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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

Resonance Energy Transfer Using ZnO Nanocrystals And Magnetism In The Mixed Metal Layered Thiophosphates, Mn1-xFexPS3(0≤x≥1)

Rakshit, Sabyasachi 04 1900 (has links) (PDF)
This thesis consists of two parts. The first part deals with the visible emission of ZnO Nanocrystals and its possible application in Resonance Energy Transfer (RET) studies. The second part of the thesis is on the magnetic properties of the layered transition metal Thiophosphates MPS3 (M = Mn, Fe), their solid solutions and intercalation compounds. Recent advances in semiconductor nanocrystals or quantum dots (QDs) as inorganic fluorophores have pioneered a new direction in the fluorescent based techniques to investigate fundamental processes in lifesciences. Their broad absorption spectra with narrow, Size-tunable emissions with high quantum e±ciency and stability under relative harsh environments have made inorganic QD's the fluorophores of choice in many applications. Among inorganic fluorophores the II-VI semiconductors based on cadmium chalcogenides are the front-runners. The cytotoxicity associated with these QDs is, however, a major drawback and has lead to the search for new nanocrystalline fluorophores that are non-toxic and possess the same favorable fluorescence properties as the Cd based QDs, viz, tunability and narrow spectral profile. ZnO Nano particles are known to exhibit two emission bands; a narrow emission band in UV around 380 nm (3.25 eV) at a wavelength just below the onset of the band gap excitation in the absorption spectra and a broad emission band in the blue-green part of the visible spectrum, with a maximum between 500 and 550 nm (2.5-2.2 eV). The UV Emission originates from the recombination of bound excitons - excited electrons in the Conduction band with holes in the valence band. The visible emission of ZnO nanocrystals is known to involve deep trap states that lie approximately midway between the Conduction and valence bands and surface defects that exist as shallow traps. In principle, visible-light-emitting ZnO nanocrystals would be ideal candidates as replacement for Cd-based fluorescent labels since they are nontoxic, less expensive, and chemically stable in air. Nanoscale ZnO, however, tends to aggregate and/or undergo Ostwald ripening be-Cause of high surface free energy resulting in an increase in crystallite size and consequent Disappearance of the visible emission. Most attempts to stabilize the ZnO nanocrystals by Capping has usually resulted in the quenching of the visible trap emission. The objective of the present study was to stabilize the visible light emission of ZnO nanocrystals, to Understand the origin and mechanism of the visible emission and to explore the possibility Of using the visible emission of ZnO in RET studies. The stabilization of visible light emission in ZnO nanocrystals was achieved by forming ZnO:MgO core-shell nanocrystals. The nanocrystals were synthesized by a sequential preparative procedure that involved formation of a ZnO core followed by an MgO shell. The Nanocrystals were characterized by using XRD, TEM, optical absorption and photoluminescence spectroscopy. These are described in Chapter 2 of the thesis. The ZnO: MgO Core-shell nanostructures exhibit stable emission in the visible for extended periods. Application of the ZnO: MgO nanocrystals either as fluorescent probes or RET studies require that they be dispersible in both polar and non-polar solvents. This as realized by appropriate choice of the capping agents (Chapter 3). ZnO: MgO nanocrystals with hydrophobic surface were obtained by capping the nanocrystals with oleic acid. The oleate capped ZnO: MgO nanocrystals are soluble in a variety of non-polar organic solvents with no change in their emission properties. Water-soluble ZnO: MgO nanocrystals were obtained by capping the ZnO:MgO nanocrystals with carboxymethyl-β-cyclodextrin (CMCD). The hydroxyl groups located at the rim of the cyclodextrin cavity renders the surface hydrophilic. The integrity of the CMCD molecules are preserved on capping and their by hydrophobic cavities available for host-guest chemistry. The visible emission of The ZnO: MgO nanocrystals are unaltered by the nature of the capping agent. The origin and mechanism of the visible emission from ZnO: MgO nanocrystals has been Investigated using time-resolved emission spectroscopy technique (Chapter 4). The time-evolution of the photoluminescence spectra show that there are, in fact, two features in the visible emission whose relative importance and efficiencies vary with time. These features originate from recombination involving trapped electrons and holes, respectively, And with efficiencies that depend on the occupancy of the trap density of states. The application of the visible emission of ZnO: MgO nanocrystals as resonance energy transfer (RET) donors in water and hydrophobic media are demonstrated. In aqueous media, the carboxymethyl β-cyclodextrin (CMCD) capped ZnO: MgO nanocrystals is able to accommodate the organic dye Nile Red by an inclusion in the anchored hydrophobic cyclodextrin cavity forming a 1:1 complex. Nile Red was chosen as the guest molecule because its absorption has appreciable overlap with ZnO: MgO visible emission, a prerequisite for RET to occur. The resonance energy transfer on the band gap excitation of The ZnO core to included Red molecules in the CMCD-ZnO: MgO-Nile Red supramolecular assembly is demonstrated in aqueous media. A similar RET process is shown to occur in the non-polar media in the oleate capped ZnO: MgO nanocrystals when Nile Red is partitioned from the solvent into hydrophobic anchored oleate chains. The wavelength dependent energy transfer in the system has been studied using time-resolved emission spectroscopic technique. The importance of trap states in giving rise to non-Forster distance dependence for the RET is highlighted. The second part of the thesis deals with magnetism in low dimensional layered transition metal thiophophates, MPS3 (M = Mn, Fe). Low dimensional magnetic systems continue to be a fertile ground for discovering new phenomena and properties. Among two-dimensional magnetic systems the insulating transition metal thiophosphates are one of the few known layered systems, in which both magnetic and crystallographic lattices are two dimensional (2D). In the metal chalcogenophosphates, the magnetic MPX3 layers are separated by a van der Waals gap that effectively rules out interlayer exchange and hence these systems are nearly perfect 2D magnetic systems, with the magnetic ions forming a honeycomb arrangement within the layer. Due to the crystallographic two-dimensional nature these materials may be intercalated by variety of molecules or ions leading to change in magnetic properties. The objective of this thesis work is to try and modify the magnetic properties of the transition metal thiophosphates either by forming solid solutions of the type, M1-xMxPS3, (M, M = Mn, Fe) or by intercalating hydrated metal ions within the layers. The structure, Bonding, reactivity and magnetic properties are briefly introduced in Chapter 7. The Scope and nature of the present work in presented towards the end of the chapter. MnPS3 and FePS3 have identical crystal structures and both order antiferromagnetically at low temperatures, TN. The in-plane magnetic structures of the antiferromagnetically ordered the Neel state in the two compounds are, however, different. In MnPS3 the spins Alternate up-down whereas in FePS3 the spins are arranged as ferromagnetic chains with Alternate chains coupled antiferromagnetically. Since the crystal structures are identical, These two compounds can form solid solutions, Mn1-xFexPS3(0≤x≥1) over the entire concentration range. The magnetic properties of the single crystals of the solid solutions was measured by using a SQUID magnetometer. This system is of interest since the contrasting Neel states of the end-members may give rise to new magnetic phenomena at intermediate composition. It is shown that the magnetic behavior falls into three distinct categories. The Mn-rich compositions behave like a dilute MnPS3 lattice, the Fe-rich compositions behave like dilute FePS3 and in the intermediate compositions a spin-glass like phase appears. The phase boundaries for these regime in Mn1-xFexPS3, 0≤x≥1 is shown to be related to the percolation threshold for a honeycomb lattice. MnPS3 is known to undergo a unusual ion-exchange intercalation reaction. Intercalation occurs by the inclusion of hydrated metal ions in the galleries of MnPS3 with charge neutrality maintained by loss of the Mn2+ ions from the layer (Equation). MnPS3 + 2xG+ (aq) → Mn1-xPS3 [G (H2O) y] 2x + xMn2+ (aq) Where G is a neutral guest species. This chemistry has been exploited to intercalate hydrated Mn2+ ions in the interlamellar space to give Mn1-xPS3[Mn(H2O)6]x. the magnetic properties of this 3D analogue of MnPS3 has been investigated in Chapter 9.
472

A Heavy Graphene Analogue amongst the Bismuth Subiodides as Host for Unusual Physical Phenomena

Rasche, Bertold 16 January 2017 (has links) (PDF)
This thesis was inspired by the discovery of Bi14Rh3I9, the first so-called weak three-dimensional topological insulator (3D-TI) and has been concerned with the topic of TIs in general. Two aspects were tackled to gain a deeper understanding of this new state of matter. On one hand, the expansion of the material’s basis and on the other hand developing a simple model of the structure and analysing it via density-functional theory (DFT) based methods. To discover new materials, a systematic investigation of the metal-rich parts of the bismuth–platinum-metal–iodine phase systems was conducted. It led to six new phases among the bismuth subiodides. Some of which, e.g. Bi14Rh3I9, share a honeycomb network of platinum-metal-centred bismuth-cubes and are the seed of a family of materials with this structural motive. The others show strand-like structures or layered structures with platinum-platinum bonds. The latter were so far unknown amongst bismuth subiodides. The honeycomb network was separately analysed and shown to host the TI properties. Structurally and electronically it can be seen as a “heavy graphene analogue”, which refers to the fact that graphene with hypothetical strong spin-orbit coupling (“heavy graphene”) was the first TI put forward by theoreticians. Apart from DFT-calculations, physical experiments confirmed the TI properties. Angle-resolved photoelectron spectroscopy (ARPES) was used to verify the electronic structure and scanning tunnelling microscopy and spectroscopy (STM and STS) to reveal the protected 1D edge states present at the cleaving surface of this material. As the arrangement of the honeycomb layer varies between the different known and newly discovered materials within this family of structures, this influence was also investigated. All further materials were also characterised by DFT-calculations and physical experiments, e.g. magnetisation and transport measurements. This thesis might give an experimental and theoretical basis for a deeper understanding of the TI state of matter. The 1D edge states on the surface of Bi14Rh3I9 could be a chance to handle spins and therefore propel spintronic research, or they could host Majorana fermions, which could be used as qubits in quantum computing.
473

Impacts of a capillary barrier on infiltration and subsurface stormflow in layered slope deposits monitored with 3-D ERT and hydrometric measurements

Hübner, Rico, Günther, Thomas, Heller, Katja, Noell, Ursula, Kleber, Arno 09 November 2017 (has links)
Identifying principles of water movement in the shallow subsurface is crucial for adequate process-based hydrological models. Hillslopes are the essential interface for water movement in catchments. The shallow subsurface on slopes typically consists of different layers with varying characteristics. The aim of this study was to draw conclusions about the infiltration behaviour, to identify water flow pathways and derive some general interpretations for the validity of the water movement on a hillslope with periglacial slope deposits (cover beds), where the layers differ in their sedimentological and hydrological properties. Especially the described varying influence of the basal layer (LB) as an impeding layer on the one hand and as a remarkable pathway for rapid subsurface stormflow on the other. We used a time lapse 3-D electrical resistivity tomography (ERT) approach combined with punctual hydrometric data to trace the spreading and the progression of an irrigation plume in layered slope deposits during two irrigation experiments. This multi-technical approach enables us to connect the high spatial resolution of the 3-D ERT with the high temporal resolution of the hydrometric devices. Infiltration through the uppermost layer was dominated by preferential flow, whereas the water flow in the deeper layers was mainly matrix flow. Subsurface stormflow due to impeding characteristic of the underlying layer occurs in form of organic layer interflow and at the interface to the first basal layer (LB1). However, the main driving factor for subsurface stormflow is the formation of a capillary barrier at the interface to the second basal layer (LB2). The capillary barrier prevents water from entering the deeper layer under unsaturated conditions and diverts the seepage water according to the slope inclination. With higher saturation, the capillary barrier breaks down and water reaches the highly conductive deeper layer. This highlights the importance of the capillary barrier effect for the prevention or activation of different flow pathways under variable hydrological conditions.
474

Horský penzion / Mountain guesthouse

Roštár, Matej January 2018 (has links)
This diploma thesis is dealing with the solution of four-floor mountain guesthouse with one floor underground and three floor overground on parcel 1953/16 in Low Tatras, Slovak republic. The parcel is situated in the cadastral region of Horná Lehota. The design of the mountain guesthouse is solving the architectonical, technical and building solutions of the object according to the requests of investor. Underground floor is designed from DT concrete blocks, which are waterproofed by the bitumen felts and thermally insulated by the extruded polysytrene. Overground floors are made from ceramic blocks HELUZ and thermally insulated by ETICS system from mineral wool. The roof of the object is made from pitched roof constructed from timber trusses, which are connected by gangnail steel sheets. The purpose of this project is to create modern and comfortable builidng, which provides pleasant environment mainly for fans of tourism and downhill skiing, but also for other visitors.
475

Problematika prostřihování otvoru dvouvrstvým polotovarem / Hole punching problematics of two layered sheet metal

Kvapil, Štěpán January 2020 (has links)
The thesis is focussed on project of a tool – a hot working clipping punch, where the hole is punched in the upsetting ends of stabilizer. We talk about punching of a two layered semi-finished product, in which burr is formed at the layer interface, which is undesirable from the point of the customer requirement. The stabilizer is mounted in the car chassis, where it is fastened to the axle with screws. The literature study is focused on the theory and problems of punching. In the practical part, several design solutions of cutter faces are discussed, from which three types of face shape were selected. This was associated with a change in the design of the ejector. Two tool materials were selected for comparison. The cutters were tested on an automatic forming centre. Finally, after summarizing and evaluating all the practical experiments, an optimal solution of a tool designed for punching a hole with a two layered semi-finished product is proposed.
476

Výzkum elektrochemických a materiálových charakteristik nově vyvinutých vrstevnatých elektrodových materiálů pro lithno-iontové baterie / The research on electrochemical and material characteristics new developed layered electrode materials for lithium-ion batteries

Kratochvíl, Miroslav January 2009 (has links)
The diploma thesis deals with electrode materials for lithium-ions accumulators, concretely layered materials prepared via new methods. The main objective of this work is dealing with new procedures prepare electrodes of newly developed layered electrode materials and subsequently their measure. Another challenge was a theoretical analysis of newly developed layered electrode materials for positive and negative electrodes and their preparation of new procedures. In this work the detailed procedures for the preparation of individual electrodes, electrolytes and other issues associated with these preparations. There were describing batteries of general, primary and secondary lithium cells, fuel cells, Lithium-ion batteries, layered materials forming the electrodes and of course the history these cells. Practical work is focused on separate measurements layered electrode materials prepared by new processes and assessment of results for individual layered materials. In the practical part has been made that the newly prepared layered electrode materials offer higher capacity and voltage.
477

Penzion pro seniory / Pension for Seniors

Vítek, Jan January 2013 (has links)
This Diploma´s thesis proceses topic Pension for Seniors. The object is situated in Božetěchova street in Brno-Královo Pole. This house is new building, three-floored and partial basemented. Basement is a technical floor. On the first floor are spaces of services and offices. On the second and the third floor are situated twenty-eight flats. Shape of the house is „L“ and its basic dimensions are 39,0 x 38,0 meters. The building is finished with a single layered flat roof. Height of house is 10,715 meters. The base structures is of conrete C16/20. The bearing walls on 1S are of monolithic reinforced concrete. Other Bering construction system is used of Porotherm. The staircase structure consists is of monolithic reinforced concrete.
478

Polyfunkční dům / Multifunctional House

Hantscherová, Lucie January 2013 (has links)
This Diploma thesis deals with the topic of multifunctional house. The building is situated on the street Pod Studánkou in Pardubice. This house is brand new building, four-storey, basementless, with a single layered flat roof. Height of the house is 13,580 meters. On the first floor there is technical hinterland and commercial places for a rent. On the second, third and fourth floor there are situated thirteen flats for a living. The foundations of the house are made of concrete C16/20. The bearing walls are made of masonry Porotherm. The external bearing walls are combined with the contact thermal-insulation. Windows and doors are triple glazed with a thermal-insulation.
479

Cloud Framework on Infrastructure as a Service / Cloud Framework on Infrastructure as a Service

Pech, David January 2013 (has links)
Práce se zabývá podrobnou analýzou požadavků na moderní aplikační rámec pro prostředí cloud. Za pomoci standardních návrhových vzorů a technik připravuje teoretický základ a pravidla, která musí uvnitř rámce platit. V práci je realizována referenční implementace a připravena demonstrační aplikace středního rozsahu, aby představila výhody plynoucí z užití frameworku.
480

Characterization of lamellar or nanostrutured materials based on transition metal oxides for liquid phase catalysis / Caractérisation des matériaux lamellaires ou nanostructurés à base d’oxydes de métaux de transition pour la catalyse en phase liquide

Fayad, Ghinwa 05 December 2018 (has links)
Les oxydes de métaux de transition lamellaires peuvent servir de catalyseurs pour la conversion de la biomasse, mais leur développement nécessite une meilleure compréhension de leurs propriétés. En conséquence, plusieurs matériaux lamellaires, tels que HNbMoO6, HNbWO6, H2W2O7 et H2WO4, ainsi qu'un nouveau type d'oxydes en couches basés sur Nb et W et caractérisés par des phases d'Aurivillius “en escalier” ont été largement caractérisés notamment par spectroscopie DRX et spectroscopie Raman. La possibilité de convertir les solides précurseurs au lithium ou bismuth en phases protonées a été étudiée. Ces oxydes ont la spécificité d'intercaler des molécules entre les couches, ce qui peut contribuer à l’activité catalytique en phase liquide. Pour identifier les rôles respectifs de l’intercalation et des propriétés de surface comme l’acidité, les matériaux ont été caractérisés en phase liquide par spectroscopie Raman en utilisant des bases organiques telles que les n-alkylamines (butylamine et octylamine) et la pyridine. L'intercalation avec des réactifs possibles, les n-alcools et le 2,5-hexanediol, a également été étudiée. L'activité catalytique de ces oxydes lamellaires a été déterminée grâce à une nouvelle réaction: la cyclo-déshdrataion du 2,5-hexanediol en 2,5-diméthyltétrahydrofurane. HNbMoO6 s’est avéré le catalyseur le plus actif, comparé à des catalyseurs acides conventionnels ou aux autres matériaux lamellaires. L’acidité et la capacité d’intercalation de ces divers matériaux lamellaires ont été comparées pour comprendre les différences observées pour l’activité catalytique. / Layered transition metal oxides have a potential as catalysts for biomass conversions, but their development necessitates a better understanding of their properties. Consequently, several layered materials such as HNbMoO6, HNbWO6, H2W2O7 and H2WO4 as well as new types of layered oxides based on Nb and W and characterized by a “stair-like” Aurivillius phases were extensively characterized notably by XRD and Raman spectroscopy. The possibility to convert the as-synthesised lithium or bismuth precursors to protonated phases was also thoroughly evaluated. Layered oxides have the specificity to intercalate molecules within their interlayer regions, which may be a key feature to catalytic activity for reactions in the liquid phase. In order to evaluate the respective roles of intercalation and surface properties such as acidity, the materials were characterized in the liquid phase by Raman spectroscopy using organic bases such as n-alkylamines (butylamine and octylamine) and pyridine. Intercalation with possible reagents, n-alcohols and 2,5-hexanediol, was also studied. The catalytic activity of these layered oxides was evaluated using a novel test reaction: the cyclo-dehydration of 2,5-hexanediol into 2,5-dimethyltetrahydrofuran. HNbMoO6 proved to be the most active catalyst, compared to conventional acidic catalysts or other layered materials. The acidity and intercalation ability of the various layered materials were compared to understand the differences observed for the catalytic activity.

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