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Witwit, Abdul-Mehdi Rahim Mohammed. "Meshing techniques for TLM diffusion problems." Thesis, University of Hull, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296281.
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Williams, Catherine F. M. "Diffusion-weighted magnetic resonance imaging techniques." Thesis, University of Aberdeen, 1998. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602003.
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The aim of this project was to compare and evaluate other, non-EPI, diffusion-weighted MRI (DWI) sequences, through imaging experiments, on a phantom and in vivo, (using a 0.95 T system) and computer simulations, and to develop improved DWI methodology which could be implemented on standard hardware. Pulsed gradient spin echo (PGSE) and diffusion-weighted STEAM are slow multiple shot sequences, with measurement times of several minutes. Both sequences are highly sensitive to patient motion, but motion artifact was virtually eliminated using navigator echo phase correction and EGG triggering when diffusion-sensitisation was in the phase-encoding direction. It was demonstrated that both sequences can provide high quality images and allow accurate and straightforward diffusion-coefficient measurement when an imaging time period in the region of 20-30 minutes is available and when diffusion-sensitisation is required in one or two directions. A third direction of diffusion-sensitisation may be feasible if more sophisticated immobilisation or phase correction techniques are employed. A choice between PGSE or STEAM for a given application should take account of the Ti and T2 values of the imaged tissues, since a higher SNR might be provided by STEAM when the T1T2 ratio is high. A diffusion-weighted CE-FAST sequence was implemented with the novel modification of acquisition of a navigator gradient-echo, which was shown to reduce motion artifact when diffusion-sensitisation was in the phase-encoding direction. However, it has been demonstrated by other workers that unknown signal losses due to motion-induced phase incoherence between signal components may remain. The SNR (normalised with respect to the square root of the imaging time) in the phantom and in white matter was similar to that obtained using PGSE, but an advantage of CE- FAST is that it can be performed in a fraction of the measurement time of PGSE. Diffusion-sensitivity was much higher than in other sequences and the diffusion- attenuation was found to agree with an analysis presented in the literature. However, a major disadvantage of the technique, which precludes its use for many DWI applications, is the requirement of accurate knowledge of Ti, T2 and flip angle in order to calculate the diffusion coefficient or tensor. Prior to a study of diffusion-weighted snapshot FLASH, the effects of magnetisation evolution during snapshot FLASH acquisition on image quality and parameter measurement accuracy were first investigated, through phantom experiments and computer simulations, in the context of a r2-weighted snapshot FLASH sequence. It was demonstrated that magnetisation evolution effects can lead to significant error in parameter measurement, but that this error can be eliminated by using crusher gradients to prevent evolved magnetisation from contributing to the acquired signal. However, qualitative effects are not entirely eliminated, since a significant degree of edge blurring may remain, and there is a 50% loss of SNR inherent to the crusher gradient technique. It was then shown, theoretically and experimentally, that in diffusion-weighted snapshot FLASH, the crusher gradient technique not only addresses the problem of magnetisation evolution, but also eliminates the effect of phase shifts arising during the diffusion-preparation sequence.
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Sekerci, Yadigar. "Some recent simulation techniques of diffusion bridge." Thesis, Växjö University, School of Mathematics and Systems Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-5749.
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We apply some recent numerical solutions to diffusion bridges written in Iacus (2008). One is an approximate scheme from Bladt and S{\o}rensen (2007), another one, from Beskos et al (2006), is an algorithm which is exact: no numerical error at given grid points!
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Rogerson, Alexandria. "New techniques in diffusion-ordered NMR spectroscopy." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/new-techniques-in-diffusionordered-nmr-spectroscopy(aa3eaee0-984b-4434-b460-8c3118a7c3b2).html.
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The analysis of mixtures is a subject that spans several different analytical techniques. In NMR, a powerful technique for this analysis is Diffusion-Ordered NMR Spectroscopy (DOSY), in which signals from different chemical species can be distinguished by their different diffusion coefficients. DOSY NMR allows an analysis of mixture components and their interactions in a non-invasive way and is proving to be an accurate and time effective method for looking at mixtures.An in-depth analysis of DOSY NMR is presented using the commercial mixture “monoacetin”. The chemically cognate species in this mixture produce complex and overlapping multiplet signals in 1H NMR that are difficult to assign and interpret. A previous analysis of this mixture used 1H NMR together with Liquid Chromatography (LC) and Gas Chromatography (GC) to identify the components present, but failed to provide complete assignments of all the signals. Here, the possibility of using DOSY as an alternative to hyphenated techniques is examined, and it is shown that a full analysis of the spectrum of “monoacetin” is possible with careful selection of experimental parameters and processing techniques, without recourse to chromatography. DOSY NMR can be ineffective when signals overlap and/or diffusion coefficients are similar. Many methods have been proposed to overcome these problems, and some of these are presented here. In order to increase resolving power, it is possible to gather further information about a mixture and incorporate this into diffusion experiments as another dimension. This creates a 3D dataset that can be analysed using a multiway method, such as PARAFAC, to extract the component spectra. This method is explored for the mixture “monoacetin” that has been partially separated by high-performance liquid chromatography. Resolution of two out of four components was achieved from poor HPLC separation; the decomposition obtained the component spectra, diffusional decay and HPLC elution profile for these components. Improved HPLC separation should result in further resolution.Diffusion coefficients of different mixture species can be manipulated by changing the matrix in which they diffuse: Matrix-Assisted DOSY (MAD). Previous techniques have involved either improving resolution in the diffusion domain or aiming to improve resolution in chemical shift. A method is presented here that simultaneously addresses both problems in a chemically-selective way, using lanthanide shift reagents. The chemically-selective binding of the LSR to mixture components can both enhance chemical shift dispersion and increase diffusion resolution in DOSY. This neatly deals with the two main drawbacks of the DOSY experiment, and is demonstrated using a mixture of an alkane, alcohol and aldehyde. The manipulation of a molecule’s electrostatic charge through pH control has been investigated, where small ions with a high charge density would be highly solvated, resulting in a change in D. The effect, however, was not measurable and so the indirect effect of pH on the interaction of charged species with the cationic micelle CTAB is presented, where an increase in resolution between of mixture of aspirin and salicylic acid is achieved.Although DOSY NMR is a powerful tool for mixture analysis, in recent years it has been used for studying molecular interactions. An example of this is presented here where species aggregate under specific conditions, a process identified by DOSY NMR.
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Clement, Meagan E. Couper David J. "Analysis techniques for diffusion tensor imaging data." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,2010.
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Thesis (DrPH)--University of North Carolina at Chapel Hill, 2008.Title from electronic title page (viewed Feb. 17, 2009). "... in partial fulfillment of the requirements for the degree of Doctorate of Public Health in the School of Public Health Department of Biostatistics." Discipline: Biostatistics; Department/School: Public Health.
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Mueller, Katherine Elisabeth. "Diffusion in polymers using quartz crystal microbalance techniques /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Ferguson, R. C. "Numerical techniques for the drift-diffusion semiconductor equations." Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362239.
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Bushby, Roger Stanley. "Joining aluminium-based composites using diffusion bonding techniques." Thesis, University of Bath, 1993. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.331934.
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Ismail, Furrukh. "Photovoltaic Process Development and innovative Techniques." Thesis, Högskolan Dalarna, Elektroteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:du-6453.
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Photovoltaic processing is one of the processes that have significance in semiconductor process line. It is complicated due to the no. of elements involved that directly or indirectly affect the processing and final yield. So mathematically or empirically we can’t say assertively about the results specially related with diffusion, antireflective coating and impurity poisoning. Here I have experimented and collected data on the mono-crystal silicon wafers with varying properties and outputs. Then by using neural network with available experimental data output required can be estimated which is further tested by the test data for authenticity. One can say that it’s a kind of process simulation with varying input of raw wafers to get desired yield of photovoltaic mono-crystal cells.
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Symeonidis, Kimon. "The Controlled Diffusion Solidification Process: Fundamentals and Principles." Worcester, Mass. : Worcester Polytechnic Institute, 2009. http://www.wpi.edu/Pubs/ETD/Available/etd-042909-102711/.
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Heinke, Lars, Despina Tzoulaki, Christian Chmelik, Florian Hibbe, and Jörg Kärger. "Assessing details of molecular motion in nanopores by combining different microscopic techniques." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189565.
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Nguyen, Quyen. "Quantitative diffusion weighted imaging : techniques and applications to perinatal asphyxia." Thesis, University College London (University of London), 2001. http://discovery.ucl.ac.uk/1382401/.
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This thesis describes the results of a study to investigate early cerebral changes in a piglet model of perinatal asphyxia using quantitative diffusion-weighted imaging (DWI) and subsequent work to develop a robust DWI technique to enable similar studies to be performed in neonates. 31Phophorus magnetic resonance spectroscopy and quantitative diffusion and T2 imaging of the cerebrum were performed in a piglet model of perinatal asphyxia. A significant decline in the ratio of phosphocreatine to inorganic phosphate concentrations ([PCr]/[Pi]) was observed during the 48 hours following the transient hypoxicischaemic (H-I) insult. The global directionally averaged apparent diffusion coefficient (ADCav) also declined significantly during the same period and a strong correlation between the [PCr]/[Pi] and ADCav was found. Strong regional and temporal variations in the cerebral response were observed following the H-I insult. In the basal ganglia and parasagittal cortex, significant decline in ADCs was seen approximately 8 hours after the H-I insult. In the thalamus, internal capsule, periventricular white matter and medial cortex, significant ADCs decline was not observed until 32 hours following the H-I insult. A significant T2 increase was observed in the internal capsule but not in the other regions of interest. To enable clinical DWI to be performed in neonates a novel `reacquisition' technique that overcomes the problem of motion artefact in DWI is presented. The reacquisition technique involves the automatic detection and reacquisition of motion-corrupted data in real-time. Computer simulations were used to demonstrate that motion-corrupted data may be detected accurately and reacquired in a time efficient manner. The reacquisition technique was implemented on a Bruker AVANCE scanner in combination with a spinecho 2DFT DWI sequence and an interleaved EPI DWI sequence. The effectiveness of the technique was demonstrated with both a computer-controlled motion phantom and neonates from an ongoing study of perinatal asphyxia.
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Brihuega-Moreno, Oscar. "Development and optimisation of diffusion MRI techniques for articular cartilage." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614690.
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Gopinathan, Navin. "Development of catalyst characterisation techniques." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571865.
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Standard catalyst characterisation techniques such as gas adsorption porosimetry and mercury porosimetry only account for some of the physical heterogeneity of the catalyst surface. They completely ignore the chemical heterogeneity present and in most cases consider pores present in the medium to be independent of each other. Thus, most results of characterisation (pore space descriptors such as BET surface area, BJH pore size distribution, mercury porosimetry surface area, etc.) are not accurate. This has been a major issue that remains to be resolved during the characterisation of fresh and coked catalysts. In this thesis, the use of a multi-component adsorption system is recommended as a step-change solution to this limitation. Two approaches are adopted. Firstly, integrated nitrogen-waternitrogen gas adsorption experiments are performed on fresh and coked catalysts. This established the significance of pore coupling by showing the presence of advanced adsorption. The method also helped to determine the location of coke deposits within catalysts and indicated that water vapour adsorption was a good probe to understand the sites responsible for coking. Secondly, coadsorption of immiscible liquids – cyclohexane and water – was performed on fresh and coked catalysts following which the displacement of cyclohexane by water was studied using NMR relaxometry and diffusometry. This novel approach takes the wettability of the surface into consideration, unlike the former methods. It is therefore a method that accounts for the chemical heterogeneity of the surface. It also helped determine the location of coke within catalysts. The different approaches are presented in the context of combustion of heavy oil in bitumen reservoirs, and the use of supercritical conditions that help to dissolve coke precursors in the isomerisation of 1-hexene. Thus, the solutions provided in this thesis are directions in which catalyst characterisation, especially distinguishing fresh and coked catalysts, and other porous materials, must be carried out.
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Helander, Thomas. "Some applications of CALPHAD techniques to diffusion reactions in gradient materials." Doctoral thesis, Stockholm : Tekniska högsk, 1999. http://www.lib.kth.se/abs99/hela0604.pdf.
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Cheung, Man-hin Matthrew, and 張文騫. "Development of diffusion and functional magnetic resonance imaging techniques for neuroscience." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47147635.
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Bachmann, Sebastian. "Estimating Molecular Weights of Organometallics in Solution with Diffusion NMR Techniques." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3DF9-7.
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Morgan, Stephen P. "Continuous wave optical techniques for imaging through scattering media." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319966.
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Heinke, Lars, Despina Tzoulaki, Christian Chmelik, Florian Hibbe, and Jörg Kärger. "Assessing details of molecular motion in nanopores by combining different microscopic techniques." Diffusion fundamentals 11 (2009) 30, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A13973.
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Chmelik, Christian, Pavel Kortunov, Sergey Vasenkov, Taro Ito, Jörg Kärger, Jan Konatowski, Jens Weitkamp, and Douglas M. Ruthven. "Transport diffusivity in zeolites: possible reasons for misleading results of macroscopic techniques." Diffusion fundamentals 2 (2005) 86, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14421.
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Dvoyashkin, Muslim, Aiping Wang, Hrishi Bhase, Sergey Vasenkov, and Clifford R. Bowers. "Single-file dynamics in nanotubular materials probed by a combination of hyperpolarized tracer exchange and diffusion NMR techniques." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-183080.
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Ries, Jonas. "Advanced Fluorescence Correlation Techniques to Study Membrane Dynamics." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1219846317196-73420.
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Fluorescence Correlation Spectroscopy (FCS) is a powerful tool to measure important physical quantities such as concentrations, diffusion coefficients, diffusion modes or binding parameters, both in solution and in membranes. However, it can suffer from severe artifacts, especially in non-ideal systems. Here we develop several novel implementations of FCS which overcome these limitations and facilitate accurate and quantitative determination of dynamic parameters in membranes. Two-focus FCS with camera-detection allows for accurate and calibration-free determination of diffusion coefficients. Confocal FCS using a laser scanning microscope provides an unprecedented positioning accuracy which enabled us to study, for the first time with FCS, dynamics in bacterial membranes. Scanning FCS with a scan path perpendicular to the membrane plane allows to correct for instabilities permitting long measurement times necessary to study slow diffusion. It can easily be extended to measure calibration-free diffusion coefficients with two-focus scanning FCS and to quantify binding with dual color scanning FCS. Spectral crosstalk can be avoided effectively by using alternating excitation. Using this method we were able to perform measurements in systems previously not accessible with FCS, such as yeast cell membranes or membranes of living zebrafish embryos. Line-scan FCS with a scan path in the membrane plane uses the parallel acquisition along the line to increase the statistical accuracy and decrease the measurement times. Knowledge of the scan speed serves as an internal calibration, enabling accurate diffusion and concentration measurements within seconds, hardly affected by photobleaching. Both realizations of scanning FCS can be easily implemented with commercial laser scanning microscopes. Often, a fluorescence background around the membrane cannot be avoided. The high surface selectivity needed in this case can be achieved efficiently by using a novel objective for FCS, the supercritical angle objective, which produces a very flat and laterally confined detection volume. Another technique with similar surface selectivity is FCS with total internal reflection excitation (TIRFCS). Due to the lack of a correct model, the accurate analysis of TIR-FCS data was previously not possible. In this work we develop such a model, enabling quantitative measurements of membrane dynamics with TIR-FCS. The novel FCS techniques developed here will have a high impact on the use of FCS to address key questions in biological systems, previously inaccessible by other methodsFluoreszenz-Korrelations-Spektroskopie (FCS) ist eine mächtige Methode, um wichtige physikalische Parameter wie Konzentrationen, Diffusionskoeffizienten, Diffusionsarten oder Bindungsparameter in Lösung und in Modell- oder Zellmembranen zu bestimmen. In nichtidealen Systemen ist FCS fehleranfällig. In dieser Arbeit entwickeln wir mehrere neuartige Realisierungen von FCS, welche diese Fehlerquellen umgehen und die genaue und quantitative Messung dynamischer Parameter in Membranen ermöglichen. Zwei-Fokus FCS mit Kamera-Detektion erlaubt eine genaue und kalibrationsfreie Messung von Diffusionskoeffizienten. Konfokale FCS mit einem Laserscanningmikroskop besitzt eine bislang unerreichte Positionsgenauigkeit, welche uns erstmals dynamische Messungen in Bakterienmembranen mit FCS ermöglichte. Scanning FCS mit einem Scanweg senkrecht zur Membran ermöglicht eine Korrektur von Instabilitäten und damit lange Messzeiten, die zur Bestimmung langsamer Diffusionskoeffizienten notwendig sind. Eine Erweiterung zur kalibrationsfreien Messung von Diffusionskoeffizienten mit Zwei-Fokus Scanning FCS und von Bindungsparametern mit Zwei-Farben Scanning FCS ist einfach. Mit diesen Methoden konnten wir in Systemen messen, die bislang FCS nicht zugänglich waren, so in Hefezellmembranen oder in Membranen lebender Zebrafischembryonen. Line-scan FCS besitzt einen Scanweg parallel zur Membran. Die parallele Messung entlang der ganzen Linie führt zu einer deutlichen Verbesserung der Statistik und damit zu kurzen Messzeiten. Die Kenntnis der Scangeschwindigkeit dient einer internen Kalibration und erlaubt eine akkurate Bestimmung von Diffusionskoeffizienten und Konzentrationen innerhalb weniger Sekunden, kaum beeinflusst vom Bleichen von Fluorophoren. Beide Arten von Scanning FCS können mit einem kommerziellen Laserscanningmikroskop realisiert werden. Häufig kann bei FCS Messungen ein fluoreszierender Hintergrund nicht vermieden werden. Hier ist eine hohe Oberflächenselektivitiät nötig, welche effizient mit einem neuartigen Objektiv erreicht werden kann. Dieses Supercritical Angle-Objektiv erzeugt ein sehr flaches und lateral begrenztes Detektionsvolumen. Eine weitere Methode mit einer ähnlich guten Oberflächenselektivität ist FCS mit Anregung über totale interne Reflektion (TIR-FCS). Bislang war eine quantitative Analyse der TIR-FCS Daten kaum möglich, da keine ausreichend genaue theoretische Beschreibung existierte. In dieser Arbeit entwickeln wir ein akkurates Modell, welches quantitative Messungen mit TIR-FCS erlaubt. Die hier entwickelten neuartgien FCS-Techniken ermöglichen die Untersuchung biologischer Fragestellungen, welche bislang keiner anderen Methode zugänglich sind
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Bassett, John. "Assessing the Spatial Diffusivity of Sound Fields in Rooms using Ambisonic Techniques." Thesis, The University of Sydney, 2012. http://hdl.handle.net/2123/8255.
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This thesis explores the means of objectively measuring diffuse sound fields contained within music performance auditoria. Although the diffuse field is considered to be an important component of the reverberant sound field there is currently no widely accepted method for its measurement. A review of methods shows that attempts to characterize the field may be divided into those methods that seek to directly measure the state of the field and those that indirectly indicate the existence of the state. The primary focus of this thesis is the application of Ambisonic techniques to capture the spatial aspects of the sound field. Initial work explores the rotation of a directional microphone in three measurement spaces. The results and modeling in idealised simulated sound fields indicate that the method may have some efficacy. The method is extended through the application of signal processing to the output of an Ambisonic microphone array. The method is tested firstly in a reverberation room that is modified progressively to produce a series of room states with incrementally increasing reverberation time. The extents of the measurement system were tested by measuring the degrees of diffusivity reached in a reverberation room. Diffusing panels were progressively added in the expectation the increases in diffusivity would be detected. The measurement was carried out in conjunction with standard absorption coefficient measurements outlined in Appendix A of ISO 354. Comparison was made between the measured field and the standard method for achieving a diffuse field in a reverberation room test facility. The final stage attempts to find correlation between physical measures of diffuse fields and listener’s subjective assessment of those fields. To that end a paired comparison test was conducted where listeners were presented music samples rendered through simulated halls where the scattering coefficients and consequently the sound field diffusivity was varied. Subjects were asked to choose which pair they preferred.
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Vanacore, Giovanni Maria. "INVESTIGATION OF Ge SURFACE DIFFUSION AND SiGe NANOSTRUCTURES BY SPECTRO-MICROSCOPY TECHNIQUES." Phd thesis, Ecole Polytechnique X, 2011. http://tel.archives-ouvertes.fr/tel-00725427.
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SiGe nanostructures on crystalline Si substrates with (001) orientation are among the most studied system in condensed matter physics and nanoscience. This interest has been mainly driven by the important potential applications in opto and nano-electronic devices thanks to the improvement of the optical and electronic properties compared to bulk systems. These features come essentially from the possibility of engineering the strain field within the nanostructures using the lattice mismatch of ~ 4 % between Ge and Si and from the spatial confinement, capable of modifying the electronic band structure leading to an increase of the charge carrier mobility. It is obvious that these applications largely depend on the control of surface processes during the growth of the nanostructures, and their performance are strongly dependent on strain relaxation and dislocation injection. Besides the technological interest, the SiGe/Si(001) system has received much attention since it is also a model for understanding the fundamental processes occurring during 3D island formation and self-organization phenomena. In fact, the lattice mismatch between Ge and Si introduces a stress field which has dramatic effects on the growth process and is responsible for a number of structural and electronic phenomena. In particular, the stored elastic energy can be partially relieved by spontaneous formation of 3D objects of nanometric size on top of a pseudomorphic SiGe wetting layer. This growth mode, called Stranski-Krastanov (SK), is a way of easily forming self-assembled nanostructures, which can be used to obtain quantum confinement of charge carriers in nanoelectronics device applications. In recent years, considerable efforts have been devoted to the growth of hetero-epitaxial SiGe nanostructures with well controlled size, shape and positioning, and with defined stoichiometry and strain state. However, some aspects still need to be addressed for a complete understanding of this system, including: (i) the competition between kinetic and thermodynamic factors for island formation, (ii) the mechanisms governing the relative growth of individual nanostructures, (iii) the interplay between SiGe intermixing and strain relaxation mechanisms. In the present work, we carry out an experimental investigation of the relationship between morphology, elemental composition, strain state and electronic structure of self-assembled and lithographically defined SiGe nanostructures by means of several spectro-microscopy techniques. The Si and Ge diffusion dynamics and the self-organization phenomena during the growth of SiGe islands have been studied by Scanning Auger Microscopy (SAM) and Atomic Force Microscopy (AFM). Micro-Raman, SAM and Scanning Transmission Electron Microscopy coupled with Electron Energy Loss Spectroscopy (STEM-EELS) techniques have been used for the investigation of the interplay between strain relaxation mechanisms and SiGe intermixing in self-assembled islands. The effects of strain and composition on the electronic band structure in lithographically defined SiGe nanostructures, in layout very close to those used in prototype devices, have been characterized with nanoscale spatial resolution joining information from Tip Enhanced Raman Spectroscopy (TERS), nanofocused X-Ray Diffraction (XRD) and Energy-Filtered PhotoElectron Emission Microscopy (PEEM). The thesis is conceptually divided in two main parts: the first, to which belong Chapters 1, 2 and 3, deals with the experimental investigation of the Ge surface diffusion and of the self-organization phenomena of SiGe islands grown in a bottom-up approach; the second, including Chapters 4 and 5, is based on the experimental characterization of the strain state and of the strain-induced effects on the electronic band structure of lithographically defined SiGe nanostructures obtained in a top-down approach Chapter 1 presents an overview on the basic processes occurring during hetero-epitaxial growth of thin solid films. In the Chapter 2 the surface diffusion of Ge on a clean and C covered Si(001) surface promoted by annealing at high temperatures in UHV of pure Ge stripes is experimentally investigated by means of in-situ Scanning Auger Microscopy. The influence of a controlled carbon coverage on the Ge surface diffusion is quantitatively studied, showing that the diffusion coefficient presents a strong dependence on carbon coverage (see Fig. 1(a)). Chapter 3 deals with the experimental investigation of the growth process of self-assembled SiGe islands on Si(001) (see Fig. 1(b)). From the size and density evolution exhibited by the nucleated islands, we propose a scenario where the island growth is essentially driven by kinetic factors within a diffusion limited regime. Finally, we investigated the interplay among SiGe intermixing and plastic relaxation, showing that the surface thermal diffusion growth method leads to the formation of coherent islands (dislocation-free), as shown in Fig. 1(c), larger than those attainable by MBE and CVD. Chapter 4 presents the mapping with nanoscale resolution of strain, composition, local work function and valence band structure of lithographically defined SiGe embedded nano-stripes using TERS and Energy-Filtered PEEM (see Fig. 1(d) showing the Ge concentration mapping of the nano-stripes as obtained by PEEM analysis). In Chapter 5 are presented the first results of a direct characterization of the strain state of lithographically defined SiGe nano-ridges using the recently developed nanofocused XRD technique. The work presented in this thesis is the outcome of an experimental PhD research project developed at the Politecnico di Milano (Milano, Italy) in co-tutorship with the École Polytechnique (Paris, France) and the French Atomic Energy Commission (CEA-Saclay, France). SAM and AFM have been performed at Department of Physics of the Politecnico di Milano. Micro-Raman Spectroscopy has been carried out at the Materials Science Department of the Università Milano-Bicocca. PEEM measurements have been realized at CEA and during two standard experimental runs at the TEMPO beamline of SOLEIL Synchrotron (France). TERS and preliminary TEM analysis have been performed at the École Polytechnique, while more extensive TEM and STEM-EELS measurements have been developed at IMM-CNR in Catania. The nano-XRD experiment has been carried out during a standard experimental run at ID13 beamline of the European Synchrotron Radiation Facility (ESRF). The close collaboration with the laboratory L-NESS in Como made available the set of the lithographically-defined investigated samples. The experimental results have been exploited in close collaboration with a theory group at the Materials Science Department of the Università Milano-Bicocca for a deeper insight into the atomic level mechanisms during island growth process.
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Woźniak, Mariusz. "CARACTÉRISATION D'AGRÉGATS DE NANOPARTICULES PAR DES TECHNIQUES DE DIFFUSION DE LA LUMIÈRE." Phd thesis, Aix-Marseille Université, 2012. http://tel.archives-ouvertes.fr/tel-00747711.
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Ce travail de thèse de doctorat propose et évalue différentes solutions pour caractériser, avec des outils optiques et électromagnétiques non intrusifs, les nanoparticules et agrégats observés dans différents systèmes physiques : suspensions colloïdales, aérosols et plasma poussiéreux. Deux types de modèles sont utilisés pour décrire la morphologie: d'agrégats fractals (p. ex. : suies issues de la combustion, de procédés plasma) et agrégats compacts (qualifiés de " Buckyballs " et observés dans des aérosols produits par séchage de nano suspensions). Nous utilisons différentes théories et modèles électromagnétiques (T-Matrice et approximations du type dipôles discrets) pour calculer les diagrammes de diffusion (ou facteur de structure optique) de ces agrégats, de même que leurs spectres d'extinction sur une large gamme spectrale. Ceci, dans le but d'inverser les données expérimentales obtenues en temps réel. Différents outils numériques originaux ont également été mis au point pour parvenir à une analyse morphologique quantitative de clichés de microscopie électronique. La validation expérimentale des outils théoriques et numériques développés au cours de ce travail est focalisée sur la spectrométrie d'extinction appliquée à des nano agrégats de silice, tungstène et silicium.
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Ali-Romson, Farida. "Détermination de coefficients de diffusion par diverses techniques de spectroscopie de fluorescence." Vandoeuvre-les-Nancy, INPL, 1991. http://www.theses.fr/1991INPLA001.
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Mattea, Carlos. "Molecular dynamics in porous media studied by Nuclear Magnetic Resonance techniques." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:289-vts-55830.
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Kaloun, Soulaimane. "Vieillissement d'un verre colloïdal : Variations sur les techniques de diffusion de la lumière." Université Louis Pasteur (Strasbourg) (1971-2008), 2005. http://www.theses.fr/2005STR13057.
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Les résultats obtenus au cours de ce travail relèvent de trois aspects fondamentaux de la phénoménologie des systèmes vitreux : le vieillissement, le rajeunissement et les effets mémoire. Nous avons développé des expériences originales de diffusion de la lumière qui utilisent des caméras CCD comme multidétecteurs. Ces techniques permettent d’effectuer en temps réel une moyenne d’ensemble de l’intensité diffusée. L’étude du vieillissement d’un verre colloïdal de Laponite a été effectuée en incorporant des particules sondes pour suivre leur dynamique sur des échelles micrométriques grandes devant la taille du grain nanométrique du système vitreux. Nous montrons que l’évolution du temps de relaxation de la structure en fonction de l’âge du système est initialement décrite par une croissance exponentielle, puis suivie d’une croissance en loi de puissance avec un exposant de l’ordre de l’unité. Dans le premier régime, la diffusion des sondes est normale, alors qu’au cours du second, dit de « full aging », la dynamique de la sonde est surdiffusive. Nous étudions d’autre part le vieillissement d’un système vitreux colloïdal de smecton sous cisaillement périodique. Les effets de rajeunissement et l’existence d’effets mémoire y sont discutés. Nous observons que la dynamique est accélérée lorsque l’on applique un cisaillement d’amplitude modérée, néanmoins cette accélération n’affecte pas la dynamique quand le cisaillement est arrêté. Nous montrons que la dynamique de la suspension à un instant après un rajeunissement total est indépendante des cisaillements effectués avant cet instant si son amplitude est inférieure à une amplitude critique nécessaire au rajeunissement total de la suspension vitreuse. Ceci nous permet d’exclure l’effet de termes mémoire dans la dynamique de nos suspensionsThe results obtained during this work concern three fundamental aspects of the phenomenology of the glassy systems: aging, the rejuvenation and the memory effects. We developed original experiments of light scattering with multi-speckle detection on CCD chips. Thanks to these techniques we were able to calculate an ensemble average of the scattered intensity in real time. We study the aging of colloidal Laponite glass by measuring the dynamic structure factor of dilute embedded tracer particles on micrometric length scales. We show that an initial aging regime, where the decay time grows exponentially with aging time is followed by a full aging regime. The dynamics of the tracers is diffusive in the exponential regime and hyperdiffusive in the full aging regime. Besides, we study the aging under a periodic shear of a concentrated suspension of saponite particles. The effects of rejuvenation and the existence of memory effects are discussed there. We observe that the dynamics is fastened by the application of a moderate shear amplitude. Nevertheless, this acceleration does not affect the dynamics of the suspension when the shear is ceased. We show that the dynamics of the suspension at any given time after complete rejuvenation is independent of the shear history before this time as soon as the amplitude of the applied shear is smaller than the characteristic shear necessary to completely rejuvenate the suspension. We thus rule out the existence of a memory effect in our suspension
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Ainte, Mohamed Iman. "NMR techniques for measuring transport phenomena in microporous materials." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270581.
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The primary aim of this thesis is to investigate and quantify the self-diffusion processes of gaseous molecules adsorbed in industrially relevant microporous zeolite materials using Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR). The main body of this work involves the use of weakly adsorbing hydrocarbon gases (CH4, C2H6 and C3H¬8) adsorbed in a large pore β-zeolite structure. This thesis describes the development of a solely PFG NMR based technique for measuring the molecular displacements of these species at varying length-scales. This enabled the characterisation of self-diffusion regimes across zeolite beds and within individual zeolite crystallites. The characterisation of self-diffusion processes within single zeolite crystallites was critical with respect to accounting for quantitative discrepancies reported in the literature between PFG NMR and alternative measurement techniques. This approach also revealed that the transitions in the Gaussian probability distributions of the molecular displacements in the aforementioned self-diffusion regimes could be recorded by varying the experimental time-scale for observing molecular motion. This technique was extended to characterise the self-diffusion processes of the aforementioned hydrocarbons in small (≤ 1 μm) and large (≥ 15 μm) zeolite crystallites to investigate the dependence of this technique on zeolite geometry. It was found that the self-diffusion coefficients within single crystallites were in good agreement with one another, despite their differing crystallite geometries. This technique was subsequently used to study the self-diffusion behaviour of two-component hydrocarbon gaseous mixtures with differing sorption properties co-adsorbed in β-zeolite. Excellent chemical shift resolution was obtained for chemically similar species using NMR spectroscopy, relaxometry and diffusometry without the use of Magic Angle Spinning (MAS). This connoted that conventional PFG NMR is capable of precisely characterising individual species in real world multi-component systems. This thesis also describes the self-diffusion of ammonia in small pore chabazite structures, which are typically used in Selective Catalytic Reduction (SCR) processes. It was found that the self-diffusion coefficient of this strongly adsorbing species increased with molecular loading up to a certain point. This peculiar behaviour implied a strong concentration and inter-molecular dependence within the zeolite structure. Lastly, the techniques which were developed at high magnetic field strengths (300 MHz) were transferred to a lower field strength (43 MHz) benchtop spectrometer at the Johnson Matthey Technology Centre (JMTC). This describes the first characterisation of mass transport behaviour of weakly interacting sorbates in zeolites using a portable spectrometer. This presents an excellent opportunity for future off-line molecular displacement measurements to be made for complex and real-world systems in a matter of minutes.
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Chatfield, Stuart R. "A study of pore structure of human dental enamel using radiotracer techniques." Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389134.
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Boutet, Jérôme. "Localisation d'inclusions fluorescentes dans les milieux diffusants à l'aide de techniques laser. Application au diagnostic médical in vivo." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY009/document.
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La tomographie de fluorescence est une méthode d'imagerie préclinique et clinique permettant de localiser des traceurs fluorescents préalablement injectés ou naturellement présents dans un organisme vivant. Ce travail de thèse à consisté, dans un premier temps, à définir l'architecture et les conditions d'utilisation optimales d'un tomographe de fluorescence continu appliqué à l'observation de tissus de faible épaisseur. On s'est en particulier attaché à traiter le problème de l'observation de tissus hétérogènes et d'organes fortement absorbants. Dans un deuxième temps, pour observer des tissus de plus grande épaisseur, nous avons montré l'apport de la mesure du temps de vol moyen des photons pour améliorer la localisation d'inclusions fluorescentes. Les performances de deux types de systèmes capables de réaliser ce type de mesure ont été comparées et nous avons proposé un protocole permettant d'en optimiser les principaux paramètres. Notre procédé a été appliqué à la problématique du guidage de biopsies prostatiques. Il pourra aussi être utilisé pour visualiser d'autres pathologies moyennant une simple adaptationFluorescence tomography is a preclinical and clinical imaging method which aims to localize fluorescent probes injected into a living organism. In this thesis work, we defined the optimal design and parameters of a continuous wave fluorescent tomograph applied to thin tissue observation. We handled the problem of observing heterogeneous and highly absorbing organs. Secondly, we showed the advantage of time of flight measurement for inclusion detection through thicker tissues. The detection performances of two types of system capable of these measurements were compared and we proposed a protocol to optimize their main parameters. This process was applied to the problematic of prostatic biopsy guiding. It would also be used to detect and localize other pathologies by means of a simple adaptation
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Chmelik, Christian, Lars Heinke, Arati Varma, Dhananjai B. Shah, Jörg Kärger, and Rajamani Krishna. "Loading dependence of diffusion in zeolites: combined benefits of microscopic measuring techniques and theoretical approaches." Diffusion fundamentals 6 (2007) 59, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14238.
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Bourdin, Vincent, Stefano Brandani, Alfeno Gunadi, Hervé Jobic, Cordula Krause, Jörg Kärger, and Wolfgang Schmidt. "Diffusion of n-alkanes in MFI-type zeolites: a comparative study with different measuring techniques." Diffusion fundamentals 2 (2005) 83, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14420.
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Giacalone, Elisabetta. "Graph-based analysis of brain structural connectivity using different diffusion MRI reconstruction techniques." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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Il cervello si può definire un network complesso in cui delle regioni sono interconnesse fra loro. L'imaging di risonanza magnetica pesato in diffusione (DWI) insieme alla trattografia, permettono di ricostruire i fasci di fibre assonali di sostanza bianca indagando la connettività strutturale tra le aree di sostanza grigia. Il "connettoma" risultante può essere analizzato e caratterizzato attraverso la graph theory. Il lavoro che ho sviluppato presso l'unità di RM funzionale del Policlinico S. Orsola-Malpighi, e il DIBINEM, Università di Bologna, si propone di ricostruire il connettoma tramite due diversi metodi trattografici probabilistici confrontando i risultati ottenuti da acquisizioni DWI con diverso numero di direzioni del gradiente di diffusione (NDGD), ma con rapporto segnale rumore (SNR) costante. È stata effettuata un’acquisizione a 66 e tre a 22-NDGD per 18 soggetti sani. Le scansioni a 22-NDGD sono state mediate fra loro per ottenere un SNR comparabile con le 66-NDGD (22avg) e poter confrontare correttamente i diversi NDGD. Questo tipo di analisi non è ancora presente in letteratura. Dopo aver segmentato il cervello in diverse aree è stata effettuata la trattografia, tramite gli algoritmi PROBTRACKX2 e iFOD2, per costruire un network pesato del connettoma. Abbiamo effettuato misure locali e globali sui network e analizzato le proprietà di small-world e l'organizzazione modulare. Tali misure sono state confrontate fra i diversi NDGD e algoritmi trattografici. Si è visto come PROBTRACKX2 risulti più sensibile alle variazioni del SNR nel confronto dei network a 22 e 22avg. Per entrambi gli algoritmi sono state misurate differenze significative fra i network a 66 e a 22avg suggerendo che l'aumento della risoluzione angolare influenza fortemente le proprietà del network. In particolare, a livello locale si evidenzia un'alterazione delle misure nodo-specifiche nelle zone della sostanza grigia profonda e nell'area fronto temporale, per entrambi gli algoritmi.
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McGuckin, C. E. "The mathematical modelling of diffusion techniques associated with osmotic dehydration of apple slices." Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329361.
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Thomas, David Lee. "Magnetic resonance imaging of diffusion and perfusion : techniques and applications to cerebral ischaemia." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391829.
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Nzikou, Jean-Mathurin. "Étude des phénomènes de diffusion des solutés ioniques par techniques voltamétrique et conductimétrique." Vandoeuvre-les-Nancy, INPL, 1995. http://www.theses.fr/1995INPL145N.
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Les phénomènes de transport constituent en eux seuls un vaste domaine d'étude qui se veut indispensable dans la compréhension des comportements des réacteurs électrochimiques et polyphasiques. Le but de ce travail a consisté à la mise en œuvre de deux différentes méthodes de détermination du coefficient de diffusion, qu'il a fallu ensuite confronter afin d'établir un quelconque lien entre elles ; nous avons de ce fait mis en œuvre la première méthode dite classique, largement utilisée en génie chimique. Elle décrit les phénomènes de manière très simple, mais demeure toutefois limitée car elle présente une inexactitude en toute rigueur ; le fait que la loi de Levich ne s'applique que dans le cas de solution diluée en est une illustration. Nous avons ensuite mis en œuvre la méthode conductimétrique qui est par contre la plus rigoureuse sur l'interprétation de l'intégralité des signaux, permettant donc de suivre des phénomènes de diffusion plus complexes et ainsi de quantifier des interactions mutuelles par le biais des coefficients de diffusion croisés. Toutefois, la restriction de son application sur certains cas spécifiques, notamment sur la limitation du domaine de concentration étudiée, en raison de la certaine saturation des sondes, fait peser en elle une faiblesse. Pourtant, la confrontation des deux méthodes a permis de constater une cohérence entre elles, et les résultats obtenus montrent que les deux méthodes ont été utilisées avec succès dans la détermination du coefficient de diffusion
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Lin, Xuelei. "Preconditioning techniques for all-at-once linear systems arising from advection diffusion equations." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/803.
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In this thesis, we mainly study preconditioning techniques for all-at-once linear systems arising from discretization of three types of time-dependent advection-diffusion equation: linear diffusion equation, constant-coefficients advection-diffusion equation, time-fractional sub-diffusion equation. The proposed preconditioners are used with Krylov subspace solvers. The preconditioner developed for linear diffusion equation is based on -circulant ap- proximation of temporal discretization. Diagonalizability, clustering of spectrum and identity-plus-low-rank decomposition are derived for the preconditioned matrix. We also show that generalized minimal residual (GMRES) solver for the preconditioned system has a linear convergence rate independent of matrix-size. The preconditioner for constant-coefficients advection-diffusion equation is based on approximating the discretization of advection term with a matrix diagonalizable by sine transform. Eigenvalues of the preconditioned matrix are proven to be lower and upper bounded by positive constants independent of discretization parameters. Moreover, as the preconditioner is based on spatial approximation, it is also applicable to steady-state problem. We show that GMRES for the preconditioned steady-state problem has a linear convergence rate independent of matrix size. The preconditioner for time-fractional sub-diffusion equation is based on approximat- ing the discretization of diffusion term with a matrix diagonalizable by sine transform. We show that the condition number of the preconditioned matrix is bounded by a constant independent of discretization parameters so that the normalized conjugate gradient (NCG) solver for the preconditioned system has a linear convergence rate independent of discretization parameters and matrix size. Fast implementations based on fast Fourier transform (FFT), fast sine transform (FST) or multigrid approximation are proposed for the developed preconditioners. Numerical results are reported to show the performance of the developed preconditioners
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Thambipillai, Vasumathy. "A study of the diffusion of mercury into cadmium telluride using mainly radioactive tracer techniques." Thesis, Coventry University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278545.
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Thermitus, Marc-Antoine. "Nouvelles techniques d'identification de la diffusivité thermique par la méthode Flash." Lyon, INSA, 1997. http://www.theses.fr/1997ISAL0029.
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Ce travail porte sur l'identification de la diffusivité thermique des matériaux opaques et isotropes par la méthode flash. Dans une première approche, on exploite non seulement le thermogramme de la face arrière mais aussi celui de la face qui reçoit l'impulsion thermique. Le rapport des des deux thermogrammes offre l'avantage d’être indépendant de la diffusion radiale de la chaleur dans l’échantillon. La diffusivité peut alors être identifiée par la méthode des moments temporels partiels. Une autre manière de tenir compte des deux thermogrammes est de calculer le rapport de leurs transformées de Laplace. Dans ce cas, en utilisant la méthode des quadripôles thermiques, on montre que l'influence de la durée et de la répartition temporelle de l'impulsion n'intervient pas. La diffusivité est alors identifiée dans le domaine de Laplace par la méthode de Levenberg-Marquardt. Cette méthode convient particulièrement aux films minces. Dans une deuxième approche, on ne considère que le thermogramme de la face arrière auquel on applique une transformation logarithmique. Le nouveau modèle obtenu est peu sensible aux pertes et à la diffusion radiale de la chaleur. On montre de plus que l'échantillon peut être assimilé à un système linéaire représenté par un modèle d'état. La diffusivité est alors identifiée en utilisant le filtre de Kalman. Cette méthode très efficace aux hautes températures et lorsque l'impulsion thermique n'est pas homogène, est bien adaptée au traitement en ligne des donnéesThe aim of this work is to propose new identification techniques of thermal diffusivity with the flash method in the case of isotropic and opaque materials. In the first approach, the temperature histories of the two faces of the sample are considered. It is shown that their ratio doesn’t depend on the radial heat diffusion within the sample. In this case, thermal diffusivity can be identified with an adapted moment method. Another way to take the two thermograms into account, is to compute the ratio of their Laplace transforms. Using the quadrupole method, it is shown that the duration of the pulse has no effect. Thermal diffusivity is then identified with the Levenberg-Marquardt method. This technique is particularly suitable for thin films. In the second approach, the logarithmic transform of the rear face temperature rise is considered. In comparison with other existing techniques, the new obtained regression model has the peculiarity to be less sensible to heat losses and to the non-uniformity of the pulse. Furthermore. A stare model is proposed, allowing the identification of thermal diffusivity with the Kalman filter. This technique is also suitable for on-line data redution
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Lechner, Ruep Ekkehard, Goetz Schuck, and Klaus Langer. "Mechanism of proton conduction in solid-state protonic conductors: method and results from investigations by QENS techniques." Diffusion fundamentals 12 (2010) 3, 2010. https://ul.qucosa.de/id/qucosa%3A13865.
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Larsson, Henrik. "Internal oxidation processing : New alloys and new simulation techniques." Doctoral thesis, KTH, Materialvetenskap, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3715.
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Nitriding and oxidising treatments of alloys for toolingpurposes have been investigated both experimentally andtheoretically. Specimens prepared by a combination of differentprocessing steps are investigated by light-optical, scanningand transmission electron microscopy and hardness measurments.The bounds of carbon and nitrogen concentration profiles duringnitriding are obtained from simulations using the DICTRA code.As a result, a new processing route to produce oxide-dispersediron-base alloys with large volume fraction of carbides issuggested. On the theoretical side the methods based on the random walktechnique have been investigated and developed further. The newmethods have been applied to study a vide range of phenomenae.g. internal oxidation, diffusion in inhomogeneous media,phase transformations and formation of porosity due to theKirkendall effect in welded joints. Probability distributionsare introduced to replace random number generators in order toincrease computational efficiency. A general method to simulatediffusional phase transformations in multicomponent systems isdeveloped and applied to ternary alloys.QC 20100506
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Jetin, Bruno. "La diffusion des innovations techniques et organisationnelles dans un pays à l'inflation élevée : l'exemple du Brésil." Paris 13, 1992. http://www.theses.fr/1992PA131014.
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Le bresil a connu au cours de la decennie 1980 une crise economique profonde qui se caracterise par une baisse de l'investissement productif, une hyperinflation rampante et une financiarisation de l7economie. Cette crise a genere une profonde incertitude et un retrecissement de l'horizon temporel des entreprises. Cette derniere evolution entre en contradiction avec les exigences du modele de la production de masse flexible, qui emerge dans les pays developpes, comme on peut le constater dans l'industrie automobile. En effet, ce nouveau paradigme socio-productif necessite de la part des entreprises des engagements de long terme. Du fait de cette contradiction, on assiste au bresil a une modernisation tronquee, c'est-a-dire a une integration des techniques, plutot qu'a une integration des principes du nouveau paradigmeBrazil has lived a decade of profund economic crisis during the 80's, which is caracterize by a fall of productive investments, a contained hyperinflation process and the automatisation of the financial spere. This crisi has generated a radical incertainty in the economy and a shortening of the temporal horizon of prevision of the enterprises. This last evolution contradicts the exigences of the productive paradigm of "flexible mass production", which is emerging in the developped economies, as the example of the automobile industry proves it. This new paradigm needs long term engagements of capital by the firms. This contradiction has lead to a truncated modernisation of the firms in brazil, which is caracterized by the integration of the technics rather than the principles of the new paradigm
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Dvoyashkin, Muslim, Aiping Wang, Hrishi Bhase, Sergey Vasenkov, and Clifford R. Bowers. "Single-file dynamics in nanotubular materials probed by a combination of hyperpolarized tracer exchange and diffusion NMR techniques." Diffusion fundamentals 20 (2013) 49, S. 1-2, 2013. https://ul.qucosa.de/id/qucosa%3A13622.
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Habib, Dayane. "Diffusion de l'hélium-3 hyperpolarisé dans le tissu pulmonaire : évaluation par différentes techniques IRM." Phd thesis, Université Paris Sud - Paris XI, 2007. http://tel.archives-ouvertes.fr/tel-00435916.
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Ce travail présente une étude expérimentale sur l'effet de la diffusion restreinte de l'hélium-3 hyperpolarisé dans l'acinus pulmonaire effectuée à bas champ magnétique 0,1 T. Plusieurs fantômes avec différentes tailles et connections modélisant l'acinus humain sain et à un stade précoce de l'emphysème ont été réalisés selon le modèle de Kitaoka. L'atténuation du signal dévie par rapport au comportement prévu de décroissance exponentielle en G2, G étant l'intensité de gradient. Cette observation indique une certaine ambiguïté sur la possibilité de quantifier de façon absolue le coefficient de diffusion apparent (ADC), sauf dans la limite G faible. Des simulations Monte-Carlo sont en bon accord avec les mesures. Des séquences originales rapides basées sur le principe des échos de spin multiples ont été développées, pour accéder à une valeur globale d'ADC à des temps longs permettant l'exploration du gaz dans toute la structure de branchement de l'acinus. Des mesures sur un modèle animal d'emphysème (rat) ont été comparées à des cartes obtenues à partir d'acquisitions standard avec petits angles de basculement, elles indiquent une augmentation systématique et toujours significative des ADC par rapport au contrôle sain, pour plusieurs protocoles de mesure. La méthode globale a une meilleure sensibilité que la cartographie standard, en outre elle donne un plus fort contraste d'ADC entre animaux sains et avec emphysème du fait de la possibilité d'employer des valeurs de G plus faibles. Ces outils de mesure de diffusion par IRM et RMN des gaz hyperpolarisés ouvrent des voies prometteuses aussi bien pour la physique de la diffusion que pour les applications médicales.
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Ebada, Mohamed. "Multipath Routing for Wireless Sensor Networks: A Hybrid Between Source Routing and Diffusion Techniques." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19887.
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In this thesis, an investigation of the performance of multipath routing in Wireless Sensor Networks (WSN) is performed. The communication in the network under study is to take place from individual nodes to the sink node. The investigation involved multipath finding methods in WSN. Also, it involves investigating the weight assignment, traffic splitting and route selection methods for the different paths discovered by each node in the WSN. Also, a comparison between Hybrid Routing Protocol, Source Routing Protocol and Diffusion Routing Protocol is performed. A simple traffic routing algorithm for each routing protocol has been developed to conceptualize how the network traffic is routed on a set of active paths. The investigation of the Hybrid, Source and Diffusion Routing Protocol involved using multiple paths simultaneously to transmit messages that belong to the same flow by using a weight assigned to each path and transmit each message as a whole. Finally, the power consumption and the QoS in terms of message delays for a WSN were investigated and compared between different protocols.
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Keshava, Murthy Krishna Nand. "Novel representation and low level computer vision techniques for manifold valued diffusion tensor MRI." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42312.
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Diffusion tensor magnetic resonance imaging (DT-MRI) is a powerful non-invasive imaging modality whose processing, analysis and visualization has become a strong focus in medical imaging research. In this modality, the direction of the water diffusion is locally modeled by a Gaussian probability density function whose covariance matrix is a second order 3 X 3 symmetric positive definite matrix, also called the tensor here. The manifold-valued nature of the data as well as its high dimensionality makes the computational analysis of DT images complex. Very often, the data dimensionality is reduced to a single scalar derived from the tensors. Another common approach has been to ignore the restriction to the manifold of symmetric second-order tensors and, instead, treat the data as a multi-valued image. In this thesis, we try to address the above challenges posed by DT data using two different approaches. Our first contribution employs a geometric approach for representing DT data as low dimensional manifold embedded in higher dimensional space and then applying mathematical tools traditionally used in the study of Riemannian geometry for formulating first order and second order differential operators for DT images. Our second contribution is an algebraic one, where the key novel idea is to represent the DT data using the 8 dimensional hypercomplex algebra-biquaternions. This approach enables the processing of DT images in a holistic manner and facilitates the seamless introduction of traditional signal processing methodologies from biquaternion theory such as computing the Fourier transform, convolution, and edge detection for DT images. The preliminary results on synthetic and real DT data show great promise in both our approaches for DT image processing. In particular, we demonstrate greater detection ability of our features over scalar based approaches such as fractional anisotropy and show novel applications of our new biquaternion tools that have not been possible before for DT images.
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Bruland, K. "British technology and Norwegian industrialization : The diffusion of textile techniques from 1845 to 1870." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375880.
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Clark, Christopher Alan. "Magnetic resonance techniques for measurement of water diffusion in the human central nervous system." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286293.
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Marquardt, Pascal [Verfasser], and Wilhelm [Akademischer Betreuer] Heinrichs. "Adaptive spectral least-squares techniques for reaction-diffusion equations / Pascal Marquardt ; Betreuer: Wilhelm Heinrichs." Duisburg, 2020. http://d-nb.info/1212362470/34.
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