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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1331

Gradient-Index Metamaterial Infrared Detector for Enhanced Photo-Response and Image Quality

Adams, Kelsa Derek 05 1900 (has links)
An enhanced thermal imaging concept made possible through the development of a gradient-indexed metamaterial infrared detector that offers broadband transmission and reflection in THz waves. This thesis proposes a proof of feasibility for a metamaterial infrared detector containing an anti-reflective coating with various geometrically varying periodic metasurfaces, a gradient-indexed dielectric multilayer for near-perfect longpass filtering, and a gradient index of refraction (GRIN) metalens for enhanced focal plane thermal imaging. 2D Rigorous Coupled-Wave Analysis (RCWA) is used for understanding the photonic gratings performance based on material selection and varying geometric structure. Finite Difference Time Domain (FDTD) is used to characterize performance for a diffractive metalens by optimizing the radius and arrangement of cylindrical nanorods to create a desired phase profile that can achieve a desired focal distance for projections on a detector for near- to far-infrared thermal imaging. Through combining a micromachined anti-reflective coating, a near-perfect longpass filter, and metamaterial GRIN metalens, infrared/THz focal plane thermal imaging can obtain faster photo-response and image quality at targeted wavelengths, which allows for scientific advancements in electro-optical devices for the Department of Defense, aerospace, and biochemical detection applications.
1332

Korrektur des LET-abhängigen Ansprechvermögens von faseroptischen Dosimetrie-Sonden

Grabs, Leopold 29 January 2021 (has links)
Viele Festkörperdosimetriesonden haben eine hohe räumliche und zeitliche Auflösung. Jedoch zeigt ihr Messsignal Quench-Effekte beim Einsatz in Protonenstrahlungsfeldern mit hohem linearen Energietransfer (LET). Ohne eine Korrektur dieses verminderten Messeffekts würde dies zu einer Unterschätzung der Dosis führen. In dieser Arbeit wurde ein Messsystem entwickelt, das auf einem an eine Lichtleitfaser gekoppelten sensitiven Volumen aus Berylliumoxid basiert, dessen Lumineszenzlicht während der Messung spektral geteilt wird. Dadurch entsteht eine zusätzliche Information, die eine Aussage über die Restreichweite und somit über den LET von Protonen am Messort ermöglicht. Es konnte gezeigt werden, dass das Signalverhältnis der beiden spektralen Anteile stark mit der Restreichweite von initial monoenergetischen Protonen korreliert. Auf dieser Basis wurde eine Korrekturfunktion implementiert, welche die Dosisunterschätzung für Protonen mit Anfangsenergien kleiner als 145 MeV gut ausgleicht. Eine beobachtete Abhängigkeit der Signalverhältnisbasierten Dosiskorrektur von der initialen Protonenenergie führt jedoch dazu, dass die Korrektur für initial höherenergetische Protonen bei hohem LET weiterhin eine unterschätzte Dosis liefert.:1 Einleitung 2 Physikalische Grundlagen zur Dosimetrie in Photonen- und Protonenfeldern 2.1 Strahlungsfeldgrößen 2.2 Wechselwirkungen von Photonen mit Materie 2.3 Wechselwirkungen geladener Teilchen mit Materie 2.4 Wichtige Größen der Dosimetrie und dosimetrische Konzepte 2.5 BeO-basierte Faser-Dosimetriesonden 3 Material und Methoden 3.1 Verwendetes Messsystem 3.2 Dosis-Kalibrierung des Messsystems im Photonen-Referenzfeld 3.3 Messungen im Protonenfeld an der UPTD 3.4 LET-abhängige Korrektur des Messeffekts 3.5 Verifikation 4 Ergebnisse 4.1 Dosis-Kalibrierung im Photonen-Referenzfeld 4.2 Messungen im Protonenfeld 4.3 LET-abhängige Korrektur des Messeffekts 4.4 Verifikation 5 Diskussion 6 Zusammenfassung / Many solid dosemeters offer high spatial and temporal resolution. However, a common problem is their quenching in regions of high linear energy transfer (LET) during measurements in proton beams. This leads to reduced measurement signal, and thus, to dose underestimation. Hence, a dose correction is necessary. In this work a dosimetric system was developed which is based on a fiber coupled sensitive volume of beryllium oxide. Its radioluminescence signal is split into two spectral parts during measurement. Thereby one can obtain additional information that enables access to the values of residual range and LET of proton beams at the point of measurement. It could be shown that there exists a strong correlation between the signal ratio of both spectral parts of luminescence and the residual range of monoenergetic proton beams. Based on this, a correction function was implemented which allows for the adjustment of dose underestimation for measurements in proton beams of initial energies less than 145 MeV. Nevertheless, the signal ratio based correction function was observed to be dependent on the initial proton beam energy. Hence, the underestimation of the dose remains in the case of higher initial proton energies in regions of high LET.:1 Einleitung 2 Physikalische Grundlagen zur Dosimetrie in Photonen- und Protonenfeldern 2.1 Strahlungsfeldgrößen 2.2 Wechselwirkungen von Photonen mit Materie 2.3 Wechselwirkungen geladener Teilchen mit Materie 2.4 Wichtige Größen der Dosimetrie und dosimetrische Konzepte 2.5 BeO-basierte Faser-Dosimetriesonden 3 Material und Methoden 3.1 Verwendetes Messsystem 3.2 Dosis-Kalibrierung des Messsystems im Photonen-Referenzfeld 3.3 Messungen im Protonenfeld an der UPTD 3.4 LET-abhängige Korrektur des Messeffekts 3.5 Verifikation 4 Ergebnisse 4.1 Dosis-Kalibrierung im Photonen-Referenzfeld 4.2 Messungen im Protonenfeld 4.3 LET-abhängige Korrektur des Messeffekts 4.4 Verifikation 5 Diskussion 6 Zusammenfassung
1333

Vývoj nových kvantově-chemických metod pro silně korelované systémy / Coupled clusters tailored by matrix product state wave functions

Antalík, Andrej January 2021 (has links)
The central problem in the modern electronic structure theory is the calculation of cor- relation energy, possibly by an approach that would account for both static and dynamic correlation in an efficient, balanced and accurate way. In this thesis, I present a collection of methods that combine the effective treatment of dynamic correlation by the coupled cluster theory with density matrix renormalization group, a well-established technique for calculations of strongly correlated systems. The connection between them is achieved via the tailored coupled clusters (TCC) ansatz, which conveniently does not impose any ad- ditional computational costs. After the successful initial assessment, we developed more efficient implementations of these methods by employing the local approaches based on pair natural orbitals. This way, we extended the range of possible applications to larger systems with thousands of basis functions. To assess the accuracy of TCC as well as its local counterparts, we performed a variety of benchmark calculations ranging from small, yet challenging systems such as the nitrogen molecule or tetramethyleneethane diradical, to larger molecules like oxo-Mn(Salen) or Fe(II)-porphyrin model. 1
1334

Composite-Cavity Organic Microlasers

Wagner, Tim 09 July 2019 (has links)
This thesis deals with the development and investigation of composite-cavity (CC) organic microresonators comprising a vertical cavity (VC) and a distributed feedback structure (DFB). Prepared as separate devices, these two resonators are extensively investigated and characterized by their far-field radiation patterns, emission spectra, and dispersion characteristics. Although the vertical and lateral systems are based on entirely different concepts leading to distinct symmetries, confinement mechanisms, and processes of optical feedback, devices produced with the same set of materials show comparable lasing thresholds. The different angular dispersions of cavity and waveguide (WG) resonances are employed in a laterally structured vertical-cavity surface-emitting laser (VCSEL), where a periodic grating serves as a diffractive coupler between these two regimes. A coherent interaction of the vertical and horizontal system is observed as pronounced anticrossings of parabolic and linear dispersion curves in the far-field spectra. As a result from this coherent coupling, the hybridized WG-VCSEL modes show stimulated emission in far-field regions, where the individual photonic structures would not reach the lasing threshold in a decoupled scenario. Efficient optical feedback in surface-normal and in-plane direction is achieved by combining a VC and a second-order DFB structure in a continuous tunable CC microresonator. The optical coupling is due to a first-order light diffraction on a second-order Bragg grating and, in the degenerate case, can be as efficient as the coupling observed in more classical cascade coupled cavities. When the system is non-degenerate, the diffraction efficiency is suppressed because of sub-coherence-length dimensions of the composite-cavity and both resonators tend to operate as independent structures, without experiencing substantial losses due to diffraction on the distributed-feedback grating. Dispersion characteristics of multiple resonances are recorded and related to calculated modes, their field profiles, and coupling efficiencies. In combination with the analysis of input-output measurements, the lasing characteristics of vertical and lateral resonances are controlled by adjusting specific design parameters of the system. For identical resonance energies, the distinct resonators show coherent interaction in the cross-coupled configuration, if the quality of the resonances and the cross-coupling efficiency meet the condition of strong photon-photon interaction. This resonant coupling has a fundamental impact on dispersion and lasing characteristics of the system. / Die vorliegende Arbeit beschäftigt sich mit der Entwicklung und Untersuchung von organischen Mikroresonatoren, die eine Kompositkavität aus einem Oberflächenemitter und einem Resonator mit verteilter Rückkopplung (DFB) beinhalten. Diese beiden Resonatortypen werden zunächst als separate Strukturen hergestellt, untersucht und über deren Intensitätsverteilungen im Fernfeld, Emissionsspektren und Dispersionseigenschaften charakterisiert. Die vertikalen und lateralen Strukturen basieren auf unterschiedlichen Konzepten, die zu völlig verschiedenartigen Symmetrien, Mechanismen des elektromagnetischen Einschlusses und Arten der optischen Rückkopplung führen. Nichtsdestotrotz weisen diese Resonatoren, die mit dem gleichen Materialsatz hergestellt wurden, ähnliche Laserschwellen auf. Die unterschiedliche winkelabhängige Dispersion von Vertikal- und Wellenleitermoden werden in einem lateral strukturierten Oberflächenemitter (VCSEL) ausgenutzt. In dieser Struktur dient eine periodisches Gitter als Kopplungselement zwischen diesen beiden Bereichen. Eine kohärente Wechselwirkung zwischen vertikalem und horizontalem System zeigt sich durch das Auftreten von ausgeprägten Antikreuzungspunkten parabolischer und gerader Dispersionskurven in den winkelaufgelösten Emissionsspektren. Die Folge dieser kohärenten Kopplung ist das Entstehen von Lasermoden in Bereichen des Fernfelds, wo die einzelnen Resonatoren im entkoppelten Zustand die Laserschwelle nicht erreichen würden. Eine wirksame optische Rückkopplung sowohl in Richtung der Oberflächennormalen als auch in lateraler Richtung wird durch die Kombination einer VCSEL und einer DFB-Struktur zweiter Ordnung in einem kontinuierlich durchstimmbaren Kompositresonator erreicht. Die optische Kopplung wird durch Beugung erster Ordnung am Bragg-Gitter zweiter Ordnung realisiert. Im entarteten Fall werden Kopplungseffizienzen beobachtet, die vergleichbar mit denen klassisch kaskadengekoppelter Mikrokavitäten sind. Für verschiedene Energieeigenwerte der zwei Resonatorkomponenten führt die im Vergleich zur Kohärenzlänge geringe Ausdehnung der Kompositkavität zu einer nahezu unabhängigen Tätigkeit der beiden Resonatoren mit nur geringen Verlusten durch Beugung an der periodischen Struktur. Die Dispersionseigenschaften von mehreren Resonanzen werden gemessen und berechneten Moden, deren Feldverteilungen und Kopplungseffizienzen zugeordnet. In Verbindung mit der Analyse der Intensitäten der Lasermoden in Abhängigkeit der Pumpleistung werden die Laserschwellen durch die Anpassung spezifischer Designparameter kontrolliert. Für identische Resonanzenergien weisen die unterschiedlichen Resonatoren eine kohärente Wechselwirkung auf, falls die Qualität der Moden und die Beugungseffizienz die Bedingung für starke Photon-Photon-Kopplung erfüllen. Diese resonante Kopplung zeigt einen fundamentalen Einfluss auf die Dispersions- und Lasereigenschaften im Kompositsystem.
1335

Regulation of the Dopamine D3 Receptor by Adenylyl Cyclase 5

Habibi Khorasani, Hedieh 10 May 2022 (has links)
The D3 dopamine receptor (D3R) belongs to D2-class of dopamine receptors (DARs) and is involved in emotion, movement, and reward. D3R dysfunction has been reported in some neuropsychiatric disorders such as addiction, cognitive deficits, depression, schizophrenia, and Parkinson’s disease. Genetic studies have shown two polymorphic variants of the D3R gene resulting from substitution of serine to glycine at position nine of the amino terminus. Isoform 5 of adenylyl cyclase (AC5) is one of the nine transmembrane bound ACs in the brain and myocardium. Previous studies in rats have shown that AC5 is expressed in the striatum, nucleus accumbens and olfactory tubercle and at lower levels in islands of Calleja, where the D3R is also expressed. Previous studies showed that although D2R and D4R inhibit ACs activity in different cell types, inhibition of ACs by D3R is weak and often undetectable. It has been shown that D3R selectively inhibits AC5 activity in human embryonic kidney 293 (HEK293) cells co-transfected with D3R and AC5. Co-expression of D3R and AC5 in brain regions which are major coordinators of normal and pathological movement, and the selective inhibition of AC5 activity by D3R raise the possibility of a functional link between AC5 and D3R in the modulation of signal transduction and trafficking. I hypothesized that AC5 plays a unique role in modulation of D3R trafficking and signaling pathways through interaction between D3R and AC5. Herein, I demonstrated an interaction between D3R and AC5 in vivo and in vitro using reciprocal co-immunoprecipitation/immunoblotting (co-IP/IB) assays. Interestingly, DA may facilitate the formation of protein complex between D3R and AC5 in vitro. Radio ligand binding assays revealed that heterodimerization of D3R polymorphic variants with AC5 does not change ligand binding affinity and expression of the D3R. Furthermore, taking advantages of GloSensor assays, selective inhibition of AC5 activity by D3Ser9 and D3Gly9 has been shown following activation by DA and quinpirole. Using ELISA studies showed that AC5 promotes cell surface expression and total expression of D3Ser9 and D3Gly9. Moreover, ELISA results suggested that AC5 facilitates DA-induced D3Ser9 endocytosis in dynamin and β-arrestin 2 dependent process, while having no effect on D3Gly9 polymorphic variant. The results also revealed that AC5 attenuates heterologous (PKC-induced) internalization of D3Ser9, while it does not have any effect on D3Gly9 heterologous internalization. My results also displayed a complex formation between D3R, AC5 and, β-arrestin 2 under basal and DA stimulation conditions, which emphasize the role of β-arrestin 2 in D3R signal transduction. Overall, a new regulatory mechanism for D3R has been suggested. My results suggested that complex formation between both D3R polymorphic variants with AC5 can regulate signaling and trafficking properties of D3R without changing the binding affinity of the receptor. These data will be meaningful for understanding of diseases and developing treatment strategies.
1336

Many-Body effects in Semiconductor Nanostructures

Wesslén, Carl-Johan January 2014 (has links)
Low dimensional semiconductor structures are modeled using techniques from the field of many-body atomic physics. B-splines are used to create a one-particle basis, used to solve the more complex many-body problems. Details on methods such as the Configuration Interaction (CI), Many-Body Perturbation Theory (MBPT) and Coupled Cluster (CC) are discussed. Results from the CC singles and doubles method are compared to other high-precision methods for the circular harmonic oscillator quantum dot. The results show a good agreement for the energy of many-body states of up to 12 electrons. Properties of elliptical quantum dots, circular quantum dots, quantum rings and concentric quantum rings are all reviewed. The effects of tilted external magnetic fields applied to the elliptical dot are discussed, and the energy splitting between the lowest singlet and triplet states is explored for varying geometrical properties. Results are compared to experimental energy splittings for the same system containing 2 electrons.
1337

Semilinear Systems of Weakly Coupled Damped Waves

Mohammed Djaouti, Abdelhamid 06 August 2018 (has links)
In this thesis we study the global existence of small data solutions to the Cauchy problem for semilinear damped wave equations with an effective dissipation term, where the data are supposed to belong to different classes of regularity. We apply these results to the Cauchy problem for weakly coupled systems of semilinear effectively damped waves with respect to the defined classes of regularity for different power nonlinearities. We also presented blow-up results for semi-linear systems with weakly coupled damped waves.
1338

Models in nonlinear condensed-matter optics: From theory to experiment

Voit, Kay-Michael 12 April 2013 (has links)
Cumulative Dissertation on models in nonlinear condensed-matter optics. In chapter 2, the coupled-wave theory first introduced by Kogelnik is reviewed and extended with emphasis on out-of-phase mixed holographic gratings. This class of gratings becomes increasingly important due to novel methods of hologram recording and new classes of materials and metamaterials like holographic polymer dispersed liquid crystals. Additionally, advances in laser technology suggest a stronger spectro- scopic view on holography. The model presented in this thesis accounts for both of these demands and provides a closed analytical solution. Chapter 3 contributes to the field of space-charge waves (SCW), which provides powerful tools for material analysis, especially in semiconductor technology. Although the underlying theory is generally understood, recent improvements of the ex- perimental techniques required extensions of the model and the interpretation of new effects. In this thesis, the existing formalism is adapted to a new method of excitation, which not only simplifies the experimental setup, allowing for easier adoption into industrial environments, but also provides insight into the direction of carrier motion. Furthermore, the model is extended to describe the influence of an external magnetic field, adding the possibility to examine the Hall mobility of carriers. Eventually, chapter 4 studies the dynamics of light induced absorption in pho- tochromic [Ru(bpy)2 (OSO)]+ . Compared to other photofunctional compounds, this molecule is nontoxic and exhibits exceptional photochromic reactions. These properties make it a promising candidate for important industrial and technological applications, ranging from data storage to non-electronic computation. For a profound analysis, the models used for the description of photofunctional molecules have been completely revised to account for the pronounced absortion changes in the material. Furthermore, a setup with orthogonal pump and probe beams is modeled and exper- imentally tested. This novel geometry is introduced to resemble common industrial setups.
1339

Transferts et réactivité de l’huile au cours du procédé de friture / Oil-related mass transfer and reactivities during deep frying process

Touffet, Maxime 29 August 2018 (has links)
La friture profonde de type batch a été étudiée dans le projet FUI Fry’In (Réf. AAP17, 2014-2018) dans le but de proposer des innovations de rupture pour des friteuses batch domestiques et professionnelles. La thèse a appuyé le projet sur la maîtrise de deux effets négatifs de la friture : i) la thermo-oxydation de l’huile responsable des mauvaises odeurs et produits de dégradation ainsi que ii) la prise d’huile généralement favorisée au détriment de son égouttage. L’étude a été réalisée en combinant des mesures directes (spectroscopie et imagerie infrarouges en mode ATR, photo-ionisation, mesures DSC, imagerie rapide…) et modélisation multi-échelle (écoulement de l’huile et égouttage lors du retrait, description lagrangienne des réactions en présence d’un écoulement, couplage avec les ciné-tiques de dissolution de l’oxygène). La complexité du processus de thermo-oxydation a été réduite en considérant les hydroperoxydes comme une forme de stockage organique de l’oxygène, qui propage l’oxydation dans des régions en anoxie. Leur décomposition produit de nombreux composés de scission, dont la nature est influencée par les conditions locales de température et de concentration en oxygène. La prise d’huile a été décrite comme le bilan net entre l’huile charriée au moment du retrait et l’huile égouttée. L’égouttage a été étudié sur des barreaux métalliques et des produits réels. Il se conduit à la formation de quatre à huit gouttes en quelques secondes. Les cinétiques de drainage anisothermes ont été prédites par un modèle mécanistique. Le mécanisme spécifique de prise d’huile en cours de friture a été aussi analysé ; il se produit uniquement dans le cas des produits préfrits congelés. / Batch deep-frying has been investigated within the collaborative project FUI Fry’In (ref. AAP17, 2014-2018) with the aim of proposing breakthrough innovations for small and medium size appliances. The PhD thesis was part of the project and focused on two specific adverse effects of deep-frying on food products: oil thermo-oxidation responsible for break-down products and off-flavors, and oil pickup process usually favored relatively to oil dripping. The work was carried out by combing direct measurements (FTIR-ATR spectroscopy and imaging, photoionization, DSC measurements, fast imaging…) and multiscale modeling (oil flow and oil dripping during product re-moval, Lagrangian description of reactions in aniso-thermal flows, coupling with oxygen dissolution kinetics). The complex problem of thermo-oxidation was split into simpler mechanisms by noticing that hydroperoxides are a kind of long-lived form of or-ganic oxygen, which trigger propagation in deep re-gions under anoxia. Their decomposition lead to various scission products, which were shown to be in-fluenced by both local temperature and oxygen con-centration. Oil uptake was described as the net balance between the amount of dragged oil during product removal and oil dripping at the tips of the product. The dripping process studied on both metal-lic sticks and real products occurs in less than few seconds and leads to a formation of four to eight drop-lets. The detailed drainage kinetics in anisothermal conditions were captured and predicted with the pro-posed mechanistic models. The specific mechanism of oil uptake during the immersion stage was eluci-dated and was shown to occur only in parfried frozen products.
1340

Modélisation numérique instationnaire pour la simulation du soudage TIG avec couplage plasma / bain de fusion / Unsteady numerical simulation of GTA welding process with plasma / weld pool coupling

Yau, Xavier 15 February 2018 (has links)
Compte tenu de l'importance de maintenir une qualité optimale des cordons de soudure et l'impossibilité d'assurer tout risque de manque de pénétration et de fusion par des contrôles non-destructifs, cette thèse permettra de développer une expertise et des outils numériques pour la simulation numérique tridimensionnelle des procédés de soudage par fusion afin de prédire la géométrie finale du cordon. Pour ce faire, on implémente une méthode de suivi d'interface afin d'améliorer la prise en compte des phénomènes thermophysiques au niveau des surfaces libres déformables. Cela permettra en outre de prendre en compte les forces agissant à la surface du bain métallique telles que la tension de surface, la gravité et la pression d'arc. Puis, il est envisagé d'améliorer l'estimation du transfert thermique entre l'arc et les pièces à assembler via un couplage instationnaire des modèles de plasma et de bain de fusion pour ainsi simuler de façon optimale la forme finale du cordon de soudure. Cette thèse permettra de traiter certaines applications industrielles spécifiques à EDF, en particulier les soudures d'étanchéité de faible épaisseur, permettant des études approfondies sur les opérations de réparations par soudage en corniche. / In order to ensure total safety during maintenance operations within nuclear power plants, it is mandatory to preserve the optimal quality of the internal weld beads. To this end, we use Computational Magnetohydrodynamics to simulate adjacent phenomena within the plasma and the weld pool in order to improve the knowledge of welding operating process. One of the difficulties is to take into account the effects induced by the thermal gradient and the variations of surfactant element concentrations on the weld pool surface known as the Marangoni effect. In order to take into account all the physical phenomena at the plasma / weld pool interface, we use an interface tracking method (Arbitrary Lagrangian-Eulerian) to improve the simulation of weld pool with free surfaces. Subsequently, it enables to capture more precisely the interfacial forces such as the Marangoni effect, the arc pressure and the gravity, and improve vertical welding simulation. Thus, this work is part of the development of a tridimensional unsteady two-way coupling in order to overcome the Gaussian boundary condition used to model the heat transfer from plasma torch towards the work piece surface. Ultimately, we could obtain an unified model for an optimal welding process simulation.

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