Dark Matter freezeout in modified cosmological scenarios

We study the effects of modifying the expansions history of the Universe on Dark Matter freezeout. We derived a modified Boltzmann equation for freeze-out for an arbitrary energy density in the early Universe and provide an analytic approach using some approximations. We then look at the required thermally averaged cross sections needed to obtain the correct relic density for the specific case where the energy density consists of radiation plus one extra component which cools faster. We compare our analytic approximation to a numerical solutions. We find that it gives reasonable results for most of the parameter space explored, being at most a factor of order one away from the measured value. We find that if the new contribution to the energy density is comparable to the radiation density, then a much smaller cross section for Dark Matter annihilation is required. This would lead to weak scale Dark Matter being much more difficult to detect and opens up the possibility that much heavier Dark Matter could undergo freezeout without violating perturbative unitarity.Comment: 9 pages, 6 figures. In this version, we added some references and fixed some typo

Multi-component dark matter from a hidden gauged SU(3)

We study Dark Matter (DM) phenomenology with multiple DM species consisting of both scalar and vector DM particles. More specifically, we study the Hidden Gauged SU(3) model of Arcadi {\it et al}. Before proceeding to the Hidden Gauged SU(3) model, we study the relic abundances of simplified multi-species DM scenarios to gain some insights when multiple species and interactions are included. In the Hidden Gauged SU(3) model, because of the large parameter space, we restrict ourselves to three representative benchmark points, each with multiple DM species. The relic densities for the benchmark points were found using a program developed to solve the coupled Boltzmann equations for an arbitrary number of interacting DM species with two particles in the final state. For each case, we varied the mass of the DM particles and then found the value of the dark SU(3) gauge coupling that gives the correct relic density. We found that in some regions of the parameter space, the DM would be difficult to observe in direct detection experiments while easier to observe in indirect detection experiments and vice versa, so that complementary measurements could help pinpoint the details of the Hidden Gauged SU(3) model. Important to this, is that even for moderate changes in input parameter values, the relative relic density of each species can change significantly resulting in large changes in the observability of multi-species DM by direct or indirect detection.Comment: 21 pages, 5 figures, 3 tables. We made major revisions to section 3 by changing the points considered and the discussion about those points; also fixed some typo

Réseaux de Bragg verticaux accordables en silicium pour le développement de microsystèmes optiques appliqués

Ce mémoire porte sur la conception de réseaux de Bragg verticaux accordables en silicium pour le développement de microsystèmes optiques. Les travaux de recherche présentés ont été effectués dans le cadre de deux projets menés par le Laboratoire de Microphotonique en collaboration respectivement avec l’Office Fédérale de Métrologie (METAS) suisse et le Laboratoire d’Optique Diagnostique et d’Imagerie (LODI). L’objectif de ces collaborations est de concevoir des microsystèmes optiques appliqués, c’est-à-dire répondant à des besoins et des problématiques précises, à partir de l’expertise du Laboratoire de Microphotonique dans le domaine des réseaux de Bragg verticaux en silicium. La collaboration avec le METAS a pour objectif d’étudier le potentiel des réseaux de Bragg verticaux accordables en silicium dans le développement de microbalances de haute précision. Plus précisément, des masses situées entre 10 mg et 10 g sont ciblées. La dimension d’un tel échantillon peut facilement atteindre l’ordre du cm3 ce qui s’avère généralement problématique pour les microsystèmes. La microbalance optique proposée est basée sur une cavité Fabry-Pérot accordable. Lorsqu’une force externe est appliquée sur le dispositif, la longueur de la cavité est modifiée et il en résulte un décalage spectral au niveau de sa résonance optique. La force appliquée peut être déterminée à partir de l’amplitude du décalage spectral observé. La microbalance a été fabriquée et caractérisée avec succès. Des sensibilités expérimentales allant de 0.51 nm/mN à 67.69 nm/mN et des résolutions absolues allant de 0.15 μN à 19.61 μN sont rapportées. La résolution relative maximale du senseur est inférieure à 100 ppm. La microbalance optique présentée est basée sur un design dans le plan. Ce type de design simplifie le procédé de fabrication et facilite l’alignement optique. L’épaisseur du substrat limite cependant la taille de la zone de charge. Afin de s’affranchir de cette limitation, un système permettant de transférer dans le plan une force ou un déplacement hors-plan a été développé. Ce système de translation est basé sur un condensateur formée par deux peignes inter-digités possédant chacun un seul degré de liberté, l’un hors-plan et l’autre dans le plan. Tout déplacement vertical au niveau du premier peigne induit un déplacement horizontal proportionnel au niveau du second peigne. Comme preuve de concept, le système de translation a été implémenté dans le design d’une seconde génération de microbalances. Des dispositifs possédant une zone de charge de 1 mm2 ont été fabriqués et caractérisés avec succès. Les résultats----------Abstracts This master thesis presents the development of applied optical microsystems based on tunable vertical silicon Bragg gratings. This work was realized within the frame of two collaborations initiated by the Microphotonics Laboratory respectively with the Federal Office of Metrology (METAS) and the Laboratory of Optical Diagnosis and Imagery (LODI). The main objective of these collaborations is to use the expertise of the Microphotonics Laboratory in tunable vertical silicon Bragg gratings in order to develop optical microsystems which address specific needs and technical issues. The objective of the collaboration with the METAS is to study the potential of tunable vertical silicon Bragg gratings in the development of high precision microbalances for macro samples. More precisely, masses ranging from 10 mg to 10 g are targeted. The dimension of such samples can easily go up to a few cm3. The optical microbalance we propose is based on a tunable Fabry-Perot cavity. When an external force is applied on the device, the length of the cavity is modified which results in a spectral shift of its optical resonance. The applied force can then be determined from the amplitude of the spectral shift observed. The microbalance was successfully fabricated and characterized. Sensibilities ranging from 0.51 nm/mN to 67.69 nm/mN and absolute resolutions ranging from 0.15 μN to 19.61 μN are reported. The maximum relative resolution of the sensor is below 100 ppm. The optical microbalance we developed is based on an in-plane design. This type of design simplifies the fabrication process and eases the optical alignment. However, the thickness of the substrate limits the area of the load patch. In order to free oneself of this limitation, a vertical to horizontal motion translation system was developed. This translation system is based on a capacitor formed by two interdigitated combs exhibiting perpendicular degrees of freedom. The out-of-plane displacement of the first comb induces a proportional in-plane displacement of the second comb. As a proof of concept, the translations system is implemented in the design of a second generation of optical microbalances. Devices exhibiting a 1 mm2 load patch were successfully fabricated and characterized. The experimental results validate the working principle of the translation system. A vertical 1.7 μm motion was transferred into a 0.26 μm horizontal displacement

Miniaturized Dielectric Elastomer Actuator for Mechanical Stimulation of Monolayer Cell Cultures

This thesis advances the field of dielectric elastomer actuators (DEAs) through the development of device designs, fabrication processes, strain characterization technique and modelling tool. It provides the first demonstration that DEAs can be interfaced with living cells, opening the door to real-world applications in mechanobiology, an important step for the development of this emerging soft-actuator technology. It also provides a practical approach towards low voltage DEAs, demonstrating a fully-printed actuator that works below 300 V, a range compatible with commercially available CMOS circuitry, hence enabling a variety of new applications for DEA-based technologies. The mechanisms by which cells can sense and react to their mechanical environment are still partly unknown, and advances in this field will contribute to better diagnosis and treatment of serious diseases like cancer. Research heavily relies on in vitro models, and there is therefore great interests in systems capable of applying precise mechanical strain on cell cultures. This thesis overcomes the many challenges of interfacing DEAs with living cells, and presents a biocompatible device which can sustain standard cell culture protocols like sterilization, incubation, and immersion in growth medium. The device can apply from -10% to 35% uniaxial strain on a small cell population (~100 cells), located in a transparent area (0.5mm x 1.5mm) of a larger biocompatible membrane. It can be mounted on an inverted microscope, where its novel design enables real-time high-resolution optical imaging of cells during stretching. With strain rates in the excess of 700 %/s, the in vivo environment can be reproduced with unprecedented accuracy. As a demonstration of the technology, in collaboration with the Vascular and Tumor Biology Laboratory at UNIL in Switzerland, a population of lymphatic endothelial cells (LECs) was cycled from 0% to 10% strain at 1 Hz for 24 h. The results show stretch-induced alignment of cells perpendicular to strain, and confirm that the device fringing electric field has no effect on LECs morphology. This is the first demonstration that DEAs can be interfaced with living cells, and the first time they are used to observe cell mechanosensitivity. The driving voltage of DEAs is typically in the kV range, which limits their possible applications. One approach to reduce the actuation voltage is to decrease the membrane thickness, which is typically in the 20-100 microns range, as reliable fabrication becomes challenging below this thickness. This thesis presents a pad-printed 3 microns thick DEA, and demonstrates that decreasing the membrane thickness to only a few microns significantly reduces the driving voltage, while maintaining good actuation performance. A radial strain of 7.5% was achieved at only 245 V, which corresponds to a strain-to-voltage-squared ratio of 125%/kV^2, the highest reported value to date. This thesis also investigates the electrodes stiffening impact, often overlooked in the design and development DEAs. It presents an analytical model which accounts for the electrodes stiffness, and presents a strain-mapping algorithm to compares the strain uniformity of 3 microns- and 30 microns-thick DEAs. The simulation results and the strain mapping measurements identify the electrodes as an important parameter that should not be neglected in the design and optimization of thin-DEAs

La dépense improductive dans l'art actuel de Michel de Broin, Thomas Hirschhorn et Santiago Sierra : une approche critique

Ce mémoire se base sur l'économie générale développée par Georges Bataille (La notion de dépense, 1933; La part maudite, 1949) afin d'approfondir la notion de dépense improductive dans l'art actuel. L'objectif principal est d'y questionner la possibilité d'une dépense qui soit réalisée en pure perte, alors que Bataille associe une fonction de liant social aux dépenses anti-utilitaires. À partir du constat qu'un pouvoir émane de la perte, il est question d'identifier si la mise en place de processus improductifs au sein de pratiques artistiques micropolitiques produit une critique de la société de croissance productiviste et de l'utilitarisme qui la sous-tend. En regard de différents phénomènes – notamment la consommation insubordonnée, l'expérience précaire et la transgression des valeurs morales – par lesquels semble se répercuter la dépense comme mécanisme de résistance en art actuel, l'analyse s'établit autour des pratiques artistiques de Michel de Broin, Thomas Hirschhorn et Santiago Sierra. Cette analyse comparative révèle un paradoxe au cœur de la pensée bataillenne : non seulement la dépense improductive ne se réalise jamais en pure perte puisqu'elle produit du sens et se signale dans la différence, mais elle semble de plus participer à la création de valeurs et à l'établissement de nouvelles autorités. Ce mémoire tente de remettre en question l'orientation critique de la notion de dépense en lien avec les transformations récentes du capitalisme postindustriel (ou post-Fordiste). Il se conclut sur le constat que la dépense improductive agit comme force motrice du système économique actuel. Dans ce contexte, l'art de la dépense se voit réduit à une forme de mimétisme où s'accentuent les risques d'une assimilation à l'ordre dominant.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : dépense improductive, anti-utilitarisme, capitalisme, perte, art actuel, art critique, Georges Bataille, Michel de Broin, Thomas Hirschhorn, Santiago Sierr

Quantum error correction benchmarks for continuous weak parity measurements

We present an experimental procedure to determine the usefulness of a measurement scheme for quantum error correction (QEC). A QEC scheme typically requires the ability to prepare entangled states, to carry out multi-qubit measurements, and to perform certain recovery operations conditioned on measurement outcomes. As a consequence, the experimental benchmark of a QEC scheme is a tall order because it requires the conjuncture of many elementary components. Our scheme opens the path to experimental benchmarks of individual components of QEC. Our numerical simulations show that certain parity measurements realized in circuit quantum electrodynamics are on the verge of being useful for QEC

Pad printing 1-10 mm thick elastomer membranes for DEAs

We present a technique for stamping patterned silicone elastomer membranes with thicknesses ranging from 1 to 10 um. Silicone elastomers are becoming the material of choice for dielectric elastomer transducers. The variety of readily available materials, their versatility in terms of film thicknesses and their excellent mechanical properties have made them a very appealing alternative to the widely used acrylic elastomer VHB from 3M. Silicone films are typically blade casted or spin coated, two complementary techniques allowing for large-area (> 10 cm x 10 cm) and ultra-thin (< 1 µm) membranes respectively. By comparison, membranes up to 5 cm x 5 cm in area and with thicknesses ranging from 1 to 10 µm can be fabricated with a stamping technique. Unlike blade casting and spin coating this technique can be used to directly pattern (in-plane) the membrane to any desired shape, thus providing great design flexibility. We demonstrated in prior work that stretchable electrodes can also be patterned by stamping. Combined with the ability to pattern silicone membranes, it enables the stamping of functional structures such as dielectric elastomer actuators (DEAs) with high level of integration (vertical integration). In this contribution we detail our fabrication process and highlight the important parameters. As a proof of concept we characterized a stamped DEA, as well as a stamped vertical electrical connection for layers interconnection

Fully printed 3 microns thick dielectric elastomer actuator

In this work we present a new fabrication technique to print thin dielectric elastomer actuators (DEAs), reducing the driving voltage below 300 V while keeping good actuation performance. With operation voltages in the kV-range, standard DEAs are limited in terms of potential applications. Using thinner membranes is one of the few existing methods to achieve lower operation voltages. Typical DEAs have membranes in the 20-100 um range, values below which membrane fabrication becomes challenging and the membrane quality and uniformity degrade. Using pad printing we produced thin silicone elastomer membranes, on which we pad-printed compliant electrodes. We then fabricated DEAs by assembling two membranes back to back. We obtain an actuation strain of 7.5% at only 245 V on a 3 um thick DEA. In order to investigate the stiffening impact of the electrodes we developed a simple DEA model that includes their mechanical properties. We also developed a strain-mapping algorithm based on optical correlation. The simulation results and the strain-mapping measurements confirm that the stiffening impact of the electrodes increases for thinner membranes. Electrodes are an important element that cannot be neglected in the design and optimization of ultra-thin DEAs