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Because of their ability to confine light, optical resonators.sup.1-3 are of great importance to science and technology, but their performance is often limited by out-of-plane-scattering losses caused by inevitable fabrication imperfections.sup.4,5. Here we theoretically propose and experimentally demonstrate a class of guided resonances in photonic crystal slabs, in which out-of-plane-scattering losses are strongly suppressed by their topological nature. These resonances arise when multiple bound states in the continuum--each carrying a topological charge.sup.6--merge in momentum space and enhance the quality factors Q of all nearby resonances in the same band. Using such resonances in the telecommunication regime, we experimentally achieve quality factors as high as 4.9 × 10.sup.5--12 times higher than those obtained with standard designs--and this enhancement remains robust for all of our samples. Our work paves the way for future explorations of topological photonics in systems with open boundary conditions and for their application to the improvement of optoelectronic devices in photonic integrated circuits. Bound states in the continuum are merged in momentum space by varying the periodicity of the photonic crystal lattice, giving high-quality-factor guided resonances that are robust to out-of-plane scattering., Author(s): Jicheng Jin [sup.1] , Xuefan Yin [sup.1] , Liangfu Ni [sup.1] , Marin Soljacic [sup.2] , Bo Zhen [sup.3] , Chao Peng [sup.1] [sup.4] Author Affiliations: (1) State Key [...]

Thomson, Rayleigh, Mie, and Raman scattering are commonly used in several disciplines in science and engineering. The techniques involve the scattering of electromagnetic radiation or particles in a sample. This paper provides a brief history for each scattering method, describes the traditional laboratory approach for implementation, and discusses current uses and variations of these four techniques. Keywords: scattering, Thomson, Rayleigh, Mie, Raman, physics, INTRODUCTION Scattering is a process in which electromagnetic waves or particles deviate from a straight line due to interference or collision within a medium. For electromagnetic radiation, modification of reflected [...]

Thomson, Rayleigh, Mie, and Raman scattering are commonly used in several disciplines in science and engineering. The techniques involve the scattering of electromagnetic radiation or particles in a sample. This paper provides a brief history for each scattering method, describes the traditional laboratory approach for implementation, and discusses current uses and variations of these four techniques. Keywords: scattering, Thomson, Rayleigh, Mie, Raman, physics, INTRODUCTION Scattering is a process in which electromagnetic waves or particles deviate from a straight line due to interference or collision within a medium. For electromagnetic radiation, modification of reflected [...]

In this paper, we investigate the possible unparticle signatures through Bhabha scattering. The numerical results show that the angular distribution with unparticle effects can be up to 42% of the one that is confirmed by Born QED and Born + 1-loop QED calculation and the total cross section with unparticle effects are about 0.04-4.24 pb. This could have important implications for unparticle searches and for the measurement of the cross section of the Bhabha scattering. Key words: theoretical physics, unparticle physics, cross section, Bhabha scattering, total effect. Nous explorons les signatures possibles de particules improbables (unparticle de Georgi) dans la diffusion de Bhabha. Les resultats numeriques montrent que la distribution angulaire avec effets des particules improbables peut etre jusqu'a 42 % de celle obtenue d'un calcul EDQde Born et EDQde Born + 1 boucle, alors que la section efficace totale avec effets des particules improbables est de l'ordre de 0.04 a 4.24 pb. Ceci pourrait avoir des consequences importantes pour la recherche des particules improbables et pour la diffusion de Bhabha. [Traduit par la Redaction] Mots-cles: physique theorique, physique des particules improbables, section efficace, diffusion de Bhabha, effet total., 1. Introduction Bhabha scattering is among the most important and carefully studied processes in particle physics. It provides a very efficient tool for luminosity at electron-positron colliders and thus mediates [...]

A mode-matching analysis articulates the coupled wave scattering in a 2D waveguide structure. An elastic plate is attached at the upper surface parallel to the axis of inlet-outlet ducts whereas a flanged junction is introduced between two flexible waveguides. The main intention is to see how choice of appropriate edge conditions and the incident forcing affect the scattered field for both structure-borne and fluid-borne vibrations. The graphical results illustrate that different physical conclusions should be drawn. Through apposite numerical results, we observe the power distributions in attenuated regions with abrupt changes of height. Such configurations are directly relevant to the models of fluid and structural interactions. Key words: scattering, flexible waveguide, non-Sturm-Liouville, mode-matching. Nous utilisons une analyse de couplage de modes pour decrire la diffusion d'ondes couplees dans un guide d'onde 2D. Une plaque elastique est fixee a la surface superieure parallele a l'axe des conduits d'entree-sortie, alors qu'un raccordement bride est introduit entre deux guides d'onde flexibles. Le but premier est d'observer comment le choix approprie de conditions aux bords et l'effet de forcage afferent affectent les vibrations portees par la structure et portees par le fluide. Les resultats graphiques illustrent comment obtenir les differentes conclusions physiques. A partir des resultats appropries, nous observons que les distributions de puissance dans les regions attenuees montrent d'abrupts changements de valeur. De tels effets sont directement pertinents pour les modeles d'interactions fluide-structure. [Traduit par la Redaction] Mots-cles: diffusion, guide d'onde flexible, couplage de modes, flux d'energie., 1. Introduction The study of non-uniform obstacles in uniform waveguide structures has received wide attention in the literature. The transmission of elastic and electromagnetic waves, underwater sound propagation, and sound [...]

Relativistic Dirac analyses are performed phenomenologically for the high-lying excited states that belong to the 2+ gamma vibrational band at the 800 MeV polarized proton inelastic scatterings from the s-d shell nuclei, [sup.24]Mg and [sup.26]Mg. Optical potential model is used and scalar and time-like vector potentials are considered as direct potentials. First-order vibrational collective models are used to obtain the transition optical potentials to accommodate the high-lying excited vibrational collective states. The complicated Dirac coupled channel equations are solved phenomenologically to reproduce the differential cross section and analyzing power data by varying the optical potential and deformation parameters. It is found that the relativistic Dirac coupled channel calculation could describe the high-lying excited states of the 2+ gamma vibrational band at the 800 MeV polarized proton inelastic scatterings from s-d shell nuclei [sup.24]Mg and [sup.26]Mg reasonably well, showing mostly better agreement with the experimental data compared to the results obtained from the nonrelativistic calculations. Calculated deformation parameters for the excited states are analyzed and compared with those of nonrelativistic calculations. Key words: Dirac phenomenology, optical potential model, collective model, inelastic proton scattering. Nous presentons des calculs relativistes phenomenologiques de Dirac pour les etats hautement excites qui appartiennent a la bande vibrationnelle gamma 2+ des noyaux de la couche s-d [sup.24]Mg et [sup.26]Mg excites par collisions inelastiques de protons polarises de 800 MeV. Nous utilisons le modele du potentiel optique, ainsi que des potentiels scalaire et vecteur de type temps comme potentiels directs. Nous utilisons des modeles collectifs vibrationnels de premier ordre pour obtenir les potentiels optiques de transition, afin d'accommoder les etats collectifs vibrationnels de haute energie. Les equations compliquees de Dirac pour canaux couples sont resolues phenomenologiquement pour reproduire les differentes sections efficaces et les donnees de pouvoir d'analyse en variant les parametres du potentiel optique et de deformation. Nous trouvons que les calculs relativistes de Dirac pour canaux couples peuvent decrire les etats hautement excites de la bande vibrationnelle gamma 2+ dans les noyaux de la couche s-d [sup.24]Mg et [sup.26]Mg excites par collision inelastiques de protons polarises de 800 MeV, tout en montrant un bien meilleur accord avec les donnees experimentales que les calculs non relativistes. Les parametres de deformation calcules ici sont analyses et compares avec ceux resultant de calculs non relativistes. [Traduit par la Redaction] Mots-cles : calcul phenomenologique de Dirac, modele du potentiel optique, modele collectif, collision inelastique de protons, collision aux energies intermediaires., 1. Introduction Relativistic Dirac approaches based on the Dirac equation have been very successful in treating nuclear reactions [1-3]. Because the Dirac analyses have proven to be very successful in [...]

Coherence phenomena arise from interference, or the addition, of wave-like amplitudes with fixed phase differences. Although coherence has been shown to yield transformative ways for improving function, advances have been confined to pristine matter and coherence was considered fragile. However, recent evidence of coherence in chemical and biological systems suggests that the phenomena are robust and can survive in the face of disorder and noise. Here we survey the state of recent discoveries, present viewpoints that suggest that coherence can be used in complex chemical systems, and discuss the role of coherence as a design element in realizing function., Author(s): Gregory D. Scholes (corresponding author) [1]; Graham R. Fleming (corresponding author) [2]; Lin X. Chen [3, 4]; Aln Aspuru-Guzik [5]; Andreas Buchleitner [6]; David F. Coker [7]; Gregory S. [...]

Inelastic collisions of protons with rubidium atoms are treated for the first time within the framework of the three channel coupled static, and frozen core approximations. The method is used for calculating partial and total cross sections with the assumption that only three channels (elastic; non-excited hydrogen, 1s-state; and excited hydrogen, 2s-state) are open. We have used the Lipmann-Schwinger equation and the Green's functions iterative numerical method technique to solve the derived coupled integro-differential equations to obtain the computer code. The present results for total hydrogen formation cross sections are in agreement with results of other available ones in a wide range of incident energy. Key words: inelastic scattering, proton-rubidium, hydrogen formation, excited hydrogen formation. Une etude des collisions inelastiques de protons sur des atomes de rubidium est presentee pour la premiere fois dans le cadre des approximations des trois canaux couples-statiques et du caurfige. La methode est utilisee pour calculer les sections efficaces partielles et totale en supposant que seuls trois canaux sont ouverts: elastique, hydrogene dans le fondamental 1s et excite 2s. Nous utilisons l'equation de Lipmann-Schwinger et la technique numerique iterative des fonctions de Green pour solutionner les equations couplees integro-differentielles derivees afin d'obtenir le code d'ordinateur. Nos resultats pour les sections efficaces totales de formation d'hydrogene sont en accord avec d'autres resultats disponibles sur une large bande de l'energie incidente. [Traduit par la Redaction] Mots-cles: collision inelastique, proton-rubidium, formation d'hydrogene, formation d'hydrogene excite. PACS Nos.: 34.80.Dp, 34.80.Gs, 34.80.Ht., 1. Introduction The appearance of intermediate states in atomic and nuclear reactions is considered one of the most interesting physical phenomena since the development of quantum theory. Theoretically the study [...]

We solve the Klein-Gordon equation in the presence of the hyperbolic tangent potential. The scattering solutions are derived in terms of hypergeometric functions. The reflection, R, and transmission, T, coefficients are calculated in terms of gamma function and, superradiance is discussed, when the reflection coefficient, R, is greater than one. PACS Nos.: 02.30.Gp, 03.65.Pm, 03.65.Nk. Nous solutionnons l'equation de Klein-Gordon en presence d'un potentiel tangent hyperbolique. Les solutions de diffusion sont ecrites a l'aide de fonctions hypergeometriques. Nous calculons les coefficients de reflexion R et de transmission T en termes de fonctions gamma et nous discutons de super-radiance, lorsque le coefficient R est plus grand que un., 1. Introduction The solution of the Klein-Gordon equation with different potentials has been extensively studied in recent years, for bound states and scattering solutions [1-7]. The scattering solutions to the [...]

In the framework of the first Born approximation and using the Dirac-Volkov formalism, we investigate the relativistic model describing the laser assisted elastic differential cross sections (DCSs) for positron scattering by the hydrogen atom. Both the DCSs for electron and positron are notably modified by the circularly polarized laser field, particularly in the regime of high energies and medium intensities. Comparing the two numerical DCSs, we recover the well-known result that the elastic scattering differential cross sections with and without laser field for a hydrogen atom by electron and positron impact are the same (Greiner and Reinhardt. Quantum Electrodynamics, 2nd ed., Springer Verlag, New York, Berlin, Heidelberg. 1994). The numerical results reveal that the differential cross section for positron--hydrogen atom scattering is significantly reduced with the increase of the electric field strength. PACS Nos.: 34.80.Qb, 12.20.Ds. Dans le cadre de la premiere approximation de Born et utilisant le formalisme de Dirac-Volkov, nous etudions le modele relativiste qui decrit la section efficace differentielle elastique de la diffusion de positrons sur des atomes d'hydrogene en presence d'un champ laser (DCSs). Les DCSs pour electrons et positrons sont affectes notablement par le champ laser a polarisation circulaire, particulierement aux hautes et moyennes intensites. Comparant les resultats numeriques pour les deux DCSs, nous retrouvons le resultat bien connu que les sections efficaces differentielles de diffusion elastique avec et sans champ laser pour des electrons et des positrons sur des atomes d'hydrogene sont les memes (Greiner et Reinhardt. Quantum Electrodynamics, 2e ed., Springer Verlag, New York, Berlin, Heidelberg. 1994). Les resultats numeriques revelent que la section efficace differentielle pour la diffusion positron-hydrogene est significativement reduite avec l'augmentation du champ electrique. [Traduit par la Redaction], 1. Introduction The solutions of the Dirac equation for the fermionic particles in an external electromagnetic field, known as the Volkov wave functions [1], have been widely used as asymptotic [...]

It is well known that multiple scattering theories are very useful in the study of nucleon-nucleus and nucleus-nucleus scattering processes. The derivation of a nonrelativistic multiple scattering theory (NRMST) is well-established and clear. A key component to the formulation of an NRMST is the ability to separate the unperturbed Hamiltonian from the residual interaction. For the relativistic problem, it is not clear how to perform this separation starting from a field theoretical Lagrangian. Instead, one starts from an infinite set of Feynman diagrams, which play the role of the kernel in the Bethe-Salpeter equation for nucleus-nucleus scattering. Once the kernel is defined, it is straightforward to develop a relativistic multiple scattering theory (RMST). To be more complete than previous studies, delta degrees of freedom are included, which is a minimum requirement to explain pion production. It is demonstrated that an RMST can be formulated by expressing the kernel in a form that is similar to the residual interaction in the NRMST. PACS No.: 11.80.La. Il est bien connu que les theories de diffusion multiple sont tres utiles dans l'etude des mecanismes nucleon- noyau et noyau-noyau. La derivation d'une theorie de diffusion multiple non relativiste (NRMST) suit un cheminement bien connu. Une composante cle de la formulation d'une NMRST repose sur la possibilite de separer le Hamiltonien non perturbe de l'interaction residuelle. Dans le cas relativiste, il n'est pas clair comment on peut faire cette separation en partant d'une theorie lagrangienne de champ. A la place, on commence avec un ensemble infini de diagrammes de Feynman qui joue le role de kernel dans l'equation de Bethe-Salpeter pour la diffusion noyau-noyau. Une fois le kernel defini, il est relativement immediat de definir une theorie de diffusion multiple relativiste (RMST). Afin d'aller au dela des etudes passees, nous incluons les degres de liberte delta, ce qui est un minimum pour expliquer la production de pions. Nous montrons qu'une RMST peut etre formulee en exprimant le kernel sous une forme similaire a l'interaction residuelle de la NRMST. [Traduit par la Redaction], 1. Introduction Multiple scattering theories (MSTs) have been used extensively for nuclear scattering problems [1-11]. Early in the development of nuclear reaction theory, it was found that the Born approximation [...]

The diffractive aspects of angular distribution have been investigated by analyzing the experimental data for a set of elastic scattering processes of [sup.6]Li by different target nuclei at different laboratory energies. The analysis of experimental data of angular distribution for elastic scattering process is performed using both Frahn-Venter and Mclntyre models. The theoretical models can reasonably reproduce the general pattern of the data, thus allowing us to extract geometrical parameters from elastic scattering processes. It is found that interpretation of the diffraction features of the data is model-independent. The values of extracted parameters, from both models, are found to be comparable to each other and to those of others. The correlation between the total reaction cross section and the incident laboratory energy for each scattering is discernible and values of total reaction cross section are found to be comparable with those of others. PACS Nos.: 25.70.-z, 25.70.Bc. Nous etudions ici les aspects diffractifs des distributions angulaires en analysant les donnees experimentales pour un ensemble de cas de diffusion elastique de [sup.6]Li sur divers noyaux cibles a differentes energies dans le laboratoire. Nous utilisons les modeles de Frahn-Venter et de Mclntyre pour analyser les donnees experimentales de diffusion elastique. Les modeles theoriques reproduisent raisonnablement bien le patron general des donnees, nous permettant d'extraire les parametres geometriques a partir du mecanisme de diffusion elastique. Nous trouvons que l'interpretation des caracteristiques de diffraction des donnees est independante du modele. Les valeurs des parametres obtenues des deux modeles sont comparables les une avec les autres et avec celles d'analyses par d'autres auteurs. On peut discerner la correlation entre la section efficace totale de reaction et l'energie incidente dans le laboratoire pour chaque cas de diffusion et les valeurs de section efficace totale de reaction obtenues sont comparables a celles d'autres auteurs. [Traduit par la Redaction], 1. Introduction In several nuclear scattering processes, the incident nucleus is strongly absorbed upon entering the target nucleus where features in the angular distribution of the scattering of complex nuclei [...]

A hyperbolic-type potential with a centrifugal term is solved approximately using the path integral approach. The radial Green's function is expressed in closed form, from which the energy spectrum and the suitably normalized wave functions of bound and scattering states are extracted for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Besides, the phase shift and the scattering function [S.sub.l] for each angular momentum l are deduced. The particular cases corresponding to the s-waves (l = 0) and the barrier potential (a = 1) are also analyzed. PACS Nos.: 03.65.Ca, 03.65.Db. Utilisant l'integrale de parcours, nous solutionnons approximativement un potentiel de type hyperbolique avec terme centrifuge. La fonction de Green radiale est exprimee sous forme analytique et nous en tirons le spectre en energie et les fonctions d'onde normalisees pour les etats lies et de diffusion correspondant a [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. De plus, nous en deduisons le dephasage et la fonction de diffusion [S.sub.l] pour chaque valeur du moment cinetique l. Nous analysons aussi les cas particuliers correspondant aux ondes s (l = 0) et la barriere de potentiel ([sigma] = 1). [Traduit par la Redaction], 1. Introduction The hyperbolical potential V(r) = D[1 - [[sigma]coth ([alpha]r)].sup.2] (1) was proposed by Schioberg [1] in 1986 in view of its application in the description of interatomic interactions [...]

A step by step transformation of the low frequency small height and slope perturbation solution into the high frequency reciprocal and dual, physical and geometrical optic solutions is presented. The familiar Kirchhoff approximations for the fields impressed by the incident plane wave upon the rough surfaces results in nonreciprocal solutions. It is shown that the surface element scattering coefficients based on the Kirchhoff approximations agree with the corresponding reciprocal physical optics solutions only at the stationary phase, specular points on the rough surfaces. While the Kirchhoff approximations and physical optics approximations are based on the characterization of the surface fields by Fresnel reflection coefficients, the corresponding surface element scatter coefficient derived for the small perturbation solution and the full wave solutions are based on the imposition of boundary conditions for the tangential components of the electric and magnetic fields. A flow graph schematically depicting the relationships between these solutions for the scattered fields is also presented. PACS Nos: 02.00, 41.00, 42.00, 84.00, 89.00 Nous presentons une transformation etape par etape da la solution de petite amplitude de basse frequence et de perturbation de pente vers des solutions reciproques de haute frequence et a la fois d'optique physique et geometrique. Les approximations habituelles de Kirchhoff pour les champs marques par l'onde plane incidente sur les surfaces rugueuses donnent des solutions non reciproques. Nous montrons que les coefficients de diffusion d'element de surface bases sur les approximations de Kirchhoff n'agreent avec les solutions d'optique physique reciproques correspondantes qu'a la phase stationnaire, les points speculaires des surfaces rugueuses. Alors que les approximations de Kirchhoff et les approximations d'optique physique sont basees sur la caracterisation des champs de surface par les coefficients de reflexion de Fresnel, les coefficients de diffusion des elements de surface correspondants obtenus de la solution en faible perturbation et les solutions ondulatoires completes sont basees sur l'imposition de conditions limites pour les composantes tangentielles des champs electrique et magnetique. Nous presentons aussi un graphe de flot qui montre schematiquement entre les solutions pour les champs diffuses. [Traduit par la Redaction], 1. Introduction In this paper the relationships between rough surface (see Figs. 1a and 1b) scattering solutions based on (i) the Kirchhoff approximation, (ii) the physical optics approximations, (iii) the [...]

The problem of spin-0 particles subject to a nonminimal vector double-step potential is explored in the context of Duffin-Kemmer-Petiau theory. Surprisingly, one can never have an incident wave totally reflected, and the transmission amplitude has complex poles corresponding to bound states. The interesting special case of bosons embedded in a sign potential with its unique bound-state solution is analyzed as a limiting case. PACS Nos: 03.65.Ge, 03.65.Pm Nous examinons le probleme des particules de spin zero soumises a un potentiel vecteur non minimal a double echelon dans le cadre de la theorie de Duffin-Kemmer-Petiau. Avec surprise, nous constatons qu'il est impossible d'avoir une onde totalement reflechie et l'amplitude de transmission a des poles complexes qui correspondent aux etats lies. Comme cas limite, nous analysons le probleme de bosons pris dans un potentiel delta deplace possedant un seul etat lie. [Traduit par la Redaction], 1. Introduction The first-order Duffin-Kemmer-Petiau (DKP) equation [1, 2] is often seen as an alternative and rather unusual form for describing spin-0 and spin-1 particles, and has been used to [...]

Long-established results for low-energy photon--photon scattering, γγ → γγ, have recently been questioned. We analyze that claim and demonstrate that it is inconsistent with experience. We demonstrate that the mistake originates from an erroneous manipulation of divergent integrals and discuss the connection with another recent claim about the Higgs decay into two photons. We show a simple way of correctly computing low-energy γγ scattering. PACS Nos: 13.60.Fz, 13.40.-f, 12.15.Lk On a remis recemment en question des resultats longtemps etablis sur la diffusion photon-photon, γγ → γγ. Nous analysons cette assertion et demontrons qu'elle est en desaccord avec l'experience. Nous montrons que l'erreur origine d'une mauvaise manipulation d'integrales divergentes et discutons une autre assertion recente sur la desintegration du Higgs en deux photons. Nous presentons une facon simple de faire correctement les calculs dans la diffusion γγ de basse energie. [Traduit par la Redaction], 1. Introduction After Dirac proposed the theory of negative energy solutions to his equation [1], it was realized that photons can interact with other photons by polarizing the vacuum. Photon-photon [...]

A three-body problem for a system of three nucleons interacting with short-range forces is discussed following effective field theory. Considering the case of a system of neutron-deuteron scattering, three-body equations are demonstrated such that the eigenvalues greater than unity are removed from the kernel leading to an equation that is renormalization-group invariant. The phase shifts are developed from a unique solution of the case of the doubled channel in neutron-deuteron scattering. The calculated neutron-deuteron phase shifts are well described below the deuteron breakup threshold. PACS Nos: 21.45.+v, 11.10.Gh, 11.80Jy, 13.75.Cs Nous analysons en theorie de champ efficace le probleme a trois corps pour un systeme de trois nucleons avec interaction de faible portee. Etudiant le cas de la diffusion neutron-deuton, nous obtenons des equations a trois corps, dont l'elimination des valeurs propres plus grandes que un mene a une equation invariante sous le groupe de renormalisation. Les dephasages sont obtenus d'une solution unique du cas a deux canaux en diffusion neutron-deuton. Les dephasages sous le seuil de desintegration du deuton sont bien decrits. [Traduit par la Redaction], 1. Introduction The Faddeev [1] equations have been shown to be successful in solving the three-nucleon problem, especially for two-body interactions with finite range [2]. Few-body systems at low energies, [...]

The study of the nuclear structure for the elements [sup.12]C, [sup.40]Ca, and [sup.6]Li has been performed in the momentum range from 0 to 0.8 GeV/c by using [K.sup.+]N phase shifts. An optical potential is used to calculate the elastic differential cross section and total cross section for [K.sup.+] scattering from [sup.12]C, [sup.40]Ca, and [sup.6]Li. Comparison with previous experiments shows better results for the elements [sup.6]Li and [sup.40]Ca and fair agreement for the element [sup.12]C. PACS Nos: 21.10.Ft, 25.80.Dj, 25.80.Nv Nous avons complete une etude de la structure nucleaire des elements [sup.12]C, [sup.40]Ca et [sup.6]Li dans le domaine allant de 0 a 0,8 GeV/c en utilisant le dephasage [K.sup.+]N. Nous utilisons un potentiel optique pour calculer la section efficace differentielle elastique et la section efficace totale dans la diffusion du [K.sup.+] sur les noyaux [sup.12]C, [sup.40]Ca et [sup.6]Li. La comparaison avec des experiences precedentes indique de meilleurs resultats pour [sup.6]Li et [sup.40]Ca et un accord raisonnable pour le [sup.12]C. [Traduit par la Redaction], 1. Introduction Study of the physics of nuclear structures requires mastery of suitable techniques to effectively obtain quantitative results of scattering between nuclei and lighter particles (mesons). The study of [...]

A numerical method to solve acoustic scattering in the time domain is presented in the present paper. Equivalent sources are embedded within a scattering surface and their strengths are determined as a function of time by the pressure-gradient boundary condition on a scattering surface. Once the strengths are determined, the equivalent sources are used to predict the scattered pressure. Linear shape functions are used to discretize the strength of the equivalent sources in time, and singular value decomposition is used to find the least-squares solution and to overcome potential numerical instabilities. The predictions are found to be in excellent agreement with the exact solutions for sound from a point monopole source and band-passed broadband sound. The method works well even at the irregular frequencies at which internal resonance modes occur. Finally, the method is used to predict the scattering of sound from a moving source. It is shown that the method has the capability to capture aperiodic characteristics very well. DOI: 10.2514/1.45132

We investigate the effect of finite bandwidth of the incident radiation on scattering by thin layers that introduce random phase or amplitude variations. In particular, we calculate the scintillation index of the propagating radiation for smoothly varying and fractal phase screens and for random telegraph wave and checkerboard amplitude screens. Increasing the bandwidth of the incident radiation reduces the fluctuations of the scattered intensity over the whole propagation path, except in the case of the smoothly varying phase screen, where geometrical optics features in the pattern persist in the focusing region. OCIS codes: 030.1640, 030.6600, 030.6140, 290.5930, 110.1758.

We present computationally efficient and accurate semiempirical models of light transfer for real-time analysis of multilayer fluorescing media exposed to normally incident excitation light. The model accounts for absorption and strong forward scattering as well as for internal reflection at the interface between the medium and the surrounding air. The absorption and scattering coefficients are assumed to be constant with depth; the fluorophore concentration is considered piecewise constant. The refractive index ranges from 1.0 to 2.0, and the transport single scattering albedo between 0.50 and 0.99. First, simple analytical expressions for local excitation fluence rate within the medium and surface fluorescence intensity emerging from its surface were derived from the two-flux approximation. Then, parameters appearing in the analytical expression previously derived were fitted to match results from more accurate Monte Carlo simulations. A single semiempirical parameter was sufficient to relate the diffuse reflectance of the medium at the excitation wavelength to the local excitation fluence rate within the medium and to the surface fluorescence emission intensity. The model predictions were compared with Monte Carlo simulations for local fluence rate and total surface fluorescence emission from (i) homogeneous semi-infinite fluorescing media, (ii) media with a semi-infinite fluorescing layer beneath a nonfluorescing layer, and (iii) media with a finite fluorescing layer embedded in a nonfluorescing semi-infinite layer. The model predictions of the local excitation fluence rate and of the total surface fluorescence emission fell to within 5% of predictions by Monte Carlo simulations for single scattering albedo greater than 0.90. The current model can be used for a wide range of applications, including noninvasive diagnosis of biological tissue. OCIS codes: 000.4430, 010.5620, 170.6280, 230.4170, 170.6510, 110.7050.

We were previously successful in representing series of Ps + H scattering resonances as mainly due to quasibound Rydberg states in either the closed [e.sup.+] + [H.sup.-] or [Ps.sup.-] + [H.sup.+] system. An obvious extension would be to investigate the analogous Ps + Ps system, as either [e.sup.+] + [Ps.sup.-] or [e.sup.-] + [Ps.sup.+]. Here we treat the system in four increasingly complete approximations: with and without including electron and positron symmetry and charge conjugation symmetry. A comparison is made with previous calculations, and in an Appendix the relationship between quasi-bound states and scattering resonances is clarified. PACS Nos: 34.50.-s, 36.10.Dr Nous avons anterieurement reussi a representer les series de resonnances de diffusion Ps + H comme etant surtout dues a des etats quasi lies de Rydberg soit dans [e.sup.+] + [H.sup.-] ferme soit dans le systeme [Ps.sup.-] + [H.sup.+]. Une extension evidente serait d'etudier le systeme analogue Ps + Ps comme soit [e.sup.+] + [Ps.sup.-], soit [e.sup.-] + [Ps.sup.+]. Nous traitons ici le systeme dans quatre approximations de plus en plus completes: avec et sans les symetries electron/positron et de conjugaison de charge. Nous comparons nos resultats avec des calculs anterieurs et nous eeclaircissons en annexe la relation entre les etats quasi lieeset les resonnances de diffusion. [Traduit par la Redaction], 1. Introduction The positronium 'atom', consisting of an electron and a positron bound electrostatically has been of theoretical interest since it was realized that such a system was analogous to [...]

We examine the zero-range limit of the finite square well in arbitrary dimensions through a systematic analysis of the reduced, s-wave, two-body, time-independent Schrodinger equation. A natural consequence of our investigation is the requirement of a delta function multiplied by a regularization operator to model the zero-range limit of the finite-square well when the dimensionality is greater than one. The case of two dimensions turns out to be surprisingly subtle, and needs to be treated separately from all other dimensions. PACS Nos: 01.40.gb, 03.65.Nk, 34.50.Cx A l'aide d'une analyse systematique de l'equation de Schrodinger independante du temps reduite a deux corps dans un etat s, nous examinons la limite de portee nulle du potentiel carre; fini dans un espace de dimensions arbitraires. Une consequence naturelle de notre procedure est l'exigence d'un operateur de regularisation multiplie: d'une fonction delta pour modeliser la limite de portee nulle dans le cas a plus d'une dimension. Le cas a deux dimensions apparait particulierement subtil et doit etre etudie separement de tous les autres cas., 1. Introduction All undergraduate students of physics familiarize themselves with the mathematical machinery of quantum mechanics by solving the one-body, one-dimensional (1D), time-independent Schrodinger equation (TISE) for a variety of [...]

We study the interrelation of the internal field of irregular particles to the far-field scattering characteristics by modifying the internal field of dipole groups. In this paper, we concentrate on the longitudinal component, i.e., the internal-field component parallel to the incident wave vector. We use the discrete-dipole approximation to determine the internal field and switch off the longitudinal component from the dipoles that have the highest energy density above a preset cutoff value. We conclude that only a relatively small number of core dipoles, about 5% of all dipoles, contribute to the negative linear polarization at intermediate scattering angles. These core dipole groups are located at the forward part of the particles. The number of core dipoles in the group becomes greater as particle asphericity increases. We find that the interference between the scattered waves from the core dipole groups, which was studied previously for spherical particles, is preserved to a large extent for nonspherical particles. OCIS codes: 290.5855, 260.3160.

Accurate and precise measurements of light scattering and extinction by atmospheric particulate matter aid understanding of tropospheric photochemistry and are required for estimates of the direct climate effects of aerosols. In this work, we report on a second generation instrument to simultaneously measure light scattering ([b.sub.scat]) and extinction ([b.sub.ext]) coefficient by dispersed aerosols. The ratio of scattering to extinction is known as the single scatter albedo (SSA); thus, the instrument is referred to as the albedometer. Extinction is measured with the well-established cavity ring-down (CRD) technique, and the scattering coefficient is determined through collection of light scattered from the CRD beam. The improved instrument allows reduction in sample volume to < 1% of the original design, and a reduction in response time by a factor of > 30. Through using a commercially available condensation particle counter (CPC), we have measured scattering ([[sigma].sub.scat]) and extinction ([[sigma].sub.ext]) cross sections for size-selected ammonium sulfate and nigrosin aerosols. In most cases, the measured scattering and extinction cross section were within 1 standard deviation of the accepted values generated from Mie theory suggesting accurate measurements are made. While measurement standard deviations for [b.sub.ext] and [b.sub.scat] were generally < 1 [Mm.sup.-1] when the measurement cell was sealed or purged with filtered air, relative standard deviations > 0.1 for these variables were observed when the particle number density was low. It is inferred that statistical fluctuations of the absolute number of particles within the probe beam leads to this effect. However, measured relative precision in albedo is always superior to that which would be mathematically propagated assuming independent measurements of [b.sub.scat] and [b.sub.ext]. Thus. this report characterizes the measurement precision achieved, evaluates the potential for systematic error to be introduced through light absorption by gases, presents comparisons with Mie theory, and provides ambient monitoring data collected on a mineral dust dominated aerosol at our location. 10.1021/ac100617j

Recent work discovered the remarkable optical scattering properties of the scales of the white beetle Cyphochilus. It was suggested that its brilliant whiteness and brightness were due to optimization of the microstructure within its scales. Here we compare the microstructure of Cyphochilus scales to those of two other white beetles, Lepidiota stigma and Calothyrza margaritifera. Extensive optical modeling and experimental data suggest that each species displays structural optimization designed to maximize optical scatter. Optimization of the scale filling fraction is observed, as well as optimization of scattering center spacing and diameter. Cyphochilus, in particular, displays a high degree of structural optimization, resulting in its bright white appearance. OCIS codes: 160.1435, 160.4236, 290.5850.

We investigate the scattering process of plane waves by a conducting half-plane between two dielectric media by introducing novel boundary conditions, in terms of soft and hard surfaces. The cases of soft and hard half-planes are studied independently. The scattered waves are examined numerically. The numerical results show that the behavior of the fields is in harmony with the theory. The transition between the two dielectric media is continuous, and the structure of the method enables one also to examine more complex geometries, such as wedges having soft and hard boundary conditions. OCIS codes: 290.0290, 290.5825, 050.0050, 050.1960.

We evaluate and compare the use of competitive neural networks, self-organizing maps, the expectation-maximization algorithm, K-means, and fuzzy C-means techniques as partitional clustering methods, when the sensitivity of the activity measurement of dynamic speckle images needs to be improved. The temporal history of the acquired intensity generated by each pixel is analyzed in a wavelet decomposition framework, and it is shown that the mean energy of its corresponding wavelet coefficients provides a suited feature space for clustering purposes. The sensitivity obtained by using the evaluated clustering techniques is also compared with the well-known methods of Konishi--Fujii, weighted generalized differences, and wavelet entropy. The performance of the partitional clustering approach is evaluated using simulated dynamic speckle patterns and also experimental data. [c] 2010 Optical Society of America OCIS codes: 100.2000, 120.3940, 120.6150.

Molecular beam scattering experiments are used to investigate reactions of S[O.sub.2] at the surface of a molten alkali carbonate eutectic at 683 K. We find that two-thirds of the S[O.sub.2] molecules that thermalize at the surface of the melt are converted to gaseous C[O.sub.2] via the reaction S[O.sub.2](g) + C[O.sup.2-.sub.3] [right arrow] C[O.sub.2](g) + S[O.sup.2-.sub.3]. The C[O.sub.2] product is formed from S[O.sub.2] in less than [10.sup.-6]s, implying that the reaction takes place in a shallow liquid region less than 100 [Angstrom] deep. The reaction probability does not vary between 683 and 883 K, further' implying a compensation between decreasing S[O.sub.2] residence time in the near-interfacial region and increasing reactivity at higher temperatures. These results demonstrate the remarkable efficiency of S[O.sub.2] [right arrow], C[O.sub.2] conversion by molten carbonates, which appear to be much more reactive than dry calcium carbonate or wet slurries commonly used for flue gas desulfurization in coal-burning power plants. flue gas desulfurization | gas scrubbing | gas-liquid reactions | liquid surface | molecular beam scattering doi/ 10.1073/pnas.0910993107

Discussions of the scattering length frequently focus on the special case of the deuteron, and sometimes statements that are not true in general are made. To obtain a deeper understanding, we study the scattering length as a function of the depth [V.sub.0] of a square well and an exponential well and show how the scattering length becomes infinite at values of [V.sub.0] for which new bound states appear at zero energy. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3279730]

The three-body scattering signature is an appendage seen on weather radar displays of reflectivity behind strong storm cells. It is caused by multiple scattering between hydrometeors and the ground. The radar equation for this phenomenon is reexamined and corrected to include the coherent wave component producing 3 dB more power than previously reported. Furthermore, the possibility to gauge hail size causing this phenomenon is explored. A model of forward scattering by spherical hail and accepted values of ground backscattering cross sections are used in an attempt to reconcile the reflectivity in this signature with observations. This work demonstrates that the signature can be caused by small- ( DOI: 10.1175/2009JAMC2300.1

The electromagnetic fields scattered when a plane wave is incident on an oblate spheroid in the side-on orientation may be calculated using a generalization of Mie theory, and the results may be decomposed in a Debye series expansion. A number of optical caustics are observed in the computed scattered intensity for the one internal reflection portion of the Debye series for scattering angles in the vicinity of the first-order rainbow, and are analyzed in terms of the rainbow, transverse cusp, and hyperbolic umbilic caustics of catastrophe optics. The specific features of these three caustics are described, as is their assembly into the global structure of the observed caustics for spheroid scattering. It is found that, for a spheroid whose radius is an order of magnitude larger than the wavelength of the incident light, the interference structure accompanying the transverse cusp and hyperbolic umbilic caustics is only partially formed. OCIS codes: 260.1960, 290.4020.

Glass surface roughness can be considered positive for certain applications in optics. Results of maskless (i.e., lithography-free) reactive-ion-etch runs are given, where (depending on etch parameters) self-masking leads to very different surface morphologies. The latter's variety allows for virtually any desired scattered visible light power portion, a result that we term dosed scattering. The surfaces are characterized, for example, by the root-mean-square roughness [[delta].sub.rms], while their optical scattering is described by the diffuse transmission as well as the Harvey parameters. Since the wavelengths [lambda] in glass are around [[delta].sub.rms], the shapes of the individual scatterers account for local refraction adding up to the usual scattering. OCIS codes: 240.0240, 290.0290.

The speckle grain close to a diffuser medium carries information about the angles at which light is scattered. We propose the extension of a technique that allows obtaining the angular distribution of the scattered intensity in the far-field speckle pattern from the near-field speckle pattern produced by strong diffusers (whose roughness is greater than the illuminating wavelength). To illustrate this technique we applied it to the light scattered from ground glass diffusers. The experimental results are compared with those obtained by direct measurement of the angular distribution of the mean scattered intensity in the far field showing good agreement with each other. The advantages over the classical far-field methods are outlined. OCIS codes: 290.5880, 240.5770, 030.6140.

We present a diffraction analysis for image formation in fluorescence confocal microscopy with divided apertures. The three-dimensional optical transform function is given, and axial resolution and transverse resolution are investigated. The results show that the employment of a divided-aperture technique in fluorescence confocal microscopy can enhance the rejection of background scattering. In addition, the axial resolution and transverse resolution can be improved by adjusting the width of the divider strip. For a given detector size, an optimum value of the divider strip width is given to obtain the best axial resolution or transverse resolution. The integrated intensity and signal-to-background ratio are also discussed. [c] 2010 Optical Society of America OCIS codes: 170.3660, 170.4580, 170.6510, 170.1530, 290.0290.

Direct aeroaconstic simulation, which simulates acoustic radiation associated with unsteady fluid flows, involves capturing waves in both aerodynamic and acoustic scales. The presence of a thermal field further complicates this simulation. There are few analytical thermal-acoustic problems that could serve as benchmark to validate computational aeroacoustics schemes. This paper attempts to seek a theoretical solution of a simple problem involving scattering of acoustic plane waves by a localized zero-heat-gain/loss thermal disturbance and use it as a benchmark to verify the validity and extent of a numerical gas-kinetic scheme based on the modeled Boltzmann equation for the study of aeroacoustics resulting from thermal-flow/acoustic interaction. Two limiting eases with different acoustic wavelengths are attempted. Theoretical solutions are established for both cases, with the center of an axisymmetric thermal disturbance located at the origin of the physical domain. The incident acoustic wave has a dimensionless amplitude given by 1 x [10.sup.-4] and is propagated from left to right of the coordinate system. The simulation of the gas-kinetic scheme is carried out using the same computational setting as for the theoretical solutions. Riemann invariants are stipulated at the open boundaries. Numerical results are compared with the theoretical solutions and good agreement is obtained for the short-wavelength case only. The discrepancy for the long-wavelength case could be partially attributed to the inappropriateness of the Riemann invariants for oblique waves at the boundaries. DOI: 10.2514/1.37398

The Klein-Gordon equation in the presence of a spatially one-dimensional Hulthen potential is solved exactly and the scattering solutions are obtained in terms of hypergeometric functions. The transmission coefficient is derived by the matching conditions on the wave functions and the conditions for the existence of transmission resonances are investigated. It is shown how the zero-reflection condition depends on the shape of the potential. PACS Nos: 03.65.Nk, 03.65.Pm Nous solutionnons exactement l'equation de Klein-Gordon en 1+1 D avec un potentiel a une dimension spatiale de Hulthen et nous obtenons les solutions de diffusion sous la forme de fonctions hypergeometriques. Le coefficient de transmission est obtenu en mariant les conditions sur les fonctions d'onde et nous etudions les conditions d'existence d'une transmission resonante. Nous montrons que la condition de reflexion nulle depend de la forme du potentiel. [Traduit par la Redaction], The study of low-momentum scattering in the Schrodinger equation in one-dimensional even potentials shows that, as momentum goes to zero, the reflection coefficient goes to unity unless the potential V(x) [...]

Imaging processes built on the Compton scattering effect are currently under intense investigation. However, despite many innovative contributions, this topic still pose a formidable mathematical and technical challenge. In this work, we argue that, in the framework of single-photon emission imaging, collecting Compton scattered radiation from an emitting object, allows to image the radiotracer distribution in vivo. Data is acquired by a stationary collimated gamma camera under the form of compounded conical projections of the activity density function. Mathematically, the image formation process is described by the so-called Compounded Conical Radon Transform (CCRT) and three-dimensional object reconstruction is based on an inversion formula of the CCRT. We perform numerical simulations to show the feasibility of this new imaging modality, which offers the remarkable advantage of operating in stationary mode without the need of bulky and cumbersome spatial rotational mechanism of conventional gamma cameras. This is highly attractive for applications in medical imaging, industrial non-destructive evaluation, nuclear waste storage surveillance and homeland security monitoring. Finally, to improve drastically the sensitivity, we introduce a new feature allowing to acquire data without mechanical collimation and support the findings with some preliminary simulation results. Index Terms--Compton imaging, Compton scattering, computed tomography imaging, SPECT, SPECT reconstruction.

The scattering resonance state of the F + [H.sub.2] reactive system has been the focus of the reactive resonance or Feshbach resonance, since the reaction can generate infrared laser. The partial potential-energy surface is constructed with the ab initio method, and the formation mechanism of the scattering resonance is studied. The resonance energy is given, and the first resonance life is estimated. The F + [H.sub.2] and F + HD reactive systems are investigated simultaneously to study the isotope effect, and some valuable results are achieved. Key words: F + [H.sub.2] system, the partial potential-energy surface, isotope effect, scattering resonance state. Compte tenu du fait que la reaction associee a l'etat de resonance de diffusion du systeme reactif F + [H.sub.2] peut generer un laser infrarouge, elle a fait l'objet d'attentions particulieres de la resonance reactive et de la resonance de Feshbach. La surface d'energie potentielle partielle a ete construite a l'aide de methodes theoriques ab initio et on a etudie le mecanisme de formation de la resonance de diffusion. On rapporte l'energie de resonance et on a evalue la vie de la premie re resonance. On a etudie d'une facon simultanee les systemes reactifs F + [H.sub.2] et F + HD afin d'evaluer l'effet isotopique et on a obtenu quelques resultats utiles. Mots-cles : systeme F + [H.sub.2], surface d'energie potentielle partielle, effet isotopique, etat de resonance de diffusion. [Traduit par la Redaction], Introduction In 1970, Kuppermann (1) predicted the existence of the scattering resonance phenomenon in elementary chemical reactions based on the calculation of quantum-scattering theory. The reactive resonance, or Feshbach resonance, [...]

An evaporative light scattering detector (ELSD) coupled with HPLC was used for the first time to characterize membranes. Polydispersed PEG-200, 600, and 1000 were selected as probe molecules to study the dependence of membrane retention on molecular weight via a gradient eluted HPLC separation coupled to ELSD detection. The results show that HPLC/ELSD is a really general and powerful technique to study the nanofiltration (NF) process since it does not require any special properties for the solutes (chromospheres or fluorophores) and possesses the required sensitivity. Especially in solvent resistant NF (SRNF), where a wide range of organic solvents is used, the ELSD detector was not affected by the interaction between solvent and solutes, which is a critical issue compared to other more common detectors.

A balloon filled with a gas that has a different sound speed than that of air has been used as an acoustic lens. One purpose of the lens is to show refraction of sound waves in an analogy to geometric optics. We discuss the physics of the balloon lens demonstration. To determine the validity of a gas-filled balloon as a classroom demonstration of an acoustic lens and to understand the corresponding phenomena, its physics is considered analytically, numerically, and experimentally. Our results show that although a geometric analogy is a good first-order approximation, scattering theory is required to fully understand the observed phenomena. Thus this demonstration can be adapted to a wide range of students, from those learning the basic principles of refraction to advanced students studying scattering.

The continuity of thought during studies of particle substructure is illustrated through the scattering experiments of Rutherford, DuMond and their collaborators, and the deep inelastic electron scattering experiments at SLAC. The spectroscopy of positronium and charmonium is compared to further illustrate the continuing validity of the basic principles of quantum mechanics. It is shown that the rate of progress in testing the continuity of old principles and identifying the need for introducing new ones is paced by particle accelerator and collider technology.

Elastic and inelastic cross sections of proton-proton and electron-proton scattering are discussed. Special attention is given to elastic scattering and to the striking difference between the data of these two kinds of experiments. It is shown that the regular charge-monopole theory explains the main features of the data. Predictions of results of CERN's Large Hadron Collider are pointed out. Keywords: Proton Structure, Magnetic Monopole, Scattering Data, 1. Introduction Scattering experiments are used as a primary tool for investigating the structure of physical objects. These experiments can be divided into several classes, depending on the kind of [...]

We have measured differential cross sections (DCSs) for the vibrationally inelastic scattering process H + o-[D.sub.2](v = 0, j = 0,2) [right arrow] H + o-[D.sub.2](v' = 1-4, j' even). Several different collision energies and nearly the entire range of populated product quantum states are studied. The products are dominantly forward-scattered in all cases. This behavior is the opposite of what is predicted by the conventional textbook mechanism, in which collisions at small impact parameters compress the bond and cause the products to recoil in the backward direction. Recent quasiclassical trajectory (QCT) calculations examining only the o-[D.sub.2](v' = 3, j') products suggest that vibrationally inelastic scattering is the result of a frustrated reaction in which the D--D bond is stretched, but not broken, during the collision. These QCT calculations provide a qualitative explanation for the observed forward-scattering, but they do not agree with experiments at the lowest values of j'. The present work shows that quantum mechanical calculations agree closely with experiments and expands upon previous results to show that forward-scattering is universally observed in vibrationally inelastic H + [D.sub.2] collisions over a broad range of conditions. fully quantum calculations | ion imaging | reaction dynamics | vibrationally inelastic scattering

The probability of scattering by ionized impurities has been calculated as function of the scattering angle for various energy values of the electrons in gallium nitride at 77 K. It is found that for electron energies higher than 0.1 eV, almost-zero angle scatterings are most prevalent. PACS Nos.: 72.10.?d, 72.20.Fr Nous avons calcule en fonction de l'angle de diffusion la probabilite de diffusion d'electrons a differentes energies par des impuretes ionisees dans du nitrure de Gallium a 77 K. Nous trouvons qu'aux energies au dela de 0.1 eV, l'angle prevalent de diffusion est 0 degres. [Traduit par la Redaction], 1. Introduction Gallium nitride, a direct band gap semiconductor, has emerged as an important material for high-power, optoelectronic as well as for high-temperature devices because of its large band gap [...]