Dissertations / Theses: 'FFDO' – Grafiati (2024)

Abstract:

The diploma thesis deals with the topic of free-form deformations. The main goal of this work were elaboration of theoretical knowledge about this issue and the programming of selected methods od free-form deformations. The first part describes the required spline theory, matrix calculus and free-form deformations. The resulting version shows three programs. The first program compares the selected free-form deformation methods to the example of the 4x4 control point grid. The second program serves as a generalization for the general case of grid of control points. The last program is based on direct manipulation of arbitrary surface point and following recomputation of the control points to obtain demanded shape.

Abstract:

Cette thèse a eu pour objet l'étude de l'influence du magnétisme sur la supraconductivité du composé borocarbure TmNi2B2C. Nous introduisons d'abord le problème de la coexistence de ces deux phénomènes coopératif a priori antagonistes. Nous y situons TmNi2B2C et décrivons également les motivations de ce travail de thèse : TmNi2B2C est un composé où une nouvelle phase supraconductrice doit être favorable, la phase FFLO. Bien que prédite depuis longtemps, une claire mise en évidence expérimentale manque encore. Nous introduisons ensuite plus précisément la classe des borocarbures et TmNi2B2C, pour décrire ensuite nos efforts effectués dans la croissance cristalline de bons échantillons monocristallins. Cette partie se termine sur la description de nos mesures de spectroscopie et de microscopie à effet tunnel. Nous avons mesuré des gaps supraconducteurs très propres et reproductibles, une première sur des supraconducteurs magnétiques. Nous décrivons ensuite le diagramme de phase supraconducteur précis que nous avons obtenu par des mesures de résistivité de TC= 11K jusqu'à 50mK. Nous expliquons sa non-monotonie par un champ critique en limite paramagnétique, à cause du champ d'échange entre les moments localisés de Tm et les électrons supraconducteurs. Des mesures d'aimantation à SQUID, nous permettent d'estimer la force de ce champ d'échange. Enfin, nous décrivons l'influence du magnétisme sur le réseau de vortex, à la recherche d'une signature de la phase FFLO. Nous avons ans un premier temps effectué des mesures de courant critique par transport qui montrent un chute à basse température en opposition avec le comportement habituel. Pour sonder l'état des vortex, nous avons utilisé une technique originale, des mesures de tension transverse. Si le comportement de la tension transverse est celui attendu à haute température (au-dessus de 3K), à basse température, on observe un changement de régime qui peut s'expliquer qualitativement par la présence de la phase FFLO
We present results on the interplay between magnetism and superconductivity in the bororcarbide TmNi2B2C. The bororcarbides are a new family where both magnetism and superconductivity coexist. First, we introduce the question of the coexistence of these two antagonistic phenomena and the aim of this Ph. D. : TmNi2B2C is a compound where a new superconducting phase should be likely to appear. This is the so-called FFLO phase. We wanted to observe this phase in TmNi2B2C. We, then, introduce more precisely the borocarbide family and TmNi2B2C in particular. We show our efforts to provide ourselves with good single crystals. We succeeded to grow good Yni2B2C single crystals, but failed to grow YNi2B2C ones. This second chapter ends with the description of our STM measurements. We have been able to have nice, reproducible gaps, which is a first for magnetic superconductors. The third chapter deals with the study of the influence of magnetism on the critical field. We measured a precise phase diagram down to 50mK with resistivity measurements. We explain its unusual shape by the Pauli limit, enhanced by the exchanged field between localized moments and the superconducting electrons. Magnetization measurements allowed us to get an estimation of the exchange constant. The last chapter deals with the influence of magnetism on the vortices lattice. We first performed some critical currents measurement by transport. The critical current diminished at low temperature though in classical superconductor, it raises. The mechanism for this feature is still to be found. We have probed the state of the vortices lattice through transverse voltage measurements. We show that, although at high temperature, this voltage behaves as expected there is a behavior change under 3K, around the temperature where the FFLO phase is expected. The change in this behavior can be qualitatively explained by the appearance of the FFLO. For a more quantitative description, some precise calculations are needed

Abstract:

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Métodos de migração baseados na equação da onda unidirecional apresentam limitações no imageamento de refletores com forte mergulho e no tratamento de ondas evanescentes. Utilizando a expansão de Padé complexa na solução da equação da onda unidirecional para imageamento em geofísica é possível tratar ondas evanescentes, estabilizando a migração e dispensando um tratamento especial para absorção nas fronteiras do domínio. Utilizando várias parcelas na expansão de Padé, refletores com forte mergulho podem ser corretamente migrados. Nesta dissertação aplicamos a equação da onda unidirecional com expansão de Padé complexa para implementar dois algoritmos de migração em profundidade pré e pós empilhamento: a migração por diferenças finitas (FD) e a migração por diferenças finitas e Fourier (FFD). O estudo das curvas de dispersão e da resposta impulsiva dos operadores de migração nos permitiu escolher o número adequado de parcelas na expansão de Padé e os coeficientes da expansão que garantem estabilidade à continuação do campo de onda para um ângulo de mergulho máximo prescrito. As implementações foram validadas nos dados Marmousi e no modelo de domo de sal da SEG/EAGE mostrando que refletores com forte mergulho foram corretamente migrados, mesmo na presença de forte variação lateral de velocidade. Esses resultados são comparados com outros métodos de migração baseados na equação da onda unidirecional ressaltando a qualidade da aproximação estudada neste trabalho.
Seismic Migration by downward continuation using the unidirectional wave equation approximationshas two shortcomings: imaging steep dip reflectors and handling evanescentwaves. Complex Padé approximations allow a better treatment of evanescent modes stabilizingthe finite difference migration, and does not require special treatment for domainboundaries. Imaging of steep dip reflectors can be improved using several terms in the Padéexpansion. This dissertation discuss the implementation and evaluation of complex Padéapproximation for finite difference migration and Fourier finite difference migration.The study of the dispersion relation and impulsive response associated to the migrationoperator is used to select the number of terms and coefficients in the Padé expansion whichassures stability for a prescribed maximum reflector dip. The implementations are validatedin the Marmousi and SEG/EAGE salt model datasets, and compared to other wave equationmigration methods. The results of FD and FFD complex Padé migrations can handle steeperdips, and present a much lower signal to noise ratio than their real valued counterparts.

Abstract:

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CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico
CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
PETROBRAS - Petróleo Brasileiro S.A.
Implementações dos métodos de migração diferença finita e Fourier (FFD) usam fatoração direcional para acelerar a performance e economizar custo computacional. Entretanto essa técnica introduz anisotropia numérica que podem erroneamente posicionar os refletores em mergulho ao longo das direções em que o não foi aplicado a fatoração no operador de migração. Implementamos a migração FFD 3D, sem usar a técnica do fatoração direcional, no domínio da frequência usando aproximação de Padé complexa. Essa aproximação elimina a anisotropia numérica ao preço de maior custo computacional buscando a solução do campo de onda para um sistema linear de banda larga. Experimentos numéricos, tanto no modelo hom*ogêneo e heterogêneo, mostram que a técnica da fatoração direcional produz notáveis erros de posicionamento dos refletores em meios com forte variação lateral de velocidade. Comparamos a performance de resolução do algoritmo de FFD usando o método iterativo gradiente biconjugado estabilizado (BICGSTAB) e o multifrontal massively parallel direct solver (MUMPS). Mostrando que a aproximação de Padé complexa é um eficiente precondicionador para o BICGSTAB, reduzindo o número de iterações em relação a aproximação de Padé real. O método iterativo BICGSTAB é mais eficiente que o método direto MUMPS, quando usamos apenas um termo da expansão de Padé complexa. Para maior ângulo de abertura do operador, mais termos da série são requeridos no operador de migração, e neste caso, a performance do método direto é mais eficiente. A validação do algoritmo e as propriedades da evolução computacional foram avaliadas para a resposta ao impulso do modelo de sal SEG/EAGE.
Fourier finite-difference (FFD) migration implementations use splitting techniques to accelerateperformace and save computational cost. However, such techniques introduce numericalanisotropy which leads to mispositioning of dipping reflectors along directions not used forsplitting the migration operator. We implement 3D FFD continuation migration withoutsplitting in the frequency-space domain using the complex Padé approximation and implicitfinite differences. This approach eliminates numerical anisotropy at the expense of a computationallymore intensive solution of a large banded linear system. Numerical experiments inhom*ogeneous and heterogeneous models show that splitting techniques produce noticiable positioningerros for models with strong lateral velocity variation. We compare the performanceof the iterative stabilized biconjugate gradient (BICGSTAB) and the multifrontal massivelyparallel direct solver (MUMPS). It turns out that the use of the complex Padé approximationprovides an effective preconditioner for the BICGSTAB, reducing the number of iterationsrelative to the real Padé expansion. The iterative BICGSTAB method is more efficient thanthe direct MUMPS method when solving for a single term in the Padé expansion. For wideangle approximations more terms are required to represent the migration operator, in thiscase direct methods are required. The algorithm is validated and the properties evaluatedcomputing the migration impulse response in the SEG/EAGE salt model.

Abstract:

The understanding of new emerging unconventional ground states is a great challenge for experimental and theoretical solid-state physicists. New ground states are developing, where different energy scales compete, leading to a high sensitivity of the system to external tuning parameters like doping, pressure or magnetic field. The exploration of superconductivity proved to be a fascinating and challenging scientific undertaking. Discovered by H. Kammerlingh Onnes in 1911, prior to the development of the quantum theory of matter, superconductivity was defying a microscopic theory for more than four decades until the BCS theory was formulated in 1957 by J. Bardeen, L. N. Cooper and J. R. Schrieffer. Superconductivity of most of the simple metals or metallic alloys is well described within the frame of the BCS scenario, however, in the last thirty years numerous new superconducting materials were found to exhibit exotic properties not accounted for by the BCS theory. Among them are included the high-Tc compounds, the heavy-fermion superconductors and as well the organic superconductors. It was the purpose of this work to probe different facets of superconductivity in heavy-fermion and in low-dimensional metallic compounds. This dissertation is divided into six chapters. After this introduction, in Chapter 1 we will outline the basic theoretical concepts later needed for the analysis of the experimental results. In Chapter 2 we briefly introduce the experimental techniques with a special focus on the new pressure cells developed during this thesis and used for the measurements presented in Chapters 3 to 5. In Chapter 3 the possible realization of the inhom*ogeneous superconducting FFLO state in CeCoIn5 is studied by specific heat measurements under hydrostatic pressure, while in Chapter 4 the results of AC specific heat experiments on UBe13 under uniaxial pressure are presented. The ambient pressure properties as well as results obtained by resistivity measurements under hydrostatic pressure on the one-dimensional metallic compounds TlxV6S8 are discussed in Chapter 5. At the end, Chapter 6 summarizes and concludes this thesis.

Abstract:

Im Jahr 1964 wurde eine Theorie der Supraleitung vorgestellt, welche Cooper-Paarbindungen mit nichtverschwindendem Gesamtimpuls berücksichtigt. Sie wird nach den maßgeblich beteiligten Physikern P. Fulde, R. A. Ferrell, A. I. Larkin und Y. N. Ovchinnikov als FFLO-Supraleitung bezeichnet [1, 2]. Aufgrund recht anspruchsvoller Voraussetzungen kommen nur wenige Festkörper-Systeme in Frage, die eine FFLO-Phase ausbilden könnten. Im Jahr 2007 konnte R. Lortz durch Messungen der spezifischen Wärme an dem organischen Supraleiter kappa-(ET)2Cu(NCS)2 einen soliden Nachweis für eine weitere thermodynamische Supraleitungs-Phase in hohen Magnetfeldern erbringen [3]. ET steht hierbei für Bis-(ethylen-dithiolo)-tetrathiafulvalen.Die Hochfeld-Phase von kappa-(ET)2Cu(NCS)2 erfüllt alle bekannten Bedingungen für einen FFLO-Zustand. Diese Arbeit befasst sich mit der Erbringung eines gleichwertigen Beweises einer thermodynamischen Hochfeld-Supraleitungs-Phase in dem quasi-zweidimensionalen und vollständig organischen Supraleiter beta\'\'-(ET)2SF5CH2CF2SO3 durch hochauflösende Messungen der spezifischen Wärme. Darüber hinaus sollte durch eine präzise Ausrichtung der Probe zum Magnetfeldvektor die Feldorientierungsabhängigkeit der spezifischen Wärme und damit der supraleitenden Phasen bestimmt werden.[1] - P. Fulde and R.A. Ferrell, Phys. Rev., 135:A550, (1964).[2] - A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp. Teor. Fiz., 47:1136,(1964).[3] - R. Lortz et al., Phys. Rev. Lett., 99:187002, (2007).

Abstract:

Objective: Full-field Digital Mammography (FFDM) is employed in breast screening for the early detection of breast cancer. High quality, artefact free, diagnostic images are crucial to the accuracy of this process. Unwanted motion during the image acquisition phase and subsequent image blurring is an unfortunate occurrence in some FFDM images. The research detailed in this thesis seeks to understand the impact of motion blur on cancer detection performance in FFDM images using novel software to perform simulation of motion, an observer study to measure the lesion detection performance and physical measures to assess the impact of simulated motion blur on image characteristics of the lesions. Method: Seven observers (15±5 years’ reporting experience) evaluated 248 cases (62 containing malignant masses, 62 containing malignant microcalcifications and 124 normal cases) for three conditions: no motion blur (0.0 mm) and two magnitudes of simulated motion blur (0.7 mm and 1.5 mm). Abnormal cases were biopsy proven. A free-response observer study was conducted to compare lesion detection performance for the three conditions. Equally weighted jackknife alternative free-response receiver operating characteristic (wJAFROC) was used as the figure of merit. A secondary analysis of data was deemed important to simulate ‘double reporting’. In this secondary analysis, six of the observers are combined with the seventh observer to evaluate the impact of combined free-response data for lesion detection and to assess if combined two observers data could reduce the impact of simulated motion blur on detection performance. To compliment this, the physical characteristics of the lesions were obtained under the three conditions in order to assess any change in characteristics of the lesions when blur is present in the image. The impact of simulated motion blur on physical characteristics of malignant masses was assessed using a conspicuity index; for microcalcifications, a new novel metric, known as dispersion index, was used. Results: wJAFROC analysis found a statistically significant difference in lesion detection performance for both masses (F (2,22) = 6.01, P=0.0084) and microcalcifications (F(2,49) = 23.14, P < 0.0001). For both lesion types, the figure of merit reduced as the magnitude of simulated motion blur increased. Statistical differences were found between some of the pairs investigated for the detection of masses (0.0mm v 0.7mm, and 0.0mm v 1.5mm) and all pairs for microcalcifications (0.0 mm v 0.7 mm, 0.0 mm v 1.5 mm, and 0.7 mm v 1.5 mm). No difference was detected between 0.7 mm and 1.5 mm for masses. For combined two observers’ data of masses, there was no statistically significant difference between single and combined free-response data for masses (F(1,6) = 4.04, p=0.1001, -0.031 (-0.070, 0.008) [treatment difference (95% CI)]. For combined data of microcalcifications, there was a statistically significant difference between single and combined free-response data (F(1,6) = 12.28, p=0.0122, -0.056 (-0.095, -0.017) [treatment difference (95% CI)]. Regarding the physical measures of masses, conspicuity index increases as the magnitude of simulated motion blur increases. Statistically significant differences were demonstrated for 0.0–0.7 mm t(22)=-6.158 (p < 0.000); 0.0–1.5 mm t(22)=-6.273 (p < 0.000); and 0.7–1.5 mm (t(22)=-6.231 (p < 0.000). Lesion edge angle decreases as the magnitude of simulated motion blur increases. Statistically significant differences were demonstrated for 0.0–0.7 mm t(22)=3.232 (p < 0.004); for 0.0–1.5 mm t(22)=6.592 (p < 0.000); and 0.7–1.5mm t(22)=2.234 (p < 0.036). For the grey level change there was no statistically significant difference as simulated motion blur increases to 0.7 and then to 1.5mm. For image noise there was a statistically significant difference, where noise reduced as simulated motion blur increased: 0.0–0.7 mm t(22)=22.95 (p < 0.000); 0.0–1.5mm t(22)=24.66 (p < 0.000); 0.7–1.5 mm t(22)=18.11 (p < 0.000). For microcalcifications, simulated motion blur had a negative impact on the ‘dispersion index’. Conclusion: Mathematical simulations of motion blur resulted in a statistically significant reduction in lesion detection performance. This reduction in performance could have implications for clinical practice. Simulated motion blur has a negative impact on the edge angle of breast masses and a negative impact on the image characteristics of microcalcifications. These changes in the image lesion characteristics appear to have a negative effect on the visual identification of breast cancer.

Abstract:

This thesis uses the paleoceancirculation proxy ²³¹Pa/²³⁰Th, coupled with water mass tracers δ¹³C and εNd, to reconstruct circulation histories for southern source waters masses in the South Atlantic, in addition to North Atlantic Deep Water (NADW) far from its source, for the last ~25 kyrs. Downcore ²³¹Pa/²³⁰Th records from a suite of cores along a depth transect in the Argentine Basin show distinct differences with depth, suggesting that ²³¹Pa/²³⁰Th ratios in sediments are reflective of conditions in only the bottom most waters. This indicates the importance of consideration of changes in water mass distribution when interpreting ²³¹Pa/²³⁰Th records. Opal and particle flux data from these cores show little correlation with ²³¹Pa/²³⁰Th values meaning that changes in ²³¹Pa/²³⁰Th cannot be explained by a local composition or particle flux effect and are instead likely to be reflecting changes in circulation. A core bathed by Antarctic Intermediate Water (AAIW) throughout the last 25 kyrs (GeoB 2107, 1045 m), has relatively high ²³¹Pa/²³⁰Th values (0.075) during the Holocene and distincly lower values (0.055) at the LGM suggesting faster AAIW transport during the last glacial. At greater depths, ²³¹Pa/²³⁰Th, δ¹³C and εNd data in core GeoB 2109 (2504 m) indicate a change in both circulation and water mass distribution on glacial-interglacial timescales, with moderate flow of Antarctic Bottom Water (AABW) at the LGM being replaced by more vigorous flow of NADW during the Holocene. On millenial timescales, ²³¹Pa/²³⁰Th values in deep cores GeoB 2109 and GeoB 2112 (4010 m) indicate enhanced production of AABW during northern hemisphere stadials, when variations in ²³¹Pa/²³⁰Th records are of opposite sign between hemispheres, supporting a possible bipolar seesaw relationship in deep water formation between hemispheres. These data indicate that the ²³¹Pa/²³⁰Th proxy can be used to reconstruct past flow rates of multiple water masses in the Argentine Basin and provide evidence that southern source water masses play a dynamic counterpart to NADW formation on abrupt as well as glacial-interglacial timescales.

Abstract:

This thesis explores the use of cyclic alkenylsiloxanes in Hiyama cross-coupling reactions for the stereospecific construction of the Z-pentaenyl system of incednam, the aglycon of incednine. The early chapters continue the investigation of the previously developed C6-C13 lynchpin cyclic diethyl alkenylsiloxane, accessed by controlled semi-hydrogenation of alkynylsiloxane. Later chapters discuss the development of a novel strategy to access the more reactive cyclic dimethyl alkenylsiloxanes and their application towards the synthesis of incednam.

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This dissertation is a study of the Futūḥ Miṣr (Conquest of Egypt) of Ibn 'Abd al-Ḥakam (d. 257/871), the earliest extant Arabic history of Egypt. Its primary aim is not to assess whether its information is 'authentic' - i.e. corresponding to an objective historical reality - though my findings are of relevance for those engaged in debates over authenticity. My goal instead is to explore the ideas about the past which are conveyed by this particular conglomeration of historical information and to propose methods through which we can expose and analyse different layers and types of authorial activity within a multi-vocal text like Futūḥ Miṣr. Ultimately, I use this analysis as the basis of a case study suggesting how we might more effectively historicise the generation and transmission of historical ideas in the early Islamic period. Part I of the thesis consists of three chapters which explore Futūḥ Miṣr as a whole, literary text which can be understood as an instantiation of the historical worldview of its composer. Part II of the thesis contains three chapters which each illuminate features of Ibn 'Abd al-Ḥakam's historical practice which are important prerequisites for the stratigraphic reading of Futūḥ Miṣr performed in Part III. Part III of the thesis uses the understanding of Ibn 'Abd al-Ḥakam's authorial techniques developed in Part II to expose the earlier packages of historical information which underpin Futūḥ Miṣr. These final three chapters demonstrate how Ibn 'Abd al-Ḥakam reinvested these pre-existing narratives with meaning at a micro-level - by interjecting commentary and accounts from other sources - and at a macro-level - by integrating them into the larger narrative structure of Futūḥ Miṣr. In sum, this thesis is the first systematic study of the sources, structure, and authorship of an early Arabic history, which both tests and expands our current understanding of the dynamics of early Islamic historical writing, and sheds light on numerous aspects of the changing uses of the past among the Muslim scholars of Umayyad and 'Abbāsid Egypt.

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ABSTRACT: There are many theories of which the doctrine development process is described, both in a generalperspective and more specific for either large or small states. Where one of them shows that smallstates have a limited ability to develop their doctrines, and are required to implement experiencesthat larger states have obtained through international operations and war. This statement is thefoundation of the thesis and is used to analyse the doctrine development process for small statesregardless of membership to a military alliance. The thesis compares Swedish and Norwegianmilitary doctrines through a case study to determine how the doctrine development process isstructured and if it complies with the arguments from the theories about doctrine development.The result of the thesis shows that the process is similar between the countries, and therefore thedoctrines are developed in a similar way, regardless of a membership to a military alliance.

Abstract:

In questo lavoro di tesi sono state studiate le caratteristiche di una macchina per tomosintesi Fujifilm AMULET Innovality in uso presso l'Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori (I.R.S.T.) di Meldola.Le valutazioni sono state fatte utilizzando diversi fantocci, uno dei quali costruito durante il lavoro di tesi. Per la valutazione delle immagini di mammografia digitale e di tomosintesi sono state seguite le linee guida della International Electrotechnical Commission (IEC) e della European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services (EUREF).Per lo studio delle mammografie digitali sono stati valutati, utilizzando i software COQ e ImageJ, i parametri di NPS, MTF e DQE.Per lo studio delle immagini di tomosintesi sono stati appositamente sviluppati degli algoritmi in linguaggio Java, integrati poi all'interno del software COQ. Il programma sviluppato ha permesso di valutare ASF, MTF, NPS e omogeneità delle immagini ricostruite.

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Modern scholars are deeply divided over the extent to which early Byzantine provinces such as Egypt adopted imperial Roman law. This thesis undertook a diachronic study of the published debt acknowledgements from Egypt and Nessana for the fifth through seventh centuries CE to examine the degree of adoption of imperial legal changes. The debt acknowledgements are one of the largest sets of papyri documents for this period, consisting of 283 Greek and fifty-seven Coptic documents. Having created a database of these documents, in their original Greek or Coptic plus an English translation and information from the major commentaries, I had an unparalleled opportunity to analyse change, both legal and socio-economic. The research shows that while many legal changes, including the requirement for regnal dating and changes in the liability of co-debtors, were generally adopted, there was resistance to other changes. For example, the interest rate reduction ordered by Justinian I in 528 was clearly disseminated because some documents reflect the reduction. Most people, however, continued to charge the earlier higher rates. Furthermore, some sectors of the population appear to have struggled with the imperial changes. Model formats for a simplified Greek debt acknowledgement and a very similar Coptic debt acknowledgement were developed and disseminated in the sixth century. These simplified formats did not use regnal dating or many of the other customary clauses of the formal Greek debt acknowledgment. The early development of these simplified formats, together with evidence of the privatisation and localisation of many imperial functions, including dispute resolution, support the view that the later sixth century experienced an unravelling of ties with the Roman Empire. The catastrophic seventh century, with its civil wars and Persian and Arab invasions, resulted in a shift in language from Greek to Coptic for personal legal documents. The disruption of the seventh century, however, only accelerated and finalised a process of change that was already well established in the sixth century.

Abstract:

U6Fe has the highest superconducting transition temperature TSC ~ 4 K out of all of the U-based compounds. Unusually, the Pauli limit (1:84TSC = 7:36 T) is less than the observed critical field for both the a and c axes in this tetragonal material. Neither Pauli or usual BCS orbital limit is apparently respected. In order to explain why superconductivity exceeds the Pauli limit, it must be considered that either the superconducting state is unaffected by paramagnetic effects, or there is a large amount of spin-orbit scattering. Superconductivity is in the dirty limit for typical samples of U6Fe, which means that the latter cannot be precluded. Another unusual property of the superconducting state of U6Fe is that TSC has a positive dependence on the applied pressure P, for P < 4 kbar. This combined with other subtle signals in various measurements have led to the suggestion that a Charge Density Wave (CDW) state may exist in U6Fe below 110 K. The CDW state is typically favoured by materials with low-dimensional structural features such as chains of atoms. Such materials, if superconductors, are also candidates to exhibit the sought-after Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, an unusual state in which the superconducting order parameter is modulated in real space. The FFLO is expected to be suppressed except in clean, Pauli limited materials. Therefore if U6Fe can be produced at high enough quality to bring the superconducting state into the clean limit, it would be a potential candidate for an FFLO state. Part of this project discusses apparatus and techniques applied with the goal of producing such quality samples of U6Fe. We have succeeded in the application of the Solid State Electrotransport (SSE) method to purifying samples, and have been able to replicate the highest Residual Resistivity Ratios (RRRs) achieved (~9, compared to 4 for typical samples), but for single crystals instead of the polycrystals produced in the past. In parallel with the progress made towards higher quality samples of U6Fe, a new X-ray scanner has been developed for grain mapping of samples. This has found application in the course of our synthesis studies. The best quality samples have been studied by X-ray diffraction on the XMaS beamline at the ESRF in Grenoble, France. Below TCDW ~ 10 K, satellites at (δH; δK; 0) = (±0:11;±0:11; 0) were observed that confirm a CDW state, albeit at much lower temperatures than anticipated. By examination of systematic satellite absences we have determined that the displacement vector → u is perpendicular to the modulation direction in k-space. Additionally it has been found that the symmetry of the lattice below TCDW is reduced from that of the room temperature I4=mcm structure. The appearance of additional Bragg peaks below ~110 K during these experiments were later cast into doubt by multiple scattering. We have, however, detected a signal in the form of a jump at ~110 K in specific heat measurements of our samples. These measurements also show a kink near to TCDW. We have additionally extended the investigation of the effect of pressure on the superconducting state. The maximum of TSC is confirmed in our samples, and the subsequent suppression of TSC and Hc2 is investigated up to 8 GPa. We have analysed our Hc2(T) curves at different pressures under a simple two-band model that fits the observed trends well and suggest that at the highest pressures U6Fe is approaching even more unusually enhanced Hc2 values.

Abstract:

Les progrès techniques réalisés dans le cadre des expériences sur les gaz de fermions ultrafroids ont engendré une émulation particulièrement importante ces dernières années. En effet, ces dispositifs expérimentaux permettent de produire des systèmes gazeux ≪ à la carte ≫, notamment grâce au phénomène de résonances de Feshbach qui permet de contrôler le signe de la longueur de diffusion a par application d'un champ magnétique extérieur. Il est alors possible de générer aussi bien une interaction attractive (a < 0) que répulsive (a > 0). La résonance de Feshbach en elle-même se trouve en a → ±∞, cette limite correspondant à un régime de fortes corrélations entre les particules. De plus, dans la région où a est positive, des états lies moléculaires (bosoniques car formés de deux fermions) peuvent se former. En-dessous d'une certaine température, une phase superfluide peut alors apparaitre, et une transition de phase continue entre l'état bosonique et l'état fermionique peut être observée (BEC-BCS crossover). En fonction de la position dans le diagramme de phases, les modes collectifs possèderont des caractéristiques (fréquence, amortissem*nt) différentes. En ce sens, ils constituent une sonde de l'état de la matière et une connaissance précise de ces modes est par conséquent très importante. Le travail présenté dans cette thèse comporte une caractérisation détaillée de plusieurs modes collectifs dans la phase normale du système atomique. L'étude repose principalement sur l'équation de Boltzmann, que nous résolvons de deux façons différentes. La première consiste à utiliser une méthode des moments ≪ améliorée ≫ (c'est-à-dire d'ordre supérieur). La seconde est numérique et a nécessité l'écriture d'un programme de simulation permettant l'incorporation de tous les effets de milieu (potentiel de champ moyen et section efficace). Une attention toute particulière a été apportée à la mise en place des simulations afin de reproduire le plus fidèlement possible les conditions expérimentales. Les techniques expérimentales permettent également désormais la création de gaz polarisés. Nous présenterons donc dans ce travail une étude de ces gaz utilisant notre programme de simulation (mise en évidence des différents régimes de collision), puis une étude plus théorique ayant pour principal objectif d'établir le diagramme de phase encore méconnu de ces gaz particuliers, et enfin de proposer une méthode de calcul des effets de milieu, les techniques habituelles utilisées pour les gaz non polarisés n'étant plus valables
Technical progress on ultra-cold Fermi gases experiments induced numerous studies for the last few years. Using these experimental setups, it is effectively possible to generate ultra-cold gases with selected properties, in particular through the Feshbach resonances phenomenon. This allows us to set the sign of the scattering length a using an external magnetic field. It is then possible to have an attractive interaction (a < 0) as well as a repulsive one (a > 0). The Feshbach resonance itself is defined for infinite values of a (positive or negative), which corresponds to a strongly interacting regime. Moreover, when a > 0, molecular bound states (bosonic because they are made with two fermionic atoms) can appear. Thus, below a critical temperature, a superfluid phase can emerge and a crossover can be observed (from the BEC to BCS superfluid states). Depending on the position on the phase diagram, frequency and damping of collective modes will be different. This is why the collective modes are good probes of the system phase. A precise extensive knowledge of their characteristics is thus very important. This thesis presents a complete study of some of these collective modes in the normal phase. This work mainly relies on the Boltzmann equation which will be solved in two different ways: firstly, with an improved (higher order) version of the so-called moments method; secondly with a numerical solution that has required to write a numerical code in order to take into account the in-medium effects (mean field potential and in-medium cross section). Particular attention has been paid to numerical simulations in order to reproduce as closely as possible the experimental conditions. Moreover, experimental procedures now allow to create spin unbalanced gases. We have shown in this work a study of these systems using the numerical resolution of the Boltzmann equation. Moreover, we have developed a theoretical approach in order to build the phase diagram of these polarized gases, which is not fully described yet. Finally, we have suggested a method to determine the in-medium effects, with the aim to solve the problem emerging with the usual method used in the balanced case

Abstract:

I examine the market reaction to the announcement of FFO by REITs using abnormal trading volume as a gauge of investors’ reaction. I also address the question of whether FFO provides more useful information to investors than net income. Lastly, I examine whether the quality of private information among traders prior to the announcement of FFO affects the level of abnormal trading volume.Using three different specifications, I find that even though the announcement of FFO leads to abnormal trading, there is no association between the level of abnormal trading volume and the size of the surprise contained in the FFO announcement. I also find, using abnormal returns as a measure of investor response, that FFO explains significantly more variance in abnormal returns than net income suggesting that FFO provides more useful information than net income.Lastly, I use the proportion of institutional holdings as a proxy for the number of informed traders to predict the amount of abnormal trading volume. I find no significant relation between abnormal trading volume and the proportion of institutional holdings. However, when I break down institutional ownership into two broad classifications, I find that the level of abnormal trading volume is significantly positively related to the holdings by mutual funds and investment advisors but negatively related to the holdings of other institutions (pension funds &.endowments, banks and insurance companies). This raises questions of whether the use of an aggregate measure of institutional ownership is appropriate in studies that examine the effect of institutional holdings.

Abstract:

L'état supraconducteur étant un condensat de paires de Cooper constitué d'électrons de moments et de spins opposés, il peut être fortement influencé par des effets de spin. Au cours de cette thèse, nous étudions l'effet d'un fort champ d'échange et d'un effet spin-orbite de type Rashba sur les propriétés supraconductrices. Dans une première partie, on étudie les effets associés à l'interaction entre supraconductivité et fort champ d'échange, se caractérisant par une transition de phase vers un état supraconducteur inhom*ogène découvert par Fulde, Ferrell, Larkin et Ovchinnikov (FFLO). On étudie tout particulièrement les fluctuations supraconductrices à l'approche de la transition de phase. On montre que ces fluctuations peuvent servir de révélateur à cette phase. Notamment, la capacité calorifique et la paraconductivité divergent de façon caractéristique à la transition vers un état modulé. On décrit également comment les effets paramagnétiques modifient les fluctuations de l'aimantation, annulant la réponse diamagnétique ou produisant des oscillations entre réponse para- et dia-magnétique. La seconde partie est dévolue aux jonctions supraconducteur-ferromagnétique (S/F). Dans les jonctions Josephson S/F/S, le champ d'échange donne lieu à des oscillations du courant critique en fonction de la longueur de la jonction, charactérisées par une alternance des états 0 et π. On prédit une transition entre les états 0 et π induite par la température, même dans la limite ballistique. Dans cette limite ballistique, on montre également que le courant de Josephson s'atténu sous la forme de lois de puissance en fonction de la longueur de la jonction, alors que le cas diffusif présente une atténuation exponentielle. On étudie ensuite la seconde harmonique de la relation courant-phase en présence d'une faible quantité d'impuretés. La dernière partie traite des effets de proximité lorsque les deux effets paramagnétique et spin-orbite sont présents dans une jonction Josephson. On montre que l'association d'une interaction Rashba et d'un champ d'échange induit un couplage direct entre les ordres magnétique et supraconducteur. En particulier, ce couplage permet de générer toute la dynamique magnétique par l'application d'une simple tension électrique.

Abstract:

Avec le développement des techniques d'analyse à haut débit, les chercheurs ont adopté des démarches de profilage systémique qui permettent l'analyse descriptive simultanée d'un grand nombre de variables. Une des diffcultés réside dans la synthèse et l'interprétation de ces nombreuses informations. Nous adoptons ici une approche de classiffcation de variables (CLV) qui permet de mettre en lumière des structures disjonctives pour la réduction de la dimensionnalité du problème, facilitant ainsi l'interprétation des données. Cependant, afin d'améliorer davantage la pertinence de ce type d'approches, deux directions d'investigation sont proposées. La première consiste à filtrer les données de sorte à écarter les variables isolées ouassociées à du bruit de fond. Une stratégie qui consiste à créer un groupe supplémentaire de variables, appelé « noise cluster", ainsi qu'une stratégie fondée sur la définition de variables latentes de groupe creuses (ou sparse) sont proposées et comparées. La seconde direction d'investigation est le développement d'une procédure de classification de variables dirigée vers l'explication d'une variable de réponse. Un algorithme itératif de classification/extraction est proposé. Il fournit une séquence de variables latentes de groupes ayant de bonnes performances en prédiction. Elles sont également simples à interpréter dans la mesure ou chaque composante prédictrice n'est associée qu'à un sous-ensemble de variables exploratoires conçu pour avoir une structure pratiquement unidimensionnelle
With the development of high-throughput analysis techniques, researchers have adopted systematic approaches to describe simultaneously a large number of variables. However, one of the important challenges lies in the diffculty to summarise and interpret this enormous quantity of information. We adopt a clustering of variables approach (CLV) which allows us to highlight disjunctive structures, and therefore, reduce the dimensionality of the problem and facilitate the interpretation of the data at hand. However, in order to further improve the relevance of such approaches, two directions of investigation are proposed. The first direction involves filtering the data by setting aside atypical variables or variables associated with noise. For this purpose, a strategy to create an additional group of variables, called noise cluster, and a strategy based on the definition of sparse latent variables are proposed and compared. The second direction concerns the development of a clustering of variables procedure directed to the explanation of a response variable. The implementation of iterative algorithms provides a sequence of group latent variables with good predictive performance. These latent variables are also easy to interpret since each predictive component is associated with a subset of variables assumed to have a one-dimensional structure

Abstract:

Resuelve el problema Guillotine Cutting Stock Problem with Demand on Varied Stock (GCSP-DVS) a través de un algoritmo FFD-Eficiente variado (FFD-E 2DGV). Además, demuestra la capacidad del algoritmo propuesto para incidir en el ahorro significativo a través del reúso de materia prima reciclable para el proceso industrial de corte bidimensional. Asimismo, compendia los resultados del algoritmo propuesto aplicado al GCSP-DVS y los resultados comparativos entre el FFD y el FFD-E aplicado al GCSP-D; generando un banco inédito para instancias de cortes 2 dimensiones de tipo guillotina sobre stock de tamaño variado y otra de demostraciones numéricas comparativas del FFD-E respecto al FFD, respectivamente. Finalmente, implementa un sistema computacional parametrizable que ejecute el algoritmo propuesto y arroje reportes de solución del citado problema GCSP con demanda sobre stock variado (GCSP-DVS).
Tesis

Abstract:

Les hétérostructures de taille nanométrique comprenant des matériaux supraconducteurs (S) en contact avec des matériaux métalliques (N) ou ferromagnétiques (F) présentent des propriétés surprenantes. L'effet de proximité dans les structures F/S/F se manifeste par l'effet vanne de spin. Dans les jonctions S/F/S, on voit l'apparition d'une transition de phase 0-p. Ces propriétés dépendent des paramètres internes du ferromagnétiques. Dans la première partie, nous étudions l'influence d'un décalage énergétique et d'une différence de masse effective pour expliquer l'effet de vanne de spin inverse qui se manifeste dans certaines hétérostructures F/S/F. On étudie la transition de phase 0-p dans le cas de décalage énergétique et d'anisotropie des surfaces de Fermi. La seconde partie est consacrée à l'étude de l'effet paramagnétique sur le diagramme (H,T) des bicouches S/N et S/S. On demontre qu'il se forme une phase de supraconductivité induite par champ magnétique à fort champ magnétique et faibles températures. Calculée en présence d'un phase supraconductrice inhom*ogène de type Fulde-Ferrell-Larkin-Ovchinikov (FFLO), on s'interesse également à l'influence des impuretés sur cette nouvelle phase supraconductrice à fort champ magnétique. La troisième partie est dévolue à l'étude des multicouches supraconducteur/métal normal(N). Le but de cette partie est d'étudier l'influence du nombre de couche et de décalage d'énergie sur la température critique, la densité d'état des multicouches S/N/.../N épaisses et de l'effet Josephson dans les multicouches S/N/.../N/S.

Abstract:

Cílem mé disertační práce je analyzovat a vyvinout parametrizační metodu pro 2D a 3D tvarové optimalizace v kontextu průmyslového aerodynamického návrhu letounu založeném na CFD simulacích. Aerodynamická tvarová optimalizace je efektivní nástroj, který si klade za cíl snížení nákladů na návrh letounů. Nástroj založený na automatickém hledání optimálního tvaru. Klíčovou částí úspěšného optimalizačního procesu je použití vhodné parametrizační metody, metody schopné garantovat možnost dosažení optimálního tvaru. Parametrizační metody obecně používané v oblasti aerodynamické tvarové optimalizace momentálně nejsou připravený na komplikované průmyslové aplikace vyskytující se u moderních dopravních letounů, které mají šípová zalomená křídla s winglety a motorovými gondolami, přechodové prvky spojující např. trup s křídlem atd.. Existuje tedy potřeba nalezení obecné parametrizační metody, která bude aplikovatelná na širokou škálu různých geometrických tvarů. Free-Form Deformation (FFD[1]) parametrizace může, vzhledem ke svým schopnostem při zacházení s geometrií, být odpovědí na tuto potřebu. Adaptivní parametrizace by se měla být schopna automaticky přizpůsobit danému tvaru tak, aby byly její kontrolní body vhodně rozmístěny. Což umožní dostatečnou kontrolu deformací objektu, která zaručí možnost vytvoření optimálního tvaru objektu a splnění geometrických omezení. Primární aplikací takové parametrizační metody je deformace tvaru objektu. Dalším navrhovaným cílem je modifikace FFD parametrizační metody pro současné deformace tvaru objektu a CFD výpočetní sítě, umožnující velké deformace objektu při zachování kvality výpočetní sítě.

Abstract:

Cette thèse porte principalement sur l'étude de modèles de fermions en interactions contenant un couplage spin-orbite. Ces modèles (i) peuvent décrire une classe de matériaux composés d'iridates sur le réseau en nid d'abeille ou (ii) pourraient être réalisés artificiellement dans des systèmes d’atomes froids. Nous avons étudié, dans un premier temps, le système à demi-remplissage avec l'interaction de Hubbard et un couplage spin-orbite anisotrope. Nous avons trouvé plusieurs phases: la phase isolant topologique pour de faibles corrélations, et deux phases avec des ordres magnétiques frustrés, l'ordre de Néel et l'ordre spiral, dans la limite de très fortes corrélations. La transition entre les régimes de faibles et de fortes corrélations est une transition de Mott dans laquelle les excitations électroniques se fractionnent en excitations de charge et de spin. Les charges sont localisées par l'interaction. Le secteur de spin présente de fortes fluctuations qui sont modélisées par un gaz d’instantons. Nous avons ensuite exploré la physique d'un système régi au demi-remplissage par le modèle de Kitaev-Heisenberg, qui présente une phase magnétique de type zig-zag. En dopant le système, autour du quart remplissage, la structure de bande présente de nouveaux centres de symétrie en plus de la symétrie d'inversion. Le couplage de spin de Kitaev-Heisenberg favorise alors la formation de paires de Cooper dans un état triplet autour de ces centres de symétrie. La condensation de ces paires de Cooper autour de ces vecteurs d'onde non triviaux se manifeste par une modulation spatiale du paramètre d'ordre supraconducteur, comme dans la supraconductivité de Fulde–Ferrell–Larkin–Ovchinnikov (FFLO). La dernière partie de la thèse propose et étudie une implémentation des phases topologiques dite de Haldane et de Kane-Mele dans un système avec deux espèces de fermions sur le réseau en nid d'abeille, stabilisée grâce à l’interaction RKKY médiée par l’espèce rapide et qui agit sur l’espèce lente
This thesis is dedicated largely to the study of theoretical models describing interacting fermions with a spin-orbit coupling. These models (i) can describe a class of 2D iridate materials on the honeycomb lattice or (ii) could be realized artificially in ultra-cold gases in optical lattices. We have studied, in the first part, the half-filled honeycomb lattice model with on-site Hubbard interaction and anisotropic spin-orbit coupling. We find several different phases: the topological insulator phase at weak coupling, and two frustrated magnetic phases, the Néel order and spiral order, in the limit of strong correlations. The transition between the weak and strong correlation regimes is a Mott transition, through which electrons are fractionalized into spins and charges. Charges are localized by the interactions. The spin sector exhibits strong fluctuations which are modeled by an instanton gas. Then, we have explored a system described by the Kitaev-Heisenberg spin Hamiltonian at half-filling, which exhibits a zig-zag magnetic order. While doping the system around the quarter filling, the band structure presents novel symmetry centers apart from the inversion symmetry point. The Kitaev-Heisenberg coupling favors the formation of triplet Cooper pairs around these new symmetry centers. The condensation of these pairs around these non-trivial wave vectors is manifested by the spatial modulation of the superconducting order parameter, by analogy to the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) superconductivity. The last part of the thesis is dedicated to an implementation of the Haldane and Kane-Mele topological phases in a system composed of two fermionic species on the honeycomb lattice. The driving mechanism is the RKKY interaction induced by the fast fermion species on the slower one

Abstract:

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Este trabalho examina a reação em mercado secundário dos preços e do volume de transação de Fundos de Investimento Imobiliário (FII) brasileiros após anúncios de resultados. Para isso, utiliza a metodologia de estudo de eventos para estimar o turnover anormal acumulado e o retorno anormal acumulado durante a janela de divulgação. Utiliza também o conceito de Funds From Operations (FFO) para calcular a performance operacional dos FIIs. Os dados das divulgações de resultado foram obtidos através de sistema que realiza a coleta diária em diferentes fontes públicas de informação. Os resultados sugerem que há evidências de violação da hipótese de mercado eficiente na forma semi-forte para os retornos dos fundos da amostra durante o período estudado.

Abstract:

The EU landfill directive has imposed a challenging set of targets for the UK to reduce the amount of waste sent to landfill. This has resulted in an increased realisation that wastes can be recycled and reprocessed into valuable products. One such area that is undergoing significant development is the composting of biodegradable waste products. The primary or secondary treatment of wastes by earthworms (vermicomposting) has been proposed as a mechanism to enhance the commercial value of composts. The commercialization of these technologies, however, requires the development of stable markets and consumer confidence in the end products. Currently, in the scientific literature, there are several reports that vermicomposts enhance plant growth; however the mechanism for this enhancement is poorly understood. The first experimental chapter of this thesis presents data from an experiment into the in-vessel co-composting of Green Wastes (GW), Green waste with Paper Pulp (GW/PP), and Green waste with Biosolids (GW/SS) using Ecopod® composting process. It aimed to determine whether compost chemistry and end-use was affected by feedstock quality. Consequently, three feedstock were made by mixing green waste with paper pulp or biosolids (paper I). Vermicomposts were subsequently produced from the three Ecopod® composts. In three separate plant growth trials the presence of vermicompost significantly affected plant growth. However, not all plant species responded in the positive manner previously reported (paper II). In cereal growth, substituting inorganic fertiliser with vermicompost did not decrease yield as long as some inorganic fertiliser was present in the feeding regime. This is true for wheat and maize (paper III, appendix 2). Similarly silage grass responded much better to applications of vermicompost than to conventional composts applied at the same rate (appendix 2). Tomatoes grown in commercial growth media substituted with vermicompost did not respond in the same way as reported in previous studies; no significant yield increases were observed. Few studies report on the effect of growing medium/ fertilising regime on vitamin content of foods. With increasing interest in organic food production systems in particular, it is becoming increasingly important that we understand the effects that growing conditions have on the nutritional properties of foods. In this case there was no effect of growing medium on ascorbic acid (vitamin C) content of tomatoes (paper IV). The final chapter (paper V) was a collaborative work with A. P. Williams and investigates the effect of earthworm digestion on the survival and proliferation of E. coli 0157 in composts and soil. Litter dwelling earthworms (e. g. Dendrobaena veneta) significantly aided the lateral movement of E. coli 0157 within compost. Our results imply that whilst long-term persistence of E. coli 0157 in soil and compost may be unaffected by the presence of earthworms, digestion from worms may aid proliferation of the pathogen during initial stages of soil or compost contamination. In summary, this thesis shows that feedstock can be used to manipulate compost product quality. After vermicomposting the plant growth response is often species specific. Our failure to replicate US studies suggests that vermicompost production methods and process management may also affect end product quality. This will hinder commercialisation of the technology. Significant further work is required to identify the method by which plant growth enhancement is facilitated by vermicomposts and to what extent this is specific to a particular vermicompost production method.

Abstract:

The isomeric structure of the neutron deficient nucleus 132Pr in themass 130-140 region of nuclear chart has been studied with the 98Mo(40Ar,p5n) 132Pr reaction at beam energies of 150 and 165MeV. Theexperiment was performed at the university of Jyväskylä , Finland where the40Ar beam was accelerated onto the target by the K130 cyclotron. TheJUROGAM II HPGe detector array was employed in conjunction with the RITUgas filled recoil separator. A new isomer has been established. Two newdelayed transitions have been observed at energies of 101 and 118 keV.Prompt transition previously established in 132Pr are in coincide with thenewly identified delayed transition. The half-life of the isomeric state in 132Prwas determined from a series of focal-plane time spectra gated on thedelayed 101 and 118kev gamma –ray transitions at both beam energies.The half-life of the isomeric state has been measured to be 2.6 (3)μs.Ongoing analysis aims to place the isomeric state in the known prompt levelscheme of 132Pr, and intrpret it's structure properties from the transitionsseen to directly feed the isomer

Abstract:

Se desarrolla un modelo basado en NURBS, BSplines4D, de representación de superficies parametrizadas en 4D. El objetivo es la representación y simulación dinámica de superficies deformables basadas en el modelo; se realiza un estudio de las ecuaciones del movimiento, asociando un funcional de energía para medir la deformación de objetos, realizando un estudio riguroso sobre los métodos de integración y de discretización, tanto temporal como espacial, determinando su adecuación para resolver el sistema de ecuaciones diferenciales generado. El movimiento y la simulación de la deformación se realizan exclusivamente usando los puntos de control 4D, obteniendo una eficiencia numérica y computacional excelentes. La determinación del modelo BSplines4D se realiza tras un estudio pormenorizado de los modelos existentes. También se ha utilizado para desarrollar un modelo, N-Scodef, de deformaciones de formas libres (FFD), utilizando deformaciones geométricas basadas en restricciones. Se han establecido las condiciones para aplicar restricciones con trayectorias no rectilíneas, representadas por curvas B-Spline 4D. La deformación se adapta de forma precisa a la forma descrita por las curvas.
Es desenvolupa un model basat en NURBS, Bsplines4D, de representació de superfícies parametritzades en 4D. L'objectiu és la representació i simulació dinàmica de superfícies deformables basades en el model; es realitza un estudi de les equacions del moviment, associant un funcional d'energia per mesurar la deformació d'objectes, realitzant un estudi rigorós sobre els mètodes d'integració i discretització, tant temporal com espacial, determinant la seva adequació per resoldre el sistema d'equacions diferencials generat. El moviment i la simulació de la deformació es realitzen exclusivament utilitzant els punts de control 4D, obtenint una eficiència numèrica i computacional excel·lents. La determinació del model Bsplines4D es realitza després d'un estudi detallat dels models existents. També s'ha utilitzat per desenvolupar un model, N-Scodef, de deformacions de formes lliures (FFD), utilitzant deformacions geomètriques basades en restriccions. S'han establert les condicions per aplicar restriccions amb trajectòries no rectilínies, representades per corbes B-Spline 4D. La deformació s'adapta de forma precisa a la forma descrita per les corbes
Bsplines4D, a NURBS based model, is presented. The model allows the representation of 4D parameterized surfaces. The objective is the representation and dynamic simulation of deformable surfaces based on this model; a study of the movement equations has been made, associating to them an energy functional to measure the objects' deformation. A rigorous study on the integration and discretization, both temporal and spatial, is made to evaluate its suitability to solve the system of differential equations generated. The movement and simulation of the deformation is performed only using the 4D control points. An excellent numeric and computational efficiency is achieved. The Bsplines4D model is obtained after a detailed study on the existent models. The model has been also used to develop a free-form deformable (FFD) model, N-Scodef, using geometric constraint-based deformations. The conditions to apply constraints with non rectilinear trajectories, based on 4D B-Spline curves, have been established. The deformations fit precisely to the curves form.

Abstract:

Sweden is home to five recognized national minorities, namely the Jews, the Roma, the Torne Valley Descendants (Tornedalians), the Swedish Finns, and the Sami population which also are an indigenous group. The Government`s Minority Policy aims at protecting and supporting the national minorities and the historical minority languages (Yiddish, Romani chib, Sami, Finnish, Meänkieli). The policy also promotes the right of youth, belonging to national minority groups in order to develop and streng then their cultural identity. This paper seeks to address the lack of involvement of Swedish Finnish youth in the so called Finnish Administrative Areas (Finskt förvaltningsområde, FFO), and how the Norrköping and Haninge municipalities tackle the issue. In this paper, a reconstruction of the intervention theory is presented with inspiration sought from the ideas of Evert Vedung, in order to see if the intentions of the legislation are implemented. In accordance to the research on how the policy is designed, the democratic theory, the theory of participation, as well as the theory of identity will be linked together to the opinions of officials. This will be done in accordance to the reconstructed intervention theory, which will be used as a tool in order to show how the selected mechanisms relate in order to describe how the policy will receive an expected result. The intervention theory is a method which is meant to be in use during the evaluation of measures done by the public organization. I have conducted audits on how each FFO approaches the problem at hand using municipality documents relating to the Swedish Finnish youth. In addition, I have interviewed municipal officials in the FFO:s of Norrköping and Haninge with the aim to get an impartial over view on how they are perceived by the Swedish Finnish youth within FFO. The result of my research indicates that local government activities in many cases can be linked to democracy theory, identity theory as well as participation theory. The mechanisms which were chosen used the recently named theories, are used to measure the municipalities offer of activities are language, interventions, activities and also the media. These theories have been used to select the mechanisms considered to be the most important deemed by the Law on the Protection of National Minorities (SFS 2009: 724[1]). [1] Lag (2009:724) om nationella minoriteter och minoritetsspråk

Abstract:

The aim of this thesis is to describe and defend ‘The Constraint-Based View’, which is a particular conception of the nature of, and relationship between, ideal and non-ideal theories of justice. Traditionally, ideal theory is characterised by the assumption of ‘full compliance’, while non-ideal theory is characterised by the assumption of ‘partial compliance’. In other words, ideal theories assume that those for whom the theory is meant to apply will be entirely willing and able to comply with the theory’s requirements, while non-ideal theories do not. In Chapter 1 of this thesis, I describe and assess this original conception as well as several alternative accounts of ideal and non-ideal theory, in order to offer a broad survey of the existing literature, and to identify the various ways that these conceptions fail to capture fully the relationship between ideal and non-ideal theory. In Chapter 2, I draw a distinction between two different approaches to theorising about justice. ‘Axiological’ or ‘A-Type’ approaches are characterised by the fact that they include almost no assumptions as inputs to the theory, and that they are not intended to provide action-guiding recommendations as part of the outputs of the theory. In contrast, ‘Practical’ or ‘P-Type’ approaches include additional assumptions as part of their inputs and are intended to form part of a process that ultimately produces action-guiding recommendations. In Chapter 3, I describe and defend my preferred conception of the relationship between ideal and non-ideal theory – the ‘Constraint-Based View’ (CBV). According to the CBV, there is a spectrum of theoretical approaches that can be more or less ideal, depending on the extent to which they include ‘soft constraints’ as part of the inputs to the theory. Soft constraints are facts about the world that can be changed, in contrast to hard constraints, which are facts about the world that cannot. I argue that this way of thinking about the relationship between ideal and non-ideal theory is more useful than the alternative conceptions considered in Chapter 1. In Chapter 4, I examine the roles that feasibility considerations should play in ideal and non-ideal theory, from the perspective of the CBV and in Chapter 5, I explain the implications of adopting the CBV for what I call ‘transitional theory’, which is concerned with the transition from the status quo towards a more ideal state of affairs. In Chapter 6, I offer an example of the CBV in action, by considering its implications for the debate over duties of justice towards future generations.

Abstract:

L’objectif de ce travail consiste en l'étude expérimentale et la modélisation du comportement thermo-hydraulique d'un fluide frigoporteur diphasique (FFD) particulier : le coulis de paraffine, en écoulement dans un canal rectangulaire simulant un échangeur à plaques. Les coulis de paraffine sont constitués de particules millimétriques de paraffine, stabilisées dans une matrice poreuse el mises en suspension dans de l'eau. Les particules de paraffines sont composées de 75% en masse de Norpar®15 et de 25% de polymère tri-block qui sert à gélifier la paraffine. Les résultats expérimentaux issus de bilans sur les veines d'essai de l'installation développée el mise en place au Centre de Thermique de Lyon (CETHIL), mettent en évidence une intensification importante du coefficient d'échange thermique, due a la présence des particules dans le fluide porteur. Pour un écoulement laminaire du coulis de paraffine dans le canal de refroidissem*nt, une multiplication moyenne par 1 ,25 à 1 ,5 du coefficient d'échange global par rapport au fluide monophasique a été enregistrée pour des fractions massiques en particules de 6 à 12 %. Par régression linéaire des résultats expérimentaux, des corrélations pour le calcul des nombres de Nusselt local et moyen sont proposées. Une approche théorique basée sur le modèle de mélanges (Mixture Mode!) a été élaborée pour étudier le comportement hydraulique et thermique du fluide frigoporteur diphasique FFD pendant son refroidissem*nt en écoulement laminaire dans un canal rectangulaire. L'évolution des valeurs expérimentales et théoriques pour la température moyenne du fluide et le coemcien1 d'échange thermique paroi - fluide montrent qu'ils sont en bon accord. Le modèle peut être considéré comme satisfaisant car les écarts entre résultats théoriques et expérimentaux n'excèdent jamais 14 %
This work concerns the experimental investigation and modelling of the thermo hydraulic behaviour of a new Iwo-phase secondary refrigerant, the paraffin slurry, flowing through a rectangular channel of a heat plate exchanger type. The paraffin slurries are made of millimetric bullets of paraffin, stabilized in an organic porous polymeric matrix, in suspension in water serving as a carrying fluid. The paraffin particles used contain 75% of paraffin called NORPAR®15 and 25% of a tri-block polymer of styrene with High Molecular Weight (HMW). The experimental results generated by the heat balances on the test sections of the experimental setup built in the Thermal Center of Lyon (CETHIL), highlight an important increase of the heat transfer coefficient, due to the particles presence in the carrying fluid. For a laminar flow of the paraffin slurry in the cold channel, an average multiplication by 1 .25 to 1.5 of the global heat transfer coefficient compared to the single-phase fluid was recorded for particles mass fractions of 6 to 12%. By regression of the experimental results, correlations for the local and average Nusselt number calculation for the laminar flows are proposed. The particularity of the presented correlations is their validity in the case of a pure fluid as we\l as for a two-phase fluid containing so\id particles. A model for the hydraulic and thermal behaviours studies of a Iwo-phase secondary refrigerant fluid during its cooling in laminar flow through a rectangular channel was developed it is based on the mixture model and to king the slip velocity into account. The evolution of the experimental and theoretical values for the fluid average temperature, the heat flow which crosses the walls and the heat transfer coefficient between the wall and fluid shows good agreement and the model is satisfactory since the variations never exceed 14%

Abstract:

This thesis is focused on the automatic detection of masses in FFDM images by using case-level information which includes bilateral, temporal and/or ipsilateral information. As a first step, FFDM images are preprocessed to improve image quality. A novel enhancement method is applied to compensate the thickness reduction in peripheral edges of the breast. Following, B-Splines image registration with Affine initialisation is used to obtain bilateral and temporal information that is incorporated in the detection stage. Finally, CC/MLO correspondence approach based on using curved epipolar lines is used in the FP stage. Furthermore, in order to add breast density information to the detection process, different methods for breast density assessment are analysed. Both, qualitative and quantitative methods are proposed and evaluated. Initial results show a better performance of the multi-image CAD approach relative to the single-image CAD approach. Sensitivity increases and the number of FPs is reduced
L’objectiu d’aquesta tesi és la detecció automàtica de masses en imatges mamogràfiques digitals fent servir informació mamogràfica bilateral, temporal i ipsilateral del pacient. Primerament, les imatges són preprocessades mitjançant un nou mètode que compensa la reducció del gruix mamari a la part perifèrica de la mama i així millora la seva qualitat. A continuació, per a obtenir la informació bilateral i temporal que s'incorporarà durant el procés de detecció, es fa servir el registre afí seguit del registre B-Splines. Finalment, la correspondència entre les vistes CC i MLO basada en l’ús de línies epipolars s’utilitzarà durant la part de reducció de falsos positius. Per tal d'afegir informació sobre la densitat de la mama analitzada, diferents mètodes d’avaluació de densitat mamària, tant qualitatius com quantitatius, han estat proposats i avaluats. Els resultats inicials mostren que el CAD multi-imatge incrementa la seva sensibilitat i redueix el nombre de falsos positius respecte l'uni-imatge

Abstract:

Climate change models predict an increase in the amount and intensity of winter rainfall in the UK. A series of experiments using both container grown plants and field trials was undertaken, to investigate the effect of winter waterlogging on the growth, development and yield of current varieties of winter wheat. The interaction of waterlogging with other factors such as summer drought, seed rate, and sowing date was also investigated. In the field, waterlogging decreased plant population, and uptake of nitrogen over winter from 50 kg/ha to 25 kg/ha. Plants formed new porous nodal roots, which were able to penetrate below the water level. All the varieties tested had a good ability to recover from damage by waterlogging. Plant dry weights per area of waterlogged plots were 50% of controls at the end of treatment in March, 75% at anthesis and 85-90% at harvest. In all varieties except Xi-19, recovery was due to increased number of tillers per plant, a higher proportion of which survived to form an ear. Xi-19 increased the number of grains per ear and the weight of individual grains. Waterlogging early in the season (autumn and early winter) killed more plants, but allowed longer for surviving plants to recover and compensate. Spring waterlogging caused the greatest decrease in grain yield. Sowing in September allowed autumn and spring tillering, thus two chances for compensatory growth. November sown plants did not tiller until spring, and if waterlogging occurred at this time yields were especially poor. Waterlogging did not make crops more vulnerable to subsequent drought or lodging, but the incidence of take-all and stem-base disease did appear to increase. Despite the lack of disparity in tolerance, varieties did appear to have different responses to waterlogging. Varieties with a higher growth rate and demand on resources due to weaker winter dormancy (Xi- 19) appeared to suffer more leaf chlorosis than those with a stronger dormancy (Claire). Deben had good ability to recover due to its high tillering rate in spring, and had the largest yield. Hereward showed the smallest decrease in yield, but had the lowest yield under control and waterlogged conditions. It was hoped that it would be possible to find a simple screening method to identify tolerant varieties at an early stage. Unfortunately plant appearance during waterlogging was not predictive of final yield. Research into stress tolerance has tended to concentrate on identifying `stress genes' but in this case it appears that multi-gene traits are more important in determining crop yield.

Abstract:

Petroleum powered vehicles emit volatile organic compounds (VOCs) through combustion that contributes to the pollution of the environment. A technique in the 1970s was developed to decrease these emissions, especially for nitrogen oxides (NOx) and sulphuric oxides (SOx) which is called exhaust gas recirculation (EGR). The technique works by recirculating a portion of the combusted gas back into the engine, this limits the NOx and SOx emissions because of lower temperatures and less available oxygen. The problems that follow these effects is the formation and condensation of acids that corrode the material of the EGR system, which are created by many different reactions. It is of importance to understand how the compounds in the EGR system behaves through analysis of authentic and simulated condensates, which is why a quantitative method for these compounds are of interest. The aim of the project was to develop a simple quantitative analysis method for formic acid, acetic acid, and lactic acid in aqueous solution, which was done at Gränges Sweden AB. The technique used for detection and quantification was gas chromatography (GC) coupled to a flame ionization detector (FID) and a water compatible polyethylene glycol (PEG) column. Fractional factorial design (FFD) was used for determination of adequate operating parameters of the GC method and the sample preparation. Sample preparation only required filtration and pH adjustment prior to direct aqueous injection (DAI) to the chromatographic instrument. Detection of the analytes was very difficult because of non-compatibility with the FID, and quantification of asymmetric peak shapes made this problem worse, omitting lactic acid from further analysis. Limit of detection (LOD) and limit of quantification (LOQ) was 490 and 1640 ppm for formic acid and 120 and 400 ppm for acetic acid, with an injection volume of 0.3 μL and split ratio 10:1. Limits were too high for every EGR sample leaving no peaks detected for the sample preparation used. Further development should be done with complementary techniques and sample reprocessing in order to quantify the compounds.

Abstract:

La première partie de cette thèse concerne les phases inhom*ogènes
FFLO. Celles-ci peuvent apparaître dans les supraconducteurs
ou les gaz d'atomes froids fermioniques en présence d'une différence
hom*ogène de potentiels chimiques entre les deux états de spin.
Nous regardons la compétition
entre les différentes phases FFLO près de la transition.
A 2D, nous utilisons une approche de type Ginzburg-Landau
pour prédire une cascade de transitions entre des phases inhom*ogènes
de plus en plus complexes.
A 3D ou la transition FFLO est du premier ordre,
nous présentons une méthode numérique
de résolution des équations quasiclassiques d'Eilenberger
basée sur un développement de Fourier.
Nous déterminons ainsi les phases inhom*ogènes de plus basse énergie.

Dans la seconde partie, nous étendons la théorie perturbative
de Bogoliubov aux quasicondensats dans une représentation densité-phase.
Nous obtenons des prédictions pour différentes observables.

Abstract:

The work of this thesis was focused on the development of high-performance algorithms for a new generation of molecular descriptors, with many advantages with respect to its predecessors, suitable for diverse applications in the field of drug design, as well as its implementation in commercial grade scientific software (Pentacle). As a first step, we developed a new algorithm (AMANDA) for discretizing molecular interaction fields which allows extracting from them the most interesting regions in an efficient way. This algorithm was incorporated into a new generation of alignmentindependent molecular descriptors, named GRIND-2. The computing speed and efficiency of the new algorithm allow the application of these descriptors in virtual screening. In addition, we developed a new alignment-independent encoding algorithm (CLACC) producing quantitative structure-activity relationship models which have better predictive ability and are easier to interpret than those obtained with other methods.
El trabajo que se presenta en esta tesis se ha centrado en el desarrollo de algoritmos de altas prestaciones para la obtención de una nueva generación de descriptores moleculares, con numerosas ventajas con respecto a sus predecesores, adecuados para diversas aplicaciones en el área del diseño de fármacos, y en su implementación en un programa científico de calidad comercial (Pentacle). Inicialmente se desarrolló un nuevo algoritmo de discretización de campos de interacción molecular (AMANDA) que permite extraer eficientemente las regiones de máximo interés. Este algoritmo fue incorporado en una nueva generación de descriptores moleculares independientes del alineamiento, denominados GRIND-2. La rapidez y eficiencia del nuevo algoritmo permitieron aplicar estos descriptores en cribados virtuales. Por último, se puso a punto un nuevo algoritmo de codificación independiente de alineamiento (CLACC) que permite obtener modelos cuantitativos de relación estructura-actividad con mejor capacidad predictiva y mucho más fáciles de interpretar que los obtenidos con otros métodos.

Abstract:

abstract: The Federal Flight Deck Officer (FFDO) program was mandated legislatively, as part of the Homeland Security Act of 2002. This study replicated earlier research that investigated pilots’ opinions of the current state of the FFDO program based on interviews. A Likert survey was created to allow simpler quantitative collection and analysis of opinions from large groups of pilots. A total of 43 airline pilots participated in this study. Responses to the Likert questions were compared with demographics, searching for significance through a Pearson chi-square test and frequencies were compared to earlier research findings. Significant chi-square results showed that those familiar with the program were more likely to agree the program should continue, it was effective, the screening and selection process of program applicants was adequate and the Federal Air Marshal Service’s management of the FFDO program was effective. Those with Military experience were more likely to disagree it was reasonable that FFDOs were required to pay for their own room and board during training or train on their own time. All those who shared an opinion agreed there should be a suggestion medium between FFDOs and their management. Unlike the prior study, all those familiar with the program agreed the weapons transportation and carriage procedures were adequate. Furthermore, all those who shared an opinion found the holster locking mechanism adequate, which was another reversal of opinion from the prior study. Similar to the prior study, pilots unanimously agree FFDOs were well trained and agreed that the program was effective and should continue.
Dissertation/Thesis
Masters Thesis Aerospace Engineering 2017

Abstract:

碩士
輔仁大學
金融與國際企業學系金融碩士班
100
The recession wave of financial crisis and European debt crisis is sweeping the whole globe and will affect the next few decades. This study focuses on real estate investment trusts (REITs), it has a stable rental income and invests real estate for its assets structure, REITs next step should repay the interest from its high debt ratio. But that is a big question whether REITs overcome the market's uncertainty. Many scholars are mostly studied the REITs equity financing, verified that the assumptions on signal theory, agency cost theory. This article towards another side-debt financing, collects the 84 REITs listed on the NYSE from 2001 to 2011 for article sample data. Uses Funds from Operations(FFO) as a proxy factor to measure cash flow uncertainty, confirms the volatility of FFO and debt ratio exist a inverse relationship, and longer IPO year, a higher proportion of total revenue does make the debt ratio increased, these conclusions also effectively support the former scholars studies. Another interesting result, REITs size does not affect the debt ratio.

Abstract:

Ultracold atomic gases have emerged as an ideal laboratory system to emulate many-body physics in an unprecedentedly controllable manner. Numerous many-body quantum states and phases have been experimentally explored and characterized using the ultracold atomic gases, offering new insights into many exciting physics ranging from condensed matters to cosmology. In this thesis, we will present a systematic numerical study of a novel experimental system, population imbalanced two-component ultracold Fermi gases. We explore the phase diagram of this system in both 3D and 1D especially focusing on the exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, which is characterized by a spatially oscillating order parameter. In 3D, we solve for the stationary states of trapped imbalanced Fermi gases in a wide range of parameter space with a home-made parallel eigen-solver for Bogoliubov-de Gennes (BdG) equations. Our results show that there exists a metastable state with a FFLO type oscillating order parameter. In 1D, we simulate the dynamical expansion of the population imbalanced Fermi gases from the trap. A numerically quasi-exact scheme, time-evolving block decimation (TEBD), is introduced for the comparative studies with the solution of the time-dependent BdG equation. Our results predict that the existence of FFLO states will leave conspicuous signatures in the density profiles during the expansion. For further understanding of the interplay between the population imbalance and two-body pairing interaction between two spin components, we also study the spin transport properties through trapped ultracold Fermi gases. The preliminary results will be discussed.

Abstract:

Two recent methods for the fast simulation of the building airflow are studied: the fast fluid dynamics (FFD) algorithm and the use of graphic processing unit (GPU) for scientific computing in building engineering. A GOOGLE SketchUp plug-in for the FFD program was also developed as a model-creating tool to enhance the accessibility of the operation and to extend the range of users. The new methods are verified to be much faster than conventional computational fluid dynamics (CFD) models and they can achieve real-time simulations. This thesis focuses on the applications of the FFD program to illustrate its functions and abilities. The application fields include but not limited to fast building airflow analysis, architectural design and urban planning associated with airflows. Although the results are not as accurate as the conventional CFD, it is designed for the needs of fast simulations and analysis with less requirement of accuracy. With further improvements in the future, the developed FFD program in this study can become an important tool to bring the engineering analysis of building simulation into the early stage of the architectural designs.

Abstract:

Im Jahr 1964 wurde eine Theorie der Supraleitung vorgestellt, welche Cooper-Paarbindungen mit nichtverschwindendem Gesamtimpuls berücksichtigt. Sie wird nach den maßgeblich beteiligten Physikern P. Fulde, R. A. Ferrell, A. I. Larkin und Y. N. Ovchinnikov als FFLO-Supraleitung bezeichnet [1, 2]. Aufgrund recht anspruchsvoller Voraussetzungen kommen nur wenige Festkörper-Systeme in Frage, die eine FFLO-Phase ausbilden könnten. Im Jahr 2007 konnte R. Lortz durch Messungen der spezifischen Wärme an dem organischen Supraleiter kappa-(ET)2Cu(NCS)2 einen soliden Nachweis für eine weitere thermodynamische Supraleitungs-Phase in hohen Magnetfeldern erbringen [3]. ET steht hierbei für Bis-(ethylen-dithiolo)-tetrathiafulvalen.Die Hochfeld-Phase von kappa-(ET)2Cu(NCS)2 erfüllt alle bekannten Bedingungen für einen FFLO-Zustand. Diese Arbeit befasst sich mit der Erbringung eines gleichwertigen Beweises einer thermodynamischen Hochfeld-Supraleitungs-Phase in dem quasi-zweidimensionalen und vollständig organischen Supraleiter beta\'\'-(ET)2SF5CH2CF2SO3 durch hochauflösende Messungen der spezifischen Wärme. Darüber hinaus sollte durch eine präzise Ausrichtung der Probe zum Magnetfeldvektor die Feldorientierungsabhängigkeit der spezifischen Wärme und damit der supraleitenden Phasen bestimmt werden.[1] - P. Fulde and R.A. Ferrell, Phys. Rev., 135:A550, (1964).[2] - A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp. Teor. Fiz., 47:1136,(1964).[3] - R. Lortz et al., Phys. Rev. Lett., 99:187002, (2007).

Abstract:

碩士
國立中山大學
財務管理學系研究所
92
This paper examines the information content of net income and cash flows for hotel and tourism industry and department store industry in Taiwan. The National Association of Real Estate Investment Trust (NATEIT) has suggested that Net Income is a misleading measure of operating performance for income-producing real estate operating companies. They assert that historical cost based depreciation is inappropriate for income-producing real estate because it is not correlated with changes in the value of those real estates. Thus, the NAREIT has promoted Funds From Operations (FFO) as a supplemental measure of operating performance. FFO is calculated as net income adding depreciation expense and excluding realized gain or loss from the sale of properties. Like the REITs, the hotel and department stores industry hold and operate income-producing real estate. We test the NAREIT proposal that FFO is a more informative measure for real estate operating companies by doing an empirical analysis for hotel industry and department store industry. The results suggest that although FFO is associated with stock market performance, it is not relatively superior to Net Income or incrementally relevant beyond Net Income. Furthermore, results on testing of individual components in deriving FFO from Net Income show that both depreciation expenses and gain or loss from sale of properties is not associated with stock price performance. This indicates that FFO excludes non-value relevant accounting data. Therefore, the test results show little evidence in supporting NAREIT’s claim that FFO is a more informative measure for real estate operating companies. Although we do not have strong evidence to indicate that FFO is a better performance measure than Net Income, it is still a value relevant information in determining the value of income-producing real estate managing companies. The recent passed Taiwan Real Estate Securitization Act provides investors a new channel to invest in income-producing real estate. While it is not likely that FFO will replace Net Income as the main performance measure of the securities under Taiwan Real Estate Securitization Act, FFO could provide investors helpful information in determining the value of these income-producing real estate securities.

Abstract:

Nowadays, subsalt oil and gas exploration is drawing more and more attention from the hydrocarbon industry. Hydrocarbon exploitation requires detailed geological information beneath the surface. Seismic imaging is a powerful tool employed by the hydrocarbon industry to provide subsurface characterization and monitoring information. Traditional wave-equation migration algorithms are based on the one- way-in-depth propagation using the scalar wave equation. These algorithms focus on downward continuing the upcoming waves. However, it is still really difficult for conventional seismic imaging methods, which have dip limitations, to get a correct image for the edge and shape of the salt body and the corresponding subsalt structure. The dip limitation problem in seismic imaging can be solved completely by switching to Reverse-Time Migration (RTM). Unlike old methods, which deal with the one-way wave equation, RTM propagator is two-way and, as a result, it no longer imposes dip limitations on the image. It can also handle complex waveforms, including prismatic waves. Therefore it is a powerful tool for subsalt imaging. RTM involves wave extrapolation forward and backward in time. In order to accurately and efficiently extrapolate the wavefield in heterogeneous media, I develop three novel methods for seismic wave modeling in both isotropic and tilted transversely isotropic (TTI) media. These methods overcome the space-wavenumber mixed-domain problem when solving the acoustic two-way wave equation. The first method involves cascading a Fourier Transform operator and a finite difference (FD) operator to form a chain operator: Fourier Finite Differences (FFD). The second method is lowrank finite differences (LFD), whose FD schemes are derived from the lowrank approximation of the mixed-domain operator and are represented using adapted coefficients. The third method is lowrank Fourier finite differences (LFFD), which use LFD to improve the accuracy of TTI FFD mothod. The first method, FFD, may have an advantage in efficiency, because it uses only one pair of multidimensional forward and inverse FFTs (fast Fourier transforms) per time step. The second method, LFD, as an accurate FD method, is free of FFTs and in return more suitable for massively parallel computing. It can also be applied to the FFD method to reduce the dispersion in TTI case, which results in the third method, LFFD. LFD and LFFD are based on lowrank approx- imation which is a general method to handle mixed-domain operators and can be easily applied to more complicated mixed-domain operators. I show pseudo-acoustic modeling in orthorhombic media by lowrank approximation as an example.
text

Abstract:

Failed fuel refers to the breach in the fuel-clad of an irradiated fuel assembly in a nuclear reactor. Neutron detection or gamma detection is commonly used in Failed Fuel Detection and Locating (FFDL) system to monitor the activity of the coolant. Though these methods offer specific advantages under different conditions of the coolant, providing both types of detectors in FFDL system is impractical. This limitation is the motivation for the detector system developed in the present work. In the present work, effort has been made for realising a detector system for simultaneous measurement of neutron and gamma activity of the coolant, thus offering a two-parameter basis for failed fuel detection. NE213 liquid scintillator was chosen for this work as it has good detection capability for both neutrons and gammas. Additionally, the neutrons and gammas interacting with NE213 detector can be separated based on pulse shape discrimination. The work reported in this thesis includes fabrication details and different steps followed in assembling the NE213 detector. Details of experimental set-up developed for pulse height analysis and pulse shape analysis are covered. Results of experiments carried out to study the response of the NE213 detector to gamma and neutron sources using pulse height analyser are presented. The absolute gamma efficiency and relative gamma efficiency of NE213 detector are calculated. Neutron–gamma separation capability of NE213 detector based pulse shape analysis system is reported. Application of the developed detector system to analyse the coolant activity in FFDL system in a reactor is described. Response of the detector is compared with the existing FFDL system at different power levels of the reactor. Since failed fuel is a rare event, it was simulated using neutron and gamma sources. Pulse shape analysis spectra obtained under simulated failed fuel condition are presented.