Dissertations / Theses on the topic 'Radiative and effective properties'
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1
Wang, Xiaojia. "Study of the radiative properties of aligned carbon nanotubes and silver nanorods." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42871.
Abstract:
Arrays of nanotubes/rods made of appropriate materials can yield unique radiative properties, such as large absorption and optical anisotropy, with broad applications from high-efficiency emitters and absorbers for energy conversion to the polarization conversion via anisotropic responses. The objective of this dissertation is to investigate the radiative properties of arrays formed by aligned carbon nanotubes (CNTs) and silver nanorods (AgNRs).
The CNT arrays used in the present study consist of multi-walled CNTs synthesized vertically on silicon substrates using thermal chemical vapor deposition. Their close-to-unity absorptance is demonstrated by measuring the directional-hemispherical reflectance in the visible and near-infrared spectral ranges using an integrating sphere. The bidirectional reflectance distribution function and angle-resolved reflectance were measured at the 635-nm wavelength. The results demonstrate that high-absorptance CNT arrays may be diffusely or specularly reflecting and have important applications in radiometry. Theoretical modeling based on the effective medium theory (EMT) and reflectivity of an anisotropic medium are developed to explain the high absorption and polarization dependence. The effective optical constants of the CNT array for both ordinary and extraordinary polarizations are quantitatively determined by fitting the angle-resolved reflectance.
The AgNR arrays used in the present study were fabricated using oblique angle deposition, which results in inclined Ag nanorods that can be modeled as an effective homogenous and optically anisotropic thin film. The spectral and directional radiative properties of AgNRs grown on different substrates, including a glass slab with a silver film, and compact disc gratings, were characterized at the 635-nm and 977-nm wavelengths for different polarizations. The results are analyzed based on the EMT, rigorous coupled-wave analysis, and anisotropic thin-film optics. The results of this dissertation help gain a better understanding of radiative properties of anisotropic nanostructures for potential applications in high-efficiency energy conversion, radiometric devices, and optical systems.
2
Guerra, Timothée. "Interaction lumière-matière dans des suspensions de nanoparticules : homogénéisation et conception de nouvelles propriétés optiques." Electronic Thesis or Diss., Orléans, 2024. http://www.theses.fr/2024ORLE1005.
Abstract:
Les milieux désordonnés composés de nanoparticules revêtent une grande importance dans de nombreuses applications, particulièrement celles liées à l'efficacité énergétique telle que le refroidissement radiatif. Dès lors, la compréhension de l'interaction lumière-matière est primordiale, mais s'avère très complexe. En effet, ces études doivent bien souvent passer par la résolution des équations de Maxwell dans des systèmes constitués de milliers de particules, permettant ainsi de prendre en compte les phénomènes de diffusion et d'interférences. De façon à réduire l'importante charge numérique qui en découle, ce travail de thèse se focalise sur des systèmes 2D en incluant quelques discussions sur des systèmes 3D. Dans ce contexte, le premier volet de ce manuscrit s'intéresse au concept d'homogénéisation pour des systèmes de particules petites par rapport à la longueur d'onde du rayonnement et pouvant présenter des résonances. Cette étude met en évidence des comportements exotiques permettant de discuter, entre autres, du lien entre homogénéisation et parties cohérente et incohérente du champ diffusé. Le second volet est dédié à l'optimisation de l'absorption du rayonnement dans des lames minces par rapport à la longueur d'onde, et composées de nanoparticules. On montre que l'utilisation exclusive de particules résonantes ne donne lieu qu'à une absorption plafonnant à 70%. Néanmoins, leur couplage avec des particules purement diffusantes permet une absorption quasi-parfaite (∼95%), par un effet similaire au couplage critique. Finalement, l'étude détaillée des mécanismes qui régissent le gain d'absorption en 2D a permis leur reproduction dans des systèmes 3DDisordered media composed of nanoparticles are of great importance in many applications, particularly those related to energy efficiency such as radiative cooling. Understanding the light-matter interaction is therefore essential, but highly complex. Indeed, these studies often involve solving Maxwell's equations in systems made up of thousands of particles, to take account of scattering and interference phenomena. In order to reduce the ensuing numerical burden, this thesis focuses on 2D systems, with some discussion of 3D systems. In this context, the first part of this manuscript focuses on the concept of homogenization for particle systems that are small relative to the radiation wavelength and may exhibit resonances. This study highlights exotic behaviours that allow us to discuss, among other things, the link between homogenization and coherent and incoherent parts of the scattered field.The second part is dedicated to optimizing the absorption of radiation in subwavelength plates made of nanoparticles. It is shown that the use of resonant particles only results in absorption up to 70%. However, combining them with purely scattering particles results in near-perfect absorption (∼95%), through an effect similar to critical coupling. Finally, a detailed study of the mechanisms governing absorption gain in 2D has enabled them to be reproduced in 3D systems
3
Burnett, P. D. S. "Radiative properties of confined plasmas." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275600.
4
Francis, Peter N. "Infrared radiative properties of clouds." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302829.
5
Garrett, Timothy J. "Radiative properties of arctic clouds /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/10090.
6
Jiang, Jingyi. "Retrieving leaf and canopy characteristics from their radiative properties using physically based models : from laboratory to satellite observations Estimation of leaf traits from reflectance measurements: comparison between methods based on vegetation indices and several versions of the PROSPECT model a model of leaf optical properties accounting for the differences between upper and lower faces Speeding up 3D radiative transfer simulations: a physically based approximation of canopy reflectance dependency on wavelength, leaf biochemical composition and soil reflectance Effective GAI for crops is best estimated from reflectance observations as compared to GAI and LAI Optimal learning for GAI and chlorophyll estimation from 1D and 3D radiative transfer model inversion: the case of wheat and maize crops observed by Sentinel2." Thesis, Avignon, 2019. http://www.theses.fr/2019AVIG0708.
Abstract:
La mesure des caractéristiques des feuilles et du couvert végétal par télédétection est un moyen efficace et non destructif d’effectuer un suivi des cultures, que ce soit pour la prise de décision dans la gestion d’itinéraires techniques an agriculture de précision ou pour le phénotypage au champ pour améliorer l'efficacité de la sélection variétale. Grâce à l’augmentation de la puissance de calcul des machines et à la disponibilité croissante d'images à haute résolution spatiale, les méthodes d’estimation peuvent maintenant bénéficier de simulations plus précises des modèles de transfert radiatif (RT) dans la végétation. L'objectif de ce travail est de proposer et d'évaluer des moyens efficaces pour estimer les caractéristiques des feuilles et du couvert végétal à partir d'observations rapprochées ou de télédétection en utilisant des modèles RT basés sur une description réaliste de la structure des feuilles et du couvert. Au niveau des feuilles, nous avons d'abord évalué la capacité des différentes versions du modèle PROSPECT à estimer des variables biochimiques comme la chlorophylle (Cab), la teneur en eau et en matière sèche. Nous avons ensuite proposé le modèle FASPECT pour décrire les différences de propriétés optiques entre les faces supérieure et inférieure des feuilles en considérant un système à quatre couches. Après avoir étalonné les coefficients d'absorption spécifiques des principaux constituants de la feuille, nous avons validé FASPECT sur 8 jeux de données. Nous avons montré que les spectres de réflectance et de transmittance des deux faces sont simulés avec une très bonne précision, et même meilleure que PROSPECT pour la face supérieure. De même, en mode inverse, les performances d'estimation de la teneur en matière sèche sont considérablement améliorées avec FASPECT par rapport à PROSPECT, et restent du même ordre de grandeur pour la chlorophylle et l’eau. Au niveau du couvert végétal, nous avons utilisé le simulateur de rendu physique réaliste LuxCoreRender pour calculer le transfert radiatif à partir d'une description 3D de l’architecture de la culture. Nous avons d’abord vérifié ses bonnes performances par comparaison aux modèles 3D les plus récents en utilisant ROMC (RAMI On Line Model Checker). Afin d’accélérer les simulations, nous avons développé une méthode qui repose sur l’utilisation d’un nombre limité de propriétés optiques du sol et des feuilles. Pour estimer les variables d'état du couvert végétal (indice de surface verte, GAI, contenu en chlorophylle du couvert (CCC) ou des feuilles (Cab), nous avons ensuite entrainé des algorithmes d’apprentissage automatique à partir de bases de données « culture spécifique » simulées avec LuxCoreRender pour le blé et le maïs et d’une base de données générique simulée avec le modèle 1D PROSAIL de transfert radiatif. Les résultats sur des simulations et sur des données in situ combinés aux images SENTINEL2 ont montré que les algorithmes spécifiques aux cultures surpassent les algorithmes génériques pour les trois variables, en particulier lorsque la structure du couvert s’éloigne de l'hypothèse 1D du milieu turbide, comme dans le cas du maïs où la structure en rang domine pendant toute une partie de la saison de croissanceMeasuring leaf and canopy characteristics from remote sensing acquisitions is an effective and non destructive way to monitor crops both for decision making within the smart agriculture practices or for phenotyping under field conditions to improve the selection efficiency. With the advancement of computer computing power and the increasing availability of high spatial resolution images, retrieval methods can now benefit from more accurate simulations of the Radiative Transfer (RT) models within the vegetation. The objective of this work is to propose and evaluate efficient ways to retrieve leaf and canopy characteristics from close and remote sensing observations by using RT models based on a realistic description of the leaf and canopy structures. At the leaf level, we first evaluated the ability of the different versions of the PROSPECT model to estimate biochemical variables like chlorophyll (Cab), water and dry matter content. We then proposed the FASPECT model to describe the optical properties differences between the upper and lower leaf faces by considering a four-layer system. After calibrating the specific absorption coefficients of the main absorbing material, we validated FASPECT against eight measured ground datasets. We showed that FASPECT simulates accurately the reflectance and transmittance spectra of the two faces and overperforms PROSPECT for the upper face measurements. Moreover, in the inverse mode, the dry matter content estimation is significantly improved with FASPECT as compared to PROSPECT. At the canopy level, we used the physically based and unbiased rendering engine, LuxCoreRender to compute the radiative transfer from a realistic 3D description of the crop structure. We checked its good performances by comparison with the state of the art 3D RT models using the RAMI online model checker. Then, we designed a speed-up method to simulate canopy reflectance from a limited number of soil and leaf optical properties. Based on crop specific databases simulated from LuxCoreRender for wheat and maize and crop generic databases simulated from a 1D RT model, we trained some machine learning inversion algorithms to retrieve canopy state variables like Green Area Index GAI, Cab and Canopy Chlorophyll Content (CCC). Results on both simulations and in situ data combined with SENTINEL2 images showed that crop specific algorithms outperform the generic one for the three variables, especially when the canopy structure breaks the 1D turbid medium assumption such as in maize where rows are dominant during a significant part of the growing season
7
Assi, Benoît [Verfasser]. "Electroweak Radiative Corrections and Effective Field Theories / Benoît Assi." Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2021. http://d-nb.info/1240835590/34.
8
Becker, H. "Controlling the radiative properties of conjugated polymers." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596510.
Abstract:
My research has focused on the effects of reflective surfaces such as metals and dielectric stacks on the light emission from conjugated polymers. Conjugated polymers have semiconducting properties which arise from the delocalisation of electrons along the polymer backbone. These plastics are efficient light-emitters both in photoluminscence (PL) and Electroluminescence (EL). One of the unique features of these materials is their broad emission spectrum. Proximity to reflective surfaces alters the radiative rate of an emitter because of interference effects. This modification to the radiative rate is a function of the dielectric properties of the mirror, the orientation of the dipole, the distance between the dipole and the mirror, the emission angle, and the emission wavelength. In addition, non-radiative energy transfer from the emitter to excitations in a metal film efficiently quench luminescence at separations less than 60 nm. I have investigated the effects of interference and non-radiative energy transfer on the emission spectra and the PL and EL quantum efficiencies of conjugated polymer structures. The PL from thin films of conjugated polymers spin-coated onto Al and Au films, with and without SiO2 spacer layers in between, was investigated. PL was found to be quenched close to the metal films. Experiments on double-layer LEDs where the distance between the emissive region can be controlled by altering the film thicknesses of the polymer layers extended those results from PL to EL. In addition, changes in the PL spectra and PL efficiency with increasing polymer-metal separation could be explained by computer-modelling the radiative power of oscillating dipoles. The results allowed design rules to be formulated which could improve the efficiency of LEDs, photovoltaic cells and microcavity devices in which the polymer film is sandwiched between two mirrors. Comparison between experiment and modelling revealed some information about the photophysics of conjugated polymers. Microcavities (Fabry-Perot resonators containing a light-emitter) modify the radiative rate of an emitter more strongly than single mirror devices. I have investigated the role of the dielectric properties of metals on the resonance wavelengths of a microcavity. It is shown that the metal film thickness influences the cavity resonances and that the angular dependence of the microcavity emission can be reduced exploiting specific properties of the metal.
9
Liu, Xianglei. "Tailoring thermal radiative properties and enhancing near-field radiative heat flux with electromagnetic metamaterials." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54960.
Abstract:
All substances above zero kelvin temperature emit fluctuating electromagnetic waves due to the random motions of charge carriers. Controlling the spectral and directional radiative properties of surfaces has wide applications in energy harvesting and thermal management. Artificial metamaterials have attracted much attention in the last decade due to their unprecedented optical and thermal properties beyond those existing in nature. This dissertation aims at tailoring radiative properties at infrared regime and enhancing the near-field radiative heat transfer by employing metamaterials. A comprehensive study is performed to investigate the extraordinary transmission, negative refraction, and tunable perfect absorption of infrared light. A polarizer is designed with an extremely high extinction ratio based on the extraordinary transmission through perforated metallic films. The extraordinary transmission of metallic gratings can be enhanced and tuned if a single layer of graphene is covered on top. Metallic metamaterials are not the unique candidate supporting exotic optical properties. Thin films of doped silicon nanowires can support negative refraction of infrared light due to the presence of hyperbolic dispersion. Long doped-silicon nanowires are found to exhibit broadband tunable perfect absorption. Besides the unique far-field properties, near-field radiative heat transfer can be mediated by metamaterials. Bringing objects with different temperatures close can enhance the radiative heat flux by orders of magnitude beyond the limit set by the Stefan-Boltzmann law. Metamaterials provide ways to make the energy transport more efficient. Very high radiative heat fluxes are shown based on carbon nanotubes, nanowires, and nanoholes using effective medium theory (EMT). The quantitative application condition of EMT is presented for metallodielectric metamaterials. Exact formulations including the scattering theory and Green’s function method are employed to investigate one- and two-dimensional gratings as well as metasurfaces when the period is not sufficiently small. New routes for enhancing near-field radiative energy transport are opened based on proposed hybridization of graphene plasmons with hyperbolic modes, hybridization of graphene plasmons with surface phonon modes, or hyperbolic graphene plasmons with open surface plasmon dispersion relation. Noncontact solid-state refrigeration is theoretically demonstrated to be feasible based on near-field thermal radiation. In addition, the investigation of near-field momentum exchange (Casimir force) between metamaterials is also conducted. Simultaneous enhancement of the near-field energy transport and suppress of the momentum exchange is theoretically achieved. A design based on repulsive Casimir force is proposed to achieve tunable stable levitation. The dissertation helps to understand the fundamental radiative energy transport and momentum exchange of metamaterials, and has significant impacts on practical applications such as design of nanoscale thermal and optical devices, local thermal management, thermal imaging beyond the diffraction limit, and thermophotovoltaic energy harvesting.
10
Bourgeois, C. Saskia. "The radiative properties of snow at Summit, Greenland /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16758.
11
Mavrogordatos, Themistoklis. "Emission properties of radiative chiral nematic liquid crystals." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/247156.
Abstract:
In this work, we calculate the density of photon states (DOS) of the normal modes in dye-doped chiral nematic liquid crystal (LC) cells in the presence of various loss mechanisms. Losses and gain are incorporated into the transmission characteristics through the introduction of a small imaginary part in the dielectric constant perpendicular and along the director, for which we assume no frequency dispersion. Theoretical results are presented on the DOS in the region of the photonic band gap for a range of values of the loss coefficient and different values of the optical anisotropy. The obtained values of the DOS at the photonic band gap edges predict a reversal of the dominant modes in the structure. Our results are found to be in good agreement with the experimentally obtained excitation thresholds in chiral nematic LC lasers. The behaviour of the DOS is also discussed for amplifying LC cells providing an additional insight to the lasing mechanism of these structures. We subsequently investigate the spontaneous emission properties, under the assumption that the electronic transition frequency is close to the photonic edge mode of the structure (resonance). We take into account the transition broadening and the decay of electromagnetic field modes supported by the so-called 'mirror-less' cavity. We employ the Jaynes-Cummings Hamiltonian to describe the electron interaction with the electromagnetic field, focusing on the mode with the diffracting polarization in the chiral nematic layer. As known in these structures, the density of photon states, calculated via the Wigner method, has distinct peaks on either side of the photonic band gap, which manifests itself as a considerable modification of the emission spectrum. We demonstrate that, near resonance, there are notable differences between the behaviour of the density of states and the spontaneous emission profile of these structures. In addition, we examine in some detail the case of the logarithmic peak exhibited in the density of states in 2D photonic structures and obtain analytic relations for the Lamb shift and the broadening of the atomic transition in the emission spectrum. The dynamical behaviour of the atom-field system is described by a system of two first order differential equations, solved using the Green's function method and the Fourier transform. The emission spectra are then calculated and compared with experimental data. Finally, we detail a new technique for the pumping of dye lasers which requires no moving parts or flushing mechanisms and is applicable to both solid state and liquid based devices. A reconfigurable hologram is used to control the position of incidence of a pump beam onto a dye laser and significant increases in device lifetimes are achieved. The technique is also applied to wavelength tune a dye laser. This offers access to higher repetition rates and larger average output powers. With higher repetition rate pump lasers it is feasible that the approach could allow such organic lasers to reach operating frequencies on the order of MHz. The unique nature of the adaptive pumping method also allows precise control of the spatial wave-front and configuration of the pumping wave which allows greater versatility and functionality to be realised. It is possible to envisage that novel pump beam profiles that optimise propagation through the medium could also be demonstrated.
12
Bantges, Richard John. "Cirrus cloud radiative properties in the thermal infrared." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.344152.
13
Cunsolo, Salvatore. "Radiative properties computational modeling of porous cellular materials." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI005/document.
Abstract:
Les transferts thermiques par rayonnement dans des mousses sont modélisés à partir de la morphologie du matériau et des propriétés de sa phase solide. Dans ce travail de thèse, une attention particulière est portée sur les modèles radiatifs de Monte Carlo. Les différentes approches d’homogénéisation telles que « Homogeneous Phase » (HPA) and « Multi Phase » (MPA) sont discutées et comparées. Des développements novateurs sont proposés pour améliorer la précision des résultats. Nos avancées permettent de générer numériquement trois types de mousses périodiques couvrant un large domaine de matériaux cellulaires: mousse à pores fermés à haute porosité, mousse à cellules ouvertes à basse et haute porosité. Pour ces dernières, des comparaisons morphologiques avec des données expérimentales tomographiques, montrent des résultats satisfaisants et tendent à valider nos modèles de génération. Des mousses dont la phase solide est opaque ont tout d’abord été étudiées. Nos simulations ont permis de trouver de nouvelles lois analytiques précises permettant d’estimer les propriétés radiatives de ces matériaux à partir de données morphologiques. Ensuite, nous avons considéré des mousses, dont la phase solide est semi transparente. La modélisation du transfert radiatif au sein de ces milieux cellulaires est plus complexe. Les méthodes de modélisation des propriétés radiatives de la littérature, HPA et MPA, sont testées. Des simulations de Monte carlo directes dans les matériaux ont permis de mettre en exergue les limites de ces modèles. Des modèles novateurs ont été proposés afin d’ améliorer la précision des simulations. Ils sont basés sur une méthode hybride directe-inverse et une modification de l’équation de transfert radiatif classique. Ces nouveaux modèles (HPA+ et MPA+) ont été testés sur un ensemble varié de morphologies générées numériquement. Les modèles améliorés sont systématiquement plus précis que les modèles existantsCellular media such as plastic, ceramic and metal foams present specific characteristics that make them interesting for a number of applications related to thermal engineering. Their ability to minimize natural convection makes them ideal candidates for insulation applications, while the high specific surface and permeability to fluid of open cell foams makes them interesting heat transfer enhancers. In addition, their permeability to light makes them an ideal candidate for thermal radiation based applications, such as porous burners or solar energy collectors. In many of these application, thermal radiation heat transfer can have a significant influence on the heat transfer process. Both accurate radiation models and accurate morphological models of the structure of the foam are required. This work provides an original contribution on both these accounts. A discussion of the literature on numerical methods for radiation heat transfer in cellular media is presented, with focus on Monte Carlo methods. Homogeneous Phase (HPA) and Multi Phase (MPA) methods are discussed. Further efforts are required to accurately model and digitally replicate of foam morphologies. Our goal is to digitally generate three commonly occurring types of foam structures, covering a large range of real materials: high-porosity open cell foams, high-porosity closed cell foams, low-porosity open-cell structures. For high-porosity open cell foams, the automated parametric digital generation technique was validated against a dataset consisting of raw morphological data obtained by tomographic analysis. The generation capabilities were then applied to parametrically investigate the influence of morphological parameters on the radiative properties (namely, the extinction coefficient) of an opaque open-cell foam. Highly accurate analytical relationships were subsequently deduced and validated by comparison with results obtained from tomography samples. Modeling radiation in foams with a semi-transparent solid phase is substantially more complex. A Direct Monte-Carlo Homogenization reference technique is proposed, that allows to simulate radiation within arbitrary cavities and calculate macroscopic radiative quantities based on a Representative Elementary Volume (REV) of cellular material. The technique is validated against full scale Monte Carlo simulations. Improvements of the existing Homogeneous Phase and Multi Phase approach are proposed, through extensive use of inverse methods and the addition of one equation to take into account specific phenomena taking place in the semi-transparent solid phase. The resulting Improved Homogenized Approaches are extensively tested by comparing them with Direct Monte Carlo Homogenization simulations and existing homogenized models, on a varied set of morphologies making full use of the previously developed digital generation techniques. The improved models consistently outperform existing homogenized models
14
Rogne, Henrik. "Thermal radiative properties of Si, GaAs, and InP." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627277.
15
Xu, Jin. "Direct aerosol radiative forcing based on measurements of aerosol radiative, chemical and physical properties in China." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/20173.
16
Nouri, Nima. "Radiative Conductivity Analysis Of Low-Density Fibrous Materials." UKnowledge, 2015. https://uknowledge.uky.edu/me_etds/66.
Abstract:
The effective radiative conductivity of fibrous material is an important part of the evaluation of the thermal performance of fibrous insulators. To better evaluate this material property, a three-dimensional direct simulation model which calculates the effective radiative conductivity of fibrous material is proposed. Two different geometries are used in this analysis.
The simplified model assumes that the fibers are in a cylindrical shape and does not require identically-sized fibers or a symmetric configuration. Using a geometry with properties resembling those of a fibrous insulator, a numerical calculation of the geometric configuration factor is carried out. The results show the dependency of thermal conductivity on temperature as well as the orientation of the fibers. The calculated conductivity values are also used in the continuum heat equation, and the results are compared to the ones obtained using the direct simulation approach, showing a good agreement.
In continue, the simulated model is replaced by a realistic geometry obtained from X-ray micro-tomography. To study the radiative heat transfer mechanism of fibrous carbon, three-dimensional direct simulation modeling is performed. A polygonal mesh computed from tomography is used to study the effect of pore geometry on the overall radiative heat transfer performance of fibrous insulators. An robust procedure is presented for numerical calculation of the geometric configuration factor to study energy-exchange processes among small surface areas of the polygonal mesh.
The methodology presented here can be applied to obtain accurate values of the effective conductivity, thereby increasing the fidelity in heat transfer analysis.
17
Sun, Wenbo. "An investigation of infrared radiative properties of cirrus clouds." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24928.pdf.
18
Chalmers, Nicky. "Using retrieved cloud properties to investigate their radiative impact." Thesis, University of Reading, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553137.
Abstract:
The cloud climate feedback has long been recognised as one of the greatest sources of uncertainty of future climate predictions. In order to narrow this uncertainty models should be evaluated in terms of cloud properties and their radiative sensitivity to those properties. Over recent years methods have been developed to retrieve cloud properties (ice and liquid water content), therefore allowing this evaluation. This thesis focuses on model validation by using retrieved cloud property information, from active remote sensing instruments at Lindenberg in Germany, as input to a radiative transfer scheme. The radiative budget of the atmosphere is simulated and can be used as a tool to assess model cloud representation and its radiative response to cloud properties. First, the radiation scheme is assessed under cloud-free conditions. The clear sky top of atmosphere (TOA) radiation budget can be modelled with an average difference of 15 W m -2 in the shortwave (SW) and 5 W m -2 in the longwave (LW) of observations. The surface radiative ftuxes are simulated with an average difference of 30 W m -2 in the SW and 12 W m-2 in the LW. After testing the sensitivity of the radiation simulations to cloud property retrieval errors, the radiation budget in the presence of cloud is calculated. Cloudy sky simulations agree with observations with an average difference of 10 W m-2 at the TOA in both the SW and LW, and at the surface, 1 W m -2 in the SW and 6 W m -2 in the LW, although the variability is larger than this indicates. A positive bias is found in the OLR simulations which is partly attributed to un-observed thin ice clouds, which consist of small particles that are beyond the sensitivity of the radar. Simulations show that these clouds reduce the OLR by -4 W m -2 , explaining a portion of this discrepancy. The cloud property data and the radiative simulations are used to assess the cloud representation, and cloud radiative response, in the ECMWF model. The temperature dependant parameterisation of mixed phase clouds is compared with observations and found to be unrealistic. The radiative impact of this error reduces the magnitude of the SW and LW simulated radiative effect by approximately 20%.
19
Brent, Kevin M. "Optimization of Fire Blanket Performance by Varying Radiative Properties." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1313767793.
20
Sweet, Julian. "RADIATIVE COUPLING AND DECAY PROPERTIES OF QUANTUM CONFINED SEMICONDUCTORS." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/194915.
Abstract:
Several contemporary research topics on the subject of light-matter coupling are addressed. Through a variety of experimental methods, the emissive and carrier correlation properties of both quantum dots (QD) and quantum wells (QW) are explored.The radiative decay properties of self-assembled indium arsenide (InAs) quantum dots grown by molecular beam epitaxy (MBE) are discussed. The measurement of radiative lifetime is used to determine dipole moment. In addition, evidence is presented of radiative lifetime reduction for quasi-resonant and strictly resonant time-resolved measurements. This lessening is attributed to carrier correlations which exist during resonant excitation but that are not present during above-band pumping. The data do not support the assertion that the shorter radiative lifetime is caused by a superradiant effect.MBE-grown Fibonacci sequence QWs exhibiting novel polaritonic properties are also introduced. These quasiperiodic structures stand apart from periodic structures in that they possess nonperiodic long-range order. Subsequent investigation of nonlinear reflectivity in the quasiperiodic structure showed excellent agreement with theoretical predictions. Of particular interest is the narrow deep dip close to the heavy hole resonance as well as the valley between the heavy hole and light hole resonance positions.
21
De, Silva A. A. "Measurement of some radiative properties of solar absorber materials." Thesis, Open University, 1986. http://oro.open.ac.uk/56922/.
Abstract:
This work describes, (i) the designing and building of two sets of apparatus, namely a Liquid Nitrogen Cooled Ditectional Emissometer and a Laser-source Spectral Bidirectional Reflectometer (ii) measurements using the above apparatus on Solar selective absorber (Maxorb, Cusorb, Skysorb, Solarcoat- 100), non-selective absorber (Nextel, Solarcoat-50) and metal (Al, Cu and brass) samples. The emissometer incorporates liquid nitrogen cooling of the sample chamber thus reducing the error due to emission from the surroundings and extending the working range of sample temperature down to about 273 K. This instrument also uses a beam chopper with a phase sensitive detection system, and a Golay-cell detector. The overall error in the emittance values measured is estimated to be ± 5%. Using the emissometer all the samples in (ii) above were studied. The directional emittance behaviour of the metals and the non-selective absorbers agree well with theoretical predictions and with measurements made by other workers. In the case of the solar selective absorbers however, a peak in the directional emittance at 20°-30° reported by Hutchins (1979) is not seen in any of the present measurements. It is suggested that the ∈/∈'(0°) vs. ∈'(0°) plot can be used in comparing the emittance properties of solar selective absorbers with their substrate metals. The bidirectional reflectometer incorporates a novel device for mounting, positioning and orienting both the sample and the detector (Sample and Detector Assembly - SDA). The relatively small dimensions of this device compared with that of other bidirertional reflectometers reported makes it convenient to use and also allows it to be housed within a light-tight enclosure that minimizes problems with stray light. Extensive measurements have been made using laser sources at λ - 633 nm and λ - 1152 nm on the same set of samples of solar absorbers (selective and non-selective) studied with the emissometer. Comparison of the bidirectional reflectance characteristics of the solar selective absorbers shows marked differences between the materials. However certain features common to 'specularly' reflecting materials and others common to 'diffusely' reflecting materials have been identified. Materials like Cusorb and Solarcoat-lOO show a combination of these. Some of these features are discussed in terms of the surface microstructure data obtained using a scanning electron microscope and a conventional stylus type instrument.
22
Allen, Clare. "The influence of multi-dimensional radiative transfer on the evolution and radiative properties of tropical convective clouds." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490579.
Abstract:
This study investigates the role of multi-dimensional (MD) solar radiation on the cloud radiative properties and cloud evolution for convective clouds using the UK Met Office Large Eddy Model (LEM) with an interactively coupled Monte Carlo (MC) radiation model. Simulations are performed with the MC scheme running in MD mode and in Independent Column Approximation (ICA) mode. These simulations have been studied to ascertain the impact and understand how MD radiation is influencing clouds differently from the lCA implementation. Since the difference between the ICA and MD radiation is greatest for clouds with large vertical extent, focus has been on warm phase shallow cumulus and mixed phase deep convective (DC) clouds. Using these two types of clouds, it . was possible to evaluate not only the effect of differing clo~d side extent but also the effect of microphysical phase on the evolution. For the cumulus case, the Small Cumulus Microphysics Study (SCMS) is used and for the DC cloud a new case study has been developed based on the Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE) observations. All simulations were performed in 2D. It is found that the MD radiation creates minor differences in the early phase of the first plume; however, these differences have an important role in affecting the secondary plumes for the warm phase cumulus SCMS caSe and cause significant changes in the mixed phase cloud properties (ice, snow, graupel) for the CRYSTAL-FACE case, altering them by as much as a factor of two in the cases studied. Detailed accounts of cloud evolution are presented and the process of how MD as opposed to ICA affects the evolution is presented in terms of radiation-cloud diminishing/enhancing effects that are developed in the work. Cloud radiative forcing (CRF) values were calculated to assess the effects of MD compared to lCA simulations for the upwelling fluxes at the TOA. A tool was developed that related the cloud geometry to the upwelling solar flux, called the effective cloud perimeter. Simulations were performed to calculate the total CRF as well as isolate effects due to geometry and cloud evolution differences. The CRF for geometry effects is up to 70Wm-2 for the SCMS case and 15vVm-2 for the CRYSTAL-FACE case. The impact of evolution is found to be up to 62\Vm-2 for the SCMS and 55\Vm-2 for the CRYSTAL-FACE case. The geometry effects are found to occur during the development and maturation stages and the evolution effects are most prominent in the later mature and dissipation stages. This research developed two tools which can be applied to other simulations. The first was the radiation-cloud diminishing/enhancing effect, which was used to help determine the impact of radiation modifying convective cloud evolutions. The second tool was the effective cloud perimeter, which was used to understand the impact of cloud features that modified the solar radiative properties. Both tools enabled a rigorous understanding of the interactive nature of radiation and cloud processes, and how these varied with ICA and MD solar radiation.
23
Ring, Harvey Brents III. "Radiative ignition of a wall jet." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/18937.
24
Charron, Luc G. "Radiative properties of molybdenum sulfide and other transition metal dichalcogenides." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26599.
Abstract:
Low temperature radiative properties of the layered transition metal dichalcogenides 2H-MoS2, 2H-WS2 and 2H-WSe 2 are investigated. Synthetically grown crystals of all three materials, natural 2H-MoS2 single crystals and several 2H-MoS2 and 2H-WS2 commercial powders are studied. Steady-state photoluminescence (PL) measurements performed on the samples reveal two distinct radiative regions in the near infrared. The first region consisting of several sharp lines is produced by bound excitons related to the halogen transport agent intercalated within the van der Waals gap of the layered compounds. The second weaker region, composed of a broad spectral band, originates from the radiative recombination between an intrinsic crystal lattice defect center and the valence band in the conditions of a strong electron-phonon coupling. Time decay analysis of the bound excitonic radiative transitions is performed with time-resolved and PL intensity ratio measurements. The spectral and temperature dependence of the total radiative emissions of all three compounds are described in the framework of a two-channel kinetic recombination model in thermal equilibrium conditions. A configuration coordinate diagram is also constructed for 2H-MoS 2. PL intensity measurements performed on the 2H-MoS2 and 2H-WS2 synthetic crystals reveal a sublinear PL dependence on excitation intensity. Finally a technique developed to intercalate halogen molecules in natural 2H-MoS2 single crystals is described.
25
Ridley, David A. "Aerosol Radiative Properties Analysed using Global Models of Aerosol Microphysics." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494262.
26
CRISCUOLI, SERENA. "Radiative properties of complex magnetic elements in the solar photosphere." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/599.
Abstract:
In this thesis I investigate the photometric and geometric properties of bright
magnetic features in the lower solar atmosphere. The contribution of these fea-
tures to Total Solar Irradiance (TSI here after) variations observed at different
temporal scales has been broadly showed during the last years. Nevertheless,
measurements and theoretical investigations of their properties, on which recon-
structions of TSI variations are based, have produced discrepant results.
In order to interpret discrepancies presented in the literature and to improve
our understanding of physical properties of magnetic elements, both experimen-
tal and theoretical aspects have been investigated.
In the first part of the thesis I show results obtained by the analysis of full
disk PSPT broad band images from Rome and Hawaii. Geometric properties
and the possible connection with photometric properties have been investigated
through the measurement of fractal dimension of features observed in chromo-
sphere. Results I obtain agree very well with the ones presented in the literature
carried out on similar data and with the same fractal dimension estimator. The
fractal dimension increases in fact with features area and reaches a plateau at
areas larger than about 1000-2000 Mm2. Nevertheless, by the analyses of im-
ages of fractals whose dimension is known by the theory, I show that fractal
dimension estimation is critically effected by pixelization, technique employed
to select magnetic structures on images and resolution. In particular the in-
crease of fractal dimension with object size is an effect of pixelization and thus
some conclusions previously drawn in the literature should be revisited.
Photometric properties are investigated by the analyses of contrast of identi-
fied features in two photospheric bands and in the chromosphere. In particular
the variation of the contrast with position on the solar disk and with object
size is investigated. I show that the contrast in the chromosphere is not depen-
dent on disk position and that in the photosphere monotonically increases from
the center toward the limb. A comparison with previously published results
shows a better agreement with authors that employed an identification meth-
ods similar to the ones I employed to select magnetic features on images. The
contrast, especially at the limb, is also critically affected by seeing. Comparison
of the scaling of average and maximum contrast with object size suggests that
the smaller magnetic elements, whose clustering forms the features analyzed,
are characterized by different photometric properties. The increase of average
contrast with object size, very similar to the increase observed for the fractal
dimension, is instead an effect of filling factor.
In order to investigate the physical origin of the results and validate some
of the conclusions drawn, 2D numerical codes based on the magnetic flux tube
model have been developed. Plane parallel gray atmosphere in LTE is supposed
and radiative and convective energy transport mechanisms have been taken
into account. In particular two classes of models are investigated. In the first
one convection is modelled by the Mixing length theory and radiation by the
radiative diffusion approximation. In the second one only radiation is taken
into account, but radiative diffusion approximation is dropped and radiative
equilibrium is imposed by an iterative scheme. The presence of the magnetic
field is mimicked by imposing a lower pressure and density in the magnetic
region. In order to evaluate the radiation field a numerical code, based on
the short characteristic technique, was developed. A detailed description of
the code, as well as results obtained by tests aimed to investigate and compare
different numerical techniques and spurious effects, are presented. The radiative
flux is finally evaluated by a quadrature scheme. At this aim two schemes
have been developed and compared. The software developed has allowed to
investigate radiation field through the flux tube models studied. I show that the
presence of a magnetic structure generates areas of different shapes and contrast
around it. These features vary with the position of the structures on the solar
disk (the sight angle) and have spatial scales smaller than the typical scale of
a flux tube (about 100 km), so resolution better than 0.1 arcsec is required to
observe them. The contrast of magnetic features varies also in function of the
optical depth, so that for the same model different center to limb variations of the
contrast can be observed. This indicates that contrast is strongly dependent on
observation wavelength, thus partially explaining the discrepant results obtained
in the literature. Investigation of the results also shows that the center to
limb variation of the contrast reflects the temperature stratification inside and
outside the tube. Measurements carried out at different wavelengths are thus
fundamental for the determination of temperature of magnetic structures and
for the investigation of their physical properties.
27
Ghaemi, Hamid. "The effective properties of composite material." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0020/MQ58036.pdf.
28
Chopra, Prateek. "Effective mechanical properties of lattice materials." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39436.
Abstract:
Lattice materials possess a spatially repeating porous microstructure or unit cell. Their usefulness lies in their multi-functionality in terms of providing high specific stiffness, thermal conductivity, energy absorption and vibration control by attenuating forcing frequencies falling within the band gap region. Analytical expressions
have been proposed in the past to predict cell geometry dependent effective material properties by considering a lattice as a network of beams in the high porosity limit. Applying these analytical techniques to complex cell geometries is cumbersome. This precludes the use of analytical methods in conducting a comparative study involving complex lattice topologies. A numerical method based on the method of long wavelengths and Bloch theory is developed here and applied to a chosen set of lattice geometries in order to compare effective material properties of infinite lattices. The proposed method requires implementation of Floquet-bloch transformation in conjunction with a Finite Element (FE) scheme. Elastic boundary layers emerge from surfaces and interfaces in a finite lattice, or an infinite lattice with defects such as cracks. Boundary layers can degrade effective
material properties. A semi-analytical formulation is developed and applied to a chosen set of topologies and the topologies with deep boundary layers are identified. The methods developed in this dissertation facilitate rapid design calculation and selection of appropriate core topologies in multifunctional design of sandwich
structures employing a lattice core.
29
Lehmann, Brian (Brian Todd). "Numerical properties of pseudo-effective divisors." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60194.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 69-71).
Suppose that X is a smooth variety and L is an effective divisor. One of the main goals of bi rational geometry is to understand the asymptotic behavior of the linear series... as m increases. The two most important features of the asymptotic behavior - the litaka dimension and the litaka fibration - are subtle and difficult to work with. In this thesis we will construct approximations to these objects that depend only on the numerical class of L. The main interest in such results arises from the Abundance Conjecture which predicts that the Iitaka fibration for Kx is determined by its numerical properties. In the second chapter we study a numerical approximation to the Iitaka dimension of L. For a nef divisor L, this quantity is a classical invariant known as the numerical dimension. There have been several proposed extensions of the numerical dimension to pseudo-effective divisors in [Nak04] and [BDPP04]. We show that these proposed definitions coincide and agree with many other natural notions. Just as in the nef case, the numerical dimension v(L) of a pseudo-effective divisor L should measure the maximum dimension of a subvariety ... such that the "positive restriction" of L is big along W. In the third chapter, we analyze how the properties of the Iitaka fibration OL for L are related to the numerical properties of L. Although the numerical dimension detects the existence of "virtual sections", it does not have a direct relationship with the Iitaka fibration. However, we do construct a rational map that only depends on the numerical class of L and approximates the Jitaka fibration. This rational map is the maximal possible fibration for which a general fiber F satisfies v(LIF) = 0. Thus, this chapter recovers and extends the work of [Eck05] from an algebraic viewpoint. Finally, we use the pseudo-effective reduction map to study the Abundance Conjecture.
by Brian Lehmann.
Ph.D.
30
Lee, Hyunjin. "Radiative properties of silicon wafers with microroughness and thin-film coatings." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-07092006-181152/.
Abstract:
Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006.Zhang, Zhuomin, Committee Chair ; Joshi, Yogendra, Committee Member ; Lee, Kok-Meng, Committee Member ; Gallivan, Martha, Committee Member ; Zhao, Yiping, Committee Member.
31
Gilbert, Dean. "Observations and calculations of radiative properties of clouds observed during RACE." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0003/MQ44171.pdf.
32
Ivanov, Vladyslav Victorovych. "Cold atoms modified radiative properties and evaporative cooling from optical traps /." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2007. http://dare.uva.nl/document/47332.
33
Taylor, Jonathan P. "The remote retrieval of stratiform water cloud radiative and microphysical properties." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357173.
34
Aasum, Yngve. "Effective properties of reservoir simulator grid blocks /." Access abstract and link to full text, 1992. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9300177.
35
Okyay, Gizem. "Impact of the morphology of soot aggregates on their radiative properties and the subsequent radiative heat transfer through sooty gaseous mixtures." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC031/document.
Abstract:
Les suies et leur caractérisation constituent des sujets de recherche très actuels dans divers domaines tels que le diagnostic de la combustion, la combustion numérique, l’optique atmosphérique, l'environnement et les applications de santé. Notre étude se concentre sur les propriétés radiatives des agrégats de suie issus de flammes de combustion ; notre objectif est de déterminer l’effet de la présence de suies sur le transfert de chaleur par rayonnement pour la simulation d'applications industrielles à haute température impliquant la combustion de gaz. Les études actuelles de modélisation du transfert de chaleur par rayonnement à travers les mélanges gazeux chargés de suies ne considèrent que l'absorption comme phénomène d'interaction rayonnement-matière. Des corrélations généralisées sont utilisées pour déterminer les propriétés radiatives des suies, soit sur la base de morphologies générées numériquement, soit plus simplement à partir de la taille moyenne des suies, de leur dimension fractale et de leur fraction volumique. Cependant, lorsque la taille de l'objet atteint l'ordre de grandeur des longueurs d'onde du rayonnement incident, l'interaction matière-rayonnement est susceptible d’être plus complexe du fait du phénomène de diffusion au niveau de l’agrégation qui ne peut plus être ignoré.Dans notre travail, nous établissons une méthodologie complète assortie d’une chaîne de calcul allant de la définition d'une morphologie de suie réaliste jusqu'au calcul du transfert de chaleur par rayonnement. À cette fin, des observations de suies émises par des flammes propane / air, méthane / air et méthane / oxygène sont effectuées par Microscopie Electronique à Balayage (MEB). La tomographie MEB est appliquée pour la première fois sur une suie issue d’une flamme propane / air, en combinaison avec la Microscopie Electronique en Transmission (MET) pour les observations. Des techniques d'analyse fractale 2D et 3D sont utilisées pour étudier les propriétés fractales d’agrégats de suie virtuels (générés numériquement) et de l'objet obtenu par la tomographie. Les propriétés radiatives des suies sont ensuite calculées en utilisant notre propre code d’Approximation Dipolaire Discrète (ADD – Discrete Dipole Approximation, ou DDA, en anglais). Une attention particulière est accordée à la modélisation ADD des suies en raison de l’indice optique complexe élevé de leur matériau constitutif, et aux méthodes numériques d’intégration directionnelle car les moyennes directionnelles des propriétés radiatives sont nécessaires pour les simulations ultérieures de transfert radiatif. La morphologie et les propriétés radiatives de l’agrégat de suie réaliste (tomographié) sont comparées à celles d'agrégats de suie numériques représentatifs, générés par un algorithme d’agrégation amas-amas limitée par la diffusion (Diffusion Limited Cluster-Cluster Aggregation, ou DLCCA, en anglais). Les compatibilités et les écarts entre les propriétés radiatives sont examinés, et les différences entre agrégats numériques représentatifs d’une part et agrégat réaliste d’autre part en termes de propriétés radiatives sont soulignées. Enfin, l'effet de la présence et de la morphologie des suies sur le transfert de chaleur par rayonnement est étudié par la résolution de l'équation du transfert radiatif en utilisant la méthode des ordonnées discrètes (Discrete Ordinates Method, ou DOM, en anglais) dans un mélange gazeux chargé de suies et dans une configuration académique 1D de plaques parallèles isothermesSoot and its characterization are of interest to researchers from various domains such as combustion diagnostics, numerical combustion, atmospheric optics, environmental and health applications. In this study, the main interest is on the radiative properties of soot aggregates issued directly from combustion flames in order to determine the effect of the presence of soot on the radiative heat transfer in the simulation of high temperature industrial applications involving gas combustion. Current studies modeling the radiative heat transfer through sooty gaseous media consider only the absorption as the main phenomenon of material-radiation interaction. Generalized correlations are used to determine the radiative properties of soot: these radiative properties are either computed over numerically generated aggregate morphologies or simply as a function of the soot average size, the fractal dimension and the volume fraction. However, the material-radiation interaction is susceptible to be more complex and morphology dependent at the aggregate level because of multiple scattering when the size of the object reaches the order of magnitude of the incident radiation wavelengths.In our work, we investigate the possibility to establish a computational methodology and workflow, starting from the definition of a realistic soot morphology up to the computation of the radiative heat transfer. To that end, observations of soot issued from propane/air, methane/air and methane/oxygen flames are performed using Scanning Electron Microscopy (SEM). SEM tomography is applied for the first time on soot issued from a propane/air flame, combined with Transmission Electron Microscopy (TEM) observations. 2D and 3D fractal analysis techniques are used to investigate the fractal properties of virtual (numerically generated) soot clusters and also of the tomography reconstructed objects. The radiative properties of soot are then computed using our in-house developed DDA (Discrete Dipole Approximation) code. Special attention is paid to the DDA modeling of soot because of the high complex extinction index of the material, and to the directional integration numerical methods because direction-averaged radiative properties are required for the subsequent radiative heat transfer simulations. The morphology and the radiative properties of the realistic morphology are compared to the ones of representative soot aggregates numerically generated by a DLCCA (Diffusion Limited Cluster-Cluster Aggregation) algorithm. The similarities and discrepancies on the radiative properties are investigated, and the differences between representative virtual aggregates on the one hand and the tomography reconstructed object on the other hand in terms of radiative properties are highlighted. Finally the effect of the presence and of the morphology of soot on the radiative heat transfer within a sooty gaseous mixture in a 1D isothermal parallel plate configuration is investigated by the resolution of the radiative transfer equation using DOM (Discrete Ordinates Method)
36
Lee, Yong-Keun. "Study of cloud properties from single-scattering, radiative forcing, and retrieval perspectives." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1734.
37
Fu, Ceji. "Radiative Properties of Emerging Materials and Radiation Heat Transfer at the Nanoscale." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4941.
Abstract:
A negative index material (NIM), which possesses simultaneously negative permittivity and permeability, is an emerging material that has caught many researchers attention after it was first demonstrated in 2001. It has been shown that electromagnetic waves propagating in NIMs have some remarkable properties such as negative phase velocities and negative refraction and hold enormous promise for applications in imaging and optical communications. This dissertation is centered on investigating the unique aspects of the radiative properties of NIMs. Photon tunneling, which relies on evanescent waves to transfer radiative energy, has important applications in thin-film structures, microscale thermophotovoltaic devices, and scanning thermal microscopes. With multilayer thin-film structures, photon tunneling is shown to be greatly enhanced using NIM layers. The enhancement is attributed to the excitation of surface or bulk polaritons, and depends on the thicknesses of the NIM layers according to the phase matching condition. A new coherent thermal emission source is proposed by pairing a negative permittivity (but positive permeability) layer with a negative permeability (but positive permittivity) layer. The merits of such a coherent thermal emission source are that coherent thermal emission occurs for both s- and p-polarizations, without use of grating structures. Zero power reflectance from an NIM for both polarizations indicates the existence of the Brewster angles for both polarizations under certain conditions. The criteria for the Brewster angle are determined analytically and presented in a regime map. The findings on the unique radiative properties of NIMs may help develop advanced energy conversion devices. Motivated by the recent advancement in scanning probe microscopy, the last part of this dissertation focuses on prediction of the radiation heat transfer between two closely spaced semi-infinite media. The objective is to investigate the dopant concentration of silicon on the near-field radiation heat transfer. It is found that the radiative energy flux can be significantly augmented by using heavily doped silicon for the two media separated at nanometric distances. Large enhancement of radiation heat transfer at the nanoscale may have an impact on the development of near-field thermal probing and nanomanufacturing techniques.
38
Abel, Steven John. "The radiative properties and direct effect of Southern African biomass burning aerosols." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417397.
39
Wang, Xuan Ph D. Massachusetts Institute of Technology. "Exploring the absorption properties and direct radiative impact of atmospheric carbonaceous aerosols." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113493.
Abstract:
Thesis: Ph. D. in Environmental Chemistry, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 125-141).
Atmospheric aerosols are important due to their adverse effects on human health and their direct and indirect radiative effects on climate, which are significant and very uncertain factors contributing to global climate change. In estimating the direct radiative effect (DRE), the absorption from carbonaceous aerosols, including black carbon (BC) and brown carbon (BrC, a component of organic aerosol, OA), are highly uncertain. This thesis addresses this uncertainty by combining models and observations to better constrain the optical properties and radiative impact of carbonaceous aerosols. First, a global model simulation (GEOS-Chem) of BC is expanded to separately treat both the aging and physical properties of BC from different sources. By combining model and observations, the global BC lifetime is found to be overestimated in previous investigations, leading to higher estimates of its warming potential. The DRE of BC is estimated to be less than one quarter of the previously reported value. Second, a new method is developed to derive BrC absorption from measurements and used to identify BrC from total absorption observations. The absorption efficiency of BrC is found to be positively correlated with the emitted BC/OA mass ratio, which is related to combustion conditions. In addition, measured BrC absorption from biomass burning plumes is found to decrease with photochemical aging with a lifetime of one day. Third, a global model simulation of BrC is developed and tested against BrC absorption measurements from aircraft campaigns in the continental United States. The BrC absorption properties from biomass burning estimated based on laboratory measurements are found to overestimate the direct measurements of ambient BrC absorption. In addition, applying a photochemical aging scheme for BrC improves the model skill. The simulation suggests that the DRE of BrC has been overestimated previously due to the lack of observational constraints from direct measurements and omission of the effects of photochemical aging. Finally, the influence of mixing state on the global absorption of carbonaceous aerosols is estimated through simplified model experiments. This thesis suggests that policies for reducing emissions of carbonaceous aerosols may have a limited impact on mitigating global climate warming.
by Xuan Wang.
Ph. D. in Environmental Chemistry
40
Takeuti, Douglas de Freitas. "Thermal radiative properties of ion-implanted silicon and titanium and cobalt silicides." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627343.
41
Reid, Jeffrey Spencer. "Emission, evolution, and radiative properties of particles from biomass burning in Brazil /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/10099.
42
Toullier, Thibaud. "Simultaneous characterization of objects temperature and radiative properties through multispectral infrared thermography." Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S038/document.
Abstract:
L'utilisation de caméras infrarouges bas coûts pour la surveillance long-terme d'infrastructures est prometteuse grâce aux dernières avancées technologiques du domaine. Une mesure précise de la température des surfaces observées in-situ se heurte au manque de connaissance des propriétés radiatives de la scène. L'utilisation d'une instrumentation multi-capteurs permet d'affiner le modèle de mesure afin d'obtenir une estimation plus précise de la température. A contrario, il est montré qu'il est toujours possible d'exploiter des données climatiques en ligne pour pallier un manque de capteur. Des méthodes bayésiennes d'estimation conjointe d'émissivité et de température sont ensuite développées et comparées aux méthodes de la littérature. Un simulateur d'échanges radiatifs diffus de scènes 3D a été implémenté afin de tester ces différentes méthodes. Ce logiciel utilise l'accélération matérielle de la machine pour réduire les temps de calcul. Les résultats numériques obtenus mettent en perspective une utilisation avancée de la thermographie infrarouge multi-spectrale pour la surveillance de structures. Cette estimation conjointe permet alors d'obtenir un estimé de la température par thermographie infrarouge avec une incertitude connueThe latest technological improvements in low-cost infrared cameras have brought new opportunities for long-term infrastructures monitoring. The accurate measurement of surfaces' temperatures is facing the lack of knowledge of radiatives properties of the scene. By using multi-sensors instrumentation, the measurement model can be refined to get a better estimate of the temperature. To overcome a lack of sensors instrumentation, it is shown that online and free available climatic data can be used. Then, Bayesian methods to estimate simultaneously the emissivity and temperature have been developed and compared to literature's methods. A radiative exchange simulator of 3D scenes have been developed to compare those different methods on numerical data. This software uses the hardware acceleration as well as a GPGPU approach to reduce the computation time. As a consequence, obtained numerical results emphasized an advanced use of multi-spectral infrared thermography for the monitoring of structures. This simultaneous estimation enables to have an estimate of the temperature by infrared thermography with a known uncertainty
43
Bulgin, Claire Elizabeth. "Improved understanding of aerosol processes using satellite observations of aerosol optical properties." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4906.
Abstract:
Atmospheric aerosols are the largest remaining uncertainty in the Earth’s radiative budget and it is important that we improve our knowledge of aerosol processes if we are to understand current radiative forcing and accurately project changes in future climate. Aerosols affect the radiation balance directly through the absorption and scattering of incoming solar radiation and indirectly through the modification of cloud microphysical properties. Understanding aerosol forcing remains challenging due to the short atmospheric residence time of aerosols resulting in large spatial and temporal heterogeneity in aerosol loading and chemical composition. Satellite retrievals are becoming increasingly important to improving our knowledge of aerosol forcing. They provide regular global data at finer spatial and temporal resolution than available through sparse groundbased point measurements or localised aircraft campaigns, but cannot unambiguously determine aerosol speciation, relying heavily on a priori assumptions. In this thesis I use data from two satellite instruments: the Along Track Scanning Radiometer 2 (ATSR-2) and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) interpreted using the Oxford-RAL Aerosol and Cloud (ORAC) retrieval scheme in three pieces of interrelated work. First I use satellite observations of aerosol optical depth a and cloud particle effective radius re from the ATSR-2 instrument in 1997 to investigate the Twomey indirect effect (IE, -δ ln re /δ ln τa) in regions of continental outflow. I generally find a negative correlation between τa and re with the strongest inverse relationships downwind of Africa. North America and eastern Asian continental outflow exhibits a strong seasonal dependence, as expected. Global values for IE range from 0.10 to 0.16, consistent with theoretical predictions. Downwind of Africa, I find that the IE is unphysically high but robust (r = −0.85) during JJA associated with high aerosol loading, and attribute this tentatively to the Twomey hypothesis accounting only for a limited number of physical properties of aerosols. Second, I test the response of the Oxford-RAL Aerosol and Cloud (ORAC) retrieval algorithm for MSG SEVIRI to changes in the aerosol properties used in the dust aerosol model, using data from the Dust Outflow and Deposition to the Ocean (DODO) flight campaign in August 2006. I find that using the observed DODO free tropospheric aerosol size distribution and refractive index compared with the dust aerosol properties from the Optical Properties of Aerosol and Cloud (OPAC) package, increases simulated top of the atmosphere radiance at 0.55 μm assuming a fixed aerosol optical depth of 0.5, by 10–15%, reaching a maximum difference at low solar zenith angles. This difference is sensitive to changes in AOD, increasing by ~2–4% between AOD of 0.4–0.6. I test the sensitivity of the retrieval to the vertical distribution of the aerosol and find that this is unimportant in determining simulated radiance at 0.55 μm. I also test the ability of the ORAC retrieval when used to produce the GlobAerosol dataset to correctly identify continental aerosol outflow from the African continent and I find that it poorly constrains aerosol speciation. I develop spatially and temporally resolved prior distributions of aerosols to inform the retrieval which incorporates five aerosol models: desert dust, maritime, biomass burning, urban and continental. I use a Saharan Dust Index and the GEOS-Chem chemistry transport model to describe dust and biomass burning aerosol outflow, and compare AOD using my speciation against the GlobAerosol retrieval during January and July 2006. I find AOD discrepancies of 0.2–1 over regions of biomass burning outflow, where AOD from my aerosol speciation and the GlobAerosol speciation can differ by as much as 50 - 70 %. Finally I use satellite observations of aerosol optical depth and cloud fraction from the MSG SEVIRI instrument to investigate the semi-direct effect of Saharan dust aerosol on marine stratocumulus cloud cover over the Atlantic during July 2006. I first use these data to study the spatial autocorrelation of aerosol optical depth and find that it is correlated over a lag of 0.1◦ (approximately 10 km at low latitudes), beyond which it rapidly decorrelates. I find a 15 % higher cloud fraction in regions with high dust loading (AOD > 0.5), compared with scenes with a lower dust loading (AOD < 0.5), which for high dust scenes increases with local static stability. I attribute this tentatively to aerosol solar shielding enhancing longwave cloud top radiative cooling which drives marine stratocumulus convection.
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Schubert, Richard [Verfasser]. "On the effective properties of suspensions / Richard Schubert." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/118185590X/34.
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Johnston, Desmond Alexander. "Gauge properties and convexity of the effective potential." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38054.
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Zhu, Junlin. "Effective properties for flow in heterogeneous porous media." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39416.
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Poladian, Leon. "Effective transport and optical properties of composite materials." Phd thesis, Department of Theoretical Physics, 1990. http://hdl.handle.net/2123/11724.
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Dauchet, Jérémi. "Analyse radiative des photobioréacteurs." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00914315.
Abstract:
L'ingénierie de la photosynthèse est une voie prometteuse en vue de produire à la fois des vecteurs énergétiques et des molécules plateformes pour palier la raréfaction des ressources fossiles. Le défi à relever est de taille car il faut réussir à mettre au point des procédés solaires de production de biomasse à constante de temps courte (quelques jours), là où une centaine de millions d'années a été nécessaire à la formation du pétrole. Cet objectif pourrait être atteint en cultivant des micro-organismes photosynthétiques dans des photobioréacteurs dont les performances cinétiques en surface et en volume seraient optimales. Une telle optimisation nécessite avant tout une analyse fine des transferts radiatifs au sein du procédé. L'analyse radiative des photobioréacteurs qui est ici proposée s'ouvre sur la détermination des propriétés d'absorption et de diffusion des suspensions de micro-organismes photosynthétiques, à partir de leurs caractéristiques morphologiques, métaboliques et structurales. Une chaîne de modélisation est construite, mise en oeuvre et validée expérimentalement pour des micro-organismes de formes simples ; à terme, la démarche développée pourra directement être étendue à des formes plus complexes. Puis, l'analyse du transfert radiatif en diffusion multiple est introduite et illustrée par différentes approximations qui apparaissent pertinentes pour une conceptualisation des photobioréacteurs, menant ainsi à la construction d'un intuitif nécessaire à leur optimisation. Enfin, la méthode de Monte Carlo est mise en oeuvre afin de résoudre rigoureusement la diffusion multiple en géométries complexes (géométries qui découlent d'une conception optimisée du procédé) et afin de calculer les performances cinétiques à l'échelle du photobioréacteur. Ce dernier calcul utilise une avancée méthodologique qui permet de traiter facilement le couplage non-linéaire du transfert radiatif à la cinétique locale de la photosynthèse (et qui laisse entrevoir de nombreuses autres applications dans d'autres domaines de la physique du transport). Ces outils de simulation mettent à profit les développements les plus récents autour de la méthode de Monte Carlo, tant sur le plan informatique (grâce à une implémentation dans l'environnement de développement EDStar) que sur le plan algorithmique : formulation intégrale, algorithmes à zéro-variance, calcul de sensibilités (le calcul des sensibilités aux paramètres géométriques est ici abordé d'une manière originale qui permet de simplifier significativement sa mise en oeuvre, pour un ensemble de configurations académiques testées). Les perspectives de ce travail seront d'utiliser les outils d'analyse développés durant cette thèse afin d'alimenter une réflexion sur l'intensification des photobioréacteurs, et d'étendre la démarche proposée à l'étude des systèmes photoréactifs dans leur ensemble.
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Zheng, Xiaoyu Forest M. Gregory. "On the effective properties of nematic polymer nano-composites." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2006. http://dc.lib.unc.edu/u?/etd,248.
Abstract:
Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2006.Title from electronic title page (viewed Oct. 10, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Mathematics." Discipline: Mathematics; Department/School: Mathematics.
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Dimas, Leon Sokratis Scheie. "Effective mechanical Properties of material models with random heterogeneities." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103706.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 191-198).
In this thesis we obtain analytical approximations to the probability distribution of the elastic tensor and fracture strengths of material models with random heterogeneities. We start by investigating the effective elastic properties of one-, two-, and three-dimensional rectangular blocks whose Young's modulus varies spatially as a lognormal random field. We decompose the spatial fluctuations of the Young's log-modulus F = In E into first- and higher-order terms and find the joint distribution of the effective elastic tensor by multiplicatively combining the term-specific effects. Through parametric analysis of the analytical solutions, we gain insight into the effective elastic properties of this class of heterogeneous materials. Building on this analysis we find analytical approximations to the probability distribution of fracture properties of one-dimensional rods and thin two-dimensional plates for systems in which: only the Young's modulus varies spatially as an isotropic lognormal field and more generally, both the Young's modulus and the local material strength vary spatially as possibly correlated lognormal fields. The properties considered are the elongation, strength, and toughness modulus at fracture initiation and at ultimate failure. For all quantities at fracture initiation our approach is analytical in I D and semi-analytical in 2D. For ultimate failure, we quantify the random effects of fracture propagation and crack arrest by fitting regression models to simulation data and combine the regressions with the distributions at fracture initiation. Through parametric analysis, we gain insight into the strengthening/weakening roles of the Euclidean dimension, size of the specimen, and the correlation, variance and correlation function of the random fields. Finally, we extend the approach to investigate the elasticity of non-lognormal random heterogeneous materials. First we investigate the elastic bulk stiffness of two-dimensional checkerboard specimens in which square tiles are randomly assigned to one of two component phases. This is a model system for multi-phase polycrystalline materials such as granitic rocks and many ceramics. We study how the bulk stiffness is affected by different characteristics of the specimen and obtain analytical approximations to the probability distribution of the effective stiffness. In particular we examine the role of percolation of the soft and stiff phases. In small specimens, we find that the onset of percolation causes significant discontinuities in the effective modulus, whereas in large specimens the influence of percolation is smaller and gradual. Secondly we study the effective stiffness of multi-phase composite systems in which the Young's modulus varies as a filtered Poisson point process and find that the homogenization approach initially developed for lognormal systems produces accurate results also for this class of non-lognormal systems.
by Leon Sokratis Scheie Dimas.
Ph. D.