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Volume 14 Issue 8
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Original Articles
Exact Travelling Wave Solutions of Discrete Planar Velocity Boltzmann Models
LÜ, Xian-qing
Chin. Phys. Lett. 1997, 14 (8): 561-564 .  
Abstract   PDF(pc) (148KB) ( 376 )
By investigating the discrete planar Boltzmann models: the square 4-velocity and the hexagonal 6-velocity models, exact travelling wave solutions can be studied in a concise way. And their exact travelling wave solutions can only be monotonic travelling wave . The conclusions of the precursors need ameliorating. This suggests a general method for obtaining nontrivial exact solutions for the similar discrete Boltzmann equation.
On the Significance of Electrical Damping in Torsion Balance
ZHOU Ze-bing, LUO Jun
Chin. Phys. Lett. 1997, 14 (8): 565-568 .  
Abstract   PDF(pc) (191KB) ( 444 )
A typical electrical damping circuit for increasing the damping coefficient of a torsion balance system in high vacuum is discussed in detail. Theoretical analysis and numerical estimation performed with typical experimental parameters show that the signal-noise ratio can be improved by partial cooling of the electrical damping circuit. This is significant for the torsion balance experiments.
Reflection Asymmetric Shapes in the Neutron-Rich 140,143Ba Isotopes
ZHU Sheng-jiang, WANG Mu-ge, J. H. Hamilton, A. V. Ramayya, B. R. S. Babu, W. C. Ma, LONG Gui-lu, DENG Jing-kang, ZHU Ling-yan, LI Ming, T. N. Ginter, J. Komicki, J. D. Cole, R. Aryaeinejadv, Y. K. Dardenne, M. W. Drigert, J. O. Rasmussen, Yu. Ts. Oganessian, M. A. Stoyer, S. Y. Chu, K. E. Gregorich, M. F. Mohar, S. G. Prussin, I. Y. Lee, N. R. Johnson, F. K. McGowan
Chin. Phys. Lett. 1997, 14 (8): 569-572 .  
Abstract   PDF(pc) (211KB) ( 412 )
Level schemes for the neutron-rich 140,143Ba nuclei have been determined by study of prompt γ-rays in spontaneous fission of 252Cf. The level pattern and enhanced E1 transitions between π = + and π = - bands show reflection asymmetric shapes with simplex quantum number s = +1 in 140Ba and s = ±i in 143Ba, respectively. The octupole deformation stability with spin variation has been discussed.
Sigma-Meson from General Color Symmetry Model for Quantum Chromodynamics
LÜ, Xiao-fu, /sup>, LIU Yu-xin, ZOU Bing-song, DING Hui-ming, ZHAO En-gang
Chin. Phys. Lett. 1997, 14 (8): 573-576 .  
Abstract   PDF(pc) (156KB) ( 286 )
The property of σ-meson or f0 (400-1200) is studied in the general color symmetry model (GCM) for quantum chromodynamics. With recent determined values of mσ, fσ and fπ in GCM, the isoscalar ππ S-wave amplitude is calculated without any free parameter. The T-matrix pole for f0 (400-1200) is found to be 1011- i 284MeV, which is very close to the Particle Data Group value (400-1200)-i(300-500) MeV.
Dilepton Distribution as a Signature for the Baryon-Rich Quark-Gluon Matter
HE Ze-jun, ZHANG Jia-ju, WANG Zi-xing, QIU Xi-jun
Chin. Phys. Lett. 1997, 14 (8): 577-580 .  
Abstract   PDF(pc) (228KB) ( 457 )
From the full stopping scenario, the dilepton production in the baryon-rich quark-gluon fireball based on a relativistic hydrodynamic model is studied, and it is found that with increasing incident energy a characteristic plateau indicating the formation of the baryon-rich quark-gluon matter appears in the total yield.
Observation of Hysteresis of the Ion Cloud Motion in an rf Trap
GAO Ke-lin, LUO Xue-li, ZHU Xi-wen, YAN Min, LI Jiao-mei
Chin. Phys. Lett. 1997, 14 (8): 581-584 .  
Abstract   PDF(pc) (195KB) ( 401 )
Variations of the hysteresis of the rf detection signals corresponding to the axial motion of an ion cloud in a Paul trap versus the detection voltage, operation parameters and number of ions have been observed. The features are explained by an extended pseudopotential model with an octupole potential correction and an effective potential from the ion cloud.
Coulomb Correction to Keldysh-Faisal-Reiss Theory for Photoionization of Atoms
CHEN Bao-zhen
Chin. Phys. Lett. 1997, 14 (8): 585-588 .  
Abstract   PDF(pc) (180KB) ( 413 )
In this paper, the Coulomb correction to Keldysh-Faisal-Reiss theory is derived in A-gauge. An application of the Coulomb correction to the photoelectric effect of H-atom is presented and the role of the gauge choice and the Coulomb correction are discussed. It is shown that the Coulomb correction plays an importaht role in the explanation of the recent energetic photoelectron spectra of He.
Optical Nutation Effect in the Three-Level System Driven by a Coherent Microwave Field
CAO Zhuo-liang, GUO Guang-can
Chin. Phys. Lett. 1997, 14 (8): 589-592 .  
Abstract   PDF(pc) (183KB) ( 344 )
In this paper, a coherent transient effect-optical nutation in Bloch form is studied semiclassically in the three-level atomic system driven by a coherent microwave field. The amplitude of the optical nutation signal field is obtained. It is found that the signal field, related to the microwave, is the overlap of two slow oscillations instead of one.
Correlation Between Multiplicative Noises and Its Effects on Two-Mode Laser
LONG Quan, CAO Li, WU Da-jin, LI Zai-guang
Chin. Phys. Lett. 1997, 14 (8): 593-596 .  
Abstract   PDF(pc) (215KB) ( 381 )
A two-mode laser cavity in which the optical paths of two modes can be separated and affected by different but correlated multiplicative noises (external disturbances) with the help of a noise introducing device is proposed. Through a corresponding mathematical model, it is found that the statistical properties of laser intensities depend strongly on the relationship between the noise correlation coefficient and the mode coupling constant.
Measurement of Plasma Rotation Velocities with Limiter Biasing on the CT-6B Tokamak
ZHOU Bao-suo, YANG Xuan-zong, WANG Long, FENG Chun-hua, JIANG Di-ming, QI Xia-zhi
Chin. Phys. Lett. 1997, 14 (8): 597-600 .  
Abstract   PDF(pc) (219KB) ( 512 )
H-mode-like phenomenon is observed with positive limiter biasing on the CT-6B Tokamak. Poloidal rotation of plasma in the boundary region is slowed and even changed its direction with positive bias, effect of positive bias on the toroidal rotation is also presented.
Formation of Large Bipolarons
CHEN Qing-hu, REN Yu-hang, JIAO Zheng-kuan, ZHANG Qi-rui
Chin. Phys. Lett. 1997, 14 (8): 601-604 .  
Abstract   PDF(pc) (225KB) ( 435 )
A variational approach is presented to calculate the ground-state energy of large bipolarons in two and three dimensions. The values of the critical coupling constant αc above which the bipolaron is stable and the critical ratio of dielectric constants ηc below which the bipolaron is stable are approximately evaluated. It is found that the stability region of bipolarons in the (l/α, η )-plane becomes larger with decreasing dimensionality.
Absolute Instability in Superlattice Miniband Transport
LEI Xiao-lin
Chin. Phys. Lett. 1997, 14 (8): 605-608 .  
Abstract   PDF(pc) (274KB) ( 395 )
The possible absolute instability in superlattice miniband transport using the hydrodynamic balance equations for arbitrary energy dispersion is investigated. In contrast to the prediction of the drift-diffusion model that in doped semiconductor superlattices absolute instability occurs closely following the onset of negative differential mobility (NDM), the present analysis shows that a wide-miniband planar superlattice may become absolutely unstable only when it is biased deep in the NDM regime. This result is in agreement with recent experimental findings.
Effect of Growth Temperature on the Band Lineup of Ge/CdTe(111) Polar Interfaces
BAN Da-yan, FANG Rong-chuan, JI XUE Jian-geng, LU Er-dong, XU Peng-shou
Chin. Phys. Lett. 1997, 14 (8): 609-612 .  
Abstract   PDF(pc) (245KB) ( 413 )
By using synchrotron radiation photoelectron spectroscopy, the band lineup of Ge/CdTe (111) interfaces grown at different temperatures have been measured. Experimental studies show that the valence band offset of Ge/CdTe (111) interface grown at room temperature is 0.88 ± 0.1 eV, which agrees well with previously reported value. While as for the interface grown at 280°C, an obvious reduction of valence band offsets is observed and attributed to sthe effect of different interface dipole.
Effect of Oxygen-Diffusion Possibly Involved in Perovskite Unit on Superconductivity of Various Oxygen-Doped Bi2Sr2CaCu208+y Single Crystals
ZHAO Xiao-ru, SUN Xue-feng, WU Wen-bin, JIA Yun-bo, ZHOU Gui-en, LI Xiao-guang, ZHANG Yu-heng
Chin. Phys. Lett. 1997, 14 (8): 613-616 .  
Abstract   PDF(pc) (235KB) ( 387 )
For a highly oriented Bi2Sr2CaCu208+y single crystal with a lower as-grown Tc of 72K, on air-annealing at 250°C for 2h, its Tc remained unchanged, while increased to 83 K after annealing for 25 h. For another crystal with a higher as-grown Tc of 86.7K and annealed under the same condition, its Tc was unchanged except for a slight improvement of ΔTc and was independent of the annealing time. X-ray diffraction showed that there were no changes of c-axis lattice parameter for the annealed crystals. If the above two crystals, after annealing at 250°C for 25 h, were further annealed at 600°C for 20 h, then Tc was increased to the same value of almost 88K and the c-axis lattice parameter showed a dramatic contraction. We suggested that the improvement of superconductivity of the sample annealed at much lower annealing temperature (250°C ) are associated with the oxygen diffusion involved in the pervoskite unit and this diffusion from the perovskite unit occurs earlier than that from Bi-O layers.
Influence of Weak Self-Field Effect on Calculated Activation Energy for Superconducting Thin Film
XU Xiao-nong, SUN Ai-min, DING Shi-ying, JIN Xin, YAO Xi-xian, YAN Shao-lin, WEN Hai-hu
Chin. Phys. Lett. 1997, 14 (8): 617-620 .  
Abstract   PDF(pc) (182KB) ( 445 )
When the applied field Ba = μ0 Ha (Ha > Hp) is perpendicular to the surface of a disk-shaped superconducting thin film with the full penetrated field Hp, the radius R, and the thickness d, a quantitative relation between the average field < B > and the magnetization M is described by < B > = μ0 [Ha + (0.81 d/R) M] for R» d , where the term μ0(0.81 d/R) M also is the average self-field of the film. Combining this relation with the magnetic flux conservation equation and the Arrhenius relation, the effective activation energy is extracted from the experimental magnetization relaxation and the dynamic magnetization relaxation, respectively.
Fractal Formation in Sputtered Films of Bi2Sr2CaCU2O7-x on Si Substrates
LIU Rong, QIAN Wen-sheng, WEI Tong-li
Chin. Phys. Lett. 1997, 14 (8): 621-624 .  
Abstract   PDF(pc) (321KB) ( 421 )
Fractal regions appearing in BSCCO films after annealing have been investigated by atomic force microscopy and transmission electron microscope. The fractal dimensions and fractal density (number of fractals per unit area) are temperature dependent. At lower annealing temperature (450°C) both the morphologies and fractal dimensions closely resemble those arising in two dimensional diffusion-limited-aggregation (DLA) simulations. The observation results show that after annealing at 600°C or higher temperature, the fractal regions changed, even disappeared, which means the growth mechanism is very different from that of traditional DLA. A random diffusion and successive nucleation model has been proposed to explain the results.
Room Temperature Electron Spin Resonance of the Purified Carbon Nanotubes Produced in Different Helium Pressures
ZHANG Hai-yan, WANG Deng-yu, XUE Xin-min, HE Yan-yang, WU Ming-mei, PENG Shao-qi
Chin. Phys. Lett. 1997, 14 (8): 625-628 .  
Abstract   PDF(pc) (405KB) ( 521 )
The electron spin resonance(ESR) of purified carbon nanotubes prepared under different helium pressures from 20.0 to 80.0kPa in arc discharge has been measured. The dependence of the ESR spin density, linewidth and g value of the purified nanotubes on the helium pressure is found. The electronic properties of purified nanotubes varying with He pressure are discussed.
Photorefraction Resistance of Na2O-Doped Lithium Niobate Single Crystals
KONG Yong-fa, WEN Jin-ke, YANG Zheng-fang
Chin. Phys. Lett. 1997, 14 (8): 629-632 .  
Abstract   PDF(pc) (241KB) ( 367 )
Na2O-doped (up to 3mol% Na in the melt) LiNbO3 crystals have been grown by the Czochraski method. The experimental results show that Na2O dopants can increase the ability of LiNbO3 to resist light-induced optical damage, but the photorefraction of LiNbO3 : Na(3 mol%) is larger than that of LiNbO3 : Na (1 mol%) and the absorption edge of the former crystal has a longer wavelength compared with that of the latter. These two abnormal phenomena were interpreted as that some ilmenite structure (NaNbO3) regions are formed in doped LiNbO3 crystals with the increasing dopant concentration of Na2O.
Field Electron Emission from Highly Graphitic Diamond Films with Ball-Like Surface Morphologies
LI Yun-jun, YAO Ning, HE Jin-tian, ZHANG Bing-lin, GONG Zhi-ben
Chin. Phys. Lett. 1997, 14 (8): 633-636 .  
Abstract   PDF(pc) (291KB) ( 399 )
Chemical vapor deposited diamond films with ball-like surface morphologies for field electron emission are reported on Mo substrates. A transparent conducting thin film anode (indium-tin oxide film coated on glass substrate) technique was used to determine the locations of field emission sites on the film cathode. The emission site density was obtained by counting damage spots on the film anode by optical microscopy. These damage spots, caused by the impact of emission electrons, corresponded to the emission sites. With the ball-like diamond films, a low turn-on filed of 2.1 V/μm and high current density of 4 mA/cm2 from an emitting area of 0.3cm2 were obtained. A field enhancement model and injection mechanism have been developed to explain the low turn-on field and high emission current.

P-Type GaN Directly Grown by Low Pressure Metalorganic Vapor Phase Epitaxy
ZHANG Guo-yi, YANG Zhi-jian, TONG Yu-zhen, JIN Si-xuan, DANG Xiao-zhong, WANG Shu-min
Chin. Phys. Lett. 1997, 14 (8): 637-640 .  
Abstract   PDF(pc) (261KB) ( 585 )
P-type GaN was grown on AI3O2 substrate by low pressure metalorganic vapor phase epitaxy without any post treatment. The p-type conduction of as-grown GaN has the typical characteristics of a light-doped or high-compensation semiconductor, that is a hole concentration of 2.2 x 1017cm-3 at 77K, which changes to n-type with an electron concentration of 2.7 x 1017 cm-3 at room temperature. After thermal annealing under a N2 ambient, it showed the characteristics of a heavy-doped semiconductor and the hole concentration was enhanced reaching a hole concentrations of 4.2 x 1017 at 77K and 5.7 x 1017 cm-3 at room temperature.
20 articles