Dissertations / Theses on the topic 'Low energy'

This thesis investigates two very different aspects of quantum gravity. In the first - and main - section, we examine the question of quantum gravitational contributions to the running of a coupling parameter alongside the various problems and issues that this raises. We treat quantum gravity as an e ective eld theory and use perturbative methods to address issues. Speci cally, we look at a '4-type scalar coupling. In a gauge-invariant way, we consider a non-minimally coupled, massive scalar eld, with non-constant background, in the presence of a cosmological constant and contrary to most of the literature, we also calculate all derivative terms. An e ective action is constructed, renormalization counterterms calculated, and we nd that, within certain bounds, gravity leads to asymptotic freedom of scalar eld theory. Furthermore, we investigate whether considering quadratic divergences in gravitational calculations can tell us anything useful. In this case we nd non-vanishing quadratic divergences. However, we also recognise the possibility that quadratic divergences are somewhat of a red herring and that by suitable eld rede nitions, we can eliminate these from our calculations. The second section of the thesis addresses the possibility of super uidity in a quark gluon plasma. We use the framework of AdS/CFT, with knowledge of black hole thermodynamics, to consider the duality between a black hole in anti-de Sitter space and a uid existing on the boundary. Initially, we look at a simple case of a black hole possessing only mass and charge in AdS spacetime and calculate such properties as the entropy, temperature and speci c heat capacity, identifying a telltale sign of a phase change (speci c heat capacity tending to in nity) and of points of vanishing viscosity (corresponding with a zero entropy). After con rming that such a boundary exists, we take a di erent approach where we calculate and interpret the solutions to a relativistic Gross-Pitaevskii equation on a sphere. On projection back to R3, the solutions are seen to be tori, which we choose to interpret as vortex rings in analogy to the expected feature of those which are known to appear in a real super uids.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 187-195).
Vibration energy harvesters work effectively only when the operating conditions match with the available vibration source. Typical resonating MEMS structures cannot be used with low-frequency, low-amplitude and unpredictable nature of ambient vibrations. Bi-stable nonlinear oscillator based energy harvesters are developed for lowering the operating frequency while widening the bandwidth, and are realized at MEMS scale for the first time. This design concept does not rely on the resonance of the MEMS structure but operates with the large snapping motion of the beam at very low frequencies when proper conditions are provided to overcome the energy barrier between the two energy wells of the structure. A fully functional piezoelectric MEMS energy harvester is designed, monolithically fabricated and tested. An electromechanical lumped parameter model is developed to analyze the nonlinear dynamics and to guide the design of the multi-layer buckled beam structure. Residual stress induced buckling is achieved through the progressive control of the deposition along the fabrication steps. Static surface profile of the released device shows bi-stable buckling of 200 [mu]m which matches very well with the design. Dynamic testing demonstrates the energy harvester operates with 35% bandwidth under 70Hz at 0.5g, operating conditions that have not been met before by MEMS vibration energy harvesters.
by Ruize Xu.
Ph. D.

This project investigated the current market regarding wireless net and the communication between the tools used for diagnostics/maintenance and an embedded system. Based on documentation obtained through interviews a demo system was created based on Bluetooth Low Energy (BLE) communication between an embedded system and an Android device. This report intends to describe the tools and methods used in the design of the demo system and the result of an analysis of the BLE communication. Bluetooth Low Energy is an exciting protocol with wide applicability within the industrial field. This project investigated the communicational possibilities between a Smartphone and a Raspberry Pi and based on the results that emerged the conclusion can be drawn that BLE is a protocol with many beneficial applications within industrial IT.
Projektet undersökte dagens marknad gällande trådlösa nät samt kommunikation mellan verktyg som används för diagnostik/underhåll och ett inbyggt system. Utifrån underlaget som erhölls genom intervjuer har ett demosystem skapats som bygger på Bluetooth Low Energy (BLE) kommunikation mellan ett inbyggt system och en Android-enhet. Denna rapport avser redogöra för de verktyg och metoder som använts för att konstruera ett demosystem samt resultatet av en analys av BLE-kommunikationen. Bluetooth Low Energy är ett spännande protokoll med stora tillämpningsmöjligheter inom industrin. Detta projekt har undersökt möjligheterna att kommunicera mellan en Smartphone och en Raspberry Pi och utifrån resultaten som uppkommit kan slutsatsen dras att BLE är ett protokoll som kan ha många och fördelaktiga tillämpningar inom Industriell IT.

Approved for public release; distribution is unlimited
The U.S. Navy has many opportunities to take advantage of energy sources that are usually wasted because these low power sources yield such low-voltages that a normal voltage converter is not efficient enough to harvest the energy. Low-voltage energy is available in many forms including solar, thermal, vibration, and electro-magnetic. The power that can be obtained from these sources on a small scale can be taken advantage of by using an ultra-low power boost converter that is specifically designed for energy harvesting applications. These energy sources with a very small footprint can be used in military and defense applications such as wireless sensor networks, industrial monitoring, and varieties of portable and wearable devices. The theory of power conversion, synchronous rectification, and maximum power point tracking is discussed. A discussion of the benefits of using an energy converter made specifically for energy harvesting is also covered. A commercially available energy harvester converter is simulated using a simulation program with integrated circuit emphasis, and a solar application is tested with hardware. The hardware experiments explore the startup sequence of the circuit, the switching profile of the converter, and a test of the circuits efficiency.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 265-270).
There have been few measurements of cross sections for neutron-proton scattering and radiative capture below 1 MeV. Those measurements which do exist are at a small number of energies and are often inconsistent with theoretical models and with each other. We have conducted several experiments with the goal of obtaining improved data on these cross sections at the University of Kentucky (UKY) and the Los Alamos Neutron Science Center (LANSCE). Feasibility studies for measuring the low energy cross section for np radiative capture have been conducted at both UKY and LANSCE, culminating in a measurement of the cross section at 0.5, 0.9, 1.5, 2.0, and 2.5 MeV at UKY, using a plastic scintillator to detect recoiling deuterons and two BGO scintillators to detect the [gamma]-ray yields at 64.6° and 106.6°. We also performed measurements of the response of BC418 plastic scintillator to low energy protons during these studies, and conducted several additional measurements of the scintillator response at LANSCE and UKY, yielding very precise results from 100 keV to 3.6 MeV. The total cross section for np scattering was measured at UKY from 150 to 800 keV by neutron transmission, measuring the neutron yields in a liquid scintillator with various targets in the beam. The cross section was determined by taking ratios of neutron yields with and without the target, giving cross sections which are independent of detector efficiency and dead time. These results fill a significant gap in the available data below 500 keV.
by Brian Daub.
Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 149-151).
Møller scattering is one of the most fundamental processes in QED. Its knowledge at high precision is necessary for a variety of modern nuclear and particle physics experiments. However, most treatments have neglected the electron mass, which is an approximation that breaks down at relevant low energies. In this thesis, existing soft-photon radiative corrections were combined with new hard-photon bremsstrahlung calculations to take into account the effect of photon emission at any photon energy. The electron mass was included at all steps. The radiative corrections were compiled into a Monte Carlo event generator. To test the results, an experiment was designed, constructed, installed, and executed at the MIT High Voltage Research Laboratory. Measurements are reported, comparing the simulated radiative Møller spectra to data at 2.5 MeV. Good agreement between the measurements and the new calculation is observed in the momentum spectrum at three angles.
by Charles S. Epstein.
Ph. D.

The rapid advancement in complimentary metal-oxide-semiconductor (CMOS) electronics has led to a reduction in the sizes of wireless sensor networks (WSN) and a subsequent decrease in their power requirements. To meet these power requirements for long time of operation, energy harvesters have been developed at the micro scale which can convert vibration energy into electrical energy. Recent studies have shown that for mechanical-to-electrical conversion at the mm-scale (or micro scale), piezoelectric mechanism provides the best output power density at low frequencies as compared to the other possible mechanisms for vibration energy harvesting (VEH). However, piezoelectric-based VEH presents a fundamental challenge at the micro scale since the resonance frequency of the structure increases as the dimension decreases. Electromagnetic induction is another voltage generation mechanism that has been utilized for VEH. However, the electromagnetic induction based VEH is limited by the magnet and coil size and the decrease in power density at the micro scale. Hybrid energy harvesting is a novel concept that allows for increased power response and increased optimization of the generated voltage. The work in this field is currently limited due to integration challenges at small dimensions. An effective design for low frequency piezoelectric VEH is presented in this work. A unique cantilever design called arc-based cantilever (ABC) is presented which exhibits low natural frequencies as compared to traditional cantilevers. A general out-of-plane vibration model for ABCs was developed that incorporated the effects of bending, torsion, transverse shear deformation and rotary inertia. Different configurations of micro ABCs were investigated through analytical modeling and validation experiments. ABC structures were fabricated for dual-phase energy harvesting from vibrations and magnetic fields. Next, a levitation-induced electromagnetic VEH concept based on double-repulsion configuration in the moving magnet composite was studied. Computational modeling clearly illustrated the advantages of the double-repulsion configuration over the single-repulsion and no-repulsion configurations. Based on the modeling results, an AA battery-sized harvester with the double-repulsion configuration was fabricated, experimentally characterized and demonstrated to charge a cell phone. The scaling analysis of electromagnetic energy harvesters was conducted to understand the performance across different length scales. A micro electromagnetic harvester was developed that exhibited softening nonlinear spring behavior, thus leading to the finding of nonlinear inflection in magnetically-levitated electromagnetic harvesters. The nonlinear inflection theory was developed to show its causal parameters. Lastly, a coupled harvester is presented that combines the piezoelectric and electromagnetic voltage mechanisms. The advantages of each mechanism were shown to positively contribute to the performance of hybrid harvester. The cantilever provided low stiffness, low frequency, and pure bending, while the magnetic system provided nonlinearity, broadband response, and increased strain (and thus voltage).
Ph. D.

Atrial fibrillation (AF) is one of the commonest cardiac arrhythmias encountered in modern medicine and is associated with deterioration in cardiac function and increased risk of stroke resulting in significant morbidity and mortality. The most recently published data indicates that AF: (i) has a prevalence of circa. 5.5 % in individuals over the age of 55 years; increasing to 17.8 % in patients greater than 85 years, (ii) confers up to a 500 % increase in the risk of related stroke, (iii) accounts for 30 - 40 % of all cardiovascular related hospital admissions; with incidence rates and associated treatment costs expected to double by 2050. For symptomatic patients where pharmacological intervention has failed, recent publications indicate that the advancement of new technologies and therapies may result from two specific lines of enquiry: (i) optimisation of the electrical defibrillation shock waveform for the lowest possible energy to achieve successful cardioversion (less than 1 J would potentially avoid the need for patient sedation) and (ii) investigation of the possible development of battery free passive implantable atrial defibrillators (thereby facilitating AF arrhythmia detection and cardioversion in a non-acute care setting).

Thesis (M.S.) -- University of Maryland, College Park, 2003.
Thesis research directed by: Dept. of Electrical and Computer Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The goal of the project is development of a project documentation for a building: Low energy block of apartments. The documentation was processed in the depressed for construction realization. It solves a four floor block of apartments with flat warm roof and partially depressed parking garage. The structure is designed with risen requirements on thermal properties. The project also solves a concept of heating system. Its energy efficiency was analysed using precise calculation acc. ČSN 73 0540 and processed statement of energy efficiency. The result energy consumption of the structure is B – very efficient.

Diploma thesis is aimed on solution of project documentation design of a four-storey low-energy block of apartments with a flat roof in the degree of project realization. The object has a collective garage on first floor and no basement. The structure is designed with the emphasis on overall energy saving, which was documented by detailed calculation of the energy performance of the building under Decree No.78 / 2013 Coll. and ČSN 73 0540-2.

The amount of greenhouse gas emissions mitigation required to prevent the most dramatic climate change scenarios postulated in the 2014 IPCC Synthesis Report is substantial. Prior analyses have examined the potential for nuclear energy to play a role in decarbonizing the energy sector, one of the largest contributors to emissions worldwide. However, advanced, non-light water reactors, while often touted as a viable alternative for development, have languished. Large light water development projects have a repeated history of extended construction timelines, re-work delays, and significant capital risk. With few exceptions, large-scale nuclear projects have demonstrated neither affordability nor economic competitiveness, and are not well suited to nations with smaller energy grids, or to replace fossil generation in the industrial process heat sector. If nuclear power is to play a role in decarbonization, new policy and technical solutions will be needed. In this manuscript, we examine key aspects of past performance across the nuclear enterprise and explore the future potential of nuclear energy worldwide, focusing on policy and technical solutions that may be needed to move nuclear power forward as a part of a low-carbon energy future. We do so first at a high level, examining the history of nuclear power research and development in the United States, the nation that historically has led the way in the development of this generating technology. A significant portion of our analysis is focused on new developments in this technology – advanced non-light water reactors and small modular reactors. We find that while there are promising technical solutions available, improved funding and focus in research and new models of deployment may be needed if nuclear is to play a continuing or future role. We also find that in examining potential new markets for the technology, a continuing focus on institutional readiness is critical.

El desarrollo de la innovación baja en carbono es necesario para generar energía suficiente y, al mismo tiempo, reducir las emisiones de gases de efecto invernadero de manera suficientemente rápida para evitar un cambio climático extremo. Esto hace con que sea fundamental el entendimiento de los factores capaces de acelerar el desarrollo y la difusión de la innovación baja en carbono. La innovación baja en carbono en el sector energético involucra diversos desafíos en función de la especificidad de sus características y dinámica, razón por la hay renovado interés en su investigación. Esta tesis doctoral reúne una serie de cinco artículos científicos que buscan explorar tópicos emergentes en torno a particular dinámica de la innovación baja en carbono, a saber: la formación de mercados líder, la diversidad tecnológica, la trayectoria tecnológica, estrategias de obtención de conocimiento, e impacto en la reducción de emisiones de gases de efecto invernadero. El primer artículo presenta una extensión del marco de referencia para análisis de mercados líder donde son adicionalmente considerados los factores referentes a la cadena de suministro y a políticas tecnológicas. Con base en la comparación del desarrollo de mercados líder en la industria eólica de Alemania, China, y Estados Unidos, este estudio demuestra el papel de los contextos de negocios y de las políticas de suporte a la innovación baja en carbono específicos de cada país. El segundo artículo explora el papel de la diversidad en el desarrollo de la innovación baja en carbono. Con base en el caso de la industria de energía fotovoltaica, nueve indicadores de diversidad tecnológica son aplicados para mapear la tendencia en la industria y su impacto en el desarrollo de nuevas innovaciones. El tercero artículo investiga la relación entre la evolución del conocimiento científico y la innovación baja en carbono en turbinas eólicas. Basándose en una nueva modelo para el análisis de citaciones, este artículo presenta nueva evidencia empírica de la relación entre desarrollo de conocimiento científico y la innovación baja en carbono. El cuarto artículo discute los resultados de una encuesta original realizada con organizaciones de investigación para analizar el impacto de diferentes estrategias de obtención de conocimiento en la innovación baja en carbono. Con base en la comparación de la investigación en energía solar y eólica, este estudio demuestra la importancia de políticas direccionadas a tecnologías específicas. Finalmente, el quinto artículo explora de que forma la rápida difusión de innovaciones bajas en carbono puede afectar su efecto en términos de reducciones de emisiones de gases de efecto invernadero. Analizando el caso de la energía eólica, este estudio demuestra el desequilibrio entre capacidad instalada y efectiva producción de energía eólica en cuatro países líderes en capacidad de generación eólica, a saber: Alemania, China, España y Estados Unidos. En resumen, esta tesis combina diferentes perspectivas de economía evolucionaria, ambiental y ecológica con estudios de innovación y clima para investigar las particular dinámica de innovación baja en carbono. Al estudiar los casos de las energías solar y eólica, esta tesis ofrece datos empíricos originales e ilustra nuevas posibilidades de suporte a la innovación baja en carbono.
Low-carbon innovation is required to match energy supply with GHG emissions reductions at a quick enough pace to avoid dangerous climate change. This calls for a deeper understanding of low-carbon innovation to explore factors capable of speeding up its development and diffusion. Low-carbon innovation in the energy sector involves a number of challenges due to its particular characteristics and dynamics which have renewed the interest in exploring its drivers. This doctoral dissertation combines a series of five research papers which address emerging issues regarding the particular dynamics of low-carbon innovation, namely: lead markets formation, technological diversity, technological trajectory, knowledge sourcing strategies and impact on GHG emissions reduction. In the first research paper, an extension of the lead market framework is developed to include supply side factors and technology policy issues. By comparing the development of lead markets in the wind power industry in China, Germany and the USA, this study shows the role of countries’ specific business contexts and policy responses on low-carbon innovation. The second study is dedicated to explore the role of diversity in low-carbon innovations. By looking at the solar photovoltaic (PV) industry, nine indicators of technological diversity are applied to map diversity trends in the industry and its impact on further innovation. Subsequently, the third research paper links scientific knowledge evolution and low-carbon innovation in wind turbines. Based on a novel approach to citation analysis, this study offers original evidence on this relationship. The fourth article is based on an original survey among research organisations to analyse the impact of distinct strategies of external knowledge sourcing on low-carbon innovation. By comparing research on solar and wind power, this study depicts the importance of technology-specific policies. The fifth and final study explores how fast deployment of low-carbon innovation can affect its potential of GHG emissions reduction. Considering the case of wind power, it addresses the mismatch between installed capacity and actual wind power output in four of the leading countries in terms of generation capacity, namely: China, the United States, Germany and Spain. In summary, this dissertation combines different perspectives from evolutionary, environmental and ecological economics with innovation and climate studies to explore the particular dynamics of low-carbon innovation. By looking at the cases of solar and wind power, this dissertation builds up original evidence and sheds new light into the possibilities of fostering innovation in low-carbon technologies.

Low-energy buildings have, in recent years, gained attention and moved towards a large-scale introduction in the residential sector. During this process, national and international criteria for energy use in buildings have become stricter and the European Union has through the Energy Performance of Buildings Directive imposed on member states to adapt their building regulations for ‘Nearly Zero Energy Buildings’, which by 2021 should be standard for new buildings. With a primary focus on new terraced and detached houses, this thesis analyses how the concept of low-energy buildings may be further developed to reduce the energy use in the residential sector. The main attention is on the technical performance in terms of indoor climate and heat consumption as well as on the market diffusion of low-energy buildings into the housing market. A multidisciplinary approach is applied, which here means that the concept of low-energy buildings is investigated from different perspectives as well as on different system levels. The thesis thus encompasses methods from both engineering and social sciences and approaches the studied areas through literature surveys, interviews, assessments and simulations. The thesis reveals how an increased process integration of the building’s energy system can improve the thermal comfort in low-energy buildings. Moreover, it makes use of learning algorithms – in this case artificial neural networks – to study how the heat consumption can be predicted in a low-energy building in the Swedish climate. The thesis further focuses on the low-energy building as an element in our society and it provides a market diffusion analysis to gain understanding of the contextualisation process. In addition, it suggests possible approaches to increase the market share of low-energy buildings.

QC 20140321

Despite remarkable advances in naval architecture in the past few years, limited effort has been expended to improve the energy efficiency of ships due to the relatively low price of fuel oil and lack of stringent environmental regulations. However, the ever-growing intercontinental trade has resulted in an increase of greenhouse gas emissions from ships that triggered the introduction of mandatory environmental measures and shifted the focus of the shipping industry towards more energy efficient designs and operations. This thesis focus is on improving the energy efficiency of ships during design and operation by adopting a direct approach to estimating the requisite thermal energy on board ships over their life cycle. This is achieved by dynamically modelling the thermal energy flows on board, drawing from the considerable developments in Building Energy Simulation (BES), which precedes developments in the maritime industry by five decades. To this end, and in broad terms, the thesis focus is on and embodies the technology transfer from the Buildings Industry to the Marine Industry ("marinisation of BES") whilst accounting for the differences and complexities implicit in some of the ship types as well as the marine environment and operations. This, in turn, necessitates focus on applicability, functionality and limitations of BES in ships with the view to enable developments to fill pertinent gaps and to demonstrate such developments with purposely selected case studies. During the investigation of the applicability of BES in ships, the main differences between ships and buildings were identified, and their effect on energy simulation was pointed out. The results of this comparison served as the basis for the marinisation of the selected building energy simulation software 'ESP-r', which was enhanced to also cater for energy flows present in the marine environment, leading to the development of 'ESP-r marine'. Despite the ability of the tool to model the majority of thermal energy flows on board ships, several modelling and computational problems were presented during the development of large accommodation models that triggered necessary simplification considerations. In an attempt to allow energy modelling of smaller groups of spaces and drop the requirements for explicit and topologically correct model representation, the geometrical decoupling of major space types was examined. A verification process based on energy simulation was used to construct guidelines, indicating acceptable assumptions for the boundary conditions of individually modelled or groups of accommodation spaces. This methodology was then used to facilitate further simplification of thermal modelling, which was achieved through the concept of space grouping that encompassed the process of the consecutive merging of adjacent spaces, until groups of spaces were represented by a single thermal zone. Throughout this process the loss of accuracy in the results was quantified, and results were used to develop design guidelines for the group representation of major types of on board spaces. All findings were used to form a methodology for the design of the most common ship accommodation spaces and relevant HVAC systems which outer performs current practices, since it provides detailed information about state variables in accommodation spaces and energy systems components, and allows for the calculation of the power consumption of the energy systems serving the accommodation over the ship's life-cycle at a low computational cost. Implementation of the methodology was exhibited with two case studies, one for a cargo and one for a passenger ship. The work undertaken and the derived results clearly demonstrate the applicability of BES to ships and the extent to which it can be simplified during the design process, thus introducing the concept of Dynamic Energy Modelling as a platform in shipping to support life-cycle energy management. This constitutes a significant development in shipping.

2008/2009
Remarkable interest has recently arisen about the search for Weakly Inter- acting Sub-eV Particles (WISPs), such as axions, Axion Like Particles (ALPs), Minicharged and chameleon particles, all of which are not included in the Stan- dard Model. Precision experiments searching for WISPs probe energy scales as high as 10^6 TeV and are complementary to accelerator experiments, where the energy scale is a few TeV. The axion, in particular, is the oldest studied and has the strongest theoretical motivation, having its origin in Quantum Chromodynamics. It was introduced for the first time in 1973 by Peccei and Quinn to solve the strong CP problem, while later on the cosmological implications of its postulated existence also became clear: it is a good candidate for the cold dark matter, and it is necessary to fully explain the evolution of galaxies. Among the different interactions of axions, the most promising for its detection, from an experimental point of view, is the coupling to two photons (Primakoff effect). Using this coupling, several bounds on the axion mass and energy scale have been set by astrophysical observations, by laboratory experiments and by the direct observation of celestial bodies, such as the Sun. Most of these considerations, as was recently recognized, not only constrain the mass and coupling of the axion, but are more generally applicable to all ALPs. The current best limits on the coupling, over a wide range of ALP masses, come from the the CAST (Cern Axion Solar Telescope) experiment at Cern, which looks for ALPs produced in the solar core. The experiment is based on the Primakoff effect in a high magnetic field, where solar ALPs can be reconverted in photons. The CAST magnet, a 10 T, 10 m long LHC superconducting dipole, is placed on a mobile platform in order to follow the Sun twice a day, during sunrise and sunset, and has two straight bores instrumented with X-ray detectors at each end. The re- generated photon flux is, in fact, expected to be peaked at a few keV. On the other hand, there are suggestions that the problem of the anomalous temperature profile of the solar corona could be solved by a mechanism which could enhance the low energy tail of the regenerated photon spectrum. A low energy photon counter has, for this reason, been designed and built to cover one of the CAST ports, at least temporarily. Low energy, low background photon counters such as the one just mentioned, are also crucial for most experiments searching for WISPs. The low energy photon counting system initially developed to be coupled to CAST will be applicable, with proper upgrades, to other WISPs search experiments. It consists of a Galilean telescope to match the CAST magnet bore cross section to an optical fiber leading photons to the sensors, passing first through an optical switch. This last device allows one to share input photons between two different detectors, and to acquire light and background data simultaneously. The sensors at the end of this chain are a photomultiplier tube and an avalanche photodiode operated in Geiger mode. Each detector was preliminary characterized on a test bench, then it was coupled to the optical system. The final integrated setup was subsequently mounted on one of the CAST magnet bores. A set of measurements, including live sun tracking, was carried out at Cern during 2007-2008. The background ob- tained there was the same measured in the test bench measurements, around 0.4 Hz, but it is clear that to progress from these preliminary measurements a lower background sensor is needed. Different types of detectors were considered and the final choice fell on a Geiger mode avalanche photodiode (G-APD) cooled at liquid nitrogen temperature. The aim is to drastically reduce the dark count rate, al- though an increase in the afterpulsing phenomenon is expected. Since the detector is designed to be operated in a scenario where a very low rate of signal photons is predicted, the afterpulsing effect can be accepted and corrected by an increase in the detector dead time. First results show that a reduction in background of a factor better than 10^4 is obtained, with no loss in quantum e ciency. In addition, an optical system based on a semitransparent mirror (transparent to X-rays and re ective for 1-2 eV photons) has been built. This setup, covering the low energy spectrum of solar ALPs, will be installed permanently on the CAST beamline. Current work is centered on further tests on the liquid nitrogen cooled G-APD concept involving different types of sensors and different layouts of the front-end read-out electronics, with a particular attention to the quenching cir- cuit, whether active or passive. Once these detector studies are completed, the final low background sensor will be installed on the CAST experiment. It is important to note that the use of a single photon counter for low energy photons having a good enough background (<1 Hz at least) is not limited to the CAST case, but is of great importance for most WISPs experimental searches, with special regard for photon regeneration experi- ments, and, in general, for the field of precision experiments in particle physics.
Negli ultimi tempi è riemerso un notevole interesse nel campo della ricerca di particelle leggere debolmenti interagenti (Weakly Interacting Sub-eV Particles - WISPs), come ad esempio assioni, particelle con comportamenti simili agli assioni (Axion Like Particles - ALPs), particelle con carica frazionaria e particelle camaleonte; tutti tipi di particelle non inclusi nel Modello Standard. Vista la loro natura debolmente interagente, la scala di energia coinvolta è dell'ordine dei 10^6 TeV, queste particelle non sono visibili nelle collisioni realizzabili negli attuali acceleratori e possono invece essere studiate in esperimenti di precisione, che, sotto questo punto di vista, diventano complementari agli esperimenti su acceleratori. L'assione in particolare è la prima particella, da un punto di vista cronologico, ad essere stata ipotizzata, ed inoltre la sua esistenza è supportata da forti basi teoriche: la sua origine va infatti ricercata all'interno della Cromodinamica Quantistica (QCD). L'assione fu introdotto per la prima volta nel 1973 da Peccei e Quinn come soluzione del problema di violazione di CP nelle interazioni forti, mentre le sue implicazioni cosmologiche risultarono chiare solo in seguito. L'assione infatti può essere considerato un buon candidato per la materia oscura fredda e la sua introduzione è necessaria per spiegare l'evoluzione delle galassie. Tra le diverse interazione degli assioni con la materia e la radiazione, la più interessante da un punto di vista sperimentale è l'accoppiamento con due fotoni (effetto Primakoff). Usando questo tipo di accoppiamento numerosi limiti, sia sulla massa dell'assione che sulle scale di energia coinvolte, possono essere ottenuti da osservazioni astrofisiche e da esperimenti di laboratorio così come dalla diretta osservazione di oggetti celesti tipo il Sole. Queste considerazioni possono essere applicate non solo all'assione ma più in generale a tutte le ALPs. Attualmente i limiti migliori sulla costante di accoppiamento, su un largo spettro di masse di ALPs, si sono ottenuti dall'esperimento CAST (Cern Axion Solar Tele- scope) al Cern, che guarda agli ALPs prodotti nel Sole. L'esperimento è basato sull'effetto Primakoff in un campo magnetico elevato, dove gli ALPs solari sono riconvertiti in fotoni. Il magnete dell'esperimento CAST è costituito da un prototipo per un dipolo superconduttore di LHC, lungo 10 m e con un campo magnetico totale di 10 T. Il magnete è posto su di un affusto mobile per poter seguire il sole durante le fasi di alba e tramonto. Alle due estremità del magnete sono disposti quattro rivelatori sensibili nel campo degli X molli. Il picco del usso di fotoni rigenerato è infatti atteso a pochi keV. Tuttavia, ci sono suggerimenti che il prob- lema ancora aperto del profilo di temperatura della corona solare può essere risolto tramite un meccanismo che contemporaneamente incrementerebbe le code a bassa energia dell'atteso usso di fotoni rigenerati. A questo scopo un contatore di fotoni sensibile nell'intervallo del visibile è stato progettato ed assemblato per coprire una delle quattro porte del magnete di CAST, almeno temporaneamente. I contatori di fotoni studiati hanno un largo campo di applicazione e possono essere usati in altri tipi di esperimenti per la ricerca di WISPs. Il sistema inizialmente sviluppato per CAST consiste in un telescopio Galileiano per accoppiare una fibra ottica all'apertura del magnete di CAST, la fibra ottica è quindi collegata ad un interruttore ottico che permette di utilizzare due rivelatori contemporaneamente. La fibra in ingresso è infatti collegata alternativamente a due fibre in uscita, in questo modo ciascun rivelatore acquisisce per metà del tempo segnale e per metà del tempo fondo, lasciando inalterato il tempo totale di integrazione. I sensori utilizzati fino ad ora al termine della catena ottica sono un tubo fotomoltiplicatore e un avalanche photodiode operato in modalità Geiger. Ciascun rivelatore è stato preliminarmente caratterizzato su un banco di prova e quindi collegato al sistema ottico. Il sistema finale è stato quindi installato su CAST. Una serie di misure, che includono reali prese dati, sono state condotte al Cern durante il 2007-2008. La misura del fondo ottenuta a CAST è stata la stessa misurata durante i test di prova a Trieste, circa 0.4 Hz, ma risulta chiaro che il vero sviluppo futuro è basato su un sensore a fondo molto più basso. A questo scopo sono stati considerati diversi tipi di sensore e la scelta finale è ricaduta su di un avalanche photodiode operato in modalità Geiger e raffreddato all'azoto liquido. Lo scopo è quello di ridurre drasticamente i conteggi di fondo, sebbene a queste temperature sia atteso un incremento del rateo di afterpulses. Tuttavia il rivelatore è pensato per essere utilizzato in un applicazione a basso rateo e quindi il fenomeno degli afterpulses può essere ridotto agendo direttamente sul tempo morto del rivelatore, cioè aumentandolo. I primi test condotti sul rivelatore mostrano un decremento del fondo pari ad un fattore meglio di 10^4, senza rilevabili variazioni in efficienza. In aggiunta a questo sistema, per ottenere un'installazione permanente sul fascio di CAST, è stato realizzato uno specchio semitrasparente, che lascia pressocchè inalterato il fascio di raggi X e invece de ette il fascio di fotoni con energia nel visibile. Il lavoro attuale è incentrato sullo sviluppo del rivelatore a basso fondo raffreddato all'azoto liquido, includendo anche lo studio di diversi tipi di sensore e diversi tipi di elettronica di lettura, con particolare attenzione all'elettronica di quenching del circuito con le varianti attiva e passiva. Una volta terminati gli studi sui diversi tipi di rivelatori, l'apparato finale sarà installato su CAST. E' comunque importante notare che l'uso di un rivelatore a singolo fotone sensibile tra 1-2 eV con un fondo sufficientemente basso (<1 Hz almeno) non è limitato all'uso su CAST ma in tutti gli altri esperimenti per la ricerca di WISPs, con particolare riguardo agli esperimenti di rigenerazione risonante, e in generale, nel campo di applicazione degli esperimenti di precisione alla fisica delle particelle.
1982

Cryptographic algorithms, like the Advanced Encryption Standard, are frequently used in todays electronic appliances. Battery operated devices are increasingly popular, creating a demand for low energy solutions. As a microcontroller is incorporated in virtually all electronic appliances, the main objective in this thesis is to evaluate possible hardware implementations of AES and implement a solution optimized for low energy consumption, suited for incorporation in a microcontroller. A good cost/performance balance is also a design goal. An existing solution based on a 32 bit architecture with support for 128 bit keys was chosen as a basis and altered in order to lower area and energy consumption. The alterations yielded a 13.6% area reduction as well as 14.2% and 3.9% reduction in energy consumption in encryption and decryption mode, respectively. In addition to alterations in the datapath, low energy techniques like clock gating and numerical strength reduction has been applied in order to further lower the energy consumption. The proposed architecture was also extended in order to accommodate 256 bit keys. Although this increased the area by 9.2%, the power consumption was still reduced by 7.6% and 1.3% in en- and decryption, compared to the architecture chosen as basis. As AES is an algorithm which easily can be parallelized, a high throughput solution utilizing a 128 bit datapath was implemented. This AES module is able to process 372.4 Mbps at an operating frequency of 32 Mhz and is based on the same architecture as the 32 bit datapath solution. In addition, this implementation yielded excellent energy per encryption figures, 24.5% lower than the 32 bit solution. The alternative to performing AES in a dedicated hardware module is to perform it using software. In order to have a basis for comparison, a software solution optimized for 32 bit architectures was implemented. Simulations show that the energy consumption attained when performing AES in the proposed hardware module is approximately 2.3% of what a software solution would use. In addition, the throughput is increased by a factor of 25. The architecture proposed in this thesis combines relatively high throughput with modest demands to area and low energy per encryption.

Understanding the radiation chemistry of water is important in many disciplines including the nuclear industry, astrochemistry, and medicine. In recent years, low-energy electrons have been paid much greater attention, due to their abundance and reactivity in irradiated materials. Electrons with energies < 20 eV may interact via the dissociative electron attachment (DEA) mechanism, which has been found to cause single-strand breaks in DNA.DEA in water involves the capture of a low energy electron by a neutral water molecule into an outer orbital and is generally accompanied by excitation of the H2O molecule, causing it to dissociate. The aim of this work is to study the OH radical produced in DEA to H2O using laser-induced fluorescence (LIF).A high-vacuum chamber equipped with low energy electron gun, molecular beam and laser system was built for gas-phase studies of DEA in water. LIF spectra were recorded from OH formed by dissociation of gas-phase H2O, for determination of the rotational and vibrational state distributions. In addition to the gas-phase studies, low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices were investigated using a combination of temperature-programmed desorption (TPD) and infrared reflection-absorption spectroscopy (IRAS).For CO trapped within approximately 50 mono-layers of the vacuum interface both reduction and oxidation products were observed including HCO, H2CO, H3CO and CH3OH, and CO2. Concentration profiles of CO versus film thickness showed two zones in the film: a near-surface zone of preferential oxidation, and a zone of preferential reduction deeper in the film. A Monte Carlo model was developed based on diffusion of H atoms through the ice lattice, which supported the experimental results.

Over recent years, distributed energy resources (DER) have been the object of many studies, which recognise and establish their emerging role in the future of power systems. Given this context, the concept of transactive energy (TE) has emerged as a central element to the vision of the future grid. The transition to the emerging TE concept requires to tap the inherent flexibility of the demand-side. In this context, the concept of peer-to-peer (P2P) energy trading between consumers and prosumers is one of the new scenarios of growing importance in the domain of distribution networks. This local energy market has been proposed as a means of efficiently managing the uptake of DER. However, the deployment of P2P energy markets at the distribution level is not clear yet. Few studies have investigated the implementation of local energy markets in distribution systems. It is necessary to examine in more detail the limitations and rules that will allow and support the electrical energy trading in a local energy market. Network constraints must be considered in order to evaluate the impact in the network and satisfy the constraints of the grid. In addition, the real benefits for end-users are not yet known. Likewise, it is not known whether this would favour power systems or not. Furthermore, market structures and agents’ strategies need also to be studied. Those factors influence the performance and efficiency of the market. Hence, there are some fundamental questions that have to be solved first in order to implement local markets. This research aims to contribute to this growing area by exploring the operation and implementation of P2P markets on distribution networks using new methodologies and tools. This study also provides a systematic analysis of other prominent DER integration approaches that have been proposed in the transition towards a transactive energy system.

Les opérateurs de Berezin--Toeplitz permettent de quantifier des fonctions, ou des symboles, sur des variétés kähleriennes compactes, et sont définies à partir du noyau de Bergman (ou de Szeg\H{o}). Nous étudions le spectre des opérateurs de Toeplitz dans un régime asymptotique qui correspond à une limite semiclassique. Cette étude est motivée par le comportement magnétique atypique observé dans certains cristaux à basse température. Nous étudions la concentration des fonctions propres des opérateurs de Toeplitz, dans des cas où les effets sous-principaux (du même ordre que le paramètre semiclassique) permet de différencier entre plusieurs configurations classiques, un effet connu en physique sous le nom de sélection quantique Nous exhibons un critère général pour la sélection quantique et nous donnons des développements asymptotiques précis de fonctions propres dans le cas Morse et Morse--Bott, ainsi que dans un cas dégénéré. Nous développons également un nouveau cadre pour le traitement du noyau de Bergman et des opérateurs de Toeplitz en régularité analytique. Nous démontrons que le noyau de Bergman admet un développement asymptotique, avec erreur exponentiellement petite, sur des variétés analytiques réelles. Nous obtenons aussi une précision exponentiellement fine dans les compositions et le spectre d'opérateurs à symbole analytique, et la décroissance exponentielle des fonctions propres
Berezin-Toeplitz operators allow to quantize functions, or symbols, on compact Kähler manifolds, and are defined using the Bergman (or Szeg\H{o}) kernel. We study the spectrum of Toeplitz operators in an asymptotic regime which corresponds to a semiclassical limit. This study is motivated by the atypic magnetic behaviour observed in certain crystals at low temperature. We study the concentration of eigenfunctions of Toeplitz operators in cases where subprincipal effects (of same order as the semiclassical parameter) discriminate between different classical configurations, an effect known in physics as quantum selection . We show a general criterion for quantum selection and we give detailed eigenfunction expansions in the Morse and Morse-Bott case, as well as in a degenerate case. We also develop a new framework in order to treat Bergman kernels and Toeplitz operators with real-analytic regularity. We prove that the Bergman kernel admits an expansion with exponentially small error on real-analytic manifolds. We also obtain exponential accuracy in compositions and spectra of operators with analytic symbols, as well as exponential decay of eigenfunctions

The aim of this diploma thesis is trying to solve difficulties connected with administrative buildings. In this thesis we are talking about possibility that administrative building can have low energy footprint. Most of energy consumption of administrative building is not created by heating but mostly by cooling and by consumption of office equipment. That is why there have been used modern equipment of the building as well as automatic control of building equipment.

In this work we discuss the role of topological degrees of freedom in very low-energy hadronic processes (vacuum polarization and vacuum birefringence). We also present an approach which enables to investigate the microscopic dynamics of non-perturbative processes: this is achieved by constructing an effective statistical theory for topological vacuum gauge configurations, by means of Lattice QCD simulations.

In this work we discuss the role of topological degrees of freedom in very low-energy hadronic processes (vacuum polarization and vacuum birefringence). We also present an approach which enables to investigate the microscopic dynamics of non-perturbative processes: this is achieved by constructing an effective statistical theory for topological vacuum gauge configurations, by means of Lattice QCD simulations.

In this dissertation work, a computer simulation model based on the Geant4 simulation package has been designed and developed to study the energy deposition and track structures of cosmic muons and their secondary electrons in tissue-like materials. The particle interactions in a cubic water volume were first simulated. To analyze the energy deposition and tracks in small structures, with the intention of studying the energy localization in nanometric structures such as DNA, the chamber was sliced in three dimentions. Validation studies have been performed by comparing the results with experimental, theoretical, and other simulation results to test the accuracy of the simulation model. A human body phantom in sea-level muon environment was modeled to measure the yearly dose to a human from cosmic muons. The yearly dose in this phantom is about 22 millirems. This is close to the accepted value for the yearly dose from cosmic radiation at sea level. Shielding cosmic muons with a concrete slab from 0 to 2 meters increased the dose received by the body. This dissertation presents an extensive study on the interactions of secondary electrons created by muons in water.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2002.
Includes bibliographical references (p. 115-119).
Building energy simulation is an important tool for evaluating the energy consumption of a building and can provide guidance in the design of a building and its mechanical systems. EnergyPlus is a new energy simulation program meant to be a major advance over existing energy simulation programs. This study uses EnergyPlus to compare several alternative low-energy cooling systems for an office building in suburban London and compare them to the chilled ceiling system installed in the actual building. Prior to modeling the full -scale building, several validation studies demonstrate the accuracy of EnergyPlus and the author's competency as an EnergyPlus user. Systems considered include displacement ventilation, traditional mixing variable air volume ventilation, night cooling, and natural ventilation. Several changes were made to the EnergyPlus source code to model these systems appropriately. Most notable are a displacement ventilation three-node vertical temperature gradient model and a simple model for prediction of the natural ventilation rate. A detailed building model is created from inputs gathered from both building design documents and measured data. An excellent comparison between simulated and measured space temperatures over a one-month period demonstrates the accuracy of the model. System comparisons show that systems using free cooling from outside air and night cooling use the least energy and have the smallest equipment. Natural ventilation alone is insufficient to maintain summer comfort within the building, but could be used within a hybrid ventilation system. Conclusions are that EnergyPlus should be adopted for general use, because it represents a major improvement over previous energy simulation programs and is capable of modeling real-world buildings. A hybrid ventilation system would have the lowest building system energy use, but displacement ventilation is also a good choice, and could be implemented with few changes to the existing building.
by Erik L. Olsen.
S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, May, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 89-91).
Inspired by emerging low-power robotic vehicles, we identify a new class of motion planning problems in which the energy consumed by the computer while planning a path can be as large as the energy consumed by the actuators during the execution of the path. As a result, minimizing energy requires minimizing both actuation energy and computing energy since computing energy is no longer negligible. We propose the first algorithm to address this new class of motion planning problems, called Computing Energy Included Motion Planning (CEIMP). CEIMP operates similarly to other anytime planning algorithms, except it stops when it estimates that while further computing may save actuation energy by finding a shorter path, the additional computing energy spent to find that path will negate those savings. The algorithm formulates a stochastic shortest path problem based on Bayesian inference to estimate future actuation energy savings from homotopic class changes. We assess the trade-off between the computing energy required to continue sampling to potentially reduce the path length, the potential future actuation energy savings due to reduction in path length, and the overhead computing energy expenditure CEIMP introduces to decide when to stop computing. We evaluate CEIMP on realistic computational experiments involving 10 MIT building floor plans, and CEIMP outperforms the average baseline of using maximum computing resources. In one representative experiment on an embedded CPU (ARM Cortex A-15), for a simulated vehicle that uses one Watt to travel one meter per second, CEIMP saves 2.1-8.9x of the total energy on average across the 10 floor plans compared to the baseline, which translates to missions that can last equivalently longer on the same battery. As the the energy to move relative to the energy to compute decreases, the energy savings with CEIMP will increase, which highlights the advantage in spending computing energy to decide when to stop computing.
by Soumya Sudhakar.
S.M.
S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 107-112).
A low-frequency, low-g piezoelectric MEMS energy harvester has been designed. Theoretically, this new generation energy harvester will generate electric power from ambient vibrations in the frequency range of 200~30OHz at excitation amplitude of 0.5g. Our previous energy harvester successfully resolved the gain-bandwidth dilemma and increased the bandwidth two orders of magnitude. By utilizing a doubly clamed beam resonator, the stretching strain triggered at large deflection stiffens the beam and transforms the dynamics to nonlinear regime, and increases the bandwidth. However, the high resonance frequency (1.3kHz) and the high-g acceleration requirement (4-5g) shown in the testing experiments limited the applications of this technology. To improve the performance of the current energy harvesters by lowering the operating frequency and excitation level, different designs have been generated and investigated. Moreover, a design framework has been formulated to improve the design in a systematic way with higher accuracy. Based on this design framework, parameter optimization has been carried out, and a quantitative design with enhanced performance has been proposed. Preliminary work on fabrication and testing setup has been done to prepare for the future experimental verification of the new design.
by Ruize Xu.
S.M.

The effects of implantation dose, energy, and annealing conditions on the microstructure and the formation and evolution of defects in the low-dose, low-energy SIMOX materials were investigated using transmission electron microscopy (TEM), scanning electron microscopy, scanning electron microscopy (SEM), optical microscopy secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectrometry (RBS). The quality of top Si layer and buried oxide layer (BOX) was also characterized with the electrical measurements. From the structural characterization of 100 keV implanted samples, it was found that the optimum dose window to form a continuous BOX layer after annealing was 3.0 to 3.5 x 10¹⁷ O⁺/cm². In addition, the formation mechanisms of dislocations and stacking faults in SIMOX materials were also proposed. The Hg-based pseudo-MOSFET technique was a very effective in-situ technique to evaluate the electrical quality of low-dose low-energy SIMOX. Based on the comparisons of device parameters of low-dose low-energy SIMOX and commercial SIMOX samples, we found that the quality of top Si layer of SIMOX sample prepared at 100 keV with a dose of 3.5 x 10¹⁷ O⁺/cm² was excellent. However, the interface properties (interfacial trap density) needed to be improved. The dielectric quality of low-dose low-energy SIMOX evaluated by breakdown voltage measurements showed a strong dependency on the microstructure of samples.

Bluetooth Low Energy (BLE) has become a popular Internet of Things (IoT) technology. However, it was originally designed to only support the star topology. This PhD thesis investigates and evaluates different Bluetooth Low Energy (BLE) mesh network approaches, including existing ones (such as the Bluetooth Mesh standard), and our own solution for IPv6-based BLE mesh networking (6BLEMesh). The thesis comprises 6 main contributions: 1.- A comprehensive survey on existing BLE mesh networking proposals and a taxonomy for BLE mesh network solutions. 2.- An energy consumption model for Bluetooth Mesh. The model allows to predict useful performance parameters, such as device average current consumption, device lifetime and energy efficiency, considering the impact of the most relevant Bluetooth Mesh parameters, i.e. PollTimeout and ReceiveWindow, as well as application parameters (e.g. the data interval for a sensor that periodically reports its readings). 3.- A new proposed IPv6-based BLE mesh networking IETF standard (in progress), called 6BLEMesh. After defining the characteristics and properties of 6BLEMesh, we evaluated it in terms of connectivity, latency, RTT, and energy consumption. 4.- For the connectivity evaluation of 6BLEMesh, we developed an analytical model that takes a set of network and scenario characteristics as inputs, and provides two main results: i) the probability of no isolation of a node, and ii) the k-connectivity of the considered network. We validated the model by simulation. 5.- An implementation, and an experimental evaluation, of 6BLEMesh. We built a three-node testbed consisting of all node types (i.e. 6LN, 6LR and 6LBR). We used three different popular commercial hardware platforms. We evaluated a number of performance parameters on the testbed, related with latency and energy consumption. Next, we characterized the current consumption patterns of the complete life cycle for different node types in the three-node testbed. We also evaluated the energy performance of a 6LN on three different platforms. We presented a 6LN current consumption model for different connInterval settings. To this end, we experimentally characterized each current consumption state in terms of its duration time and average current consumption value. We illustrated the impact of connInterval on energy performance. 6.- A comparison between Bluetooth Mesh and 6BLEMesh, in terms of protocol stack, protocol encapsulation overhead, end-toend latency, energy consumption, message transmission count, end-to-end reliability, variable topology robustness and Internet connectivity. Bluetooth Mesh and 6BLEMesh offer fundamentally different BLE mesh networking solutions. Their performance depends significantly on their parameter configuration. Nevertheless, the following conclusions can be obtained. Bluetooth Mesh exhibits slightly greater protocol encapsulation overhead than 6BLEmesh. Both Bluetooth Mesh and 6BLEMesh offer flexibility to configure per-hop latency. For a given latency target, 6BLEMesh offers lower energy consumption. In terms of message transmission count, both solutions may offer relatively similar performance for small networks; however, BLEMesh scales better with network size and density. 6BLEMesh approaches ideal packet delivery probability in the presence of bit errors for most parameter settings (at the expense of latency increase), whereas Bluetooth Mesh requires path diversity to achieve similar performance. Bluetooth Mesh does not suffer the connectivity gaps experimented by 6BLEMesh due to topology changes. Finally, 6BLEMesh naturally supports IP-based Internet connectivity, whereas Bluetooth Mesh requires a protocol translation gateway.
Bluetooth Low Energy (BLE) ha esdevingut una tecnologia popular per a Internet of Things (loT). Ara bé, va ser originalment dissenyada per suportar només la topologia en estrella. Aquesta tesi doctoral investiga i avalua diferents alternatives de xarxa mesh BLE, incloent alternatives existents (com l'estandard Bluetooth Mesh), i la nostra propia solució basada en IPv6, 6BLEMesh. Aquesta tesi comprén 6 contribucions·principals: 1.- Una revisió exhaustiva de l'estat de l'art i una taxonomia de les xarxes mesh BLE. 2.- Un model de consum d'energia per Bluetooth Mesh. El model permet predir parametres de rendiment útils, tals com consum de corrent, temps de vida del dispositiu i eficiéncia energética, considerant !'impacte deis principals parametres de Bluetooth Mesh (PollTimeout i ReceiveWindow) i a nivell d'aplicació. 3.- Un nou estandard (en progrés) anomenat 6BLEMesh. Després de definir les característiques de 6BLEMesh, aquesta solució ha estat avaluada en termes de connectivitat, laténcia, RTT i consum d'energia. 4.- Per a l'avaluació de connectivitat de 6BLEMesh, hem desenvolupat un model analític que proporciona dos resultats principals: i) probabilitat de no arllament d'un node i ii) k-connectivitat de la xarxa considerada. Hem validat el model mitjani;:ant simulació. .- Una imP.lementació, i una avaluació experimental, de 6BLEMesh. S'ha construrt un testbed de tres nodes, que comprén 5tots els tipus de node principals (6LN, 6LR i 6LBR). S'han usat tres plataformes hardware diferents. S'han avaluat diversos parametres de rendiment en el testbed, relacionats amb laténcia i consum d'energia. A continuació, s'ha caracteritzat els patrons de consum de corren! d'un ciclde de vida complet per als diferents tipus de nodes en el testbed. També s'han avaluat les prestacions d'energia d'un 6LN en tres plataformes diferents. S'ha presenta! un model de consum de corren! d'un 6LN per a diferents valors de connlnterval. Per aquest fi, s'ha caracteritzat emplricament cada estat de consum de corrent en termes de la seva durada i consum de corrent. 6.- Una comparativa entre Bluetooth Mesh i 6BLEMesh, en termes de pila de protocols, overhead d'encapsulament de protocol, laténcia extrem a extrem, consum d'energia, nombre de missatges transmesos, fiabilitat extrem a extrem, robustesa davant de topologies variables, i connexió a Internet. Bluetooth Mesh i 6BLEMesh són solucions de BLE mesh networking fonamentalment diferents. Les seves prestacions depenen de la seva configuració de parametres. Ara bé, es poden extreure les següents conclusions. Bluetooth Mesh mostra un overhead d'encapsulament de protocol lleugerament superior al de 6BLEmesh. Tots dos, Bluetooth Mesh i 6BLEMesh, ofereixen flexibilitat per configurar la laténcia per cada salt. Per un target de laténcia doni¡it, 6BLEMesh ofereix un consum d'energia inferior. En termes de nombre de missatges transmesos, les dues solucions ofereixen prestacions relativament similars per a xarxes petites. Ara bé, 6BLEMesh escala millor amb la mida i la densitat de la xarxa. 6BLEMesh s'aproxima a una probabilitat d'entrega de paquets ideal en preséncia d'errors de bit (amb un increment en la laténcia), mentre que Bluetooth Mesh requereix diversitat de caml per assolir unes prestacions similars. Bluetooth Mesh no pateix els gaps de connectivitat que experimenta 6BLLEMesh a causa de canvis en la topología. Finalment, 6BLEMesh suporta de forma natural la connectivitat amb Internet basada en IP, mentre que Bluetooth Mesh requereix un gateway de traducció de protocols.

The π-p → γn and π-p → π⁰n reactions were studied for laboratory pion kinetic energies of 50, 66, 80, 95, 110, and 125 MeV at 9 angles between 30° and 140°, using a large Nal(Tl) detector, TINA. The results are much more accurate than previous data. The radiative capture differential cross-sections are compared with previous data and with several calculations and will specify more precisely the isoscalar amplitudes in multipole analyses. They are consistent with earlier data and confirm the principle of detailed balance, but indicate that the theoretical calculations cannot reproduce the nucleon data adequately below resonance. The charge exchange differential cross-sections are obtained by unfolding the energy spectra of the π⁰ γ-ray decay, and agree with the Karlsruhe and VPI phase-shift analyses. Pion-nucleon phase-shifts and scattering lengths are calculated and the results are in good agreement with data from the elastic scattering channels and support isospin invariance in this energy region.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

Dispositifs photovoltaïques d'aujourd'hui convertissent l'énergie solaire en électricité de manière propre, renouvelable et inépuisable et représentent un remplacement possible pour les combustibles fossiles. Toutefois, afin de rivaliser avec les sources d'énergie classiques une augmentation significative de l'efficacité de conversion est inévitable. Dans ce travail, nous nous concentrons sur des aspects pouvant propulser le rendement de conversion au-dessus des limites de cellules présentes. La première partie de l'étude est consacrée à de nouvelles idées théoriques considérés comme le photovoltaïque de 3ème génération, alors que le plus d'intérêt est maintenu à étudier les avantages possibles de la multiplication d'électrons faible seuil. Dans la deuxième partie de l'étude, nous développons un modèle qui permet un traitement précis des propriétés optiques et de transport des structures de silicium avec des interfaces enterrées. Les analyses théoriques et expérimentales approfondies des structures existantes MIND sont ensuite effectuées. En étudiant le flux exacte et la distribution d'énergie à l'intérieur de plusieurs structures dans le cadre de leur géométrie, nous estimons les rendements quantiques possibles et les comparer avec les résultats expérimentaux. Grâce aux moyens de simulations numériques couplées avec caractérisation expérimentale, nous extrayons l'efficacité de la collecte de porteur de cellules étudiées. De nouveaux effets sont observés, une telle augmentation possible de l'efficacité de la collecte au-dessus de l'unité. Une analyse plus approfondie des résultats expérimentaux couplés avec l'étude numérique suit quelques explications classiques et non classiques de l'augmentation de l'efficacité de la collecte ou l'augmentation résultante de l'efficacité quantique. Avec la plupart des explications classiques exclu, nous concluons que l'explication la plus probable, mais non définitive de cet effet peut être interprété comme le résultat d'une multiplication des porteurs faible seuil
Photovoltaic devices of today convert solar energy into electricity in a clean, renewable and inexhaustible way and represent a possible replacement for the fossil fuels. However, in order to compete with classical energy sources a significant increase in the conversion efficiency is inevitable. In this work, we concentrate on the aspects able to raise the conversion efficiency above the limitations of present cells. The first part of the study is devoted to new theoretical ideas considered as 3rd generation photovoltaics, while the most interest is kept at studying the possible benefits of electron multiplication at low-energies. In the second part of the study, we develop a model that allows a precise treatment of optical and transport properties of silicon structures with buried interfaces. Extensive theoretical and experimental analyses of existing MIND structures are then conducted. By studying the exact flux and power distribution inside several structures in conjunction with their geometry, we estimate the possible quantum efficiencies and compare them with experimental results. Through the means of numerical simulations coupled with experimental characterization, we extract the carrier collection efficiency of studied cells. New effects are being observed, such a possible increase in collection efficiency above unity. A deeper analysis of the experimental results coupled with the numerical study analyzes several classical and non-classical explanations of the increase in collection efficiency or the resulting increase in the quantum efficiency. With most of the classical explanations ruled out, we conclude that the most probable, but not definitiveexplanation of this effect can be interpreted as the result of a low-energy carrier multiplication

Wireless communication is becoming more common, a relatively new technology within the area is Bluetooth Low Energy. It’s been developed to be energy efficient and in regard to compatibility. Alongside the growth of wireless technology, scientists and companies are looking for new areas of use. One of these is localization, which means to determine the position of a moving device with the use of stationary devices, an example of this would be GPS.This report means to evaluate indoor localization using Bluetooth Low Energy and was made for Combitech AB in Jönköping. The purpose of the work was to determine with what accuracy and precision the position of a moving device could be estimated. The report will answer the following questions: With what accuracy and precision can the position of a device be determined within a test area of varying size using Bluetooth Low Energy? Is the accuracy and precision affected by the environment?The authors chose an inductive reasoning and therefore intended to answer the questions with the help of experimental studies. A system consisting of both software and hardware was developed and was then used to conduct multiple rounds of tests, where the size of the area and the environment was varied.By evaluating the data gathered from said tests and comparing it to theoretical studies and prior research credible results were obtained. The accuracy appears to decrease as the distance between the units is increased, however a deeper analysis shows that the difference is smaller below 500 cm. No correlation is found between environment and accuracy. When three stationary units, forming a triangle with 400 cm between the vertices, are used to determine the position of a fourth the achieved accuracy is 65 cm. During the tests the precision is not shown to decrease with distance, it seems to vary independently. However, as the environment is changed a noticeable difference is observed. In a gymnasium the standard deviation was calculated to 0.38 RSSIwhereas in an office environment it was 0.99 RSSI. In regard to the given results the authors conclude that Bluetooth Low Energy shows some potential for the use in indoor positioning systems. A possible scenario where the technology would be well suited would be when the units need to work of a coin cell battery for a large period of time, while the system must support multiple types of units and a rough estimation of the position is adequate.
Trådlös kommunikation blir allt mer vanlig i vår vardag, en relativt ny teknik inom detta område är Bluetooth Low Energy som utvecklats med avseende på energieffektivitet och kompabilitet. Parallellt med den trådlösa teknikens spridning letar forskare, såväl som företag, efter nya användningsområden. En av dessa är lokalisering, vilket innebär att med fasta enheter avgöra rörliga enheters position, ett exempel på detta är GPS. Detta arbete handlar om att utvärdera inomhuslokalisering med Bluetooth Low Energy och gjordes på uppdrag av Combitech AB i Jönköping. Syftet var att undersöka med vilken noggrannhet och precision en rörlig enhets position kunde avgöras. Rapporten kommer att besvara följande frågeställningar: Med vilken noggrannhet och precision kan man med Bluetooth Low Energy avgöra en enhets position inom ett testområde med varierande storlek? Påverkas noggrannhet och precision av omgivningen?Författarna valde en induktiv metod och ämnade därför besvara frågeställningarna med hjälp av experimentella studier. Ett testsystem bestående av hård- samt mjukvara utvecklades varpå tester utfördes i flera omgångar, där storlek på område och omgivning varierades. Genom utvärdering av testdata i förhållande till teoretiska studier och tidigare forskning kunde trovärdiga resultat nås. Noggrannheten tycks minska då avståndet mellan enheter ökas, djupare analys pekar på en mindre förlust under 500 cm. Det observeras dock inget samband mellan noggrannhet och omgivning. Då tre fasta enheter placeras med ett inbördes avstånd på 400 cm kan positionen avgöras med 65 cm noggrannhet. Precisionen påverkas under testerna inte av avstånd, signalstyrkevärdena varierar helt oberoende av detta. Vid skifte av omgivning tydliggörs dock en markant skillnad i resultat. I en idrottshall beräknades standardavvikelsen till 0,38 RSSI medan den i en kontorsmiljö var 0,99 RSSI.Författarna drar utifrån det uppnådda resultat slutsatsen att Bluetooth Low Energy har viss potential att användas för inomhuslokalisering. Exempel på ett möjligt scenario där tekniken anses väl lämpad är då de fasta enheterna måste drivas av knappcellsbatterier under en lång tidsperiod, att systemet skall stödja en mängd olika enheter samt att en grov uppskattning av position är tillräcklig.

The aim of this project is to design, simulate, and implement a privacy enhancement protocol over BLE advertising channels. The design of the privacy enhancement is generic and modular. Due to the risk of privacy disclosure and device tracking by adversary, the main focus will be put on designing and implementing message confidentiality, replay prevention, and anti-tracking of device over BLE advertising channels. Bluetooth core specification 4.1 is used as baseline for design and implementation. In order to provide resistance against replay attacks and device tracking, this project has taken counter approach. It proposes a 3-way handshake protocol for nonce Rs deployment. There are two nonces Ra and Rs involved in the 3-way handshake protocol. The advertiser generates a nonce Ra as challenge sent to the scanner, which assures of freshness of the advertising session. Then the scanner generates a nonce Rs for advertising confidentiality and replay prevention. After the nonce Rs is deployed successfully from the scanner to the advertiser, the local counters Receiving (RX) and Transmitting (TX) on both sides are initialized to be Rs which protects all the following advertisement in the advertising session.To accommodate to open BLE advertising channels a handling mechanism of counter out-of-synchronization is given in system design. Moreover, to avoid unnecessary power consumption in the BLE devices then mitigation for Denial-of-service (DoS) is also proposed. In addition, advertising confidentiality, replay prevention, and antitracking of device have been simulated in Scyther and also been integrated into the code. The functional tests have been done in a realistic testing environment. The results show that the added functionalities work as designed.

Approved for public release; distribution is unlimited
Piezoelectricity is a material property that generates an electric charge proportional to the mechanical stress placed on the material. This phenomenon was first discovered by the Curie brothers in 1880. This material property gives the ability to turn vibrations into an electrical waveform, but power electronics is necessary to harness this low-level energy. AC power is often produced at the power plant level in modern society; however, low voltage AC power is widely available in vibrational form. The U.S. Navy may be able to utilize piezoelectric technology to harness wasted vibrational energy. Some of these applications include inserting a piezoelectric harvester in shoes to supply small amounts of power to cell phones or utilizing motion energy to provide power to iPod chargers. The power electronics that provides full bridge rectification and step down conversion, which achieves AC-DC power harvesting, is discussed. Also discussed is a breakdown of possible applications for such a device as well as the benefits of turning AC power into DC. A Linear Technology LTC-3588-1 integrated circuit was simulated in software and demonstrated in hardware. The hardware experiment showed that the software accurately predicted the performance of the chip.

Cosmologists are interested in topological defects as a possible source for the primordial density perturbations which seeded structure formation through gravitational instability. In this thesis, the gravitational properties of various topological defects are studied in the context of low-energy string theory, a likely modification of Einstein gravity at the high energy scales prevalent in the early universe. We consider in turn global monopole, local monopole, global cosmic string and global texture defects, allowing for an arbitrary coupling of defects to the string theory dilaton. For global defects we find the following behaviour. If the dilaton is massless, this modification to general relativity generically destroys the global good behaviour of the monopole and cosmic string, making their spacetimes singular. For the texture non-singular spacetimes exist, but only for certain values of the matter-dilaton coupling, dependent on the gravitational strength of the defect; in addition, this non-singular behaviour exists only in a certain frame. In the case of a massive dilaton, the metric behaviour of these defects is similar to that found in Einstein gravity, though we find they generically induce a long-range dilaton cloud. For the local monopole, which we study only in the presence of a massless dilaton, a rich variety of behaviour is found. For particular parameter values the local monopole spacetime approximates that of an extremal dilaton black hole.