<p>Radiative thermal management has become increasingly more relevant within the past few decades due to the avocation for higher efficiency buildings, increases in</p> <p>power densities with decreases in form factors, and cutting-edge technologies for space exploration. This research focuses on engineering coatings with spectrally selective optical properties to achieve ultra-efficient thermal management via passive radiative cooling of both terrestrial and extraterrestrial applications. Terrestrial radiative cooling is a phenomenon of passively cooling exterior surfaces below ambient temperatures by engineering coatings to exhibit low absorptance in the solar spectrum (0.25 μm< λ <2.5 μm), such that a minimal amount of solar irradiation is absorbed, and high emittance in the transmissive portion of the atmosphere (8 μm< λ <13μm), i.e. the sky window, to lose heat to deep-space for a net cooling effect. Deep-space is considered to be an infinite heat sink at 3 K. Extraterrestrial radiative cooling requires the same criteria as terrestrial radiative cooling, however, there is no atmosphere to block a portion of the solar irradiation or the emission from the surface. A key requirement for achieving passive radiative cooling for an ideal emitter during daytime is a total solar reflection >85%, and every 1% above this threshold results in ≈10 W/m2 gain in cooling power. Here, recognizing the broadband nature of solar irradiation, we propose and test a new concept of enhancing solar reflection at a given particle volume concentration by using hierarchical particle sizes, which we hypothesize to scatter each band of the solar spectrum, i.e. VIS, NIR and UV effectively. The hypothesis is tested using a TiO2 nanoparticle-acrylic system. Using the Mie Theory, the scattering and absorption efficiencies and asymmetric parameter</p> <p>of nanoparticles with different sizes and combinations are calculated, then the Monte Carlo Method is used to solve the Radiative Transfer Equation. An overall total solar</p> <p>reflection of ≈91%, which is higher than the ≈78% and ≈88% for 100 nm and 400 nm single particle sizes, respectively was achieved from our hypothesis.</p> <p>With increasingly better RC materials being demonstrated in literature, there is a growing need to understand the real-world utility and benefit of RC with regards</p> <p>to energy savings. A fundamental limit of current radiative cooling systems is that only the top surface facing deep-space can provide the radiative cooling effect, while</p> <p>the bottom surface cannot. Here, we propose and experimentally demonstrate a concept of “concentrated radiative cooling” by nesting a radiative cooling system in a mid-infrared reflective trough, so that the lower surface, which does not contribute to radiative cooling in previous systems, can radiate heat to deep-space via the reflective</p> <p>trough. Field experiments show that the temperature drop of a radiative cooling pipe with the trough is more than double that of the standalone radiative cooling</p> <p>pipe. Furthermore, by integrating the concentrated radiative cooling system as a preconditioner in an air conditioning system, we predict electricity savings of > 75% in Phoenix, AZ, and > 80% in Reno, NV, for a single-story commercial building. We further look into unique applications of radiative cooling for outdoor enclosures</p> <p>of electrical equipment, as demonstrated with a case study of coating pole-type distribution transformers. Utilizing RC paint on the exterior of the case would allow further dissipation of heat to deep-space, as well as, increase the solar reflectance to lessen the heat load on the case. A single 25 kVA pole-type transformer is modeled</p> <p>via CFD with two different exterior case coatings, the standard grey coatings commonly utilized and an RC coating, BaSO4 paint, is analyzed under different operating loads. The RC coating demonstrates great benefits from a thermal management perspective</p> <p>and a gain in the lifetime of the windings. The RC coating cooled a 25 kVA distribution transformer’s core by > 11oC when compared to the standard case and even shows below ambient cooling of the case under minimal heat generations. The lifetime of the distribution transformers was increased by a minimum of 55% when comparing the standard case to the case with a radiative cooling paint based on the Aging Acceleration Factor. A more traditional application of radiative cooling paints is to utilize them on the exterior of buildings to offset the cooling energy demand for air conditioning. This work develops a high-fidelity RC model which accounts for pertinent weather factors including precipitable water, sky clearness, and dynamic convective heat transfer coefficients based on wind speed to further understand the energy savings. We implement our RC model on a single-story residential building to study the impact of RC in every unique ASHRAE climate zone in the United States using the 16 DOE recommended representative cities. Our results show > 7% and > 12% cooling energy savings across the United States for NREL’s building and typical buildings, respectively. Furthermore, warm climates yield the greatest cooling energy savings of up to 22% and 46% for the NREL and the Typical building, respectively. Extraterrestrial radiative thermal management is becoming increasingly pertinent with the development of new space technologies and the need to discover what is beyond</p> <p>our world. Space presents extreme thermal environments for radiative transfer, from a total eclipse case where the body radiates to deep space at 3 K to a full solar load where 1400 W/m2 is radiated onto the surface and a hybrid of both situations. The goal of this work is to engineer micropatterned Lanthanum Strontium Manganite</p> <p>(LSM) Barium Sulfate (BaSO4) coatings as efficient variable emissivity coatings (VECs). The photon transport through the micropatterned system is modeled using</p> <p>geometric optics and Monte Carlo coupled with geometric optics to obtain the coatings reflectivity, transmissivity, and emissivity to predict the ideal reflectivity and</p> <p>emissivity of the micropatterns. Then the micropatterned LSM coatings are experimentally fabricated using screen printing on a BaSO4 paint layer. The coatings are</p> <p>characterized by their temperature-dependent variable emissivity and solar absorptivity from the dual-layer micropatterned coatings. Furthermore, a computational model for a body-mounted cylindrical radiator was developed to investigate the real implications a VEC can have on crewed space vehicles, as well as define some target guidelines for VEC’s to achieve in future technologies.</p>

Le sondeur infrarouge hyperspectral IASI (Interféromètre Atmosphérique de Sondage Infrarouge), développé conjointement par le CNES et EUMETSAT à bord du satellite européen Metop, permet, entre autres, le sondage de la température, de l'humidité ainsi que la restitution de paramètres de surface. Bien que l'on tire le meilleur parti de ces données sur la mer, leur utilisation est encore limitée au-dessus des terres dans le contexte de la prévision numérique du temps, à cause de l'incertitude plus grande sur l'émissivité et la température de surface (Ts). Ces erreurs se répercutent sur la qualité des simulations de transfert radiatif et empêche l'utilisation de ces mesures dans les modèles de prévision numérique du temps. Seuls les canaux non sensibles à la surface terrestre sont assimilés de façon opérationnelle, limitant ainsi le potentiel de sondage aux couches atmosphériques les plus élevées. Cette thèse a pour but l'amélioration de la description des paramètres de surface dans le modèle global ARPEGE de Météo-France en vue de l'assimilation des données du sondeur IASI sur les continents. Nous avons d'abord cherché à améliorer la modélisation de la surface (émissivité et Ts) sur les continents dans le modèle ARPEGE. Pour cela, différents atlas d'émissivité ont été intégrés dans ce modèle : l'un a été calculé à partir des données MODIS (Moderate-Resolution Imaging Spectroradiometer) par l'Université du Wisconsin et le second a été construit à partir des produits IASI de niveau 2 (L2) développés par EUMETSAT. La Ts a ensuite été restituée à partir de canaux de surface IASI en profitant d'une meilleure connaissance de l'émissivité de surface donnée par ces atlas. Ces Ts ont été évaluées par comparaison avec les produits MODIS de la NASA et les produits IASI L2 d'EUMETSAT. Ces comparaisons nous ont permis de sélectionner une combinaison de canaux qui fournit les meilleures estimations de Ts. L'utilisation d'une modélisation de surface réaliste a contribué à l'amélioration de la qualité des simulations de transfert radiatif pour les canaux sensibles à la surface. Les radiances IASI sensibles à la surface ont alors pu être assimilées sur les continents dans le modèle ARPEGE en ciel clair et en utilisant la paramétrisation de surface définie précédemment. Les impacts sur la qualité des analyses et des prévisions ont été étudiés. La prise en compte d'une émissivité et d'une Ts précises a permis d'augmenter significativement le nombre d'observations assimilées. Les principales améliorations concernent les prévisions de géopotentiel et de température pour des pressions inférieures à 400~hPa (en dehors des tropiques). Enfin, dans un cadre plus spécifique et climatologique, nous nous sommes intéressés à la validation de l'utilisation des données IASI en Antarctique durant la campagne Concordiasi. Cette étude a permis d'améliorer les profils inversés de température et de vapeur d'eau par comparaison avec les profils provenant du modèle. L'amélioration est particulièrement importante pour la température de surface. Dans ce cadre, les Ts restituées dans cette thèse ont été comparées à Concordia et au Pôle Sud avec des mesures in-situ et se sont révélées particulièrement précises à Concordia. / The Infrared Atmospheric Sounding Interferometer (IASI), on-board the EUMETSAT Polar System Metop satellite, is developed by CNES in the framework of a co-operation agreement with EUMETSAT. IASI enables, amongst other, infrared soundings of temperature, moisture and retrievals of surface parameters. However in the numerical weather prediction context, these observations are not as intensively used over land as they are over sea because of larger uncertainties about land emissivity and land surface temperature (LST). These uncertainties have an impact on the quality of radiative transfer simulation and hinder the use of these measurements in numerical weather prediction models. Only channels that are not sensitive to the surface are currently assimilated in operations, which limits the potential of sounding instruments to the highest atmospheric layers. This PhD aims to improve the description of land surface parameters in the ARPEGE global model of Météo-France to assimilate IASI data over land. First of all, we tried to improve the surface modelling (surface emissivity and LST) over land in the ARPEGE model. To this end, two emissivity atlases were integrated in this model. The first one is the emissivity climatology computed from the IASI Level-2 products from EUMETSAT and the second one is the global high spectral resolution infrared land surface emissivity database (called UWIREMIS) developed by the Space Science and Engineering Center at University of Wisconsin. Hence, the LST was retrieved from IASI surface channels using these atlases as input parameters in the radiative transfer model. These LSTs were compared to land LST products: the MODIS (Moderate-Resolution Imaging Spectroradiometer) products from the NASA and the IASI Level-2 products from EUMETSAT. These comparisons enabled us to choose the IASI channel combination that provided the best LST estimates. The use of a realistic surface modelling contributed to improve the quality of radiative transfer simulations for surface sensitive channels. Then, surface sensitive IASI radiances were assimilated over land in ARPEGE in clear sky conditions using the surface parameters as previously defined. The impact on analysis and forecast quality was studied. The use of good estimates of surface emissivity and LST significantly increased the number of assimilated observations. The main improvements are for geopotential and temperature forecasts for pressure levels lower than 400~hPa (except in the tropics and in the stratosphere). Finally, from a climatological point of view and within the more specific framework of the Concordiasi campaign, we assessed and validated the use of IASI data in Antarctica. The temperature and humidity retrieved in this particular study proved of better quality than the model profiles, as assessed against the sonde measurements. The improvement is particularly striking for surface temperature. In this framework, the LST retrieved in this PhD were compared with in situ measurements at Concordia and at South Pole station. These estimates are of a great accuracy at Concordia.

Cette thèse porte sur l’étude de l’émissivité et de l’opacité dans les plasmas de fusion inertielle (FCI), et des processus atomiques dans les plasmas de fusion magnétique (FCM).En FCI, nous avons étudié les spectres d’émissivité du hohlraum de l’approche indirecte et d’opacité des dopants de l’ablateur. Leur connaissance permet d’améliorer la compression de la cible de D-T et ainsi favoriser les réactions de fusion. Nous avons caractérisé les spectres lié-lié de l’or, du carbone et du germanium au moyen de méthodes détaillées (code PPP) mais qui s’avèrent coûteuses en temps de calculs et limitées quand le nombre de niveaux/ions augmente. Pour optimiser le temps de calcul sans perdre en précision, une méthode hybride détaillée/statistique (code SCO-RCG) a fait l’objet de comparaison/validation avec le code PPP sur des cas tests. Cette approche a ensuite été appliquée au calcul de l’opacité totale (lié-lié, lié-libre, libre-libre) pour tous les états d’ionisation du germanium et du silicium. Les spectres obtenus sont ensuite comparés dans une large gamme d’énergies en vue d’optimiser la compression de la cible.En FCM, à partir d’expériences effectuées sur les tokamaks Tore Supra (CEA Cadarache) et ASDEX Upgrade (Max Planck Institut, Garching), nous nous proposons de développer une nouvelle base de données de physique atomique (sections efficaces, taux des processus,…) à l’aide du code HULLAC pour analyser des coefficients de transport. Le but de cette étude est la sensibilité aux données atomiques de la reconstruction des coefficients de transport par le code ITC. Pour le cas de l’argon, les sections efficaces de quelques processus sont présentées et les coefficients de taux sont comparés à ceux provenant du consortium ADAS. / The thesis is devoted on the study of emissivity and opacity in inertial confinement fusion plasmas (ICF), and on atomic processes in magnetic fusion plasmas (MCF).In ICF, we have studied the emissivity of the hohlraum and the opacity of ablator’s dopants in the indirect drive scheme. The knowledge of these quantities allows the improvement of the target compression and, as a consequence, the fusion reactions. We have characterized the bound-bound spectrum of gold, carbon and germanium with detailed line calculation (PPP code). Such calculations are time consuming and thus restricted to small numbers of levels/ions. To optimize the time calculation without lack of precision, a hybrid approach statistical/detailed (SCO-RCG code) was compared with the PPP code for test cases. Then the hybrid approach was applied to total opacity calculations (bound-bound, bound-free and free-free transitions) for each ionization state of germanium and silicon. The spectra are compared in a large temperature range in order to optimize the target compression.In MCF, from experiences carried out on Tore Supra (CEA Cadarache) and ASDEX Upgrade (Max Planck Institut, Garching) tokomak, we have provided new atomic data (cross sections, rates of processes) with the HULLAC code in order to analyze the transport coefficients. The aim of this study is the sensitivity of atomic data on the reconstruction of transport coefficients by the ITC code. For the argon case, the cross sections of some processes are presented and the rate coefficients are compared to those of ADAS consortium.

Entre els accidents greus que poden ocórrer a les instal·lacions industrials o durant el transport de substàncies perilloses, els dolls de foc presenten un especial interès. Tot i que tenen una distància relativament més curta d'afectació que altres accidents greus, es caracteritzen per originar grans fluxos de calor i, en cas de contacte de la flama amb un equip, originen sovint un efecte domino, desencadenant una subseqüent explosió, incendi o altres esdeveniments amb greus conseqüències.Diversos estudis experimentals i teòrics han estat efectuats; no obstant això, la majoria d'aquests han estat enfocats a dolls de foc a escala de laboratori, flames subsòniques o torxes, les condicions de les quals difereixen significativament d'aquelles trobades en dolls de foc accidentals reals, que normalment assoleixen majors longituds de flama i velocitats de sortida sònica. Aquesta manca d'investigació és la raó per explicar perquè els dolls de foc eren encara molt mal coneguts i la predicció dels seus efectes i conseqüències era encara un problema. Aquesta tesi ha estat elaborada per a obtenir informació nova i útil sobre els dolls de foc, millorant la comprensió de la seva geometría i de les característiques tèrmiques, mitjançant l'anàlisi, l'experimentació i el modelatge matemàtic.Aquest estudi s'ha centrat alhora en dades existents i en noves dades experimentals, implicant Aixa dolls de foc verticals i horitzontals alliberats en absència de vent, implicant diversos combustibles (hidrogen, metà i propà). L'estudi comprèn una àmplia gamma de variables d'operació (velocitats de sortida del combustible, pressions en la canonada i diàmetres d'orifici de sortida). L'estudi experimental ha implicat dolls de foc amb flames de fins a 10.3 m de longitud i 1.5 m d'amplada. El combustible utilitzat ha estat propà, amb velocitats de sortida sònica i subsònica, utilitzant diversos diàmetres d'orifici de sortida. Els dolls de foc han estat filmats amb dues càmeres de vídeo (VHS) i una càmera termográfica d'alta velocitat (IR). Les principals característiques geomètriques de les flames (dimensions i forma) han estat analitzades en funció de la velocitat de sortida del combustible,del flux màssic i del diàmetre d'orifici de sortida. L'anàlisi i tractament d'imatges infraroges i de les mesures obtingudes amb tres sensors de flux de calor situats a diferents distàncies de la sortida del doll de foc han permès l'obtenció de les seves principals característiques de radiació: flux de calor irradiat als voltants (persones i instal·lacions) en funció de la distancia, poder emissiu i emisivitat de les flames. Diverses expressions han estat proposades per estimar les dimensions de la flama en funció de diverses variables (flux màssic, diàmetre d'orifici de sortida i nombres de Froude i Reynolds). Els resultats i expressions obtinguts en aquest estudi contribueixen a una millor comprensió dels dolls de foc, representant un avanç en les metodologies i l'establiment de noves mesures, normes i polítiques de planificació per a la prevenció i/o el control d'aquest tipus d'accident greu amb foc, tant en establiments industrials com en el transport de materials perillosos. / Among the major accidents that can occur in processing plants or in the transportation of hazardous materials, jet fires are of particular interest. Although they have a relatively shorter distance of influence than other major accidents, they are characterized by high heat fluxes and if there is flame impingement they can originate a domino effect, leading to a subsequent explosion, large fire, or other events with severe effects. Several experimental and theoretical studies have been carried out; however, most of those works have been focused on small-scale jet fires, subsonic flames or flares, the conditions of which significantly differ from those found in real accidental jet fires, usually reaching larger flame lengths and sonic exit velocities. This lack of research is the reason to explain why the current knowledge of jet fires was still rather poor and the accurate prediction of their effects and consequences was still a problem. The present thesis has been addressed to produce a significant amount of novel and useful information on jet fires, by improving understanding of jet fire structure, reach and radiative features, through analyses, experiment and mathematical modelling. This study has been focused on both existing and also new experimental jet flame data, comprising all together, turbulent non-premixed jet flames vertically and horizontally released into still air, involving several fuels (hydrogen, methane and propane), over a wide range of operational conditions (jet exit velocities, release pressures and pipe diameters). The experimental study developed in this thesis has concerned relatively large jet fires with flames of up to 10.3 m in length and 1.5 m in width. The fuel was propane, and both sonic and subsonic jet exit velocities were obtained from different outlet diameters. The jet fires were filmed with two videocameras registering visible light (VHS) and a thermographic camera (IR). The main geometrical features of the flames were analyzed as a function of the fuel velocity, mass flow rate and jet outlet diameter: jet flame size and flame shape. The treatment of infrared images and measurements obtained from three heat flow sensors located at different distances from the jet fire outlet also led the main radiative features of jet fires to be obtained: incident thermal radiation heat over a target, surface emissive power and emissivity of the flames.Expressions for estimating jet flame reach as a function of several variables (mass flow rate, orifice exit diameter, Froude and Reynolds numbers) have also been proposed. The results and the expressions obtained in this study contribute to a better understanding of jet fires for accurate risk assessment, allowing the obtention of important advances in risk assessment methodologies and the establishment of new measures, regulations, and risk planning policies for the prevention and/or control of this type of major fire, occurred world-wide in industrial establishments and in the transportation of hazardous materials.

No description available.

Thermal management and energy input are required to maintain working fluids, i.e., liquefied natural gas, liquid nitrogen, and multi-phase fluids within their optimal working conditions. Increasing a pipes thermal resistance, e.g., utilizing vacuum insulation, is one method of minimizing energy input. A dual-wall concentric pipe employing a vacuum in the annulus, along with low emissivity surface coatings, is an achievable and economically viable solution. In this study, an experimental setup was designed and utilized to measure the air leakage mass flow rate for single-wall unloaded and mechanically loaded dual-wall fiber reinforced polymeric composite specimens. The mass flow rates were used to develop intrinsic permeability coefficients to quantify leakage, and to determine the maximum serviceable pipe length for a mechanical vacuum pump. In addition, thermal resistance equations were developed to quantify the theoretical heat loss, and an economic study was performed to ascertain the viability for three applications. / Applied Mechanics

L’échange d’énergie par rayonnement est proportionnel à l’émissivité. Ce facteur dépend de la température et de la longueur d’onde mais aussi de l’état de surface, de la composition et de la phase. Sa mesure précise est donc toujours un défi à cause des influences connues ou inconnues. Par rapport à d’autres travaux, le but de ce travail est de l’étudier dans des conditions extrêmes, des températures cryogéniques aux hautes températures : Nous avons ainsi étudié à 80K l’absorption d’un diélectrique pour la protection thermique d’un satellite et celles de surfaces en or de différentes rugosités. A la température ambiante nous avons déterminé par une méthode en réflexion, l’émission de vitrages dans le but de la recherche d‘économie d’énergie. Nous avons aussi étudié la variation de l’émissivité pendant le changement de phase solidus-liquidus et α-β de second ordre. Autour de 100°C le soufre devient plus émissif lorsqu’il passe du solide au liquide mais par contre il n’y a pas de différence sur l’émissivité pour ses deux variétés allotropiques principales. A une beaucoup plus haute température, le silicium liquide se comporte comme un métal avec une émissivité très faible et un saut net a été constaté à son passage au point de fusion. Une variation marquée de l’émissivité pour les deux phases solides du SiC a été observée entre 8-11μm dans notre étude. Contrairement aux résultats de la littérature, les sommets d’émissivité diminuent progressivement avec l’augmentation de la température. Enfin trois points X, longueur d’onde où l’émissivité ne dépend pas de la température, ont été observés pour chaque phase. / Heat transferred by radiation is proportional to the emissivity. This coefficient depends not only on the wavelength and the temperature, but also on the surfaceroughness, the chemical composition and the phase. A precise measurement is always a challenge because of the known and unknown factors. Compared with others, this thesis aims at the studies in extreme conditions, from cryogenic temperature to very high temperature: The absorptivity of a dielectric applied to the thermal protector for the satellite and the emissivity of gold surfaces with different roughness have been measured at 80K. The emissivity of different windows has been determined by the reflection method at room temperature for the research of energy saving. We have also studied the variation of the emissivity during the solid to liquid and α-β phase transition. The sulfur becomes more emissive when it changes from solid to liquid around 100°C, but there is no difference on the emissivity between its two major allotropies. The liquid silicon behaves like a metal with a very low emissivity and an obvious bound has been measured when it crosses its melting point. A marked variation of the emissivity of SiC for its two solid-state phases has been observed between 8-11μm. Contrary to other results, the peak values of the emissivity attenuate with the increase of temperature. Finally, three X points at which the emissivity doesn’t depend on the temperature have been measured for each phase.

In recent years, advances in deep optical, and especially deep near-infrared imaging with the Hubble Space Telescope (HST) and wide-field ground-based telescopes such as VISTA, have revolutionized our understanding of the cosmological evolution of galaxies and supermassive black-holes (as manifest through active galactic nuclei; AGN). In particular, the dynamic range provided by the survey `wedding cake' of available HST+ground-based optical/IR data offers new opportunities to push the meaningful statistical study of galaxy and AGN evolution out to high redshifts. Much recent attention has focused, unsurprisingly, on using these new data to push studies of galaxy formation back to within a billion years of the Big Bang, and exploring the role of young galaxies in driving cosmic hydrogen reionization during the crucial era corresponding to redshifts z ≃ 6-10. However, these data have not been as thoroughly exploited at intermediate redshifts, and have only recently been used to explore black-hole/AGN evolution. In this thesis I utilise the latest deep optical/near-infrared imaging and spectroscopy to explore three key facets of cosmological evolution. First, I present a new, robust measurement of the evolving rest-frame ultraviolet (UV) galaxy luminosity function (LF) over the key redshift range from z ≃ 2 to z ≃ 4. My results are based on the high dynamic range provided by combining the Hubble Ultra Deep Field (HUDF), CANDELS/GOODS-South, and UltraVISTA/COSMOS surveys. I utilise the unparalleled multi-frequency photometry available in this survey `wedding cake' to compile complete galaxy samples at z ≃ 2; 3; 4 via photometric redshifts (calibrated against the latest spectroscopy). This study is important as the peak of star-formation is shown to happen within a redshift range z = 2 - 4 and determining the exact epoch that the galaxies were forming most of their stars depends significantly on the UV luminosity density which requires robust measurements of the galaxy UV luminosity function and its accurate parameterization. My new determinations of the UV LF extend from M1500 ≃ -22 (AB mag) down to M1500 =-14.5, -15.5 and -16 at z ≃2, 3 and 4 respectively (thus reaching ≃ 3-4 magnitudes fainter than previous blank-field studies at z ≃ 2 - 3). At z ≃ 2 - 3 I find a much shallower faint-end slope (α = -1:32 ± 0:03) than the steeper values (α ≃ -1:7) reported in the literature, and show that this new measurement is robust. By z ≃ 4 the faint-end slope has steepened slightly, to α = -1:43 ± 0:04, and I show that these measurements are consistent with the overall evolutionary trend from z = 0 to z = 8. I then calculate the UV luminosity density (and hence unobscured star-formation density) and show that it peaks at z ≃ 2:5 - 3, when the Universe was ≃ 2:5 Gyr old. Second, I have used these data to revisit the possibility that X-ray AGN played a significant role in cosmic hydrogen reionization which is one of the major processes in the formation of the Universe we see today. Hence, it is really important to understand this phenomenon thoroughly by studying the properties of sources capable of ionising photons, such as star-forming galaxies and high redshift AGNs. Although most recent studies have suggested that the emerging population of young star-forming galaxies can bathe the Universe in sufficient high-energy photons to complete reionization by z ≃ 6, some authors have reasserted the potentially important role of high-redshift AGN in the hydrogen reionization process. In an effort to clarify this situation, I reinvestigate a claimed sample of 22 X-ray detected active galactic nuclei (AGN) at redshifts z > 4, which has reignited the debate as to whether young galaxies or AGN reionized the Universe. These sources lie within the GOODS-S/CANDELS field, and I examine both the robustness of the claimed X-ray detections (within the Chandra 4Ms imaging) and perform an independent analysis of the photometric redshifts of the optical/infrared counterparts. I confirm the reality of only 15 of the 22 reported X-ray detections, and moreover find that only 12 of the 22 optical/infrared counterpart galaxies actually lie robustly at z > 4. I recalculate the evolving far-UV (1500Å) luminosity density produced by AGN at high redshift, and find that it declines rapidly from z ≃ 4 to z ≃ 6, in agreement with several other recent studies of the evolving AGN luminosity function. The associated rapid decline in inferred hydrogen-ionizing emissivity contributed by AGN falls an order-of-magnitude short of the level required to maintain hydrogen ionization at z ≃ 6. I conclude that AGNs make a very minor contribution to cosmic hydrogen reionization. Finally, I have utilized the deep optical/near-infrared survey data to explore the prevalence of quenched/passive galaxies at high redshift. Applying a robust method to isolate passive galaxies from star-forming galaxies is the key to improving our understanding of the quenching process. Focusing primarily on the deep HUDF data-set, I have revisited the effectiveness of simple colour-colour (UVJ) selection techniques in isolating robust samples of quenched galaxies, and find that dust plays a more important role in this selection process than has been previously appreciated. Through careful SED fitting I successfully isolate a sample of apparently dust-free quiescent galaxies in the redshift range 0:5 < z < 4:5 but (at least in the HUDF) fail to find any galaxy which has remained truly quiescent for > 1 Gyr. I conclude by focusing on the properties of a refined/robust sample of apparently quenched galaxies at z > 3, and in particular establishing the contribution of quenched galaxies to stellar-mass density at early times. I conclude with a summary of my findings, and a brief discussion of the most promising avenues for future advances with the next generation of facilities, such as the James Webb Space Telescope (JWST).

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O estudo de superfÃcies seletivas para coletores solares tÃrmicos, hà alguns anos, enfoca o uso de pastas e tintas para recobrir chapas de cobre ou alumÃnio, formando a placa absorvedora do coletor. Essas tintas ou pastas sÃo eletrodepositadas em placas metÃlicas, sendo este processo muitas vezes responsÃvel pelo levado custo de superfÃcies seletivas. O uso de compÃsitos obtidos a partir do Ãxido de cromo, Ãxido de ferro e Ãxido de titÃnio em um processo cerÃmico, utilizando a tÃcnica de deposiÃÃo por screen-printing pode ser uma alternativa para a obtenÃÃo de novas superfÃcies seletivas que tenham eficiÃncia prÃxima Ãs tintas e pastas jà comercializadas e com baixo custo de fabricaÃÃo. O objetivo deste trabalho à obter e caracterizar superfÃcies seletivas à base de cromo, ferro e titÃnio e comparÃ-las com outras superfÃcies jà comercializadas (Ãxidos metÃlicos), encontrar os valores da absortividade e caracterizar as mesmas por espectroscopÃa raman e infavermelho. / The study of selective coating for thermal solar collectors has been carried out with focus on the use of selective paints and coatings for copper and aluminum plates, which are used to manufacture the absorber plate. The processes, such as electrodeposition, used in these paints and coatings are expensive and they increasing the price of the final product. The use of composite obtained from chromium oxide, iron oxide, and titanium oxide in a ceramic process using the screen-printing deposition technique is an alternative to develop new selective coating with approximately the same thermal efficiency, but at a lower cost than the commercial ones. The results show that the absorptivity values measured with the new coatings are close to those presented by the manufacturers in the commercial sufaces. The objective is to obtain and characterize selective surfaces based on chromium, iron and titanium and compares them to other areas already marketed (metal oxides), find the values of absorptivity and characterize them by raman and infrared spectroscopy.

Orientador: Rosana Maria Caram / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-19T03:21:43Z (GMT). No. of bitstreams: 1 Roriz_VictorFigueiredo_D.pdf: 10020580 bytes, checksum: b85781c508b837b2a89be30231390421 (MD5) Previous issue date: 2011 / Resumo: Saliências e reentrâncias existentes nas superfícies típicas das edificações, tanto na escala da rugosidade quanto das ondulações (de uma telha, por exemplo), constituem obstáculos que podem diferenciar o comportamento das mesmas em relação aos fluxos por radiação, se comparadas a superfícies perfeitamente lisas e planas. Absortividades e emissividades são propriedades dos materiais, enquanto absortâncias e emitâncias são características das superfícies, sendo influenciadas não apenas pelo material de que são constituídas, mas também por sua geometria. Esta pesquisa objetivou verificar tais influências, por meio de desenvolvimentos teóricos, e por procedimentos experimentais. Foi desenvolvido um modelo teórico de cálculo para o chamado "efeito cavidade", que permite estimar as absortâncias e emitâncias efetivas de uma superfície. As estimativas resultantes foram comparadas às obtidas em procedimentos clássicos para cálculo deste mesmo efeito. Foram realizados ensaios de campo, a céu aberto e sob condições climáticas reais, possibilitando uma análise do fenômeno na presença de outros fluxos de calor e sob a influência das diversas variáveis do clima. Para complementar os dados, experimentos foram realizados sob condições controladas, possibilitando aferir o modelo teórico. A fim de quantificar as implicações dos efeitos acima mencionados, simulações foram feitas no software EnergyPlus, considerando uma edificação de geometria simples, submetida ao clima da cidade de Brasília, com diferentes propriedades radiantes para as telhas. Adotando-se absortâncias e emitâncias efetivas, as simulações revelaram diferenças acima de 2.5oC nas temperaturas internas do ar, em relação às obtidas supondo-se que a cobertura fosse lisa e plana. No caso de uso de condicionadores de ar, esta diferença pode provocar uma variação de até 30% nas estimativas de consumo de energia elétrica. A pesquisa demonstrou que, para as superfícies normalmente encontradas nas edificações, o modelo proposto é adequado e pode contribuir para o aperfeiçoamento dos estudos de comportamento térmico e energético dos edifícios / Abstract: On surfaces perfectly flat and smooth, there are no obstacles to the radiant flow. However, typical surfaces of buildings have bumps and hollows that can significantly change the behaviour of them. The absorptivity and emissivity are properties of materials, while the emittance and absorptance are surface characteristics, being influenced not only by the material they are made, but also by its geometry and surface feature. This research aimed to verify such influences by means of theoretical and experimental procedures. A theoretical model for calculating the so-called "cavity effect" was developed, which allows to estimate the effective absorptance and Emittance of a surface. The resulting estimates were compared with those obtained in classical procedures for calculating the same effect. Field tests were conducted under actual weather conditions, allowing an analysis of the phenomenon in the presence of other heat fluxes and under the influence of different climate variables. To complement the data, experiments were performed under controlled conditions, allowing to test the theoretical model. In order to quantify the implications of the effects mentioned above, simulations were made with the software EnergyPlus considering a simple geometry building, submitted to the climate of the city of Brasilia, with different radiant properties of the roofs Adopting effective absorptances and emittance, simulation results show differences of up to 2.5 ° C in the internal air temperature, compared to those obtained ignoring the influences that the ripples of the tiles have on radiant flows. Considering the use of air conditioners, this could represent up to 30% variation in the energy consumption estimative. Research has shown that for surfaces typically found in buildings, the proposed model is adequate and may contribute to the improvement of thermal and behavioral studies of buildings / Doutorado / Arquitetura e Construção / Doutor em Engenharia Civil