Dissertations / Theses: 'ALLIED APPLICATIONS'

1

Rowlands, Anne Justine. "Applications of near infra-red Fourier transform Raman spectroscopy to photographic and allied chemistry." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387073.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Dyer, M. R. "Observation of the stress distribution in crushed glass with applications to soil reinforcement." Thesis, University of Oxford, 1985. http://ora.ox.ac.uk/objects/uuid:98dee0c7-5e27-45b7-aef8-01bd56240671.

Full text

Abstract:

The research described in this dissertation follows on from the study made by Jewell (1980)into the effects of tensile reinforcement on the mechanical behaviour of sand. For this study Jewell used the direct shear test with reinforcement placed about the central plane as shown in fig. 1.1. The direct shear test was chosen for the following reasons. (1) The reinforcement variables could be better controlled and examined in a unit cell test than in modular field studies of soil reinforcement systems. (2) The pattern of deformation is similar to that experienced by soil in which a rupture band develops, with the principal axes of stress, strain and strain increment free to rotate as is the case in model and field structures. (3) The overall shear strength of the sample is measured directly at the boundaries of the apparatus. The direct shear tests were monitored by boundary measurements and internal measurements using a radiographic technique. The findings are outlined below with reference made to relevant observations by other researchers. 1) The optimum orientation for a relatively flexible steel grid was found to be approximately along the direction of principal tensile strains in the unreinforced sand, see fig.1.2. This indicated that the reinforcement functioned by limiting tensile strains in the sand. McGown et al. (1978) obtained a similar result for plane strain cell tests on sand containing a single layer of flexible reinforcement. However in both studies the reinforcement was observed to waken the sand. Jewell recognized weakening to occur when the steel grid was placed along the direction of principal compressive strains in the unreinforced sand. This was attributed to a reduction in vertical effective stress. McGown et al. observed weakening of the sand when the reinforcement orientation approached the rupture band which developed in the sand alone. This was recognized to be the direction of zero-extension in the unreinforced sand. The weakening was linked to a lower bond between soil and reinforcement than soil alone. 2) Internal strains determined by Jewell showed the tensile reinforcement modified strains in the sand over a well defined zone, see fig.1.3. This resulted in a significant rotation of principal axes of strain increment, with the bond of major strains which developed across the centre of the box in the unreinforced sand being prohibited from forming. This agreed with boundary measurements, indicating the reinforcement functioned by limiting tensile strains in the sand. Consequently a less favourable mode of failure took place. The limit of rotation of principal axes of strain increment was understood to be the alignment of a direction of zero-extension in the sand with the reinforcement. These findings agree with the ideas expressed by Basset and Last (1978) on the mode of action of tensile reinforcement, which in particular was related to the effect of tensile reinforcement on the strain field in a reinforced earth wall as shown in fig.1.4. 3) For efficient use of tensile reinforcement it was demonstrated that the bond with sand should be as high as possible. This could be achieved by roughening the surface. Alternatively, the bond was improved by introducing openings or apertures in the reinforcement, changing the shape to a grid. It appeared that the bond for a suitably proportioned grid could be as high as for a fully roughened surface. 4) The longitudinal stiffness of tensile reinforcement was observed to affect the magnitude and rate of increase in strength in the direct shear tests. The rupture strain of tensile reinforcement relative to maximum tensile strains of the soil, under the same operational stress conditions, have also been observed to influence the reinforcing effect in terms of its limiting behaviour, i.e. whether brittle or ductile (McGown, et al. 1978). With regards to the performance of reinforced earth walls, Al-Hussanini and Perry (1976) observed that steel reinforced strips produced a stiffer and stronger structure than a more extensible fabric reinforcement, even though surface roughness was less. The importance of reinforcement tensile stiffness is recognized in limit equilibrium designs for tensile reinforced soil structures by limiting the available reinforcement force to the tensile strains that can develop in the soil (e.g. Jewell 1985). For highly structured non-woven and composite geotextiles, McGown et al. (1982) demonstrated that the stress-strain behaviour can be significantly affected by soil confinement. Testing wider strips in isolation was not found to replicate the effects of soil confinement. Another factor which needs to be considered when assessing the tensile property of a polymer reinforcement is creep. McGown et al. (1984) illustrated an appropriate method of interpreting creep data using isochronous curves, which enable long term laboratory test data to be extrapolated to the design life of the soil structure. 5) The strain and hence stress fields in the reinforced direct shear tests have been shown to be complex and non-uniform. However Jewell successfully modelled the variation of reinforcing effect for tensile reinforcement at different orientations by using a simple limit equilibrium analysis, see fig.1.5. The effect of the tensile reinforcement force was represented as: - an increase in the normal effective stress acting on the central plane of the box due to the normal component of the force and - a reduction in the applied shear stress due to the parallel component of the force to the central plane. Subsequently this analysis has been applied to limit equilibrium design methods for reinforcing soil retaining walls and embankments, Jewell et al. 1984, and Jewell 1982 respectively. 6) A reduction in the reinforcing effect for individual reinforcement due to the presence of other reinforcement was observed in the shear box. This loss of efficiency of individual reinforcement was termed interference. Interference between tensile reinforcement has also been studied by Guilloux et al. (1979) for the pull-out resistance from soil. However interference between reinforcement has yet to be introduced into a limit equilibrium design method.

APA, Harvard, Vancouver, ISO, and other styles

3

Greenaway, Rebecca L. "Palladium-catalysed cyclisations of bromoenynamides in the synthesis and applications of amidodienes." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:d49aad2d-65ce-4af1-acda-e90921d34a1a.

Full text

Abstract:

The aim of this work was to investigate palladium-catalysed cyclisations of bromoenynamides in the synthesis of amidodienes, which on further reaction or oxidation can lead to a diverse range of heteroaromatic systems. Building upon work within the Anderson group on the palladium-catalysed cyclisations of bromoenynes, we have been able to successfully apply a palladium-catalysed carbopalladation/Stille coupling/electrocyclisation cascade to bromoenynamides and then further develop this to incorporate a Suzuki coupling, leading to bicyclic amidodienes which can undergo selective oxidation to a range of heteroaromatics including indolines, indoles, tetrahydroquinolines and benzazepines. During the investigations into the cascade cyclisation, a reductive cyclisation was discovered which enabled access to a range of monocyclic amidodienes. These could subsequently be subjected to a series of Diels-Alder cycloadditions (thermal, Lewis acid-catalysed, arynes) and oxidations to afford a complimentary range of heteroaromatic systems. Whilst this methodology was successful with bromoenynamides, extension of its application to bromoenynhydrazides, with the hope of accessing a relatively unusual range of heteroaromatic structures including indazoles, cinnolines and diazepines, proved to be more problematic. Finally, expansion of the cascade methodology into a fully intramolecular cyclisation, enabled studies towards the synthesis of the trikentrin family of natural products to be conducted.

APA, Harvard, Vancouver, ISO, and other styles

4

Falco, Camillo. "Sustainable biomass-derived hydrothermal carbons for energy applications." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2012/5978/.

Full text

Abstract:

The need to reduce humankind reliance on fossil fuels by exploiting sustainably the planet renewable resources is a major driving force determining the focus of modern material research. For this reason great interest is nowadays focused on finding alternatives to fossil fuels derived products/materials. For the short term the most promising substitute is undoubtedly biomass, since it is the only renewable and sustainable alternative to fossil fuels as carbon source. As a consequence efforts, aimed at finding new synthetic approaches to convert biomass and its derivatives into carbon-based materials, are constantly increasing. In this regard, hydrothermal carbonisation (HTC) has shown to be an effective means of conversion of biomass-derived precursors into functional carbon materials. However the attempts to convert raw biomass, in particular lignocellulosic one, directly into such products have certainly been rarer. Unlocking the direct use of these raw materials as carbon precursors would definitely be beneficial in terms of HTC sustainability. For this reason, in this thesis the HTC of carbohydrate and protein-rich biomass was systematically investigated, in order to obtain more insights on the potentials of this thermochemical processing technique in relation to the production of functional carbon materials from crude biomass. First a detailed investigation on the HTC conversion mechanism of lignocellulosic biomass and its single components (i.e. cellulose, lignin) was developed based on a comparison with glucose HTC, which was adopted as a reference model. In the glucose case it was demonstrated that varying the HTC temperature allowed tuning the chemical structure of the synthesised carbon materials from a highly cross-linked furan-based structure (T = 180oC) to a carbon framework composed of polyaromatic arene-like domains. When cellulose or lignocellulosic biomass was used as carbon precursor, the furan rich structure could not be isolated at any of the investigated processing conditions. These evidences were indicative of a different HTC conversion mechanism for cellulose, involving reactions that are commonly observed during pyrolytic processes. The evolution of glucose-derived HTC carbon chemical structure upon pyrolysis was also investigated. These studies revealed that upon heat treatment (Investigated temperatures 350 – 900 oC) the furan-based structure was progressively converted into highly curved aromatic pre-graphenic domains. This thermal degradation process was observed to produce an increasingly more hydrophobic surface and considerable microporosity within the HTC carbon structure. In order to introduce porosity in the HTC carbons derived from lignocellulosic biomass, KOH chemical activation was investigated as an HTC post-synthesis functionalisation step. These studies demonstrated that HTC carbons are excellent precursors for the production of highly microporous activated carbons (ACs) and that the porosity development upon KOH chemical activation is dependent on the chemical structure of the HTC carbon, tuned by employing different HTC temperatures. Preliminary testing of the ACs for CO2 capture or high pressure CH4 storage yielded very promising results, since the measured uptakes of both adsorbates (i.e. CO2 and CH4) were comparable to top-performing and commercially available adsorbents, usually employed for these end-applications. The combined use of HTC and KOH chemical activation was also employed to produce highly microporous N-doped ACs from microalgae. The hydrothermal treatment of the microalgae substrate was observed to cause the depletion of the protein and carbohydrate fractions and the near complete loss (i.e. 90%) of the microalgae N-content, as liquid hydrolysis/degradation products. The obtained carbonaceous product showed a predominantly aliphatic character indicating the presence of alkyl chains presumably derived from the lipid fractions. Addition of glucose to the initial reaction mixture was found out to be extremely beneficial, because it allowed the fixation of a higher N amount, in the algae derived HTC carbons (i.e.  60%), and the attainment of higher product yields (50%). Both positive effects were attributed to Maillard type cascade reactions taking place between the monosaccharides and the microalgae derived liquid hydrolysis/degradation products, which were in this way recovered from the liquid phase. KOH chemical activation of the microalgae/glucose mixture derived HTC carbons produced highly microporous N-doped carbons. Although the activation process led to a major reduction of the N-content, the retained N-amount in the ACs was still considerable. These features render these materials ideal candidates for supercapacitors electrodes, since they provide extremely high surface areas, for the formation of electric double-layer, coupled to abundant heteroatom doping (i.e. N and O) necessary to obtain a pseudocapacitance contribution.
Die Notwendigkeit, die Abhängigkeit der Menschheit von fossilen Brennstoffen zu reduzieren ist die treibende Kraft hinter aktuellen Forschungsanstrengungen in den Materialwissenschaften. Folglich besteht heutzutage ein erhebliches Interesse daran Alternativen zu Materialien, die aus fossilen Resourcen gewonnen werden, zu finden. Kurzfristig ist zweifellos Biomasse die vielversprechendste Alternative, da sie aus heutiger Sicht die einzige nicht-fossile, nachhaltige und nachwachsende Kohlenstoffquelle ist. Konsequenterweise werden die Antrengungen neue Syntheseansätze zur Konvertierung von Biomasse und ihren Derivaten in kohlenstoffbasierten Materialien forwährend erhöht. In diesem Zusammenhang hat sich die Hydrothermalkarbonisierung (HTC) als sehr vielseitiges Werkzeug zur Konvertierung von Biomasse-basierten Ausgangsstoffen in funktionale Kohlenstoffmaterialien herausgestellt. Dennoch gibt es bisher wenige Ansätze um rohe Biomasse, genauer gesagt Lignicellulose, direkt in funktionale Materialien umzusetzen. Könnte der direkte Einsatz von roher Biomasse Verfahren wie der HTC zugänglich gemacht werden, würde dies die Nachhaltigkeit des Verfahrens immens steigern. Daher wurde in dieser Dissertation die Hydrothermalkarbonisierung von kohlenhydratreicher (d. h. Lignicelluse) und proteinreicher (d. h. Microalgae) Biomasse systematisch analysiert. Diese Untersuchung galt dem Ziel einen besseren Einblick in das Potential dieser thermochemischen Verarbeitungsmethode funktionale Kohlenstoffmaterialien aus unverarbeiteter Biomasse hervorzubringen zu gewinnen. Die hergestellten Materialien wurden mittels chemischer Aktivierung nachträglich weiter behandelt. Dieser zusätzliche Verarbeitungsschritt ermöglichte die Herstellung hochporöser aktiverter Kohlenstoffe (AC). Die aus Lignicellulose gewonnenen ACs zeigten exzellente Eigenschaften bei der Aufnahme von CO2 und der Hochdruckspeicherung von CH4 währen die aus Microalgae gewonnen Eigenschaften an den Tag legten (z. B. hohe Oberfläche und N-Dotierung), welche sie zu vielversprechenden Materialien für Superkondensatoren machen. Die in dieser Dissertation präsentierte Arbeit zeigte außergewöhnliche Fortschritte in Richtung der Anwendung von unbehandelter Biomasse als Ausgangsmaterial für die Produktion von funktionalen Kohlenstoffen.

APA, Harvard, Vancouver, ISO, and other styles

5

Reed, Stephen. "Synthesis and characterisation of novel glycosidase substrates and evaluation of applications in biomedical science." Thesis, Northumbria University, 2010. http://nrl.northumbria.ac.uk/1101/.

Full text

Abstract:

The last fifty years has seen an increase in the production of synthetic or artificial enzyme substrates used to identify and quantify enzymes. These substrates have found applications in a range of biomedical science disciplines. Used in biochemistry and clinical chemistry to identify and measure enzymes, some of these substrates have been adapted for use in microbiology, particularly bacterial diagnosis and, in more recent years, molecular biology. The use of artificial chromogenic and fluorogenic enzyme substrates to identify certain bacteria is now common place in medical laboratories worldwide. Not all bacteria can be identified with existing and commercially available artificial substrates. Some of these can be slow to yield results, imprecise, expensive or require a technical method too complicated to provide a viable laboratory test. Therefore, the search for new, more efficient, biochemical tests has progressed, with novel substrates and inventive applications being developed continually. In this study, core compounds were synthesised by various condensation reactions and their characteristics evaluated with respect to colouration/fluorescence and possible enhancement of these properties by metal chelation. Promising candidates were selected for glycosidation, via modified Koenigs-Knorr reactions, in an attempt to synthesise artificial substrates. Several commercially available core molecules were also subjected to glycosidation. The more successful substrates included glycosides of alizarin, nitrosalicylaldehyde and 3- hydroxyflavone. The galactoside of nitrosalicylaldehyde was evaluated in solid agar media and found to be selective for certain Gram-negative bacteria. When similarly investigated, the 3- hydroxyflavone-β-D-glucoside showed the possibility of being used in a procedure for the isolation of the clinically significant pathogens including Listeria monocytogenes. The enzyme kinetics of β-glucosidase with this substrate were also determined in a novel fluorescence assay and compared favourably to the well documented 4-methylumbelliferyl-β-D-glucopyranoside. Alizarin-2-yl-β-D-galactoside and p-naphtholbenzein-β-D-galactoside were successfully utilized for the screening of recombinant and non-recombinant Escherichia coli transformants produced routinely in molecular biology. Aminopeptidase substrates have been shown to be useful for the detection of enzymes which hydrolyse peptides that are specific to certain bacteria. To allow the evaluation of novel aminopeptidase substrates, that were to be subsequently synthesised, a cost effective, large scale source of recombinant leucyl aminopeptidase enzyme was developed via gene cloning techniques. Consequently, the products of this study may serve a beneficial purpose in future enzymatic investigations, medical diagnosis and molecular biology.

APA, Harvard, Vancouver, ISO, and other styles

6

Fellinger, Tim-Patrick. "Hydrothermal and ionothermal carbon structures : from carbon negative materials to energy applications." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2012/5782/.

Full text

Abstract:

The needs for sustainable energy generation, but also a sustainable chemistry display the basic motivation of the current thesis. By different single investigated cases, which are all related to the element carbon, the work can be devided into two major topics. At first, the sustainable synthesis of “useful” carbon materials employing the process of hydrothermal carbonisation (HC) is described. In the second part, the synthesis of heteroatom - containing carbon materials for electrochemical and fuel cell applications employing ionic liquid precursors is presented. On base of a thorough review of the literature on hydrothermolysis and hydrothermal carbonisation of sugars in addition to the chemistry of hydroxymethylfurfural, mechanistic considerations of the formation of hydrothermal carbon are proposed. On the base of these reaction schemes, the mineral borax, is introduced as an additive for the hydrothermal carbonisation of glucose. It was found to be a highly active catalyst, resulting in decreased reaction times and increased carbon yields. The chemical impact of borax, in the following is exploited for the modification of the micro- and nanostructure of hydrothermal carbon. From the borax - mediated aggregation of those primary species, widely applicable, low density, pure hydrothermal carbon aerogels with high porosities and specific surface areas are produced. To conclude the first section of the thesis, a short series of experiments is carried out, for the purpose of demonstrating the applicability of the HC model to “real” biowaste i.e. watermelon waste as feedstock for the production of useful materials. In part two cyano - containing ionic liquids are employed as precursors for the synthesis of high - performance, heteroatom - containing carbon materials. By varying the ionic liquid precursor and the carbonisation conditions, it was possible to design highly active non - metal electrocatalyst for the reduction of oxygen. In the direct reduction of oxygen to water (like used in polymer electrolyte fuel cells), compared to commercial platinum catalysts, astonishing activities are observed. In another example the selective and very cost efficient electrochemical synthesis of hydrogen peroxide is presented. In a last example the synthesis of graphitic boron carbon nitrides from the ionic liquid 1 - Ethyl - 3 - methylimidazolium - tetracyanoborate is investigated in detail. Due to the employment of unreactive salts as a new tool to generate high surface area these materials were first time shown to be another class of non - precious metal oxygen reduction electrocatalyst.
Die Notwendigkeit einer nachhaltigen Energiewirtschaft, sowie der nachhaltigen Chemie stellen die Motivation der vorgelegten Arbeit. Auf Grundlage separater Untersuchungen, die jeweils in engem Bezug zum Element Kohlenstoff stehen, kann die Arbeit in zwei Themenfelder geordnet werden. Der erste Teil behandelt die nachhaltige Herstellung nützlicher Kohlenmaterialien mit Hilfe des Verfahrens der hydrothermalen Carbonisierung. Im zweiten Teil wird die Synthese von Bor und Stickstoff angereicherten Kohlen aus ionischen Flüssigkeiten für elektrochemische Anwendungen abgehandelt. Insbesondere geht es um die Anwendung in Wasserstoff-Brennstoffzellen. Als Ergebnis einer sorgfältigen Literatur¬zusammenfassung der Bereiche Hydrothermolyse, hydrothermale Carbonisierung und Chemie des Hydroxymethylfurfurals wird ein chemisch-mechanistisches Modell zur Entstehung der Hydrothemalkohle vorgestellt. Auf der Basis dieses Modells wird ein neues Additiv zur hydrothermalen Carbonisierung von Zuckern vorgestellt. Die Verwendung des einfachen Additivs, genauer Borax, erlaubt eine wesentlich verkürzte und zu niedrigeren Temperaturen hin verschobene Prozessführung mit höheren Ausbeuten. Anhand des mechanistischen Modells wird ein Einfluss auf die Reaktion von Zuckern mit der reaktiven Kohlenvorstufe (Hydroxymethylfurfural) identifiziert. Die chemische Wirkung des Minerals Borax in der hydrothermalen Carbonisierung wird im Folgenden zur Herstellung vielfältig anwendbarer, hochporöser Kohlen mit einstellbarer Partikelgröße genutzt. Zum Abschluss des ersten Teils ist in einer Serie einfacher Experimente die Anwendbarkeit des mechanischen Modells auf die Verwendung „echter“ Biomasse in Form von Wassermelonenabfall gezeigt. Im zweiten Teil werden verschiedene cyano-haltige ionische Flüssigkeiten zur ionothermalen Synthese von Hochleistungskohlen verwendet. Durch Variation der ionischen Flüssigkeiten und Verwendung unterschiedlicher Synthesebedingungen wird die Herstellung hochaktiver, metallfreier Katalysatoren für die elektrochemische Reduktion von Sauerstoff erreicht. In der direkten Reduktion von Sauerstoff zu Wasser (wie sie in Brennstoffzellen Anwendung findet) werden, verglichen zu konventionellen Platin-basierten elektrochemischen Katalysatoren, erstaunliche Aktivitäten erreicht. In einem anderen Beispiel wird die selektive Herstellung von Wasserstoffperoxid zu sehr geringen Kosten vorgestellt. Abschließend wird anhand der Verwendung der ionischen Flüssigkeit 1-Ethyl-3-methylimidazolium-tetracyanoborat eine detaillierte Betrachtung zur Herstellung von graphitischem Borcarbonitrid vorgestellt. Unter Verwendung unreaktiver Salze, als einfaches Werkzeug zur Einführung großer inneren Oberflächen wird erstmals die elektrokatalytische Aktivität eines solchen Materials in der elektrochemischen Sauerstoffreduktion gezeigt.

APA, Harvard, Vancouver, ISO, and other styles

7

Cummings, Beth L. "Applications of infrared laser spectroscopy to breath analysis." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:5b6e0624-5982-457c-b13c-61484bace371.

Full text

Abstract:

The work presented in this thesis is concerned with development of spectroscopic detection methods based on absorption spectroscopy using semiconductor lasers, with particular ref- erence to the ﬁeld of medical diagnostics through breath analysis. The ﬁrst part of this thesis deals with the design and testing of a prototype analyser for simultaneous monitoring of the exchange gases O₂ , CO₂ and H₂O in breath. The aim of this analyser is to provide information required to monitor respiration, with potential use in intensive care monitoring or during anaesthesia. The relatively high concentrations of these gases in breath and read- ily available diode laser sources make detection in the near-infrared (NIR) ideal. However, the relatively weakly absorbing A-band O₂ transitions at 760 nm require the application of a sensitive spectroscopic method, cavity enhanced absorption spectroscopy (CEAS). In contrast, CO₂ and H₂O are monitored using direct single pass absorption spectroscopy, with transitions arising from the 2ν₁ + ν₃ band at 2 μm and ν₁ + ν₃ band at 1.3 μm, respectively. It has been demonstrated that these gases can be detected simultaneously over a short pathlength (2.74 - 4 cm) in the respiratory ﬂow by combining various spectroscopic methodologies and real-time data analysis. This analyser is shown to offer a viable alter- native for monitoring respiration, exhibiting absolute detection limits of changes of 0.26 % O₂ , 0.02 % CO₂ and 0.003 % H₂O with a 10 ms time resolution, which are comparable to current mass spectrometry based methods, but without their inherent delays. Following this, investigations into the detection of the main gas constituents in breath in the NIR employing noise-reduction modulation based spectroscopic techniques, namely wavelength and frequency modulation (WMS and FMS respectively) are also reported. The described WMS studies on water at 1.37 μm provide a demonstration of conventional WMS detection, as well as a “proof-of-principle” example of a relatively new approach to calibrating the non-absolute information obtained from a WMS absorption signal. Typically WMS spectra are calibrated using mixtures of known gas concentrations or an absolute direct absorption spectrum where possible. In this work however, a self-calibrating method, the phasor decomposition method (PDM), is employed and the returned concentration from this calibration is compared to direct absorption measurement. From this, the calculated concentration using the PDM is found to differ by 9 % from the concentration value obtained by direct absorption, providing an alternative method of calibration for when direct absorption measurements are not possible. The use of FMS in the NIR is also demonstrated as a potential alternative to CEAS for monitoring O₂ at 760 nm. FMS detection is performed on atmospherically broadened O₂ and a time-normalised α_min(t) of 2.45 ×10⁻⁶ cm⁻¹ s^1/2 is obtained, which is two orders of magnitude less sensitive than the value of α_min(t) = 2.35 ×10⁻⁸ cm⁻¹ s^1/2 obtained with CEAS. This combined with the experimental requirements of an FMS system, make its use for detection of O₂ a less practicable option compared to CEAS for real-time breath analysis. The latter work in this thesis involves a change in focus to detection of trace gases in breath in the mid-infrared (MIR). The move of spectroscopic detection to the MIR exploits the larger absorption cross-sections available in this region, and to achieve this, a relatively new form of semiconductor laser, the quantum cascade laser (QCL) is used. The design of a continuous wave QCL spectrometer at 8 μm and its operating characteristics are demon- strated and improvements in its performances are also discussed. This QCL system is then utilised to demonstrate the potential of monitoring species in breath, namely the narrow- band absorber methane and the broadband absorber acetone, taking into consideration the potential interference from other absorbing species in breath and the diﬀerent spectroscopic characteristics exhibited by these molecules. Finally, the potential to further improve the sensitive detection of trace gases in breath in the MIR is also investigated with studies on the use of CEAS and multipass cells. In this work, the molecule of interest is the biomarker OCS, using transitions of the 2ν₂ band at 1031 cm⁻¹ , that are probed using a 10 μm QCL. The application of CEAS in the MIR is not as well developed as in the NIR, and the experimental consequences of using optical cavities at these wavelengths, where equipment tends to be more limited, are investigated and sensitivities discussed in the context of other literature. The experimental procedure of optimising a cavity for CEAS using the off-axis alignment method is also studied in detail, as well as the addition of WMS to further improve the signal quality. An effective absorption pathlength of ∼ 100 m was achieved in the cavity, with a bandwidth reduced α_min(BW) of 1.7 ×10⁻⁷ cm⁻¹ Hz^−1/2 using WMS CEAS achieved. With the poorer quality optics and limitations in equipment in the MIR for CEAS experiments, the use of a multipass cell, a 238 m Herriott cell, is also investigated as an alternative to the use of an optical cavity at 10 μm. Detection of OCS using direct absorption and WMS is demonstrated in the Herriott cell, achieving α_min(BW) = 2.03×10⁻⁸ cm⁻¹ Hz^−1/2 using WMS. This shows an improvement in sensitivity compared to WMS CEAS, and also shows the potential for future work on biomarker detection, as it approaches the ∼ ppb levels required for breath analysis.

APA, Harvard, Vancouver, ISO, and other styles

8

Ghavami, Navid. "Ultra-wideband imaging techniques for medical applications." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:6f590d26-ee7c-41d7-a89b-393c864c9d82.

Full text

Abstract:

Ultra-wideband (UWB) radio techniques have long promised good contrast and high resolution for imaging human tissue and tumours; however, to date, this promise has not entirely been realised. In recent years, microwave imaging has been recognised as a promising non-ionising and non-invasive alternative screening technology, gaining its applicability to breast cancer by the significant contrast in the dielectric properties at microwave frequencies of normal and malignant tissues. This thesis deals with the development of two novel imaging methods based on UWB microwave signals. First, the mode-matching (MM) Bessel-functions-based algorithm, which enables the identification of the presence and location of significant scatterers inside cylindrically-shaped objects is introduced. Next, with the aim of investigating more general 3D problems, the Huygens principle (HP) based procedure is presented. Using HP to forward propagate the waves removes the need to apply matrix generation/inversion. Moreover, HP method provides better performance when compared to conventional time-domain approaches; specifically, the signal to clutter ratio reaches 8 dB, which matches the best figures that have been published. In addition to their simplicity, the two proposed methodologies permit the capture of a minimum dielectric contrast of 1:2, the extent to which different tissues, or differing conditions of tissues, can be discriminated in the final image. Moreover, UWB allows all the information in the frequency domain to be utilised, by combining information gathered from the individual frequencies to construct a consistent image with a resolution of approximately one quarter of the shortest wavelength in the dielectric medium. The power levels used and the specific absorption rates are well within safety limits, while the bandwidths satisfy the UWB definition of being at least 20% of the centre frequencies. It follows that the methodologies permit the detection and location of significant scatterers inside a volume. Validation of the techniques through both simulations and measurements have been performed and presented, illustrating the effectiveness of the methods.

APA, Harvard, Vancouver, ISO, and other styles

9

Gingell, Alexander David. "Applications of Coulomb crystals in cold chemistry." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:3b93832d-b9eb-49e1-b4a4-1bb43d7c9c00.

Full text

Abstract:

This thesis describes the study of a range of ion-molecule reactions at very low collision energies using a newly developed experimental technique which involves the reaction of velocity-selected beams of translationally cold neutral molecules with very low kinetic energy ion ensembles. These studies have been enabled by the construction of a new apparatus for trapping and laser-cooling gas phase atomic ions (⁴⁰Ca⁺). The laser-cooling process results in the formation of ordered, low kinetic energy, lattice-like ion structures, also known as "Coulomb crystals". The properties of single and multicomponent Coulomb crystals (which may also involve molecular ions), and their manipulation via modulation of the applied fields, are explored experimentally and with the use of molecular dynamics simulations. Variations in the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of ⁴⁰Ca⁺ involved with the laser cooling cycle, and these are modelled within an appropriate theoretical framework. The imaging of ⁴⁰Ca⁺ fluorescence as a function of time allows the study of various ion-molecule reactions at collision energies around 300 K, with single ion sensitivity. These reaction studies are extended to low-temperature (collision energies close to 1 K), by combination of the ion trap apparatus with a bent quadrupole guide velocity-selector. Ion-molecule collision energies are shown to be variable over a short range through a change in the quadrupole guide voltage, or the ion trapping parameters; the effect of these modulations on the rate constant is explored for Ca⁺ + CH₃F. Bimolecular rate constants for the reactions of ⁴⁰Ca⁺ with CH₃F, CH₂F₂ and CH₃Cl have been determined for a range of ⁴⁰Ca⁺ state populations, allowing resolution of the global rate contributions from the ground and combined excited states. These results are analysed in the context of capture theories and ab initio electronic structure calculations. In each case, suppression of the ground state rate constant is explained by the presence of either a submerged or real barrier on the ground state potential surface. Rates of reaction from the combined excited states are generally found to be in line with capture theories, and in some cases variation is found between the high and low collision energy regimes. Molecular product ions generated in these experiments have been shown to be sympathetically-cooled into the crystal structure, and subsequently identified through resonance-excitation mass spectrometry. Molecular ions were also produced by multiphoton laser ionisation of a thermal background gas of OCS molecules. An ion-molecule reaction involving a molecular ion, that of charge transfer between OCS⁺ and ND₃, has been studied at a collision energy near 1 K for the first time using sympathetically-cooled OCS⁺ and velocity-selected ND₃. These experiments illustrate the generality of the techniques described herein, and should lead to many possibilities for future studies.

APA, Harvard, Vancouver, ISO, and other styles

10

Walker, Ann L. (Ann Lee). "Strategic Planning Applications in Postsecondary Institutions with Accredited Physical Therapy Educational Programs." Thesis, University of North Texas, 1990. https://digital.library.unt.edu/ark:/67531/metadc331640/.

Full text

Abstract:

Although strategic planning has been used successfully in most major business institutions, higher education has been slow to adopt this management technique. Involvement in planning is a critical issue for allied health educational programs, such as physical therapy, which are relatively new to the academic environment. These programs face a continual need to update their curricula and clinical education based on rapid changes in the health care delivery system and the profession. The problem of this study was to determine the extent to which the strategic planning process is currently applied in institutions in the United States which offer accredited physical therapy educational programs. The population of this study was made up of the chief executive officers of the 115 public and independent institutions that offer physical therapy educational programs. Selected experts on strategic planning and chief executive officers were surveyed in two phases using a mailed questionnaire designed to measure the organization, characteristics, and impact of strategic planning in institutions that offer accredited physical therapy educational programs. Seventy-three percent of the chief executive officers responded, and 50.9 percent indicated their involvement with strategic planning by completing the questionnaire. The findings indicate that, although there is general agreement between the experts and the chief executive officers concerning the characteristics of strategic planning, differences exist. Differences were also identified between academic health centers and other types of institutions, between public and independent institutions, and between institutions by type of physical therapy degree offered. It was concluded that, in the opinion of the chief executive officers, strategic planning processes are being practiced in institutions that offer physical therapy programs, that this process is compatible with academic collegiality, that changes are made in policies and programs but not in the mission, that although faculty members including those from physical therapy are involved, the role and the involvement of these individuals is unclear, and that information-gathering and evaluation methods could be refined.

APA, Harvard, Vancouver, ISO, and other styles

11

Epps, Susan Bramlett, and Alison L. Barton. "Enhancing Student Motivation Using Self-Determination Theory: Practical Applications for the Online Environment." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etsu-works/2568.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Engelhard, Sonja, Michael U. Kumke, and Hans-Gerd Löhmannsröben. "OPQS – optical process and quality sensing : exemplary applications in the beerbrewing and polyurethane foaming processes." Universität Potsdam, 2006. http://opus.kobv.de/ubp/volltexte/2007/1219/.

Full text

Abstract:

Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near-infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant.

APA, Harvard, Vancouver, ISO, and other styles

13

Wang, Chao. "Microfluidics for particle manipulation : new simulation techniques for novel devices and applications." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:8125980e-0603-4425-b0fa-89a4fdfdf464.

Full text

Abstract:

This thesis focuses on fundamental aspects of microfluidic systems and applies relevant findings to innovative designs for advanced particle manipulation applications. Computational Fluid Dynamics (CFD) is adopted for fluid modeling, based on the Finite Volume method. The accuracy of the solutions obtained is confirmed by grid sensitivity analysis and by comparisons with experimental work. Curved microchannel features and the induced Dean flow are studied through a parametric space exploration and simulations. The Lagrange-Euler coupling method – Surface Marker Point methodology – is applied to simulate large-size particles (of comparable size to the channel). Through this simulation approach, all the forces on such particles are directly derived through solving the governing equations and the influence of these particles on the flow is considered in a fully coupled manner. A new approach – the Frozen Flow & Flow Correction Coefficient method – is developed, making trans-relaxation-time simulations possible and improving computational efficiency significantly, for 3D simulations of arbitrary shape and size microparticles in complicated microfluidic channels. Detailed comparisons between simulation results and experiments involving particle sedimentation and particle equilibrium position have been conducted for methodology validation. Mechanisms of hydrodynamic particle manipulation are then studied, including hydrodynamic focusing and separation. It is found that the Tubular Pinch effect, Dean flow and the Radial Pressure Gradient effect interact to yield two distinct particle separation mechanisms. For advanced applications, particle focusing, non-magnetic and magnetic separation for neutrally buoyant particles are proposed, based on newly gained insight on the above-mentioned mechanisms. Appropriate channel designs have been proposed both for particle focusing and size-based particle separation, while the vertical-magnetic-Dean separation scheme is highlighted for magnetic separation. Finally, a new integrated system is proposed, that combines the above novel designs into a device-like ensemble. It promises to offer functionality for biomaterial separation and detection, including different types of cells, antigens and biomarkers.

APA, Harvard, Vancouver, ISO, and other styles

14

Walker, Richard James. "Quantum cascade laser spectroscopy : developments and applications." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:5021ac50-c69d-4a1d-8071-e59ffed9fcb8.

Full text

Abstract:

This thesis presents work examining the characteristics and applicability of quantum cascade lasers. An introduction is given explaining both the desire for a widely tunable, narrow bandwidth device working in the midinfrared, as well as detailing the ways in which quantum cascade lasers (QCLs) fulfill these requirements. The development and manufacture of QCLs are then discussed. The experimental section of this thesis is then split into three parts. Chapter 2 concerns the characterisation and application of several pulsed QCLs. The intrapulse mode of operation is employed and the effect of the resulting rapid frequency chirp upon molecular spectra is investigated in the form of rapid passage signals. The evolution of said rapid passage signals is then investigated as a function of chromophore pressure and identity, with different QCLs, chirp rates, and optical path lengths. The prospect of producing population transfer with chirped lasers is discussed. Chapters 3, 4, and 5 are then concerned with the application and characterisation of continuous wave QCLs. In these chapters a widely tunable commercially produced EC-QCL is utilised as well as two DFB QCLs, one of which is used in tandem with a home-made mount and temperature controller. In Chapter 3 a number of sensitive detection techniques are compared with the employment of wavelength modulation spectroscopy, long path cells and optical cavities, and the narrow bandwidth of QCLs utilised to determine a previously unknown spectral constant of DBr. Chapters 4 and 5 then utilise the high power of an external cavity quantum cascade laser in sub-Doppler Lamb-dip and polarisation spectroscopy measurements and then a pump-probe experiment. The laser linewidth is investigated on a millisecond timescale returning a current noise limited value of c.a. 2 MHz and the fundamental linewidth of the device investigated by altering the injection current. Chapter 5 is concerned with the pump-probe experiment, directly measuring the hot band absorption in a ladder like transition (R(6.5)$_\frac{1}{2}$ $v=1\leftarrow0$ and P(7.5)$_\frac{1}{2}$ $v=1\leftarrow0$). The Bennett peak in the hot band is observed with a DFB-QCL swept at $\sim 0.15$ MHz ns$^{-1}$ and is seen not just as a pump bandwidth limited lineshape, but as a highly velocity selected rapid passage signal. The effect of pressure, pump and probe scan rate and power upon this rapid passage signal is also studied. It is further noted that rapid thermalisation occurs within $v=1$ such that at pressures above c.a. 30 mTorr a broad NO doublet absorption is observed beneath the Bennett peak from which a total population transfer of c.a. $16 \%$ can be estimated. Finally an experiment is discussed in which this population transfer could be increased for use in secondary applications. Chapter 6 then presents initial measurements with two prototype pulsed 3.3 \si{\micro\metre} QCLs considering the prospects of such devices. A Fabry-P\'rot device is first studied using a Fourier transform spectrometer and temperature tuning used to produce a spectrum of the Q-branch of CH$_4$ around 3025 cm$^$. Experiments are then performed using a DFB QCL investigating the chirp rate of the system as an indicator of the rate of heat accumulation within the system. Heat management is of particular consideration when the sea-change is made from pulsed to continuous devices. For this device absorption spectra of two CH$_4$ transitions at 2971 cm$^$ are used to determine the chirp rate, which is found to be c.a. 1.8 GHz ns$^$, at least an order of magnitude higher than that of the longer wavelength pulsed devices considered in Chapter 2.

APA, Harvard, Vancouver, ISO, and other styles

15

Fechler, Nina. "Salts as highly diverse porogens : functional ionic liquid-derived carbons and carbon-based composites for energy-related applications." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2013/6477/.

Full text

Abstract:

The present thesis is to be brought into line with the current need for alternative and sustainable approaches toward energy management and materials design. In this context, carbon in particular has become the material of choice in many fields such as energy conversion and storage. Herein, three main topics are covered: 1)An alternative synthesis strategy toward highly porous functional carbons with tunable porosity using ordinary salts as porogen (denoted as “salt templating”) 2)The one-pot synthesis of porous metal nitride containing functional carbon composites 3)The combination of both approaches, enabling the generation of highly porous composites with finely tunable properties All approaches have in common that they are based on the utilization of ionic liquids, salts which are liquid below 100 °C, as precursors. Just recently, ionic liquids were shown to be versatile precursors for the generation of heteroatom-doped carbons since the liquid state and a negligible vapor pressure are highly advantageous properties. However, in most cases the products do not possess any porosity which is essential for many applications. In the first part, “salt templating”, the utilization of salts as diverse and sustainable porogens, is introduced. Exemplarily shown for ionic liquid derived nitrogen- and nitrogen-boron-co-doped carbons, the control of the porosity and morphology on the nanometer scale by salt templating is presented. The studies within this thesis were conducted with the ionic liquids 1-Butyl-3-methyl-pyridinium dicyanamide (Bmp-dca), 1-Ethyl-3-methyl-imidazolium dicyanamide (Emim-dca) and 1 Ethyl 3-methyl-imidazolium tetracyanoborate (Emim-tcb). The materials are generated through thermal treatment of precursor mixtures containing one of the ionic liquids and a porogen salt. By simple removal of the non-carbonizable template salt with water, functional graphitic carbons with pore sizes ranging from micro- to mesoporous and surface areas up to 2000 m2g-1 are obtained. The carbon morphologies, which presumably originate from different onsets of demixing, mainly depend on the nature of the porogen salt whereas the nature of the ionic liquid plays a minor role. Thus, a structural effect of the porogen salt rather than activation can be assumed. This offers an alternative to conventional activation and templating methods, enabling to avoid multiple-step and energy-consuming synthesis pathways as well as employment of hazardous chemicals for the template removal. The composition of the carbons can be altered via the heat-treatment procedure, thus at lower synthesis temperatures rather polymeric carbonaceous materials with a high degree of functional groups and high surface areas are accessible. First results suggest the suitability of the materials for CO2 utilization. In order to further illustrate the potential of ionic liquids as carbon precursors and to expand the class of carbons which can be obtained, the ionic liquid 1-Ethyl-3-methyl-imidazolium thiocyanate (Emim-scn) is introduced for the generation of nitrogen-sulfur-co-doped carbons in combination with the already studied ionic liquids Bmp-dca and Emim-dca. Here, the salt templating approach should also be applicable eventually further illustrating the potential of salt templating, too. In the second part, a one-pot and template-free synthesis approach toward inherently porous metal nitride nanoparticle containing nitrogen-doped carbon composites is presented. Since ionic liquids also offer outstanding solubility properties, the materials can be generated through the carbonization of homogeneous solutions of an ionic liquid acting as nitrogen as well as carbon source and the respective metal precursor. The metal content and surface area are easily tunable via the initial metal precursor amount. Furthermore, it is also possible to synthesize composites with ternary nitride nanoparticles whose composition is adjustable by the metal ratio in the precursor solution. Finally, both approaches are combined into salt templating of the one-pot composites. This opens the way to the one-step synthesis of composites with tunable composition, particle size as well as precisely controllable porosity and morphology. Thereby, common synthesis strategies where the product composition is often negatively affected by the template removal procedure can be avoided. The composites are further shown to be suitable as electrodes for supercapacitors. Here, different properties such as porosity, metal content and particle size are investigated and discussed with respect to their influence on the energy storage performance. Because a variety of ionic liquids, metal precursors and salts can be combined and a simple closed-loop process including salt recycling is imaginable, the approaches present a promising platform toward sustainable materials design.
Die vorliegende Arbeit basiert auf der Notwendigkeit für eine alternative und nachhaltige Energiewirtschaft sowie alternativer Herstellungsmethoden der damit verbundenen Materialien. Hierbei kommt besonders Kohlenstoffen und kohlenstoffbasierten Systemen eine hohe Bedeutung zu. Im Rahmen der Dissertation wurden drei Ansätze verfolgt, die zu der Entwicklung alternativer Strategien zur Herstellung poröser Heteroatom-enthaltender Kohlenstoffe und deren Komposite beitragen. Die Materialien wurden des Weiteren für die CO2 Nutzung sowie Energiespeicherung in Form von Superkondensatoren getestet. Allen Materialien ist gemeinsam, dass sie ausgehend von ionischen Flüssigkeiten, Salze mit einem Schmelzpunkt unterhalb von 100 °C, als Kohlenstoffvorstufe durch Hochtemperaturverfahren hergestellt wurden. Im ersten Teil wird ein alternatives und nachhaltiges Verfahren zur Herstellung hochporöser Stickstoff und Stickstoff-Bor-haltiger Kohlenstoffe vorgestellt. Bei dieser als „Salztemplatierung“ bezeichneten Methode werden herkömmliche Salze als Porogen verwendet. Damit sind sehr hohe Oberflächen erreichbar, die neben der Porengröße und dem Porenvolumen durch die Variation der Salzspezies und Salzmenge einstellbar sind. Dies bietet gegenüber herkömmlichen Templatierungsverfahren den Vorteil, dass das Salz nach erfolgter Karbonisierung der ionischen Flüssigkeit in Anwesenheit der nicht karbonisierbaren Salzspezies einfach mit Wasser auswaschbar ist. Hierbei ist ein Recyclingprozess denkbar. Bei hohen Synthesetemperaturen werden graphitische, bei niedrigen hochfunktionalisierte, polymerartige Produkte erhalten. Letztere erwiesen sich als vielversprechende Materialien für die CO2 Nutzung. Unter Verwendung einer bisher nicht eingesetzten ionische Flüssigkeit konnte weiterhin die Einführung von Schwefel als Heteroatom ermöglicht werden. Im zweiten Teil wird eine Templat-freie Einschrittsynthese von porösen Kompositen aus Metallnitrid Nanopartikeln und Stickstoff-dotiertem Kohlenstoff vorgestellt. Die Materialien werden ausgehend von einer Lösung aus einer ionischen Flüssigkeit und einem Metallvorläufer hergestellt, wobei die ionische Flüssigkeit sowohl als Kohlenstoffvorläufer als auch als Stickstoffquelle für die Metallnitride dient. Der Metallgehalt, das Metallverhältnis in ternären Nitriden und die Oberfläche sind über den Anteil des Metallvorläufers einstellbar. Schließlich werden beide Ansätze zur Salztemplatierung von den Kompositen kombiniert. Dadurch wird die Einschrittsynthese von Kompositen mit einstellbarer Oberfläche, Zusammensetzung, Partikelgröße und Morphologie ermöglicht. Diese Materialien wurden schließlich als Elektroden für Superkondensatoren getestet und der Einfluss verschiedener Parameter auf die Leistungsfähigkeit untersucht. Aufgrund verschiedener Kombinationsmöglichkeiten von ionischen Flüssigkeiten, Metallvorläufern und Salzen, stellen die hier präsentierten Ansätze eine vielversprechende Plattform für die nachhaltige Materialsynthese dar.

APA, Harvard, Vancouver, ISO, and other styles

16

Wu, Yimin A. "Towards large area single crystalline two dimensional atomic crystals for nanotechnology applications." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:bdb827e5-f3fd-4806-8085-0206e67c7144.

Full text

Abstract:

Nanomaterials have attracted great interest due to the unique physical properties and great potential in the applications of nanoscale devices. Two dimensional atomic crystals, which are atomic thickness, especially graphene, have triggered the gold rush recently due to the fascinating high mobility at room temperature for future electronics. The crystal structure of nanomaterials will have great influence on their physical properties. Thus, this thesis is focused on developing the methods to control the crystal structure of nanomaterials, namely quantum dots as semiconductor, boron nitride (BN) as insulator, graphene as semimetal, with low cost for their applications in photonics, structural support and electronics. In this thesis, firstly, Mn doped ZnSe quantum dots have been synthesized using colloidal synthesis. The shape control of Mn doped ZnSe quantum dots has been achieved from branched to spherical by switching the injection temperature from kinetics to thermodynamics region. Injection rates have been found to have effect on controlling the crystal phase from zinc blende to wurtzite. The structural-property relationship has been investigated. It is found that the spherical wurtzite Mn doped ZnSe quantum dots have the highest quantum yield comparing with other shape or crystal phase of the dots. Then, the Mn doped ZnSe quantum dots were deposited onto the BN sheets, which were micron-sized and fabricated by chemical exfoliation, for high resolution imaging. It is the first demonstration of utilizing ultrathin carbon free 2D atomic crystal as support for high resolution imaging. Phase contrast images reveal moiré interference patterns between nanocrystals and BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes using a newly developed equation method. Double diffraction is observed and has been analyzed using a vector method. As only a few microns sized 2D atomic crystal, like BN, can be fabricated by the chemical exfoliation. Chemical vapour deposition (CVD) is as used as an alternative to fabricate large area graphene. The mechanism and growth dynamics of graphene domains have been investigated using Cu catalyzed atmospheric pressure CVD. Rectangular few layer graphene domains were synthesized for the first time. It only grows on the Cu grains with (111) orientation due to the interplay between atomic structure of Cu lattice and graphene domains. Hexagonal graphene domains can form on nearly all non-(111) Cu surfaces. The few layer hexagonal single crystal graphene domains were aligned in their crystallographic orientation over millimetre scale. In order to improve the alignment and reduce the layer of graphene domains, a novel method is invented to perform the CVD reaction above the melting point of copper (1090 ºC) and using molybdenum or tungsten to prevent the balling of the copper from dewetting. By controlling the amount of hydrogen during the growth, individual single crystal domains of monolayer over 200 µm are produced determined by electron diffraction mapping. Raman mapping shows the monolayer nature of graphene grown by this method. This graphene exhibits a linear dispersion relationship and no sign of doping. The large scale alignment of monolayer hexagonal graphene domains with epitaxial relationship on Cu is the key to get wafer-sized single crystal monolayer graphene films. This paves the way for industry scale production of 2D single crystal graphene.

APA, Harvard, Vancouver, ISO, and other styles

17

Ramraj, Varun. "Exploiting whole-PDB analysis in novel bioinformatics applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6c59c813-2a4c-440c-940b-d334c02dd075.

Full text

Abstract:

The Protein Data Bank (PDB) is the definitive electronic repository for experimentally-derived protein structures, composed mainly of those determined by X-ray crystallography. Approximately 200 new structures are added weekly to the PDB, and at the time of writing, it contains approximately 97,000 structures. This represents an expanding wealth of high-quality information but there seem to be few bioinformatics tools that consider and analyse these data as an ensemble. This thesis explores the development of three efficient, fast algorithms and software implementations to study protein structure using the entire PDB. The first project is a crystal-form matching tool that takes a unit cell and quickly (< 1 second) retrieves the most related matches from the PDB. The unit cell matches are combined with sequence alignments using a novel Family Clustering Algorithm to display the results in a user-friendly way. The software tool, Nearest-cell, has been incorporated into the X-ray data collection pipeline at the Diamond Light Source, and is also available as a public web service. The bulk of the thesis is devoted to the study and prediction of protein disorder. Initially, trying to update and extend an existing predictor, RONN, the limitations of the method were exposed and a novel predictor (called MoreRONN) was developed that incorporates a novel sequence-based clustering approach to disorder data inferred from the PDB and DisProt. MoreRONN is now clearly the best-in-class disorder predictor and will soon be offered as a public web service. The third project explores the development of a clustering algorithm for protein structural fragments that can work on the scale of the whole PDB. While protein structures have long been clustered into loose families, there has to date been no comprehensive analytical clustering of short (~6 residue) fragments. A novel fragment clustering tool was built that is now leading to a public database of fragment families and representative structural fragments that should prove extremely helpful for both basic understanding and experimentation. Together, these three projects exemplify how cutting-edge computational approaches applied to extensive protein structure libraries can provide user-friendly tools that address critical everyday issues for structural biologists.

APA, Harvard, Vancouver, ISO, and other styles

18

Wang, Zeng. "Laser-based detection and tracking of dynamic objects." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c7f2da08-fa1e-4121-b06b-31aad16ecddd.

Full text

Abstract:

In this thesis, we present three main contributions to laser-based detection and tracking of dynamic objects, from both a model-based point of view and a model-free point of view, with an emphasis on applications to autonomous driving. A segmentation-based detector is first proposed to provide an end-to-end detection of the classes car, pedestrian and bicyclist in 3D laser data amongst significant background clutter. We postulate that, for the particular classes considered, solving a binary classification task outperforms approaches that tackle the multi-class problem directly. This is confirmed using custom and third-party datasets gathered of urban street scenes. The sliding window approach to object detection, while ubiquitous in the Computer Vision community, is largely neglected in laser-based object detectors, possibly due to its perceived computational inefficiency. We give a second thought to this opinion in this thesis, and demonstrate that, by fully exploiting the sparsity of the problem, exhaustive window searching in 3D can be made efficient. We prove the mathematical equivalence between sparse convolution and voting, and devise an efficient algorithm to compute exactly the detection scores at all window locations, processing a complete Velodyne scan containing 100K points in less than half a second. Its superior performance is demonstrated on the KITTI dataset, and compares commensurably with state of the art vision approaches. A new model-free approach to detection and tracking of moving objects with a 2D lidar is then proposed aiming at detecting dynamic objects of arbitrary shapes and classes. Objects are modelled by a set of rigidly attached sample points along their boundaries whose positions are initialised with and updated by raw laser measurements, allowing a flexible, nonparametric representation. Dealing with raw laser points poses a significant challenge to data association. We propose a hierarchical approach, and present a new variant of the well-known Joint Compatibility Branch and Bound algorithm to handle large numbers of measurements. The system is systematically calibrated on real world data containing 7.5K labelled object examples and validated on 6K test cases. Its performance is demonstrated over an existing industry standard targeted at the same problem domain as well as a classical approach to model-free tracking.

APA, Harvard, Vancouver, ISO, and other styles

19

Deshpande, Atul Suresh. "Fabrication of porous metal oxides for catalytic application using templating techniques." Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/112/.

Full text

Abstract:

Nanostrukturierte Materialien zeichnen sich dadurch aus, dass sie aus sehr kleinen Baueinheiten zusammengesetzt sind. Typischerweise liegt die Grössenordnung dieser Bausteine im Bereich von einigen Nanometern. Ein Nanometer entspricht 10-9 Meter. Dadurch bekommen nanostrukturierte Materialien oft verbesserte, vielfach sogar ganz neue Eigenschaften, die für viele heutige wie auch zukünftige Anwendungen von Vorteil sind.

Ein Weg, um solche nanostrukturierte Materialien herzustellen, ist die sogenannte „Templatierungsmethode“. Das Templat besteht aus einem einzelnen Molekül, einer Ansammlung von Molekülen oder aus einem festen Objekt. Beim Aufbau des nanostrukturierten Materials wirkt das Templat als Schablone oder als Gussform und beeinflusst damit die Struktur des Endproduktes. Normalerweise besteht dieser Prozess aus mehreren Schritten. Zuerst wird der Raum um das Templat mit dem Ausgangsstoff umhüllt oder ausgefüllt, dann wird der Ausgangsstoff chemisch in das gewünschte Endprodukt umgewandelt, wobei das Templat die Endform kontrolliert und am Schluss wird das Templat entfernt. Das geschieht meistens durch Erhitzen. Als Ausgangsstoff können dabei einzelne Moleküle verwendet werden, die sich leicht in das Endprodukt umwandeln lassen, oder aber vorgeformte Partikelchen, die nur noch zur entsprechenden Form angeordnet werden müssen.

In dieser Arbeit wurden poröse Metalloxid-Kügelchen hergestellt, die aus einem Gemisch aus Titanoxid und entweder Aluminium-, Gallium- oder Indiumoxid bestehen. Als Template wurden poröse Kunststoffkügelchen eingesetzt, die man sonst für Chromatographiezwecke braucht. Bei der Synthese wurden die Poren der Kunststoffkügelchen mit dem Ausgangsmaterial gefüllt und mit Wasser in ein amorphes Netzwerk umgewandelt. Danach werden die Kügelchen erhitzt, wobei das Kunststofftemplat zersetzt wird. Gleichzeitig wird das amorphe Gerüst in stabile, kristalline Wände umgewandelt, die die Form der Kügelchen auch dann noch behalten, wenn das Templat verschwunden ist. Mit einem ähnlichen Prozess wurden auch Kügelchen aus Cer-Zirkonoxid erhalten. Als Ausgangsstoff wurden dabei aber vorgeformte Cer-Zirkonoxid-Nanopartikel eingesetzt, die in die Poren der Kunststofftemplatkügelchen hinein diffundieren. Diese Cer-Zirkonoxid-Nanopartikel lassen sich auch für die Herstellung von porösen Pulvern verwenden, wobei dann nicht Polymerkügelchen, sondern hochgeordnete Ansammlungen von Block Copolymeren als Template verwendet werden.

Form, Struktur und Eigenschaften all dieser Materialien wurden systematisch unter Anwendung verschiedenster Analysemethoden untersucht. Die auf Titanoxid-basierten Kügelchen wurden auch auf ihre photokatalytische Verwendung zum Abbau von umweltschädlichem 2-Chlorophenol untersucht. Die Cer-Zirkonoxid-Kügelchen wurden für die Herstellung von Wasserstoff aus Methanol getestet. Wasserstoff gilt als hoffungsvoller, sauberer Energieträger der Zukunft und kommt in Brennstoffzellen zum Einsatz.
Nanostructured materials are the materials having structural features on the scale of nanometers i.e. 10-9 m. the structural features can enhance the natural properties of the materials or induce additional properties, which are useful for day to technology as well as the future technologies

One way to synthesize nanostructured materials is using templating techniques. The templating process involves use of a certain “mould” or “scaffold” to generate the structure. The mould is called as the template, can be a single molecule or assembly of molecule or a larger object, which has its own structure. The product material can be obtained by filling the space around the template with a “precursor”, transformation of precursor into the desired material and then removal of template to get product. The precursor can be any chemical moiety that can be easily transformed in to the desired material. Alternatively the desired material is processed into very tiny bricks or “nano building blocks (NBB)” and the product is obtained by arrangement of the NBB by using a scaffold.

We synthesized porous metal oxide spheres of namely TiO2-M2O3: titanium dioxide- M-oxide (M = aluminum, gallium and indium) TiO2-M2O3 and cerium oxide-zirconium oxide solid solution. We used porous polymeric beads as templates. These beads used for chromatographic purposes. For the synthesis of TiO2-M2O3 we used metal- alkoxides as precursor. The pore of beads were filled with precursor and then reacted with water to give transformation of the precursor to amorphous oxide network. The network is crystallized and template is removed by heat treatment at high temperatures. In a similar way we obtained porous spheres of CexZr1-xO2. For this we synthesized nanoparticle of CexZr1-xO2 and used then for the templating process to obtain porous CexZr1-xO2 spheres.

Additionally, using the same nanoparticles we synthesized nano-porous powder using self-assembly process between a block-copolymers scaffold and nanoparticles.

Morphological and physico-chemical properties of these materials were studies systematically by using various analytical techniques

TiO2-M2O3 material were tested for photocatalytic degradation of 2-Chlorophenol a poisonous pollutant. While CexZr1-xO2 spheres were tested for methanol steam reforming reaction to generate hydrogen, which is a fuel for future generation power sources like fuel cells. All the materials showed good catalytic performance.

APA, Harvard, Vancouver, ISO, and other styles

20

Gaganatsou, Paraskevi. "Lithium and indium quinoneoximic complexes and their application in scintillation counting." Thesis, London Metropolitan University, 1987. http://repository.londonmet.ac.uk/3082/.

Full text

Abstract:

Several complexes of lithium derived from 1,2-naphthoquinone 1-oxime and 1,2-naphthoquinone 2-oxime have been prepared and characterised using analytical, spectroscopic and thermal gravimetric techniques. I.r. studies indicate that the ligands in these complexes are essentially quinoneoximic in character. For the complex Li(1-nqo)(1-nqoH).Eton the quinoneoximic character has been confirmed by X-ray crystallography. All the lithium complexes were found to be stable towards atmospheric oxygen and water. Their reactivity towards dimethylacetylene dicarboxylate was investigated and compared to that of the copper quinoneoximato complexes. Each of the lithium complexes reacted readily with the acetylene dicarboxylate to give a novel nucleophilic addition product isomeric to the Diels-Alder adduct (1,4-oxazine) obtained from the copper complexes. Re-examination of the behaviour of the copper quinoneoximato complexes towards dimethylacetylene dicarboxylate has given an insight to the mechanism of the reaction and has shown that the copper complexes also act as catalysts in the conversion of 1,4-oxazine derivatives to 1,3-oxazoles. Several lithium carboxylato and dithiocarbamato complexes have been prepared. For the dithiocarbamato complexes a new synthetic method involving the reaction of carbon disulphide and the amine with lithium chloride was developed during this study. Solubility studies were carried out on several complexes of types Li(RCO,), Li(R-NCS,)(R-NCSSH), Ll(nqo) and M(qo) (M = Li, Na2 K, Ni, Co) in polar and non-polar solvents. Maximum solubility was observed in pyridine, dimethylsulphoxlde and ethanol. The scintillation efficiency of pyridine, dimethylsulphoxide and ethanol was examined in commercially available scintillator mixtures and in scintillator mixtures developed during this study. The scintillation efficiency of the lithium complexes derived from the mono-oximes of 1,2-naphthoqulnone, carboxylic and dlthlocarbamlc acids was also investigated. The latter two set of complexes proved promising for loading liquid scintillation counters, when present as 'solid' in the scintillator mixture.

APA, Harvard, Vancouver, ISO, and other styles

21

Hardester, Bryan Matthew. "An analysis and compositional application of trombonist John Allred's improvisational style." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/4852.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Marshall, Helen. "Exploration, Development and Application of Z-Shim and Allied Methods for Signal Recovery in Single-Shot Echo Planar Imaging." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487314.

Full text

Abstract:

Echo planar imaging (EPI) is widely used for applications where speed and/or sensitivity are essential, such as functional MRI (fMRI) and perfusion MRI. Gradient echo EPI suffers from signal drop-out due to through-slice magnetic field (Bo) inhomogeneity, which prevents certain brain areas from being imaged, e.g. around the frontal sinus and auditory canals. Signal loss can be corrected using the z-shim method, which approximates local 80 variations as linear and recovers signal by applying an opposite refocusing gradient. However, the required gradient is spatially varying and unknown, and. each refocused image requires a separate acquisition. Multiple z-shims are required for full correction making the method inefficient. Signal loss increases with increasing magnetic field strength. The need for an effective correction strategy is driven by the current trend towards high field strengths of 3T and above. This work explores signal loss and recovery in the brain at 3T, and investigates signal loss correction methods culminating in a method which achieves successful signal recovery from two optimally chosen z-shims. The linear approximation made by z-shim methods was found to be valid for the majority of pixels in the brain ,at 3T. Parallel imaging in the through-slice direction to reconstruct points of the k-space slice profile not originally measured was investigated but found to be limited by current hardware. An efficient signal loss correction method was developed which requires only two optimally spaced zshims, positioned by a rapid calibration method for maximum signal recovery. Full signal restoration (to within 2% of the correct value) was achieved in 96% of all brain pixels for 3mm slices, and partial correction in pixels outside this range. This method was applied to a language fMRI study which suffers from signal loss, and recovered activation in regions of 80 inhomogeneity revealing language activation not detectable by conventional fMRI.

APA, Harvard, Vancouver, ISO, and other styles

23

Yu, Hai-Sui. "Cavity expansion theory and its application to the analysis of pressuremeters." Thesis, University of Oxford, 1990. http://ora.ox.ac.uk/objects/uuid:96cfe772-8f4b-4995-a890-1138c2be1458.

Full text

Abstract:

The successful application of in-situ testing of soils heavily depends on development of methods of interpretation of the tests. The purpose of this thesis is to develop a consistent theoretical basis for the interpretation of pressuremeter tests in cohesive and frictional materials. The research programme is based on cavity expansion theory with additional details provided by a large strain finite element analysis. A unified analytical solution is developed for the expansion and contraction of both cylindrical and spherical cavities in dilatant elastic-plastic soils. For the first time, explicit solutions for the pressure-expansion and pressure-contraction relationships are derived without any restriction being imposed on the magnitude of the deformation. In addition, the finite element method is adopted for solving the cavity expansion problem. This is mainly due to the fact that only in special cases when simple material models and boundary conditions are involved has it been possible to solve the problem analytically. A finite element analysis of the cone-pressuremeter test in sand is described. A series of two-dimensional finite element calculations on both the self-boring pressuremeter test and the cone-pressuremeter test is performed. In modelling the penetration process of cone-pressuremeter tests, the stresses evaluated by the cavity expansion theory are used as the starting condition for the finite element analysis. Emphasis is placed on quantifying the effects of pressuremeter geometry on derived deformation and strength parameters. In the finite element formulation, a special effort is devoted to developing a lower order finite element suitable for analysing axisymmetric elastic-plastic problems which involve incompressibility constraints. The formulation of a new six-noded isoparametric displacement finite element is presented. To account for large strain (rotation) effects, an Eulerian description of deformation is adopted and the Jaumann stress rate is used in the soil constitutive equations. The suitability of the conventional interpretation methods for pressuremeter tests is critically assessed in the light of the finite element results. Based on the numerical results, improved procedures for obtaining in-situ soil parameters from pressuremeter tests in both clay and sand have been proposed.

APA, Harvard, Vancouver, ISO, and other styles

24

JOUINOT, PATRICE. "Developpements de l'essai de disques sous pression. Applications a la fragilisation par l'hydrogene d'aciers faiblement allies." Paris 6, 1991. http://www.theses.fr/1991PA066531.

Full text

Abstract:

Nous avons apporte plusieurs perfectionnements a la technique experimentale des essais de disques sous pression: automatisation des equipements, grandes vitesses de pressurisation, mesure de la temperature et de la fleche au pole du disque pendant l'essai. Grace a l'essai de disques et a des observations macroscopiques et microscopiques avant et apres essai, nous avons etudie les proprietes mecaniques et la fragilisation par l'hydrogene (fph) de six aciers faiblement allies pour oleoducs. Les proprietes mecaniques mesurees avec l'essai de disques sont en accord avec celles determinees en traction et en durete; de plus, les fractographies ont montre que la pression de rupture sous helium diminue lorsque le disque contient des inclusions. Plus les aciers etudies sont sensibles a la corrosion sous contrainte en milieu h2s, plus leur indice de fragilisation par l'hydrogene est eleve. Avec les micrographies et les microfractographies, nous avons montre que les aciers doivent contenir peu d'inclusions, surtout si elles sont alignees, pour resister a la fph. De plus, les micrographies montrent que la fph est reduite si la microstructure est homogene; les fissures se developpent au niveau des interfaces ferrite-perlite et/ou aux joints de grains. La fph de l'acier a structure bainitique est relativement elevee; elle semble liee a la distribution irreguliere des precipites dans la matrice

APA, Harvard, Vancouver, ISO, and other styles

25

Likitlersuang, Suched. "A hyperplasticity model for clay behaviour : an application to Bangkok clay." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:56dbe556-c58b-439f-b8fa-9e092f139309.

Full text

Abstract:

The main purpose of this thesis is the development of a new constitutive soil model emphasising the use of thermodynamic principles. This new approach to plasticity modelling, termed ‘hyperplasticity’, was first developed by Collins and Houlsby (1997) and Houlsby and Puzrin (2000). This idea has been further extended to continuous hyperplasticity in which smooth transitions between elastic and plastic behaviour can be modelled (Puzrin and Houlsby, 2001b). Applying hyperplasticity to this research, a kinematic hardening model specified by means of two scalar functionals is used to accommodate the effect of stress history on stiffness. A rate-dependent calculation for an approximation of the incremental stress-strain response is introduced. The model developed in the research is named ‘kinematic hardening modified Cam-clay (KHMCC) model’ and requires eight parameters (plus an extra parameter for rate-dependent analysis). Triaxial test results from the Asian Institute of Technology (AIT) and cyclic undrained triaxial data from Chulalongkorn University are employed to establish the soil parameters for the new model. The model is initially developed in terms of triaxial stress-strain parameters for the purpose of comparison with the experimental data on Bangkok clay. The model is expressed in FORTRAN code for implementation into the OXFEM finite element program. Two examples of real geotechnical projects in Bangkok (a road embankment and tunnelling in soft ground) are analysed under plane strain conditions. Comparisons of the numerical analysis results with field data are made. In addition, factors affecting the results of the analysis such as stress history and K0, are investigated.

APA, Harvard, Vancouver, ISO, and other styles

26

Garcia-Hermosa, M. Isabel. "Morphodynamics of sand mounds in shallow flows." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:c6ef38f8-d098-4ce5-b0f0-38e2ebe6caf5.

Full text

Abstract:

Large-scale bed features are often encountered in coastal waters, and include sandbanks and spoil heaps. The morphodynamic development of such features involves complicated nonlinear interactions between the flow hydrodynamics, sediment transport, and bed profile. Numerical modelling of the morphodynamic evolution and migration of large-scale bed features is necessary in order to understand their long-term behaviour in response to changing environmental conditions. This thesis describes detailed measurements of the morphodynamics of sand mounds in unidirectional and oscillatory (tidal) flows, undertaken at the U.K. Coastal Research Facility (UKCRF). High quality data were collected, including water velocities, water levels and overhead images. The parameters tested are: three types of mound shape (circular and elliptical in plan shape, and Gaussian, cosine and triangular in cross-section); underlying fixed or mobile bed conditions; and initial crest height (submerged, surface-touching and surface-piercing). Peak flow velocities are about 0.5 m/s, the sand median grain size is 0.454 mm, and transport occurring mostly as bedload. When analysing the data, the bed contours are determined by digitising the shoreline at different water levels. From these plots, the volume, height, and centroid position of the mound are calculated. A large-scale fit method, based on a Gaussian function has been used to separate small-scale ripples from the large-scale bed structure during the evolution of an isolated sand mound or spoil heap. The bed profile after the ripples are removed is comparable to typical predictions by shallow-flow numerical solvers. The UKCRF experiments investigated the morphodynamic response of a bed mound to hydrodynamic forcing: shape changes, migration rates, volume decay and sediment transport rates. The measured migration rate and decay of a submerged sand mound in the UKCRF are found to be in satisfactory agreement with results from various theoretical models, such as the analytical solution derived by De Vriend. Numerical predictions of mound evolution by a commercial code, PISCES, are also presented for a fully submerged sand mound; the bed evolution is reasonably similar to that observed in the UKCRF. The data provided as a result of the research reported in this thesis provide insight into the behaviour of sand mounds in steady and unsteady flows at laboratory scale, and should also be useful for benchmark (validation) purposes to numerical modellers of large-scale morphodynamics.

APA, Harvard, Vancouver, ISO, and other styles

27

McInerney, Robert E. "Decision making under uncertainty." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:a34e87ad-8330-42df-8ba6-d55f10529331.

Full text

Abstract:

Operating and interacting in an environment requires the ability to manage uncertainty and to choose definite courses of action. In this thesis we look to Bayesian probability theory as the means to achieve the former, and find that through rigorous application of the rules it prescribes we can, in theory, solve problems of decision making under uncertainty. Unfortunately such methodology is intractable in realworld problems, and thus approximation of one form or another is inevitable. Many techniques make use of heuristic procedures for managing uncertainty. We note that such methods suffer unreliable performance and rely on the specification of ad-hoc variables. Performance is often judged according to long-term asymptotic performance measures which we also believe ignores the most complex and relevant parts of the problem domain. We therefore look to develop principled approximate methods that preserve the meaning of Bayesian theory but operate with the scalability of heuristics. We start doing this by looking at function approximation in continuous state and action spaces using Gaussian Processes. We develop a novel family of covariance functions which allow tractable inference methods to accommodate some of the uncertainty lost by not following full Bayesian inference. We also investigate the exploration versus exploitation tradeoff in the context of the Multi-Armed Bandit, and demonstrate that principled approximations behave close to optimal behaviour and perform significantly better than heuristics on a range of experimental test beds.

APA, Harvard, Vancouver, ISO, and other styles

28

Barnes, Edward Owen. "Advances in electrochemical simulation and its application to electroanalysis." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:59bb14a9-180f-4883-9dca-e90d3f1d1ac5.

Full text

Abstract:

This thesis is concerned with the simulation of various electrochemical experiments and its application to electroanalysis. Chapter 1 outlines the fundamental principles of electrochemistry which are of importance for the reading of this thesis. Chapter 2 then outlines the methods used in the numerical simulation of electrochemical experiments. Chapters 3 and 4 are concerned with the electrochemistry of nanoparticles, and how this is affected by the presence of near wall hindered diffusion. In Chapter 3, a computational model to simulate anodic particle coulometry of nanoparticles in the presence of hindered diffusion is developed, and the effect of this hindered diffusion investigated. The model is then applied to simulate experimental data. Chapter 4 looks at the effect of hindered diffusion on the adsorption of nanoparticles on electrode surfaces, and investigates the effects of this adsorption on electrochemical experiments with nanoparticles generally. Chapters 5, 6 and 7 are concerned with band electrodes in isolation, in a pair and in an array respectively. In Chapter 5, a model to simulate double potential step chronoamperometry at an individual band electrode is developed, and used to successfully simulate experimental data. Chapter 6 looks at dual band electrodes used in generator-collector mode, and how this can be used to simultaneously measure the concentration of two species in solution. Chapter 7 looks at interdigitated arrays of band and ring electrodes in generator-collector mode, and develops a model to simulate cyclic voltammetry in both cases, as well as investigating under what conditions interdigitated ring arrays may be modelled as interdigitated band arrays. Chapter 8 develops a model to simulate chronoamperometry and cyclic voltammetry at porous electrodes, and investigates the consequences for electroanalysis of having a porous layer. Finally, Chapter 9 investigates the Marcus-Hush theory of electron transfer kinetics, and looks at the effect of the kinetically limited currents resulting from this theory to the equivalence relation between microdisc electrodes and sphere-on-a-surface electrodes.

APA, Harvard, Vancouver, ISO, and other styles

29

Hernandez, Garcia Hugo Fernando. "Multiscale simulation of heterophase polymerization : application to the synthesis of multicomponent colloidal polymer particles." Phd thesis, Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/2503/.

Full text

Abstract:

Heterophase polymerization is a technique widely used for the synthesis of high performance polymeric materials with applications including paints, inks, adhesives, synthetic rubber, biomedical applications and many others. Due to the heterogeneous nature of the process, many different relevant length and time scales can be identified. Each of these scales has a direct influence on the kinetics of polymerization and on the physicochemical and performance properties of the final product. Therefore, from the point of view of product and process design and optimization, the understanding of each of these relevant scales and their integration into one single model is a very promising route for reducing the time-to-market in the development of new products, for increasing the productivity and profitability of existing processes, and for designing products with improved performance or cost/performance ratio. The process considered is the synthesis of structured or composite polymer particles by multi-stage seeded emulsion polymerization. This type of process is used for the preparation of high performance materials where a synergistic behavior of two or more different types of polymers is obtained. Some examples include the synthesis of core-shell or multilayered particles for improved impact strength materials and for high resistance coatings and adhesives. The kinetics of the most relevant events taking place in an emulsion polymerization process has been investigated using suitable numerical simulation techniques at their corresponding time and length scales. These methods, which include Molecular Dynamics (MD) simulation, Brownian Dynamics (BD) simulation and kinetic Monte Carlo (kMC) simulation, have been found to be very powerful and highly useful for gaining a deeper insight and achieving a better understanding and a more accurate description of all phenomena involved in emulsion polymerization processes, and can be potentially extended to investigate any type of heterogeneous process. The novel approach of using these kinetic-based numerical simulation methods can be regarded as a complement to the traditional thermodynamic-based macroscopic description of emulsion polymerization. The particular events investigated include molecular diffusion, diffusion-controlled polymerization reactions, particle formation, absorption/desorption of radicals and monomer, and the colloidal aggregation of polymer particles. Using BD simulation it was possible to precisely determine the kinetics of absorption/desorption of molecular species by polymer particles, and to simulate the colloidal aggregation of polymer particles. For diluted systems, a very good agreement between BD simulation and the classical theory developed by Smoluchowski was obtained. However, for concentrated systems, significant deviations from the ideal behavior predicted by Smoluchowski were evidenced. BD simulation was found to be a very valuable tool for the investigation of emulsion polymerization processes especially when the spatial and geometrical complexity of the system cannot be neglected, as is the case of concentrated dispersions, non-spherical particles, structured polymer particles, particles with non-uniform monomer concentration, and so on. In addition, BD simulation was used to describe non-equilibrium monomer swelling kinetics, which is not possible using the traditional thermodynamic approach because it is only valid for systems at equilibrium. The description of diffusion-controlled polymerization reactions was successfully achieved using a new stochastic algorithm for the kMC simulation of imperfectly mixed systems (SSA-IM). In contrast to the traditional stochastic simulation algorithm (SSA) and the deterministic rate of reaction equations, instead of assuming perfect mixing in the whole reactor, the new SSA-IM determines the volume perfectly mixed between two consecutive reactions as a function of the diffusion coefficient of the reacting species. Using this approach it was possible to describe, using a single set of kinetic parameters, typical mass transfer limitations effects during a free radical batch polymerization such as the cage effect, the gel effect and the glass effect. Using multiscale integration it was possible to investigate the formation of secondary particles during the seeded emulsion polymerization of vinyl acetate over a polystyrene seed. Three different cases of radical generation were considered: generation of radicals by thermal decomposition of water-soluble initiating compounds, generation of radicals by a redox reaction at the surface of the particles, and generation of radicals by thermal decomposition of surface-active initiators "inisurfs" attached to the surface of the particles. The simulation results demonstrated the satisfactory reduction in secondary particles formation achieved when the locus of radical generation is controlled close to the particles surface.
Eine der industriell am meisten verwendeten Methoden zur Herstellung von Hochleistungspolymeren ist die Heterophasenpolymerisation. Industriell von besonderer Bedeutung ist die sogenannte Saatemulsionspolymerisation bei der kleine Saatteilchen durch die sequentielle Zugabe von weiteren Monomeren gezielt modifiziert werden, um Kompositpolymerteilchen mit den gewünschten mechanischen und chemischen Gebrauchseigenschaften herzustellen. Ein häufig auftretendes Problem während dieser Art der Heterophasenpolymerisation ist die Bildung von neuen, kleinen Teilchen im Polymerisationsverlauf. Diese sogenannte sekundäre Teilchenbildung muss vermieden werden, da sie die Herstellung der gewünschten Teilchen mit den angestrebten Eigenschaften verhindert. Ein spezieller Fall der Saatemulsionspolymerisation ist die Kombination von Vinylacetat als Monomer, das auf Saatteilchen aus Polystyrol polymerisieren soll. Die Unterdrückung der Teilchenneubildung ist in diesem Beispiel besonders schwierig, da Vinylacetat eine sehr hohe Wasserlöslichkeit besitzt. In der vorliegenden Arbeit wurden zur Lösung der Aufgabenstellung verschiedene numerische Simulierungsalgorithmen verwendet, die entsprechend den charakteristischen Längen- und Zeitskalen der im Verlauf der Polymerisation ablaufenden Prozesse ausgewählt wurden, um die passenden Bedingungen für die Unterdrückung der sekundären Teilchenbildung zu finden. Die verwendeten numerischen Methoden umfassen Molekulare Dynamik Simulationen, die benutzt werden, um molekulare Bewegungen zu berechnen; Brownsche Dynamik Simulationen, die benutzt werden, um die zufälligen Bewegungen der kolloidalen Teilchen und der molekularen Spezies zu beschreiben, und kinetische Monte Carlo Simulationen, die das zufällige Auftreten von individuellen physikalischen oder chemischen Ereignissen modellieren. Durch die Kombination dieser Methoden ist es möglich, alle für die Beschreibung der Polymerisation relevanten Phänomene zu berücksichtigen. Damit können nicht nur die Reaktionsgeschwindigkeit und die Produktivität des Prozesses simuliert werden sondern auch Aussagen bezüglich der physikalischen und chemischen Eigenschaften des Produktes sowie den Applikationseigenschaften getroffen werden. In dieser Arbeit wurden zum ersten Mal Modelle für die unterschiedlichen Längen- und Zeitskalen bei Heterophasenpolymerisationen entwickelt und erfolgreich zur Modellierung des Prozesses angewendet. Die Ergebnisse führten zu bedeutenden Verbesserungen der Theorie von Emulsionspolymerisationen insbesondere für die Beschreibung des Massenaustausches zwischen den Phasen (bspw. Radikaleintritt in und Radikalaustritt aus die Polymerteilchen), der Bildung von neuen Teilchen, und der Polymerisationskinetik unter den heterogenen Reaktionsbedingungen mit uneinheitlicher Durchmischung.

APA, Harvard, Vancouver, ISO, and other styles

30

Hunt, Julian David. "Integration of rationale management with multi-criteria decision analysis, probabilistic forecasting and semantics : application to the UK energy sector." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:2cc24d23-3e93-42e0-bb7a-6e39a65d7425.

Full text

Abstract:

This thesis presents a new integrated tool and decision support framework to approach complex problems resulting from the interaction of many multi-criteria issues. The framework is embedded in an integrated tool called OUTDO (Oxford University Tool for Decision Organisation). OUTDO integrates Multi-Criteria Decision Analysis (MCDA), decision rationale management with a modified Issue-Based Information Systems (IBIS) representation, and probabilistic forecasting to effectively capture the essential reasons why decisions are made and to dynamically re-use the rationale. In doing so, it allows exploration of how changes in external parameters affect complicated and uncertain decision making processes in the present and in the future. Once the decision maker constructs his or her own decision process, OUTDO checks if the decision process is consistent and coherent and looks for possible ways to improve it using three new semantic-based decision support approaches. For this reason, two ontologies (the Decision Ontology and the Energy Ontology) were integrated into OUTDO to provide it with these semantic capabilities. The Decision Ontology keeps a record of the decision rationale extracted from OUTDO and the Energy Ontology describes the energy generation domain, focusing on the water requirement in thermoelectric power plants. A case study, with the objective of recommending electricity generation and steam condensation technologies for ten different regions in the UK, is used to verify OUTDO’s features and reach conclusions about the overall work.

APA, Harvard, Vancouver, ISO, and other styles

31

Auger, Jacques. "Analyse et synthèse de substances allélochimiques des allium (liliacées) et synthèse d'analogues : applications à quelques comportements d'insectes inféodés ou non au poireau (allium porrum L.)." Tours, 1987. http://www.theses.fr/1987TOUR4012.

Full text

Abstract:

L'odeur de poireau, a son émission, contient du thiosulfinate de propyle et peu ou pas de disulfures. Les fèces des a. A. Et p. X. Contiennent des disulfures. Différents produits de références et des analogues ont été synthétisés et testées en olfactométrie vis a vis des larves de plusieurs papillons. L'odeur des feces de a. A. Et p. X. Attire d. P. , parasitoide de ces espèces. L'incidence des différentes substances sur le comportement de ponte des adultes de a. A. Est etudiée.

APA, Harvard, Vancouver, ISO, and other styles

32

Ehland, Andreas. "Vibrations of precast and partially prestressed floor systems under moving loads : development of a dynamic fork-lift truck model for vibration serviceability analysis and its application." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:9820a6a3-6b98-44b3-89e0-3aadb818b606.

Full text

Abstract:

This project studies the dynamic response of a composite floor system to excitations from moving fork-lift trucks. The floor system analysed is a system of precast and partially prestressed double-tee elements with a cast in-situ topping. Currently, there are concerns whether the vibrations caused by fork-lift trucks might exceed acceptable limits due to an ongoing trend towards structures of higher slenderness. This study investigates the mechanical background of the excitation and the current design of the floor system. The study is divided into three major chapters: Dynamic fork-lift truck model A dynamic load model of a fork-lift truck is developed which can be used in the analytical verification of the vibration serviceability of structures. The model is based on tests performed on four fork-lift trucks in various configurations. The tests are analysed for the spectrum of accelerations. The analysis results in a simple two-degree-of-freedom model. Its only variables are velocity and time. All other values are constant throughout a simulation and depend on the geometry of the specific fork-lift truck and its payload. The frequencies and phase delays are constants and they are verified as eigen-frequencies of a three-degree-of-freedom model. FE-simulation of vibrations of a composite floor system The fork-lift truck model is applied to a three-dimensional model of a composite floor system. The finiteelement model is developed to simulate the construction process of the composite floor system and its influence on the in-service properties of the structure. As part of this work a preliminary investigation of the damping potential of the joint between precast and cast in-situ concrete is undertaken. A linear time-step analysis of the structure is performed and the nodal accelerations are analysed for their magnitude, dependence on the excitation and frequency content. Field test In order to verify the FE-model of the floor system and the results of the dynamic analysis a field test was undertaken: a floor system was monitored under service conditions. The field data comprise the accelerations of the floor and the forklift truck and the position of the truck relative to the points of measurement. A comparison of the field data and the simulation results proves the validity of both the dynamic fork-lift truck model and the FE-model of the floor system.

APA, Harvard, Vancouver, ISO, and other styles

33

Makuch, Martin. "Circumplanetary dust dynamics application to Martian dust tori and Enceladus dust plumes /." Phd thesis, [S.l.] : [s.n.], 2007. http://opus.kobv.de/ubp/volltexte/2007/1440.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Metzke, Sarah. "Synthesis and characterization of transition metal nitrides and carbides for catalysis and electrochemistry application." Bachelor's thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/6983/.

Full text

Abstract:

It was the goal of this work to explore two different synthesis pathways using green chemistry. The first part of this thesis is focusing on the use of the urea-glass route towards single phase manganese nitride and manganese nitride/oxide nano-composites embedded in carbon, while the second part of the thesis is focusing on the use of the “saccharide route” (namely cellulose, sucrose, glucose and lignin) towards metal (Ni0), metal alloy (Pd0.9Ni0.1, Pd0.5Ni0.5, Fe0.5Ni0.5, Cu0.5Ni0.5 and W0.15Ni0.85) and ternary carbide (Mn0.75Fe2.25C) nanoparticles embedded in carbon. In the interest of battery application, MnN0.43 nanoparticles surrounded by a graphitic shell and embedded in carbon with a high surface area (79 m^2/g) were synthesized, following a previously set route.The comparison of the material characteristics before and after the discharge showed no remarkable difference in terms of composition and just slight differences in the morphological point of view, meaning the particles are stable but agglomerate. The graphitic shell is contributing to the resistance of the material and leads to a fine cyclic stability over 140 cycles of 230 mAh/g after the first charge/discharge and coulombic efficiencies close to 100%. Due to the low voltage towards Li/Li+ and the low polarization, it might be an attractive anode material for lithium ion batteries. However, the capacity is still noticeably lower than the theoretical value for MnN0.43. A mixture of MnN0.43 and MnO nanoparticles embedded in carbon (surface area 93 m^2/g) was able to improve the cyclic stability to over 160 cycles giving a capacity of 811 mAh/g, which is considerably higher than the capacity of the conventional material graphite (372 mAh/g). This nano-composite seems to agglomerate less during the process of discharge. Interestingly, although the capacity is much higher than of the single phase manganese nitride, the nano-composite seems to only contain MnN0.43 nanoparticles after the process of discharge with no oxide phase to be found. Concerning catalysis application, different metal, metal alloy, and metal carbide nanoparticles were synthesized using the saccharide route. At first, systems that were already investigated before, being Pd0.9Ni0.1, Pd0.5Ni0.5, Fe0.5Ni0.5 and Mn0.75Fe2.25C using cellulose as the carbon source were prepared and tested in an alkylation reaction of toluene with benzylchloride. Unexpectedly, the metal alloys did not show any catalytic activity, but the ternary carbide Mn0.75Fe2.25C showed fine catalytic activity of 98% conversion after 9 hour reaction time (110 °C). In a second step, the saccharide route was modified towards other carbon sources and carbon to metal ratios in order to improve the homogeneity of the samples and accessibility of the particle surfaces. The used carbon sources sucrose and glucose are similar in their basic structure of carbohydrates, but reducing the (polymeric) chain length. Indeed, the cellulose could be successfully replaced by sucrose and glucose. A lower carbon to metal ratio was found to influence the size, homogeneity and accessibility (as evidenced by TEM) of the samples. Since sucrose is an aliment, glucose is the better choice as a carbon source. Using glucose, the synthesis of Cu0.5Ni0.5 and W0.15Ni0.85 nano-composites was also possible, although the later was never obtained as pure phase. These alloy nano-composites were tested, along with nickel0 nanoparticles also prepared with glucose and on their catalytic activity towards the reduction of phenylacetylene. The results obtained let believe that any (poly) saccharide, including lignin, could be used as carbon source. The nickel0 nano-composites prepared with lignin as a carbon source were tested along with those prepared with cellulose and sucrose for their catalytic activity in the transfer hydrogenation of nitrobenzene (results compared with exposed nickel nanoparticles and nickel supported on carbon) leading to very promising results. Based on the urea-glass route and the saccharide route, simple equipment and transition metals, it was possible to have a one-pot synthesize with scale-up possibilities towards new material that can be applied in catalysis and battery systems.
Im Rahmen dieser Arbeit wird sowohl die Synthese von Mangannitrid- und -oxid-Nanopartikeln, als auch die Synthese verschiedener Metall- und Legierungsnanopartikel untersucht. Einen Schwerpunkt stellt dabei die Optimierung der Synthese unter den Gesichtspunkten der Nachhaltigkeit dar, was sich insbesondere in der Verwendung diverser nachwachsender Rohstoffe als Kohlenstoffquelle äußert. Für eine mögliche Anwendung in Akkumulatoren werden mit Graphit ummantelte MnN0.43-Nanopartikel mit einer großen Oberfläche (79 m^2/g) synthetisiert. Diese werden exemplarischen Ladezyklen unterzogen, wobei eine strukturelle und auch elektrochemische Stabilität festgestellt werden kann. Eine Mischung der Mangannitride mit Manganoxiden führt zu einer weiteren Verbesserung der Ladekapazität und einer weiteren Oberflächenvergrößerung (93 m^2/g). Die Langlebigkeit der Strukturen wird durch die Einbettung der Nanopartikel in Kohlenstoff unterstützt und kann zu einer Anwendung als Anodenmaterial in den heutzutage vielfach verwendeten Lithiumionen-Akkus führen. Im Sinne der Nachhaltigkeit ist auch die Entwicklung von Katalysatoren. Dabei soll insbesondere die Verwendung von Lignin, was als Bestandteil vieler Pflanzen zwar leicht verfügbar, aber unglücklicherweise bisher chemisch unverwertbar ist, fokussiert werden. Um sich diesem Ziel zu nähern und entsprechende Mechanismen zur Reduktion des Lignins zu entwickeln, werden in dieser Arbeit zunächst verschiedene Kohlenstoffquellen (wie Cellulose, Sucrose und Glucose) zur Synthese von reduktiven Katalysatoren untersucht. Der Kohlenstoff dient dabei sowohl als preiswertes Reduktionsmittel für Metallsalze zur Gewinnung von Metallnanopartikel als auch zur Stabilisierung ebendieser. Es werden vielfältige Legierungen mit Nickel (z.B. Pd0.9Ni0.1, Pd0.5.Ni0.5, Fe0.5.Ni0.5, und Cu0.5.Ni0.5) aber auch ternäre Carbide (z.B. Mn0.75Fe2.25C) erhalten, die schon in ersten Alkylierungs- und Hydrierungsreaktionen ein großes Potential als Katalysatoren zeigen. Um die erhaltenen Nanopartikel in zukünftigen Anwendungen nutzbar zu machen, ist eine ausführliche Charakterisierung unabdingbar. Auch die Ergebnisse der zahlreichen durchgeführten Analysen werden in dieser Arbeit zusammengestellt und bilden gemeinsam mit den optimierten Syntheserouten einen tiefgreifenden Überblick über dieses Forschungsfeld.

APA, Harvard, Vancouver, ISO, and other styles

35

Mondal, Suvendu Sekhar. "Design of isostructural metal-imidazolate frameworks : application for gas storage." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/6969/.

Full text

Abstract:

The sharply rising level of atmospheric carbon dioxide resulting from anthropogenic emissions is one of the greatest environmental concerns facing our civilization today. Metal-organic frameworks (MOFs) are a new class of materials that constructed by metal-containing nodes bonded to organic bridging ligands. MOFs could serve as an ideal platform for the development of next generation CO2 capture materials owing to their large capacity for the adsorption of gases and their structural and chemical tunability. The ability to rationally select the framework components is expected to allow the affinity of the internal pore surface toward CO2 to be precisely controlled, facilitating materials properties that are optimized for the specific type of CO2 capture to be performed (post-combustion capture, precombustion capture, or oxy-fuel combustion) and potentially even for the specific power plant in which the capture system is to be installed. For this reason, significant effort has been made in recent years in improving the gas separation performance of MOFs and some studies evaluating the prospects of deploying these materials in real-world CO2 capture systems have begun to emerge. We have developed six new MOFs, denoted as IFPs (IFP-5, -6, -7, -8, -9, -10, IFP = Imidazolate Framework Potsdam) and two hydrogen-bonded molecular building block (MBB, named as 1 and 2 for Zn and Co based, respectively) have been synthesized, characterized and applied for gas storage. The structure of IFP possesses 1D hexagonal channels. Metal centre and the substituent groups of C2 position of the linker protrude into the open channels and determine their accessible diameter. Interestingly, the channel diameters (range : 0.3 to 5.2 Å) for IFP structures are tuned by the metal centre (Zn, Co and Cd) and substituent of C2 position of the imidazolate linker. Moreover hydrogen bonded MBB of 1 and 2 is formed an in situ functionalization of a ligand under solvothermal condition. Two different types of channels are observed for 1 and 2. Materials contain solvent accessible void space. Solvent could be easily removed by under high vacuum. The porous framework has maintained the crystalline integrity even without solvent molecules. N2, H2, CO2 and CH4 gas sorption isotherms were performed. Gas uptake capacities are comparable with other frameworks. Gas uptake capacity is reduced when the channel diameter is narrow. For example, the channel diameter of IFP-5 (channel diameter: 3.8 Å) is slightly lower than that of IFP-1 (channel diameter: 4.2 Å); hence, the gas uptake capacity and Brunauer-Emmett-Teller (BET) surface area are slightly lower than IFP-1. The selectivity does not depend only on the size of the gas components (kinetic diameter: CO2 3.3 Å, N2 3.6 Å and CH4 3.8 ) but also on the polarizability of the surface and of the gas components. IFP-5 and-6 have the potential applications for the separation of CO2 and CH4 from N2-containing gas mixtures and CO2 and CH4 containing gas mixtures. Gas sorption isotherms of IFP-7, -8, -9, -10 exhibited hysteretic behavior due to flexible alkoxy (e.g., methoxy and ethoxy) substituents. Such phenomenon is a kind of gate effects which is rarely observed in microporous MOFs. IFP-7 (Zn-centred) has a flexible methoxy substituent. This is the first example where a flexible methoxy substituent shows the gate opening behavior in a MOF. Presence of methoxy functional group at the hexagonal channels, IFP-7 acted as molecular gate for N2 gas. Due to polar methoxy group and channel walls, wide hysteretic isotherm was observed during gas uptake. The N2 The estimated BET surface area for 1 is 471 m2 g-1 and the Langmuir surface area is 570 m2 g-1. However, such surface area is slightly higher than azolate-based hydrogen-bonded supramolecular assemblies and also comparable and higher than some hydrogen-bonded porous organic molecules.
Metallorganische Gerüstverbindungen (MOFs) sind eine neue Klasse von porösen Koordinationspolymeren, die aus Metall-Knoten und verbrückenden Liganden bestehen. MOFs können Gasgemische trennen und Gase speichern. Aufgrund ihres modularen Aufbaus können die MOF-Eigenschaften systematisch variiert werden. Ein wichtiges Ziel für das Design von MOFs ist die Synthese von Materialien, die eine hohe selektive Aufnahmefähigkeit und -kapazität für Kohlenstoffdioxid besitzen. Im Rahmen der Arbeit ist es gelungen sechs neue MOFs (IFP-5, -6, -7, -8, -9 und -10) zu synthetisieren. Diese MOFs tragen die Kurzbezeichnung IFP. IFP steht als Abkürzung für Imidazolat-Framework-Potsdam (Imidazolat-basierte Gerüstverbindung Potsdam). In diesen IFPs wurde der Metallknoten (Zink, Cobalt, Cadmium) und der Brückenligand, ein 2-substituiertes Imidazolat-amid-imidat, in der Position variiert, um gute und selektive Sorptionseigenschaften für Kohlenstoffdioxid zu erzielen. Von den synthetisierten Verbindungen hat das IFP-5 die besten Sorptionseigenschaften für Kohlenstoffdioxid. Es konnte weiter gezeigt werden, dass sich die IFP-Struktur bei der Wahl von geeigneten Substituenten 2, wie z.B. Methoxy und Ethoxy auch für das Design von gate-opening (Tür-öffnenden) Effekten eignet. Diese Effekte können wiederum genutzt werden, um selektiv Gasmischungen zu trennen. Wenn man das 4,5-Dicyano-2-methoxy-imidazol in Gegenwart von Zink- und Cobalt-Salzen unter solvothermalen Bedingungen zur Reaktion bringt, erhält man beispiellose supramolekulare Wasserstoffbrückenbindungen zu einem dreidimensionalen Netzwerk, die mit Kanälen verknüpft sind. Diese Kanäle können von Lösungsmittelmolekülen (Wasser und Dimethylformamid) befreit werden und Gase aufnehmen. Insgesamt besteht nun die neue MOF-Klasse der Imidazolat-basierten IFPs aus Vertretern. Das Potential der 2-substituierten 4,5-Dicyanoimidazole ist nicht nur auf die Bildung von porösen Koordinationspolymeren beschränkt, sondern kann auch für die Synthese von bisher unbekannten supramolekularen Strukturen genutzt werden.

APA, Harvard, Vancouver, ISO, and other styles

36

Dowdall, James. "Wave Blocking Phenomena and Ecological Applications." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/33155.

Full text

Abstract:

The growing flow of people and goods around the globe has allowed new, non-native species to establish and spread in already fragile ecosystems. The introduction of invasive species can have a detrimental impact on the already established species. Thus, it is important that we understand the mechanisms that facilitate or prevent invasion. Since reaction-diffusion invasion models produce travelling waves we can study invasion by looking at the mechanisms that allow for wave propagation failure, or wave-blocking. In this thesis we consider a perturbed reaction-diffusion model in which the perturbation resides in either the reaction or diffusion term. In doing so we exploit the underlying symmetry of our problem to define a region in the appropriate parameter space that leads to wave blocking. As a demonstrative example we apply our theory to the bistable equation and consider the effects of various perturbations.

APA, Harvard, Vancouver, ISO, and other styles

37

Korzycka, Karolina Anna. "Two-photon sensitive protecting groups for biological application." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:7e895ed2-04a5-4c0b-9105-74461eae8796.

Full text

Abstract:

Caged compounds are a class of photosensitive reagents used to stimulate cells with spatial control down to a sub-cellular level, and millisecond temporal control. They comprise of biologically important molecule which is modified with a photolabile protecting group. In the absence of light, caged compounds are physiologically silent but irradiation with light induces the release of biologically active species. Illumination under two-photon conditions is particularly advantageous as it enables restriction of the photolysis volume to ~1 fL and it provides deeper penetration into scattering samples. This thesis reports the development of new protecting groups for two-photon uncaging in neuroscience. Mechanistically, the deprotection in these novel groups is designed to operate via an intramolecular photoinduced electron transfer (PeT) between the absorbing unit (electron-donor) and the release module (electron-acceptor). The modular design of these cages ensures separation of absorption and release steps, and allows each process to be tuned and optimized independently. Chapter 1 provides an introduction to the two-photon absorption phenomenon and a historic overview of the uncaging technique. It also discusses recent advances in the development of two-photon sensitive probes used in neuroscience. Chapter 2 describes the exploration of molecular designs for novel protecting groups. A two-photon absorbing dye (electron-donor; fluorene dye) and three different release units (electron-acceptors; nitrobenzyl, pyridinium and phenacyl) were identified as suitable building blocks for the current project. Efficiency of the intramolecular electron transfer between chosen units was evaluated using model dyads which constitute covalently linked electron-donor and acceptor species. Chapter 3 is devoted to the synthesis and photophysical evaluation of nitrobenzyl-based protecting group. Chapter 4 describes the preparation of pyridinium-derived protecting group and demonstrates PeT-mediated release of tryptophan and GABA under one- and two-photon excitation. Hydrolytic instability of pyridinium esters is highlighted. Chapter 5 reports the synthesis, hydrolytic stability and one-photon uncaging efficiency of phenacyl-based derivatives. Chapter 6 discusses properties of developed caged compounds and compares them with other compounds reported in literature. It contains overall conclusions and outlook for the current project. Chapter 7 details the experimental procedures and the characterization of compounds synthesized during this work.

APA, Harvard, Vancouver, ISO, and other styles

38

Snell, Robert Henry. "Development and application of asymmetric C-N bond formation." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:512e617a-2b01-45f3-86ae-c0cf4b874149.

Full text

Abstract:

A synthetic investigation on the chemistry of cyclotryptamine derived natural products, with a particular focus on the synthesis of the trimeric-alkaloid, hodgkinsine. Methodology has been developed to tackle this complex natural product which utilises a desymmetrization approach; this strategy hinges on the development and applications of asymmetric C-N bond forming reactions. Chapter one examines elements of symmetry in natural products, looking in particular at the synthesis of compounds which contain cyclotryptamine functionality. Chapter two contains a brief review of enantioselective desymmetrization paying attention, if possible, on its application in the synthesis of natural products. In the remaining chapters we discuss our own progress and results in our pursuit of an efficient enantioselective total synthesis of hodgkinsine.

APA, Harvard, Vancouver, ISO, and other styles

39

Luís, Rafael Domingos Garanito. "Nonautonomous difference equations with applications." Doctoral thesis, Universidade da Madeira, 2011. http://hdl.handle.net/10400.13/206.

Full text

Abstract:

This work is divided in two parts. In the first part we develop the theory of discrete nonautonomous dynamical systems. In particular, we investigate skew-product dynamical system, periodicity, stability, center manifold, and bifurcation. In the second part we present some concrete models that are used in ecology/biology and economics. In addition to developing the mathematical theory of these models, we use simulations to construct graphs that illustrate and describe the dynamics of the models. One of the main contributions of this dissertation is the study of the stability of some concrete nonlinear maps using the center manifold theory. Moreover, the second contribution is the study of bifurcation, and in particular the construction of bifurcation diagrams in the parameter space of the autonomous Ricker competition model. Since the dynamics of the Ricker competition model is similar to the logistic competition model, we believe that there exists a certain class of two-dimensional maps with which we can generalize our results. Finally, using the Brouwer’s fixed point theorem and the construction of a compact invariant and convex subset of the space, we present a proof of the existence of a positive periodic solution of the nonautonomous Ricker competition model.
Henrique Oliveira and Saber Elaydi

APA, Harvard, Vancouver, ISO, and other styles

40

Gabrielli, Andrea. "Mini-robotic applications for miniaturized assembly tasks." Doctoral thesis, Università Politecnica delle Marche, 2009. http://hdl.handle.net/11566/242341.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Presland, Katayune. "Synthesis, properties and applications of cadmium based nanoparticles emitting from 400-750 nm." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/synthesis-properties-and-applications-of-cadmium-based-nanoparticles-emitting-from-400--750-nm(7c86b6aa-d5ad-4eb1-9d65-898da886e67c).html.

Full text

Abstract:

This thesis concerns the synthesis of cadmium based nanoparticles that emitted from 400 to the near infrared (NIR) region. Once synthesised they can be possibly used as biomarkers once encapsulated in microspheres. A brief introduction to the area of nanomaterials is also provided. The focus of this thesis is split into three main categories. Firstly core/shell nanoparticles were synthesised due to their ability to emit over a large range of wavelengths. Alloyed nanoparticles were then synthesised due to their ability of being very good photoemitters. Finally core/shell/shell nanoparticles were synthesised as they had the ability of emitting in the NIR region. This thesis is split into five main chapters. The first chapter is a brief introduction to the field of nanomaterials, analysis techniques and current and possible future applications. Chapters 2, 3, and 4 contain the main research carried out with brief synthetic methods and detailed analysis and characterization. Chapter 5 contains detailed synthetic methods with experimental conditions and specific equipment used for this research.

APA, Harvard, Vancouver, ISO, and other styles

42

Woldetsadik, Kebede. "Shallot (Allium cepa var. ascolonicum) responses to plant nutrients and soil moisture in a sub-humid tropical climate /." Alnarp : Dept. of Crop Science, Swedish Univ. of Agricultural Sciences, 2003. http://epsilon.slu.se/a367.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Lublinski, Alf Erko. "Geographical business clusters concepts for cluster identification with an application to an alleged aeronautics cluster in Northern Germany /." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965586456.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Boulahrouf, Abdelhak. "Étude des alliages plomb calcium faiblement alliés en calcium destinés à la fabrication des grilles d'accumulateurs de la nouvelle génération." Nancy 1, 1989. http://www.theses.fr/1989NAN10008.

Full text

Abstract:

Étude du durcissement des alliages PBCA et du mécanisme de la transformation discontinue responsable du durcissement. Influence de la vitesse de refroidissement et du pourcentage de calcium. Simulation de la déformation plastique de l'opération de mise en forme par laminage

APA, Harvard, Vancouver, ISO, and other styles

45

Melin, Nicholas O'Brien. "Application of Bennett mechanisms to long-span shelters." Thesis, University of Oxford, 2004. http://ora.ox.ac.uk/objects/uuid:9c7938c7-7ee4-4c9c-9748-6a3a56a0d179.

Full text

Abstract:

Rapidly assembled tent structures are temporary enclosures used to house people or goods. Their uses vary to include recreation, refugee housing, and military shelters. The structural concepts applied in these shelters are as variable as their uses. Some make use of a tensioned fabric and pole system to provide structural strength. Others have a load-bearing frame with attached fabric skin. Further variants make use of inflatable arches or consist of modular containers. Analysis of a number of different types of rapidly assembled tent structures reveals an area where innovation can occur. Conflicts in the last ten years suggest that rapidly assembled shelters for both military purposes and humanitarian relief have the greatest need for innovative solutions. Existing shelters used by the military lack the versatility and speed of deployment necessary in modern conflict. The lack of scalability in the designs makes it difficult to use an existing tent in different situations. They are slow to construct, heavy, and difficult to transport in large numbers. These problems suggest that there is a need for new shelters that better meet the needs of the military. The application of deployable structures technology meets military's needs for structures with the advantages of a small compacted volume, rapid assembly, and ease of deployment. This makes them ideal for application to shelter structures. The aim of this dissertation was to develop a new type of deployable, long-span shelter frame based upon tiled Bennett mechanisms. An overlapping combination of equilateral Bennett mechanisms yields a structure that opens into a half-cylinder shape, providing an enclosed space useful and applicable to the problem of deployable shelters. The specific application considered in the design portion of this process will be a long-span deployable shelter capable of housing military helicopters. This report details the development of the Bennett Shelter concept. Its deployed and compacted geometries are explored, and a procedure for determining structural properties and dimensions is presented. The full concept for the structure, from outer covering to foundation support is then detailed. Loads affecting the structure are determined, and the process of modelling and analysing the structure is then considered. Optimisation of the structure with respect to weight and serviceability requirements is conducted using a number of different materials, and full analysis of the optimal geometries is completed. As no method exists for evaluating the effect of imperfections on the deployment of overconstrained mechanisms, a procedure is derived. The effects of manufacturing imperfections on deployment of the Bennett mechanism are then explored using the method. A full examination of the variation of energy within the Bennett Shelter during deployment provides valuable insight into the performance of the structure. With the above analysis complete, it is shown that the Bennett Shelter is viable as a long-span deployable shelter.

APA, Harvard, Vancouver, ISO, and other styles

46

Blaineau, Pierre. "Restitution de la microtexture parente à partir de la microtexture héritée mesurée par EBSD : une application aux aciers faiblement alliés." Thesis, Metz, 2010. http://www.theses.fr/2010METZ042S.

Full text

Abstract:

L’état métallurgique de l’austénite avant le dernier refroidissement (taille de grain, texture, écrouissage …) ne peux pas directement être caractérisée car elle se transforme lors du dernier refroidissement or elle influence remarquablement les propriétés d’emploi des aciers. Ce travail de thèse propose une méthode automatique indirecte pour restituer la microtexture austénitique à partir de la seule information de la microtexture, mesurée par EBSD, des phases héritées (martensite, bainite) à basse température. Cette méthode nécessite trois prérequis : 1) La présence d’une relation d’orientation entre l’austénite parente et le produit de transformation 2) la phase héritée s’est formée dans le grain avec lequel elle est en relation d’orientation et 3) il y a un nombre de variant suffisant. Sa validation a été effectuée sur des exemples numériques et pour les aciers faiblement alliés. La restitution des contours austénitiques est efficace mais sensible aux variants en relation d’orientation avec plusieurs grains parents adjacents. Ces situations ambigües sont principalement générées par la présence de macles dans la phase parente ou par sélection de variants aux joints de grains austénitiques. Dans ce cas, il est possible d’améliorer la qualité de la restitution des contours parents (notamment les contours de macles) en prenante en compte des informations topologiques. Ces méthodes de restitution permettent par conséquent de repérer les macles ou la sélection de variants aux joints de grains γ et donc de mieux analyser les mécanismes d’héritage de texture locale. Donc les méthodes développées peuvent être généralisées à d’autres transformations de phase
The metallurgical state of the austenite before the last cooling (grain size, texture, strain hardening ...) cannot be directly characterized because the austenite transforms during the last cooling. However, it influences remarkably the in use properties of steels. This thesis proposes an indirect automatic method to restore the austenitic microtexture from the microtexture of the inherited phases (martensite, bainite) at low temperature, measured by EBSD. This method requires three prerequisites: 1) the presence of an orientation relationship between the parent austenite and the transformation product, 2) the inherited phase has to be formed in the grain with which it is related and 3) there is a sufficient number of variants. Its validation has been performed both on numerical examples and for low alloyed steels. The restitution of austenitic grain boundaries is efficient but sensitive to variants in orientation relationship with several adjacent parent grains. These ambiguous situations are mainly generated by the presence of twins in austenite grains or by selection of variants at the austenitic grain boundaries. In this case, it is possible to improve the quality of the restitution of the parent contours (especially the twins boundaries) by taking into account topological information. These restitution methods consequently allow to identify twins or variant selection at grain boundaries and thus to better analyze local texture inheritance mechanisms. Therefore, the developed methods can be generalized to other phase transformations

APA, Harvard, Vancouver, ISO, and other styles

47

Auger, Jacques. "Analyse et synthèse des substances allélochimiques des Allium (Lilacées) et synthèse d'analogues applications à quelques comportements d'insectes inféodés ou non au poireau... /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376024499.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Zhang, Zhao. "Synthesis, characterization and electrochemical hydrogen storage properties of mechanicalyl alloyed Ti-Mg-Ni : application as negative electrode for Ni-MH battery." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCA006/document.

Full text

Abstract:

Le stockage de l'hydrogène est l'un des plus grands problèmes techniques qui restreignent l'application pratique de l'hydrogène. Les hydrures métalliques sont considérés comme la solution principale à ce problème puisqu'ils peuvent absorber et désorber de façon réversible une grande quantité d'hydrogène sous une température et une pression modérées. Par ailleurs, les hydrures métalliques utilisés comme électrodes négatives dans les accumulateurs Nickel-Métal Hydrure (Ni-MH) sont également les composants clés des performances de ces derniers.Dans cette thèse, les alliages métalliques TiMgNix, MgTi1-xNix et TiMg1-xNix ont été synthétisés par broyage mécanique à partir de poudres élémentaires. La microstructure et les transformations de phase des échantillons préparés ont été caractérisées par DRX, MEB et MET (avec microanalyse EDS).Les propriétés d'hydrogénation ont été mesurées par réaction d'hydrogène solide-gaz et par des essais électrochimiques. Un diagramme de composition-capacité 3D a été établi sur la base du diagramme de phase ternaire Ti-Mg-Ni. Un procédé de broyage en deux étapes a été mis en œuvre pour améliorer les performances électrochimiques des alliages Ti-Mg-Ni.De plus, les alliages TiNi1-xCux ont été synthétisés par broyage mécanique et ensuite recuits. L 'influence de la substitution du nickel par le cuivre sur la structure et les propriétés électrochimiques est étudiée en utilisant une double approche: expérimentale et par simulation.Les résultats obtenus par la théorie de la fonctionnelle de la densité (DFT) en utilisant le programme CASTEP montrent que l'enthalpie de formation et l'énergie d'adsorption de l¿hydrogène de la phase pseudo-binaire Ti(Ni, Cu) sont en bon accord avec les résultats expérimentaux
The storage of hydrogen is one of the biggest technical problem that restrict the practical application of hydrogen. Metal hydrides are mainly regarded as the solution facing to this issue since it can reversibly absorb and desorb big amount of hydrogen under moderate temperature and pressure. Meanwhile, metal hydrides used as the negative electrodes of Ni-MH batteries are also the key components to the battery performance.In this thesis, the metallic composite TiMgNix, MgTi1-xNix and TiMg1-xNix were synthesized by mechanical alloying from elemental powder. The microstructure and phase transformation of prepared samples were characterized by XRD, SEM, TEM (EDS support). The hydrogenation properties were measured by hydrogen solid-gas reaction and electrochemical tests. Based on the Ti-Mg-Ni ternary phase diagram, a 3D composition-capacity diagram have been established. Two-step mill process was proposed for meliorating the electrochemical performance of Ti-Mg-Ni alloys.Additionally, TiNi1-xCux alloys had been synthesized by mechanical alloying and subsequent annealing and studied using experimental and computational approaches. The influence of Cu substitution for Ni on the phase structure and electrochemical properties are investigated. The first principle calculation was carried out to study the formation enthalpy and hydrogen adsorption energy of pseudo-binary Ti(Ni, Cu) phase. The computational results are in good agreement with experimental results

APA, Harvard, Vancouver, ISO, and other styles

49

GRASSI, ROBERTO. "Application of pneumatic technology in advanced robotic systems." Doctoral thesis, Politecnico di Torino, 2007. http://hdl.handle.net/11583/2502137.

Full text

Abstract:

The purpose of this work is to show two experimental applications of pneumatics to innovative robotic devices, in which are summarized most of the aspects here presented. After a short digression with examples of modern pneumatic solutions the author will concentrate on two research subjects describing the specifications and the solutions that were implemented. They are two different research themes in the field of robotics, which were carried out with the extensive use of pneumatics. The variety of topics is noticeable, the first project to be described is a six degrees of freedom (DoF) haptic interface that was fully actuated with pneumatic cylinders. The second project consists in a climbing robot that uses pneumatic elements even as its own structure; originally designed for home window cleaning; it comprises also an innovative drying solution based on the Coanda effect.

APA, Harvard, Vancouver, ISO, and other styles

50

Farhoudi, Mohammad Hassan. "Multi-plane routing practical applications in future all-IP access networks." Thesis, King's College London (University of London), 2018. https://kclpure.kcl.ac.uk/portal/en/theses/multiplane-routing-practical-applications-in-future-allip-access-networks(be4b52e5-c43f-4b23-8a58-8ccd8c5b8eff).html.

Full text

Abstract:

The Internet has proven to be a major contributor to the world and has had a significant impact on many aspects of our lives over the past decades. It continues to have the potential to impact societies, businesses and governments in different ways. Despite the clear significance of Internet as a key enabler of a big technological revolution, there are rising challenges associated with the exponential growth of the Internet. In addition, accelerated in part by the massive increase in devices and the capabilities of those devices, Internet traffic is increasingly becoming more dynamic and demanding. Meanwhile, users expect a quality delivery facilitated by service providers across the mobile networks from core to access. Internet Protocol (IP) as the underlying foundation for the next-generation networks is becoming increasingly relevant considering the ubiquitous installed IP infrastructure. Correspondingly, different suggestions are being explored about the facilitation of next-generation access networks via IP mechanisms, with a growing trend towards a flat IP structure and novel topological set-ups in the backhaul. With the expected surge in global IP traffic, service providers would need to adapt accordingly to operate disruption and loss free networks supported with the developing IP infrastructure. This calls for a consistent routing optimization strategy to minimize loss in data transmission. Hence, a resilient, efficient and easily implementable routing paradigm that employs suitable Traffic Engineering (TE) techniques aligned with the developing nature of future access networks must be applied. It becomes imperative that the routing considerations for IP access networks converge with the ones found in conventional intra-domain routing. Multi-Plane Routing (MPR) is a routing optimization approach that consolidates various aspects in an all-IP access network infrastructure and consists of both offline and online TE approaches. MPR integrates the recent multi-topology approach that leverages multiple alternative paths (for each Ingress-Egress pair) through a network that divides the physical network topology into several logical routing planes facilitating path diversity. In this thesis, MPR is extended from a practical prospective in line with the architectural evolution of access networks and the introduction of new traffic types and applications. The offline and online TE strategies of MPR have been modified to suit the flattened network architecture. Correspondingly, a MPR-based TE approach is proposed considering two different scenarios to reflect the evolution in the architectural design of access network structures under a realistic traffic scenario. It becomes evident that for ranges of topologies, MPR’s utilization of the whole topology in building path diversity in networks, allows for significant improvement of networks’ capacity, performance and support for meshing. Moreover, with the rise of different traffic types of various nature, Quality of Service (QoS) is increasingly becoming important. Tactile Internet is considered in this thesis in addition to other traffic applications. To this end, a novel routing technique which accommodates for the strict requirements of this new traffic type in access networks architectures will be proposed. Validation of the proposed techniques through simulations have been performed and presented, illustrating the effectiveness of the proposed methods.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'ALLIED APPLICATIONS'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles