This study deals with crystal orientation effect along with the effects of microstructure on the pile-ups which affect the nanoindentation measurements. Two metal classes, face centered cubic (FCC) and body centered cubic (BCC, are dealt with in the present study. The objective of this study was to find out the degree of inaccuracy induced in nanoindentation measurements by the inherent pile-ups and sink-ins. Also, it was the intention to find out how the formation of pile-ups is dependant upon the crystal structure and orientation of the plane of indentation. Nanoindentation, Nanovision, scanning electron microscopy, electron dispersive spectroscopy and electron backscattered diffraction techniques were used to determine the sample composition and crystal orientation. Surface topographical features like indentation pile-ups and sink-ins were measured and the effect of crystal orientation on them was studied. The results show that pile-up formation is not a random phenomenon, but is quite characteristic of the material. It depends on the type of stress imposed by a specific indenter, the depth of penetration, the microstructure and orientation of the plane of indentation. Pile-ups are formed along specific directions on a plane and this formation as well as the pile-up height and the contact radii with the indenter is dependant on the aforesaid parameters. These pile-ups affect the mechanical properties like elastic modulus and hardness measurements which are pivotal variables for specific applications in micro and nano scale devices.

This thesis deals with the use of non-metallic highly thermally conductive materials, more concrete-ly special plastic materials, enriched with highly thermally conductive additives, for the purpose of passive cooling of a given heat source. The thesis compares the effectivity of these heat sinks with the classically used materials, specifically aluminium. The thesis is divided into two main sections, theoretical and practical. The theoretical part deals with a constantly growing need of LED (Light Emitting Diode) chips cooling in automotive head-lamps, where the new materials could be put into effect, analyses possible replacement of classic aluminium heat sinks with different materials with a significantly lower thermal conductivity and introduces problems of such materials. The practical part applies the problematic described in the theoretical one on the actually produced heat sinks, which are compared among themselves, with regard to their method of production, as well as with aluminium counterpart in different conditions. Furthermore, the problematic of de-signing a heat sink made from material which is characteristic for its highly anisotropic thermal con-ductivity is dealt with. The end of the thesis shows the importance of heat dissipation via radiation, which can have a great significance in case of plastic heat sinks and in a specific applications.

The existence of a coordinate system can often improve the routing in a wireless sensor network. While most coordinate systems correspond to the geometrical or geographical coordinates, in recent years researchers had proposed the use of virtual coordinates. Virtual coordinates depend only on the topology of the network as defined by the connectivity of the nodes, without requiring geographical information. The work in this thesis extends the use of virtual coordinates to scenarios where the wireless sensor network has a mobile sink. One reason to use a mobile sink is to distribute the energy consumption more evenly among the sensor nodes and thus extend the life-time of the network. We developed two algorithms, MS-DVCR and CU-DVCR which perform routing towards a mobile sink using virtual coordinates. In contrast to the baseline virtual coordinate routing MS-DVCR limits routing updates triggered by the sink movement to a local area around the sink. In contrast, CU-DVCR limits the route updates to a circular area on the boundary of the local area. We describe the design justification and the implementation of these algorithms. Using a set of experimental studies, we show that MS-DVCR and CU-DVCR achieve a lower energy consumption compared to the baseline virtual coordinate routing without any noticeable impact on routing performance. In addition, CU-DVCR provides a lower energy consumption than MS-DVCR for the case of a fast moving sink.

No description available.

Heat pipes are passive heat transfer devices in which a working fluid is sealed inside a metal enclosure. Properly designed wick structures on the inner surface of the heat pipe are critical as the wick aids in the return of the condensed liquid from the cold end back to the hot end where the vaporization-condensation cycle begins again. Additive manufacturing techniques allow for manufacturing complex parts that are typically not feasible with conventional manufacturing methods. Thus, additive manufacturing opens the possibility to develop high performance heat pipes with complex shapes. In this study, an additive manufacturing technique called Binder Jetting is used to fabricate a fully operational compact (78 mm x 48 mm x 8 mm) flat plate heat pipe. Rectangular grooves with converging cross section along the length act as the wicking structure. A converging cross section was designed to enhance the capillary force and to demonstrate the capability of additive manufacturing to manufacture complex shapes. This work describes the challenges associated with the development of heat pipes using additive manufacturing such as de-powdering and sintering. Multiple de-powdering holes and internal support pillars to improve the structural strength of the heat pipe were provided in order to overcome the manufacturing constraints. The heat pipe was experimentally characterized for thermal performance with acetone as the working fluid for two different power inputs. The heat pipe operated successfully with a 25% increase in effective thermal conductivity when compared to solid copper. / Master of Science / The number of transistors in electronic packages has been on an increasing trend in recent decades. Simultaneously there has been a push to package electronics into smaller regions. This increase in transistor density has resulted in thermal management changes of increased heat flux and localization of hotspots. Heat pipes are being used to overcome these challenges. Heat pipes are passive heat transfer devices in which a working fluid is sealed inside a metal enclosure. The fluid is vaporized at one end and condensed at the other end in order to efficiently move heat through the pipe by taking advantage of the latent heats of vaporization and condensation of the fluid. Properly designed wick structures on the inner surface of the heat pipe are used to move the condensed fluid from the cold end back to the hot end, and the wick is a critical component in a heat pipe. Additive manufacturing techniques offer the opportunity to manufacture complex parts that are typically not feasible with conventional manufacturing methods. Thus, additive manufacturing opens the possibility to develop high performance heat pipes with complex shapes as well as the ability to integrate heat exchangers with the heat source. In this study, an additive manufacturing technique called Binder Jetting is used to fabricate a fully operational compact (78 mm x 48 mm x 8 mm) flat plate heat pipe. Rectangular grooves with converging cross section along the length act as the wicking structure. This work describes the challenges associated with the development of heat pipes using additive manufacturing such as depowdering and sintering. The heat pipe was experimentally characterized for thermal performance with acetone as the working fluid for two different power inputs. The heat pipe was found to operate successfully with a 25% increase in effective thermal conductivity when compared with solid copper.

In the present paper, an attempt is made to obtain the potential distribution in the case of two such charges, a source-sink combination, located on the axis of a bore hole drilled through an infinite, homogeneous medium.

Yes / This article presents the homotopy perturbation method (HPM) employed to investigate the effects of inclination on the thermal behavior of a porous fin heat sink. The study aims to review the thermal characterization of heat sink with the inclined porous fin of rectangular geometry. The study establishes that heat sink of an inclined porous fin shows a higher thermal performance compared to a heat sink of equal dimension with a vertical porous fin. In addition, the study also shows that the performance of inclined or tilted fin increases with decrease in length–thickness aspect ratio. The study further reveals that increase in the internal heat generation variable decreases the fin temperature gradient, which invariably decreases the heat transfer of the fin. The obtained results using HPM highlights the accuracy of the present method for the analysis of nonlinear heat transfer problems, as it agrees well with the established results of Runge–Kutta. / Supported in part by the Tertiary Education Trust Fund of Federal Government of Nigeria, and the European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016SECRET-722424.

Le travail présenté dans cette thèse est dédié à l’étude d’un absorbeur bistable continu basé sur le principe du "Nonlinear Energy Sink" (NES) et son utilisation pour l’atténuation des vibrations d’un système mécanique à plusieurs degrés de liberté sous excitation acoustique. Le modèle analytique du comportement linéaire de l’absorbeur ainsi que le modèle numérique complet ont été présentés, analysés et validés par des séries d’expériences. Le complexité du transfert énergétique ciblé ("Targeted Energy Transfer" ou TET) entre l'absorbeur et le système primaire à contrôler n’a pas permis une description analytique simple. Nous avons donc choisi de concentrer cette étude sur l’exploration expérimentale et numérique de l’absorbeur couplé à des systèmes mécaniques sous excitations harmonique et aléatoire ainsi que sur l’identification des mécanismes de transfert d’énergie. Le système couplé a montré une dynamique très riche du fait de différents régimes de TET qui ont été décrits dans la littérature pour d’autres types de NES. Ce projet a été financé par Saint-Gobain. L’absorbeur a été adapté pour l’application prévue par la direction industrielle de la thèse: contrôle des vibrations de la double paroi sous excitation acoustique afin d’améliorer l’isolation acoustique fournie par le système.Les connaissances qualitatives sur la dynamique de l’absorbeur obtenues à partir des résultats expérimentaux et numériques, ainsi que l’analogie avec les autres types de NES, ont permis la création d’un absorbeur qui répond à la problématique posée. Les moyens pour l’optimisation et le développement de l’absorbeur ont été identifiés et les simulations préliminaires ont été fournies. / The work presented in this thesis is dedicated to the study of a continuous bistable absorber based on the principle of Nonlinear Energy Sink (NES) and its use for the vibration mitigation of a many-degree-offreedom mechanical systems under acoustic excitation. The analytical model of the linear behavior of the absorber and its complete numerical model were presented, analyzed and validated by series of experiments. The complexity of the Targeted Energy Transfer (TET) between the absorber and the primary system did not allow a simple analytical description. We have chosen to concentrate this study on the experimental and numerical exploration of the absorber coupled to mechanical systems under harmonic and random excitations, as well as on the identification of the mechanisms of energy transfer. The coupled system have shown very rich dynamics as it possessed different regimes of TET, which were earlier described in literature for other types of NES. This project was funded by Saint-Gobain. The absorber was adapted for the application foreseen by the industrial supervisors of the PhD: the vibration control of partitioning double walls under acoustic excitation so that to improve the acoustic isolation provided by the system. The qualitative knowledge on the absorber dynamics obtained from the experimental and numerical results, as well as the analogy with the other types of NES, permitted the creation of an absorber which corresponds to the problematic. The ways for the further optimization and development of the absorber were identified and preliminary simulations were provided.

Ce mémoire est consacré à l'étude d'un absorbeur dynamique non linéaire hybride passif-actif (ADNLH) pour la réduction du bruit en basses-fréquences. La partie passive de l'ADNLH est une membrane en latex à déformée non linéaire dont la face avant est couplée au champ acoustique que l'on souhaite réduire. Cette membrane se comporte comme un oscillateur non linéaire et fait partie de la famille des absorbeurs non linéaires connus sous le nom de Nonlinear Energy Sink (NES). La face arrière de la membrane est encoffrée et un dispositif de contrôle actif est inclus dans le volume d'encoffrement. Ce dispositif est conçu pour modifier la raideur linéaire et l'amortissement de la membrane. Des précédents travaux ont été réalisés uniquement sur la partie passive (la membrane) et ont permis de valider le principe de pompage énergétique dans le domaine acoustique. Cependant la membrane seule possède des limitations (notamment le seuil de déclenchement du pompage) qui restreignent les applications possibles. L'objectif de l'ADNLH est d'améliorer les performances du pompage énergétique acoustique en modifiant les propriétés linéaires de la membrane grâce à la boucle d'asservissement. Dans un premier temps une étude théorique et expérimentale est réalisée sur l'ADNLH. L'ADNLH est ensuite couplé à un tube résonant avec une excitation sinusoïdale et en bruit blanc. Il permet bien d'écrêter le premier pic de résonance du tube avec de meilleures performances que la version passive. Enfin l'ADNLH est installé dans une salle peu amortie. Il permet d'atténuer la première résonance acoustique de la salle dans le cas d'une excitation sinusoïdale. / This thesis is devoted to the study of a hybrid passive-active nonlinear dynamic absorber for the reduction of noise in low frequencies. The passive part of the ADNLH is a membrane in latex with a nonlinear deformation and its front face coupled to the acoustic field to be reduced. This membrane is acting as a nonlinear oscillator and is part of the family of absorbers known as Nonlinear Sink Energy (NES). The rear face is enclosed and a active device is included inside this enclosure. This device is designed in order to modify the linear stiffness and the damping of the membrane. Previous work has been done only on the passive part (the membrane) and has validated the principle of energy pumping for Acoustics. However the membrane has some limitations (like the threshold of energy pumping) that restrain the practical applications. The goal of the ADNLH is to improve the performance of the energy pumping by modifying the linear properties of the membrane with the help of the active device. In a first time an experimental and theoretical study of the ADNLH is done. Then the ADNLH is coupled to a tube of air thanks to an academic assembly under a sinusoidal excitation or broadband. It allows to cut the top off the first acoustic resonance of the tube with better performances than the membrane alone. At last the ADNLH is set inside a weakly damped room. The ADNLH allows to attenuate the first resonance of the room in the case of a sinusoidal excitation. One also shows that the control of the damping of the membrane is the key parameter for the performance of the ADNLH.

<p>Vissa utländska forskare som kom till Sverige kunde från och med 1984 erbjudas skattelättnader genom en speciell lag om beskattning av utländska forskare. Syftet med lagstiftningen var att locka kompetent personal med spetskunskaper till anställningar i Sverige. Under slutet av 1990-talet uppkom frågan om det behövdes en reformering av lagstiftningen eftersom detta skett i andra nordiska länder. De reformerade expertbeskattningsreglerna infördes 2001. Lagstiftningen erbjuder sedan dess förutom forskare även experter, specialister, personer med företagsledande uppgifter och andra nyckelpersoner en möjlighet att få del av skattelättnader. De som uppfyller lagens krav kan undanta 25 procent av lön, arvode eller liknande ersättning från beskattning. Vidare beskattas ej ersättningar för utgifter som den utländske personen har haft för flyttning till eller från Sverige, två resor per år per familjemedlem mellan hemlandet och Sverige samt avgifter för barns skolgång i grundskola och gymnasieskola eller liknande. I förarbetena ges ingen utförlig beskrivning för exakt vilka personalkategorier eller yrken som ska ha möjligheten att ta del av skattelättnaderna i egenskap av expert. En individuell bedömning får göras i varje enskilt fall, men kompetensnivån hos den sökande ska vara hög och det ska vara svårt att rekrytera någon med liknande kunskaper inom Sverige för att skattelättnaderna ska kunna komma ifråga. Det anges i propositionen att de tilltänkta personerna ska vara verksamma inom tekniskt avancerade och kunskapsintensiva verksamheter där Sverige har ett intresse av att kunna konkurrera om internationellarbetskraft.I praxis har det funnits en tendens att fokus vid bedömningen av vem som kan ses som expert hamnar på just det tekniska området även om andra branscher inte utesluts av ordalydelsen i förarbetena och inte heller i lagtextens utformning. Det är inom det tekniska området som de flesta beviljade expertbeskattningsansökningar har förekommit. Bedömningen av vem som kan omfattas av expertbegreppet har således varit sträng. Det finns dock undantag. Kammarrätten beviljade under 2008 en chefsdirigent skattelättnader eftersom denne kunde anses vara expert i en kunskapsintensiv bransch. Det går således inte att fastslå generellt vem som omfattas av expertbegreppet i lagens mening och inte heller generellt bestämma inom vilka yrken eller personalkategorier experter kan förekomma. Det verkar som att expertbegreppet genom den senaste tidens utveckling i praxis i framtiden kan få en ny vidare innebörd där andra yrkeskategorier än de mer klassiska inom industrin och högteknologiska branscher kan komma att omfattas av expertbegreppet.</p>