Les applications thérapeutiques de la neurostimulation ultrasonore représentent un terrain de recherche très prometteur, auquel il fait défaut un modèle valide décrivant les biomécanismes sous-jacents. Le premier objectif de ce travail de thèse était de proposer un modèle nerveux propice à une étude mécanistique du phénomène de neurostimulation ultrasonore. L’objectif suivant était de prouver l’intérêt d’exploiter ce modèle pour recueillir des informations concernant les interactions biophysiques ayant lieu entre les ultrasons (US) focalisés et le système nerveux. La majorité des études réalisées a porté sur le système nerveux du ver de terre commun, Lumbricus terrestris. Elles ont consisté d’une part à comparer entre elles les caractéristiques temporelles des réponses nerveuses associées à différentes modalités de stimulation, et d’autre part à évaluer l’influence de chacun des paramètres acoustiques du stimulus ultrasonore sur le taux de succès de neurostimulation (NSR). Dans les deux cas, la méthodologie suivie reposait sur l’administration de différents stimuli aléatoirement alternés. Complémentairement, le rôle joué par la cavitation acoustique a été étudié. La faisabilité de la stimulation du système nerveux du ver de terre, au moyen d’US et dans des conditions in vivo, a été prouvée. Les aires sensorielles et la dynamique de réponses associées aux trois modalités de stimulation ont été caractérisées. Il a été conclu que, dans ce modèle nerveux invertébré, pendant le phénomène de neurostimulation ultrasonore, les structures nerveuses interagissant fonctionnellement avec les US sont les nerfs afférents segmentaux. Les résultats des études paramétriques ont indiqué que le NSR augmente avec l’intensité acoustique, la durée de pulse et la fréquence de répétition des pulses. Il a été proposé que la structure nerveuse visée est sensible à la « force de radiation moyenne » transportée par le stimulus US, indépendamment des paramètres menant à cette valeur / Ultrasound neurostimulation applied to therapy is a promising field of research but still lacks of a validated model explaining the biomechanisms underlying the phenomenon. The first objective of this PhD thesis was to propose a nervous model suited for a mechanistic study of the phenomenon of ultrasound neurostimulation. In a second time, it was intended to practically prove the interest of this model by using it to gain knowledge regarding the biophysical interactions between focused ultrasound and the nervous system. Studies were performed on the nervous system of the anesthetized earthworm, Lumbricus terrestris. They consisted in either comparing the timings of the nervous responses associated with different modalities of stimulation, or evaluating the influence of each acoustic parameter on the neurostimulation success rate (NSR). In both cases, the methodology followed was to administer randomly mixed sequences of different stimuli. The feasibility of the in vivo activation of the anesthetized earthworm’s nervous system was proven. The sensory fields and response dynamics associated with the three modalities of stimulation were characterized. The parametric studies indicated that the NSR increases with pulse amplitude, pulse duration, pulse repetition frequency, but is more weakly influenced by the harmonic content and number of pulses. By applying a causal approach to interpret the results, we concluded that, in this nervous model, during the phenomenon of ultrasound neurostimulation, the structures functionally responding to the ultrasound stimulus are the segmental afferent nerves. We hypothesize that the main interaction with the axonal regions is mediated by ultrasound radiation force, without excluding the involvement of other biomechanisms

The search for extra-terrestrial life is guided by the classification of promising candidate worlds. In this classification the habitable zone acts as a measure for the perceived habitability of a circumstellar body. Habitable zone definitions vary between using a conservative and an optimistic limit. As the Sun progresses through stages of stellar evolution previously uninhabitable outer moons may receive sufficient heating for the existence of liquid water on their surface. To evaluate the possibility for life on these moons the time inside the habitable zone is calculated and compared to estimates for the time for life to develop on Earth. For these calculations the stellar evolution models of PARSEC and Dartmouth are employed. A class of moons is discovered whose time inside the habitable zone is longest during the horizontal branch evolutionary phase (fueled by helium burning in the core). Since the horizontal branch luminosity is near constant, this class is of particular interest due to being less dependent on a stabilizing climate mechanism to regulate atmospheric composition needed to counteract luminosity changes. Ultimately, it is found that regardless of moon, stellar evolution model, and habitable zone definition no post-main sequence time inside the habitable zone is as long as the time for life to arise on Earth. / <p>Research presentation</p>

The cloud and haze properties in the troposphere and stratosphere of Saturn are investigated in this thesis by analysing Cassini/VIMS spectra at 0.8-3.5 μm and 4.5-5.1 μm. The aerosol properties are derived from VIMS data by using the retrieval tool NEMESIS developed at the University of Oxford. Near-infared VIMS data between 4.5 and 5.1 μm are mainly sensitive to deeper tropospheric levels down to approximately 5 bar. At such pressure levels, thermochemical models predict the formation of condensed clouds made of ammonia and ammonium hydrosulphide ices, although none of these species has been spectrally detected so far. In addition, phosphine and ammonia are responsible for most of the gaseous absorption at these wavelengths. Therefore, the cloud properties and gas distributions can be retrieved from VIMS near-infared spectra. In this thesis, the analysis of limb-darkening data at 4.5-5.1 μm is performed in order to constrain the aerosol properties in Saturn’s atmosphere. The best-fitting model consists of a scattering cloud between 2 and 3 bar, and a scattering haze layer which can be placed anywhere between 10 and 500 mbar. The composition is still poorly constrained for both the deep cloud and haze layer. The haze physical and optical properties can however be independently retrieved from VIMS near-infrared spectra at shorter wavelengths in the 0.8-3.5 μm spectral range. Saturn’s hazes in the troposphere and stratosphere reflect the sunlight at 0.8-3.5 μm. The properties and vertical structure of tropospheric and stratospheric hazes are then investigated from VIMS reflection spectra in the near-infared. The latitudinal variation of haze properties is compared to a thermal feature known as "the temperature knee", corresponding to a local increase of temperature right below the tropopause. The north-south temperature variations in the troposphere are obtained from the analysis of thermal infrared data measured with the Composite InfraRed Spectromete (CIRS) instrument on board Cassini. Finally, VIMS near-infrared data at 0.8-3.5 and 4.5-5.1 μm are combined in order to obtain a cloud and haze model coherent with both wavelength ranges.

This thesis presents the experimental work performed on the spectrin protein. The aim of the work was to study the direct interactions of spectrin, the cytoskeleton of RBCs, with membrane lipid to determine its effects on the mechanical properties of the lipid bilayer. Motivation for this work came from a lack of unanimity in the field of spectrin, and the hypothesized potential of the protein to perforate giant unilamellar vesicles. The work aimed to investigate and determine how spectrin-lipid interactions influence membrane mesoscopic morphology and biophysics in ways that could ultimately be important to cellular function. For this purpose, a protocol was implemented to take into account the different aspects of the binding. Direct visualisation of the spectrin-lipid interaction and distribution was achieved using confocal fluorescence microscopy. Changes in the mechanical properties of the membrane were investigated using the micropipette aspiration technique. Finally the thermodynamics of the interaction were considered with isothermal titration calorimetry experiments. This allowed evaluation of the protein-lipid interaction in a complete and coherent manner. Experiments were also performed on another elastic protein, alpha-elastin, for comparison. In addition to its similarities with spectrin (both possess hydrophobic domains and entropy elasticity), elastin is auto-fluorescent which makes it an attractive model protein. Elastin was also used as a sample model to implement new techniques using nonlinear optics microscopy.

Orbicular and comb layer textures in igneous environments are evidence of an unusual heating and cooling regime in small pockets at the edges of crystallizing magmas. Changes in the composition of a magma spark rapid changes in temperature, which cause the temporary suppression of normal crystal nucleation. As the superheated or supercooled magma returns to equilibrium temperature, crystallization occurs exclusively on pre-existing nucleation surfaces (floating xenoliths or wall rocks), creating orbicular and comb layering textures. Orbs and comb layers collected from two localities in the central Sierra Nevada Batholith were analyzed to determine 1) how they formed and 2) what their formation history reveals about the emplacement histories of their respective host plutons. Geochemical analysis including XRF, U-Pb dating and Sr-Nd and O isotope analysis was used to constrain the characteristics of the orbicular magma. Cathodoluminescence as well as macro and microscale petrography was used to determine the specific growth history of the orbs and comb layers. This study shows that orbs and comb layers from both localities formed due to superheating caused by the influx of water into the orbicular melt. Subsequent cooling was caused by mixing–induced depolymerization and fluid enrichment (Big Meadows Creek) or emplacement into a cooler host rock (Deer Creek). Both locations studied are 2–3 Ma younger than their host plutons, indicating that the processes which form orb and comb layers may cause late melting and magma remobilization in larger plutons.

Spintronics in metallic multilayers, composed of ferromagnetic (F) and non-magnetic (N) metals, grew out of two complementary discoveries. The first, Giant Magnetoresistance (GMR), refers to a change in multilayer resistance when the relative orientation of magnetic moments in adjacent F-layers is altered by an applied magnetic field. The second, Spin-Transfer-Torque (STT), involves a change in the relative orientation of F-layer moments by an electrical current. This novel physical phenomenon offers unprecedented spatial and temporal control over the magnetic state of a ferromagnet and has tremendous potential in a broad range of technologies, including magnetic memory and recording. Because of its small size (<10nm), point contact is a very efficient probe of electrical transport properties in extremely small sample volumes yet inaccessible with other techniques. We have observed the point-contact excitations in magnetic multilayers at room temperature and extended the capabilities of our point-contact technique to include the sensitivity to wavelengths of the current-induced spin waves. Recently MacDonald and coworkers have predicted that similar to ferromagnetic multilayers, the magnetic state of an antiferromagnetic (AFM) system can affect its transport properties and result in antiferromagnetic analogue of giant magnetoresistance (GMR) = AGMR; while high enough electrical current density can affect the magnetic state of the system via spin-transfer-torque effect. We show that a high density dc current injected from a point contact into an exchange-biased spin valve (EBSV) can systematically change the exchange bias, increasing or decreasing it depending on the current direction. This is the first evidence for current-induced effects on magnetic moments in antiferromagnetic (FeMn or IrMn) metals. We searched for AGMR in multilayers containing different combinations of AFM=FeMn and F=CoFe layers. At low currents, no magnetoresistance (MR) was observed in any samples suggesting that no AGMR is present in these samples. In samples containing F-layers, high current densities sometimes produced a small positive MR – largest resistance at high fields. For a given contact resistance, this MR was usually larger for thicker F-layers, and for a given current, it was usually larger for larger contact resistances (smaller contacts). We tentatively attribute this positive MR to suppression at high currents of spin accumulation induced around and within the F-layers. / text

We report on a search for short -period binary systems composed of pairs of evolved stars. The search is being carried out concurrently with a program to characterize the kinematical properties of two different samples of stars. Each sample has produced one close binary candidate for which further spectroscopic observations are planned. We also recapitulate the discovery of a close detached binary system composed of two cool DA white dwarfs, and we discuss the null results of Ha observations of the suspected white dwarf /brown dwarf system G 29-38.

In this study we present photometric predictions for C-type Asymptotic Giant Branch Stars (AGB) stars from Eriksson et al. (2014) for the James Webb Space Telescope (JWST) and the Wide-field Infrared Survey Explorer (WISE) instruments. The photometric predictions we have done are for JWST’s general purpose wide-band filters on NIRCam and MIRI covering wavelengths of 0.7 — 21 microns. AGB stars contribute substantially to the integrated light of intermediate-age stellar popula- tions and is a substantial source of the metals (especially carbon) in galaxies. Studies of AGB stars are (among other reasons) important for the understanding of the chemical evolution and dust cycle of galaxies. Since the JWST is scheduled for launch in 2018 it should be a high priority to prepare observing strategies. With these predictions we hope it will be possible to optimize observing strategies of AGB stars and maximize the science return of JWST. By testing our method on Whitelock et al. (2006) objects from the WISE catalog and comparing them with our photometric results based on Eriksson et al. (2014) we have been able to fit 20 objects with models. The photometric data set can be accessed at: http://www.astro.uu.se/AGBmodels/ / I den här studien har jag gjort fotometriska förutsägelser för asymptotis- ka jättegrensstjärnor (AGB-stjärnor) av C typ från Eriksson et al. (2014) modifierade för instrument ombord på James Webb Space Telescope (JWST) och Wide-field Infrared Survey Explorer (WISE). AGB-stjärnor bidrar kraftigt till det totala ljuset av stjärnor av intermediär ålder och är också en stor källa till metaller (speciellt kol) i galaxer. Studier av AGB stjärnor är viktiga av flera anledningar, däribland för att förstå den kemiska evolutionen och stoftcykler i galaxer. JWST är planerad att skjutas upp 2018 och fram till dess bör det vara en hög prioritet att förbereda observeringsstrategier. Med den fotometriska datan i den här studien hoppas vi att användare av JWST kommer kunna optimera sina observeringsstrategier av AGB-stjärnor och få ut så mycket som möjligt av sin obseravtionstid med teleskopet. Vi har testat metoden genom att titta på objekt från Whitelock et al. (2006) i WISE-katalogen och jämföra dem med de fotometriska resultaten baserade på modellerna från Eriksson et al. (2014). På detta sett har vi lyckats matcha 20 objekt med modeller. Den fotometriska datan går att ladda ner ifrån: http://www.astro.uu.se/AGBmodels/

The Giant Magellan Telescope (GMT) primary mirror consists of seven 8.4 m light-weight honeycomb mirrors that are being manufactured at the Richard F. Caris Mirror Lab (RFCML), University of Arizona. In order to manufacture the largest and most aspheric astronomical mirrors various high precision fabrication technologies have been developed, researched and implemented at the RFCML. The unique 8.4 m (in mirror diameter) capacity fabrication facilities are fully equipped with large optical generator (LOG), large polishing machine (LPM), stressed lap, rigid conformal lap (RC lap) and their process simulation/optimization intelligence called MATRIX. While the core capability and key manufacturing technologies have been well demonstrated by completing the first GMT off-axis segment, there have been significant hardware and software level improvements in order to improve and enhance the GMT primary mirror manufacturing efficiency. The new and improved manufacturing technology plays a key role to realize GMT, the next generation extremely large telescope enabling new science and discoveries, with high fabrication efficiency and confidence.

The Richard F. Caris Mirror Lab at the University of Arizona is responsible for production of the eight 8.4 m segments for the primary mirror of the Giant Magellan Telescope, including one spare off-axis segment. We report on the successful casting of Segment 4, the center segment. Prior to generating the optical surface of Segment 2, we carried out a major upgrade of our 8.4 m Large Optical Generator. The upgrade includes new hardware and software to improve accuracy, safety, reliability and ease of use. We are currently carrying out an upgrade of our 8.4 m polishing machine that includes improved orbital polishing capabilities. We added and modified several components of the optical tests during the manufacture of Segment 1, and we have continued to improve the systems in preparation for Segments 2-8. We completed two projects that were prior commitments before GMT Segment 2: casting and polishing the combined primary and tertiary mirrors for the LSST, and casting and generating a 6.5 m mirror for the Tokyo Atacama Observatory.