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Volume 32 Issue 06
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Critical Behavior of the Energy Gap and Its Relation with the Berry Phase Close to the Excited State Quantum Phase Transition in the Lipkin Model
YUAN Zi-Gang, ZHANG Ping
Chin. Phys. Lett. 2015, 32 (06): 060301 .   DOI: 10.1088/0256-307X/32/6/060301
Abstract   PDF(pc) (681KB) ( 568 )

In our previous work [Phys. Rev. A 85 (2012) 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann–Feynman theorem, we derive the relation between the energy gap and the Berry phase closed to the excited state quantum phase transition (ESQPT) in the Lipkin model. It is found that the energy gap is approximately linearly dependent on the Berry phase being closed to the ESQPT for large N. As a result, the critical behavior of the energy gap is similar to that of the Berry phase. In addition, we also perform a semiclassical qualitative analysis about the critical behavior of the energy gap.

Robustness of Genuine Tripartite Entanglement under Collective Dephasing
Chin. Phys. Lett. 2015, 32 (06): 060302 .   DOI: 10.1088/0256-307X/32/6/060302
Abstract   PDF(pc) (492KB) ( 387 )

We study the robustness of genuine multipartite entanglement for a system of three qubits under collective dephasing. Using a computable entanglement monotone for multipartite systems, we find that almost every state is quite robust under this type of decoherence. We analyze random states and weighted graph states at infinity and find all of them to be genuinely entangled.

Quantum State Transfer among Three Ring-Connected Atoms
GUO Yan-Qing, DENG Yao, PEI Pei, TONG Dian-Min, WANG Dian-Fu, MI Dong
Chin. Phys. Lett. 2015, 32 (06): 060303 .   DOI: 10.1088/0256-307X/32/6/060303
Abstract   PDF(pc) (770KB) ( 364 )
A robust quantum state transfer scheme is discussed for three atoms that are trapped by separated cavities linked via optical fibers in a ring connection. It is shown that, under the effective three-atom Ising model, an arbitrary unknown quantum state can be transferred from one atom to another deterministically via an auxiliary atom with maximum unit fidelity. The only required operation for this scheme is replicating turning on/off the local laser fields applied to the atoms for two steps with time cost √2π/Γ0. The scheme is insensitive to cavity leakage and atomic position due to the condition Δκ?g. Another advantage of this scheme is that the cooperative influence of spontaneous emission and operating time error can reduce the time cost for maximum fidelity and thus can speed up the implementation of quantum state transfer.
The Coherence of a Dipolar Condensate in a Harmonic Potential Superimposed to a Deep Lattice
WANG Long, YU Zi-Fa, XUE Ju-Kui
Chin. Phys. Lett. 2015, 32 (06): 060304 .   DOI: 10.1088/0256-307X/32/6/060304
Abstract   PDF(pc) (668KB) ( 278 )
Within the mean-field model, the coherent matter waves of a dipolar condensate in a harmonic potential superimposed to a deep lattice are investigated by the variational principle. It is shown that, in a harmonic potential superimposed to a deep lattice, it is possible to control the decoherence of Bloch oscillations due to the fact that the on-site and the inter-site dipolar interactions can not only damp out Bloch oscillations but also maintain long-lived Bloch oscillations under the certain condition. In particular, long-lived Bloch oscillations of dipolar condensate can be realized when the dipolar interaction, the contact interaction, the frequency of the harmonic potential and initial width of the wave packet satisfy an analytical condition. Thus the decoherence of Bloch oscillation can be controlled by adjusting the dipolar interaction, the contact interaction, the frequency of harmonic potential and the initial width of the wave packet.
The Effect of Quantum Coins on the Spreading of Binary Disordered Quantum Walk
ZHAO Jing, HU Ya-Yun, TONG Pei-Qing
Chin. Phys. Lett. 2015, 32 (06): 060501 .   DOI: 10.1088/0256-307X/32/6/060501
Abstract   PDF(pc) (882KB) ( 453 )
The dynamical and static disordered quantum walks were extensively studied recently. It is found that, for the dynamical disorder case, the transport behavior of particles is diffusive, and for the static disorder case the transport behavior is localized. In this work, we study the effect of quantum coins on the transport behaviors of the binary disordered quantum walks. We find that once the coins satisfy certain conditions, the sub-ballistic spreading could be found in binary dynamical disorder quantum walks, and the sub-ballistic, diffusive and sub-diffusive spreadings could be found in binary static disorder quantum walks. We obtain the necessary conditions for those abnormal diffusive behaviors.
The Dependence of Chimera States on Initial Conditions
FENG Yue-E, LI Hai-Hong
Chin. Phys. Lett. 2015, 32 (06): 060502 .   DOI: 10.1088/0256-307X/32/6/060502
Abstract   PDF(pc) (544KB) ( 585 )
A chimera state consisting of both coherent and incoherent groups is a fascinating spatial pattern in non-locally coupled identical oscillators. It is thought that random initial conditions hardly evolve to chimera states. In this work, we study the dependence of chimera states on initial conditions. We show that random initial conditions may lead to chimera states and the chance of realizing chimera states becomes increasing when the model parameters are moving away from the boundary of their stable regime.
Description of the Shape Coexistence in 98Mo with IBM2
ZHANG Da-Li, YUAN Shu-Qing, DING Bin-Gang,
Chin. Phys. Lett. 2015, 32 (06): 062101 .   DOI: 10.1088/0256-307X/32/6/062101
Abstract   PDF(pc) (477KB) ( 346 )
We investigate the properties of the low-lying states and the relevant shape dynamics of 98Mo within the framework of the proton-neutron interacting boson model (IBM2). By considering the relative energy of the d proton boson to be different from that of the neutron bosons, the low-lying levels and the key observable B(E2) transition branching ratios are calculated. The characteristic feature of the energy spectrum and the most crucial available structure indicator indicate that the substantial mixing between the spherical-vibrational and γ-unstable shapes in 98Mo. The calculation results of the overall deformation in 98Mo are almost the same for both the ground and the first excited 0+ states, showing a weak deformation. While the triaxiality parameter indicates that the mostly triaxial shape with some oblate for the ground state, and the triaxial shape with some prolate for the excited 0+2 state, being equilibrium shapes of spherical-vibrational and γ-unstable in 98Mo.
Azimuthal Asymmetry of Pion-Meson Emission around the Projectile and Target Sides in Au+Au Collision at 1A GeV
WANG Ting-Ting, LU Ming, MA Yu-Gang, FANG De-Qing, WANG Shan-Shan, ZHANG Guo-Qiang
Chin. Phys. Lett. 2015, 32 (06): 062501 .   DOI: 10.1088/0256-307X/32/6/062501
Abstract   PDF(pc) (1007KB) ( 273 )

The ratio of the number of emitted pions from the target side to that from the projectile side at target rapidity within the reaction plane is investigated for the study of the pion dynamics with an isospin-dependent quantum molecular dynamic model. The results show that high-energy pions are emitted preferentially towards the target side and, therefore, they are freezed out at the early stage of the collision. By contrast, low-energy pions are emitted predominantly in the opposite direction, which means that they are emitted in a later stage. This argument is based on the shadowing effect caused by the interaction of pions with the spectator matter in peripheral collisions at target or projectile rapidities. This phenomenon disappears in the central collision or at midrapidity due to the weaker shadowing effect. The calculated ratios are also compared with the experimental data.

A High-Precision Calculation of Bond Length and Spectroscopic Constants of Hg2 Based on the Coupled-Cluster Theory with Spin–Orbit Coupling
TU Zhe-Yan, WANG Wen-Liang
Chin. Phys. Lett. 2015, 32 (06): 063101 .   DOI: 10.1088/0256-307X/32/6/063101
Abstract   PDF(pc) (434KB) ( 8360 )
Based on the two-component relativistic effective core potential and matched basis sets cc-pwcvnz-pp (n=Q, 5), combining the completed basis-set extrapolation of electronic correlation energy and the fourth-order polynomial fitting technique, the bond length and spectroscopic constants of Hg2 are studied by the coupled cluster theory with spin–orbit coupling. Spin–orbit coupling is included in the post Hartree–Fock procedure, i.e., in the coupled-cluster iteration, to obtain more reliable theoretical results. The results show that our theoretical values agree with the experimental values very well and will be helpful to understand the spectral character of Hg2.
Population Distribution of Excited States in Cs Electrodeless Discharge Lamp
ZHU Chuan-Wen, TAO Zhi-Ming, CHEN Mo, LIU Zhong-Zheng, ZHANG Xiao-Gang, ZHANG Sheng-Nan, CHEN Jing-Biao
Chin. Phys. Lett. 2015, 32 (06): 063201 .   DOI: 10.1088/0256-307X/32/6/063201
Abstract   PDF(pc) (522KB) ( 298 )
We measure the intensity of fluorescence spectral lines of Cs atoms in an electrodeless discharge lamp from visible light to the near-infrared region of 400–1000 nm. To build an excited state Faraday anomalous dispersion optical filter, the population ratios between the excited states are calculated by rate equations and the spontaneous transition probabilities. The electrodeless discharge lamp with populations in the excited states can be used to realize the frequency stabilization reference for lasers at multiwavelength and the excited state Faraday anomalous dispersion optical filter for submarine communication applications in blue–green wavelengths to simplify the system.
Charge Resonance Enhanced Multiple Ionization of H2O Molecules in Intense Laser Fields
LIU Hong, LI Min, XIE Xi-Guo, WU Cong, DENG Yong-Kai, WU Cheng-Yin, GONG Qi-Huang, LIU Yun-Quan
Chin. Phys. Lett. 2015, 32 (06): 063301 .   DOI: 10.1088/0256-307X/32/6/063301
Abstract   PDF(pc) (1534KB) ( 356 )
We perform a kinetically complete measurement on the fragmentation of Coulomb explosion of H2O molecules in intense few-cycle linearly and circularly polarized laser fields. Both the fragmentations of H2O3+ and H2O4+ reveal the concerted pathway of dissociation. The length of the O–H bond prior to the Coulomb explosion of both molecular ions is sensitive to the laser pulse duration and laser intensity. However, the bending angle of H–O–H is less sensitive to the pulse duration and laser intensity. We introduce the mechanism of charge resonance enhanced double ionization to elucidate the triple (or quadruple) dissociative ionization dynamics of H2O, in which two electrons are non-adiabatically localized at the protons of the precursor ion H2O+ (or H2O2+) and are released simultaneously due to the over barrier ionization in the combined laser field and molecular ionic potential. Such charge resonance enhanced multiple ionization is not suppressed in few-cycle laser fields and elliptically polarized laser fields.
Generation of Isolated Attosecond Pulse from Asymmetric Molecular Ions by Introducing Half-Cycle-Like Laser Fields
LIU Sha-Sha, MIAO Xiang-Yang
Chin. Phys. Lett. 2015, 32 (06): 063302 .   DOI: 10.1088/0256-307X/32/6/063302
Abstract   PDF(pc) (707KB) ( 271 )
We propose an efficient method for the generation of an isolated attosecond pulse from the asymmetric molecular ions HeH2+ by adding a half-cycle-like field (HCLF) to the fundamental driving laser field. The high-order harmonic generation (HHG) is investigated by numerically solving the time-dependent Schr?dinger equation. By performing the time-frequency distributions and the electronic wave packet probability densities, we find that the optimizing combined field is not only useful for extending the HHG cutoff, but also for simplifying the recombination channels through controlling the electron localization. In addition, by adjusting the intensity of the HCLF, a dominant short quantum path is selected to contribute the HHG spectrum. As a result, a 75-as isolated attosecond pulse is obtained by superposing a proper range of the harmonics.
Photon Statistical Properties of Single Terrylene Molecules in P-Terphenyl Crystals
HAN Bai-Ping, ZHENG Yu-Jun, HU Feng, FAN Qiu-Bo
Chin. Phys. Lett. 2015, 32 (06): 063303 .   DOI: 10.1088/0256-307X/32/6/063303
Abstract   PDF(pc) (597KB) ( 343 )
We consider the photon emission statistical properties of a single molecule under pump-probe field driving, using the generating function method. The first- and second-order moments of statistical quantities are presented. Derived from the first-order moment, the line shapes are in good agreement with the experimental results. Derived from the second-order moment, Mandel's Q parameters show an obvious quantum effect of photon statistical distribution, i.e., the anti-bunching effect.
A kW Continuous-Wave Ytterbium-Doped All-Fiber Laser Oscillator with Domestic Fiber Components and Gain Fiber
LIAO Lei, LIU Peng, XING Ying-Bin, WANG Yi-Bo, PENG Jing-Gang, DAI Neng-Li, LI Jin-Yan, HE Bing, ZHOU Jun
Chin. Phys. Lett. 2015, 32 (06): 064201 .   DOI: 10.1088/0256-307X/32/6/064201
Abstract   PDF(pc) (810KB) ( 695 )
We demonstrate a kW continuous-wave ytterbium-doped all-fiber laser oscillator with all domestic fiber components: a 7×1 fused fiber bundle combiner, a fiber Bragg grating and a double-clad gain fiber. The oscillator operates at 1079.48 nm with 80.94% slope efficiency and shows no limit of temperature and nonlinear effects. These indicate that the passive fiber components and the gain fiber are all qualified for the high power environment. No evidence of the signal power roll-over shows that this oscillator possesses the capacity to higher output with available pump power.
Probing of Ultrafast Plasmon Dynamics on Gold Bowtie Nanostructure Using Photoemission Electron Microscopy
QIN Jiang, JI Bo-Yu, HAO Zuo-Qiang, LIN Jing-Quan
Chin. Phys. Lett. 2015, 32 (06): 064202 .   DOI: 10.1088/0256-307X/32/6/064202
Abstract   PDF(pc) (790KB) ( 449 )
We report the direct imaging of plasmon on the tips of nano-prisms in a bowtie structure excited by 7 fs laser pulses and probing of ultrafast plasmon dynamics by combining the pump-probe technology with three-photon photoemission electron microscopy. Different photoemission patterns induced by the plasmon effect are observed when the bowties are excited by s- and p-polarized femtosecond laser pulses. A series of images of the evolution of local surface plasmon modes on different tips of the bowtie are obtained by the time-resolved three-photon photoemission electron microscopy, and the result discloses that plasmon excitation is dominated by the interference of the pump and probe pulses within the first 13 fs of the delay time, and thereafter the individual plasmon starts to oscillate on its own characteristic resonant frequencies.
Optimization of High Power 1.55-µm Single Lateral Mode Fabry–Perot Ridge Waveguide Lasers
KE Qing, TAN Shao-Yang, LU Dan, ZHANG Rui-Kang, WANG Wei, JI Chen
Chin. Phys. Lett. 2015, 32 (06): 064203 .   DOI: 10.1088/0256-307X/32/6/064203
Abstract   PDF(pc) (622KB) ( 511 )
Optimization of the high power single-lateral-mode double-trench ridge waveguide semiconductor laser based on InGaAsP/InP quantum-well heterostructures with a separate confinement layer is reported. Two different waveguide structures of Fabry–Perot lasers emitting at a wavelength of 1.55 μm are fabricated. The influence of an effective lateral refractive index step on the maximum output power is investigated. A cw single mode output power of 165 mW is obtained for a 1-mm-long uncoated laser.
Propagation of Partially Coherent Elegant Hermite-Cosh-Gaussian Beam in Non-Kolmogorov Turbulence
ZHANG Wen-Fu, LIAN Jie, WANG Ying-Shun, HU Xue-Yuan, SUN Zhao-Zong, ZHAO Ming-Lin, WANG Ying, LI Meng-Meng
Chin. Phys. Lett. 2015, 32 (06): 064204 .   DOI: 10.1088/0256-307X/32/6/064204
Abstract   PDF(pc) (758KB) ( 284 )
Based on the extended Huygens–Fresnel integral, analytical propagation expressions for the rms beam width and angular of partially coherent elegant Hermite cosh Gaussian beam (EHChGB) in non-Kolmogorov turbulence are derived. The effects of exponent value, inner and outer scales of non-Kolmogorov turbulence on partially coherent EHChGB are investigated quantitatively.
Simultaneously Suppressing Low-Frequency and Relaxation Oscillation Intensity Noise in a DBR Single-Frequency Phosphate Fiber Laser
XIAO Yu, LI Can, XU Shan-Hui, FENG Zhou-Ming, YANG Chang-Sheng, ZHAO Qi-Lai, YANG Zhong-Min
Chin. Phys. Lett. 2015, 32 (06): 064205 .   DOI: 10.1088/0256-307X/32/6/064205
Abstract   PDF(pc) (654KB) ( 432 )
Effective multiple optoelectronic feedback circuits for simultaneously suppressing low-frequency and relaxation oscillation intensity noise in a single-frequency phosphate fiber laser are demonstrated. The forward transfer function, which relates the laser output intensity to the pump modulations, is measured and analyzed. A custom two-path feedback system operating at different frequency bands is designed to adjust the pump current directly. The relative intensity noise is decreased by 20 dB from 0.2 to 5 kHz and over 10 dB from 5 to 10 kHz. The relaxation oscillation peak is suppressed by 22 dB. In addition, a long term (24 h) laser instability of less than 0.05% is achieved.
Extraordinary Optical Confinement in a Silicon Slot Waveguide with Metallic Gratings
LIANG Han, ZHAN Ke-Tao, HOU Zhi-Ling
Chin. Phys. Lett. 2015, 32 (06): 064206 .   DOI: 10.1088/0256-307X/32/6/064206
Abstract   PDF(pc) (551KB) ( 274 )
We present a silicon slot waveguide with metallic gratings embedded on the silicon surface in the slot region. The dependence of the optical coupling between two silicon wires on the width of the metal gap and the slot size are studied in detail. The results show that the optical field in the slot region with metallic gratings is significantly enhanced compared with the traditional slot waveguide due to the surface plasmon polaritons coupling on metallic gratings. The extraordinary optical confinement is attributed to the low effective dielectric constant of metallic gratings. The effective dielectric constant decreases with the increasing wavelength, and reaches the minimum when the width of the metal gap is about 0.01 times the wavelength.
Effect of In Diffusion on the Property of Blue Light-Emitting Diodes
ZENG Yong-Ping, LIU Wen-Jie, WENG Guo-En, ZHAO Wan-Ru, ZUO Hai-Jie, YU Jian, ZHANG Jiang-Yong, YING Lei-Ying, ZHANG Bao-Ping
Chin. Phys. Lett. 2015, 32 (06): 064207 .   DOI: 10.1088/0256-307X/32/6/064207
Abstract   PDF(pc) (681KB) ( 305 )
In diffusion to blue light-emitting diode (LED) wafers is performed by the inductive coupled plasma (ICP) treatment of a covering layer of indium tin oxide (ITO) on the wafer surface. The electrical property of the p-type contact is improved and the redshift of photoluminescence (PL) from the InGaN quantum well of the wafer is found. Measurements by x-ray photoelectron spectroscopy (XPS) demonstrate that In atoms have diffused into p-GaN. Reflectance spectra of the sample surface reveal the variation caused by the ICP treatment. A model of compensation of the in-plane strain of the InGaN layer is used to explain the redshift of the PL data. Finally, LEDs are fabricated by using as-grown and ICP-treated wafers and their properties are compared. Under an injection current of 20 mA, LEDs with ICP-induced In doping show a decrease of 0.3 V in the forward voltage and an increase of 23% in the light output, respectively.
In-Fiber Mach–Zehnder Interferometer Based on Waist-Enlarged Taper and Core-Mismatching for Strain Sensing
ZHANG Yun-Shan, QIAO Xue-Guang, SHAO Min, LIU Qin-Peng
Chin. Phys. Lett. 2015, 32 (06): 064208 .   DOI: 10.1088/0256-307X/32/6/064208
Abstract   PDF(pc) (803KB) ( 429 )
An in-fiber Mach–Zehnder interferometer for strain measurement is proposed and experimentally demonstrated. The sensor consists of a taper followed by a short section of a multi-mode fiber (MMF) and a dispersion compensating fiber (DCF), which is sandwiched between two single mode fibers (SMFs). The taper is used as a fiber coupler to excite cladding modes in the SMF, and these cladding modes transmit within the MMF and the DCF. The core mode and the cladding modes interfere in the DCF–SMF fusion point to form intermodal interference. A well-defined interference spectrum is obtained in the experiment. Selected interference dips are used to measure the strain changes. The experimental results show that this device is sensitive to strain with the wavelength-referenced sensitivity of 2.6 pm/μ? and the power-referenced sensitivity of 0.0027 dB/μ?, respectively.
Stable Q-Switched Yb:NaY(WO4)2 Laser with Cr4+:YAG Saturable Absorber
LAN Rui-Jun
Chin. Phys. Lett. 2015, 32 (06): 064209 .   DOI: 10.1088/0256-307X/32/6/064209
Abstract   PDF(pc) (574KB) ( 270 )
The passively Q-switched Yb:NaY(WO4)2 (Yb:NaYW) laser is studied. By using Cr4+:YAG as the saturable absorber, a very stable pulse train is obtained. At a high pump power, the pulse to pulse timing jitter is measured to be less than 2% and the amplitude fluctuation is less than 4%. A Q-switched average output power of 2.3 W at 1029 nm is generated with a slope efficiency of 33.9%; the one-dimensional intensity distribution of the laser facula is of the Gaussian type. The output repetition rate, pulse energy, pulse width and peak power are 33.3 kHz, 70 μJ, 36 ns and 2.0 kW, respectively. The passively Q-switched process is simulated by solving the rate equations, the simulated results are in good agreement with the experimental data.
Transverse Optical Properties of the Eu3+:Y2SiO5 Crystal in Electromagnetically Induced Transparency
YANG Li-Ru, WANG Chun-Fang, ZHANG Da-Wei
Chin. Phys. Lett. 2015, 32 (06): 064210 .   DOI: 10.1088/0256-307X/32/6/064210
Abstract   PDF(pc) (732KB) ( 281 )
According to density matrix equations of the interaction between light and matter, the expression for the susceptibility of the Eu3+:Y2SiO5 crystal is obtained. When the control field is a Gaussian beam, we investigate and analyze the influence of probe detuning, the Rabi frequency of the control field and the laser line width on the transverse optical properties. We also analyze the influence of the dope-ion concentration on electromagnetically induced transparency (EIT). The analysis result indicates that the transmission is not a monotonic function of the dope-ion concentration. Based on the influences of various parameters on the transverse optical properties, we choose the appropriate parameters to realize the desired EIT and gradient refractive index, which has applications in focusing and imaging.
Cold Atom Cloud with High Optical Depth Measured with Large Duty Cycle
ZHANG Jun, GU Zhen-Jie, QIAN Peng, HAN Zhi-Guang, CHEN Jie-Fei
Chin. Phys. Lett. 2015, 32 (06): 064211 .   DOI: 10.1088/0256-307X/32/6/064211
Abstract   PDF(pc) (514KB) ( 472 )
We present a cold atom system with a dark-line two-dimensional magneto-optical trap, to increase the atomic density by suppressing the atomic radiation pressure. Optical depth (OD) and duty cycle are used to evaluate the system performance. We demonstrate a 100% increase in OD with the dark line, and obtain an ultrahigh OD of 264 with 10% for the duty cycle. Also, with an efficient dark line region, the OD could maintain above 100 with duty cycle as high as 30%. The cold atomic ensemble with an ultrahigh OD with a 10%–30% duty cycle is particularly advantageous in quantum information processing and communication.
On the Fundamental Mode Love Wave in Devices Incorporating Thick Viscoelastic Layers
LIU Jian-Sheng, WANG Li-Jun, HE Shi-Tang
Chin. Phys. Lett. 2015, 32 (06): 064301 .   DOI: 10.1088/0256-307X/32/6/064301
Abstract   PDF(pc) (535KB) ( 275 )
A detailed investigation is presented for Love waves (LWs) with thick viscoelastic guiding layers. A theoretical calculation and an experiment are carried out for LW devices incorporating an SU-8 guiding layer, an ST-90° X quartz substrate and two 28-μm periodic interdigital transducers. Both the calculated and the measured results show an increase in propagation velocity when h/λ>0.05. The measured insertion loss of LWs is consistent with the calculated propagation loss. The insertion loss of bulk waves is also measured and is compared with that of LWs.
The Effects of Seamounts on Sound Propagation in Deep Water
LI Wen, LI Zheng-Lin, ZHANG Ren-He, QIN Ji-Xing, LI Jun, NAN Ming-Xing
Chin. Phys. Lett. 2015, 32 (06): 064302 .   DOI: 10.1088/0256-307X/32/6/064302
Abstract   PDF(pc) (1659KB) ( 328 )
A propagation experiment was conducted in the South China Sea in 2014 with a flat bottom and seamounts respectively by using explosive sources. The effects of seamounts on sound propagation are analyzed by using the broadband signals. It is observed that the transmission loss (TL) decreases up to 7 dB for the signals in the first shadow zone due to the seamount reflection. Moreover, the TL might increase more than 30 dB in the converge zone due to the shadowing by seamounts. Abnormal TLs and pulse arrival structures at different ranges are explained by using the ray and wave theory. The experimental TLs and arrival pulses are compared with the numerical results and found to be in good agreement.
Horizontal-Longitudinal Correlations of Acoustic Field in Deep Water
LI Jun, LI Zheng-Lin, REN Yun, LI Wen, ZHANG Ren-He
Chin. Phys. Lett. 2015, 32 (06): 064303 .   DOI: 10.1088/0256-307X/32/6/064303
Abstract   PDF(pc) (632KB) ( 293 )
The horizontal-longitudinal correlations of the acoustic field in deep water are investigated based on the experimental data obtained in the South China Sea. It is shown that the horizontal-longitudinal correlation coefficients in the convergence zone are high, and the correlation length is consistent with the convergence zone width, which depends on the receiver depth and range. The horizontal-longitudinal correlation coefficients in the convergence zone also have a division structure for the deeper receiver. The signals from the second part of the convergence zone are still correlated with the reference signal in the first part. The horizontal-longitudinal correlation coefficients in the shadow zone are lower than that in the convergence zone, and the correlation length in the shadow zone is also much shorter than that in the convergence zone. The numerical simulation results by using the normal modes theory are qualitatively consistent with the experimental results.
Electron Cyclotron Emission Imaging Observations of m/n=1/1 and Higher Harmonic Modes during Sawtooth Oscillation in ICRF Heating Plasma on EAST
AZAM Hussain, GAO Bing-Xi, LIU Wan-Dong, XIE Jin-Lin, the EAST Team
Chin. Phys. Lett. 2015, 32 (06): 065201 .   DOI: 10.1088/0256-307X/32/6/065201
Abstract   PDF(pc) (1500KB) ( 242 )
The m/n=1/1 and its higher harmonic modes are observed in sawtooth oscillations by using the novel high-resolution 2D ECE imaging system on the experimental advanced superconducting Tokamak (EAST). Higher harmonic modes are appearing for a short time during the crash phase of sawtooth oscillation in lower βp plasma, which is not the preferable position in the poloidal cross section. These modes generate sharp pressure points on the inversion radius during the crash phase of sawtooth oscillation. Furthermore, reconnection events proceed in two distinctive phases. In the first phase, a small amount of heat is expelled through the weak reconnection while in the second phase the remaining large quantity of heat and particles emerged rapidly from the hot core to the peripheral region of the inversion radius. In addition, these harmonic modes are only found before and after the ICRF pulse, while in the ICRF pulse only the (1,1) mode exists in the sawtooth oscillation.
Negative Refraction in a Lossy Plasma Layer
PENG Li, GUO Bin, GAO Ming-Xiang, CAI Xin
Chin. Phys. Lett. 2015, 32 (06): 065202 .   DOI: 10.1088/0256-307X/32/6/065202
Abstract   PDF(pc) (539KB) ( 293 )
Negative refraction at the interface between air and a lossy plasma layer is theoretically analyzed based on the inhomogeneous wave theory. The phenomenon of negative refraction, which arises from the negative refraction angle, can occur when a transverse magnetic wave is incident from air to the lossy plasma layer under certain conditions. The formula of the negative refraction angle is derived, and the dependences of the negative refraction angle on the angle of incidence, frequency of incidence, and lossy plasma layer are analytically investigated. The parameter dependences of the effects are calculated and discussed.
Simulation of Plasma Disruptions for HL-2M with the DINA Code
Chin. Phys. Lett. 2015, 32 (06): 065203 .   DOI: 10.1088/0256-307X/32/6/065203
Abstract   PDF(pc) (1807KB) ( 578 )
Plasma disruption is often an unavoidable aspect of tokamak operations. It may cause severe damage to in-vessel components such as the vacuum vessel conductors, the first wall and the divertor target plates. Two types of disruption, the hot-plasma vertical displacement event and the major disruption with a cold-plasma vertical displacement event, are simulated by the DINA code for HL-2M. The time evolutions of the plasma current, the halo current, the magnetic axis, the minor radius, the elongation as well as the electromagnetic force and eddy currents on the vacuum vessel during the thermal quench and the current quench are investigated. By comparing the electromagnetic forces before and after the disruption, we find that the disruption causes great damage to the vacuum vessel conductors. In addition, the hot-plasma vertical displacement event is more dangerous than the major disruption with the cold-plasma vertical displacement event.
Enhanced Magnetic and Dielectric Properties in Low-Content Tb-Doped BiFeO3 Nanoparticles
GUO Min-Chen, LIU Wei-Fang, WU Ping, ZHANG Hong, XU Xun-Ling, WANG Shou-Yu, RAO Guang-Hui
Chin. Phys. Lett. 2015, 32 (06): 066101 .   DOI: 10.1088/0256-307X/32/6/066101
Abstract   PDF(pc) (1649KB) ( 419 )
Bi1?xTbxFeO3 (x=0, 0.01, 0.03 and 0.05) nanoparticles are synthesized by the sol-gel method. A single phase perovskite rhombohedral structure of all the samples is established from the Rietveld refined XRD patterns. The substitution of Tb3+ ions to Bi3+ decreases the particle size and enhances the ferromagnetic properties of this system. Interestingly a large maximum magnetization value of 1.73 emu/g at 50 kOe can be observed in 1% Tb-doped sample at 300 K. The decrease in band gap may result from the reduced particle size, while the leakage current density also decreases, which is mainly explained by the variation of oxygen vacancies.
Bismuth Effects on Electronic Levels in GaSb(Bi)/AlGaSb Quantum Wells Probed by Infrared Photoreflectance
CHEN Xi-Ren, SONG Yu-Xin, ZHU Liang-Qing, QI Zhen, ZHU Liang, ZHA Fang-Xing, GUO Shao-Ling, WANG Shu-Min, SHAO Jun
Chin. Phys. Lett. 2015, 32 (06): 067301 .   DOI: 10.1088/0256-307X/32/6/067301
Abstract   PDF(pc) (533KB) ( 414 )
GaSb(Bi)/Al0.2Ga0.8Sb single quantum wells are characterized by a Fourier transform infrared spectrometer-based photoreflectance method at 77 K. Spatially direct and indirect transitions between the electronic levels at and above the effective band gap are well resolved. The shifts of the electronic levels with Bi incorporation are identified quantitatively. The results show that the upshift of the valence band edge is clarified to be dominant, while the Bi-induced downshift of the conduction band edge does exist and contributes to the band gap reduction in the GaSbBi quantum-well layer by (29±6)%.
First-Principles Calculations of the Quantum Size Effects on the Stability and Reactivity of Ultrathin Ru(0001) Films
WU Ming-Yi, JIA Yu, SUN Qiang
Chin. Phys. Lett. 2015, 32 (06): 067302 .   DOI: 10.1088/0256-307X/32/6/067302
Abstract   PDF(pc) (665KB) ( 282 )
We carry out first-principles calculations of Ru(0001) films up to 30 monolayers (MLs) to study the quantum size effect (QSE) of Ru films for two cases: the freestanding Ru films and Ru films on Pt(111) substrates. Our studies show that the properties of these films (surface energy, work-function, charge density decay length in a vacuum and chemical reactivity) exhibit pronounced oscillatory behavior as a function of the film thickness, with an oscillation period of about four MLs for both cases due to the relationship of the match between the Fermi wave vector and the film thickness. Due to the localization of d-electron of Ru films, these quantum oscillations almost disappear when the thickness of the film is more than ~20 ML for the free standing Ru films, while for the Ru films on Pt substrates the oscillations disappear quickly when the thickness of the film is beyond ~13 ML. Our results reveal that the stability and reactivity of the Ru films could be tailored through QSE and the Ru bilayer grown on Pt substrates observed in the experiment is also related to the effect.
Identification of Topological Surface State in PdTe2 Superconductor by Angle-Resolved Photoemission Spectroscopy
LIU Yan, ZHAO Jian-Zhou, YU Li, LIN Cheng-Tian, LIANG Ai-Ji, HU Cheng, DING Ying, XU Yu, HE Shao-Long, ZHAO Lin, LIU Guo-Dong, DONG Xiao-Li, ZHANG Jun, CHEN Chuang-Tian, XU Zu-Yan, WENG Hong-Ming, DAI Xi, FANG Zhong, ZHOU Xing-Jiang
Chin. Phys. Lett. 2015, 32 (06): 067303 .   DOI: 10.1088/0256-307X/32/6/067303
Abstract   PDF(pc) (3441KB) ( 368 )

High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc at 1.7 K. Combined with theoretical calculations, we discover for the first time the existence of topologically nontrivial surface state with Dirac cone in PbTe2 superconductor. It is located at the Brillouin zone center and possesses helical spin texture. Distinct from the usual three-dimensional topological insulators where the Dirac cone of the surface state lies at the Fermi level, the Dirac point of the surface state in PdTe2 lies deeply below the Fermi level at ∼1.75 eV binding energy and is well separated from the bulk states. The identification of topological surface state in PdTe2 superconductor deeply below the Fermi level provides a unique system to explore new phenomena and properties and opens a door for finding new topological materials in transition metal chalcogenides.

Electronic Structure, Irreversibility Line and Magnetoresistance of Cu0.3Bi2Se3 Superconductor
YI He-Mian, CHEN Chao-Yu, SUN Xuan, XIE Zhuo-Jin, FENG Ya, LIANG Ai-Ji, PENG Ying-Ying, HE Shao-Long, ZHAO Lin, LIU Guo-Dong, DONG Xiao-Li, ZHANG Jun, CHEN Chuang-Tian, XU Zu-Yan, GU Gen-Da, ZHOU Xing-Jiang
Chin. Phys. Lett. 2015, 32 (06): 067401 .   DOI: 10.1088/0256-307X/32/6/067401
Abstract   PDF(pc) (1331KB) ( 403 )

CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ∼4000 Oe for the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9 K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. These observations provide useful information for further study of this possible candidate for topological superconductors.

Possible p-Wave Superconductivity in Epitaxial Bi/Ni Bilayers
GONG Xin-Xin, ZHOU He-Xin, XU Peng-Chao, YUE Di, ZHU Kai, JIN Xiao-Feng, TIAN He, ZHAO Ge-Jian, CHEN Ting-Yong
Chin. Phys. Lett. 2015, 32 (06): 067402 .   DOI: 10.1088/0256-307X/32/6/067402
Abstract   PDF(pc) (1247KB) ( 1302 )

Superconductivity (SC) is one of the most intriguing physical phenomena in nature. Nucleation of SC has long been considered highly unfavorable if not impossible near ferromagnetism, in low dimensionality and, above all, out of non-superconductor. Here we report observation of SC with TC near 4 K in Ni/Bi bilayers that defies all known paradigms of superconductivity, where neither ferromagnetic Ni film nor rhombohedra Bi film is superconducting in isolation. This highly unusual SC is independent of the growth order (Ni/Bi or Bi/Ni), but highly sensitive to the constituent layer thicknesses. Most importantly, the SC, distinctively non-s pairing, is triggered from, but does not occur at, the Bi/Ni interface. Using point contact Andreev reflection, we show evidences that the unique SC, naturally compatible with magnetism, is triplet p-wave pairing.

Evaluation of the Ultrafast Thermal Manipulation of Magnetization Precession in Ferromagnetic Semiconductor (Ga,Mn)As
LI Hang, ZHANG Xin-Hui
Chin. Phys. Lett. 2015, 32 (06): 067501 .   DOI: 10.1088/0256-307X/32/6/067501
Abstract   PDF(pc) (671KB) ( 228 )
We present a quantitative evaluation study of the thermal effect responsible for laser-triggered collective magnetization dynamics in a ferromagnetic (Ga,Mn)As film without applying the external magnetic field by employing the pump-probe magneto-optical spectroscopy. Our observation shows that the effect of ultrafast laser heating on the manipulation of magnetization precession in a (Ga,Mn)As film is not exactly equivalent to that of the ambient temperature increase, and needs to be carefully analyzed by considering the temperature-dependent specific heat of (Ga,Mn)As. The transient modulation of magnetocrystalline anisotropy via ultrafast laser heating at low temperature exhibits a higher sensitivity than that at high temperature. The quantitative analysis of the laser-heating manipulated magnetization precession presented in this work is helpful for evaluating the laser-triggered ultrafast magnetization dynamics in (Ga,Mn)As films.
Magnetization Reversal Process of Single Crystal α-Fe Containing a Nonmagnetic Particle
LI Yi, XU Ben, HU Shen-Yang, LI Yu-Lan, LI Qiu-Lin, LIU Wei
Chin. Phys. Lett. 2015, 32 (06): 067502 .   DOI: 10.1088/0256-307X/32/6/067502
Abstract   PDF(pc) (939KB) ( 256 )
The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau–Lifshitz–Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.
Nitrogen-Induced Change of Magnetic Properties in Antiperovskite-Type Carbide: Mn3InC
MALIK Muhammad-Imran, SUN Ying, DENG Si-Hao, SHI Ke-Wen, HU Peng-Wei, WANG Cong
Chin. Phys. Lett. 2015, 32 (06): 067503 .   DOI: 10.1088/0256-307X/32/6/067503
Abstract   PDF(pc) (1127KB) ( 338 )
The effects of N substitution on the magnetic properties of Mn3InC1?xNx (0.0≤x≤0.7) are investigated systematically. Partial substitution of N for C leads to the monotonic reduction in both the Curie temperature TC and saturated magnetization MS. The final results obtained from thermo-magnetic curves demonstrate that Mn3InC1?xNx samples show a magnetic phase transition from a paramagnetic (PM) state to a ferrimagnetic (FIM) state consisting of ferromagnetic (FM) and antiferromagnetic (AFM) components. In addition, there is a competition between the AFM component and the FM component in the FIM state with the change of the N-doped content. Magnetic measurements of Mn3InC at 100 Oe and 5000 Oe indicate the metastability and the coexistence of different magnetic phases at lower temperature. The spans of FIM phase broaden gradually with further N doping. The mechanism for the induction of the complicated magnetic state is still in controversy. However, the results clearly show that the doping at the X site in antiperovskite Mn3AX materials is as useful as that of the A and Mn sites.
Magnetic Field Measurement with Heisenberg Limit Based on Solid Spin NOON State
ZHOU Lei-Ming, DONG Yang, SUN Fang-Wen
Chin. Phys. Lett. 2015, 32 (06): 067601 .   DOI: 10.1088/0256-307X/32/6/067601
Abstract   PDF(pc) (586KB) ( 340 )
The maximum entangled number state (NOON state) can improve the sensitivity of physical quantity measurement to the Heisenberg limit 1/N. In this work, the magnetic field measurement based on the individual solid spin NOON state is investigated. Based on the tunable effective coupling coefficient, we propose a generation scheme of the three-spin NOON state, i.e, the Greenberger–Horne–Zeilinger (GHZ) state, and discussed the measurement resolution reduction due to decoherence. It is unnecessary to entangle spins as many as possible when decoherence exists. In practice, defect spins in diamond and 31P donors with long coherence time can be applied with current techniques in the nano-scaled high resolution magnetic measurement.
Graphene-Based Tunable Polarization Insensitive Dual-Band Metamaterial Absorber at Mid-Infrared Frequencies
ZHANG Yu-Ping, LI Tong-Tong, LV Huan-Huan, HUANG Xiao-Yan, ZHANG Xiao, XU Shi-Lin, ZHANG Hui-Yun
Chin. Phys. Lett. 2015, 32 (06): 068101 .   DOI: 10.1088/0256-307X/32/6/068101
Abstract   PDF(pc) (643KB) ( 557 )
A graphene-based tunable dual-band metamaterial absorber which is polarization insensitive is numerically proposed at mid-infrared frequencies. In numerical simulation the metamaterial absorber exhibits two absorption peaks at the resonance wavelengths of 6.246 μm and 6.837 μm when the Fermi level of graphene is fixed at 0.6 eV. Absorption spectra at different Fermi levels of graphene are displayed and tuning functions are discussed in detail. Both the resonance wavelengths of the absorber blue shift with the increase in Fermi level of graphene. Moreover, the surface current distributions on the gold resonator and ground plane at the two resonance wavelengths are simulated to deeply understand the physical mechanism of resonance absorption.
Theoretical and Experimental Optimization of InGaAs Channels in GaAs PHEMT Structure
GAO Han-Chao, YIN Zhi-Jun
Chin. Phys. Lett. 2015, 32 (06): 068102 .   DOI: 10.1088/0256-307X/32/6/068102
Abstract   PDF(pc) (545KB) ( 309 )
The ground-state energy level (GEL) and electron distribution of GaAs pseudomorphic high-electron-mobility transistors (PHEMTs) are analyzed by a self-consistent solution to the Schr?dinger–Poisson equations. The indium composition and thickness of the InGaAs channel are optimized according to the GEL position. The GEL position is not in direct proportion to 1/d2 (d is the channel thickness) by considering the influence of electron distribution in the InGaAs channel. Indium composition 0.22 and channel thickness 9 nm are obtained by considering the mismatch between InGaAs and AlGaAs. Several PHEMT samples are grown according to the theoretical results and mobility 6300 cm2/V?s is achieved.
Simulation of Dendritic Growth with Melt Convection in Solidification of Ternary Alloys
SUN Dong-Ke, ZHANG Qing-Yu, CAO Wei-Sheng, ZHU Ming-Fang
Chin. Phys. Lett. 2015, 32 (06): 068103 .   DOI: 10.1088/0256-307X/32/6/068103
Abstract   PDF(pc) (808KB) ( 325 )
A cellular automaton-lattice Boltzmann coupled model is extended to study the dendritic growth with melt convection in the solidification of ternary alloys. With a CALPHAD-based phase equilibrium engine, the effects of melt convection, solutal diffusion, interface curvature and preferred growth orientation are incorporated into the coupled model. After model validation, the multi dendritic growth of the Al-4.0 wt%Cu-1.0 wt%Mg alloy is simulated under the conditions of pure diffusion and melt convection. The result shows that the dendritic growth behavior, the final microstructure and microsegregation are significantly influenced by melt convection in the solidification.
Molecular Beam Epitaxy Growth and Scanning Tunneling Microscopy Study of Pyrite CuSe2 Films on SrTiO3
PENG Jun-Ping, ZHANG Hui-Min, SONG Can-Li, JIANG Ye-Ping, WANG Li-Li, HE Ke, XUE Qi-Kun, MA Xu-Cun
Chin. Phys. Lett. 2015, 32 (06): 068104 .   DOI: 10.1088/0256-307X/32/6/068104
Abstract   PDF(pc) (1056KB) ( 417 )
We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide (CuSe2) films on SrTiO3(001). Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski–Krastanov (layer-plus-island) mode with a preferential orientation of (111). Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2×√3 and √3×√3-R30°. The Cu termination is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.
Set Programming Method and Performance Improvement of Phase Change Random Access Memory Arrays
FAN Xi, CHEN Hou-Peng, WANG Qian, WANG Yue-Qing, LV Shi-Long, LIU Yan, SONG Zhi-Tang, FENG Gao-Ming, LIU Bo
Chin. Phys. Lett. 2015, 32 (06): 068301 .   DOI: 10.1088/0256-307X/32/6/068301
Abstract   PDF(pc) (850KB) ( 310 )
A novel slow-down set waveform is proposed to improve the set performance and a 1 kb phase change random access memory chip fabricated with a 130 nm CMOS technology is implemented to investigate the set performance by different set programming strategies based on this new set pulse. The amplitude difference (I1?I2) of the set pulse is proved to be a crucial parameter for set programming. We observe and analyze the cell characteristics with different I1?I2 by means of thermal simulations and high-resolution transmission electron microscopy, which reveal that an incomplete set programming will occur when the proposed slow-down pulse is set with an improperly high I1?I2. This will lead to an amorphous residue in the active region. We also discuss the programming method to avoid the set performance degradations.
Ultralow Specific on-Resistance Trench MOSFET with a U-Shaped Extended Gate
WANG Zhuo, LI Peng-Cheng, ZHANG Bo, FAN Yuan-Hang, XU Qing, LUO Xiao-Rong
Chin. Phys. Lett. 2015, 32 (06): 068501 .   DOI: 10.1088/0256-307X/32/6/068501
Abstract   PDF(pc) (838KB) ( 341 )
An ultralow specific on-resistance (Ron,sp) trench metal-oxide-semiconductor field effect transistor (MOSFET) with an improved off-state breakdown voltage (BV) is proposed. It features a U-shaped gate around the drift region and an oxide trench inserted in the drift region (UG MOSFET). In the on-state, the U-shaped gate induces a high density electron accumulation layer along its sidewall, which provides a low-resistance current path from the source to the drain, realizing an ultralow Ron,sp. The value of Ron,sp is almost independent of the drift doping concentration, and thus the UG MOSFET breaks through the contradiction relationship between Ron,sp and the off-state BV. Moreover, the oxide trench folds the drift region, enabling the UG MOSFET to support a high BV with a shortened cell pitch. The UG MOSFET achieves an Ron,sp of 2 mΩ?cm2 and an improved BV of 216 V, superior to the best existing state-of-the-art transistors at the same BV level.
The Cu Based AlGaN/GaN Schottky Barrier Diode
LI Di, JIA Li-Fang, FAN Zhong-Chao, CHENG Zhe, WANG Xiao-Dong, YANG Fu-Hua, HE Zhi
Chin. Phys. Lett. 2015, 32 (06): 068502 .   DOI: 10.1088/0256-307X/32/6/068502
Abstract   PDF(pc) (734KB) ( 374 )
The electrical characteristics of Cu and Ni/Al AlGaN/GaN Schottky barrier diodes on Si substrates are compared. The onset voltage of Cu Schottky diodes is about 0.4 V less than the Ni/Al contact. For the Cu/Ni Schottky contact, the leakage current is 4.7×10?7 A/mm at ?10 V. After annealing, the leakage current is decreased to 3.7×10?7 A/mm for 400°C or 4.6×10?8 A/mm for 500°C, respectively. The electrical property is affected by the thickness ratio of Cu to Ni. The Cu/Ni for 80/20 nm shows a low onset voltage, while the Cu/Ni for 20/80 nm shows a low leakage current. Both breakdown voltages are above 720 V.
A Strategy for Magnifying Vibration in High-Energy Orbits of a Bistable Oscillator at Low Excitation Levels
WANG Guang-Qing, LIAO Wei-Hsin
Chin. Phys. Lett. 2015, 32 (06): 068503 .   DOI: 10.1088/0256-307X/32/6/068503
Abstract   PDF(pc) (1081KB) ( 261 )
This work focuses on how to maintain a high-energy orbit motion of a bistable oscillator when subjected to a low level excitation. An elastic magnifier (EM) positioned between the base and the bistable oscillator is used to magnify the base vibration displacement to significantly enhance the output characteristics of the bistable oscillator. The dimensionless electromechanical equations of the bistable oscillator with an EM are derived, and the effects of the mass and stiffness ratios between the EM and the bistable oscillator on the output displacement are studied. It is shown that the jump phenomenon occurs at a lower excitation level with increasing the mass and stiffness ratios. With the comparison of the displacement trajectories and the phase portraits obtained from experiments, it is validated that the bistable oscillator with an EM can effectively oscillate in a high-energy orbit and can generate a superior output vibration at a low excitation level as compared with the bistable oscillator without an EM.
Dynamics of Nano-Chain Diffusing in Porous Media
CHEN Jiang-Xing, ZHENG Qiang, HUANG Chun-Yun, XU Jiang-Rong, YING He-Ping
Chin. Phys. Lett. 2015, 32 (06): 068701 .   DOI: 10.1088/0256-307X/32/6/068701
Abstract   PDF(pc) (1293KB) ( 268 )
A coarse-grained model is proposed to study the dynamics of a nano-chain diffusing in porous media. The simulation utilizes a hybrid method which combines stochastic rotation dynamics with molecular dynamics. Solvent molecules are explicitly taken into account to represent the hydrodynamic interactions and random fluctuations. The conformation, relaxation, and diffusion properties of a polymer chain are investigated by changing the density degree of the obstacle matrix. It is found that the average size of the chain is a non-monotonic function of the obstacle volume fraction φ. A dense environment may contribute to extending a linear chain, which can be characterized by larger exponents in the corresponding power law. The relaxation behavior of a stretched chain to a steady state shows dramatic crossover from exponent to power-law relaxation when the values of φ are increased. The dependence of the diffusion coefficient on the chain size is also studied. Various kinds of scaling properties are presented and discussed. The results can give additional insight into the density effect of porous media on polymer structure and dynamics.
Structural Modeling and Characteristics Analysis of Flow Interaction Networks in the Internet
WU Xiao-Yu, GU Ren-Tao, PAN Zhuo-Ya, JIN Wei-Qi, JI Yue-Feng
Chin. Phys. Lett. 2015, 32 (06): 068901 .   DOI: 10.1088/0256-307X/32/6/068901
Abstract   PDF(pc) (512KB) ( 319 )
Applying network duality and elastic mechanics, we investigate the interactions among Internet flows by constructing a weighted undirected network, where the vertices and the edges represent the flows and the mutual dependence between flows, respectively. Based on the obtained flow interaction network, we find the existence of 'super flow' in the Internet, indicating that some flows have a great impact on a huge number of other flows; moreover, one flow can spread its influence to another through a limited quantity of flows (less than 5 in the experimental simulations), which shows strong small-world characteristics like the social network. To reflect the flow interactions in the physical network congestion evaluation, the 'congestion coefficient' is proposed as a new metric which shows a finer observation on congestion than the conventional one.
Erratum: Laser-Induced Graphite Plasma Kinetic Spectroscopy under Different Ambient Pressures [Chin. Phys. Lett. Vol. 32, No. 4, 043201(2015)]
K. Chaudhary, S. Rosalan, M. S. Aziz, M. Bahadoran, J Ali, P. P. Yupapin, N. Bidin, Saktioto
Chin. Phys. Lett. 2015, 32 (06): 069901 .   DOI: 10.1088/0256-307X/32/6/069901
Abstract   PDF(pc) (189KB) ( 157 )
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