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Volume 16 Issue 8
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Original Articles
New < q,n|| Representation for Studing Two-Mode Nonlinear Phase Operator
FAN Hong-yi, ZOU Hui
Chin. Phys. Lett. 1999, 16 (8): 547-549 .  
Abstract   PDF(pc) (206KB) ( 382 )
A new complete and orthonormal < q,n|| representation is constructed in which Hradil’s two-mode phase operator R exhibits its phase behavior manifestly and can be put into R = Σq=-∞Σn=0 ||q-1,n> < q, n||, which resembles S-G phase operator (N + l)-1/2a = Σn=1|n–l > < n|. The corresponding phase state is also obtained, which is quaJified to make up a phase representation.

Temperature Fluctuations in Laser-Solid Interaction
WEI Xue-qin, ZHENG Qi-guang, LI Zai-guang
Chin. Phys. Lett. 1999, 16 (8): 550-552 .  
Abstract   PDF(pc) (222KB) ( 397 )
Epoxylite,polymethylmethacrylate and aluminum are irradiated by a cw CO2 laser and their temperature fluctuations are measured by the infrared thermal imagers. It is reported that the temperature fluctuation becomes stronger with increase of the laser-solid interaction time in the experiment, which is in good agreement with the theory prediction. Furthermore, the temperature fluctuation is experimentally studied while the material is melted or vaporized.
Levy Stability Index from Multifractal Spectrum
HU Yuan, YU Mei-ling, LIU Lian-shou
Chin. Phys. Lett. 1999, 16 (8): 553-554 .  
Abstract   PDF(pc) (159KB) ( 340 )
A method for extracting the Levy stability index μ from the multi-fractal spectrum f(α) in high energy multipar-ticle production is proposed. This index is an important parameter, characterizing the non-linear behaviour of dynamical fluctuations in high energy collisions. Using the random cascading α model as an example, the validity of this method is tested. It is shown that this method, based on a linear fit, is consistent with and more accurate than the usual method, which gets the Levy index through fitting the ratio of qth to 2nd order multi-fractal (Rényi) dimensions to the Peschanski formula.
Observation of the New Heavy Neutron-Rich Isotope 238Th
YUANG Shuang-gui, YANG Wei-fan, HE Jian-jun, XU Yan-bing, MA Tao-tao, XIONG sing, LI Zong-wei
Chin. Phys. Lett. 1999, 16 (8): 555-556 .  
Abstract   PDF(pc) (184KB) ( 349 )
A new nuclide 238Th was produced via multinucleon transfer reaction by 60 MeV/u 18O ion irradiation of the natural uranium. The thorium was radiochemically separated from the mixture of uranium and reaction products. The growth and decay of 238Pa gamma rays was observed, identifying the 238Pa parent as 238Th. The half-life of 238Th was determined to be 9.4±2.0min.

Coherent Bremsstrahlung at Beijing Electron-Positron Collider
DING Yi-bing, V. G. Serbo,
Chin. Phys. Lett. 1999, 16 (8): 557-559 .  
Abstract   PDF(pc) (275KB) ( 307 )
The main characteristics of coherent bremsstrahlung (CBS) for the Beijing Electron-Positron Collider are calculated. At this collider dNγ~3 x 108 dEγ/Eγ photons of CBS will be emitted for a single collision of the beams in the energy range Eγ< 240 eV. It seems that CBS can be a potential tool for optimizing collisions and measuring beam parameters. Indeed, the bunch length σz can be found from the CBS spectrum because critical energy Ec ∝ 1/σz; the horizontal transverse bunch size σx is related to dNγ∝1/σx2. In addition, CBS may be very useful for a fast control over an impact parameter R between the colliding bunch axes.

Spectroscopic Properties of Perturbed Ba 6p3/2ns Autoionizing States
LÜ, Jun, DAI Chang-jian, LI Cong-qi, LIU Zheng-dong, TANG Jing-chang
Chin. Phys. Lett. 1999, 16 (8): 560-562 .  
Abstract   PDF(pc) (247KB) ( 493 )
The excitation spectra of the Ba 6p3/2ns ( J = 1) autoionizing states with n ranging from 8 to 12 are measured using multistep laser excitation scheme. The measurements manifest that these states are strongly perturbed by the degenerate 6p1/2nl states, as the resonance profiles are structured according to the corresponding perturbing states. The experimental data are well reproduced by multichannel-quantum-defect theory, with the parameters obtained from a previous R-matrix calculation.
Chemical Shifts of 23Na in NaCl Crystal Specimens Implanted with Xenon Ions
LIANG Jia-chang, , XU Zhou, LE Xiao-yun, ZHAO Wei-jiang, YU Fu-chun, LIU Zhi, CHEN Rong-ti, SUN Xian-ping, ZHENG Xi-zhi, DU Yo-ru, ZHAO Ming-xin, SHEN Lian-fang, GU Hong-en, LI Yi, SU Yi
Chin. Phys. Lett. 1999, 16 (8): 563-564 .  
Abstract   PDF(pc) (170KB) ( 382 )
Na clusters containing 10 to less than 1000 metal sodium atoms and blisters containing xenon inclusions were formed in NaCl crystal specimens prepared by xenon ion implantation to single crystal NaCl with Auences more than or equal to 2 x 1016/cm2 at the energy of 36keV. Experiments indicated that on the condition of xenon ion Auences more than or equal to 1 x 1017/cm2 the xenon inside the inclusions formed in NaCl crystal specimens is in solid state and the solid state molecules NaXe are formed through the Combination of Xe with Na in Na clusters. The chemical shift of 23Na in solid state molecules NaXe relative to 23Na in single crystal NaCl was measured and is equal to -17ppm.
Image Storage Based on Photoinduced Alignment in Azobenzene Liquid-Crystalline Films
WANG Chang-shun, CHEN Guo-jian, CHEN Yong-mei, WEI Zhen-qian, YANG Yan-qiang, FEI Hao-sheng
Chin. Phys. Lett. 1999, 16 (8): 565-567 .  
Abstract   PDF(pc) (247KB) ( 361 )
Image storage based on photoinduced alignment in azobenzene liquid-crystalline films is reported. Measurements reveal that the liquid-crystalline film possesses large photoinduced birefringence (Δn~10-2 and permanent optical storage characteristics. The photoinduced alignment process is used for storing images. It is clearly demonstrated that the alignment of the azo chromophores as well as the stored image can be controlled by choosing the appropriate polarization of the irradiating light.

Transmission Probability of an Ultracold Three-Level Atom Through a Micromaser Cavity
ZHANG Zhi-ming, ZHOU Shi-kang, XIA Yu-xing, CHEN Ying-li, XIE Sheng-wu
Chin. Phys. Lett. 1999, 16 (8): 568-570 .  
Abstract   PDF(pc) (189KB) ( 399 )
The transmission probability of an ultracold cascade three-level atom through a micromaser cavity is calculated and analyzed. It is shown that the micromaser cavity can be used as a velocity selector for ultracold three-level atoms, and the velocity selectivity is better for three-level atoms than for two-level atoms.
Structure Effect of Squarylium Cyanine Dyes on Third-Order Optical Nonlinearities in Ground and Excited States
LIU Xu-chun, XU Gang, SI Jin-hai, YE Pei-xian, LIN Tong, PENG Bi-xian
Chin. Phys. Lett. 1999, 16 (8): 571-573 .  
Abstract   PDF(pc) (265KB) ( 355 )
A series of squarylium cyanine dyes with different substituents were synthesized and the third-order optical nonlinearities of their ground and excited states were investigated by backward degenerate four-wave-mixing. For the ground state, the molecular hyperpolarizability γg increases with the red-shift of the absorption peak λabmax, of the squaraine with different substituents, whereas for the excited-state molecular hyperpolarizability γe, the nonlinear enhancement γeg decreases, which may indicate that in the excited state the electron accepting-donating ability of different substituents changes in the reverse order compared with the order in the ground state.

Electron Swarm Behavior in Nonuniform Field
OUYANG Ji-ting
Chin. Phys. Lett. 1999, 16 (8): 574-576 .  
Abstract   PDF(pc) (224KB) ( 368 )
The comparison of the electron transport properties is presented under nonuniform fields with their local fields in oxygen. The electron swarm parameters are calculated by using Monte Carlo simulation. The results show that there are relatively more electrons distributing in the high-energy range for the decreasing field than the local field, while less for the increasing field, compared with the uniform field. The effective ionization coefficients for the decreasing field are larger than the equilibrium values, and vice versa for the increasing field. The different behavior of the electron swarms in increasing and/or decreasing field is considered to be the reason of the dependence of the discharge current and the corona inception voltage on the electrode polarity during the surface discharge.
Nonlinear Coupling of Langmuir Wave and Dust- Acoustic Wave in Plasmas with the Variable-charge grains
CHEN Yin-hua, LU Wei
Chin. Phys. Lett. 1999, 16 (8): 577-579 .  
Abstract   PDF(pc) (205KB) ( 459 )
Nonlinear interaction of the Langmuir wave and the dust-acoustic wave in plasmas with the variable-charge grains has been investigated. In the approximation of small amplitude, we find the solution of envelope soliton for the nonlinear Langmuir wave. The results show that the amplitude of envelope soliton increases with the increasing
of dust grain density
Plasma Generation in Air by Intense Laser Pulses with Various Pulse Durations
QIN Yuan-dong, YANG Hong, WANG Shu-feng, ZHU Chang-jun, GONG Qi-huang
Chin. Phys. Lett. 1999, 16 (8): 580-582 .  
Abstract   PDF(pc) (279KB) ( 445 )
We have studied the plasma generation through collecting the charged particles produced in laser-induced break-down in atmospheric air. This breakdovn is produced by ultrashort laser pulses with various durations ranging from 200fs to 2ps at a fixed pulse energy of 8mJ. We found that the plasma yield increases first with the increment of pulse duration and then reaches a plateau at a duration longer than 500fs. The generated plasma temperature is estimated to be higher than 5x 105 K .
Local Atomic Structure of Piperidyl Nd Dithiocarbamate
WU Zhong-hua, GUO Lin, JU Xin, HU Tian-dou, LI Qian-shu, ZHU He-sun,
Chin. Phys. Lett. 1999, 16 (8): 583-585 .  
Abstract   PDF(pc) (224KB) ( 361 )
The atomic structure of a novel rare earth complex consisting of Nd and the sulfur-containing ligand pipdtc (C5H10NCS-2) has been studied with extended x-ray absorption fine structure (EXAFS} and x-ray diffraction techniques. The complex of formula Nd(pipdtc)4N(CH3)4 crystallizes in the monoclinic space group P21/n with the following lattice parameters, a = 22.685(2), b = 20.332(2), c = 17.1270(10)Å, β = 100.570(10)o, Z = 8. The calculated density is 1.47g/cm3. A new derivative method is used to remove the post-edge absorption background including the multielectron excitation effect. The EXAFS results demonstrate that there are about eight S and four O atoms around Nd with the Nd-S bond length of 2.916Å and the Nd-O bond length of 2.415Å, respectively. This implies that the powder of this complex is not stable and is easy to oxidize in air. The possible change of structure before and after oxidation is discussed.
Interaction Between Dopants and Native Defects in Zn Doped p-InP Observed by Positron Annihilation
CHEN Zhi-quan, WANG Zhu, WANG Shao-jie
Chin. Phys. Lett. 1999, 16 (8): 586-588 .  
Abstract   PDF(pc) (219KB) ( 361 )
Positron lifetime spectra were measured for three Zn doped p-InP samples as a function of temperature. Interaction of Zn dopants and native P vacancies was observed under thermal activation. It is found that the formation of Zn-Vp complex has a correlation with the carrier concentration. The formation mechanism of the complex was tentatively discussed.
Internal Friction in Bi-material Specimens
CHEN Gang, ZHU Zhen-gang, SHUI Jia-peng
Chin. Phys. Lett. 1999, 16 (8): 589-590 .  
Abstract   PDF(pc) (151KB) ( 310 )
A new kind of bi-material specimen is employed in an inverted torsion pendulum to study the internal friction in liquids, and especially in materials during liquid-solid or solid-liquid transitions. Vibration systems containing a bi-material specimen with a solid or a liquid inner material can be described by using a modified three-parameter mechanical model. The theoretical results agree well with experimental data.
Effect of Carbon Content on Mechanoreduction of Copper Oxide
LIU Lin, YUAN Song-liu, DONG Yuan-da, CUI Kun
Chin. Phys. Lett. 1999, 16 (8): 591-593 .  
Abstract   PDF(pc) (347KB) ( 346 )
The reduction of CuO with different amount of carbon (CuO:C=2:1, 2:1.5, and 2:2, in molar ratio) induced by ball milling is examined by x-ray diffraction and transmission electron microscopy. It is found that reduction process is closely related to the carbon content. CuO can be completely converted into Cu if an excessive C is used (i.e., C = 1.5 or 2.0mol). However, the reduction of CuO follows a two-step process, CuO→Cu→Cu2O, if the mixture only contains a nominal C content (i.e., C = 1 mol). A tentative model in terms of solid state reaction at the interfaces is proposed to explain the effect of carbon content on the mechanoreduction of CuO.
Ground-State Properties of an Artificial Molecule: a Simple Model Calculation for the Double Quantum Dot
YOU Jian-qiang, ZHENG Hou-zhi
Chin. Phys. Lett. 1999, 16 (8): 594-596 .  
Abstract   PDF(pc) (229KB) ( 363 )
The ground state of a double quantum-dot structure is studied by a simplified Anderson-type model. Numerical calculations reveal that the ground-state 1evel of this artificial molecule increases with the increasing single particle level of the dot, and also increases with the decreasing transfer integrals. We show the staircase feature of the electron occupation and the properties of the ground-state eigenvector by varying the single particle level of the dot.
Colossal Magnetoresistance of Polycrystalline (La0.7Tb0.3)2/3Cal/3MnO3 at Low Drive Field
WANG Jing-hua, CHEN Ting-yong, WU Jian-hua, DAI Dao-sheng, NIE Jia-cai, ZHAO Bai-ru
Chin. Phys. Lett. 1999, 16 (8): 597-599 .  
Abstract   PDF(pc) (267KB) ( 388 )
The magnetic and electric properties of polycrystalline (La0.7Tb0.3)2/3Cal/3MnO3 were investigated. A spin glass-paramagnetic transition and metal-insulator transition were observed near 45K, and there exists continuous volume change in the range of measured temperature. At 60 K, a large anisotropic magnetostriction and a volume magnetostriction correspond to an isotropic colossal magnetoresistance (CMR) with the magnitude of more than 40% at an applied field of ±0.1 T. Our results demonstrate that the transition is of second-order in nature and CMR could be caused by spin-charge coupling in this compound.

Mechanism of the Curie-Weiss Law in Ferroelectrics
ZHANG Lei, ZHONG Wei-lie, WANG Chun-lei, PENG Yi-ping, ZHANG Qun*
Chin. Phys. Lett. 1999, 16 (8): 600-601 .  
Abstract   PDF(pc) (168KB) ( 352 )
A simple double-well potential model is established. It shows that the nature of the low-frequency dielectric constant in ferroelectrics is the additional hopping of the off-center ions in multi-site potential. The co-operative effect causes the fact that the Curie-Weiss law is obeyed. The mechanism of the molecular field is clarified.

Study of Blue Emission from Nano-SiC Powders During Rapid Thermal Annealing
LIU Yu-zhen, SHI Wan-quan, HUANG Yun-lan, LIU Shi-xiang, HAN Yi-qin, LU Zhong-qian, TAN Shou-hong, JIANG Dong-liang
Chin. Phys. Lett. 1999, 16 (8): 602-604 .  
Abstract   PDF(pc) (213KB) ( 421 )
Nanometric SiC powder was prepared by chemical vapor deposition at 1100°C, and samples were subsequently treated by rapid thermal annealing at 600-1100°C. The intensities of the blue photoluminescence were then measured a t room temperature. The peak intensity at 2.56 eV (484 nm) rises with annealing temperature, reaching a value about 9.2 times as high at 800°C, then drops very quickly at 900°C. Based on the results of x-ray diffraction, infrared spectroscopy, x-ray photoelectron spectroscopy and transmission electron microscopy, we conclude that the amounts of the twofold coordinated Si on the surface of the nanometric SiC particles play an important role in the photoluminescence intensity.
Electroluminescence from Indium Tin Oxide Film/Nanoscale Si Oxide/p-Si Structure
WANG Yong-qiang, ZHAO Tai-ping, CUI Xiao-ming, MA Zhen-chang, ZONG Wan-hua, QIN Guo-gang,
Chin. Phys. Lett. 1999, 16 (8): 605-607 .  
Abstract   PDF(pc) (287KB) ( 380 )
After an Si oxide layer of 3nm thickness had been grown by using magnetron sputtering on a p-type Si (100) substrate, an indium tin oxide (ITO) film was deposited onto the Si oxide layer by using electron beam deposition. Electroluminescence (EL) from such an ITO/Si oxide/p-type Si structure was measured under a forward bias of 5V or more. Its EL power efficiency is about eight times as large as that of a semitransparent Au/Si oxide (3nm)/p-Si structure. The experimental results indicate that the greater EL power efficiency is due not only to the higher optical transparency of the ITO film compared with Au film in a range of 300 to 900nm, but also to some new luminescence centers introduced in the Si oxide layer during the ITO deposition process.
Electron Field Emission from Nitrogen Ion Implantat ion Diamond-Like Carbon Film
MA Hui-zhong, ZHANG Lan, YAO Ning, LI Yun-jun, ZHANG Bing-lin, HU Huan-ling
Chin. Phys. Lett. 1999, 16 (8): 608-609 .  
Abstract   PDF(pc) (185KB) ( 295 )
The electron field emission from both diamond-like carbon(DLC) and nitrogen doped diamond-like carbon films by ion implantation was studied. The DLC films were deposited on a molybdenum layer coated on ceramic by using pulsed laser deposition. The field emission measurements show that the incorporation of nitrogen in DLC films can increase current density and lower the turn-on field from 9 to 4 V/μm, which indicate that the nitrogen doped DLC films have a potential application as field emission materials for flat panel displays.
Some Considerations on Optical Confinement and Free Carrier Confinement of Quantum Cascade Lasers
YANG Quan-kui, LI Ai-zhen
Chin. Phys. Lett. 1999, 16 (8): 610-612 .  
Abstract   PDF(pc) (251KB) ( 404 )
Calculating the refractive index dispersions considering the influence of doping concentration on refractive indices, we have illustrated the heavily doped contact layers, n = 1 x 1019cm-3 for λ ~ 9 μm, and n ~ 1 x 1020cm-3 for λ = 5μm quantum cascade lasers, to suppress the refractive indices and get sufficient optical confinement. By calculating the transmission of energies through a graded gap superlattice, it is demonstrated that for energies E1 and E2 (the two lower states) the electrons can easily get through the graded gap superlattice. While for energy E3 the graded gap superlattice creates a minigap (the transmission of the energies E1 and E2 is 102 times more than that of E3). In this way, the electrical confinement can be achieved.
Electron-Electron Interaction Effect on the Conformational Soliton of Deoxyribonucleic Acid
ZHANG Ling-yun, SUN Hong, LIN Jia-ti
Chin. Phys. Lett. 1999, 16 (8): 613-615 .  
Abstract   PDF(pc) (221KB) ( 454 )
The local conformational behavior of deoxyribonucleic acid (DNA) has been discussed by considering the electron-electron interaction. We set up the coupled nonlinear equations to describe the interaction between the longitudinal displacement of DNA backbone and the electronic wave function. Under the case of approximated condition, we obtain the analytic solution of the electronic wave function and longitudinal displacement. The influence of electron-electron interaction upon the parameters of conformational soliton such as the amplitude and width have been revaluated. With the increasing of electron-electron interaction, the amplitude and half-width will increase.
Dynamo Effect Due to Plasma Motion
YANG Zhi-liang, JING Hai-rong
Chin. Phys. Lett. 1999, 16 (8): 616-618 .  
Abstract   PDF(pc) (206KB) ( 359 )
On the basic Maxwell equations in moving media, the magnetic induction equation in the moving plasma is derived. A more efficient dynamo transforming kinetic energy of the moving plasma to magnetic energy is obtained with this equation. This model of dynamo possesses to oscillatory solutions. The oscillation of magnetic field can explain the variation of the solar magnetic field.
Abundances of the Neutron-Capture Elements in Metal-Poor Halo Star HD 126238
LI Ji, ZHANG Bo, WEI Guo-qiang, ZHANG Li-ping, PENG Qiu-he,
Chin. Phys. Lett. 1999, 16 (8): 619-621 .  
Abstract   PDF(pc) (239KB) ( 378 )
Using the new observations of several neutron-capture elements in metal-poor star HD 126238, combining a computer model and the method of least square, we accurately compute the component coefficients C1, C2, and C3. The results are C1 = 2.52, C2 = 0.26, C3 = 0.31. Then employing the values of the component coefficients, we determine the relative contributions of the r-process and the s-process to the abundances of neutron-capture elements in the HD 126238, and predict the abundances of all the neutron-capture elements in this metal-poor star. The predictions agree well with the observations.

Cosmic Ray Composition in the “Knee”Region Deduced from the Lateral Distribution of Cerenkov Light Emitted in Extensive Air Showers
ZHA Min, CHUENG Tsang, DING Lin-kai, GAO Xiao-yu, GENG Qing-xi, LIU Chang-qin, NG Pun-Hon, YANG Hong-tao, ZHU Qing-qi
Chin. Phys. Lett. 1999, 16 (8): 622-624 .  
Abstract   PDF(pc) (208KB) ( 387 )
We report the first result of measurements of the lateral distribution of Cerenkov light associated with cosmic ray extensive air showers with size between 105.0 and 106.6 observed in the Liangwang Mountain Observatory, 90 km east of Kunming City in China. The change trend towards heavy nucleus dominance of the primary cosmic ray composition in the “Knee”region is deduced with the aid of a Monte Carlo simulation.

28 articles