Vol. 50, No. 5 (2001)
NUMERICAL SIMULATION OF BISTATIC SCATTERING FROM FRACTAL ROUGH SURFACE BY FAST FORWARD-BACKWARD METHOD
2001, 50 (5): 797-804. doi: 10.7498/aps.50.797
In order to numerically simulate bistatic scattering from fractal rough surface at low grazing angle incidence, a hybrid approach of the forward-backward method (FBM) with spectral-accelerated algorithm (SAA) is developed to solve the magnetic field integral equation. Numerical bistatic scattering from one-dimensional perfect conducting fractal rough surface realized by the Monte Carlo method with and without the presence of a regular object is accomplished, Linear relationship between the envelope slope of bistatic scattering pattern and the fractal dimension is discussed.
2001, 50 (5): 805-810. doi: 10.7498/aps.50.805
The equations of motion of variable-mass nonlinear nonholonomic dynamical systems in Poincaré-Chetaev variables have been studied. Firstly, the Poincaré-Chetaev variables x1,x2,…,xn and more with n-m holonomic constraints and m-l nonlinear nonholonomic constraints of Chetaev type were introduced. Secondly, the equations of Chaplygin's form, Nielsen's form and Appell's form were derived from the D'Alembert-Lagrange principle for a variable-mass mechanical system. Finally, the problem of equivalence between the Chaplygin's equations and the Appell's equations was discussed. Then the theory is illustrated by an example due to Appell.
SYMMETRY AND INVARIANT IN GENERALIZED MECHANICAL SYSTEMS IN THE HIGH-DIMENSIONAL EXTENDED PHASE SPACE
2001, 50 (5): 811-815. doi: 10.7498/aps.50.811
By means of the invariance of Hamilton’s action under infinitesimal transformation in the high-dimensional extended phase space, the symmetry and invariant of the generalized holonomic conservative and nonconservative mechanical systems and some related propositions are obtained. Finally one example is given.
2001, 50 (5): 816-819. doi: 10.7498/aps.50.816
We have studied the Lie symmetries of a constrained Hamiltonian system only with the second type of constraints,and establised the determining equations, the restriction equations and the additional restriction equations. The conditions under which a Lie symmetry can lead to a conserved quantity and the form of the quantity were given.
2001, 50 (5): 820-824. doi: 10.7498/aps.50.820
The experimental simulation method is introduced into the quantum mechanics.A vibrating chord system with a stationary stote equation in a form similar to that of the stationary Schr?dinger equation is designed.The system offers the theoretical and experimental methods for the simulation solution to the stationary Schr?dinger equation.The results of the macroscopical simulation presents a macroscopical analogy for the understanding of the Schr?dinger equation.
2001, 50 (5): 825-831. doi: 10.7498/aps.50.825
This paper researches Fock state space structure and supersymmetry mechanics of parasystem consisting of one degree of freedom of paraboson and one degree of freedom parafermion in the case of the same order p.It is shown that except for the four extreme special states,there is an intrinsic double-degeneracy in the state space structure of a parasystem.Moreover,it is also discovered that the parasystem possesses a hidden intrinsic supersymmetry in addition to the dynamic supersymmetry,and the intrinsic supersymmetry plays a key role in the exact supersymmetry of a parasystem.
2001, 50 (5): 832-836. doi: 10.7498/aps.50.832
The smashed electromagnetic wave is a new electromagnetic wave, which is transmitted by the transfinite sources with the transfinite phases in a part area. It has a much different character from the general electromagnetic wave, its wave character is nearly disappeared. So its transmission through a conductor almost is enhanced by a hundred times, and this transmission is achieved by particle diffusion. It has a character to keep its initial resting place on the earth, thus its movement willbe in the opposite direction of that of a moving carrier.
2001, 50 (5): 837-840. doi: 10.7498/aps.50.837
The MKDV equation (ut+6u2ux+uxxx=0) is simulated by the 5-speed lattice Boltzmann method of 0(ε)precision,then the result is compared with the soliton solution of the MKDV equation. They inosculate with each other.
THE INFLUENCE OF WEAK PARAMETRIC PERIODIC PERTURBATION ON SAFE BASIN AND THE CONTROL OF THE FRACTAL EROSION BASIN
2001, 50 (5): 841-846. doi: 10.7498/aps.50.841
In this paper,the influence of weak parameter periodic perturbation on the safe basin of a nonlinear oscillator is studied.The results show that the fractal erosion of the safe basin is enhanced when the system is perturbed by the periodic signal at some definite frequencies.On the other hand,the fractal erosion basin is suppressed by the periodic perturbation at other frequencies,for this case there exists an optimal perturbation frequency.Furthermore,based on the obtained results,a method used to control the fractal erosion basin is presented.Melnikov's method is used to interpret this control method,and the robustness of the control of the fractal erosion basin is also discussed.
2001, 50 (5): 847-850. doi: 10.7498/aps.50.847
A novel adaptive control method is proposed for a class of chaotic systems with uncertain parameters,based on Lyaponov function.Using the presented method,a controller is developed,which can remove chaos in nonlinear systems and make the system asymptotically stabilizing to any desired smooth orbit.The controller is directly constructed by analytic formula without knowing unknown bounds about uncertain parameters in advance.Computer simulation example is given to validate the proposed approach.
2001, 50 (5): 851-855. doi: 10.7498/aps.50.851
The scaling properties of the nonlocal Lai-Das Sarma-Villain equation are studied by using dynamic renormalization-group(DRG) analysis and scaling approach,respectively.The DRG analysis shows that the nonlocal nature of the nonlinear term can produce new fixed points with continuously varying exponents, depending on both the nonlocal interaction parameter ρ and the substrate dimension d.The scaling exponents in both weak- and strong-coupling regions are obtained by scaling approach.The exponents obtained in the weak-coupling region well match the results of the DRG analysis.
2001, 50 (5): 856-859. doi: 10.7498/aps.50.856
The research for the absorptance of materials is significant to the development of laser material processing.The measurement method is the foundation of the absorptance research.In this paper the lumped method based on heat transfer is established for the absorptance of laser,and the measuring apparatus is also built up.As examples,the absorptance of laser is measured for several ordinary engineering materials.
ATOMIC AND MOLECULAR PHYSICS
2001, 50 (5): 860-864. doi: 10.7498/aps.50.860
The measurement and analysis were carried out on the Si(111) surface implanted by N+1,N+2,N+10 cluster ions with high doses (1.7×1017ions/cm2) at 76keV energy using ellipsometry,Fourier-transform infrared (FT-IR) absorption spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy.It was found that the medium layer containing Si-N bond on the surface appeared,and their complex refractive index turned into real;however,at the same implantation dose their surface morphologies were different from each other.Expect for a few pittings,the N+1-implanted surface had a best fineness (average roughness Ra≈4.2nm), close to the unimplanted original surface.The N+2-implanted surface had a black dendritic area,and had a poorer fineness (Ra≈16nm).While in the N+10-implanted surface appeared a ripple structure,with the poorest fineness (Ra≈40nm).It was indicated that the roughness of the material surface increased with the ion size and fluence at the high energy in contrast to the cluster implantation at the low energy.
CLASSICAL AREA OF PHENOMENOLOGY
THEORY AND EXPERIMENT FOR THE CHARACTERIZATION OF RANDOM SURFACES BY THE AVERAGE INTENSITY OF IMAGE SPECKLES OF VARIABLE APERTURES
2001, 50 (5): 865-870. doi: 10.7498/aps.50.865
Using the Gaussian correlation model of random surfaces, we conduct the theoretical derivation of the image-plane intensity produced by a weak scatterer in the 4f optical filtering system.Then the method is proposed for characterizing the square-root-mean deviation roughness and lateral correlation length.This method uses the derived theoretical expressions to fit the experimentally measured curve of image speckle intensity versus the radius of filtering aperture,and the two surface parameters can be extracted simultaneously.In the experiment,random surface samples are specially made and their surface parameters are measured. The results conforms with those obtained by atomic force microscopy,which shows that the method of this paper is of good accuracy.
2001, 50 (5): 871-874. doi: 10.7498/aps.50.871
The thresholds of laser-induced darkening in different optical and laser glasses irradiated by a 800nm, 120fs, 1kHz Ti:sapphire laser are reported for the first time. The ESR spectra of irradiated glass show laser-induced darkening results from color-center generation. The glasses are transparent in the wavelength of 800nm, so we suggest that color-center is generated through multi-photon absorption.
TIMING JITTER INDUCED BY AMPLIFIED SPONTANEOUS EMISSION IN A FEMTOSECOND MODE-LOCKED SOLID-STATE LASER
2001, 50 (5): 875-879. doi: 10.7498/aps.50.875
We have derived a set of motion equations for the amplitude,the inverse pulse width,the chirp,the frequency,the central position of the pulse and the phase in a mode locked solid-state laser.In the hypothesis of the low and white noise,the timing jitter induced by the amplified spontaneous emission was estimated for a Ti:sapphire laser with the chirp.It is found that for a certain mode-locked solid-state laser with a pulse profile of sech2(1.763t/τ),the jitter is approximatively a linear function of the net group delay dispersion (GDD),and turns to be larger with increasing GDD ;however,it cannot be reduced to zero even if the GDD is completely compensated.
2001, 50 (5): 880-885. doi: 10.7498/aps.50.880
The impact of linear loss on the evolution of screening-photovoltaic (SP) spatial solitons in biased photovoltaic-photorefractive crystals is investigated.Our numerical study indicates that the loss not only results in the decrease of the amplitude of the soliton beam,but also results in the change of the shape of the soliton beam.For the bright SP soliton,the soliton width increases as the propagation distance increases for the SP soliton with low-intensity at the input,whereas the soliton width decreases initially and then increases as the propagation distance increases, and there is a propagation distance in which the soliton width returns to its value at the input for the SP soliton with high-intensity at the input.For the dark SP soliton,the soliton width increases as the propagation distance increases whether the SP soliton has low-or high-intensity at the input.Though the effect of loss on the evolution of SP soliton can be ignored if the propagation distance is short enough,the loss is eventually expected to destroy these solitons at long distance.
2001, 50 (5): 886-891. doi: 10.7498/aps.50.886
We observed for the first time (to our knowledge) a new type of all optical double-quasi-steady-state photorefractive spatial soliton in a Cu:KNSBN crystal.The soliton was created without an applied electric field but with an inducing laser beam.An all optical switching effect was found in the formation of the soliton.
2001, 50 (5): 892-896. doi: 10.7498/aps.50.892
The experimental results demonstrate that an amorphous colloidal crystal possesses a quasi-complete photonic band gap. The bandwidth and the wavelength of the forbidden gap in the amorphous crystal do not change along with the variation of the incident angle. The bandwidth of the stop band is much larger than that in the silica colloidal single crystal. The results also show that quasi-complete photonic band gap can be observed in an amorphous colloidal crystal with a low refractive index. The quasi-complete photonic band gap results from the fact that the symmetry of lattice is decreased in amorphous colloidal crystal.
ANALYTICAL EXPRESSION OF SECOND-ORDER AND THIRD ORDER DISPERSIONS IN THREE-ELEMENT RESONATOR USED FOR KERR LENS MODE-LOCKING
2001, 50 (5): 897-903. doi: 10.7498/aps.50.897
In this paper,we give an analytical expression of second-and third-order dispersions for three-element cavity.The variations of the second- and third-order dispersions owing to the changing of Ti:Al2O3 crystal and prismatic output coupler are calculated.The results provide a theoretical basis for the design of three-element cavity.
2001, 50 (5): 904-909. doi: 10.7498/aps.50.904
The propagation and switching of short optical pulses in a three-core nonlinear fiber coupler have been investigated with a variation method within the framework of the Lagrangian density formulation.The analytical solutions were directly obtained from the coupled nonlinear Schr?dinger equations.It is shown that the soliton switching behavior predicted by the present analytical method agrees well with the results from numerical analysis.In addition,the coupling length and the switching threshold of solitons in a nonlinear coupler were obtained.
2001, 50 (5): 910-913. doi: 10.7498/aps.50.910
The irreversibility of ferroelectric phase transition has been studied by using irreversible thermodynamics.Heat stagnation of the first-order ferroelectric phase transition and polydomain configuration of ferroelectrics can be explained on the basis of the principle of minimum entropy production.A conclusion has been derived that the heat stagnation is not an intrinsic property of a system in which a first-order ferroelectric phase transition arises.The finiteness of the system's surface is connected with the heat stagnation.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2001, 50 (5): 914-920. doi: 10.7498/aps.50.914
The ablating model of a bulk target irradiated by a pulse laser is set up.Using the simple energy balance considerations,the relationship of the ablating surface's location with the time is derived.By adiabatic approximation,the continuous-temperature condition and conservation of energy,we find out all the boundary conditions.By using the combination of analytical method and integral-approximation method,and solving the heat flow equation,the temperature distribution of soild and liquid phases' as functions of time and location are obtained,the interface of solid and liquid phase is also derived.In addition,the results are compared with other published data.Finally,most of the calculated results present are on excimer-laser irradiated target Al,although the calculations can be easily extended to laser irradiation of other targets.
2001, 50 (5): 921-925. doi: 10.7498/aps.50.921
The mechanism of the fast ignition in laser fusion and ultra-intense and ultra-short-pulse laser plasma interaction are analysed theoretically and simulated numerically.Two-and Two and half-dimensional cloud-in-cell simulation codes are developed and simulation results for ultra-intense and ultra-short-pulse laser propagating in an inhomogeneous plasma and the boring velocity and the depth of the hole are presented,as well as the parameter index of the laser device of fast ignition in laser fusion.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2001, 50 (5): 926-932. doi: 10.7498/aps.50.926
A new finite-difference iterative method is used to calculate the distribution of the liquid crystal directors under an applied voltage.Numerical results for twisted nematic,super twisted nematic,and hybrid nematic cells are given.In comparison with Newton's method and the relaxation method, it in shown that the new method is simpler,more stable to give accurate results for various types of liquid crystal cells.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2001, 50 (5): 933-937. doi: 10.7498/aps.50.933
The exchange interaction is considered to play the dominant role in the quenching of 5D0—7F2 emission of Eu3+ in Y2O3 nanocrystals.Luminescence decay curves of 5D0-7F2 of Eu3+ in two sizes of nanocrystals were measured.We fit the luminescence decay curve by the Inokuti-Hirayama theory.The efficiencies of energy transfer of exchange interaction were calculated.The difference between theoretical and experimental curves of efficiency was analyzed.
ERROR ANALYSIS FOR MEASUREMENTS OF MICROWAVE SURFACE RESISTANCE OF HIGH-TEMPERATURE SUPERCONDUCTORS BY DIELECTRIC RESONATOR METHOD
2001, 50 (5): 938-941. doi: 10.7498/aps.50.938
In this paper the relations between the errors in measurements for the microwave surface resistance of a high-temperature superconducting thin film and the geometry and frequency of a parallel plate dielectric resonator were analyzed. The results showed that the influence of the 2a/L(ratio of the diameter of the dielectric rod to its length), the b/a (ratio of the radius of the metal cavity to the radius of the dielectric rod) and the frequency f on the error and the measurable minimum surface resistance Rsmin is quite important. The curves obtained in this paper could be used to design the dielectric resonators of parallel plate type. The error of order of 1% and Rsmin of the order of micro-ohm could be obtained by proper choosing 2a/L, b/a and f.
2001, 50 (5): 942-947. doi: 10.7498/aps.50.942
The dynamic phase transition has been studied in the three-dimensional kinetic Ising model in the presence of a time-varying(sinusoidal)magnetic field by Monte Carlo simulation.The nature of the transition is characterized by studying the distribution of the order parameter.The system is in contact with an isothermal heat bath at temperature T.We varied the magnitude of the magnetic field,keeping the frequency of the magnetic field unchanged.For the lower values of the environment temperature the transition is discontinuous and it is continuous for higher values of the environment temperature,indicating the existence of a tricritical point (TCP) on the phase boundary.The TCP shifts towards higher temperature region with the decrease of frequency.i.e:TTCP=1.33×e(-ω/30.7)
2001, 50 (5): 948-952. doi: 10.7498/aps.50.948
The Monte Carlo method was employed to perform the numerical simulation for classical discrete diluted Heisenberg spin system driven by an oscillating external magnetic field. To form the diluted spin system based on isotropic Heisenberg model, we introduced in the Hamiltonian of a typical Heisenberg model both random anisotropy energy term characterizing amorphous state with a proportion X and uniaxial anisotropy energy term representing crystalline state with a proportion 1-X. The dynamical transition behavior of the Spin system mentioned above, hysteresis loop scaled with parameter X and random as well as uniaxial anisotropy constant D and A, respectively, was studied in detail. It has been put forward a scaling relationship between hysteresis loop area and parameter X, A and D as below: Aarea-AδDηXσ . The main conclusions can be summarized below:(1)At a specific value X(defined as Xmin), the investigated system gains minimal hysteresis which has been proved experimentally in our another investigation. (2) The exponents δ,η and σ of the diluted spin system are universal constants, and the sum of δ+η(～0.9) equals the exponent δ,η of single either uniaxial or random anisotropy spin system. (3)The specific value Xmin versus logarithm of the ratio of A/D shows a peculiar sigmoidal trend.
2001, 50 (5): 953-957. doi: 10.7498/aps.50.953
We report the displaced hysteresis loops in the annealed amorphous alloys Fe65.9Cr11.6Si7.5B15 and Fe60Co5.9Cr11.6Si7.5B15. The effects of measuring field Hm, temperature T and time t on the displacement HD have been studied. On the basis of the magnetostatic interaction between the hard particle resulting from the annealing and the residual amorphous soft matrix, the experiments could be well explained by the unidirectional anisotropy model.
ANALYSIS OF THE EXISTENCE OF MAGNETOSTATIC SOLITONS IN FERROMAGNETIC FILMS UNDER THE INFLUENCE OF CARRIERS
2001, 50 (5): 958-963. doi: 10.7498/aps.50.958
Under the influence of semiconductor carriers, within certain frequencies, along the direction of propagation perpendicular to the external magnetic field, magnetostatic surface wave can develop into magnetostatic solitons, with the group velocity and phase velocity being opposite to each other, and the magnitude of the velocity changes with the carriers density.
When the photon energy of an incident light is close to E0+Δ0 of Hg1-xCdxTe, we observe the resonant Raman scattering, “forbidden” resonant enhancement Raman scattering and the second-order resonant Raman scattering. We have analyzed the reason why we can observe the weak “forbidden” TO2 mode from the principal (100) face of Hg1-xCdxTe in the case of no resonant scattering; and also analyzed the reason why the “forbidden” TO2 mode from the principal (100) face of Hg1-xCdxTe increases significantly in the case of no resonant scattering. According to our analysis, we find that the second-order resonant Raman scattering by two LO phonons is caused largely by the interband Fr?hlich interaction.
2001, 50 (5): 968-972. doi: 10.7498/aps.50.968
Variation of fluorescence background in the Raman spectrum was investigated versus laser power, which was measured on Cd0.96Zn0.04Te surface at low temperatures. The fluorescence signals “burning out” were observed, accompanied by a red shift of the material's phonon peaks. It was shown that the “burning out” of the fluorescence signals was correlated to the transformation of the crystal surface structure, which was directly indicated by the red shift of the phonons. The exciting laser should be responsible for the structure transformation.
2001, 50 (5): 973-976. doi: 10.7498/aps.50.973
Pure green and narrow bandwidth emission from organic bilayer electroluminescent devices were presented by using Tb3+∶(SA)3 as hole-transporting layer and emissive layer, and high fluorescent material Alq3 acting as electron-transporting layer. It proves that the emission comes from carriers' recombination after their tunneling through the inner interface (Tb3+∶(SA)3/Alq3) in the bilayer ITO/Tb3+∶(SA)3(40nm)/Alq3(55 nm)/Al diode. The spectrum of the bilayer devices varies with the thickness of the electron-transporting layer. Keeping the thickness of Tb3+∶(SA)3 layer constant, there is no emission from Alq3 layer when Alq3 layer reduces to 12 nm; meanwhile, pure green and narrow bandwidth emission can be observed. Thus, it provides a simple way to obtain high luminance and long-term stability by reducing electron- or hole-transporting layer, especially, by using a lanthanide complex for emissive layer.
ENHANCED PHOTOEMISSION FROM METAL NANOPARTICLE COMPOSITE THIN FILMS (Ag-BaO) DOPED WITH RARE-EARTH ELEMENTS
2001, 50 (5): 977-980. doi: 10.7498/aps.50.977
A metal nanoparticles-composite thin film (Ag-BaO), doped by rare-earth elements, was grown by vacuum deposition. Compared with the normal Ag-BaO thin film, the photoemission current of the doped Ag-BaO thin film increases by about 40%. The transmission electron micrograph indicated that Ag nanoparticles become smaller when doped with rare-earth. With the smaller size of Ag nanoparticles, photoelectrons are easier to transgress from Ag nanoparticles via tunnel effect. Thus the photomission current increases.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2001, 50 (5): 981-985. doi: 10.7498/aps.50.981
The Au/PZT/BIT/p-Si heterostructure was fabricated by pulsed laser deposition technique. The effect of introducing a BIT buffer layer between the PZT films and Si substrate on the crystallinity, the ferroelectric characteristics and the electrical characteristics of the ferroelectric film system, as well as the conductivity behavior of the Au/PZT/BIT/p-Si heterostructure were investigated. The PZT films deposited on p-Si with a BIT buffer layer were found to grow with a preferred orientation along(110) direction. In the case of identical thickness(400?nm) of ferroelectric layer, the PZT/BIT multilayer ferroelectric thin films showed a better ferroelectric property than PZT thin films. The clockwise rotational C-V hysteresis loop of the Au/PZT/BIT/p-Si heterostructure indicated that the PZT/BIT ferroelectric thin films had controlled the Si surface potential and showed a characteristic of polarization-type switching. The current-voltage (I-V) curves showed that the heterostructure was conductive only in the one voltage direction and the leakage currents are too low to identify in the opposite direction. The conduction in low voltage region displays an ohmic behavior and the current transportation in ferroelectric thin films at the high voltage region is ascribed to the space-charge limited current. The remnant polarization of the PZT/BIT films system remained tobe 90% of the initial value after 109 bipolar switching cycles.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Using the first and third law of the black hole mechanics, we have derived the formula of the Planck absolute entrory of the black hole. The formula represents that the entrory of the black hole should be proprotional to the total area of the inner and outer horizons. And we have proven that the Planck absolute entrory of the black hole should be the classical thermodynamic entropy.
2001, 50 (5): 990-993. doi: 10.7498/aps.50.990
Nanometer scale data recording has been achieved on p-nitrobenzonitrile thin films using scanning tunneling microscopy.When a series of voltage pulse is applied between the STM tip and the highly ordered pyrolytic graphite substrate, structural transition at molecular scale has been observed directly for PNBN thin films.The recording mechanism is attributed to local structural transition at molecular scale,i.e.,from a crystalline state to a disordered one.The former corresponds to a high electrical resistance,and the latter to a low resistance.
2001, 50 (5): 994-1000. doi: 10.7498/aps.50.994
The use of the state-of-the-art laser facility makes it possible to create conditions of the same or similar to those in the astrophysical processes.The introduction of the astrophysics-relevant ideas in laser-plasma experiments is propitious to the understanding of the astrophysical phenomena.However,the great difference between the laser-produced plasmas and the astrophysical processes makes it awkward to model the latter by laser-plasma experiments.This paper addresses the physical backgrounds for modeling the astrophysical plasmas by laser plasmas, connecting these two kinds of plasmas by scaling laws.Thus,allowing the creation of experimental test beds where observations and models can be quantitatively compared with laser-plasma data.Special attentions are paid on the possibilities of using home-made laser facilities to model astrophysical phenomena.