Vol. 52, No. 2 (2003)

Iterative approach of high-order scattering solution for vector radiative transfer of inhomogeneous media layer
Liang Zi-Chang, Jin Ya-Qiu
2003, 52 (2): 247-255. doi: 10.7498/aps.52.247
Abstract +
By stratifying a random scattering media into thin multi-layers in z direction,the first-order scattering solution of each thin layer with Fourier transform is employed to derive high-order scattering solution of the whole random media.An iterative approach to solve high-order scattering solution of a vector radiative transfer (VRT) equation is newly developed.Numerical results are well compared with the Mueller matrix solutions of the first-order for a layer medium,second-order for a half-space,and also the results of the discrete ordinates and eigen-analysis method.It demonstrates that our approach is as feasible,effective and especially applicable to high-order solutions of VRT for both bistatic scattering and thermal emission of inhomogeneous non-spherical scattering media.
Stability for the equilibrium state of rotational relativistic Birkhoffian systems
Chen Li-Qun, Xue Yun, Fu Jing-Li
2003, 52 (2): 256-261. doi: 10.7498/aps.52.256
Abstract +
The stability for equilibrium state of rotational relativistic Birkhoffian systems is studied.The equilibrium state equations, the disturbance equation and the first approximation equation are given.The stability criteria for equilibrium state,and the stability criteria of the direct method for the rotational relativistic Birkhoffian autonomous systems are obtained.The relationship of the stability of equilibrium state between rotational relativistic Birkhoffian systems and rotational classical Birkhoffian systems are discussed. Two examples are presented to illustrate the results.
A Darboux transformation and new exact solutions for Broer-Kaup system
Li Zhi-Bin, Zhou Zhen-Jiang
2003, 52 (2): 262-266. doi: 10.7498/aps.52.262
Abstract +
An explicit Darboux transformation for Broer-Kaup (BK) system is constructed with the aid of the elemental solutions of its Lax pairs.From the Darboux transformation,the new two-soliton solutions for BK system are obtained.
Explicit and exact solutions of the combined KdV equation
Shi Yu-ren, Lü Ke-Pu, Duan Wen-Shan, Hong Xue-Ren, Zhao Jin-Bao, Yang Hong-Juan
2003, 52 (2): 267-270. doi: 10.7498/aps.52.267
Abstract +
With the aid of computer algebraic system “Mathematica” and by using the hyperbola function method,the exact and solitary wave solutions of the combined KdV equation are obtained,including the bell-like and the kink solitary wave solutions.The thought based on the hyperbola function method is extended,and more explicit and exact solutions are successfully derived,including shock wave type solutions with break point and exponential function type solutions.This method can be used also to solve other nonlinear evolution equation(s).
A time-dependent damped harmonic oscillator with a force quadratic in velocity
Huang Bo-Wen
2003, 52 (2): 271-275. doi: 10.7498/aps.52.271
Abstract +
A time-dependent damped harmonic oscillator with a nonconservative force quadratic in velocity (THOFQV) is described by an appropriate Lagrangian,and hence the general solution of THOFQV can be found.The solution of the Schrdinger equation for the system,such as the eigenfunctions and eigenvalues,is derived by utilizing these invariant operators.
Synchronization of a class of chaotic systems in the presence of perturbation by an observer
Guan Xin-Ping, He Yan-Hui, Fan Zheng-Ping
2003, 52 (2): 276-280. doi: 10.7498/aps.52.276
Abstract +
Synchronization problem in the presence of perturbation is considered,and the nolinear part of the chaotic system is nt in output feedback form.In this paper,we first transfer the system and obtain a nonfull order system.Second,we construct a synchronous system based on the nonlinear observer idea and realize the synchronization.Finally numerical example is illustrated and the simulation results verify the conclusion of this paper.
Control of a unified chaotic system
Tao Chao-Hai, Lu Jun-An
2003, 52 (2): 281-284. doi: 10.7498/aps.52.281
Abstract +
The paper addressed the self-feedback control,dislocation feedback control and adaptive control strategies for a unified chaotic system.The strict theoretical proof was put forward,numerical simulations were provided to show the effectiveness of these methods.The deficiency of Ref.[10] was also corrected.
A statistical property to recover coarsely initial conditions from coupled map lattices
Tong Qin-Ye, Zeng Yi-Cheng
2003, 52 (2): 285-291. doi: 10.7498/aps.52.285
Abstract +
To recover the initial signals in coupled map lattices (CMLs) is a key work when CMLs are applied to signal processing.In this paper,a method to roughly recover the initial signal is proposed.Numerical simulations show that the mean of recovered initial conditions from the coupled map lattices is equal to that of the given(real value),and the variance of recovered initial conditions is less than that of the given.For explaining these properties,when a Logistic map is coupled to others,it is taben as undergoing a transformation.Meanwhile,some interesting phenomena are found to sort two sequences obtained under Logistic mapping with different parameters.The results in this paper is heuristic for CMLs study and coupled nonlinear measurement etc.
Adaptive fuzzy synchronization of chaotic systems with uncertainties
Jun Yoneyama, Yue Dong
2003, 52 (2): 292-297. doi: 10.7498/aps.52.292
Abstract +
This paper is concerned with the synchronization problem of a class of chaotic systems with uncertainties.A novel design method for the adaptive fuzzy synchronization is proposed based on a Takagi-Sugeno(T-S) fuzzy dynamical model.The proposed methods can be appliced not only to the chaotic systems with the same structures,but also to the chaotic systems with different structures.To demonstrate the effectiveness of our method,simulation results of synchronization are finally given for the Lorenz system and Rossler system.
The imaging of chemical samples with a scanning near-field infrared microscope
Wang Qian, Xu Jin-Qiang, Wu Jin, Li Yong-Gui
2003, 52 (2): 298-301. doi: 10.7498/aps.52.298
Abstract +
The imaging research of chemical samples by using a scanning near-field infrared microscope(SNIM) was described in this paper. And this microscope use Beijing Free Electron Laser as its illuminating light. Fram the SNIM image, we can make a precise decision about the sample composition and the percentage of each component in a 10μm×10μm—102μm×102μm region.
Trapping effect modeling for SiC power MESFETs
Yang Lin-An, Zhang Yi-Men, Yu Chun-Li, Zhang Yu-Ming
2003, 52 (2): 302-306. doi: 10.7498/aps.52.302
Abstract +
An analytical trapping modle, which utilizes concise parameters to describe the impact of deep level traps in the p-buffer layer on the output characteristics, is proposed for 4H-SiC RF power MESFET. This model is simple in calculations compared with normally used 2D numerical model. It also takes into account the self-heating effect that plays an important role in saturated region of I-V characteristics. The description of transconductance degradation, drain conductance decrease and pinch-off voltage dispersion caused by the traps is easily derived by theoretical analysis. The result shows good agreement between simulations and measurements.
Studies on the potential energy curves of heteronuclear diatomic molecules using energy consistent method
Li Xin-Xi, Sun Wei-Guo, Feng Hao
2003, 52 (2): 307-311. doi: 10.7498/aps.52.307
Abstract +
The potential energy curves of some heteronuclear diatomic molecules are studies using the energy consistent method (ECM) for the electronic states of Clf-A3Π1, ClF-B0+(3Π),CH-X2Π,BH-X1Σ+,XeO-d1Σ+,LaF-X1Σ+,Li7D-X1Σ+,NaRb-X1Σ+,KRb-(2)3Σ+ and KRb-21Π. The results show that the ECM potentials are in excellent agreement with the known Rydberg-Klein-Ress(RKR) data, and are superior to the frequently used Morse potential and Huxley-Murrell-Sorbie(HMS) potential. The EGM potential can give reliable potential data at the molecular asymptote and the dissociation region where the RKR results may not be available.
Calculation of electron capture probabilities in collisions of O5+ ion with H atom
Wang Jun, Wang Li-Guang
2003, 52 (2): 312-315. doi: 10.7498/aps.52.312
Abstract +
A method, in which the wave function is expanded with the atomic orbitals added to the electron transfer factor to correct the boundary condition, is used to study the collisions between O5+ ion and H atom. After calculating the initial channel potential energy of O5++H system, the good agreement between calculation and experiment shows that optimized calculation factors are highy reliable. The electron capture probabilities vs time in the interaction of O5+ ion with H atom (8Σ states) are calculated at an impact factor b=8.0 a.u. and an impact speed v=220.0 a.u. by using the core approximation and the optimized factors.
Study on the properties of the dynamic partially coherent speckle in the Fresnel and Fraunhofer diffraction regions
Teng Shu-Yun, Liu Man, Liu Li-Ren, Xu Zhi-Zhan, Cheng Chuan-Fu
2003, 52 (2): 316-323. doi: 10.7498/aps.52.316
Abstract +
We have studied the properties of the dynamic partially coherent speckles in the Fresnel and Fraunhofer diffraction regions. We use the theory of propagation of the mutual intensity in partially coherent light, and derive the general form of the spatio-temporal cross-correlation functions of the dynamic speckle intensities produced by a moving diffusing object. Based on these theoretical expressions, the characteristics of the movement and the boiling of the dynamic partially coherent speckles are discussed. By choosing the proper extended incoherent light source and by adjusting the parameters of the optical setup, we have observed experimentally the partially coherent speckle in the Fresnel and Fraunhofer diffraction regions. Then we study qualitatively the movement and the boiling of the speckles. Using techniques of photon counting and automatic data acquisition, we have measured the temporal evolution of the speckle intensity in the Fraunhofer plane as the object moves, and thus measured the cross-correlation of the speckles versus the temporal increment. The experimental data are in agreement with the theoretical results.
Photic intensity distribution simulations of biological tissues with polystyrene spheres
Guo Hong-Lian, Cheng Bing-Ying, Zhang Dao-Zhong
2003, 52 (2): 324-327. doi: 10.7498/aps.52.324
Abstract +
The photic intensity distributions of biological tissues which are sensitive to light such as mesophyll cell of green plant, epidermal cell of animal, compound eye of insect are simulated with single and periodically arrayed 3-μm-diameter polystyrene spheres in water. The results show that the photic intensity distributions are very different in different cross sections of spheres. Within the section of spheres, the photic intensity distributions pressent well-regulated pattern, which out of the sphere the distributions are similar to that of lens imaging. In addition, the difference of the distributions between single and periodically arrayed spheres in cross section is obvious. The distribution of the latter presents the correlativity of spheres.
Measurement of superposition of orbit angular momentum states of photons by fork-like grating
Ye Fang-Wei, Li Yong-Ping
2003, 52 (2): 328-331. doi: 10.7498/aps.52.328
Abstract +
Laguerre-Gaussian(LG) mode carries a well-defined orbit angular momentum. We have designed a fork-like grating to measure the superposition of two LG modes. It is useful in the high-dimensional quantum communication.
Preparation of squeezed even coherence state and its nonclassical properties
Ji Ying-Hua
2003, 52 (2): 332-336. doi: 10.7498/aps.52.332
Abstract +
By keeping the frequency of non-dissipative mesoscopic LC circuit a constant and its parameter varying with the step function, the quantum state of the circuit evolves to a squeezed even coherent state from the initial even coherent state. The nonclassical properties, not only squeezing but also antibunching effects, appear in the circuit by adjusting its inductor parameter under the squeezed even coherent state.
The squeezing of angular momentum and its evolutions in atomic Schrdinger cat states
Dong Chuan-Hua
2003, 52 (2): 337-344. doi: 10.7498/aps.52.337
Abstract +
The atomic coherent states will evolve to the atomic Schrdinger cat states at some special times in a low-Q acvity. The fluctuations and higher-order fluctuations of angular momentum in these atomic Schrdinger cat states are discussed. According to the uncertainty principle, the squeezing and higher-order squeezing for atomic angular momentum are investigated. It shows that the atomic Schrdinger cat states can be squeezed to second-and sixth-order, but cannot be squeezed to fourth-order. The properties of squeezing of atomic Schrdinger cat states formed by superposing infinite terms of atomic coherent states are identical with those of atomic coherent states.
Interference enhancement of two-photon absorption caused by a pair of coherent superposition levels in Na
Zhang Yan-Liang, Jiang Li, Sun Zhen-Rong, Ding Liang-En, Wang Zu-Geng, Niu Yue-Ping
2003, 52 (2): 345-348. doi: 10.7498/aps.52.345
Abstract +
In the sodium dimer rhomb-type four-level system with a pair of coherent superposition levels, the interference enhancement of two-photon absorption caused by coherent superposition of the coupling levels is experimentally observed. The calculated results using density matrix equation are in good agreement with the experimental results.
A dynamical analysis on V-shaped solid laser resonator and the improved one
Zhang Guang-Yin, Zhang Chao-Bo, Jiao Zhi-Yong, Ding Xin, Yan Cai-Fan, Huang Hui
2003, 52 (2): 349-354. doi: 10.7498/aps.52.349
Abstract +
We have analyzed the dynamics of the general V-shaped solid laser resonator in detail and pointed out its advantage and shortcoming. Its crucial shortcoming is the appearance of a high-loss region when the dynamics factor approaches 1ft≈1l1-f, and in this case the laser cannot run. In order to overcome this weakness, we have introduced a kind of improved V-shaped resonator proposed by Liu Jun-hai, and based on this we put forward an improved more compact V-shaped resonator.
Heat-induced undulation in the distribution of diode-pumped solid-state laser
Guo Zhen, Cai De-Fang, Wen Jian-Guo, Xue Hai-Zhong, Tang Ying-De, Fu Jun-Mei, Wang Shi-Yu
2003, 52 (2): 355-361. doi: 10.7498/aps.52.355
Abstract +
A theoretical model has been adopted to analysis the unsteady thermal effects in a laser medium. It is based on the fact that the internal dissipation power is always unequal to the heat removed from the surface. According to this, the case in a laser diode pumped solid-state laser has been studied. The result obtained shows that the fluctuations in the laser beam strongly depend on those of the temperature in the heat sink. It was also shown that the dissymmetric temperature distribution of the heat sink distorts the shape of the laser beam. A set of experiments has been carefully designed to proved these conclusions.
Measurement of femtosecond laser pulses using SHG frequency-resolved optical gating technique
Wang Zhao-Hua, Wei Zhi-Yi, Teng Hao, Wang Peng, Zhang Jie
2003, 52 (2): 362-366. doi: 10.7498/aps.52.362
Abstract +
We present a measurement of femtosecond laser pulses using the technique of second harmonic generation frequency-resolved optical gating (FROG) in this paper. Based on the data of the correlation signal in time and frequency domains, we obtained the detailed information on pulse shape, bandwidth, pulse duration and phase by using the retrieval algorithm program. The pulse duration is in reasonable agreement with the measurements using an interferometric autocorrelator.
The analytical calculation of temperature distribution in doping processes of Zn/InP induced by continuous wave laser
Tian Hong-Tao, Chen Chao
2003, 52 (2): 367-371. doi: 10.7498/aps.52.367
Abstract +
Based on the experiment, the process of doping of Zn/InP Indued by continuous wave laser was analysed. A brief visual analytical form of temperature distribution on a finite double-material irradiated by a continuous wave laser is presented under the third boundary condition in one-dimensional heat conduction.
Second harmonic theory of two coupled oscillators in chiral molecular media
Zheng Yang-Dong, Li Jun-Qing, Li Chun-Fei
2003, 52 (2): 372-376. doi: 10.7498/aps.52.372
Abstract +
We have derived the hyperpolarizability of a chiral molecule from the model of coupled two-oscillators in second-harmonic generation. We gave the susecptibility of a thin film. We discussed the influence of microscopic parameters of a molecule on the efficiency of second-harmonic generation through the relationship of hyperpolarizabilities and susceptibilities. We also have simulated the spectrum of rotational angle of polarization state. Our theoretical results fit the known experimental facts.
Screening-photovoltaic solitons affected by the photovoltaic effect of a background beam
Wang Xiao-Sheng, Ouyang Shi-Gen, She Wei-Long
2003, 52 (2): 378-382. doi: 10.7498/aps.52.378
Abstract +
The photovoltaic effect of a background beam do not affect the spatial-charge field in a photovoltaic crystal with a constant external applied field, but has an effect on the current density in the crystal.If the crystal is connected with an external circuit which includes a resistor and a constant voltage source, the photovoltaic effect of the background beam will affect the full width at half maximum of the solitons, even switch the bright solitons, to the dark solitons, or vice versa.
The general solution of noncircular uniform optical waveguides in an arbitrary coordinate system and applications
Dong Hui, Fu Song-Nian, Wu Chong-Qing, Liu Hai-Tao
2003, 52 (2): 383-389. doi: 10.7498/aps.52.383
Abstract +
This paper presents the general solution of noncircular uniform waveguides in an arbitrary coordinate system. It can be expressed as exp{i(+ΔβV)z}E0(x,y),where V is a matrix depending uniquely on the angle θ between polarization principal axis (PPA) and coordinate axis. As a kind of application, we give the method to find , Δβ and V(θ) in the weak-guided fiber, whose distortion is smaller.It is easier to use it for analyzing the effect of birefringence decreasing due to the lognitudinal asymmetry in a fiber, compared with Jones matrix.
Fused biconical taper all-wave coupler
Zhang Rui-Feng, Ge Chun-Feng, Wang Shu-Hui, Hu Zhi-Yong, Li Shi-Chen
2003, 52 (2): 390-394. doi: 10.7498/aps.52.390
Abstract +
This paper, on the basis of coupled-mode equations, analyzes the bandwidth characteristic of asymmetric fused biconical taper (FBT) coupler, and proposes and proves a solution of all-wave coupler (O+E+S+C+L band).We also succeed in making all-wave couplers with a bandwidth of 390nm, while the excess loss is only 0.1 dB and the coupling ratio is 1∶99
The influence and control of incoherent irradiation on photorefractive nonlinearity of LiNbO3:Fe crystal
Yang Li-Sen, Wang Da-Yun, Liu Si-Min, Chen Xiao-Hu, Guo Ru, Gao Yuan-Mei, Huang Chun-Fu, Zhao Hong-E, Lu Yi
2003, 52 (2): 395-400. doi: 10.7498/aps.52.395
Abstract +
In this paper,we study the influence of incoherent irradiation on the conversion process from self-defocusing to self-focusing in LiNbO3:Fe crystal under the open-circuit condition.We observe that the incoherent irradiation can increase the refractive index change, fasten greatly the process of self-defocuisng, self-focusing and the conversion from the former to the latter in LiNbO3:Fe crystal, whether it propagates along the direction of the incident light or the opposite direction. When the incoherent light illuminates the crystal in certain time intervals repeatedly, the transmissivity can rise up and fall down quickly, the obvicus switching effect is observed. The change of the refractive index controlled by the incoherent irradiation can be applied in the all-optical switch.
The choke effect on a two-dimensional granular flow and the relation with its speed
Bao De-Song, Zhang Xun-Sheng, Xu Guang-Lei, Pan Zheng-Quan, Tang Xiao-Wei, Lu Kun- Quan
2003, 52 (2): 401-404. doi: 10.7498/aps.52.401
Abstract +
The motion of granular wafers relative to its speed and the opening-size at choke point has been studied experimentally on a two-dimensional conveyer belt. The result shows that there is a critical speed vc when the opening-size d is fixed. The rate of flow Q increases linearly with the speed v, when v<vc.The change of the Q-v curve occurs at the speed of vc.The critical speed vc is dependent on the opening-size d. The interaction between the granular wafers is changed when altering the speed or the opening-size at the choke point, and affects the motion of granular flow.
Phase transition of solid-liquid electrorheological system in flow percess
Zhao Xiao-Peng, Gao Xiu-Min, Gao Xiang-Yang, Gao Dan-Jun
2003, 52 (2): 405-410. doi: 10.7498/aps.52.405
Abstract +
Considering the short-range interaction of multi-particles, we have employed the equivalent plate conductivity model to simulate the phase transition of solid-liquid electrorheological(ER) fluids in flow process. We also devised experiment to observe the phase transition of ER fluids. The conclusions show that under the certain pressure the ER fluids begin to flow, here the flow is the two-phase flow. But when the strength of external electric field reaches a certain threshold value, the particles in ER fluids stop flowing, so the flow of ER fluids changes into one-phase flow, the phase transition happens. The phase transition observed in our experiment complies with the simulation fundamentally. The threshold strength of external electric field increases with the increasing pressure, and decreases with the concentration of particles in ER fluids.
Electron temperature measurement of low-energy laser produced plasma using iso-electronic x-ray spectroscopy
Yang Jia-Min, Ding Yao-Nan, Chen Bo, Zheng Zhi-Jian, Yang Guo-Hong, Zhang Bao-Han, Wang Yao-Mei, Zhang Wen-Hai
2003, 52 (2): 411-414. doi: 10.7498/aps.52.411
Abstract +
Low-Z CHO targets were illuminated by a low-energy laser beam on Xingguang laser facility to produce relatively low-temperature plasma. The ratios of spectrum intensity of the carbon ions to the oxygen ions have been measured by a 2400 lines per millimeter grating spectrometer in order to obtain the electron temperature. The diagnostics on low electron temperature has been developed.
Studies on the mechanism of energy transformation in implosion processes of the Z-pinches
Ning Cheng, Yang Zhen-Hua, Ding Ning
2003, 52 (2): 415-420. doi: 10.7498/aps.52.415
Abstract +
In this paper, the energy transformation processes in neon gas-puff pinch and Al wire-array pinch were studied numerically by means of one-dimensional three-temperature radiation magneto-hydrodynamic code. In the Z-pinch, the main energy transformation process is the Coulomb collision process between ions and electrons. The second one is the photoelectric process and bremsstrahlung radiation process. The energy transformation in the Compton scattering process can be neglected in the computation. The x-ray energy radiated from Z-pinch was produced mainly by the photoelectric excitation and recombination process, and also by the bremsstrahlung radiation process and Compton scattering process. Numerical analysis indicates that the x-ray radiation energy can be larger or smaller than the maximal plasma kinetic energy. In our numerical simulation, the radiation energy from neon gas-puff pinch is smaller than the maximal plasma kinetic energy, however, that from Al wire-array pinch is larger than the maximal plasma kinetic energy. They are all smaller than the work done by magnetic pressure. The electric energy consumed by Ohm heating is rather small.
A maser instability driven by an electron beam
Wu Ching-Sheng, Chen Yan-Ping, Zhou Guo-Cheng
2003, 52 (2): 421-427. doi: 10.7498/aps.52.421
Abstract +
The theory of a maser-instabiligy driven by a beam of weakly relativistic electrons is discussed. The main purpose of this paper is to complement the derivation of the expressin for the growth rate. An approximation, which enables us to see the physics associated with the growth rate more clearly, is suggested. Moreover, some essential numerical results are also presented.
Equilibrium optimization code opeq and results of applying it to HT-7U
Zha Xue-Jun, Zhu Si-Zheng, Yu Qing-Quan
2003, 52 (2): 428-433. doi: 10.7498/aps.52.428
Abstract +
The plasma equilibrium configuration has a strong impact on the confinement and MHD stability in tokamaks. For designing a tokamak device, it is an important issue to determine the sites and currents of poloidal coils which have some constraint conditions from physics and engineering with a prescribed equilibrium shape of the plasma. In this paper, an effective method based on multi-variables equilibrium optimization is given. The method can optimize poloidal coils when the previously prescribed plasma parameters are treated as an object function. We apply it to HT-7U equilibrium calculation, and abtain good results.
Theoretical study on nonlinear resonances of a charged micro-particle in a RF sheath
Hou Lu-Jing, Wang You-Nian
2003, 52 (2): 434-441. doi: 10.7498/aps.52.434
Abstract +
A self-consistent model is proposed here to study the nonlinear resonance and the hysteresis phenomena in the vertical oscillations of a charged micro-particle in a RF sheath. In this model, the charging process of the micro-particle and the sheath dynamics is considered self-consistently. And also, various forces acting on the particle are fully taken into account in the Newton's equations of the micro-particle. By solving the equation, we simulate the motions of the micro-particle in the sheath, under the excitations of the probe. Numerical results reproduce well the recent experimental observations; at the same time, we find that these nonlinearities are not only due to the structure of the sheath, but also due to the charging process of the micro-particle, ion drag force, neutral gas friction and the excitation of the probe.
Two fractal structures of methyl-modified Silica gels by SAXS
Wang Jun, Dong Bao-Zhong, Xu Yao, Li Zhi-Hong, Fan Wen-Hao, Wu Dong, Sun Yu-Han
2003, 52 (2): 442-447. doi: 10.7498/aps.52.442
Abstract +
With tetraethoxysilane [Si(OC2H5)4,TEOS] and methyltriethoxysilane [CH3Si(OC2H5)3,MTES] as precursors, two kinds of methyl-modified silica gels were prepared by the two-step method and co-hydrolysis method. The gels were tested at the small angle x-ray scattering(SAXS) Station of Beijing Synchrotron Radiation Facility(BSRF). We calculated the average particle diameter and the special surface area between the two phases. On the basis of these data the fractal characters of gels were analyzed, and two fractal structures were found in all the samples. The two fractal dimensions indicated two fractal structures on two scales, i.e., from primary SiO2 particles to first-aggregates and from first-aggregates to clusters. Aided by transmission electronic microscope(TEM) we confirmed the two different microstructures of the gels prepared using the two different methods. It can be said that SAXS is a powerful technigue to study microstructures of gel systems by studying its fractal structure.
Rapid dendritic growth in an undercooled Ni-Cu alloy under the microgravity condition
Yang Chun, Chen Min, Guo Zeng-Yuan, Yao Wen-Jing, Han Xiu-Jun, Wei Bing-Bo
2003, 52 (2): 448-453. doi: 10.7498/aps.52.448
Abstract +
Droplets of Ni-50%Cu alloy with different sizes are rapidly solidified under the condition of microgravity and containerless state within a 3m drop tube. With the increase of undercooling, the microstructural evolution has shown a transition from coarse dendrites to equiaxed grains. The maximum cooling rate of 8×103K/s and the undercooling up to 218K(014TL) are obtained in experiment. Based on a theoretic analysis, the heterogeneous nucleation occurs preferably in Ni-50%Cu droplets. The nucleation rate exceeds 1012 m-3s-1. The rapid dendritic growth of Ni-50%Cu alloy proceeds from the solutal-diffusion-controlled to the thermal-diffusion-controlled growth with the enhancement of undercooling. Under the undercooling of 68K, the segregation degree of liquid at the growing interface reaches a maximum value.
Effects of substrates on silicon oxide nanowires growth by thermal chemical vapor deposition
Yan Xiao-Qin, Liu Zu-Qin, Tang Dong-Sheng, Ci Li-Jie, Liu Dong-Fang, Zhou Zhen-Ping, Liang Ying-Xin, Yuan Hua-Jun, Zhou Wei-Ya, Wang Gang
2003, 52 (2): 454-458. doi: 10.7498/aps.52.454
Abstract +
Silicon oxide nanowires, grown on (100) Si wafers with the oxide layer about 100nm in thickness and on quartz plates, are investigated by exposing to the same conditions in a thermal chemical vapor deposition reactor at a temperature about 860℃. Field-emission scanning electron microscopy, transmission electron microscope equipped with energy-dispersive x-ray analysis were used to characterize the samples. The results show that a large amount of amorphous silicon oxide nanowires was obtained. The morphology, size and chemical composition of the silicon oxide nanowires grown on different substrates are quite different. The reasons of forming different characteristic silicon oxide nanowires were discussed.
Theoretical study on defects associated with oxygen vacancy in PbWO4 crystal
Yao Ming-Zhen, Gu Mu
2003, 52 (2): 459-462. doi: 10.7498/aps.52.459
Abstract +
In this study, the defect associated with oxygen vacancy VO in lead tungstate crystals(PbWO4), was investigated by the relativistic self-consistent discrete variational embedded cluster method. We focused on the density state and the effect of color centre induced by VO on the surroundings. The results showed that, VO could produce the WO3+F+ defect in the crystal, and the existence of F+ could result in the absorption of 420nm. In addition, there was not F centre in the PbWO4 crystal.
A study on the electronic structure,superconductivity,and optical properties of MgCNi
Tan Ming-Qiu, Tao Xiang-Ming, Xu Xiao-Jun, He Jun-Hui, Ye Gao-Xiang
2003, 52 (2): 463-467. doi: 10.7498/aps.52.463
Abstract +
In this article the density functional theory and LDA are used to study the electronic and optical properties of newly discovered alloy superconductor MgCNi3.The calculated results exhibit that the conduction bands in this compound are derived by Ni 3d and C 2p states.The top valence states have essentially Ni 3d characters and the C 2p states occupy the region from 4.0eV to 7.0eV below Fermi energy.EF locates just at the step slope of sharply structured Ni 3dyz+zx and 3d3z2-r2 peaks near EF.The doping carriers from Mg atoms destroy the magnetic order.The calculated optical properties show that the optical conductivity in the energy range 0—12eV are contributed from the Ni 3d to Ni 4s and C 2p transitions.The density of states near Fermi energy N(EF) is evaluated to be 5.50 (states/eV·cell)which yielded a Sommerfeld constant γcal~4.45mJ/mol·K2.We conclude that the mechanism of superconductivity in MgCNi3 has the type of BCS with strong electron-phonon coupling.
The ground state and persistent current of mesoscopic Aharonov-Bohm ring embedded with a quantum dot
Ye Jian-Fei, Ye Fei, Ding Guo-Hui
2003, 52 (2): 468-472. doi: 10.7498/aps.52.468
Abstract +
An interacting quantum dot inserted in an Aharonov-Bohm ring is investigated.The explicit expression of the ground-state energy and the persistent current of the system are obtained by a second-order variational perturbation approximation method.The numerical results of the Kondo temperature and the ground-state persistent current of the system are also given under the condition that the Coulomb repulsion is infinite.
Behaviors of multi-node superconducting rings in external magnetic field
Xie Fei-Xiang, Wang Fu-Ren, Ma Ping, Dai Yuan-Dong, Liu Xin-Yuan
2003, 52 (2): 473-477. doi: 10.7498/aps.52.473
Abstract +
Numerical simulations and analyses have been applied to find the relationships between magnetic flux,ring current,free energy of superconducting rings and external magnetic field.It is found that a double-junction superconducting ring has a different behavior from a single-junction ring.When the Ic values are identical,a double-junction ring has a non-hysteresis behavior when β<2.The hysteresis exists only when β≥2.And a double-junction ring has a double-branch solution with 2Φ0 period.
The dependence of exchange bias of Ni81Fe19/Ni100-xMnx bilayers on the Mn content and the thickness of Ni100-xMnx
Dai Bo, Cai Jian-Wang, Lai Wu-Yan
2003, 52 (2): 478-482. doi: 10.7498/aps.52.478
Abstract +
By adjusting the Mn concentration,we systematically investigated the magnetic properties,especially the exchange bias field(Hex),in Ni81Fe19/Ni100-xMnx bilayers.In the range of 534≤x≤600,the largest exchange bias field(~175kA/m)was achieved,and at the same time the reduction of magnetic moment due to the Mn diffusion into the Ni81Fe19 layer was lower than 20%.High-angle x-ray diffraction(XRD)showed a variation of Ni100-xMnx lattice parameters when altering the Mn content:the more the Mn content,the larger the lattice parameters.It was found that the as-deposited Ni100-xMnx films with their lattice parameters close to those of θ-phase of NiMn alloy could be transformed into θ-phase relatively easily.Finally, the exchange bias of the bilayers with different Ni100-xMnx thicknesses was studied.We first obtain a 80 kA/m exchange bias field in the Ni81Fe19(150nm)/Ni100-xMnx(90nm)bilayers when Mn content increases to 706% after annealed at 240℃ for 5h,while the magnetic moment of the ferromagnetic layer was nearly umchanged.
Self-assembled two-dimensional structure of magnetic cobalt nanocrystals
Wang Yu-Ping, Shen Cheng-Min, Su Yi-Kun, Yang Hai-Tao, Yang Tian-Zhong, Gao Hong-Jun
2003, 52 (2): 483-486. doi: 10.7498/aps.52.483
Abstract +
Synthesis of monodisperse Cobalt nanocrystals by high temperature diol reduction methods in the presence oleic acid and triocethylphosphine stabilizers were reported.The mean size of the Co nanocrystals is about 14±19nm and a standard deviation of the diameter is less than 2%.The structure and the surface valency state of the Co nanocrystals were measured by XRD,Uv-vis,XPS and TEM.The monodisperse Cobalt nanocrystals can be assembled to form a two-dimensional hexagonal close-packed structure.
Compensation for the demagnetizing field in remanence measurements of perpendicular magnetic recording films
Feng Jie
2003, 52 (2): 487-491. doi: 10.7498/aps.52.487
Abstract +
It is necessary to compensate for the demagnetizing field in remanence measurements of perpendicular magnetic recording films.In this paper,a new method of compensating for the demagnetizing field is proposed and an effective reverse field Heff is used to evaluate the dc demagnetization remanence curves,isothermal remanent magnetization curves,and the ΔM plots for perpendicular magnetic recording films.The demagnetization factor N is important for this method,and three methods are used to estimate the value of N. The results of the ΔM plots indicate that the intergranular interactions in Ba ferrite films seem to be of exchange coupling,while those in Co-Cr-Ta films are of magnetostatic interactions.
Studies on magnetic and magneto-optical properties of Pt976Mn26/Co multilayers
Chen Liang-Yao, Liang Bing-Qing, Wang Hai, Tang Yun-Jun, Wang Yin-Jun, Zhou Xun
2003, 52 (2): 492-497. doi: 10.7498/aps.52.492
Abstract +
A series of Co/Pt974Mn26(xPtMn nm)modulated multilayers with the thickness of PtMn layer x ranging from 096 to 168nm have been prepared by a magnetron sputtering system on 40nm thick PtMn buffer.With combined small-and large-angle x-ray analyses,the layered and crystal structure of the samples were investigated.Magnetic hysteresis loops and perpendicular magnetic anisotropy(PMA) were obtained by means of altermating-gradient magnetometer(AGM) and magnetic torque methods.Saturation magnetization,PMA and the Kerr spectrum of the samples were also investigated.Through analyses,we obtained the variation of Kerr rotation with the increase of PtMn thickness,which was ascribed to the reduction of the polarization of Pt atom and the interlayer alloys.
The preparation and properties of bilayer manganite films
Cha Li-Mei, Zhang Peng-Xiang, H.U.Habermeier
2003, 52 (2): 498-502. doi: 10.7498/aps.52.498
Abstract +
The bilayer manganite film La2-2xSr1+2xMn2O7(x=032)were successfully prepared by pulsed laser deposition(PLD)method.By controlling the parameters of deposition,the fabricated films are of single phase and grown well on two kinds of substrates with different lattice constants.After measurements of transport property,it is found that there is 80K deference between the two cusp temperatures in resistivity-temperature curves(TM-I) of the two films grown on SrTiO(001) and NdGaO(110).At the same time,the resistivity of the film on SrTiO(001)is 50 times higher than that of the film on NdGaO(110).We studied the influence of the interface strain and found that the lattice mismatch between substate and film is the main reason of the above observations.Tensile strain decreases TM-I with increasing resistivity and compressed strain has an opposite effect.Using double exchange model by Zener,we found that these results can be explained qualitatively.
Photocurrent spectra of very long wavelength GaAs/AlGaAs quantum well infrared photodetector
Zi Jian, Yuan Xian-Zhang, Li Ning, Chen Xiao-Shuang, Shen Xue-Chu, Lu Wei
2003, 52 (2): 503-507. doi: 10.7498/aps.52.503
Abstract +
The photocurrent spectra characteristics of the 15μm very long wavelength GaAs/AlGaAs quantum well infrared photo detector(QWIP) have been investigated.The two photocurrent response peaks, which have a Gaussian lineshape due to the random fluctuation of the well width,are attributed to the transitions from the ground state E0 to the first excited state E1 and the third excited state E3 in the well,respectively.The transition peaks shift linearly to higher energy as the bias across the detector increases.Taking into account electrons exchange effect,we find that the theoretical calculation using the transfer matrix method agrees well with the experimental data.
Spectroscopic properties and thermal stability of a new erbium-doped bismuth-based glass
Yang Jian-Hu, Dai Shi-Xun, Wen Lei, Liu Zhu-Ping, Hu Li-Li, Jiang Zhong-Hong
2003, 52 (2): 508-514. doi: 10.7498/aps.52.508
Abstract +
The absorption spectra,emission spectra and thermal stability of Er3+-doped (85-x)Bi2O3-(10+x)B2O3-5Na2O(x=0,5,10,15,20,25 mol%)glasses were investigated in this work.The Ωt(t=2,4,6)(Ω2=(352—386)×10-20cm2,Ω4=(138—152)×10-20cm2,Ω6=(093—117)×10-20cm2)parameters were calculated by Judd-Ofelt theory.The stimulated emission cross sections(σe=(70—95)×10-21cm2)of the Er3+ ion 4I13/2→4I15/2 transition were calculated using the McCumber theory.The FWHMs(FWHM=57—79nm) of the 4I13/2→4I15/2 emission and lifetimes of 4I13/2 level(τm=265—159ms)of Er3+ ions were measured.The thermal stability of the glasses were analyzed.The compositional dependence of optical parameters of Er3+ ions were studied,with the increases of B2O3 content in the glass.The parameters Ωt(t=2,4,6),FWHM,and temperature difference of ΔT=Tx-Tg increase monotonically,while the measured lifetime decreases.The optical properties of Er3+ in different glass hosts were compared.The results show that our Er3+-doped bismuth-based glass is much more beneficial for optical amplifier to realize broadband and high gain amplification.