• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 356
  • 228
  • 61
  • 47
  • 23
  • 19
  • 10
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • Tagged with
  • 913
  • 913
  • 208
  • 205
  • 162
  • 159
  • 122
  • 111
  • 88
  • 86
  • 75
  • 71
  • 71
  • 65
  • 59
  • 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.
441

Accurate Energetics Across the Periodic Table Via Quantum Chemistry

Peterson, Charles Campbell 12 1900 (has links)
Greater understanding and accurate predictions of structural, thermochemical, and spectroscopic properties of chemical compounds is critical for the advancements of not only basic science, but also in applications needed for the growth and health of the U.S. economy. This dissertation includes new ab initio composite approaches to predict accurate energetics of lanthanide-containing compounds including relativistic effects, and optimization of parameters for semi-empirical methods for transition metals. Studies of properties and energetics of chemical compounds through various computational methods are also the focus of this research, including the C-O bond cleavage of dimethyl ether by transition metal ions, the study of thermochemical and structural properties of small silicon containing compounds with the Multi-Reference correlation consistent Composite Approach, the development of a composite method for heavy element systems, spectroscopic of compounds containing noble gases and metals (ArxZn and ArxAg+ where x = 1, 2), and the effects due to Basis Set Superposition Error (BSSE) on these van der Waals complexes.
442

Substance flow analysis of rare earth elements and precious metals from end-of-life vehicles including next-generation vehicles / 次世代自動車を含む使用済み自動車からの希土類元素と貴金属の物質フロー分析

Xu, Guochang 23 July 2019 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22011号 / 工博第4623号 / 新制||工||1720(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 酒井 伸一, 教授 高岡 昌輝, 准教授 平井 康宏 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
443

Crystal Structural Control of Nanomaterials toward High-Performance Permanent Magnets / 高性能永久磁石創製を目指したナノ材料の結晶構造制御

Matsumoto, Kenshi 25 November 2019 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22114号 / 理博第4541号 / 新制||理||1652(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 若宮 淳志 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM
444

Water and rock geochemical characterization to clarify fluid circulation process in transitional geothermal reservoir with a case study of the Wayang Windu field, West Java, Indonesia / 水と岩石の地球化学的特徴抽出による遷移型地熱貯留層での流体循環プロセスの解明とインドネシア西ジャワ ワヤン ウインドゥ地区への適用

Riostantieka, Mayandari Shoedarto 23 March 2020 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22425号 / 工博第4686号 / 新制||工||1731(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 小池 克明, 教授 立川 康人, 准教授 柏谷 公希 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
445

Design of rare-earth-doped inorganic phosphors and luminescence enhancement by plasmonic effects / 希土類添加無機蛍光体の設計とプラズモンの効果によるルミネセンスの増強

Gao, Yuan 23 March 2020 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22452号 / 工博第4713号 / 新制||工||1736(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 田中 勝久, 教授 三浦 清貴, 教授 藤田 晃司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
446

Spatially Explicit Assessment of Environmental Impacts in the Electronics Sector

Kali Diane Frost (11813585) 09 December 2021 (has links)
<div>As society rapidly migrates to digitized services, the Information, Communications, and Technology (ICT) sector is projected to sustain a 16% compound annual growth rate (CAGR) over the next five years, surpassing $1 trillion in revenue by 2024. The hardware infrastructure that supports ICT growth, such as semiconductor chips and hard disk drives (HDDs), is also experiencing parallel growth trajectories. Thus, large technology companies need to understand the environmental implications of growth in these vital components within their supply chains, as they strive to reach ambitious targets for carbon, water, and waste reduction.</div><div><br></div><div>Life cycle assessment (LCA) is a powerful tool for measuring environmental impacts along the life cycle of a product and is implemented here to measure emissions and resource use in the semiconductor and HDD manufacturing supply chains, and to quantify the benefits of circularity for HDD components. However, to understand how environmental impacts of a manufacturing process relate to the landscapes (i.e. ecosystems) where manufacturing occurs, one must look to methods beyond LCA. </div><div><br></div><div>Footprinting methods are a promising tool for bridging the gap between LCA process data inventories and site-specific impacts on ecosystems. Further, the footprint assesses the total volume of emission over a time period, which is aligned with the concept of absolute sustainability. As such, regionalized footprint methods for freshwater use in the semiconductor industry and toxic chemical pollution for the HDD rare earth magnet supply chain were undertaken. In each case, data from the LCA literature or custom LCAs were used as the basis for the life cycle inventory, but advanced methods including regional databases of water scarcity and toxicity factors were used to quantify and communicate impacts. Further, geographic information systems (GIS) were used to allocate emissions or water use from a manufacturing facility with their associated watershed, which enabled aggregation of data across various geographies (i.e. watershed, region, country). </div><div><br></div><div>This work implements multi-disciplinary methods, databases, and tools with the aim to bring water and chemical footprinting methods a step closer towards meaningful assessment of a product’s impact on local, regional, and planetary boundaries. </div><div><br></div>
447

Toward lanthanide containing coordination polymers and nanomaterials

Unknown Date (has links)
The focus of this thesis is to develop lanthanide (Ln) luminescent materials through the exploration of coordination polymers and nanomaterials. Herein, dimethyl-3,4- furanedicarboxylate acid undergoes hydrolysis under hydrothermal conditions to form coordination polymers with lanthanide ions. The resulting coordination polymers exhibited luminescent properties, with quantum yields and lifetimes for the Eu-and Tb-CP of 1.14+-0.32% and 0.387=-0.0001 mx, and 3.33=-0.82% and 0.769=-0.006 ms, respectively. While the incorporation of lanthanides was not achieved in this work, progress toward the production of pure phase InP in the nanoregime has been made, using a low-cost, hydrothermal method. Through SEM and PXRD conflict, it is believed that pure INP particles with a size range of 58-81 nm were successfully synthesized. / by Natalie E. Greig. / Thesis (M.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.
448

Réactions intramoléculaires de formation de liaison carbone – oxygène, sur des systèmes insaturés non activés, catalysées par des complexes de terres rares / Intramolecular C-O bond formation of non-activated insaturations catalyzed by rare earth complexes

Carlino, Romain 26 October 2016 (has links)
Ce travail de thèse s’est focalisé sur la formation de liaisons carbone-oxygène à partir d’alcènes et d’allènes non activés via des réactions intramoléculaires d’hydroalcoxylation ou d’hydroacylalcoxylation catalysées par des complexes de terres rares.Premièrement, la version racémique de ces réactions catalysées par deux systèmes différents a été étudiée : les tri-alkyls ainsi que les triflates de terres rares. Lors de cette étude, les différents effets stériques ou électroniques ainsi que les différentes substitutions sur l’insaturation ont été évalués. Pour les deux systèmes catalytiques, une sélectivité Markovnikov a été mise en évidence ; pour chacun de ces systèmes catalytiques deux mécanismes différents sont proposés. En effet, en plus des propriétés acide de Lewis, le fait que les alkyls de terres rares soient des bases de Brønsted, explique la différence de comportement catalytique des deux systèmes.Par la suite, ces réactions ont été étudiées dans leur version asymétrique. Pour cela, différents ligands chiraux ont été associés au triflate de scandium ; d’autre part, de nouveaux complexes mono-alkyl binaphtolate de terres rares dérivés des tri-alkyls ont également été synthétisés. Avec ces derniers, des éthers cycliques ont été obtenus avec des excès énantiomériques allant jusqu’à 34%.Etant donné que les triflates de terres rares ont montré une très bonne activité et que les mono-alkyl binaphtolates de scandium et d’yttrium ont conduit à d’encourageantes énantiosélectivités, il a été proposé de créer un nouveau complexe de terre rare muni de ligands chiraux associés par des liaisons ioniques ; les premiers essais de préparation de binaphtolate monotriflate de scandium et d’yttrium sont très prometteurs.Enfin, dans le cadre d’une collaboration, de nouveaux complexes de terres rares comportant des ligands dérivés de la BINAM ont été synthétisés et une étude RMN HMBC ¹H/¹ ⁵N a été réalisée afin de déterminer les différences forces de liaisons métal-azote. Ces complexes chiraux ont été notamment utilisés afin de mettre en évidence le concept de ligand relai avec la réalisation monotope de deux réactions métallocatalysée et organocatalysée consécutives. / This thesis is focused on intramolecular carbon-oxygen bond formation of non-activated alkenes and allenes by hydroalkoxylation or hydroacylalkoxylation reactions catalyzed by rare earths complexes.Firstly, the racemic version of these reactions catalyzed by two different systems has been studied: tri-alkyls and triflate rare earth. In this study, different steric or electronic effects and different substitutions on insaturations have been evaluated. For both systems, Markovnikov selectivity was evidenced; two different mechanisms for each system have been proposed. Indeed, in addition to the Lewis acid properties, the fact that rare earth alkyls are also Brønsted bases, could explain the difference of catalytic behavior of these systems.Thereafter, enantioselective versions of these reactions have been studied. For that, different chiral ligands have been associated on scandium triflate; on the other hand, new mono-alkyl binaphtholate complexes from tri-alkyl complexes have been synthesized. Therewith, cyclic ethers have been obtained with enantiomeric excesses up to 34%.As triflate rare earths have shown an excellent activity and yttrium and scandium mono-alkyl binaphtholate led to encouraging enantioselectivity, it has been proposed to create a new rare earth complex with chiral ligand associated with ionic bonds; the first tests of scandium and yttrium binaphtholate monotriflate preparation are very promising.Finally, in the frame of a collaboration, new rare earth complexes bearing ligands derived from BINAM have been synthesized and a HMBC ¹H/¹ ⁵N NMR study have been realized to determine the strength of the different carbon-nitrogen bonds. These chiral complexes have been especially used to highlight the concept of relay ligand with one pot consequent metallocatalyzed and organocatalyzed reactions.
449

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.
450

Rare-Earth Elements in the Swedish Alum Shale Formation: A Study of Apatites in Fetsjön, Västerbotten / Sällsynta jordartsmetaller i Sveriges alunskiffer: en studie av apatiter i Fetsjön, Västerbotten

Engström, Fredrik January 2019 (has links)
The Caledonian alum shales of Sweden host a vast number of economically interesting metals. In Fetsjön, Västerbotten, the shales contain significant amounts of rare-earth elements, vanadium, molybdenum and uranium. As metals with a multitude of high-technological applications, the former rare-earth elements (REEs) are particularly attractive in a world where the supply may be exhausted as the demand continuously increase while new deposits are not being discovered fast enough. Meanwhile, the latter uranium notably constitutes as an unwanted secondary product during the extraction of rare-earth elements. As the mineral association of the REEs in Fetsjön is unknown, the intent of this study is to analyze and thus determine their mineralogical expression. The assumed REE-bearing mineral apatite was confirmed to host the rare-earths in the Fetsjön shales after microscopy and spectrometry analyses.

Page generated in 0.0472 seconds