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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

AFM surface force measurements between hydrophobized gold surfaces

Wang, Jialin 08 October 2008 (has links)
In 1982, Israelachvili and Pashley reported the first measurements of a hitherto unknown attractive force between two mica surfaces hydrophobized in cetyltrimethylammonium bromide (CTAB) solutions. Follow-up experiments conducted by many investigators confirmed their results, while others suggested that the "hydrophobic force" is an artifact due to nanobubbles (or cavitation). Evidences for the latter included the discontinuities (or steps) in the force versus distance curves and the pancake-shaped nano-bubbles seen in atomic force microscopic (AFM) images. Recent measurements conducted in degassed water showed, however, smooth force versus distance curves, indicating that the hydrophobic force is not an artifact due to nanobubbles.1, 2 Still other investigators3, 4 suggested that the long-range attraction observed between hydrophobic surfaces is due to the correlation between the patches of adsorbed ionic surfactant and the patches of unoccupied surface. For this theory to work, it is necessary that the charged patches be laterally mobile to account for the strong attractive forces observed in experiment. In an effort to test this theory, AFM force measurements were conducted with gold substrates hydrophobized by self-assembly of alkanethiols and xanthates of different chain lengths. The results showed long-range attractions despite the fact that the hydrophobizing agents chemisorb on gold and, hence, the adsorption layer is immobile. When the gold surfaces were hydrophobized in a 1 Ã 10-3 M thiol-in-ethanol solution for an extended period of time, the force curves exhibited steps. These results indicate that the long-range attractions are caused by the coalescence of bubbles, as was also reported by Ederth.5 The steps disappeared, however, when the species adsorbed on top of the chemisorbed monolayer were removed by solvent washing, or when the gold substrates were hydrophobized in a 1 Ã 10-5 M solution for a relatively short period of time. AFM force measurements were also conducted between gold substrates coated with short-chain thiols and xanthates to obtain hydrophobic surfaces with water contact angles (ï ±) of less than 90o. Long-range attractions were still observed despite the fact that cavitation is thermodynamically not possible. Having shown that hydrophobic force is not due to coalescence of pre-existing bubbles, cavitation, or correlation of charged patches, the next set of force measurements was conducted in ethanol-water mixtures. The attractive forces became weaker and shorter-ranged than in pure water and pure ethanol. According to the Derjaguin's approximation6, an attractive force arises from the decrease in the excess free energy (ï §f) of the thin film between two hydrophobic surfaces.7 Thus, the stronger hydrophobic forces observed in pure water and pure ethanol can be attributed to the stronger cohesive energy of the liquid due to stronger H-bonding. Further, the increase in hydrophobic force with decreasing separation between two hydrophobic surfaces indicates that the H-bonded structure becomes stronger in the vicinity of hydrophobic surfaces. The force measurements conducted at different temperatures in the range of 10-40C showed that the hydrophobic attraction between macroscopic surfaces causes a decrease in film entropy (Sf), which confirms that the hydrophobic force is due to the structuring of water in the thin film between two hydrophobic surfaces. The results showed also that the hydrophobic interaction entails a reduction in the excess film enthalpy (Hf), which may be associated with the formation of partial (or full) clathrates formed in the vicinity of hydrophobic surfaces. The presence of the clathrates is supported by the recent finding that the density of water in the vicinity of hydrophobic surfaces is lower than in the bulk.8 / Ph. D.
82

Bradford Non-Lethal Weapons Research Project (BNLWRP). Research Report No. 7.

Davison, N., Lewer, N. January 2005 (has links)
yes / The length of this Bradford Non-Lethal Weapons Research Project Report No.7 again reflects the interest related to non-lethal weapons from academics, research institutes, policy makers, the police and the military. A number of reports, particularly concerning the Taser electro-shock weapon, have been published from these sectors since our last BNLWRP Report No.6 in October 2004. Some, such as the Amnesty International (U.S. and Canada) have again raised, and stressed, the concerns about the safety of the weapon and the number of deaths associated with its use. Others, such as the Joint Non-Lethal Weapons Human Effects Center of Excellence (HECOE), Human Effectiveness and Risk Characterization of the Electromuscular Incapacitation Device ¿ A Limited Analysis of the TASER. (March 2005) concluded that the Taser was relatively safe, but that further research was needed into potential bio-effects, and for continual development into a safer weapon. Reaction to these reports was mixed. Some US legislators called for limitations on the use of Tasers, more accountability, and the detailed recording of incidents in which they were used.1 Others called for a ban on their use until more testing was carried out regarding their potentially harmful effects. A number of US police forces stopped the use of Taser, slowed down the deployment and ordering of the weapons, reviewed their rules of engagement and reporting, and revisited their operational guidelines. The International Association of Chiefs of Police (IACP) published the Electro- Muscular Disruption Technology (EMDT). A Nine-Step Strategy For Effective Deployment. (April 2005) as a response to these growing concerns. Certain elements of the media, especially The Arizona Republic2 and others, took a hostile view of what they considered the scandal of the number of deaths and associated serious injuries caused by the Taser. Taser International challenged allegations that their weapon was directly responsible for these deaths and quoted reports, such as the Madison Police Department report (February 2005), the study by McDaniel, W & Stratbucker, R & Nerheim, M & Brewer, J. Cardiac Safety of Neuromuscular Incapacitating Defensive Devices (January 2005), and the U.K. DOMILL Statement (March 2005) to support their view. The controversy continues. Other than Tasers, there are still few reports of the newer non-lethal technologies actually being deployed in operations. The exception to this is the Long Range Acoustic Device (LRAD), which is now in widespread use in Iraq. Little additional information has appeared regarding the `active denial¿ weapon we have described in previous reports.
83

Forecasting Highly-Aggregate Internet Time Series Using Wavelet Techniques

Edwards, Samuel Zachary 28 August 2006 (has links)
The U.S. Coast Guard maintains a network structure to connect its nation-wide assets. This paper analyzes and models four highly aggregate traces of the traffic to/from the Coast Guard Data Network ship-shore nodes, so that the models may be used to predict future system demand. These internet traces (polled at 5â 40â intervals) are shown to adhere to a Gaussian distribution upon detrending, which imposes limits to the exponential distribution of higher time-resolution traces. Wavelet estimation of the Hurst-parameter is shown to outperform estimation by another common method (Sample-Variances). The First Differences method of detrending proved problematic to this analysis and is shown to decorrelate AR(1) processes where 0.65< phi1 <1.35 and correlate AR(1) processes with phi1 <-0.25. The Hannan-Rissanen method for estimating (phi,theta) is employed to analyze this series and a one-step ahead forecast is generated. / Master of Science
84

Computational modeling of biological barriers

Wennberg, Christian January 2016 (has links)
One of the most important aspects for all life on this planet is the act to keep their biological processes in a state where they do not reach equilibrium. One part in the upholding of this imbalanced state is the barrier between the cells and their surroundings, created by the cell membrane. Additionally, terrestrial animal life often requires a barrier that protects the organism's body from external hazards and water loss. As an alternative to experiments, the investigation of the processes occurring at these barriers can be performed by using molecular dynamics simulations. Through this method we can obtain an atomistic description of the dynamics associated with events that are not accessible to experimental setups.  In this thesis the first paper presents an improved particle-mesh Ewald method for the calculation of long-range Lennard-Jones interactions in molecular dynamics simulations, which solves the historical performance problem of the method. The second paper demonstrate an improved implementation, with a higher accuracy, that only incurs a performance loss of roughly 15% compared to conventional simulations using the Gromacs simulation package. Furthermore, the third paper presents a study of cholesterol's effect on the permeation of six different solutes across a variety of lipid bilayers. A laterally inhomogeneous permeability in cholesterol-containing membranes is proposed as an explanation for the large differences between experimental permeabilities and calculated partition coefficients in simulations. The fourth paper contains a coarse-grained simulation study of a proposed structural transformation in ceramide bilayer structures, during the formation of the stratum corneum. The simulations show that glycosylceramides are able to stabilize a three-dimensionally folded bilayer structure, while simulations with ceramides collapse into a lamellar bilayer structure. / <p>QC 20160308</p>
85

HIGH ALTITUDE TRANSMITTER FLIGHT TESTING

Brown, K. D., Sorensen, Trevor 10 1900 (has links)
International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper describes a high altitude experimental flight test platform developed by the University of Kansas (KU) and the National Nuclear Security Administration’s Kansas City Plant (NNSA’s Kansas City Plant) for high altitude payload flight testing. This platform is called the Kansas University Balloon Experiment Satellite (KUBESat). The paper describes the flight test platform and experimental flight test results captured at Fort Riley, KS from characterization of the KCP developed Distributed Transmitter (DTX).
86

Mudanças estruturais na proteína príon celular induzidas por alteração de pH

Thompson, Helen Nathalia January 2012 (has links)
Os príons são proteínas que causam um grupo de doenças neurodegenerativas invariavelmente fatais, sendo uma das mais conhecidas a encefalopatia espongiforme bovina (ou doença da vaca louca). A proteína príon celular (PrPc), rica em estrutura α-helicoidal, sofre uma mudança na sua estrutura secundária produzindo a proteína patológica (PrPSc; o príon) na qual prevalecem folhas-β. Devido a falta de dados de estruturais de alta resolução dos príons, simulações de DM podem ser particularmente úteis para estudar o redobramento de PrP. Estudos experimentais e computacionais, descritos na literatura, indicam que a utilização de pH ácido é capaz de criar alguma instabilidade estrutural, produzindo um ganho de estrutura-β na região N-terminal antes desestruturada. Este trabalho se propõe a investigar computacionalmente as mudanças estruturais na proteína príon celular do hamster Sírio induzidas por alteração de pH. Para isso, foi avaliada a influência do uso de diferentes campos de força (GROMOS, AMBER e OPLS), diferentes estados de protonação dos resíduos de histidina, diferentes condições iniciais e diferentes métodos de cálculo de interações eletrostáticas de longo alcance (GRF e SPME). A partir da evolução temporal das estruturas secundárias, foi observada uma forte dependência dos resultados com o uso de diferentes parâmetros de simulação. De fato, a tendência de pH descrita na literatura não foi claramente observada neste trabalho. Isso pode estar associado com a necessidade de se investir mais em múltiplas simulações de dinâmica molecular para quantificar com maior precisão o comportamento estrutural dos fragmentos protéicos em cada pH de estudo. / Prions are proteins that cause a group of invariably fatal neurodegenerative diseases, one of the most known being bovine spongiform encephalopathy (or mad cow disease). The cellular prion protein (PrPc), rich in α-helical structure, undergoes a change in its secondary structure producing the pathological protein (PrPSc, the prion) in which β-sheet structure prevails. Because of the lack of high-resolution prion structural data, MD simulations can be particularly useful to study PrP misfolding. Experimental and computational studies, described in literature, indicate that the use of low pH is capable to create some structural instability, producing a gain of β-structure content in the otherwise unstructured N-terminal region. This work aims to investigate computationally structural changes in the cellular prion protein of Syrian hamster induced by pH change. For this, we evaluated the influence of different force fields (GROMOS, AMBER and OPLS), different protonation states of histidine residues, different initial conditions and different methods for calculating long-range electrostatic interactions (GRF and SPME). From the time evolution of the secondary structures, we observed a strong dependence on the simulation parameters. In fact, the pH tendency described in literature was not clearly observed in this work. It may be associated with the need to invest more in multiple molecular dynamics simulations to quantify more accurately the structural behavior of the protein fragments in each pH study.
87

Contribuição para a análise de teletráfego com dependência de longa duração. / Contribution to the analysis of network traffic with long-range dependence.

Lipas Augusto, Marcelo 07 April 2009 (has links)
A utilização de modelos de teletrafego que contemplem caractersticas tais como autossimilaridade e dependencia de longa duraçao tem se mostrado cada vez mais como sendo ponto-chave na correta caracterizaçao do teletrafego Local Area Network (LAN) e Wide Area Network (WAN) [1, 2]. Tal caracterizaçao e necessaria para o monitoramento e controle de teletrafego em redes convergentes [3]. Nesse contexto, a questão da estimaçao precisa do parâmetro de autossimilaridade, denominado de parâmetro de Hurst, torna-se essencial. Entretanto, estudos comprovam que, alem da dependência de longa duraçao, redes WAN podem, não raramente, apresentar caractersticas mistas de dependência de longa e de curta duraçao [4, 5]. Enquanto vasta literatura cientca, tanto teorica como pratica, tem abordado com anco a questão da acuracia de diversos estimadores para o parâmetro de Hurst [6, 7, 8, 9], pouca atenção tem sido dada a questão da estimação deste parâmetro na presenca de dependência de curta duração. O presente trabalho de pesquisa concentrou-se no estudo dos metodos de estimaçao do parametro de Hurst baseados no espectro wavelet, em particular atraves do metodo de Abry-Veitch [10] { baseado na transformada Discrete Wavelet Transform (DWT) { e atraves do espectro obtido atraves da transformada Discrete Wavelet Packet Transform (DWPT). Os resultados baseados no metodo de Abry-Veitch demonstram que, atraves de um ajuste apropriado dos par^ametros de estimaçao, tal metodo permite uma estimaçao robusta na presenca de componentes com dependencia de curta duraçao, mesmo em situaçoes de mudanca de regime de tal componente, caracterstica desejavel para a estimaçao em tempo real do parametro de Hurst. Entretanto, a dispersao consideravel apresentada, em alguns casos, pelas estimativas do metodo de Abry-Veitch, motivou o estudo da utilizaçao do espectro wavelet obtido via transformada DWPT para realizaçao da estimaçao do parametro de Hurst. Os resultados indicam que a utilizaçao de tal transformada gera um espectro wavelet tal que e possvel detectar a presenca ou não de componentes com dependencia de curta duraçao. Ao final, os resultados da pesquisa realizada são sumarizados e utilizados em uma proposta de mecanismo de estimaçao do parametro de Hurst em tempo real, na presenca simultanea de componentes de dependencia de longa e curta duracão. / The use of network trac models that hold self-similar and long-range dependence characteristics have shown to be a key element on the correct characterization of Local Area Network (LAN) and Wide Area Network (WAN) network trac [1, 2]. Such characterization is necessary to monitor and control the network trac in converged networks [3]. In this context, the accurate estimation of the selfsimilarity parameter, named Hurst parameter, is a major issue. However, studies show that, besides the long-range dependence, WAN network trac may, not uncommonly, present mixed long and short-range dependence characteristics [4, 5]. While great part of either theoretical or practical scientic literature has been focused on the issue of Hurst parameter estimator accuracy [6, 7, 8, 9], little attention has been given to the estimation of such parameter in the presence of short-range dependence. This research work has focused on the study of the Hurst parameter estimation methods based on the wavelet spectrum, specially through the Abry-Veitch method [10] { which is based on the Discrete Wavelet Transform (DWT) transform { and through the wavelet spectrum based on the Discrete Wavelet Packet Transform (DWPT) transform. The results based on the Abry-Veitch method show that, through a suitable adjustment of the estimation parameters, such method yields a robust estimation in the presence of short-range dependence components, even in changing conditions of such component, a desirable characteristic for the real-time estimation of the Hurst parameter. However, the signi cant dispersion presented, occasionally, by the Abry-Veitch method estimates motivated the research of the usage of the wavelet spectrum obtained via DWPT transform to estimate the Hurst parameter. The results show that the usage of such transform generates such a wavelet spectrum that it is possible to detect whether short-range dependence components are present, or not, in the analyzed series. At the end, the research results are summarized and used to propose a realtime Hurst parameter estimation mechanism, in the presence of simultaneous long- and short-range dependence components.
88

Analysis of non-stationary (seasonal/cyclical) long memory processes / L'analyse de processus non-stationnaire long mémoire saisonnier et cyclique

Zhu, Beijia 20 May 2013 (has links)
La mémoire longue, aussi appelée la dépendance à long terme (LRD), est couramment détectée dans l’analyse de séries chronologiques dans de nombreux domaines, par exemple,en finance, en économétrie, en hydrologie, etc. Donc l’étude des séries temporelles à mémoire longue est d’une grande valeur. L’introduction du processus ARFIMA (fractionally autoregressive integrated moving average) établit une relation entre l’intégration fractionnaire et la mémoire longue, et ce modèle a trouvé son pouvoir de prévision à long terme, d’où il est devenu l’un des modèles à mémoire longue plus populaires dans la littérature statistique. Précisément, un processus à longue mémoire ARFIMA (p, d, q) est défini comme suit : Φ(B)(I − B)d (Xt − µ) = Θ(B)εt, t ∈ Z, où Φ(z) = 1 − ϕ1z − · · · − ϕpzp et Θ(z) = 1 + · · · + θ1zθpzq sont des polynômes d’ordre p et q, respectivement, avec des racines en dehors du cercle unité; εt est un bruit blanc Gaussien avec une variance constante σ2ε. Lorsque d ∈ (−1/2,1/2), {Xt} est stationnaire et inversible. Cependant, l’hypothèse a priori de la stationnarité des données réelles n’est pas raisonnable. Par conséquent, de nombreux auteurs ont fait leurs efforts pour proposer des estimateurs applicables au cas non-stationnaire. Ensuite, quelques questions se lèvent : quel estimateurs doit être choisi pour applications, et à quoi on doit faire attention lors de l’utilisation de ces estimateurs. Donc à l’aide de la simulation de Monte Carlo à échantillon fini, nous effectuons une comparaison complète des estimateurs semi-paramétriques, y compris les estimateurs de Fourier et les estimateurs d’ondelettes, dans le cadre des séries non-stationnaires. À la suite de cette étude comparative, nous avons que (i) sans bonnes échelles taillées, les estimateurs d’ondelettes sont fortement biaisés et ils ont généralement une performance inférieure à ceux de Fourier; (ii) tous les estimateurs étudiés sont robustes à la présence d’une tendance linéaire en temps dans le niveau de {Xt} et des effets GARCH dans la variance de {Xt}; (iii) dans une situation où le probabilité de transition est bas, la consistance des estimateurs quand même tient aux changements de régime dans le niveau de {Xt}, mais les changements ont une contamination au résultat d’estimation; encore, l’estimateur d’ondelettes de log-regression fonctionne mal dans ce cas; et (iv) en général, l’estimateur complètement étendu de Whittle avec un polynôme locale (fully-extended local polynomial Whittle Fourier estimator) est préféré pour une utilisation pratique, et cet estimateur nécessite une bande (i.e. un nombre de fréquences utilisés dans l’estimation) plus grande que les autres estimateurs de Fourier considérés dans ces travaux. / Long memory, also called long range dependence (LRD), is commonly detected in the analysis of real-life time series data in many areas; for example, in finance, in econometrics, in hydrology, etc. Therefore the study of long-memory time series is of great value. The introduction of ARFIMA (fractionally autoregressive integrated moving average) process established a relationship between the fractional integration and long memory, and this model has found its power in long-term forecasting, hence it has become one of the most popular long-memory models in the statistical literature. Specifically, an ARFIMA(p,d,q) process X, is defined as follows: cD(B)(I - B)d X, = 8(B)c, , where cD(z)=l-~lz-•••-~pzP and 8(z)=1-B1z- .. •-Bqzq are polynomials of order $p$ and $q$, respectively, with roots outside the unit circle; and c, is Gaussian white noise with a constant variance a2 . When c" X, is stationary and invertible. However, the a priori assumption on stationarity of real-life data is not reasonable. Therefore many statisticians have made their efforts to propose estimators applicable to the non-stationary case. Then questions arise that which estimator should be chosen for applications; and what we should pay attention to when using these estimators. Therefore we make a comprehensive finite sample comparison of semi-parametric Fourier and wavelet estimators under the non-stationary ARFIMA setting. ln light of this comparison study, we have that (i) without proper scale trimming the wavelet estimators are heavily biased and the y generally have an inferior performance to the Fourier ones; (ii) ail the estimators under investigation are robust to the presence of a linear time trend in levels of XI and the GARCH effects in variance of XI; (iii) the consistency of the estimators still holds in the presence of regime switches in levels of XI , however, it tangibly contaminates the estimation results. Moreover, the log-regression wavelet estimator works badly in this situation with small and medium sample sizes; and (iv) fully-extended local polynomial Whittle Fourier (fextLPWF) estimator is preferred for a practical utilization, and the fextLPWF estimator requires a wider bandwidth than the other Fourier estimators.
89

Contribuição para a análise de teletráfego com dependência de longa duração. / Contribution to the analysis of network traffic with long-range dependence.

Marcelo Lipas Augusto 07 April 2009 (has links)
A utilização de modelos de teletrafego que contemplem caractersticas tais como autossimilaridade e dependencia de longa duraçao tem se mostrado cada vez mais como sendo ponto-chave na correta caracterizaçao do teletrafego Local Area Network (LAN) e Wide Area Network (WAN) [1, 2]. Tal caracterizaçao e necessaria para o monitoramento e controle de teletrafego em redes convergentes [3]. Nesse contexto, a questão da estimaçao precisa do parâmetro de autossimilaridade, denominado de parâmetro de Hurst, torna-se essencial. Entretanto, estudos comprovam que, alem da dependência de longa duraçao, redes WAN podem, não raramente, apresentar caractersticas mistas de dependência de longa e de curta duraçao [4, 5]. Enquanto vasta literatura cientca, tanto teorica como pratica, tem abordado com anco a questão da acuracia de diversos estimadores para o parâmetro de Hurst [6, 7, 8, 9], pouca atenção tem sido dada a questão da estimação deste parâmetro na presenca de dependência de curta duração. O presente trabalho de pesquisa concentrou-se no estudo dos metodos de estimaçao do parametro de Hurst baseados no espectro wavelet, em particular atraves do metodo de Abry-Veitch [10] { baseado na transformada Discrete Wavelet Transform (DWT) { e atraves do espectro obtido atraves da transformada Discrete Wavelet Packet Transform (DWPT). Os resultados baseados no metodo de Abry-Veitch demonstram que, atraves de um ajuste apropriado dos par^ametros de estimaçao, tal metodo permite uma estimaçao robusta na presenca de componentes com dependencia de curta duraçao, mesmo em situaçoes de mudanca de regime de tal componente, caracterstica desejavel para a estimaçao em tempo real do parametro de Hurst. Entretanto, a dispersao consideravel apresentada, em alguns casos, pelas estimativas do metodo de Abry-Veitch, motivou o estudo da utilizaçao do espectro wavelet obtido via transformada DWPT para realizaçao da estimaçao do parametro de Hurst. Os resultados indicam que a utilizaçao de tal transformada gera um espectro wavelet tal que e possvel detectar a presenca ou não de componentes com dependencia de curta duraçao. Ao final, os resultados da pesquisa realizada são sumarizados e utilizados em uma proposta de mecanismo de estimaçao do parametro de Hurst em tempo real, na presenca simultanea de componentes de dependencia de longa e curta duracão. / The use of network trac models that hold self-similar and long-range dependence characteristics have shown to be a key element on the correct characterization of Local Area Network (LAN) and Wide Area Network (WAN) network trac [1, 2]. Such characterization is necessary to monitor and control the network trac in converged networks [3]. In this context, the accurate estimation of the selfsimilarity parameter, named Hurst parameter, is a major issue. However, studies show that, besides the long-range dependence, WAN network trac may, not uncommonly, present mixed long and short-range dependence characteristics [4, 5]. While great part of either theoretical or practical scientic literature has been focused on the issue of Hurst parameter estimator accuracy [6, 7, 8, 9], little attention has been given to the estimation of such parameter in the presence of short-range dependence. This research work has focused on the study of the Hurst parameter estimation methods based on the wavelet spectrum, specially through the Abry-Veitch method [10] { which is based on the Discrete Wavelet Transform (DWT) transform { and through the wavelet spectrum based on the Discrete Wavelet Packet Transform (DWPT) transform. The results based on the Abry-Veitch method show that, through a suitable adjustment of the estimation parameters, such method yields a robust estimation in the presence of short-range dependence components, even in changing conditions of such component, a desirable characteristic for the real-time estimation of the Hurst parameter. However, the signi cant dispersion presented, occasionally, by the Abry-Veitch method estimates motivated the research of the usage of the wavelet spectrum obtained via DWPT transform to estimate the Hurst parameter. The results show that the usage of such transform generates such a wavelet spectrum that it is possible to detect whether short-range dependence components are present, or not, in the analyzed series. At the end, the research results are summarized and used to propose a realtime Hurst parameter estimation mechanism, in the presence of simultaneous long- and short-range dependence components.
90

Design and implementation of power management strategies for long range radio module with energy harvesting / Conception et implémentation de stratégies de gestion d'énergie pour noeuds radio longue portée avec récupération d'énergie

Gléonec, Philip-Dylan 08 February 2019 (has links)
L'avènement de l'Internet des Objets a permis de déployer de nombreux réseaux de capteurs sans-fil. Ces réseaux sont utilisés dans des domaines aussi variés que l'agriculture, l'industrie ou la ville intelligente, où ils permettent d'optimiser finement les processus. Ces appareils sont le plus souvent alimentés par des piles ou batteries, ce qui limite leur autonomie. De plus, il n'est pas toujours possible ou financièrement viable de changer ou recharger les batteries. Une solution possible est d'alimenter ces capteurs en récupérant l'énergie présente dans l'environnement alentour. Ces sources d'énergie sont cependant peu fiables, et le capteur doit être capable d'éviter de vider complètement sa réserve d'énergie. Afin de moduler sa consommation d'énergie, le capteur peut adapter sa qualité de service à ses capacités énergétiques. L'appareil peut ainsi fonctionner en continu sans interruption de service. Cette thèse présente les méthodes utilisées pour la conception d'un capteur entièrement autonome alimenté par récupération d'énergie ambiante, communiquant sur un réseau longue portée LoRa. Afin d'assurer l'alimentation électrique, une carte permettant de récupérer de l'énergie depuis plusieurs sources d'énergie simultanément a été conçue. Un module logiciel de gestion d'énergie a ensuite été développé afin de calculer un budget énergétique que le capteur peut dépenser, et choisir la meilleure manière de dépenser ce budget pour exécuter une ou plusieurs tâches. Ce travail a ainsi permis le développement d'un prototype de produit industriel entièrement autonome en énergie. / The advent of the Internet of Things has enabled the roll-out of a multitude of Wireless Sensor Networks. These networks can be used in various fields, such as agriculture, industry or the smart city, where they facilitate fine optimization of processes. These devices are often powered by primary or rechargeable batteries, which limits their battery life. Moreover, it is sometimes not possible or financially viable to change and/or recharge these batteries. A possible solution is to harvest energy from the environment to power these sensors. But these energy sources are unreliable, and the sensor must be able to prevent the complete depletion of its energy storage. In order to adapt its energy consumption, the node can match its quality of service to its energetical capabilities. Thus, the device can continuously operate without any service interruption. This thesis presents the methods used for the conception of a completely autonomous sensor, powered by energy harvesting and communicating through a long range LoRa network. In order to ensure its power supply, a board has been designed to harvest energy from multiple energy sources simultaneously. A power management software module has then been developed to calculate an energy budget the sensor can use, and to choose the best way to spend this budget over one or multiple tasks. This work has enabled the development of an energy autonomous industrial sensor prototype.

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