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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.
471

Mineralisation and biomineralisation of radionuclides

Brookshaw, Diana Roumenova January 2013 (has links)
Management of contamination from industrial activities and wastes from nuclear power generation and weapons development are arguably amongst the greatest challenges facing humanity currently and into the future. Understanding the mobility of toxic radioactive elements is essential for successful remediation strategies and safe management of our nuclear waste legacy (DEFRA, 2008). Interactions between minerals and radionuclides, such as sorption and precipitation, govern the mobility of the contaminants through the subsurface environment. Microbial metabolic processes (redox cycling or release of metabolites) have the potential to affect drastically these abiotic interactions. Microbially-driven mineralisation processes could provide long-term solid-phase-capture solutions to radionuclide contamination problems and support safety cases for geological disposal of radioactive waste. The recent advancements at the intersection between mineralogy, microbiology and radiochemistry were reviewed with the aid of a cluster analysis (Self-Organising Map). This is a relatively novel method of creating a map of the ‘research landscape’ which provides a visual summary of the reviewed literature and can help to identify areas of promising and active research as well as less researched interdisciplinary areas. It is the first time this tool has been applied to research literature on this interdisciplinary topic, and it highlighted the need to gain further understanding of ternary systems including bacteria, minerals and radionuclides. The analysis showed that phyllosilicates are of interest, but few studies have explored the properties of the Fe(II)/Fe(III)-containing micas biotite and chlorite. The ability of model Fe(III)-reducing microorganisms to reduce Fe(III) in biotite and chlorite was demonstrated in batch model systems. In chlorite, approximately 20% and in biotite ~40% of the bulk Fe(III) was transformed to Fe(II) by this reduction. To our knowledge, this is the first study to show the availability of Fe(III) in biotite for such reduction and the ability of the model organism Shewanella oneidensis MR-1 to conserve energy for growth using Fe(III) in biotite as the sole electron acceptor. The microbial Fe(III) reduction led to a decrease in the sorption of Cs and Sr by chlorite, but had very little effect on sorption to biotite. The data indicate that remediation strategies based on microbial Fe(III) reduction may exacerbate the movement of Cs and Sr through strata where sorption is dominated by phyllosilicates, particularly chlorite. While microbial Fe(III) reduction had only a slight effect on the sorption properties of biotite and chlorite, it drastically altered their redox properties. Previously bioreduced biotite and chlorite readily removed Cr(VI), Tc(VII) and Np(V) by surface-mediated reduction. The minerals were also able to reduce U(VI), but solution chemistry affected this reaction, reflecting the complexity of the biogeochemistry of this actinide. Overall, this work highlights the importance of decoupling microbial and geochemical processes in developing a holistic understanding of radionuclide behaviour in the environment. This body of work forms the thesis is entitled ‘Mineralisation and Biomineralisation of radionuclides’, and was prepared by Diana Roumenova Brookshaw for submission in August 2013 for the degree of Doctor of Philosophy to the University of Manchester.
472

La Extensión del Convenio Arbitral a partes no Signatarias en Europa: ¿Un enfoque uniforme?

Silva Romero, Eduardo, Velarde Saffer, Luis Miguel 09 April 2018 (has links)
Hoy en día no existe duda de que un convenio arbitral puede ser extendido a partes no signatarias. Un caso en el que esto puede ocurrir es cuando la parte no signataria tiene una participación activa en el iter contractual, es decir, en la negociación, celebración, ejecución y/o terminación del contrato que contiene un convenio arbitral. Diversos tribunales arbitrales internacionales han concluido que esta participación activa del no signatario prueba su consentimiento implícito al arbitraje.El consentimiento es un elemento fundamental del arbitraje y, como tal, su ausencia conlleva la anulación del laudo. En este contexto, más allá de la postura de los tribunales arbitrales, es necesario conocer cuál es la postura quehan adoptado las cortes (por ejemplo, en vía de anulación del laudo) al analizar la existencia de consentimiento implícito. ¿Han adoptado una postura rígida o flexible? Este artículo aborda esta cuestión. Concretamente, los autores presentan un estudio de las decisiones emitidas por las cortes de Inglaterra, Suecia, Suiza, España y Francia que refleja una distinta postura (más o menos rígida) respecto del consentimiento implícito.
473

The Experience of Freedom: A Leap of Faith / La experiencia de la libertad: un salto de fe

Valdez, Martín 10 April 2018 (has links)
This paper seeks to interpret Fear and Trembling’s paradox of faith together with Kant’s examination of the problem of freedom, in order to reconcile Kierkegaard’s thought with rationalism, but at the same time, to enrich the latter with a more existential language. It argues that, at the ground of all ethics, a certain experience beyond the limits of reason is found, albeit not an irrational one. / El siguiente trabajo busca interpretar la paradoja de la fe presente en Temor y temblor a la luz de la problemática kantiana en torno a la libertad, de tal modo que podamos reconciliar el pensamiento de Kierkegaard con el racionalismo, pero al mismo tiempo, enriquecer a este último con un discurso de carácter existencial. Sostendremos que a la base de toda ética se encuentra una experiencia más allá de los límites de la razón, pero no por ello irracional.
474

Impact of different catchments on the Brownification of Lake Bolmen

Chileshe, Kaela January 2020 (has links)
Increased DOC and Fe concentrations from terrestrial landscapes has led to the browning of boreal surface waters. The negative societal and ecological impacts of brownification are increased cost of water purification, increased presences of algae and cyanobacteria, loss of ecosystem services and reduced recreational value. Impacts of climate change, changes in land use and reduced sulfur deposition have been identified as drivers of brownification. While it has been recognized that DOC and Fe from terrestrial landscapes is increasing, little has been done to understand the impact of different land use practices on brownification. This research aims at evaluating the DOC and Fe runoff from spruce plantations, clear-cuts and wetland landscapes and determining the export of DOC from these landscapes into humic lakes. To do that, streams running through these three different land use types were sampled for water colour, pH, temperature, conductivity, DOC and Fe both at upstream and downstream of each land use type. Further, water discharge was calculated with the help of flow speed measurements and stream profiling (width, depth and channel shape). DOC (but not Fe) concentrations changed significantly depending on land use type. Wetlands lead to reduced DOC concentrations, whereas especially spruce plantations lead to increased stream water DOC concentrations.
475

Combustion Synthesis of Nanomaterials Using Various Flame Configurations

Ismail, Mohamed 02 1900 (has links)
Titanium dioxide (TiO2) is an important semiconducting metal oxide and is expected to play an important role in future applications related to photonic crystals, energy storage, and photocatalysis. Two aspects regarding the combustion synthesis have been investigated; scale-up in laboratory synthesis and advanced nanoparticle synthesis. Concerning the scale-up issue, a novel curved wall-jet (CWJ) burner was designed for flame synthesis. This was achieved by injecting precursors of TiO2 through a central port into different flames zones that were stabilized by supplying fuel/air mixtures as an annular-inward jet over the curved wall. This provides a rapid mixing of precursors in the reaction zone with hot products. In order to increase the contact surface between the precursor and reactants as well as its residence time within the hot products, we proposed two different modifications. The CWJ burner was modified by adding a poppet valve on top of the central port to deliver the precursor tangentially into the recirculating flow upstream within the recirculation zone. Another modification was made by adopting double-slit curved wall-jet (DS-CWJ) configuration, one for the reacting mixture and the other for the precursor instead of the central port. Particle growth of titanium dioxide (TiO2) nanoparticles and their phases were investigated. Ethylene (C2H4), propane (C3H8), and methane (CH4) were used with varying equivalence ratio and Reynolds number and titanium tetraisopropoxide (TTIP) was the precursor. Flow field and flame structure were quantified using particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) techniques, respectively. TiO2 nanoparticles were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman Spectroscopy, and BET nitrogen adsorption for surface area analysis. The flow field quantified by PIV consisted of a wall-jet region leading to a recirculation zone, an interaction jet region, followed by a merged-jet region. The modified CWJ burner revealed appreciable mixing characteristics between the precursor and combustion gases within these regions, with a slight increase in the axial velocity due to the precursor injection. This led to more uniformity in particle size distribution of the synthesized nanoparticles with the poppet valve (first modification). The double-slit modification improved the uniformity of generated nanoparticles at a very wide range of stable experimental conditions. Images of OH fluorescence showed that flames are tightly attached to the burner tip and TTIP has no influence on these flames structures. The particle size was slightly affected by the operating conditions. The phase of TiO2 nanoparticles was mainly dependent on the equivalence ratio and fuel type, which impact flame height, heat release rate and high temperature residence time of the precursor vapor. For ethylene and methane flames, the anatase content is proportional to the equivalence ratio, whereas it is inversely proportional in the case of propane flames. The anatase content reduced by 8% as we changed Re between 8,000 and 19,000, implying that the Re has a slight effect on the anatase content. The synthesized TiO2 nanoparticles exhibited high crystallinity and the anatase phase was dominant at high equivalence ratios (φ >1.6) for C2H4, and at low equivalence ratios (φ <1.3) for the C3H8 flame. Concerning advanced nanoparticle synthesis, a multiple diffusion burner and flame spray pyrolysis (FSP) were adopted in this study to investigate the effect of doping/coating on TiO2 nanoparticles. The nanoparticles were characterized by the previously mentioned techniques in addition to thermogravimetric analysis (TGA) for carbon content, X-ray photoelectron spectroscopy (XPS) for surface chemistry, ultraviolet-visible spectroscopy (UV-vis) for light absorbance, inductively coupled plasma (ICP) for metal traces, and superconducting quantum interference device (SQUID) for magnetic properties. Results from multi diffusion burner show that doping TiO2 with vanadium changes the phase from anatase to rutile while doping and coating with carbon or SiO2 does not affect the phase. Doping with iron reduces the band gab of TiO2 particles by reducing the conduction band. FSP results show that iron doping changes the valance band of the nanoparticles and enhances their paramagnetic behavior as well as better light absorption than pure titania, which make these particles good candidates for photocatalytic applications.
476

Analysis of Soil-Tire Interaction Using a Two-Dimensional Finite Element-Discrete Element Method / 2次元有限要素-離散要素法による土-タイヤ相互作用解析

Nishiyama, Kenta 25 November 2019 (has links)
京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13294号 / 論農博第2877号 / 新制||農||1073(附属図書館) / 学位論文||R1||N5239(農学部図書室) / (主査)教授 清水 浩, 准教授 中嶋 洋, 教授 飯田 訓久 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM
477

Modifikace kvazikrystalických kompaktů SPS pomocí technologie elektronového paprsku / Modification of SPS quasicrystalline compacts via electron beam treatment

Poczklán, Ladislav January 2018 (has links)
The quasicrystals are characterized by unusual rotational symmetries that are not observed in the crystalline materials, which is the cause of their interesting material properties. Because of that a particular attention was paid to quasicrystalline structures in the literature research. The research also contains a description of electron beam technology, spark plasma sintering method and introduction to the problematics of wear. As the default materials for the experimental part were selected Titanium Grade 2 powder and Cristome A5 powder which was partially composed of quasicrystalline phase. The first series of samples was sintered only from powder Cristome A5. The second series was sintered from the mixture of 80 % Titanium Grade 2 powder and 20 % Cristome A5 powder. For the compaction of samples spark plasma sintering technology was selected. Samples were then systematically modified by electron beam and subjected to pin on disc tests. Samples modified at 750 °C had the best wear resistance. Samples modified at 1150 °C contained increased amount of quasicrystalline phase.
478

Určení kinetických parametrů reakcí pomocí DSC měření / determination of kinetic parameter of reactions using DSC

Kopecký, Jan January 2018 (has links)
The master thesis deals with DSC measurments a calculation of kinetic parameters. In the theoretical part, iron alotropy is briefly described, followed by a description of the DSC analysis itself. The thesis also includes division and derivation of isoconversional methods for calculating the activation energy. In the experimental part, a series of measurments is perfomed on pure iron prepared by Cold Spray method. In the paper the influence of deformation on the Curie temperature of the magnetic transformation in -Fe and transformation > is investigated. The activation energy is calculated for transformation > for different degrees of deformation. The degree of deformation is monitored by channeling contrast.
479

ThMn₁₂型非平衡磁石母材の結晶構造と磁気特性に関する研究

鈴木, 啓幸 23 September 2020 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22774号 / 工博第4773号 / 新制||工||1746(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 中村 裕之, 教授 田中 功, 教授 吉村 一良 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
480

Formminneslegeringar : En jämförandestudie mellan en ny typ av förstärkning och traditionella förstärkning av broar

Alhali, Sara January 2021 (has links)
Den industriella revolutionen kom med behovet av att bygga byggnader och broar, till en början förstod man inte vikten av armering och förstärkning av konstruktion. Men med tiden behövde man komma på någon strategi att göra konstruktionen starkare och mer hållbar, och det var då man började använda sig av förstärkning. I dagens moderna samhälle är det vanligare att bygga med betong, betong är det viktigaste byggmaterialet i världen. Det har flera egenskaper som garanterar en lång livslängd för konstruktionen; dess hållbarhet och styvhet är av störst intresse för att designa betongkonstruktioner. Andra egenskaper såsom täthet och bearbetbarhet är också viktiga. För att utnyttja betongegenskaperna korrekt måste nästan alla strukturer förstärkas på ett eller annat sätt. Därför har man under en lång period gjort stora forskningar på hur man kan göra betong starkt i draghållfasthet och inte bara i tryck. Moderna komplicerade konstruktionsformer kräver nya förstärkningsmetoder, komplexiteten i den nya strukturen både när det gäller höjd och bredd har nödvändiggjort behovet av nya metoder för betongarmering. En metod är användningen av järn-baserade minneslegeringar (Fe-SMA), genom forskning har det visat sig vara en effektiv metod för armering av stål. SMAs har unika egenskaper och det mest speciella är att det återgår till sin ursprungliga form även när det har deformerats. Som ett resultat av detta möjliggör det förstärkning av betong av vilken form och storlek som helst, de goda limegenskaperna hos betong och järn gör installationen komplett. Detta examensarbete resulterade att SMA har väldigt unika egenskaper som kommer att göra stora skillnader i byggbranschen. Detta gäller främst hos broar och är en väldigt aktuell metod som har förmågan att anpassa sig till den omgivande miljön. Utöver det kan den även justera sig själv för att säkerställa optimal och säker drift under normala och svåra belastnings villkor och det minimala kravet för underhåll.

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