Scattering of Klein–Gordon particles by a Kink-like potential

The Klein–Gordon equation for the non-minimal vector and a scalar Kink-like potential is solved in terms of the hypergeometric functions. The scattering problem, i.e. the transmission and reflection coefficients, is studied as well.     

Linear approximation in classical scattering by a moliégre potential

Abstract

In the context of a Monte Carlo simulation of channeling, it is shown how the scattering angle of an ion by a Molière potential can be calculated by linear interpolation. In the case of impulse approximation, this reduces the computing time to ?1/17 of that needed by the usual procedure.

The maximum error introduced by the linear approximation is calculated as a function of the interval width used for interpolation. Using Firsov's inversion formula, the corresponding approximation to the atomic potential is also evaluted. It is shown that such approximation is very good, if compared with the present knowledge of atomic potential.     

On a new mechanism of polariton–polariton scattering

Condensate states of a two-dimensional exciton–polariton system have been considered under the conditions of direct resonant photoexcitation. It has been theoretically predicted that splitting of eigenmodes with orthogonal polarizations leads to the emergence of a new channel of parametric scattering. A polariton condensate spontaneously decays into a set of states in a finite region of the momentum space, thus leading to a strong inhomogeneity in the distributions of the intensity and polarization even in the case of a strictly constant amplitude and zero in-plane momentum of the external field. The new scattering mechanism makes possible self-oscillating and chaotic states of polariton systems.     

Experimental attempt to detect stimulated “diffusion” scattering by particles in liquid

The change in the shape of the correlation function of the intensity of light scattered by particles in liquid, i.e., the appearance of a cosine component, with increasing excitation radiation intensity, is observed. The amplitude of this component increases with the intensity of exciting radiation. A quadratic component appears in the dependence of the scattering intensity on the exciting radiation intensity. These results point to the appearance of stimulated “diffusion” scattering by particle concentration fluctuations.     

On the solution of a “2D Coulomb + Aharonov-Bohm” problem: oscillator strengths in the discrete spectrum and scattering

In this paper we present an exact analytic solution of the Schrödinger equation both inthe discrete and continuous spectra for the combination of a 2D Coulomb potential and theAharonov-Bohm flux. We analyze the influence of the Aharonov-Bohm flux on the energyspectrum of such a system and show that its presence leads to the broadening of theelectron density in the bound states with the given value of the principal quantum number.We have shown that the scattering phase shift, which determines theS-matrix, can be represented as a sum of the Aharonov-Bohm scatteringphase, first obtained by Henneberger, and a “modified” 2D Coulomb phase. We have noticed,that the Aharonov-Bohm scattering phase has a full analogy with the “quantum defect” forsuch a system. We have shown also, that the presence of the Aharonov-Bohm flux affects theradiation spectrum of the electron in this case, and this fact is demonstrated bycalculations of the corresponding oscillator strengths. The explicit analytic expressionfor the scattering cross section on such a system is found in the frame of the eikonalapproach. Obtained formula contains the two exact limiting cases, namely, the “pure” 2DCoulomb scattering as well as the “pure” Aharonov-Bohm effect. The mutual influence of a2D Coulomb potential and the Aharonov-Bohm flux is also discussed.     

Visualization of the sound scattering by a cylinder

The schlieren method is applied to visualizing the sound scattering ofa cylinder immersed in the liquids.Images of the echoes,caused by normal andoblique incidence from a cylinder,are obtained for two kinds of liquids:(1)theliquid is composed of a transparent liquid;and(2)the liquid is composed of twonon-mixable transparent liquids.It is found experimentally that the echo canbe caused by the discontinaites in the shadow zone.This fact is utilized to dem-onstrate the locus of the helical surface wave creeping along the surface of thecylinder.For such cases the three-dimensional image can be described by thismethod and has not to use the system with special appliances and complexalgorithm.     

On the theory of “true” three particle scattering

The Hulthen, Kohn and Schwinger-type variational principles for the phase of true three particle scattering is formulated using the method of the hyperspherical basis. The optical theorem for such processes is proved.     

Investigation of unburned carbon particles in fly ash by means of laser light scattering

A new optical method to determine the percentage of unburned carbon particles in fly ash from combustion of pulverized coal has been developed. The technique exploits the different properties of particles of ash and coal in the elastic scattering of polarized light.     

On the nature of striped phases: striped phases as a stage of “melting” of 2D crystals

We discuss striped phases as a state of matter intermediate between two extreme states: a crystalline state and a segregated state. We argue that this state is very sensitive to weak interactions, compared to those stabilizing a crystalline state, and to anisotropies. Moreover, under suitable conditions a 2D system in a striped phase decouples into (quasi) 1D chains. These observations are based on results of our studies of an extension of a microscopic quantum model of crystallization, proposed originally by Kennedy and Lieb.     

Conditional stability of diatomic molecule driven by a weak laser field

Using a direct perturbation method, we investigate the stability of a diatomic molecule modelled by a weakly laser-driven Morse oscillator. It is shown that stationary state solution of the system is stable in the sense of Lyapunov and the periodical one possesses conditional stability, namely its stability depends on the initial conditions and system parameters. The corresponding sufficient and necessary conditions are established that indicate the stable states associated with some discrete energies. The results reveal how a diatomic molecule can be stabilized or dissociated with a weak laser, and demonstrate that the mathematical conditional stability works in the considered physical system.     

Analysis of a 2D “liquid” plasma lattice

To study the structural and dynamical properties of a 2D dusty plasma lattice, a set of experiments were performed in an environment of radio frequency discharge. Based on the results of one of the experiments, pair correlation function, bond-orientational correlation function and mean square displacement of such a system were computed and analyzed. The bond-orientational correlation function is found to fit in with the law of e-r, and the mean square displacement is found to increase monotonously with time, both of which, together with the pair correlation function, indicate that the two-dimensional dusty plasma lattice formed in the experiment stayed in a "liquid" state.     

Analysis of a 2D “liquid”plasma lattice

Adustyplasmacanbedefinedasacomplicatedplasmacontainingsmallsolidmattercalleddustgrainsordustparticles,whichareusuallychargednegatively,duetoelectronshighermobilitythanion,bycollectingelectronsandionsfromthebackgroundplasma.Theuniverseisfilledwithdustyplasmassuchasplanetaryrings,comettails,andnebulae.Also,inindustrialplasmaprocessing,particulatessuspendedinplasmaarethemajorcontaminationinsemiconductormanufacture.Studiesondustyplasmahavebeenextendedtofar-flungtopicssuchaswaves,instabilities,stro…     

Mössbauer spectra obtained by modulation of a scattering crystal

We have carried out numerous experiments with supersources having intensities in the 100 Curie range. These sources usually require massive shielding, and are not easily moved to carry out Mössbauer spectroscopy. Several of these sources can be used with microfoil conversion electron (MICE) detectors, but they cannot be moved easily either because of the delicate microfoils used, which ideally have thicknesses less than the range of the internally converted electrons. Here, we describe a technique for doing Mössbauer spectroscopy by oscillating a monochromating crystal parallel to the reciprocal lattice vector of the Bragg reflection, this being used to filter out extraneous photons from the beam. Specifically, an LiF crystal is used in diffraction experiments as a filter to scatter the 46.5-keV Mössbauer gamma rays from¹⁸³Ta by setting it at the (200) Bragg reflection. In the present measurements, the LiF crystal was mounted in the transmission mode and oscillated with a crank along the scattering vectorQ to produce the velocity modulation, with the source, sample and absorber all at rest. The velocity components of the filtering crystal along the incident and scattered beams cause the measured linewidth to be equal to the usual Mössbauer width divided by 2 sin, where is the Bragg angle. Measured widths for the (200), (400), (600) and (800) Bragg reflections agreed with the calculated values of 12.08, 6.04, 4.03 and 3.02 cm/s, within our experimental uncertainties. The technique could have applications not only to MICE detectors, but also to very narrow resonances such as⁶⁷Zn, where the increased velocities required for small Bragg angles could be an advantage and lead to enhanced resolution.     

Patterning of small particles by a surfactant-enhanced Marangoni-Bénard instability

Evaporating drops provide a means of organizing particles suspended within them. Here, the manner in which surfactants alter these patterns is studied as a function of the surface state of an insoluble monolayer at the drop interface. The surface state is visualized throughout the drop evolution using fluorescence microscopy. A regime of surfactant coverage is identified that creates conditions that enhance the Marangoni-Bénard instability. This result was not anticipated in prior studies, in which surfactants are predicted to prevent this instability. These data demonstrate that, by tuning the liquid-gas boundary condition, the patterns formed from an evaporating drop can be controlled.     

Floquet scattering through a parity–time symmetric oscillating potential

We investigate the scattering of a particle from a trapping potential that is subjected to weak, parity–time symmetric periodic drivings. Using the Floquet theory, we derive the scattering matrix and calculate the transmittance of the incident particle. When the driving is purely coherent, our calculation recovers the known result and the transmission spectrum shows the familiar, bound-state-induced Fano resonances. When the driving is purely incoherent, we find the Fano resonances still occur, ...     

On the spectrum of Schrödinger operators with a random potential

We investigate the spectrum of Schrödinger operatorsH of the type:H =–+q _i ()f(x–x _i + _i ())(q _i () and _i () independent identically distributed random variables,i ^d ). We establish a strong connection between the spectrum ofH and the spectra of deterministic periodic Schrödinger operators. From this we derive a condition for the existence of forbidden zones in the spectrum ofH . For random one- and three-dimensional Kronig-Penney potentials the spectrum is given explicitly.     

Acceleration of ions by “slow” intense laser light in low-density targets

The mechanism of synchronized acceleration of ions by slow intense laser light is studied in application to available low-density targets of a new generation, which open prospects for experimental detection of a new effect of acceleration of protons.     

Characterization of spherical core–shell particles by static light scattering. Estimation of the core- and particle-size distributions

A numerical method is proposed for the characterization of core–shell spherical particles from static light scattering (SLS) measurements. The method is able to estimate the core size distribution (CSD) and the particle size distribution (PSD), through the following two-step procedure: (i) the estimation of the bivariate core–particle size distribution (C–PSD), by solving a linear ill-conditioned inverse problem through a generalized Tikhonov regularization strategy, and (ii) the calculation of the CSD and the PSD from the estimated C–PSD. First, the method was evaluated on the basis of several simulated examples, with polystyrene–poly(methyl methacrylate) core–shell particles of different CSDs and PSDs. Then, two samples of hematite–Yttrium basic carbonate core–shell particles were successfully characterized. In all analyzed examples, acceptable estimates of the PSD and the average diameter of the CSD were obtained. Based on the single-scattering Mie theory, the proposed method is an effective tool for characterizing core–shell colloidal particles larger than their Rayleigh limits without requiring any a-priori assumption on the shapes of the size distributions. Under such conditions, the PSDs can always be adequately estimated, while acceptable CSD estimates are obtained when the core/shell particles exhibit either a high optical contrast, or a moderate optical contrast but with a high ‘average core diameter’/‘average particle diameter’ ratio.