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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.
51

Optimalizace návrhu energetické renovace školských budov / Optimisation of energy renovation of school buildings

Mocová, Pavla January 2018 (has links)
The dissertation thesis is focused on a methodology of optimal design energy renovation of school buildings. The thesis is focused on the analysis of selected school buildings during the last 100 years of construction in the first phase. At this phase, are found some important information, especially in terms of the energy performance of the building envelope and results of this parts. Last but not least, CO2 emissions were detected. In the next part of this work, one selected school is assessed in terms of the quality of the environment, due to the evaluation of microbial microclimate on building structures, CO2 concentration and daylight. CO2 concentration and classroom daylight is addressed both for the original and for the new state. Another point of this thesis is the appreciation of the size of the classrooms in the schools both in terms of typological principles and in terms of the average size of classrooms. The daylight assessment is performed on these selected sizes, which is a part of the "PaMo I" design tool. In the next phase of the dissertation was created the design tool "PaMo I". This tool solves the evaluation of the renovation of school buildings from the point of view of the thermal engineering in connection with the influence of the daylight illumination on the classrooms of the school buildings by the thickness of the insulation system and the replacement of the windows. Part of the design tool is also the financial quantification of the investment, the payback period and the impact on the environment of the individual variants. The choice of variant options has been used when making a design tool user decision. The result of this work is a design tool which will help in deciding and finding the optimal alternative to the energy renovation of a school building in connection with daylighting inside classrooms.
52

ELECTRONIC AND OPTICAL PROPERTIES OF FIRST-ROW TRANSITION METALS IN 4H-SIC FOR PHOTOCONDUCTIVE SWITCHING

Timothy Sean Wolfe (11203593) 29 July 2021 (has links)
<div>Photoconductive Semiconductor Switches (PCSS) are metal-semiconductor-metal devices used to switch an electrical signal through photoconduction. Rapidly switched PCSS under high bias voltages have shown remarkable potential for high power electronic and electromagnetic wave generation, but are dependent on precise optoelectronic material parameters such as defect ionization energy and optical absorption. These properties can be measured but are difficult to attribute definitively to specific defects and materials without the aid of high-accuracy, predictive modeling and simulation. This work combines well-established methods for first principles electronic structure calculations such as Density Functional Theory (DFT) with novel modern approaches such as Local Moment Counter Charge (LMCC) boundary conditions to adequately describe charge states and Maximally Localized Wannier Functions (MLWF) to render the summation of optical excitation paths as computationally tractable. This approach is demonstrated to overcome previous barriers to obtaining reliable qualitative or quantitative results, such as DFT band gap narrowing and the prohibitive computational cost of coupled electron-phonon processes. This work contributes electronic structure calculations of 4H-SiC doped with first-row transition metals (V through Ni) that are consistent with prior published work where applicable and add new possibilities for prospective semi-insulating metal-semiconductor systems where investigating new dopant possibilities. The results indicate a spectrum of highly localized, mid-gap, spin-dependent defect energy levels which suggest a wider range of potential amphoteric dopants suitable for producing semi-insulating material. Additionally, this work contributes MLWF-based calculations of phonon-resolved optical properties in 3C and 4H-SiC, indirect gap semiconductors, which accurately produce the expected onset of optical absorption informed by experiment. These results were further expanded upon with small V-doped cells of 4H-SiC, which while not fully converged in terms of cell size still provided a qualitative point of comparison to the ground state results for determining the true optical excitation energy required for substantial photoconductivity. The subsequent speculative analysis suggests the importance of anisotropic absorption and alternative metal defects for optimizing high current optoelectronic devices such as PCSS.</div>
53

THE EFFECT OF MOLECULAR DESIGN ON SPIN DENSITY LOCALIZATION AND RADICAL-INITIATED DEGRADATION OF CONJUGATED RADICAL CATIONS

Kaelon Athena Jenkins (16613448) 19 July 2023 (has links)
<p> Radical species are essential in modern chemistry. In addition to fundamental chemistry, their unique chemical bonding and distinct physicochemical features serve critical functions in materials science in the form of organic electronics. Due to their high reactivity, radicals of the main group element are often transient. In recent years, remarkably stable radicals are often stabilized by π-delocalization, sterically demanding side groups, carbenes, and weakly coordinating anions. The impacts of modifications such as electron-donating, electron-withdrawing, and end-capping on the spin density distribution and thermodynamic and kinetic stability of archetypal radical-driven processes such as dimerization are not well understood. This dissertation aims to track the perturbation of spin density from EDG and EWG modifications, provide mechanistic insight into the radical-initiated reactions of conjugated radical cations, and establish correlations between molecular design and thermochemical properties and their resulting kinetic stability by computationally evaluating these characteristics against experimental data. The disclosed connections give useful new recommendations for the rational design of thermodynamically and kinetically stable novel materials.</p>
54

Rheology of suspension of fibers: Microscopic interaction to macroscopic rheology

Md Monsurul Islam Khan (6911054) 21 July 2023 (has links)
<p>Fibre suspensions in the fluid medium are common in industry, biology, and the environment. Industrial examples of concentrated suspensions include fresh concrete, uncured solid rocket fuel, and biomass slurries; natural examples include silt transfer in rivers and red blood cells in the blood.  These suspensions often include a Newtonian fluid as their suspending medium; still, these suspensions exhibit a plethora of non-Newtonian properties, such as yield stresses, rate-dependent rheology, and normal stresses, to name a few. Other than volume fraction, the type of fiber material, the presence of fluid-fiber or fiber-fiber interactions such as hydrodynamic, Brownian, colloidal, frictional, chemical, and/or electrostatic determine the rheological behavior of suspension. The average inter-fiber gaps between the neighboring fibers decrease significantly as the suspension volume fraction move towards a concentrated regime. As a result, in this regime, inter-fiber interactions become dominant.  Moreover, the surface asperities are present on the fiber surface even in the case of so-called smooth fibers, as fibers in real suspensions are not perfectly smooth. Hence, contact forces arising from the direct touching of the fibers become one of the essential factors in determining the rheology of suspensions.</p> <p>We first describe the causes of yield stress, shear thinning, and normal stress differences in fibre suspensions. We model the fibers as inextensible continuous flexible slender bodies with the Euler-Bernoulli beam equation governing their dynamics suspended in an incompressible Newtonian fluid. The fiber dynamics and fluid flow coupling is achieved using the immersed boundary method (IBM). In addition, the fiber surface roughness lead to inter-fiber contacts resulting in normal and tangential forces between the fibers, which follow Coulomb’s law of<br> friction. The surface roughness is modeled as hemispherical protrusions on the fiber surfaces. In addition to the comparison of the computational model to the experimental results, we demonstrate that attractive interactions lead to yield stress and shear thinning rheology.</p> <p>Furthermore, we investigate the effects of fiber aspect ratio, roughness, flexibility, and volume fraction on the rheology of concentrated suspensions. We find that the suspension viscosity increases with increasing the volume fraction, roughness, fiber rigidity, and aspect ratio. The increase in relative viscosity is the macroscopic manifestation of a similar increase  in the microscopic contact contribution with these parameters. In addition, we observe positive and negative first and second normal stress differences, respectively, in agreement with previous experiments. Lastly, we propose a modified Maron-Pierce law to quantify the the jamming volume fraction with varying fiber aspect ratio and roughness. Additionally, we provide a constitutive model to calculate the viscosity at various volume fractions, aspect ratios, and shear rates.</p>
55

LIGHT AND CHEMISTRY AT THE INTERFACE OF THEORY AND EXPERIMENT

James Ulcickas (8713962) 17 April 2020 (has links)
Optics are a powerful probe of chemical structure that can often be linked to theoretical predictions, providing robustness as a measurement tool. Not only do optical interactions like second harmonic generation (SHG), single and two-photon excited fluorescence (TPEF), and infrared absorption provide chemical specificity at the molecular and macromolecular scale, but the ability to image enables mapping heterogeneous behavior across complex systems such as biological tissue. This thesis will discuss nonlinear and linear optics, leveraging theoretical predictions to provide frameworks for interpreting analytical measurement. In turn, the causal mechanistic understanding provided by these frameworks will enable structurally specific quantitative tools with a special emphasis on application in biological imaging. The thesis will begin with an introduction to 2nd order nonlinear optics and the polarization analysis thereof, covering both the Jones framework for polarization analysis and the design of experiment. Novel experimental architectures aimed at reducing 1/f noise in polarization analysis will be discussed, leveraging both rapid modulation in time through electro-optic modulators (Chapter 2), as well as fixed-optic spatial modulation approaches (Chapter 3). In addition, challenges in polarization-dependent imaging within turbid systems will be addressed with the discussion of a theoretical framework to model SHG occurring from unpolarized light (Chapter 4). The application of this framework to thick tissue imaging for analysis of collagen local structure can provide a method for characterizing changes in tissue morphology associated with some common cancers (Chapter 5). In addition to discussion of nonlinear optical phenomena, a novel mechanism for electric dipole allowed fluorescence-detected circular dichroism will be introduced (Chapter 6). Tackling challenges associated with label-free chemically specific imaging, the construction of a novel infrared hyperspectral microscope for chemical classification in complex mixtures will be presented (Chapter 7). The thesis will conclude with a discussion of the inherent disadvantages in taking the traditional paradigm of modeling and measuring chemistry separately and provide the multi-agent consensus equilibrium (MACE) framework as an alternative to the classic meet-in-the-middle approach (Chapter 8). Spanning topics from pure theoretical descriptions of light-matter interaction to full experimental work, this thesis aims to unify these two fronts. <br>

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