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1
Del, Fré Samuel. „Études théoriques de la photodésorption d'analogues de glaces moléculaires interstellaires : application au monoxyde de carbone“. Electronic Thesis or Diss., Université de Lille (2022-....), 2024. http://www.theses.fr/2024ULILR039.
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Des quantités inhabituelles de molécules en phase gazeuse sont détectées dans les régions froides (environ 10 K) du milieu interstellaire (ISM), principalement attribuées à la désorption non thermique de molécules depuis les glaces déposées sur les grains de poussière. En particulier, la désorption induite par les rayons ultraviolets du vide (photodésorption VUV) est considérée comme étant une voie de désorption majoritaire dans les régions de l'ISM dominées par les photons. Les investigations expérimentales ont révélé que dans les glaces pures de monoxyde de carbone (CO), espèce omniprésente dans l'ISM, la photodésorption VUV peut suivre un mécanisme indirect de désorption induite par transition électronique (DIET) pour les photons dont l'énergie est comprise entre 7 et 10 eV. Néanmoins, la compréhension des mécanismes moléculaires sous-jacents reste un sujet de débat scientifique. Dans ce contexte astrochimique, nous présentons une étude théorique combinée utilisant la dynamique moléculaire ab initio (AIMD) basée sur la théorie de la fonctionnelle de la densité (DFT) et des potentiels machine learning (PML) construits avec des réseaux de neurones artificiels (ANN), afin d'étudier la dernière partie du mécanisme DIET dans les glaces amorphes de CO. Ici, une molécule CO hautement excitée vibrationnellement (v = 40) au centre d'un agrégat composé de 50 molécules de CO, initialement optimisé puis thermalisé à 15 K, déclenche, la désorption indirecte de molécules de surface. Nos résultats théoriques révèlent que le processus de désorption consiste en 3 étapes fondamentales qui commence par une attraction mutuelle entre la molécule excitée vibrationnellement et une ou deux molécules voisines, activée par l'étirement de la liaison CO et favorisée par l'effet stérique des molécules environnantes. Cela est suivi par une séquence de transferts d'énergie initiée par une collision, se concluant en la désorption de molécules CO vibrationnellement froides dans 88% des trajectoires AIMD. De plus, les distributions théoriques de l'énergie interne et translationnelle des molécules désorbées concordent remarquablement avec les résultats expérimentaux, ce qui soutient le rôle crucial de la relaxation vibrationnelle dans le processus de désorption. Enfin, les premiers PML construits à partir des simulations AIMD, sont capables d'ajuster avec précision la surface d'énergie potentielle multidimensionnelle du système, permettant de prédire efficacement les énergies des agrégats et les forces atomiques. Les simulations de dynamique moléculaire classique utilisant ces potentiels sont plus de 1800 fois plus rapides que celles basées sur l'AIMD, tout en offrant des précisions similaires à ceux de la DFTUnusual amounts of gas-phase molecules are detected in the cold regions (around 10 K) of the interstellar medium (ISM), primarily attributed to the non-thermal desorption of molecules from ices deposited on dust grains. In particular, vacuum ultraviolet (VUV) photon-induced desorption (photodesorption) is considered a major desorption pathway in photon-dominated regions of the ISM. Experimental investigations have revealed that in pure carbon monoxide (CO) ices, a ubiquitous species in the ISM, VUV photodesorption can follow an indirect mechanism of desorption induced by electronic transitions (DIET) for photons with energy between 7 and 10 eV. Nevertheless, the understanding of the underlying molecular mechanisms remains a topic of scientific debate. In this astrochemical context, we present a combined theoretical study using ab initio molecular dynamics (AIMD) based on density functional theory (DFT) and machine learning potentials (PML) constructed with artificial neural networks (ANN) to study the final part of the DIET mechanism in amorphous CO ices. Here, a highly vibrationally excited CO molecule (v = 40) at the center of an aggregate initially composed of 50 CO molecules, optimized and then thermalized at 15 K, triggers the indirect desorption of surface molecules. Our theoretical results reveal that the desorption process consists of three fundamental steps, beginning with a mutual attraction between the vibrationally excited molecule and one or two neighboring molecules, activated by CO bond stretching and facilitated by the steric effect of surrounding molecules. This is followed by a sequence of energy transfers initiated by a collision, resulting in the desorption of vibrationally cold CO molecules in 88% of the AIMD trajectories. Additionally, the theoretical distributions of the internal and translational energy of desorbed molecules remarkably match experimental results, supporting the crucial role of vibrational relaxation in the desorption process. Finally, the first PML constructed from AIMD simulations accurately fit the multidimensional potential energy surface of the system, allowing efficient prediction of aggregate energies and atomic forces. Classical molecular dynamics simulations using these potentials are over 1800 times faster than those based on AIMD while offering precision comparable to DFT
2
MacKenzie, Todd. „New methods for deblending spectral energy distributions in confused imaging“. Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/56192.
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The submillimetre band is ideal for studying high-redshift star-forming galaxies, but such studies are hampered by the poor resolution of single-dish telescopes. Interferometric follow-up has shown that many sources are in fact comprised of multiple sources. For many such targets, confusion-limited Herschel observations that target the peak of their far-infrared emission are also available. Many methods for analysing these data have been developed, but most follow the traditional approach of extracting fluxes before model spectral energy distributions are fit, which erases degeneracies among fitting parameters and glosses over the intricacies of confusion noise. We have developed a forward-modelling method in order to tackle this problem in a more statistically rigorous way, which combines source deblending and spectral energy distribution fitting into the same procedure. We adapt our method to three independent projects, all of which benefit from our improved methodology. We investigate a "giant submillimetre arc" behind a massive foreground cluster and uncover seven multiply imaged galaxies, of which six are found to be at a redshift of z~2.9, and possibly constitute an interacting galaxy group. Using our new method, we disentangle the arc into its contributing components and constrain their far-IR properties. Using confusion limited Herschel-SPIRE imaging, the far-IR properties LABOCA detected submillimetre sources can be constrained. Despite such sources often breaking up in high-resolution ALMA imaging, existing studies have implemented traditional fitting methods. We apply our new forward modelling method to re-derive constraints on the far-infrared properties of these sources, exploring selection effects on this sample, while highlighting the benefits of our fitting approach. Finally, we present SCUBA-2 follow-up of 51 candidate proto-cluster fields undergoing enhanced star-formation. With the accompanying Herschel-SPIRE observations and a realistic dust temperature prior, we provide photometric redshift and far-IR luminosity estimates for 172 SCUBA-2 selected sources within the Planck overdensity fields. We find a redshift distribution similar to sources found in cosmological surveys, although our fields are enhanced in both density of sources and star formation rate density over a wide range of redshifts.Science, Faculty of
Physics and Astronomy, Department of
Graduate
3
Hornsey, Richard Ian. „Factors affecting ion energy distributions in liquid metal ion sources“. Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236154.
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4
Turrell, Arthur Edward. „Processes driving non-Maxwellian distributions in high energy density plasmas“. Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18083.
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The purpose of this thesis is to explore the driving of non-Maxwellian distributions of particles in high energy density plasmas in a few select cases, with particular reference to efforts to produce a net gain in energy via inertial confinement fusion (ICF). Non-Maxwellian distributions are typically short-lived, as distributions are forced toward equilibrium by collisions, and are rarely static as a net transfer of energy must occur to sustain them. This makes non-Maxwellian distributions challenging to study with conventional approaches to plasma physics. The strategy adopted in this work to understand their evolution, and their effects, is a kinetic approach in which particles are individually accounted for. The specific cases presented are that of degenerate electrons during the heating of the cold fuel shell in hotspot ignition schemes, ion-ion inverse bremsstrahlung absorption of laser radiation, and large-angle Coulomb collisions. New computational algorithms based on the Monte Carlo technique are presented, and are capable of modelling the salient aspects of the phenomena explored. Important results which form part of this thesis include that conventional models underestimate degenerate electron temperatures long after the plasma ceases to be degenerate, that it may be possible to induce temperatures of keV in light-ion species with high power, short pulse lasers, and that consideration of large-angle collisions changes interactions in a plasma in several significant ways. Of most interest are the ability of large-angle collisions to decrease equilibration times, drive athermal tails on distribution functions, and increase the overall yield from fusion reactions relative to small-angle only simulations.
5
Yang, Guangyuan. „The Energy Goodness-of-fit Test for Univariate Stable Distributions“. Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1339476355.
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6
Stins, O. W. M. „A Retarding Field Energy Analyser to measure the Energy Distributions of Liquid Metal Ion Sources“. Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-32306.
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7
Stins, O. W. M. „A Retarding Field Energy Analyser to measure the Energy Distributions of Liquid Metal Ion Sources“. Forschungszentrum Rossendorf, 1994. https://hzdr.qucosa.de/id/qucosa%3A22057.
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8
Horwat, Stephen M. „Continuous distributions of non-dilatonic branes“. Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31235.
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In this thesis we construct new supergravity solutions representing continuous distributions of D3, M2, and M5-branes. These solutions are completely specified by the harmonic function H , which is determined by solving 12H=0 in carefully chosen coordinate systems with SO( n) x SO(D⊥ - n) symmetry. Afterwards, we calculate the corresponding charge distributions using a generalized Gauss's law type argument. These solutions are asymtoptically AdS in the near horizon limit.
9
Fretwell, Tracey Ann. „Monte Carlo simulation of energy intensity distributions for electron beam lithography“. Thesis, University of Manchester, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.576984.
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10
Dahlgren, David. „Monte Carlo simulations of Linear Energy Transfer distributions in radiation therapy“. Thesis, Uppsala universitet, Högenergifysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446550.
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In radiotherapy, a quantity asked for by clinics when calculating a treatment plan, along withdose, is linear energy transfer. Linear energy transfer is defined as the absorbed energy intissue per particle track length and has been shown to increase with relative biologicaleffectiveness untill the overkilling effect. In this master thesis the dose averaged linear energytransfer from proton and carbon ion beams was simulated using the FLUKA multi purposeMonte Carlo code. The simulated distributions have been compared to algorithms fromRaySearch Laboratories AB in order to investigate the agreement between the computationmethods. For the proton computation algorithm improvements to the current scoring algorithmwere also implemented. A first version of the linear energy transfer validation code was alsoconstructed. Scoring of linear energy transfer in the RaySearch algorithm was done with theproton Monte Carlo dose engine and the carbon pencil beam dose engine. The results indicatedthat the dose averaged linear energy transfer from RaySearch Laboratories agreed well for lowenergies for both proton and carbon beams. For higher energies shape differences were notedwhen using both a small and large field size. The protons, the RaySearch algorithm initiallyoverestimates the linear energy transfer which could result from fluence differences in FLUKAcompared to the RaySearch algorithm. For carbon ions, the difference could stem from someloss of information in the tables used to calculate the linear energy transfer in the RaySearchalgorithm. From validation γ-tests the proton linear energy transfer passed for (3%/3mm) and(1%/1mm) with no voxels out of tolerance. γ-tests for the carbon linear energy transfer passedwith no voxels out of tolerance for (5%/5mm) and a fail rate of 2.92% for (3%/3mm).
11
Ignace, Richard. „Long-Wavelength, Free–Free Spectral Energy Distributions from Porous Stellar Winds“. Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etsu-works/2685.
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The influence of macroclumps for free–free spectral energy distributions (SEDs) of ionized winds is considered. The goal is to emphasize distinctions between microclumping and macroclumping effects. Microclumping can alter SED slopes and flux levels if the volume filling factor of the clumps varies with radius; however, the modifications are independent of the clump geometry. To what extent does macroclumping alter SED slopes and flux levels? In addressing the question, two specific types of macroclump geometries are explored: shell fragments (pancake-shaped) and spherical clumps. Analytic and semi-analytic results are derived in the limiting case that clumps never obscure one another. Numerical calculations based on a porosity formalism is used when clumps do overlap. Under the assumptions of a constant expansion, isothermal, and fixed ionization wind, the fragment model leads to results that are essentially identical to the microclumping result. Mass-loss rate determinations are not affected by porosity effects for shell fragments. By contrast, spherical clumps can lead to a reduction in long-wavelength fluxes, but the reductions are only significant for extreme volume filling factors.
12
Zhou, Li. „A Retarding-potential Analyzer for Measuring Energy Distributions in Electron Beams“. PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4744.
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An energy analyzer for electron beams, based on a retarding-potential method, has been studied both experimentally and theoretically. In this method a potential energy barrier at right-angles to the beam acts as a high-pass energy filter allowing electrons having energies greater than the barrier height to pass through while turning back electrons of lower energy. The potential barrier in the present study was created by applying a negative potential to an electrode consisting of a 600/inch hexagonal copper mesh or an electrode having a pair of single apertures in series (compound aperture). Two different compound apertures, of diameters 0.4 mm and 1.0 mm, were used. The retarding electrode was mounted between two grounded outer electrodes having openings centered on the axis for entrance and exit of electrons. The barrier height was adjusted by means of a small variable bias voltage between the electron gun cathode and the retarding electrode. Auxiliary electron lenses external to the retarding module were used to satisfy the conditions that the beam be normal to the retarding electrode and, for an imaging filter, that an image plane be focused at the retarding electrode. A beam having a narrow distribution of energies was used to calibrate the energy analyzer as a function of bias voltage for the three different configurations of retarding electrode. The calibration curves were then compared with the transmission curve for a beam having a broadened energy distribution. The feasibility of obtaining a filtered image was explored by observing the image of a fine mesh focused into an aperture of the retarding electrode. The experiments were carried out for a beam voltage of 15 kV. At this beam voltage the energy resolution is poor, being 3. 6 volts for the smaller compound aperture, 3. 7 volts for the mesh, and 5.2 volts for the larger compound aperture. Typically, electrostatic analyzers operate on a beam which has been decelerated to low energies before entering the analyzer, in which case the energy resolution is proportionately better. For example, at 150 V the above resolution figures would be 0.036, 0.037, and 0.052, respectively. In view of the potential for high energy-resolution and the attractive features of in-line, rotationally-symmetric systems, it is felt that the retarding-potential analyzer is a promising candidate for further development.
13
Vidal, García Alba. „Modeling and interpretation of the ultraviolet spectral energy distributions of primeval galaxies“. Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066667/document.
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Je combine de nouveaux modèles de production de radiations stellaires et de transport radiatif à travers le milieu interstellaire (MI). Cela permet de caractériser les étoiles ainsi que le MI neutre et ionisé dans des galaxies formant des étoiles (GFE), via des raies ultraviolettes dans leur spectre. J'évalue la fiabilité des modèles stellaires en ajustant dans l'ultraviolet les indices d'absorption mesurés dans les spectres stellaires de 10 amas d'étoiles dans le Grand Nuage de Magellan. Je montre que négliger l'échantillonnage stochastique de la fonction de masse initiale stellaire de ces amas jeunes et peu massifs a une faible influence dans l'estimation d'âge et de métallicité, mais peut entraîner une surestimation significative des estimations de leur masse. Ensuite, je développe une approche basée sur une description épurée des principales caractéristiques du MI, afin de calculer de manière auto-cohérente l'influence combinée de l'émission et de l'absorption de ce milieu dans le spectre ultraviolet des GFE. Ce modèle tient compte du transport radiatif aussi bien à travers les couches intérieures ionisées, qu'à travers les couches extérieures neutres des nuages de formation d'étoiles ainsi que le milieu diffus entre ces nuages. J'utilise cette approche pour étudier la signature enchevêtrée des étoiles, du milieu neutre et du milieu ionisé dans les spectres ultraviolets des GFE. J'obtiens que la plupart des indices stellaires dans l'ultraviolet sont susceptibles de présenter une contamination par le MI qui augmente avec la métallicité. Enfin, j'identifie des raies d'émission et d'absorption interstellaires pouvant discriminer efficacement les différentes phases du MII combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. I start by assessing the reliability of the stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large-Magellanic-Cloud clusters. In doing so, I find that neglecting stochastic sampling of the stellar initial mass function in these young low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, I develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. My model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. I use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. I find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. I also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM
14
Evans, Thomas M. „The measurement and calculation of nanodosimetric energy distributions for electrons and photons“. Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19264.
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15
Dickenson, Andrew C. „Measurement and simulation of ion energy distributions in a reactive ion etcher“. Thesis, University of Bristol, 1994. http://hdl.handle.net/1983/2e692fca-5cd1-48da-bb7e-6bb76a1bb23b.
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16
Greenwood, Claire-Louise. „Energy and angular distributions of ions induced by electron stimulated desorption from surfaces“. Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240517.
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17
Eggers, Hans Christoph. „Intermittency, moments and correlations in distributions of particles created in high-energy collisions“. Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185422.
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Intermittency, as introduced into multiparticle production by Bialas and Peschanski, has become a fruitful and rapidly growing industry. The original concept of intermittency in the form of the Alpha model is discussed in detail and suggestions for extensions are made. We analyze the factorial moments measured by different experimental collaborations in terms of their nontrivial many-particle correlations, the cumulants. A large fraction of measured moments is shown to originate in two-particle correlations. The validity of the Linked Pair ansatz is tested and found to be acceptable to fourth order for hadronic collisions but uncertain for nuclear collisions. A cumulant decomposition for bin-bin correlations is derived, and a general formalism is developed for treating correlations of particle distributions consisting of several distinct populations, such as particles of different charge.
18
Dickson, Ewan Cameron Mackenzie. „Photospheric albedo and the measurement of energy and angular electron distributions in solar flares“. Thesis, University of Glasgow, 2013. http://theses.gla.ac.uk/4196/.
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In this thesis I examine the role of Compton back-scatter of solar flare Hard X-rays, also known as albedo, in the inference of the parent electron spectrum. I consider how albedo affects measurements of the energy and angular distributions when the mean electron flux spectrum in a solar flare is inferred using regularised inversion techniques. The angular distribution of the accelerated electron spectrum is a key parameter in the understanding of the acceleration and propagation mechanisms that occur in solar flares. However, the anisotropy of energetic electrons is still a poorly known quantity, with observational studies producing evidence for an isotropic distribution and theoretical models mainly considering the strongly beamed case. First we investigate the effect of albedo on the observed spectrum for a variety of commonly considered analytic forms of the pitch angle distribution. As albedo is the result of the scattering of X-ray photons emitted downwards towards the photosphere different angular distributions are likely to exhibit a varying amount of albedo reflection, in particular, downward directed beams of electrons are likely to produce spectra which are strongly influenced by albedo. The low-energy cut-off of the non-thermal electron spectrum is another significant parameter which it is important to understand, as its value can have strong implications for the total energy contained in the flare. However, both albedo and a low energy cut-off will cause a flattening of the observed X-ray spectrum at low energies. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) X-ray data base has been searched to find solar flares with weak thermal components and flat photon spectra in the 15 - 20 keV energy range. Using the method of Tikhonov Regularisation, we determine the mean electron flux distribution from count spectra of a selection of these events. We have found 18 cases which exhibit a statistically significant local minimum (a dip) in the range of 10 - 20 keV. The positions and spectral indices of events with low-energy cut-off indicate that such features are likely to be the result of photospheric albedo. It is shown that if the isotropic albedo correction was applied, all low-energy cut-offs in the mean electron spectrum were removed. The effect of photospheric albedo on the observed X-ray spectrum suggest RHESSI observations can be used to infer the anisotropy in the angular distribution of X-ray emitting electrons. A bi-directional approximation is applied and regularized inversion is performed for eight large flare events viewed by RHESSI to deduce the electron spectra in both downward (towards the photosphere) and upward (away form the photosphere) directions. The electron spectra and the electron anisotropy ratios are calculated for broad energy range from about 10 and up to ~ 300 keV near the peak of the flares. The variation of electron anisotropy over short periods of time intervals lasting 4, 8 and 16 seconds near the impulsive peak has been examined. The results show little evidence for strong anisotropy and the mean electron flux spectra are consistent with the isotropic electron distribution. The inferred X-ray emitting electron spectrum is likely to have been modified from the accelerated or injected distribution by transport effects thus models of electron transport are necessary to connect the observations. We use the method of stochastic simulations to investigate the effect of Coulomb collisions on an electron beam propagating through a coronal loop. These simulations suggest that the effect of Coulomb collisions on a uniformly downward directed beam as envisaged in the collisional thick target model is not strong enough to sufficiently scatter the pitch angle distribution to be consistent with the measurements made in the previous chapter. Furthermore these simulations suggest that for the conditions studied the constraints inferred in Chapter 4 are only consistent with a low level of anisotropy in the injected electron distribution.
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Ackerman, Jonathan R. „Unsteady energy separation and base pressure distributions in subsonic crossflow around a circular cylinder“. Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/30214.
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Eckert and Weise first measured time-averaged energy separation behind a circular cylinder in 1943- Although a significant amount of work has been carried out on the subject since Eckert and Weise's discovery no time-resolved measurements have been made of the phenomenon at high subsonic Mach numbers. The aim of this project was to make these measurements, along with those of surface pressure. Energy separation and base pressure are investigated at high subsonic Mach numbers, behind a circular cylinder in crossflow, for the first time.;The measurement of energy separation has involved developing a novel operating procedure for a high frequency response thin film total temperature probe, allowing it to be heated in stagnant conditions while keeping the wind tunnel running, hi addition the analysis of the results has involved the development of a fully automated phase lock averaging routine.;The principal original contribution of this work is to demonstrate clearly that unsteady energy separation occurs as a result of vortex shedding at high subsonic Mach numbers. The time-resolved measurements show how the areas of increased and decreased total temperature and total pressure are related. The results also give, a good qualitative description of the shape of the vortex street, showing the presence of interconnecting ribs and the areas of maximum entropy increase and thus drag creation.;The surface pressure results have permitted the study of how Strouhal number, drag, base drag and vortex shedding mechanisms change with Mach number. Of particular note they show that the vortex mechanism present in the permanent shock wave regime does not replace that present in the intermediate shock wave regime but rather develops from it.
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Dodson-Robinson, Sarah E., Kate Y. L. Su, Geoff Bryden, Paul Harvey und Joel D. Green. „HERSCHEL OBSERVATIONS AND UPDATED SPECTRAL ENERGY DISTRIBUTIONS OF FIVE SUNLIKE STARS WITH DEBRIS DISKS“. IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622672.
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Observations from the Herschel Space Observatory have more than doubled the number of wide debris disks orbiting Sunlike stars to include over 30 systems with R > 100 AU. Here we present new Herschel PACS and re-analyzed Spitzer MIPS photometry of five Sunlike stars with wide debris disks, from Kuiper belt size to R > 150 AU. The disk surrounding HD 105211 is well resolved, with an angular extent of >14" along the major axis, and the disks of HD 33636, HD 50554, and HD 52265 are extended beyond the PACS PSF size (50% of energy enclosed within radius 4.23"). HD 105211 also has a 24 mu m infrared excess that was previously overlooked because of a poorly constrained photospheric model. Archival Spitzer IRS observations indicate that the disks have small grains of minimum radius a(min) similar to 3 mu m, although the a(min) is larger than the radiation pressure blowout size in all systems. If modeled as single-temperature blackbodies, the disk temperatures would all be <60 K. Our radiative transfer models predict actual disk radii approximately twice the radius of model blackbody disks. We find that the Herschel photometry traces dust near the source population of planetesimals. The disk luminosities are in the range 2 x 10(-5) <= L/L-circle dot <= 2 x 10(-4) , consistent with collisions in icy planetesimal belts stirred by Pluto-size dwarf planets.
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Haman, John T. „The energy goodness-of-fit test and E-M type estimator forasymmetric Laplace distributions“. Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1524756256837676.
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Wilking, B. A., C. J. Lada und E. R. Young. „IRAS Observations of the Rho Ophiuchi Infrared Cluster: Spectral Energy Distributions and Luminosity Function“. Steward Observatory, The University of Arizona (Tucson, Arizona), 1988. http://hdl.handle.net/10150/623919.
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Perez-Ramos, Redamy. „DISTRIBUTIONS ET CORRÉLATIONS HADRONIQUES EN CHROMODYNAMIQUE QUANTIQUE DANS L'APPROXIMATION DES "PETIT X"“. Phd thesis, Université Paris-Diderot - Paris VII, 2006. http://tel.archives-ouvertes.fr/tel-00108167.
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Dans le cadre de l'approximation MLLA de la Chromodynamique Quantique, nous calculons analytiquement, pour des jets hadroniques à très haute énergie, les distributions inclusives en fonction de l'impulsion transverse du hadron émergent, ainsi que les corrélations à 2 particules. Dans un premier temps, nous obtenons, pour le spectre inclusif et pour les corrélations, les solutions exactes des équations d'évolution partoniques, qui sont ensuites calculées à petit x dans l'approximation du ``spectre limite''. La méthode du col nous permet enfin de généraliser les résultats précédents au delà de cette limite. Nos résultats pour les distributions inclusives sont en très bon accord avec les données expérimentales (Tevatron), et améliorent très sensiblement ceux obtenus dans les travaux antérieurs pour les corrélations. La comparaison avec les données à venir (Tevatron, LHC) fournira un test supplémentaire de l'hypothèse de dualité locale parton-hadron, ainsi que de la nécessité éventuelle d'inclure des corrections d'ordre supérieur (next-to-MLLA).
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Hickox, Ryan C., Adam D. Myers, Jenny E. Greene, Kevin N. Hainline, Nadia L. Zakamska und Michael A. DiPompeo. „Composite Spectral Energy Distributions and Infrared–Optical Colors of Type 1 and Type 2 Quasars“. IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626048.
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We present observed mid-infrared and optical colors and composite spectral energy distributions (SEDs) of type 1 (broad-line) and 2 (narrow-line) quasars selected from Sloan Digital Sky Survey (SDSS) spectroscopy. A significant fraction of powerful quasars are obscured by dust and are difficult to detect in optical photometric or spectroscopic surveys. However, these may be more easily identified on the basis of mid-infrared (MIR) colors and SEDs. Using samples of SDSS type 1 and 2 matched in redshift and [O III] luminosity, we produce composite rest-frame 0.2-15 mu m SEDs based on SDSS, UKIDSS, and Wide-field Infrared Survey Explorer photometry and perform model fits using simple galaxy and quasar SED templates. The SEDs of type 1 and 2 quasars are remarkably similar, with the differences explained primarily by the extinction of the quasar component in the type 2 systems. For both types of quasar, the flux of the active galactic nucleus (AGN) relative to the host galaxy increases with AGN luminosity (L-[O III]) and redder observed MIR color, but we find only weak dependencies of the composite SEDs on mechanical jet power as determined through radio luminosity. We conclude that luminous quasars can be effectively selected using simple MIR color criteria similar to those identified previously (W1-W2 > 0.7; Vega), although these criteria miss many heavily obscured objects. Obscured quasars can be further identified based on optical-IR colors (for example, (u-W3[AB])> 1.4(W1-W2[Vega])+ 3.2). These results illustrate the power of large statistical studies of obscured quasars selected on the basis of MIR and optical photometry.
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Jenner, Clare Elizabeth. „A new semi-analytical treatment of the effect of supernovae on ULIRG spectral energy distributions“. Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1446241/.
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This work presents a method for generating synthetic spectra of Ultra-Luminous Infrared Galaxies (ULIRGS) using AGN, HII region and supernovae source functions. The AGN element represents the far-infrared contribution to the ULIRG spectrum from an energetic central engine. It is modelled using a quasar source embedded in an axi-symmetric dusty torus. The radiative transfer of flux (RT) is then simulated and the AGN emergent spectral energy distributions (SEDs) generated. The HII region solution is then developed. A stellar evolutionary synthesis code is used to generate instantaneous burst (ISB) source functions which decay in time. The evolution of the gas and dust density in a spherically-symmetric, dense GMC, under the influence of a time-dependent ionizing source flux, is derived. Having irradiated the dust distribution with the source cluster SED, the RT is calculated and the HII region SEDs obtained. The impact of supernovae energy on a GMC already ionized by stellar flux is then considered. Using the standard pressure-driven expansion model of e.g., Weaver et al. (1977) the radial evolution of a superbubble expanding under the influence of a continuous super novae energy function is derived. The superbubble is modelled in both an adiabatic rapid expansion phase and in an isothermal momentum-conserving phase. As the superbubble expands, upstream gas is swept into a thin shell trapped on its surface and the gas density enhancement is modelled using simple shock physics. Having generated expressions for the evolution of the shell gas temperature, it is linked to the dust density via a temperature dependent condensation factor. Finally expressions are developed to quantify the evolution of the optical depth along a line of sight. It is found that the star formation efficiency (SFE) has a profound effect on the radial evolution of the optical depth distributions in GMCs generating marked differences in behaviour between and high and low SFEs. Low SFE models have shells below the dust condensation temperature at the GMC boundary R2w and the extinction, having initially been in decline, recovers to more substantial values in a dust reformation scenario. These systems tend to be optically thick for most of their evolution. Those models classified high SFE have supershell temperatures in excess of the dust condensation temperature at R2w and the extinction distribution drops precipitously and reaches very low values (< 1) at R2w- It then remains low for some time before a small recovery in extinction occurs as the shell dust condenses out. These systems tend to be optically thin for most of their life-times. It is the more powerful supernovae source functions included in the modelled space which generate the high SFE extinction behaviour and vice versa. Having derived the dust density distributions they are irradiated by the appropriate central source cluster SED and the RT simulated to generate the emergent SEDs. These are similarly categorised as low and high SFE. The low SFE model SEDs appear to be representative of systems where the dust acts as an enshrouding bolometer and most it not all UV and optical radiation is reprocessed and re-emitted into the infrared. Conversely, the high SFE model SEDs are optically revealed and exhibit substantial, only mildly attenuated source flux at short wavelengths for the majority of their evolution. The emergent AGN and starburst (ISB HII region and supernovae) SEDs are then combined in pairs to form a ULIRG SED Library. These SEDs are matched to the published data for a sample of six nearby (redshift z < 1) ULIRGS. No model ULIRG SED is found to have a better than 40% probability of belonging to the same population distribution as the published data. This is found to be most likely the result of using an ISB source function. The starburst SED library is therefore extended to approximate constant star formation (CSFRA) using a time decay parameterization and the ULIRGs refitted. In each case a model ULIRG SED was found to match the observations with a better than 5% probability of non-random fit, which suggests that a constant rather than ISB star formation mode is perhaps more appropriate in ULIRGs. Using the CSFRA component of the best-fitting model ULIRG SED, estimates are made for the star formation rate, starburst age and the implied merger and interaction state for each ULIRG. In all case these quantities agree favourably with the literature. Each ULIRG was fitted with a CSFRA SED element originating in the high SFE group of models. This was found to be a direct result of fitting the upper limits to the short wavelength (A < 3m) flux data points, as it is the high SFE SEDs that are optically revealed.
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Opperman, Logan J. „Sequential Inference and Nonparametric Goodness-of-Fit Tests for Certain Types of Skewed Distributions“. Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1560856288455652.
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Robitaille, Thomas Pierre. „Star formation across the galaxy : observations and modelling of the spectral energy distributions of young stars /“. St Andrews, 2009. http://hdl.handle.net/10023/733.
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Robitaille, Thomas P. „Star formation across the galaxy : observations and modelling of the spectral energy distributions of young stars“. Thesis, University of St Andrews, 2009. http://hdl.handle.net/10023/733.
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In the last few decades, the emergence of large-scale infrared surveys has led to a revolution in the study of star formation. In particular, NASA’s Spitzer Space Telescope has recently carried out mid- and far-infrared observations of numerous star formation regions with unprecedented resolution and sensitivity, and has uncovered thousands of forming stars. In combination with present and future large-scale near-infrared and sub-mm surveys, spectral energy distributions from near-infrared to mm wavelengths will be available for these thousands of young stars. Never before has there been such a wealth of multi-wavelength data for so many young stars. Traditional techniques for studying the physical properties of young stars through their spectral energy distributions have usually focused either on the analysis of many sources using simple observational diagnostics such as colours or spectral indices, or on the analysis of a few sources through the detailed modelling of their full spectral energy distributions. The work presented in the first part of this thesis aims to bridge these two techniques through the efficient modelling of the spectral energy distributions of many young stars. In particular, the technique developed for this work makes it straightforward to find out how well different physical parameters are constrained, whether any parameters are degenerate, and whether additional data would resolve the degeneracies. In the second part of this thesis, a census of intrinsically red sources observed by Spitzer in the Galactic plane is presented, including a catalogue of over 11,000 likely young stellar objects. This sample of sources is the largest uniformly selected sample of young stars to date, and effectively provides a map of the sites of star formation in the mid-plane of the Milky-Way. In parallel, this census has uncovered over 7,000 candidate asymptotic giant branch stars, of which over 1,000 are variable at 4.5 or 8.0 microns.
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Assef, Roberto Jose. „Properties of Active Galactic Nuclei and Galaxies: Spectral Energy Distributions, Luminosity Functions and Black Hole Masses“. The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1281369360.
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Laidet, Julien. „High Energy Collisions of Dense Hadrons in Quantum Chromodynamics : LHC Phenomenology and Universality of Parton Distributions“. Palaiseau, Ecole polytechnique, 2013. http://pastel.archives-ouvertes.fr/pastel-00875951.
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Lorsque l'impulsion longitudinale des partons contenus dans un hadron ultra-relativiste diminue, on observe un accroissement de leur densité. Quand la densité approche une valeur d'ordre dollar1/\alpha_sdollard, elle n'augmente plus, elle sature. Ces effets de haute densité semblent être correctement décrits par la théorie effective du "Color Glass Condensate". Du point de vue expérimental, le LHC est le meilleur outil jamais disponible pour atteindre la phase saturée de la matière hadronique. Pour cette raison, la physique de la saturation est une branche très active de la QCD dans les années passées et à venir car la théorie et les expériences peuvent être comparées. En premier lieu, je discute de la phénoménologie des collisions proton-plomb qui ont eu lieu à l'hiver 2013 et dont les données sont sur le point d'être disponibles. Je calcule la section efficace pour la production de deux gluons qui est l'observable la plus simple pour trouver des preuves quantitatives de la saturation dans le régime cinématique du LHC. Je traite également la limite des états finaux fortement corrélés à grandes impulsions transverses et, par la même occasion, généralise la distribution de partons au régime dense. Le second sujet principal est l'évolution quantique des spectres de gluons et de quarks dans les collisions noyau-noyau, ayant à l'esprit son caractère universel. Ce résultat est déjà connu pour les gluons et je détaille ici le calcul avec attention. Pour les quarks, l'universalité n'a toujours pas été prouvée mais je dérive une formule de récursion intermédiaire entre l'ordre dominant et l'ordre sous-dominant qui constitue une étape cruciale dans l'extraction de l'évolution quantique. Enfin, je présente brievement un travail indépendant de théorie des groupes. Je détaille une méthode personnelle permettant de calculer des traces impliquant un nombre arbritraire de générateurs, une situation souvent rencontrée dans les calculs de QCDAs the value of the longitudinal momentum carried by partons in a ultra-relativistic hadron becomes small, one observes a growth of their density. When the parton density becomes close to a value of order dollar1/\alpha_sdollar, it does not grow any longer, it saturates. These high density effects seem to be well described by the Color Glass Condensate effective field theory. On the experimental side, the LHC provides the best tool ever for reaching the saturated phase of hadronic matter. For this reason saturation physics is a very active branch of QCD during these past and coming years since saturation theories and experimental data can be compared. I first deal with the phenomenology of the proton-lead collisions performed in winter 2013 at the LHC and whose data are about to be available. I compute the di-gluon production cross-section which provides the simplest observable for finding quantitative evidences of saturation in the kinematic range of the LHC. I also discuss the limit of the strongly correlated final state at large transverse momenta and by the way, generalize parton distribution to dense regime. The second main topic is the quantum evolution of the quark and gluon spectra in nucleus-nucleus collisions having in mind the proof of its universal character. This result is already known for gluons and here I detail the calculation carefully. For quarks universality has not been proved yet but I derive an intermediate leading order to next-to leading order recursion relation which is a crucial step for extracting the quantum evolution. Finally I briefly present an independent work in group theory. I detail a method I used for computing traces involving an arbitrary number of group generators, a situation often encountered in QCD calculations
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Dance, Michael Raymond Jr. „Hydroxide Formation and Carbon Species Distributions During High-Temperature Kraft Black Liquor Gasification“. Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7189.
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This work focuses on high-temperature kraft black liquor gasification in the presence of H2O and CO2 in a laboratory-scale Laminar Entrained-Flow Reactor (LEFR). The effects of gasification conditions on hydroxide formation, carbon gasification rate, carbonate carbon and fixed carbon levels, alkali metal and sulfur species retention, and char yield were studied at atmospheric pressure and at 900-1000oC, and at residence times of 0.5-1.5 s.
The results suggest that carbon gasification rates may be enhanced in the presence of H2O and CO2, with fixed carbon conversions of up to 95% at the earliest residence times at 1000oC. CO2 and H2O gasifying agents cause a significant increase in carbonate formation, with 22% of the initial carbon input forming carbonate as compared to 16% with one gasifying agent. Carbonate levels increase to a maximum level and then decrease at 900oC, but at 1000oC, carbonate decomposition processes are more dominant and cause lower levels of carbonate even at early residence times. The results show that alkali metal retention is high until vaporization occurs after 1.4 s at 900oC and at early residence times at 1000oC. Moreover, the results indicate that sulfur retention is an exothermic process, as sulfur capture increases with temperature.
At 900oC, no hydroxide is produced until after 1.4 s, but at 1000oC, hydroxide appears to form readily even at the earliest residence times studied. The char product yields a maximum mole percent of 18-19% hydroxide, starting at intermediate residence times at 1000oC. Generally, hydroxide is not produced until fixed carbon conversions approach 95%. The results can be explained in terms of the interactions of phenolate and carboxylate catalytic moieties in the char product. The hydroxide formation results suggest that it may be possible to develop a gasification-causticization process that does not require external chemicals and would make the energy-efficient and environmentally friendly black liquor gasification technology an economic reality.
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Polowin, Joel Evan Carleton University Dissertation Chemistry. „The effects of potential energy surface features on product vibrational distributions for the reaction F + H [subscript] 2 -] HF + H“. Ottawa, 1988.
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Ekanayake, Gemunu. „Determination of Stellar Parameters through the Use of All Available Flux Data and Model Spectral Energy Distributions“. UKnowledge, 2017. http://uknowledge.uky.edu/physastron_etds/44.
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Basic stellar atmospheric parameters, such as effective temperature, surface gravity, and metallicity plays a vital role in the characterization of various stellar populations in the Milky Way. The Stellar parameters can be measured by adopting one or more observational techniques, such as spectroscopy, photometry, interferometry, etc. Finding new and innovative ways to combine these observational data to derive reliable stellar parameters and to use them to characterize some of the stellar populations in our galaxy is the main goal of this thesis.
Our initial work, based on the spectroscopic and photometric data available in literature, had the objective of calibrating the stellar parameters from a range of available flux observations from far-UV to far-IR. Much effort has been made to estimate probability distributions of the stellar parameters using Bayesian inference, rather than point estimates.
We applied these techniques to blue straggler stars (BSSs) in the galactic field, which are thought to be a product of mass transfer mechanism associated with binary stars. Using photometry available in SDSS and GALEX surveys we identified 85 stars with UV excess in their spectral energy distribution (SED) : indication of a hot white dwarf companion to BSS. To determine the parameter distributions (mass, temperature and age) of the WD companions, we developed algorithms that could fit binary model atmospheres to the observed SED. The WD mass distribution peaks at 0.4M , suggests the primary formation channel of field BSSs is Case-B mass transfer, i.e. when the donor star is in red giant phase of its evolution. Based on stellar evolutionary models, we estimate the lower limit of binary mass transfer efficiency β ~ 0.5.
Next, we have focused on the Canis Major overdensity (CMO), a substructure located at low galactic latitude in the Milky Way, where the interstellar reddening (E(B-V )) due to dust is significantly high. In this study we estimated the reddening, metallicity distribution and kinematics of the CMO using a sample of red clump (RC) stars. The averageE(B-V)(~0.19)is consistent with that measured from Schlegel maps (Schlegal et.al. 1998). The overall metallicity and kinematic distribution is in agreement with the previous estimates of the disk stars. But the measured mean alpha element abundance is relatively larger with respect to the expected value for disk stars.
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Niyazov, Rustam. „Measurements of Correlated Pair Momentum Distributions in {sup 3}He(e,e{prime}pp)n with CLAS“. Washington, D.C : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Energy Research ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/824882-21uB5k/native/.
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Thesis (Ph.D.); Submitted to Old Dominion Univ., Norfolk, VA (US); 1 May 2003.Published through the Information Bridge: DOE Scientific and Technical Information. "JLAB-PHY-03-36" "DOE/ER/40150-2739" Rustam Niyazov. 05/01/2003. Report is also available in paper and microfiche from NTIS.
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Kelly, Madeleine N. „The Temperature Dependence of Grain Boundary Complexion Transitions and Their Effect on the Grain Boundary Character and Energy Distributions“. Thesis, Carnegie Mellon University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10604582.
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Abrupt changes in grain boundary energy (GBE) and character are associated with a change in GB complexion, GB mobility and exaggerated grain growth. In this thesis, complexion transitions and their effect of relative GBE and GB character distributions (GBCD) are studied for ceramics: europium doped spinel (Eu doped spinel), yttria doped (Y-doped), undoped alumina (Al 2O3), and strontium titanate (SrTiO3).
The population of GB planes (GBPD) of Eu doped spinel was investigated at temperatures before and after a previously identified a complexion transition. The microstructure changed from unimodal (1400 °C) to bimodal (1600 °C) and the relative area of {111} increased. This information was used to understand the GBs involved in the transition.
Atomic force microscopy was used to measure relative GBE from thermal grooves on the surfaces of Al2O3, 100 ppm Y-doped Al 2O3, and 500 ppm Y-doped Al2O3 heated between 1350 °C and 1650 °C. The relative GBE of Al2O 3 decreased slightly with increased temperature. When the doped samples were heated, there was an overall increase in the relative GBE, interrupted by abrupt reductions (increases) in relative GBE (mobility) between 1450 °C and 1550 °C. When the 100 ppm Y-doped sample was cooled, there was an increase in the relative GBE at the same complexion transition temperature, indicating that the transition is reversible.
Relative GBE was measured from thermal grooves on (SrTiO3 in a region of non-Arrhenius grain growth. Between 1350 °C and 1390 °C, an abrupt decrease in relative GBE and exaggerated grain growth indicated that a complexion transition occurred. Solidified liquid eutectic wet the boundaries at 1550 °C so these GB interfaces could not be compared to the lower temperatures.
3D microstructures of samples heated below (1350 °C), within (1390 °C), and above (1425 °C) the non-Arrhenius region in (SrTiO3 were measured. Internal dihedral angles indicated that slowly growing grains have lower GBE than more rapidly growing grains. Low GBE grains increased in fraction with increased temperature until 1425 °C. The GBE distribution and GBCD at 1425 °C indicated a correlated high population and low energy for the {001}, the (111) sigma 3 and (2¯21) sigma 9 GBs.
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Kelly, Madeleine Nicole. „The Temperature Dependence of Grain Boundary Complexion Transitions and Their Effect on the Grain Boundary Character and Energy Distributions“. Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1005.
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Bezuidenhout, Jacques. „Cross sections and analysing power energy-sharing distributions of valence (p,2p)-knockout from 208Pb with a projectile of 200MeV“. Thesis, Stellenbosch : Stellenbosch University, 2000. http://hdl.handle.net/10019.1/51668.
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Thesis (MSc)--Stellenbosch University, 2000.ENGLISH ABSTRACT: The aim of this work was to study the 208Pb(p,2p)207Tl quasi-free knockout process. The experimental data were measured at the National Accelerator Centre using incident polarised protons of 200 MeV. The two scattered particles, from the knockout reaction, were detected in coincidence and their energies were determined using a magnetic spectrometer and a solid state detector telescope. Cross section and analysing power energy distributions were extracted from the experimental measurements and these were compared with theoretical values for the Distorted Wave Impulse Approximation. The theoretical cross-section calculations predict the experimental cross-section distribution well for all combinations of distorting potentials and bound states that were investigated, both with regard to shape, as well as absolute magnitude. However the theoretical analysing power distributions did not agree with the experimental quantities. Therefore it is not clear whether the analysing power is a useful tool to extract information on the specifics of the quasi-free reaction mechanism. The spectroscopic factors were found to be consistent with the results obtained in previous studies, thereby inspiring confidence that the problem with the analysing power distribution is not ascribable to a possible deficiency in the experimental techniques exploited in this work.
AFRIKAANSE OPSOMMING: Die doel van die studie was om die kwasi vrye 208pb(p,2p )207TI verstrooingsproses te ondersoek. Die eksperimentele data is ingewin by die Nasionale Versnellingsentrum deur gebruik te maak van 'n 200 MeV gepolariseerde proton bundel. Die twee verstrooide deeltjies is in koïnsidens gemeet. Vir die metings is 'n magnetiese spektrometer en 'n vastetoestand detektorteleskoop gebruik. Die kansvlak- en analiseervermoë-energieverdelings is uit die eksperimentele data verkry en is vergelyk met die berekenings van die Vervormde Golf Impuls Benadering. Die teoretiese kansvlak berekening het die eksperimetele data goed voorspel, vir die verskillende parametrisering van potensiaal en gebonde toestande. Die berekeninge het goed ooreengestem met betrekking tot beide vorm en absolute grootheid. Die berekende analiseervermoë het egter nie goed met die eksperimentele data ooreengestem nie. Dit is dus nie duidelik of die analiseervermoë 'n handige instrument is om inligting oor die betrokke kwasi-vrye reaksie meganisme te bekom nie. Die spektroskopiese faktore was in ooreenstemming met resultate wat in vorige studies verkry is. Dit versterk vertroue dat die probleem met die analiseervermoë nie toegeskryf kan word aan die eksperimentele tegniek wat gebruik is nie.
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Lawther, D., M. Vestergaard, S. Raimundo und D. Grupe. „A catalogue of optical to X-ray spectral energy distributions of z ≈ 2 quasars observed with Swift – I. First results“. OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623803.
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We present the Swift optical to X-ray spectral energy distributions (SEDs) of 44 quasars at redshifts z approximate to 2 observed by Swift, part of a larger program to establish and characterize the optical through X-ray SEDs of moderate-redshift quasars. Here, we outline our analysis approach and present preliminary analysis and results for the first third of the full quasar sample. Not all quasars in the sample are detected in X-rays; all of the X-ray-detected objects so far are radio loud. As expected for radio-loud objects, they are X-ray bright relative to radioquiet quasars of comparable optical luminosities, with an average alpha(ox) = 1.39 +/- 0.03 (where alpha(ox) is the power-law slope connecting the monochromatic flux at 2500 angstrom and at 2 keV), and display hard X-ray spectra. We find integrated 3000 angstrom-25 keV accretion luminosities of between 0.7 x 10(46) erg s (1) and 5.2 x 10(47) erg s (1). Based on single-epoch spectroscopic virial black hole mass estimates, we find that these quasars are accreting at substantial Eddington fractions, 0.1 less than or similar to L/L-Edd less than or similar to 1.
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Okafor, Izuchukwu Francis. „Influence of Circumferential Spans of Heat Flux Distributions on Secondary Flow, Heat Transfer and Friction Factors for a Linear Focusing Solar Collector Type Absorber Tube“. Thesis, University of Pretoria, 2017. http://hdl.handle.net/2263/64173.
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Solar collector absorber tubes play a critical role in converting incident solar heat flux into absorbed thermal energy and transferring it to a heat transfer fluid. In this study a single horizontally orientated absorber tube was investigated numerically in terms of the influence of different circumferential spans of symmetrical and asymmetrical heat flux distributions on buoyancy-driven secondary flow, internal heat transfer and friction factor characteristics. Three types of circumferential heat flux boundaries were considered, namely fully uniform, partial uniform and sinusoidal non-uniform heat flux distributions. Both gravitational symmetry and asymmetry for non-uniform heat flux distributions were investigated to cover symmetry angles in terms of the gravitational field (g) of 0° (symmetrical case), 20°, 30°, 40° and 60°.
Different sized stainless steel absorber tubes having a length of 10 m, and inner diameters of 62.7 mm, 52.5 mm, 40.9 mm and 35.1 mm were considered. Three dimensional steady-state simulations were performed for water as working fluid, covering laminar flow Reynolds numbers ranging from 130 to 2200, as well as for turbulent flow Reynolds numbers ranging from 3030 to 202 600. Buoyancy effects, temperature dependent fluid thermal properties, tube-wall heat conduction and the external wall heat losses by convection and radiation were taken into consideration. Average internal heat transfer coefficients, local internal heat transfer coefficients, Richardson numbers and overall friction factors were obtained for different angular spans of incident heat flux, inlet fluid temperatures, heat flux intensities and outer wall thermal conditions
Laminar flow results indicated that the angular span, angular position, and intensity of the applied external heat flux all have significant influences on the buoyancy induced mixed convection inside the tube. This resulted in significant variations in the internal heat transfer coefficients and the friction factor which are not well described by classical empirical correlations. Buoyancy induced secondary flow significantly enhanced the internal heat transfer coefficient and significantly increased the friction factor compared to forced convection cases. Higher heat transfer coefficients and friction factors were obtained for non-uniform heat flux distributions compared to uniform heat flux distributions and were found to be dependent on the angle span and position of the heat flux. Higher inlet temperatures resulted in increased Nusselt numbers and lower friction factors, while higher external heat loss resulted in lower Nusselts numbers and lower friction factors. An increase in the asymmetry of the heat flux distribution resulted in a reduction of the Nusselt number and friction factor.
Even though turbulent flow cases with a Reynolds number range of approximately 3000 to 9000 were also influenced by buoyancy driven secondary flow, and followed the same parameter trends, it occurred to a lesser extent compared to the laminar flow cases. Turbulent flow cases with Reynolds numbers higher than 9100, exhibited little dependence on secondary flow effects and indicates the suitability of classical fully uniform heat flux heat transfer and friction factor correlations for highly turbulent flow irrespective of the distribution or intensity of the heat flux.Thesis (PhD)--University of Pretoria, 2017.
Advanced Engineering Centre of Excellence at the University of Pretoria, NRF, TESP, NAC, and SOLAR Hub with the Stellenbosch University, EEDSM Hub and CSIR is highly acknowledged and duly appreciated.
Mechanical and Aeronautical Engineering
PhD
Unrestricted
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Barcellos, Luiz Felipe Fracasso Chaves. „On a continuous energy Monte Carlo simulator for neutron interactions in reactor core material considering up-scattering effects in the thermal energy region“. reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/142675.
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Neste trabalho o transporte de nêutrons é simulado em materiais presentes no núcleo de reatores. O espectro de nêutrons é decomposto como uma soma de três distribuições de probabilidade. Duas das distribuições preservam sua forma com o tempo, mas não necessariamente sua integral. Uma das duas distribuições é devido ao espectro de fissão, isto é, altas energias de nêutrons, a outra é uma distribuição de Maxwell-Boltzmann para nêutrons de baixas energias (térmicos). A terceira distribuição tem uma forma a priori desconhecida e que pode variar com o tempo, sendo determinada a partir de uma simulação Monte Carlo com acompanhamento dos nêutrons e suas interações com dependência contínua de energia. Isto é obtido pela parametrização das seções de choque dos materiais do reator com funções contínuas, incluindo as regiões de ressonâncias resolvidas e não resolvidas. O objetivo deste trabalho é implementar efeitos de up-scattering através do tratamento estat ístico da população de nêutrons na distribuição térmica. O programa de simulação calcula apenas down-scattering, pois o cálculo do up-scattering microscópico aumenta signi_cativamente tempo de processamento computacional. Além de contornar esse problema, pode-se reconhecer que up-scattering é dominante na região de energia mais baixa do espectro, onde assume-se que as condições de equilíbrio térmico para nêutrons imersos em seu ambiente são válidas. A otimização pode, assim, ser atingida pela manutenção do espectro de Maxwell- Boltzmann, isto é, up-scattering é simulado por um tratamento estatístico da população de nêutrons. Esta simulação é realizada utilizando-se dependência energética contínua, e, como um primeiro caso a ser estudado assume-se um regime recorrente. As três distribuições calculadas são então utilizadas no código Monte Carlo para calcular os passos Monte Carlo subsequentes.In this work the neutron transport is simulated in reactor core materials. The neutron spectrum is decomposed as a sum of three probability distributions. Two of the distributions preserve shape with time but not necessarily the integral. One of the two distributions is due to prompt ssion, i.e. high neutron energies and the second a Maxwell-Boltzmann distribution for low (thermal) neutron energies. The third distribution has an a priori unknown and possibly variable shape with time and is determined from a Monte Carlo simulation with tracking and interaction with continuous energy dependence. This is done by the parametrization of the material cross sections with continuous functions, including the resolved and unresolved resonances region. The objective of this work is to implement up-scattering e ects through the treatment of the neutron population in the thermal distribution. The simulation program only computes down-scattering, for the calculation of microscopic upscattering increases signi cantly computational processing time. In order to circumvent this problem, one may recognize that up-scattering is dominant towards the lower energy end of the spectrum, where we assume that thermal equilibrium conditions for neutrons immersed in their environment holds. The optimization may thus be achieved by the maintenance of the Maxwell-Boltzmann spectrum, i.e. up-scattering is simulated by a statistical treatment of the neutron population. This simulation is performed using continuous energy dependence, and as a rst case to be studied we assume a recurrent regime. The three calculated distributions are then used in the Monte Carlo code to compute the Monte Carlo steps with subsequent updates.
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Mabiala, Justin. „Analyzing power and cross section distributions of the 12C (p,pα)8Be cluster knockout reaction at an incident energy of 100 MeV“. Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4012.
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Thesis (PhD (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: The (p, pα) reaction on 12C was investigated experimentally using polarized incident protons of 100 MeV. Coincident data, which were obtained at ten quasifree angle pairs for proton angles ranging from 25◦ to 110◦, were analyzed in terms of the distorted-wave impulse approximation (DWIA). Calculated energy-sharing cross section and analyzing power distributions reproduce the data reasonably well. The observed agreement allows the extraction of distorted momentum distributions from experimental data. These distributions are very consistent over a wide range of angle pairs at which cross section energy-sharing distributions vary considerably. Since measurements of analyzing powers were made, spin-orbit distortions were included in the DWIA calculations. The effects of spin-orbit distortions were found to be very small near zero recoil momentum and did not destroy the validity of the factorization approximation where the two-body p-α cross section enters as a multiplicative factor in the three-body (p, pα) cross section expression. Spectroscopic factors derived from the data are fairly consistent with the trend of the theoretical predictions. Analyzing power data also follow the trend of free p-4He scattering data, and comparisons with DWIA predictions are in reasonable agreement. The theory reproduces also very well analyzing power angular distributions of the projectile-cluster two-body scattering at large angular momentum of the residual nucleus. This indicates that a quasifree knockout mechanism dominates the reaction. The two-body interaction response between the projectile and the α cluster was found to resemble the scattering of protons from a free α particle to a remarkable degree, the present results strongly imply the existence of preformed α clusters in 12C.
AFRIKAANSE OPSOMMING: Die (p, pα) reaksie op 12C is eksperimenteel ondersoek deur middel van gepolariseerde protone met n invalsenergie van 100 MeV. Ko¨ınsidensie data, wat verkry is by tien kwasievrye hoekpare, met proton hoeke tussen 25◦ en 110◦, is geanaliseer in terme van die vervormde-golf-impuls-benadering (DWIA). Die berekende energie-verdeelde kansvlak en analiseervermo¨e verspreidings reproduseer die data redelik goed. Die waargenome ooreenstemming maak dit moontlik om vervormde momentumverdelings uit die eksperimentele data te verkry. Aangesien analiseervermo¨e metings gedoen is, is spin-baan wisselwerking by die DWIA berekenige ingesluit. Die bydra as gevolg van spin-baan wisselwerking blyk baie klein te wees naby nul terugslag momentum en het nie die geldigheid van die faktoriseringsbenadering, waartydens die twee-deeltjie, p-α kansvlak as ’n vermenigvuldigingsfaktor in die uitdrukking vir die drie-deeltjie (p, pα) kansvlak verskyn, vernietig nie. Spektroskopiese faktore wat uit die data herlei is, is redelik konsistent met die verloop van die teoretiese voorspellings. Analiseervermo¨e data volg ook die verloop van die vrye p-4He verstrooiings-data en vergelyk redelik goed met DWIA voorspellings. Die teorie reproduseer ook die hoekverdelings in die analiseervermo¨e van die twee-deeltjie projektiel-bondel verstrooiing by groot hoekmomentum waardes vir die oorblywende kern baie goed. Dit dui daarop dat ’n kwasie-vrye uitslaanmeganisme die reaksie domineer. Die twee-deeltjie wisselwerkingsgedrag tussen die projektiel en die α-bondel toon sterk ooreenkomste met die verstrooiing van protone vanaf ’n vrye α-deeltjie. Die huidige resultate lewer sterk bewyse vir die bestaan van voorafgevormde α-bondels in 12C.
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Bernhard, John Michael. „Work Function Study of Iridium Oxide and Molybdenum Using UPS and Simultaneous Fowler-Nordheim I-V Plots with Field Emission Energy Distributions“. Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc2211/.
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The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using X-ray Photoelectron Spectroscopy and X-ray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and Fowler-Nordheim I-V plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated.
Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous research. The analytic chamber used in the field emission analysis demonstrated the ability to independently determine the value and changes in work function and emitter geometry by simultaneous measurement of the Field Emission Energy Distribution and Fowler-Nordheim I-V plots from single emitters.
Iridium oxide coating was found to enhance the stability of molybdenum emission tips with a relatively low work function of 4.2 eV and inhibited the formation of high work function molybdenum oxides. However, the method of deposition of iridium and annealing in oxygen to form iridium oxide on molybdenum emitters left rather severe cracking in the protective oxide coating exposing the molybdenum substrate.
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Taulbee, Timothy Dale. „Measurement and model prediction of proton-recoil track length distributions in NTA film dosimeters for neutron energy spectroscopy and retrospective dose assessment“. Cincinnati, Ohio : University of Cincinnati, 2009. http://www.ohiolink.edu/etd/view.cgi?acc_num=ucin1235764236.
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Thesis (Ph.D.)--University of Cincinnati, 2009.Advisors: Henry Spitz PhD (Committee Chair), Bingjing Su PhD (Committee Member), John Christenson PhD (Committee Member). Title from electronic thesis title page (viewed May 1, 2009). Keywords: NTA; proton-recoil; neutron spectroscopy; dose assessment; track length; Monte Carlo; neutron transport; neutron interactions. Includes abstract. Includes bibliographical references.
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Lanz, Lauranne. „Constraining the Evolution of Galaxies over the Interaction Sequence with Multiwavelength Observations and Simulations“. Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11129.
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Interactions are crucial for galaxy formation and profoundly affect their evolution. However, our understanding of the impact of interactions on star formation and activity of the central supermassive black hole remains incomplete. In the canonical picture of the interaction process, these processes are expected to undergo a strong enhancement, but some recent studies have not found this prediction to be true in a statistically meaningful sense. This thesis uses a sample of local interactions observed from the ultraviolet to the far-infrared and a suite of N-body hydrodynamic simulations of interactions to examine the evolution of star formation, stellar mass, dust properties, and spectral energy distributions (SEDs) over the interaction sequence.Astronomy
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Kamenetska, Masha. „Modeling the affect of dark matter distributions in the Milky Way on the component of the cosmic rays energy spectrum as incident on Earth“. Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32902.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (leaves 51-53).
In this thesis, we investigate the effect of dark matter distribution in the galaxy on the positron spectrum on earth. We wrote code to simulate two district dark matter distribution functions as well as the annihilations which convert them into positrons. We then channeled the results into a galaxy propagation software package GALPROP and obtained a positron spectrum on earth. Our results suggest that while no dramatic differences emerge in the spectrum as a result of varying dark matter distributions, further studies are needed to confidently establish the exact nature of the relationship between the ellipticity of the dark matter profile and the positron spectrum. trajectories for other research designs are made clear as a result of this project.
by Masha Kamenetska.
S.B.
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Laidet, Julien. „Collisions à Haute Energie de Hadrons Denses en Chromodynamique Quantique : Phénoménologie du LHC et Universalité des Distributions de Partons“. Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00875951.
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Lorsque l'impulsion longitudinale des partons contenus dans un hadron ultra-relativiste diminue, on observe un accroissement de leur densité. Quand la densité approche une valeur d'ordre $1/\alpha_s$, elle n'augmente plus, elle sature. Ces effets de haute densité semblent être correctement décrits par la théorie effective du "Color Glass Condensate". Du point de vue expérimental, le LHC est le meilleur outil jamais disponible pour atteindre la phase saturée de la matière hadronique. Pour cette raison, la physique de la saturation est une branche très active de la QCD dans les années passées et à venir car la théorie et les expériences peuvent être comparées. En premier lieu, je discute de la phénoménologie des collisions proton-plomb qui ont eu lieu à l'hiver 2013 et dont les données sont sur le point d'être disponibles. Je calcule la section efficace pour la production de deux gluons qui est l'observable la plus simple pour trouver des preuves quantitatives de la saturation dans le régime cinématique du LHC. Je traite également la limite des états finaux fortement corrélés à grandes impulsions transverses et, par la même occasion, généralise la distribution de partons au régime dense. Le second sujet principal est l'évolution quantique des spectres de gluons et de quarks dans les collisions noyau-noyau, ayant à l'esprit son caractère universel. Ce résultat est déjà connu pour les gluons et je détaille ici le calcul avec attention. Pour les quarks, l'universalité n'a toujours pas été prouvée mais je dérive une formule de récursion intermédiaire entre l'ordre dominant et l'ordre sous-dominant qui constitue une étape cruciale dans l'extraction de l'évolution quantique. Enfin, je présente brievement un travail indépendant de théorie des groupes. Je détaille une méthode personnelle permettant de calculer des traces impliquant un nombre arbritraire de générateurs, une situation souvent rencontrée dans les calculs de QCD.
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Mowat, Christopher. „Star formation in the Gould Belt : a submillimetre perspective“. Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34652.
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This thesis presents my work characterising star formation in Gould Belt molecular clouds using submillimetre observations from SCUBA-2 on the James Clerk Maxwell Telescope (JCMT). I use these observations alongside data from previously published surveys using instruments including the Spitzer Space Telescope. I investigate the effect of including submillimetre data on the numbers, classifications and lifetimes of Young Stellar Objects (YSOs) in Gould Belt molecular clouds, particularly protostars. Following a literature review, I use SCUBA-2 450 and 850 μm observations to characterise star formation in the Lupus I molecular cloud. A total of eleven previously identified YSOs are detected with SCUBA-2, as well as eleven starless cores. Two cores have masses greater than the Jeans mass, and one has a virial parameter of 1.1 0.4, meaning these cores could be unstable against collapse. I use submillimetre emission to calculate disk masses, and find that one YSO has a disk mass greater than the minimum mass solar nebula. I find that Lupus I has a high percentage of both protostars and Very Low Luminosity Objects (VeLLOs). I also fit YSO Spectral Energy Distributions (SEDs) with models, allowing protostellar envelope masses and temperatures to be calculated, and interstellar extinction to be constrained for some YSOs. The signs of recent and future star formation support the hypothesis that a shock has triggered a star forming event in Lupus I. I also use SCUBA-2 data in conjunction with archival Spitzer and Herschel data to produce SEDs for five new candidate First Hydrostatic Cores (FHSCs) in Serpens South. These observations were then fit with models by the first author of this work, Alison Young. This work was able to identify two of the FHSC candidates as probable FHSCs, and constrain the rotation rate and inclination of one of them. I use JCMT Gould Belt Survey (GBS) observations of ten molecular clouds to produce an updated catalogue of protostars in these clouds. I use the FellWalker algorithm to find individual sources in the SCUBA-2 maps, and match them to the Spitzer YSO catalogue of Dunham et al. (2015). I use bolometric temperature to classify 362 out of 592 candidates as Class 0 or Class I protostars - a factor of two increase compared to the Spitzer catalogue due to improved submillimetre coverage. I find that protostellar lifetimes of 0.59 – 0.89 Myr - approximately 25 % longer than previously estimated. I also calculate protostellar luminosities, envelope masses, and envelope temperatures, and examine the distributions. Finally, I newly identify 19 protostars as VeLLOs, and increase the number of known VeLLOs in these clouds by a factor of two.
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Bäckebo, Markus. „The influence of particle size distribution on bio-coal gasification rate as related to packed beds of particles“. Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79084.
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This thesis is a part of a collaboration between Höganäs AB and Luleå University of Technology, aiming at replacing fossil process coal with bio-coal in their sponge iron process. The difference in gasification reactivity, i.e. reaction rate, between fossil coals and bio-coals is the major challenge in the endeavor to decrease the climate impact of the existing process. The goal of this thesis is to develop a model of reaction rate for bio-coals in relation to particle size distribution. Different particle size distributions were combined and tested to see how that affects the effective reaction rate. Within the scope of this work, gasification reactivities of different materials, including coal, cokes, and bio-coals, were determined. Three bio-coals were selected to study the effect of particle size distribution on reactivity. Kinetic parameters were determined by using thermogravimetric analysis in the temperature range of 770-850 °C while varying CO2 partial pressure between 0.1-0.4 atm. The effect of particle size on the reaction rate was investigated by using particles with diameter between 0.18 and 6.3 mm. The effect of particle size distribution on the reactivity of bio-coal in a packed bed was carried out in a macro thermogravimetric reactor with a constant bed volume of 6.5 cm3 at 980 °C and 40% (vol.) of CO2. The experimental investigation in three different rate-limiting steps was done for one bio-coal sample, i.e. Cortus Bark bio-coal. The activation energy of the bio-coal was 187 kJ mol-1, and the reaction order was 0.365. For the internal diffusion control regime, an increase in particle size resulted in low reaction rate. The effective diffusivity calculated from the Thiele modulus model was 1.41*10-5 m2 s-1. For the external diffusion control regime, an increase in particle size increased the reaction rate up to a certain point where it plateaued at >1 mm. By choosing two discrete particle size distributions, where a smaller average distribution can fit into a larger average distribution the reaction rate was lowered by 30% compared to only using a single narrow particle size distribution. This solution decreased the difference of apparent reaction rate in a packed bed between the bio-coal and anthracite from 6.5 times to 4.5 times. At the moment the model is not generalized for all bio-coals. However, the developed methodology can be routinely applied to assess the different bio-coal samples. One possible error can be that pyrolysis influences the gasification rate for bio-coal that is pyrolyzed below the temperature of the gasification test. There is a clear correlation between particle size distributions, bulk density, and apparent reactivity. By mixing two distributions the reaction rate of Cortus Bark was reduced from 6.5 times the reaction rate of anthracite to 4.5.
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Beauvais, March Hélène. „Modelisation des distributions de dose sur l'axe pour les faisceaux de photons de haute energie utilises en radiotherapie“. Toulouse 3, 1987. http://www.theses.fr/1987TOU30074.
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He, Yanping. „Representations of boundary layer cloudiness and surface wind probability distributions in subtropical marine stratus and stratocumulus regions“. Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/22585.
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Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2007.Committee Chair: Dr. Robert E. Dickinson; Committee Member: Dr. Irina Sokolik; Committee Member: Dr. Judth Curry; Committee Member: Dr. Peter Webster; Committee Member: Dr. Rong Fu.