Academic literature on the topic 'Scattering nonlocality'

Roles of the nonlocality in the two-baryon potential derived from the quark cluster model, especially in the one from the quark Pauli-blocking effect on the kinetic term, is investigated by employing the inverse scattering problem. This effect can be understood by changing the degrees of the mixing between the incoming wave and the 0ℓ state of the inter-baryon-cluster wave function; which can be expressed by a baryon potential with high nonlocality. We look into the properties of this nonlocal potential by comparing it to the on-shell equivalent local potential. Their off-shell behaviors are very different from each other in the channels where the Pauli-blocking effect is large. The off-shell behavior of the nonlocal potential, however, seems to be simulated well when we keep the nonlocality of the potential between the 0s state and the other states.

We solve the nd scattering in the Faddeev formalism, employing the NN sector of the quark-model baryon-baryon interaction fss2. The energy-dependence of the NN interaction, inherent to the (3q)-(3q) resonating-group formulation, is eliminated by the standard off-shell transformation utilizing the [Formula: see text] factor, where N is the normalization kernel for the (3q)-(3q) system. This procedure yields an extra nonlocality to the quark-model exchange kernel, which is very important to reproduce all the observables for the bound state and elastic scattering below En ≤ 65 MeV .

The neutron-deuteron (nd) scattering is studied in the Faddeev formalism, employing the NN sector of the quark-model baryon-baryon interaction fss2. The energy-dependence of the NN interaction, inherent to the resonating-group formulation of two three-quark clusters, is eliminated by the standard off-shell transformation utilizing the square root of the normalization kernel. This procedure yields an extra nonlocality to the quark-model exchange kernel, which is very important to reproduce all the observables for the bound state and the elastic scattering below En ≤ 65 MeV . The deuteron breakup differential cross sections are also examined.

Une bonne compréhension et une bonne capacité de prédiction de la section efficace de diffusion de neutron est essentielle à un grand nombre de technologies nucléaires, parmi lesquelles les réacteurs à fission. Pour les noyaux déformés, le calcul des observables de diffusion de nucléon pour la voie élastique et les premiers états excités de basse énergie requiert l'utilisation de calcul en voies couplées. Des potentiels optique et de transition phénoménologiques locaux sont le plus couramment utilisés dans les analyses par voies couplées, mais leur précision en dehors de leur domaine d'ajustement est imprévisible. Des approches microscopiques sont en cours de développement pour augmenter les capacités prédictives et résoudre les problèmes d'extrapolation. Un potentiel obtenu microscopiquement est non local, et de récentes études ont souligné l'importance de traiter explicitement cette non localité sans passer par une procédure de localisation. Notre but dans ce travail est d'étudier dans une approche microscopique, sans paramètre ajustable, l'impact de la non localité des potentiels sur les observables de diffusion de nucléon sur noyau cible. Pour ce faire, nous étudions la diffusion de neutron avec la matrice G de Melbourne qui représente l'interaction entre le projectile et un nucléon de la cible, et nous utilisons la RPA pour décrire la structure de la cible dans le cadre de nos premières applications sur le ⁹⁰Zr. Pour pouvoir étudier aussi des noyaux déformés, nous menons notre étude dans le cadre des voies couplées. La première partie de ce document contient la dérivation, faite dans un cadre unique et cohérent, des équations couplées pour la diffusion de nucléons et des potentiels microscopiques obtenues avec la matrice G de Melbourne et une description de la cible via la RPA. La deuxième partie est dédiée à la présentation des codes que nous avons développés durant ce projet de thèse : MINOLOP pour le calcul de potentiels microscopiques à partir de la matrice G de Melbourne et d'informations de structure données sous la forme d'une densité à 1 corps, et ECANOL pour la résolution des équations en voies couplées avec des potentiels non locaux en entrée. Enfin, nous présentons nos premières applications basées sur ces deux codes : l'étude d'émission de pré-équilibre due à des excitations à 2 phonons dans le ⁹⁰Zr
A good understanding and prediction capacity of neutron scattering cross sections is crucial to many nuclear technologies, among which all kinds of reactors based on fission process. For deformed nuclei, the computation of scattering observables for the elastic channel and the first, low-lying excited states requires coupled channel calculations. Local, phenomenological optical and macroscopic transition potentials are the most commonly used in coupled channel analyses, but their accuracy outside of their fitting range remains unpredictable. Microscopic approaches are being developed in order to improve prediction power and solve the extrapolation issue. Potentials obtained microscopically are nonlocal, and recent studies have emphasized the importance of treating explicitly this nonlocality, without using a localization procedure. Our goal in the present work is to study in a quantum framework with no adjustable parameter, the impact of the nonlocality of potentials on scattering observables of nucleon-nucleus reactions. To achieve this we study neutron scattering with the Melbourne G matrix, which represents the interaction between the projectile and one nucleon of the target, and we describe the target’s structure using the RPA for our first applications to ⁹⁰Zr. In order to be able to study also deformed nuclei, we do our study in the coupled channel framework. The first part of this paper is dedicated to the derivation in a unique, consistent scope of coupled equations for nucleon-nucleus scattering and of the potentials obtained with the Melbourne G matrix and RPA structure input. Secondly, we describe the codes which we wrote during this Ph.D. project: MINOLOP for the computation of microscopic potentials using the Melbourne G matrix and structure inputs given in terms of a 1-body density, and ECANOL for the resolution of coupled channel equations using nonlocal potentials as input. Eventually, we present our first applications using these two codes to study pre-equilibrium emissions due to 2-phonon excitations in ⁹⁰Zr

In dieser Arbeit werden die nichtlokalen sowie nichtlinearen Eigenschaften plasmonischer Nanopartikel behandelt, wie sie im hydrodynamischen Modell enthalten sind. Das hydrodynamische Materialmodell stellt eine Erweiterung des Drude Modells dar, in der Korrekturen in der Beschreibung des Elektronenplasmas berücksichtigt werden. Einer ausführlichen Einführung des Materialmodells folgt eine analytische Diskussion der Auswirkungen der Nichtlokalität am Beispiel eines einzelnen Zylinders. Hierbei werden die durch die Nichtlokalität herbeigeführten Frequenzverschiebungen in den Streu- und Absorptionsspektren quantifiziert und asymptotisch behandelt. Des Weiteren wird mit Hilfe einer konformen Abbildung das Problem eines zylindrischen Dimers in der Elektrostatischen Näherung gelöst und die Moden der Struktur bestimmt. Diese Untersuchungen dienen als maßgebliche Grundlage für weiterführende numerische Studien die mit der diskontinuierlichen Galerkin Zeitraummethode durchgeführt werden. Die durch die analytischen Betrachtungen gewonnene Kenntnis der Moden ermöglicht es, im Zusammenhang mit gruppentheoretischen Betrachtungen und numerischen Untersuchungen, rigorose Auswahlregeln für die Anregung der Moden durch lineare und nichtlineare Prozesse aufzustellen. In weiterführenden numerischen Simulationen werden außerdem Strukturen niedrigerer Symmetrie, auf die sich die Auswahlregeln übertragen lassen, untersucht. Zudem werden numerische Studien präsentiert in denen der Einfluss der Nichtlokalität auf Feldüberhöhungen in Dimeren und doppel-resonantes Verhalten (es liegt sowohl bei der Frequenz des eingestrahlten Lichtes als auch bei der zweiten harmonischen eine Resonanz vor) untersucht werden.
This thesis deals with the nonlocal and nonlinear properties of plasmonic nanoparticles, as described by the hydrodynamic model. The hydrodynamic material model represents an extension of the Drude model that contains corrections to the descriptions of the electron plasma. After a thorough derivation of the material model, analytical discussions of nonlocality are presented for the example of a single cylinder. The frequency shifts in the scattering and absorption spectra are quantified and treated asymptotically. Furthermore, by applying a conformal map, the problem of a cylindrical dimer is solved in the electrostatic limit and the modes of the structure are determined. These investigations lay the foundations for numerical investigations which are performed employing the discontinuous Galerkin time domain method. The analytical knowledge of the modes, in conjunction with group theoretical considerations and numerical analysis, enables the formulation of rigorous selection rules for the excitation of modes by linear and nonlinear processes. In further numerical studies, the influence of nonlocality on the field enhancement in dimer structures and double-resonant behavior (a resonance is found at the frequency of the incoming light and at the second harmonic) are investigated.

Nanoscale optical energy concentration and focusing is crucial for many high-throughput nanomanufacturing applications, such as material processing, imaging and lithography. The use of surface plasmons has resulted in the rapid development of nanofocusing devices and techniques at spatial confinements as good as a few nanometers associated with strong nonlocal plasmonic response. However, operations of these plasmonic nanofocusing structures usually require extremely high optical energy density at nanoscale, which leads to intense structure heating and causes unreliable device functions and short device lifetimes. In many plasmonic applications, optical heating has become a very important issue, which has not been investigated intensively yet. In these structures, the ballistic transport and interface scattering of the energy carriers both become significant because the characteristic lengths of the devices are comparable to or smaller than the mean free paths of the carriers. A comprehensive model is desired to understand the heat generation and transport inside the plasmonic nanofocusing structures. This work studied the electromagnetic and optothermal responses of plasmonic nanofocusing nanostructures. At the nanometer length scale, the local optical response and diffusive thermal model are no longer sufficient to describe the device optothermal response because of the strong interactions between energy carriers and the ballistic nature of carriers. Here, we used the hydrodynamic Drude model to consider the nonlocality of plasmonic response and calculate the heat generation inside the metallic nanostructures. Starting from Boltzmann transport equation, we derived the energy transport equations for both electron and phonon systems under the relaxation-time approximations. The obtained multi-carrier ballistic-diffusive model was used to study the non-equilibrium heat transports inside the structures. We assume that the ballistic electrons originate from boundaries and the electron-photon couplings inside the structure, experiencing out-scattering only in the material. The optically-generated “hot” electrons are considered as ballistic and are treated separately from the “ordinary” electrons which are in local thermal equilibrium and have significantly lower energies. Meanwhile, the electron-phonon couplings are considered under the non-equilibrium conditions between the electron and phonon systems. Using our model, we further investigated the transient optothermal responses of a one-dimensional (1D) plasmonic nanofocusing structure. In comparison to the diffusive transport description, our multi-carrier ballistic-diffusive model can more accurately describe the optothermal responses of the plasmonic nanofocusing structures which are crucial for predicting the performance and the lifetime of the plasmonic nanofocusing devices.