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Valivarthi, Mohan Varma, and Hema Chandra Babu Muthyala. "A Finite Element Time Relaxation Method." Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-17728.
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In our project we discuss a finite element time-relaxation method for high Reynolds number flows. The key idea consists of using local projections on polynomials defined on macro element of each pair of two elements sharing a face. We give the formulation for the scalar convection–diffusion equation and a numerical illustration.
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Jouravleva, Svetlana. "Dielectric relaxation time spectroscopy for tissue characterisation." Thesis, Oxford Brookes University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364927.
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Worsley, Richard Edward. "Time-resolved relaxation processes in quantum wells." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295867.
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KUMAR, VINAYAK. "ANALOG SIMULATION TIME REDUCTION BASED ON VARIABLE TOLERANCE RELAXATION." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163019325.
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Beyea, Steven Donald. "Magnetic resonance imaging (MRI) and relaxation time mapping of concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ65451.pdf.
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Ye, Yufeng 1971. "The study of long time relaxation behavior of metallocene polyethylene /." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31081.
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The long time relaxation behavior of linear and long chain branched (LCB) metallocene polyethylene (mPE) is very important for understanding their flow properties. One linear and four LCB mPEs were studied in shear creep and recovery measurements. All the mPEs have similar molecular weight and molecular weight distribution but different levels of long chain branching. A technique was developed to eliminate the effect of non-ideal start-up at the beginning of creep experiment and the small residual stress that exists during the creep recovery period. It is found that the existence of long chain branching is responsible for the increasing of the zero shear viscosity, the steady state compliance and the longest relaxation time. The retardation and relaxation spectrums were calculated from the creep compliance. The dynamic compliance calculated using retardation spectrum is compared with that measured directly. Both are in very good agreement. These observations are compared with the molecular dynamics theory.
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Nordin, Adrian, and Simon Nylén. "Real-time Snow Simulator using Iterative-relaxation and Boundary Handling." Thesis, Blekinge Tekniska Högskola, Institutionen för datavetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-21788.
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Background Physics-based snow simulation in real time is an unexplored area, the reason being the difficulty introduced by the multitude of factors that affect the snow behaviour, such as cohesion, thermodynamics, and compression. Simulating snow in real time when considering these factors can become computationally demanding. However, the continued advancement of graphics processing units makes the exploration of real-time snow simulation attractive. Recently published research on real time physics-based snow simulation shows promising results in a parallel solution and will serve as motivation and base for this thesis. Objectives This thesis aims to improve the time-step of a previously proposed method using an iterative method and improve the snow behaviour with a particle-based boundary handling implementation. The aim consists of the following objectives. Integrate an iterative method, extend the snow behaviour with additional snow types, and implement a particle-based boundary handling method with two-way coupling. The proposed method should remain comparable to the original method in terms of snow behaviour. In order to gather results, the methods are measured in performance and used in a questionnaire to analyse the behaviour. Methods An iterative method along with a particle-based boundary handling method is implemented. The methods are both measured and compared using quantitative tests. Additionally, a questionnaire is deployed to gather qualitative results about the behaviour of the snow. Results The proposed method outperforms the original method in terms of time-step size. The proposed method is capable of increasing the time-step tenfold while decreasing the execution time by approximately eight times. Finally, the results from the questionnaire verify the perceived naturalism of the snow and its comparability to the original method. Conclusions The proposed method can perform with an increased time-step and a lower execution time compared to the original method, at the cost of time spent per frame. Lastly, the snow is perceived as natural with the boundary handling method at a significance level of 1 %.Bakgrund Fysikbaserad snösimulering i realtid är ett outforskat område, anledning till detta är mängden faktorer som påverkar snö, exempelvis sammanhållning, termodynamik och kompression. Simulering av snö i realtid som tar hänsyn till dessa faktorer kan bli beräkningsmässigt krävande, däremot har den växande utvecklingen av grafikprocessorer gjort utforskning av realtidsmetoder ytterligare attraktivt. Nyligen publicerad forskning inom fysikbaserade snösimuleringar i realtid visar lovande resultat i en parallell lösning och kommer att användas som motivering samt bas i detta examensarbete. Syfte Detta examensarbete syftar till att förbättra tidsstegen i en tidigare implementerad metod med hjälp av att använda ett iterativt tillvägagångssätt samt förbättra snöbeteendet med en partikelbaserad gränshanteringsimplementation. Syftet är uppdelat i följande mål. Integrera en iterativ metod, utöka snöbeteendet med ytterligare snötyper, och implementera en partikelbaserad gränshanteringsmetod med tvåvägskoppling. Den föreslagna metoden ska förhålla sig jämförbar med originalmetoden med avseende på snöbeteendet. Slutligen för att samla in resultat mäts metoderna i prestanda och dessutom används ett frågeformulär för att analysera beteendet. Metod En iterativ metod tillsammans med en partikelbaserad gränshanteringsmetod är implementerad. Båda metoderna mäts och jämförs med hjälp av kvantitativa tester. Dessutom distribueras ett kvalitativt frågeformulär för att samla resultat om snöns beteende. Resultat Den föreslagna metoden tillåter större tidsteg än originalmetoden. Den iterativa metoden är kapabel till att förstora tidsstegen tiofaldigt, samtidigt som den sänker exekveringstiden till en åttondel. Resultaten verifierar den uppfattade naturligheten av snön och jämförelsebarheten till originalmetoden. Slutsatser Den föreslagna metoden kan prestera med ett större tidssteg och en lägre exekveringstid jämfört med originalet i utbyte av högre tid spenderad per bildruta. Slutligen uppfattas snön som naturlig i sammankoppling med gränshanteringsmetoden vid en signifikansnivå på 1 %.
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Shiu, Kai Pong. "Study of relaxation time of mechanically aligned polystyrene thin films /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202003%20SHIU.
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Yamamoto, Takashi. "Studies on long time relaxation of multi-arm star polymers." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/148862.
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Doran, Simon John. "An exploration of the role of relaxometry in quantitative magnetic resonance imaging." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308229.
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Schumacher, Kimberly Lydia. "Femtosecond time-resolved intersubband relaxation measurements in GaAs/AlGaAs quantum wells." Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/270439.
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Pon, Carlos (Carlos Roberto) Carleton University Dissertation Engineering Electronics. "Time warping - waveform relaxation (TW - WR) in a distributed simulation environment." Ottawa, 1995.
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Parsaeian, Azita. "Fluctuations in the Relaxation of Structural Glasses." Ohio University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1257449080.
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Chang, Yung-Yeh. "A Time-efficient Method for Accurate T1 Mapping of The Human Brain." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2626.
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The signal resulting from the IR-FSE sequence has been thoroughly analyzed in order to improve the accuracy of quantitative T1 mapping of the human brain. Several optimized post-processing algorithms have been studied and compared in terms of their T1 mapping accuracy. The modified multipoint two-parameter fitting method was found to produce less underestimation compared to the traditional multipoint three-parameter fitting method, and therefore, to result in a smaller T1 estimation error. Two correction methods were proposed to reduce the underestimation problem which is commonly seen in IR-FSE sequences used for measuring T1, especially when a large turbo factor is used. The intra-scan linear regression method corrects the systematic error effectively but the RMSE may still increase due to the increase of uncertainty in sequences with large turbo factors. The weighted fitting model corrects not only the systematic error but also the random error and therefore the aggregate RMSE for T1 mapping can be effectively reduced. A new fitting model that uses only three different TI measurements for T1 estimation was proposed. The performance for the three-point fitting method is as good as that of the multipoint fitting method with correction in the phantom simulation. In addition, a new ordering scheme that implements the three-point fitting method is proposed; it is theoretically able to reduce the total scan time by 1/3 compared to the TESO-IRFSE sequence. The performance of the three-point fitting method on the real human brain is also evaluated, and the T1 mapping results are consistent to with the conventional IR-FSE sequence. More samples of true anatomy are needed to thoroughly evaluate the performance of the proposed techniques when applied to T1 mapping of the human brain.
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Hayes, Gary Robert. "Ultrafast relaxation processes in semiconductors studied by femtosecond time-resolved photoluminescence spectroscopy." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263051.
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Zybell, Sabine. "Relaxation dynamics in photoexcited semiconductor quantum wells studied by time-resolved photoluminiscence." Helmholtz-Zentrum Dresden - Rossendorf, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-197703.
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Gegenstand der vorliegenden Arbeit ist die Untersuchung der Photolumineszenzdynamik von Halbleiter-Quantentöpfen (Quantum Wells), die durch Anregung von Intraband-Übergängen mittels resonanter Laserpulse im mittleren Infrarot- und Terahertz-Spektralbereich verändert wird. Diese Zweifarbenexperimente wurden mit Hilfe eines optischen Aufbaus für zeitaufgelöste Photolumineszenzspektroskopie am Großgerät Freie-Elektronen Laser FELBE am Helmholtz-Zentrum Dresden-Rossendorf realisiert. Zeitlich verzögert zur gepulsten optischen Anregung über die Bandlücke wurden Intersubband- oder Intraexziton-Übergange in den Quantum Wells resonant angeregt. Die dadurch erreichte Ladungsträgerumverteilung zeigt sich in einer deutlichen Verringerung der Photolumineszenzintensität zum Zeitpunkt des zweiten Anregepulses, die im Folgenden als Photolumineszenz-Quenching bezeichnet wird.
Zunächst wird die Stärke des Photolumineszenz-Quenchings in Abhängigkeit der Polarisationsrichtung des midinfraroten Laserstrahls ausgewertet. Während die Absorption durch freie Ladungsträger für beide Polarisationsrichtungen nachweisbar ist, wird experimentell gezeigt, dass Intersubbandabsorption nur möglich ist, wenn ein Anteil der anregenden Strahlung senkrecht zur Quantum-Well-Ebene polarisiert ist.
Das Photolumineszenzsignal ist überwiegend an der energetischen Position der 1s-Exzitonresonanz unterhalb der Bandkante messbar. Die intraexzitonischen Übergangsenergien in Quantum Wells liegen typischerweise im Terahertzbereich. Unter intraexzitonischer 1s-2p Anregung erscheint auch auf dieser Energieskala ein abrupter Intensitätsverlust in der langsam abklingenden Photolumineszenztransiente. Erstmalig wurde im Photolumineszenzspektrum bei höheren Energien im Abstand der Terahertz-Photonenenergie ein zusätzliches 2s-Photolumineszenzsignal detektiert. Eine detaillierte theoretische Beschreibung dieses Problems durch unsere Kooperationspartner Koch et al. von der Phillips-Universität Marburg zeigt, dass unter intraexzitonischer 1s-2p Anregung eine effiziente Coulombstreuung zwischen den nahezu entarteten exzitonischen 2p- und 2s-Zustanden stattfindet. Während der 2p-Zustand optisch dunkel ist, kann die 2s-Population strahlend rekombinieren, was zu dem besagten 2s-Photolumineszenzsignal führt. Die Zeitkonstanten der untersuchten Ladungsträgerdynamik werden durch ein phänomenologisches Modell bestimmt, das die experimentellen Kurven sehr gut abbildet. Es wird ein Ratengleichungsmodell eingeführt, bei dem die involvierten Zustände auf optisch helle und optisch dunkle Besetzungsdichten reduziert werden.
Darüber hinaus werden mit einem modifizierten Versuchsaufbau die Terahertz-induzierten Photolumineszenzsignaturen von Magnetoexzitonen untersucht. Die Stärke des 1s-Photolumineszenz-Quenchings ändert sich dabei entsprechend der magnetoexzitonischen Übergänge, die im betrachteten Feldstärkebereich zwischen 0T und 7T liegen. Für Magnetfelder größer als 3T sind keine 2s-Photolumineszenzsignale mehr messbar, da durch das externe magnetische Feld die Entartung der 2p- und 2s-Zustände aufgehoben wird.
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Zybell, Sabine. "Relaxation dynamics in photoexcited semiconductor quantum wells studied by time-resolved photoluminiscence." Helmholtz-Zentrum Dresden - Rossendorf, 2015. https://hzdr.qucosa.de/id/qucosa%3A22319.
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Gegenstand der vorliegenden Arbeit ist die Untersuchung der Photolumineszenzdynamik von Halbleiter-Quantentöpfen (Quantum Wells), die durch Anregung von Intraband-Übergängen mittels resonanter Laserpulse im mittleren Infrarot- und Terahertz-Spektralbereich verändert wird. Diese Zweifarbenexperimente wurden mit Hilfe eines optischen Aufbaus für zeitaufgelöste Photolumineszenzspektroskopie am Großgerät Freie-Elektronen Laser FELBE am Helmholtz-Zentrum Dresden-Rossendorf realisiert. Zeitlich verzögert zur gepulsten optischen Anregung über die Bandlücke wurden Intersubband- oder Intraexziton-Übergange in den Quantum Wells resonant angeregt. Die dadurch erreichte Ladungsträgerumverteilung zeigt sich in einer deutlichen Verringerung der Photolumineszenzintensität zum Zeitpunkt des zweiten Anregepulses, die im Folgenden als Photolumineszenz-Quenching bezeichnet wird.
Zunächst wird die Stärke des Photolumineszenz-Quenchings in Abhängigkeit der Polarisationsrichtung des midinfraroten Laserstrahls ausgewertet. Während die Absorption durch freie Ladungsträger für beide Polarisationsrichtungen nachweisbar ist, wird experimentell gezeigt, dass Intersubbandabsorption nur möglich ist, wenn ein Anteil der anregenden Strahlung senkrecht zur Quantum-Well-Ebene polarisiert ist.
Das Photolumineszenzsignal ist überwiegend an der energetischen Position der 1s-Exzitonresonanz unterhalb der Bandkante messbar. Die intraexzitonischen Übergangsenergien in Quantum Wells liegen typischerweise im Terahertzbereich. Unter intraexzitonischer 1s-2p Anregung erscheint auch auf dieser Energieskala ein abrupter Intensitätsverlust in der langsam abklingenden Photolumineszenztransiente. Erstmalig wurde im Photolumineszenzspektrum bei höheren Energien im Abstand der Terahertz-Photonenenergie ein zusätzliches 2s-Photolumineszenzsignal detektiert. Eine detaillierte theoretische Beschreibung dieses Problems durch unsere Kooperationspartner Koch et al. von der Phillips-Universität Marburg zeigt, dass unter intraexzitonischer 1s-2p Anregung eine effiziente Coulombstreuung zwischen den nahezu entarteten exzitonischen 2p- und 2s-Zustanden stattfindet. Während der 2p-Zustand optisch dunkel ist, kann die 2s-Population strahlend rekombinieren, was zu dem besagten 2s-Photolumineszenzsignal führt. Die Zeitkonstanten der untersuchten Ladungsträgerdynamik werden durch ein phänomenologisches Modell bestimmt, das die experimentellen Kurven sehr gut abbildet. Es wird ein Ratengleichungsmodell eingeführt, bei dem die involvierten Zustände auf optisch helle und optisch dunkle Besetzungsdichten reduziert werden.
Darüber hinaus werden mit einem modifizierten Versuchsaufbau die Terahertz-induzierten Photolumineszenzsignaturen von Magnetoexzitonen untersucht. Die Stärke des 1s-Photolumineszenz-Quenchings ändert sich dabei entsprechend der magnetoexzitonischen Übergänge, die im betrachteten Feldstärkebereich zwischen 0T und 7T liegen. Für Magnetfelder größer als 3T sind keine 2s-Photolumineszenzsignale mehr messbar, da durch das externe magnetische Feld die Entartung der 2p- und 2s-Zustände aufgehoben wird.
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Zybell, Sabine. "Relaxation dynamics in photoexcited semiconductor quantum wells studied by time-resolved photoluminescence." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-187690.
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Gegenstand der vorliegenden Arbeit ist die Untersuchung der Photoluminenzenzdynamik von Halbleiter-Quantentöpfen (Quantum Wells), die durch Anregung von Intraband-Übergängen mittels resonanter Laserpulse im mittleren Infrarot- und Terahertz-Spektralbereich verändert wird. Diese Zweifarbenexperimente wurden mit Hilfe eines optischen Aufbaus für zeitaufgelöste Photolumineszenzspektroskopie am Großgerät Freie-Elektronen Laser FELBE am Helmholtz-Zentrum Dresden-Rossendorf realisiert. Zeitlich verzögert zur gepulsten optischen Anregung über die Bandlücke wurden Intersubband- oder Intraexziton-Übergänge in den Quantum Wells resonant angeregt.
Die dadurch erreichte Ladungsträgerumverteilung zeigt sich in einer deutlichen Verringerung der Photolumineszenzintensität zum Zeitpunkt des zweiten Anregepulses, die im Folgenden als Photolumineszenz-Quenching bezeichnet wird. Zunächst wird die Stärke des Photolumineszenz-Quenchings in Abhängigkeit der Polarisationsrichtung des midinfraroten Laserstrahls ausgewertet. Während die Absorption durch freie Ladungsträger für beide Polarisationsrichtungen nachweisbar ist, wird experimentell gezeigt, dass Intersubbandabsorption nur möglich ist, wenn ein Anteil der anregenden Strahlung senkrecht zur Quantum-Well-Ebene polarisiert ist.
Das Photolumineszenzsignal ist überwiegend an der energetischen Position der 1s-Exzitonresonanz unterhalb der Bandkante messbar. Die intraexzitonischen Übergangsenergien in Quantum Wells liegen typischerweise im Terahertzbereich. Unter intraexzitonischer 1s-2p Anregung erscheint auch auf dieser Energieskala ein abrupter Intensitätsverlust in der langsam abklingenden Photolumineszenztransiente. Erstmalig wurde im Photolumineszenzspektrum bei höheren Energien im Abstand der Terahertz-Photonenenergie ein zusätzliches 2s-Photolumineszenzsignal detektiert.
Eine detaillierte theoretische Beschreibung dieses Problems durch unsere Kooperationspartner Koch et al. von der Phillips-Universität Marburg zeigt, dass unter intraexzitonischer 1s-2p Anregung eine effziente Coulombstreuung zwischen den nahezu entarteten exzitonischen 2p- und 2s-Zuständen stattfindet. Während der 2p-Zustand optisch dunkel ist, kann die 2s-Population strahlend rekombinieren, was zu dem besagten 2s-Photolumineszenzsignal führt. Die Zeitkonstanten der untersuchten Ladungsträgerdynamik werden durch ein phänomenologisches Modell bestimmt, das die experimentellen Kurven sehr gut abbildet.
Es wird ein Ratengleichungsmodell eingeführt, bei dem die involvierten Zustände auf optisch helle und optisch dunkle Besetzungsdichten reduziert werden. Darüber hinaus werden mit einem modifizierten Versuchsaufbau die Terahertz-induzierten Photolumineszenzsignaturen von Magnetoexzitonen untersucht. Die Stärke des 1s-Photolumineszenz-Quenchings ändert sich dabei entsprechend der magnetoexzitonischen Übergänge, die im betrachteten Feldstärkebereich zwischen 0T und 7T liegen. Für Magnetfelder größer als 3T sind keine 2s-Photolumineszenzsignale mehr messbar, da durch das externe magnetische Feld die Entartung der 2p- und 2s-Zustände aufgehoben wird.
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Phillips, Paul Stewart. "Magnetic resonance line-shape and relaxation time studies of rotational diffusion in liquids." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25956.
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A new numerical analysis method, dispersion vs. absorption plots (DISPA), has been developed for ESR. This method may be used for semi-quantitative line-shape studies and is useful both as a diagnostic and analytical tool. In addition it provides a method of automatic phasing for magnetic resonance spectra. Numerous examples of its applications, both simulated and experimental are presented, with emphasis on spin-probe studies. The digital acquisition and processing methods used for these studies are also briefly discussed.
ESR and NMR relaxation time studies of the bis(dialkyl-N-carbodithioate) metal(II) class of spin-probes have been performed. The T₁,'s of ¹³C and ²H enriched nickel complex were measured by NMR. The line-widths of ⁶³Cu complex were measured by ESR and analysed by Redfield theory. The two sets of results were combined to give the principal elements of the rotational diffusion tensor for the pyrollidine derivative in toluene. This is the first time that ESR and NMR studies have been combined to measure a diffusion tensor. A general strategy for this approach is presented.
ESR data from previous work has been re-analysed in the light of the new results. The analysis shows that the commonly used assumption of isotropic diffusion is extremely misleading.Science, Faculty of
Chemistry, Department of
Graduate
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Turo, Diego. "A relaxation approach for time domain modelling of sound propagation in porous media." Thesis, University of Salford, 2011. http://usir.salford.ac.uk/26948/.
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In the present study a relaxation approach to modelling sound propagation in porous media has been developed. A frequency domain model has been formulated and is shown to allow an analytical transformation of the governing equations in the time domain. The model proposed is an extension of an earlier work by Wilson at al. (1997) and is based on the use of two relaxation times. The model presented requires a set of six measurable parameters, e.g. static flow resistivity, porosity, tortuosity, thermal permeability, viscous and thermal characteristic lengths. It will be shown that the model satisfies the physically correct low and high frequency limits evaluated by Johnson et al. (1987) and therefore allows the prediction of a porous material's behaviour in a wide range of frequencies (and pulse durations when used in time domain). It will also be demonstrated that two different model formulations are necessary depending on the material shape factor values and physical reasons for this are identified. The model has been validated by performing laboratory measurements and numerical simulations in both frequency and time domains for a range of granular and fibrous porous materials. The well-known equivalent fluid model by Johnson et al. (1987), Champoux and Allard (1991) and Lafarge et al. (1997) has been formulated analytically in the time domain and its predictions are compared with those of the relaxation model and the data. In the last section of the work a nonlinear model is developed for finite amplitude sound propagation in porous media and validated using laboratory data for acoustic pulses with different durations and amplitudes.
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Tan, Xin. "Molecular reorientational relaxation and excited state dynamics probed by time-resolved fluorescence spectroscopy /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486474078049178.
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Pandit, Rajib K. "Local Fluctuations in the Relaxation Rate in Glassy Systems." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1542389277929449.
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Sabesan, Vaidhyanathan. "Detection and Frequency Estimation of Nonlinear Systems using Step Relaxation Technique." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1505203318448279.
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Mavimbela, Gcina A. "Time Reparametrization Symmetry and Spatial-Temporal Fluctuations in Glasses." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1354211400.
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Huen, Isaac Kwong-Ping. "Assessment of placental and fetal oxygenation in normal and abnormal pregnancy using magnetic resonance imaging." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/assessment-of-placental-and-fetal-oxygenation-in-normal-and-abnormal-pregnancy-using-magnetic-resonance-imaging(8cd3f9a2-22cb-4c95-bee3-06b5c4bfc2d2).html.
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Fetal growth restriction (FGR) is a common pregnancy complication resulting in increased neonatal mortality and morbidity. The aetiology of fetal growth restriction is not fully understood, but abnormalities in placental development are, leading to abnormalities in placental structure which are thought to affect supply of oxygen to the fetus. The source of fetal hypoxia is unknown due to the difficulty in obtaining oxygenation data in the context of pregnancy using existing techniques. There is also an absence of data relating to oxygenation in FGR pregnancies. Oxygen-Enhanced MRI (OE-MRI) and Blood Oxygen-Level Dependent (BOLD) MRI permit noninvasive acquisition of data related to changes in the concentration of dissolved oxygen (pO2) and changes in hemoglobin saturation (sO2) under air- and oxygen- breathing (hyperoxic challenge).The aim of this project was to determine whether MRI methods can provide information relating to placental oxygenation in normal and FGR-compromised pregnancy, to investigate fetal brain oxygenation and to assess the potential confound of placental perfusion changes under hyperoxic challenge. After optimization of sequences in non-pregnant volunteers, similar pO2 and sO2 increases under hyperoxic challenge were seen in normal and FGR pregnancy. This suggested placental oxygenation was similar and that fetal extraction of oxygen may be a likelier cause of fetal hypoxia. Normal fetal brain oxygenation was found not to increase under hyperoxic challenge, which may be due to hemodynamic adaptation to limit cerebral hyperoxygenation. Finally, the robustness of these oxygenation results was supported by the lack of placental perfusion changes observed under hyperoxia using Arterial Spin Labeling (ASL).In conclusion, MRI methods successfully provided information on placental and fetal oxygenation in normal and abnormal pregnancy, obtaining novel data informing the aetiology of FGR and the physiology of the fetal brain.
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Shah, Falak Dipak. "Time-dependent behavior of pretensioned stainless steel bars used for structural rehabilitation and retrofitting." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53063.
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The objective of this study is to characterize the long-term behavior of an austenitic-ferritic stainless steel-based pretensioned system for strengthening reinforced concrete bridge pier caps in shear. Stress relaxation experiments were conducted on UNS S32101 stainless steel bars subjected to various initial stresses and temperatures within the low homologous temperature (LHT) regime. Data from these experiments were used to develop a viscoplastic constitutive model to describe the long-term time- and temperature-dependent behavior of the stainless steel bars. This mechanics-based approach is integrated with an analytical method based on strut-and-tie analysis to compute the shear strength of reinforced concrete pier caps strengthened with this external pretensioned system.
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Gilbert, Valérie. "The effect of time-scale truncation and data errors on the linear relaxation spectrum." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1995. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/MQ37298.pdf.
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Dunn, DeRome Osmond. "Modeling cycle and time dependent creep/relaxation effects on fatigue lives of notched members." Diss., Virginia Polytechnic Institute and State University, 1991. http://hdl.handle.net/10919/54823.
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Mechanical cyclic variations in mean stress and strain amplitude is a well-known occurrence for metals even at room temperature. Many fatigue analysis procedures ignore these variations. Fatigue analysis which included both time and cycle dependent mechanical material behavior for metals at room temperature had not been previously studied except for the case of creep. An investigation studying transient mechanical effects on Ti-6Al-4V titanium and 7475-T651 Al alloys was done to determine how great an effect transients at room temperature would have on fatigue life under cyclic conditions. The mechanical material response was modeled using viscoplasticity constitutive laws and Neuber’s rule eliminating the need for finite element modeling of uniaxially loaded notched members. However, the Nenber’s modeling may be used with any material constitutive law. The procedures for fatigue damage used cycle counting to compute strain amplitude and mean stress. Since a large amount of fatigue data is reported as strain-life curves, the fatigue analysis was developed using this fatigue data although it did not include transients. If favorable results are obtained, development of modeling and testing to include transients in strain-life fatigue data could be avoided, and the existing fatigue data base utilized.
Experimental work was undertaken and nonlinear optimization techniques used to compute model constants for the two alloys. However, small amounts of rate dependence was found for cyclic strain control testing. The viscoplasticity models became stiff when rate dependence was low causing numerical problems, and model constants for the viscoplastic constitutive law could not be determined since convergence was not achieved. Also, only small amounts of transient static stress relaxation was observed for extended hold periods.
Finally, experimental verification was done for the local surface stresses in a notched member under load using advanced x-ray stress equipment. Measurements during brief pauses were made over a cycle. From the x-ray results, an anomalous surface behavior was observed. The surface yielded before the bulk material with the lower surface yielding seeming to be time dependent in nature. Since rolled plates of the alloys were used, texture was measured and studied in the form of pole figures, and extreme texture was found for both alloys. However. successful x-ray measurements were made for the alloys studied even though assuming linear d-spacing versus sin²ψ. Finally. x-ray measurements for a cycled notched member, exhibited relaxation of mean stress and not relaxation of residual stress.Ph. D.
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Okubo, Gosuke. "The relationship between Aging and T1 relaxation time in deep gray matter: A voxel-based analysis." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225482.
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Goulkhah, Mohammad (Monty). "Waveform relaxation based hardware-in-the-loop simulation." Cigre Canada, 2014. http://hdl.handle.net/1993/31012.
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This thesis introduces an alternative potentially low cost solution for hardware-in-the-loop (HIL) simulation based on the waveform relaxation (WR) method. The WR tech-nique is extended so that, without the need for a real-time simulator, the behaviour of an actual piece of physical hardware can nevertheless be tested as though it were connected to a large external electrical network. This is achieved by simulating the external network on an off-line electromagnetic transients (EMT) simulation program, and utilizing iterative exchange of waveforms between the simulation and the hardware by means of a spe-cialized Real-Time Player/Recorder (RTPR) interface device. The approach is referred to as waveform relaxation based hardware-in-the-loop (WR-HIL) simulation.
To make the method possible, the thesis introduces several new innovations for stabi-lizing and accelerating the WR-HIL algorithm. It is shown that the classical WR shows poor or no convergence when at least one of the subsystems is an actual device. The noise and analog-digital converters’ quantization errors and other hardware disturbances can affect the waveforms and cause the WR to diverge. Therefore, the application of the WR method in performing HIL simulation is not straightforward and the classical WR need to be modified accordingly.
Three convergence techniques are proposed to improve the WR-HIL simulation con-vergence. Each technique is evaluated by an experimental example. The stability of the WR-HIL simulation is studied and a stabilization technique is proposed to provide suffi-cient conditions for the simulation stability.
The approach is also extended to include the optimization of the parameters of power system controllers located in geographically distant places. The WR-HIL simulation technique is presented with several examples. At the end of the thesis, suggestions for the future work are presented.February 2016
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Loskutov, Valentin. "Dependence of the relaxation time T 2 on a fluid flow velocity in a porous media." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-183839.
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Loskutov, Valentin. "Dependence of the relaxation time T 2 on a fluid flow velocity in a porous media." Diffusion fundamentels 20 (2013) 94, S. 1-2, 2013. https://ul.qucosa.de/id/qucosa%3A13683.
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Bezant, Christopher David. "Application of THz pulses in semiconductor relaxation and biomedical imaging studies." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325712.
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Iglesias, Oscar. "Time Dependent Processes in Magnetic Systems." Doctoral thesis, Universitat de Barcelona, 2002. http://hdl.handle.net/10803/662613.
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En este trabajo se presentan modelos para el estudio de los procesos de dependencia en el tiempo de las propiedades magnéticas de diferentes tipos de materiales magnéticos, básicamente sistemas de partículas pequeñas y capas delgadas con aplicación en el campo del almacenamiento magnético. A lo largo del mismo se han estudiado las distintas problemáticas asociadas al creciente aumento de la densidad de grabación en soportes magnéticos.
En primer lugar se han considerado los efectos de tamaño finito y de superficie asociados a la reducción del tamaño de las partículas magnéticas a través de simulaciones Monte Carlo de un modelo reticular para una única partícula de maghemita. Se han estudiado también los efectos de desmagnetización térmica a través de un modelo fenomenológico para la relajación magnética basado en llamada ley de escala Tln(t/to). A través de cálculos numéricos basados en este modelo y su aplicación a medidas experimentales, se ha mostrado como el modelo permite extraer información de las barreras de energía microscópicas responsables de la relajación, incluso cuando ésta se da en presencia de un campo magnético. La existencia de interacciones dipolares entre partículas puede también incorporarse dentro del marco del anterior modelo fenomenológico. A través de un análisis de la relajación calculadas mediante simulación en la ley de relajación y en la estructura de las distribuciones de barreras energéticas. Se han tratado también sistemas con más complejidad de interacciones magnéticas como son las capas delgadas, modelizadas a través de redes bidimensionales de espines con anisotropía perpendicular al plano. Las simulaciones realizadas para distintos valores de la interacción dipolar y de intercambio reproducen la gran variedad de estructuras magnéticas observadas en sistemas reales.
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Delsaute, Brice. "New approach for Monitoring and Modeling of the Creep and Shrinkage behaviour of Cement Pastes, Mortars and Concretes since Setting Time." Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC1104/document.
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Lors de la construction de structure réalisée en plusieurs phases de bétonnage, les déformations du béton sont restreintes durant son durcissement. Quand le retrait est restreint, des contraintes de traction sont induites dans le matériau et un risque de fissuration est présent. Il est alors nécessaire de modéliser l’évolution des propriétés au jeune âge afin de prédire le comportement de la structure durant le jeune âge du béton. La difficulté réside dans le fait que la modélisation des propriétés du béton doit être basée sur des données expérimentales au jeune âge et que ces données doivent être obtenues automatiquement car le durcissement du béton se produit rapidement pendant les premières heures et les premiers jours. La thèse porte sur l’étude expérimentale et numérique des propriétés au jeune âge des matériaux à base de ciment et plus particulièrement sur le développement des déformations endogènes, le coefficient de dilatation thermique, le module d’élasticité et le fluage propre en compression et en traction. A cet effet, un travail complet a été réalisé à l'ULB et à l’Ifsttar impliquant le développement d'une nouvelle approche avec de nouvelles procédures d'essai et la conception de nouveaux dispositifs d'essai pour générer des données expérimentales depuis la prise du matériau. La méthodologie est basée sur deux méthodes d'essai répété. Pour la caractérisation du comportement viscoélastique d'un béton depuis sa prise, un essai de chargement permanent couplé à un essai avec des chargements répétés de plusieurs minutes est nécessaire. Les déformations endogènes, le coefficient de dilatation thermique et la prise sont caractérisés avec des variations thermiques répétées sur un échantillon de béton. Cette nouvelle approche a été définie sur un béton ordinaire et ensuite étendue sur l’étude de 4 paramètres pertinents : le rapport eau-ciment, l'effet de restriction de l'agrégat sur la pâte de ciment dans le développement des propriétés du béton au jeune âge, la substitution du ciment par des additions minérales et la différence de comportement en traction et en compression. Sur la base de ces résultats expérimentaux, de nouveaux modèles ont été développés pour la caractérisation des propriétés au jeune âge de matériaux cimentaires depuis le temps de prise. Une version adaptée de la modélisation du fluage propre dans le Code modèle 2010 est également proposéeFor usual concrete structure built in several phases, concrete deformations are restrained during the hardening process. When shrinkage is restrained, tensile stresses are induced and a cracking risk occurs. Modelling the evolution of an early age set of parameters on concrete is necessary to predict the early age behaviour of concrete structures. The difficulty lies in the fact that the modelling of concrete properties must be based on experimental data at early age and this data must be obtained automatically because the hardening process of the concrete takes place rapidly during the first hours and also the first days. The thesis deals with experimental and numerical study of the early age properties of cement based materials and more specifically the development of the autogenous deformation, the coefficient of thermal expansion, the E-modulus and the basic creep in compression and tension. For this purpose, a comprehensive work was carried out at ULB and Ifsttar involving the development of a new approach with new test procedures and the design of new testing devices to generate experimental data since the setting of the material. The methodology is based on two repeated testing methods. For the characterization of the viscoelastic behaviour of a concrete since setting, a permanent loading coupled to a test with repeated minute-long loadings is needed. Whereas, the autogenous strain, the coefficient of thermal expansion and the setting are characterized with repeated thermal variations on a concrete sample. The new approach was defined on an ordinary concrete and then extended to the study of the following parameters: the water-cement ratio, the restrained effect of aggregate on the cement paste in the development of concrete properties at early age, the substitution of cement by mineral addition and the difference of behaviour in tension and in compression. Based on these experimental results, new models were developed for the characterization of the early age properties of cement based materials since setting time. An adapted version of the Model Code 2010 for the modelling of basic creep is also proposed
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Shahabi, Sagedeh Sadat. "Non-invasive Monitoring of Degradation of Poly (lactide-co-glycolide) Hollow Fiber Channel for Recovery of Spinal Cord Injury Using Magnetic Resonance Imaging." Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23566.
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Spinal cord injury (SCI) leads to axonal damage and limits the ability of the brain to communicate with the rest of the body. Several bioengineered approaches have been developed for the recovery of SCI. Among these techniques, degradable guidance tubes have shown promising results. However, design of nerve guide tubes requires several design considerations and has been a significant challenge. To assess the efficacy of a prototypical implanted nerve guide tubes, it is essential to perform continuous monitoring. In this respect, magnetic resonance imaging (MRI) is one of the most reliable imaging techniques as it offers the ability to achieve extraordinary high temporal and spatial resolution in addition to its non-invasive features. In spite of the excellent image quality of non-enhanced MRI various types of contrast agents have been developed to further enhance the contrast and allow improved visualization. The MRI contrast agents principally work by shortening the T1 or T2 relaxation times of protons located nearby.
The presented study was intended to evaluate the in vitro degradation of the nerve guide tubes made of poly (lactic-co-glycolic acid) (PLGA). PLGA tubes incorporated with different concentrations of superparamagnetic iron oxide (SPIO) were scanned by MRI 3T on weekly basis during the degradation period. Spin-echo (SE) sequence with various echo times (TEs) ranged from 13.3 to 314.4 msec was applied. T2 mapping was computed using in-house algorithm developed in Matlab. Least square fit was used to find the slope of the decay curve by plotting log intensity on the y-axis and echo time on the x-axis. The average T2 values were calculated.
Mass loss and water uptake of the degrading tubes were also measured weekly. Moreover, the micro-structural changes of the tubes were investigated using the scanning electron microscope (SEM). The MRI results showed that the concentration of SPIO affects the signal intensity of the T2 weighted images reducing the T2 relaxation time value. Accordingly, a linear correlation between SPIO concentration and T2 relaxation time was found. At the beginning of degradation, the SPIO nanoparticles were trapped within the polymeric network. Therefore, water penetration was the predominant factor affecting the T2 relaxation times. At week 5, a significant mass loss was observed. From this stage onwards, the trapped SPIO were released from the polymeric network increasing T2 relaxation time dramatically. According to SEM images, the size of the pores in PLGA guide tubes was increased with the degradation. Approaching the end of degradation, shrinkage of the tubes was observed and the degraded nerve guide tubes were shown to be collapsed. Similar shape variation was observed in T2 weighted MR images.
In summary, this study provided an approach to non-invasive monitoring of degradation behavior of nerve guide tubes using contrast enhancement. The developed technique is of great importance since it opened an insight to non-invasive monitoring of tissue engineered scaffolds for in vivo studies.
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Muggli, Mark W. "Physical Aging and Characterization of Engineering Thermoplastics and Thermoplastic Modified Epoxies." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/40509.
Full textAbstract:
In this work the relationship between physical properties, such as physical aging and relaxation time distributions, and chemical structure for a variety of polymeric systems were investigated. Although there is a vast amount of physical aging data for polymers, most of these studies do not attempt to correlate structure with physical aging. Therefore, a set of engineering thermoplastics was examined with the goal of relating certain of their characteristic molecular dimensions to their mechanical and volumetric physical aging attributes.Another series of polymeric materials, based on a poly(ether sulfone) backbone, and having various endgroups differing in size, was also studied to determine physical aging rates and relaxation time distributions. Furthermore, it was concluded that the density of the poly(ether sulfones) increased while the glass transition temperature decreased as the endgroup became smaller.Thermoplastic toughened epoxies were also examined to clarify the importance of covalent bonds between toughener and epoxy on physical aging, relaxation time distributions and fracture toughness. In these studies the covalently bonded tougheners differed from their non-reactive counterparts in the rates of volumetric physical aging at high temperatures for the difunctional epoxy. The solvent resistance of the reactive thermoplastic toughened tetrafunctional epoxy was higher than the non-reactive thermoplastic toughened system. The tetrafunctional epoxies with the reactive toughener also had higher toughener glass transition temperatures.Ph. D.
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Koirala, Sandhaya. "Localization dynamics of paraexcitons and their lattice relaxation at oxygen vacancies in cuprous oxide." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/189651.
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Jullian, Christelle Francoise. "Investigation of polarization switching over broad time and field domains in various ferroelectrics." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/9853.
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Investigations of polarization switching over broad time and electric field domains, in various modified Pb-based perovskite ferroelectrics, were systematically performed by ferroelectric switching current transient and bipolar drive P-E responses. Studies were performed from E«Ec to E»Ec, where Ec is the coercive field These investigations have shown the presence of broad relaxation time distributions for the switching process, which can extend over several decades in order of magnitude in time, and where the distribution is strongly dependent on the applied electric field.
By performing the study of domain dynamics and polarization switching over extremely broad time domains (10⁻⁸ t < 10² sec), more complete information has been obtained that allows for development of a better mechanistic understanding. Prior polarization kinetics studies have focused on relatively narrow time ranges, and were fit to the Avarami equation, which contains a single relaxation time. However, our broad band width polarization dynamics and frequency relaxation studies have been fit to multiple stretched exponential functions extending over decades of order of magnitude in the time domain. Stretched exponential functions for domain nuclei formation, and for domain variant growth have been found. For example, [001]c, [110]c, and [111]c oriented PZN-4.5%PT crystals, nucleation was found to be a volume process (n=3) rather than just a domain wall restricted process. Consequently, nucleation is heterogeneous. And, growth of a domain variant with reversed polarization was found to be a boundary process (n=2), involving diffuse or rough domain walls. We have extended these studies to various types of ferroelectrics including hard, soft and relaxor types.Master of Science
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Kubach, Miriam Rabea [Verfasser]. "Quantification of the longitudinal relaxation time for in vivo MRI : influence of magnetisation transfer / Miriam Rabea Kubach." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1025884574/34.
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Harvey, Pierre Dominique. "Applications of vibrational spectroscopy and NMR spin-lattice relaxation time measurements to organometallic and organic molecular crystals." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=73986.
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Carlin, Dominic Alexander. "An investigation into the importance of T2 relaxation and echo time choice for accurate metabolite biomarker quantification." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7194/.
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Metabolite concentrations are fundamental biomarkers of disease. With increasing interest in personalised medicine, this work assessed the accuracy of non-invasive metabolite quantification with magnetic resonance spectroscopy (MRS) using a combination of simulations, phantom and in vivo data. No optimal echo time (TE) was found for measuring a range of key metabolites with quantification accuracy generally influenced more by data quality than TE choice. The T2 relaxation times of water and metabolites with MRS dominated by a singlet could be estimated using 2 TEs and were found to be significantly different in paediatric brain tumours compared with normal brain, varying between tumour types. The T2 relaxation times of paediatric brain tumours were significantly shorter at 3T compared with 1.5T. Metabolite concentrations for individual patients were most affected by changes in the T2 relaxation time of water which is quick to measure. A clinical JPRESS protocol was developed which aids assignment of overlapping metabolites using changes of MRS with TE. Overall, measurement of MRS with a short TE reduces inaccuracies associated with variability in metabolite T2 and does not tend to lead to worse quantification of overlapping resonances. Further improvements in concentration accuracy can be obtained by measuring case-specific water T2.
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Chen, Ping-Shun. "Cost minimization in multi−commodity multi−mode generalized networks with time windows." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4779.
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The purpose of this research is to develop a heuristic algorithm to minimize total
costs in multi-commodity, multi-mode generalized networks with time windows
problems. The proposed mathematical model incorporates features of the congestion of
vehicle flows and time restriction of delivering commodities. The heuristic algorithm,
HA, has two phases. Phase 1 provides lower and upper bounds based on Lagrangian
relaxations with subgradient methods. Phase 2 applies two methods, early due date with
overdue-date costs and total transportation costs, to search for an improved upper bound.
Two application networks are used to test HA for small and medium-scale
problems. A different number of commodities and various lengths of planning time
periods are generated. Results show that HA can provide good feasible solutions within
the reasonable range of optimal solutions. If optimal solutions are unknown, the average
gap between lower and upper bounds is 0.0239. Minimal and maximal gaps are 0.0007
and 0.3330. If optimal solutions are known, the maximal gap between upper bounds and
optimal solutions is less than 10% ranges of optimal solutions.
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Hannila, I. (Ilkka). "T2 relaxation of articular cartilage:normal variation, repeatability and detection of patellar cartilage lesions." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526212043.
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Abstract Cartilage-related diseases such as osteoarthritis (OA) are a major cause of disability and decrease in the quality of life. Moreover OA causes a heavy economical burden on the social welfare and health care systems. Conventional magnetic resonance imaging (MRI) provides accurate noninvasive method of morphological evaluation of the articular cartilage. However, there are early degenerative changes in the articular cartilage that can be evaluated with modern quantitative MRI methods prior to the signs of cartilage loss. In this study, T2 relaxation time of the articular cartilage was further evaluated in 1.5T in vivo using clinical patients and asymptomatic volunteers. The detection of focal patellar cartilage lesions in T2 mapping as compared to standard clinical MRI was evaluated. T2 mapping showed more lesions than the clinical MRI, and in T2 maps the lesions appeared generally wider. This suggests that T2-mapping is feasible in the clinical setting and may reveal cartilage lesions not seen in the standard knee MRI. The normal topographical variation of T2 relaxation time of articular cartilage in different compartments of the knee joint and at different zones of cartilage in young healthy adults was assessed. T2 values were significantly higher in the superficial zone as compared to the deep tissue at all locations and there was remarkable variation in T2 relaxation between different locations. The normal variation in cartilage T2 within a joint is significant and should be acknowledged when pathology-related T2 changes are investigated. The short- and long-term repeatability of T2 relaxation time measurements of articular cartilage in the knee joint was assessed. The results showed mostly good repeatability, and with careful patient positioning T2 relaxation time at the different cartilage surfaces of the knee can be accurately determinedTiivistelmä Nivelrikko, joka usein liittyy nivelruston vaurioitumiseen, aiheuttaa merkittävää toimintakyvyn ja elämänlaadun heikentymistä ikääntyvässä väestössä. Lisäksi nivelrikosta aiheutuu merkittäviä kustannuksia sosiaali- ja terveydenhuollolle. Magneettikuvaus on tarkka kajoamaton menetelmä rustovaurioiden arvioimiseksi. Kuitenkin rustovaurion alkuvaiheessa tapahtuu ruston sisäisiä rakenteellisia ja biokemiallisia muutoksia, joita on mahdollista arvioida uusilla kvantitatiivisilla magneettikuvausmenetelmillä ennen varsinaisten rustopuutosten kehittymistä. Tässä tutkimuksessa tutkittiin ruston T2-relaksaatioaikamittausta 1.5T magneettikuvauslaitteella sekä potilasaineistossa että vapaaehtoisilla. Tutkimuksessa verrattiin paikallisten rustomuutosten havaitsemisen herk¬kyyttä T2-relaksaatioaikakartoituksen ja tavanomaisen kliinisen magneetti¬kuvauksen välillä kliinisessä potilasaineistossa. T2-relaksaatiomittaus osoitti useampia muutoksia kuin kliininen magneettikuvaus ja muutokset olivat yleensä laajempia. Voidaan olettaa, että T2-relaksaatioaikamittaus soveltuu kliiniseen käyttöön ja voi osoittaa tavanomaisessa magneettikuvauksessa näkymättömiä rustomuutoksia. Tutkimuksessa arvioitiin ruston T2-relaksaatioajan paikkakohtaista ja kerroksittaista vaihtelua polven nivelpintojen eri alueilla nuorten vapaaehtoisten aineistossa. T2-relaksaatioaika oli merkitsevästi pidempi ruston pinnallisessa kuin syvässä kerroksessa kaikilla nivelpintojen alueilla. Lisäksi T2-relaksaatioajassa oli merkittävää normaalia vaihtelua eri alueiden välillä ja tämä tulisi huomioida ruston patologisia muutoksia arvioitaessa. Tutkimuksessa arvioitiin polven ruston T2-relaksaatioajan lyhyen ja pitkän aikavälin toistettavuutta vapaaehtoisaineistossa. Tulokset osoittivat enimmäkseen hyvää toistettavuutta ja huolellisella asettelulla voidaan ruston T2-relaksaatioaika mitata luotettavasti polven nivelpintojen eri alueilla
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Galbraith, Martin Christopher Edward [Verfasser]. "Time-resolved spectroscopy with attosecond pulses and pulse trains: ultrafast relaxation in benzene cations / Martin Christopher Edward Galbraith." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1124465170/34.
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Glancy, Paul Michael. "Terahertz time domain spectroscopy (THz-TDS) of hydrated biomolecular polymers and monomers." Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=153&did=1906549291&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270496277&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Vita. Includes abstract. Includes bibliographical references (leaves 148-155). Issued in print and online. Available via ProQuest Digital Dissertations.
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Raya, García del Olmo José María. "Voxel-based assessment of disease progression in articular cartilage with MRI follow-up examinations of the T2 relaxation time." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-108411.
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Lau, Wai-ping, and 劉偉平. "Minimising the calculation time of the cluster program by choosing theminimum convergent cluster size and the best relaxation factor." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B29760392.
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Kwan, Kermit S. Jr. "The Role of Penetrant Structure on the Transport and Mechanical Properties of a Thermoset Adhesive." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30666.
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In this work the relationships between penetrant structure, its transport properties, and its effects on the mechanical properties of a polymer matrix were investigated. Although there is a vast amount of data on the diffusion of low molecular weight molecules into polymeric materials and on the mechanical properties of various polymer-penetrant systems, no attempts have been made to inter-relate the two properties with respect to the chemical structure of the diffusant. Therefore, two series of penetrants - n-alkanes and esters - were examined in this context, with the goal of correlating molecular size, shape, and chemical nature of the penetrant to its final transport and matrix mechanical properties. These correlations have been demonstrated to allow quantitative prediction of one property, given a reasonable set of data on the other parameters.
A series of n-alkanes (C6-C17) and esters (C5-C17) have been used to separate the effects of penetrant size and shape, from those due to polymer-penetrant interactions, in the diffusion through a polyamide polymeric adhesive. These effects have been taken into account in order to yield a qualitative relationship that allows for prediction of diffusivity based upon penetrant structural information. Transport properties have been analyzed using mass uptake experiments as well as an in-situ FTIR-ATR technique to provide detailed kinetic as well as thermodynamic information on this process.
The phenomenon of diffusion and its effects on the resulting dynamic mechanical response of a matrix polymeric adhesive have been studied in great detail using the method of reduced variables. The concept of a diffusion-time shift factor (log aDt) has been introduced to create doubly-reduced master curves, taking into account the effects of temperature and the variations in the polymer mechanical response due to the existence of a low molecular weight penetrant.Ph. D.
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KHARCHEVA, Anna. "Anomalous diffusion and nonlinear relaxation phenomena in stochastic models of interdisciplinary physics." Doctoral thesis, Università degli Studi di Palermo, 2020. http://hdl.handle.net/10447/430665.
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The study of nonlinear dynamical systems in the presence of both Gaussian and non-Gaussian noise sources is the topic of this research work. In particular, after shortly present new theoretical results for statistical characteristics in the framework of Markovian theory, we analyse four different physical systems in the presence of Levy noise source. (a) The residence time problem of a particle subject to a non-Gaussian noise source in arbitrary potential profile was analyzed and the exact analytical results for the statistical characteristics of the residence time for anomalous diffusion in the form of Levy flights in fully unstable potential profile was obtained. Noise enhanced stability phenomenon was found in the system investigated. (b) The correlation time of the particle coordinate as a function of the height of potential barrier, the position of potential wells and noise intensity was investigated in the case of confined steady-state Levy flights with Levy index alpha=1, that is Cauchy noise, in the symmetric bistable quartic potential. (c) The stationary spectral characteristics of superdiffusion of Levy flights in one-dimensional confinement potential profiles were investigated both theoretically and numerically. Specifically, for Cauchy stable noise we calculated the steady-state probability density function for an infinitely deep rectangular potential well and for a symmetric steep potential well. (d) For two-dimensional diffusion the general Kolmogorov equation for the joint probability density function of particle coordinates was obtained by functional methods directly from two Langevin equations with statistically independent non-Gaussian noise sources. We compared the properties of Brownian diffusion and Levy flights in parabolic potential with radial symmetry. Afterwards, we analyzed the nonlinear relaxation in the presence of
Gaussian noise for the stochastic switching dynamics of the memristors. We have studied three different models. (a) We started from
consideration of the simplest model of resistive switching. (b) Further, the charge-controlled and the current-controlled ideal Chua memristors with external Gaussian noise were investigated. For both cases we have obtained exact analytical expressions for the probability density function of the charge flowing through the memristor and of the memristance. (c) Moreover, we proposed a stochastic macroscopic model of a memristor, based on a generalization of known approaches and experimental results. Steady-state concentration of defects for different boundary conditions was found. Also we analysed how the concentration of defects is changed with time under arbitrary values of external voltage, noise intensity, effective diffusion coefficient and other parameters. An examination of the results was performed, the possible implications of this work and the future development of this study were outlined.