|
Resonance-Radiation Force Exerted by a Circularly Polarized Light on an Atomic Wave Packet
YE Yong-Hua, ZENG Gao-Jian, LI Jin-Hui
Chin. Phys. Lett. 2006, 23 (1):
13-16
.
We study the behaviour of an atomic wave packet in a circularly polarized light, and especially give the calculation of the radiative force exerted by the circularly polarized light on the atomic wave packet under the resonance condition. A general method of the calculation is presented and the result is interesting. For example, under the condition that the wave packet is very narrow or/and the interaction is very strong, no matter whether the atom is initially in its ground state or excited state, as time approaches to infinity, the resonance-radiation force exerted by the light on the atom approaches to zero. If the atom is initially in its ground state and excited state with the probability 1/2 respectively, and if the momentum density is a even function, then the resonance-radiation force exerted by the light on the atom is equal to zero.
|
|
Astrophysical Reaction Rates of the 8Li(p,\pmb \gamma)9Beg.s. Direct Capture Reaction
SU Jun, LI Zhi-Hong, GUO Bing, LIU Wei-Ping, BAI Xi-Xiang, ZENG Sheng, LIAN Gang, YAN Sheng-Quan, WANG Bao-Xiang, WANG You-Bao
Chin. Phys. Lett. 2006, 23 (1):
55-57
.
Based on the angular distribution of the 8Li(d,n)9Beg.s. reaction at Ec.m.=8.0MeV and distorted wave Born approximation analysis, the single particle spectroscopic factor S1,3/2 for the ground state of 9Be = 8Li otimes p is derived to be 0.64 ± 0.21. In addition, we deduce the astrophysical S-factors and rates of the 8Li(p,γ)9Beg.s. direct capture reaction at energies of astrophysical interests.
|
|
First Principles Study on NaxLi1-xFePO4 As Cathode Material for Rechargeable Lithium Batteries
OUYANG Chu-Ying, WANG De-Yu, SHI Si-Qi, WANG Zhao-Xiang, LI Hong, HUANG Xue-Jie, CHEN Li-Quan
Chin. Phys. Lett. 2006, 23 (1):
61-64
.
The electronic structure and ionic dynamic properties of pure and Na doped (Li site) LiFePO4 have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of the undoped one, indicating of better electronic conductive properties. First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion. The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway, indicating that the ionic conductive property is also improved, as compared with the high valance doping (such as Cr) cases.
|
|
A Method for Determining the Phase Transition Point of the Bose--Einstein Condensation by Judging the Fitting Errors
MA Xiu-Quan, CHEN Shuai, YANG Fan, XIA Lin, ZHOU Xiao-Ji, WANG Yi-Qiu, CHEN Xu-Zong,
Chin. Phys. Lett. 2006, 23 (1):
79-82
.
In this paper, We demonstrate an approach to determine the phase transition point and critical temperature of Bose-Einstein condensation. During the fitting sequence of time-of-flight images, for just one picture we take four kinds of different calculations instead of only one. By calculating the quantitative least-square errors, which have always been neglected before, we find out that this value can act as a criterion to judge the status of atom clouds. Using this criterion, we can not only discriminate the status around the phase transition point, but can also find the critical point precisely. Also with this method, we can achieve the totally automatical running of calculating programs without human's judgments.
|
|
Multi-Electron Processes in 13C6+ Ions with Neon Collisions in Energy Region 4.15--11.08keV/u
RUAN Fang-Fang, CAI Xiao-Hong, YU De-Yang, LU Rong-Chun, SHAO Cao-Jie, LU Jun, CUI Ying, SHAO Jian-Xiong, XU Xu, ZHANG Hong-Qiang, DING Bao-Wei, YANG Zhi-Hu, CHEN Xi-Meng
Chin. Phys. Lett. 2006, 23 (1):
95-98
.
The cross-section ratios of double-, triple-, quadruple-, and the total multi-electron processes to the single electron capture process (σDE/σSC, σTE/σSC, σQE/σSC and σME/σSC as well as the relative ratios among reaction channels in double-electron active, triple-electron active and quadruple-electron active are measured in 13C6+--Ne collision in the energy region of 4.15--11.08keV/u by employing position-sensitive and time-of-flight coincident techniques. It is determined that the cross-section ratios σDE/σSC, σTE/σSC, σQE/σSC and σME/σSC are approximately the constants of 0.20±0.03, 0.16±0.04, 0.06±0.02 and 0.42±0.05. These values are obviously smaller than the predictions of the molecular Coulomb over-the-barrier model (MCBM) [J. Phys. B 23 (1990) 4293], the extended classical over-the-barrier model (ECBM) [J. Phys. B 19 (1986) 2925] and the semiempirical scaling laws (SL) [Phys. Rev. A 54 (1996) 4127]. However, the relative ratios among partial processes of DE, TE and QE are found to depend on collision energy, which suggests that the collision dynamics depends on the collision velocity. The limitation of velocity-independent character of ECBM, MCBM and SL is undoubtedly shown.
|
|
Nonparaxial Dark-Hollow Gaussian Beams
GAO Zeng-Hui, LÜ, Bai-Da
Chin. Phys. Lett. 2006, 23 (1):
106-109
.
The concept of nonparaxial dark-hollow Gaussian beams (DHGBs) is introduced. By using the Rayleigh--Sommerfeld diffraction integral, the analytical propagation equation of DHGBs in free space is derived. The on-axis intensity, far-field equation and, in particular, paraxial expressions are given and treated as special cases of our result. It is shown that the parameter f =1/kw0 with k being the wave number and w0 being the waist width determines the nonparaxiality of DHGBs. However, the parameter range, within which the paraxial approach is valid, depends on the propagation distance. The beam order affects the beam profile and position of maximum on-axis intensity.
|
|
High Efficiency Pulse Acetone Liquid Raman Laser Using DCM Fluorescent Dye as the Enhancement Medium
CHENG Andrew Yuk-Sun, YANG Jing-Guo, CHAN Mau-Hing
Chin. Phys. Lett. 2006, 23 (1):
135-138
.
Pumped by a frequency-doubled Nd:YAG laser, 10-Hz repetition rate, 320-mJ pump energy, and 5.1-ns pulse width, a liquid Raman laser using acetone as the Raman shifting medium has been established. The residual pump laser pulse and the generated Stokes pulse are directed to a DCM dye cell for energy enhancement of the Stokes pulse. The Raman laser system is capable to produce a laser pulse at wavelength 630nm, with single pulse energy of 120mJ, peak power of 70MW and an average power of 1200mW. The energy conversion efficiency is 37.5%, or equivalently a quantum efficiency of 44.5%.
|
|
Effects of Flow Rate Variation on SiCln (n<3) Densities in SiCl4 Plasmas
WANG Zhao-Kui, LIN Kui-Xun, LIN Xuan-Ying, LOU Yan-Hui, ZHU Zu-Song
Chin. Phys. Lett. 2006, 23 (1):
169-171
.
Radicals produced by the plasma enhanced chemistry vapour deposition technique in SiCl4 plasma are identified by mass spectrometry using our newly proposed straight-line fit method. Since flow rate is one of the most important parameters in depositing thin films, we present the effects of SiCl4 flow rate variation on SiCln (n<3) densities. The experimental results demonstrate that Si and SiCln (n=1,2) densities decrease with increasing SiCl4 flow rate. After reaching the minimum values at a flow rate of 17 and 13sccm, respectively, Si and SiCln (n=1,2) densities slightly increase with further increase of flow rate to 20.5sccm. These results could be interpreted to which the depletion fraction of SiCl4 decreases and the residence time of SiCl4 molecule becomes shorter, with the increasing SiCl4 flow rate. In order to obtain high-quality poly-Si films with high growth rate, it is better to use smaller flow rate of SiCl4 source gas for depositing films.
|
|
Relaxation of Dense Electron Plasma Induced by Femtosecond Laser in Dielectric Materials
SUN Quan, JIANG Hong-Bing, LIU Yi, ZHOU Yong-Heng, YANG Hong, GONG Qi-Huang
Chin. Phys. Lett. 2006, 23 (1):
192-192
.
Electron plasma induced by a focused femtosecond pulse (130fs, 800nm) in dielectric materials (Soda Lime glass, K9 glass, and SiO2 crystal) is investigated by pump-probe shadow imaging technology. The relaxation of the electron plasma in the conduction band is discussed. In SiO2 crystals, a fast self-trapping process with a trapping time of 150fs is observed, which is similar to that in fused silica. However, in Soda Lime glass and K9 glass, no self-trapping occurs, and two decay processes are found: one is the energy relaxation process of conduction electrons within several picoseconds, another is an electron-hole recombination process with a timescale of 100ps. The electron collision time τ in the conduction band is also measured to be in the order of 1fs in all of these materials.
|
|
Monte Carlo Simulation of Magnetization Behaviour of Co Nanowires
ZHONG Ke-Hua, HUANG Zhi-Gao, FENG Qian, JIANG Li-Qin, YANG Yan-Min, CHEN Zhi-Gao
Chin. Phys. Lett. 2006, 23 (1):
200-203
.
Based on the Monte Carlo method, we simulate the magnetization curves with various magnetic field orientations for various single Co nanowires at room temperature. The simulated switching field as a function of angle θ between the field and the wire axis is consistent well with the experimental data. Correspondingly, the coercivity as a function of angle θ is presented, which together with the switching field plays an important role on explaining the magnetic reversal mechanism. It is found that the angular dependence of coercivity depends on the diameter of nanowires, and the coercivity and switching field versus θ deviate markedly from the prediction from the classical uniform rotation mode in the chain-of-sphere model. Furthermore, the magnetic reversal configurations display that magnetization reversal in the wires with small diameters is a nucleation-propagation process, and it is similar to the curling spread process in the larger wires.
|
|
Studies of Spectroscopic Ellipsometry in Cd1-xMnxTe/CdTe Superlattices
CHEN Chen-Jia, WANG Xue-Zhong, Vittorio BELLANI, Angiolino STELLA
Chin. Phys. Lett. 2006, 23 (1):
207-210
.
Cd1-xMnxTe/CdTe superlattices and thin films were grown by molecular beam epitaxy on GaAs (001) substrates. Spectroscopic ellipsometry measurements were performed on Cd1-xMnxTe/CdTe superlattices with compositions x=0.4, 0.8, and Cd1-xMnx thin films with x=0.2, 0.4, 0.6 at room temperature in the photon energy range 1.4--5eV. In superlattices the pseudodielectric functions measured by ellipsometry show specific features related to the exciton transition between quantized interbands. The exciton transitions related to the heavy holes of 11H, 22H, and 33H are observed and identified. In thin films spectroscopic ellipsometry allows the clear identification of the energy gap E0. Additionally, critical point transitions are observable in both the spectra of the superlattices and films. Photoreflectance spectra were also performed at room temperature in order to compare with our ellipsometry results. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with our experimental spectra. Ellipsometry appears to be a suited technique to monitor the MBE growth, ultimately also in situ, of diluted magnetic low-dimensional systems.
|
|
Grow Large High-Quality Diamonds with Different Seed Surfaces
ZANG Chuan-Yi, JIA Xiao-Peng, MA Hong-An, LI Shang-Sheng, TIAN Yu, XIAO Hong-Yu
Chin. Phys. Lett. 2006, 23 (1):
214-216
.
Large high-quality type Ib diamond crystals have been grown with different seed surfaces by temperature gradient method at 5.5GPa, 1500--1600K, with NiMnCo alloy as the metal solvent. Compared with {100} as the growth surface, the growth region of large high-quality diamond crystals with {111} as the growth surface at a higher growth rate shifts markedly from lower temperatures (suitable for {100}-facet growth) to higher temperatures (suitable for {111}-facet growth). However, regardless of different growth surfaces, {100} or {111}, the grown crystals of sheet-shaped shape are most difficult for metal inclusions to be trapped into, and whether or not matched growth between the seed surfaces and the growth temperatures determines the crystal shapes. In view of the growth rates, large high-quality diamond crystals of sheet-shaped shapes can be grown at a growth rate of above 2.5mg/h, while the growth rate of large high-quality diamond c
|
|
Agglomeration Evolution of Nano-Particles Aluminium in Normal Incident
YAN Zheng-Xin, WU Jing-He, HU Dong, YANG Xiang-Dong
Chin. Phys. Lett. 2006, 23 (1):
217-219
.
Agglomeration behaviour of nano-particle aluminium (nano-Al) in normal incident shock waves is investigated by our devised shock tube technology. The morphology, particle size, agglomeration process of nano-Al studied in normal incident shock waves are comprehensible evaluated by x-ray diffraction, transmission electron microscopy and scanning electron microscopy. The above-mentioned techniques show that the high strength and temperature of incident shock wave give a chance for activity of nano-Al in the reactions and decrease the agglomeration, and the morphology of agglomeration is affected by the temperature of nano-Al reaction region. The dynamic temperature of reaction region determined by the intensity ratio of two AlO bands is 2602K, which is closer to nano-Al actual reacted temperature than the determined temperature of ordinary methods (i.e. six channel instantaneous optical pyrometer; plank black body radiation law, etc.)
|
|
A New Type of Terahertz Waveguides
LOU Shu-Qin, GUO Tie-Ying, FANG Hong, LI Hong-Lei, JIAN Shui-Sheng
Chin. Phys. Lett. 2006, 23 (1):
235-238
.
A new type of THz waveguides, which employs a solid polyethylene rod as the core and polyethylene tubes in a periodic array of square lattice as the cladding, is proposed. Optical properties of this new THz waveguide, especially in dispersion, confinement loss and single mode property, are investigated in detail with the plane wave expansion method and the beam propagation method. Numerical results demonstrate that the new THz waveguide can reach not only low dispersion but also low confinement loss at single mode propagation. Therefore, the square lattice structure is a better candidate as THz waveguides than the triangular ones.
|
|
Fast Theoretical Simulation for Design of Helical Flux Compression Generators
YANG Xian-Jun, DONG Zhi-Wei
Chin. Phys. Lett. 2006, 23 (1):
249-251
.
A theoretical scheme is derived to achieve the numerical simulation of helical flux compression generator (HFCG) design, by which not only any physical approximation is not made, but also numerical simulation can be fast obtained. In particular, an analytic formula to calculate the inductance is deduced, which is extremely close to the experimental results. The physical process of relevant interesting physical quantity, such as inductance, enlarging current, and magnetic flux density, can be calculated to compare with the experimentally quantitative results.
|
|
Stability of Random Networks under Evolution of Attack and Repair
CHI Li-Ping, YANG Chun-Bin, CAI Xu
Chin. Phys. Lett. 2006, 23 (1):
263-266
.
With a simple model, we study the stability of random networks under the evolution of attack and repair. We introduce a new quantity, i.e. invulnerability I(s), to describe the stability of the system. It is found that the network can evolve to a stationary state. The stationary value Ic has a power-law dependence on the initial average degree , with the slope about -1.5. In the stationary state, the degree distribution is a normal distribution, rather than a typical Poisson distribution for general random graphs. The clustering coefficient in the stationary state is much larger than that in the initial state. The stability of the network depends only on the initial average degree , which increases rapidly with the decrease of .
|
|
Influence of Hyperon on 1S0 Superfluidity of Nucleons in Neutron Star Matter
CHEN Wei, LAM Yu-Yiu, WEN De-Hua, LIU Liang-Gang
Chin. Phys. Lett. 2006, 23 (1):
271-274
.
We investigate the property of 1S0 superfluidity of neutrons and protons in the neutron star matter. On the basis of the result, we study the effects of hyperons on the 1S0 pairing gaps of the two species of the particles. The parameter sets we use are for the Hartree approximation of the relativistic σ-ω model and the mean field approximation of the Walecka model, respectively. The predicted domain of superfluidity is very close to other works, whereas differences appear in the predicted value of the maximum gap. It is found that Σ-, Λ and Ξ- have some influences, the scales of which depend on hyperon-meson coupling constants we use besides other factors, on the 10 superfluidity of protons in some density range, and do not have influence on superfluidity of neutrons. Other hyperons have no influence on the 1S0 superfluidity of neutron and proton due to these hyperons appearing after 1S0 neutron and proton pairs disappear.
|
78 articles
|