Etude du confinement acoustique dans des nano-structures métalliques et semiconductrices par diffusion Ramanbasse fréquence.

Inelastic light scattering spectroscopies (Raman/Brillouin) are a versatile tool to study thermal phonons at various scales. In nano-granular media, the study of acoustic phonons with a wavelength much greater than the grain diameter D (λ/D >> 1) allows one to characterize the macroscopic elasticity governed by Hertz law of the contact. The validity of Hertz law is studied for powders made of oxide nanoparticles a few nanometers in diameter. When the phonon half-wavelength reaches the confinement dimension (diameter D for spheres, thickness e for plates) propagation is forbidden and mechanical resonances occur. Low frequency Raman spectroscopy has been used to characterize the acoustic resonances of semiconducting nanoplatelets “dressed” with an organic surfactant layer. When the thickness becomes thin enough (e ~ 1 nm), the resonance frequency is significantly downshifted compared to a free platelet, attributed to a mass load effect due to the organic molecules. When the confining object is a metallic nano-dimer, both plasmonic and acoustic hybridization occur at the same time. The resonant excitation of the dimeric plasmon allows one to observe down to single nano-object scale the inelastic scattering by dimer hybridized dipolar vibration modes l=1 as well as non-hybridized modes with higher angular momentum l >2, known to be Raman inactive in this size range according to previously established selection rules. Possibilities for a new plasmon-vibration coupling mechanism are discussed.Les spectroscopies de diffusion inélastique de la lumière (Raman/Brillouin) sont un outilversatile qui permet d’étudier les phonons thermiques de la matière à différentes échelles.En particulier, lorsque le milieu possède une nano-structuration, un phénomène derésonance mécanique nait du confinement des phonons dont la longueur d’ondecorrespond au critère λ = 2L, où L est la longueur de confinement. Ces résonances ontété jusque-là majoritairement caractérisées dans le cas de nanoparticules sphériques (aussiappelées modes de Lamb pour un confinement 3D), mais les expériences de diffusioninélastique restent malgré tout peu sensibles aux effets d’interaction entre les résonateurs.Cette thèse est donc dédiée à l’étude de ces effets d’interaction depuis le cas simple d’undimère de nanoparticules métalliques couplées d’un point de vue plasmonique etmécanique, jusqu’à une assemblée désorganisée de N nanoparticules d’oxydes (dans lecas de TiO2 et ZrO2). Dans le cas de dimères métalliques, l’excitation résonante duplasmon longitudinal résulte en une forte exaltation de la diffusion par les modes devibration dipolaires hybridés, ainsi que par des modes de vibration de plus haut momentangulaire. Le Raman résonant est également mis à profit pour l’étude d’autres géométriesde confinement telles que des nanoplaquettes semi-conductrices colloidales de CdS etCdSe. Il est montré que le mode de respiration des nanoplaquettes est sensible à la massemoléculaire du manteau organique recouvrant la surface, ouvrant la voie à desapplications en termes de nanobalances basées sur les vibrations acoustiques de nano-objets

Interactions visio-haptiques pour la coordination et la conscience situationnelle partagée en environnement virtuel collaboratif

La communication haptique interpersonnelle est communément utilisée pour se saluer, se féliciter, ou de manière indirecte pour manipuler des objets lourds. Pourtant, la modalité haptique est absente des systèmes de communication à distance usuels. Les progrès récents de l'informatique et des réseaux de communication ont permis l'émergence d'environnements virtuels collaboratifs offrant un retour haptique aux utilisateurs. Les environnements virtuels collaboratifs constituent une solution prometteuse pour faciliter le travail collaboratif à distance. Les contextes applicatifs sont nombreux : entrainement militaire, assemblage mécanique, manipulation moléculaire, conception assistée par ordinateur.Toutefois, les utilisateurs d'environnements virtuels collaboratifs sont confrontés à deux types de problématiques : celles liées aux environnements virtuels 3D et celles liées à la collaboration à distance. En effet, il est difficile pour un utilisateur peu expérimenté d'interagir avec un environnement virtuel 3D. Se déplacer et manipuler des objets dans ce type d'environnement nécessite une bonne représentation mentale de l'espace.De plus, la collaboration à distance limite les possibilités et la qualité de la communication. Les informations dont disposent les utilisateurs sur leurs partenaires sont donc réduites. Dans ce contexte, la coordination des actions entre les utilisateurs devient plus complexe.L'objectif de ces travaux de thèse est donc de proposer des méthodes d'interaction visio-haptique pour faciliter la coordination et augmenter l'attention mutuelle entre les utilisateurs. Via l'amélioration de la coordination et de l'attention inter-utilisateurs, une augmentation des performances et de l'efficacité du travail collaboratif est escomptée.Trois types d'interactions fondamentales sont abordées dans un contexte collaboratif : la coordination des sélections, le paramétrage des sélections et la manipulation collaborative d'objet. Pour chacune des tâches d'interactions précédemment citées, des méthodes d'interaction ainsi que des outils de coordination et de communication ont été proposé et évalué.Ces travaux de thèse présentent les points forts mais aussi les défauts des méthodes d'interaction collaboratives fortement couplées. Les résultats obtenus montrent également l'importance de la communication haptique dans la collaboration à distance.Haptic interpersonal communication is commonly used to salute, to congratulate, or indirectly to manipulate heavy objects. However, the haptic feedback is missing from the common communication systems. Recent developments in telecommunications and computer capabilities have made possible the use of haptic feedback in collaborative virtual environments. Collaborative virtual environments are a promising solution to facilitate remote work collaboration. They have many applications like: military training, engineering design, e-learning or video games.Nevertheless, users of collaborative virtual environments have to face several issues. First, interacting with a virtual environment is not a straightforward task. Navigate and manipulate objects in a virtual environment requires a good mental representation of space. Secondly, remote collaboration limits the communication quality because even the best video conference system can't support all the richness of a face to face communication. Information available on the partners are reduced thus coordinate actions between users become a complex task.The aim of this thesis is to propose visual haptic interactions to simplify coordination and increase mutual awareness between the users. Through the improvement of coordination and mutual awareness an increase of team performance and work efficiency is expected.Three kind of fundamental 3D interactions are addressed in collaborative context: the coordination of selections, the setting of selections and the manipulation of objects. For each of these three of fundamental interactions, several methods of interaction and tools of coordination are proposed and assessed.The findings of this thesis highlight the strengths and the weaknesses of the closely coupled method of interactions. The results of the experiments also confirm the importance of haptic communication in remote collaboration.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Modeling Approach for the Prediction of Transient and Permanent Degradations of Image Sensors in Complex Radiation Environments

A modeling approach is proposed to predict the transient and permanent degradation of image sensors in complex radiation environments. The example of the OMEGA facility is used throughout the paper. A first Geant4 simulation allows the modeling of the radiation environment (particles, energies, timing) at various locations in the facility. The image sensor degradation is then calculated for this particular environment. The permanent degradation, i.e. dark current increase, is first calculated using an analytical model from the literature. Additional experimental validations of this model are also presented. The transient degradation, i.e. distribution of perturbed pixels, is finally simulated with Geant4 and validated in comparison with experimental data

Vulnerability of CMOS image sensors in megajoule class laser harsh environment

CMOS image sensors (CIS) are promising candidates as part of optical imagers for the plasma diagnostics devoted to the study of fusion by inertial confinement. However, the harsh radiative environment of Megajoule Class Lasers threatens the performances of these optical sensors. In this paper, the vulnerability of CIS to the transient and mixed pulsed radiation environment associated with such facilities is investigated during an experiment at the OMEGA facility at the Laboratory for Laser Energetics (LLE), Rochester, NY, USA. The transient and permanent effects of the 14 MeV neutron pulse on CIS are presented. The behavior of the tested CIS shows that active pixel sensors (APS) exhibit a better hardness to this harsh environment than a CCD. A first order extrapolation of the reported results to the higher level of radiation expected for Megajoule Class Laser facilities (Laser Megajoule in France or National Ignition Facility in the USA) shows that temporarily saturated pixels due to transient neutron-induced single event effects will be the major issue for the development of radiation-tolerant plasma diagnostic instruments whereas the permanent degradation of the CIS related to displacement damage or total ionizing dose effects could be reduced by applying well known mitigation techniques

Vulnerability of optical detection systems to megajoule class laser radiative environment

The Laser MegaJoule (LMJ) facility will host inertial confinement fusion experiments in order to achieve ignition by imploding a Deuterium-Tritium filled microballoon [1]. In this context an X-ray imaging system is necessary to diagnose the core size and the shape of the target in the 10-100 keV band. Such a diagnostic will be composed of two parts: an X-ray optical system and a detection assembly. The survivability of each element of this diagnostic has to be ensured within the mixed pulse consisting of X-rays, gamma rays and 14 MeV neutrons created by fusion reactions. The design of this diagnostic will take into account optics and detectors vulnerability to neutron yield of at least 1016. In this work, we will present the main results of our vulnerability studies and of our hardening-by-system and hardening-by-design studies

Hardening approach to use CMOS image sensors for fusion by inertial confinement diagnostics

A hardening method is proposed to enable the use of CMOS image sensors for Fusion by Inertial Confinement Diagnostics. The mitigation technique improves their radiation tolerance using a reset mode implemented in the device. The results obtained evidence a reduction of more than 70% in the number of transient white pixels induced in the pixel array by the mixed neutron and γ-ray pulsed radiation environment

Daptomycin resistance mechanisms in clinically derived Staphylococcus aureus strains assessed by a combined transcriptomics and proteomics approach

Objectives The development of daptomycin resistance in Staphylococcus aureus is associated with clinical treatment failures. The mechanism(s) of such resistance have not been clearly defined. Methods We studied an isogenic daptomycin-susceptible (DAPS) and daptomycin-resistant (DAPR) S. aureus strain pair (616; 701) from a patient with relapsing endocarditis during daptomycin treatment, using comparative transcriptomic and proteomic techniques. Results Minor differences in the genome content were found between strains by DNA hybridization. Transcriptomic analyses identified a number of genes differentially expressed in important functional categories: cell division; metabolism of bacterial envelopes; and global regulation. Of note, the DAPR isolate exhibited reduced expression of the major cell wall autolysis gene coincident with the up-regulation of genes involved in cell wall teichoic acid production. Using quantitative (q)RT-PCR on the gene cadre putatively involved in cationic peptide resistance, we formulated a putative regulatory network compatible with microarray data sets, mainly implicating bacterial envelopes. Of interest, qRT-PCR of this same gene cadre from two distinct isogenic DAPS/DAPR clinical strain pairs revealed evidence of other strain-dependent networks operative in the DAPR phenotype. Comparative proteomics of 616 versus 701 revealed a differential abundance of proteins in various functional categories, including cell wall-associated targets and biofilm formation proteins. Phenotypically, strains 616 and 701 showed major differences in their ability to develop bacterial biofilms in the presence of the antibacterial lipid, oleic acid. Conclusions Compatible with previous in vitro observations, in vivo-acquired DAPR in S. aureus is a complex, multistep phenomenon involving: (i) strain-dependent phenotypes; (ii) transcriptome adaptation; and (iii) modification of the lipid and protein contents of cellular envelope

Screening for Staphylococcal Superantigen Genes Shows No Correlation with the Presence or the Severity of Chronic Rhinosinusitis and Nasal Polyposis

BACKGROUND: Staphylococcus aureus secretes numerous exotoxins which may exhibit superantigenic properties. Whereas the virulence of several of them is well documented, their exact biological effects are not fully understood. Exotoxins may influence the immune and inflammatory state of various organs, including the sinonasal mucosa: their possible involvement in chronic rhinosinusitis has been suggested and is one of the main trends in current research. The aim of this study was to investigate whether the presence of any of the 22 currently known staphylococcal exotoxin genes could be correlated with chronic rhinosinusitis. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a prospective, multi-centred European study, analysing 93 Staphylococcus aureus positive swabs taken from the middle meatus of patients suffering from chronic rhinosinusitis, with or without nasal polyposis, and controls. Strains were systematically tested for the presence of the 22 currently known exotoxin genes and genotyped according to their agr groups. No direct correlation was observed between chronic rhinosinusitis, with or without nasal polyposis, and either agr groups or the presence of the most studied exotoxins genes (egc, sea, seb, pvl, exfoliatins or tsst-1). However, genes for enterotoxins P and Q were frequently observed in nasal polyposis for the first time, but absent in the control group. The number of exotoxin genes detected was not statistically different among the 3 patient groups. CONCLUSIONS/SIGNIFICANCE: Unlike many previous studies have been suggesting, we did not find any evident correlation between staphylococcal exotoxin genes and the presence or severity of chronic rhinosinusitis with or without nasal polyposis

Anthropocène : Plan B, création de connaissances pour répondre aux enjeux sociétaux de manière soutenable dans les limites planétaires

De nombreuses recherches et en particulier celles sur les limites planétaires ont montré que nous dépassons actuellement plusieurs limites globales, ce qui questionne fortement la soutenabilité de nos sociétés contemporaines à forte empreinte écologique. Cette prise de conscience se généralise et a fait croître à une vitesse importante les attentes sociétales de visions alternatives à un futur basé sur le seul progrès technologique et/ou une croissance économique infinie.Nous souhaitons faire face à ces constats et aux attentes qu’ils génèrent, sans greenwashing et sans nous en remettre à une croissance verte que nous savons impossible depuis longtemps et notamment par les travaux commandités par le Club de Rome. Impossibilité qui a été rappelée récemment à notre mémoire par une note de l’UE. Pour cela nous souhaitons engager l’UGA dans la construction, sur le long terme, d’une communauté scientifique transdisciplinaire. Nous proposons de développer des recherches complémentaires et alternatives à celles basées sur la double hypothèse d’un éternel progrès technologique et d’une croissance économique qui serait nécessairement vertueuse sur le plan social. Ces recherches auront pour objectif principal d’appréhender la dimension systémique et complexe des questions de dépassement écologique.Pour cela nous savons que nous pouvons d’ores et déjà appuyer notre démarche sur plusieurs collectifs de personnels et d’étudiants nés spontanément dans différentes structures de l’UGA. Leur diversité de profils et de disciplines constitue un atout précieux pour construire une approche transdisciplinaire. Nous pensons donc qu’il est utile et pertinent d’essayer de fédérer ces initiatives dans une démarche collective commune de production de connaissances