Multiple scattering of an obliquely incident plane acoustic wave from a grating of immersed cylindrical shells

The study of the interaction of acoustic waves with cylindrical structures has numerous applications including the ultrasonic nondestructive testing of materials. In this paper, using a new mathematical model presented for the scattering of obliquely incident plane acoustic waves from a grating of immersed cylindrical shells, a detailed study of the resonant interaction of A-wave resonances originating from the shells is conducted. The nature of A-wave resonances and the effect of center-to-center distance of the shells on these resonances are examined. It is observed that this resonant interaction not only results in the splitting of A-wave resonances, but also causes an increase in resonance amplitudes. This interaction phenomenon is not seen in Rayleigh, whispering gallery and guided wave resonances. It is also shown that increasing the angle of wave incidence to the grating weakens the A-wave resonant interactions. The numerical results obtained from the mathematical model are compared to experimental results available in the literature for gratings composed of two and three aluminum shells. The numerical results are in very good agreement with their experimental counterparts.     

超冷钠原子弹性散射特性的精确计算

基于精确的原子之间相互作用势,系统研究了钠原子在超冷温度下的弹性散射特性,精确计算了钠原子间碰撞时的s波散射长度、有效力程、p波散射长度以及束缚态数目等散射参数.超冷温度下单重态和三重态原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现,计算发现单重态和三重态散射截面分别存在显著的f波和i波形状共振.应用简并内态近似方法获得了超精细态相互作用时的s波散射长度,所得结果与精确值比较符合.     

Super scattering phenomenon in active spherical nanoparticles

Localized surface electromagnetic resonances in spherical nanoparticles with gain are investigated by using the Mie theory. Due to the coupling between the gain and resonances, super scattering phenomenon is raised and the total scattering efficiency is increased by over six orders of magnitude. The dual frequency resonance induced by the electric dipole term of the particle is observed. The distributions of electromagnetic field and the Poynting vector around nanoparticles are provided for better understanding different multipole resonances. Finally, the scattering properties of active spherical nanoparticles are investigated when the sizes of nanoparticles are beyond the quasi-static limit. It is noticed that more highorder multipole resonances can be excited with the increase of the radius. Besides, all resonances dominated by multipole magnetic terms can only appear in dielectric materials.     

Pure elastic resonance scattering for submerged elastic objects with separable geometries

I.IntroductionTheResonanceScatteringTheory(RST)wasdevelopedasabasicmethodtoanalyzesoundscatteringfromelasticobjectsimmersedinwater.Itwasusedtocylindricalandspher-icalgeometries,includingsolidandshellobjects.TheRSTinvestigatesmainlytheresonancespectrumofscatteredwavefromanelasticobjectexcitedbytheincidentwave.Theresonallcespectrum,namedthe'AcousticSpectroscoPy',reflectsmaterialcharactersoftheobjectsandcanbeusedtoidentifythetarget.Theresonallcespectraareisolatedbysubtractingfromthescattere…     

Investigating the absolute phase information in acoustic wave resonance scattering

The aim of this work is to investigate the absolute phase information in resonance acoustic scattering by spheres and cylinders and place this work in the broader context of scattering in which the properties of the magnitude and (processed) phase have been examined in a more general way than in the classical resonance scattering theory (RST). Here, comparisons are made between the classical and modified RST formalisms of acoustic resonance scattering. Experimental and theoretical backscattering form functions are obtained and discussed. It is shown that the magnitude and processed (unwrapped) phase can be correctly obtained through the classical RST, suggesting that the modified RST formalism offers little new practical advantage. Furthermore, the absolute phase is shown to be very sensitive to object’s resonances, suggesting that the unwrapped phase may be considered as an efficient tool, along with the magnitude information, to carry out remote (active) classification of targets in underwater acoustics applications. The combination of absolute phase information with the magnitude data offers a complementary advantage in the identification of resonances from cylinders and spheres.     

Scattering on plasmonic nanostructures arrays modeled with a surface integral formulation

The surface integral formulation is a flexible, multiscale and accurate tool to simulate light scattering on nanostructures. Its generalization to periodic arrays is introduced in this paper. The general electromagnetic scattering problem is reduced to a discretizated model using the Method of Moments on the surface of the scatterers in the unit cell. The study of the resonances of an array of bowtie antennas illustrates the main features of the method. When placed into an array, the bowtie antennas show additional resonances compared to those of an individual antenna. Using the surface integral formulation, we are able to investigate both near-field and far-field properties of these resonances, with a high level of accuracy.     

η-production on the proton via electromagnetic and hadronic probes

The reactions π~-p→ηn and γp→ηp are investigated within a dynamical coupled-channels model of meson production reactions in the nucleon resonance region. The meson-baryon channels included are πN, ηN, π△, σN, and ρN. The direct η-photoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU(6) O(3) symmetry. In the models search, the following known nucleon resonances are embodied: S_(11)(1535), S_(11)(1650), P_(11)(1440), P_(11)(1710), P_(13)(1720), D_(13)(1520), D_(13)(1700), D_(15)(1675), and F_(15)(1680). Data for the π~-p→ηn reaction from threshold up to a total center-of-mass energy of W ≈ 2 GeV are satisfactorily reproduced. For the photoproduction channel, two additional higher mass known resonances, P_(13)(1900) and F_(15)(2000), are also considered. However, reproducing the data for γp→ηp requires, within our approach, two new nucleon resonances, for which we extract mass and width.     

A review of the effects of light scattering on the dynamics of irregularly shaped dust grains in the Solar System

The various aspects of the interaction of electromagnetic radiation with cosmic dust particles are discussed. In particular, attention is paid to discrepancies between optical and physical behavior of realistically shaped particles and volume equivalent homogeneous spheres. The dynamical evolution of morphologically non-identical particles which are driven by gravity, electromagnetic radiation and the Lorentz forces can dramatically differ. Although spherical particles often enable analytical calculations, an orbital evolution of spheres cannot be considered as a representative evolution for real cosmic dust particles. The effect of electromagnetic radiation on the motion of dust grains plays a crucial role here. While irregularly shaped interstellar dust particles may be captured in the Solar System, the spherical particles will not survive due to close encounters with the Sun. Spherical grains can be captured almost only in the evaporation region (in the vicinity of the Sun), where they are destroyed due to high temperatures. The spherical dust particles ejected from comets will monotonously inspiral toward the Sun subject to the Poynting-Robertson effect. However, the non-spherical particles of the same origin may be temporarily stabilized at some heliocentric distances and thus their lifetime may be much longer than that for the Mie spheres. Some dust particles may also be captured in mean-motion resonances with planets (commensurability resonances). While spherical particles are always characterized by the secular decrease of the semi-major axes near mean-motion resonances, this may not be true for non-spherical particles. Resonant captures of arbitrarily shaped dust grains exist for exterior and interior mean-motion resonances with planets.     

Application of the diffraction trace formula to the three-disk scattering system

The diffraction trace formula derived previously and the spectral determinant are tested on the open three-disk scattering system. The system contains a generic and exponentially growing number of diffraction periodic orbits. In spite of this it is shown that even the scattering resonances with large imaginary part can be reproduced semiclassically. The nontrivial interplay of the diffraction periodic orbits with the usual geometrical orbits produces the fine structure of the complicated spectrum of scattering resonances, which are beyond the resolution of the conventional periodic orbit theory.     

Giant resonances in90Zr and116Sn

The giant resonance region in⁹⁰Zr and¹¹⁶Sn excited by 270 MeV helions has been measured up to about 35 MeV excitation energy. The low and the high energy octupole resonances are seen prominently in addition to the quadrupole and the monopole resonances. The angular distribution data for the various multipoles are satisfactorily explained by the collective model calculations. The percentatge energy weighted sum rule strengths have been determined for all the prominent resonances.     

Resonance properties from a coupled channel meson exchange model

In this talk, I present the results on the pole structure of pion-nucleon scattering in an analytic model based on meson exchange. The analytic properties of scattering amplitudes provide important informa-tion. Besides the cuts, the poles and zeros on the different Riemann sheets determine the global behavior of the amplitude on the physical axis. Pole positions and residues allow for a parameterization of resonances in a well-defined way, free of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate resonance contributions in different reactions.     

Acoustic scattering from cylindrical shells: Guided waves and resonances of the liquid column

Recent studies of acoustic scattering have allowed the explanation of the existence of additional lines in the resonance spectrum of an elastic solid cylinder immersed in water by the examination of natural modes. A first group of natural modes, related to the propagation of the circumferential waves (Rayleigh, Whispering Gallery waves), is detected when the cylinder is insonified perpendicularly to its axis. A second group of natural modes related to the guided waves which propagate in the direction parallel to the axis of the cylinder is detected when it is insonified obliquely. In this Paper, the authors examine the acoustic scattering from cylindrical shells filled with a fluid (air or liquid) by the method of isolation and identification of resonances (MIIR). It allows resonance spectra to be obtained; in addition, the mode number, n, given by the identification, makes it possible to separate the resonances into different series. It is possible to explain the experimental resonance spectra of a liquid-filled tube insonified perpendicularly to its axis with a non-perfect directive transducer, by the calculation of the eigenfrequencies of the different parts of the target. The authors show the great importance of the guided waves along the axis and of the resonances of the liquid column when the shell is filled with a liquid. The resonance spectra of liquid-filled targets and the reradiation patterns giving by MIIR, i.e. after the end of excitation, are shown for the first time.     

Oscillatory magnetoconductivity of a two-dimensional electron system due to phonon scattering

Summary A quantum-statistical theory of magnetophonon resonance oscillations in two-dimensional systems has been developed, starting from the resolvent representation of Kubo's formula and its proper connected diagram expansion. Non-polar and polar optical-phonon scattering has been considered and the results show, as anticipated based on the physical considerations and experimental observations, conductivity oscillations as a function of magnetic field with the magnetophonon resonances occurring at the phonon frequencies {ie1539-1} {ie1539-2}=cyclotron frequency). Divergences occurring in the magnetoconductivity near the magnetophonon resonances are removed by using the full resolvent operator in the tetradic self-energy operator of an electron. These additional terms provide necessary damping of the magnetophonon resonance oscillations. The present results are also shown to be qualitatively similar to those obtained by others using quantum Boltzmann's equation approach to quantum transport theory.     

K-Li冷碰撞散射特性的理论研究

本文应用量子方法和半经典方法计算了表征锂(6Li,7Li) 原子和钾(39K,40K,41K) 原子间超冷碰撞特性的散射参数,如s波散射长度,有效力程,p波散射长度等。超冷温度下6Li-39K单重态和三重态原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现,计算发现单重态和三重态散射截面均存在显著的i波形状共振. 此外,本文应用简并内态近似获得了超精细态相互作用时的s波散射长度.     

Accurate calculation of the elastic scattering properties of ^7Li atoms at ultralow temperatures

The elastic scattering properties for collisions between two ^7Li atoms are investigated in the cold and ultracold regimes separately. Based on recent theoretical and experimental results, we present the improved hybrid potentials for the singlet X^1 ∑g^＋ and triplet a^3 ∑u^＋ ground states of the Li2, Our calculated values for the scattering lengths α and the effective ranges re are compared with previous ones, and found them to be in good agreement. The scattering lengths are 34.6α0 for the singlet state and -27.6α0 for the triplet state. Shape resonances occur in the collisions at low energies. We also calculate the total cross sections and the energy positions of shape resonances for both X^1 ∑g^＋ and a^3 ∑u^＋ states.     

Control of light scattering by nanoparticles with optically-induced magnetic responses

Conventional approaches to control and shape the scattering pattems of light generated by different nanostructures are mostly based on engineering of their electric response due to the fact that most metallic nanostructures support only electric resonances in the optical frequency range. Recently, fuelled by the fast development in the fields of metamaterials and plasmonics, artificial optically-induced magnetic responses have been demonstrated for various nanostructures. This kind of response can be employed to provide an extra degree of freedom for the efficient control and shaping of the scattering patterns of nanoparticles and nanoantennas. Here we review the recent progress in this research direction of nanoparticle scattering shaping and control through the interference of both electric and optically-induced magnetic responses. We discuss the magnetic resonances supported by various structures in different spectral regimes, and then summarize the original results on the scattering shaping involving both electric and magnetic responses, based on the interference of both spectrally separated （with different resonant wavelengths） and overlapped dipoles （with the same resonant wavelength）, and also other higher-order modes. Finally, we discuss the scattering control utilizing Fano resonances associated with the magnetic responses.     

Normal incidence Raman scattering enhancement in double-cavity microresonators

We report on the observation of huge enhancements of the Raman scattering efficiency at quasi-backscattering due to double optical resonances in a microcavity. The structure, based on a double-cavity configuration separated by a central mirror, was specifically designed and grown by molecular beam epitaxy to achieve a large splitting, close to the energy of the LO phonon of GaAs, between the two confined photon modes.     

超冷温度下钾和铯原子间弹性散射特性的精确计算

本文分别用量子方法和半经典方法计算了超冷钾和铯原子之间弹性碰撞的s波散射长度,有效力程和p波散射长度等散射参数. 超冷温度下³⁹K-¹³³Cs原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现, 计算发现单重态和三重态截面分别存在显著的g波和d波形状共振.另外,本文应用简并内态近似方法获得了⁴¹K-¹³³Cs 超精细态相互作用时的s波散射长度.     

Fano-type resonances induced by a boson mode in Andreev conductance

We study spectroscopic signatures of a monochromatic boson mode interacting with a T-shape double quantum dot coupled between the metallic and superconducting leads.Focusing on a weak interdot coupling,we find that the proximity effect together with the bosonic mode are responsible for the series of Fano-type resonances appearing simultaneously at negative and positive energies.We investigate these interferometric features and discuss their influence on the subgap Andreev conductance taking into account the correlation effects driven by the Coulomb repulsion.