive interferences in the vicinage effect.
Proton Acceleration with Nano-Scale Micro-Structured Target by Circularly Polarized Laser Pulse
JIN Zhang-Ying, SHEN Bai-Fei, ZHANG Xiao-Mei, WANG Feng-Chao, WENMeng, JI Liang-Liang, XU Jian-Cai, WANG Wen-Peng
Chin. Phys. Lett. 2009, 26 (12): 125404 .   DOI: 10.1088/0256-307X/26/12/125404
Abstract   PDF(pc) (904KB) ( 382 )
Two dimensional particle-in-cell simulations are taken to study the interaction of a circularly polarized laser pulse with a nano-scale micro-structured target. The protons which are doped in the rear side of the target experience the electrostatic fields caused by both the radiation pressure driven shock and the target normal sheath at the rear side of the target. A quasimonoenergetic proton bunch with central energy of about 11MeV and energy spread of ∆ ε/ε about 0.18 is achieved by using a 3.45×1019 W/cm2, 66fs laser pulse. A comparison with the case of linearly polarized laser pulse and the same target condition is considered.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Fabrication of Co/CoO Exchange Bias System by Ion Implantation and Its Magnetic Properties
FA Tao, XIANG Qing-Pei, YAO Shu-De
Chin. Phys. Lett. 2009, 26 (12): 126101 .   DOI: 10.1088/0256-307X/26/12/126101
Abstract   PDF(pc) (415KB) ( 463 )
We use ion implantation as a new approach to build an anti-ferromagnetic (AFM) cluster embedded exchange bias (EB) system. Co film with thickness of 130nm is deposited on the Si (111) substrate using magnetron sputtering, 60keV O+ is chosen to implanted into the Co film to form CoO AFM clusters coupling with Co matrix at the interface. By measuring the hysteresis loop after field-cooling, significant shifts of loop along the applied field are confirmed. When increasing the implantation dose to 2×1017/cm2 and annealed samples in N2 atmosphere, we obtain the highest HEB to 458Oe.
Density Functional Theory Approach for Charged Hard Sphere Fluids Confined in Spherical Micro-Cavity
KANG Yan-Shuang, , WANG Hai-Jun,
Chin. Phys. Lett. 2009, 26 (12): 126102 .   DOI: 10.1088/0256-307X/26/12/126102
Abstract   PDF(pc) (420KB) ( 717 )
Within the framework of the density functional theory for classical fluids, the equilibrium density profiles of charged hard sphere fluid confined in micro-cavity are studied by means of the modified fundamental measure theory. The dimension of micro-cavity, the charge of hard sphere and the applied electric field are found to have significant effects on the density profiles. In particular, it is shown that Coulomb interaction, excluded volume interaction and applied electric field play the central role in controlling the aggregated structure of the system.
A Unified Guide to Two Opposite Size Effects in Nano Elastic Materials
TANG Yi-Zhe, ZHENG Zhi-Jun, XIA Meng-Fen, BAI Yi-Long
Chin. Phys. Lett. 2009, 26 (12): 126201 .   DOI: 10.1088/0256-307X/26/12/126201
Abstract   PDF(pc) (478KB) ( 397 )
The microstructural variation near surface of nano elastic materials is analyzed based on different potentials. The atomic/molecular mechanism underlying the variation and its effect on elastic modulus are such that the nature of long-range interactions (attractive or repulsive) in the atomic/molecular potentials essentially governs the variation near surface (looser or tighter) and results in two opposite size effects (decreasing or increasing modulus) with decreasing size.
Buckling Analysis of Soft Nanostructure in Nanoimprinting
FENG Kan, LI Zheng
Chin. Phys. Lett. 2009, 26 (12): 126202 .   DOI: 10.1088/0256-307X/26/12/126202
Abstract   PDF(pc) (379KB) ( 446 )
Nanoimprint lithography is an economical and convenient method for manufacturing nanostructures, which has developed very quickly and has been widely used in the nanoindustry. However, during the process of nanoimprinting, mechanical instabilities of soft nanostructures could lead to buckling. In order to study the mechanism of this problem, we analyze the buckling of one vertical elastic column under its own weight. Based on the comparison between two critical heights of different substrates (rigid and elastic), we conclude that the approximation of considering the substrate as rigid is acceptable. Furthermore the interaction between columns with the deformation of a substrate could lead to collective buckling. Our theoretical calculations show that whether the columns are elastic or rigid makes little difference for the buckling modes.
Capillary Forces between Submillimeter Spheres and Flat Surfaces at Constant Liquid Volumes
WANG Le-Feng, RONG Wei-Bin, SUN Li-Ning, CHEN Li-Guo, SHAO Bing
Chin. Phys. Lett. 2009, 26 (12): 126801 .   DOI: 10.1088/0256-307X/26/12/126801
Abstract   PDF(pc) (900KB) ( 897 )
We investigate the capillary forces between submillimeter spheres and flat surfaces at constant liquid volumes theoretically and experimentally. An iterative method is used to estimate the capillary force with contact angles as the boundary conditions and the constant volume as a constraint. The theoretical analysis shows that the maximum capillary force between them decreases with the increase of the liquid bridge volume at small contact angles. The experimental results show that the force is smaller than the theoretical values at the initial separation distances. It is also observed that the force first increases and then decreases with an increasing separation distance in some cases. These phenomena of capillary forces hysteresis are explained according to the wetting hysteresis.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Anomalous Pressure Behavior of N-Cluster Emissions in GaAs0.973Sb0.022N0.005
WANG Wen-Jie, DENG Jia-Jun, FU Xing-Qiu, HU Bing, DING Kun
Chin. Phys. Lett. 2009, 26 (12): 127101 .   DOI: 10.1088/0256-307X/26/12/127101
Abstract   PDF(pc) (870KB) ( 453 )
Photoluminescence of GaAs0.973Sb0.022N0.005 is investigated at different temperatures and pressures. Both the alloy band edge and the N-related emissions, which show different temperature and pressure dependences, are observed. The pressure coefficients obtained in the pressure range 0-1.4GPa for the band edge and N-related emissions are 67 and 45meV/GPa, respectively. The N-related emissions shift to a higher energy in the lower pressure range and then begin to redshift at about 8.5GPa. This redshift is possibly caused by the increase of the X-valley component in the N-related states with increasing pressure.
Transition Metal Silicide Nanowires Growth and Electrical Characterization
PENG Zu-Lin, LIANG S., DENG Luo-Gen
Chin. Phys. Lett. 2009, 26 (12): 127301 .   DOI: 10.1088/0256-307X/26/12/127301
Abstract   PDF(pc) (715KB) ( 511 )
We report the characterization of self-assembled epitaxially grown transition metal, Fe, Co, Ni, silicide nanowires (TM-NW) growth and electrical transport properties. NWs grown by reactive deposition epitaxy on various silicon surfaces show a dimension of 10nm by 5nm, and several micrometers in length. NW orientations strongly depend on substrate crystal orientation, and follow the substrate symmetry. By using conductive-AFM (c-AFM), the electron transport properties of one single NW were measured, the resistivity of crystalline nickel silicide NW was estimated to be 2×10-2Ω・cm.
Spin Interference in Rectangle Loop Based on Rashba and Dresselhaus Spin-Orbit Interactions
NI Jia-Ting, LIANG Xiao-Wan, CHEN Bin, T. Koga,
Chin. Phys. Lett. 2009, 26 (12): 127302 .   DOI: 10.1088/0256-307X/26/12/127302
Abstract   PDF(pc) (328KB) ( 378 )
We demonstrate the amplitude and spin polarization of AAS oscillation changing with Rashba spin-orbit interaction (SOI) and Dresselhaus SOI. The amplitude and spin polarization of AB oscillation changing with Rashba SOI and Dresselhaus SOI are demonstrated as well. The ideal quasi-one-dimensional square loop does not exist in reality, therefore to match the experiment better we should consider the shape of the rectangle loop in theory.
Photoinduced Magnetization Change in Multiferroic YbFe2O4
LI Chang-Hui, LIU Yi, WANG Fen, LUO Xuan, SUN Yu-Ping, ZHANG Xiang-Qun, CHENG Zhao-Hua, SUN Yang
Chin. Phys. Lett. 2009, 26 (12): 127501 .   DOI: 10.1088/0256-307X/26/12/127501
Abstract   PDF(pc) (448KB) ( 367 )
We investigate the influence of laser illumination on the magnetization in multiferroic YbFe2O4 single crystals. A photoinduced magnetization change is confirmed in both ab plane and the c-axis directions. The temperature dependence of the photoinduced magnetization reduction excludes laser heating as the cause. In terms of the breakdown of charge order driven by laser illumination, the photoinduced magnetization change provides strong evidence for the spin-charge coupling in YbFe2O4. This photomagnetic effect based on charge-order-induced multiferroicity could be used for the non-thermal optical control of magnetization.
Bond-Alternating Antiferromagnetic S=1/2 Heisenberg Ladder with Ferromagnetic Diagonal Coupling
LI An-Kang, LU Jun-Zhe, MA Lei
Chin. Phys. Lett. 2009, 26 (12): 127502 .   DOI: 10.1088/0256-307X/26/12/127502
Abstract   PDF(pc) (403KB) ( 726 )
Using the density matrix renormalization group method, we determine the phase diagram of a frustrated bond-alternating S=1/2 Heisenberg ladder with ferro-antiferromagnetic couplings at zero temperature. With the interactions between spins along the rungs set, we identify three spin-gapped phases (the Haldane phase, the singlet phase and the dimer phase) in the whole parameter range. The analysis of our data shows that two-leg spin bond-alternating ladders have a rich phase diagram if both rung and diagonal couplings are taken into account.
Micromagnetic Simulation of Transfer Curve in Giant-Magnetoresistive Head
SHE Sheng-Xian, WEI Dan, ZHENG Yang, QU Bing-Jun, REN Tian-Ling, LIU Xi, WEI Fu-Lin
Chin. Phys. Lett. 2009, 26 (12): 127503 .   DOI: 10.1088/0256-307X/26/12/127503
Abstract   PDF(pc) (444KB) ( 655 )
The transfer curve of the giant-magnetoresistive (GMR) magnetic head represents its most important property in applications, and it is calculated by the micromagnetic modeling of the free layer and the pinned layer in the heart of the GMR head. Affections of the bias hard magnetic layer and the anti-ferromagnetic pinning layer are modeled by effective magnetic fields. The simulated transfer curve agrees with experiment quite well, therefore the values of these effective magnetic fields can be determined by the model. A synthetic antiferromagnetic spin valve structure GMR head is also analyzed for comparison.
Dependence of Junction Voltage Saturation on Uniformity and Quality of Laser Diode Bars
LIANG Qing-Cheng, SHI Jia-Wei, GUO Shu-Xu, LIU Kui-Xue, CAO Jun-Sheng
Chin. Phys. Lett. 2009, 26 (12): 127504 .   DOI: 10.1088/0256-307X/26/12/127504
Abstract   PDF(pc) (445KB) ( 418 )
The dependence of the sinkage at the threshold of the electric derivative curve (IdV/dI-I) on the uniformity and the quality of the laser diode bar is analyzed. By using the equations derived from the equivalent circuits of the bars, the influence of the bar uniformity on the depth of the dip is investigated in theory under certain conditions. Furthermore, the experimental results based on the presented technique indicate that the depth of the dip is interrelated to the uniformity and the quality of the corresponding bar. The present technique can be used conveniently and effectively to measure the laser diode bars in practice.
Fe-Vacancy-Induced Ferromagnetism in Tetragonal FeSe Thin Films
LI Yong-Feng, LIU Gui-Bin, SHI Li-Jie, LIU Bang-Gui
Chin. Phys. Lett. 2009, 26 (12): 127505 .   DOI: 10.1088/0256-307X/26/12/127505
Abstract   PDF(pc) (605KB) ( 532 )
Motivated by recent experiments, we investigate structural, electronic, and magnetic properties of tetragonal FeSe with Fe vacancies using the state-of-the-art first-principles method. We show that Fe vacancies tend to stay in the same one of the two sublattices and thus induce ferromagnetism in the ground-state phase. Our calculated net moment is in good agreement with the experimental data available. Therefore, the ferromagnetism observed in tetragonal FeSe thin films is explained. It could be made controllable soon for spintronic applications.
Thermal Stability and Humidity Resistance of ScTaO4 Modified (K0.5Na0.5)NbO3 Ceramics
ZHENG Li-Mei, WANG Jin-Feng, WANG Chun-Ming, WU Qing-Zao, ZANG Guo-Zhong
Chin. Phys. Lett. 2009, 26 (12): 127701 .   DOI: 10.1088/0256-307X/26/12/127701
Abstract   PDF(pc) (1151KB) ( 535 )
Lead-free (Na0.5K0.5)NbO3-xmol% ScTaO4 (x=0-1.5) ceramics are prepared using the conventional solid-state reaction method and their properties are investigated in detail. The results indicate that the piezoelectric properties and density are improved by the introduction of ScTaO4. Due to the high orthorhombic-tetragonal phase transition temperature TO-T (around 200°C), stable piezoelectric properties against temperature are obtained. In a wide temperature range of 15-160°C, kp of the (Na0.5K0.5)NbO3-0.5mol% ScTaO4 ceramic remains almost unchanged and d31 increases slightly from 59pC/N to 71pC/N. The deliquescent problem is effectively solved by the addition of ScTaO4. The piezoelectric properties of ScTaO4 modified (Na0.5K0.5)NbO3 ceramics show no obvious reduction and dielectric loss increases slightly after 120h of immersion. From the analysis, it is suggested that the density is an important factor that improves the humidity resistance of the specimens.
Ultrafast Photophysics of Star-Like Molecules with Benzene and Triazine Core
FENG Wen-Ke, KONG Sheng, XIAO Li-Xin, MENG Kang, WANG Shu-Feng, GONG Qi-Huang
Chin. Phys. Lett. 2009, 26 (12): 127801 .   DOI: 10.1088/0256-307X/26/12/127801
Abstract   PDF(pc) (454KB) ( 471 )
Static and transient spectroscopic characters of newly synthesized start-like molecules, 1,3,5-tri(10-butyl-3-propenyl-10H-phenothiazine)-benzene (TP3B) and 2,4,6-tri(10-butyl-3-propenyl -10H-phenothiazine)-[1,3,5]triazine (TP3T), are studied using static, picosecond fluorescence and femtosecond transient absorption spectroscopy. The results show that when the benzene group is in the center, a large conjugation system is formed, while a fast electron-transfer process happens when the center group is triazine.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Effect of Poly(Ether Urethane) Introduction on the Performance of Polymer Electrolyte for All-Solid-State Dye-Sensitized Solar Cells
ZHOU Yan-Fang, XIANG Wan-Chun, FANG Shi-Bi, CHEN Shen, ZHOU Xiao-Wen, ZHANG Jing-Bo, LIN Yuan
Chin. Phys. Lett. 2009, 26 (12): 128201 .   DOI: 10.1088/0256-307X/26/12/128201
Abstract   PDF(pc) (1108KB) ( 634 )
The introduction of poly(ether urethane) (PEUR) into polymer electrolyte based on poly(ethylene oxide), LiI and I2, has significantly increased the ionic conductivity by nearly two orders of magnitudes. An increment of I3- diffusion coefficient is also observed. All-solid-state dye-sensitized solar cells are constructed using the polymer electrolytes. It was found that PEUR incorporation has a beneficial effect on the enhancement of open circuit voltage VOC by shifting the band edge of TiO2 to a negative value. Scanning
electron microscope images indicate the perfect interfacial contact between the TiO2 electrode and the blend electrolyte.
An SPICE Model for PCM Based on Arrhenius Equation
LI Xi, SONG Zhi-Tang, CAI Dao-Lin, CHEN Xiao-Gang, JIA Xiao-Ling
Chin. Phys. Lett. 2009, 26 (12): 128501 .   DOI: 10.1088/0256-307X/26/12/128501
Abstract   PDF(pc) (442KB) ( 759 )
Based on the temperature dependence of the Arrhenius law, an HSPICE compact module using Verilog-A language for phase change memory (PCM) is presented. In the model of this HSPICE compact module, the basic theory that the resistance of the amorphous semiconductor has relations with the activation energy and temperature is used, and an assumption that this theory can be expanded to describe the crystalline semiconductor is employed. Moreover, since an objective reality that the resistance of the semiconductor determines the temperature and the temperature affects the resistance inversely is inevitable, coupling with such positive feedback, this model can reproduce the real-time characteristics of the memory cell accurately. The simulation results show that this model can reproduce the features of the PCM cell well. It can be used in the PCM circuit design and further analysis.
High-Current Multi-Finger Mesa InGaAs/InP DHBTs
JIN Zhi, CHENG Wei, SU Yong-Bo, LIU Xin-Yu, XU An-Huai, QI Ming
Chin. Phys. Lett. 2009, 26 (12): 128502 .   DOI: 10.1088/0256-307X/26/12/128502
Abstract   PDF(pc) (997KB) ( 429 )
Characteristics of single- and multi-finger mesa InGaAs/InP double heterojunction bipolar transistors (DHBTs) are compared. The current gain decreases with the increasing number nf of the emitter fingers due to the mutual thermal interaction between the fingers. The Kirk current can be as high as 150mA for four-finger DHBT. No degradation of the peak of the current gain cutoff frequency ft is found for multi-finger DHBTs. The peak of the maximum oscillation frequency fmax decreases with an increase of nf due to the increasing parasitic resistance of the base. The results are very helpful for applications of the common-base DHBTs in power amplifiers operating at very high frequencies.
Further Discussion on Polaron Existence in Dry DNA
LI Xiao-Hong, ZHANG Yu-Yu, LIU Tao, WANG Ke-Lin,
Chin. Phys. Lett. 2009, 26 (12): 128701 .   DOI: 10.1088/0256-307X/26/12/128701
Abstract   PDF(pc) (297KB) ( 343 )
We study the interaction between holes and molecular vibrations on dry DNA by using the extended Firsov's model. The ground state energy, calculated by using two Hilbert spaces, Fock state space and coherent state space, is confirmed. The polaron binding energy, defined with the ground state energy, is 0.014eV, much less than the thermal energy 0.026eV at room temperature 300K, which means that polarons are difficult to form self-trapping at room temperature and Anderson localization will prevent a metallic state on dry DNA. The results are consistent with the available experiments.
Robustness of Complex Networks under Attack and Repair
HU Bin, LI Fang, ZHOU Hou-Shun
Chin. Phys. Lett. 2009, 26 (12): 128901 .   DOI: 10.1088/0256-307X/26/12/128901
Abstract   PDF(pc) (328KB) ( 660 )
To study the robustness of complex networks under attack and repair, we introduce a repair model of complex networks. Based on the model, we introduce two new quantities, i.e. attack fraction fa and the maximum degree of the nodes that have never been attacked ~Ka, to study analytically the critical attack fraction and the relative size of the giant component of complex networks under attack and repair, using the method of generating function. We show analytically and numerically that the repair strategy significantly enhances the robustness of the scale-free network and the effect of robustness improvement is better for the scale-free networks with a smaller degree exponent. We discuss the application of our theory in relation to the
understanding of robustness of complex networks with reparability.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Resonant Scattering of Relativistic Outer Zone Electrons by Plasmaspheric Plume Electromagnetic Ion Cyclotron Waves
SU Zhen-Peng, ZHENG Hui-Nan
Chin. Phys. Lett. 2009, 26 (12): 129401 .   DOI: 10.1088/0256-307X/26/12/129401
Abstract   PDF(pc) (368KB) ( 517 )
The bounce-averaged Fokker-Planck equation is solved to study the relativistic electron phase space density (PSD) evolution in the outer radiation belt due to resonant interactions with plasmaspheric plume electromagnetic ion cyclotron (EMIC) waves. It is found that the PSDs of relativistic electrons can be depleted by 1-3 orders of magnitude in 5h, supporting the previous finding that resonant interactions with EMIC waves may account for the frequently observed relativistic electron flux dropouts in the outer radiation belt during the main phase of a storm. The significant precipitation loss of ~MeV electrons is primarily induced by the EMIC waves in H+ and He+ bands. The rapid remove of highly relativistic electrons (>5MeV) is mainly driven by the EMIC waves in O+ band at lower pitch-angles, as well as the EMIC waves in H+ and He+ bands at larger pitch-angles. Moreover, a stronger depletion of relativistic electrons is found to occur over a wider pitch angle range when EMIC waves are centering relatively higher in the band.
Two-Component Model for the Interstellar Scattering along the Line of Sight to the Pulsar PSR B0136+57
ZHOU Ai-Zhi, TAN Jin-Yu, Ali Esamdin, WU Xin-Ji
Chin. Phys. Lett. 2009, 26 (12): 129701 .   DOI: 10.1088/0256-307X/26/12/129701
Abstract   PDF(pc) (413KB) ( 377 )
A rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum is discussed. It is assumed that the interstellar scattering medium is composed of a thin screen ISM and an extended interstellar medium. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than the single extended medium model along the line of sight to the pulsar PSR B0136+57.
COMMENTS AND ERRATA
Erratum: Numerical Calculation on the SAW Propagation Properties at x-Cut of Ferroelectric PMN-33%PT Single Crystals [Chin. Phys. Lett. 26 (2009) 064301]
ZHANG Wei, LI Xiu-Ming, ZHANG Rui, HUANG Nai-Xing, CAO Wen-Wu,
Chin. Phys. Lett. 2009, 26 (12): 129901 .   DOI: 10.1088/0256-307X/26/12/129901
Abstract   PDF(pc) (208KB) ( 314 )
Erratum:Dynamics of Forster Energy Transfer in Pyridium Salt-Doped Thin Films [Chin. Phys. Lett. 26 (2009) 077806]
Chin. Phys. Lett. 2009, 26 (12): 129902 .   DOI: 10.1088/0256-307X/26/12/129902
Abstract   PDF(pc) (159KB) ( 308 )
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