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Vol. 54, No. 10 (2005)

2005-05-20
GENERAL
A meshless method with complex variables for elasticity
Cheng Yu-Min, Li Jiu-Hong
2005, 54 (10): 4463-4471. doi: 10.7498/aps.54.4463
Abstract +
The moving least-square approximation with complex variables (MLSCV) is developed on the basis of moving least-square approximation. The advantages of MLSCV are that the approximation function of a 2-D problem is formed with 1-D basis function, and the meshless method obtained has greater computational efficiency. A meshless method with complex variables for 2-D elasticity is then presented using MLSCV, and the formulae of the meshless method with complex variables are obtained. Compared with the conventional meshless method, the meshless method with complex variables introduced in this paper has greater precision and computational efficiency. Some examples are given.
Exact solutions of nonlinear Shr?dinger equations
Pu Li-Chun, Lin Zong-Bing, Zhang Xue-Feng, Wang Ben-Ju, Jiang Yi, Yan Tian-Yan
2005, 54 (10): 4472-4477. doi: 10.7498/aps.54.4472
Abstract +
A Maple language process is utilized to find the traveling wave accurate solutions and their restricting condition equation for nonlinear Schrdinger equations with coupling characteristic without any assumptions. The expressions are arbitrary and cover all coupling solutions and non-coupling solutions. The calculation and characteristic analysis for the coupling solutions can explain the coupling effect of traveling wave solition solutions of the helix chain movement model for the alpha-helix protein and reveal the direction in which the protein activation and function are increased and fixed. The research methods in this paper provide certain ways for obtaining the traveling wave accurate solutions of the coupling nonlinear differential equations.
Simulation of x-ray transmission through a capillary
Wu Peng-Ju, Li Yu-De, Lin Xiao-Yan, Liu An-Dong, Sun Tian-Xi
2005, 54 (10): 4478-4482. doi: 10.7498/aps.54.4478
Abstract +
A ray-tracing theory for the X-ray transmission in a capillary is described based on which a calculation model is built. The transmission efficiency and intensity distribution curve through a capillary are numerically calculated. The simulation results are in good agreement with the experimental results and previous simulations.
Higher order Lagrange equations of holonomic potential mechanical system
Zhang Xiang-Wu
2005, 54 (10): 4483-4487. doi: 10.7498/aps.54.4483
Abstract +
First, the theorem on energy of higher order velocity of the holonomic potential mechanical system is presented with on explaining of the physical meaning of energy of higher order velocity of the system. The general criterion of potential mechanical system is then presented. On this basis, the higher order Lagrange function is introduced,the higher order Lagrange equations of holonomic potential mechanical system are derived, and the higher order cyclic integral and the integral of higher order generalized energy of the system are obtained.
Symmetries and conserved quantities of mechanical systems with unilateral holonomic constraints in phase space
Zhang Yi
2005, 54 (10): 4488-4495. doi: 10.7498/aps.54.4488
Abstract +
The symmetries and conserved quantities of mechanical systems with unilateral holonomic constraints in extended phase space is studied. The differential equations of motion of the systems are established. The criterions of Noether symmetry, Lie symmetry and Mei symmetry are given, and the relations between the symmetries are researched. The Noether conserved quantity and two types of new conserved quantities, called the Hojman quantity and Mei quantity, for the systems are obtained, and intrinsic relations between the three symmetries and three types of conserved quantities are researched. An example is given to illustrate the application of the results.
The ideal velocity field of ship waves on a viscous fluid
Wu Yun-Gang, Tao Ming-De
2005, 54 (10): 4496-4500. doi: 10.7498/aps.54.4496
Abstract +
The method used by Ursell to solve the problem of ship waves on an inviscid fluid is extended to the viscous case and the ideal velocity filed is deduced. The singularity on two critical lines deduced by employing the steepest descent method to get the asymptotic expression of integral is eliminated. It is convenient for use in the SAR technique.
Abundant Jacobi elliptic function solutions of nonlinear evolution equations
Lü Da-Zhao
2005, 54 (10): 4501-4505. doi: 10.7498/aps.54.4501
Abstract +
In this paper, the twelve Jacobi elliptic functions are divided into four groups, and a new general Jacobi elliptic function expansion method is proposed to construct abundant doubly periodic Jacobi elliptic function solutions of nonlinear evolution equations. By this method, many exact doubly periodic solutions are obtained which shows the powerfulness of this method. When the modulus m→1 or 0, these solutions degenerate to the corresponding solitary wave solutions, shock wave solutions or trigonometric function (singly periodic) solutions.
Using trial equation method to solve the exact solutions for two kinds of KdV equations with variable coefficients
Liu Cheng-Shi
2005, 54 (10): 4506-4510. doi: 10.7498/aps.54.4506
Abstract +
Trial equation method was applied to nonlinear evolution equations with variable coefficients. As examples, exact solutions for two kinds of KdV equations with variable coefficients were obtained. Some of these results were new.
Characteristics of the band structure in two-dimensional phononic crystals with complex lattices
Zhao Fang, Yuan Li-Bo
2005, 54 (10): 4511-4516. doi: 10.7498/aps.54.4511
Abstract +
The band structure of two-dimensional phononic crystals with complex lattices is analyzed using the plane-wave algorithm in this paper. Phononic crystals composed of two-dimensional arrays of periodic aluminium alloy cylinders in air are calculated. Band structures of two types of complex lattices, the honeycomb and the Kagome lattices, are presented. The band structures of complex lattices and simple lattices are compared. It is concluded that compared with simple lattices, the band-gap of complex lattices are located at lower frequency fields. When the filling fraction is between 0.091 and 0.6046, the complex lattices have larger band gaps and gain an advantage over simple lattices. In addition, the gap map is introduced to illustrate the influences of the filling fraction on the number, the width and the limit frequency of the band-gap.
General WGHZ state and its disentanglement and probabilistic teleportation
Liu Min, Huang Yong-Chang
2005, 54 (10): 4517-4523. doi: 10.7498/aps.54.4517
Abstract +
A general WGHZ state is given, different entanglement W states are deduced by means of the general WGHZ state, different disentanglement conditions are obtained. When taking different complex coefficients of the general WGHZ state as zero, there are different disentanglements, and different W states and different Bell basic vectors are achieved. The above disentanglement results agree with the results obtained from the usual disentanglement condition of decomposable property of density matrices. By constructing a 5×5 diagonal projection transformation matrix, the problem of the recovery of state distortion is salved when using general entanglement channels and not introducing an accessorial state, and the diagonal projection transformation matrix UM is different to that of the other references and is a direct transformion matrix. Furthermore, the problem of probabilistic teleportation of a general WGHZ state is solved without introducing an accessorial state using the general entanglement channels. The diagonal projection transformation matrix method developed in this paper may be directly generalized to probabilistic teleportation of general entanglement states.
Discussion on the transformation property between the configuration wavefunction of the equivalent-electron and the Young tableau
Hu Kun-Ming
2005, 54 (10): 4524-4525. doi: 10.7498/aps.54.4524
Abstract +
The transformation property between the configuration wavefunction of the equivalent-electron and the Young tableau is pointed out to be unitary but not to be Hermite unitary. And a sign error of the spectrum item wavefunction is presented.
Quantum fluctuation in the time-dependent linearly driven degenerate parametric amplification
Zhao Chao-Ying, Tan Wei-Han
2005, 54 (10): 4526-4531. doi: 10.7498/aps.54.4526
Abstract +
A systematic theory of quantum fluctuation in the time-dependent linearly driven parametric amplification is developed. At first, a time-dependent linearly driven Fokker-Planck equation for the degenerate optical parametric amplification system is deduced when the pump depletion is considered, and then the quantum fluctuation below or near the threshold is evaluated, which is in agreement with that obtained by the linear theory or perturbation expansion near the threshold. Above the threshold, the short-time behavior of our solution is close to the linearization approximation; however, with the increase of interaction time τ, the long-time behavior of our solution shows that the squeezing is quite different from the linear theory.
The dynamical mechanism of A-B effect and its testing scheme
Wang Rui-Feng
2005, 54 (10): 4532-4537. doi: 10.7498/aps.54.4532
Abstract +
The dynamical mechanism of A-B effect is discussed in detail. It is found that A-B effect is due to the superposition of the magnetic field produced by the moving charges with that in the solenoid, rathor than the existence of vector potential A. If such a magnetic field superposition can be prevented, the A-B effect will disappear, even though the vector potential A still exists in space. To verify this conclusion, a new experimental scheme is suggested.
Spectra analysis of the two-dimensional elliptic billiards
Xu Xue-You, Zhang Yan-Hui, Huang Fa-Zhong, Lin Sheng-Lu, Du Meng-Li
2005, 54 (10): 4538-4542. doi: 10.7498/aps.54.4538
Abstract +
The correspondence between the quantum spectra and the classical orbits of the two-dimensional elliptic billiards is investigated. In order to study systems without analytic solutions in the future, an expansion method for stationary states (EMSS) to get highly accurate numerical solutions is applied and tested. The closed-orbit theory was extended to the open orbit case. By comparing the Fourier-transformed spectra with the classical orbits, we find that the peak positions in the quantum spectra match with the lengths of the classical orbits with small numerical differences. This is another example showing that semiclassical method provides a bridge between quantum and classical mechanics.
Series solution for relative-rotation motion equation
Zhao Wu, Liu Bin
2005, 54 (10): 4543-4548. doi: 10.7498/aps.54.4543
Abstract +
For solving the difficult calculation problem of nonlinear differential equation of motion of complex revolving shaft in relative rotation , a new decoupled equation was proposed by using series method, which expands the nonlinear differential equation into a series of algebraic equations and the series solution is obtained. Based on the result of the research , the veracious speed fluctuation of revolving shaft in relative rotation in practice can be calculated for the steady state. The method also provides a technology for error detachment of measuring apparatus calibration and a highly effective algorithm for torsional vibration real-time on-line monitor of heavy-duty and complex revolving shaft.
Eigenvalues of volume and area in the spin network representation
Shao Chang-Gui, Chen Yi-Han, Ma Wei-Chuan, Shao Dan, Shao Liang
2005, 54 (10): 4549-4555. doi: 10.7498/aps.54.4549
Abstract +
By antisymmetrizing the action of grasp and binor identity, it is proved that the spin network states of 3-valent and any-valent are the eigenstates of the volume operator and the area operator, respectively. The formulas 2-32l3p∑ipσpτpρ and 2-1l2p∑jpl(j) for calculating the eigenvalue spectrums of volume and area, respectively, are obtained.
Influence of the ingot solidification microstructure on the formation kinetics of icosahedral quasicrystalline phase during the crystallization of the corresponding amorphous alloy
Tong Yu-Quan, Shen Bao-Cheng, Gan Yu-Sheng, Yan Zhi-Jie
2005, 54 (10): 4556-4561. doi: 10.7498/aps.54.4556
Abstract +
Zr65Al7.5Cu12.5Ni10Ag5 ingots with different solidification microstructures are obtained by repeated arc melting of origin ingots. Under the same conditions, slices of amorphous alloys can be produced by suction casting in a copper mold. Differential scanning calorimetry (DSC) is employed to investigate the crystallization kinetics of the amorphous alloys. X-ray diffraction patterns (XRD) show that icosahedral quasicrystalline phase (I-phase) precipitates as primary phase during the crystallization of Zr65Al7.5Cu12.5Ni10Ag5 amorphous alloys. The results of Kissinger analyses suggest that the amorphous alloys made from the ingot with finer microstructure show better thermal stability, and that the I-phase precipitated becomes more stable against decomposition. Within the frame of structure heredity, the influence of ingot microstructure on the formation kinetics of I-phase during the crystallization of corresponding amorphous alloys is discussed.
One-way Hash function construction based on two-dimensional hyper-chaotic mappings
Peng Fei, Qiu Shui-Sheng, Long Min
2005, 54 (10): 4562-4568. doi: 10.7498/aps.54.4562
Abstract +
The design of an efficient one-way Hash function with good performance is a hot spot in modern cryptography researches. In this paper, a Hash function construction method based on two-dimensional hyper-chaotic mappings is proposed. The initial values of the two-dimensional hyper-chaotic system come from the chaotic sequence, produced by a series of operations including chaotic mappings and linear transformation based on the plain text, and then modulates the signals resulting from the iteration of the hyper-chaotic system to construct a one-way Hash function. Simulation and analysis demonstrate that the new method has the merit of convenience, high sensitivity to initial values, good Hash performance, weak collision property, and better security.
On the prediction of chaotic time series using a new generalized radial basis function neural networks
Li Jun, Liu Jun-Hua
2005, 54 (10): 4569-4577. doi: 10.7498/aps.54.4569
Abstract +
Radial basis function (RBF) networks have been widely used for function approximation and pattern classification as an alternative to conventional feedforward neural networks. A novel generalized RBF neural network model is presented. The form of RBF is determined by a generator function, and then an easily implementable gradient decent learning algorithm for training the new generalized RBF networks is given. Simultaneously, a fast dynamic learning algorithm based on Kalman filter is also proposed to improve the performance and accelerate the convergence speed of the new generalized RBF networks. The generalized RBF neural networks based on Kalman filtering dynamic learning algorithm is then applied to the chaotic time series prediction on the Mackey-Glass equation and the Henon map to test the validity of this proposed model. Simulation results show that the new generalized RBF networks can accurately predict chaotic time series. It provides an attractive approach to study the properties of complex nonlinear system model and chaotic time series.
Adaptive multi-variable generalized predictive control and synchronization of chaotic systems
Dong En-Zeng, Chen Zeng-Qiang, Yuan Zhu-Zhi
2005, 54 (10): 4578-4583. doi: 10.7498/aps.54.4578
Abstract +
This paper presents a β type multi-variable generalized predictive control method for control and synchronization of chaotic systems. Using this method, the chaotic Lorenz system, Rossler system and Chua's circuit system can be controlled to track the discretionary reference signal. The effectiveness of the proposed method is verified by numerical simulations. The advantages of the proposed method are that it can realize effective control and synchronization of chaotic systems without the knowledge of its precise model.
A fast algorithm for generalized predictive control and synchronization of Hénon chaotic systems
Liu Fu-Cai, Liang Xiao-Ming
2005, 54 (10): 4584-4589. doi: 10.7498/aps.54.4584
Abstract +
A kind of generalized predictive control and synchronization algorithm with terminal sliding model equation restriction for Hénon chaotic system is proposed. This algorithm combines the generalized predictive control with sliding-model control which has been applied to Hénon chaotic systems, and the soft coefficient to input signal, in which the inverse matrix does not require calculation. The method needs smaller computer memory and the computational speed is higher. The ability of tracking the reference signal and restraining the parameter perturbation and stochastic disturbance are improved. Simulated results show the effectiveness and speed of this algorithm.
Synchronization of a critical chaotic system with Lorenz system and Chen system
Ning Di, Lu Jun-An
2005, 54 (10): 4590-4595. doi: 10.7498/aps.54.4590
Abstract +
A nonlinear feedback controller is designed to make the first state of a new chaotic system track an arbitrary smooth reference signal at an exponential rate. In addition, Chaos synchronization between two different chaotic systems by using active control is presented. This technique is applied to achieve chaos synchronization between the critical system, Lorenz system and Chen system. Numerical simulations are madc to verify the results.
Optimization of scaled probabilistic cleaning methods
Jiang Ke-Yu, Cai Zhi-Ming
2005, 54 (10): 4596-4601. doi: 10.7498/aps.54.4596
Abstract +
The scaled probabilistic cleaning method is one of nonlinear noise reduction methods for chaotic time series, whose calculation quantity and needed memory volume increase exponentially with the number of reference points and the embedding dimension because of the joint processing of all data points in phase space. An optimized method, which modifies the estimation of forward probabilities and transition probabilities is proposed, and the computing workload is reduced to about 0.27 times that of the original method without degradation in noise reduction performance. The implementation of the method for the long time series also reduces the needed memory size.
A new scheme of suppression of spiral and spatiotemporal chaos in centric field
Pu Zhong-Sheng, Feng Wang-Jun, Li Wei-Xue, Ma Jun
2005, 54 (10): 4602-4609. doi: 10.7498/aps.54.4602
Abstract +
Suppression of spiral in centric field is investigated. The spiral is suppressed by circumrotating the system with mechanical force. It is the first time spiral is supressed and spatiotemporal chaos dispelled using this scheme. The Fitzhugh-Nagumo equation and Panfilov equation are investigated, and numerical simulation shows that the scheme is effective and robust to certain white noise.
Bifurcation of safe basins in softening Duffing oscillator under bounded noise excitation
Rong Hai-Wu, Wang Xiang-Dong, Xu Wei, Fang Tong
2005, 54 (10): 4610-4613. doi: 10.7498/aps.54.4610
Abstract +
The erosion of the safe basins of a softening Duffing oscillator under harmonic or bounded random noise is studied in detail using the Monte-Carlo method. As an alternative, stochastic bifurcation may be defined as a sudden change in the character of the stochastic safe basin when the bifurcation parameter of the system passes through a critical value. This definition applies equally well either to randomly perturbed motion, or to purely deterministic motion. It is found that random noise may destroy the integrity of safe basins and bring about stochastic bifurcation, hence make the system more unsafe.
The traffic flow of two-lane system with vehicle mixing
Tan Hui-Li, Kong Ling-Jiang, Liu Mu-Ren, Zheng Rong-Sen
2005, 54 (10): 4614-4620. doi: 10.7498/aps.54.4614
Abstract +
A cellular automaton model for two-lane traffic with vehicle mixing basing on the Nagel-Schreckenberg (NaSch) model is proposed. With different parameters, we simulated the traffic flow of the two-lane system when the vehicle densities of lanes are equal or different respectively. The fundamental diagrams of the traffic flow are given. According to the analysis, the traffic state could be divided into three regions.The nonsymmetry of car density on two lanes has important influence on the traffic flow.
Cellular automaton traffic flow model considering intelligent transportation system
Ge Hong-Xia, Dai Shi-Qiang, Zhu Hui-Bing
2005, 54 (10): 4621-4626. doi: 10.7498/aps.54.4621
Abstract +
A novel cellular automaton model for traffic flow on highway is proposed considering Intelligent Transportation System (ITS). Based on the Nagel-Schreckenberg model (NS for short), it includes effective gap and brake light. Moreover, a novel concept about the variable security gap is introduced. The simulation shows that the road capacity of the modified ITS cellular automaton model is higher than the measured data on certain highway, further indicating the important role of ITS,enlarged traffic flow and suppressed traffic jam. The mixed traffic flow related to two different vehicles' velocity is studied. The simulation shows even few slow vehicles will lead to drastic decrease of traffic flow, which demonstrates the necessity to implement strictly special fast lane.
Synthesis, characterization and properties of B0.44C0.27N0.29 compound
Su Wen-Hui, Bai Suo-Zhu, Yao Bin
2005, 54 (10): 4627-4632. doi: 10.7498/aps.54.4627
Abstract +
B-C-N compounds with different structures were synthesized by chemical reaction between Boracic acid and melamine, combined with heat treatment under vacuum and high pressure. An amorphous B-C-N precursor was prepared at 1273K under 10-3Pa. This amorphous B-C-N behaves as an insulator below 920K, and transforms into semiconductor above 920K. The B-C-N semiconductor shows different conductivity-temperature relationship in the temperature ranges of 973—1003K and 1013—1073K, and has conductivity activation energy of 0.34eV in the former range and 1.10eV in the latter range, indicating that conductivity mechanism of the B-C-N amorphous semiconductor is different in the two temperature ranges. Annealed for 40min. at 1473K under 3.5GPa, the amorphous B-C-N precursor crystallizes into hexagonal B0.44C0.27N0.29(h-BCN) compound with lattice constants of a=0.2515nm and c=0.6684nm. Four strong Raman scattering peaks were observed at 1330,1364,1588 and 1617cm-1 in the h-BCN, of which the peaks located at 1330 and 1617cm-1 are considered as characteristic Raman peaks of the h-BCN.
Optical absorption, Raman spectra and TEM study of Ag nanoparticles formed by ion implantation into a-SiO2
Liu Xiang-Fei, Ren Feng, Jiang Chang-Zhong, Fu Qiang
2005, 54 (10): 4633-4637. doi: 10.7498/aps.54.4633
Abstract +
Silver nanoparticles are formed by ion implantation into amorphous silica matrix at 200 keV at room temperature with doses of 1×1016, 5×1016 and 1×1017 cm-2. The sizes,distributions and shapes of the silver nanoparticles in the samples were obtained by transmission electron microscopy, which is greatly influenced by the dose. The effect of size,distribution and shape of the silver nanoparticles to the optical resonant absorption peak is been discussed. Optical absorption spectra of samples implanted with 5×1016 and 1×1017Ag+ cm-2 showed absorption peaks shifted to red, the intensity of absorption peak increased and shoulder peaks appeared, compared with the absorption spectra of the sample implanted with 1×1016Ag cm-2. The red-shift of absorption peaks and the appearance of shoulder peaks are due to the increasing volume factor and the multipolar plasmon induced by the interaction of nanoparticles, respectively. Raman scattering spectroscopy indicates that there are many defects in the high-dose implanted samples. Nanocavities in the large Ag nanoparticles are discovered in the sample with the dose of 1×1017 cm-2 possibly due to the aggregation of implant-induced silicon and oxygen atoms in Ag nanoparticles.
Experimental research on the sensitivity of wavelength modulation by signal processing
Yuan Yi-Qian, Shao Jie, Gao Xiao-Ming, Cao Zhen-Song, Yang Yong, Pei Shi-Xin, Zhang Wei-Jun
2005, 54 (10): 4638-4642. doi: 10.7498/aps.54.4638
Abstract +
We present a signal-processing system developed for enhancing the sensitivity of absorption measurement based on tunable diode laser wavelength modulation spectroscopy. A signal-to-noise ratio enhancement of an order of magnitude was observed when digital signal-processing algorithms were applied to wavelength modulation spectrometers in the near-infrared,at the same time a new spectra was found by observation of CO2 near 1.53 μm. These algorithms include digital low-pass filters, multiple averages, and a least squares fit. Digital signal processing has a practical advantage over other noise suppression techniques because it is easy to implement and adapt able to all experiments.
NUCLEAR PHYSICS
A high sensitive fission neutron detector system with a lead slot collimator
Huo Yu-Kun, Ouyang Xiao-Ping, Wang Qun-Shu, Li Zhen-Fu, Ma Yian-Liang, Zhang Qian-Mei, Zhang Guo-Guang, Jin Yu-Ren
2005, 54 (10): 4643-4647. doi: 10.7498/aps.54.4643
Abstract +
A fission neutron detector system with frontward-extended lead slot collimator has been developed and tested. By designing the slot collimator and developing large area PIN detectors as well as large area fissionable target with thin Be backing, this detector system can reach high neutron sensitivities up to 10-16C·cm2, which is about 4-5 orders of magnitude higher than that of existing fission detectors,and high n/γ discrimination ratio up to 30.
ATOMIC AND MOLECULAR PHYSICS
Calculation of the transition spectra of sodium atom via TDDFT
Gu Bin, Jin Nian-Qing, Wang Zhi-Ping, Zeng Xiang-Hua
2005, 54 (10): 4648-4653. doi: 10.7498/aps.54.4648
Abstract +
The time dependant density functional theory(TDDFT) and local density approximation (LDA) are used to calculate the transition spectra of sodium atom. Several excited energy levels of valence-electron and the corresponding electronic wave function distribution are calculated in detail. The characteristic transition Rydberg series spectra of sodium are given. The calculated results agree with the experiment data very well, which is a good evidence for the applicability of TDDFT to the description of the excited system.
Temperature measurement from the Raman spectra of porous silicon
Bai Ying, Mo Yu-Jun, Lan Yan-Na
2005, 54 (10): 4654-4658. doi: 10.7498/aps.54.4654
Abstract +
Raman spectra of porous silicon are obtained using 457.5nm laser line, from which some relations between peak parameters and laser powers are obtained. Our previous theoretical research demonstrated that the increase of laser power leads to the increase of local temperature, and this results in the shrink of local size which gives rise to the variation of a series of peak parameters. In this article we discuss and calculate in detail the influence of laser power on the local temperature of porous silicon, which set the experimental basis for the quantitative measurement of temperature utilizing Raman spectrum.
A novel beam-splitter for surface wave-guided atoms or molecules
Yin Jian-Ping, Ji Xian-Ming
2005, 54 (10): 4659-4665. doi: 10.7498/aps.54.4659
Abstract +
We propose a new scheme to form a surface Y- or X-shaped beam splitter for optically wave-guided atoms (or molecules) and its Mach-Zehnder interferometer by using the combination of a binary π phase plate and a micro-cylindrical lens. The physics idea and basic principle of our beam splitter are introduced, and the analytic relationships between the intensity distribution (or the intensity gradient, or the splitting distance, and splitting-path width) and the parameters of our optical system are derived and discussed. The potential applications of the beam splitter and its experimental feasibility are discussed. Our study shows that the design is novel and the scheme is simple, and it can be used to construct various integrated atom- (or molecule-) optical elements with surface micro-structures, and even to form some all-optically integrated atom (or molecular) chips.
Study of 46.8MeV p+12C inelastic scattering
Gu Yun-Ting, Feng Lu-Yan, Tao Jun-Quan, Huang Tian-Heng, Luo Chun, Ma Wei-Xing
2005, 54 (10): 4666-4668. doi: 10.7498/aps.54.4666
Abstract +
The inelastic scattering of 46.8MeV antiproton by 12C leading to the excitation of one normal parity T=0 levels is studied in the framework of Glauber model. The transition densities obtained from fitting to the electron scattering data and the three annihilation potentials derived from analysis of p—p scattering data are used in the calculation. The inelastic angular distribution for exciting the lowest normal parity T=0 states in 12C at 4.44MeV (Jπ=2+) by 46.8MeV antiproton are calculated by selecting potential parameter suitably. The results are seen to be in fairly good agreement with the available experimental data. The results are given by comparing the elementary two-body amplitudes.
EMS investigation of inner valance orbital 1a" for butanone
Li Gui-Qin, Deng Jing-Kang, Li Bin, Ren Xue-Guang, Ning Chuan-Gang, Zhang Shu-Feng, Su Guo-Lin
2005, 54 (10): 4669-4672. doi: 10.7498/aps.54.4669
Abstract +
The binding energy and the spherically averaged momentum distributions of orbital 1a″for butanone have been investigated by high resolution electron momentum spectroscopy (ΔE=1.15eV, Δp=0.1a.u.). The impact energy was 1200eV plus binding energy (i.e. 1206—1242eV) and symmetric non-coplanar kinematics was employed. The experimental binding energy spectra have been compared with published photoelectron spectra. The momentum profile of 1a″ orbital has been compared on a quantitative basis with theoretical calculations using Hartree-Fock method and Density Functional Theory. The position density and momentum density for 1a″ orbital are presented.
Theoretical study of cross sections of excitation and ionization for electron-ion impact in average-atomic model
Tian Ming-Feng, Meng Xu-Jun, Zhu Xi-Rui, Jiang Min-Hao, Wang Zhi-Gang
2005, 54 (10): 4673-4679. doi: 10.7498/aps.54.4673
Abstract +
By using a distorted-wave Born exchange approximation method in averaged-atomic model, we calculated the direct excitation and direct ionization cross sections of several ions in plasmas. The ionization cross sections of ions at different temperatures or different plasma densities are systematically studied. It is found that due to the shift of the energy levels produced by the effects of the temperature and the density of plasma, the ionization cross sections of ions in plasmas are rather different from those of free atoms.
Electronic structure of the surface of LaNi5 crystal
Lin Shao-Jie, Zheng Hao-Ping
2005, 54 (10): 4680-4687. doi: 10.7498/aps.54.4680
Abstract +
The spin-polarized, all-electron, full-potential ab initio calculations have been performed for the electronic structure of the surface of LaNi5 crystal using the self-consistent cluster-embedding (SCCE) calculation method. The geometrical surface structure of LaNi5 crystal and its electronic structure having lowest ground-state energy are obtained, with the full relaxation of atomic positions along the direction perpendicular to the surface. On the surface of LaNi5 crystal, it is found that the La atom protruded out, and the Ni atoms caved in, so the surface becomes uneven which increases the contacting area with the hydrogen. The effective volume of the surface layer rises by 9%, which is in favour of the absorption of hydrogen. The Fermi level of the surface of LaNi5 crystal, which is made mainly of the 3d electrons of Ni,is much higher than that of body LaNi5. The valence band is not fully filled, which shows the metallic property. For the first two layers of the surface of LaNi5 crystal, there are 1.15 electrons transferred from La to Ni, and the two layers have small opposite spin magnetic moments which shows the paramagnetism. The density of state (DOS) of the valence band is obtained. The ionization potential and the electron affinity are calculated by the transition-state mathod. All calculated results show that although the properties of the surface of LaNi5 crystal are significantly different from that of body LaNi5, they are very similar to that of hydride LaNi5H7, so the structure of the surface of LaNi5 crystal is in favour of the absorption of hydrogen.
CLASSICAL AREA OF PHENOMENOLOGY
Experiment on PR SEW of SBN crystal
Zhang Tian-Hao, Lu Yan-Zhen, Kang Hui-Zhen, Yang Da-Peng, Zheng Jian-Ya, Fang Zhe-Yu, Lou Ci-Bo, Yang Jia, Yang Hui-Zhan, Yin Mei-Rong
2005, 54 (10): 4688-4691. doi: 10.7498/aps.54.4688
Abstract +
Photorefractive surface electromagnetic wave (PR SEW) at the interface between SBN crystal and air based on drift and diffusion mechanism was observed experimentally for the first time. PR SEW can be formed when laser beam was incident at an angle of 55° in proper ratio of signal beam to background beam, and the intensity of PR SEW increases along with the increasing of additional electric field.
Ultraslow light propagation in a solid
Fan Bao-Hua, Zhang Yun-Dong, Yuan Ping
2005, 54 (10): 4692-4695. doi: 10.7498/aps.54.4692
Abstract +
With the spectral hole-burning effect resulting from coherent population oscillation in the homogenously broadened material, the ultraslow light propagation phenomenon with the group velocity as slow as 27.55±0.05m/s at room temperature in a ruby crystal is observed. And the group velocity in ruby crystal depends on the amplitude modulation frequency, the power of laser beam and the orientation of the crystal lattice. Lower frequency or higher power leads to slower group velocity.
Study of the multipass amplification of the chirped pulse and its inverse problem
Chu Xiao-Liang, Zhang Bin, Cai Bang-Wei, Wei Xiao-Feng, Zhu Qi-Hua, Huang Xiao-Jun, Yuan Xiao-Dong, Zeng Xiao-Ming, Liu Lan-Qin, Wang Xiao, Wang Xiao-Dong, Zhou Kai-Nan, Guo Yi
2005, 54 (10): 4696-4700. doi: 10.7498/aps.54.4696
Abstract +
The multipass amplification characters of the chirped pulse in gain medium were studied with the Schrdinger equation and population equation. The inverse problem of multipass amplification of the chirped pulse was studied and simulated by means of the Split-step Fourier and iteration methods, to find the profile of the input pulse from the given output pulse and multipass amplification parameters. The results are useful for the multipass amplification and design of the pulse shaping of the chirped pulse.
Optical feedback characteristics of two orthogonally polarized light beams in a HeNe laser during cavity tuning
Liu Gang, Zhang Shu-Lian, Xu Ting, Zhu Jun, Li Yan
2005, 54 (10): 4701-4709. doi: 10.7498/aps.54.4701
Abstract +
We can get optical feedback signals of the two orthogonally polarized light beams in a HeNe laser during the cavity tuning process when the period of the driving signal of the feedback mirror is set much shorter than that of the cavity mirror. The experiments are done under three different optical feedback conditions: only perpendicular light is fed back, only parallel light is fed back and both lights are fed back. When both lights are fed back, there is a phase delay less then 180 degrees between the two lights' intensity curves. When only one polarized light is fed back into the laser cavity, the two lights' intensity curves are inverted with respect to each other. We can subtract one light's intensity curve from the other one to improve the sensitivity of the optical feedback system. Especially when only perpendicular light is fed back, both lights' modulation amplitudes are large in a wide range of gain curve with the DC component stable. This property can be used to reduce the miscount of the system.
Nonparaxial propagation of Gaussian beam in arbitrary linearly polarized state
Zhou Guo-Quan
2005, 54 (10): 4710-4717. doi: 10.7498/aps.54.4710
Abstract +
The forming of transmitted-aperture in Sb layer of Super-RENS was studied based on laser-induced thermal model with Gauss assumption. The optical transmit model was created with optical admittance characteristic matrix. A numerical simulation was carried out by FEMLAB to understand the forming process of the aperture. The simulation results showed that transmitted aperture would not be formed until the exposure power exceeded a threshold within a certain pulse time, further more, the aperture size would be increased if the power was raised. The static writing experiment for transmitted-aperture type Super-RENS was carried out. The experiment results well agree with the simulation. It is concluded that a laser-induced thermal model could well describe the forming of aperture in Sb layer of transmitted-aperture type Super-RENS in optical data storage.
Laser-induced thermal analysis for mask layer of transmitted-aperture type super-RENS in optical storage
Shen Quan-Hong, Xu Duan-Yi, Qi Guo-Sheng, Hu Heng, Liu Rong
2005, 54 (10): 4718-4722. doi: 10.7498/aps.54.4718
Abstract +
The forming of transmitted-aperture in Sb layer of Super-RENS was studied based on laser-induced thermal model with Gauss assumption. The optical transmit model was created with optical admittance characteristic matrix. A numerical simulation was carried out by FEMLAB to understand the forming process of the aperture. The simulation results showed that transmitted aperture would not be formed until the exposure power exceeded a threshold within a certain pulse time, further more, the aperture size would be increased if the power was raised. The static writing experiment for transmitted-aperture type Super-RENS was carried out. The experiment results well agree with the simulation. It is concluded that a laser-induced thermal model could well describe the forming of aperture in Sb layer of transmitted-aperture type Super-RENS in optical data storage.
The effect of mass center motion on a two-level atom emission spectrum
Zhao Li-Yan, Guo Hong
2005, 54 (10): 4723-4729. doi: 10.7498/aps.54.4723
Abstract +
The emission spectrum of a two-level atom in a harmonic trap is studied. It is shown that atomic motion do not affect the atomic spectrum phase sensitivity when there is no correlation between atomic mass center motion and the field. With the increase of the average energy of atomic center motion, the peaks move towards each other, their heights change with the state of the field and atomic motion. When there is correlation between atomic mass center motion and the field, the atomic spectrum becomes insensitive to the relative phase between the field and the atomic dipole. Under certain conditions, there are fewer peaks, and they become higher and narrower.
Scheme for quantum information processing via Λ-type atoms interacting with bimodal cavity field
Song Ke-Hui
2005, 54 (10): 4730-4735. doi: 10.7498/aps.54.4730
Abstract +
Some schemes for the entanglement generation of two and three distant cavity-fields and the distant transfer of a qubit atomic state and atomic entangled state are presented. The realization of entanglement swapping without measurement on Bell basis vectors and the operation of swap gate are proposed. These schemes are all based on Λ-type atoms interacting with bimodal under one-photon detuning and two-photon resonance. Finally, a discussion of experimental feasibility is given.
Ultrafast electronic dymamics during femtosecond laser-induced damage in omnidirectional reflector
Sun Hai-Yi, Jia Tian-Qing, Li Xiao-Xi, Xu Shi-Zhen, Feng Dong-Hai, Li Cheng-Bin, Wang Xiao-Feng, Xu Zhi-Zhan
2005, 54 (10): 4736-4740. doi: 10.7498/aps.54.4736
Abstract +
The use of optical frequency domain phase conjugation (FDPC) to suppress pulse impairments due to cross-phase modulation (XPM) in optical fiber systems is propo sed. Evolution of Gaussian pulses in the system using midway FDPC is analyzed thoretically and simulated numerically. It is found that pulse waveform impairmen ts induced by XPM can be suppressed effectively by FDPC. The impairments due to group-velocity dispersion and self-phase modulation can be suppressed simultaneously. Suitable initial time delay and pulse chirp of pulses can improve the suppression and compensation for the distortion.
Numerical simulation of x-ray lasers pumped by grazing incidence pulses
Yan Fei, Zhang Jie, Dong Quan-Li, Lu Xin, Li Ying-Jun
2005, 54 (10): 4741-4746. doi: 10.7498/aps.54.4741
Abstract +
Numerical simulation of the Ni-like Mo x-ray laser at 189 nm (4d→4p, J=0→1) pumped by grazing incidence pulses is performed using a modified one-dimensional hydrodynamic code MEDUSA. By comparing the electron density, the electron temperature, and the absorbed laser energy density obtained by the grazing incidence and the normal incidence schemes respectively, it is clearly shown that the absorption efficiency is greatly increased in the grazing incidence scheme due to the increased absorption of driver laser in the gain region.
Suppression of pulse impairments due to cross-phase modulation by frequency domain phase conjugation
Bu Yang, Wang Xiang-Zhao
2005, 54 (10): 4747-4753. doi: 10.7498/aps.54.4747
Abstract +
The use of optical frequency domain phase conjugation (FDPC) to suppress pulse impairments due to cross-phase modulation (XPM) in optical fiber systems is proposed. Evolution of Gaussian pulses in the system using midway FDPC is analyzed theoretically and simulated numerically. It is found that pulse waveform impairments induced by XPM can be suppressed effectively by FDPC. The impairments due to group-velocity dispersion and self-phase modulation can be suppressed simultaneously. Suitable initial time delay and pulse chirp of pulses can improve the suppression and compensation for the distortion.frequency domain phase conjugation, cross-phase modulation, group-velocity dispersion, self-phase modulation can be suppressed simultaneously. Suitable initial time delay and pulse chirp of pulses can improve the suppression and compensation for the distortion.
Singly resonant optical parametric oscillator with intracavity optical amplification
Deng Cheng-Xian, Li Zheng-Jia, Zhu Chang-Hong
2005, 54 (10): 4754-4760. doi: 10.7498/aps.54.4754
Abstract +
The Gaussian beam theory has been developed to describe the power characteristics of the steady-state operating ring cavity singly resonant optical parametric oscillator (SRO) with intracavity optical amplification (ICOASRO). The threshold of SRO can be greatly lowered with suitable parameters of the optical amplifier. Under the mean-field approximation, there are four operating domains for a ICOASRO without the second-order nonlinear coupling, meanwhile there exits a minimum pump threshold for the SRO. The characteristics of the end-pumped laser gain medium used as optical amplifier is considered. The generalized characteristics of SRO are also considered in the derivation.
The effect of electrode configuration in domain broadening of periodically poled LiNbO3
Wang Ting, Ma Bo-Qin, Sheng Yan, Cheng Bing-Ying, Zhang Dao-Zhong
2005, 54 (10): 4761-4764. doi: 10.7498/aps.54.4761
Abstract +
The effect of LiNbO3 electrode with three different configurations o n domain broadening by using poling method appling external electric field applying exter nal electric field is studied. The effect of poling electrode configuration in d omain broadening is studied. The experiment demonstrated that under the same pol ing condition, the broadening velocities are 0.089μm/ms and 0.011μm/ms when th e angle between the poling electrode and the diagonals of hexagonal domain nucl eus are 90°and 0°,respectively, therefore the circumstance of 90°angle betwe en poling electrode and the diagonals of hexagonal domain nucleus should be avoi ded in fabricating one-dimension nonlinear photonic crystal.
Group velocity self-matching in noncollinear optical parametric generation with a type-Ⅰ phase-matched BBO crystal
Ma Jing, Zhang Ruo-Bing, Liu Bo, Zhu Chen, Zhang Wei-Li, Zhang Zhi-Gang, Wang Qing-Yue
2005, 54 (10): 4765-4769. doi: 10.7498/aps.54.4765
Abstract +
Noncollinear parametric superfluorescence (NPS) is obtained in the visible regio n by pumping a type-Ⅰ phase-matched BBO crystal with the second harmonic of an amplified Ti:sapphire laser at 1kHz repetition rate. The variation of the noncol linear angle and the wavelength at the peak intensity of the NPS with the phase- matched angle is studied, and the variations of the group velocity mismatch (GVM ) with the noncollinear angle and the phase-matched angle in the three-wave inte raction is calculated theoretically. The results indicate that the type-Ⅰ phase -matched NPS ring is centrosymmetric with respect to the pump beam on the observ ation screen. Along the NPS direction at the peak intensity, the GVM is minimal and the effective interaction length is maximal for the three waves. The angular distribution of the NPS intensity is ascribed to phase velocity and group veloc ity self-matching among interacting pulses. The theory and the experiment provid e an ideal geometrical model for reducing the GVM between three waves, and provi de a theoretical guidance and experimental verification for obtaining parametric pulses with higher gain and shorter duration in femtosecond optical parametric amplification.
PBG structures of two-dimensional magnetic photonic crystals in square lattice
Che Ming, Zhou Yun-Song, Wang Fu-He, Gu Ben-Yuan
2005, 54 (10): 4770-4775. doi: 10.7498/aps.54.4770
Abstract +
Photonic band gap(PBG) structures of the two-dimensional magnetic photonic crystals (MPCs) are calculated by use of the plane-wave expansion method. The MPCs consist of magnetic pillars in rectangular, square, hexagonal and circular shapes, respectively embedded in dielectric medium in a square lattice. The optimal MPC samples that possess the largest gap-mid gap ratio for each type of MPC are obtained by scanning the three parameters(permeability, filling factor and rotating angle). The changes of the PBG structures are investigated when varying independently each parameter and fixing the others. Calculated results show that the frequency in the middle of the PBG hardly changes with the variation in filling factor or rotating angle, but decreases monotonicly with the increase of the per meability. The PBG width increases to a top value and then decreases with the in crease of each parameter.
Transient and steady-state multi-wave nonlinear optical properties of liquid crystal film
Hou Gang, Xu Ze-Da, Miao Ming-Chuan, Fan Shang-Chun
2005, 54 (10): 4776-4781. doi: 10.7498/aps.54.4776
Abstract +
Transient and steady-state multi-wave mixing experiments are carried out on the novel azo+c-tube liquid crystal sample. The shape of the diffracted multi-wave consists of rings under Ar+(514.5nm) laser pump light, and th e nonlinear refractive index is n~0.8. Using different polarization states of the pump laser light field, different reorientation models of liquid crystal molecules ar e observed. On the other hand, a Nd:YAG(532nm)pulsed laser is used, polarizati on holographic gratings are detected by a He-Ne (632.8nm)laser beam. Different p rocesses of liquid crystal molecular reorientation are also detected using the o -light beam and e-light beam of a He-Ne (632.8nm)laser.
Fast tunable electro-optic polymer waveguide gratings
Wang Yi-Ping, Chen Jian-Ping, Li Xin-Wan, Zhou Jun-He, Shen Hao, Shi Chang-Hai, Zhang Xiao-Hong, Hong Jian-Xun, Ye Ai-Lun
2005, 54 (10): 4782-4788. doi: 10.7498/aps.54.4782
Abstract +
A novel fast tunable electro-optic (EO) polymer waveguide grating is proposed an d designed. Its resonant wavelength can be linearly tuned by first-order EO effe ct with a high sensitivity of 6.1pm/V. Its spectrum characteristics depend stron gly on many optical parameters of grating, such as refractive index modulation, modulation function, grating period and period number. Material selection, fabri cation technology, EO tunability and polarization dependence of the polymer wave guide grating are also discussed. This waveguide grating not only dispenses with the slow wavelength tuning and large-scale integration inconvenience of convent ional optic fiber gratings, but have many advantages, such as high resonant wave length tuning sensitivity, using same fabrication technology as semiconductor de vices, and polarization independence.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
RCS of 2-D target loaded with anisotropic magnetized plasma computed by FDTD
Xu Li-Jun, Liu Shao-Bin, Yuan Nai-Chang
2005, 54 (10): 4789-4793. doi: 10.7498/aps.54.4789
Abstract +
The finite-difference time-domain(FDTD) method is extended to two dimensional anisotropic dispersive media-magnetized-plasma using Z transformation for the f ist time. The problem which incorporates both anisotropy and frequency dispersio n at the same time is solved for the electromagnetic wave propagation. The two d imensional FDTD formulations for anisotropic magnetized plasma are derived. The method is applied to the electromagnetic scattering of perfectly conducting cyli nder coated with anisotropic magnetized plasma. By simulating the interaction of electromagnetic wave with magnetized plasma, some bistatic numerical results ar e obtained, which indicate that an appropriate plasma coating may efficiently re duce the RCS of a metallic target.
Investigation of void in dust clouds in reactive plasma
Wu Jing, Zhang Peng-Yun, Song Qiao-Li, Zhang Jia-Liang, Wang De-Zhen
2005, 54 (10): 4794-4798. doi: 10.7498/aps.54.4794
Abstract +
The void in the sheath of a radio-frequency(rf) dusty plasma is investigated experimentally. Dust particles in our experiment are created in situ using mixed reactive gases silane and ethane. Dust particles in radio frequency discharges form crystalline structure and display instabilities under certain conditions. The behaviour of the dust void as a function of rf power and gas pressure is stu died.
Calculation of neutron spectrum in ultraintense laser-plasmas interactions
Chen Zheng-Lin, Kodama R., Zhang Yi, Li Yu-Tong, Zhang Jie
2005, 54 (10): 4799-4802. doi: 10.7498/aps.54.4799
Abstract +
The neutron spectrum of D-D reaction in ultraintense laser-plasma interaction is calculated. Using Maxwellian and Gauss distribution, the temperature and angular distribution of the deuterons are obtained by fitting the experimental neutron spectrum.
Experimental study of optical emission from the rear surface in ultrashort ultra-intense laser interaction with solid targets
Yang Xiang-Dong, Wang Guang-Chang, Zhang Shuang-Gen, Wang Xiang-Xian, Zheng Zhi-Jian, Gu Yu-Qiu, Liu Hong-Jie, Wen Tian-Shu, Ge Fang-Fang, Jiao Chun-Ye, Zhou Wei-Min
2005, 54 (10): 4803-4807. doi: 10.7498/aps.54.4803
Abstract +
Optical emission generated by hot electrons passing through solid targets is measured from the rear surface of a metallic foil. The integrated image taken by CC D camera shows that the optical emission forms a ring, on the edge of the ring t here is a bright localized signal, which is the optical transition radiation (OT R). The optical emission spectrum shows a series of sharp nonperiodic peaks bet ween 300—500nm,obviously near 400nm(2ω). The sharp peaks are ascribed to the c oherent transition radiation (CTR) of hot electron-beam microbunching generated by v×B acceleration mechanism. The OTR intensity decreases with the increase of the target thickness.
Numerical simulation of filamentary discharge controlled by dielectric barrier at atmospheric pressure
Zhang Yuan-Tao, Wang De-Zhen, Wang Yan-Hui
2005, 54 (10): 4808-4815. doi: 10.7498/aps.54.4808
Abstract +
The spatio-temporal evolution of filamentary discharge in dielectric barrier dis charge at atmospheric pressure is studied. A two-dimensional model was solved wi th uniform initial conditions. The simulation results reveal that the breakdowns take place continuously at different positions and gradually spread all over th e discharge space. It is found that under certain conditions the splitting and u niting of filaments can occur, which has been observed in experiments. The split ting of filaments leads to the generation of new filament and the uniting reduce s the number density of filaments in discharge space. The simulation shows that the charges on barrier surface play a dominant role in determining the global sp atio-temporal evolution of filamentary discharge.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Thermal shock effect on diamond-like carbon thin films induced by pulsed-laser
Niu Yan-Xiong, Huang Feng, Duan Xiao-Feng, Wang Yue-Feng, Zhang Peng, Yu Ye, Yao Jian-Quan, He Chen-Juan
2005, 54 (10): 4816-4821. doi: 10.7498/aps.54.4816
Abstract +
When high power laser irradiates the infrared imaging system, the system will be injured or destroyed. The damage to the systems varies for different laser wavelengths. The infrared windows are generally coated with diamond-like carbon(DLC) thin films to protect itself and improve the permeation rate. When the incid ent laser's wavelength lies outside the infrared system response wave band, lase r destroys the DLC films firstly. The DLC films' damage mechanism induced by pul sed laser is studied with the 1.06μm laser. The thermal shock effect model of D LC films is proposed. The temperature and stress distributions are deduced throu gh solving the thermal conduction equation and stress-balance equation. The theo retical analysis shows that thermal stress fracture dominants in the damage mech anism. When the irradiation energy density is E0=100mJ·cm-2 , the pressu re on the surface of DLC films at about 40μm from the center of laser facula ex ceeds the rupture intensity, the film will break and peel off. The theoretical a nalysis matches the experimental results basically, and the correctness of the t hermal shock effect model is confirmed.
The study of depth distribution for ion with low energy implanted into plant seeds and mechanism of biological effect
Lu Ting, Zhou Hong-Yu, Ding Xiao-Ji, Wang Xin-Fu, Zhu Guang-Hua
2005, 54 (10): 4822-4826. doi: 10.7498/aps.54.4822
Abstract +
The depth distribution of 200keV Vanadium ions implanted into the dry peanut seeds have been determined by SEM+EDAX, PIXE, TPLSM and PAT. The results of measurements show that the depth of ion with low energy implanted into the dry peanut seeds are much greater than the value of depth calculated by of TRIM95 program. The mechanism of biological effect of ion with low energy implanted to the plant seed was discussed.
Molecular dynamics studies on vacancy-interstitial annihilation in silicon
Qiao Yong-Hong, Wang Shao-Qing
2005, 54 (10): 4827-4835. doi: 10.7498/aps.54.4827
Abstract +
Molecular dynamics (MD) simulation is performed to study the vacancy-interstitial annihilation in crystalline silicon. We choose the Stillinger-Weber potential , which is commonly used for silicon, to describe the interaction between atoms. The system is relaxed under 300K and 1400K respectively. We have found that is the preferred recombination direction and propose the presence of an energy barrier in the direction. From the calculated value of energy barrier alon g we give a reasonable explanation for the difference between Tang's and Z awadzki's data.
Molecular dynamics simulation of strain effects on surface melting for metal Cu
Wang Hai-Long, Wang Xiu-Xi, Liang Hai-Yi
2005, 54 (10): 4836-4841. doi: 10.7498/aps.54.4836
Abstract +
Molecular dynamics simulations of surface melting process at different strain values were performed for metal Cu(110). The variation of the structure and energy in the system and the movement of the interface position between solid and liquid during surface melting were observed. The interaction between atoms in the system adopts the embedded atom potential proposed by Mishin. Cu(110) surface pr emelts below thermal melting point and the thickness of quasi-liquid film grows with temperature increasing. Beyond the thermal melting point, the velocity of t he interface between solid and liquid is linearly proportional to temperature, t he melting point is extrapolated to be 1380K which accords with the experimental data of 1358K. Strain lowers the melting point and accelerates the premelting p rocess. The thickness of quasi-liquid grows with increasing strain at the same t emperature. The increase of solid free energy induced by strain is the main fact or that decreases surface thermal stability, the direction of strain relative to the surface stress also effects the premelting process.
Modeling analysis of gradient-index coatings prepared by reactive magnetron sputtering
Shao Jian-Da, Wang Ying-Jian, Fan Zheng-Xiu, Shen Zi-Cai
2005, 54 (10): 4842-4845. doi: 10.7498/aps.54.4842
Abstract +
The formation mechanism of gradient-index coatings by reactive magnetron sputtering is discussed. A practical modeling of gradient-index coatings is propose d, the relationship between refractive index of coatings and pressure of reactiv e gas is established. Next, we discussed the changing rule of partial-pressure o f reactive gas with time requivcd for obtaining a desired refractive index of g radient coatings under specific deposition conditions. A linear coating is tak en as example to illustrate how to get the relationship between partial-pressure of reactive gas and time.
The coherent growth and mechanical properties of non-isostructural TiN/TiB2 nanomultilayers
Wei Lun, Mei Fang-Hua, Shao Nan, Dong Yun-Shan, Li Ge-Yang
2005, 54 (10): 4846-4851. doi: 10.7498/aps.54.4846
Abstract +
TiN/TiB2 nanomutlialyers with different TiB2 layer thickne ss were prepared using multi-target magnetron sputtering method. The effects of TiB2 layer thickness on the growth structure and mechanical properti es of nanomultialyers were studied by X-ray diffraction, high-resolution transmi ssion electron microscopy and nanoindentation respectively. The results reveal t hat the normally amorphous TiB2 layers crystallize in close-packed he xagonal structure when its thickness is less than 2.9 nm due to the template eff ect of cubic TiN layers. Coherent growth is found between TiN and TiB2 layers with the orientation relationship of {111}TiN//{0001}Ti B2,〈110〉TiN//〈1120〉TiB2. Because of th e lattice misfit, an alternating tensile/compressive stress field develops in th e nanomultilayers, which leads to the anomalous enhancement of hardness and elas tic modulus. Maximum hardness and elastic modulus of 46.9 and 465GPa are obtaine d at TiB2 layer thickness of 0.6nm. With increasing TiB2 l ayer thickness, amorphous TiB2 forms and blocks the coherent growth of the multilayers. Consequently, the hardness and elastic modulus of the films decrease gradually.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Effect of micropore on hydrogen adsorption of single walled carbon nanotubes
Zheng Hong, Wang Shao-Qing, Cheng Hui-Ming
2005, 54 (10): 4852-4856. doi: 10.7498/aps.54.4852
Abstract +
Using grand canonical ensemble Monte Carlo method,the effect of micropores,mainly the hollow cores of single-walled carbon nanotubes(SWNTs) and the interstitial channel among SWNTs,on the hydrogen adsorption of SWNTs was studied.Comparing with experimental observations,it was found that the hollow cores of SWNTs are the dominant sites for hydrogen adsorption,The overlap and efficiency of the adsorption potential inside a SWNT were analyzed,and it was found that the hydrogen adsorption capacity of the SWNTs is improved when the diameter of the SWNTs is around 2nm.The calculation also showed that the interstitial channel among SWNTs can become effective sites for hydrogen adsorption when the gap between two SWNTs increases.
Defect production and formation of helium-vacancy clusters in cascades of α-iron with different concentration of helium
Gao Fei, Zu Xiao-Tao, Xiao Hai-Yan, Yang Li, Yang Shu-Zheng, Liu Ke-Zhao
2005, 54 (10): 4857-4862. doi: 10.7498/aps.54.4857
Abstract +
The low-temperature displacement cascades in α-Fe with different concentrations of substitutional He atoms are simulated by molecular dynamics (MD) methods. Primary knock-on atom (PKA) energy, Ep , from 500eV to 5keV is cons idered for irradiation temperature of 100K. The concentration of He in Fe varies from 1% to 5%. The results are compared with those obtained in pure α-Fe. We f ind the number of Frenkel pairs (NF) in Fe with low concentration of He atoms is nearly equal to those in pure Fe, but increases with increasing He c oncentration. The present study demonstrates for the first time that He-vacancy bubbles can be nucleated directly from displacement cascades, even at low tempe rature at which the vacancies are not mobile. However, the efficiency of He-vaca ncy clusters increases with increasing the concentration of He for the same ener gy recoils, and increases with increasing Ep for the same concentrati on of He. The mechanisms of He bubble nucleation in displacement cascades are di scussed in detail.
Effect of high temperature rapid thermal annealing on flow pattern defects in heavily Sb-doped CZSi
Zhou Qi-Gang, Wang Jing, Liu Cai-Chi, Sun Wei-Zhong, Zhang Jian-Qiang, Sun Shi-Long, Zhao Li-Wei, Zhang Jian-Feng, Hao Qiu-Yan
2005, 54 (10): 4863-4866. doi: 10.7498/aps.54.4863
Abstract +
Flow pattern defects(FPDs) in as-grown and rapid thermal annealed heavily Sb-dop ed silicon wafers was investigated. The experimental results show that the dens ity of FPDs can be reduced after high temperature annealing, and H2 is the most effective annealing atmosphere. The mechanism of elimination of FPDs is also discussed from the relationship between heavily doping Sb and interstit ial oxygen concentration. The heavily doping Sb influences not only the distribu tion of initial oxygen concentration in CZSi wafer, but also the formation and h eat behavior of grown-in void defects.
Self-organization of ordered surface patterns in nearly free sustained Al films
Zhang Yong-Ju, Yu Sen-Jiang
2005, 54 (10): 4867-4873. doi: 10.7498/aps.54.4867
Abstract +
A nearly free sustained aluminum film system has been successfully fabricated o n liquid substrates by thermal evaporation method. The ordered surface pattern s with band-shaped structure, propagating from the film edges to the central reg ions, are systematically studied. The formation of these patterns is strongly d ependent on the experimental conditions (such as the nominal film thickness, de position rate, growth period in vacuum etc.) and the growth mechanism can be tra ced to a three-stage process. The experiment proves that the ordered patterns re sult from the free diffusion and aggregation of the Al atoms and atomic clusters on the liquid surfaces driven by the internal stress. Further theoretical analy sis shows that due to the characteristic boundary condition and interactions bet ween the metallic films and the liquid substrates, the nearly free sustained Al films may contain a series of sinusoidal stress distributions with different amp litudes and frequencies, and their composition results in the formation of the o rdered surface patterns.
Fabrication of intrinsic microcrystalline silicon thin films used for solar cells and its structure
Zhao Ying, Gao Yang-Tao, Zhu Feng, Wei Chang-Chun, Sun Jian, Geng Xin-Hua, Zhang Xiao-Dan, Xiong Shao-Zhen
2005, 54 (10): 4874-4878. doi: 10.7498/aps.54.4874
Abstract +
Microcrystalline silicon thin films used for solar cells were deposited at different silane concentrations and reaction pressures by VHF-PECVD.Study of materials structure was conducted by Raman spectra and x-ray diffraction. In the range of experiment, microcrystalline silicon thin films prepared under different cond itions all have (220) preferential orientation. Microcrystalline silicon solar c ells with conversion efficiency up to 7.1% were fabricated. The structure of sol ar cells was glass/ZnO/p(μc-Si:H)/i(μc-Si:H)/n(a-Si:H/Al). There was no Zno ba ck reflector and the thickness of solar cells was only 1.2μm.
Magnetism and transport properties of Heusler alloy Co2TiSn
Zhang Wei, Qian Zheng-Nan, Sui Yu, Liu Yu-Qiang, Su Wen-Hui, Zhang Ming, Liu Zhu-Hong, Liu Guo-Dong, Wu Guang-Heng
2005, 54 (10): 4879-4883. doi: 10.7498/aps.54.4879
Abstract +
Magnetism and transport properties of the Heusler alloy Co2TiSn are s tudied. The results show this alloy exhibits ferrimagnetic structure at low fiel d. Both resistance and Hall resistivity show anomalies below 8K. An analysis is given for the microscopic scattering mechanisms of electric transport. The origi n of anomalous Hall effect is discussed.
Pseudoelasticity of Co50Ni22Ga28:Fex single crystal at room temperature and high temperature of 100℃
Dai Xue-Fang, Liu Guo-Dong, Liu Zhu-Hong, Wu Guang-Heng, Chen Jing-Lan
2005, 54 (10): 4884-4888. doi: 10.7498/aps.54.4884
Abstract +
The pseudo-quaternary Heusler alloys Co50Ni22Ga28:Fex (x=0,1.5,2,2.5) single crystals have been synthesized. Excell ent pseudoelasticities were observed in compression, bending and torsion. At roo m temperature, the perfect pseudoelastic strains of 4% and 6.7% were obtained in the [100] and [110] directions of the Co50Ni22Ga 28:Fe2 single crystal under compression, respectively. The stre ss-strain curve for the Co50Ni22Ga28:Fe1.5 single crystals shows an indistinct platform on loading, and an intermar tensitic transformation occurs with unloading. The platform of the curve on load ing becomes clear and the intermartensitic transformation with unloading becomes indistinct at the high temperature of 100℃. Pseudoelastic strains of 5.5% wer e obtained in the [001] direction of the Co50Ni22Ga 28 :Fe2.5 single crystal. In addition, the single crystals show strong elastic anisotropy.
Preparation and magnetic properties of nanocomposite Nd28Fe66B6 /Fe50Co50 bilayer films
Ao Qi, Zhang Wa-Li, Zhang Yi, Wu Jian-Sheng
2005, 54 (10): 4889-4893. doi: 10.7498/aps.54.4889
Abstract +
The nanocomposite Nd28Fe66B6/Fe50Co50 bilayer films with Mo underlayer and overlayer have been fabricated on Si substrates. All the samples prepared have perpendicular anisotropy and th e hysteresis loops are simple single loops for fixed Nd-Fe-B layer thickness (10 nm) and different FeCo layer thickness (dFeCo =1—100nm). The shape a nd the behavior of the initial loops and the minor loops suggest that wall pinni ng is the dominant coercivity mechanism in these films. The magnetization of the se samples is found to increase with increasing FeCo layer thickness for a fixed Nd-Fe-B layer thickness and the coercivity of films decrease with increasing Fe Co layer thickness. The sample of maximum energy product is 160×103A/m for dFeCo =5nm at room temperature. The enhancement of the rema nence and energy products in nanocomposite bilayer films is attributed to the ex change coupling between the magnetically soft and hard phases.
Dopant effects on martensitic transition and magnetic properties of Ni51.5Mn25Ga23.5 materials
Zhu Zhi-Yong, Wang Wen-Quan, Miao Yuan-Hua, Wang Yan-Song, Chen Li-Jie, Dai Xue-Fang, Liu Guo-Dong, Chen Jing-Lan, Wu Guang-Heng
2005, 54 (10): 4894-4897. doi: 10.7498/aps.54.4894
Abstract +
Ni51.5Mn23M2Ga23.5 materials are to reveal the dopant effect on the martensitic transition and the magnetic propert ies. We found that the dopants Ti, Zr, Hf, V, Nb, and Ta lower the martensitic transition temperature of the sample, but W increases it. The martensitic trans ition temperature is very sensitive to the atomic size when the valence electron ic concentration keeps constant for the doping elements. The dopants Ti, Zr, Hf or V decrease the magnetic moment of Mn atom in the martensite at low temperatur e, while Nb, Ta or W enhance it. A corresponding variation of TC of t he materials is not observed, which indicates that the influence of the lattice change of martensitic transition on the magnetic properties should also be ta lken into account.
Effect of Ag and Ti underlayer on the ordering in Fe/Pt multilayers
Feng Chun, Teng Jiao, Yang Tao, Yu Guang-Hua, Li Bao-He
2005, 54 (10): 4898-4902. doi: 10.7498/aps.54.4898
Abstract +
The Fe/Pt multilayers with Ag,Ti,Cu,Cr,Pt and Ta underlayers were prepared by DC magnetron sputtering on the heated glass substrates.After vacuum annealing at d ifferent temperatures, the FePt thin films with L10 ordering phase ( L10-FePt) were obtained. Results showed that the Ag and Ti underlaye r prompt the ordering of FePt thin films, and the ordering temperature of FePt- L10 phase is reduced by at least 150℃. It is also worth noting tha t the annealing time is shorter and the magnetic performance is excellent. The m agnetic performance of samples with Ag underlayer is not sensitive to temperatur e at relative higher annealing temperature, whereas the coercivity of samples wi th Ti underlayer decreases obviously when the annealing temperature is higher th an 500℃. After annealing at 400℃ for 20 min, the in-plane coercivity of sample s with Ag and Ti underlayer can be as high as 597kA/m, and 654kA/m, respectivel y, and the ratio of remanent magnetization to saturation magnetization reaches 0 .81 and 0.94, respectively, implying the potential of the films as future magnet ic recording media of ultrahigh density.
Composition-modulated hybrid tunnel junctions of La1-xSrxMnO3
Du Yong-Sheng, Yan Hui, Ying Qi-Ming, Zhang Guo-Cheng, Yu Dun-Bo, Feng Jia-Feng, Han Xiu-Feng
2005, 54 (10): 4903-4908. doi: 10.7498/aps.54.4903
Abstract +
Tunnel magnetoresistance junctions with the structure of SrTiO3-sub/ La0.7Sr0.3MnO3(100nm)/La0.96Sr 0.04MnO3 (5nm)/La0.7Sr0.3MnO3 (100nm)/Ir22Mn78(15nm)/Ni79Fe21(5nm)/Pt(20nm) were micro-fabricated with lithography and Ar ion etching. T he first three epitaxial layers of La0.7Sr0.3MnO3(100nm)/La0.96Sr0.04MnO3 (5nm)/La0.7Sr0.3MnO3 (100nm) were deposited on single crystal (0 01) SrTiO3-substrate by magnetron sputtering and heat treatment, the n the spinning and top conducting layers of Ir22Mn78(1 5nm)/Ni79Fe21(5nm)/Pt(20nm) were continuously fabricat ed on top the three epitaxial layers by normal magnetron sputtering. The coloss al TMR ratio of 3270% was observed at 4.2K under the external magnetic field of 8 T. The polarization value of 97% for the La0.7Sr0.3MnO3 is well consistent with the theoretical value of 100%. The present r esults directly indicate the half-metallic ferromagnetism in La0.7Sr0.3MnO3. The high TMR value can possibly be attributed to the good interface due to the perfect barrier.
Characterization of transitions in MnFeP0.45As0.55 compound
Zhu Zhi-Yong, Wang Wen-Quan, Miao Yuan-Hua, Wang Yan-Song, Chen Li-Jie, Dai Xue-Fang, Liu Guo-Dong, Chen Jing-Lan, Wu Guang-Heng
2005, 54 (10): 4909-4913. doi: 10.7498/aps.54.4909
Abstract +
The resistance, magnetization and strain measurements have been carried out on MnFeP0.45As0.55 compound. We found that, at variance with what is commonly believed, the critical temperature points for the first order t ransition, paramagnetism-ferromagnetism transition, and lattice anomaly are not identical. The first order transition goes on in a quite wide temperature range with a thermal hysteresis of about 10K. In the duration of the first order trans ition, the paramagnetism-ferromagnetism transition is observed, which indicates that they are not related to the lattice anomaly. Thus, we attribute it to the continuous change of the lattice parameters due to the structure transition bas ed on our observation and Zach et al.'s work. On the other hand, the lattice ano maly occurs at lower temperature than that of the first order structural and mag netic transitions. We conclude that it is a magnetostrictive behavior associate d with the magnetoelastic coupling below the Curie temperature.
Mechanism of nonlinear dielectric constant of BaTiO3-based ceramics under high DC electric field
Liang Rui-Hong, Dong Xian-Lin, Chen Ying, Cao Fei, Wang Yong-Ling
2005, 54 (10): 4914-4919. doi: 10.7498/aps.54.4914
Abstract +
Ba0.6Sr0.4TiO3(BST) and Ba(Zrx Ti1-x)O3(BZT) (x=0.25,0.3,0.35,0.4) ceramics were pr epared by traditional ceramic processing and their structural, dielectric proper ties as well as the mechanism of its nonlinear dielectric constant under dc elec tric field were systemically examined. The results show that the phenomenologic al theory of Devonshire can be applied to BST system when the material is in the paraelectric state, and the equations εr(app)εr(0)=1[1 +αε3r(0)E2]1/3 and ε(E)=ε1 -ε2E2+ε3E4 can give a quanti tative explaination of its nonlinear dielectric behavior under high DC electric field. where εr(0) and εr(app) are the dielectric cons tants under zero DC field and under the applied field respectively, α is the an harmonic coefficient, E is the strength of electric field, ε(F) is the dielect ric constant under the applied field and ε1,ε2,ε3 is linear, nonlinear and high order dielectric constant respectively . When the BST system is in the ferroelectric or phase transition state, the dom ain and domain wall's extrinsic contributions to the nonlinear dielectric consta nt cannot be neglected, and the extrinsic contributions decrease with the increa se of the strength of the electric field. For the relaxor-like BZT system, even if it is in paraelectric state, the extrinsic contribution of polar microregion s to the nonlinear dielectric constant can be markedly observed. With the incre ase of the strength of the electric field and temperature, this contribution dec reases.
Theoretical study of influence of substrate microdefects on optical properties of dielectric thin films
Liu Shou-Hua, Shao Jian-Da, Fan Zheng-Xiu, Shen Jian, Shen Zi-Cai, Kong Wei-Jin, Huang Jian-Bing
2005, 54 (10): 4920-4925. doi: 10.7498/aps.54.4920
Abstract +
Based on the theory of inhomogeneous thin films, a model for refractive index of stratified dielectric substrate is firstly put forward. The substrate can be divided into surface layer, subsurface layer and bulk layer in turn. Both the s urface layer and subsurface layer, whose refractive indices obey statistical dis tributions, are equivalent to inhomogeneous thin films. They can be separated in to N1 and N2 sublayers respetively which are regarded as homogenous thin films. Subsequently, theoretical analysis was carried out utili zing the characteristic matrix method of optical thin films. Numerical calculati on for optical properties of single layer dielectric thin films was carried out. The computing results indicate that microdefects in surface layer and subsurfac e layer of the substrate alter the equivalent refractive indices of the thin film and the substrate, which leads to the deviation of pseudo-Brewster angles and assembling reflectance from ideal conditions. Meanwhile, these microdefects change the propagation characteristics in thin film and substrate, as a result t he phase shift of reflection and phase difference deviate from ideal conditions. In addition, this model is also suitable for calculating the influence of micr odefects in the substrate on optical propertied of multilayer dielectric thin fi lms.
Spectroscopic properties of Er3+-doped alkaline/alkaline-earth metal modified fluorophosphate glasses
Li Tao, Zhang Qin-Yuan, Feng Zhou-Ming, Zhao Chun, Jiang Zhong-Hong
2005, 54 (10): 4926-4932. doi: 10.7498/aps.54.4926
Abstract +
This paper reports the spectroscopic properties of Er3+-doped Al(PO 3)3-based fluorophosphate glasses for 1.5μm optical ampl ifiers. Effects of alkaline/alkaline-earth metal composition on the spectroscopi c properties of Er3+ in fluorophosphate glasses are investigated. A strong correlation between the alkaline/alkaline-earth metal content and the s pectroscopic parameters, such as absorption and emission cross sections, Judd-Of elt intensity parameters and upconversion emission intensity, has been observed. The fluorophosphate glass with 12 mol% potassium fluoride exhibits the largest calculated stimulated-emission cross-section of 7.83×10-21cm2 and the smallest upconversion emission intensity among the fluorophosphate studied. The fluorophosphate glass with 23 mol% strontium fluoride has a broadb and near-infrared emission at 1.5μm with a full width at half-maximum over 65nm and a long upper level fluorescence lifetime of 8.6ms.
Efficient coupling from dielectric rib waveguide to two-dimensional photonic crystal waveguide
Bai Ning-Feng, Liu Xu, Xiao Jin-Biao, Zhang Ming-De, Sun Xiao-Han
2005, 54 (10): 4933-4937. doi: 10.7498/aps.54.4933
Abstract +
An efficient adiabatic coupling is presented in this paper for coupling light between rib dielectric waveguide and 2D photonic crystal waveguide (PCW). Using planar wave expand (PWE) method and FDTD method, the linear and nonlinear taper profiles are compared. Following with these, some widths of the entrance of the taper are compared and the best width is given. Simulation result have proved that transmission ratio above 95% can be obtained in a wider frequency range by usin g a cosine taper profile than line taper profile.
Generation and detection of terahertz radiation on reactive ion etched ZnTe surfaces
He Li-Rong, Gu Chun-Ming, Shen Wen-Zhong, Cao Jun-Cheng, Hiroshi Ogawa, Guo Qi-Xin
2005, 54 (10): 4938-4943. doi: 10.7498/aps.54.4938
Abstract +
Electro-optic sampling technique is employed to reveal the generation of teraher tz (THz) radiation via optical rectification from reactive ion etched ZnTe surfa ces. The pulsewidth of the observed THz radiation is ~0.25ps. The electro-optic coefficient of the ZnTe samples is found to decrease with the increase of the r adio frequency (RF) power. By calculating the frequency response function, we di scuss the THz bandwidth under different values of RF plasma power.
Investigation of diamond-like-carbon films prepared by unbalanced magnetron sputtering
Zhang Shou-Zhong, Du Jian, Ma Pei-Ning, Yang Wu-Bao, Fan Song-Hua, Zhang Gu-Ling
2005, 54 (10): 4944-4948. doi: 10.7498/aps.54.4944
Abstract +
Using unbalanced magnetron sputtering method, smooth, dense and uniform diamond like carbon films (DLC) with high diamond phase content are deposited.Based on testing and analysis of deposition mechanism, we conclude that with smaller s puttering clusters and higher collision frequency between the sputtering cluster and environment molecules, and more suitable momentum of the sputtering cluste r impacting on the substrate, higher content of diamond phase in the film will result. Scanning electron micrograph shows that there are no obvious grains in this film. The micro-hardness is about 11 GPa, bulk elastic modulus is about 120 GPa as tested by nano-indentation. The optical transmittance is about 89%, ref raction coefficient is 1.952, and the deposition rate is 0.724μm/h as calculate d from the FTIR spectra.
Synthesis of carbon nanotubes using alumina template and its thermal annealing effects
Wang Sen, Yu Guo-Jun, Gong Jin-Long, Zhu De-Zhang, He Sui-Xia, Zhu Zhi-Yuan, Xu Hong-Jie
2005, 54 (10): 4949-4954. doi: 10.7498/aps.54.4949
Abstract +
Highly uniform multiwall carbon nanotubes (MWCNTs) were synthesized using templ ate confining growth technique in combination with high temperature annealing. Scanning electron microscopy (SEM) images show that the morphology and dimensi on of raw carbon nanotubes (CNTs) synthesized by template confining growth techn ique is completely controlled by the template structure. Transmission electron m icroscopy (TEM) and x-ray powder diffraction (XRD) studies reveal that the tube wall has a mixed structure of amorphous carbon and graphite nanocrystallites. To reduce crystallite defects and the content of amorphous carbon, a series of hig h temperature annealing (1100—2400℃) of the raw CNTs were carried out. In addi tion, the tube wall crystallization behavior under high temperature was prelimin arily studied. The experiment results show that high temperature annealing is an effective way to improve the quality of MWCNTs.
Fragmentation in DNA double-strand breaks
Wei Zhi-Yong, Zang Li-Hui, Li Ming, Fan Wo, Xu Yu-Jie
2005, 54 (10): 4955-4960. doi: 10.7498/aps.54.4955
Abstract +
DNA double strand breaks are important lesions induced by irradiations. Random breakage model or quantification supported by this concept is suitable to analyze DNA double strand break data induced by low LET radiation,but deviation from random breakage model is more evident in high LET radiation data analysis. In this work we develop a new method , statistical fragmentation model , to analyze the fragmentation process of DNA double strand breaks. After charged particles enter the biological cell, they produce ionizations along their tracks, and transfer their energies to the cells and break the cellular DNA strands into fragments. The probable distribution of the fragments is obtained under the condition in wh ich the entropy is maximum. Under the approximation E≈E0+E1l+E2l2, the distribution functions are obtained as exp( αl+βl2) . There are two components, the one proportional to exp(βl2),mainly contributes to the low mass fragment yields, the other comp onent, proportional to exp(αl),decreases slowly as the mass of the fragments i ncreases. Numerical solution of the constraint equations provides parameters α and β. Experimental data , especially when the energy deposition is higher, sup port the statistical fragmentation model.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Numerical modeling of non-linear characteristics for barotropic atmosphere with external forcing
Dai Xin-Gang, Wang Ping
2005, 54 (10): 4961-4970. doi: 10.7498/aps.54.4961
Abstract +
Some characteristics of barotropic atmosphere are illustrated by numerical modeling, basing on a potential vorticity equation with forcing, dissipation, and non -linear interaction. For the barotropic potential vorticity equation (named the barotropic model) on a β-plane channel its solution is a stationary, wave-like pattern under a certain thermal forcing, while a quasi-periodic oscillation betw een two essential flow patterns appears if north-south thermal heating and wave- like topography are added as the model forcing. The oscillation has a period abo ut 15d, very similar to atmospheric index cycle in middle and high latitudes. Th e low-index pattern corresponds to a blocking flow, whereas the high index one i s an intensive westerly flow. More oscillation solutions are expected when the e quation is under periodic boundary condition with a strong thermal forcing, and a similar quasi-periodic solution can be obtained, which also results from a wav e topography forcing. However, its low index pattern is symmetrical, and differe nt from the blocking pattern produced by the β-plane model. When the heating fo rcing becomes weak, there also exists a stationary solution. Therefore, the char acteristics of atmospheric index cycle may not be soundly manifested by an analy tical solution or numerical solution under periodic boundary condition using low -order spectrum method that approximates the barotropic model in the β-plane ch annel.
LETTERS
Conserved quantity and stability of Birkhoffian system
Xu Zhi-Xin
2005, 54 (10): 4971-4973. doi: 10.7498/aps.54.4971
Abstract +
It is showed that Stability of Birkhoffian system can be determined by its conserved quantities. If a conserved quantity or a combination of some conserved quantities became a Liapunov function,then it can be used to study the stability of equilibrium and the stability of motion of the system.
The two generalized solutions for the stationary axisymmetric vacuum garvitational field
Wu Ya-Bo, Dong Peng, Zhao Guo-Ming, Deng Xue-Mei
2005, 54 (10): 4974-4978. doi: 10.7498/aps.54.4974
Abstract +
In this paper by applying Ehlers transformation to Schwarzschild and Kerr soluti ons of Ernst equation and introducing the proper coordinate transformations, the two solutions of the Ernst equation, i.e., the so called generalized NUT-Taub ( GNT) solution and generalized Kerr-NUT (GKN) solution are obtained, which not on ly can reduce to the well-known Schwarzschild and Kerr solutions when the parame ter L=0, but also can also reduce to the NUT-Taub metric and Kerr-NUT metric res pectively when the parameter LM and if taking 1-LM2≈1. It is showe d that in the NUT-Taub and Kerr-NUT solutions the range of value for the paramet er l (interpreted as the gravomagnetic monopole) can't be arbitrary and should be limited by mass of the source to |l|M.
Effect of pre-pulses on capillary discharge soft x-ray laser
Zheng Wu-Di, Peng Hui-Min, Cheng Yuan-Li, Luan Bo-Han, Wu Yin-Chu, Zhao Yong-Peng, Wang Qi, Yang Da-Wei
2005, 54 (10): 4979-4984. doi: 10.7498/aps.54.4979
Abstract +
On a capillary discharge setup lasing in Ne-like Ar at 46.9nm, the ablation of c apillary wall was investigated for polythene and alumina material at both of inh erent 2—5kA-pre-pulse of setup and separate pre-pulse of 20A by measuring soft x ray emission from the capillary discharged. For inherent pre-pulse and polythe ne capillary, the ablation is too large to create uniform plasma columns and it is impossible to obtain lasing. In the case of 20A-pre-pulse and alumina capilla ry, the ablation decreased remarkably and the laser spike pulse was distinguishe d on an x-ray diode because the uniform Z-Pinch plasma column had formed.