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Volume 17 Issue 11
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Original Articles
Some Special Types of Multisoliton Solutions of the Nizhnik-Novikov-Vesselov Equation
LOU Sen-Yue
Chin. Phys. Lett. 2000, 17 (11): 781-783 .  
Abstract   PDF(pc) (232KB) ( 595 )
Using the standard truncated Painlevé analysis, we have obtained some new special types of soliton solutions of a (2+1)-dimensional integrable model, the Nizhnik-Novikov-Vesselov equation. Starting from the standard truncation approach in the Painlevé analysis, one can obtain a Bäcklund transformation to find a new solution from a known one. Usually, one can obtain only a single solitary wave solution from the Bäcklund transformation related to the truncated Painlevé analysis starting from the trivial vacuum solution. In this paper, we find some special types of the multisoliton solutions from the truncated Painlevé analysis and the trivial vacuum solution.
A Scheme for Realizing the Continuous Wave Atom Laser
ZHOU Xiao-Ji, WANG Yi-Qiu, YANG Dong-Hai
Chin. Phys. Lett. 2000, 17 (11): 784-786 .  
Abstract   PDF(pc) (290KB) ( 391 )
We propose a scheme for realizing the long-term continuous output of an atom laser. In this scheme the cold atoms in several subsidiary Bose-Einstein condensates (BEC) will be coupled one by one in turn into one main BEC which serves for the continuous output of a coherent atomic beam. We discuss the process of the phase unification of the newly entered BEC atoms with the remaining atoms in the main BEC trap. An ideal dynamical equilibrium can be established when the transition rate of the uncondensed atoms transforming into the condensate and the decay rate of coupling output satisfy some conditions. The coupling method from the subsidiary BEC to the main BEC and the time rates of all different processes are considered.
(EC+β+) Decay of 128Ce
LI Zhan-Kui, XU Shu-Wei, XIE Yuan-Xiang, ZHANG Tian-Mei, MA Rui-Chang, GUO Ying-Xiang, GE Yuan-Xiu, WANG Chun-Fang, GUO Bin, XING Jian-Ping, DU Jin-Zhou
Chin. Phys. Lett. 2000, 17 (11): 787-788 .  
Abstract   PDF(pc) (176KB) ( 357 )
The (EC+β+) decay of 128Ce was reinvestigated in the116Sn (l6O, 4n) reaction by using a helium-jet tape transport system. The decay γ rays of 128Ce were unambiguously described from those of 129Ce after taking the comparing experiments of 16O+116Sn and 16O+117Sn. Based on x-γ and γ-γ coincidence measurements, a detailed (EC+β+) decay scheme of 128Ce has been proposed which modifies the previous one, and takes accounts of 100 observed γ-lines.
One- and Two-Neutron Transfer Reactions in 11Be+208Pb and Mechanism of Lowering Fusion Barrier
WANG Ning, LI Zhu-Xia, WU Xi-Zhen, WANG Nan, SUN Xiu-Quan
Chin. Phys. Lett. 2000, 17 (11): 789-791 .  
Abstract   PDF(pc) (293KB) ( 478 )
We study one- and two-neutron transfer reactions in 11Be+208Pb by using the quantum molecular dynamics model. We find that lowering about 1-2 MeV of the potential barrier of 208Pb for fusion is gained when two neutrons separated from 11Be enter into 208Pb. Whereas no significant change of potential barrier is found when only the halo neutron separated from 11Be enters into 208Pb. The dynamical interplay between suppression and enhancement effects on the fusion probability in reaction 11Be+208Pb stemming from the easy separation of halo neutron and the long extending of neutron distribution is discussed.

Analysis on Origin of Oscillation of H Moment in High-Energy hh Collision
WU Tao, ZHOU Dai-Cui
Chin. Phys. Lett. 2000, 17 (11): 792-794 .  
Abstract   PDF(pc) (213KB) ( 443 )
Multiplicity distributions of negative binomial distribution (NBD) and modified NBD are obtained from a birth process model with an immigration. The ratio of factorial cumulant moment to factorial moment, i.e., H moment is calculated from different multiplicity distributions of NBD, modified NBD and the three fireball model, which shows an oscillatory behavior when there is a truncation of multiplicity. The oscillation of H moment is related to the common character of the truncated multiplicity distributions.
Momentum Profile and Final Correlation Effects of Iso-butane Inner Valence by Binary (e, 2e) Spectroscopy
DENG Jing-Kang, LI Gui-Qin, HE Yao, HUANG Jian-Dong, DENG Hui, WANG Xiao-Dong, WANG Fang, ZHANG Yi-An, NING Chuan-Gang, GAO Nai-Fei, WANG Yan, CHEN Xue-Jun, ZHENG Yan-You
Chin. Phys. Lett. 2000, 17 (11): 795-797 .  
Abstract   PDF(pc) (321KB) ( 474 )
The binding energy spectra and the momentum distributions of the valence orbitals of iso-butane, also known as methylpropane (CH3CH(CH3)CH3), are studied by using a high resolution binary (e, 2e) electron momentum spectrometer, at an impact energy of 1200eV plus the binding energy (8-32eV) with symmetric non-coplanar kinematics. Binding energy spectra of the valence shell are obtained at a coincidence energy resolution of 0.95 eV in full width at halfmaximum. The experimental momentum profiles of the inner valence orbitals are obtained and compared with the theoretical momentum distributions calculated by using Hartree-Fock and density functional theory methods with the basis sets 6-31G and 6-311++G**. The pole strengths of the inner orbitals are estimated and the final correlation effects are discussed.
Information Entropy and Squeezing of Quantum Fluctuations in a Two-Level Atom
FANG Mao-Fa, ZHOU Peng, S. Swain
Chin. Phys. Lett. 2000, 17 (11): 798-800 .  
Abstract   PDF(pc) (264KB) ( 558 )
We study the atomic squeezing in the language of the quantum information theory. A rigorous entropy uncertainty relation which suits for characterizing the squeezing of a two-level atoms is obtained, and a general definition of information entropy squeezing in the two-level atoms is given. The information entropy squeezing of two-level atoms interacting with a single-mode quantum field is examined. Our results show that the information entropy is a superior measure of the quantum uncertainty of atomic observable, also is a remarkable good precision measure of atomic squeezing. When the population difference of two-level atom is zero, the definition of atomic squeezing based on the Heisenberg uncertainty relation is trivial, while the definition of information entropy squeezing of the atom based on the entropy uncertainty relation is valid and can provide full information on the atomic squeezing in any cases.
High-Order Stimulated Raman Emission and Two-Photon Stimulated Emission by Photodissociation of PbI2 Molecules
MAN Bao-Yuan, ZHANG Jie, NI Pei-Gen, ZHANG Dao-Zhong
Chin. Phys. Lett. 2000, 17 (11): 801-803 .  
Abstract   PDF(pc) (249KB) ( 322 )
When focusing YAG laser pulses at 266nm into a heat-pipe oven containing PbI2 molecules vapor, four red line emissions at 626.0, 619.8, 613.7 and 621.8nm are observed. The photodissociation mechanism of PbI2 molecules and the possible generation channels of these four line emissions are given. Moreover, the dependence of the emission at 626.0nm on incident laser energy and heat-pipe temperature is measured. The experimental observation is well supported by the photodissociation mechanism proposed by us.

Saturable Nonlinearity in Photovoltaic-Photorefractive Crystals Under Open-circuit Condition
GUO Ru, LING Zhen-Fang, CHEN Xiao-Hu, ZHANG Guo-Quan, ZHANG Xin-Zheng, WEN Hai-Dong, JIANG Ying, LIU Si-Min
Chin. Phys. Lett. 2000, 17 (11): 804-805 .  
Abstract   PDF(pc) (199KB) ( 410 )
We show that the refractive index change induced by a focused incident beam with an additional incoherent uniform illumination in photovoltaic-photorefractive crystals under open-circuit condition has a saturable nonlinearity form. The incoherent uniform background illumination can be used to increase the effective dark irradiance. The formation time of the photovoltaic soliton can be decreased by keeping the intensity of the soliton at a higher value without over-saturation by use of the background illumination.
Generation of Pedestal-free 10 GHz Pulses from a Comb-Like Dispersion Profiled Fiber Compressor and Its Application in Supercontinuum Generation
HAN Ming, LOU Cai-Yun, WU Yue, CHANG Guo-Qing, GAO Yi-Zhi, LI Yu-Hua
Chin. Phys. Lett. 2000, 17 (11): 806-808 .  
Abstract   PDF(pc) (258KB) ( 373 )
We built a pulse compressor using a comb-like dispersion-profiled fiber (CDPF). The CDPF consists of 12-segment fibers with the dispersion alternatively high and low. Using this compressor and a 17dBm Erbium-doped fiber amplifier, the 10GHz, 12ps pulses generated from an actively mode-locked Er3+ doped fiber ring laser was compressed to ~ 2ps without pedestal. We also show that compared with the high order soliton pulse compressor, the power efficiency can be doubled in supercontinuum generation by using the pump pulses compressed by this CDPF compressor.

Nonlinear Transmission Property of the Excited State Proton Transfer Molecule 7-Hydroxyquinoline
XIAO Dong, ZHANG Gui-Lan, WANG Hai-Yan, TANG Guo-Qing, CHEN Wen-Ju
Chin. Phys. Lett. 2000, 17 (11): 809-811 .  
Abstract   PDF(pc) (225KB) ( 396 )
Nonlinear transmission property of 7-hydroxyquinoline with excited state proton transfer effect was investigated at 355 and 532nm using picosecond laser pulses. The experiment result shows that the transmissivity of 7-hydroxyquinoline is nonlinear at 355nm but it is linear at 532nm. The nonlinear transmissivity of 7-hydroxyquinoline originates from the larger nonlinearity of anion and cation formed in excited state proton transfer process. Therefore, 7-hydroxyquinoline might be used as ultrafast optical amplitude limit material.
Investigation of the Parametric Field from a Focusing Source by Using Superposition of Gaussian Beams
ZHANG Dong, GONG Xiu-Fen, LU Rong-Rong
Chin. Phys. Lett. 2000, 17 (11): 812-814 .  
Abstract   PDF(pc) (199KB) ( 402 )
The superposition method of Gaussian beams is extended to describe the acoustical parametric field from a focusing source. The axial sound pressure of the difference frequency wave 1MHz generated due to the interaction of two primary wave 3.5 and 4.5MHz is theoretically calculated by using 10 items of Gaussian functions. Experimental results coincide well with the calculated results except for the case at the vicinity of the focusing source.
Dust-Acoustic Solitons in Dusty Plasma with Two-Temperature Ions
XIE Bai-Song, , HE Kai-Fen, HUANG Zu-Qia
Chin. Phys. Lett. 2000, 17 (11): 815-817 .  
Abstract   PDF(pc) (249KB) ( 511 )
Dust-acoustic solitons in dusty plasmas with two-temperature isothermal ions are investigated by considering an effect of self-consistent dust-charge variation. Employing the reductive perturbation technique we derived dust-acoustic solitons. It is found that both rarefactive and compressive solitons exist and the approximate similarity law which holds in dust-charge-fluctuation plasma system with one-temperature ion does not survive in the present studied dusty plasma with two-temperature isothermal ions.
Diagnostics of Femtosecond Laser-Plasmas Using Fundamental and Second Harmonic Emission
ZHAO Li-Zeng, ZHANG Ping, FENG Bao-Hua, WEI Zhi-Yi, ZHANG Jie
Chin. Phys. Lett. 2000, 17 (11): 818-820 .  
Abstract   PDF(pc) (306KB) ( 330 )
By observing the fundamental and second harmonic emission from a plasma produced by a 150fs, 5mJ laser at 800nm, the electron temperature, the expansion speed and the scalelength of the plasma have been diagnosed. Moreover the polarization of the fundamental and second harmonic emission has been studied. This could be a useful diagnostic for modulation at the critical surface of the plasma.
Comparison between Cooling Rate Dependence of Macroscopic and Microscopic Quantities in Simulated Aluminium Glass
LIU Chang-Song, ZHU Zhen-Gang
Chin. Phys. Lett. 2000, 17 (11): 821-823 .  
Abstract   PDF(pc) (251KB) ( 373 )
Constant-pressure molecular dynamics simulations and an analysis of the local atomic structures have been performed to study the cooling rate dependence of some macroscopic and microscopic quantities in aluminium glass. Macroscopic quantities, enthalpy and density, see an observable but small dependence on the cooling rate. Icosahedral ordering units exhibit strong cooling rate dependence, which is responsible for the dependence of the enthalpy and the density on the cooling rate; while the almost independence of some microstructural units such as the 1541, 1431 and 1421 pairs of the cooling rate may lead to a small dependence of the enthalpy and the density on the cooling rate.
Effects of the Wetting Particles on Phase Separation of Binary Mixtures
LIU Ji-Wen, MA Yu-Qiang
Chin. Phys. Lett. 2000, 17 (11): 824-826 .  
Abstract   PDF(pc) (408KB) ( 485 )
We study phase separation of binary mixtures in the presence of mobile particles by the lattice Monte Carlo simulation. The presence of mobile particles changes the morphology of the domain growth, in agreement with earlier experimental result. By varying the wetting interaction strength, we can control the speed of phase separation, and find a critical wetting strength beyond which the growth of the domains slows down. We propose a novel scaling function which describes the growth of the domain size L(t) as a function of time. It suggests an applicable way to tune the speed of phase separation by the coupling between the phase decomposition and the mobile particle-wetting process.
Au/Ti/p-Diamond Ohmic Contacts Prepared by Radio-Frequency Sputtering
ZHEN Cong-Mian, LIU Xue-Qin, YAN Zhi-Jun, GONG Heng-Xiang, WANG Yin-Yue
Chin. Phys. Lett. 2000, 17 (11): 827-828 .  
Abstract   PDF(pc) (169KB) ( 336 )
The as-deposited Au/Ti/p-diamond contacts prepared by rf sputtering are ohmic. The ohmic characteristics of the contacts are improved after annealing. As for the as-deposited and annealed contacts, the specific contact resistivities of 2.886 x 10-3 and 2.040 x 10-4 Ω.cm2 are obtained, respectively. The x-ray photoelectron spectroscopy analysis indicates that the titanium carbide formation occurs at the interface between titanium and the diamond substrate in the as-deposited state, and no TiO2 is observed.
Photoinduced Charge Transfer in MBB-PPV/C60 Composite Film
GUO Li-Jun, MA Guo-Hong, SHAN Fu-Kai, MO Yu-Jun, QIAN Shi-Xiong
Chin. Phys. Lett. 2000, 17 (11): 829-831 .  
Abstract   PDF(pc) (262KB) ( 474 )
The photoconductive properties of MBB-PPV/C60 composite films fabricated by the physical jet deposition (PJD) technique have been studied on the basis of the photoinduced charge transfer process. Under the photoex-citation, the transverse photoconductivity of the composite films is greatly enhanced by 4 orders of magnitude due to the efficient excitation transfer process from MBB-PPV (as donor) to C60 (as acceptor) occurring at the interface, the separation of charges and the existence of in-layer free carriers. The results indicate that the conjugated polymer/fullerene composite films optimized by an appropriate configuration have potential applications in photoelectric devices and photonic fields.
Enhancement of Curie Temperature and Magnetoresistance in the Perovskit es La2/3Cal/3Mnl-xSixO3
LI Run-Wei, WANG Zhi-Hong, SUN Ji-Rong, CHEN Xin, SHEN Bao-Gen
Chin. Phys. Lett. 2000, 17 (11): 832-834 .  
Abstract   PDF(pc) (243KB) ( 431 )
Structural, magnetic, and transport properties of perovskite La2/3Cal/3Mnl-xSixO3(x = 0, 0.025, 0.05) have been studied. The incorporation of Si decreases the overall resistivity, but obviously increases the Curie temperature (TC), metal-insulator transition temperature (TP), and the magnetoresistance ratio MR (defined as [R(0) - R(H)]/R(0)) near room temperature. Comparing with La2/3Cal/3MnO3 the TC , TP, and MR of the sample with x = 0.05 increase by 30, 45K, and 20%, respectively. Lattice effects may play a more important role than the magnetic dilution in the case of low Si substitution.
Giant Magneto-Impedance Effect in Sandwiched FeSiB/Cu/FeSiB Films
ZHOU Yong, YANG Chun-Sheng, YU Jin-Qiang, ZHAO Xiao-Lin, MAO Hai-Ping
Chin. Phys. Lett. 2000, 17 (11): 835-837 .  
Abstract   PDF(pc) (253KB) ( 565 )
Giant magneto-impedance (GMI) effect has been realized in the sandwiched FeSiB/Cu/FeSiB films. With magnetic field Ha and ac current applied along the longitudinal direction of the sample, the GMI ratio increases with the increasing Ha, reaching a positive maximum value, and then decreases to negative values with further increase of magnetic field. Field dependence of the GMI ratio also indicates that the magnetic field corresponding to the maximum GMI ratio is different for various frequencies. The positive maximum GMI ratio is 17.2% for Ha=1600A/m and frequency of 3 MHz. In addition, the films display a large negative GMI ratio with a magnetic field applied along the transverse direction and the value of the GMI ratio is about -13.4% for Ha=5600A/m and frequency of 3 MHz.
Photoluminescence and Microstructure of the Erbium-Doped Hydrogenated Amorphous SiOx(O < x < 2)
LIANG Jian-Jun, , CHEN Wei-De, , WANG Yong-Qian, , HE Jie, , ZHENG Wei-Min, WANG Zhan-Guo
Chin. Phys. Lett. 2000, 17 (11): 838-840 .  
Abstract   PDF(pc) (240KB) ( 353 )
The hydrogenated amorphous SiOx films (a-SiOx:H) with various oxygen contents have been prepared using plasma enhanced chemical vapor deposition technique. The films were implanted with erbium and annealed by rapid thermal annealing. An intense photoluminescence (PL) of Er at 1.54μm has been observed at 77K and at room temperature. The PL intensity depends strongly on both the oxygen content of the film and the rapid thermal annealing temperature and reaches its maximum if the ratio of O/Si in the film is approximately equal to 1.0 at 77K and to 1.76 at room temperature. The microstructure of the film also has strong influences on the PL intensity. The PL intensity at 250K is slightly more than a half of that at 15K. It means that the temperature quenching effect of the PL intensity is very weak.

Observation of As-Grown Defects in Zn-Doped GaAs by Positron Lifetime Spectra
WANG Zhu, WANG Shao-Jie, CHEN Zhi-Quan
Chin. Phys. Lett. 2000, 17 (11): 841-843 .  
Abstract   PDF(pc) (292KB) ( 348 )
Positron lifetime spectra were measured for the Zn-doped p-type GaAs. In comparing the horizontal-Bridgman-method-grown and the floating-zone-method grown p- type GaAs with the liquid-encapsulation-Czochralski-grown p-type GaAs samples, positron trapping into vacancy type defects was observed in the former two grown p-type GaAs. Shallow positron traps were detected, and the dominant ones were attributed to acceptor the in p-type GaAs.
Effect of Si/Sil-yCy/Si Barriers on the Characteristics of Sil-xGex/Si Resonant Tunneling Structures
HAN Ping, CHENG Xue-Mei
Chin. Phys. Lett. 2000, 17 (11): 844-846 .  
Abstract   PDF(pc) (286KB) ( 362 )
P-type double barrier resonant tunneling diodes (RTD) with the single Si0.6Ge0.4 quantum well and double Si0.6Ge0.4spacer have been realized by using an ultra clean low-pressure chemical vapor deposition system. The effect of Si1-yCy layer on the characteristics of the devices was shown by comparing the current-voltage (I-V) characteristics of RTD’s of the barriers of Si layers with that of Si/ Si1-yCy/Si structures. The peak voltage was gradually increased and the resonant current decreased obviously with increasing C content in the Si/ Si1-yCy/Si barriers. The origin of the phenomena above can be attributed to the C related deep acceptor levels in the Si/ Si1-yCy/Si barriers. The possible mechanism for the observed I- V characteristics was shown more clearly by increasing C content to 3% and changing the thicknesses of Si and Si1-yCy layers in the Si/Si1-yCy/Si barriers.
TI2Ba2CaCu2Ox Bicrystal Junction DC-SQUID Magnetometers Operating in Unshielded Environment
HAN Bing, CHEN Geng-Hua, ZHANG Li-Hua, ZHAO Shi-Ping, YANG Qian-Sheng, YAN Shao-Lin, LU Rong-Tao
Chin. Phys. Lett. 2000, 17 (11): 847-849 .  
Abstract   PDF(pc) (366KB) ( 511 )
We fabricated direct-current superconducting quantum interference device magnetometers with single layer epi-taxial Tl2Ba2CaCu2Ox films on 36.8o SrTiO3 bicrystal substrates. The white Aux noise and the field-flux transformation coefficient of the devices are 1.5 x 10-5Φ0/√Hz and 40 nT/Φ0, respectively. The magnetometers can work in unshielded environment.
Some New Observing Features of a Solar Radio Spectral Event on August 25,1999
XU Fu-Ying, LIU Yu-Ying, YAO Qi-Jun, FU Qi-Jun, MENG Xuan, WU Hong-Ao
Chin. Phys. Lett. 2000, 17 (11): 850-852 .  
Abstract   PDF(pc) (263KB) ( 387 )
A broadband solar radio type III burst was observed on August 25,1999 at Purple Mountain Observatory with waveband of 4.5-7.5 GHz. It was also observed at Beijing Astronomical Observatory with waveband of 5.2-7.6 GHz. Therefore, it is the first common spectral event observed in China. The type III bursts are gathered into more than 10 groups and drift in opposite directions, but the reverse drifting prevails. The largest bandwidth of type III burst reaches ≥3 GHz and may be the broadest bandwidth of the reverse type III burst ever observed up to the present. Some new observing characteristics of fine structures are found, for example, fiber-like, V-shaped and neck-ring-like structures. Especially, the neck-ring-like structure is probably first discovered in cm waveband and may be the evidence of twisted rope of magnetic lines.

A New Approach to Evolution of Black Hole Accretion Disks
WANG Ding-Xiong, LEI Wei-Hua, XIAO Kan
Chin. Phys. Lett. 2000, 17 (11): 853-855 .  
Abstract   PDF(pc) (181KB) ( 366 )
Evolution of black hole (BH) accretion disks is investigated by a new approach, in which the evolution of the central BH can be derived in terms of BH spin directly, and the evolution characteristics of the concerning BH parameters are shown more easily and obviously. As an example, the unusual evolution characteristics of angular velocity of BH horizon and that of accreting particles at the inner edge of the disk are derived by considering the Blandford-Znajek process.
Cosmic Wave Functions with the Brans-Dicke Theory
ZHU Zong-Hong
Chin. Phys. Lett. 2000, 17 (11): 856-858 .  
Abstract   PDF(pc) (265KB) ( 555 )
Using the standard Wentzel-Kramers-Brillouin method, the Wheeler-DeWitt equation for the Brans-Dicke theory is solved under three kinds of boundary conditions (proposed by Hartle-Hawking, Vilenkin and Linde, respectively). It is found that, although the gravitational and cosmological “constants”are dynamical and time-dependent in the classical models, they will acquire constant values when the universe comes from the quantum creation, and that in particular, the amplitude of the resulting wave function under Linde or Vilenkin boundary conditions reaches its maximum if the cosmological constant is the minimum.

27 articles