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Volume 19 Issue 12
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Original Articles
Variable Separation and Exact Solutions to Generalized Nonlinear Diffusion Equations
ZHANG Shun-Li, LOU Sen-Yue, QU Chang-Zheng
Chin. Phys. Lett. 2002, 19 (12): 1741-1744 .  
Abstract   PDF(pc) (223KB) ( 411 )
We study in detail a method to find the generalized nonlinear diffusion equations, which can be solved by means of the variable separation approach. A complete list of canonical forms for such equations, which admit the functional separable solutions, is obtained and some exact solutions to the resulting equations are described.
Energy Distribution in SU(1,1) Coherent State of Hydrogen
ZENG Gao-Jian
Chin. Phys. Lett. 2002, 19 (12): 1745-1748 .  
Abstract   PDF(pc) (579KB) ( 305 )
We construct an SU(1,1) coherent state for hydrogen, we discuss its properties, and we give the energy distribution law of the atom. The coherent state may be used to describe the atomic states of discrete spectrum.
Dispelling the Anthropic Principle from the Dimensionality Arguments
WU Zhong-Chao
Chin. Phys. Lett. 2002, 19 (12): 1749-1751 .  
Abstract   PDF(pc) (186KB) ( 413 )
It is shown that in d = 11 supergravity, under a very reasonable ansatz, the nearly flat space-time in which we are living must be four-dimensional without appealing to the anthropic principle. Can we dispel the anthropic principle completely from cosmology?
Distribution Characteristics of Dirac Energy Levels in Non-Kerr Space-time
YANG Xue-Te, YANG Shu-Zheng
Chin. Phys. Lett. 2002, 19 (12): 1752-1754 .  
Abstract   PDF(pc) (271KB) ( 304 )
The distribution of Dirac energy levels in a non-Kerr black hole space-time is related to an arbitrary set of multiple moments determined by the parameters αn. A singular point appears on the event horizon of the black hole, at which the Dirac energy levels have obvious distribution characteristics and are different from those in the space-time of the Kerr black hole.

Brick Walls for Nonstationary Black Holes
LI Zhong-Heng, MI Li-Qin, ZHAO Zheng
Chin. Phys. Lett. 2002, 19 (12): 1755-1758 .  
Abstract   PDF(pc) (220KB) ( 583 )
The validity condition of the brick-wall model is analysed in nonstationary space-time. It is shown that the model holds only in thin regions, only by using tortoise coordinates, near the event horizon of a slowly varying (quasi-stationary) black hole. The reason for the use of tortoise coordinates is that the stationary state solutions of quantum field equations in other coordinates do not exist for any region in nonstationary space-time. Meanwhile, the quantum corrections to the entropy of the Vaidya-Bonner black hole due to the spin fields are calculated in terms of the brick-wall model.

Phenomenon of Repeated Current Reversals in the Brownian Ratchet
YANG Ming, CAO Li, , WU Da-Jin, , LI Xiang-Lian
Chin. Phys. Lett. 2002, 19 (12): 1759-1762 .  
Abstract   PDF(pc) (312KB) ( 348 )
We study the probability current of the Brownian particles in a tilted periodic piecewise linear “saw-tooth” potential. It is found that the stationary probability current would take on a maximum value at a given additive noise if the intensity of the multiplicative noise is appropriate and at the same time both of the two noises are correlated; and the direction of the stationary probability current is reversed more than once upon some certain correlation intensities between both noises. It is proven that the occurrence of current reversal is only dependent on the relative intensity of the multiplicative and additive noises, but has nothing to do with the absolute intensities of the two noises.
Control of Semiquantum Chaos by Nonfeedback Method
LIU Bao-Wei, DONG Jin-Ming, WU Gang, HE Wei-Zhong
Chin. Phys. Lett. 2002, 19 (12): 1763-1766 .  
Abstract   PDF(pc) (667KB) ( 431 )
We numerically study the dynamic behaviour of coupled chaotic oscillators in a so-called semiquantum chaotic system in which one is classical and the other is quantum mechanical. Fourier spectra of the classical oscillator and the wave function of ground state of the quantum part have been investigated, when small pulse perturbations are applied. It is found that the semiquantum chaos can also be successfully controlled by the nonfeedback method.
Projection Operator and Propagator for an Arbitrary Integral Spin
HUANG Shi-Zhong, , RUAN Tu-Nan, WU Ning, ZHENG Zhi-Peng,
Chin. Phys. Lett. 2002, 19 (12): 1767-1770 .  
Abstract   PDF(pc) (218KB) ( 366 )
Based on the solution of the Bargmann-Wigner equation for an arbitrary integral spin, a direct derivation of the projection operator and propagator for an arbitrary integral spin is presented. The explicit form for the spin projection operators constructed by Behrends and Fronsdal is confirmed, the commutation rules and a general expression for the Feynman propagator for a free particle of arbitrary integral spin are deduced.
Pairing Field and Moments of Inertia of Superdeformed Nuclei
CHEN Yong-Jing, CHEN Yong-Shou, XU Fu-Xin
Chin. Phys. Lett. 2002, 19 (12): 1771-1774 .  
Abstract   PDF(pc) (469KB) ( 457 )
We have systematically analysed the dynamic moments of inertia of the experimental superdeformed (SD) bands observed in the A = 190, 150, and 60-80 mass regions as functions of rotational frequency. By combination of the different mass regions, the dramatic features of the dynamic moments of inertia were found and explained based on the calculations of the pairing fields of SD nuclei with the anisotropic harmonic oscillator quadrupole pairing Hartree-Fock-Bogoliubov model.

Hyperon Halos in Λ Hypernuclei in the Relativistic Continuum Hartree-Bogoliubov Theory
LÜ, Hong-Feng, MENG Jie,
Chin. Phys. Lett. 2002, 19 (12): 1775-1778 .  
Abstract   PDF(pc) (418KB) ( 392 )
We investigate the existences of a single-Λ hyperon halo in 153ΛC and a two-Λ hyperon halo in 164ΛC. Ground-state properties of hyperon carbon isotopes, such as density distributions, single particle levels in the canonical basis, the binding energy, Λ separation energy and radii, are calculated and discussed by using the relativistic continuum Hartree-Bogoliubov theory. The hyperon halo phenomenon in 153ΛC and 164ΛC is supported by the discussion on the weakly bound state 1p3/2, extended density distribution and small separation energy of the Λ hyperon.
Search for the Chiral Band in the N = 71 Odd-Odd Nucleus 126Cs
LI Xian-Feng, MA Ying-Jun, LIU Yun-Zuo, LU Jing-Bin, ZHAO Guang-Yi, YIN Li-Chang, MENG Rui, ZHANG Zhen-Long, WEN Li-Jun, ZHOU Xiao-Hong, GUO Ying-Xiang, LEI Xiang-Guo, LIU Zhong, HE Jian-Jun, ZHENG Yong
Chin. Phys. Lett. 2002, 19 (12): 1779-1781 .  
Abstract   PDF(pc) (397KB) ( 491 )
High-spin states in 126Cs are studied via the 116Cd(14N, 4n) reaction at a beam energy of 65 MeV. The sideband of the πh11/2 vh11/2 yrast band, a ΔI = 2 band known from previous study, is developed into a ΔI = 1 coupled structure at low spins. This sideband is assigned to be built on the same configuration as the yrast band according to the measured ratios of directional correlation of orientation and observed alignment properties. On the basis of comparisons with the previously proposed chiral doublet bands for 128,130Cs, the observed two πh11/2 vh11/2 bands are proposed to be candidates for chiral doublet bands in 126Cs.
Computer Simulation for the Formation of Insulator Layer of Silicon on Insulator by N+ and O+ Co-implantation
LIN Qing, ZHU Ming, LIU Xiang-Hua, XIE Xin-Yun, LIN Cheng-Lu
Chin. Phys. Lett. 2002, 19 (12): 1782-1784 .  
Abstract   PDF(pc) (481KB) ( 418 )
A buried sandwiched layer consisting of silicon dioxide (upper
part), silicon oxynitride (medium part) and silicon nitride (lower part) is formed by N+ and O+ co-implantation in silicon wafers at a constant temperature of 550°C. The microstructure is performed by cross-sectional transmission electron microscopy. To predict the quality of the buried sandwiched layer, we study the computer simulation for the formation of the SIMON (separation by implantation of oxygen and nitrogen) structure. The simulation programme for SIMOX (separation by implantation of oxygen) is improved in order to be applied in O+ and N+ co-implantation on the basis of different formation mechanism between SIMOX and SIMNI (separation by implantation of nitrogen) structures. There is a good agreement between experiment and simulation results verifying the theoretical model and presumption in the programme.
Novel Bismuth Nanotubes
SU Chang-Rong, LI Jia-Ming,
Chin. Phys. Lett. 2002, 19 (12): 1785-1787 .  
Abstract   PDF(pc) (423KB) ( 668 )
Theoretical investigations show that bismuth nanotubes are semiconductors for all diameters. For small diameter bismuth nanotubes, the band structures and bandgaps vary strongly with the strong hybridization effect. When the diameters are larger than 18Å, the bandgaps of Bi (n,n) and (n,0) nanotubes approach to 0.63 eV, corresponding to the bandgap of bismuth sheet at the Γ point. Thus, bismuth nanotubes are expected to be a potential semiconductor nanomaterial in future nanoelectronics.
Dynamical Transition of Myoglobin and Cu/Zn Superoxide Dismutase Revealed by Molecular Dynamics Simulation
ZHANG Li-Li, ZHANG Jian-Hua, ZHOU Lin-Xiang
Chin. Phys. Lett. 2002, 19 (12): 1788-1791 .  
Abstract   PDF(pc) (498KB) ( 479 )
We have carried out parallel molecular dynamics simulations of
solvated and non-solvated myoglobin and solvated Cu/Zn superoxide dismutase at different temperatures. By analysis of several methods, the simulations reproduce the quasielastic neutron scattering experimental results. Below 200 K these two proteins behave as harmonic solids with essentially only vibrational motion, while above this temperature, there is a striking dynamic transition into anharmonic motion. Moreover, the simulations further show that water molecules play an important role for this dynamical transition. There is no such sharp dynamical transition in non-solvated proteins and the higher the solvate density is, the steeper at transition point the curve of mean square displacement versus temperature will be. The simulations also display that the dynamical transition is a general property for globular protein and this transition temperature is a demarcation of enzyme activity.
Electronic Wave Packet in a Quantized Electromagnetic Field
CHENG Tai-Wang, XUE Yan-Li, LI Xiao-Feng, WU Ling-An, FU Pan-Ming
Chin. Phys. Lett. 2002, 19 (12): 1792-1794 .  
Abstract   PDF(pc) (303KB) ( 346 )
We study a non-stationary electronic wave packet in a quantized
electromagnetic field. Generally, the electron and field become
entangled as the electronic wave packet evolves. Here we find that, when the initial photon state is a coherent one, the wavefunction of the system can be factorized if we neglect the transferred photon number. In this case, the quantized-field calculation is equivalent to the semi-classical calculation.
Electron Momentum Spectroscopy of the Frontier Orbitals of Chlorodifluoromethane
XU Chun-Kai, CHEN Xiang-Jun, JIAChang-Chun, ZHANG Xu-Huai, YIN Xiao-Feng, SHAN Xu, WEI Zheng, XU Ke-Zun
Chin. Phys. Lett. 2002, 19 (12): 1795-1797 .  
Abstract   PDF(pc) (317KB) ( 314 )
We report on the first measurement of the electron momentum distributions of the three outermost valence orbitals for chlorodifluoro-methane (CHF2Cl) by a binary (e, 2e) electron momentum spectroscopy. The experimental data are compared with Hartree-Fock and density functional theory (DFT) calculations employing 6-31 G, 6-311++G** and AUG-cc-pVQZ basis sets. For the summed momentum distribution of 8a'+5a''+7a' orbitals, the DFT/AUG-cc-pVQZ calculation gives the best fit. A very large and diffuse basis set, AUG-cc-pVQZ, is employed in the calculations to approach the Hartree-Fock limit of basis set, but improvement of the calculation quality is little in comparison with that calculated with 6-311++G** basis set. This indicates that 6-311++G** basis set is nearly saturated for the calculations of these three orbitals of CHF2Cl, and it is unnecessary to employ a larger basis set in the calculations.
A Measurement Method of Time Jitter of a Laser Pulse with Respect to the Radio-Frequency Wave Phase in a Photocathode Radio-Frequency Gun
LIU Sheng-Guang, LI Yong-Gui, WANG Ming-Kai
Chin. Phys. Lett. 2002, 19 (12): 1798-1800 .  
Abstract   PDF(pc) (303KB) ( 374 )
In a photo-cathode radio-frequency (rf) gun, the micro-bunched charge output from the gun is dependent linearly on the laser injection phase, due to the Scottay effect in the process of photoemission and the procedure of the eletron lognitudinal acceleration. Based on this principle, a new method is proposed, which should be utilized to measure the time jitter between the driving laser pulse and the rf phase with a very high resolution of a few tens of femtoseconds.
Dynamic Polariton and Quantum State Swapping Between an Electromagnetic Field and Atomic Ensemble
WANG Kai-Ge, YANG Guo-Jian
Chin. Phys. Lett. 2002, 19 (12): 1801-1804 .  
Abstract   PDF(pc) (223KB) ( 415 )
We analyse a dynamical swapping of the quantum state in coupled harmonic oscillators. The result can be applied to the interaction of a single-mode field with atomic ensemble in the weak field case. Similar to the case of electromagnetic induced transparency (EIT), a dynamic polariton is formed. Therefore, the quantum state of the field can be completely mapped on to the atomic medium and vice versa. Using this dynamical swapping and the adiabatic transfer in the EIT between the field and atomic ensemble, we propose a scheme in which both the quantum and the coherent information can be transferred from one field to another.
Atomic Interaction Effects on Electromagnetically Induced Transparency and Slow Light in Ultracold Bose Gas
HU Zheng-Feng, DU Chun-Guang, LI Dai-Jun, LI Shi-Qun,
Chin. Phys. Lett. 2002, 19 (12): 1805-1807 .  
Abstract   PDF(pc) (301KB) ( 437 )
We investigate electromagnetically induced transparency and slow group velocity of light in ultracold Bose gas with a two-photon Raman process. The properties of electromagnetically induced transparency and light speed can be changed by controlling the atomic interaction. Atomic interaction can be used as a knob to control the optical properties of atomic media. This can be realized in experiment by using the Feshbach resonance technique.
Efficient Diode-Pumped Passively Q-Switched Nd:GdVO4 Lasers
LIU Jie, JIA Yu-Lei, YANG Ji-Min, DU Juan, HE Jing-Liang
Chin. Phys. Lett. 2002, 19 (12): 1808-1810 .  
Abstract   PDF(pc) (368KB) ( 548 )
An efficient diode-pumped Nd:GdVO4 laser passively Q-switched by a Cr4+:YAG as an saturable absorber was developed. A KTP crystal is used for the extra-cavity second-harmonic generation (SHG) and a BBO crystal for the sum frequency mixing (SFM). The green output power is 172 mW at incident pump power of 8 W. The ultraviolet (UV) output power is measured to be 20 mW at the same pump power. The peak power of UV laser is 143 W with the pulse repetition rate of 14 kHz and pulse width of 10 ns.

Properties and Stability of Nanosecond Optical Limiting of Gold Nanoclusters
QU Shi-Liang, FU Shi-You, LI Hua-Jun, GENG Yao-Hui, SONG Ying-Lin, LIU Shu-Tian, LI Yu-Liang, ZHU Cong-Shan
Chin. Phys. Lett. 2002, 19 (12): 1811-1814 .  
Abstract   PDF(pc) (415KB) ( 355 )
Optical limitation (OL) performances of the gold nanoclusters protected by C60-tpy have been investigated with 8-ns pulses at 532 nm. The experimental results show that the nanocomposite possesses the OL effects superior to C60 in toluene. The main mechanism of OL is attributed to the nonlinear absorption and subsequently induced nonlinear scattering during excitation of the pulse. Ageing of the nanocomposite chloroform solution in air lowers the OL performances by a factor of 2.4, which can be due to the formation of aggregates of large gold particles.
A Hybrid Optical Bistable Device Based on a Fibre Bragg Grating
LI Jun-Qing, CHEN Qiang, LI Qiang-Hua, LI Chun-Fei
Chin. Phys. Lett. 2002, 19 (12): 1815-1818 .  
Abstract   PDF(pc) (418KB) ( 323 )
We propose a hybrid optical bistable device based on a fibre Bragg grating. The experimental setup is designed by using real communication components. The optical bistable characteristics are simulated. The feedback nonlinearity and the delay time of the device are emphasized. We discuss the potential of such a device in sensor application.
Modification of Absorption of a Bulk Material by Photonic Crystals
XI Yong-Gang, WANG Xin, HU Xin-Hua, LIU Xiao-Han, ZI Jian
Chin. Phys. Lett. 2002, 19 (12): 1819-1821 .  
Abstract   PDF(pc) (362KB) ( 351 )
We show theoretically that it is possible to modify absorption of a bulk absorbing material by inserting another non-absorbing dielectric slab periodically to form one-dimensional photonic crystals. It is found that, for frequencies within photonic bandgaps, absorptance is always suppressed. For frequencies located at photonic bands, absorptance can be suppressed or enhanced, which depends on the relative values of the real refactive index of the absorbing and non-absorbing dielectric layers.
An All-Fibre Dynamic Gain Equalizer Based on a Novel Long-Period Fibre Grating Written by High-Frequency CO2 Laser Pulses
RAO Yun-Jiang, ZHU Tao, RAN Zeng-Ling, JIANG Jian
Chin. Phys. Lett. 2002, 19 (12): 1822-1824 .  
Abstract   PDF(pc) (412KB) ( 596 )
An all-fibre dynamic gain equalizer based on a novel long-period fibre grating (LPFG) written on a photosensitive fibre by high-frequency CO2 laser pulses is demonstrated for the dynamic gain flattening of Er-doped fibre amplifiers. The resonant peak amplitude of such a dynamic gain equalizer can be adjusted linearly by bending the LPFG. The gain profile of the Er-doped fibre amplifier constructed has been flattened to within ±0.7 dB over a 32 nm bandwidth using such a device.
Sound Field Calculations of Elliptical Pistons by the Superposition of Two-Dimensional Gaussian Beams
ZHANG Yu, LIU Jin-Qiu, DING De-Sheng
Chin. Phys. Lett. 2002, 19 (12): 1825-1827 .  
Abstract   PDF(pc) (330KB) ( 347 )
We present an alternative approach to calculate the sound field of ultrasonic transducers. The distribution function of sources is expanded into the superposition of a series of two-dimensional Gaussian functions. The corresponding radiated sound field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions. This treatment does not require the condition that the shape of source is of circular axial-symmetry. A numerical example is presented for the uniform elliptical piston transducer and is in good agreement with the results given by complicated computation.
Acoustic Nonlinear Behaviour of Microbubble Contrast Agent
YU Jin-Fei, LU Rong-Rong, GONG Xiu-Fen, William T. Shi
Chin. Phys. Lett. 2002, 19 (12): 1828-1830 .  
Abstract   PDF(pc) (429KB) ( 506 )
We have investigated the nonlinear characteristics of a microbubble contrast agent SonazoidR (Nycomed, Norway), including the second, third, 1/2-order, 3/2-order and 5/2-order harmonics. We have measured the 1/2-order subharmonic response to different transmit sound pressure. It is found that subharmonic signals can not be generated until the acoustic pressure reached a certain value, which is the most difference subharmonic from high harmonics. This result is favorable for the further study of the subharmonic in the bubbly liquid. The 3/2-order ultraharmoic response to acoustic pressure was also measured.
Lattice Bhatnagar-Gross-Krook Simulation of Stratified Backward-Facing Step Flow
GUO Wei-Bin, SHI Bao-Chang, WANG Neng-Chao, GUO Zhao-Li
Chin. Phys. Lett. 2002, 19 (12): 1831-1834 .  
Abstract   PDF(pc) (486KB) ( 328 )
We perform a numerical simulation for steady stably-stratified flow over a two-dimensional backward-facing step with the Froude number of 16/9, the Reynolds number of 800 and the Prandtl number of 1.0 by using a newly developed thermal lattice Bhatnagar-Gross-Krook model. A detailed analysis is presented. Excellent agreement between the present results and other numerical data shows that the lattice-Boltzmann method is an efficient simulation method for complex flows.
A New Method for the Analysis of Relative Permeability in Porous Media
XU You-Sheng, WU Feng-Min,
Chin. Phys. Lett. 2002, 19 (12): 1835-1837 .  
Abstract   PDF(pc) (345KB) ( 541 )
By combining three-dimensional digital microtomography techniques with the lattice Boltzmann method, a new methodology is used to analyse the relative permeability of multiphase flow in porous media. The results indicate that the two coupling coefficients K12 and K21 have the same magnitude, therefore the Onsager reciprocity still holds. The results also agree well with the results of pipe flow numerical experiments.
Conditional Analysis and Biorthogonal Decomposition of Plasma Turbulence in the CT-6B Tokamak
DONG Li-Fang, ZHANG Qing-Li, WANG Long
Chin. Phys. Lett. 2002, 19 (12): 1838-1840 .  
Abstract   PDF(pc) (411KB) ( 384 )
Coherent structures in the CT-6B Tokamak plasma turbulence are detected by using conditional averaging. The results show that the coherent structures are short-lived and do not propagate in the radial direction. The biorthogonal decomposition technique is adopted to analyse further the coherent structure in the turbulence. The time evolution and spatial distribution of the coherent structure are obtained.
Characteristics of Plasma Shock Waves Generated in the Pulsed Laser Ablation Process
LI Zhi-Hua, ZHANG Duan-Ming, YU Bo-Ming, GUAN Li
Chin. Phys. Lett. 2002, 19 (12): 1841-1843 .  
Abstract   PDF(pc) (335KB) ( 576 )
We modify the Sedov theory to describe plasma shock waves generated in a pulsed laser ablating process. We also study the propagation characteristics of plasma shock waves during the preparation process of functional thin films deposited by a pulsed laser. In particular, We discuss in detail the temporal behaviour of energy causing the difference of the propagation characteristics between the plasma shock wave and the ideal shock wave in point explosion model. Under the same experimental conditions, the theoretical results calculated with our modified Sedov theory are in good agreement with the existent experimental data.
Lattice Disorder and Photoluminescence of Er-Implanted AlN Crystalline Films
LU Fei, A. Rizzi, R. Carius
Chin. Phys. Lett. 2002, 19 (12): 1844-1846 .  
Abstract   PDF(pc) (395KB) ( 446 )
AlN crystalline films have been grown on SiC substrates by molecular beam epitaxy. Er doping was carried out by implantation with energy 180 keV to fluence of 1 x 15ions/cm2. The as-implanted samples were then annealed at 650, 800, 950, and 1100°C respectively, to remove defects and to make Er ions optically active. The annealing up to 1100°C did not exert significant influence on either Er distribution or the profiles of implant-induced lattice damage. Strong 1.54μm photoluminescence was observed in Er-implanted AlN at room temperature. The experimental results indicated that the photoluminescence lifetime can be improved by increasing the annealing temperature. The maximum photoluminescence lifetime was measured to be 2.3 ms.
Co-time-Resolvable Diffraction and New Tunneling Electronics
YI Lin
Chin. Phys. Lett. 2002, 19 (12): 1847-1849 .  
Abstract   PDF(pc) (330KB) ( 334 )
With the help of the perturbation method and the Feynman path integral technique, we analytically demonstrate that, when the electronic spectrum of a mesoscopic box is measured through two connecting leads, there exists a class of new diffraction phenomena in the coherence time domain, based on the new coherent tunneling model. It is shown that the new diffraction effect determines the minimal resolvable coherence time to the Heisenberg limit. In particular, Fraunhofer optical phenomena, such as missing order and grating effects, can be reproduced in the meso-systems. The predicted periodic oscillations as a function of voltage are in excellent agreement with experimental observations.
Transport Properties in a One-Dimensional Chain with Randomly Side-Coupled Impurities
HU Dong-Sheng, ZHANG Gui-Ping, XIONG Shi-Jie
Chin. Phys. Lett. 2002, 19 (12): 1850-1852 .  
Abstract   PDF(pc) (315KB) ( 387 )
We investigate the transport properties of a one-dimensional (1D) chain with randomly side-coupled impurities. By using the transfer matrix technique, we present numerical results of the transmission coefficient as a function of the electron energy. It is found that an extended state will be shown in such a random 1D system if the impurities are side-coupled to the chain with not only the nearest-neighbouring bonds but also the next-nearest-neighbouring-bonds. We present an analytic expression for the energy of this extended state, which is determined by the strength of the nearest and next-nearest couplings between the impurities and the chain. The obtained results can be used to explain the transport properties of DNA chains and other quasi-1D organic structures.
Pt/Au Schottky Contacts to Modulation-Doped AlxGa1-xN/GaN Heterosturctures Using Pre-deposition Surface Treatment
LIU Jie, SHEN Bo, WANG Mao-Jun, ZHOU Yu-Gang, ZHENG Ze-Wei, ZHANG Rong, SHI Yi, ZHENG You-Dou, T. Someya, Y. Arakawa
Chin. Phys. Lett. 2002, 19 (12): 1853-1855 .  
Abstract   PDF(pc) (436KB) ( 471 )
Pt/Au Schottky contacts were fabricated on modulation-doped Al0.22GaN0.78/GaN heterostructures. Some different pre-deposition surface treatments were used to prevent the formation of the native oxide layer on the Al0.22GaN0.78 surface. X-ray photoelectron spectroscopy (XPS) measurements indicate that the pre-deposition surface treatment with boiling (NH4)2S solution can remove the native oxide layer on the Al0.22GaN0.78 surface effectively. The highest Schottky barrier height of 1.13 eV was obtained on the (NH4)2S-treated Al0.22GaN0.78 heterostructure.
Electret Characteristics of Hybrid Films Consisting of Porous Polytetrafluoroethylene and Teflon Fluoroethylenepropylene with Corona Charging
CHEN Gang-Jin, HAN Gao-Rong, Rudi Danz, Burkhard Elling
Chin. Phys. Lett. 2002, 19 (12): 1856-1858 .  
Abstract   PDF(pc) (404KB) ( 669 )
We have prepared hybrid films consisting of porous polytetrafluoroethylene (PTFE) and Teflon fluoroethylenepropylene (FEP) and we have investigated their charge dynamics of injection, transport and trapping using corona charging, isothermal and thermally stimulated surface-potential decay measurement. The results indicate that the hybrid film samples show different electret characteristics when charged through side PTFE or side FEP. The samples charged negatively through side porous PTFE show the best charge stability. Their charge dynamics differs very much from a single film. The effect of corona polarity on the electret behaviour in the hybrid film is very large. The experimental results are explained with the three structure level model of charge storage in electrets.
Fabrication of Intrinsic Josephson Junctions on Bi2Sr2CaCu2O8+δ Single Crystals with Reproducible Surface Junctions
ZHU Xiao-Bo, ZHAO Shi-Ping, CHEN Geng-Hua, XIE Si-Shen, YANG Qian-Sheng
Chin. Phys. Lett. 2002, 19 (12): 1859-1862 .  
Abstract   PDF(pc) (379KB) ( 360 )
Intrinsic Josephson junctions on Bi2Sr2CaCu2O8+δ single crystals are successfully fabricated using photolithography and Ar ion milling. Here we discuss the properties of the surface CuO2/metal bilayers and surface junctions prepared with different crystal cleavage conditions and metal film deposition techniques. We show that by cleaving the crystal at liquid nitrogen temperature in vacuum, the contents of the (interstitial) oxygen in the Bi-O layers become stable upon cleavage, leading to a CuO2/metal bilayer and to surface junctions with reproducible properties. These results can be useful for practical device fabrications as well as for the studies of the contact properties between high Tc superconductors and normal metals.

Superconductivity of Bi1.6Pb0.4Sr2Ca3Cu4O12
Atilla Coskun, Ahmet Ekicibil, Bekir Ö, zccelik
Chin. Phys. Lett. 2002, 19 (12): 1863-1865 .  
Abstract   PDF(pc) (539KB) ( 353 )
The superconducting ceramics Bi1.6Pb0.4Sr2Ca3Cu4O12 have been prepared by melt-casting method. A zero resistance temperature at 60 K has been observed. It has been found that the superconducting phase temperature Tc increases with increasing sintering temperature. The effect of Pb content on the superconductivity of the ceramic has been studied. The microstructure of the sample has been investigated by scanning electron microscopy. Phase analysis has been carried out by x-ray diffraction patterns and energy dispersive analysis through x-ray spectroscopy.
Substantial Enhancements of Low-Field Magnetoresistance at Temperatures near 77 K with Doping 4% Cu at Mn Sites of La2/3Ca1/3MnO3 Synthesized at 1000°C
YUAN Song-Liu, ZHANG Guo-Hong, LIU Li, TANG Jie, ZHANG Li-Jiang, ZHONG Qiang-Hua, YANG Ying-Ping, FENG Wen, LIU Sheng, CHEN Wei, XIA Zheng-Cai
Chin. Phys. Lett. 2002, 19 (12): 1866-1869 .  
Abstract   PDF(pc) (520KB) ( 438 )
We report on investigations of magnetoresistance (MR) in polycrystalline La2/3Ca1/3Mn1-xCuxO3 (x = 0 and 4%) samples prepared by the sol-gel method followed a sintering treatment at 1000°C. For the x = 4% sample, the most remarkable MR effect appears at temperatures near 77 K and for magnetic fields lower than 1 T. For fields ~ 0.3 T and at temperatures ~ 77 K, the x = 4% sample exhibits giant MR effect with M0 (≡ Δρ/ρ (H = 0)) between ~ 50 and ~ 70%, comparable to the so-called colossal MR response observed in the x = 0 sample for the 3 T field.
Magnetostriction Dependence of the Relaxation Frequency in the Magnetoimpedance Effect for Amorphous and Nanocrystalline Ribbons
M.L.Sánchez, V.M.Prida, B.Hernando, G.V.Kurlyandskaya, J.D.Santos, M.Tejedor, M.Vázquez
Chin. Phys. Lett. 2002, 19 (12): 1870-1873 .  
Abstract   PDF(pc) (427KB) ( 610 )
The Magnetoimpedance effect and changes of the relaxation frequency fx are studied in CoFeSiB and CoFeMoSiB amorphous and FeCuNbSiB nanocrystalline ribbons. The evolution of the magnetostriction constant λs and relaxation frequency is analysed for the states with different magnetic anisotropies induced in the same ribbons. A monotonical decrease of the relaxation frequency is observed for shifting of λs towards positive values.
Influence of Boundary Condition and Diffusion Coefficient on the Accuracy of Diffusion Theory in Steady-State Spatially Resolved Diffuse Reflectance of Biological Tissues
ZHANG Lian-Shun, ZHANG Chun-Ping, WANG Xin-Yu, QI Sheng-Wen, XU Tang, TIAN Jiang-Guo, ZHANG Guang-Yin
Chin. Phys. Lett. 2002, 19 (12): 1874-1876 .  
Abstract   PDF(pc) (325KB) ( 474 )
The applicability of diffusion theory for the determination of tissue optical properties from steady-state diffuse reflectance is investigated. Analytical expressions from diffusion theory using the two most commonly assumed boundary conditions at the air-tissue interface and the two definitions of the diffusion coefficient are compared with Monte Carlo simulations. The effects of the choice of the boundary conditions and diffusion coefficients on the accuracy of the findings for the optical parameters are quantified, and criteria for accurate curve-fitting algorithms are developed. It is shown that the error in deriving the optical coefficients is considerably smaller for the solution which uses the extrapolated boundary condition and the diffusion coefficient independence of absorption coefficient, compared to the other three solutions.


Preparation of a Waveguide Array in Flame Hydrolysis Deposited GeO2-SiO2 Glasses by Excimer-Laser Irradiation
WU Yuan-Da, XING Hua, ZHANG Le-Tian, LI Ai-Wu, YU Yong-Sen, ZHANG Yu-Shu
Chin. Phys. Lett. 2002, 19 (12): 1877-1879 .  
Abstract   PDF(pc) (383KB) ( 421 )
SiO2 glass films doped with GeO2 were prepared by the flame hydrolysis deposition method, then annealed at 1200°C. After exposure to high pressure hydrogen, the as-deposited films were irradiated with excimer laser pulses operated at 248 nm. The induced refractive index change (the growth of index change was 0.33%) was measured by a spectroscopic ellipsometer. A waveguide array has been written in the film by irradiation through a phase mask.
A New Method for the Raman Spectra Calculation of Vitreous or Molten Silicate
WU Yong-Quan, JIANG Guo-Chang, YOU Jing-Lin, HOU Huai-Yu, CHEN Hui
Chin. Phys. Lett. 2002, 19 (12): 1880-1883 .  
Abstract   PDF(pc) (566KB) ( 509 )
A new method is deduced to calculate the Raman spectra of vitreous or molten silicate. This method includes five steps: (i) molecular dynamics simulation to generate thousands of vitreous or molten configurations in equilibrium; (ii) decomposing the configurations into five kinds of defined tetrahedral units; (iii) normal vibrational analysis with Wilson's GF matrix method for the eigen frequencies and eigen vectors of each tetrahedral unit; (iv) Raman intensities calculation for each vibrational mode by utilizing the electro-optical parameter method and bond polarizability model; (v) accumulating the data of frequencies and corresponding intensities to form the partial Raman spectral line of each defined tetrahedral unit and finally the envelope.
Enhanced Brightness of Eu3+ Complex in Organic Electroluminescent Devices by Using Another Rare-Earth Ion
BAI Feng, DENG Zhen-Bo, GAO Xin, LI Yong, XU Yi-Zhuang, WU Jin-Guang
Chin. Phys. Lett. 2002, 19 (12): 1884-1886 .  
Abstract   PDF(pc) (517KB) ( 423 )
Rare-earth ions Tb3+ ion and La3+ ion were used as a bridge to improve the energy transfer from the polymer to an Eu complex. The material Tb(La 0.5Eu0.5(BSA)3phen was synthesized and used as the emission layer in the device: ITO/PVK:Tb(La)0.5Eu0.5(BSA)3phen/Alq/Al. The two device were compared in details and it was found that the device used La0.5Eu0.5(BSA)3phen as the emission material had better Monochromatic characteristics with the maximal brightness of 102 cd/m2 and the colour coordinates x = 0.55 and y = 0.36.
Cooperative Trends in a Modified Image Scoring Model
ANDREASEN Jonathan, OU-YANG Qi
Chin. Phys. Lett. 2002, 19 (12): 1887-1889 .  
Abstract   PDF(pc) (305KB) ( 302 )
The evolution of modern cooperative trends now seen in society have not yet been easily explained. After extensive computational studies and theoretical analysis, Nowak and Sigmund proposed that cooperation was established largely due to the emergence of indirect reciprocity. Our previous studies show that a high information flow rate stimulates cooperation in a society. In this study we find that the decrease of cooperation cost will make a society more cooperative, and the inheritance of wealth will induce cooperation in the society even when the exchange rate is comparatively low. We also study the distribution of knowledge according to wealth. We find that, for this model, cooperation is slightly less likely to occur if the exchange rate is low.
Phenomenon of Energy Concentration in High-Energy Family Events of Cosmic Rays
WANG He, WANG Yong-Gang, DAI Zhi-Qiang, XUE Liang, FENG Cun-Feng, ZHANG Xue-Yao, LI Jin-Yu, ZHANG Nai-Jian, HE Mao, WANG Cheng-Rui, REN Jing-Ru, LU Sui-Ling
Chin. Phys. Lett. 2002, 19 (12): 1890-1892 .  
Abstract   PDF(pc) (260KB) ( 412 )
The phenomenon of energy concentration in high-energy family events of cosmic rays is studied by comparing the results of family events of total visible energies 100-400 TeV observed in Kanbala emulsion chamber experiment with the Monte Carlo simulation data. The simulation is made by program CORSIKA in which QGSJET is applied as the hadronic interaction model, and the chemical composition of primary cosmic rays is obtained from the rigidity-cut model and the extrapolation of new results of direct measurements. This shows that the whole distribution tendency of the rate of energy concentration of simulated family events is basically consistent with that of the experiment.
45 articles