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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.
1

A study of structure, electrical and optical properties of some vanadate glasses

Hosseini, A. A. January 1982 (has links)
Studies of semiconducting glasses have become of great interest in recent years because of their importance in the theory of solid state physics and in their applicability to electronic devices. Of these classes of materials the transition metal oxide glasses are much the most thoroughly studied. In these glasses the transition metal oxide e. g. V205-TiO2-MoO39 WO3, Cu0 is a major constituent i.e > 50 mol%. We start this work with a discussion about a critical review of the history, formation and modern theory of non-crystalline semiconductors in general and glassy state in particular. The aim of the experimental work in present study is to check the validity of the theories and models proposed so far to explain the origin and the nature of the charge carriers, structure, electrical and optical properties of some transition metal oxide glasses based on vanadium pentoxide. For this purpose series of binary V205-P205 glass samples containing 50 to 90 mol% V205 as well as ternary V2015-P205-Te02 glasses containing 60 mol% V2051 (40-x) mol% P205 and x mol% Te02 in which x varies from 5 to 35 were prepared by normal cooling from the melt. It was found that the glass forming region of the system under consideration is fairly large and in binary V205-P205 systems, glass with up to 95 moll V205 could be prepared. Density measurements indicate that in binary V205 - P205 glasses the density increases linearly with increasing V205 content and in ternary V205 - P205 - TeO2 systems density increases with increasing Te02 content. It was also found that the density of both systems are affected by annealing temperature. Electron spin resonance (E.S.R.) studies show that in vanadate glasses, the vanadium exists in more than one valency state mainly V5+ and V4+ of which V4+ is paramagnetic and detectable by E. S. R. This could be taken as some evidence of a hopping conduction mechanism in vanadate glasses and conduction is due to transfer of charge form V4+ to V5+ ions and this is discussed in the terms of small polaron. It is found that the conduction in these glasses is Ohmic up to a field of the order of 4x 105 Vcm-1 with an activation energy range from 0.31 to 0.48 e.V depending on composition and independent of temperatures in our range of temperature (above room temperature). Above this field conduction becomes non-Ohmic which is found to be due to lowering the potential barrier of the carriers at high electric field as was predicted by Poole and Frenkel. Memory switching is observed in thin blown film samples of both binary and ternary glass systems, which is associated with field-induced crystallization of a localized region and formation of conductive channel in the switched area due to self heating effect. In other words the conducting zone consists of VO2 crystals which possess more metal-like conductivity. Infra-red absorption spectra of these glasses revealed that some of the absorption bands of glasses and crystalline V205 are similar which is some evidence that the vanadium ions exists in six-fold co-ordination in disordered glassy systems as well as ordered crystalline V205. The fundamental absorption edge of these glasses occurs in the short wave length region of the visible and is dependent on composition, and the fundamental absorption arises form direct forbidden transitions and occurs at a photon energy of about 1.9-2.6 e.V depending on composition. The absorption edge in these glasses is found to be of the same order of magnitude as that in crystalline V205.
2

THERMAL SYSTEM ANALYSIS OF AN ELECTRIC VEHICLE AND THE INFLUENCE OF CABIN GLASS PROPERTIES

Andrew Penning (14202806) 01 December 2022 (has links)
<p>  </p> <p>As consumer adoption and total energy consumption of electric vehicles continues to rapidly increase, it is important to develop comprehensive system modeling frameworks that consider the complex interactions of their mechanical, electrical, and thermal subsystems to guide component technology development. This thesis studies the influence of cabin glass properties on the performance of an electric vehicle thermal system and overall cabin design considerations. The work first builds a generic long-range electric vehicle dynamic thermal system model while considering the system architecture, component sizing, control scheme, and glass properties. This comprehensive system model is used to assess the influence of cabin glass radiative properties on vehicle performance. The system model incorporates simplified models for all salient components in the electric traction drive, cabin HVAC, and battery subsystems, and uses a higher fidelity cabin thermal model that is able to capture the individual properties of the cabin glass used in the vehicle. To study the cabin model in isolation, a heat-up scenario is used to find that a cabin air temperature reduction of 8 °C through the use of different glass properties alone. Additionally, the cabin model is run repeatedly to produce a large data set that is trained using a machine learning regression model. This surrogate regression model that is used to reduce the computational time allowing for fast studies of glass properties and build an application engineering tool. The overall system performance is then evaluated under a dynamic NEDC drive cycle which is repeated until battery depletion to determine a vehicle range. A system validation is done on the HVAC subsystem by using steady-state thermodynamic analysis and comparing to the dynamic system model. This results in good agreement between four different subsystem modeling approaches. The system model is used to study five different glazing design cases, each corresponding to different transmission and reflection properties of the glass, by predicting their impact on the vehicle range. The cases span all theoretically possible glass properties while also enabling inspection of practical glass technologies that are available or under development to be adopted in modern electric vehicles. The influence of glass on vehicle range is then further compared at various locations across the United States to understand and illustrate the effects of ambient conditions and solar load. The system model predicts a vehicle range of 188.5 miles under a high solar loading scenario typical for Phoenix, AZ using traditional glass properties, which increases to a range of 221.6 miles using high-performance glass properties, representing a significant potential gain of 33.1 miles using technologies available on the market today. Under this same loading scenario, the glass properties at their extreme physical limits could theoretically affect the vehicle range by up to 92.5 miles. The influence of the glass properties is location-specific, and the model predicts that using the same glass at different locations can affect the range of vehicle by up to 100.8 miles for traditional glass properties and 73.4 miles for high-performance glass properties. </p>

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