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Volume 29 Issue 4
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GENERAL
New Mechanical Feature of Two-Solitary Wave to the KdV Equation
DAI Zheng-De**, WU Feng-Xia, LIU Jun and MU Gui
Chin. Phys. Lett. 2012, 29 (4): 040201 .   DOI: 10.1088/0256-307X/29/4/040201
Abstract   PDF(pc) (815KB) ( 1007 )
New breather solitary solution and two-solitary solutions depending on constant equilibrium solution to the Korteweg de Vries equation are obtained by using an extended homoclinic test approach. A new mechanical feature of a two-solitary wave, namely, dependence of propagation direction and shape on position of equilibrium point, is investigated.
New Exact Solutions to the (2+1)-Dimensional Ablowitz–Kaup–Newell–Segur Equation: Modification of the Extended Homoclinic Test Approach
Mohammad Najafi**,Maliheh Najafi,M. T. Darvishi
Chin. Phys. Lett. 2012, 29 (4): 040202 .   DOI: 10.1088/0256-307X/29/4/040202
Abstract   PDF(pc) (646KB) ( 1442 )
By means of modification of the extended homoclinic test approach (mEHTA), we obtain some new exact soliton solutions for the (2+1)-dimensional Ablowitz-Kaup-Newell-Segur (AKNS) equation by obtaining a bilinear closed form for it.
Anomalous Temperature Effects of the Entanglement of Two Coupled Qubits in Independent Environments
SHAN Chuan-Jia,**,CAO Shuai,XUE Zheng-Yuan,ZHU Shi-Liang
Chin. Phys. Lett. 2012, 29 (4): 040301 .   DOI: 10.1088/0256-307X/29/4/040301
Abstract   PDF(pc) (705KB) ( 681 )
We investigate the entanglement dynamical behavior of two coupled qubits via a Heisenberg XX interaction, which are connected with two independent finite temperature heat baths. By numerical simulations of the quantum master equation, it is found that the interesting phenomena of entanglement sudden death (ESD) as well as sudden birth (ESB) appear during the evolution process for particular initial states. We also show that two critical temperatures T1 (determining that the quantum state is entangled or separable) and T2 (where maximal stationary entanglement can be observed) exist, and stationary entanglement exhibits a non-monotonic behavior as a function of the finite temperature noise strength. These results enlarge the domain of the reasonable experimental temperature where stationary entanglement can be observable.
Enhancing Quantum Discord in Cavity QED by Applying Classical Driving Field
QIAN Yi,XU Jing-Bo**
Chin. Phys. Lett. 2012, 29 (4): 040302 .   DOI: 10.1088/0256-307X/29/4/040302
Abstract   PDF(pc) (1106KB) ( 623 )
We investigate the quantum discord dynamics in a cavity quantum electrodynamics system, which consists of two noninteracting two-level atoms driven by independent optical fields and classical fields, and find that the quantum discord vanishes only asymptotically although entanglement disappears suddenly during the time evolution in the absence of classical fields. It is shown that the amount of quantum discord can be increased by adjusting the classical driving fields because the increasing degree of the amount of quantum mutual information is greater than classical correlation by applying the classical driving fields. Finally, the influence of the classical driving field on the fidelity of the system is also examined.
New Geometry with All Killing Vectors Spanning the Poincaré Algebra
HUANG Chao-Guang,**,TIAN Yu,WU Xiao-Ning,XU Zhan,ZHOU Bin
Chin. Phys. Lett. 2012, 29 (4): 040303 .   DOI: 10.1088/0256-307X/29/4/040303
Abstract   PDF(pc) (474KB) ( 557 )
The new four-dimensional geometry whose Killing vectors span the Poincaré algebra is presented and its structure is analyzed. The new geometry can be regarded as the Poincaré-invariant solution of the degenerate extension of the vacuum Einstein field equations with a negative cosmological constant and provides a static cosmological spacetime with a Lobachevsky space. The motion of free particles in the spacetime is discussed.
Fermi-Decay Law of Bose–Einstein Condensate Trapped in an Anharmonic Potential
LIU Yuan,JIA Ya-Fei,LI Wei-Dong**
Chin. Phys. Lett. 2012, 29 (4): 040304 .   DOI: 10.1088/0256-307X/29/4/040304
Abstract   PDF(pc) (553KB) ( 478 )
The Fermi-decay law of Bose–Einstein condensate, which is trapped by a cigar-shaped anharmonic trap and subjected to a weak random perturbation, is investigated by numerically calculating quantum fidelity (Loschmidt echo), to reveal the coherence loss of the condensate. We find that there are three indispensable factors, anharmonic trap, weak random perturbation and nonlinear interaction, in charging of the Fermi-decay law. The anharmonic trap creates anharmonic oscillations, and the weak random perturbation causes coherence loss by disturbing their coherent oscillations, while the nonlinear interaction enhances the loss to the Fermi-decay law. Based on the Fermi-decay law, some suggestions are presented to prolong the coherent time during coherently manipulating condensates.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Boundary Conditions for NHEK through Effective Action Approach
CHEN Bin,NING Bo**,ZHANG Jia-Ju
Chin. Phys. Lett. 2012, 29 (4): 041101 .   DOI: 10.1088/0256-307X/29/4/041101
Abstract   PDF(pc) (425KB) ( 398 )
We study the asymptotic symmetry group (ASG) of the near horizon geometry of extreme Kerr black hole through the effective action approach developed by Porfyriadis and Wilczek (arXiv:1007.1031v1[gr-qc]). By requiring a finite boundary effective action, we derive a new set of asymptotic Killing vectors and boundary conditions, which are much more relaxed than the ones proposed by Matsuo Y et al. [Nucl. Phys. B 825 (2010) 231], and still allow a copy of a conformal group as its ASG. In the covariant formalism, the asymptotic charges are finite, with the corresponding central charge vanishing. By using the quasi-local charge and introducing a plausible cut-off, we find that the higher order terms of the asymptotic Killing vectors, which could not be determined through the effective action approach, contribute to the central charge as well. We also show that the boundary conditions suggested by Guica et al. [Phys. Rev. D 80 (2009) 124008] lead to a divergent first-order boundary effective action.
An Extra Phase for Two-Mode Coherent States Displaced in Noncommutative Phase Space
YAN Long,FENG Xun-Li**,ZHANG Zhi-Ming,LIU Song-Hao
Chin. Phys. Lett. 2012, 29 (4): 041102 .   DOI: 10.1088/0256-307X/29/4/041102
Abstract   PDF(pc) (457KB) ( 584 )
Using deformed boson algebra, we study the property of two-mode coherent states in noncommutative phase space. When a two-mode field evolves in the noncommutative phase space, it can acquire an extra θ-dependent phase compared to the case of commutative space. This phase is detectable and may be used to test noncommutativity.
Wigner Solution to the Quark Gap Equation in the Nonzero Current Quark Mass
JIANG Yu,GONG Hao,SUN Wei-Min,ZONG Hong-Shi,**
Chin. Phys. Lett. 2012, 29 (4): 041201 .   DOI: 10.1088/0256-307X/29/4/041201
Abstract   PDF(pc) (504KB) ( 422 )
From the graphical representation of the Dyson–Schwinger equation for the dressed gluon propagator it is shown that the gluon propagator in the Wigner phase should be different from that in the Nambu phase. Based on this analysis, we propose a modified gluon propagator to reflect this fact. With such a modified gluon propagator, in the framework of the Nambu–Jona–Lasinio (NJL) model, we obtain the Wigner solution to the quark gap equation at finite current quark mass, which has not been found in literature. This provides a new point of view to study partial restoration of chiral symmetry at finite temperature and chemical potential.
Non-Standard ZZ Production with Leptonic Decays at the Large Hadron Collider
SUN Hao**
Chin. Phys. Lett. 2012, 29 (4): 041401 .   DOI: 10.1088/0256-307X/29/4/041401
Abstract   PDF(pc) (527KB) ( 387 )
The prospects of anomalous ZZγ and ZZZ triple gauge boson couplings are investigated at the Large Hadron Collider (LHC) through an excess of events in ZZ diboson production. Two such channels are selected and the tree level results including leptonic final states are discussed: ZZ→ℓ11+2-2+ and ZZ→ℓ+νν(ℓ,ℓ1,2=e,μ). The results in the full finite width method are compared with the narrow width approximation (NWA) method in detail. Besides the Z boson transverse momentum distributions, the azimuthal angle between the Z boson decay to fermions, ΔΦ, and their separations in the pseudo−rapidity-azimuthal angle plane, ΔR, as well as the sensitivity on anomalous couplings are displayed at the 14 TeV LHC.
The Perturbed Puma Model
RONG Shu-Jun*,LIU Qiu-Yu
Chin. Phys. Lett. 2012, 29 (4): 041402 .   DOI: 10.1088/0256-307X/29/4/041402
Abstract   PDF(pc) (407KB) ( 389 )
The puma model on the basis of the Lorentz and CPT violation may bring an economical interpretation to the conventional neutrinos oscillation and part of the anomalous oscillations. We study the effect of the perturbation to the puma model. In the case of the first-order perturbation which keeps the (23) interchange symmetry, the mixing matrix element Ue3 is always zero. The nonzero mixing matrix element Ue3 is obtained in the second-order perturbation that breaks the (23) interchange symmetry.
NUCLEAR PHYSICS
Odd Systems in Deformed Relativistic Hartree Bogoliubov Theory in Continuum
LI Lu-Lu,MENG Jie,P. Ring,ZHAO En-Guang,ZHOU Shan-Gui,**
Chin. Phys. Lett. 2012, 29 (4): 042101 .   DOI: 10.1088/0256-307X/29/4/042101
Abstract   PDF(pc) (490KB) ( 523 )
In order to describe the exotic nuclear structure in unstable odd-A or odd−odd nuclei, the deformed relativistic Hartree Bogoliubov theory in continuum is extended to incorporate the blocking effect due to the odd nucleon. For a microscopic and self-consistent description of pairing correlations, continuum, deformation, blocking effects, and the extended spatial density distribution in exotic nuclei, the deformed relativistic Hartree Bogoliubov equations are solved in a Woods–Saxon basis in which the radial wave functions have a proper asymptotic behavior at large r. The formalism and numerical details are provided. The code is checked by comparing the results with those of spherical relativistic continuum Hartree Bogoliubov theory in the nucleus 19O. The prolate deformed nucleus 15C is studied by examining the neutron levels and density distributions.
Nucleon Effective Mass in Asymmetric Nuclear Matter within Extended Brueckner Approach
GAN Sheng-Xin,ZUO Wei**,U. Lombardo
Chin. Phys. Lett. 2012, 29 (4): 042102 .   DOI: 10.1088/0256-307X/29/4/042102
Abstract   PDF(pc) (625KB) ( 537 )
The on-shell properties of the nucleon effective mass in asymmetric nuclear matter are investigated in the framework of an extended Brueckner–Hartree–Fock (BHF) approach. The proton and neutron effective masses in neutron-rich nuclear matter are predicted by including both the effect of ground state correlations and the three-body force (TBF) rearrangement contribution. Within this framework, the neutron effective mass is predicted to be larger than the proton one in neutron-rich nuclear matter, i.e., mn*mp*. The effect of ground state correlations turns out to be dominated at low densities and it leads to a strong enhancement of the effective mass. The TBF rearrangement contribution becomes predominant over the effect of ground state correlations at high densities and it reduces remarkably the absolute magnitude of the isospin splitting of the neutron and proton effective masses in neutron-rich matter at high densities.
Measured and Simulated Performance of a Four-Segmented Clover Detector
ZHANG Ning-Tao**,LEI Xiang-Guo,ZHANG Yu-Hu,ZHOU Xiao-Hong,LIU Min-Liang,GUO Ying-Xiang,FANG Yong-De,LI Shi-Cheng,ZHOU Hou-Bing,DING Bing,WANG Hai-Xia,WU Xiao-Guang,HE Chuang-Ye,ZHENG Yun
Chin. Phys. Lett. 2012, 29 (4): 042901 .   DOI: 10.1088/0256-307X/29/4/042901
Abstract   PDF(pc) (528KB) ( 907 )
Gamma rays with energies between 80 keV and 1500 keV produced by 133Ba and 152Eu standard sources are measured with the clover detector. Relative efficiencies and add-back factors are determined in both crystals and full clover modes. The add-back characteristics have been calculated using Monte-Carlo simulation code Geant4. The simulation and measurements agree very well.
ATOMIC AND MOLECULAR PHYSICS
Effect of Rotational Excitation on Stereodynamics for the Reactive Collision Between N(2D) and H2
CHENG Jie,YUE Xian-Fang**,FENG Hai-Ran
Chin. Phys. Lett. 2012, 29 (4): 043101 .   DOI: 10.1088/0256-307X/29/4/043101
Abstract   PDF(pc) (2154KB) ( 460 )
Effect of rotational excitation on stereodynamics for the N( 2D)+H2(v=0, j=0−5)→NH(v', j')+H collision reactions is investigated by employing the quasiclassical trajectory method. Based on an accurate 12A" potential energy surface, three angular distributions P(θr ), P(φr ), P(θrr ), and polarized−dependent differential cross section 2π/σ dσ00 /dωt are calculated at a collision energy of 5.1 kcal/mol. It is found that the P(θr ) distribution has a distinct peak at about θr=90°. The P(φr ) distribution has a small peak at about φr=270° and no peak at about φr=90°. This implies that the product angular momentum j' is not only aligned perpendicular to k, but also orientated to the negative direction of the y axis. The product rotational alignment and orientation become increasingly weaker with an increase of the rotational quantum number j of H2. Analysis of trajectory propagation demonstrates that the title collision reaction has a dominant indirect insertion mechanism and a minor direct H-abstraction mechanism.
Fluorescence and Auger Decay Properties of the Core-Excited F-Like Ions from Ne to Kr
WANG Xiang-Li,DONG Chen-Zhong**,SU Mao-Gen,KOIKE Fumihiro
Chin. Phys. Lett. 2012, 29 (4): 043201 .   DOI: 10.1088/0256-307X/29/4/043201
Abstract   PDF(pc) (566KB) ( 349 )
We systematically study the decay properties of the K−shell excited F-like ions with 10≤Z ≤36 based on the multiconfiguration Dirac–Fock method. The Breit interaction, the QED corrections and the nuclear finite mass effects are also considered as perturbation. Auger transition rates, radiative, Auger and natural widths, as well as fluorescence and Auger yields for K−shell excited F-like ions are presented. It is shown by means of concrete figures that the decay properties change significantly with the increase of the atomic number Z; the Auger rate is overtaken at Z=30 by the radiative decay rate. Several fitting formulae for the radiative and Auger widths and the fluorescence yields have been evaluated which is expected to be useful in plasma analysis and plasma modeling.
Photodetachment of a Homo-Nuclear Linear Tetra-Atomic Negative Molecular Ion
A. Rahman,Iftikhar Ahmad**,A. Afaq,H. J. Zhao
Chin. Phys. Lett. 2012, 29 (4): 043301 .   DOI: 10.1088/0256-307X/29/4/043301
Abstract   PDF(pc) (446KB) ( 407 )
The photodetachment of a homo-nuclear linear tetra-atomic negative molecular ion is studied theoretically for an arbitrary laser polarization. An expression for the total cross section is obtained by using an extended version of the two center model, where each center acts as a source of coherent photodetached-electron waves. Strong oscillations on observation plane, placed at a large distance from the ion, are observed. The amplitude of these oscillations is maximum when the laser polarization is parallel to the molecular axis. Furthermore, the amplitude decreases as the angle between the laser polarization and molecular axis increases and consequently vanishes when they are perpendicular to each other. It is also found that if the distance between the adjacent centers is very small or very large, then the amplitude of oscillations is negligibly small.
Valence-Shell Excitations of Nitrous Oxide Studied by Fast Electron Impact
LIU Ya-Wei,WANG You-Yan,ZHU Lin-Fan**
Chin. Phys. Lett. 2012, 29 (4): 043302 .   DOI: 10.1088/0256-307X/29/4/043302
Abstract   PDF(pc) (678KB) ( 351 )
The valence-shell excitations of nitrous oxide are studied by fast electron energy loss spectroscopy. From the spectra measured at 2.5 keV and scattering angles of 3.5°–8.5°, it is found that the asymmetric peak of the transition B1Δ can be well fitted by Haarhoff−Van der Linde function, while the symmetric peaks of the transitions of C1Π and D1Σ+ can be well fitted by the Voigt function. The parameters of the peak profiles of B1Δ, C1Π and D1Σ+, i.e., their energy level positions and linewidths, are determined. With the aid of these parameters, the overlapping spectra measured at the low−energy electron impact can be deconvolved, which provides the possibility to determine the quantitative differential cross sections. The present results also show that the peak profiles of the transitions of B1Δ, C1Π and D1Σ+ are independent of the momentum transfer.
Quantitative Analysis for Monitoring Formulation of Lubricating Oil Using Terahertz Time-Domain Transmission Spectroscopy
TIAN Lu,ZHAO Kun,**,ZHOU Qing-Li,SHI Yu-Lei,ZHANG Cun-Lin
Chin. Phys. Lett. 2012, 29 (4): 043901 .   DOI: 10.1088/0256-307X/29/4/043901
Abstract   PDF(pc) (834KB) ( 806 )
The quantitative analysis of zinc isopropyl-isooctyl-dithiophosphate (T204) mixed with lube base oil from Korea with viscosity index 70 (T204-Korea70) is presented by using terahertz time-domain spectroscopy (THz-TDS). Compared with the middle-infrared spectra of zinc n-butyl-isooctyl-dithiophosphate (T202) and T204, THz spectra of T202 and T204 show the weak broad absorption bands. Then, the absorption coefficients of the T204-Korea70 system follow Beer's law at the concentration from 0.124 to 4.024%. The experimental absorption spectra of T204-Korea70 agree with the calculated ones based on the standard absorption coefficients of T204 and Korea70. The quantitative analysis enables a strategy to monitor the formulation of lubricating oil in real time.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Phases in a General Chaotic Three-Coupled-Laser Array
ZHOU Liang,DUAN Kai-Liang**
Chin. Phys. Lett. 2012, 29 (4): 044201 .   DOI: 10.1088/0256-307X/29/4/044201
Abstract   PDF(pc) (3053KB) ( 495 )
Phases in a general chaotic three-coupled-laser array are numerically investigated. Phase attractors are firstly found to exist within corresponding basins of attraction on the projection plane of phase differences of the three-coupled-laser array. Whether the chaos appears or not is related not only to the coupling strength but also to the initial phase differences. For a large coupling strength new phase attractors can occur. With the increase of coupling strength, the three-coupled-laser array has a great chance of resulting in a quiescent to chaotic state. Based on these results, we present the method to reach phase-locking when the coupling strength is strong.
Interference of a Narrowband Biphoton with Double Electromagnetically Induced Transparency in an N-Type System
CHEN Peng,QIAN Jun,CHEN Dong-Yuan,HU Zheng-Feng**,WANG Yu-Zhu**
Chin. Phys. Lett. 2012, 29 (4): 044202 .   DOI: 10.1088/0256-307X/29/4/044202
Abstract   PDF(pc) (546KB) ( 520 )
We predict the possibility of the interference of narrow-band biphotons generated by spontaneous four-wave mixing with double electromagnetically induced transparency configuration in cold atoms. In an N-type four-level system, an auxiliary optical field Ωm can create double transparency windows for anti-Stokes photons. When the slow light effects in the double transparency windows are very strong, two four-wave mixing channels could exist due to the splitting of the phase matching condition. The biphoton generated from the two four-wave mixing channels can cause interference and shows Rabi oscillations in two-photon correlation. This interference mechanism will complement the understanding of interference at the two-photon level.
THz Output Improvement in a Photomixer with a Resonant-Cavity-Enhanced Structure
DU Ming-Di,SUN Jun-Qiang**,CHENG Wen-Long
Chin. Phys. Lett. 2012, 29 (4): 044203 .   DOI: 10.1088/0256-307X/29/4/044203
Abstract   PDF(pc) (483KB) ( 673 )
We carry out a detailed theoretical study on THz coherent generation in an LTG-GaAs photomixer with a resonant-cavity-enhanced (RCE) structure. In the structure, an improvement in THz output can be achieved by increasing the quantum efficiency. Under optimized structure parameters, the maximum quantum efficiency of the RCE photomixer is 93%, which is 2.82 times higher than that of the case without an RCE structure. The corresponding THz output ratio of the two structures is found to be about eight in the whole range of the lower frequency at the same incident optical power.
The Improved Power of the Central Lobe in the Beam Combination and High Power Output
LIU Hou-Kang,XUE Yu-Hao,LI Zhen,HE Bing**,ZHOU Jun**,DING Ya-Qian,JIAO Meng-Li,LIU Chi,QI Yun-Feng,WEI Yun-Rong,DONG Jing-Xing,LOU Qi-Hong
Chin. Phys. Lett. 2012, 29 (4): 044204 .   DOI: 10.1088/0256-307X/29/4/044204
Abstract   PDF(pc) (1569KB) ( 428 )
In order to increase the power fraction of the central lobe in the coherent beam combination of lasers in an array, the effects of the distance factor of near-field distribution on far-field interference patterns are calculated and demonstrated experimentally. An improved beam array of interwoven distribution is demonstrated to enable the power in the central lobe to reach 41%. An optimized mirror array is carefully designed to obtain a high duty ratio, which is up to 53.3% at a high power level. By using these optimized methods and designs, the passive phase locking of eight Yb-doped fiber amplifiers with ring cavities are obtained, and a pleasing interference pattern with 87% visibility is observed. The maximum coherent output power of the system is up to 1066 W.
RZ-DQPSK Signal Amplitude Regeneration Using a Semiconductor Optical Amplifier
WU Wen-Han,HUANG Xi,YU Yu**,ZHANG Xin-Liang
Chin. Phys. Lett. 2012, 29 (4): 044205 .   DOI: 10.1088/0256-307X/29/4/044205
Abstract   PDF(pc) (609KB) ( 473 )
An all-optical return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) signal regeneration scheme is experimentally demonstrated. Thanks to the gain saturation effect, common quantum-well semiconductor optical amplifiers have the ability to regenerate the amplitude distorted RZ-DQPSK signal, so amplitude noise can be reduced while phase information will not be distorted. A significant eye-opening improvement and a negative power penalty of about 1 dB can be achieved for an 80 Gb/s RZ-DQPSK signal.
Multivariate Analysis of Laser-Induced Breakdown Spectroscopy for Discrimination between Explosives and Plastics
WANG Qian-Qian**,LIU Kai,ZHAO Hua
Chin. Phys. Lett. 2012, 29 (4): 044206 .   DOI: 10.1088/0256-307X/29/4/044206
Abstract   PDF(pc) (508KB) ( 773 )
A method to distinguish explosives from plastics using laser-induced breakdown spectroscopy is discussed. A model for classification with cross-validation theory is built based on the partial least-square discriminant analysis method. Seven types of plastics and one explosive are used as samples to test the model. The experimental results demonstrate that laser-induced breakdown spectroscopy has the capacity to discriminate explosives from plastics combined with chemometrics methods. The results could be useful for prospective research of laser-induced breakdown spectroscopy on the differentiation of explosives and other materials.
Measurement of the Velocities of Nanoparticles in Flowing Nanofluids using the Zero-Crossing Laser Speckle Method
YAN Qin,LU Jian,NI Xiao-Wu**
Chin. Phys. Lett. 2012, 29 (4): 044207 .   DOI: 10.1088/0256-307X/29/4/044207
Abstract   PDF(pc) (589KB) ( 526 )
A zero-crossing dynamic speckle method is proposed to determine the velocities of nanoparticles in nanofluids. A Gaussian laser beam is used to illuminate nanofluids in a pipe, and the dynamic speckles are detected by a spatially integrating detector with an aperture. The integrated speckle intensity signal is processed by a computer and the zero-crossing rate is counted. The velocity of the nanoparticles can be determined from its relationship to zero-crossing rate. The results show that the nanoparticles exhibit features of flowing nanofluids, and when the average velocity of the nanofluids is 53.4 mm/s, the average velocity of the nanoparticles is 51.8±5.1 mm/s.
A High-Power Single-Frequency 540 nm Laser Obtained by Intracavity Frequency Doubling of an Nd:YAP Laser
ZHENG Yao-Hui**,WANG Ya-Jun,PENG Kun-Chi
Chin. Phys. Lett. 2012, 29 (4): 044208 .   DOI: 10.1088/0256-307X/29/4/044208
Abstract   PDF(pc) (686KB) ( 509 )
By analyzing the relation between the transmission of the output mirror and the output power in an intracavity frequency doubling laser, we choose an optimal transmission of the output mirror according to the laser application requirements. As a result, a high-power single-frequency laser at 540 nm is obtained with a maximum output power of 8 W and a power stability of ±1% for three hours, whose beam quality M2 is better than 1.2. At the same time, a moderate FW power of 1.2 W is coupled out, which is enough to meet the requirements for local oscillation light and injected signal optical beams in quantum optics experiments.
Design and Fabrication of a Monolithic Optoelectronic Integrated Circuit Chip Based on CMOS Compatible Technology
GUO Wei-Feng,ZHAO Yong,WANG Wan-Jun,SHAO Hai-Feng,YANG Jian-Yi,JIANG Xiao-Qing**
Chin. Phys. Lett. 2012, 29 (4): 044209 .   DOI: 10.1088/0256-307X/29/4/044209
Abstract   PDF(pc) (1008KB) ( 821 )
A monolithic optoelectronic integrated circuit chip on a silicon-on-insulator is designed and fabricated based on complementary metal oxide semiconductor compatible technology. The chip integrates an optical Mach–Zehnder modulator (MZM) and a CMOS driving circuit with the amplification function. Test results show that the extinction ratio of the MZM is close to 20 dB and the small-signal gain of the CMOS driving circuit is about 26.9 dB. A 50 mV 10 MHz sine wave signal is amplified by the driving circuit, and then drives the MZM successfully.
A 171.4 W Diode-Side-Pumped Q-Switched 2 µm Tm:YAG Laser with a 10 kHz Repetition Rate
CAO Dong,DU Shi-Feng**,PENG Qin-Jun,BO Yong,XU Jia-Lin,GUO Ya-Ding,ZHANG Jing-Yuan,CUI Da-Fu,XU Zu-Yan
Chin. Phys. Lett. 2012, 29 (4): 044210 .   DOI: 10.1088/0256-307X/29/4/044210
Abstract   PDF(pc) (607KB) ( 714 )
A 785 nm diode-side-pumped high-power high-pulse-repetition-frequency Q-switched 2 µm Tm:YAG laser system is reported. Under a pump power of 1300 W, a 171.4 W average output power is achieved at a pulse repetition frequency of 10 kHz. To our knowledge, this is the highest average output power for a diode−pumped all solid-state Q-switched 2 µm Tm:YAG laser. The laser output corresponds to an optical-to-optical conversion efficiency of 13.3% and a slope efficiency of 18.9%.
The Structure Evolution of Fused Silica Induced by CO2 Laser Irradiation
LIU Chun-Ming,JIANG Yong,LUO Cheng-Si,SHI Xiao-Yan,REN Wei,XIANG Xia,WANG Hai-Jun,HE Shao-Bo,YUAN Xiao-Dong**,LV Hai-Bing,ZHENG Wan-Guo,ZU Xiao-Tao
Chin. Phys. Lett. 2012, 29 (4): 044211 .   DOI: 10.1088/0256-307X/29/4/044211
Abstract   PDF(pc) (724KB) ( 744 )
The structure evolution of fused silica induced by CO2 laser irradiation (with a wavelength of 10.6 µm ) is studied in detail. In the non-evaporation mitigation process, the irradiation time should be long enough to completely eliminate damage. However, there is a raised rim around the mitigated site. The rim height is enhanced when the irradiation time increases, and the mitigated site can lead to off-axis and on-axis downstream light intensification. Volume shrinkage occurs during the irradiation and rapid cooling processes, and this may be due to a decrease in the Si–O–Si bond angle. The distribution of debris overlaps with the maximum phase retardance induced by stress. The debris arouses an enhanced light absorption in the region from 220 nm to 800 nm.
Polarization Stability of a Double-Loop Interferometer Based on a Planar 3×3 Coupler
WANG Ya-Ping,**,WU Chong-Qing,YAN Ping
Chin. Phys. Lett. 2012, 29 (4): 044212 .   DOI: 10.1088/0256-307X/29/4/044212
Abstract   PDF(pc) (1105KB) ( 427 )
An interferometer with double loops based on a planar 3×3 coupler is proposed. The main factors that cause the instability of the polarization state are obtained by theoretical analysis and experiment. Furthermore, the stability of the polarization state is described quantitatively by the time-varying vector of polarization. Using these effective measures, interference with a stable polarization state at all times is achieved.
Effects of Input Spectra on the Threshold of Modulation Instability in a Single-Mode Fiber
CHEN Wei,MENG Zhou**,ZHOU Hui-Juan,LUO Hong
Chin. Phys. Lett. 2012, 29 (4): 044213 .   DOI: 10.1088/0256-307X/29/4/044213
Abstract   PDF(pc) (604KB) ( 416 )
We investigate modulation instability (MI) in the presence of a monochromatic spectrum and on the background of a broadband amplified spontaneous emission spectrum induced by an erbium-doped fiber amplifier, respectively. For the former case, the MI threshold is ∼110 mW, which agrees well with the theoretical value. However, for the latter case, the threshold is as high as ∼170 mW, which indicates that the MI threshold depends on the shape of the input spectrum and that the broadband spectrum has a higher threshold than the monochromatic one.
Producing and Distinguishing χ-Type Four-Qubit States in Flux Qubits
GAO Gui-Long,SONG Fu-Quan,HUANG Shou-Sheng,WANG Yan-Wei,FAN Zhi-Qiang,YUAN Xian-Zhang,JIANG Nian-Quan**
Chin. Phys. Lett. 2012, 29 (4): 044214 .   DOI: 10.1088/0256-307X/29/4/044214
Abstract   PDF(pc) (547KB) ( 400 )
We propose an effective method to produce four-qubit χ-type entangled states by using flux qubits coupled to an LC circuit which acts as a quantum data bus (QDB). In our scheme, the interaction is mediated by the exchange of virtual rather than real photons because of the large detuning between flux qubits and QDB, and then QDB-induced loss can be effectively avoided. The experimental feasibility of the scheme is also presented.
Attenuation of Rayleigh Surface Waves in a Porous Material
DEBBOUB Salima**,BOUMAÏ, ZA Youcef,BOUDOUR Amar,TAHRAOUI Tarek
Chin. Phys. Lett. 2012, 29 (4): 044301 .   DOI: 10.1088/0256-307X/29/4/044301
Abstract   PDF(pc) (558KB) ( 613 )
Using acoustic microscopy at higher frequency, we show the velocity evolutions of surface acoustic waves, in particular Rayleigh waves that depend on porosity for a mesoporous silicon layer. The velocities are obtained from different V(z) curves, which are determined experimentally at a frequency of 600 MHz. The analysis of V(z) data yields attenuation that is directly dependent on porosity. On the other hand, αN attenuation has been modeled and allows us to investigate its influence on the velocity VR of the propagation for Rayleigh waves.
A Novel Method for Measuring the Temperature in the Active Region of Semiconductor Modules
LIU Jing,FENG Shi-Wei**,ZHANG Guang-Chen,ZHU Hui,GUO Chun-Sheng,QIAO Yan-Bin,LI Jing-Wan
Chin. Phys. Lett. 2012, 29 (4): 044401 .   DOI: 10.1088/0256-307X/29/4/044401
Abstract   PDF(pc) (544KB) ( 390 )
The temperature in the active region of semiconductor modules can be measured by a vacuum system method. The test device is positioned on a vacuum test platform and heated in two ways, from the chip and from the case, to identify the required heat to establish stable temperature gradients for the two processes, respectively. A complementary relationship between the temperatures under the two heating methods is found. By injecting the total heat into the device, the resulting uniform temperature can be derived from the temperature curves of the chip and case. It is demonstrated that the temperature obtained from this vacuum system method is equivalent to the normal operating temperature of the device in the atmosphere. Further comparison of our result with that of the electrical method also shows good agreement.
Accurate Period Approximation for Any Simple Pendulum Amplitude
XUE De-Sheng,ZHOU Zhao,GAO Mei-Zhen**
Chin. Phys. Lett. 2012, 29 (4): 044601 .   DOI: 10.1088/0256-307X/29/4/044601
Abstract   PDF(pc) (632KB) ( 587 )
Accurate approximate analytical formulae of the pendulum period composed of a few elementary functions for any amplitude are constructed. Based on an approximation of the elliptic integral, two new logarithmic formulae for large amplitude close to 180° are obtained. Considering the trigonometric function modulation results from the dependence of relative error on the amplitude, we realize accurate approximation period expressions for any amplitude between 0 and 180°. A relative error less than 0.02% is achieved for any amplitude. This kind of modulation is also effective for other large-amplitude logarithmic approximation expressions.
The Effect of Gas Leaks on Underground Gas Storage Performance During Development and Operation
SHI Lei**,XIONG Wei,GAO Shu-Sheng
Chin. Phys. Lett. 2012, 29 (4): 044602 .   DOI: 10.1088/0256-307X/29/4/044602
Abstract   PDF(pc) (614KB) ( 1044 )
Underground gas storage is an efficient tool for matching the constant supply of gas to the variable demands of the market. Gas escaping from a storage field may cause environmental and safety problems. We present a physical simulation together with actual field data to evaluate the caprock of underground gas storage in the Jing-Bian area. The effect of gas leaks on the performance of gas storage is analyzed by using the type curves of the injection-withdrawal cycle.
Characterization of the Flow Separation of a Variable Camber Airfoil
YANG Wen-Chao,WANG Hui,YANG Jian-Ting,YANG Ji-Ming**
Chin. Phys. Lett. 2012, 29 (4): 044701 .   DOI: 10.1088/0256-307X/29/4/044701
Abstract   PDF(pc) (1296KB) ( 1068 )
An experimental investigation is carried out to study the flow separation behaviors of a variable camber airfoil. The aerodynamic load measurements and related flow visualization show that there are two types of stalls caused by the deformation on the camber: the leading-edge stall and the trailing-edge stall. Static measurements of aerodynamic force show a drastic leading-edge stall, while the serial measurements on an airfoil with camber deformation illustrate a trailing-edge stall and gradual bending-over on the aerodynamic coefficient curve. Under flow separation circumstances, the flow structure is related not only to current boundary conditions, but also the previous flow characteristics, so the quasi-steady aerodynamic characteristics are significantly distinct from those of the static measurements.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Operational Tau Approximation for the Fokker–Planck Equation
S. S. Dehcheshmeh*,S. Karimi Vanani,J. S. Hafshejani
Chin. Phys. Lett. 2012, 29 (4): 045201 .   DOI: 10.1088/0256-307X/29/4/045201
Abstract   PDF(pc) (423KB) ( 478 )
An extension of the operational Tau method (OTM) is used to solve the Fokker–Planck equation arising in many physical problems. This extension yields an algebraic equivalent representation of the desired problem using arbitrary polynomial basis functions to decrease the size of the computations. The structure, properties and advantages of the OTM are presented, and some illustrative linear and nonlinear experiments are given to show the capability and efficiency of the proposed algorithm.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
The Effects of Femtosecond Laser Irradiation and Thermal Annealing on the Optoelectronic Properties of Silicon Supersaturated with Sulfur
HU Shao-Xu,HAN Pei-De**,GAO Li-Peng,MAO Xue,LI Xin-Yi,FAN Yu-Jie
Chin. Phys. Lett. 2012, 29 (4): 046101 .   DOI: 10.1088/0256-307X/29/4/046101
Abstract   PDF(pc) (599KB) ( 432 )
Electrochemical capacitance-voltage profiling, Raman and absorption spectroscopy measurements are employed to characterize the electronic and optical properties of silicon supersaturated with sulfur above the equilibrium solubility limit. Silicon wafers are ion implanted with 50 keV 32S+ to a dose of 1×1016 ions/cm2 and subsequently irradiated by femtosecond pulses at a fluence of 0.2 J/cm2, followed by thermal annealing at 825 K for 30 min. The spectral response of the photodiode fabricated from the laser-irradiated sample is also investigated. It is found that femtosecond laser irradiation and subsequent thermal annealing can electrically and optically activate the supersaturated sulfur dopant in silicon, as well as reduce the implantation-induced damage in the silicon lattice.
Multiphase Equation of States of the Solid and Liquid Phases of Al and Ta
LI Ying-Hua,CHANG Jing-Zhen LI Xue-Mei,ZHANG Lin**
Chin. Phys. Lett. 2012, 29 (4): 046201 .   DOI: 10.1088/0256-307X/29/4/046201
Abstract   PDF(pc) (676KB) ( 443 )
The multiphase equation of states (EOSs) of both the solid and liquid phases of Al and Ta are presented. These EOSs are carried out on the basis of the Helmholtz free energy, where the ion vibration free energy is evaluated from the mean field potential (MFP) model we recently proposed [Physica B 406 (2011) 4163]. The calculated results show that our multiphase EOSs can give a good reproduction of the measured phase diagrams and other experimental data, including static high-pressure measurements, shock Hugoniots and the thermodynamic quantities of these metals.
Enhanced Surface Premelting of Ni90Si10 Nanoparticles
LÜ, Yong-Jun**
Chin. Phys. Lett. 2012, 29 (4): 046401 .   DOI: 10.1088/0256-307X/29/4/046401
Abstract   PDF(pc) (673KB) ( 366 )
Molecular dynamics simulations are used to investigate the melting of Ni90Si10 nanoparticles. The melting is found to originate from the surface prematurely. By means of the bond order parameter, the thickness of the surface liquid layer during surface premelting is calculated. The results show that the thickness of the liquid layer increases in a logarithmic−type manner on heating to the melting temperature, which is larger than the values of elemental Ni nanoparticles. Furthermore, the temperature range associated with the premelting of Ni90Si10 nanoparticles is wider. Both theory and simulations indicate that the high Si concentration of the surface liquid layer formed via surface segregation during crystallization due to Gibbs adsorption is the main reason for enhanced surface premelting. The simulations suggest that the crystallization process used to prepare samples greatly influences the melting behavior of nanoparticles.
Specific Heat in a Typical Metallic Glass Former
KE Hai-Bo,ZHAO Zuo-Feng,WEN Ping**,WANG Wei-Hua
Chin. Phys. Lett. 2012, 29 (4): 046402 .   DOI: 10.1088/0256-307X/29/4/046402
Abstract   PDF(pc) (578KB) ( 643 )

The specific heat in a typical Pd40Ni10Cu30P20 metallic glass forming system is investigated. It is found that the specific heat of the metallic liquid is around 4.7R (R is the gas constant) and that it is almost independent of temperature. The glass transition observed during cooling is accompanied by a decrease in the specific heat of 1.5R. The specific heat of the metallic glass is similar to that of its crystalline phases, contributed mainly from atomic vibrations. Combined with the results of the structural relaxation and diffusivities, we demonstrate an intrinsic connection between the atomic motion and the specific heat in the metallic glass-forming liquid. The results support the idea that glass transition is a process accompanied by the freezing of most of the atomic transitional motions in a metallic supercooled liquid during cooling.

The Impact of HCl Precleaning and Sulfur Passivation on the Al2O3/Ge Interface in Ge Metal-Oxide-Semiconductor Capacitors
XUE Bai-Qing,CHANG Hu-Dong,SUN Bing,WANG Sheng-Kai,LIU Hong-Gang**
Chin. Phys. Lett. 2012, 29 (4): 046801 .   DOI: 10.1088/0256-307X/29/4/046801
Abstract   PDF(pc) (847KB) ( 1466 )
Surface treatment for Ge substrates using hydrogen chlorine cleaning and chemical passivation are investigated on AuTi/Al2O3/Ge metal−oxide-semiconductor capacitors. After hydrogen chlorine cleaning, a smooth Ge surface almost free from native oxide is demonstrated by atomic force microscopy and x-ray photoelectron spectroscopy observations. Passivation using a hydrogen chlorine solution is found to form a chlorine-terminated surface, while aqueous ammonium sulfide pretreatment results in a surface terminated by Ge-S bonding. Compared with chlorine-passivated samples, the sulfur-passivated ones show less frequency dispersion and better thermal stability based on capacitance-voltage characterizations. The samples with HCl pre-cleaning and (NH4)2S passivation show less frequency dispersion than the HF pre−cleaning and (NH4)2S passivated ones. The surface treatment process using hydrogen chlorine cleaning followed by aqueous ammonium sulfide passivation demonstrates a promising way to improve gate dielectric/Ge interface quality.
Solid Phase Reactions of Ni-GaAs Alloys for High Mobility III–V MOSFET Applications
LU Li,CHANG Hu-Dong,SUN Bing,WANG Hong,XUE Bai-Qing,ZHAO Wei,LIU Hong-Gang**
Chin. Phys. Lett. 2012, 29 (4): 046802 .   DOI: 10.1088/0256-307X/29/4/046802
Abstract   PDF(pc) (866KB) ( 753 )
The solid phase reactions of Ni with GaAs substrates are investigated. The experimental results reveal that the Ni-GaAs solid phase reaction forms a ternary phase of Ni2GaAs when annealing temperatures are in the range 250–300°C. As the annealing temperature increases to 400°C, the Ni2GaAs phase starts to decompose due to NiAs phase precipitation. Ni−GaAs alloys processed at 400°C with a 3 min annealing time demonstrate a sheet resistance of 30 Ω/square after unreacted Ni removal in hot diluted−HCl solutions. Therefore, Ni-GaAs alloys formed by solid phase reaction could be promising metallic source/drain structures with significant low series resistance for high mobility III–V metal-oxide-semiconductor field effect transistor (MOSFET) applications.
Mapping the Diffusion Potential of a Reconstructed Au(111) Surface at Nanometer Scale with 2D Molecular Gas
YAN Shi-Chao,XIE Nan,GONG Hui-Qi,SUN Qian,GUO Yang,SHAN Xin-Yan,LU Xing-Hua**
Chin. Phys. Lett. 2012, 29 (4): 046803 .   DOI: 10.1088/0256-307X/29/4/046803
Abstract   PDF(pc) (953KB) ( 359 )

The adsorption and diffusion behaviors of benzene molecules on an Au(111) surface are investigated by low-temperature scanning tunneling microscopy. A herringbone surface reconstruction of the Au(111) surface is imaged with atomic resolution, and significantly different behaviors are observed for benzene molecules adsorbed on step edges and terraces. The electric field induced modification in the molecular diffusion potential is revealed with a 2D molecular gas model, and a new method is developed to map the diffusion potential over the reconstructed Au(111) surface at the nanometer scale.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Non-Equilibrium Quantum Entanglement in Biological Systems
LI Hong-Rong**,ZHANG Pei,GAO Hong,BI Wen-Ting,ALAMRI M. D.,LI Fu-Li
Chin. Phys. Lett. 2012, 29 (4): 047101 .   DOI: 10.1088/0256-307X/29/4/047101
Abstract   PDF(pc) (434KB) ( 464 )
A non-equilibrium model of a classically driven quantum harmonic oscillator is proposed to explain persistent quantum entanglement in biological systems at ambient temperature. The conditions for periodic entanglement generation are derived. Our results support the evidence that biological systems may have quantum entanglement at biological temperatures.
The Kondo and Fano Effects in Triple Quantum Dots Coupled to Noncollinear Ferromagnetic Leads
HUANG Rui**,MING Shan-Wen,WANG Yong
Chin. Phys. Lett. 2012, 29 (4): 047201 .   DOI: 10.1088/0256-307X/29/4/047201
Abstract   PDF(pc) (649KB) ( 362 )
We use the equation-of-motion technique and non-equilibrium Green's function theory to study the Kondo effect and the Fano effect in triple quantum dots (QDs) coupled to symmetrically ferromagnetic leads whose magnetic moments are noncollinear. We address the question of how the noncollinear ferromagnetic leads influence the Kondo effect and how the side-coupled QDs present Fano interference. The results show that the spin splitting of the density of state (DOS) takes place in an intermediate direction between the magnetic moments in the two leads. When interdot coupling strength ti is nonzero, Fano interference begins to play a major role in complicating the DOS of QD0.
The Electronic Structure of Coupled Semiconductor Quantum Dots Arranged as a Graphene Hexagonal Lattice under a Magnetic Field
PENG Juan**,LI Shu-Shen
Chin. Phys. Lett. 2012, 29 (4): 047301 .   DOI: 10.1088/0256-307X/29/4/047301
Abstract   PDF(pc) (2110KB) ( 657 )
We study the electronic spectrum of coupled quantum dots (QDs) arranged as a graphene hexagonal lattice in the presence of an external perpendicular magnetic field. In our tight-binding model, the effect of the magnetic field is included in both the Peierls phase of the Hamiltonian and the tight-binding basis Wannier function. The energy of the system is analyzed when the magnetic flux through the lattice unit cell is a rational fraction of the quantum flux. The calculated spectrum has recursive properties, similar to those of the classical Hofstadter butterfly. However, unlike the ideal Hofstadter butterfly structure, our result is asymmetric since the impacts of the specific material and the magnetic field on the wavefunctions are included, making the results more realistic.
Electronic Transport Properties of an Anthraquinone-Based Molecular Switch with Carbon Nanotube Electrodes
ZHAO Peng**,LIU De-Sheng,
Chin. Phys. Lett. 2012, 29 (4): 047302 .   DOI: 10.1088/0256-307X/29/4/047302
Abstract   PDF(pc) (1280KB) ( 710 )
Based on the nonequilibrium Green's function method and density functional theory calculations, we theoretically investigate the electronic transport properties of an anthraquinone-based molecular switch with carbon nanotube electrodes. The molecules that comprise the switch can convert between reduced hydroquinone (HQ) and oxidized anthraquinne (AQ) states via redox reactions. Our results show that the on-off ratio is increased one order of magnitude when compared to the case of gold electrodes. Moreover, an obvious negative differential resistance behavior at much low bias (0.07 V) is observed in the HQ form.
Solution Fabrication of a Superconducting MgB2 Coated Conductor on Stainless Steel
WANG Yin-Bo,CHEN Li-Ping,**,ZHANG Chen,WANG Yue,GUO Zheng-Shan,CHEN Yi-Ling,FENG Qing-Rong**,GAN Zi-Zhao
Chin. Phys. Lett. 2012, 29 (4): 047401 .   DOI: 10.1088/0256-307X/29/4/047401
Abstract   PDF(pc) (672KB) ( 484 )
We report the solution fabrication of a MgB2 coated conductor on a stainless steel substrate. The precursor solution of Mg(BH4)2 diethyl ether is initially synthesized by refluxing the milled mixture of NaBH4 and MgCl2 in diethyl ether. Then the Mg(BH4)2 diethyl ether is spin coated on a stainless steel substrate and annealed in Mg vapor, which yields a homogeneous MgB2 coated conductor. X−ray diffraction indicates that the grown MgB2 coated conductor is polycrystalline. It has a superconducting transition temperature of 34–37 K. The slope of the upper critical field HC increases with decreasing temperature, and the extrapolated value of HC(0) reaches ∼28 T. The critical current density estimated by the Bean model is JC (25 K, 0 T)∼106 A⋅cm−2. These parameters indicate that the solution method is potentially able to produce MgB2 coated conductors that can satisfy application purposes.
Magnetoresistance Effect in Antiferromagnet-Based Nanogranular Films
CHEN Feng-Liang,ZHOU Shi-Ming**
Chin. Phys. Lett. 2012, 29 (4): 047501 .   DOI: 10.1088/0256-307X/29/4/047501
Abstract   PDF(pc) (591KB) ( 401 )
Magnetic and magneto-transport properties of nano-structured CoO-Ag granular films are reported. Apparent magnetization hysteresis is observed for low CoO contents and becomes weaker with increasing CoO content. Magnetoresistance (MR) ratio has a maximal value near 84vol% CoO and is reduced at low CoO contents. It decreases with increasing temperature and disappears near the Néel temperature of CoO. The uncompensated magnetic moments of CoO particles have been clearly demonstrated by MR effect.
Size Segregation and Super-Domain Mediated by Dipolar Interactions in 3-D Iron Nanoparticle Assemblies
SI Ping-Zhan**,WANG Hai-Xia,JIANG Wei,CHEN Chun-Qiang,HU Xiu-Kun,LIU Jin-Jun,LEE Jung-Goo,CHOI Chul-Jin
Chin. Phys. Lett. 2012, 29 (4): 047502 .   DOI: 10.1088/0256-307X/29/4/047502
Abstract   PDF(pc) (1929KB) ( 364 )
We report the phenomenon of size segregation and the experimental evidence for the presence of correlated areas mediated by dipolar interactions in three-dimensional Fe nanoparticle assemblies. Iron nanoparticles dispersed in ethanol assemble into tabular whiskers (8µm×40µm in cross section with lengths up to 10 cm) due to dipolar interactions. Magnetic force microscopy observations on iron nanoparticle compact assemblies prove the local magnetic correlation of the Fe nanoparticles due to dipolar coupling and the formation of domain-like structures in expanded dimensions. Magnetic measurements show that the coercivity and the low field magnetic susceptibility of the Fe nanoparticle assemblies increase while the saturation magnetization decreases with the increasing inter-particle distance.
First-Principles Study of Doped Half-Metallic Spinels: Cu0.5Zn0.5Cr2S4, Cu0.5Cd0.5Cr2S4, Li0.5Zn0.5Cr2O4 and Li0.5Zn0.5Cr2S4
ZHOU Tie-Ge,LIU Zhi-Qiang**,ZUO Xu
Chin. Phys. Lett. 2012, 29 (4): 047503 .   DOI: 10.1088/0256-307X/29/4/047503
Abstract   PDF(pc) (706KB) ( 582 )
Electronic structure and magnetic properties of Cu0.5Zn0.5Cr2S4, Cu0.5Cd0.5Cr2S4, Li0.5Zn0.5Cr2O4 and Li0.5Zn0.5 Cr2S4 are investigated using the first−principles calculation based on the density functional theory. GGA+U exchange correlation is used in the calculation to correct the effective Coulomb repulsion energy of Cr underestimated by LSDA or GGA. The calculation results reveal that half−metallic Cu0.5Zn0.5Cr2S4 and Cu0.5Cd0.5Cr2S4 can be achieved by doping CuCr2S4 with Zn or Cd, though CuCr2S4 is not half−metallic. Half-metallic LiCr2O4 is experimentally unstable, but half−metallic Li0.5Zn0.5Cr2O4 and Li0.5Zn0.5Cr2S4 can be achieved by doping Li into experimentally stable ZnCr2O4 and ZnCr2S4, though ZnCr2O4 and ZnCr2S4 are not half−metallic. The influence of +U on the electronic structure and half-metallicity of the doped systems is also presented.
Switchable Ferroelectric Diode Effect and Piezoelectric Properties of Bi0.9La0.1FeO3 Ceramics
GONG Yu-Fei,WU Ping,LIU Wei-Fang**,WANG Shou-Yu,LIU Guang-Yao,RAO Guang-Hui
Chin. Phys. Lett. 2012, 29 (4): 047701 .   DOI: 10.1088/0256-307X/29/4/047701
Abstract   PDF(pc) (708KB) ( 482 )
Multiferroic ceramics Bi0.9La0.1FeO3 are synthesized by solid−state reactions and sintered at various temperatures. The rhombohedral structure with the space group R3c is confirmed by means of x−ray diffraction, and their multiferroic properties are investigated. Bi0.9La0.1FeO3 ceramics sintered at 880°C are found to have the lowest leakage current density and the largest saturated polarization among all the samples. A diode−like current-voltage hysteresis that could be switched by an external voltage is observed in the Bi0.9La0.1FeO3 ceramics. A typical "butterfly" shaped strain−versus-voltage curve is shown with a maximum strain of 0.09% at 7 kV. Room-temperature magnetization exhibits a hysteresis loop, indicating that the modulation of the spin structure of BiFeO3 has been suppressed.
Pyroelectric Study on Dipolar Alignment in 0.69Pb(Mg1/3Nb2/3)O3−0.31PbTiO3 Single Crystals
ZHAO Liang,SHEN Ming-Rong*,CAO Wen-Wu
Chin. Phys. Lett. 2012, 29 (4): 047702 .   DOI: 10.1088/0256-307X/29/4/047702
Abstract   PDF(pc) (713KB) ( 365 )
Pyroelectric measurements are conducted during zero-field heating in [001], [110] and [111] poled 0.69Pb(Mg1/3 Nb2/3)O3−0.31PbTiO3 single crystals. Compared to the room−temperature-poled samples, the crystals poled by using the field cooling method show broad but well recognizable pyroelectric current peaks near 190°C, which is much higher than the Curie point (126°C) of the crystal. We propose that this peak of the crystals poled by field-cooling above the Curie point is ascribed to the order-disorder transition of the dipoles in polar nano-regions formed at the Burns temperature.
Helium-Related Defect Evolution in Titanium Films by Slow Positron Beam Analysis
LI Yue,DENG Ai-Hong,**,ZHOU Yu-Lu,ZHOU Bing,WANG Kang,HOU Qing,SHI Li-Qun,QIN Xiu-Bo,WANG Bao-Yi
Chin. Phys. Lett. 2012, 29 (4): 047801 .   DOI: 10.1088/0256-307X/29/4/047801
Abstract   PDF(pc) (665KB) ( 531 )
Various helium-containing titanium films were deposited on Si substrates by magnetron sputtering under different helium/argon (He/Ar) ambiances. Helium concentrations and corresponding depth profiles in the Ti films are obtained by elastic recoil detection analysis (ERDA). X-ray diffraction (XRD) measurements are carried out to evaluate the crystallization of the titanium films. Vacancy-type defects and their depth profiles were revealed by slow positron beam analysis (SPBA). It is found that the defect-characteristic parameter S rises with the increment of the He/Ar flow ratios. The variation of S indicates the formation and evolution of various He-related defects, with uniform distribution into the depth around 400 nm.
Super-Resolution Imaging by using a Metallic Rod Array in the Near Infrared Region
YAO Jie,YE Yong-Hong**
Chin. Phys. Lett. 2012, 29 (4): 047802 .   DOI: 10.1088/0256-307X/29/4/047802
Abstract   PDF(pc) (1150KB) ( 452 )
An array of metallic rods can transport details below the diffraction limit of an object from the front face to the back face. This super-resolution imaging system has been studied in the microwave, mid-infrared and optical range. We investigate its performance in the near infrared (1550 nm) region. Numerical simulations show that the near-field components of dipole sources are transferred by the excitation and propagation of the surface plasmon mode of the rods. The appropriate length of rods is determined by the excited surface plasmon mode. The spatial resolution is greatly affected by the loss of metal.
Influence of Lanthanum on the Microstructural and Dielectric Properties of Polycrystalline Ba(Ti0.5Fe0.5)O3
M. R. Shah**,A. K. M. Akther Hossain
Chin. Phys. Lett. 2012, 29 (4): 047803 .   DOI: 10.1088/0256-307X/29/4/047803
Abstract   PDF(pc) (888KB) ( 540 )
Various polycrystalline Ba1−xLax(Ti0.5Fe0.5)O3 are prepared by using the standard solid state reaction technique. Pellet shaped samples prepared from each composition are sintered at 1200°C for 5 h. X-ray diffraction patterns of these compositions confirm the formation of a single phase perovskite structure. The lattice parameters are decreased but the average grain size increases with the increase of La content. The dielectric constant, dielectric loss and ac conductivity are studied as a function of frequency for various compositions, and their behaviors are explained on the basis of the Maxwell–Wagner model. A three-times enhancement of the dielectric constant is observed with the increase of La content.
Frequency Selective Propagation by Employing Fabry–Perot Nanocavities in a Subwavelength Double-slit Structure
M. Afshari Bavil,SUN Xiu-Dong*,HUANG Feng
Chin. Phys. Lett. 2012, 29 (4): 047804 .   DOI: 10.1088/0256-307X/29/4/047804
Abstract   PDF(pc) (1031KB) ( 440 )
By embedding a nanocavity adjacent to one or both of slits in a subwavelength double-slit structure, frequency selective propagation through the slits is demonstrated. When the incident light wavelength corresponds to the cavity resonance mode, the electromagnetic wave passing through the slit will be trapped within the nanocavity. Therefore, the double slit operates as a single slit and light propagation is solely allowed through the partner slit. These wavelengths are determined by applying the Fabry–Perot resonance condition for the nanocavities. Various geometrical structures result in different effective refractive indexes. Thus, the effective refractive index and consequently the attenuation wavelength can be adjusted by choosing the appropriate parameters of the nanocavity. Our theoretical predictions are in good agreement with 2D finite-difference time-domain simulation.
Leakage Current Simulation of Insulating Thin Film Irradiated by a Nonpenetrating Electron Beam
ZHANG Hai-Bo**,LI Wei-Qin,CAO Meng
Chin. Phys. Lett. 2012, 29 (4): 047901 .   DOI: 10.1088/0256-307X/29/4/047901
Abstract   PDF(pc) (469KB) ( 509 )
We perform numerical simulations of the leakage current characteristics of an insulating thin film of SiO2 negatively charged by a low-energy nonpenetrating focused electron beam. For the formation of leakage current, electrons are demonstrated to turn from diffusion to drift after clearing the minimum potential barrier due to electron-hole separation. In the equilibrium state, the leakage current increases approximately linearly with the increasing primary beam current and energy. It also increases with the increasing film thickness and trap density, and with the decreasing electron mobility, in which the film thickness has a greater influence. Validated by some existing experiments, the simulation results provide a new perspective for the negative charging effects of insulating samples due to the low-energy focused electron beam.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Growth of Ge/Si(100) Nanostructures by Radio-Frequency Magnetron Sputtering: the Role of Annealing Temperature
ALIREZA Samavati**,S. K. Ghoshal,Z. Othaman
Chin. Phys. Lett. 2012, 29 (4): 048101 .   DOI: 10.1088/0256-307X/29/4/048101
Abstract   PDF(pc) (900KB) ( 649 )
Surface morphologies of Ge islands deposited on Si(100) substrates are characterized and their optical properties determined. Samples are prepared by rf magnetron sputtering in a high-vacuum chamber and are annealed at 600°C, 700°C and 800°C for 2 min at nitrogen ambient pressure. Atomic force microscopy, field emission scanning electron microscopy, visible photoluminescence (PL) and energy dispersive x−ray spectroscopy are employed. The results for the annealing temperature-dependent sample morphology and the optical properties are presented. The density, size and roughness are found to be strongly influenced by the annealing temperature. A red shift of ∼0.29 eV in the PL peak is observed with increasing annealing temperature.
Fine Structural and Carbon Source Analysis for Diamond Crystal Growth using an Fe-Ni-C System at High Pressure and High Temperature
FAN Xiao-Hong,XU Bin**,NIU Zhen,ZHAI Tong-Guang,TIAN Bin
Chin. Phys. Lett. 2012, 29 (4): 048102 .   DOI: 10.1088/0256-307X/29/4/048102
Abstract   PDF(pc) (2803KB) ( 425 )
Diamond is synthesized in an Fe-Ni-C system at high pressure and high temperature, the C sp3 content profile through different thicknesses of interface between diamond and the catalyst film is measured by using electron energy loss spectroscopy. It is found that the C sp3 content varies from 87.33% to 78.15% when the measured position is located at the inner face near the diamond and then changes to 6 µm further away. Transmission electron microscope examinations show that there are different phases in the interface, such as Fe3C, γ−(Fe,Ni), and graphite, but the graphite phase diminishes gradually towards the inner face of the interface. These results profoundly indicate that the carbon atoms, required for diamond growth, could only come from the carbon-rich phase, Fe3C, but not directly from the graphite. It is possible that carbon atoms from the graphite in the interface first react with Fe atoms to produce carbide Fe3C during diamond synthesis at high pressure and high temperature. The Fe3C finally decomposes into carbon atoms with the sp3 electron state at the interface to form the diamond.
Emergence and Decline of Scientific Paradigms in a Two-Group System
ZHANG Feng-Li,ZHANG Mei**
Chin. Phys. Lett. 2012, 29 (4): 048701 .   DOI: 10.1088/0256-307X/29/4/048701
Abstract   PDF(pc) (669KB) ( 393 )
Idea spreading is an important process in science and society. In this work, we study this spreading process in a population consisting of two groups based on a recent model proposed by Bornholdt et al. We consider two types of division in the population: regular and random division. We find some interesting phenomena, for example, the exchange of dominant ideas between the two groups in the cases of regular and the random division, and the appearance of a novel stage in which a few ideas interact strongly to seek a balance.
The Efficiency of a Small-World Functional Brain Network
ZHAO Qing-Bai,ZHANG Xiao-Fei,SUI Dan-Ni,ZHOU Zhi-Jin,CHEN Qi-Cai,TANG Yi-Yuan,**
Chin. Phys. Lett. 2012, 29 (4): 048702 .   DOI: 10.1088/0256-307X/29/4/048702
Abstract   PDF(pc) (740KB) ( 546 )
We investigate whether the small-world topology of a functional brain network means high information processing efficiency by calculating the correlation between the small-world measures of a functional brain network and behavioral reaction during an imagery task. Functional brain networks are constructed by multichannel event-related potential data, in which the electrodes are the nodes and the functional connectivities between them are the edges. The results show that the correlation between small-world measures and reaction time is task-specific, such that in global imagery, there is a positive correlation between the clustering coefficient and reaction time, while in local imagery the average path length is positively correlated with the reaction time. This suggests that the efficiency of a functional brain network is task-dependent.
An Improved Adaptive model for Information Recommending and Spreading
CHEN Duan-Bing**,GAO Hui
Chin. Phys. Lett. 2012, 29 (4): 048901 .   DOI: 10.1088/0256-307X/29/4/048901
Abstract   PDF(pc) (715KB) ( 523 )
People in the Internet era have to cope with information overload and expend great effort on finding what they need. Recent experiments indicate that recommendations based on users' past activities are usually less favored than those based on social relationships, and thus many researchers have proposed adaptive algorithms on social recommendation. However, in those methods, quite a number of users have little chance to recommend information, which might prevent valuable information from spreading. We present an improved algorithm that allows more users to have enough followers to spread information. Experimental results demonstrate that both recommendation precision and spreading effectiveness of our method can be improved significantly.
Community Detection by Neighborhood Similarity
LIU Xu,XIE Zheng,YI Dong-Yun**
Chin. Phys. Lett. 2012, 29 (4): 048902 .   DOI: 10.1088/0256-307X/29/4/048902
Abstract   PDF(pc) (474KB) ( 568 )
Detection of the community structure in a network is important for understanding the structure and dynamics of the network. By exploring the neighborhood of vertices, a local similarity metric is proposed, which can be quickly computed. The resulting similarity matrix retains the same support as the adjacency matrix. Based on local similarity, an agglomerative hierarchical clustering algorithm is proposed for community detection. The algorithm is implemented by an efficient max-heap data structure and runs in nearly linear time, thus is capable of dealing with large sparse networks with tens of thousands of nodes. Experiments on synthesized and real-world networks demonstrate that our method is efficient to detect community structures, and the proposed metric is the most suitable one among all the tested similarity indices.
Dynamical Influence of Nodes Revisited: A Markov Chain Analysis of Epidemic Process on Networks
LI Ping, ZHANG Jie, XU Xiao-Ke, SMALL Michael
Chin. Phys. Lett. 2012, 29 (4): 048903 .   DOI: 10.1088/0256-307X/29/4/048903
Abstract   PDF(pc) (518KB) ( 670 )
We provide a theoretical analysis of node importance from the perspective of dynamical processes on networks. In particular, using Markov chain analysis of the susceptible-infected-susceptible (SIS) epidemic model on networks, we derive the node importance in terms of dynamical behaviors on network in a theoretical way. It is found that this quantity happens to be the eigenvector centrality under some conditions, which bridges the topological centrality measure of the nodes with the dynamical influence of the nodes for the dynamical process. We furthermore discuss the condition under which the eigenvector centrality is valid for dynamical phenomena on networks.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
In Situ Observation of Gypsum-Anhydrite Transition at High Pressure and High Temperature
LIU Chuan-Jiang,ZHENG Hai-Fei**
Chin. Phys. Lett. 2012, 29 (4): 049101 .   DOI: 10.1088/0256-307X/29/4/049101
Abstract   PDF(pc) (1096KB) ( 954 )
An in-situ Raman spectroscopic study of gypsum-anhydrite transition under a saturated water condition at high pressure and high temperature is performed using a hydrothermal diamond anvil cell (HDAC). The experimental results show that gypsum dissolvs in water at ambient temperature and above 496 MPa. With increasing temperature, the anhydrite (CaSO4) phase precipitates at 250–320°C in the pressure range of 1.0–1.5 GPa, indicating that under a saturated water condition, both stable conditions of pressure and temperature and high levels of Ca and SO4 ion concentrations in aqueous solution are essential for the formation of anhydrite. A linear relationship between the pressure and temperature for the precipitation of anhydrite is established as P(GPa)=0.0068T−0.7126 (250°C≤T≤320°C). Anhydrite remained stable during rapid cooling of the sample chamber, showing that the gypsum-anhydrite transition involving both dissolution and precipitation processes is irreversible at high pressure and high temperature.
Effect of Ultrastrong Magnetic Field on the Electron Capture in the Stellar Surroundings
WANG Kun,LUO Zhi-Quan**,LI Ying-Lin
Chin. Phys. Lett. 2012, 29 (4): 049701 .   DOI: 10.1088/0256-307X/29/4/049701
Abstract   PDF(pc) (494KB) ( 427 )
Using the nuclear shell model, we study the influence of ultra-strong magnetic field on the electron capture nuclei reactions 56,58Co→56,58Fe, 56,57Ni→56,57Co, 52,53Fe→52,53Mn and 57,60Cu→57,60Ni. The results show that the electron capture rates of most iron group nuclei are increased greatly in the ultrastrong magnetic field, and even exceed three orders of magnitude in the range from 5×1013 G to 2.5×1017 G.
70 articles