Vol. 54, No. 9 (2005)
2005, 54 (9): 3967-3970. doi: 10.7498/aps.54.3967
The oscillation for a class of coupled systems in the El Nio-Southern Oscillatio n (ENSO) mechanism is studied. Using the perturbation theory and perturbative me thod, the uniformly valid asymptotic expansions of the solution for a class of E NSO model are obtained easily.
2005, 54 (9): 3971-3974. doi: 10.7498/aps.54.3971
A class of models of equator sea-air coupled oscillators is studied. Using the perturbative method the asymptotic solution of the corresponding model is obtained.
A generalized Chaplygin system is written in the form of containing the Lagrangian of the system which admits a reduction to an unconstrained system under certain conditions. This paper presents these conditions and two examples are given to illustrate the application of the result.
2005, 54 (9): 3978-3982. doi: 10.7498/aps.54.3978
Starting from Newtonian kinetic equations of a particle system, the energy of higher order-velocity of the system is introduced; higher-order Lagrange equations, higher-order Nielsen equations and higher-order Appell equations of a holonomic mechanical system are derived, from which we prove that the three kinds of higher-order differential equations of motion of the holonomic system are equivalent to each other. The result indicates that the higher-order differential equations of motion of the holonomic system reveal the relationship between the chan ges of the system's motion state and the rate of change of force at every order, which cannot be obtained by using Newtonian kinetic equations and the tradition al analytical mechanical equations. Therefore, the higher-order differential equ ations of motion of the holonomic system are a complement to the second-order di fferential equations of motion, including Newtonian kinetic equations and the tr aditional Lagrange equations, Nielsen equations and Appell equations.
2005, 54 (9): 3983-3986. doi: 10.7498/aps.54.3983
The Mei symmetry, i.e.the form invariance, of a Vacco system is studied. The Definition and the determining equation of Mei symmetry in the Vacco system are given. The relations among the Mei symmetry, the Lie symmetry and the Noether symmetry are studied, and the conserved quantities of the Vacco system are obtained. An example is finally given to illustrate the application of the result of this paper.
Steadiness of relatively rotation dynamics equation and it’s solution for a kind stickiness flexibility coefficient
2005, 54 (9): 3987-3991. doi: 10.7498/aps.54.3987
Establishing a kind stickiness flexibility rotation dynamics equation of the cylinder between random two cross sections,discussing steadiness of relatively rotation angle.Gaining solution for a kind stickiness flexibility coefficient because the equation is non-homogeneous ordinary differential equation group of order 2 linear of variable coefficient,and there isn't unified solution to this equation group.
A direct algebraic method to obtain solitary solutions of nonlinear differential-difference equations
2005, 54 (9): 3992-3994. doi: 10.7498/aps.54.3992
In this letter, we extend a direct method for constructing solitary solutions of nonlinear differential-difference equations.Hybrid lattice equations are chosen to illustrate this method.As a result, several solitary solutions are obtained with the help of Maple.This method can also be used in other nonlinear differential-difference equations.
2005, 54 (9): 3995-3999. doi: 10.7498/aps.54.3995
A theoretical scheme for multi-user quantum authentication and key distribution in a network is proposed. Similar to the authentication architecture of the netw ork in classical cryptography, a distributed client/server architecture with the shared Einstein-Podolsky-Rosen(EPR) entangled pairs between each user and his t rusted server used for the authentication and key distribution is proposed. Base d on this architecture, any-to-any multi-user quantum authentication and key dis tribution is realized. The trusted server only provides the authentication betwe en users and swaps the entanglement between the particles so as to entangle the particles of the two users who want to communicate secretly. The key generation is performed by the requesting user. Each user in a network only shares Einstein -Podolsky-Rosen entangled pairs with the trusted server and communicates with th e trusted server through the classical channel and quantum channel. Users need n ot share EPR entangled pairs with each other so that the number of EPR pairs in the network is reduced from O(n2) to O(n).
A new approach to study the dynamics of the deformation of vesicles discrete-space variational method
2005, 54 (9): 4000-4005. doi: 10.7498/aps.54.4000
A new approach, namely discrete-space variational method(DSVM) is developed to study the dynamics of deformation of a two-dimensional vesicle. It can overcome the difficulties in the previously analytical or numerical methods which were de signed to solve the shape-equation of the vesicle. Also it is a correct and stab le method because its computational results accord well with those gained by the other methods. Furthermore, it can be used to describe the three-dimensional ve sicle without any symmetry, and takes into account the long-range interaction fo r avoiding the intersection of membranes.
2005, 54 (9): 4006-4011. doi: 10.7498/aps.54.4006
A Hash function construction method based on spatiotemporal chaos is proposed. We take the rumor after linearly transformed as a group of initial values and utilize the one-way coupled map lattice of spatiotemporal chaos to iterate the grou p of initial values concurrently.Then in spatiotemporal chaos convergence the pr oper items of the chaos convergence produced in the last space are linearly tran sformed into Hash value of 128 bits.The result obtained shows that the Hash func tion based on spatiotemporal chaos have advantages of irreversibility,weak colli sion and sensitivity to initial values.The method has a stronger secret performa nce than the Hash function based on low-dimensional chaos maps, and it is simple to be realized.
Synchronization of chaotic neural networks based on adaptive inverse control and its applications in secure communications
2005, 54 (9): 4012-4018. doi: 10.7498/aps.54.4012
Based on adaptive inverse control theory, a new chaotic neural networks synchron ous system and its secure communication are designed. The synchronization of cha otic neural networks system in the presence of perturbation is studied. The prop osed method can overcome effectively the noise pollution of channel in transmitt ing information. The numerical experiments show that the proposed secure communi cation scheme has advantages of flexible implementation, fast synchronization, h igh-quality recovery of information and large amounts of secret key for informat ion encryption.
2005, 54 (9): 4019-4025. doi: 10.7498/aps.54.4019
A new chaos control method based on Least-Square Support Vector Machines (LS-SVM) is proposed which has the excellent nonlinearity approximation ability and b etter generalization capability. Many chaotic systems can be composed into a sum of a linear and a nonlinear parts. LS-SVM has been applied in off-line identification of nonlinear part in continuous chaos system, and the identification mode l has been joined in system to compensate nonlinearity. Subsequently a linear st ate feedback controller has been developed to drive chaotic system to desirable points. It is proven by simulations for three representative continuous chaotic systems that the proposed method is effective to control the chaotic system and closed-loop system with state feedback, and the LS-SVM approximator is stable.
2005, 54 (9): 4026-4030. doi: 10.7498/aps.54.4026
This paper investigates the synchronization of two linearly coupled unified chaotic systems. A new sufficient condition of global asymptotic synchronization is attained from the theory of stability of time-varying systems. In addition, compared with the previously proposed method, the sufficient condition for the synchronization of two linearly coupled unified chaotic systems is simpler and le ss conservative, and the range of coupled coefficients is wider. Numerical simul ation shows the effectiveness and feasibility of this method.
2005, 54 (9): 4031-4037. doi: 10.7498/aps.54.4031
To analyze the security of tangent-delay ellipse reflecting cavity-map system (TD-ERCS) from the point view of cryptography, a simple pseudo-random number generator (PRNG) is proposed with parallel TD-ERCS in this paper. Users' keys are n o longer fixed, and can be chosen in the interval [264, 26 72] arbitr arily in the PRNG. By testing the basic statistic characteristics such as equili brium, runs and correlation of the binary pseudo-random sequences (viz. TD-ERCS sequences) being generated from the PRNG, and comparing with m-sequences, the lo gistic sequences, Chebyshev sequences and SCQC sequences, the experimental resul ts show that TD-ERCS sequences have better statistic characteristics.
2005, 54 (9): 4038-4043. doi: 10.7498/aps.54.4038
This paper studies how to suppress the abnormal vibration in a dynamic system wi th clearance. The abnormal vibration contains the bifurcations or chaotic motio n due to the change of some parameters of the nonlinear system. This paper prop oses a method to suppress chaotic motion by applying an external periodical for ce to the system. The periodical force is adjusted according to some real-time a lgorism related to an error between real-time states and the states when the sy stem is stable. This method has been applied to a two-degree-freedom impact vibration system. With numerical simulation, the effectiveness of the method is demonstrated.
Studies on the density profiles of square-well chain fluid confined in a slit pore by density functional theory
2005, 54 (9): 4044-4052. doi: 10.7498/aps.54.4044
The density profiles of square-well chain fluid confined in two planar walls are calculated using density-functional theory based on the weighted-density appro ximation of Yethiraj. The free energy functional of the system consists of an id eal part and excess part. We obtain the excess part by the equation of state of corresponding uniform system combined with the weighted-density approximation. We adopted respectively the equations of state based on cavity correlation fun ction and the statistically associating fluid theory. The calculated density pro files are compared with the corresponding Monte Carlo simulation data at differe nt chain lengths, temperatures, volume fractions and different attractions of t he wall. For a square-well chain fluid confined in two hard planar walls, result s from both equations of state are in good agreement with that of the Monte Car lo simulations at high temperature and high volume fraction. Both results devia te from the Monte Carlo result at low temperature and low volume fraction. The density profile in hard wall slit pore calculated from the equation of state of SAFT-VR is in better agreement with the available simulation data than that fro m the equation of state developed by Liu et al. We find that the equation of st ate has significant influence on theoretical prediction. For the walls with attr active forces, predictions from both equations of state deviate from the simula tion data. This deviation results from the increasing non-uniformity of the flu ids. Therefore, more suitable weighted-density function is needed to improve the density-functional theory.
2005, 54 (9): 4053-4057. doi: 10.7498/aps.54.4053
The electric-field-induced strain in Rh-doped BaTiO3 single crystals increases with increasing ageing time at 80℃. After 27 days' ageing, the strain can reach 1.11% under bipolar field cycling conditions. However, the strain under mo nopolar field cycles is strongly dependent on the drive frequency and reaches as high as 0.95% at frequency of 0.01Hz. The hysteresis loop (P-E curve) of the aged sample is similar to a wasp-waisted hysteresis loop. Ageing can significant ly improve the electro-strain effect in the Rh-doped BaTiO3 crystal a nd make t he BaTiO3 crystal a promising and lead-free material for novel applic ations in ultra-large strain and nonlinear actuators.
2005, 54 (9): 4058-4064. doi: 10.7498/aps.54.4058
Present methods using spectral reflected imaging for detection of lint trash suf fer from some fundamental limitation because the trash almost has the same refl ected characteristic as the lint. To effectively detect the trash in lint, a met hod using transmitted imaging technique was proposed and the experimental pheno menon was analyzed in detail. The transmitted imaging model was constructed bas ed on analyzing the trash and lint absorption characteristics. And the impacts o n imaging target by the type and energy of light source as well as thickness an d velocity of lint movement were also discussed. After analyzing the transmitted photo propagation characteristic, a method of capturing non-diffuse photo using high-speed CCD and statistic filtering processing was developed for enhancement of the imaging target. Furthermore, the relation between the exposure time of high-speed CCD and the target distinctness was determined. The result indicated that the method is effective to acquire a distinct target image using the transmitted imaging detection and imaging target enhancement. And the image is consistent with the actual target. This method not only can provide an effective way to detect the white and colorless trash in cotton, but also can be applied to other imaging system such as the infrared and other band spectral imaging. It is believed that this weak target transmitted imaging system is an effective way to detect wcak target.
Study of the technique of 4-face coated pyramid prism for measurement of upper atmospheric wind field
2005, 54 (9): 4065-4071. doi: 10.7498/aps.54.4065
The principle of measurement of upper atmospheric wind field has been described first by using the technique of 4-face coated pyramid prism (CPP). If the anti-r efraction films is coated by λ/4（λwavelength）stepped optical path difference (OPD), there can be obtained 4 interference intensities for one fringe simultan eously to measure the upper atmospheric wind field. After correlative parameters of CPP technique are calculated, the CPP's vertex angle must be larger than 24 degree and the width of symmetric incident beam to CPP vertex may be less than 8 mm by LF7 prism and MgF2 anti-refraction films, so that it can be use d to dete ct the upper atmospheric wind for 9°×9° interferometer's field of view (FOV) and CCD 4.5°×4.5°. Finally, we made a simulation test for 2-face coated prism , two group of speckle patterns of deflection light and intensities on CCD have been obtained for prism vertex angle 60° and ９０°. By copying the two-speckl e patterns to obtain CPP's four ones, it can achieve “four intensities way" for upper atmospheric wind field measurement. The test result is made sure of this way to measure the atmospheric wind. This way has developed the technique of pas sive measurement of wind field.
2005, 54 (9): 4072-4078. doi: 10.7498/aps.54.4072
The preliminary experimental results obtained for the energy spectra of high-power ion beam(HPIB) with a pile of thin films on FLASH Ⅱ accelerator are reported. Code was developed to calculate the theoretical energy-loss of proton and C ion beams transmited through the Mylar films with different thickness. T he apertures of Faraday Cups are covered with Mylar films of different thicknes s, and then the signal attenuations can be recorded with oscilloscope. The energ y spectra of HPIB and the diode voltage are obtained according to the signal al lenuations. The diode voltage measured with a pile of thin films agrees with the voltage measured with a differential ring. And the ion number versus time curv e was given. In addition, the ion energy of HPIB is also measured with Thomson spectrometer and time of flight method and the results agree with those measured with a pile of thin films.
Because the central wavelength of terahertz (THz) pulse is long, the spatial resolution of the THz detection is limited to sub-millimeter due to the diffraction effect. We report a new THz microscopy by attaching an electro-optical crystal directly to a thin generation crystal. By focusing tightly the optical pump beam, the detected spatial resolution can reach several microns. In additior this mechanism cacan avoid the loss of intensity and spectrum components. In this letter, the configuration and characteristics of this device are described in details.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2005, 54 (9): 4084-4086. doi: 10.7498/aps.54.4084
By using the two approaches, Regge trajectory and meson mixing, we estimate the mass of the isoscalar state ( composed mostly of ss— quarks) of the 3１Ｓ０ meson nonet. The two approa ches respectively give the values of 1853 MeV and 1849±12 MeV, which would be useful for searching for the candidate of this state experimently.
2005, 54 (9): 4087-4091. doi: 10.7498/aps.54.4087
In this paper, the one-dimensional time-dependent Schrdinger equation is numerically solved; in muon-catalysed fusion, the influence of different laser inte nsities and wavelengths on the μ3He ionization is studied. Resul ts show t hat the ionization probability is about 2.7 percent when the magnitude of laser intensity is from 1019 to 1023W/cm2, an d can increase obviously wh en the laser intensity reaches 3.0×1024 W/cm2. Furthe rmore, the ionizat ion probability increases with the laser intensity and wavelength, that is, to e nhance the efficiency of the muon-catalysed fusion.
2005, 54 (9): 4092-4096. doi: 10.7498/aps.54.4092
The tan2x potential is introduced to describe the interaction between a partic le and a crystal.In the frame of quantum mechanics, Schrdinger equation is red uced to the hypergeometric equation.The eigenvalues are calculated also.It is sh own that the conformity between the theory and the experiment is good.
Polarization direction modulation for spin-polarized electrons with liquid crystal variable retarder
2005, 54 (9): 4097-4100. doi: 10.7498/aps.54.4097
The production of spin-polarized electrons and the modulation of polarization direction with liquid crystal variable retarder (LCVR) are discussed. The LCVR ca n play the roles of 1/4, 1/2, 3/4 and whole-wave plates with special voltages in the optical system. And the advantages of using LCVR instead of Pockels cell an d 1/4λ plate are the insensitivity to the incident photon direction, and the va riability of retardation over a large wavelength range without mechanical moveme nt. The polarization direction of spin-polarized electrons can be modulated easi ly by switching the helicity of the circularly polarized light. In order to dete rmine the photon polarization, the spinning polarimeter is developed. And the re sult is also described.
ATOMIC AND MOLECULAR PHYSICS
2005, 54 (9): 4101-4107. doi: 10.7498/aps.54.4101
On the basis of dynamic criterion for free electrons, a traditional averaged atomic model (AAM 1) is improved in several aspects. The continuum radial wave function in central field approximation is normalized in a certain boundary condition. The contributions of the free electrons are dealt with in four parts to improve the precision of electron pressure. The condition of normal density is spontaneously satisfied. As samples electron pressure of Iron, Nickel, Lead and Americium are calculated and compared with the results other theories and experiments.
2005, 54 (9): 4108-4112. doi: 10.7498/aps.54.4108
The ionization energy spectrum and the spherically averaged momentum distribution of 1a′ inner valance orbital for cyclopentene have been investigated by using a high resolution (ΔE=1.15eV, Δp≈0.1a.u.) electron momentum spectrometer. The impact energy was 1200eV plus binding energy (i.e. 1202—1234eV) and a symmet ric non-coplanar kinematics was employed. The experimental momentum profile of the 1a′ inner valence orbital is obtained and compared with the theoretical m omentum distributions calculated by using Hartree-Fock and density functional th eory methods with the basis sets STO-3G, 6-31G, 6-311++G** and au g-cc-pVTZ. The pole strength of the 1a′ inner valence orbital is estimated and the electron correlation effects are discussed.
Theoretical calculation of vertical migration velocity for helium-radon cluster ions under ideal condition
2005, 54 (9): 4113-4116. doi: 10.7498/aps.54.4113
The process in which the helium-radon clusters come into being was discussed.According to the traditional theory of mechanics,the theoretical calculation formula of vertical migration velocity for helium-radon clusters has been deduced.The maximal velocity and the time needed for the helium-radon clusters being accelerated to the maximal velocity are also given.
2005, 54 (9): 4117-4123. doi: 10.7498/aps.54.4117
Geometric structures, electronic states and energies of GanP and GanP2 (n= 1—7) clusters have been studied using the density functional theory. Structural optimization and frequency analysis were carried out at the B3LYP/6-31G* level.All ground states of GanP and GanP2 (n=1—7) clusters have been obtained.Our calculations reveal that there exists a transition from planar to spacial structures at n=5 with increasing cluster size. The strong P-P bond is favored over P-Ga in GanP2 (n=1—7) clusters. Among different GanP and GanP2 (n=1—7) clusters, Ga3P,Ga4P, GaP2, Ga2P2 and Ga4P2 are more stable. Their stability tends to reduce with the increase of the number of total atoms.
CLASSICAL AREA OF PHENOMENOLOGY
2005, 54 (9): 4124-4128. doi: 10.7498/aps.54.4124
Terahertz radiation generated by ultra short laser pulses has a broad band width in the far-infrared band.It is a new research field on terahertz wave interacting with materials,especially bio-materials.In this paper we studied five kinds of vegetable oil and two kinds of animal fats under different states using THz-TDS(THz time-domain spectroscopy).The refractive index and absorption coefficient of these materials are presented in the range from 0.2 to 1.6THz.The result hows that different oils have different refractive indices.The refractive indic es of vegetable oils have a gentle decline and the refractive indices of animal fats increase with temperature.The coefficients of absorption also increase with frequency.It's a meaningful result for the applications of biomedical sensing a nd imaging.
2005, 54 (9): 4129-4135. doi: 10.7498/aps.54.4129
The dynamical properties and spectrum characteristics of a Λ-type atom with an external field embedded in three-dimensional photonic crystals are investigated . With the help of numerical calculation and theoretical analysis, we find that the populations of the upper and lower levels display quasi-oscillation, and the frequency and amplitude of the oscillation is greatly affected by the intensity of the external-driving field Ω, the detuning δ and the background decay of the upper level γ. Ｓpontaneous emission of the atom is apparently influenced by the relative position of the upper level from the forbidden gap. Furthermore, the properties of the emission field around the atom are analyzed by means of s pontaneous emission spectrum.
2005, 54 (9): 4136-4140. doi: 10.7498/aps.54.4136
We have observed the reduction of group velocity of light via electromagnetically induced transparency (EIT) and measured the dependence of pulse delay on the one-photon detuning in a three-level Λ-type atomic system. The results show that due to the effect of Doppler broadening the light speed reduction is signif icant in a range of ±600MHz one-photon detuning. Under the condition of consid ering the Doppler shift of frequency, the pulse delay as a function of the one-p hoton detuning is numerically calculated. The experimental measurements are in g ood agreement with the theoretical results. These researches provide theoretical and experimental references for controlling the group velocity of light by mean s of one-photon detuning.
2005, 54 (9): 4141-4145. doi: 10.7498/aps.54.4141
The high-polarized single-photon emission in single anisotropic InGaAs quantum d ots excited by linear pulse excitation was discussed. The expression of the pola rization and cross relaxation between two orthogonal eigenstates was given. It w as revealed that the cross relaxation increased with intensity of the excitation , which resulted in the decrease of polarization factor with the input pulse a rea.
2005, 54 (9): 4146-4150. doi: 10.7498/aps.54.4146
Based on the avalanche model, the evolution of femtosecond laser induced micro-e xplosion in fused silica was investigated. The microscopic processes, including the production of conduction band electron (CBE), laser energy deposition, CBE a nd energy diffusion were solved by a finite element method in two-dimensional cy lindrical coordinates. The accumulated net charge and the electrostatic field we re also calculated. The results indicate that the CBE and energy diffusions play an important role in the micro-explosion in dielectrics.
2005, 54 (9): 4151-4156. doi: 10.7498/aps.54.4151
On the basis of the multi-longitude theory of stimulated Brillouin scattering (S BS), a group of coupling wave equations without limitation to the mode separatio n of a laser was deduced while the random initial phases of the multi-longitudin al modes were introduced for SBS pumped by a free-operating laser. The dependenc es of broadband SBS threshold on the bandwidth of the laser, the number of the l aser modes, the mode separation of the laser, the linewidth of Brillouin, and th e ratio of the SBS interaction length to the laser coherence length were discuss ed in detail. And the theoretical results were consistent with the experimental results reported.
Hyperfine stucture during nanocrystallization of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy irradiated by laser
2005, 54 (9): 4157-4163. doi: 10.7498/aps.54.4157
The material composed of a definite amount of nanocrystalline phase α-Fe(Si) with a double-phase structure was produced by laser irradiation on the amorphous Fe735Cu1Nb3Si135B9 alloy with a laser power ranging from 50 to 300W, scanning speed 20mm/s, laser beam spot 20mm. Hyperfine structures of the nanocrystallized samples were analyzed by Mssbauer spectra. Experimental result shows that after the CO2 laser irradiated on the amorphous allo y Fe735Cu1Nb3Si135B 9, its hyperfine magnetic field dist ribution transformed from a single peak to double peaks with the change of laser power. When irradiated at a high laser power, it formed a double-peak structure and the peaks moved to a high field position. Nanocrystallization of amorphous Fe7 35Cu1Nb3Si135B9 ir radiated by a higher laser power produces fou r hyperfine structures, i.e. two primary crystal phases with relatively small hy perfine magnetic field and two nanocrystalline phases with a relatively large hy perfine magnetic field. The major crystal phase is the α-Fe(Si) phase of DO3 whose hyperfine magnetic field is comparatively larger (17—25MA/m).
2005, 54 (9): 4164-4168. doi: 10.7498/aps.54.4164
The efficient amplification of stimulated Raman scattering in Acetone enhanced by dicyanomethylene(DCM) dye fluorescence and the amplification characteristics are reported in this paper. Under the various concentrations of DCM, various inte nsities of input Stokes signal and various pump laser intensities, the input and output Stokes wave intensities are measured in the experiment. At the concentration of 2×10-4 mol/L for DCM solution in ethanol, the bigg est enhan cement factor of Stokes wave reaches 57 The higher the intensity of pump l aser or input Stokes signal, the higher the intensity of output Stokes wave, an d if the input Stokes is too high, the enhancement coefficient may decrease, the so-called enhancement saturation.
Theoretical model and characteristics investigations of dual-channel optical chaotic communication system
2005, 54 (9): 4169-4175. doi: 10.7498/aps.54.4169
A theoretical model characterizing a recent experiment of dual-channel optical chaotic communication has been presented, and is proved to be reasonable by comparing the numerical simulation with the experimental results. After deducing the transmission function of semiconductor laser by small-signal analysis, how toreasonably select the system parameters in order to realize the effective transmission of signal has been specified. Moreover, the cross talk between two channels has been analyzed quantitatively. For a 250MHz modulation message, the nume rical simulation shows that it can be hidden efficiently during the transmission in the system and decoded easily.
2005, 54 (9): 4176-4181. doi: 10.7498/aps.54.4176
We have investigated the accuracy of wavelet analysis of spectral shearing inter ferometry signal with noisy data. Specifically, we have examined at the effects of additive noise, multiplicative noise, and quantization of the interferogram o n the reconstruction of the spectral phase, and revealed that the wavelet transf orm is a robust technique to retrieve spectral phase from the noise background. We also show that the phase of a femtosecond pulse can be identified from the tr ace of wavelet transform.
2005, 54 (9): 4182-4185. doi: 10.7498/aps.54.4182
A low-threshold self-starting Kerr-lens mode-locked Ti:sapphire laser was demons trated by use of a tight focusing cavity design and a semiconductor saturable-ab sorber mirror (SESAM). With a 3% and a 12% output couplers, we achieved mode-loc king thresholds as low as 390 and 600mW, respectively. Stable femtosecond laser pulses with average power of 114mW were generated for pump power at 12W, which corresponds to a typical duration of 17fs and bandwidth of 47nm. The pump power range for mode-locking covers from 600 mW to 48W at a 12% output coupler, an d the mode-locking stability is improved.
2005, 54 (9): 4186-4191. doi: 10.7498/aps.54.4186
In this paper the author proposes a new method to solve the nonlinear “loop” soliton equation,that is,to directly find the solution of the analytic function U(ξ) of the equation by using the traveling wave parameter ξ and the power ser ies expansion, and to find the exact solution of the equation (including the sol itary wave solution) by directly observing the variation of the equation using M atLab to depict the functional relationship of U(ξ)-ξ for the cases of c→ligh t speed and c→sound speed.This method should be helpful in solving difficult no nlinear soliton equations.
Buckling of a single wall carbon nanotube under an axial pressure based on the nonlocal elastic theory
2005, 54 (9): 4192-4197. doi: 10.7498/aps.54.4192
A shallow shell model is developed for the elastic buckling of a single wall car bon nanotube under a uniform external axial pressure by using the nonlocal elastic theory. Effects of the small size scale are incorporated in the formulation Critical conditions are given under the axial buckling pressure for a single-w all carbon nanotube. Influences of the small size scale on the axial buckling pr essure are found. It is concluded that the axial buckling pressure for a carbon nanotube could be overestimated by the classic shell model without considering t he effect of the small size scale.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2005, 54 (9): 4198-4202. doi: 10.7498/aps.54.4198
Ion extraction from laser-induced plasma is one of the key problems in atomic vapor laser isotope separation (AVLIS) engineering. In an electrostatic field, the plasma potential is higher than both electrodes due to the plasma shield effect. And sheaths exist on both sides of the electrodes. Using numerical simulation, it has been proven that ions can be extracted by the positive electrode. In conventional ion extraction experiments using an electrostatic field, the ions are only collected at the negative electrode. We focused on the positive electrode as well as the negative collector in our experiments. The Faraday cups, fix ed on both electrodes, were used to collect the extracted ions and avoid the eff ect of power supply. As a result, the positive electrode can also extract ions. The collection ratio of positive and negative collectors decreases, as the appli ed voltage increases.
Acceleration of a pre-accelerated electron by an ultra-short and ultra-intense laser pulse in vacuum
2005, 54 (9): 4203-4207. doi: 10.7498/aps.54.4203
Acceleration of a pre-accelerated electron by an ultra-short and ultra-intense laser pulse in vacuum has been explored. The deceleration by the descending part of the laser pulse can be neglected when the pre-accelerated electron is accelerated by the ascending part of the pulse. Because the acceleration dist ance is much longer than for a initially stationary electron, the energy gain is much larger. The net energy gain can be up to 01GeV with a laser intensity of 1019W/cm2 and an initial electron energy of 45Me V. Final energy ga in of the electron as a function of its initial condition and laser parameters h as also been discussed.
Electron capture and violent acceleration by a tightly focused ultra-short ultra-intense laser pulse in vacuum
2005, 54 (9): 4208-4212. doi: 10.7498/aps.54.4208
A low-energy relativistic free electron capture and violently acceleration by a tightly focused ultra-short ultra-intense laser pulse in vacuum is presented in this paper. The results show that the electron is mainly accelerated by the long itudinal ponderomotive force and the energy gain is sensitively dependent on the retarded time, initial energy and the incident angle of electron. On the other hand, the energy gain is not very sensitive to the pulse width when it is larger than 10λ.
2005, 54 (9): 4213-4216. doi: 10.7498/aps.54.4213
The magnetic and dielectric properties of the ferroelectromagnet(FEM) Pb(Fe1／2Nb1／2)O3 (PFN) single crystals have be en investigated.Anoma lies i n the dielectric constant as a function of temperature have been observed near i ts Neltemperature of ～143K，which are indicative of the so-called magnet oelectric coupling between the ferroelectric and antiferromagnetic orders in thi s compound.It is demonstrated that a weak magnetic transition appeared at the te mperature a little below the Nel temperature，which confirms the earlier predi ction from the Monte Carlo simulation in a qualitative sense.The magnetic hyster esis measurement proves that there does exists a weak magnetic order in PFN crys tal below its Nel temperature.
Density modulation produced by ultrashort laser pulses and the phase reflection induced in underdense plasmas
2005, 54 (9): 4217-4222. doi: 10.7498/aps.54.4217
It is shown theoretically and by particle-in-cell simulations that the interferi ng fields of the incident and reflected laser pulses can produce deep plasma den sity modulations in underdense pre-plasmas.This occurs within a few tens of lase r cycles if the incident laser pulse is at moderate intensities such as 10 15W／cm2Such density modulations can serve as a Bragg reflector ,which results in phase reflection from underdense plasmas.Because the deep dens ity modulations are just a period of half a wavelength in the plasma，the reflec ted wave reaches the maximum by resonance with a reflectivity up to near 100％.T he phase reflection can also be observed from the plasma with a linear density p rofile，which can significantly reduce the laser absorption by fusion targets.
2005, 54 (9): 4223-4228. doi: 10.7498/aps.54.4223
The dispersion equation of a coaxial arbitrary-shaped-groove slow-wave structure is derived by means of an approximate field-theory analysis，in which the continuous profile of the groove is approximately replaced by a series of recta ngular steps，and the field continuity at the interface of two neighboring step s and the matching conditions at the interface between the groove region and central region are employed.The simulation results by CST MWS are in good agreement with the numerical calculation results of the dispersion equation.We have calculated the dispersion characteristics and the coupling impedance of the slo w-wave structures with some special groove shape.It shows that the dispersion c haracteristic of the triangle-groove structure is the weakest and the coupling i mpedance of it is the least, while the dispersion characteristic of the inverted -trapezoid-groove structure is the strongest and the coupling impedance of it is the largest.
2005, 54 (9): 4229-4235. doi: 10.7498/aps.54.4229
The beam shape distortion of the pseudospark pulsed electron beam in transmissi on has been observed by the beam bombardment of the color changeable film and t he single crystal silicon. Based on the beam self-pinch effect, the mechanisms of the beam shape distortion have been analyzed by the theoretical calculation of the radial force of electron beam. The results showed that the elliptic beam shape was caused by the azimuthal magnetic field of transient currents, which past through the parallel charging capacitor, and the method for solving beam shape distortion in transmission was also presented.
2005, 54 (9): 4236-4239. doi: 10.7498/aps.54.4236
Stable localized hexagonal structure is obtained in Ar dielectric barrier discharge. Its spatiotemporal dynamics is measured. It is found that the discharge moment of the middle filament always precedes that of others. The interval between two adjacent discharges of one micro-discharge varies between a long interval an d a short one alternatively. The experimental results are analyzed and explained by a discharge model of wall charges. It is shown that the filament is affected not only by its own field but also by other filaments during the discharge.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2005, 54 (9): 4240-4244. doi: 10.7498/aps.54.4240
The R(Fe, Mo)12 (R=Nd, Y, Dy) samples have been prepared and measure d by x-ray diffraction at different temperatures. The crystal lattice constant s and degree of the thermal expansion along the different axes are calculated. As a result, we consider that the abnormally thermal expansion of R(Fe, Mo)12 compounds is mainly determined by the Fe-Fe interaction. According to structural parameters of Nd(Fe, Mo)12, the anomaly is caused not on ly by the short Fe-Fe interaction as the previous explanation on other R-Fe inte rmetallic compounds but also by the other strongly positive Fe-Fe interactions. The mechanism of the substitution by Mo affecting the thermal expansion anomal ies is also discussed.
2005, 54 (9): 4245-4250. doi: 10.7498/aps.54.4245
Freezing processes of liquid Cu nanoclusters with atoms of 147，309 and 561 are performed by means of molecular dynamics，which show that the structures of the obtained solid nanoclusters at room temperature are governed by the cooling rate and the clusters' sizes: the smaller clusters and the slower cooling rate bring the icosahedra structures more favorably, and contrarily， for the larger clust ers and the faster cooling rate，the face centered cubic structures will be expe cted in our simulation time. The physical mechanisms of this phenomenon are also discussed in this paper.
Nano-sized graphite patterns were obtained by tailoring graphite sheets using different methods. With focused ion beam etching we are able to produce grooves of minimum width ～ 30 nm. However, at the edges of the grooves there deposit with Ga-C compound which prevents the easy cleavage of the graphite sheets. With electron beam lithography and reactive ion etching techniques we are able to produce graphite patterns of sizes down to 50 nm. Three different types of masks are tested, and the results are compared and discussed.
2005, 54 (9): 4256-4262. doi: 10.7498/aps.54.4256
According to the research of the mesoscopic structure of Fe73.5Cu 1Nb 3Si135B9 by AFM, we propose a model for n anostructured soft magnetic properties; and explain the influence of the frequency on the magnetic properti es successfully using the model. The model possesses the characteristic of Herze r's or Ji Song's model, and supplement their deficiency. We also study the influ ence of the conductivity σ and the permeability μ on the magnetic properties o f Fe73.5Cu1Nb3Si135B9 for the first time.
2005, 54 (9): 4263-4268. doi: 10.7498/aps.54.4263
In this work, amorphous carbon nanowires(ACNWs), formed during ion irradiating m ulti-wall carbon nanotubes (MWCNTs), were annealed at a high temperature of 2400 ℃. Transmission electron microscopy observations revealed that the body of ACNW s had transformed to a tube-like structure similar to that of the original MWCNT s, but the tip structure had various forms and was quite different from the orig inal MWCNTs. Based on the results, we proposed a conceptual model of phase trans ition mechanism.
2005, 54 (9): 4269-4272. doi: 10.7498/aps.54.4269
Transparent and crack-free γ-LiAlO2 single crystal was grown by quic k Czochra lski technique. However, high melting point and easy volatilization degraded the quality of the crystal. The fall with at half maximum(FWHM) value dropped from 1169arcsec to 442arcsec when the crystal was modified by vapor transport equ ilibrium(VTE) technique. But when the temperature of VTE was 1300℃, the FWHM va lue increased to 552arcsec. The ［100］-orientation thermal expansion coeffici ent of the as-grown crystal was 176798×10-6/K, while that alon g the ［0 01］-orientation was 107664×10-6/K. After three VTE treatments , the cor responding thermal expansion coefficients decreased to 166539×10-6/K and 101784×10-6/K, respectively.
2005, 54 (9): 4273-4278. doi: 10.7498/aps.54.4273
The stacking fault in crystals of GaN was studied by high-resolution electron microscope images in combination with image deconvolution. The principle of deconvolution for high-resolution electron microscope images is briefly introduced. It is demonstrated that an image originally does not intuitively reflect the examined crystal structure can be transformed into the structure image. The stacking faults in crystals of GaN were observed with the high-resolution microscope. The image deconvolution was performed for the image, and the atomic configuration in the defect core is seen clearly in the deconvoluted image. Based on this, the type of stacking fault has been determined. Besides, the effectiveness of image deconvolution in studying crystal defects is discussed.
2005, 54 (9): 4279-4284. doi: 10.7498/aps.54.4279
The phonon frequencies at the center of Brillouin zone in a series of chiral single-wall carbon nanotubes were calculated numerically, in which the curvature effect was treated appropriately. According to the numerical results, the classification of the vibration modes for chiral tubes at the center of Brillouin zone were analysed. The relations between frequency-chirality and frequency-tube diameter for 12 non-degenerate vibration modes were illustrated.
2005, 54 (9): 4285-4293. doi: 10.7498/aps.54.4285
The effects of lattice vibration on the system in which the electron is weakly coupled with bulk longitudinal optical phonons and strongly coupled with interfac e optical phonons in an infinite quantum well were studied by using Tokuda' line ar-combination operator and a modified LLP variational method. The expressions for the effective mass of the polaron in a quantum well QW as functions of the we ll's width and temperature were derived. In particular, the law of the change of the vibration frequency of the polaron changing with well's width and temperatu re are obtained. Numerical results of the effective mass and the vibration frequ ency of the polaron for KI/AgCl/KI QW show that the vibration frequency and the effective mass of the polaron decrease with increasing well's width and temperat ure, but the contribution of the interaction between the electron and the differ ent branches of phonons to the effective mass and the vibration frequency and th e change of their variation with the well's width and temperature are greatly di fferent.
Effect of the laser power density on the properties and structures of the diamond-like carbon films deposited by pulsed laser ablation of graphite
2005, 54 (9): 4294-4299. doi: 10.7498/aps.54.4294
Diamond-like carbon films were deposited by high-frequency and high-power pulse d XeC1 excimer laser ablation of pyrolytic graphite targets in a high vacuum ch amber at room temperature. The effects of the laser power density on the propert ies and structures of the films were studied by setting the laser power density on the target at 108, 109 and 1010W/cm2. The optical transparency and the optical band gap as well as the electron diffraction patterns and Raman spectra of the films were investigated. The results demonstrated that the stru ctures of the films varied from amorphous to nanocrystalline diamond with the l aser power density increasing from 108 to 1010W/cm2.
The dynamic control of the templates in selectivity growth from their isomers and the growth mechanism of CVD diamond
2005, 54 (9): 4300-4308. doi: 10.7498/aps.54.4300
The key role of templates in the process of large-scale growth of ordered metastable phase and that of selectivity growth from their isomers with approximately equal free energy have been emphasized. Considering the rational elements in the existing models, the dynamics and thermodynamics theory for the growth process of diamond films have been given: 1) The chemical potential of carbon atoms is higher in the state of hydrocarbon gases than in the solid state. The carbon atoms in hydrocarbon gases may drop down to graphite or diamond surface that has a lower chemical potential. 2) The gas-state carbon atoms may change into the solid state through surface reactions. 3) The effect of surface of the template is a major factor for controlling the way of conversion of the gas-state carbon atoms. The different surfaces (surfaces with different orientations of graphite and diamond) can choose the different structure and energy state of the carbon atoms dropped onto them.4) Therefore, several kinds of different and independent surface reaction processes can occur at different sites of the substrate. These reactions correspond to the growths on different surfaces; 5) The orientation and velocity of these surface reactions are affected by the thermodynamic factors of neighboring surfaces. The direction of interaction determines whether growth or etching occurs for certain crystal surface. Growth of diamond and etching of graphite may be realized in a special range of temperature, of pressu re, of flow ratio of different gases. 6) The critical condition of nucleation wa s determined by the thermodynamic conditions such as local crystal lattice struc ture of the substrate, bonding structure, the gas temperature on the substrate s urface, pressure, the fractional pressure of different kinds of gases, and so on . 7) The plasma system that has energy exchange with the surroundings, and a ser ies of chemical reactions that occur in the gas phase can only provide the requi red non-equilibrium thermodynamic and chemical conditions to keep the growth of certain solid phase surface. The surfaces of diamond and graphite have the chara cter of template, they will dominate the epitaxy pattern of themselves. Heteroge neous substrates have certain local microstructure to play the role of a local t emplate for new phase nucleation. Different local microstructures caused by diff erent substrates, processing method and different chemical conditions will deter mine the orientation character,of the film.
Structural and optical properties of MgxZn1-xO thin films deposited by radio frequency magnetron sputtering
2005, 54 (9): 4309-4312. doi: 10.7498/aps.54.4309
MgxZn1-xO films(0≤x≤030) have been prepared on sap phire substrates by radio frequency magnetron sputtering at a substrate tempera ture of 80℃. Optical and structural properties of the MgxZn1-x O films were studied using transmittance and x-ray diffraction (XRD)spect ra. XRD patterns indicate that the MgxZn1-xO films have he xagonal wurtzite single-phase structure of ZnO and a preferred orientation with the c-axis perpendicular to the substrates without any significant formation o f a separated MgO phase. The c-axis lattice constant of the MgxZn1-xO films decreases gradually with increasing Mg content. Sharp absorp tion edge appeared in the transmittance spectra of the MgxZn1-x O films, the fundamental band gap of the MgxZn1-xO f ilms were estimated, which increases almost linearly from 3.32 eV at x=0 to 3.9 6 eV at x=030
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Molecular dynamics simulations of various metastable structures on Si(001) at different temperatures
2005, 54 (9): 4313-4318. doi: 10.7498/aps.54.4313
By using Stillinger-Weber potential, we have carried out the constant temperature molecular dynamics simulations of surface structures on Si(001) at different temperatures. Our results show that the dimers rearranged into p(2×1) cell are the primary structure on Si(001) surface. Besides this, trimers and c(2×2) metastable structures as well as two-dangling-bond single atoms are observed on the surface at different temperatures. Up to the surface melting temperature, these metastable structures disappear and the simple p(2×1) structure remains on the surface.
2005, 54 (9): 4319-4323. doi: 10.7498/aps.54.4319
Ultraviolet photoelectron spectroscopic(UPS) measurements of the tri (β-naphthyl) phosphine (TNP) film deposited on the Ag(110) surface were made. The TNP derived valence features are located at 38，63，93and 110 eV below Fermi level, and the top of the highest occupied molecular orbital(HOMO) of TNP is located at 25 eV in binding energy. The work function of Ag(110) is about 43 eV, and upon deposition of TNP, the work function decreases to the saturated value of 38 eV. Based on the UPS measurements, the energy level alignment at the interface of TNP/Ag(110) is given, and the results indicate a weak interaction between TNP and the Ag substrate.
Studies of quantum confinement effects of excitons in semiconductor crystallites with the B-spline technique
2005, 54 (9): 4324-4328. doi: 10.7498/aps.54.4324
The behaviors of the ground-state energies and binding energies of the confined excitons in larger CdTe quantum dots(25—35nm) and the smaller CdS quantum dots(025—35nm) are studied variationally by means of the B-spline technique based on the effective mass approximation method. It is shown from the studie s that:(1) The ground-state energies and binding energies of the confined excito ns in the larger quantum dots are not sensitive to the barrier height of potenti al and the dielectric constant of surrounding material as compared to those of s mall quantum dots; (2) The behaviors of the ground-state energies and binding en ergies of the confined excitons in larger quantum dots are very different with t hose of smaller quantum dots (3)The B-spline technique is a better one to descri be the status of excitons confined by quantum wall or well, and this method is f it to calculate the multi-layer quantum dot accurately.
Synthesis of GaN nanowires and nano-pyramids in a two-hot-boat chemical vapor deposition system via an In-doping technique
2005, 54 (9): 4329-4333. doi: 10.7498/aps.54.4329
A two-hot-boat chemical vapor deposition system was modified from a thermal evaporation equipment. This system has the advantage of high vacuum, rapid heating rate and temperature separately controlled boats for the source and samples. These are in favor of synthesizing compound semiconducting nano-materials. By the system, we have synthesized high-quality wurtzite single crystal GaN nanowires and nanotip triangle pyramids via an in-situ doping indium surfactant technique on Si and 3C-SiC epilayer/Si substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and photoluminescence measurements. The GaN nanotip triangle pyramids, synthesized with this novel method, have potential application in electronic/ photonic devices for field-emission and laser.
2005, 54 (9): 4334-4339. doi: 10.7498/aps.54.4334
Direct wafer bonded InP-GaAs structures are studied by FTIR infrared absorbance spectra and FESEM cross-sectional observations. Experiments show that the non-uniformity of bonding pressure during the fabricating step results in the appearance of a spacer-layer at the InP-GaAs interface. By melting wax and filling it into this spacer-layer, locally unbonded areas can be characterized upon the opt ical absorbance peaks at 3.509 μm. The 3.509 μm absorbance-intensity mapping images the non-uniform distribution of bonding pressure, which was obtained by t wo-dimensionally scanning measurement of infrared spectra of samples. Uniformly bonded InP-GaAs structures with uninterrupted interface are fabricated after imp roving the uniformity of pressure of fixture, which will be prospect of preparin g for large scale wafer bonding structures such as optical micro-cavity structur es.
2005, 54 (9): 4340-4344. doi: 10.7498/aps.54.4340
The thermal stability is improved in a magnetic tunnel junction with a nano-oxide layer induced between the antiferromagnetic and pinned ferromagnetic layers, in which the annealing temperature is increased about 40℃. By using Rutherford backscattering spectroscopy, it has been found that the interdiffusion of Mn atoms, responsible for the decrease of TMR during the annealing process, is uppressed across such nano-oxide layer.
2005, 54 (9): 4345-4349. doi: 10.7498/aps.54.4345
Numerical method has been used to analyze the opto-thermionic refrigeration proc ess of semiconductor heterostructure. Based on the drift-diffusion model, curren t continuity equation and Poisson equation are employed to calculate the distrib ution of carriers, the radiative recombination rate and the Auger recombination rate of the semiconductor. In addition, we have calculated the effect of the cha nging of barrier height and the doping density on the refrigeration rate. Thus t he optimum conditions of opto-thermionic refrigeration have been obtained based on these results. This work is of great significance for guiding the experiment research in the future.
2005, 54 (9): 4350-4353. doi: 10.7498/aps.54.4350
Using the result of model-solid theory,we have obtained the relationship between bandgap and strain of Si1-xGex alloy on Si(100) subs trate with x<085 . It was shown that the deviation between the bandgap of strained SiGe and relax ed SiGe is proportional to the strain. According to the theoretical result, a no vel method was suggested to determine the strain state of SiGe/Si through measur ing the bandgap. The strain in the SiGe/Si multi-quantum wells was measured using the new method and the results had good agreement with that from XRD measurement.
2005, 54 (9): 4354-4358. doi: 10.7498/aps.54.4354
The unjustifiable or mistake in the previous magnetism theories has been pointed out in this paper. For a N-electron system with Heisenberg exchange integral A 1+A2 （A1>0, A2ex=-2A1ii ·sj-2A2ii·sj，not H ex=-2Aii·s j as in the previous magnetism theories, where A=A1+A 2. The role of the mi nor term in the exchange Hamilton was considered. Based on the principle of supe rposition of state, the eigenstate of the system with Heisenberg exchange integr al A=A1+A2 （A1>0, A2 21+A22(A11〉+A2‖2 〉), and t he energy (relative to exchange interaction) eigenvalue E =-Nz（A1-A2）-2NzA 22A1+A2=-Nz（A2-A1）-2NzA21A1+A2,were attained，wh ere z is t he number of the nearest neighbours electrons, 1〉 means the state of the syste m when the spins of all electrons in the system arrange parallelly (the parallel spins state, for simply)，2〉 means the state when the spins of all electrons o r the nearest neighbor electrons in the system arrange antiparallelly (the antip arallel spins state, for simply). When A1 =A2≠0 ，X〉=12( 1〉+2〉)， and E=- NzA1, the system is in the spin glass（SG）state，the probabilities o f paralle l and antiparallel arrange for every pair of spins of electron of nearest neighb ours in the system are equal. When A1≠A２，the probabilit ies are not equal, and there coexist the parallel spins state and SG or the antiparallel spins sta te and SG， X〉=1A21+A22［(A1-A2)1〉+A2(1〉+2〉)］,orX〉=1A21+A22［(A2-A1 )2〉+A1(1〉+2〉)］. When the parallel spins st ate and SG or the antiparallel spins state and SG coexist, the energy of the sys tem is lower than that when only FM or AFM exists as in previous theory. Weiss f erromagnetic state or Neel anti ferromagnetic state is just a special state when A1=0 or A2=0.
The temperature and field dependences of the specific heat of single-crystal NdMnO3 were investigated from 2K to 200K under different fields up to 8 T.Corresponding to the Type-A antiferromagnetic (A-AF) phase transition in the Mn sub-lattice,the specific heat under zero field exhibited a sharp λ-shaped peak at about 85K,which was depressed and broadened and changed smoothly with the increa se of magnetic field.But the entropy change due to the magnetic order is only 26% of the expected value,which might arise from the extension of the magnetic flu ctuation in a larger temperature range.The specific heat curves exhibited a shou lder-shaped Schottky-like anomaly below 20K,whose maximum shifts gradually to higher temperatures with the magnetic field.By considering the contributions to the specific heat at low temperatures,the above phenomena can be interpreted in terms of the model of effective molecular field (Hmf) at Nd 3+ site that causes the splitting of the ground state doublet (GSD) of Nd3+.The specific heat below 20K under different magnetic fields was successfully fitted,through which the meaningful parameters,including the splitting of the GSD of Nd3+,Debye temperature and the A-AF spin wave stiffness coefficient s,as well as their field dependence were obtained.It was found that the ferromagnetic component of the Mn sub-lattice caused by the GdFeO3-type octahedron ro tation could be the origin of the Hmf.
2005, 54 (9): 4365-4369. doi: 10.7498/aps.54.4365
Using the Fourier transformation method,we accurately solved the Gauss Model with long-range interactions on the d-dimensional hyper-cubic lattices and the two-dimensional triangular lattices.The long-range interactions we considered here include power exponential decreasing,exponential decreasing and natural logarithmic decreasing.At the same time the critical behavior of the Gauss Model with long-range interactions decaying as r-α on two-dimensional triangular lattices is studied.The critical points of the system under these circumstances are calculated.According to the results we have obtained,we can easily compare the effect of different types of long-range interactions on the critical behavior of the system.As will be seen,for the existence of long-range interactions,the critical temperature of the system rises to some extent.And the effect of the long-range interaction on the critical temperature depends on its decaying rate.
2005, 54 (9): 4370-4373. doi: 10.7498/aps.54.4370
Fe and FePd nanowires were fabricated by electrodeposition in porous anodic aluminum oxide template. Both Fe and Fe0.95Pd0.05 nanowires have a (110) preferred orientation with a diameter of 60nm . This diameter is suitable f or investigating the behavior of traced Pd in FePd nanowire. With the traced Pd alloying in Fe nanowire, the crystalline anisotropy overpowers the shape anisotr opy, changing the magnetic domain structure and increasing the pinning of domain wall. Thus the Fe0.95Pd0.05 nanowire shows a str ong parallel-to-the-wire anisotropy with improved squareness and coercivity.
2005, 54 (9): 4374-4378. doi: 10.7498/aps.54.4374
The influence of temperature (in the range of 2—390K) on the magnetic moment,and magnetoresistance has been investigated in this paper. It is found that the magnetoelectric properties, particularly the Curie temperature TC, th e metal-insulator transition temperature, Tmi, and the maximum m agnetoresistance TMR, of La0.8Ba0.2MnO 3 are closely related to the valence of Mn in the oxides. La0.８Ba０.2M nO3 synthesize d with 2+ Mn oxides exhibited the lower resistivity, and a Curie temp erature c loser to room temperature (290K) compared with that synthesized with 3+ Mn ox ides. It can be concluded that the magnetoelectric properties of La0.8Ba 0.2MnO3 are dependent on the Mn valence of oxides. This cou ld be attribut ed to the influence of oxygen vacancy concentration variation on the Mn4+ /M n3+ ratio in the resultant compounds during solid sintering react ion, which results from the valence difference of oxide precursors.
2005, 54 (9): 4379-4383. doi: 10.7498/aps.54.4379
Temperature dependence of longitudinal and transverse ultrasonic velocities and attenuations of the single-phase polycrystalline LaCoO3 were presente d. A clear softening in the longitudinal ultrasonic velocity accompanied by a sharp peak in attenuation were observed near the spin-state transition temperature(≈90K), which did not appear in the transverse mode measurement. This anomalous ultraso nic behavior further demonstrates that the spin-state transition of Co3+ ions in LaCoO3 near 90K are more likely from a low spin state (LS,t62ge 0g) to an intermediate spin state (IS,t5 2ge1g ) than to a high s pin state (HS,t42ge2g ). A b ig attenuation peak accompanied by a slight softening in velocity was observed near 200K in both longitudinal and tr ansverse modes, which was probably caused by the relaxation of the local distort ions originating from Jahn-Teller effect of the randomly distributed IS state Co 3+ ions.
2005, 54 (9): 4384-4388. doi: 10.7498/aps.54.4384
Variation of the coercivity induced by increasing Cr and Co contents and adding inpurities of Mo and Zr in FeCrCo alloys was investigated using Mssbauer spec tra, fransmission electron microscopy, x-ray diffraction, and magnetic measureme nt. A coercivity as high as 76kA/m is obtained, which is one and half times high er than that (40—52kA/m) of the common alloy. Mssbauer spectra shows that the microstructure of the high-coercivity alloy is apparently different from that of the traditional FeCrCo alloy. The alloy is single-phase after solution treat ment, the non-magnetic γ phase, which weakens the magnetic properties, does no t appear. During the thermomagnetic treatment, the atomic distribution is rearra nged, and leads to the formation of the α2 phase, the spinodal struc ture with the two-phase (α1 +α2 ) in the alloy fully forms after step-tempering. It might be beneficial for forming the high coercivity in alloy. Comparied with th e low-coercivity case, more of the α1 phase exist in the spinodal st ructure.
2005, 54 (9): 4389-4394. doi: 10.7498/aps.54.4389
We have studied the magnetic properties, microstructure, and mechanical properti es of a high-coercivity FeCrCo alloy. Based on the experiments, the high-coerciv ity can be obtained by selecting suitable composition and heat treatment process . According to the TEM and XRD results, we drew a conclusion that the main eleme nt and the minor metallic dopants control effectively the conformation of phases . Thermomagnetic treatment induces the separation of the ferromagnetic and param agnetic phases, and a spinodal structure forms that results in magnetic-hardenin g. The large composition contrast between the two phases could improve the coer civity of the FeCrCo alloy obviously
2005, 54 (9): 4395-4399. doi: 10.7498/aps.54.4395
In this paper,the relationship between the mechanical properties and the microstructure of a high-coercivity FeCrCo alloy was studied.Measurements on bending strength and fracture toughness showed that the mechanical properties of the high-coercivity FeCrCo alloy are much lower than the conventional FeCrCo alloy.TEM micrographs showed that the composition contrast between the two phases in the high-coercivity alloy is larger;XRD results indicated that the peak intensities of the high-coercivity alloy is lower and the half-peak-width is larger,which indicated that the spinodal decomposition processes are more successfully in the high-coercivity alloy.The enlargement of the composition contrast between α1 and α2 leads to the increase of crystal mismatch,the st rength of the alloy improved,but the ductility deteriorated,that is the reason why the mechanical properties of the high-coercivity alloy is poor.
Influence of pressure expanding treatment on electret properties of positively corona charged cellular PP films
2005, 54 (9): 4400-4405. doi: 10.7498/aps.54.4400
Pressure expanding treatment is an effective method for improving the piezoelect ric activity of cellular PP films. In this work, the character of trap-level dis tribution for positively corona charged cellular PP films and the influence of t he pressure expanding treatment on its charge stability and charge transportatio n have been studied by means of thermal pulse technique, surface potential decay measurements, SEM and TSD spectrum analyses, etc. The results point out that th ere are three kinds of traps with different energy values in the range of middl e energy level for the cellular PP films, i.e. most of the deep traps and the shallow traps in the bulk, and most of the traps with middle energy values near the free surface. The pressure expanding treatment changes the state of traps a nd also, to a certain extent, reduces the charge storage stability of the cellul ar PP films, but has not impact on its charge transportation rule, in which the slow retrapping effect is dominant.
Structures and dielectric properties of (Ba0.7Sr0.3)TiO3/LaNiO3 hetero-structure films prepared by sol-gel technique
2005, 54 (9): 4406-4410. doi: 10.7498/aps.54.4406
(Ba0.7Sr0.3)TiO３/LaNiO３ he tero-structure films have been prepared on Si(100) substrate by an improved sol-gel technique. The structures and d ielectric properties for the films have been evaluated as a function of crystall ization temperature. It was found that LaNiO３ films show the lowest resistivi ty after annealing at 750 ℃ in flowing O２ for 30 min. C-V and I-V measureme nts revealed that the (Ba0.7Sr0.3)TiO３ films have excellent diele ctric properties. The dielectric constant of the (Ba0.7Sr0 .3)TiO３ film annealed at 750 ℃ is larger than 300 under the measuring conditions of 50 kHz, zero bias voltage and room temperature. The maximum leakage current dens ity of the hetero-structure is about 1.2×１０－６ A/cm２ under a bias voltage of 6 V.
Mode-controlled four-wave-mixing in the birefringent microstructure fiber by femtosecond laser pulses
2005, 54 (9): 4411-4415. doi: 10.7498/aps.54.4411
Birefringent microstructure fibers are shown to allow efficient gereration of anti-Stokes line emission as a result of four-wave-mixing in higher mode by using unamplified femtosecond Ti:sapphire laser pulses.Intense blue-shifted lines with different central wavelength were generated in the high-delta (i.e.high-air filling in the cladding) microstructure fiber with axis sizes 50 and 46 μm by femtosecond laser pulses with 35-fs in duration,820nm in central wavelength and 4nJ in energy per pulse.The experimental result shows that phase-matched four-wa ve mixing in higher-order modes of microstructure fibers allows unprecedentedly high efficiencies of anti-Stokes frequency conversion to be achieved for subnano joule femtosecond laser pulses.The dependence factor of the four waves mixing in birefringent microstructure fiber is compared and analyzed.Good agreement betwe en the theory and experiment is achieved.
2005, 54 (9): 4416-4421. doi: 10.7498/aps.54.4416
SnO２ nano-crystalline grains with sizes in the range of 4—80 nm ar e systematically investigated using Raman spectroscopy. Besides SnO２ fundam ental-fre quency modes, a few weak Raman modes and a very strong and broad photoluminescen ce peak at about 700 nm can be observed. Our results show that bulk properties o f nano-SnO２ diminish but the defect-, surface-, and size-related fea tures dis play as grain size decreases. A critical size that divides respective predominan ce is determined to be about 20 nm. Bulk spectra with spectroscopic line broaden ing and position shifting, a surface mode and interface mode around 571 cm －１and 351 cm－１, as well as the O-H vibration modes of the water mol ecu les in SnO２ nanograins are characteristics of Raman spectra of nano- SnO２ with grain size below 20 nm. They are related to the microstructure change of the nanograins, i.e. they reflect the change of grain size, surface, and the in teraction between nanograins.
2005, 54 (9): 4422-4426. doi: 10.7498/aps.54.4422
The laser properties of Q-switched Cr3+,Yb3+,Er3+:phosphate gl asses have been studied in this work.Rotating prism Q-switched laser at 1.53μm was obtained at room temperature in this erbium glass pumped by flash lamp.The b est laser properties are realized in the glass with 0.5wt% Er2O3 concentrati on.The properties include 14.5mJ threshold energy,9.6mJ maximum laser output and 0.55% slope efficiency.The laser properties of Cr14 was compared with QE-7S pro duced by Kigre under the same experimental condition.It is deduced from experime ntal results that the former has a higher threshold energy,maximum laser output and slope efficiency.
2005, 54 (9): 4427-4432. doi: 10.7498/aps.54.4427
The tellurite glass 70TeO2-20WO3-10ZnO in different Tm3+-doping co ncentration were prepared. According to the absorption spectra,the Judd-Oflet strength parameters were calculated by using Judd-Ofelt theory. The spontaneous-emission probabilities,branch ratios and radiative lifetime of each level of Tm3＋ were given.The emission spectra of Tm3＋-doping in various concentrations were studied.The effective bandwidth and stimulated emission cross-section at the peak wavelength of the emission band were also investigated. Aft er comparing the spectral properties at various Tm3＋ concentra tions, we concluded that the luminescence intensity and effective bandwidth were maximum when the Tm3＋-doping concentration ranges from 0.8wt%—1wt%. The Tm3＋-doped tellurite glass is an ideal host for optical ampli fier working on S-band.
2005, 54 (9): 4433-4438. doi: 10.7498/aps.54.4433
The influence of annealing temperature on the photo-luminescence (PL) of high co ncentration Er/Yb co-doped Al２O３ films was studied. The relationship betwe en PL spectra and microstructure of the films at various annealing temperatures was revealed by analyzing the dependence of the intensity and the full width at half-maximum of the PL spectra on the annealing temperature. The PL measurement shows that the annealing behavior may be split into three different regimes. Bel ow 750℃, the intensity increases with the increase of annealing temperature wit h a small slope, which corresponds to the amorphous Al２O３ films. Between 800℃ and 900℃, the PL intensity increases considerably, where the microstructure of the films was identified to be composed of γ-Al２O３ grains in nano-meter scale; At the temperature of 1000℃, the intensity of PL spectrum decre ases to a very low level, γ-Al２O３ grains and the segreg ation of Er2O ３ and Yb2O３ phases were observed by using transmis sion electron microscopy . Furthermore, the dependence of PL spectrum shape on the PL intensity of sub-le vel transition was analyzed and discussed by fitting the PL spectra at various t emperatures．
2005, 54 (9): 4439-4444. doi: 10.7498/aps.54.4439
Infrared emissivity of high quality indium tin oxide (ITO) film has been calcula ted based on the infrared radiation theory and thin film optical theory, the the oretical curves and the testing curves basically agree with each other. It is concluded that when the sheet resistance is less than 30Ω, the theoretical val ue of infrared emissivity of ITO films on the infrared wave band of 8μm to 14μ m will be less than 0.1. Therefore, the ITO film of practical sheet resistance less than 10Ω has good infrared stealthy capability. Physical mechanism of low infrared emissivity for ITO film is discussed, and the critical sheet resistance of low infrared emissivity, which conduce to the theoretical study and the ma nufacture of infrared stealthy ITO film, is put forward in this paper.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
A study on the effect of Fraunhofer structure on the measurement of atmospheric pollutants with differential optical absorption spectroscopy
2005, 54 (9): 4445-4450. doi: 10.7498/aps.54.4445
During the measurment of atmospheric environment with differential optical absorption spectroscopy, stray light of the sun will be added to the measurment spectrum and the Fraunhofer structure in the solar radiation could affect the measurement of NO２, CH2O, HONO etc. But if it is treated as a k ind of `component' of atmosphere and retrieved with other atmospheric components together, its ef fect on the measurement could be restricted to a minimum.
A method of characteristic LIF spectral signatures separation based on radial basis function networks
2005, 54 (9): 4451-4457. doi: 10.7498/aps.54.4451
The separation of characteristic spectral signatures plays an important role in the laser induced fluorescence (LIF) system used for monitoring dissolved organic matter (DOM) in polluted water,which has advantages of high sensitivity,fast detection,remote measurement,etc. In this paper,a method of characteristic spectral signatures separation based on radial basis function networks (RBFN) will be presented. Using this method,we separated the spectral components of laser,Raman and fluorescence of DOM from the LIF spectral. The concentration of DOM in polluted water can be retrieved from the separated spectrums.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2005, 54 (9): 4458-4462. doi: 10.7498/aps.54.4458
We demonstrate that a new class of stable composite soliton exists in a two-dimensional lattice. It can be produced by the evolution of a stationary solution of nonlinear Schrdinger equation with a periodic potential modulation. We emphasize that this new kind of composite soliton is different from the dipole soliton reported before though they seem alike. The components of the soliton exchange energy during the propagations and the total energy of soliton conserves.