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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.
291

Vlivy působící na vznik a velikost interpenetrační vrstvy při lakování polykarbonátových výlisků / Influences on the Creation and Size of Interpenetration Layers During Lacquering of Polycarbonate Moldings

Svobodová, Hana January 2020 (has links)
Diploma thesis is focused on influences on the creation and size of interpenetration layers during lacquering of polycarbonate mouldings. In the diploma thesis there is a complete description of the production of the external lens for the automobile headlight. The experimental part consists of five experiments. The subject of the experiment is to find the most optimal process settings or other solutions that would lead to positive results of chemical tests. During the tests the individual phases of the production process are examined. After each experiment follows execution and evaluation of chemical tests in the reliability laboratory.
292

Studium optických vlastností tenkých vrstev prekurzorů pro přípravu monokrystalů perovskitů FAPbBr3 / Study of optical properties of thin films of perovskiteFAPbBr3 precursors

Smolková, Denisa January 2021 (has links)
This thesis examines the preparation of thin layers of material for photovoltaic applications with focused on perovskites and determining their optical properties. Basic information about the photovoltaic panels, especially about the perovskites, and the preparation of thin layers is supplied in the theoretical section. This section includes description of optical properties and the main method of study of optical properties, spectroscopic ellipsometry. Experimental section is focused on the preparation of thin layers of perovskites FAPbBr3 and its precursors by spin-coating. Optical properties are evaluated using profilometry, UV VIS spectrometry and spectroscopic ellipsometry. The conclusion summarizes the results of this experiment with focused on comparison of ellipsometric spectrums of perovskites and its precursors.
293

Studium homogenity tenkých vrstev organických materiálů / Study of organic materials thin film homogenity

Lacinová, Eva January 2008 (has links)
This thesis deals with study homogeneity of thin organic layers using image analysis. The theoretical parts deal with preparation thin layers and some methods examining their surface, especially optical microscopy and profilometry. Optical microscope NIKON ECLIPSE E200, digital camera NIKON 5400 and computer was used for study homogeneity of organic layers by image analysis. Images of the organic layer and single electrodes, which were steamed on organic layer, were surveyed. Homogeneity of surfaces layers was assessed by errors related with common moments (roughness average, root mean square roughness, skewness, and kurtosis). Differences between single samples in connection with size their common moments and homogeneity are discussed at the close of this work.
294

Tenké transparentní vrstvy pro elektrochromní součástky / Thin layer for electrochromic devices

Pelčák, Vít January 2008 (has links)
This diploma thesis deals with creation of transparent conductive layers on glass substrate, which serve as underlay for electrochromic layers. Zinc acetate dissolved in methane and distilled water serves as basis of solution. We are searching for optimal amount of either Fluor or Boron in depositted solutions to achieve best transparency and layer conductivity.
295

Výzkum a vývoj technologie povrchových vrstev součástí valivých a kluzných ložisek / Research and Development of Technology for Surface Layers of Roll and Sliding Bearings Components

Němcová, Aneta January 2008 (has links)
To increase of bearing steels properties are research and development of surface modifications well above dedicated, in present. Basic requirements to the surface modifications are high wear resistance and good temperature resistance (origin by friction). Surface modifications can not negatively influence properties of bearing steels as a substrate. One of the possibilities can be used surface modifications used for high temperature applications. These are based on saturation of substrate surface layer by Al (and Si) elements. This work deals with preparing of Al and Al-Si diffusion layers from slurries on 100Cr6 bearing steel surface and study of elements interaction between coating and bearing steel as a substrate during proceeding of protective layers at high temperatures. To elements interaction study light microscopy, scanning electron microscopy equipped by energy dispersive microanalyses, glow discharge optical emission spectrometry and microhardness measurement methods were used. To the evaluation of layer thickness image analyses was used.
296

Synthèse et résistance mécanique des couches d'oxyde de zirconium / Synthesis and mechanical strength of zirconium oxide layers

Djuidje Dzumgam, Josiane Christelle 30 January 2018 (has links)
Le dépôt MOCVD, l’oxydation naturelle sous air et l’oxydation naturelle suivie d’un dépôt MOCVD ont été utilisés pour synthétiser des couches de zircone d’environ 1 µm d’épaisseur. Dans un premier temps, nous avons déterminé les conditions optimales pour le dépôt MOCVD sur le 304L et le Zy-4, à 400°C et 500°C. Les deux autres techniques nous ont permis d’obtenir des couches plus épaisses et de compositions différentes en termes de fractions de phases quadratique et monoclinique. Nous avons caractérisé les phases et les contraintes résiduelles dans les couches par DRX. Grâce à un chargement de flexion ou de traction dans l’enceinte d’un MEB, nous avons réalisé des essais de multifissuration. Sur le Zy-4, nous avons obtenu le schéma classique d’endommagement : apparition de fissures perpendiculaires à la direction d’extension, augmentation du nombre de fissures jusqu’à saturation de la multifissuration. Sur le 304L, nous avons observé une hétérogénéité de fissuration pour les couches les moins épaisses, qui peut être due à la taille des grains du substrat par rapport à l’épaisseur de couche. On montre que la distance entre les fissures à saturation ne dépend ni des phases, ni des contraintes résiduelles. Elle varie linéairement avec l’épaisseur de la couche. La modélisation par éléments finis des essais de flexion nous a permis d’obtenir la contrainte à l’amorçage des fissures. La résistance des couches ne dépend pas de la fraction de phase quadratique et ne semble pas dépendre des contraintes résiduelles, mais elle décroît lorsque l’épaisseur croît. La prise en compte des contraintes résiduelles pour expliquer l’amorçage des fissures conduit à supposer que ces contraintes sont fortement hétérogènes dans les couches. / MOCVD deposition, air thermal oxidation and thermal oxidation followed by MOCVD deposition were used to produce the zirconia layers. First, in order to obtain films of controlled thickness (a few microns), we determined the optimal MOCVD deposition conditions on the 304L and Zy-4, at 400°C and 500°C. The two other techniques allowed us to obtain thicker layers of different tetragonal phase fractions. The volume fraction of tetragonal phase of zirconia and the residual stresses in the layers was characterized by DRX. Multiple cracking tests were performed inside a SEM through bending or tensile tests. On the Zy-4, we obtained the classic damage scheme: cracks perpendicular to the extension direction appear and multiply until saturation. On the 304L, cracks were localized for the thinner layers; this may be due to the grain size of the substrate with respect to the layer thickness. For the layers obtained on Zy-4, the minimal distance between the cracks does not depend neither of the tetragonal phase fraction nor of the residual stresses. It varies linearly with the layer thickness. Using the finite element method, the stress at fracture initiation was obtained. It decreases with the increase of the layer thickness independently of the tetragonal phase fraction and of the residual stresses. To take into account the residual stresses in assessment of the layer strength, high residual stress gradient have to be supposed.
297

Évolution microstructurale et transition de phase induites par faisceaux d’ions dans des couches minces épitaxiées d’oxydes de terres rares / Microstructural evolution and phase transition induced by ion beams in epitaxial thin layers of rare earth oxides

Mejai, Najah 27 April 2017 (has links)
Après dopage, les oxydes de terres rares peuvent acquérir des propriétés optiques intéressantes pour les dispositifs d’optoélectronique du futur. Ces matériaux peuvent aussi être utilisés comme absorbant neutronique dans les réacteurs nucléaires. Que ce soit pendant le processus de dopage ou en réacteur, ces oxydes sont soumis à des conditions d’irradiation aux ions intenses. Il est alors important de comprendre leur comportement dans cet environnement extrême. C’est l’objectif de cette thèse durant laquelle a été menée une étude fondamentale de matériaux modèles (couches épitaxiées assimilables à des monocristaux) sous irradiation ionique. Les principaux résultats montrent qu’un changement de phase, de cubique à monoclinique, se produit sous irradiation. Cette transition, qui n’est pas directement pilotée par l’énergie déposée par les ions, a lieu en plusieurs étapes liées à des évolutions microstructurales distinctes. Enfin, la composition joue un rôle sur le changement de structure, l’oxyde de Gadolinium étant plus rapidement transformé que l’oxyde d’Erbium. / After doping, the rare earth oxides can acquire interesting optical properties for the optoelectronic devices of the future. These materials can also be used as neutron absorbers in nuclear reactors. Whether during the doping process or in the reactor, these oxides are subjected to irradiation conditions with intense ions. It is important to understand their behavior in this extreme environment. This is the objective of this thesis during which a fundamental study of model materials(epitaxial layers assimilable to single crystals)under ionic irradiation was conducted. The main results show that a phase change, from cubic to monoclinic, occurs under irradiation. This transition, which is not directly driven by the energy deposited by the ions, takes place in several stages linked to distinct microstructural evolutions. Finally, the composition plays a role in the change of structure, gadolinium oxide being more rapidly transformed than Erbium oxide.
298

Understanding a Block of Layers in Deep Neural Networks: Optimization, Probabilistic and Tropical Geometric Perspectives

Bibi, Adel 04 1900 (has links)
This dissertation aims at theoretically studying a block of layers that is common in al- most all deep learning models. The block of layers of interest is the composition of an affine layer followed by a nonlinear activation that is followed by another affine layer. We study this block from three perspectives. (i) An Optimization Perspective. Is it possible that the output of the forward pass through this block is an optimal solution to a certain convex optimization problem? We show an equivalency between the forward pass through this block and a single iteration of deterministic and stochastic algorithms solving a ten- sor formulated convex optimization problem. As consequence, we derive for the first time a formula for computing the singular values of convolutional layers surpassing the need for the prohibitive construction of the underlying linear operator. Thereafter, we show that several deep networks can have this block replaced with the corresponding optimiza- tion algorithm predicted by our theory resulting in networks with improved generalization performance. (ii) A Probabilistic Perspective. Is it possible to analytically analyze the output of a deep network upon subjecting the input to Gaussian noise? To that regard, we derive analytical formulas for the first and second moments of this block under Gaussian input noise. We demonstrate that the derived expressions can be used to efficiently analyze the output of an arbitrary deep network in addition to constructing Gaussian adversarial attacks surpassing any need for prohibitive data augmentation procedures. (iii) A Tropi- cal Geometry Perspective. Is it possible to characterize the decision boundaries of this block as a geometric structure representing a solution set to a certain class of polynomials (tropical polynomials)? If so, then, is it possible to utilize this geometric representation of the decision boundaries for novel reformulations to classical computer vision and machine learning tasks on arbitrary deep networks? We show that the decision boundaries of this block are a subset of a tropical hypersurface, which is intimately related to a the polytope that is the convex hull of two zonotopes. We utilize this geometric characterization to shed lights on new perspectives of network pruning.
299

Instability and Transition on a Sliced Cone with a Finite-Span Compression Ramp at Mach 6

Gregory R McKiernan (8793053) 04 May 2020 (has links)
<div>Initial experiments on separated shock/boundary-layer interactions were carried out within the Boeing/AFOSR Mach-6 Quiet Tunnel. Measurements were made of hypersonic laminar-turbulent transition within the separation above a compression corner. This wind tunnel features freestream fluctuations that are similar to those in</div><div>flight. The present work focuses on the role of traveling instabilities within the shear layer above the separation bubble.</div><div>A 7 degree half-angle cone with a slice and a finite-span compression ramp was designed and tested. Due to a lack of space for post-reattachment sensors, early designs of this</div><div>generic geometry did not allow for measurement of a post-reattachment boundary layer. Oil flow and heat transfer measurements showed that by lengthening the ramp, the post-reattachment boundary layer could be measured. A parametric study was completed to determine that a 20 degree ramp angle caused reattachment at 45% of the</div><div>total ramp length and provided the best flow field for boundary-layer transition measurements.</div><div>Surface pressure fluctuation measurements showed post-reattachment wave packets and turbulent spots. The presence of wave packets suggests that a shear-layer</div><div>instability might be present. Pressure fluctuation magnitudes showed a consistent transition Reynolds numbers of 900000, based on freestream conditions and distance</div><div>from the nosetip. Pressure fluctuations grew exponentially from less than 1% to roughly 10% of tangent-wedge surface pressure during transition.</div><div>A high-voltage pulsed plasma perturber was used to introduce controlled disturbances into the boundary layer. The concept was demonstrated on a straight 7 degree half-angle circular cone. The perturbations successfully excited the second-mode instability at naturally unstable frequencies. The maximum second-mode amplitudes prior to transition were measured to be about 10% of the mean surface static pressure. </div><div>The plasma perturber was then used to disturb the boundary layer just upstream of the separation bubble on the cone with the slice and ramp. A traveling instability was measured post-reattachment but the transition location did not change for any tested condition. It appears that the excited shear-layer instability was not the dominant mechanism of transition.</div>
300

Příprava a optické vlastnosti oxidových scintilačních materiálů / Preparation and optical properties of scintillation oxide layers

Hanuš, Martin January 2016 (has links)
In this work we studied properties of garnet scintillator layers (RxLu3-xAl5O12, RxY3-xAl5O12) doped by rare earth ions (Ce, Pr, Tb), orthosilicates (Y2SiO5; R = Ce, Tb) and influence of Sc codoping on Pr3+ and Tb3+ emissions. The Zr codoping on Ce3+ emission in orthosilicates was also studied. The samples were prepared by liquid phase epitaxy. The studied materials show high quantum efficiency and good chemical and mechanical stability. They represent ideal materials for 2D imaging devices. We studied optical absorption, excitation and emission spectra and scintillation properties (radiolunescence and photoelectron yield). The aim was to determine the properties of grown layers and their comparison to Czochralski grown single crystals. We looked for the impact of melt and growth conditions on measured layer properties. We also tried to determine optimal amount of dopants in layer. We used PbO - B2O3 and BaO - BaF2 - B2O3 fluxes. Using these fluxes, we succeeded in growing layers with less intrinsic defects in crystal lattice in comparison to single crystals. In grown layers of thickness from 1 to 30 µm higher dopant concentration was achieved than in single crystals.

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