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Metallic bilayer samples of Mo(400 Å)/ Al(substrate) were characterized using Rutherford Backscattering Spectroscopy after first being irradiated with Xe ion beam having an energy of 1.8 MeV. The computer code RUMP was then used to simulate the RBS spectra. The interdiffusion at the interface was considered in terms of thermal spike induced atomic migration. It was found that the coupling of the chemical effect with spike is significant with regard to mixing of the bilayer samples. Furthermore, in addition to the initial contamination of carbon atoms on the surface and at the interface, more carbon atoms were found to be picked up by the surface, this carbon w.as from the vacuum pumps and tended to migrate into the surface once irradiation dose exceeded 11 x 10¹⁵cm². A semi-empirical model was developed for ion beam mixing taking into account collisional mixing and thermal spike effects, as well as the thermal spike shape. The collisional mixing part was accounted for by the Kinchin-Pease model, or, alternatively dynamic Monte Carlo simulation. For the thermal spike, the ion beam mixing parameter Dt/Φ was derived to be proportional to ( - F_D /ΔH_coh)^2+μ, where F_D is the damage energy deposited per unit path length, ΔH_coh is the cohesive energy of the target materials, and µ is a constant dependent on the spike shape and point defect density in the spike regions. The thermal spike introduces a nonlinear effect in the mixing process, distinguishing itself from the linear effect of ballistic mixing. The shape of the thermal spike that best fit the experimental results depends on the magnitude of the cascade density. For relatively high density collisional cascades, where thermal spikes start to be important, it was found that a spherical spike model was more consistent with experimental measurements at low temperatures. However, for extremely high density collisional cascade regions, a cylindrical shaped spike gave better results. The atomic migration energy in the spike regions is scaled by a factor of one out of 8.6 of cohesive energy. The migration mechanism was recognized to be interstitial-dominated one. / M.S.

L'hydrolyse enzymatique de la P-lactoglobuline (p-lg) par la trypsine permet la libération de différents peptides dont plusieurs possèdent des propriétés fonctionnelles et bioactives. Un phénomène d'agrégation inattendu a été observé durant la concentration par osmose inverse (01) d'un hydrolysat trypsique de P-lg. Des travaux récents démontrent qu'un peptide particulier, le peptide B-lg fl-8, initie l'agrégation observée dans l'hydrolysat de /?-lg floculé via le phénomène d'auto-assemblage peptidique. L'auto-assemblage peptidique est un type particulier d'agrégation selon lequel des peptides polymérisent spontanément ensemble afin de former des nanostructures bien définies comme des nanotubes, des nanofibres et des hydrogels. Le but de cette étude était d'étudier les interactions moléculaires impliquées dans le phénomène d'auto-assemblage du peptide /?-lg fl-8, d'une part en étudiant les conditions physico-chimiques qui déclenchent l'auto-assemblage et la formation de nanofibres et d'hydrogels et, d'autre part, en étudiant l'impact de la séquence d'acides aminés sur l'auto-assemblage. Les résultats ont d'abord démontré que l'auto-assemblage du peptide B-lg fl-8 était régi par les conditions de pH et par la concentration en peptide et que la force ionique ainsi que la température n'influençaient pas l'auto-assemblage. Les résultats ont aussi démontré que plusieurs interactions moléculaires (hydrophobes, électrostatiques, liens hydrogène) étaient impliquées dans l'auto-assemblage en feuillets P du peptide B-lg fl-8. Plus précisément, il a été démontré que l'extrémité hydrophobe du peptide était essentielle pour déclencher l'auto-assemblage en feuillets P et que les interactions électrostatiques provenant de l'extrémité hydrophile contribuaient considérablement à conserver un équilibre précis entre les interactions hydrophobes et électrostatiques nécessaires pour déclencher l'auto-assemblage. Globalement, les résultats démontrent qu'il est possible de concevoir à partir de l'auto-assemblage peptidique en feuillets P des hydrogels avec des propriétés particulières, de diversifier les conditions physico-chimiques qui déclenchent la formation de ces matériaux et de générer des nanostructures présentant des morphologies très différentes.

Les études de la multifragmentation dans les collisions d'ions lourds aux énergies de Fermi se sont intensifiées dès les années 90 avec le développement des détecteurs et outils pour récolter et trier la quasi totalité des réactions nucléaires. Dans la première partie de ce travail, on a étudié les collisions centrales du système Ni+Ni à 32, 40, 52, 64, 74, 82 et 90A MeV, à l'aide du multidétecteur INDRA. Nous avons sélectionné les collisions centrales par une Analyse Factorielle Discriminante. La confrontation des données avec le modèle SMM a permis d'établir que la forme de la source est allongée dans la direction du faisceau (" = 1:7) et d'extraire l'énergie d'expansion de cette source (0:75, 1:7 et 2:4A MeV pour les énergies incidentes de 32, 40 et 52A MeV, respectivement). La recherche d'un signal de transition de phase a été abordée avec diverses analyses. Celle concernant les capacités calorifiques s'est traduite par la mise en évidence d'un signal expérimental à 32A MeV mais dont l'interprétation reste délicate compte tenu des perturbations apportées par les hypothèses indispensables à la reconstruction des fragments au freeze-out. La méthode des corrélations en charges, qui permet de rechercher des signaux "fossiles" de fragments de taille égale issus de la décomposition spinodale, permet de conclure à une surproduction de fragments de taille égale à 52A MeV. La recherche d'une signature d'un comportement critique montre que, m^eme si les fonctions d'échelle se regroupent en deux familles distinctes, la loi d'échelle n'est pas vérifiée de façon rigoureuse pour le système à 52A MeV, ce qui peut s'interpréter comme une transition d'une phase ordonnée à plus basse énergie vers une phase désordonnée à plus haute énergie. Par ailleurs, l'étude des mécanismes des réactions dans les collisions d'ions lourds aux énergies de Fermi montre la prédominance du caractère binaire de la collision, un processus qui conduit à la formation de deux sources. Récemment, on s'est intéressé aux fragments de fission binaire formés après la première étape des collisions profondément inélastiques, en posant la question sur l'aspect statistique en fonction de l'aspect dynamique de la fission. Afin de comprendre l'origine de production de ces fragments, la corrélation entre les deux plus gros fragments résultant des réactions Ni+C, Mg, Zn et Au a été étudiée. Les distributions angulaires indiquent que les deux plus gros fragments sont alignés dans la direction du quasi-projectile (QP). En étudiant les fonctions de corrélation, nous avons constaté que le QP se brise à proximité de la cible. Ceci suggère que l'intervalle de temps entre la séparation du QP et la quasi-cible et la désintégration du QP est suffisamment court pour que les fragments du QP ressentent le champ coulombien de la cible. La corrélation entre la taille et la vitesse des fragments nous suggère que c'est la déformation du QP engendrée lors de la collision entre la cible et le projectile qui provoque sa cassure binaire. / Studies of multifragmentation in collisions of heavy ions in the Fermi energy domain has been intensified with the development of the techniques to extract the most violent collisions. In first part of this work, we studied central collisions of the Ni+Ni system at 32, 40, 52, 64, 74, 82 and 90A MeV, measured with the INDRA multidetector. We selected central collisions with the Discriminant Analysis Method. The confrontation of experimental data with SMM model shows that the mean shape of the source is elongated along the beam axis (" = 1:7) and makes it possible to extract the expansion energy of the source (0:75, 1:7 and 2:4A MeV at 32, 40 and 52A MeV respectively). We have shown that the fact that we have a source which is not completely equilibrated does not allow to conclude from the existence of a liquid-gas phase transition of nuclear matter using the heat capacities. The method of charge correlations shows an overproduction of events with equal size fragments at 52A MeV. The search for a signature of critical behaviors shows that, even if functions of scale gather in two families distinct, the law of scale is not verified in a rigorous way for the system at 52A MeV, which can be interpreted like a transition from an ordered phase at lower energies towards a disordered phase at higher energies. On the other hand, heavy ion collisions in the Fermi energy domain are known to be dominated by deep inelastic scattering, a process leading to the formation of two partners in the reaction exit channel. Recently, an increasing interest has been devoted to binary fission of fragments at the end of the deep inelastic scattering stage, with the related studies usually addressing the question of the statistical versus dynamical aspects of the fission process. In order to understand the origin of production of these fragments, projectile binary breakup has been investigated in Ni+C, Mg, Zn and Au. The fragment angular distributions exhibit an anisotropic pattern showing that breakup is aligned with the direction of scattered quasi-projectile (QP). The correlation functions of the two heaviest fragments have been studied as a function of charge asymmetry. They suggest that the QP decays while still in close proximity of the target. The correlation between the charge and velocity of the two heavy fragments shows that the binary breakup of the QP might originate from an important deformation of the projectile by the target.

The model investigated, exhibits and defines in mathematical expressions all the laws of common mechanical behavior of an inelastic solid. As a result, it excels the more common models discussed in the introduction not only in completeness of behavior, but also in possibilities of application In a practical sense, it is of interest to note the similarity between the stress-strain curves of the model and those of some aluminum alloys, Duralumin, magnesium and copperâ ¢ The creep and strain recovery curve of Fig. (20) is in close agreement with that of real metals discussed by Nadai (l5). This seems to indicate that the model will be useful in giving mathematical equations for the behavior of these metals under different test conditions. / Master of Science

<p dir="ltr">Complex physical systems provide a fertile ground for exploring various phenomena owing to the quantum nature inherent in their structure. Atoms and molecules not only serve as realistic systems for experimental investigation, but also exhibit a complexity stemming from their many-body interactions which is of significant theoretical interest. This thesis delves into the domain of ultracold collisions between different interacting species (where temperature T < 1mK), and introduces novel applications for probing such systems, particularly focusing on molecular formation via photoassociation. Molecular interactions, in comparison to their atomic counterparts, present heightened complexity. The interplay of electrostatic forces among electrons and nuclei intricately couples all degrees of freedom within a single molecule. Historically, the exploration of quantum dynamics between molecules was pioneered by Born and Oppenheimer. Their seminal work involved solving Schrödinger’s equation in two steps. First step is addressing a portion of the molecular Hamiltonian where the nuclei are clamped in space (adiabatic). This adiabatic solution yields effective potentials between nuclei, encapsulating the integrated influence of the surrounding electronic cloud. The second step is to solve for the nuclear degrees of freedom in the vicinity of the effective potentials. The validity of the Born-Oppenheimer approximation stems from the substantial mass disparity between electrons and nuclei, enabling a quasi-separation of the electronic and nuclear Hamiltonians. The first order Born-Oppenheimer approximation assumes a partial separation of the molecular wave function Ψmolecule ≈ ΞvibrationYrotationalΦelectronic.</p><p dir="ltr"> A comprehensive treatment is provided for systems with numerous degrees of freedom, elucidating how the Born-Oppenheimer approximation manifests when applied to molecules. This chapter also encapsulates the principal findings from collision theory and photoassociation spectroscopy, as well as foundational techniques underpinning this thesis. Spectroscopic investigations encompass four relevant transition types: boundbound (Rabi oscillations), bound-free (photoionization), free-free (elastic scattering), and free-bound (photoassociation) transitions. Photoassociation (PA) spectroscopy probes laserinduced processes where the reactants interact through a channel |i〉, and can absorb one or more photons causing a transition to a bound state in an excited channel |f〉. The excited complex usually decays with a high probability to the ground state of the formed molecule. The same process can be utilized experimentally to prepare a cold molecule in its vibrational ground state . Diatomic PA has been of great theoretical and experimental interest in recent years. Herein, we present a theoretical inquiry into photoassociation within triatomic systems, with a particular focus on alkali atom-dimer systems, and introduce a method for calculating PA rates.</p><p dir="ltr">Moreover, this thesis presents different methods for shielding polar molecules from their short-range interactions where inelastic collisions and chemical reactions can occur with high probability. Shielding polar molecules has been shown to suppress inelastic collisions substantially between two molecules. A technique to shield two polar molecules in their ground state is studied and applied to model collisions in a gas of ground state (NaCs) molecules at temperatures T ≈ 100nK. The results show a region of interactions between two polar molecules that has an extremely long-range nature and is well isolated from the short-range losses, allowing for long-range spectroscopic studies. A new long-range regime of molecular physics arises in the study of shielded molecules where long-range vibrational tetramer states form. Different tetramer formation pathways are studied within a range of different shielding parameters. In fact, microwave shielding provides a region to study collisions between polar molecules, and controls their dynamics without worrying about shortrange losses. It has also been applied in the observation of a Bose gas of polar molecules.</p>

Contact inhibition of locomotion (CIL), a migratory mechanism, first introduced by Abercrombie and Heaysman in 1953 is now a fundamental driving force in developmental, repair and disease biology. Much of what we know of CIL stems from studies done on 2D substrates which are unable to provide the essential biophysical cue of fibrous extracellular matrix curvature. Here we inquired if the same rules are applicable for cells attached to and migrating persistently on suspended and aligned ECM-mimicking nanofibers. Using two elongated cell shapes (spindle attached to one fiber, and parallel attached to two fibers), we quantitate CIL rules for spindle-spindle, parallel-parallel and spindle-parallel collisions. Two approaching spindles do not repolarize upon contact but rather continue to migrate past one another. Contrastingly, approaching parallel cells establish distinct CIL, with only one cell repolarizing upon contact followed by migration of both cells as a cohesive unit in the repolarization direction. Interestingly, for the case of spindle and parallel cell collision, we find the parallel cell to shift the morphology to that of spindle and continue persistent movement without repolarization. To account for effect of cell speed, we also quantitate CIL collisions between daughter and non-dividing cells. While spindle-spindle collisions result in cells still walking by, for parallel-parallel collisions, we capture rare events of a daughter cell pushing the non-dividing cell. With increasing population numbers, we observe formation of cell streams that collapse into spheroids. Single cells are able to invade along fibers from the spheroids and are then subject to same CIL conditions, thus providing a platform with cyclic CIL. The presented coupling of experimental and analytical framework provides new insights in contextually relevant CIL and predictive capabilities in cell migration decision steps. / Master of Science / Contact inhibition of locomotion (CIL) is a migratory process that can lead to a change in migration direction through protrusion inhibition of single cells. First described in 1953, the traditional model of CIL shows that on a 2D substrate, two migrating cells experience a decrease in protrusive behavior upon contacting each other, followed by repolarization, and migration away from one another. However, a cell's extracellular matrix (ECM) is fibrous in nature, and how cells maintain standard CIL rules in fibrous environments remains unclear. Here, using suspended, aligned nanofibers created using a non-electrospinning Spinneret based Tunable Engineered Parameters (STEP) method, we investigate CIL decision steps of two fibroblast cells approaching each other in two shapes: spindle cells attached to single fibers, and parallel cells attached to two fibers. Most spindle cells approaching each other do not switch direction upon contact, but rather continue to migrate past each other, termed a walk past. Contrastingly, approaching parallel cells display unique CIL whereby only one cell repolarizes and reverses its migration direction. Subsequently, both cells remain in contact while migrating in the repolarization direction. Interestingly, we report that both spindle and parallel CIL are also affected by speed post cell division. Altogether, for the first time, we introduce a platform to understand cell shape driven CIL geometrical rules in ECM mimicking environments.

Les collisions d'ions lourds aux énergies intermédiaires produisent, pour des collisions semi-périphériques, une zone de mi-rapidité. Il a été montré expérimentalement que cette zone a un ratio N/Z plus élevé que le système. Deux explications sont généralement admises pour expliquer ce phénomène : le gradient isovectoriel et l'agrégation rapide de particules symétriques. Cependant, la force de Coulomb peut créer une migration des protons qui peut expliquer une partie de cet enrichissement. Pour vérifier cette hypothèse, des simulations ont été effectuées avec un programme se basant sur l'approche BUU. Lors des simulations, certaines émissions non-physiques ont été observées et ont dû être supprimées de l'analyse par différents moyens. Lorsque ces émissions sont retirées, les simulations montrent un enrichissement de la zone de mi-rapidité qui ne peut être dû qu'à la force de Coulomb. Cet enrichissement présente un maximum en fonction de l'énergie du faisceau. L'effet de migration créé par la force de Coulomb n'arrive cependant pas à expliquer tout l'enrichissement.

A minimum-norm method has been developed for solving the coupled integro-differential equations describing the scattering of positrons by one-electron targets in which the rearrangement channels for positronium formation have been explicitly included. The minimum-norm method, applied to this application for the first time in this thesis, is an enhancement of a previously reported least-squares method which has enabled the extension to a significantly larger basis consisting of up to 26 states on the direct centre, including pseudostates, and 3 states on the positronium. The method has been applied here to e+-H and e+-He+ scattering; cross-sections have been produced for the latter over a range of energies up to 250 eV. The basis was found to be large enough to produce smooth cross sections and little evidence of pseudoresonance structure was found. The results are the first converged cross sections to be calculated for e+-He+ scattering using the coupled channel approximation. Results for e+-H scattering compare well with the work of other authors. A highly efficient parallel code was developed for solving the largest coupling cases. The results prove the minimum-norm approach to be an accurate and reliable method for large-scale coupled channel calculations involving rearrangement collisions. Also in this thesis, the capture of slow antiprotons by atomic hydrogen and positronium has been simulated by the Classical Trajectory Monte Carlo (CTMC) method. Statistically accurate cross sections for protonium and antihydrogen formation have been obtained and the energy dependence of the process established. Antihydrogen formation from antiproton collisions with positronium in the presence of a laser has also been simulated with the CTMC method and the effects of laser polarisation, frequency and intensity studied. Enhancements of the antihydrogen formation cross section were observed and it is suggested that more sophisticated calculations should be undertaken