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Volume 27 Issue 9
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GENERAL
New Type Soliton Solutions to Korteweg-de Vries and Benjamin-Bona-Mahony Equations
LIU Yu
Chin. Phys. Lett. 2010, 27 (9): 090201 .   DOI: 10.1088/0256-307X/27/9/090201
Abstract   PDF(pc) (413KB) ( 777 )

We study the Korteweg-de Vries equation and the Benjamin-Bona-Mahony equation, and obtain three kinds of new type soliton solutions, i.e. peakon solutions, double-peak (peaked-point and peaked-compacton) soliton solutions. A double solitary wave with blow-up points is also contained.

Effect of Geometric Distance on Agreement Dynamics of Naming Game
HAO Jia-Bo, YANG Han-Xin, LIU Run-Ran, WANG Bing-Hong, ZHANG Zhi-Yuan
Chin. Phys. Lett. 2010, 27 (9): 090202 .   DOI: 10.1088/0256-307X/27/9/090202
Abstract   PDF(pc) (548KB) ( 643 )
We investigate the naming game on geometric networks. The geometric networks are constructed by adding geometric links to two-dimensional regular lattices. It is found that the agreement time is a non-monotonic function of the geometric distance and there exists an optimal value of the geometric distance resulting in the shortest agreement time. All these results show that the geometric distance plays an important role in the evolutionary process of the language game. Our results also show that the convergence time strongly depends on the number of adding links.
An Application of a Generalized Version of the Dressing Method to Integration of a Variable-Coefficient Dirac System
SU Ting, WANG Zhi-Wei
Chin. Phys. Lett. 2010, 27 (9): 090203 .   DOI: 10.1088/0256-307X/27/9/090203
Abstract   PDF(pc) (387KB) ( 376 )

By using the generalized version of the dressing method, we consider a Dirac system. The types of nonlinear evolution equations discussed involve the integrable variable-coefficient Dirac equation and the defocusing nonlinear Schrödinger equation. As an application, their explicit solutions and Lax pairs are given.

A New Quantum Key Distribution Scheme Based on Frequency and Time Coding
ZHU Chang-Hua, PEI Chang-Xing, QUAN Dong-Xiao, GAO Jing-Liang, CHEN Nan, YI Yun-Hui
Chin. Phys. Lett. 2010, 27 (9): 090301 .   DOI: 10.1088/0256-307X/27/9/090301
Abstract   PDF(pc) (439KB) ( 552 )

A new scheme of quantum key distribution (QKD) using frequency and time coding is proposed, in which the security is based on the frequency-time uncertainty relation. In this scheme, the binary information sequence is encoded randomly on either the central frequency or the time delay of the optical pulse at the sender. The central frequency of the single photon pulse is set as ω1 for bit 0 and set as ω2 for bit 1 when frequency coding is selected. However, the single photon pulse is not delayed for bit 0 and is delayed in τ for 1 when time coding is selected. At the receiver, either the frequency or the time delay of the pulse is measured randomly, and the final key is obtained after basis comparison, data reconciliation and privacy amplification. With the proposed method, the effect of the noise in the fiber channel and environment on the QKD system can be reduced effectively.

Wigner Functions for the Bateman System on Noncommutative Phase Space
HENG Tai-Hua, LIN Bing-Sheng, JING Si-Cong
Chin. Phys. Lett. 2010, 27 (9): 090302 .   DOI: 10.1088/0256-307X/27/9/090302
Abstract   PDF(pc) (422KB) ( 458 )

We study an important dissipation system, i.e. the Bateman model on noncommutative phase space. Using the method of deformation quantization, we calculate the Exp functions, and then derive the Wigner functions and the corresponding energy spectra.

Testing Evolution Equation for Entanglement of Two-Qubit Systems in Noisy Channels on Ensemble Quantum Computers
ZHANG Han, , LUO Jun, REN Ting-Ting, , SUN Xian-Ping,
Chin. Phys. Lett. 2010, 27 (9): 090303 .   DOI: 10.1088/0256-307X/27/9/090303
Abstract   PDF(pc) (493KB) ( 448 )

We report the experimental demonstration of decoherence dynamics of entanglement for the four Bell states in two-qubit nuclear-spin systems on ensemble quantum computers. Using artificial error operators to simulate noisy channels, we experimentally investigate the effect of noises on the four Bell states, and furthermore observe the time evolution of entanglement for the four Bell states in different noisy channels by calculating concurrences. Our experimental results show that the concurrences of the different Bell states under the same artificial error operations have the same values within the experimental error, and are independent of the different Bell states. These experimental results verify the theoretical evolution equation developed by Konrad et al.[Nature Phys. 4(2008)99] for two-qubit entanglement.

A New Approach for Constructing New Coherent-Entangled State Representations
MA Shan-Jun, XU Xue-Xiang
Chin. Phys. Lett. 2010, 27 (9): 090304 .   DOI: 10.1088/0256-307X/27/9/090304
Abstract   PDF(pc) (379KB) ( 375 )

A convenient approach for deriving new quantum mechanical coherent-entangled state representations is proposed to construct the integration of unity in normally ordered Gaussian operator forms and then decomposing it as projection operators. As examples, the n-mode complicated entangled state representations are derived and their application is presented.

From the Thermo Wigner Operator to the Thermo Husimi Operator in Thermo Field Dynamics
XU Xue-Fen, ZHU Shi-Qun
Chin. Phys. Lett. 2010, 27 (9): 090305 .   DOI: 10.1088/0256-307X/27/9/090305
Abstract   PDF(pc) (388KB) ( 367 )

Using the thermo entangled state representation and based on the thermo Wigner operator we first introduce the thermo Husimi operator, which turns out to be a projective operator of the thermo squeezed coherent state, therefore the positive definite property of Husimi distribution function can be insured. In addition, we find the use of the thermo Husimi operator in simplifying the form of master equations.

Entanglement of Superpositions of Orthogonal Maximally Entangled States
ZHANG Dao-Hua, ZHOU Duan-Lu, FAN Heng
Chin. Phys. Lett. 2010, 27 (9): 090306 .   DOI: 10.1088/0256-307X/27/9/090306
Abstract   PDF(pc) (413KB) ( 521 )

We study the entanglement properties of the superposed state of orthogonal maximally entangled states. It is shown that the superposed state is maximally entangled and the superposed state is separable. The relation between the superposed state and the mutually unbiased state is discussed.

Cryptanalysis and Improvement of Two GHZ-State-Based QSDC Protocols
GUO Fen-Zhuo, QIN Su-Juan, WEN Qiao-Yan, ZHU Fu-Chen
Chin. Phys. Lett. 2010, 27 (9): 090307 .   DOI: 10.1088/0256-307X/27/9/090307
Abstract   PDF(pc) (383KB) ( 423 )

In a recent paper[J. Korean. Phys. Soc. 49(2006)459], two GHZ-state-based quantum secure direct communication protocols were presented. Here we point out that an eavesdropper can utilize a special property of GHZ states, i.e. "correlation-elicitable" to obtain half information of the transmitted secrets without being detected in both protocols. The particular attack strategy is demonstrated in detail. Furthermore, a possible improvement is proposed, which makes the protocols secure against this kind of attack.

Analytical Approach to Space- and Time-Fractional Burgers Equations
Ahmet Y�, ld�, r�, m, Syed Tauseef Mohyud-Din**
Chin. Phys. Lett. 2010, 27 (9): 090501 .   DOI: 10.1088/0256-307X/27/9/090501
Abstract   PDF(pc) (1519KB) ( 667 )

A scheme is developed to study numerical solution of the space- and time-fractional Burgers equations under initial conditions by the homotopy analysis method. The fractional derivatives are considered in the Caputo sense. The solutions are given in the form of series with easily computable terms. Numerical solutions are calculated for the fractional Burgers equation to show the nature of solution as the fractional derivative parameter is changed.

Thermodynamic Performance Characteristics of an Irreversible Micro-Brownian Heat Engine Driven by Temperature Difference
ZHANG Yan-Ping, HE Ji-Zhou
Chin. Phys. Lett. 2010, 27 (9): 090502 .   DOI: 10.1088/0256-307X/27/9/090502
Abstract   PDF(pc) (527KB) ( 449 )

Based on the master equation describing the particles jump among barriers, the expressions of current, efficiency and power output of the heat engine are derived analytically. The general performance characteristic curves are plotted from the numerical calculation. It is found that the power output-efficiency curve is a loop-shaped one which is similar to the one for a real irreversible heat engine. When the heat flow via the kinetic energy is neglected, the power output-efficiency curve is an open-shaped one which is similar to the one for an endroeversible heat engine.

Chaotic System Identification Based on a Fuzzy Wiener Model with Particle Swarm Optimization
LI Yong, TANG Ying-Gan
Chin. Phys. Lett. 2010, 27 (9): 090503 .   DOI: 10.1088/0256-307X/27/9/090503
Abstract   PDF(pc) (561KB) ( 585 )

A fuzzy Wiener model is proposed to identify chaotic systems. The proposed fuzzy Wiener model consists of two parts, one is a linear dynamic subsystem and the other is a static nonlinear part, which is represented by the Takagi-Sugeno fuzzy model. Identification of chaotic systems is converted to find optimal parameters of the fuzzy Wiener model by minimizing the state error between the original chaotic system and the fuzzy Wiener model. Particle swarm optimization algorithm, a global optimizer, is used to search the optimal parameter of the fuzzy Wiener model. The proposed method can identify the parameters of the linear part and nonlinear part simultaneously. Numerical simulations for Henón and Lozi chaotic system identification show the effectiveness of the proposed method.

Fast-Scale and Slow-Scale Subharmonic Oscillation of Valley Current-Mode Controlled Buck Converter
ZHOU Guo-Hua, XU Jian-Ping, BAO Bo-Cheng, ZHANG Fei, LIU Xue-Shan
Chin. Phys. Lett. 2010, 27 (9): 090504 .   DOI: 10.1088/0256-307X/27/9/090504
Abstract   PDF(pc) (639KB) ( 781 )

A valley current-mode (VCM) controlled buck converter with current source load (CSI) has complex phenomena of fast-scale and slow-scale subharmonic oscillations. The piecewise smooth switching model of the VCM controlled buck converter with CSI is established. It is found that attractive regions of fast-scale and slow-scale subharmonic oscillations exist in the bifurcation diagram, and two tori exist in the corresponding Poincaré mapping. The research results by time-domain simulation indicate that U-type subharmonic oscillation (SO) constituted by SO and frequency-reduced subharmonic oscillation (FSO) exists in inductor current, and sine-type SO constituted by fast scale and low scale exists in output voltage respectively. Experimental results are given to verify the analysis and simulation results.

Bosons or Fermions in 1D Power Potential Trap with Repulsive Delta Function Interaction
MA Zhong-Qi, C. N. Yang,
Chin. Phys. Lett. 2010, 27 (9): 090505 .   DOI: 10.1088/0256-307X/27/9/090505
Abstract   PDF(pc) (680KB) ( 471 )

We study the ground state of a 1D many Boson or Fermion system with repulsive delta function interparticle interaction trapped in an external potential V(x) = |x|a/2 where a>0.

Stochastic Resonance in a Time-Delayed Bistable System Driven by Square-Wave Signal
GUO Feng, ZHOU Yu-Rong, ZHANG Yu
Chin. Phys. Lett. 2010, 27 (9): 090506 .   DOI: 10.1088/0256-307X/27/9/090506
Abstract   PDF(pc) (483KB) ( 620 )

Stochastic resonance in a time-delayed bistable system subject to asymmetric dichotomous noise and multiplicative and additive white noise is investigated. Using small time delay approximation, we obtain the expression of the signal-to-noise ratio (SNR). It is found that the SNR is a non-monotonic function of the delayed times, of the amplitude of the input square-wave signal, as well as of the asymmetry of the dichotomous noise. In addition, the SNR varies non-monotonously with the system parameters, with the intensities of the multiplicative and additive noise, as well as with the correlate rate of the dichotomous noise.

NUCLEAR PHYSICS
Effects of Pairing Correlations on Formation of Proton Halo in 9C
HAN Rui, LI Jia-Xing, YAO Jiang-Ming, JI Juan-Xia, WANG Jian-Song, HU Qiang
Chin. Phys. Lett. 2010, 27 (9): 092101 .   DOI: 10.1088/0256-307X/27/9/092101
Abstract   PDF(pc) (619KB) ( 551 )

Properties for the ground state of 9C are studied in the relativistic continuum Hartree-Bogoliubov theory with the NLSH, NLLN and TM2 effective interactions. Pairing correlations are taken into account by a density-dependent δ-force with the pairing strength for protons determined by fitting either to the experimental binding energy or to the odd-even mass difference from the five-point formula. The effects of pairing correlations on the formation of proton halo in the ground state of 9C are examined. The halo structure is shown to be formed by the partially occupied valence proton levels p3/2 and p1/2.

Elastic Scattering of 6He + p at 82.3MeV/nucleon
FAISAL Jamil-Qureshi, LOU Jian-Ling, YE Yan-Lin, CAO Zhong-Xin, JIANG Dong-Xing, ZHENG Tao, HUA Hui, LI Zhi-Huan, LI Xiang-Qing, GE Yu-Cheng, PANG Dan-Yang, LI Qi-Te, XIAO Jun, LV Lin-Hui, QIAO Rui, YOU Hai-Bo, CHEN Rui-Jiu, LU Fei, Sakurai H, Otsu H, Nishimura M, Sakaguchi S, Baba H, Togano Y, Yoneda K, LI Chen, WANG Shuo, WANG He, LI Kuo-Ang, Nakamura T, Nakayama Y, Kondo Y, Deguchi S, Satou Y, Tshoo K H
Chin. Phys. Lett. 2010, 27 (9): 092501 .   DOI: 10.1088/0256-307X/27/9/092501
Abstract   PDF(pc) (1702KB) ( 532 )

Differential cross sections for the elastic scattering of halo nucleus 6He on proton target were measured at 82.3MeV/u. The experimental results are well reproduced by optical model calculations using global potential KD02 with a reduction of the depth of real volume part by a factor of 0.7. A systematic analysis shows that this behavior might be related to the weakly bound property of unstable nuclei.

ATOMIC AND MOLECULAR PHYSICS
Dynamics of H2 in Intense Femtosecond Laser Field
ZHU Jing-Yi, LIU Ben-Kang, WANG Yan-Qiu, HE Hai-Xiang, WANG Li
Chin. Phys. Lett. 2010, 27 (9): 093301 .   DOI: 10.1088/0256-307X/27/9/093301
Abstract   PDF(pc) (703KB) ( 460 )

Fragmentation of H2 in femtosecond laser field is studied by using velocity map ion imaging method and 70 fs laser at 405 nm and 810 nm from 0.3 to 3.0×1014 W/cm2. Angular distributions from Coulomb explosion are independent of the laser wavelengths and intensities, which means the explosion starts from the same electronic state. Angular distributions from dissociation channels in the 810 nm laser field broaden with the laser intensity. Lobe structures in angular distributions from Coulomb explosion and above threshold dissociation channels are reported. Fine structures in the distribution of internuclear distances are observed.

Rovibrational Formation of Ultracold NaH Molecules Induced by an Ultrashort Laser Pulse
SU Qian-Zhen, YU Jie, NIU Ying-Yu, CONG Shu-Lin
Chin. Phys. Lett. 2010, 27 (9): 093401 .   DOI: 10.1088/0256-307X/27/9/093401
Abstract   PDF(pc) (612KB) ( 399 )

The formation of the NaH molecule from unaligned ultracold atoms via photoassociation (PA) is theoretically investigated by numerically solving the time-dependent Schrödinger equation including the vibrational and rotational degrees of freedom. The PA processes via one- and two-photon excitations are described. The calculated results show that the associated molecule can be prepared to a desired rovibrational state of the ground electronic state for NaH. Compared with the one-photon association probability, the two-photon association probability is obviously enhanced.

Photoabsorption Spectra of (SiO2)n (n≤5) Clusters on the Basis of Time-Dependent Density Functional Theory
LIU Dan-Dan, ZHANG Hong
Chin. Phys. Lett. 2010, 27 (9): 093601 .   DOI: 10.1088/0256-307X/27/9/093601
Abstract   PDF(pc) (671KB) ( 402 )

The photoabsorption spectra of (SiO2)n (n=2-5) clusters [including isomers (D3h,D2d) structures of (SiO2)3 and (C2v,D2h,D4h) structures of (SiO2)4] are calculated by using time-dependent density-function theory. The equilibrium geometries, the binding energy, the gap between the highest occupied and lowest unoccupied molecular orbitals and vertical ionization potential for corresponding structures are computed using several methods with different types of the basis functions. It is found that the polarizability functions are necessary for the basis functions when optimize the structures of silicon oxide clusters. For different geometries of various clusters and the related isomers, their spectra are very different. Meanwhile, the comparison between using local-density generalized-gradient approximations for exchange-correlation potentials shows that both the calculated spectra present the same spectral feature. We suggest that the calculated photoabsorption spectra could be taken as a tool to elucidate the isomers and clusters structure.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Influence of Filling Medium of Holes on the Negative-Index Response of Sandwiched Metamaterials
WANG Xu-Dong, YE Yong-Hong, MA Ji, JIANG Mei-Ping
Chin. Phys. Lett. 2010, 27 (9): 094101 .   DOI: 10.1088/0256-307X/27/9/094101
Abstract   PDF(pc) (894KB) ( 582 )

We numerically study the negative index properties of sandwiched metamaterials, perforated with a square array of circle holes filled with different media. Transmission spectra indicate that the filling medium can effectively change the position of the localized resonant peak, while keeping the position of the other transmission peaks hardly changed. Reflection spectra and retrieved effective impedance verify that an appropriate choice of the filling medium can provide a perfect impedance match. Due to the perfect impedance match, the electromagnetic responses of the negative index band based on the internal surface plasmon polaritons change in many aspects, such as a stronger magnetic resonance, a higher figure of merit and a narrower negative refractive index band.

Detection of Perfect Cloak in Time Domain
SU Yu-Huan, SHI Jin-Wei, LIU Da-He, YANG Guo-Jian
Chin. Phys. Lett. 2010, 27 (9): 094102 .   DOI: 10.1088/0256-307X/27/9/094102
Abstract   PDF(pc) (803KB) ( 393 )

We propose a method for detecting perfect invisible cloak based on the scattering of the materials of the cloak. The position of the detected cloak can also be determined. The demonstration shows that the detecting effect is obvious, and the accuracy of the detection is high.

The Axial Spatial Evolution of Optical Field near the Talbot Plane of a Grating
LU Yun-Qing, LI Pei-Li, ZHENG Jia-Jin
Chin. Phys. Lett. 2010, 27 (9): 094201 .   DOI: 10.1088/0256-307X/27/9/094201
Abstract   PDF(pc) (536KB) ( 402 )

The diffraction field distribution of a high density grating with a period of 2.5λ is analyzed with the finite-difference time-domain (FDTD) method. The numerical results show the axial spatial evolution of the optical field near the 1/2 Talbot plane of the grating, which is verified by experiment with the scanning near-field optical microscopy (SNOM) technique. It should be helpful for understanding more clearly the diffraction behavior of a high density grating in micro- and nano-optics and be beneficial for applications of the Talbot effect, such as the near-field photolithography.

Effect of Zeroth-Order beam on Azobenzene Polymer Surface Relief Gratings Fabricated by Phase-Mask Method
WU Wen-Xuan, LUO Yan-Hua, CHENG Xu-Sheng, TIAN Xiu-Jie, QIU Wei-Wei, REN Xi-Feng, ZHU Bing, ZHANG Qi-Jin,
Chin. Phys. Lett. 2010, 27 (9): 094202 .   DOI: 10.1088/0256-307X/27/9/094202
Abstract   PDF(pc) (897KB) ( 405 )

In the fabrication of surface relief gratings (SRGs) on azobenzene polymer films with a zeroth-order suppressed diffraction phase mask, it is found that the SRGs' relief figure and period change with the irradiation time, and the period is doubled after a critical time. The time dependence of the changes in the SRG forming process is investigated by theoretical analysis and experiments. An optimum time range for inscription of the sub-micron SRGs is determined to be 5-8 min in terms of both the theoretical and experimental results.

Range-Gated Laser Stroboscopic Imaging for Night Remote Surveillance
WANG Xin-Wei, ZHOU Yan, FAN Song-Tao, HE Jun, LIU Yu-Liang
Chin. Phys. Lett. 2010, 27 (9): 094203 .   DOI: 10.1088/0256-307X/27/9/094203
Abstract   PDF(pc) (566KB) ( 791 )

For night remote surveillance, we present a method, the range-gated laser stroboscopic imaging(RGLSI), which uses a new kind of time delay integration mode to integrate target signals so that night remote surveillance can be realized by a low-energy illuminated laser. The time delay integration in this method has no influence on the video frame rate. Compared with the traditional range-gated laser imaging, RGLSI can reduce scintillation and target speckle effects and significantly improve the image signal-to-noise ratio analyzed. Even under low light level and low visibility conditions, the RGLSI system can effectively work. In a preliminary experiment, we have detected and recognized a railway bridge one kilometer away under a visibility of six kilometers, when the effective illuminated energy is 29.5 μJ.

A Two-Stage S-Band Erbium-Doped Fiber Amplifier Based on W-type Erbium-Doped Fiber
DING Lei, JIA Yuan-Yuan, XING Jun-Bo, ZHANG Zhen, SUN Jian-Jun, LU Ke-Cheng
Chin. Phys. Lett. 2010, 27 (9): 094204 .   DOI: 10.1088/0256-307X/27/9/094204
Abstract   PDF(pc) (396KB) ( 538 )

An S-band erbium-doped fiber (EDF) amplifier based on a W-type EDF designed by ourselves is demonstrated by employing a two-stage double-pass configuration. The amplifier provides a bandwidth of 34 nm (1486-1520 nm) for the gain over 20 dB. The maximal gain of 32.8 dB is achieved at 1501 nm and the corresponding noise figure is 6.0 dB. The proposed amplifier has a promising foreground in extending the current network to the S band.

Enhanced Surface-Plasmon-Polariton Interference for Nanolithography by a Micro-Cylinder-Lens Array
LIANG Hui-Min, WANG Jing-Quan, FAN Feng, QIN Ai-Li, ZHANG Chun-Yuan, CHENG Hui
Chin. Phys. Lett. 2010, 27 (9): 094205 .   DOI: 10.1088/0256-307X/27/9/094205
Abstract   PDF(pc) (684KB) ( 408 )

A practical interference lithography scheme based on surface plasmon polaritions (SPPs) is suggested. In this scheme, a micro-cylinder-lens array is employed to generate the evanescent wave (EW) carrying much energy. When the top of the cylinder lenses are in close contact with a metal film coated on a resist, the energy of EW will launch strong SPPs and form enhanced interference nanopatterns in the resist. The simulation results confirm that a high quality nanopattern with a critical dimension of λ/7 can be achieved in the resistance. The analysis results indicate that the height of the cylinder lenses can provide a large tolerance to decrease the fabrication difficulty of this element.

An Experiment for Generating the 14-Tone Stable Carriers Using Recirculating Frequency Shifter
TIAN Feng, ZHANG Xiao-Guang, LI Jian-Ping, XI Li-Xia
Chin. Phys. Lett. 2010, 27 (9): 094206 .   DOI: 10.1088/0256-307X/27/9/094206
Abstract   PDF(pc) (539KB) ( 443 )

In experiment, the generation of 14-tone stable carriers with recirculating frequency shifter is realized. Some factors that impact the performance of the carrier generation are discussed. It is experimentally found that the balance and the insertion loss of the inphase/quadrature (I/Q) modulator, the accurate π/2 phase difference and equal power level of two rf signals which are applied to the two ports of the I/Q modulator, the gain of the optical amplifier, the bandwidth and sharp window spectrum of the tunable filter and the stability of the optical signals' states of polarization fed into I/Q modulator, play important roles in the generation of a stable multi-tone carrier source. By employing appropriate techniques we obtain 14-tone stable carriers in the experiment.

Wafer-Level Testable High-Speed Silicon Microring Modulator Integrated with Grating Couplers
XIAO Xi, ZHU Yu, XU Hai-Hua, ZHOU Liang, HU Ying-Tao, LI Zhi-Yong, LI Yun-Tao, YU Yu-De, YU Jin-Zhong
Chin. Phys. Lett. 2010, 27 (9): 094207 .   DOI: 10.1088/0256-307X/27/9/094207
Abstract   PDF(pc) (1206KB) ( 454 )

A wafer-level testable silicon-on-insulator-based microring modulator is demonstrated with high modulation speed, to which the grating couplers are integrated as the fiber-to-chip interfaces. Cost-efficient fabrications are realized with the help of optical structure and etching depth designs. Grating couplers and waveguides are patterned and etched together with the same slab thickness. Finally we obtain a 3-dB coupling bandwidth of about 60 nm and 10 Gb/s nonreturn-to-zero modulation by wafer-level optical and electrical measurements.

High-Frequency Einstein-Podolsky-Rosen Entanglement via Atomic Memory Effects in Four-Wave Mixing
ZHANG Xue-Hua, HU Xiang-Ming, KONG Ling-Feng, ZHANG Xiu
Chin. Phys. Lett. 2010, 27 (9): 094208 .   DOI: 10.1088/0256-307X/27/9/094208
Abstract   PDF(pc) (570KB) ( 386 )

Atomic memory effects occur when the atomic relaxation times are comparable to or much longer than the cavity relaxation times. We show that by using the memory effects, it is possible to obtain high-frequency Einstein-Podolsky-Rosen entanglement between a pair of Stokes and anti-Stokes fields in a four-wave mixing system. The physical origin is traced to the dynamical Stark splittings of dressed states due to the parametrically amplified fields. This mechanism provides an alternative and efficient way for sideband entanglement.

An Optical Labeling Scheme with Novel DPSK/PPM Orthogonal Modulation
ZHOU Rui, XIN Xiang-Jun, WANG Yong-Jun, ZHANG Zi-Xing, YU Chong-Xiu
Chin. Phys. Lett. 2010, 27 (9): 094209 .   DOI: 10.1088/0256-307X/27/9/094209
Abstract   PDF(pc) (911KB) ( 447 )

A novel differential-phase-shift-keying (DPSK)/pulse-position-modulation (PPM) orthogonal modulation is proposed for optical labeling applications, with PPM data as the high-speed payload and DPSK signal as the optical label. The systematic setup for the proposed scheme and research on bit-error rate is presented. The results show that at the bit-error rate of 10-9, the power penalties for 70 km fiber transmission are in the range of 1-3 dB to DPSK label and 5-6 dB to PPM payload in our simulation system. This is under the condition that the large extinction ratio of 18-19 dB is used for the intensity modulators of the PPM payload, with a well received DPSK label. Thus the feasibility of the proposed scheme for all optical transmission networks is clearly verified.

Imaging for Borehole Wall by a Cylindrical Linear Phased Array
ZHANG Bi-Xing, SHI Fang-Fang, WU Xian-Mei, GONG Jun-Jie, ZHANG Cheng-Guang
Chin. Phys. Lett. 2010, 27 (9): 094301 .   DOI: 10.1088/0256-307X/27/9/094301
Abstract   PDF(pc) (931KB) ( 489 )

A new ultrasonic cylindrical linear phased array (CLPA) transducer is designed and fabricated for the borehole wall imaging in petroleum logging based on the previous theoretical researches. First, the CLPA transducer, which is made up of numbers of the piezoelectric elements distributed on the surface of a cylinder uniformly, is designed and fabricated. By transmitting and receiving acoustic waves with 16 active elements and using different groups of the elements under the control of the electric system, the CLPA can scan all areas of the borehole wall dynamically and rapidly without a traditional mechanism around the borehole axis. Then, the theoretical and experimental investigations are conducted in detail for the borehole wall scanning and imaging by the steel pipe and casing borehole with defects distributed in different shapes and directions. It is shown by experiments that the CLPA transducer has good focusing characteristic and good resolution for the borehole wall imaging in acoustic logging.

Pharmacokinetic Monitoring of Indocyanine Green for Tumor Detection Using Photoacoustic Imaging
YANG Si-Hua, YIN Guang-Zhi, XING Da
Chin. Phys. Lett. 2010, 27 (9): 094302 .   DOI: 10.1088/0256-307X/27/9/094302
Abstract   PDF(pc) (580KB) ( 625 )

We report tumor detection using a photoacoustic technique for the imaging of angiogenesis and monitoring of agent pharmacokinetics on an animal model. We take 532-nm laser pulses to excite photoacoustic signals of blood vessels with acquisition by a broadband hydrophone, and the morphological characteristics of tumor angiogenesis are successfully image depicted. Furthermore, tumor pharmacokinetics is preformed and analyzed with fast multielement photoacoustic imaging of the intravenous-injected indocyanine green (ICG). Photoacoustic signals of ICG are excited with 805 nm laser pulses and recorded by transducer array as a function of time. The difference between the photoacoustic signal from the tumor side and that from the normal side is observed, and the ICG clearance velocity in the tumor area is found to lag behind that in the normal area. Experimental results demonstrate that photoacoustic imaging of morphological parameter and pharmacokinetics with specific agent may provide high sensitive approach for tumor detection and localization.

Effect of Tissue Inhomogeneity on Nonlinear Propagation of Focused Ultrasound
LIU Zhen-Bo, FAN Ting-Bo, GUO Xia-Sheng, ZHANG Dong
Chin. Phys. Lett. 2010, 27 (9): 094303 .   DOI: 10.1088/0256-307X/27/9/094303
Abstract   PDF(pc) (1065KB) ( 428 )

We study the influence of tissue inhomogeneity on the focused ultrasound based on the phase screen model and the acoustic nonlinear equation. The inhomogeneous tissue is considered as a combination of a homogeneous medium and a phase aberration screen. Six polyethylene (PE) plates with various correlation lengths and standard deviations are made to mimic the inhomogeneity induced by the human body abdominal. Results indicate that the correlation length affects the side lobe structure of the beam pattern; while the standard deviation is associated with the focusing capability. This study provides a theoretical and experimental basis for the development of a precise treatment plan for high intensity focused ultrasound.

A Spectral Coupled-Mode Formulation for Sound Propagation around Axisymmetric Seamounts
LUO Wen-Yu, SCHMIDT Henrik
Chin. Phys. Lett. 2010, 27 (9): 094304 .   DOI: 10.1088/0256-307X/27/9/094304
Abstract   PDF(pc) (454KB) ( 349 )

A spectral coupled-mode solution of the three-dimensional (3D) acoustic field generated by a point source in the presence of an axisymmetric seamount is developed. Based on the same theoretical foundation as the formulation presented by Taroudakis [J. Comput. Acoust. 4 (1996) 101], the present approach combines a spectral decomposition in azimuth with a coupled-mode theory for two-way range-dependent propagation. However, the earlier formulations are severely limited in terms of frequency, size and geometry of the seamount, the seabed composition, and the distance between the source and the seamount, and are therefore severely limited in regard to realistic seamount problems. Without changing the fundamental theoretical foundation, the present approach applies a number of modifications to the formulation, leading to orders of magnitude improvement in numerical efficiency for realistic problems. Therefore, realistic propagation and scattering scenarios can be modeled, including effects of seamount roughness and realistic sedimentary structure.

Simulation of Non-Newtonian Blood Flow by Lattice Boltzman Method
JI Yu-Pin, KANG Xiu-Ying, LIU Da-He
Chin. Phys. Lett. 2010, 27 (9): 094701 .   DOI: 10.1088/0256-307X/27/9/094701
Abstract   PDF(pc) (1082KB) ( 497 )

Blood flow under various conditions of vessel is simulated as a non-Newtonian fluid by the two-dimensional Lattice Boltzmann method, in which the Casson model is used to express the relationship between viscosity and shear rate of the blood. The flow field distributions at certain sites near the narrowing and bifurcation of the vessel explain the hemodynamic mechanism of the predilection of the atherosclerotic lesions for these sites which are consistent with that found by medical studies.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Effects of Perpendicular Thermal Velocities on the Transverse Instability in Electron Phase Space Holes
WU Ming-Yu, WU Hong, LU Quan-Ming, XUE Bing-Sen
Chin. Phys. Lett. 2010, 27 (9): 095201 .   DOI: 10.1088/0256-307X/27/9/095201
Abstract   PDF(pc) (754KB) ( 441 )

A multi-dimensional electron phase-space hole (electron hole) is considered to be unstable to the transverse instability. We perform two-dimensional (2D) particle-in-cell (PIC) simulations to study the evolutions of electron holes in weakly magnetized plasma (Ωepe, where Ωe and ωpe are the electron gyrofrequency and plasma frequency, respectively), and the effects of perpendicular thermal velocities on the transverse instability are investigated. The transverse instability can cause decay of the electron holes. We find that with the increasing perpendicular thermal velocity tending to stabilize the transverse instability, the corresponding wave numbers decrease.

K-Shell Spectra from CH-Tamped Aluminum Layers Irradiated with Intense Femtosecond Laser Pulses
XIONG Gang, ZHAO Yang, SHANG Wan-Li, HU Zhi-Min, ZHU Tuo, WEI Min-Xi, YANG Guo-Hong, ZHANG Ji-Yan, YANG Jia-Min
Chin. Phys. Lett. 2010, 27 (9): 095202 .   DOI: 10.1088/0256-307X/27/9/095202
Abstract   PDF(pc) (561KB) ( 441 )

X-ray spectra of H-like and He-like aluminum ions from aluminum buried in CH layers irradiated with 30 fs, 200 TW laser are measured. The electron temperature and density are derived from line ratios of the He-α resonance line to its satellite lines. Typical temperatures of 490-646 eV and electron densities up to 7×1020 cm-3 are obtained. The results show that the electron density increases and temperature decreases with the increasing CH thickness.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Effect of Zn Interstitials on Enhancing Ultraviolet Emission of ZnO Films Deposited by MOCVD
ZHONG Ze, SUN Li-Jie, CHEN Xiao-Qing, WU Xiao-Peng, FU Zhu-Xi
Chin. Phys. Lett. 2010, 27 (9): 096101 .   DOI: 10.1088/0256-307X/27/9/096101
Abstract   PDF(pc) (582KB) ( 862 )

ZnO films are grown on Si (111) substrates by a metal organic chemical vapor deposition method. Samples with different stoichiometric composition of Zn and O are obtained by varying II/VI molar ratio between 3 and 1/3 in precursors. The x-ray photoelectron spectroscopy and photoluminescence results show that the ultraviolet emission enhances with the increasing Zn/O composition ratio of the samples. It is suggested that the superfluous Zn atoms pile up at interstitial positions to form Zn interstitial defects. The radiated recombination of the coupling of free excitons with donor Zn interstitial enhances the ultraviolet emission of the samples.

Condensation Behavior of Ag Aggregates on Liquid Surfaces
ZHANG Xiao-Fei, ZHANG Chu-Hang, LV Neng, XIE Jian-Ping, YE Gao-Xiang,
Chin. Phys. Lett. 2010, 27 (9): 096102 .   DOI: 10.1088/0256-307X/27/9/096102
Abstract   PDF(pc) (763KB) ( 396 )

We report a condensation behavior of silver aggregates on silicone oil surfaces. The deposited Ag atoms diffuse and aggregate on the oil surface, and then form granular clusters and ramified islands. The apparent Ag coverage of the total area increases linearly with the nominal film thickness h for h< 0.9nm. However, the coverage exhibits a fluctuation behavior for 1.0nm < h < 2.5nm. It is found that the anomalous behavior of the coverage is resulted from a characteristic material condensation process in the aggregates.

Small-Angle X-Ray Scattering Study on Nanostructures of Polyimide Films
LIU Xiao-Xu, YIN Jing-Hua, SUN Dao-Bin, BU Wen-Bin, CHENG Wei-Dong, WU Zhong-Hua
Chin. Phys. Lett. 2010, 27 (9): 096103 .   DOI: 10.1088/0256-307X/27/9/096103
Abstract   PDF(pc) (741KB) ( 665 )

Inorganic nanohybrid polyimide (PI) is widely applied in electrical and electronic devices for its outstanding insulating properties. Samples 100CR and 100NH are made in Dupont. Among them, 100NH is a kind of pure PI films; however, 100CR is a kind of inorganic nanohybrid PI films with excellent corona-resistance. The nanostructure of PI films is investigated with small-angle x-ray scattering technique and transmission electron microscopy (TEM). The normalized volume fractions of the scatterers in the specimens are obtained with a tangent-by-tangent data analysis for the small-angle x-ray scattering data. The multi-hierarchical scatterers of 100NH can be divided into two dominant components, i.e., the sharp component and the wide component. The sharp component is corresponding to the contribution of PI molecular chains, and the wide component includes the aggregates formed by PI molecular chains and the film has nested dual-fractal characteristics, nevertheless the 100CR film possesses three types of scale scattering made up of inorganic nanoparticles, molecular chains and aggregates. The present films have multi-fractal structures. The distribution and structure of scattering body of two kinds of PI films are analyzed. The results of SAXS agree well with those of TEM methods.

Structural, Electronic and Elastic Properties of Cubic Perovskites SrSnO3 and SrZrO3 under Hydrostatic Pressure Effect
SHI Li-Wei, DUAN Yi-Feng, YANG Xian-Qing, QIN Li-Xia
Chin. Phys. Lett. 2010, 27 (9): 096201 .   DOI: 10.1088/0256-307X/27/9/096201
Abstract   PDF(pc) (741KB) ( 1419 )

Using the plane-wave pesudopotential (PWPP) method within the generalized gradient approximation (GGA), we investigate the hydrostatic pressure induced effect on the structural, electronic and elastic properties of cubic perovskites SrSnO3 and SrZrO3. The pressure dependence of the lattice constants, some indirect and direct band gaps, the upper valence bandwidths, the elastic stiffness constants and the aggregate elastic moduli, as well as the Debye temperature are investigated. Our calculated ground-state results are in good agreement with the available experimental and theoretical data.

Preparation of Thermo-Stable Bulk Metallic Glass of Nd60Cu20Ni10Al10 by Rapid Compression
YUAN Chao-Sheng, LIU Xiu-Ru, SHEN Ru, SUN Zhen-Ya, CHEN Bo, LV Shi-Jie, HE Zhu, HU Yun, HONG Shi-Ming
Chin. Phys. Lett. 2010, 27 (9): 096202 .   DOI: 10.1088/0256-307X/27/9/096202
Abstract   PDF(pc) (573KB) ( 366 )

Melt of Nd60Cu20Ni10Al10 alloy is solidified by rapid compression from 0.1 to 5.5 GPa at 793 K and from 0.1 to 3.2 GPa at 873 K within 20 ms, separately. A fully bulk metallic glass is obtained by the rapid compression method. By comparing with as-cast bulk metallic glass (BMG), it is found that Nd60Cu20Ni10Al10 BMG prepared by rapid compression exhibits a higher thermodynamic stability and a paramagnetic property. The relationship between the glass-formation temperature and the pressure in rapid compression for the BMG is demonstrated in the P-T phase diagram.

Collective Modes and Elastic Constants of Liquid Al83Cu17 Binary Alloy
B. Y. Thakore, S. G. Khambholja, P. H. Suthar, N. K. Bhatt, A. R. Jani
Chin. Phys. Lett. 2010, 27 (9): 096203 .   DOI: 10.1088/0256-307X/27/9/096203
Abstract   PDF(pc) (654KB) ( 519 )

The collective dynamics (longitudinal and transverse phonon modes) are studied for aluminum-copper (Al-Cu) binary alloy in terms of the eigen-frequencies of the localized collective excitations. The model pseudopotential formalism is employed using a self-consistent phonon scheme by involving multiple scattering and phonon eigen-frequencies. These frequencies are expressed in terms of many-body correlation functions of atoms as well as of interatomic potential. The important ingredients in the present study are the pair-potential and pair-correlation functions. The most recent and sparingly used local field correlation functions are employed to investigate the influence of the screening effects on the vibrational dynamics of non-crystalline Al83Cu17 binary alloy. The results for the elastic constants like bulk modulus BT, rigidity modulus G, Poisson's ratio ξ, Young's modulus Y, Debye temperature θD, propagation velocity of elastic waves and dispersion curves are reported based on the collective modes of this binary alloys. The present results are consistent and confirm the applicability of model potential and self-consistent phonon theory for such studies.

A Three-Component Model Suitable for Natural and Ventilated Cavitation
JI Bin, LUO Xian-Wu, ZHANG Yao, RAN Hong-Juan, XU Hong-Yuan, WU Yu-Lin
Chin. Phys. Lett. 2010, 27 (9): 096401 .   DOI: 10.1088/0256-307X/27/9/096401
Abstract   PDF(pc) (589KB) ( 741 )

A three-component model based on mass transfer equation is proposed to simulate both the natural and ventilated cavitations. In the present cavitation model, the content of nuclei in the local flow field is updated synchronously, and is coupled with the Rayleigh-Plesset equation so as to capture the cavity development. The proposed model is applied for simulating the cavitating flow around a super-cavitating vehicle in different cavitation conditions. In the case of the natural cavitation simulation, the predicted cavitation characteristics including the cavity length and cavity diameter agrees fairly well with the analytical results. In the case of the mixed cavitation simulation, the gas ventilation obviously influences the development of cavity. With the increase of the gas ventilated rate, the natural cavitation is suppressed remarkably, and a super cavitation is formed even at a relatively larger natural cavitation number.

First-Principles Study of the γ Angle Deformation Path in the Wurtzite-to-Rocksalt Phase Transition in Aluminum Nitride
CAI Ying-Xiang, XU Rui
Chin. Phys. Lett. 2010, 27 (9): 096402 .   DOI: 10.1088/0256-307X/27/9/096402
Abstract   PDF(pc) (1795KB) ( 382 )

A new transition path (γ angle deformation path) is put forward and used to characterize the wurtzite-rocksalt transition in AlN. The enthalpy surface and the contour plot of enthalpy difference at equilibrium pressure are obtained by first-principles pseudopotential method within the generalized gradient approximation. The phase transition is needed to overcome two barriers and a metaphase arises between them. The total barrier height is 0.26 eV. The pressure region of the phase transition is estimated to be 13.9-23.5 GPa, in which the experimental result is well located. Along the least barrier path, the changes of density of states and the fields of charge density difference are investigated. The similarities and differences between γ angle deformation path and the orthorhombic deformation path are analyzed.

AFM and XPS Study of Glass Surface Coated with Titania Nanofilms by Sol-Gel Method
JI Guo-Jun, SHI Zhi-Ming
Chin. Phys. Lett. 2010, 27 (9): 096801 .   DOI: 10.1088/0256-307X/27/9/096801
Abstract   PDF(pc) (732KB) ( 811 )

Ce3+-doped and undoped TiO2 nanofilms are prepared on glass surface using a sol-gel method. Crystal structure, surface morphology, chemical composition and element distribution of both glass substrates and TiO2 films were characterized by x-ray diffractometer (XRD), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). The XRD results indicate that the Ce3+-doped TiO2 films are solely composed of the anatase phase whereas in the undoped films a small amount of the rutile phase of TiO2 is present. AFM observations show that there exist many micro-cracks and micro-holes on glass substrate surface. In contrast, the surface of pure titania films is crack-free and the average crystallite size of the films is less than 50 nm. For the films doped with Ce3+, not only does it appear to be more uniform and compact, but also the corresponding crystal size is decreased. XPS results indicate that element interdiffusion occurs between the titania nanofilm and the glass substrate during the sintering process. The film is firmly adhered onto the glass surface through the chemical combination of Ti-O-Si bonds, and the combination is more enhanced by Ce3+-doping.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Tuning Bandgap of Si-C Heterofullerene-Based Aanotubes by H Adsorption
LI Ji-Ling, YANG Guo-Wei, ZHAO Ming-Wen, LIU Xiang-Dong, XIA Yue-Yuan**
Chin. Phys. Lett. 2010, 27 (9): 097101 .   DOI: 10.1088/0256-307X/27/9/097101
Abstract   PDF(pc) (638KB) ( 444 )

We theoretically show that H atoms can be chemically adsorbed onto the surface of the Si-C heterofullerene-based nanotubes. The adsorbing energy of the H atom on Si-C heterofullerene-based nanotubes is in the range of 4.28-5.66 eV without any barrier for the H atom to approach to the Si-C heterofullerene-based nanotubes. The band-gap of Si-C heterofullerene-based nanotubes can be dramatically modified by introducing dopant states, i.e., there is a transition from semiconductor to conductor of the Si-C heterofullerene-based nanotubes induced by the adsorption of the H atom. These results actually open a way to tune electronic properties of heterofullerene-based nanotubes and thus may propose an efficient pathway for band structure engineering.

A Density Functional Study of Atomic Carbon Adsorption on δ-Pu(111) Surface
WEI Hong-Yuan, XIONG Xiao-Ling, SONG Hong-Tao, LUO Shun-Zhong
Chin. Phys. Lett. 2010, 27 (9): 097102 .   DOI: 10.1088/0256-307X/27/9/097102
Abstract   PDF(pc) (849KB) ( 426 )

Adsorption of atomic carbon on δ-Pu(111) surface is investigated systematically using density functional theory with RPBE functional. The adsorption energies, adsorption structures, Mulliken population, work functions, layer and projected density of states are calculated in wide ranges of coverage, which have never been studied before as far as we know. It is found that the hcp-hollow sites is the energetically favorable site for all the coverage range considered. The repulsive interaction is identified, and the adsorption energy decreases with the coverage, while work function increases linearly with the coverage. It is found that the C-Pu interaction is very strong due to the hybridization between the C 2p states and the Pu 5f, Pu 6p,Pu 6d states of topmost layer Plutonium atoms.

Generation and Quantum Interference of Entangled Electron-Hole Pairs in a Hanbury Brown and Twiss Interferometer
ZHANG Qing-Yun, WANG Bai-Geng, SHEN Rui, XING Ding-Yu
Chin. Phys. Lett. 2010, 27 (9): 097401 .   DOI: 10.1088/0256-307X/27/9/097401
Abstract   PDF(pc) (731KB) ( 400 )

The Hanbury-Brown-Twiss interferometer is proposed to serve as a detector of the crossed Andreev reflection and to generate entangled electron-hole pairs. It is shown that the non-local electron and hole induced by the crossed Andreev reflection are entangled. Quantum interference of the entangled electron-hole pairs gives rise to a new measurable effect of the phase difference between two superconductors in the cross correlation. The present theoretical predictions can be experimentally realized within the present-day microelectronic technology.

Soft Magnetic Thin Films FeCoHfO for High-Frequency Noise Suppression Applications
LU Guang-Duo, ZHANG Huai-Wu, TANG Xiao-Li
Chin. Phys. Lett. 2010, 27 (9): 097501 .   DOI: 10.1088/0256-307X/27/9/097501
Abstract   PDF(pc) (946KB) ( 561 )

A series of FeCoHfO films were fabricated by dc magnetron reactive sputtering at varying partial pressure of oxygen (P O2) from 0 to 11.7%, and the electrical and magnetic properties of films have been studied. It is shown that optimal Fe43.29Co19.51Hf7.49O29.71 films with desired properties can be obtained when the films were prepared under PO2= 5.1%. The films show superior properties of low coercivity, Hc~5.5 Oe, relatively high saturation magnetization, 4πMs~18.3 kG, high anisotropy field Hk~EM>65 Oe, and high electrical resistivity ρ~2675 µΩcm. Permeability spectra shows that the natural ferromagnetic resonant frequency is as high as ~3.1 GHz. The combined merits of the film make the films taken as an ideal candidate material for high-frequency applications such as noise suppressor. In addition, the effects of the film thickness and annealing treatment on the magnetic properties are also reported.

Fabrication, Structural and Magnetic Properties for Aligned MnBi
LIU Yong-Sheng, ZHANG Jin-Cang, REN Zhong-Ming), GU Min-An, YANG Jing-Jing, CAO Shi-Xun, YANG Zheng-Long
Chin. Phys. Lett. 2010, 27 (9): 097502 .   DOI: 10.1088/0256-307X/27/9/097502
Abstract   PDF(pc) (815KB) ( 508 )

MnBi compound is fabricated under a magnetic field of 1 T, and the c-axis of hexagonal MnBi crystal is aligned parallel to the magnetic field direction. The saturation magnetization Ms decreases with the increase of temperature. At temperatures below 200 K, the coercive field Hc is about 150 Oe, while the coercive field Hc increases with temperature above 200 K. From 200 K to 300 K, the remnant magnetization Mr and the Mr/Ms increase with the temperature. Below 200 K, Mr and Mr/Ms reach roughly a constant value. However, there is an abnormal increase at 100 K in Hc, Mr and Mr/Ms, which comes from a spin-reorientation in MnBi. Magnetization results show the spin-reorientation for MnBi at about 91 K due to the variations of the anisotropy constants.

Magnetization Switching in a Small Disk with Shape Anisotropy
LÜ, Dong-Li, XU Chen
Chin. Phys. Lett. 2010, 27 (9): 097503 .   DOI: 10.1088/0256-307X/27/9/097503
Abstract   PDF(pc) (503KB) ( 401 )

We study the precessional switching of a single domain, uniaxial magnetic disk with shape anisotropy by the micromagnetic simulation. The results show that magnetic switching can be driven by a smaller magnetic field pulse in an elliptic disk with its long semiaxis perpendicular to the easy axis than in a circular disk. The shape anisotropy can change the height of the energy barrier, thus we may obtain an optimal fast magnetization switching by tuning the aspect ratio of the disk under the thermal stability condition. The switching behavior of the elliptic and circular disks is studied in detail. It is found that only properly choosing the pulse amplitude and duration can realize the fast precessional switching.

Modulation of Insulator-Metal Transition Temperature by Visible Light in La7/8Sr1/8MnO3 Thin Film
HU Ling, SUN Yu-Ping, WANG Bo, LUO Xuan, SHENG Zhi-Gao, ZHU Xue-Bin, SONG Wen-Hai, YANG Zhao-Rong, DAI Jian-Ming
Chin. Phys. Lett. 2010, 27 (9): 097504 .   DOI: 10.1088/0256-307X/27/9/097504
Abstract   PDF(pc) (606KB) ( 384 )

Effects of magnetic field and light illumination on the electrical transport properties of La7/8Sr1/8MnO3 thin film grown on a Si substrate are investigated. The film shows an insulator-metal transition at TP≈191.9 K and a low-temperature resistance minimum at Tmin48 K in darkness. Both magnetic field and light illumination shift the insulator-metal transition temperature TP to be higher, while the low-temperature transport properties of the film induced by them show different trends. That is, the magnetic field and light illumination make the Tmin shift to lower and higher temperatures, respectively. The enhancement of both TP and Tmin under light illumination could be explained in terms of photoinduced hole-doping and demagnetization effects of La7/8Sr1/8MnO3.

Structural and Magnetic Properties of Nd(Fe,Mo)12Nx Compounds Produced by Strip-Casting Method
LIU Shun-Quan, HAN Jing-Zhi, WANG Chang-Sheng, YANG Jin-Bo, DU Hong-Lin, YANG Ying-Chang
Chin. Phys. Lett. 2010, 27 (9): 097505 .   DOI: 10.1088/0256-307X/27/9/097505
Abstract   PDF(pc) (575KB) ( 404 )

The strip casting (SC) technique is employed to fabricate Nd(Fe,Mo)12Nx magnets. The crystallographic structure, intrinsic and permanent magnetic properties, as well as the microstructures of the compound are investigated. There are prominent advantages for the SC Nd-Fe-Mo alloys and their nitrides when compared with the samples prepared by the conventional casting (CC) method: (1) SC technique rebounds to the formation of the compounds crystallizing in a ThMn12-type structure. A single-phased host alloy Nd(Fe,Mo)12 can be directly prepared by strip casting without any isothermal annealing. Accordingly, lower energy cost and less rare earth demand notablely benefit the manufacture processing from a point of economizing. (2) The intrinsic magnetic properties, such as Curie temperature Tc, saturation magnetization Ms and anisotropy field Ha of the SC sample exceed the CC sample due to a phase forming condition with less-Mo-depended. (3) The microstructure studies also demonstrate that the SC compound contains finer grains, better-proportioned phase distribution than the CC compound. Optimized final particles are observed aligned in their easy axis and the energy product of powder sample is up to (BH)max~22 MGOe (176 kJ/m3).

Controllable Ultra Low- k by Via-Typed Air Gap with the Better Design Margin for Logic Devices below 45nm Node
CHOI Youn-Ok, KIM Sang-Yong
Chin. Phys. Lett. 2010, 27 (9): 097701 .   DOI: 10.1088/0256-307X/27/9/097701
Abstract   PDF(pc) (601KB) ( 793 )

By changing the air gap to a via-typed air gap, the height of the air gap is reduced up to about 50% compared to the height of the trench-typed air gap. The controllable (1≤k <2.9) ultra low-k is also easily fabricated by adjusting the space of the via-typed air gap. The via-typed air gap makes the design margin better due to its lower height in the dense and narrow lines.

Polymer Light-Emitting Diode Using Conductive Polymer as the Anode Layer
LIANG Chun-Jun, ZOU Hui, HE Zhi-Qun, ZHANG Chun-Xiu, LI Dan, WANG Yong-Sheng
Chin. Phys. Lett. 2010, 27 (9): 097801 .   DOI: 10.1088/0256-307X/27/9/097801
Abstract   PDF(pc) (542KB) ( 1417 )

The analysis based on series equivalent circuit indicates that the resistance of electrode layers is the major factor limiting the current density of polymer light-emitting diodes (PLEDs) at higher voltages. The conductivity of 790 S/cm for the PEDOT:PSS film is achieved by secondary doping. At a thickness of 240 nm, the sheet resistance of the polymer layer is 51 Ω/sq, which is comparable to that of ITO films. The current density and luminance of the PLEDs with the polymer anode layer is higher than the ITO anode device, suggesting that it is feasible to replace ITO anode with a highly conductive polymer in PLEDs.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Light-Induced Agglomeration and Diffusion of Different Particles with Optical Tweezers
LI Xue-Cong, SUN Xiu-Dong, LIU Hong-Peng, ZHANG Jian-Long
Chin. Phys. Lett. 2010, 27 (9): 098101 .   DOI: 10.1088/0256-307X/27/9/098101
Abstract   PDF(pc) (669KB) ( 352 )

The dynamic process of light-induced agglomeration of carbon nanotubes (CNTs), C60 and Escherichia coli (E.coli) in aqueous solutions is demonstrated using an optical tweezers system. Based on the results, the diameter of the agglomerated region and the agglomeration rate increase with the increasing laser power. After the saturation-stable period, CNTs diffuse completely, C60 clusters only diffuse partially, and E. coli never diffuses in the agglomeration region. Theoretical analyses show that the molecular polarization and thermal diffusion of particles play crucial roles in the diffusion process. The results indicate the possibility of using light to aggregate and sort nanoparticles.

Preparation and Characteristics of Nanoscale Diamond-Like Carbon Films for Resistive Memory Applications
FU Di, XIE Dan, ZHANG Chen-Hui, ZHANG Di, NIU Jie-Bin, QIAN He, LIU Li-Tian,
Chin. Phys. Lett. 2010, 27 (9): 098102 .   DOI: 10.1088/0256-307X/27/9/098102
Abstract   PDF(pc) (688KB) ( 612 )

We propose diamond-like carbon (DLC) as the resistance change material for nonvolatile memory applications. Nanoscale DLC films are prepared by filtered cathodic vacuum arc technique and integrated to W/DLC/W structure devices. The deposited DLC film has a thickness of about 20 nm and high sp3 fraction content. Reversible bistable resistive switching from a high resistance state to a low resistance state, and vice versa, is observed under appropriate unipolar stimulation pulses. High resistance switching ratio (larger than a thousand times) and low level of switching power (about 11 μW) are demonstrated. We propose that the mechanism of the repetitive resistive switching is the growth and breakage of conductive sp2-like filaments in the predominantly sp3-type insulating carbon upon applications of voltage pulses, which is consistent with the experimental results.

Spin Injection from Ferromagnetic Metal Directly into Non-Magnetic Semiconductor under Different Injection Currents
DENG Ning, TANG Jian-Shi, ZHANG Lei, ZHANG Shu-Chao, CHEN Pei-Yi
Chin. Phys. Lett. 2010, 27 (9): 098501 .   DOI: 10.1088/0256-307X/27/9/098501
Abstract   PDF(pc) (534KB) ( 400 )

For ferromagnetic metal (FM)/semiconductor (SC) structure with ohmic contact, the effect of carrier polarization in the semiconductor combined with drift part of injection current on current polarization is investigated. Based on the general model we established here, spin injection efficiency under different injection current levels is calculated. Under a reasonable high injection current, current polarization in the semiconductor is actually much larger than that predicted by the conductivity mismatch model because the effect of carrier polarization is enhanced by the increasing drift current. An appreciable current polarization of 1% could be achieved for the FM/SC structure via ohmic contact, which means that efficient spin injection from FM into SC via ohmic contact is possible. The reported dependence of current polarization on temperature is verified quantitatively. To achieve even larger spin injection efficiency, a gradient doping semiconductor is suggested to enhance the drift current effect.

Wetting Layer Effect on Optical Gain of Strained CdTe/ZnTe Pyramidal Quantum Dots
Seoung-Hwan Park, Woo-Pyo Hong
Chin. Phys. Lett. 2010, 27 (9): 098502 .   DOI: 10.1088/0256-307X/27/9/098502
Abstract   PDF(pc) (710KB) ( 403 )

The optical properties of strained CdTe/ZnTe pyramidal quantum dots (QDs) are investigated as a function of the wetting layer thickness using an eight-band strain-dependent k.p Hamiltonian. The ground-state subband energies in the conduction and valence bands rapidly decreases with the increasing wetting layer thickness. This is attributed to the reduction of subband energies in both the conduction and the valence bands due to the strain effect. The optical gain peak on the shorter wavelength side decreases with the increasing wetting layer thickness. On the other hand, the gain peak on the longer wavelength side is nearly independent of the wetting layer thickness. The decrease in the gain peak on the shorter wavelength side is related to the decrease in matrix elements corresponding to transitions between higher subbands such as (3,4) and (4,3).

Synergistic Effect of Auto-Activation and Small RNA Regulation on Gene Expression
XIONG Li-Ping, MA Yu-Qiang, TANG Lei-Han
Chin. Phys. Lett. 2010, 27 (9): 098701 .   DOI: 10.1088/0256-307X/27/9/098701
Abstract   PDF(pc) (491KB) ( 379 )

Auto-activation and small ribonucleic acid (RNA)-mediated regulation are two important mechanisms in controlling gene expression. We study the synergistic effect of these two regulations on gene expression. It is found that under this combinatorial regulation, gene expression exhibits bistable behaviors at the transition regime, while each of these two regulations, if working solely, only leads to monostability. Within the stochastic framework, the base pairing strength between sRNA and mRNA plays an important role in controlling the transition time between on and off states. The noise strength of protein number in the off state approaches 1 and is smaller than that in the on state. The noise strength also depends on which parameters, the feedback strength or the synthesis rate of small RNA, are tuned in switching the gene expression on and off. Our findings may provide a new insight into gene-regulation mechanism and can be applied in synthetic biology.

Phase Transition of the Pair Contact Process Model in a Fragmented Network
HUA Da-Yin, WANG Lie-Yan
Chin. Phys. Lett. 2010, 27 (9): 098901 .   DOI: 10.1088/0256-307X/27/9/098901
Abstract   PDF(pc) (614KB) ( 432 )

We investigate the phase transition of the pair contact process (PCP) model in a fragmented network. The network is formed by rewiring the link between two nearest neighbors to another randomly selected site in one dimension with a probability q. When the average degree <k>=2, the system exhibits a structure transition and the lattice is fragmented into several isolated subgraphs, it is shown that a giant cluster appears and its node fraction does not change nearly for q>0. Furthermore, it is found that the critical behavior of the continuous phase transition for the PCP model is different from the directed percolation (DP) class and the estimated values of the critical exponents are independent of the rewiring probability for q>0. We conjecture that the structure transition for <k> =2 takes an important role in the change of the critical behavior of the continuous phase transition.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
The Surface Gravitational Redshift of a Proto Neutron Star
ZHAO Xian-Feng
Chin. Phys. Lett. 2010, 27 (9): 099701 .   DOI: 10.1088/0256-307X/27/9/099701
Abstract   PDF(pc) (741KB) ( 461 )

The influence of the σ* and Φ mesons on the surface gravitational redshift of a proto neutron star is investigated within the framework of relativistic mean field theory for the baryon octet {n,p,Λ,Σ-0, Σ+-0} system. It is found that, compared with those without considering the contribution of σ* and Φ mesons, the surface gravitational redshift decreases, corresponding to the maximum value of the mass decreasing from 0.2220 to 0.1937, about 12.7%. It is also found that the appearance of σ* and Φ mesons makes the surface gravitational redshift as a function of M/R decrease too, with M and R being the mass and radius of the proto neutron star.

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