La récupération de l’énergie ambiante pour alimenter les systèmes électroniques devient de plus en plus une réalité grâce à la miniaturisation et la diminution importante de leur consommation. Dans ce but, nous avons développé une nouvelle famille de microgénérateurs thermoélectriques capables de produire quelques microwatts dès lors qu’une différence de température de quelques degrés est accessible. Ces microgénérateurs ont été réalisés avec des matériaux non polluants afin de tenir compte des contraintes environnementales qui apparaitront certainement dans un futur proche. Le principe de fonctionnement, classique, est basé sur l’effet Seebeck qui permet de convertir une différence de température en force électromotrice à l’aide d’une thermopile planaire réalisée en couches minces. Pour obtenir de bons résultats, il est nécessaire de concevoir puis de dimensionner précisément une structure tridimensionnelle permettant de transformer un flux de chaleur en une multitude de différences de température au niveau des thermocouples constituant la thermopile. La centrale de technologie silicium de l’IEMN nous a permis de fabriquer plusieurs familles des microgénérateurs correspondant à ces concepts en utilisant les procédés standards de micro-usinage du silicium. Bien sur, avant d’entreprendre une telle réalisation, un modèle analytique approché ainsi qu’un modèle numérique 3D ont été établis afin que le microgénérateur puisse délivrer le maximum de puissance électrique. Les dispositifs réalisés en centrale de technologie ont été caractérisés sur des bancs de mesure développés à cette fin et les résultats obtenus sont proches de ceux attendus. / Energy harvesting for the power supply of electronic systems becomes more and more a reality thanks to the miniaturization and the major reduction in their consumption. In this aim, we developed a new family of thermoelectric microgenerators able to produce a few microwatts when a temperature difference of a few degrees is accessible. These micro generators were carried out with non-polluting materials in order to take into account the environmental requirements which will certainly appear in a near future. The principle of operation is based on the Seebeck effect which makes it possible to convert a temperature difference into electromotive force using a planar thermopile fabricated with thin layers process. To obtain good performances it is necessary to design a three-dimensional structure to transform a heat flux into a multitude of temperature differences onto the thermocouples’ junctions of the thermopile. The silicon technology platform of IEMN enabled us to manufacture several families of micro generators corresponding to these concepts by using the standard processes of silicon micromachining. Of course, before undertaking such a realization, an approximate analytical model as well as a 3D numerical model was established in order to obtain the maximum of electrical power output that the microgenerator can deliver. The devices fabricated in our technology platform were characterized on specific set-up specially developed and experimental results are close to those expected.

The current misplaced focus on short-term climate policies is a product both of domestic political exigencies and badly flawed technical analyses. A prime example of the latter is a recent U.S. Department of Energy study, prepared by five national laboratories. The 5-Labs study assumes —- incorrectly —- that technical solutions are readily at hand. Worse, advocates of short-term emissions targets under the Framework Convention on Climate Change are using this study to justify the subsidy of existing energy technologies —- diverting resources from the effective long-term technology response that will be needed if the climate picture darkens. / Includes bibliographical references (p. 15-16). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/)

The TAR DNA-binding protein (TDP-43) is a heterogeneous nuclear ribonucleprotein that is involved in multiple stages of RNA processing. Mutations in the TDP-43 gene and mislocalization of TDP-43 protein have been implicated in a growing number of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Here, we show that TDP-43 negatively regulates innate immune gene expression in response to RNA virus sensing. Perturbation of TDP-43 protein expression leads to an increase in antiviral gene expression in a variety of human and mouse cells. Crosslinked RNA immunoprecipitation (CLIP) experiments revealed that TDP-43 binds to type I interferon (IFN) and interferon stimulated gene (ISGs) transcripts. Using massively parallel 3’ UTR reporter assays coupled with high throughput sequencing (MPRA-seq), we identified polyadenylation signal sequences in the 3' UTRs of innate immune genes to be specifically regulated by TDP-43. Surprisingly, IFN and ISG mRNA decay rates are faster in TDP-43-perturbed cells. Using a metabolic labeling approach to measure nascent transcript generation, we found that perturbation of TDP-43 expression leads to an increase in antiviral gene transcription rates. Additionally, RNA polymerase II (pol II) chromatin immunoprecipitation (ChIP) confirmed that there is greater pol II occupancy on innate immune genes when TDP-43 is depleted. Although TDP-43 perturbation has no effect on an isolated \(IFN\beta\) promoter reporter, we found that TDP-43 inhibits \(IFN\beta\) promoter activity when the \(IFN\beta\) 3' UTR sequence is inserted downstream of the \(IFN\beta\) promoter element, suggesting a novel mechanism of 3' UTR-mediated promoter cis-regulation.

Connexin 43 (Cx43) is a gap junction protein that enables direct cell-to-cell communication in many tissues of the body and stressful environments such as injury and hypoxia affect its expression. In addition to affecting Cx43 expression, hypoxia also retards wound-healing rates. Using rat corneal organ cultures, this thesis aims to define hypoxia's role in the expression and localization of Cx43 in wounded corneas. Tissue samples were stained immunohistochemically at three different time points after injury, 2.5 hours, 5 hours, and 18 hours. It was determined that under hypoxic conditions, Cx43 is more highly expressed than under normoxic conditions after injury. While Cx43 expression follows the same spatial pattern throughout the healing process in the cornea under both normoxic and hypoxic conditions, the pattern is delayed under hypoxic conditions. These results provide a possible reason why wound closure is delayed in low oxygen environments.

Magnesium alloys exhibit desirable properties for use in transportation technology. In particular, the low density and high specific strength of these alloys is of interest to the aerospace community. However, the concerns of flammability and susceptibility to corrosion have limited the use of magnesium alloys within the aircraft cabin. This work studies a magnesium alloy containing rare earth elements designed to increase resistance to ignition while lowering rate of corrosion. The microstructure of the alloy was documented using scanning electron microscopy. Specimens underwent salt spray testing and the corrosion products were examined using energy dispersive spectroscopy.

Transactive response DNA-binding protein of 43 kDa (TDP-43) is the major protein found within pathological inclusions in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD) (Neumann et al., 2006). TDP-43 is a ubiquitously expressed protein mainly involved in RNA metabolism. It is a member of the heterogeneous nuclear ribonucleoprotein (hnRNP) family and in its normal state is predominantly found in the nucleus. In its pathological state TDP-43 is cleaved, phosphorylated, ubiquitinated, and located in cytoplasmic or nuclear inclusions. Along with ALS and FTLD, TDP-43 is also observed in many other neurodegenerative diseases. Pathological TDP-43 inclusions have been previously reported in cases of Chronic Traumatic Encephalopathy (CTE) (King et al., 2010)(McKee et al., 2010)(Saing et al., 2012)(Hazrati et al., 2013), however no previous study has reported on the incidence and extent of TDP-43 cellular inclusions in a large cohort of autopsy cases diagnosed with CTE. This study finds that TDP-43 inclusions are a frequent feature of CTE, as TDP-43 inclusions are identified in 43% (20/47) of subjects in a CTE+, FTLD-, low-likelihood-of-AD cohort. Furthermore, this study finds that in CTE there is no consistent initial focus of TDP-43 pathology which spreads to neighboring regions as the disease progresses. Despite the lack of a clear progression of TDP-43 pathology, a TDP Staging Scheme for CTE which accurately reflects the extent and severity of TDP-43 pathology in not only the study cohort, but likely in all subjects without FTLD, was established. Four stages were identified: TDP Stage 0 showed no TDP-43 inclusions in the substantia nigra, dorsolateral frontal cortex, or dentate gyrus; TDP Stage 1 showed inclusions in either the substantia nigra or the dorsolateral frontal cortex; TDP Stage 2 showed inclusions either in the dentate gyrus or in both the substantia nigra and the dorsolateral frontal cortex; and TDP Stage 3 showed inclusions in the substantia nigra, dorsolateral frontal cortex, and dentate gyrus. Finally, a correlation was found between the presence of TDP-43 inclusions and the levels of activated microglia in the dorsolateral frontal cortex of CTE+ subjects. This finding aligns with the theory that the pathological changes of TDP-43 found in CTE are driven by the pro-inflammatory cytokines released by chronically activated microglia.

Les convertisseurs thermoélectriques conventionnels, exploitant l’effet Seebeck, sont constitués de matériaux massifs. Ce principe de conversion est fortement limité par les propriétés antagonistes de tout matériau massif à savoir la conductivité électrique et la conductivité thermique. De manière alternative, une technique de conversion directe basée sur l’émission thermoélectronique a été développée et révèle un rendement élevé à haute température. Le principe d’injection thermoélectronique est fortement limité par le travail de sortie, barrière énergétique que doit surmonter un électron pour être extrait de l’électrode. Un moyen de contourner cette difficulté est de fonctionnaliser la surface des électrodes avec un matériau à faible travail de sortie, typiquement 1eV. Le potassium et le césium ainsi que leurs oxydes ont été identifiés par la littérature comme matériaux candidats pour la fonctionnalisation de surface des électrodes réduisant considérablement leur travail de sortie, entre 0.4eV et 0.9eV. Leur utilisation a permis d’élargir le domaine de température pour lequel le convertisseur d’énergie thermoélectronique est efficace, s’approchant davantage du rendement limite de conversion de Carnot. / One main challenge associated with solid-state thermoelectric materials is to combine electron-crystal electrical conductivity and phonon-glass thermal properties that are difficult to conciliate. A markedly different principle of thermoelectric conversion is based on the micro thermionic generator that exploits electron injection and heat rejection across two electrodes, hot and cold, immersed in vacuum, a promising pathway to new electronic devices. To properly operate thermionic emission converters near room temperature, highly efficient emitting electrodes must be integrated. This naturally motivates the development and characterization of thin films that feature a very low work function lower than 1eV. Even better than alkalis like K and Cs, their oxides have been reported to produce work functions as low as 0.4 and 0.9eV respectively. The work function of the electrodes of the micro thermionic generator has been effectively reduced and the efficiency is much closer than the Carnot limit.

La thermoélectricité convertit fiablement l’énergie thermique en énergie électrique de manière directe, silencieusement et sans vibrations. Dans le contexte des réserves limitées en énergies fossiles, de l’effet de serre et de besoin énergétiques mondiaux en hausse, la récupération d’énergie thermique dissipée peut être une solution d'appoint. Un bon matériau thermoélectrique intègre des propriétés antagonistes : haute conductivité électrique (σ) et faible conductivité thermique (κ). La thermoélectricité conventionnelle utilise des matériaux nocifs, complexes, coûteux et incompatible avec des techniques de fabrication massive ex. CMOS rendant la thermoélectricité peu populaire sur le marché. En revanche, les matériaux CMOS, à savoir le silicium (Si), le germanium (Ge) et le silicium-germanium (SixGe1-x), sont simples, facilement approvisionnables et industriellement compatibles. Ils offrent une excellente conductivité électrique (σ) mais leur utilisation dans la thermoélectricité est limitée par une conductivité thermique (κ) trop élevée. Les progrès récents dans les domaines de micro et nano-fabrication permettent de réduire κ sans affecter σ. Cela permet de fabriquer des générateurs thermoélectriques (TEG) compatibles CMOS, tout en gardant une production massive réduisant le coût. Les simulations présentées placent Si, Ge et SixGe1-x dans une position compétitive par rapport aux matériaux thermoélectriques conventionnels, à condition de réduire substantiellement κ. Une réduction de la conductivité thermique d'un facteur 3 a été expérimentalement démontrée dans des membranes de Si intégrées au sein d'une plateforme micrométrique conçue, fabriquée et caractérisée dans le cadre de cette thèse. / Thermoelectricity converts heat into electric energy in a silent, direct, vibrationless and reliable way. In light of limited reserves in fossil fuels, increasing greenhouse effect and constantly rising worldwide demand in energy, recovering heat losses can be a solution. Good thermoelectric material integrates antagonistic properties: high crystal-like electrical (σ) and low glass-like thermal (κ) conductivities. Conventional thermoelectricity uses materials that are harmful, complex, expensive and incompatible with mainstream fabrication technologies e.g. CMOS making thermoelectricity unpopular. In constrast, CMOS materials, namely Silicon (Si), Germanium (Ge) and Silicon-Germanium (SixGe1-x), are simple, easy-to-get, cheap and industrially compatible offering a high electrical conductivity (σ). However, their usage in thermoelectricity is hindered due to a prohibitive thermal conductivity (κ). Recent progress in nano- and micro-fabrication opened new possibilities to reduce κ with minor impact on σ. This opportunity enables fabrication of CMOS compatible ThermoElectric Generators (TEGs) enabling massive production and cost reduction which can significantly popularize TEGs on the market. Our modelling approach place Si, Ge and SixGe1-x in a competitive position compared with conventional thermoelectrics providing that their high bulk κ can be substantially reduced. Within the framework of this thesis, a 3-fold size induced κ reduction in Si is experimentally obtained based on a micrometer measurement platform that has been designed, fabricated and characterized in this work.

La thermoélectricité rencontre un intérêt croissant ces dernières années comme source d'énergie alternative pour l’alimentation de dispositifs micro- et nano- électroniques. Les matériaux thermoélectriques transforment par effet Seebeck une différence de température en énergie électrique utile. Dans les dispositifs thermoélectriques, l’énergie perdue en général sous forme de chaleur résiduelle peut ainsi être recyclée en utilisant les gradients de température existants. L'efficacité thermoélectrique dépend des propriétés électroniques du matériau et de sa conductivité thermique κ. Le silicium présente une très bonne conductivité électrique et un coefficient Seebeck prometteur, mais sa conductivité thermique phononique limite fortement son potentiel pour des applications thermoélectriques, du moins sous forme de matériau massif. Par contre, la nanostructuration du silicium en couches minces, et a fortiori la fabrication de cristaux phononiques permet de réduire fortement la conductivité thermique. Dans ce travail, des simulations de dynamique moléculaire sont réalisées pour confirmer cette stratégie et permettre la définition d'un design optimal de membranes perforées. De plus, le travail expérimental montre différentes méthodologies de fabrication de membranes phononiques de silicium intégrées dans une plate-forme de métrologie. Plusieurs techniques de caractérisation (Electrothermique, Raman et Microscopie à sonde thermique) ont ensuite été utilisées pour déterminer la conductivité thermique des membranes. Une réduction considérable de κ est obtenue pour le silicium, permettant d’envisager l’intégration de ces membranes dans un convertisseur thermoélectrique. / In the last twenty years, the continuous seek for alternative energy sources to power micro- and nano-electronic devices has marked the rise of interest toward thermoelectricity. Thermoelectric materials can turn directly, by Seebeck effect, the temperature difference into useful electric power. The energy lost as waste heat can be re-used as a power source. It is known that, to improve thermoelectric efficiency, an important role is played by material’s electronic properties and its thermal conductivity. Silicon exhibits very good electrical conductivity and Seebeck parameter, but its lattice thermal conductivity represents the bigger obstacle for thermoelectric applications, preventing its direct integration as bulk material. It has been demonstrated that nanostructuring silicon in thin films enables the reduction of thermal conductivity down to one order of magnitude. Furthermore, a supplementary decrease of thermal conductivity is possible by periodical patterning of the silicon thin film in a photonic-like way, creating Phononic Crystals (PnCs). In our work molecular dynamics simulations are performed to confirm the trend envisaged and allow the definition of an optimal design for the patterned membranes. Moreover, our experimental work lists different fabrication methodologies of silicon phononic engineered membranes integrate into a metrology platform. Several characterization techniques (Electrothermal , Raman thermometry, Scanning Thermal Microscopy) are used to determine the membranes thermal conductivity. A considerable reduction of κ is obtained for silicon, paving the way for a prospective integration of those membranes into a thermoelectric converter.

Pt. 1. Electromechanical impedance matrix--Pt. 2. Electrical driving point impedance and admittance. / by W. Roth. / "July 3, 1947." / Includes bibliographical references. / Army Signal Corps Contract W36-039 sc-32037