Chin. Phys. Lett.

Volume 24 Issue 5

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Hall Effects on Unsteady Magnetohydrodynamic Flow of a Third Grade Fluid

K. Fakhar, XU Zhen-Li, CHENG Yi

Chin. Phys. Lett. 2007, 24 (5): 1129-1132 .

Abstract

PDF(pc) (256KB) ( 469 )

The unsteady magnetohydrodynamic flow of an electrically conducting viscous incompressible third grade fluid bounded by an infinite porous plate is studied with the Hall effect. An external uniform magnetic field is applied perpendicular to the plate and the fluid motion is subjected to a uniform suction and injection. Similarity transformations are employed to reduce the non-linear equations governing the flow under discussion to two ordinary differential
equations (with and without dispersion terms). Using the finite difference scheme, numerical solutions represented by graphs with reference to the various involved parameters of interest are discussed and appropriate conclusions are drawn.

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Stability of Motion of a Nonholonomic System

MEI Feng-Xiang, XIE Jia-Fang, GANG Tie-Qiang

Chin. Phys. Lett. 2007, 24 (5): 1133-1135 .

Abstract

PDF(pc) (186KB) ( 445 )

Perturbation differential equations of motion of a general nonholonomic system subjected to the ideal nonholonomic constraints of Chetaev's type are established, and the equation of variation of energy is deduced by using the perturbation equations of the system. A criterion of the stability is obtained and an example is given to illustrate the application of the result.

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Non-Adiabatic Geometric Phase in a Dispersive Interaction System

Ji-Bing, LI Jia-Hua, LV Xin-You, ZHENG An-Shou,

Chin. Phys. Lett. 2007, 24 (5): 1136-1139 .

Abstract

PDF(pc) (246KB) ( 409 )

We investigate the geometric phase and dynamic phase of a two-level fermionic system with dispersive interaction, driven by a quantized bosonic field which is simultaneously subjected to parametric amplification. It is found that the geometric phase is induced by a counterpart of the Stark shift. This effect is due to distinct shifts in the field frequency induced by interaction between different states (|e> and |g>) and cavity field, and a simple geometric interpretation of this phenomenon is given, which is helpful to understand the natural origin of the geometric phase.

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Quantum Tricritical Point in the Spin-Boson Model with an Ohmic Bath

CHEN Wen, CHEN Zhi-De

Chin. Phys. Lett. 2007, 24 (5): 1140-1143 .

Abstract

PDF(pc) (252KB) ( 692 )

The dynamics of the spin-boson model with an Ohmic bath at finite temperature is studied by a variational calculation. Numerical solution of the self-consistent equation derived from the variational method shows that the transition from incoherent to coherent phases is discontinuous. It indicates that (T=0,s=1) is a tricritical point, i.e. the transition changes from continuous to discontinuous by tuning from T=0 to T≠0. The discontinuous transition at finite temperature is analysed by Landau theory and the relation to the experimental observation on the coherent state is also discussed.

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Probabilistic Controlled Teleportation of a Triplet W State

JIANG Wei-Xing, FANG Jian-Xing, ZHU Shi-Qun, SHA Jin-Qiao

Chin. Phys. Lett. 2007, 24 (5): 1144-1146 .

Abstract

PDF(pc) (212KB) ( 512 )

A scheme for probabilistic controlled teleportation of a triplet W
state from the sender Alice to the distant receiver Bob is proposed.
In this scheme, an m-qubit GHZ state serves as the control parameter.
The m control qubits are shared by m(s₁,s_2^... s_m) spatially-separated supervisors. With the aid of local operations and individual measurements, including Bell-state measurement, Von Neumann measurement, and mutual classical communication, etc., Bob can faithfully reconstruct the original state by performing relevant unitary transformations. However, even if one participant does not cooperate during the process, the receiver Bob cannot fully recover the original state. This protocol can be extended to probabilistic controlled teleportation of an arbitrary N-qubit state and some other N-qubit entangled states.

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Scalable Quantum Secret Sharing Extended from Quantum Key Distribution

LIU Wei-Tao, LIANG Lin-Mei, LI Cheng-Zu, YUAN Jian-Min

Chin. Phys. Lett. 2007, 24 (5): 1147-1150 .

Abstract

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We suggest a general approach for extending quantum key distribution (QKD) protocols possessing discrete rotational symmetry into quantum secret sharing (QSS) schemes among multiparty, under certain conditions. Only local unitary operations are required for this generalization based on the almost mature technologies of QKD. Theoretically, the number of the participating partners can be arbitrary high. As an application of this method, we propose a fault-tolerant QSS protocol based on a fault-tolerant QKD implementation. The 6-state protocol is also discussed.

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Controlled Teleportation of an Arbitrary Multi-Qudit State in a General Form with d-Dimensional Greenberger--Horne--Zeilinger States

LI Xi-Han, , DENG Fu-Guo, , ZHOU Hong-Yu,

Chin. Phys. Lett. 2007, 24 (5): 1151-1153 .

Abstract

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A general scheme for controlled teleportation of an arbitrary multi-qudit state with d-dimensional Greenberger--Horne--Zeilinger (GHZ) states is proposed. For an arbitrary m-qudit state, the sender Alice performs m generalized Bell-state projective measurements on her 2m qudits and the controllers need only take some single-particle measurements. The receiver Charlie can reconstruct the unknown m-qudit state by performing some single-qudit unitary operations on her particles if she cooperates with all the controllers. As the quantum channel is a sequence of maximally entangled GHZ states, the intrinsic efficiency for qudits in this scheme approaches 100% in principle.

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Quantum Key Distribution against Trojan Horse Attacks

CAI Qing-Yu, LV Hua,

Chin. Phys. Lett. 2007, 24 (5): 1154-1157 .

Abstract

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Realistic experimental apparatus of quantum cryptography are imperfect,
which may be utilized by a potential eavesdropper to eavesdrop on the
communication. We show that quantum communication may be improved with
quantum teleportation and entanglement swapping, which is robustly secure
against the most general Trojan horse attacks. Our scheme is not an
improvement of the communication apparatus, but the improvement of
quantum communication protocol itself. We show that our modified schemes
may be implemented with current technology.

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Thermodynamic Interpretation of Field Equations at Horizon of BTZ Black Hole

M. Akbar

Chin. Phys. Lett. 2007, 24 (5): 1158-1161 .

Abstract

PDF(pc) (205KB) ( 405 )

A spacetime horizon comprising with a black hole singularity acts like a boundary of a thermal system associated with the notions of temperature
and entropy. In the case of static metric of Banados--Teitelboim--Zanelli (BTZ) black hole, the field equations near the horizon boundary can be expressed as a thermal identity dE = TdS + P_rdA, where E = M is the mass of BTZ black hole, dA is the change in the area of the black hole horizon when the horizon is displaced infinitesimally small, P_r is the radial pressure provided by the source of Einstein equations, S= 4πa is the entropy and T =k/2π is the Hawking temperature associated with the horizon. This approach is studied further to generalize it for non-static BTZ black hole, showing that it is also possible to interpret the field equation near horizon as a thermodynamic identity dE = TdS + P_rdA +Ω₊dJ, where Ω₊ is the angular velocity and J is the angular momentum of BTZ black hole. These results indicate that the field equations for BTZ black hole possess intrinsic thermodynamic properties near the horizon.

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Stochastic Resonance in the Tumour Cell Growth Model

CAI Jian-Chun, WANG Can-Jun, MEI Dong-Cheng

Chin. Phys. Lett. 2007, 24 (5): 1162-1165 .

Abstract

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The phenomenon of stochastic resonance (SR) in the tumour cell growth model subjected cross-correlated noises is investigated. When a weakly periodic signal is added to the system, the signal-to-noise ratio R_SNR is derived by the quasi-steady-state probability distribution function and the adiabatic elimination method. Based on the derived R_SNR, the effects of these parameters (the cross-correlated strength λ and the cross-correlated time τ) are analysed by numerical calculation. It is found that the existence of a maximum in R_SNR is the identifying characteristic of the SR phenomenon. The maximum of R_SNRdecreases with the increase of λ and increases with the increase of τ.

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Secure and Efficient Pseudorandom Bit Generator for Chaotic Stream Ciphers

WANG Xiao-Min, ZHANG Jia-Shu

Chin. Phys. Lett. 2007, 24 (5): 1166-1169 .

Abstract

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Based on the entropy criterion and n-dimensional uniform distribution of nonlinear digital filter (NDF), we present an efficient NDF-based seudorandom bit generator (NDF-PRBG) for chaotic stream ciphers. The cryptographic properties of the proposed NDF-PRBG are analysed, and some experiments are made. The results show that it has desirable cryptographic properties, and can be used to construct secure stream ciphers with high speed.

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Differential System's Nonlinear Behaviour of Real Nonlinear Dynamical Systems

YANG Zheng-Ling, WANG Wei-Wei, YIN Zhen-Xing, ZHANG Jun, CHEN Xi

Chin. Phys. Lett. 2007, 24 (5): 1170-1172 .

Abstract

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Chaos attractor behaviour is usually preserved if the four basic arithmetic perations, i.e. addition, subtraction, multiplication, division, or their compound,
are applied. First-order differential systems of one-dimensional real discrete dynamical systems and nonautonomous real continuous-time dynamical systems are also dynamical systems and their Lyapunov exponents are kept, if they are twice differentiable. These two conclusions are shown here by the definitions of dynamical system and Lyapunov exponent. Numerical simulations support our analytical results. The conclusions can apply to higher order differential systems if their corresponding order differentials exist.

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Exact Analytic N-Soliton-Like Solution in Wronskian Form for a Generalized Variable-Coefficient Korteweg--de Vries Model from Plasmas and Fluid Dynamics

ZHANG Chun-Yi, YAO Zhen-Zhi, ZHU Hong-Wu, XU Tao, LI Juan, MENG Xiang-Hua, GAO Yi-Tian

Chin. Phys. Lett. 2007, 24 (5): 1173-1176 .

Abstract

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Applicable in fluid dynamics and plasmas, a generalized variable-coefficient Korteweg--de Vries (vcKdV) model is investigated. The bilinear form and analytic N-soliton-like solution for such a model are derived by the Hirota method and Wronskian technique. Additionally, the bilinear auto-Backlund transformation between (N-1)-soliton-like and N-soliton-like solutions is verified.

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Improvements and New Evaluation of NIM4 Caesium Fountain Clock at NIM in 2005--2006

LI Tian-Chu, LI Ming-Shou, LIN Ping-Wei, WANG Ping, CHEN Wei-Liang, LIU Nian-Feng, LIN Yi-Ge

Chin. Phys. Lett. 2007, 24 (5): 1177-1179 .

Abstract

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The NIM4 caesium fountain clock has been operating stably and sub-continually since August 2003. We present our improvements on NIM4 in 2005--06 and the most recent evaluation for its frequency shifts with an uncertainty of 5×10^-15. A 203-day comparison between NIM4 and GPS time shows an agreement of 2×10^-14. Finally the construction of the NIM5 transportable caesium fountain clock is briefly reported.

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Raman and X-Ray Investigation of Pyrope Garnet (Mg _0.76 Fe _0.14 Ca _0.10)₃Al₂Si₃O₁₂ under High Pressure

MA Yan-Mei, CHEN Hai-Yong, LI Xue-Fei, GAO Ling-Ling, CUI Qi-Liang, ZOUGuang-Tian

Chin. Phys. Lett. 2007, 24 (5): 1180-1182 .

Abstract

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The compressional behaviour of natural pyrope garnet is investigated by using angle-dispersive synchrotron radiation x-ray diffraction and Raman spectroscopy in a diamond anvil cell at room temperature. The pressure-induced phase transition does not occur under given pressure. The equation of state of pyrope garnet is determined under pressure up to 25.3GPa. The bulk modulus K_T0 is 199GPa, with its first pressure derivative K'_T0 fixed to 4. The Raman spectra of pyrope garnet are studied. A new Raman peak nearly at 743cm^-1 is observed in a bending vibration of the SiO₄tetrahedra frequency range at pressure of about 28GPa. We suggest that the new Raman peak results from the lattice distortion of the SiO₄ tetrahedra. All the Raman frequencies continuously increase with the increasing pressure. The average pressure derivative of the high frequency modes (650--1000cm^-1) is larger than that of the low frequency (smaller than 650cm^-1). Based on these data, the mode Gruneisen parameters for pyrope are obtained.

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Van der Waals interactions and Photoelectric Effect in Noncommutative Quantum Mechanics

LI Kang, CHAMOUN Nidal,

Chin. Phys. Lett. 2007, 24 (5): 1183-1186 .

Abstract

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We calculate the long-range Van der Waals force and the photoelectric cross section in a noncommutative setup. It is argued that non-commutativity effects could not be discerned for the Van der Waals interactions. The result for the photoelectric effect shows deviation from the usual commutative one, which in principle can be used to put bounds on the space--space non-commutativity parameter.

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Calculation of the Longitudinal Structure Function from Regge-Like Behaviour of the Gluon Distribution Function in Leading Order Approximation at Low x

G.R. Boroun, B. Rezaie

Chin. Phys. Lett. 2007, 24 (5): 1187-1190 .

Abstract

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We present the calculations of F_L longitudinal structure functions from DGLAP evolution equation in leading order (LO) at low-x, assuming the Regge-like behaviour of gluon distribution at this limit. The calculated results are compared with the H1 data and QCD fit. It is shown that the obtained results are very close to the mentioned methods. The proposed simple analytical relation for F_L provides a t-evolution equation for the determination of the longitudinal structure function at low-x. All the results can consistently be
described within the framework of perturbative QCD, which essentially shows increases as x decreases.

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Shear Viscosity to Non-Equilibrium Entropy Density Ratio of Hot Quark--Gluon Plasma at Finite Chemical Potential

LIU Hui, HOU De-Fu, LI Jia-Rong

Chin. Phys. Lett. 2007, 24 (5): 1191-1194 .

Abstract

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In the framework of irreversible thermodynamics, we study the transport properties of hot quark--gluon plasmas. The viscous entropy production at
finite chemical potential as well as the shear viscosity to non-equilibrium entropy density ratio is investigated in weakly coupled limit by using kinetic theory. The results show that the chemical potential contributes positively to their ratio compared to the pure temperature case. The ratio exhibits two boundaries in the coupling strength in which a minimum value of 0.42 is found at α_s=0.6.

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Mesons in the Constituent Quark Model

WANG Li, PING Jia-Lun,

Chin. Phys. Lett. 2007, 24 (5): 1195-1198 .

Abstract

PDF(pc) (244KB) ( 393 )

The quark--antiquark (qq) spectrum is studied by solving the Schrodinger equation in the framework of non-relativistic constituent quark model. An overall good fit to the experimental data of meson is obtained. The interactions between quark and antiquark consist of quadratic colour confinement-exchange, one-gluon-exchange, and Goldstone-boson-exchange potentials.

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Exploration of Pseudospin Symmetry in the Resonant States

ZHANG Shi-Sheng, SUN Bao-Hua, ZHOU Shan-Gui,

Chin. Phys. Lett. 2007, 24 (5): 1199-1202 .

Abstract

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Taking ¹²⁰Sn as an example, we discuss the pseudospin symmetry in the single proton resonant states by examining the energies, widths and the wavefunctions. The information of the single proton resonant states in spherical nuclei are extracted from an analytic continuation in the coupling constant method within the framework of the self-consistent relativistic mean field theory under the relativistic boundary condition. We find small energy splitting in a pair of pseudospin partners in the resonant states. The lower components of the Dirac wavefunctions of a pseudospin doublet agree well in the region where nuclear potential dominates. It is concluded that the pseudospin symmetry is also well conserved for the resonant states in realistic nuclei.

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Identification of a New Band and Its Signature Inversion in ¹⁷⁴Re

ZHANG Yu-Hu, GUO Song, ZHOU Xiao-Hong, MA Long, GUO Wen-Tao, Oshima M., Toh Y., Koizumi M., Osa A., Kimura A., Hatsukawa Y., Sugawara M., Kusakari H.

Chin. Phys. Lett. 2007, 24 (5): 1203-1206 .

Abstract

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High spin states in 174Re are investigated via the ¹⁵²Sm(²⁷Al,5nγ)¹⁷⁴Re reaction and γ-γ coincidence relationships are analysed carefully. A new band is identified due to its spectroscopic connection with the known π1/2^-[541]_⊕^ν1/2^-[521] band. This band is proposed to be the ground-state band built on the π 1/2^- [541]⊕ν5/2^- [512] configuration in view of the low-lying intrinsic states in the neighbouring odd-mass nuclei. It is of particular interesting
that the new band exhibits a phenomenon of low-spin signature inversion,
providing a new situation for theoretical investigations.

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Calculations of Optical Rotation from Density Functional Theory

Antonio Canal Neto, Francisco Elias Jorge

Chin. Phys. Lett. 2007, 24 (5): 1207-1209 .

Abstract

PDF(pc) (200KB) ( 604 )

Density function theory calculations of frequency-dependent optical
rotations [αl]_ω for three rigid chiral molecules are reported. Calculations have been carried out at the sodium D line frequency, using the ADZP basis set and a wide variety of functionals. Gauge-invariant atomic orbitals are used to guarantee origin-independent values of [α]_D. In addition, study of geometry
dependence of [α]_D is reported. Using the geometries optimized at
the B3LYP/ADZP level, the mean absolute deviation of B3LYP/ADZP and
experimental [α]_D values yields 60.1°/(dm g/cm³). According to our knowledge, this value has not been achieved until now with any other model.

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Impact of Viscosity on DNA Dynamics

S. ZDRAVKOVIC, M. V. SATARIC

Chin. Phys. Lett. 2007, 24 (5): 1210-1213 .

Abstract

PDF(pc) (226KB) ( 594 )

We study the influence of viscosity on DNA dynamics. By employing the nonlinear Peyrard--Bishop--Dauxois (PBD) model, it is shown that the DNA dynamics can be explained by a solution of a complex nonlinear Schrodinger equation (CNLSE). This is the nonlinear Schrodinger equation (NLSE) with a nonlinear parameter being a complex number. We compare real and maginary parts of this nonlinear parameter and show that the latter one should not be negligible, which means that the CNLSE should be solved numerically.

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Theoretical Study of Relativistic Retardation Effects: the Abnormal Fine Structure of OII

CHEN Shao-Hao, HAN Xiao-Ying, WANG Xiao-Lu, LI Jia-Ming,

Chin. Phys. Lett. 2007, 24 (5): 1214-1216 .

Abstract

PDF(pc) (225KB) ( 545 )

Using multi-configuration Dirac--Fock and relativistic configuration interaction methods with high-order corrections, we report our precise calculation results of the fine-structure energy levels of the ground-state configuration of OII (1s²2s²2p³). Our calculated fine-structure splittings of ²D_3/2,5/2 and ²P _1/2,3/2 are abnormal. We elucidate that the transverse (Breit) interaction, i.e. relativistic retardation effect, plays an important role for the abnormal fine-structure splittings. Our calculation results are in good agreement with experimental measurements.

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Experimental Improvement of Signal of a Single Laser-Cooled Trapped ⁴⁰Ca⁺ Ion

SHU Hua-Lin, , GUO Bin, , GUAN Hua, , LIU Qu, , HUANG Xue-Ren, GAO Ke-Lin,

Chin. Phys. Lett. 2007, 24 (5): 1217-1219 .

Abstract

PDF(pc) (383KB) ( 623 )

A single ⁴⁰Ca⁺ ion is loaded in a miniature Paul trap and the probability of directly loading a single ion is above 50%. The signal-to-noise ratio and the storage time for a single ion have been improved by minimizing the ion micromotion and locking a 397nm cooling laser to a Fabry--Perot interferometer and optogalvanic signal. From the fluorescence spectrum, the ion temperature is estimated to be about 5mK.

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A Theoretical Study of Super-Excited States of F₂

ZHANG Wei-Hua, HE Chun-long, HAO Yu-Song, MO Yu-Xiang, LI Jia-Ming,

Chin. Phys. Lett. 2007, 24 (5): 1220-1223 .

Abstract

PDF(pc) (247KB) ( 649 )

In the framework of quantum defect theory, we study super-excited states
of F₂ molecules which can dissociate into F⁺(³P _2,1,0) and F-(¹S₀) ion-pair. Based on our calculation, we present a vibrational resolved assignment of the high precision photofragment yield spectra for F^-from the F₂ ion-pair production.

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Appropriate Gate Time for Single Molecular Photon Detection Based on Optimal Signal-to-Noise Ratio Analyses

DONG Shuang-Li, HUANG Tao, LIU Yuan, WANG Jun, XIAO Lian-Tuan, JIA Suo-Tang

Chin. Phys. Lett. 2007, 24 (5): 1224-1227 .

Abstract

PDF(pc) (254KB) ( 528 )

Signal-to-noise ratio of fluorescence detection from a single molecule is analysed by using time-gated techniques. It is found that the optimal signal-to-noise ratio can be obtained by choosing an appropriate gate time with a certain optical background. The dependences of molecular fluorescence lifetime and the optimal signal-to-noise ratio on the appropriate gate time are respectively discussed with two kinds of background sources, chaotic state with uniform distribution and coherent state with exponential distribution in time domain. For chaotic state background we find that a certain range for appropriate gate time can be obtained with a definite fluorescence lifetime, larger fluorescence lifetime would lower the value of optimal signal-to-noise
ratios. For coherent state background we find that there is also a narrow range of appropriate gate time when lifetime of single molecule is less than that of background photons.

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Electrostatic Surface Trap for Cold Polar Molecules with a Charged Circular Wire

MA Hui, ZHOU Bei, LIAO Bin, YIN Jian-Ping

Chin. Phys. Lett. 2007, 24 (5): 1228-1230 .

Abstract

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We propose a novel scheme to trap cold polar molecules on the surface of an insulating substrate (i.e. a chip) by using an inhomogeneous electrostatic field, which is generated by the combination of a circular charged wire (a ring electrode) and a grounded metal plate. The spatial distributions of the electrostatic field from the above charged wire layout and its Stark potentials for CO molecules are calculated. Our study shows that when the voltage
applied to the wire is U=15kV, a ring radius is R=5mm, the thickness of the insulating substrate is b=5mm, and a wire radius is r=1mm, the maximum efficient trapping potential (i.e., as equivalent temperature) for CO molecules is greater than 141.7mK, which is high enough to trap cold polar molecules with a temperature of 50mK in the low-field-seeking states.

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Study on Non-Sequential Double Ionization of Aligned Diatomic Molecules in Strong Laser Fields

LI Yan, CHEN Jing, YANG Shi-Ping, LIU Jie

Chin. Phys. Lett. 2007, 24 (5): 1231-1233 .

Abstract

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We develop a semiclassical model to describe the non-sequential double ionization of aligned diatomic molecules in an intense linearly polarized field. It is found that in the tunnelling regime, the oriented molecule shows geometric effects on double ionization process when aligned parallel and perpendicular to the external field. Our results are qualitatively consistent with the recent experimental observations.

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Partial Wave Cross Sections for Collisions between Helium Atoms and Hydrogen Halide Molecules

YU Chun-Ri, CHENG Xin-Lu, YANG Xiang-Dong

Chin. Phys. Lett. 2007, 24 (5): 1234-1237 .

Abstract

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The close-coupling method is utilized to calculate partial cross sections for elastic and inelastic scattering of He atoms with HX (X=F, Cl, Br) molecule based on the CCSD (T) potential energy surfaces obtained in the previous research. The calculation is performed at the incident energy of 200meV. The rationality of our results has been confirmed by comparison with the available theoretical results. The tendency of the elastic and inelastic rotational excitation partial wave cross sections varying with the reduced mass of the three systems is obtained.

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Surface Planar Ion Chip for Linear Radio-Frequency Paul Traps

WAN Jin-Yin, QU Qiu-Zhi, ZHOU Zi-Chao, LI Xiao-Lin, WANG Yu-Zhu, LIU Liang

Chin. Phys. Lett. 2007, 24 (5): 1238-1241 .

Abstract

PDF(pc) (969KB) ( 591 )

We propose a surface planar ion chip which forms a linear radio frequency Paul ion trap. The electrodes reside in the two planes of a chip, and the trap axis is located above the chip surface. Its electric field and potential distribution are similar to the standard linear radio frequency Paul ion trap. This ion trap geometry may be greatly meaningful for quantum information processing.

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Frequency Response of Multilayer Media Comprised of Double-Negative and Double-Positive Slabs

Cumali Sabah, Savas Uckun

Chin. Phys. Lett. 2007, 24 (5): 1242-1244 .

Abstract

PDF(pc) (206KB) ( 715 )

We present the interactions of the electromagnetic waves with multilayer media formed by double-negative and double-positive slabs to find the frequency response of the structure. The double-negative slabs are analytically realized by using the frequency dispersive cold plasma medium. Numerical examples are performed using an in-house developed simulation programme code. The variation of the reflectance and the transmittance with the emphasis on the plasma frequencies is observed in these examples.

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Controlling of Slope of Carrier--Envelope Phase of Few-Cycle Laser Pulses on Propagation Distance near the Focus

ZHOU Yong-Heng, JIANG Hong-Bing, GONG Qi-Huang

Chin. Phys. Lett. 2007, 24 (5): 1245-1247 .

Abstract

PDF(pc) (211KB) ( 500 )

The effect of focusing geometry on slope of carrier--envelope (CE) phase Ф_CE versus propagation distance from the focus in few-cycle laser pulses is investigated. The slope could be adjusted by changing the distance L between the waist of the incident beam and the lens. At the focus, ∂Ф_CE/∂ (z/z_R)=0 when L=0, and ∂Ф_CE/ References | Related Articles | Metrics -->

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Optical Amplification and Slow Light Based on Two-Wave Mixing at Large Modulation Depth

ZHANG Yun-Dong, YE Jian-Bo, QIU Wei

Chin. Phys. Lett. 2007, 24 (5): 1248-1251 .

Abstract

PDF(pc) (293KB) ( 497 )

Based on Kukhtarev's equations, we derive the formulae of intensity-coupling coefficient, the phase-coupling coefficient and the group velocity at large modulation depth. It is theoretically shown that the signal beam can be amplified after passing through the photorefractive crystal and the group velocity reduced to m/s, even cm/s. Meanwhile, we also analyse the influence of the thermal excitation rate and the large signal effects on optical amplification and reduction of light propagation in photorefractive two-wave mixing.

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Focusing of Partially Coherent Vortex Beams by an Aperture Lens

RAO Lian-Zhou, PU Ji-Xiong

Chin. Phys. Lett. 2007, 24 (5): 1252-1255 .

Abstract

PDF(pc) (491KB) ( 483 )

The focusing properties of partially coherent vortex wave fields are studied. Expressions are derived for the intensity distribution and the degree of coherence near the geometrical focus. It is found that the size of coherence vortex dark core in the focal region depends on the topological charges and normalized coherence lengths. It is found that the desired vortex dark core near the geometrical focus can be generated by choosing appropriate values of parameters. The degree of coherence possesses a pair of phase singularities regions in the geometrical focus neighbourhood.

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Anomalous Effects of Driving Field Linewidth on a One-Atom Dressed-State Laser

YANG Jin-Jin, Hu Xiang-Ming

Chin. Phys. Lett. 2007, 24 (5): 1256-1259 .

Abstract

PDF(pc) (244KB) ( 461 )

We examine the effects of driving field linewidth on a one-atom dressed state laser. Unexpectedly, the linewidth leads to anomalous effects on the cavity field. The mean photon number of the cavity field is raised or the normalized variance is reduced to a certain degree as the linewidth increases for an appropriate range of parameters. The responsible mechanism is attributed to the fluctuation-induced modification of the electromagnetic reservoir where the atom stays.

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A Radio Frequency Field Guide Using Field Induced Adiabatic Potential

YAN Bo, LI Xiao-Lin, KE Min, WANG Yu-Zhu

Chin. Phys. Lett. 2007, 24 (5): 1260-1263 .

Abstract

PDF(pc) (253KB) ( 492 )

We study the behaviour of atoms in a field with both static magnetic field and radio frequency (rf) magnetic field. We calculate the adiabatic potential of atoms numerically beyond the usually rotating wave approximation, and it is pointed that there is a great difference between using these two methods. We find the preconditions when RWA is valid. In the extreme of static field
almost parallel to rf field, we reach an analytic formula. Finally, we apply this method to ⁸⁷Rb and propose a guide based on an rf field on atom chip.

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Q-Switched Large-Mode-Area Yb-Doped Fibre Laser Using GaAs as Saturable Absorber

FU Sheng-Gui, GUO Zhan-Cheng, SI Li-Bin, ZHAO Ying, YUAN Shu-Zhong, DONG Xiao-Yi

Chin. Phys. Lett. 2007, 24 (5): 1264-1266 .

Abstract

PDF(pc) (381KB) ( 430 )

A passive Q-switched large-mode-area Yb-doped fibre laser is demonstrated using a GaAs wafer as the saturable absorber. A high Yb doping concentration double-clad fibre with a core diameter of 30μm and a numerical aperture of 0.07 is used to increase the laser gain volume, permitting greater energy storage and higher output power than conventional fibres. The maximum average output power is 7.2W at 1080nm wavelength, with the shortest pulse duration of 580ns and the highest peak power of 161W when the laser is pumped with a 25W diode laser operating at 976nm. The repetition rate increases with the pump power linearly and the highest repetition rate of 77kHz is obtained in the experiment.

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Multiple-Pulse Operation in Passively Mode-Locked Fibre Laser with Positive Dispersion Cavity

GAO Wei-Qing, ZHENG Huan, XU Li-Xin, WANG An-Ting, MING Hai, ANQi, HE Hu-Cheng, WANG Yun-Cai

Chin. Phys. Lett. 2007, 24 (5): 1267-1269 .

Abstract

PDF(pc) (241KB) ( 478 )

We report the observation of rectangular shape spectrum in passively mode-locked fibre laser with positive dispersion cavity. The spectrum is broad and flat, and 3dB bandwidth can be up to 17.61nm. Multiple-pulse operation is observed in our laser system. The spectrum width, pulse energy, pulse width and peak power of the mode-locked laser output change with the appearance of multiple-pulse operation.

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A Bidirectional, Diode-Pumped, Passively Mode-Locked Nd:YVO₄ Ring Laser with a Low-Temperature-Grown Semiconductor Saturable Absorber Mirror

CAI Zhi-Qiang, YAO Jian-Quan, WANG Peng, WANG Yong-Gang, ZHANG Zhi-Gang

Chin. Phys. Lett. 2007, 24 (5): 1270-1272 .

Abstract

PDF(pc) (236KB) ( 575 )

We report the operation of a bidirectional picosecond pulsed ring Nd:YVO₄ laser based on a low-temperature-grown semiconductor saturable absorber mirror. Except for the laser crystal, the six-mirror ring laser cavity has no intra-cavity elements such as focusing lens or mirror. The bidirectional mode locked pluses are obtained at the repetition rate of 117.5MHz, pulse duration of 81ps, power of 2×200mW.

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Calculation of the Spatio-Temporal Dynamics of Q-switched Yb³⁺:YAG Laser with an Unstable Cavity and a Super-Gaussian Mirror

CAO Ding-Xiang, ZHENG Wan-Guo, Wang Xiao-Feng, YU Hai-Wu, HEShao-Bo, Tan Ji-Chun

Chin. Phys. Lett. 2007, 24 (5): 1273-1275 .

Abstract

PDF(pc) (264KB) ( 457 )

A numerical simulation used to compute the spatio-temporal dynamics of pulse formation of diode-pumped Q-switched Yb:YAG laser is carried out. The model takes the laser amplification and gain saturation, the properties of the laser cavity, and the diffractive effects of the laser disc into account. The numerical calculation is performed for a confocal positive-branch unstable resonator with a super Gaussian coupling mirror. The simulation results show that the laser pulse starts from a Gaussian intensity distribution and becomes rapidly non-Gaussian. The corresponding beam quality M² factor is seen to vary approximately from 1.5 at the beginning of the formation of pulse to more than 10 in the tail of the pulse, with a value of 11.6 at the peak of the pulse.

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Generation of 17-TW 23-fs Pulses with a Two-Stage Ti:Sapphire Amplifier at Repetition Rate 10Hz

LI Chuang, LU Xiao-Ming, WANG Cheng, LENG Yu-Xin, LIANG Xiao-Yan, LI Ru-Xin, XU Zhi-Zhan

Chin. Phys. Lett. 2007, 24 (5): 1276-1278 .

Abstract

PDF(pc) (232KB) ( 594 )

We have developed a two-stage Ti:sapphire amplifier system which can produce 17-TW/23-fs pulses at a repetition rate 10Hz. A birefringent plate is used in the regenerative amplifier to alleviate gain narrowing, while an all-reflective cylindrical-mirror-based pulse stretcher and an acousto-optic programmable dispersive filter (AOPDF) are used to compensate for the higher order dispersion of the system.

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Interaction of Nonlocal Incoherent White-Light Solitons

HUANG Chun-Fu, GUO Qi

Chin. Phys. Lett. 2007, 24 (5): 1279-1282 .

Abstract

PDF(pc) (441KB) ( 473 )

The propagation and interaction of nonlocal incoherent white-light solitons in strongly nonlocal kerr media is investigated. Numerical simulations show that the interaction properties of nonlocal incoherent white-light solitons are different from the case in local media. The interactions of nonlocal incoherent white-light solitons are always attractive independent of their relative phase,
while the other parameters such as the extent of nonlocality and the input power have a great impact on the soliton interactions. Pertinent numerical examples are presented to show their propagation and interaction behaviour further.

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Er³⁺ and Yb³⁺ Codoped Phosphate Laser Glass for High Power Flashlamp Pumping

FANG Yong-Zheng, JIN Ming-Lin, WEN Lei, LI Shun-Guang, HU Li-Li

Chin. Phys. Lett. 2007, 24 (5): 1283-1286 .

Abstract

PDF(pc) (238KB) ( 1336 )

A novel Yb ³⁺ -Er ³⁺ codoped phosphate glass for high power flashlamp pumping and high repetition rate laser at 1.54μm, designated EAT5-2, is developed. The weight-loss rate of is 1.3×10^-5gcm^-2 h^-1 in boiling water, which is comparable to Kigre's QX--Er glass. Some spectroscopic parameters are analysed by Judd--Ofelt theory and McCumber theory. The emission cross
section is calculated to be 0.73×10 ^-20 cm². The thermo-mechanical roperties of EAT5-2 are modified after an ion-exchange chemical strengthening process in a KNO₃/NaNO₃ molten salt bath. The thresholds for optical damage from the flashlamp pumping are tested on glass rods. A repetition rate of 15Hz is achieved for chemically strengthened glass. The laser experimental results at 1.54μm from flashlamp pumping are also reported.

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Thin Films Used for Write-Once Blue Laser Recording

ZHOU Ying, GENG Yong-You, GU Dong-Hong, ZHU Qing, JIANG Zhi

Chin. Phys. Lett. 2007, 24 (5): 1287-1289 .

Abstract

PDF(pc) (285KB) ( 573 )

SbO_x thin films are deposited by reactive dc-magnetron sputtering from an antimony metal target in Ar+O₂ with the relative O₂content 7%. It is found that the as-deposited films can represent a two-component system comprising amorphous Sb and amorphous Sb₂O₃. The crystallization of Sb is responsible for the changes of optical properties of the films. The results of the static test show that the SbO_x thin films have good writing sensitivity
for blue laser beams and the recording marks are very clear and circular. High reflectivity contrast of about 41% is obtained at a writing power 6mW and writing pulse width 300ns. In addition, the films show a good stability after reading 10000 times.

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A Novel Woodpile Three-Dimensional Terahertz Photonic Crystal

LIU Huan, YAO Jian-Quan, ZHENG Fang-Hua, XU De-Gang, WANG Peng

Chin. Phys. Lett. 2007, 24 (5): 1290-1293 .

Abstract

PDF(pc) (437KB) ( 644 )

A novel woodpile lattice structure is proposed. Based on plane wave expansion (PWE) method, the complete photonic band gaps (PBGs) of the
novel woodpile three-dimensional (3D) terahertz (THz) photonic crystal (PC) with a decreasing symmetry relative to a face-centred-tetragonal ( fct) symmetry are optimized by varying some structural parameters and the highest band gap ratio can reach 27.61%. Compared to the traditional woodpile lattice, the novel woodpile lattice has a wider range of the filling ratios to gain high quality PBGs, which provides greater convenience for the manufacturing process. The novel woodpile 3D PC will be very promising for materials of THz functional components.

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Highly Birefringent Honeycomb Photonic Bandgap Fibre

FANG Hong, LOU Shu-Qin, GUO Tie-Ying, JIAN Shui-Sheng

Chin. Phys. Lett. 2007, 24 (5): 1294-1297 .

Abstract

PDF(pc) (428KB) ( 455 )

A new structure of highly birefringent honeycomb photonic bandgap fibres (PBGFs), including an elliptical air hole in its solid core, is proposed and analysed by using full vectorial plane wave expansion method. From the numerical results it is confirmed that the proposed PBGF has birefringence of the order of 10^-3. Moreover, there are two single-polarization single-mode ranges at varying normalized wavelength, in one of which only the slow-axis mode exists, and in the other only the fast-axis mode exists, which has not been achieved in index-guiding photonic crystal fibres so far.

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Theoretical Design of Single-Polarization Single-Mode Microstructured Polymer Optical Fibres

REN Li-Yong, WANG Han-Yi, ZHANG Ya-Ni, YAO Bao-Li, ZHAO Wei

Chin. Phys. Lett. 2007, 24 (5): 1298-1301 .

Abstract

PDF(pc) (251KB) ( 616 )

Using the full-vector plane-wave expansion method, a kind of PMMA-based
polarization-maintaining microstructured optical fibre (PM-mPOF) is theoretically studied. Dependence of the cutoff wavelengths of the two
orthogonal polarization states (polarized along the two principal axes
of PM-mPOF) on the structure parameters of the fibre is investigated in
detail. A single-polarization single-mode (SPSM) PM-mPOF working in the
visible region is designed and optimized with the result of the maximum
SPSM bandwidth of 140nm.

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Ultra-Narrow Dual-Channel Filter Based on Symmetrical Sampled Fibre Bragg Grating

LIU Xue-Ming, WANG Lei-Ran, GONG Yong-Kang, WANG Tao, LU Ke-Qing, ZHANG Tong-Yi, ZHAO Wei

Chin. Phys. Lett. 2007, 24 (5): 1302-1204 .

Abstract

PDF(pc) (236KB) ( 544 )

A kind of ultra-narrow dual-channel filter is proposed in principle and demonstrated experimentally. This filter is designed by means of two sampled fibre Bragg gratings (SFBGs), where one is periodic 0--π sampling and the other is symmetrical spatial sampling. The former can create two stopbands in the transmission spectra and the latter can produce two ultra-narrow passbands. Our filter has the 3-dB bandwidth of about 1pm, whose value is two orders of magnitude less than the bandwidth of the traditional SFBG filters. The proposed filter has a merit that the channel spacing remains unchanged when tuning the filter.

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Directional Propagation Characteristics of Flexural Waves in Two-Dimensional Thin-Plate Phononic Crystals

WEN Ji-Hong, YU Dian-Long, WANG Gang, ZHAO Hong-Gang, LIU Yao-Zong, WEN Xi-Sen

Chin. Phys. Lett. 2007, 24 (5): 1305-1308 .

Abstract

PDF(pc) (775KB) ( 701 )

The propagation characteristics of flexural waves in two-dimensional thin-plate phononic crystals (PCs) are analysed with the plane wave expansion (PWE) method to yield phase constant surfaces, which predict high directivity of flexural wave propagation for certain frequencies outside the band gap. The prediction is validated through the computation of the harmonic responses of a finite structure with 9×9 unit cells. The results indicate that directional propagation of flexural waves is an inherent characteristic of two-dimensional thin-plate PCs while specific effects of the directional propagation in a finite structure vary with the positions of excitations.

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A New Method for Calculation of Single Seismic Phase of Cylindrically Multilayered Media Including Liquid Interlayer

SONG Ruo-Long, WANG Ke-Xie, ZHANG Hong-Bing, HAN Wei

Chin. Phys. Lett. 2007, 24 (5): 1309-1312 .

Abstract

PDF(pc) (541KB) ( 477 )

A new method based on generalized reflection and transmission (R/T) coefficients method is proposed to calculate the single seismic phase (SSP) of cylindrically multilayered media including liquid interlayer. The use of normalization factors and normalized Lame coefficients makes the algorithm stable numerically. Using the modified R/T matrices, we derive the iterative expressions of generalized R/T matrices, and by using the iterative relation we determine the SSP of each interface and the full waveforms. To show the superiority of this new approach for investigating of reflection and ransmission properties of cylindrically multilayered media, we simulate the full
waveforms and SSPs of cased hole model with annulus I (casing-cement
interface) channelling (or, cross-flow). The generalized reflection coefficient spectra and SSPs of interfaces obtained show the propagation mechanism of each component of full waveform clearly.

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A Novel Model of Interaural Time Difference Based on Spatial Fourier Analysis

ZHONG Xiao-Li, XIE Bo-Sun

Chin. Phys. Lett. 2007, 24 (5): 1313-1316 .

Abstract

PDF(pc) (242KB) ( 568 )

Based on the spatial Fourier analysis, a statistical model of the individualized interaural time difference (ITD) is derived from the head-related transfer function database for a Chinese subject. The model reflects the spatial left--right symmetry and front--back asymmetry of ITD. Moreover, by using three anatomical parameters of head and pinna, the model is able to predict individualized ITD in the horizontal plane. Performance of the four subjects outside the database demonstrates that the mean of the total error is less than 20μs, while the lateral performance is inferior to that at other directions.

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Rotational and Vibrational Temperatures of Atmospheric Double rc Argon--Nitrogen Plasma

YAN Jian-Hua, TU Xin, MA Zeng-Yi, CEN Ke-Fa, B. G. Cheron

Chin. Phys. Lett. 2007, 24 (5): 1317-1321 .

Abstract

PDF(pc) (419KB) ( 798 )

The spectroscopic technique is employed to study the emission of
atmospheric argon--nitrogen plasma jet generated by an original dc
double anode plasma torch. The molecular bands of the N₂⁺
first negative system are observed at the torch exit and chosen to
evaluate the rotational and vibrational temperatures in comparison with
the simulated spectra. The excitation temperature (T_exc ≈9600K) is determined from the Boltzmann plot method. The results show that the rotational, vibrational, electron and kinetic temperatures are in good agreement with one another, which indicates that the core region of atmospheric double arc argon--nitrogen plasma jet at the torch exit is close to the local thermodynamic equilibrium state under our experimental conditions.

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Length Dependence of Thermal Conductivity of Single-Walled Carbon Nanotubes

PAN Rui-Qin, XU Zi-Jian, ZHU Zhi-Yuan

Chin. Phys. Lett. 2007, 24 (5): 1321-1323 .

Abstract

PDF(pc) (221KB) ( 811 )

Dependence of the thermal conductivity on the length of two armchair single-walled carbon nanotubes (SWNTs) is studied by the nonequilibrium molecular dynamics (MD) method with Brenner II potential. The thermal conductivities are calculated for (5, 5) and (7, 7) SWNTs with lengths ranging from 22 to 155nm. The results show that the thermal conductivity of SWNTs is sensitive to the length and it does not converge to a finite value when the tube length increases up to 155nm, however it obeys a power law relation.

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Numerical Simulation of the Elastic Shrinkage Induced by Portevin--Le Chatelier Effect

JIANG Hui-Feng, ZHANG Qing-Chuan, CHEN Xue-Dong, FAN Zhi-Chao, CHEN Zhong-Jia, WU Xiao-Ping

Chin. Phys. Lett. 2007, 24 (5): 1324-1326 .

Abstract

PDF(pc) (485KB) ( 422 )

A new one-dimensional phenomenological model based on the dynamic strain
aging mechanism is developed. In order to account for the elastic shrinkage induced by the Portevin--Le Chatelier effect, elastic deformation is considered under the boundary conditions of the present model. The simulated results are found to be in good agreement with the experimental observations.

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Energy of a Polaron in a Wurtzite Nitride Finite Parabolic Quantum Well

ZHAO Feng-Qi, GONG Jian,

Chin. Phys. Lett. 2007, 24 (5): 1327-1330 .

Abstract

PDF(pc) (244KB) ( 569 )

The effects of electron--phonon interaction on energy levels of a polaron in
a wurtzite nitride finite parabolic quantum well (PQW) are studied by using a modified Lee--Low--Pines variational method. The ground state, first excited state, and transition energy of the polaron in the GaN/Al _0.3 Ga _0.7 N wurtzite PQW are calculated by taking account of the influence of confined LO(TO)-like phonon modes and the half-space LO(TO)-like phonon modes and considering the anisotropy of all kinds of phonon modes. The numerical results are given and discussed. The results show that the electron--phonon interaction strongly affects the energy levels of the polaron, and the contributions from phonons to the energy of a polaron in a wurtzite nitride PQW are greater than that in an AlGaAs PQW. This indicates that the electron--phonon interaction in a wurtzite nitride PQW is not negligible.

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Miscibility of Two Components in a Binary Mixture of 9-Phenyl Anthracene Mixed with Stearic Acid or Polymethyl Methacrylate at Air--Water Interface

P. K. Paul, Md. N. Islam, D. Bhattacharjee, S. A. Hussain

Chin. Phys. Lett. 2007, 24 (5): 1331-1334 .

Abstract

PDF(pc) (362KB) ( 478 )

We report the miscibility characteristics of two components in a binary mixture of 9-phenyl anthracene (PA) mixed with stearic acid (SA) or polymethyl methacrylate (PMMA). The behaviour of surface pressure versus area per molecule isotherms reveal that the area per molecule decreases systematically with increasing molefractions of PA. The characteristics of areas per molecule versus molefractions and collapse pressure vs molefraction indicate that various interactions involved among the sample and matrix molecules. The interaction scheme is found to change with the change in surface pressure and molefraction of mixing. Scanning electron microscopic study confirms the aggregation of PA molecules in the mixed films.

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A Modified Glass Formation Criterion for Various Glass Forming Liquids with Higher Reliability

X. H. Du, J. C. Huang

Chin. Phys. Lett. 2007, 24 (5): 1335-1338 .

Abstract

PDF(pc) (255KB) ( 435 )

A modified indicator of the glass forming ability (GFA) from the previous γ=T_x/(T_l+T_g) for various glass forming liquids is proposed based on a conceptual approach which combines more acceptable physical metallurgy views in terms of the time-temperature-transformation diagrams. It is found that the glass
forming ability for glass forming liquids is closely associated mainly with two factors, i.e. (2T_x-T_g) and T_l (wherein T_xis the onset crystallization temperature, T_g the glass transition temperature, and T_lthe liquidus temperature), and could be predicated by a unified parameter γ_mdefined as (2T_x-T_g)/T_l. This approach is confirmed and validated by experimental data in various glass forming systems including oxide glasses, cryoprotectants and metallic glasses, which all shows a higher reliability when their glass forming ability is predicted by the modified parameter.

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Thermodynamics Properties of Mesoscopic Quantum Nanowire Devices

Attia A. AwadAlla, Adel H. Phillips

Chin. Phys. Lett. 2007, 24 (5): 1339-1341 .

Abstract

PDF(pc) (208KB) ( 448 )

We investigate the thermodynamics properties of mesoscopic quantum nanowire devices, such as the effect of electron-phonon relaxation time, Peltier coefficient, carrier concentration, frequency of this field, and channel width. The influence of time-varying fields on the transport through such device has been taken into consideration. This device is modelled as nanowires connecting to two reservoirs. The two-dimensional electron gas in a GaAs--AlGaAs heterojunction has a Fermi wave length which is a hundred times larger than that in a metal. The results show the oscillatory behaviour of dependence of the thermo power on frequency of the induced field. These
results agree with the existing experiments and may be important for
electronic nanodevices.

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New Power Lateral Double Diffused Metal--Oxide--Semiconductor Transistor with a Folded Accumulation Layer

DUAN Bao-Xing, ZHANG Bo, LI Zhao-Ji

Chin. Phys. Lett. 2007, 24 (5): 1342-1345 .

Abstract

PDF(pc) (382KB) ( 688 )

A new lateral double diffused metal oxide semiconductor field effect transistor with a double-charge accumulation layer using a folded silicon substrate is proposed to improve the performance of the breakdown voltage and specific on-resistance. Three kinds of technologies, which are the additional electric field modulation effect, majority carrier accumulation and increasing the effective conduction area, are applied simultaneously by a semi-insulating
polycrystalline silicon layer deposited over the top of thin oxide covering the drift region. It is indicated that by the simulator, the ideal silicon limits of the breakdown voltage and specific on-resistance have been broken due to the complete three-dimensional reduced surface field effect and the doubled majority carrier accumulation layer.

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Form of Scaling Function in Quantum Hall Plateau Transitions

TU Tao, ZHAO Yong-Jie GUO Guo-Ping, HAO Xiao-Jie, GUO Guang-Can

Chin. Phys. Lett. 2007, 24 (5): 1346-1349 .

Abstract

PDF(pc) (246KB) ( 577 )

We have measured the temperature dependence of the resistance R _xxand R_xy of a two-dimensional electron system in the regime of the quantum Hall plateau transition. We observe for our sample a considerable large critical exponent k ～ 0.66-0.77, which may be due to the dominant electron-phonon scattering. Further we find a simple exponential form of R_xx=R_cexp (-s) in agreement with the theoretically proposed universal scaling function.

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Photovoltaic and Electroluminescence Characters in Hybrid ZnO and Conjugated Polymer Bulk Heterojunction Devices

LIU Jun-Peng, QU Sheng-Chun, XU Ying, CHEN Yong-Hai, ZENG Xiang-Bo, WANG Zhi-Jie, ZHOU Hui-Ying, WANG Zhan-Guo

Chin. Phys. Lett. 2007, 24 (5): 1350-1353 .

Abstract

PDF(pc) (257KB) ( 630 )

We report electroluminescence in hybrid ZnO and conjugated polymer poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) bulk heterojunction photovoltaic cells. Photoluminescence quenching experimental results indicate that the ultrafast photoinduced electron transfer occurs from MDMO-PPV to ZnO under illumination. The ultrafast photoinduced electron transfer effect is induced because ZnO has an electron affinity about 1.2eV greater than that of MDMO-PPV. Electron `back transfer' can occur if the interfacial barrier between ZnO and MDMO-PPV can be overcome by applying a substantial electric field. Therefore, electroluminescence action due to the fact that the back transfer effect can be observed in the ZnO:MDMO-PPV devices since a forward bias is applied. The photovoltaic and electroluminescence actions in the same ZnO:MDMO-PPV device can be induced by different injection ways: photoinjection and electrical injection. The devices are expected to provide an opportunity for dual functionality devices
with photovoltaic effect and electroluminescence character.

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Spin Transport Properties of the One-Dimensional Heisenberg Chain: Bethe-Ansatz Solution with Twist Boundary Conditions

ZHANG Qiu-Lan, GU Shi-Jian

Chin. Phys. Lett. 2007, 24 (5): 1354-1356 .

Abstract

PDF(pc) (220KB) ( 484 )

Based on the Bethe-Ansatz solution of the one-dimensional Heisenberg model under twist boundary conditions, we study the spectra of the persistent current carried by the low-lying excited states. It is shown that though the energy spectra of spin-singlet and spin-triplet excitations are degenerate, their persistent current spectra are quite different.

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Effects of Slight Plastic Deformation on Magnetic Properties and Giant Magnetoimpedance of FeCoCrSiB Amorphous Ribbons

S. O. Volchkov, M. A. Cerdeira, V. V. Gubernatorov, E. I. Duhan, A. P. Potapov, V. A. Lukshina

Chin. Phys. Lett. 2007, 24 (5): 1357-1360 .

Abstract

PDF(pc) (342KB) ( 742 )

Slight plastic deformation of 0 to 1% by cold rolling is proposed as a treatment which may modify the responses of magnetoimpedance (MI)
sensor with an amorphous ribbon used as a sensitive element. The dependence of the magnetic properties of melt spun Fe₃Co₆₇Cr₃Si₁₅B₁₂ amorphous ribbons and their MI responses in the initial state and after slight plastic deformation on the value of the deformation were comparatively analysed. The shape of the hysteresis loops shows a clear correlation with the value of the deformation. The variations of the total impedance, the real and the imaginary components, are measured for the current intensity of 1.5mA for the frequency of 10MHz. Slight plastic deformation affects both real and imaginary components and allows a control of the shape of the MI curves in a small field in a range usually used in biomedical applications. The roposed deformation treatments can be useful for the construction of the MI sensitive elements with a new type of the responses.

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Positive and Negative Pulse Etching Method of Porous Silicon Fabrication

GE Jin, YIN Wen-Jing, LONG Yong-Fu, DING Xun-Min, HOU Xiao-Yuan

Chin. Phys. Lett. 2007, 24 (5): 1361-1364 .

Abstract

PDF(pc) (845KB) ( 465 )

We present a new method in which both positive and negative pulses are
used to etch silicon for fabrication of porous silicon (PS) monolayer. The optical thickness and morphology of PS monolayer fabricated with different negative pulse voltages are investigated by means of reflectance spectra, scanning electron microscopy and photoluminescence spectra. It is found that with this method the PS monolayer is thicker and more uniform. The micropores also appear to be more regular than those made by common positive pulse etching. This phenomenon is attributed to the vertical etching effect of the PS monolayer being strengthened while lateral etching process is restrained. The
explanation we propose is that negative pulse can help the hydrogen cations (H⁺) in the electrolyte move into the micropores of PS monolayer. These H⁺ ions combine with the Si atoms on the wall of new-formed micropores, leading to formation of Si--H bonds. The formation of Si--H bonds results in a hole depletion layer near the micropore wall surface, which decreases hole density on the surface, preventing the micropore wall from being eroded laterally by F^-anions. Therefore during the positive pulse period the etching reaction
occurs exclusively only at the bottom of the micropores where lots of holes are provided by the anode.

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Strain Effect on Photoluminescences from InGaN MQWs with Different Barriers Grown by MOCVD

YU Tong-Jun, KANG Xiang-Ning, PAN Yao-Bo, QIN Zhi-Xin, CHEN Zhi-Zhong, YANG Zhi-Jian, ZHANG Guo-Yi

Chin. Phys. Lett. 2007, 24 (5): 1365-1367 .

Abstract

PDF(pc) (225KB) ( 730 )

InGaN/GaN MQWs, InGaN/AlGaN MQWs and InGaN/AlInGaN MQWs are grown on (0001) sapphire substrates by MOCVD. Membrane samples are fabricated by laser lift-off technology. The photoluminescence spectra of membranes show a blue shift of peak positions in InGaN/GaN MQWs, a red shift of peak
positions in InGaN/AlGaN MQWs and no shift of peak positions in InGaN/AlInGaN MQWs from those of samples with substrates. Different
changes in Raman scattering spectra and HR-XRD (0002) profile of InGaN/AlInGaN MQWs, from those of InGaN/GaN MQWs and InGaN/AlGaN MQWs, are observed. The fact that the strain changes differently among InGaN MQWs with different barriers is confirmed. The AlInGaN barrier could adjust the residual stress for the least strain-induced electric field in InGaN/AlInGaN quantum wells.

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Temperature Dependence of the Fluorescence Emission Intensity of Eu/TiO₂ Nanocrystals

ZENG Qing-Guang, DING Ze-Jun, JU Xin, WANG Yi, SHENG Ye-Qing

Chin. Phys. Lett. 2007, 24 (5): 1368-1371 .

Abstract

PDF(pc) (409KB) ( 655 )

The samples of europium ions doped titanium dioxide (Eu³+/TiO²) nanocrystals are synthesized by a modified sol-gel method with hydrothermal treatment. The x-ray diffraction and scanning electron microscopy are used to characterize the sample. The temperature-dependent fluorescence emission effect of Eu³⁺-doped samples is investigated. It is found that under the excitation of 514.5nm light, the emission intensity of Eu³⁺ reaches a maximum value at 450K among various Eu ³⁺ dopant concentrations in
Eu³⁺/TiO₂ nanocrystals. The variation of the emission intensity may be attributed to the photon-assist absorption and the temperature-quenching effect.

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Structural Change in Au³⁺-Doped BK7 Glass Irradiated by Femtosecond Laser

DING Ting, WANG Li, ZHOU Shi-Feng, BAO Jia-Xing, QIU Jian-Rong

Chin. Phys. Lett. 2007, 24 (5): 1372-1375 .

Abstract

PDF(pc) (436KB) ( 601 )

We report on structural change in an Au ³⁺ -doped BK7 glass irradiated by an infrared femtosecond laser at 800nm. A grating structure is inscribed in the glass sample. The glass sample is then annealed at various temperatures. Structural change of the grating is observed by an optical microscope. Absorption spectra indicate that colour centres are induced after the laser irradiation, and they decrease with increasing annealing temperature. Au nanoparticles are precipitated at high temperatures (≥600°C). The mechanisms of the phenomena are discussed.

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Enhanced Electroluminescent Efficiency Based on Functionalized Europium Complexes in Polymer Light-Emitting Diodes

ZHANG Yong, WANG Lei, LI Chun, ZENG Wen-Jin, SHI Hua-Hong, CAO Yong

Chin. Phys. Lett. 2007, 24 (5): 1376-1379 .

Abstract

PDF(pc) (274KB) ( 697 )

Efficient red polymer light-emitting diodes are fabricated with the single active layer from the blends of poly(N-vinylcarbazole) (PVK) in the presence of 30wt.% electron-transporting compound 2-(4-biphenylyl)-5-(p-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and europium complexes. The polyphenylene functionalized europium complex shows an enhanced electroluminescent efficiency due to the large site-isolation effect. For the polyphenylene functionalized europium complex, the maximum external quantum efficiency of 1.90% and luminous efficiency of 2.01cd A^-1 are achieved with emission peak at 612nm. The maximum brightness is more than 300cd m^-2.

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Organic Light Emitting Diodes with an Organic Acceptor/Donor Interface Involved in Hole Injection

CAO Guo-Hua, QIN Da-Shan, GUAN Min, CAO Jun-Song, ZENG Yi-Ping, LIJin-Min

Chin. Phys. Lett. 2007, 24 (5): 1380-1382 .

Abstract

PDF(pc) (222KB) ( 577 )

Organic light emitting diodes with an interface of organic acceptor 3-, 4-, 9-, 10-perylenetetracarboxylic dianhydride (PTCDA) and donor copper phthalocyanine (CuPc) involved in hole injection are fabricated. As compared to the conventional device using a 5nm CuPc hole injection layer, the device using an interface of 10nm PTCDA and 5nm CuPc layers shows much lower operating voltage with an increase of about 46% in the maximum power efficiency. The enhanced device performance is attributed to the efficient hole generation at the PTCDA/CuPc interface. This study provides a new way of designing hole injection.

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Enhancement of Stability of Polymer Light-Emitting Diodes by Post Annealing

YAO Bing, XIE Zhi-Yuan, YANG Jun-Wei, CHENG Yan-Xiang, WANG Li-Xiang

Chin. Phys. Lett. 2007, 24 (5): 1383-1835 .

Abstract

PDF(pc) (226KB) ( 528 )

We investigate the effect of thermal annealing before and after cathode deposition on the stability of polymer light-emitting diodes (PLEDs) based on green fluorescent polyfluorene derivative. The annealed PLEDs exhibit improved charge transport and red-shift emission compared to the as-fabricated device. The stability of the PLEDs is largely enhanced by post-annealing before and after Ca deposition, which is attributed to the enhanced charge transport and the intimate contact between the cathode and the emissive layer.

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Enhanced Green Electrophosphorescence from Oxadiazole-Functionalized Iridium Complex-Doped Devices Using Poly(9,9-Dioctylfluorene) Instead of Poly(N-Vinylcarbazole) as a Host Matrix

LUO Cui-Ping, ZHOU Ji, WANG Lei, Deng Ji-Yong, QIN Zhi-Jun, ZHU Mei-Xiang, ZHU Wei-Guo,

Chin. Phys. Lett. 2007, 24 (5): 1386-1389 .

Abstract

PDF(pc) (279KB) ( 604 )

Optoelectronic properties of the oxadiazole-functionalized iridium complex-doped polymer light-emitting devices (PLEDs) are demonstrated with two different polymeric host matrices at the dopant concentrations 1--8%. The devices using a blend of poly(9,9-dioctylfluorene)(PFO) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a host matrix exhibited a maximum luminance efficiency of 11.3cd/A at 17.6mA/cm². In contrast, the devices using a blend of poly(N-vinylcarbazole) (PVK) and PBD as a host matrix reveal only a peak luminance efficiency of 6.5cd/A at 4.1mA/cm². The
significantly enhanced electrophosphorescent emissions are observed in the devices with the PFO-PBD blend as a host matrix. This indicates that choice of polymers in the host matrices is crucial to achieve highly efficient phosphorescent dye-doped PLEDs.

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Effect of Reactor Pressure on Qualities of GaN Layers Grown by Hydride Vapour Phase Epitaxy

QIU Kai, YIN Zhi-Jun, LI Xin-Hua, ZHONG Fei, JI Chang-Jian, HAN Qi-Feng, CAO Xian-Cun, CHEN Jia-Rong, LUO Xiang-Dong, WANG Yu-Qi

Chin. Phys. Lett. 2007, 24 (5): 1390-1392 .

Abstract

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The influence of reactor pressure on GaN layers grown by hydride vapour
phase epitaxy (HVPE) is investigated. By decreasing the reactor pressure from 0.7 to 0.5atm, the GaN layer growth mode changes from the island-like one to the step flow. The improvements in structural and optical properties and surface morphology of GaN layers are observed in the step flow growth mode. The results clearly indicate that the reactor pressure, similarly to the growth temperature, is one of the important parameters to influence the qualities of GaN epilayers grown by HVPE, due to the change of growth mode.

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MOCVD Growth and Characterization of Epitaxial Al_xGa_1-x N Films

LI Liang, ZHANG Rong, XIE Zi-Li, ZHANG Yu, XIU Xiang-Qian, LIU Bin, CHEN Lin, YU Hui-Qiang, HAN Ping, GONG Hai-Mei, ZHENG You-Dou

Chin. Phys. Lett. 2007, 24 (5): 1393-1396 .

Abstract

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We study the growth of Al_xGa_1-x N epilayers on (0001) sapphire by low-pressure MOCVD, using a low-temperature AlN buffer. By varying the input flow rates of trimethylgallium (TMGa), we obtain crack-free AlGaN films in the whole range of composition. A linear relationship between gas and solid Al
content is observed. The structural properties of the layers (x = 0-1)
are investigated by x-ray diffraction, atomic force microscopy (AFM) and scanning electron microscopy (SEM). It is found that a two-direction growth appears along the c-axis and the (10\11) directions for x≥0.45. From the results of Raman spectroscopy, we suggest that the compressive stain and the lack of mobility of Al adatoms can induce the formation of (10\11) grains.

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Photoinduced Resistance Change in an Oxygen-Deficient La _0.9 Sr _0.1 MnO _3-δ Thin Film

YAN Zi-Jie, YUAN Xiao, GAO Guo-Mian, LUO Bing-Cheng, JIN Ke-Xin, CHEN Chang-Le

Chin. Phys. Lett. 2007, 24 (5): 1397-1399 .

Abstract

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Photoinduced resistance change (△R/R) in an oxygen-deficient La_0.9Sr_0.1MnO_3-δ thin film is studied. At room temperature, the resistance change of about 30% and response time of about 75ns are observed under the illumination with a 532nm laser pulse of 7ns and light power of 750mW. It is also found that △R/R changes with the light power. The phenomena are explained in terms of the photoinduced hole carriers and localized insulator-to-metal transition, which may have potential applications in optoelectronic
devices.

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Effect of Pretreatment of TaN Substrates on Atomic Layer Deposition Growth of Ru Thin Films

ZHOU Mi, CHEN Tao, TAN Jing-Jing, RU Guo-Ping, JIANG Yu-Long, LIU Ran, QU Xin-Ping

Chin. Phys. Lett. 2007, 24 (5): 1400-1402 .

Abstract

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The polycrystalline ruthenium films are grown on TaN substrates by atomic layer deposition (ALD) using bis(cyclopentadienyl) ruthenium [RuCp₂] and oxygen as ruthenium precursor and reactant respectively at a deposition temperature of 330°C. The low-energy Ar ion bombardment and Ru pre-deposition are performed to the underlying TaN substrates before ALD process in order to improve the Ru nucleation. X-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy are carried out to characterize the properties of ALD Ru films. The results show that the nucleation density of Ru films with Ar⁺ bombardment to the underlying TaN substrates is much higher than that of the ones without any pretreatment. The possible reasons are discussed.

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Detection Wavelength of Strained In_xGa_1-x As/GaAs Very-Long-Wavelength Quantum Well Infrared Photodetectors

XIONG Da-Yuan, LI Ning, LI Zhi-Feng, ZHEN Hong-Lou, LU Wei

Chin. Phys. Lett. 2007, 24 (5): 1403-1406 .

Abstract

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Detection wavelength is one of the key performance indices of infrared
photodetectors. We study the character of detection wavelength of the
strained In_xGa_1-x As/GaAs very-long-wavelength (>12μm) quantum well infrared photodetectors (VLW-QWIPs) characterized by the photoluminescence (PL) and photocurrent (PC) measurements. Based on the theoretical calculation and experimental data, we have built a practical model for the In_xGa_1-x As/GaAs strained VLW-QWIPs, from which the interband transitions, intersubband transition and peak detection wavelength can be determined. Afterwards, the dependences of detection wavelength and device operation mode on the In mole fraction and In_xGa _1-x As well width are presented, which will be helpful for device design and optimization.

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Elastic Interaction between a String of Cells and an Individual Cell

WU Heng-An, LONG Rong, WANG Xiu-Xi, WANG Feng-Chao

Chin. Phys. Lett. 2007, 24 (5): 1407-1409 .

Abstract

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The elastic interaction between a string of cells and an individual cell on an elastic substrate is investigated numerically using the force-dipole model. This interaction is found to be of short range, and the cut-off distance is about 1.4 times of the length of the cell. The energy-minimization distance is about half the cellular length. The specific relationship between the cellular reorientation and the cellular position are obtained quantitatively. A critical distance is
found, and the cellular orientation has an abrupt change at this transition point.

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Analysis of Density Wave in Two-Lane Traffic

TANG Tie-Qiao, HUANG Hai-Jun, XU Xiang-Yang, XUE Yu

Chin. Phys. Lett. 2007, 24 (5): 1410-1413 .

Abstract

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We use the car-following model ( Phys. Rev. E 72 (2005) 066124) to further analyse the two-lane traffic waves. Our numerical results show that in the two-lane traffic, there exist triangular shock, soliton wave and kink wave which appear in the stable, mestastable and unstable regions of headway-sensitivity space, respectively. Compared with the single-lane traffic, it is found that the lateral distance has little effect on the formation of triangular
shock and soliton wave although the lateral distance can enlarge the stable region and can reduce the mestastable and unstable regions.

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Analysis of Possible Evolution of Dark Energy by Using a Power Series

WANG Wei, GUI Yuan-Xing, SHAO Ying

Chin. Phys. Lett. 2007, 24 (5): 1414-1416 .

Abstract

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We simulate the density of dark energy by using a power series to analyse the possible evolution of dark energy. The parameters are constrained from the newly released Gold sample of the supernova dataset. The evolutions of dark energy, as the power series from two free parameters to five free parameters, have the common and the different characters. We may conclude that either the density of dark energy possibly oscillates or increases after
it decreases to a minimum value. Accordingly, the state equation of dark energy oscillates or evolves from ω_de>-1 in the past to ω_de<-1 around the present epoch.

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Neutron-Capture Elements in the Double-Enhanced Star HE 1305-0007: a New s- and r-Process Paradigm

CUI Wen-Yuan, , CUI Dong-Nuan, DU Yun-Shuang, ZHANG Bo,

Chin. Phys. Lett. 2007, 24 (5): 1417-1420 .

Abstract

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The star HE 1305-0007 is a metal-poor double-enhanced star with metallicity [Fe/H] =-2.0, which is just at the upper limit of the metallicity for the observed double-enhanced stars. Using a parametric model, we find that almost all s-elements were made in a single neutron exposure. This star should be a member of a post-common-envelope binary. After the s-process material has
experienced only one neutron exposure in the nucleosynthesis region and is dredged-up to its envelope, the AGB evolution is terminated by the onset of common-envelope evolution. Based on the high radial-velocity of HE 1305-0007, we speculate that the star could be a runaway star from a binary system, in which the AIC event has occurred and produced the r-process elements.

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Two Kinds of Magnetic Connection in Black-Hole Accretion Disc

Chin. Phys. Lett. 2007, 24 (5): 1421-1424 .

Abstract

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We discuss two kinds of magnetic connection (MC) in the black hole (BH)
accretion disc: the magnetic connection between the BH and the disc (MCHD) and that between the plunging region and the disc (MCPD). The magnetic field configuration is produced by an electric current flowing at the inner edge of the disc. It turns out that the transfer direction of energy and angular omentum depends on the BH spin and a parameter λ for adjusting the angular velocities of the plunging matter, which corresponds to at most five regions in the disc. The effect of MCPD results in a much steeper emissivity than a standard accretion disc in the inner disc, however it fails to reach the observation range 4.3--5.5 in several objects, such as Seyfert 1 galaxy MCG-6-30-15, microquasars XTE J1650-500 and GX 399-4.

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Comparison of Supernovae Datasets Constraints on Dark Energy

ZHANG Cheng-Wu, XU Li-Xin, CHANG Bao-Rong, LIU Hong-Ya

Chin. Phys. Lett. 2007, 24 (5): 1425-1428 .

Abstract

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Cosmological measurements suggest that our universe contains a dark energy component. In order to study the dark energy evolution, we constrain a parameterized dark energy equation of state w(z)=w₀ + w₁z/1+z using the recent observational datasets: 157 Gold type Ia supernovae and the newly released 182 Gold type Ia supernovae by the maximum likelihood method. It is found that the best fit w(z) crosses -1 in the past and the present best fit value of w(0)<-1 obtained from 157 Gold-type Ia supernovae. The crossing of -1 is not realized and w₀=-1 is not ruled out in 1σ confidence level for the 182 Gold-type Ia supernovae. It is also found that the range of parameter w₀ is wide even in 1σ confidence level and the best fit w(z) is sensitive to the prior of Ωm.

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