Electronic and vibrational spectroscopy of cold protonated amino acids in the gas phase

In this thesis report, we describe a novel home-built instrument designed to study the spectroscopy of biomolecular ions in the gas phase and at low temperature, and we present the first experimental results obtained on protonated aromatic amino acids. The apparatus consists in a tandem mass spectrometer equipped with a nanospray ion source and a cryocooled 22-pole ion trap. The charged species produced by the source traverse a first quadrupole mass filter and mass-selected ions are then accumulated and thermalized in the ion trap, where their vibrational temperature can be lowered to ~ 10 K. Two setups allow us to generate ultraviolet and infrared laser light to spectroscopically probe the trapped ions by photodissociation. The resulting fragment ions are finally released from the trap and mass analyzed by a second quadrupole spectrometer. Photodissociation electronic spectra have been measured for the protonated amino acids tryptophan (TrpH+) and tyrosine (TyrH+), as well as for hydrated complexes of the former. The spectrum of TyrH+ exhibits sharp, fully resolved vibronic transitions, which attests to the low temperature of the ions. In contrast, that of tryptophan shows a broad absorption band that covers several hundreds of wavenumbers. This has been attributed to lifetime broadening related to an ultrafast (< ~ 100 fs) deactivation mechanism of the TrpH+ S1(ππ*) excited state. This phenomenon is caused by a strong coupling between this ππ* state and a nearby dissociative state of πσ* character mainly localized on the charged ammonium group. Solvation of TrpH+ by only two water molecules is sufficient to significantly destabilize the σ* orbitals and reduce that coupling, which results in a longer excited-state lifetime and a fully resolved electronic spectrum. These interpretations are supported by ab initio and density functional theory (DFT) calculations. Infrared-ultraviolet double resonance spectroscopic techniques have been successfully implemented to identify the different conformers of TyrH+ and doubly hydrated protonated tryptophan (TrpH+·W2) by measuring conformer-specific vibrational and electronic spectra for each of them. By comparison with the results of DFT geometry and harmonic frequency calculations, we could confidently determine the structures of the TyrH+ conformers and suggest possible assignments for those of TrpH+·W2. Two important stabilizing interactions could be inferred from these results: (i) the attraction between the charged ammonium group and the π-electron cloud of the aromatic ring; (ii) the hydrogen-bonding interaction of a donor water molecule to the acceptor indole ring of TrpH+·W2

Cortical mapping of the infraspinatus muscle in healthy individuals

Background : While cortical representations of intrinsic hand muscles have been extensively studied in healthy individuals, little is known about the representation of proximal upper limb muscles. Improving our understanding of normal shoulder function is important, given that shoulder musculoskeletal disorders affect approximately 20% of the population and are suspected to involve changes in central motor representations. The purpose of the study is to describe the motor representation (motor evoked potentials (MEP) amplitude at the hotspot, map area, normalized map volume and center of gravity) of the infraspinatus muscle in healthy individuals, and to explore the potential influence of hand dominance on this representation (i.e. symmetry of the excitability and of the location of motor map between sides), as well as the effect of age and gender on motor excitability. Results : Fifteen healthy participants took part in this study. No significant asymmetry between sides was observed for motor excitability (p = 0.14), map area (p = 0.73) and normalized map volume (p = 0.34). Moreover, no side x intensity interaction was found (p = 0.54), indicating similar stimulus response properties. No difference between sides was found in the location of infraspinatus motor representation, either in the mediolateral or anteroposterior axis (p > 0.10). Neither age nor gender influenced aMT (p > 0.58) or MEP size (p > 0.61). Conclusions : As the cortical representation of infraspinatus muscles was found to be symmetric between sides, both in terms of excitability and location, comparisons between the intact and affected side could be performed in clinical studies, regardless of whether the dominant or non-dominant side is affected. The next step will be to characterize corticospinal excitability and map parameters in populations with shoulder disorders

Emergence et risques sanitaires associés à la tremblante atypique ovine

Les encéphalopathies spongiformes transmissibles (EST ou « maladies à prions ») sont des maladies neurodégénératives affectant de nombreuses espèces de Mammifères, dont l’archétype est la tremblante des ovins. Ces maladies sont dues à la transconformation d’une protéine cellulaire (PrPc), codée par le gène PRNP, en une isoforme anormale (PrPSc) s’accumulant dans les tissus des individus atteints (système nerveux central notamment). Il est désormais admis que cette protéine anormale représente l’agent responsable de ces maladies. Décrite en 1998 en Norvège, la tremblante « atypique » des ovins constitue une nouvelle forme d’EST dont de nombreuses caractéristiques restent encore méconnues. Elle semble affecter préférentiellement des animaux de génotypes considérés jusqu’alors comme résistants aux EST. Cette caractéristique pourrait remettre en question la politique actuelle de sélection génétique mise en place à l’échelle européenne pour contrôler et éradiquer les maladies à prions dans l’espèce ovine. La question du risque que représente l’exposition à ce nouvel agent pour l’homme et les autres espèces animales demeure entière

Coherent beam superposition of ten diode lasers with a Dammann grating

We demonstrate the use of a binary diffractive optical element in a very simple setup to convert the multilobed beam from a low fill factor array of coherent laser diodes into a quasi-Gaussian beam. The phase profile of the grating is determined with a phase retrieval algorithm. Experimentally, the conversion efficiency reaches more than 44%. We also establish that this setup can be used to make an effective measurement of the coherency of the laser array

Multiple necking pattern in nonlinear elastic bars subjected to dynamic stretching: the role of defects and inertia

In this paper we explore the inception and development of multiple necks in incompressible nonlinear elastic bars subjected to dynamic stretching. The goal is to elucidate the role played by a spatial-localized defect of the strain rate field in the necking pattern that emerges in the bars at large strains. For that task, we have used two different approaches: (1) finite element simulations and (2) linear stability analyses. The finite element simulations have revealed that, while the defect of the strain rate field speeds up the development of the necking pattern in the late stages of the localization process, the characteristic (average) neck spacing is largely independent of the defect within a wide range of defect amplitudes. The numerical results have been rationalized with the linear stability analyses, which enabled to explain the average spacing characterizing the necking pattern at high strain rates. Moreover, the numerical calculations have also shown that, due to inertia effects, the core of the localization process occurs during the post-uniform deformation regime of the bar, at strains larger than the one based on the Considère criterion. This phenomenon of neck retardation is shown to have a meaningful influence on the necking pattern.AVR and JARM are indebted to the Ministerio de Economía y Competitividad de España (Projects EUIN2015-62556 and DPI2014- 57989-P ) for the financial support which permitted to conduct part of this work. AM and JARM acknowledge the support by the French State through the program Investment in the future operated by the National Research Agency (ANR) and referenced by ANR-11-LABX- 0 0 08-01 (LabEx DAMAS). The research leading to these results has received funding from the European Union’s Horizon2020 Programme (Excellent Sci- ence, Marie Sklodowska-Curie Actions) under REA grant agreement 675602 (Project OUTCOME)

Rôle de l'inertie microscopique lors de la rupture dynamique de matériaux ductiles

Ces travaux portent sur la modélisation de l'endommagement ductile de matériaux métalliques. Un modèle d'endommagement continu à base micromécanique a été mis point. L'originalité de celui-ci est qu'il incorpore des effets d'inertie liés aux mouvements de matière à l'échelle de microstructure du matériau. Ce modèle a été intégré dans un code de calculs par EF. Les simulations réalisées montrent que l'inertie microscopique pourrait jouer un rôle important lors de la rupture dynamique. En outre, elle induit un effet régularisant qui réduit la sensibilité au maillage lors des simulations

Simulation 2D thermomécanique des cartes de circuit imprimé avec composants enterrés

Depuis quelques années, dans le but d’augmenter la densité et les performances des cartes électroniques, des composants sont enfouis dans les couches internes de circuit imprimé. Une évaluation de la fiabilité de cette technologie est nécessaire avant utilisation au sein de cartes électroniques soumises à des environnements sévères pendant de longues durées. Afin d’étudier le comportement thermomécanique de ces cartes, des simulations par éléments finis ont été réalisées. Les composants enfouis sont soumis à un chargement thermomécanique complexe durant le procédé d’assemblage, notamment de flexion composée, due à un rétreint des résines et des préimprégnés

Comportement dynamique des matériaux ductiles. Modèle d'endommagement élasto-viscoplastique et simulation numérique du test d'impact de plaques

La rupture ductile des matériaux métalliques est un processus se déroulant en trois étapes : la nucléation, la croissance et la coalescence de vides. Aux grandes vitesses de sollicitation, les effets de micro-inertie, engendrés par la croissance rapide des cavités, influencent le comportement macroscopique du matériau. Nous proposons dans un premier temps un modèle d'endommagement dynamique par nucléation et croissance de vides, basé sur une approche d'homogénéisation. Ce modèle tient compte du comportement élasto-viscoplastique du matériau et est une extension de précédents travaux. Dans un second temps, le modèle est implanté dans le code de calculs par éléments finis Abaqus/Explicit via un sous-programme utilisateur Vumat. Les résultats de simulations numériques du test d'impact de plaques révèlent une bonne concordance avec les données expérimentales sur le tantale obtenues par Roy (2003) et permettent d'interpréter finement les expériences