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Volume 24 Issue 2
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Original Articles
Wronskian Form of N-Soliton Solution for the (2+1)-Dimensional Breaking Soliton Equation
SU Ting, GENG Xian-Guo, MA Yun-Ling,
Chin. Phys. Lett. 2007, 24 (2): 305-307 .  
Abstract   PDF(pc) (193KB) ( 1891 )
The Wronskian form of N-soliton solution for the (2+1)-dimensional breaking soliton equation is obtained by resorting to the Hirota direct method.
Discrete Integrable Couplings of the Volterra Lattice
YAO Yu-Qin, ZHANG Yu-Feng, CHEN Deng-Yuan
Chin. Phys. Lett. 2007, 24 (2): 308-311 .  
Abstract   PDF(pc) (185KB) ( 900 )
A practicable way to construct discrete integrable couplings is proposed
by making use of two types of semi-direct sum Lie algebras. As its
application, two kinds of discrete integrable couplings of the Volterra
lattice are worked out.
Multisymplectic Euler Box Scheme for the KdV Equation
WANG Yu-Shun, WANG Bin, CHEN Xin
Chin. Phys. Lett. 2007, 24 (2): 312-314 .  
Abstract   PDF(pc) (206KB) ( 789 )
We investigate the multisymplectic Euler box scheme for the Korteweg--de Vries (KdV) equation. A new completely explicit six-point scheme is derived. Numerical experiments of the new scheme with comparisons to the Zabusky- Kruskal scheme, the multisymplectic 12-point scheme, the narrow box scheme and the spectral method are made to show nice numerical stability and ability to preserve the integral invariant for long-time integration.
Bound State Solutions of Klein--Gordon Equation with the Kratzer Potential
M. Kocak
Chin. Phys. Lett. 2007, 24 (2): 315-317 .  
Abstract   PDF(pc) (169KB) ( 959 )
The relativistic problem of spinless particle subject to a Kratzer potential is nalysed. Bound state solutions for s-waves are found by separating the Klein--Gordon equation into two parts. Unlike the similar works in the iterature, the separation make it possible to see explicitly the relativistic ontributions, if any, to the solution in the non-relativistic limit.
Recovery of Graded Index Profile of Planar Waveguide by Cubic Spline Function
YANG Yong, CHEN Xian-Feng, LIAO Wei-Jun, XIA Yu-Xing
Chin. Phys. Lett. 2007, 24 (2): 318-321 .  
Abstract   PDF(pc) (249KB) ( 706 )
A method is proposed to recover the refractive index profile of graded
waveguide from the effective indices by a cubic spline interpolation
function. Numerical analysis of several typical index distributions show
that the refractive index profile can be reconstructed closely to its
exact profile by the presented interpolation model.
An Implementation of a Positive Operator Valued Measure
YAN Feng-Li, GAO Ting, LI You- Chen
Chin. Phys. Lett. 2007, 24 (2): 322-325 .  
Abstract   PDF(pc) (192KB) ( 565 )

We present an implementation of the positive operator valued measure (POVM). By using this POVM, one can realize the probabilistic teleportation of an unknown two-particle state.

Classical Capacity for a Continuous Variable Teleportation Channel
QIN Tao, ZHAO Mei-Sheng, ZHANG Yong-De,
Chin. Phys. Lett. 2007, 24 (2): 326-329 .  
Abstract   PDF(pc) (223KB) ( 669 )
The process of quantum teleportation can be considered as a quantum channel. The exact classical capacity of the continuous variable teleportation channel is presented and the channel fidelity is also derived.
Dynamical and Geometric Phases of a Two Energy-Level Bose--Einstein Condensate Interacting with a Laser Field
YU Zhao-Xian, JIAO Zhi-Yong, JIN Shuo, WANG Ji-Suo
Chin. Phys. Lett. 2007, 24 (2): 330-332 .  
Abstract   PDF(pc) (207KB) ( 511 )
By using of the invariant theory, we study a two energy-level Bose--Einstein condensate interacting with a time-dependent laser field, the dynamical and geometric phases are given respectively. The Aharonov--Anandan phase is also obtained under the cyclical evolution.
Massive Particle's Tunnelling from Black Hole with Topological Defect
HAN Yi-Wen
Chin. Phys. Lett. 2007, 24 (2): 333-335 .  
Abstract   PDF(pc) (186KB) ( 494 )
We extend Zhang and Zhao's recent work to black hole with topological defect whose Arnowitt--Deser--Misner mass is no longer identical to its mass parameter. The behaviour of the tunnelling massive particles is investigated, and the emission rate at which massive particles tunnel across the event horizon of the black hole is calculated. The result is consistent with an underlying unitary theory, and takes the same functional form as that of mass-less particles.
Teleportation of Mixture of Diagonal Bell States via Bound Entangled States
Chin. Phys. Lett. 2007, 24 (2): 336-339 .  
Abstract   PDF(pc) (190KB) ( 542 )
We propose a protocol for teleportation of arbitrary mixture of diagonal Bell states, it is shown that the channel can be constructed with either pure aximally entangled states or mixed bound entangled states. We also present protocols to realize the controlled teleportation of mixture of diagonal Bell states via multi-particle mixed states. Our results show that bound entangled states are also important and useful resources in quantum communication tasks.
Feasible Scheme for Teleportation of an Arbitrary N-Atom State with Thermal Cavity
TAN Xiao-Hui, FANG Xi-Ming, WANG Guo-You
Chin. Phys. Lett. 2007, 24 (2): 340-343 .  
Abstract   PDF(pc) (214KB) ( 625 )
We present a scheme for teleportation of an arbitrary N-atom state without Bell state measurement in thermal cavity QED, and show the feasibility in experiment. Our scheme is also insensitive to both cavity decay and thermal field, and the fidelity of teleportation is only slightly affected by the erimental errors. In addition, the success probability reaches 1.0.
Possible Realization of Cluster States and Quantum Information Transfer in Cavity QED via Raman Transition
ZHAN Zhi-Ming, LI Wei-Bin
Chin. Phys. Lett. 2007, 24 (2): 344-347 .  
Abstract   PDF(pc) (194KB) ( 680 )
We present a scheme to generate cluster states with many atoms in cavity QED via Raman transition. In this scheme, no transfer of quantum information between the atoms and cavities is required, the cavity fields are only virtually excited and thus the cavity decay is suppressed during the generation of cluster states. The atoms are always populated in the two ground states. Therefore, the scheme is insensitive to the atomic spontaneous emission and cavity decay. We also show how to transfer quantum information from one atom to another.
Generation of Multipartite Ionic Entangled States only by Single-Qubit Measurements via Linear Optical Elements
DONG Ping, CAO Zhuo-Liang
Chin. Phys. Lett. 2007, 24 (2): 348-351 .  
Abstract   PDF(pc) (216KB) ( 739 )
We propose a scheme for generation of multipartite ionic Greenberger--Horne--Zeilinger (GHZ) states only by single-qubit measurements. Our scheme not only does not need joint measurements but also avoids the difficulty of synchronizing the arrival time of the two scattered photons, which is faced by the previous schemes. Therefore our entanglement generation scheme can
be implemented more easily than the schemes based on atomic interference in experiment.
A Scheme for Generating Entangled Squeezed States Based on Cavity QED
ZHANG Zhi-Ming, YANG Jian, YU Ya-Fei
Chin. Phys. Lett. 2007, 24 (2): 352-354 .  
Abstract   PDF(pc) (181KB) ( 676 )
We propose a scheme for generating entangled squeezed vacuum states of electromagnetical fields. The scheme is based on cavity QED. In this scheme, an atom interacts, successively, with a classical field, two quantum cavity fields, and another classical field. By detecting the final states of the atom, the two quantum cavity fields will be projected to an entangled state.
On the Energy-Momentum Problem in Static Einstein Universe
S. Aygün, I. Tarhan, H. Baysal,
Chin. Phys. Lett. 2007, 24 (2): 355-358 .  
Abstract   PDF(pc) (161KB) ( 845 )
The energy-momentum distributions of Einstein's simplest static geometrical model for an isotropic and homogeneous universe are evaluated. For this purpose, Einstein, Bergmann--Thomson, Landau--Lifshitz (LL), Moller and Papapetrou energy-momentum complexes are used in general relativity. While Einstein and Bergmann--Thomson complexes give exactly the same results, LL and Papapetrou energy-momentum complexes do not provide the same energy densities. The Moller energy-momentum density is found to be zero everywhere in Einstein's universe. Also, several spacetimes are the limiting cases considered here.
Controlling Spatiotemporal Chaos with a Generalized Feedback Method
GAO Ji-Hua, ZHENG Zhi-Gang
Chin. Phys. Lett. 2007, 24 (2): 359-362 .  
Abstract   PDF(pc) (234KB) ( 616 )
The usual linear variable feedback control method is extended to a generalized function feedback scheme. The scheme is applied to high-dimensional spatiotemporal systems. By a combination of local generalized feedback control and the spatial coupling effect among elements, turbulent motion can be successfully eliminated.
Resonant Response of Rectangular AFM Cantilever in Liquid
CHEN Yu-Hang, HUANG Wen-Hao
Chin. Phys. Lett. 2007, 24 (2): 363-365 .  
Abstract   PDF(pc) (189KB) ( 414 )
Dynamic characteristics of atomic force microscopy (AFM) cantilevers can be influenced by their working media. We perform an experimental study on the resonant responses of rectangular AFM cantilevers with different sizes immersed in various viscous fluids. The measured resonance frequencies in liquids are used to validate several theoretical models. Comparison shows the analytical model proposed by Sader [J. Appl. Phys. 84 (1998) 64] can give the best agreement with the experimental results with the maximum relative error nearly 16% for all the cantilevers in different liquids. The ratio between the resonant frequencies in air and water is almost independent of the cantilever length, which is consistent with the theoretical analyses.
Determination of Tungsten Layer Profiles in Bilayer Structures Using X-Ray Reflectivity Method
XU Yao, WANG Zhan-Shan, WANG Bei, WANG Hong-Chang, WU Wen-Juan, ZHANG Shu-Min, ZHANG Zhong, WANG Feng-Li, QIN Shu-Ji, CHEN Ling-Yan
Chin. Phys. Lett. 2007, 24 (2): 366-369 .  
Abstract   PDF(pc) (216KB) ( 681 )
An effectual method is presented to determine the profiles of a tungsten (W) layer, such as the density, the thickness and the roughness in the multilayer structures, using the x-ray reflectivity technique. To avoid oxidation effects of tungsten, a B4C capping layer is deposited onto to the W layer. To observe the profiles of the tungsten layer with different thicknesses, three groups of W/B4C bilayers with different thicknesses are prepared by using ultra high vacuum dc magnetron sputtering and measured by an x-ray diffractometer. A type of genetic algorithm called the differential evolution is used to simulate
the measurement data so as to obtain the parameters of bilayers. According to the simulation, it is shown that the W layer density varies from 95.26% to 97.51% compared to the bulk. In our experiment, the deposition rate is .044nm/s, and the thickness is varied in the range of 9.8--19.4nm.
Multisymplectic Geometry and Its Applications for the Schrodinger Equation in Quantum Mechanics
CHEN Jing-Bo
Chin. Phys. Lett. 2007, 24 (2): 370-373 .  
Abstract   PDF(pc) (202KB) ( 595 )
Multisymplectic geometry for the Schrödinger equation in quantum mechanics is presented. This formalism of multisymplectic geometry provides a concise and complete introduction to the Schrödinger equation. The Schrödinger equation, its associated energy and momentum evolution equations, and the multisymplectic form are derived directly from the variational principle. Some applications are also explored.
A Light-Cone QCD Inspired Meson Model with a Relativistic Confining Potential in Momentum Space
LI Lei, WANG Shun-Jin, ZHOU Shan-Gui, ZHANG Guang-Biao
Chin. Phys. Lett. 2007, 24 (2): 374-377 .  
Abstract   PDF(pc) (232KB) ( 405 )
For describing the radial excited states a relativistic confining potential in momentum space is included in the meson effective light-cone Hamiltonian. The meson eigen equations are transformed from the front form to the instant form and formulated in total angular representation. Details about numerically solving these equations are discussed, mainly focusing on treating ingularities arising from one-gluon exchange interactions and confinement. The results of pseudo-scalar mesons indicate that the improved meson effective light-cone Hamiltonian can describe the ground states and radial excited states well. Some radial excited states are also predicted and waiting for experimental test.
Partner of η2(1645) in the 11 D2 Meson Nonet
FENG Xue-Chao, JIANG Feng-Chun
Chin. Phys. Lett. 2007, 24 (2): 378-380 .  
Abstract   PDF(pc) (196KB) ( 562 )

In the qˉq ˉquark model, the states π2(1670) and η2(1645) are assigned as the 11D2 meson nonet. The partner of state η2(1645) needs further confirmation in the experiments. We employ the meson--meson mixing and the Regge trajectory methods to calculate the mass of the partner of state η2(1645) to be 1879.8MeV and 1863± 24MeV respectively. We also calculate the strong decay width in the 3P0 decay model. These predictions can be compared with experiments in the future.

Spontaneous Electro-Weak Symmetry Breaking and Cold Dark Matter
ZHU Shou-Hua
Chin. Phys. Lett. 2007, 24 (2): 381-384 .  
Abstract   PDF(pc) (660KB) ( 554 )
In the standard model, the weak gauge bosons and fermions obtain mass after spontaneous electro-weak symmetry breaking, which is realized by one fundamental scalar field, namely the Higgs field. We study the simplest scalar cold dark matter model in which the scalar cold dark matter also obtains mass by interaction with the weak-doublet Higgs field, in the same way as those of weak gauge bosons and fermions. Our study shows that the correct cold dark matter relic abundance within 3σ uncertainty (0.093 <Ωdm h2 < 0.129) and experimentally allowed Higgs boson mass (114.4≤ mh ≤ 208GeV) constrain the scalar dark matter mass within 48≤e mS ≤78GeV. This result is in excellent agreement with the result of de Boer et al. (50~100GeV). Such a kind of dark matter annihilation can account for the observed gamma rays excess (10σ) at EGRET for nergies above 1GeV in comparison with the expectations from conventional Galactic models. We also investigate other phenomenological consequences of this model. For example, the Higgs boson decays dominantly into scalar cold dark matter if its mass lies within 48~64GeV.
Isoscaling in Statistical Sequential Decay Model
TIAN Wen-Dong, MA Yu-Gang, CAI Xiang-Zhou, FANG De-Qing, GUO Wei, MA Chun-Wang, LIU Gui-Hua, SHEN Wen-Qing, SHI Yu, SU Qian-Min, WANG Hong-Wei, WANG Kun, YAN Ting-ZHi
Chin. Phys. Lett. 2007, 24 (2): 385-388 .  
Abstract   PDF(pc) (262KB) ( 542 )
A sequential decay model is used to study isoscaling, i.e. the factorization of the isotope ratios from sources of different isospins and sizes over a broad range of excitation energies, into fugacity terms of proton and neutron umber, R21(N,Z)=Y2(N,Z)/Y1(N,Z)=Cexp(αN+βZ). It is found that the isoscaling parameters α and β have a strong dependence on the isospin difference of equilibrated source and excitation energy, no significant influence of the ource size on α and β has been observed. It is found that α and β decrease with the excitation energy and are linear functions of 1/T and β(Z/A)2 or △(N/A)2 of the
sources. Symmetry energy coefficient Csym is constrained from the relationship of α and source △(Z/A)2, β and source △(N/A)2.
Structures of NΩ and △Ω Dibaryons
DAI Lian-Rong, ZHANG Dan, LI Chun-Ran, TONG Lei
Chin. Phys. Lett. 2007, 24 (2): 389-392 .  
Abstract   PDF(pc) (232KB) ( 574 )
We study the structures of NΩ and △Ω systems in the extended chiral SU(3) quark model by solving a resonating group method equation. The results show that both systems are weakly bound states and changed into unbound states if we consider the mixing of scalar mesons.
Origin of Unexpected Isotopic Trends in Synthesis of Superheavy Nuclei
LIU Zu-Hua, BAO Jing-Dong,
Chin. Phys. Lett. 2007, 24 (2): 393-396 .  
Abstract   PDF(pc) (239KB) ( 336 )

We investigate the dependence of the yield of superheavy nuclei with Z=110, 112, 114 on the neutron excess of the projectile nucleus with a two-parameter Smoluchowski equation. It is confirmed that in some cases, the cold fusion reactions with less neutron excess are more favourable than those with more neutron excess. In order to probe the origin of these unexpected isotopic trends, we also investigate the probabilities of capture, fusion and survival in the cold fusion reactions in detail. It is found that the maximal ER cross sections of the superheavy nuclei exponentially increase as a function of Bf-Sn with Bf being the fission barrier and Sn being the neutron separation energy. Although the probabilities of capture and fusion have some influences, the unexpected isotopic trends mainly due to the ependence of the ER cross sections on the Bf-Sn value. Therefore, the reactions with larger Bf-Sn values should be more favourable for synthesis of superheavy nuclei.

Calculation of Interaction Potentials between Spherical and Deformed Nuclei
ZHANG Gao-Long, ZHANG Huan-Qiao, LIU Zu-Hua, ZHANG Chun-Lei, LIN Cheng-Jian, YANG Feng, AN Guang-Peng, JIA Hui-Ming, WU Zhen-Dong, XU Xin-Xing, BAI Chun-Lin, YU Ning
Chin. Phys. Lett. 2007, 24 (2): 397-399 .  
Abstract   PDF(pc) (227KB) ( 670 )
The interaction potential for spherical-deformed reaction partners is calculated. The shape, separation and orientation dependence of the
interaction potential and fusion cross section of the system 32S+154Sm are investigated within the double-folding model of the deformed nuclei. The effective nucleon-nucleon interaction is taken to be the M3Y-Reid potential. The density is considered for three terms of the expansion using the truncated multipole expansion method, which is a deformed Fermi shape with quadrupole and hexadecapole for the density distribution of 154Sm. It is found for the interaction potential that the height and the position of barrier strongly depend on the deformations, the orientation angle of the deformed nucleus, and hence produce great effects on fusion cross section. The integrated fusion cross section is in good agreement with the experimental data.
Photodetachment of a Negative Hydrogen Molecular Ion near an Interface
Chin. Phys. Lett. 2007, 24 (2): 400-403 .  
Abstract   PDF(pc) (214KB) ( 585 )
Photodetachment of a negative hydrogen molecular ion near an interface is studied by using the two-centre model and the closed orbit theory. The calculation results show that the photodetachment cross section is related to the distance between the two centres in the H2- and different molecular ion-interface distances. The comparison between the cross section of H2- near an interface with the section of Hˉ shows that at the equilibrium distance of two centres and at low photon energy, the photodetachment cross section of H2- is about twice the cross section of Hˉ, which shows that the interference of the two nuclei is very strong; when the distance between the two centres is large, the section of H2- is almost the same as the cross section of Hˉ near one interface, which indicates that the interference effect of the two centres anishes.
Low-Energy Rate Enhancement in Recombination Processes of Electrons into Bare Uranium Ions
WU Yong, ZENG Si-Liang, DUAN Bin, YAN Jun, WANG Jian-Guo, DONG Chen-Zhong, MA Xin-Wen
Chin. Phys. Lett. 2007, 24 (2): 404-407 .  
Abstract   PDF(pc) (251KB) ( 522 )

Based on the Dirac--Fork--Slater method combined with the multichannel quantum defect theory, the recombination processes of electrons into bare uranium ions (U 92+ ) are investigated in the relative energy range close to zero, and the x-ray spectrum emitted in the direct radiative recombination and cascades processes are simulated. Compared with the recent measurement, it is found that the rate enhancement comes from the additional populations on high Rydberg states. These additional populations may be produced by other recombination mechanisms, such as the external electric-magnetic effects and the many-body correlation effects, which still remains an open problem.

Coupled-Channel Optical Calculations for e+--Rb Collision at Intermediate Energies
ZHANG Yong-Zhi, ZHOU Ya-Jun, XU Tian-Fu
Chin. Phys. Lett. 2007, 24 (2): 408-410 .  
Abstract   PDF(pc) (201KB) ( 507 )
We present the calculation of total cross sections for positron scattering by Rb at intermediate energies by using the coupled-channel optical method, in which an equivalent-local optical potential has been used to describe the continuum and rearrangement process. The present total cross sections are in good agreement with the measurements of Parikh et al. [Phys. Rev. A 47 (1993) 1535] and other theoretical calculation results. Our results show three peaks in the vicinity of 47eV, which have not been found in the revious measurements and theoretical calculations.
Aggregation Behaviour of Cationic Diblock Copolymer (MTAC)10(BA)16: MesoDyn Simulation Study
CAO Xiao-Rong, TAN Ye-Bang, XU Gui-Ying
Chin. Phys. Lett. 2007, 24 (2): 411-413 .  
Abstract   PDF(pc) (201KB) ( 534 )
The aggregation behaviour of an amphiphilic cationic block copolymer (MTAC)10(BA)16 in aqueous solution is investigated by MesoDyn simulation. Simulation results show that (MTAC)10(BA)16 can form spherical, irregular and network aggregates with the increasing volume fraction. The time evolution of order parameter shows that the process of aggregate formation can be divided into diffusion control stage and hydrophobic interaction control stage, while the time evolution of energy indicates that the aggregate formation is driven by enthalpy but not entropy. The order parameter of the hydrophobic blocks BA increases with the increasing (MTAC)10(BA)16 concentration, while the time needed for system balance has the contrary trend.
Giant Birefringence of Lithium Niobate Crystals in the Terahertz Region
SUN Yi-Min, MAO Zong-Liang, HOU Bi-Hui, LIU Guo-Qing, WANG Li
Chin. Phys. Lett. 2007, 24 (2): 414-417 .  
Abstract   PDF(pc) (253KB) ( 1032 )
Terahertz time-domain spectroscopy (THz-TDS) is used to study the spectral response of lithium niobate crystals (LiNbO3) in the far infrared region. The optical constants are derived from the measured complex refractive index. A giant birefringence is observed in this material, and the average refractive-index difference between the ordinary wave and the extraordinary wave, no-ne, can reach up to about 1.6. Such a large birefringence is attributed to the different phonon modes of A1(z) and E(x,y). This unusual property makes LiNbO3 a promising material to be used as a functional material in the terahertz region, e.g. employed as wave-plates and polarization separators.
The First-Quantized Theory of Photons
WANG Zhi-Yong, XIONG Cai-Dong, Keller Ole
Chin. Phys. Lett. 2007, 24 (2): 418-420 .  
Abstract   PDF(pc) (205KB) ( 585 )
In near-field optics and optical tunnelling theory, photon wave mechanics, i.e. the first-quantized theory of photons, allows us to address the spatial field localization problem in a flexible manner which links smoothly to classical electromagnetics. We develop photon wave mechanics in a rigorous and unified way, based on which field quantization is obtained in a new way.
Strong Correlation of Fluorescence Photons without Quantum Interference
HU Xiang-Ming, WANG Fei
Chin. Phys. Lett. 2007, 24 (2): 421-423 .  
Abstract   PDF(pc) (193KB) ( 517 )
It has been predicted that a driven three-level V atom can emit strongly correlated fluorescence photons in the presence of quantum interference. Here we examine the effects of quantum interference on the intensity correlation of fluorescence photons emitted from a driven three-level Λ atom. Unexpectedly, strong correlation occurs without quantum interference. The quantum interference tends to reduce the correlation function to a normal level. The essential difference between these two cases is traced to the different effects of quantum interference on coherent population trapping (CPT). For the V atom, quantum interference and coherent excitation combine to lead to CPT. For the Λ atom, owever, the quantum interference tends to spoil CPT while the coherent excitation induces the effect.
Coherent Population Trapping Induced by Phase Modulated and Fluctuating Fields
WANG Jian, HU Xiang-Ming
Chin. Phys. Lett. 2007, 24 (2): 424-427 .  
Abstract   PDF(pc) (227KB) ( 541 )
We examine the effects of cross correlated phase fluctuations on the
coherent population trapping (CPT) induced by a pair of phase-modulated
fields with equal modulation frequencies in a three-level Λ system.
The maximal coherence of -0.5, which appears when CPT occurs for equal
modulation indices, is preserved in the presence of the critically
cross-correlated fluctuations. Unexpectedly, the non-maximal coherence,
which is established when CPT is obtained for different modulation indices, is
significantly enhanced due to the critically cross-correlated fluctuations.
Six-Fold Degenerate Dark States in a Four-Level Atomic System
WU Jin-Hui, CUI Cui-Li, BA Nuo, MA Qi-Rong, GUO Xiu-Zhen
Chin. Phys. Lett. 2007, 24 (2): 428-431 .  
Abstract   PDF(pc) (219KB) ( 513 )
With all driving fields on Raman resonance, a tripod-type atomic system quickly evolves into a dark state decoupled from the lossy excited level. The dark state depends strongly on field Rabi frequencies, spontaneous decay rates, and the initial atomic population in a complicated way. Analytical results reveal that it is a sixfold degenerate dark state with its three components superposed both coherently and incoherently due to population redistribution from spontaneous emission.
Two-Time Intensity Correlations and Multiple Interference Mechanisms in a Driven Cascade Atom
WANG Fei, HU Xiang-Ming
Chin. Phys. Lett. 2007, 24 (2): 432-435 .  
Abstract   PDF(pc) (226KB) ( 362 )
We examine the intensity correlation functions of the two fluorescent fields that are emitted from the top and middle states of a doubly driven three-level atom in the cascade configuration. Novel interference effects are shown. (i) Both of the fluorescent fields have anticorrelations which can exist for long times when the applied fields are on the two-photon resonance and far off one-photon resonances. (ii) Both of the fluorescent fields have strong correlations when the applied fields are far off one- and two-photon resonances. In particular, the extremely strong correlation occurs for the photons emitted from the top state. The above phenomena are traced to the multiple interference mechanisms.
Dynamical Properties of a Single-Mode Laser Driven by Quadratic Pump Noise
Chin. Phys. Lett. 2007, 24 (2): 436-439 .  
Abstract   PDF(pc) (211KB) ( 496 )
We propose a single-mode laser model driven by quadratic pump noise with cross correlation between the real and imaginary parts of the pump noise. The effect of the cross-correlation coefficient λp between the real and imaginary parts of the pump noise on dynamical properties is studied by using of the linear approximation. The theoretical expressions of intensity correlation function λ(t), normalized intensity fluctuation λ(0) are calculated. It is found that the most conspicuous effects of λp on both the intensity correlation function and the normalized intensity fluctuation appear at λp=0.5, but not at |λp|=1.
Laser Performance of Nd:GGG Operating at 938nm
ZHANG Chun-Yu, GAO Chun-Qing, ZHANG Ling, WEI Zhi-Yi, ZHANG Zhi-Guo
Chin. Phys. Lett. 2007, 24 (2): 440-441 .  
Abstract   PDF(pc) (181KB) ( 599 )
We report an efficient diode-pumped Nd-doped Gadolinium gallium garnet
(GGG) continuous-wave (CW) laser operating at 938nm. Laser action of
1.6at.% Nd-doped GGG crystals with different lengths and temperatures
are also investigated. The maximum output power of 620mW is obtained
at the incident pump power of 5.0W with a slope efficiency of 15%.
Self-Deflection of Dark Screening Spatial Solitons Based on Higher-Order Space Charge Field
ZHANG Guang-Yong, LIU Jin-Song, LIU Shi-Xiong, WANG Cheng, ZHANG Hui-Lan
Chin. Phys. Lett. 2007, 24 (2): 442-445 .  
Abstract   PDF(pc) (210KB) ( 719 )
The effects of higher-order space charge field on the self-deflection of dark screening spatial solitons in biased photorefractive crystals are numerically investigated under steady-state conditions. The expression for an induced space-charge electric field including higher-order space-charge field terms is obtained. Numerical results indicate that dark solitons possess a self-deflection process during propagation, and the solitons always bend in the direction of the c axis of the crystal. The self-deflection of dark solitons can experience considerable increase especially in the regime of high bias field strengths.

Interaction between Two-Dimensional White-Light Photovoltaic Dark Spatial Solitons
LIU Zhao-Hong, LIU Si-Min, GUO Ru, GAO Yuan-Mei, SONG Tao, ZHU Nan, QU Di
Chin. Phys. Lett. 2007, 24 (2): 446-449 .  
Abstract   PDF(pc) (213KB) ( 638 )
Using fully incoherent white light emitted from an incandescent bulb (a line source) and amplitude mask, we study experimentally the interaction between two 2D white-light photovoltaic dark spatial solitons with three different separations (40μm, 50μm and 60μm) and arrangement directions (parallel to, perpendicular to and tilted at 45° with respect to the crystalline c axis) propagating in parallel in close proximity in self-defocusing LiNbO3:Fe crystal. Experimental results reveal that a 2D white-light dark soliton pair only experiences attractive forces when their mutual separation is sufficiently small (<60μm), and the degree of the attraction depends on their mutual separation and their arrangement direction. When the separation is larger than 60μm, the interaction is not evident.
Temperature Dependence of Photoinduced Birefringence in an Azobenzene Polymer
XU Hong-Tao, WANG Chang-Shun, PAN Xu, ZHANG Xiao-Qiang, WANG Chuan-Yu, SUN Cun-Ying
Chin. Phys. Lett. 2007, 24 (2): 450-453 .  
Abstract   PDF(pc) (201KB) ( 635 )
The photoinduced birefringence in an azobenzene polymer is investigated at different temperatures between -20°C to 50°C. It is found that there is a peak value of photoinduced birefringence in the temperature dependence of the photoinduced birefringence under a certain pumping intensity. With the pump light in 90mW/cm2, the peak value of the photoinduced birefringence appeared at about 0°C. The effect of temperature on the photoinduced birefringence is discussed using the competition mechanism between the photoinduced reorientation and the thermal random motion.
Reducing Insertion Loss of Photonic Crystal Couplers by Suppressing the Remained Power
MAO Xiao-Yu, WANG Jian-Feng, HUANG Yi-Dong, ZHANG Wei, PENG Jiang-De
Chin. Phys. Lett. 2007, 24 (2): 454-457 .  
Abstract   PDF(pc) (175KB) ( 620 )
We find that the increasing coupling strength can lead to a decreasing density of power inside the waveguide of a photonic crystal waveguide (PC-WG) directional coupler, which is called the mode power remaining phenomenon. This phenomenon is detrimental to achieving low insertion loss of the coupler. An improved structure of the PC-WG directional coupler is proposed by simply increasing the radii of air holes in the post coupling region. The simulation results demonstrate that the insertion loss can be reduced dramatically by suppressing the remained power, and therefore both the short coupling length (8μm) and low insertion loss (lower than 0.5dB) can be obtained.
High-Sensitivity Sensor Based on Surface Plasmon Resonance Enhanced Lateral Optical Beam Displacements
YANG Xiao-Yan, LIU De-Ming, XIE Wen-Chong, LI Chun-Fang
Chin. Phys. Lett. 2007, 24 (2): 458-461 .  
Abstract   PDF(pc) (233KB) ( 504 )
We present a new optical sensor based on surface plasmon resonance (SPR) enhanced lateral optical beam displacements. Compared with the traditional SPR methods, the new method provides higher sensitivity to the sensor system. Theoretical simulations show that the refractive index (RI) detection sensitivity of the SPR sensor based on the displacement measurement has a strong dependence on the thickness of the metal film. When the optimal thickness of the metal film is selected, the RI resolution of the SPR sensor is predicted to be 2.2×10-7 refractive index units (RIU). Furthermore, it is found that the incidence angle can be used as a parameter to adjust the operating range of the sensor to different refractive index ranges.
Effects of Periodically Inhomogeneous Birefringence on Dark-Bright Vector Soliton Propagation and Interaction
LI Hong, D. N. Wang
Chin. Phys. Lett. 2007, 24 (2): 462-464 .  
Abstract   PDF(pc) (164KB) ( 544 )
The effects of periodically inhomogeneous birefringence on dark--bright vector soliton propagation and interaction are investigated by the numerical method. The birefringence leads to the submergence of the dark soliton and the disintegration of the bright soliton, and enhances the interaction between the neighbouring solitons. The system performance is determined by the bright soliton because the dark soliton has robust features. Finally, the avoidance and the effective control are introduced, and the controlling mechanism is
Analysis of Temperature Dependence of Silicon-on-Insulator Thermo-Optic Attenuator
LI Yun-Tao, YU Jin-Zhong, CHEN Yuan-Yuan, SUN Fei, CHEN Shao-Wu
Chin. Phys. Lett. 2007, 24 (2): 465-467 .  
Abstract   PDF(pc) (174KB) ( 553 )
The temperature dependence of silicon-on-insulator thermo-optic attenuators is analysed, which originates from the temperature dependence of characteristics of multimode interference. The attenuator depth and power consumption are independent of temperature while the insertion loss depends on the temperature heavily. The variation of the insertion loss decreases from 4.3dB to 1dB as the temperature increases from 273K to 343K.
Transmission Frequency Properties of Elastic Waves along a Hetero-Phononic Crystal Waveguide
YAO Yuan-Wei, HOU Zhi-Lin, LIU You-Yan
Chin. Phys. Lett. 2007, 24 (2): 468-470 .  
Abstract   PDF(pc) (216KB) ( 731 )
We investigate the propagation properties of hetero-phononic crystal waveguides by the improved eigen-mode matching theory, which can be used
at same time to calculate both the transmission (reflection) coefficient and band structure. The numerical results show that the transmission frequency range is the same as the common range for two uniform waveguides composing the hetero-system, and the gap of any composite waveguide is also the gap of the hetero-phononic crystals waveguide.
Geoacoustic Inversion Based on Dispersion Characteristic of Normal Modes in Shallow Water
LI Zheng-Lin, ZHANG Ren-He
Chin. Phys. Lett. 2007, 24 (2): 471-474 .  
Abstract   PDF(pc) (232KB) ( 435 )
A geoacoustic inversion method based on dispersion characteristic of normal modes is presented. An adaptive time-frequency analysis technique with a high resolution in both time and frequency domains is applied to derive the dispersion characteristic of normal modes from the broadband propagation signal. The bottom acoustic parameters are inverted by matching the calculated group delays of normal modes with the experimental data. Finally, some experimental results which could validate the inversion method are given.
Transition to Chaos in the Floating Half Zone Convection
AA Yan, CAO Zhong-Hua, HU Wen-Rui
Chin. Phys. Lett. 2007, 24 (2): 475-478 .  
Abstract   PDF(pc) (216KB) ( 477 )
The transition process from steady convection to chaos is experimentally studied in thermocapillary convections of floating half zone. The onset of temperature oscillations in the liquid bridge of floating half zone and further transitions of the temporal convective behaviour are detected by measuring the temperature in the liquid bridge. The fast Fourier transform reveals the frequency and amplitude characteristics of the flow transition. The experimental results indicate the existence of a sequence of period-doubling bifurcations that culminate in chaos. The measured Feigenbaum numbers are δ2 = 4.69 and δ4 = 4.6, which are comparable with the theoretical asymptotic value δ = 4.669.
Monte Carlo Simulation of Optical Properties of Wake Bubbles
CAO Jing, WANG Jiang-An, JIANG Xing-Zhou, SHI Sheng-Wei
Chin. Phys. Lett. 2007, 24 (2): 479-482 .  
Abstract   PDF(pc) (215KB) ( 392 )
Based on Mie scattering theory and the theory of multiple light scattering, the light scattering properties of air bubbles in a wake are analysed by Monte Carlo simulation. The results show that backscattering is enhanced obviously due to the existence of bubbles, especially with the increase of bubble density, and that it is feasible to use the Monte Carlo method to study the properties of light scattering by air bubbles.
Magnetic Behaviour and Heating Effect of Fe3O4 Ferrofluids Composed of Monodisperse Nanoparticles
ZHANG Li-Ying, DOU Yong-Hua, ZHANG Ling, GU Hong-Chen
Chin. Phys. Lett. 2007, 24 (2): 483-486 .  
Abstract   PDF(pc) (219KB) ( 682 )
Fe3O4 ferrofluids containing monodisperse Fe3O4 nanoparticles with different diameters of 8, 12, 16 and 18nm are prepared by using high-temperature solution phase reaction. The particles have single crystal structures with arrow size distributions. At room temperature, the 8-nm ferrofluid shows perparamagnetic behaviour, whereas the others display hysteresis properties and the coercivity increases with the increasing particle size. The spin glass-like behaviour and cusps near 190K are observed on all ferrofluids according to the temperature variation of field-cooled (FC) and zero-field-cooled (ZFC) magnetization measurements. The cusps are found to be associated with the freezing point of the solvent. As a comparison, the ferrofluids are dried and the FC and ZFC magnetization curves of powdery samples are also nvestigated. It is found that the blocking temperatures for the powdery samples are higher than those for their corresponding ferrofluids. Moreover, the size dependent heating effect of the ferrofluids is also investigated in ac magnetic field with a frequency of 55kHz and amplitude of 200Oe.
Estimation of Charge Exchange Recombination Emission Based on Diagnostic Neutral Beam on the Experimental Advanced Superconducting Tokamak
ZHANG Xian-Mei, WAN Bao-Nian, WU Zhen-Wei
Chin. Phys. Lett. 2007, 24 (2): 487-489 .  
Abstract   PDF(pc) (219KB) ( 525 )
Diagnostic neutral beam (DNB) attenuation and charge exchange recombination emission are estimated on EAST tokamak. Approximately 40% of the beam with the energy of 50\,keV can reach the plasma centre (r=0) for the typical parameters of the Experimental Advanced Superconducting Tokamak (EAST) plasma. Emissivities of CVI (n=8→7, 529.0nm) and OVIII (n=10→9, 607.0nm) visible charge exchange recombination emissions based on the DNB are estimated. The emissivities of the visible bremsstrahlung emission near this wavelength are also calculated for comparison. The results show that the charge exchange recombination emission is about two orders of magnitude greater than the bremsstrahlung emission. It is theoretically indicated that the ratio of signal of charge exchange recombination spectroscopy to the noise from background bremsstrahlung emission, S/N, is large enough in the EAST tokamak with the typical designed parameters. The present results are helpful for experiment design of charge-exchange recombination spectroscopy based on the DNB in the EAST tokamak.
Magneto-Hydrodynamic High-n Ballooning Mode Instability of an Analytic Axi-Symmetric Toroidal Equilibrium with Arbitrary Aspect Ratio
SHI Bing-Ren, LI Ji-Quan
Chin. Phys. Lett. 2007, 24 (2): 490-493 .  
Abstract   PDF(pc) (222KB) ( 673 )
An exact ballooning mode eigen-equation is derived to study stability of axi-symmetric toroidal plasma with arbitrary aspect ratio, including the tokamak, the finite aspect ratio and the spherical torus plasmas. For comparison with the widely used (s-α) model, an analytic exact equilibrium configuration with circular magnetic surfaces is analysed in detail. It is indicated that the (s-α) model needs to be improved for more realistic configurations.
Deuterium Clusters Fusion Induced by the Intense Femtosecond laser Pulse
LIU Hong-Jie, ZHENG Zhi-Jian, GU Yu-Qiu, ZHANG Bao-Han, RHEE Yong-Joo, NAM Sung-Mo, HAN Jae-Min, RHEE Yong-Woo, YEA Kwon-Hae, CHEN Jia-Bin, WANG Hong-Bin, JIAO Chun-Ye, HE Ying-Ling, WEN Tian-Shu, WEN Xian-Lun, CHEN Ming
Chin. Phys. Lett. 2007, 24 (2): 494-496 .  
Abstract   PDF(pc) (219KB) ( 592 )
Neutrons (2.45MeV) from deuterium cluster fusion induced by the intense femtosecond (30fs) laser pulse are experimentally demonstrated. The average neutron yield 103 per shot is obtained. It is found that the yield slightly increases with the increasing laser spot size. No neutron can be observed when the laser intensity I<4.3×1015W/cm2.
Hybrid Method for Tokamak MHD Equilibrium Configuration Reconstruction
HE Hong-Da, DONG Jia-Qi, ZHANG Jin-Hua, JIANG Hai-Bin
Chin. Phys. Lett. 2007, 24 (2): 497-500 .  
Abstract   PDF(pc) (249KB) ( 545 )
A hybrid method for tokamak MHD equilibrium configuration reconstruction is proposed and employed in the modified EFIT code. This method uses the free boundary tokamak equilibrium configuration reconstruction algorithm with one boundary point fixed. The results show that the position of the fixed point has explicit effects on the reconstructed divertor configurations. In particular, the separatrix of the reconstructed divertor configuration precisely passes the required position when the hybrid method is used in the reconstruction. The profiles of plasma parameters such as pressure and safety factor for reconstructed HL-2A tokamak configurations with the hybrid and the free boundary methods are compared. The possibility for applications of the method to swing the separatrix strike point on the divertor target plate is discussed.
High Coupling Efficiency Generation in Water Confined Laser Plasma Propulsion
ZHENG Zhi-Yuan, ZHANG Yi, ZHOU Wei-Gong, LU Xin, LI Yu-Tong, ZHANG Jie
Chin. Phys. Lett. 2007, 24 (2): 501-503 .  
Abstract   PDF(pc) (186KB) ( 687 )
High coupling efficiency generation in water confined laser plasma propulsion is investigated. It is found that the coupling efficiency is enhanced over thirty times in water confined ablation compared to that of direct ablation. From calculation of the ablation pressure induced by the plasma on the target surface, it is realized that high coupling efficiency is attributed to the confinement of the water layer on the plasma expansion.
Determination of the Surface Tension of Liquid Fe 77.5 Cu13Mo 9.5 Ternary Monotectic Alloy
WANG Hai-Peng, CHANG Jian, LUO Bing-Chi, WEI Bing-Bo
Chin. Phys. Lett. 2007, 24 (2): 504-507 .  
Abstract   PDF(pc) (213KB) ( 804 )
Thermophysical properties of undercooled liquid monotectic alloys are usually difficult to be determined because of the great difficulty in achieving large undercoolings. We measure the surface tension of liquid Fe 77.5 Cu13Mo 9.5 monotectic alloy by an electromagnetic oscillating drop method over a wide temperature range from 1577 to 1784K, including both superheated and undercooled states. A good linear relationship exists between the surface tension and temperature. The surface tension value is 1.588N/m at the monotectic temperature of 1703K, and its temperature coefficient is -3.7×10 -4 Nm -1 K -1. Based on the Butler equation, the surface tension is also calculated theoretically. The experimental and calculated results indicate that the effect of the enriched element on droplet surface is much more conspicuous than the other elements to decrease the surface tension.
Solute Distribution within Rapidly Grown Fe--Co Single Phase
YAO Wen-Jing, DAI Fu-Ping, WEI Bing-Bo
Chin. Phys. Lett. 2007, 24 (2): 508-511 .  
Abstract   PDF(pc) (259KB) ( 450 )
Rapid growth of Fe--Co single phase is accomplished by rapid solidification in a drop tube. (Fe,Co) grains are refined with the decrease of alloy droplet diameters. Energy dispersive spectroscopy analysis indicates that icrosegregation in (Fe,Co) single phase becomes lower with the reduction of droplet diameters. The experimental results with theoretical calculation reveal that the microsegregation is efficiently suppressed with the increase of undercooling. The free energies of intrinsic segregation for Fe-30wt.%Co, Fe-40wt.%Co and Fe-50wt.%Co alloys are -47.17, -27.57 and -6.57kJ/mol, respectively. The dependence of free energy of segregation on composition and undercooling has been deduced.
An Experimental Study of In-Situ Phase Fraction in Jet Pump Using Electrical Resistance Tomography Technique
XU Jing-Yu, WANG Mi, WU Ying-Xiang, H. I. SCHLABERG, ZHENG Zhi-Chu, R. A. WILLIAMS
Chin. Phys. Lett. 2007, 24 (2): 512-515 .  
Abstract   PDF(pc) (223KB) ( 1023 )
We perform the experiments to investigate in-situ phase fraction in a jet pump using the electrical resistance tomography (ERT) technique. A new jet pump with ERT sensors is designed to measure in-situ phase fraction and flow regime. The study is based on laboratory experiments that are carried out on a 50-mm vertical flow rig for various gas and liquid phase superficial velocities. The different flow patterns of gas liquid in the jet pump and vertical pipe are studied using the ERT technique. The results suggest that the ERT system can be used to successfully produce images of gas--liquid flow patterns with frames rates of 58fps and the in-situ phase fraction with frame rates of 5fps can be obtained. The visualizations of a rapid mixing process in the throat of a jet pump obtained in this work provide a reliable basis for theoretical study and optimal design of jet pumps.
A Comparison between AlN Films Grown by MOCVD Using Dimethylethylamine Alane and Trimethylaluminium as the Aluminium Precursors
HU Wei-Guo, LIU Xiang-Lin, ZHANG Pan-Feng, ZHAO Feng-Ai, JIAO Chun-Mei, WEI Hong-Yuan, ZHANG Ri-Qing, WU Jie-Jun, CONG Guang-Wei, PAN Yi
Chin. Phys. Lett. 2007, 24 (2): 516-517 .  
Abstract   PDF(pc) (238KB) ( 1505 )
Aluminium nitride (AlN) films grown with dimethylethylamine alane (DMEAA) are compared with the ones grown with trimethylaluminium (TMA). In the high-resolution x-ray diffraction Ω scans, the full width at half maximum (FWHM) of (0002) AlN films grown with DMEAA is about 0.70 deg, while the FWHM of (0002) AlN films grown with TMA is only 0.11 deg. The surface morphologies of the films are different, and the rms roughnesses of the surface are approximately identical. The rms roughness of AlN films grown with DMEAA is 47.4nm, and grown with TMA is 69.4nm. Although using DMEAA as the aluminium precursor cannot improve the AlN crystal quality, AlN growth can be reached at low temperature of 673K. Thus, DMEAA is an alternative aluminium precursor to deposit AlN film at low growth temperatures.
Alternating-Current Conductivity for a Two-Channel Interacting Quantum Wire
PENG De-Jun, CHENG Fang, ZHOU Guang-Hui,
Chin. Phys. Lett. 2007, 24 (2): 520-523 .  
Abstract   PDF(pc) (206KB) ( 602 )
We investigate theoretically the ac conductivity of a clean two-channel spinless quantum wire in the presence of both short-ranged intra- and inter-channel electron--electron interactions. In the Luttinger-liquid regime, we formulize the action functional of the system with an external time-varying
electric field. The obtained expression of ac conductivity for the system within linear response theory is generally an oscillation function of the interaction strength, the driving frequency as well as the measured position in the wire. The numerical examples demonstrate that the amplitude of ac conductivity is renormalized by the both interactions, and the dc conductivity of the system with inter-channel interaction is smaller than that without inter-channel interaction.
First-Principles Study of Electronic Structure of the Laves Phase ZrFe2
ZHANG Chang-Wen, ZHANG Zhong, WANG Shao-Qing, LI Hua, DONG Jian-Min, XING Nai-Sheng, GUO Yong-Quan, LI Wei
Chin. Phys. Lett. 2007, 24 (2): 524-526 .  
Abstract   PDF(pc) (219KB) ( 910 )

We perform the ab initio calculation for obtaining the density of states and magnetic properties of ZrFe2 Laves phase compound based on the method of augmented plane waves plus local orbital. The results indicate that the ferromagnetic state is more stable than the paramagnetic one, but with a slightly larger volume. The 3d-4d exchange interactions between Fe and Zr electrons lead to the antiparallel coupling for Fe 3d and Zr 4d states, which is
responsible for the ferrimagnetic ordering of the compound. The resulting magnetic moment of about 1.98μB for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin states causes a moment of about -0.44μB. Moreover, the resulting magnetic moments with the generalized gradient approximation are more consistent with experimental values than that of the local-spin density approximation.

Broadband and High Efficient 1530nm Emission from Oxyfluoride Glass Ceramics Codoped with Er 3+ and Yb 3+ Ions
LIU Bao-Rong, ZHAO Li-Juan, SUN Jian, YU Hua, SONG Jie, XU Jing-Jun,
Chin. Phys. Lett. 2007, 24 (2): 527-529 .  
Abstract   PDF(pc) (206KB) ( 468 )
The emission at 1530nm and its applications in optical communications
are discussed. The efficient width of the emission band Δeff, which is up to 91nm, is larger as compared with silica-based glass, bismuth glass and ZrF4--BaF2--LaF3--AlF3--NaF (ZBLAN) glass doped by Er 3+ ions. Under the excitation of 785\,nm laser, the emission integral intensity of 1530nm increases about five times in the glass ceramics higher than that in the glass. This is explained by the quantum cutting process by two-photon emission with phonon assistance. The results indicate that the glass ceramics are a promising candidate for developing broadband optical amplifiers in wavelength-division multiplexed systems.
Ultraviolet Photoelectric Effect in ZrO2 Single Crystals
XING Jie, WANG Xu, ZHAO Kun , LI Jie, JIN Kui-Juan, HE Meng, ZHENG Dong-Ning, LÜ, Hui-Bin
Chin. Phys. Lett. 2007, 24 (2): 530-531 .  
Abstract   PDF(pc) (175KB) ( 345 )
Nanosecond photoelectric effect is observed in a ZrO2 single crystal at ambient temperature for the first time. The rise time is 20ns and the full width at half maximum is about 30ns for the photovoltaic pulse when the wafer surface of the ZrO2 single crystal is irradiated by 248nm KrF laser pulses. The experimental results show that ZrO2 single crystals may be a potential candidate in UV photodetectors.
Magnetic Quantum Tunnelling in Faster Relaxation Process in Mn12Ac Molecular Magnets
LIU Hai-Qing, SU Shao-Kui, JING Xiu-Nian, LIU Ying, HE Lun-Hua, GE Pei-Wen, YAN Qi-Wei, WANG Yun-Ping
Chin. Phys. Lett. 2007, 24 (2): 532-535 .  
Abstract   PDF(pc) (212KB) ( 481 )
The field-tuned ac susceptibility of Mn12Ac single crystal has been measured as functions of temperature and frequency. Two relaxation processes appear in our measurement. One is related to the magnetic quantum tunnelling of a collective spin S=12 by a 61K magnetic barrier and it has been well studied, while the other is faster than the former and its mechanism is unclear. We find that the relaxation time for the faster process shows the minima at H=0 and H=3.4kOe, indicating that the quantum tunnelling also takes place in this process while the resonant fields are different from what we have known before.
Structural Stability of CaCuMn6O12 under High Pressure and Low Temperature
ZHANG Wang, YAO Li-De, YOU Shu-Jie, YANG Liu-Xiang, YANG Hua, LI Feng-Ying, CHEN Liang-Chen, BAO Zhong-Xing, LI Xiao-Dong, LIU Jing, JIN Chang-Qing, YU Ri-Cheng
Chin. Phys. Lett. 2007, 24 (2): 536-538 .  
Abstract   PDF(pc) (244KB) ( 528 )

In situ high pressure energy-dispersive x-ray synchrotron radiation diffraction and resistance experiments are carried out on CaCuMn6O12. Its crystal structure is stable in the measured pressure range. The equation of state of CaCuMn6O12 is obtained from the V/V0-P relationship (V and V0 are the volumes at pressure P and at atmosphere). The bulk modulus B0 is calculated based on the Birch--Murnaghan equation. Low temperature x-ray diffraction shows no phase transition occurring down to 160K.

Dynamic Phase-Mapping of Domain Nucleation in MgO:LiNbO3 Crystal by Digital Holographic Interferometry
QU Wei-Juan, LIU De-An, ZHI Ya-Nan, LUAN Zhu, LIU Li-Ren
Chin. Phys. Lett. 2007, 24 (2): 539-542 .  
Abstract   PDF(pc) (225KB) ( 311 )
The quantitative phase-mapping of the domain nucleation in MgO:LiNbO3 crystals is presented by using the digital holographic interferometry. An unexpected peak phase at the beginning of the domain nucleation is observed and it is lowered as the spreading of the domain nucleus. The existence of the nucleus changes the moving speed of the domain wall by pinning it for 3s. Such in-situ quantitative analysis of the domain nucleation process is a key to optimizing domain structure fabrication.
UV--vis Absorption and PL Properties of Self-Assembled Silicon Nanotubes
ZHANG Zheng-Hua, LIU Han-Mao, XIONG Yuan-Qin, XU Wei-Jian, TANG Yuan-Hong
Chin. Phys. Lett. 2007, 24 (2): 543-545 .  
Abstract   PDF(pc) (192KB) ( 806 )
Silicon nanotubes (SiNTs) are novel one-dimensional nanomaterials, which
have potential applications in nano-photoelectric devices, sensors and field-emission devices. The self-assembled silicon nanotubes have clear structures without metal catalysts. The structures are confirmed by TEM and HRTEM, and the UV- vis absorption spectra with an absorption peak near 685nm and PL spectra with widened strong emission near 436nm are measured by UV--vis spectrometer and spectrofluorophotometer.
An Experimental Study of Mg Aggregation in AA5754 Alloys byPositron Annihilation Spectroscopy
HUANG Chang-Hong, MA Li, CHEN Zhi-Quan, WANG Zhu, WANG Xiao-Wei, ZHANG Hong-Yan
Chin. Phys. Lett. 2007, 24 (2): 546-548 .  
Abstract   PDF(pc) (217KB) ( 561 )
Defects in an AA5754 (Al-3.0%Mg) alloy are investigated by coincidence Doppler broadening spectroscopy and positron lifetime spectroscopy. The
results indicate enhancement of positron trapping by Mg atoms in this Al--Mg alloy after quenching treatment at 623K, which may be due to the formation of vacancy-Mg complexes or the aggregation of Mg near the vacancy sites. It is speculated that the aggregation of Mg atoms in the moderate temperature range is responsible for cracking in spot welding of AA5754 alloys.
Effects of Proton Irradiation on a CMOS Image Sensor
HUANG Qiang, MENG Xiang-Ti
Chin. Phys. Lett. 2007, 24 (2): 549-551 .  
Abstract   PDF(pc) (181KB) ( 652 )
We perform 9MeV proton irradiation of a complementary metal oxide semiconductor (CMOS) image sensor at doses from 1×109 to 4×1010 cm-2. In general, the average brightness of dark output images increases with an increasing dose, and reaches the maximum at 1×1010 cm -2. The captured
colour images become very blurry at 4×1010 cm-2. These can be explained by change of concentrations of irradiation-induced electron-hole pairs and vacancies in the various layers of CMOS image sensor calculated by the TRIM simulation programme with dose.
Effects of Substrate Temperature and Nitrogen Pressure on Growth of AlN Films by Pulsed Laser Deposition
LV Lei, LI Qing-Shan, LI Li, ZHANG Li-Chun, WANG Cai-Feng, QI Hong-Xia
Chin. Phys. Lett. 2007, 24 (2): 552-554 .  
Abstract   PDF(pc) (215KB) ( 667 )
Highly oriented aluminium nitride (AlN) films are grown on p-Si (100) substrates by pulsed laser deposition, and their characteristics of structure and composition are studied by x-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The results show that the deposited films exhibit good crystalline properties with a sharp x-ray diffraction peak at 2θ=33.15°corresponding to AlN h<100> crystalline orientation. The influences of substrate temperature and ambient nitrogen (N2) pressure on the crystallinity of AlN films are remarkable. At room temperature, when the ambient N2 pressure arises from 5×10-6 Pa to 5Pa, the crystallinity of the film becomes better. When the substrate temperature is 600°C, the film has the best crystallinity at 0.05Pa. Furthermore, the effects of substrate temperature and ambient N2 pressure on the combination of Al-N bonds and surface morphology of AlN films are also studied.
Efficiency Enhancement of Dye-Sensitized Solar Cells: Using Salt CuI as an Additive in an Ionic Liquid
CHEN Lie-Hang, XUE Bo-Fei, LIU Xi-Zhe, LI Ke-Xin, LUO Yan-Hong, MENG Qing-Bo, WANG Rui-Lin, CHEN Li-Quan
Chin. Phys. Lett. 2007, 24 (2): 555-558 .  
Abstract   PDF(pc) (219KB) ( 1127 )
Energy conversion efficiency of the dye-sensitized solar cell is improved from 3.5% to 4.5% by adding a small amount of CuI into an ionic liquid electrolyte. It is found that other copper-I salts, for example, CuBr, have the same effect for the dye-sensitized solar cell. Experimental results show that no Cu 2+ ions exist in this electrolyte. It is suggested that this improvement is caused by the adsorption of Cu+ onto the TiO2 porous film.
A New Dopant of NaN3 for High-Concentration-Nitrogen Diamond Synthesized by HPHT
LIANG Zhong-Zhu, JIA Xiao-Peng, Hisao Kanda, MA Hong-An, WANG Dong-Mei, LIU Wan-Qiang, YU Run-Ze
Chin. Phys. Lett. 2007, 24 (2): 559-562 .  
Abstract   PDF(pc) (216KB) ( 671 )
Nitrogen is successfully doped in diamond by adding sodium azide (NaN3) as the source of nitrogen to the graphite and iron powders. The diamond crystals with high nitrogen concentration, 1000--2200ppm, which contain the same concentrations of nitrogen with natural diamond, have been synthesized by using the system of iron-carbon-additive NaN3. The nitrogen concentrations in diamond increase with the increasing content of NaN3. When the content of NaN3 is increased to 0.7--1.3wt.%, the nitrogen concentration in the diamond almost remains in a nitrogen concentration range from 1250ppm to 2200ppm, which is the highest value and several times higher than that in the diamond synthesized by a conventional method without additive NaN3 under high pressure and high temperature (HPHT) conditions.
Optical Characterization of β-FeSi2 Thin Films Prepared by Femtosecond Laser Ablation
ZHOU You-Hua, YANG Guang, ZHANG Zhi-Hua, LONG Hua, DUAN Xiao-Feng, GAO Yi-Hua, ZHENG Qi-Guang, LU Pei-Xiang
Chin. Phys. Lett. 2007, 24 (2): 563-566 .  
Abstract   PDF(pc) (257KB) ( 734 )
Iron disilicide thin films are prepared on fused quartz using femtosecond laser deposition (FsPLD) with a FeSi2 alloy target. X-ray diffraction results indicate the films are single-phase, orthorhombic, β-FeSi2. Field scanning electron microscopy, high resolution transmission electron microscopy, UV--VIS--NIR spectroscopy and Raman microscope are used to characterize the structure,
composition, and optical properties of the β-FeSi2 films. Normal incidence spectral transmittance and reflectance data indicate a minimum, direct energy gap of 0.85eV. The two most intense lines of Raman scattering peaked at 181.3cm-1 and 235.6cm-1 for the film on fused quartz, and at 191.2cm-1 and 243.8cm-1 for the film on Si (100), are observed.
Analytical Interaction of the Acoustic Wave and Turbulent Flame
TENG Hong-Hui, JIANG Zong-Lin
Chin. Phys. Lett. 2007, 24 (2): 567-569 .  
Abstract   PDF(pc) (188KB) ( 415 )
A modified resonance model of a weakly turbulent flame in a high-frequency acoustic wave is derived analytically. Under the mechanism of Darrieus--Landau instability, the amplitude of flame wrinkles, which is as functions of the expansion coefficient and the perturbation wave number, increases greatly independent of the `stationary' turbulence. The high perturbation wave number makes the resonance easier to be triggered but weakened with respect to the extra acoustic wave. In a closed burning chamber with the acoustic wave induced by the flame itself, the high perturbation wave number is to restrain the resonance for a realistic flame.
Terahertz Detection with Twin Superconductor--Insulator--Superconductor Tunnel Junctions
LI Jing, WANG Ming-Jye, SHI Sheng-Cai, Hiroshi Matsuo
Chin. Phys. Lett. 2007, 24 (2): 570-573 .  
Abstract   PDF(pc) (212KB) ( 656 )
Terahertz detection with twin superconductor--insulator--superconductor (SIS) tunnel junctions, which are connected in parallel via an inductive thin-film superconducting microstrip line, is mainly studied. Firstly, we investigate the direct-detection response of a superconducting twin-junction device by means of a Fourier transform spectrometer. Secondly, we construct a direct-detection model of twin SIS tunnel junctions. The superconducting twin-junction device is then simulated in terms of the constructed model. The simulation result is found to be in good agreement with the measured one. In addition, we observe that the direct-detection response of the device is consistent with the noise temperature behaviour.
Single-Photon Detection at Telecom Wavelengths
SUN Zhi-Bin, MA Hai-Qiang, LEI Ming, WANG Di, LIU Zhao-Jie, YANG Han-Dong, WU Ling-An, ZHAI Guang-Jie, FENG Ji
Chin. Phys. Lett. 2007, 24 (2): 574-576 .  
Abstract   PDF(pc) (201KB) ( 559 )
A single-photon detector based on an InGaAs avalanche photodiode has been developed for use at telecom wavelengths. A suitable delay and sampling gate modulation circuit are used to prevent positive and negative transient pulses from influencing the detection of true photon induced avalanches. A monostable trigger circuit eliminates the influence of avalanche peak jitter, and a dead time modulation feedback control circuit decreases the afterpulsing. From performance tests we find that at the optimum operation point, the quantum efficiency is 12% and the dark count rate 1.5×10-6ns-1, with a detection rate of 500kHz.
Walks on Weighted Networks
WU An-Cai, XU Xin-Jian, WU Zhi-Xi, WANG Ying-Hai
Chin. Phys. Lett. 2007, 24 (2): 577-580 .  
Abstract   PDF(pc) (251KB) ( 527 )
We investigate the dynamics of random walks on weighted networks. Assuming that the edge weight and the node strength are used as local information by a random walker. Two kinds of walks, weight-dependent walk and strength-dependent walk, are studied. Exact expressions for stationary distribution and average return time are derived and confirmed by computer simulations. The distribution of average return time and the mean-square displacement are calculated for two walks on the Barrat--Barthelemy--Vespignani (BBV) networks. It is found that a weight-dependent walker can arrive at a new territory more easily than a strength-dependent one.
Periodic Wave of Epidemic Spreading in Community Networks
ZHOU Yin-Zuo, LIU Zong-Hua, ZHOU Jie
Chin. Phys. Lett. 2007, 24 (2): 581-584 .  
Abstract   PDF(pc) (266KB) ( 829 )
It was reported by Cummings et al. [Nature 427(2004)344] that there are periodic waves in the spatiotemporal data of epidemics. For understanding the mechanism, we study the epidemic spreading on community networks by both the SIS model and the SIRS model. We find that with the increase of infection rate, the number of total infected nodes may be stabilized at a fixed point, oscillatory waves, and periodic cycles. Moreover, the epidemic spreading in the SIS model can be explained by an analytic map.
Bianchi Type-III String Cosmological Models with Time Dependent Bulk Viscosity
Chin. Phys. Lett. 2007, 24 (2): 585-588 .  
Abstract   PDF(pc) (210KB) ( 578 )
Bianchi type-III string cosmological models with bulk viscous fluid for massive string are investigated. To obtain the determinate model of the universe, we assume that the coefficient of bulk viscosity ξ is inversely proportional to the expansion θ in the model and expansion θ in the model is proportional to the shear σ. This leads to B = l Cn, where l and n are constants. Behaviour of the model in the presence and absence of bulk viscosity is discussed. The physical implications of the models are also discussed in detail.
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