The present work consists of two parts: experimental study of natural ventilation in a model room and the flow associated with a source-sink pair. The first part describes the natural ventilation of a model room of size 300mmx 300mm x 300mm with water as the fluid medium. It is insulated by air gaps on the four sides and at the top. A constant heat flux of 3148W/m2 has been maintained on the bottom surface of the room. This ‘room’ is surrounded by a large exterior tank containing water. The changes in temperature of the bottom, the interior and the exterior have been measured using T-type thermocouples. There are three openings each on two opposing sides of the model room. For any experiment, only one opening on each side is kept open. Fluid enters or leaves these openings and the flow is driven entirely by buoyancy forces. Three configurations have been studied: (1) The bottom opening at the inlet side and the top opening at the outlet side are open, (2) the bottom opening at the inlet side and the middle opening at the outlet side are open, and (3) the middle opening at the inlet side and the top opening at the outlet side are open. Shadowgraph technique is used for visualization. The buoyancy causes flow to enter through the bottom opening and leave through the top opening. At the openings, buoyant jets are observed and which have higher or lower relative densities. The buoyant jet at the inlet interacts with the plumes on the heated bottom plate. From these visualizations, it appears that free convection at bottom plate will be affected by the buoyant jets at the openings and the degree to which it is affected depends on the position and size of openings and distance between inlet and outlet. The flow rate due to the natural ventilation depends on the bottom surface heat flux and the height difference between the openings. The temperatures of the floor, the interior and the exterior are calculated using a simple mathematical model (Hunt and Linden [1999]). The mathematical model assumes well mixed conditions within the room and accounts for losses at the openings. The values of temperatures obtained in the experiments are reasonably well predicted by the mathematical model. The second part of the work is concerned with the interaction of a source -sink pair. The source consists of fluid issuing out of a nozzle in the form of a jet and the sink is a pipe that is kept some distance from the source pipe. Such source -sink pairs are observed in many situations including data centers, and collection of fresh water from a large reservoir that has also a discharge of pollutants. The main parameters of the problem are source and sink flow rates, the axial and lateral separations of the source and sink, and the angle between the axes of source and sink. Of concern is the percentage of source fluid that enters the sink as a function of these parameters. The experiments have been carried in a large glass water tank. The source nozzle diameter is 6mm and the sink pipe diameter is either 10mm or 20mm. The horizontal and vertical separations and angles between these source and sink pipes are adjustable. The Reynolds numbers of the source jet is about 3200. Experiments were done with the sink flow rate equal to, lower or higher than the source flow rate. The flow was visualized using KMnO4 dye and planar Laser Induced Fluorescence (LIF). The velocity fields for some cases were obtained using Particle Image Velocitymetry (PIV). To obtain the efficiency (that is percentage of source fluid entering the sink pipe), titration method is used. A small amount of hydrochloric acid (HCL) is added in the jet fluid through the overhead tank and the fluid collected at the sink is titrated with the Sodium hydroxide (NaOH) as base and Phenolphthalein as the pH indicator. The main characteristics of the jet, without a sink, were measured using PIV. The velocity profiles, jet widths and volume flow rates at various axial locations were obtained and compared with results reported in the literature for similar Reynolds number jets. For 100%, 70%, 50% and 25% efficiencies or removals and for zero lateral separations, the sink flow rate is about 1.5 times the flow rate predicted on the basis of jet properties at that point in the absence of a sink. The sink flow rate to obtain a certain efficiency increase dramatically with lateral separation; for example, when the lateral separation is about one half jet width, the required sink flow rate to obtain a certain efficiency increases by about five times. The sink diameter and the angle between source and the sink axes don’t influence efficiencies as much as the lateral separation. Data from our all experiments have been consolidated in the form of correlations that can be used for design of appropriate sinks for removal of heat and pollutants.

Disputats. Universität Hohenheim, 2002. / Haves kun i elektronisk udg.

L'objectif de cette thèse est d'étudier le contrôle passif des vibrations avec un absorbeur non linéaire de type Nonlinear Energy Sink (NES) à Vibro-Impact (VI). Plusieurs aspects ont été étudiés : l’influence des paramètres sur les régimes vibratoires observés, l’optimisation du design sous différentes excitations, l'application sur des systèmes vibratoires non linéaires et enfin l'étude de deux NES-VI en parallèle.Tout d'abord, l’influence des paramètres de design sur les régimes vibratoires et les bifurcations est étudiée de façon analytique, numérique et expérimentale. Ainsi différentes bifurcations et des réponses fortement modulées de type chaotique sont présentées.Ensuite, l’efficacité des régimes vibratoires est comparée, le mécanisme ainsi décrit constitue la base de l’optimisation du design de l’absorbeur face à différents types d’excitation.Le mécanisme d’activation du NES-VI est étudié analytiquement puis validé expérimentalement. Un critère d’optimisation du design est proposé, puis appliqué sur différents systèmes au comportement vibratoire non linéaire.Finalement, dans le but d’améliorer l’efficacité et la robustesse, le montage de deux NES-VI en parallèle est étudié expérimentalement. Le principe d’activation séparé est alors observé. / The objective of this thesis is to study the passive control of vibration by a Vibro-Impact (VI) Nonlinear Energy Sink (NES). Several aspects have been developed: the influence of parameters on response regimes, the optimization design mechanism under different excitations, the application to vibration control of nonlinear systems and the study of two VI NES in parallel.Firstly, the influence of parameters on response regimes and bifurcation is analytically, numerically and experimentally studied, respectively. Different bifurcation routes and chaotic strongly modulated response are presented.Then, the efficiency of typical response regimes is compared, and its mechanism lays the foundation for the optimization design of different parameters under different types of excitation.Thirdly, the activation characteristic of VI NES is analytically studied and experimentally validated. An optimization design criterion is proposed for the vibration control of nonlinear system.Finally, the vibration control by two VI NES in parallel is experimentally studied with the purpose of efficiency and robustness improvement. The principle of separate activation of VI NES is observed

Medlemskapet i EU har fått effekter på den direkta beskattningens område då internrättsliga skatteregler måste utformas i enlighet med EUF-fördraget. Icke-bosatta som tillfälligt arbetar i Sverige beskattas enligt en definitiv källskatt i SINK eller A-SINK. Beskattning sker på bruttoinkomsten, kostnadsavdrag medges inte. Vidare medges inte heller avdrag som är kopplade till den skattskyldiges personliga förhållanden. Mot bakgrund av EUDs praxis fastställdes SINK och A-SINK vara oförenliga med de fria rörligheterna i fördraget. Oförenligheten bestod i den diskriminering som uppstod då en icke-bosatt beskattades hårdare än en bosatt person i motsvarande situation. Genom att i SINK och A-SINK införa en möjlighet för den icke-bosatta att bli undantagen beskattning enligt respektive lag för att istället bli beskattad enligt IL, var lagstiftarens uppfattning att den fastställda diskrimineringen neutraliserades. I mars 2010 meddelade EUD dom i C-440/08 Gielen. I målet fastställdes att en valmöjlighet inte neutraliserar en diskriminering. Den intressanta frågan är huruvida SINK och A-SINK, mot bakgrund av Gielen, anses utgöra diskriminering av icke bosatta, då kostnadsavdrag och personliga avdrag inte medges. Mer generellt kan frågan ställas om möjligheten att välja behandling innebär att icke-bosatta inte längre diskrimineras.   Enligt författaren utgör SINK och A-SINK en diskriminering av icke-bosatta då valmöjligheten inte är tillräcklig för att åtgärda den oförenlighet som tidigare fastställdes. Författaren anser att lagstiftaren, i detta avseende, har missuppfattat principen om likabehandling med följden att SINK och A-SINK står inför en ytterligare EU-anpassning. Möjligen har den definitiva källskatten i SINK och A-SINK spelat ut sin rätt.

Doubling transistor count for every two years in a computer chip, transmitter and receiver (T/R) module of a phased-array antenna that demands higher power with smaller dimensions are all results of miniaturization in electronics packaging. These technologies nowadays depend on improvement of reliable high performance heat sink to perform in narrower volumes. Employing microchannels or open cell metal foam heat sinks are two recently developing promising methods of cooling high heat fluxes. Although recent studies especially on microchannels can give a rough estimate on performances of these two methods, since using metal foams as heat sinks is still needed further studies, a direct experimental comparison of heat exchanger performances of these two techniques is still needed especially for thermal design engineers to decide the method of cooling. For this study, microchannels with channel widths of 300 &micro / m, 420 &micro / m, 500 &micro / m and 900 &micro / m were produced. Also, 92% porous 10, 20 and 40 ppi 6101-T6 open cell aluminum metal foams with compression factors 1,2, and 3 that have the same finned volume of microchannels with exactly same dimensions were used to manufacture heat sinks with method of vacuum brazing. They all have tested under same conditions with volumetric flow rate ranging from 0,167 l/min to 1,33 l/min and 60 W of heat power. Channel height was 4 mm for all heat sinks and distilled water used as cooling fluid. After experiments, pressure drops and thermal resistances were compared with tabulated and graphical forms. Also, the use of metal foam and microchannel heat sinks were highlighted with their advantages and disadvantages for future projects.

Les réseaux de capteurs sans fils linéaires (RdCSL) sont un cas particulier de réseaux de capteurs sans fils où les nœuds de capteurs sont déployés le long de multiples lignes. les RdCSL sont utilisés pour la surveillance des infrastructures routières, ferroviaires, des conduites de gaz, d’eau, de pétrole et de cours d’eau. Les solutions classiques de formation de topologie et d’adressage proposées ne sont pas adaptées à l’environnement des RdCSFL. En effet les paramètres initiaux utilisés par ces protocoles tels que le nombre maximum de nœuds fils (Cm), nombre maximum de nœuds routeurs fils Rm, profondeur maximum de l’arbre (Lm), occasionnent un gaspillage de l’espace d’adressage disponible pour les nœuds et limitent la profondeur de l’arbre adressable (15 sauts pour ZigBee). D’autres solutions adaptées pour les RdCSFL utilisent une organisation en cluster des nœuds du réseau et sont basées elles aussi sur des paramètres fixés à l’avance tels quel le nombre maximum de cluster fils par cluster. De plus, ces solutions requièrent beaucoup d’interventions manuelles sur les nœuds de capteurs (choix des chefs de cluster par exemple) et ne favorisent pas une adaptation face aux changements du RdCSL tels que l’ajout d’un ensemble de nœuds de capteurs. Dans cette thèse, nous proposons donc des protocoles permettant la construction automatique de topologies logiques, l’adressage et le routage pour des réseaux de capteurs sans fil linéaires. Nos protocoles fournissent aussi des mécanismes de gestion dynamique d’un RdSFL avec l’ajout de nouveaux nœuds, la réallocation d’adresses pour les nœuds en cas d’épuisement de blocs d’adresses et la gestion du routage vers plusieurs puits du réseau. Nos différents protocoles sont évalués grâce au simulateur Castalia/Omnet++. Les résultats de nos simulations montrent que nos protocoles permettent de construire un RdCSFL connecté avec peu de nœuds orphelins (nœuds sans adresses logiques) et sans limitations de profondeur. Nous montrons aussi, grâce à nos simulations, que nos contributions permettent d’ajouter un grand nombres de nœuds à un RdCSFL existant de n’importe quelle taille et s’adaptent au déploiement de plusieurs puits et au routage multi-puits et permettent d’améliorer le ratio et la latence de paquets livrés dans les RdCSFL. / Linear wireless sensor network (LWSN) are a sub-case of wireless sensor network where sensor nodes are roughly deployed through multiple long lines with branches. LWSN are used to monitor infrastructures such as roads, pipelines, and naturals entities such as rivers.Classical solutions of topology construction and addressing are inefficient on LWSN . Indeed, with initials networks parameters such as the maximum number of children per node (Cm), the maximum number of children routers per node (Rm), and the maximum tree depth, a solution like ZigBee causes a waste of available address space of network nodes and limit the depth of the addressable tree to 15 hops. Other solutions proposed for LWSN use a cluster-tree organisation and are based on initial network parameters such as the maximum number of children clusters per cluster. In addition, these solutions require a lot of manual intervention on different sensor nodes and do not allow adaptation for a network extension (addition of a set of new sensor nodes). In this thesis, we propose protocols to allow the automatic construction of topologies, the addressing and the data routing for linear wireless sensor networks. Our contribution also provides mechanisms for dynamic management of LWSN (addition of new nodes, addresses reallocation, and data routing to multiple sink nodes). Our different protocols are evaluated using Castalia/Omnet++ simulator. Results of our simulations show that our protocols allow a construction of connected LWSN with very few orphan nodes and without depth limitations. We also show that our contribution allows to add many new nodes on different LWSN, and adapts to the deployment of multiple sinks to improve the ratio and the latency of data delivery packets.

Les travaux présentés dans cette thèse s’intéressent au contrôle passif des systèmes soumis à une excitation harmonique à l’aide d’absorbeurs non-linéaires de type Nonlinear Energy Sink (NES). Plusieurs voies de recherches ont été dégagées visant : l’étude expérimentale du pompage énergétique, l’étude d’un type de NES alternatif puis la proposition d’une application pour le contrôle passif de l’instabilité de broutement en usinage.L’étude théorique d’un oscillateur linéaire couplé à un NES à raideur purement cubique permet de mettre en évidence les régimes de relaxation. Une procédure de dimensionnement est développée et appliquée à la réalisation d’un dispositif expérimental.La partie suivante est consacrée à l’étude d’un NES à vibro-impact (NES-VI). L’analyse théorique permet de révéler une stratégie de contrôle analogue aux cycles de relaxation observés dans le cas du NES à raideur cubique. Un dispositif expérimental est ensuite élaboré et permet de retrouver ces cycles de relaxation.La dernière partie est dédiée au contrôle passif de l’instabilité de broutement en tournage. La faisabilité à l’aide d’un NES à raideur cubique et d’un NES-VI est établie par l’étude théorique. Le contrôle passif à l’aide d’un NES-VI est réalisé expérimentalement / The work presented in this thesis deal with the passive control of dynamic systems subjected to an harmonic forcing using a Nonlinear Energy Sink (NES). Several research ways have been identified : the experimental study of an harmonic oscillator with an embedded NES, the study of an alternative type of NES and an application for the passive control of chatter instability during machining operations.The theoretical analysis of an harmonically oscillator with an embedded NES with cubic stiffness coupling allow us to reveal the relaxation cycles. A design procedure is presented and applied to the realization of an experimental setup.The next section is devoted to the study of a vibro-impact NES (VI-NES). The theoretical analysis gives an insight on analog relaxation cycle similar to those observed with a NES with cubic stiffness. An experimental setup is presented and these relaxation cycles are observed.In the last section, the idea of passively controling the chatter instability during turning operation using a NES is studied. This possibility is demonstrated theoretically as well for a classic cubic NES as for a VI-NES. This passive control is performed experimentally and a reduction of the vibration amplitude is observed

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.

The purpose of this study was to examine how preschool children, 4-5 years, think, reason and explain an everyday physical phenomena. The phenomenon’s that was chosen for this study is the Archimedes principle and density. The study was conducted through qualitative semi-structured interviews that took place while the experiments were carried out by the children. This method was chosen to make it possible to follow the children´s reasoning about the subject of physics in preschool and to let them lead the conversation and let them explain the result. The result shows that children in the study have experience and knowledge about the phenomenon of why objects float or sink. Even if they don’t have knowledge of Archimedes´ principle or density, they can come up with their own conclusions of why objects float or sink, based on their past experiences and knowledge. Some of the children approach an explanation of these phenomena, without using the scientific concepts. / Syftet med studien är att undersöka hur förskolebarn, 4-5 år, tänker, resonerar och förklarar vardagliga fysikaliska fenomen. Fenomenen som valts till denna studie är Arkimedes princip och densitet. Genomförandet av studien bygger på kvalitativa semistrukturerade intervjuer som genomfördes i samband med att experimentet utfördes. Metoden valdes för att undvika att barnen bara svarade ja eller nej på frågorna, utan det skulle finnas utrymme och möjlighet för barnen att förklara sina tankar och idéer. I denna studie var barnens tankar det viktiga och intressanta, hur de resonerade och förklarade fenomenet. Resultatet visar att barnen i studien har erfarenhet och kunskap om fenomenet varför föremål flyter eller sjunker. Även om de inte har kunskap om Arkimedes princip eller densitet kan de komma med egna slutsatser till varför föremål flyter eller sjunker, baserat på deras tidigare erfarenheter och kunskaper, och några barn närmar sig en förklaring av dessa fenomen, utan att använda sig av de vetenskapliga begreppen.

Seagrass meadows may play a substantial role in climate change mitigation as they are capable to sequester and store substantial amounts of anthropogenic carbon in plant biomass and, more importantly, in their underlying sediments. In this PhD thesis, the carbon-burial potential was assessed by quantifying the amount of organic carbon stored in different seagrass meadows, each dominated by one of the four major seagrass species in the Western Indian Ocean region. Impacts of anthropogenic disturbances on biomass carbon allocation, greenhouse gas emission (methane and nitrous oxide) and production of sulphide were investigated in Chwaka Bay, Zanzibar. The findings showed that east African seagrass meadows generally have high carbon sink capacity. The storage of sedimentary organic carbon, however, varied among seagrass habitats and across sites, and was up to five-fold higher in seagrass sediment to those of nearby unvegetated sediments. Seagrass meadows in eutrophicated sites had higher sedimentary organic carbon content, and substantially higher emission rates of nitrous oxides and methane, compared to more pristine meadows. Disturbances in terms of shading and simulated grazing of seagrass affected several processes, with major decreases in seagrass primary productivity, net community production and biomass carbon, in turn influencing seagrass carbon sequestration as well as stimulating anaerobic microbial processes. In addition, production of sulphide in the sediment and methane emissions from the sediment surface increased significantly when disturbed. At present, seagrass meadows in the Western Indian Ocean have high carbon sink capacity. This important ecosystem service is, however, highly threatened due to regional anthropogenic pressure, which may change the role of blue carbon rich habitats, such as seagrass meadows, from being a sink to a source of greenhouse gases. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.</p>