The demand for clean and environmentally benign energy resources has been a great concern in the last two decades. To alleviate the associated environmental problems, reduction of the use of fossil fuels by developing more cost-effective renewable energy technologies becomes more and more significant. Among various types of renewable energy sources, solar energy and bioenergy take a great proportion. This dissertation focuses on the heat transfer and flow in solar energy and bioenergy systems, specifically for Thermal Energy Storage (TES) systems in Concentrated Solar Power (CSP) plants and open-channel algal culture raceways for biofuel production. The first part of this dissertation is the discussion about mathematical modeling, numerical simulation and experimental investigation of solar TES system. First of all, in order to accurately and efficiently simulate the conjugate heat transfer between Heat Transfer Fluid (HTF) and filler material in four different solid-fluid TES configurations, formulas of an effective heat transfer coefficient were theoretically developed and presented by extending the validity of Lumped Capacitance Method (LCM) to large Biot number, as well as verifications/validations to this simplified model. Secondly, to provide design guidelines for TES system in CSP plant using Phase Change Materials (PCM), a general storage tank volume sizing strategy and an energy storage startup strategy were proposed using the enthalpy-based 1D transient model. Then experimental investigations were conducted to explore a novel thermal storage material. The thermal storage performances were also compared between this novel storage material and concrete at a temperature range from 400 °C to 500 °C. It is recommended to apply this novel thermal storage material to replace concrete at high operating temperatures in sensible heat TES systems. The second part of this dissertation mainly focuses on the numerical and experimental study of an open-channel algae culture raceway for biofuel production. According to the proposed flow field design of ARID-HV algal raceway, experiments and numerical simulation have been conducted to understand the enhancement of flow mixing in the flow field of ARID-HV raceway by cutting slots on top of the dam near the dead zones. A new method was proposed to quantitatively evaluate the flow mixing by using the statistics of temporal and spatial distribution of the massless fluid particles (centered in each cell at the inlet surface) in the raceway collecting the data of path-lines of fluid particles from CFD results. It is hoped that this method can be applied to assist the algal raceway flow field design as well as other engineering applications. The third part introduces the details about the construction work of a high temperature molten salt test loop. Because of the limited operating temperature of conventional synthetic oils, in order to obtain higher energy conversion efficiency, higher operating temperature is always desirable in a CSP plant which leads to the requirement of new generation of HTF. Currently, a halide salt eutectic mixture (NaCl-KCl-ZnCl₂) as a potential HTF for future CSP applications has been proposed by a multi-institute research team, led by University of Arizona. The thermophysical properties of the halide eutectic salt have been measured. However, this new developed halide eutectic salt has not been tested in a circulating loop at a high operating temperature for the measurement of heat transfer coefficient. It is a significant effort to build such a test system due to extremely high operating temperature. As a consequence, in the third part of this dissertation, details about the design of the lab-scale test system and all the equipment items will be introduced. The investigations included in this dissertation for the heat transfer and flow in solar energy and bioenergy systems are of particular interest to the renewable energy engineering community. It is expected that the proposed methods can provide useful information for engineers and researchers.

Ce travail de thèse consiste au développement de méthodes statistiques pour détecter des com- portements anormaux dans les données fonctionnelles que produit le satellite tout au long de sa vie. Un premier travail a été de comprendre comment mettre en évidence les anomalies grâce à des projections sur des bases de fonctions. En complément de cette revue des projections, nous avons appliqué plusieurs méthodes de détection d’anomalies, telles que la One-Class SVM et le Local Outlier Factor (LOF). En plus de ces deux méthodes, nous avons développé notre propre méthode pour prendre en compte la saisonnalité des courbes que nous considérons. En se basant sur cette étude, nous avons développé une nouvelle procédure pour sélectionner automatiquement les coefficients les plus intéressants pour la détection d’anomalies dans un cadre semi-supervisé. Notre méthode est une procédure de tests multiples où nous appliquons un test à deux échantillons à tous les niveaux de coefficients. Nous nous sommes également intéressés aux covariances des télémesures entre elles pour la détection d’anomalies. Pour cela, nous cherchons à comparer les covariances entre un groupe de télémesures pour deux journées, ou périodes consécutives. Nous avons appliqué trois tests sta- tistiques ayant des angles d’approche différents. Nous avons également développé dans ce but un nouveau test asymptotique. Outre la démonstration de la convergence de notre test, nous démontrons par des exemples que ce test est dans la pratique le plus puissant sur les données dont nous disposons. Dans cette thèse, nous avons abordé plusieurs aspects de la détection d’anomalies dans les données fonctionnelles issues des satellites. Pour chacune des méthodes, nous avons pu détecter toutes les anomalies, améliorant sensiblement le taux de fausses alarmes. / In this PhD, we have developed statistical methods to detect abnormal events in all the functional data produced by the satellite all through its lifecycle. The data we are dealing with come from two main phases in the satellite’s life, telemetries and test data. A first work on this thesis was to understand how to highlight the outliers thanks to projections onto functional bases. On these projections, we have also applied several outlier detection methods, such as the One-Class SVM, the Local Outlier Factor (LOF). In addition to these two methods, we have developed our own outlier detection method, by taking into account the seasonality of the data we consider. Based on this study, we have developed an original procedure to select automatically the most interesting coefficients in a semi-supervised framework for the outlier detection, from a given projection. Our method is a multiple testing procedure where we apply the two sample-test to all the levels of coefficients.We have also chosen to analyze the covariance matrices representing the covariance of the te- lemetries between themselves for the outlier detection in multivariate data. In this purpose, we are comparing the covariance of a cluster of several telemetries deriving from two consecutive days, or consecutive orbit periods. We have applied three statistical tests targeting this same issue with different approaches. We have also developed an original asymptotic test, inspired by both first tests. In addition to the proof of the convergence of this test, we demonstrate thanks to examples that this new test is the most powerful. In this PhD, we have tackled several aspects of the anomaly detection in the functional data deriving from satellites. For each of these methods, we have detected all the major anomalies, improving significantly the false discovery rate.

Magister Philosophiae - MPhil

Le stockage d’énergie joue un rôle très important dans le secteur énergétique. Concernant le stockage thermique, il est indispensable pour le fonctionnement en continue des centrales solaires à concentration (CSP) ou pour la récupération des chaleurs perdues dans des installations industrielles. Il y a de nos jours un besoin urgent de nouveaux matériaux performants pour remplacer les matériaux conventionnels à base de nitrate pour un fonctionnement à haute température. La présente thèse porte sur le développement de nouveaux matériaux à base de phosphates pour le stockage de la chaleur sensible. C’est la première étude sur l’utilisation des phosphates dans le stockage de la chaleur. Deux approches ont été explorées : le développement des matériaux liquides et des matériaux céramiques monolithiques. Dans la partie des matériaux liquides, l’objectif est de développer des phosphates ayant le même principe de fonctionnement que les sels fondus. Un grand nombre de phosphates a été étudié et les premiers critères d’évaluation sont les températures de fusion, d’évaporation ou de décomposition et la stabilité thermique. Le ternaire M(PO)3 (M = Li, Na, K avec 33,3% molaire de chaque alkali) peut fonctionner à l’état liquide entre 390 et 850°C alors que l’acide polyphosphorique peut fonctionner jusqu’à 200°C (température de solidification restant à déterminer). Concernant les matériaux céramiques, l’étude sur les monolithes de phosphates purs montre des difficultés lors de la mise en forme et la médiocre performance mécanique de ces matériaux. Le travail s’est ensuite focalisé sur les mélanges argileux-sable/phosphates. L’ajout de phosphates est indispensable pour améliorer les propriétés thermiques et mécaniques des céramiques traditionnelles de terre cuite. L’influence de la température de cuisson, la nature des phosphates et la granulométrie des phosphates a été étudié. Les propriétés physiques, thermiques, mécaniques, thermophysiques, thermomécaniques et la stabilité thermique de ces céramiques ont été étudiées entre 30 et 1000°C. Les résultats obtenus ont montré la bonne compétitivité des céramiques à base du mélange argileux-sable/phosphates par rapport aux autres matériaux de stockage thermique solides tels que le béton, les roches naturelles...Le potentiel d’application de ces céramiques a été démontré par des tests de stockage de type thermocline à l’échelle pilote utilisant les meilleurs matériaux monolithiques et de l’air comme fluide caloporteur. Différents paramètres comme la température d’entrée (350 à 850°C) et le débit du fluide caloporteur ont été étudiés pour les deux phases de charge et de décharge. En parallèle, un modèle 1D a été développé avec COMSOL-multiphysics pour simuler des étapes de charges et de décharges. Le modèle décrit les échanges de chaleur entre le solide, l'air et la paroi et tient compte de tous les paramètres liés au stockage thermocline. Les résultats de simulation sont en bon accord avec les données expérimentales obtenues lors des tests à l'échelle pilote. Ce travail a montré de forts intérêts des matériaux à base de phosphates pour le stockage thermique à des différentes gammes de températures couvrant toutes les technologies CSP et la chaleur fatale industrielle. / Energy storage plays a very important role in the energy sector. Concerning the thermal energy storage (TES), it is indispensable for the continuous operation of concentrated solar power plants (CSP) as well as for the recovery of waste heat from industrial facilities. However, there is currently an urgency to develop new TES materials in order to support nitrate-based molten salts, which are up-to-date the only commercial TES materials. This work aimed to develop new phosphate-based materials for sensible heat storage. This is the first study on the use of phosphates as heat storage material. Both liquid and solid phosphate-based materials were developed and their properties and performances in TES were investigated. For liquid materials, the goal is to design phosphates which have the similar operation principle to nitrate-molten salts. This means they are under liquid state when working as TES materials. Different alkali polyphosphates (M(PO)3, M = Li, Na, K) were studied and the first assessment criteria was the melting point, boiling point and thermal stability. Two potential materials were identified. The first one was the ternary mixture of alkali polyphosphates ( Li33.3 Na33.3 K33.3(PO)3 ) which exists under liquid form between 390 and 850°C. The second one was polyphophoric acid ( HPO3.n H2O ) which exist in liquid form up to 200°C. Its melting point will be determined. For solid phosphate-based materials, the utilization of a selected synthetic phosphate or raw phosphate ore without any additive met a major difficulty of shaping step, and the products obtained exhibited poor mechanical performances. The work is then focused on ternary mixtures of clay-sand/phosphates. With this concept, phosphates played the role of additives to improve the properties of traditional fired clay ceramics for TES purposes. Thus, a parametric study was carried out for different clay-sand/phosphate mixtures. The influence of the firing temperature, the nature of phosphates and the granulometry of phosphates were investigated. The physical, thermal, mechanical, thermophysical, and thermomechanical properties and the thermal stability were studied between 30 and 1000°C. The best product was made of 76.24 wt.% clay, 19.06 wt.% sand and 4.7 wt.% hydroxyapatite - a synthetic phosphate and 80 wt.% clay, 15 wt.% sand and 5 wt.% raw phosphate ore. They were competitive versus other solid TES materials such as concrete, natural rocks etc. The potential application of these ceramics was experimentally demonstrated by using a pilot-scale TES system with air as heat transfer fluid. Both charging and discharging phases were successfully repeated several times with various inlet air temperatures (from 350 to 850°C) and air flow rates. Finally, a dynamic 1D model was developed using Comsol Multiphysics software to simulate the charging and discharging phases of the pilot-scale TES tests. This model took into account the role of air, solid ceramic and reservoir wall and integrated all the parameters that impacted the temperature profile in the storage tank. The simulation results matched well with experimental data.

Thermal energy storage (TES) systems are technologies with the potential to enhance the efficiency and the flexibility of the coming 4th generation low temperature district heating (LTDH). Their integration would enable the creation of smarter, more efficient networks, benefiting both the utilities and the end consumers. This study aims at developing a comparative assessment of TES systems, both latent and sensible heat based. First, a techno-economic analysis of several TES systems is conducted to evaluate their suitability to be integrated into LTDH. Then, potential scenarios of TES integration are proposed and analysed in a case study of an active LTDH network. This is complemented with a review of current DH legislation focused on the Swedish case, with the aim of taking into consideration the present situation, and changes that may support some technologies over others. The results of the analysis show that sensible heat storage is still preferred to latent heat when coupled with LTDH: the cost per kWh stored is still 15% higher, at least, for latent heat in systems below 5MWh of storage size; though, they require just half of the volume. However, it is expected that the cost of latent heat storage systems will decline in the future, making them more competitive. From a system perspective, the introduction of TES systems into the network results in an increase in flexibility leading to lower heat production costs by load shifting. It is achieved by running the production units with lower marginal heat production costs for longer periods and with higher efficiency, and thus reducing the operating hours of the other more expensive operating units during peak load conditions. In the case study, savings in the magnitude of 0.5k EUR/year are achieved through this operational strategy, with an investment cost of 2k EUR to purchase a water tank. These results may also be extended to the case when heat generation is replaced by renewable, intermittent energy sources; thus increasing profits, reducing fuel consumption, and consequently emissions. This study represents a step forward in the development of a more efficient DH system through the integration of TES, which will play a crucial role in future smart energy system. / Thermal energy storage (TES) eller Termisk energilagring är en teknologi med potentialen att öka effektivitet och flexibilitet i den kommande fjärde generationens fjärrvärme (LTDH). Studien har som mål att kartlägga en komparativ uppskattning av TES systemen, baserad både på latent och sensibel värme. Resultaten visar att lagring av sensibel värme är att föredra före latent värme när den kopplas med LTDH: pris per lagrade kWh kvarstår som 15% högre än för latent värme i system under 5 MWh av lagringsutrymme; dock fordrar de endast hälften av volymen. Utifrån systemperspektiv innebär introduktionen av TES system i nätverket en ökning av flexibilitet vilket leder till reducerade värmeproduktionskostnaderna i mindre belastning. I fallstudien nås en sparnivå av femhundra euro per år genom denna operativa strategi, med en investering av 2000 euro för inköp av vattentank. Resultaten kan också vidgas till en situation där värmeproduktionen ersätts av förnybara, intermittenta energikällor; till detta medföljer högre vinster, lägre bruk av bränsle vilket skulle innebära lägre utsläpp. Studien kan ses som ett steg framåt mot skapandet av en mer effektiv DH system genom integrationen av TES, vilket kommer att spela en betydande roll i framtida smarta energisystem.

The Diploma thesis Angels in the Bible. The role of angels in biblical texts tries to describe the role of angels in the Bible based on the contexts containing the term angel. Then it analyzes and briefly characterizes individual texts of the Old and New Testament in which the term angel occures. With the help of this analysis it is possible to observe what role did the angels serve: they announced the birth of a son, God's election, God's commands, they become the life savers, leaders and protectors of the Israel nation and executors of God's punishment. An angel - interpreter acts in the apocalyptic texts. In the New Testament, angels also announce the birth of Jesus and John the Baptist, announce the God's will to people, they announce the resurrection and protect the church similarly to Israel. The most angels figure in the Book of Revelation and they play all roles known from apocalyptic literature: angel - interpreter, angel - guardian, as well as angels who participate on the heavenly council and effect the judgement according to the God's commands.

<p>  </p> <p>Concentrated solar power (CSP) is a technology that utilizes focused sunlight to heat a high-temperature medium (such as a molten salt). Heat from this medium can be transferred to a working fluid (such as supercritical CO2) that is then used to drive a turbine to generate electricity. Alternatively, the hot medium/fluid can be pumped into tanks for thermal energy storage (TES), for heat extraction later to generate dispatchable electricity and/or for electricity production at night or on cloudy days. By increasing the fluid temperature to <u>></u>750oC and utilizing TES, CSP can become more cost competitive with fossil-based electricity production. Current CSP systems utilize molten nitrate salts for heat transfer and TES that are known to thermally degrade at temperatures >600oC. To achieve temperatures <u>></u>750oC, molten chloride salts, such as ternary MgCl2-KCl-NaCl compositions, are being considered as heat transfer and thermal energy fluids for next generation CSP plants due to their higher temperature stability, low cost, and availability. </p> <p>In this work, it was demonstrated that MgCl2-containing molten salts are prone to oxidation in ambient air at 750oC, which can enhance corrosion of the containment materials and alter the thermophysical properties of the fluid. An alternative, low-cost, earth-abundant, MgCl2-free, oxidation-resistant molten salt, a eutectic CaCl2-NaCl composition, was developed, along with a corrosion mitigation strategy, to enable the slow growth of protective oxide layers on metals that are resistant to dissolution by such MgCl2-free molten chloride salts. </p> <p>This strategy was expanded to other low-cost, oxidation resistant compositions, such as eutectic BaCl2-CaCl2-KCl-NaCl with tailored chemical and thermophysical properties for CSP and TES. The melting temperature, heat capacity, oxidation resistance, and crystallization behavior were measured for eutectic a BaCl2-CaCl2-KCl-NaCl(17.5-47.8-3.3-31.4 mol%) (BCKN) salt and a MgCl2-KCl-NaCl (40-40-20 mol%) salt. BCKN salt was shown to have a similar melting temperature while having a higher heat capacity and far better oxidation resistance. </p> <p>The corrosion of the nickel-based superalloy Haynes 214 was studied in molten MgCl2-KCl-NaCl (40-40-20 mol%) salt at 750oC under inert atmosphere conditions using a custom-built rotating-disc corrosion testing apparatus that maintained laminar fluid flow on the sample. Non-protective external Cr-, Al-, and Mg- oxide layers were formed on Haynes 214 that were prone to spallation. Internal oxidation of Al was also observed along with Cr depletion zones within Haynes 214.  Corrosion kinetics were evaluated to quantify the role of fluid flow for application of this alloy for use in containment and transportation of this molten chloride salt. </p>

The global need to eliminate CO2 emissions and its consequent reduction in the use of fossil fuels drives the ongoing energy transition that highly involves the research achievements of the scientific community to reach the goals of this purpose. Renewable sources like photovoltaic and wind energy, are central to this endeavor, however, the intermittency of natural resources makes it non-dispatchable and energy storage is fundamental. According to the European Roadmap [1] just a 60% of the CO2 emissions reduction goal can be achieved with available technologies and existing energy. However, the production, use and specially storage opportunities that hydrogen offers can drive non-dispatchable renewable sources to achieve its full potential by clearing up the intermittency problem as well as covering the remained 40% gap. This master's thesis aims to investigate the techno-economic feasibility of integrating a Solid Oxide Electrolyzer Cell (SOEC) into a hybrid PV-CSP(sCO2) plant. The study focuses on assessing various indicators related to electricity, energy, and hydrogen production prices. To achieve this, three different integration strategies within the hybrid PV-CSP(sCO2) plant were selected for analysis: Soec using heat from the particles coming from the receiver, soec using heat coming from the particles available in the thermal energy storage (TES) and soec recovering heat from the sCO2 power block. A sensitivity analysis was conducted on different PV sizes (MWp), battery capacities (MWh), and SOEC installed capacities (MWh) to investigate the technology's potential in the plant and determine optimal sizing of subsystems. However, the individual optimization of economic indicators presented technical and economic challenges. Scenarios allowing individual optimization of hydrogen production prices (€/kg H2) resulted in 10.9, 11.7, and 14.6 €/kg h2 for receiver, TES, and sCO2 integration strategy, respectively. These scenarios, however, require high SOEC installed capacities, leading to elevated electricity and energy production prices. On the other hand, the individual optimization of electricity and energy production prices led to better and lower results when no hydrogen production presence within the plant. However, this analysis also showed that soec capacities below 5MWh together with no installation of batteries and a new definition for calculating hydrogen production prices (LCOH) allows feasible integration of hydrogen production within the plant. LCOH(€/kg h2) results were 10.2€/kg h2, 7.6€/kg h2, and 9.4€/kg h2 for receiver, TES, and sCO2, respectively, for a soec installed capacity of 0.5MWh (119m2 size) along with energy production values not exceeding 101€/MWh. While the results present a favorable outlook for SOEC installations based on literature review data [2] [3] [4] they still face challenges when competing with the cost-efficient PEM technology, which offers 4.5-5.5€/kg H2 [5] without storage. Nonetheless, this research contributes valuable insights into the integration of SOEC technology within hybrid renewable energy systems and provides a comprehensive analysis of the techno-economic aspects related to hydrogen production following different integration strategies. The findings may inform decision-making processes and promote further advancements in sustainable energy solutions. / Det globala behovet av att eliminera CO2utsläpp och därmed minska användningen av fossila bränslen driver pågående energiomställning, som starkt involverar forskningsresultaten från vetenskapssamhället för att nå syftet med detta mål. Förnybara källor som solceller och vindkraft är centrala i detta arbete, men intermittensen hos naturliga resurser gör dem icke disponibla och energilagring är grundläggande. Enligt den europeiska vägkartan [1] kan endast 60% av målet att minska CO2-utsläppen uppnås med tillgängliga teknologier och befintlig energi. Produktionen, användningen och särskilt lagringsmöjligheterna som väte erbjuder kan emellertid driva icke-disponibla förnybara källor att nå sin fulla potential genom att lösa intermitt ensproblemet och täcka den återstående 40% klyftan. Detta examensarbete syftar till att undersöka den tekniskekonomiska genomförbarheten av att integrera en fastoxid elektrolysör (SOEC) i en hybrid PV CSP(sCO2)-anläggning. Studien fokuserar på att utvärde ra olika indikatorer relaterade till el-, energi- och vätgasproduktionspriser. För att uppnå detta har tre olika integrationsstrategier inom hybrid PV CSP(sCO2) anläggningen valts för analys: SOEC med hjälp av värme från partiklar som kommer från mottagaren, SOEC med hjälp av värme från partiklar som finns i termisk energilagring (TES) och SOEC som återvinner värme från sCO2-kraftblocket. En känslighetsanalys har genomförts för olika PVstorlekar (MWp), batterikapaciteter (MWh) och SOEC installerade kapacit eter (MWh) för att undersöka teknologins potential i anläggningen och bestämma optimal dimensionering av delsystem. Resultaten från individuell optimering av ekonomiska indikatorer ledde dock till flera tekniska och ekonomiska utmaningar. Scenarier som tillåter individuell optimering av vätgasproduktionspriser (€/kg H2) resulterade i 10, 9, 11, 7 respektive 14,6 €/kg H2 för mottagare, TES och sCO2 integrationsstrategi. Dessa scenarier kräver dock höga SOEC installerade kapaciteter, vilket leder till höga el och energipriser. Å andra sidan ledde individuell optimering av el och energiproduktionspriser till bättre och lägre resultat när ingen vätgasproduktion fanns i anläggningen. Denna analys visade också att SOEC kapaciteter under 5MWh tillsammans med ingen installation av batterier och en ny definition för beräkning av vätgasproduktionspriser (LCOH) möjliggör genomförbar integration av vätgasproduktion i anläggningen. LCOH (€/kg H2) resultaten var 10,2 €/kg h2 , 7 ,6 €/kg h2 respektive 9,4 €/kg h2 för mottagare, TES och sCO2, för en SOEC installerad kapacitet på 0,5 MWh (storlek 119m2) tillsammans med energiproduktionsvärden som inte överstiger 101 €/MWh. Medan resultaten visar en gynnsam utsikt för SOECinstallationer baserat på data från litteraturöversikter [2] [3] [4], står de ändå inför utmaningar när de konkurrerar med den kostnadseffektiva PEM teknologin, som erbjuder 4,5-5,5 €/kg H2 [5] utan lagring. Trots detta bidrar forskningen med värdefulla insikter i integrationen av SOEC teknologi i hybrid förnybara energisystem och ger en omfattande an alys av de teknisk-ekonomiska aspekterna relaterade till vätgasproduktion enligt olika integrationsstrategier. Resultaten kan informera beslutsprocesser och främja ytterligare framsteg inom hållbara energilösningar.

Il lavoro di tesi si è focalizzato sullo studio dell’arousal come indice psicofisiologico di attivazione e sull’applicazione della metodica di stimolazione elettrica transcranica (tES) non invasiva con lo scopo di modulare tale indice. L’obiettivo è stato quello di indagare se, applicando la tES, fosse possibile migliorare la performance di soggetti giovani sani in compiti di tipo cognitivo. Il progetto di ricerca si è sviluppato in 2 studi principali per un totale di 4 esperimenti. Tali studi hanno previsto l’acquisizione e la successiva analisi sia di dati comportamentali (tempi di reazione, accuratezza), che di indici psicofisiologici (conduttanza cutanea, diametro pupillare). I risultati hanno evidenziato che è possibile modulare l’arousal con dei “bursts” di stimolazione elettrica transcranica, somministrati in concomitanza di stimoli salienti per il soggetto. Tale modulazione si è manifestata con una riduzione dei tempi di reazione ed un contemporaneo aumento della risposta di conduttanza cutanea. Questi dati supportano la possibilità di utilizzare questo protocollo in pazienti con difficoltà di attenzione o altri problemi cognitivi per aumentare l’efficacia di interventi di riabilitazione. / The thesis analyzed the role of the arousal as a psychophysiological index of activation, and the application of non-invasive transcranial electrical stimulation (tES) technique with the aim to modulate this index. In this work we investigated if the application of tES could increase the performance of healthy young subjects during cognitive tasks. The thesis is based on 2 main studies for a total of 4 experiments with the recording of behavioural (reaction times, accuracy) and psychophysiological (skin conductance, pupil diameter) indeces. The results showed that it is possible to modulate arousal with bursts of tES, administered during the presentation of salient stimuli for the subject. This modulation resulted in a reduction of reaction times and an increase of the skin conductance response. These data support the possibility to use this protocol of stimulation with patients with attentional and other cognitive deficits in a rehabilitative context.

Depuis sa découverte en 1964, l’étude du Fond Diffus Cosmologique dans le domaine des longueurs d’ondes millimétriques est devenue un enjeu majeur de la recherche expérimentale dans le domaine de la cosmologie. En particulier, ses anisotropies en température, mesurées pour la première fois par le satellite COBE puis plus finement par l’expérience WMAP et le satellite PLANCK. L’existence prédite d’anisotropies de polarisation du Fond Diffus Cosmologique est fait actuellement parti du champ d’expérimentation privilégié de l’étude du CMB. En effet, la preuve d’existence des modes B de polarisation, signature unique des ondes gravitationnelles primordiales, fait actuellement l’objet d’une recherche expérimentale intensive par le biais notamment de l’instrument BICEP2 qui aurait détecté sa signature en 2014 dans des valeurs du rapport tenseur sur scalaire r = 0,2. Le projet QUBIC fait parti de ces expériences destinées à révéler les modes B de polarisation grâce à son instrument basé sur la technique des interféromètres et sur le développement de matrice de bolomètres, demandant un champ d’investigation poussé englobant, entre autre, la physique des solides, la physique des basses températures et la cosmologie. La thèse présentée ici se situe dans ce cadre, avec pour objectif l’élaboration d’une matrice de bolomètres dont la performance et l’optimisation devrait permettre d’acquérir la sensibilité nécessaire à l’observation des modes B de polarisation. Les différentes techniques expérimentales acquises au CSNSM d’Orsay permettent en effet d’envisager l’optimisation des éléments clé de la matrice de bolomètre en s’appuyant notamment sur l’alliage amorphe de NbxSi1-x pour l’élaboration d’un senseur thermique optimisé, et sur un matériau novateur, l’alliage de titane-vanadium, pour la mise au point d’un absorbeur de rayonnement supraconducteur efficace, dont la faible chaleur spécifique doit permettre d’atteindre un temps de réponse du détecteur de l’ordre de la dizaine de milliseconde, valeur du temps de réponse nécessaire à une lecture efficace du signal du Fond Diffus Cosmologique. Le manuscrit de thèse ici présent a pour ambition de développer les principes physiques nécessaires au champ d’investigation du travail à accomplir. Ainsi, cette étude propose d’élaborer les différents éléments d’un bolomètre, réunissant un senseur thermique optimisé ainsi qu’un absorbeur de rayonnement de faible chaleur spécifique, permettant d’envisager la mise au point d’une matrice de bolomètres optimisée dans le cadre du projet QUBIC dont la campagne d’observation est prévue courant 2015 au dôme C du pôle Sud. / Since its discovery in 1964, the study of the Cosmic Microwave Background (CMB) in the field as of millimetre-length wavelengths became a major stake of experimental research in the field of cosmology. In particular, its anisotropies in temperature, measured for the first time by satellite COBE then more finely by the experiment WMAP and the PLANCK satellite. The predicted existence of anisotropies of polarization of the Cosmic Microwave Background is currently been part of the privileged field of experimentation of the study of the CMB. Indeed, the proof of exists modes B of polarization, single signature of the paramount gravitational waves, currently is the object of an intensive experimental research by the means in particular of the instrument BICEP2 which would have detected its signature in 2014 in values of the tensor report on scalar R = 0.2. Project QUBIC makes party of these experiments intended to reveal the modes B of polarization thanks to its instrument based on the technique of the interferometers and the development of bolometers array, asking for a thorough field of investigation including, amongst other things, the solid state physics, the physics of the low temperatures and cosmology. The thesis presented here is within this framework, with for objective making of a bolometers array whose performance and optimization should make it possible to acquire the necessary sensitivity to the observation of the B-mode polarization. The various experimental techniques acquired with the CSNSM of Orsay indeed make it possible to consider the optimization of the key elements of the bolometers array while being pressed in particular on amorphous alloy of NbxSi1-x for making of an optimized thermal sensor, and on an innovative material, titanium-vanadium alloy, for the clarification of an effective superconducting absorber of radiation, whose low specific heat must make it possible to reach a response time of the detector about ten millisecond, value of the response time necessary to an effective reading of the signal of the Cosmic Microwave Background. The manuscript of thesis here present has as an ambition to develop the physical principles necessary to the field of investigation of work to be achieved. Thus, this study proposes to work out the various elements of a bolometer, joining together a thermal sensor optimized as well as an absorber of radiation of low specific heat, making it possible to consider the clarification of a bolometers array optimized within the framework of the project QUBIC whose observation campaign is envisaged during 2015 with the dome C of the south pole.