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Zomrawy, Elrashid. "Relaxation creativity." This title; PDF viewer required Home page for entire collection, 2007. http://archives.udmercy.edu:8080/dspace/handle/10429/9.
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Pop, Cristina-Maria. "Non-equilibrium relaxation." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-151719.
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Moser, Michele R., and Eys P. van. "Relaxation Skills Training." Digital Commons @ East Tennessee State University, 2008. https://dc.etsu.edu/etsu-works/4975.
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Milliken, T., L. Craigen, and Rebekah Byrd. "Stress Busting with the Relaxation Response: Creative Approaches to Relaxation Techniques." Digital Commons @ East Tennessee State University, 2012. https://dc.etsu.edu/etsu-works/925.
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Benton, Kara. "Effects of music assisted relaxation versus relaxation alone on quality of sleep." Scholarly Commons, 2011. https://scholarlycommons.pacific.edu/uop_etds/792.
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This study examined the effects of music on improving quality of sleep. Participants were randomly assigned to either a music assisted relaxation or a relaxation alone condition. Individuals in both groups were taught varying relaxation methods and were provided with a relaxation script which incorporated each of the methods. Those in the music assisted relaxation condition were allowed to select their top two pieces from a list of relaxing music. The selections were placed on a CD being played in the background while a relaxation script was read. Those in the relaxation alone condition received a CD with the same relaxation script heard by those in the music assisted relaxation condition. Global sleep scores (as measured by the Pittsburgh Sleep Quality Index) were taken on the first and last days of the experiment. Examining individual and group scores showed no statistically significant difference between music assisted relaxation and relaxation alone. Discussion focuses on the implications for future research in the area of music's effect on sleep quality.
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Gerhardt, Peter Wenzel. "Schnelle Relaxation von Clustern." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972080589.
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Crossman, Statter Gregory Christopher. "Collisional relaxation in plasmas." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27637.
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The energy relaxation of two types of fully ionized plasma systems are determined with the solution of the Fokker-Planck equation. In both cases the plasma constituents are treated as being point-like and structureless and the plasma relaxes collisionally in the absence of spatial gradients and external electric and magnetic fields.
The first plasma system consists of one plasma species dilutely dispersed in a second plasma which acts as a heat bath at equilibrium. The initial energy distribution of the dilute constituent is chosen to be a delta function and the approach to a Maxwellian distribution at the heat bath temperature is determined.
The second plasma system consists of just one plasma species which initially
possesses a bi-Maxwellian ion velocity distribution function (VDF). The average of the kinetic energy, mScience, Faculty of
Chemistry, Department of
Graduate
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McKenzie, Charles A. "Fast acquisition relaxation mapping." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0018/NQ58110.pdf.
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Cohen, Albert. "Relaxation methods in micromagnetics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ61544.pdf.
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Woldt, E. "Relaxation in metallic glasses." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382709.
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Yang, Y. H. "Relaxation method to lofargram." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA237342.
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Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Lee, C.H. Second Reader: Hippenstiel, R. "June 1990." Description based on title screen as viewed on October 20, 2009. Author(s) subject terms: Relaxation method applied to lofargram. Includes bibliographical references (p. 63-64). Also available in print.
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Willis, Maureen. "Muon spin relaxation as a probe of electron spin relaxation in organic semiconductors." Thesis, Queen Mary, University of London, 2012. http://qmro.qmul.ac.uk/xmlui/handle/123456789/5392.
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The purpose of this thesis is to study the electron spin relaxation (eSR) in small organic molecular semiconductors using the muon spin relaxation (MuSR) technique. One of the inherent problems in utilising the spin degree of freedom is the lack of understanding of the fundamental mechanisms behind spin relaxation. Two interactions have been proposed as the dominant mechanisms behind the spin relaxation, the Hyper ne interaction (HFI) and the Spin Orbit (SO) interaction. There remains much debate over the models for these interactions and their exact role, a contention that drives the work carried out in this thesis. The MuSR technique is utilised providing a novel molecular scale probe sensitive to relaxation rates in the range of 0.01-10 MHz. The Avoided Level crossing (ALC) MuSR application is useful in accessing the spin relaxation information. Temperature dependent ALC-MuSR measurements are performed for a selection of functionalised acenes and Quinolate molecules. Transverse eld MuSR measurements are also taken to determine the Hyper ne coupling constants present. DFT and semi-empirical computational methods are employed to determine theoretical values for the isotropic and anisotropic terms and the suitability of these methods was discussed. It is concluded that an intra-molecular eSR is present in all small organic molecular semiconductors. The mechanism behind this eSR was found not to be the HFI but in fact the SO interaction. It is also determined that the eSR is coupling to the vibrations in the molecule and a possible theory based on the curvature of the molecule from the vibrational modes inducing an enhanced SO coupling is proposed, which results in the eSR. The nal part of this thesis looks at the future experiments that have been initiated or can be conducted to further the understanding of spin relaxation and determine the role of a vibrationally enhanced SO coupling.
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He, Yinglan. "The Impact of Music Relaxation on Affect and Relaxation of Stressed Female College Students." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1524172499066518.
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Barelli, Eleonora. "Dielectric relaxation in biological materials." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9102/.
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The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important in order to explain various phenomena in Solid-State Physics and in Physics of Biological Materials.
Indeed, during the last two centuries, many scientists have tried to explain and model the dielectric relaxation. Starting from the Kohlrausch model and passing through the ideal Debye one, they arrived at more com- plex models that try to explain the experimentally observed distributions of relaxation times, including the classical (Cole-Cole, Davidson-Cole and Havriliak-Negami) and the more recent ones (Hilfer, Jonscher, Weron, etc.).
The purpose of this thesis is to discuss a variety of models carrying out the analysis both in the frequency and in the time domain. Particular attention is devoted to the three classical models, that are studied using a transcendental function known as Mittag-Leffler function. We highlight that one of the most important properties of this function, its complete monotonicity, is an essential property for the physical acceptability and realizability of the models.
Lo studio delle proprietà dielettriche riguarda l’immagazzinamento e la dissipazione di energia elettrica e magnetica nei materiali. I dielettrici sono importanti al fine di spiegare vari fenomeni nell’ambito della Fisica dello Stato Solido e della Fisica dei Materiali Biologici.
Infatti, durante i due secoli passati, molti scienziati hanno tentato di spiegare e modellizzare il rilassamento dielettrico. A partire dal modello di Kohlrausch e passando attraverso quello ideale di Debye, sono giunti a modelli più complessi che tentano di spiegare la distribuzione osservata sperimentalmente di tempi di rilassamento, tra i quali modelli abbiamo quelli classici (Cole-Cole, Davidson-Cole e Havriliak-Negami) e quelli più recenti (Hilfer, Jonscher, Weron, etc.).
L’obiettivo di questa tesi è discutere vari modelli, conducendo l’analisi sia nel dominio delle frequenze sia in quello dei tempi. Particolare attenzione è rivolta ai tre modelli classici, i quali sono studiati utilizzando una funzione trascendente nota come funzione di Mittag-Leffler. Evidenziamo come una delle più importanti proprietà di questa funzione, la sua completa monotonia, è una proprietà essenziale per l’accettabilità fisica e la realizzabilità dei modelli.
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Howlett, John David. "Size Function Based Mesh Relaxation." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd761.pdf.
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Rösner, Peter Christian. "Mechanische Relaxation in komplexen Fluiden." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971978824.
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Romanini, Michela. "Relaxation dynamics in disordered systems." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/317384.
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The nature of the glass transition and of the glassy state is a fundamental and still unsolved problem of condensed matter physics. Many liquids can be supercooled below their melting point without crystallizing, that is, without acquiring translational and orientational order. As the temperature of a supercooled liquid is lowered, the characteristic timescale of moleuclar motions, called relaxation time, increases until it becomes comparable to the timescale of human experimentation. This takes place at the glass transition temperature and leads to a non-equilibrium state of matter, called a ¿structural glass¿, in which a liquid-like lack of order is combined with solid-like elastic properties. Glass transitions are also observed in systems where there is only orientational disorder, such as orientationally disordered (OD) crystals or plastic crystals, which are translationally ordered solids in which the constituent molecules display reorientational motions about their centres of mass. Upon supercooling an OD crystal, the orientational disorder can ¿freeze¿, yielding a so-called ¿orientational glass¿.
In molecular materials forming structural or orientational glasses, the most important molecular dynamics process is the cooperative motion of the molecules, referred to as primary relaxation, whose freezing marks the transition to the glass state characterized by static disorder. The main difference between orientational and structural glasses is that in the former the freezing involves exclusively the rotational degrees of freedom of the molecules, while in the latter all six molecular degrees of freedom (i.e., both orientational and translational ones) are frozen. Orientational glasses are therefore systems with fewer degrees of freedom than structural glasses. This simplification, together with the fact that many OD phases are characterized by a crystal lattice with high symmetry, makes OD phases a model playground to investigate the nature of the glass transition. Other than the primary relaxation, there can be also so-called ¿secondary relaxations¿, usually characterized by shorter relaxation time than the primary process. Secondary relaxations may have different origins; for example, they can be due to conformational fluctuations or intramolecular vibrations; in many cases a special kind of secondary relaxation is observed, which is the single-molecule precursor process of the primary relaxation.
This thesis focuses on the effect of pressure and temperature on the dynamics of several pure compounds and binary mixtures forming structural or orientational glasses. We present a comparative study between two structural glass formers (ternidazole and the mixture of m-fluoroaniline with m-xylene), a plastic binary mixed crystal (neopenthyl alchol and neopentyl glycol), and two materials displaying statistical orientational disorder (2-adamantanone and pentachloronitrobenzene). In all cases a primary relaxation is present, associated with the collective motion of the molecules, and in most cases also secondary relaxations are observed. For each material, we analyse the temperature- and pressure-dependence of the various molecular relaxation and discuss the origin of secondary processes. One of the most important results of the thesis is the presence of secondary relaxations also in systems with low-dimensional disorder that behave similarly to the secondary relaxations observed in structural glasses.La naturaleza de la transición vítrea es un problema fundamental y aún no resuelto de la física de la materia condensada. Muchos líquidos pueden ser superenfriados por debajo de su temperatura de fusión sin que cristalicen, es decir, sin que adquieran orden traslacional y orientacional. Cuando la temperatura de un líquido superenfriado baja, el tiempo característico de los movimientos moleculares, llamado tiempo de relajación, aumenta hasta llegar a tiempos comparables con el tiempo característico de los experimentos y de la observación humana. Esto ocurre a una temperatura llamada temperatura de transición vítrea y lleva a un estado de non-equilibrio del material llamado ¿vidrio estructural¿, en el que la ausencia de orden de largo alcance típica del estado líquido se combina con las propiedades elásticas propias de un sólido ordenado. Las transiciones vítreas se pueden observar también en sistemas caracterizados por desorden exclusivamente orientacional, como en los cristales orientacionalmente desordenados (OD) o cristales plásticos. Estos son sólidos traslacionalmente ordenados en los que las moléculas tienen movimientos de reorientación alrededor de sus centros de masa, que están fijos. Superenfriando un cristal OD se obtiene un ¿vidrio orientacional¿ en el cual este desorden orientacional está congelado. El proceso dinámico más importante que caracteriza los materiales moleculares que forman vidrios estructurales u orientacionales es el movimiento cooperativo de las moléculas conocido como relajación primaria. Su congelamiento marca la transición al estado vítreo caracterizado por un desorden estático. La diferencia principal entre los vidrios orientacionales y estructurales es que en los primeros el congelamiento involucra sólo los grados de libertad de rotación, mientras que en los segundos todos los seis grados de libertad moleculares (orientacionales y traslacionales) están congelados. Por tanto, los vidrios orientacionales son sistemas con menos grados de libertad respecto los vidrios estructurales y pueden considerarse como sistemas modelo para investigar la transición vítrea, ya que además muchas fases OD están caracterizadas por redes cristalinas de alta simetría. Además de la relajación primaria, existen también relajaciones secundarias caracterizadas por tiempos de relajación más cortos con respecto al proceso primario. Estas relajaciones secundarias pueden tener diferentes orígenes: por ejemplo, pueden ser debidas a fluctuaciones de la conformación molecular o a vibraciones de enlaces intramoleculares; en muchos casos se observa una relajación secundaria que es considerada como la precursora del proceso primario (relajación Johari-Goldstein). Esta tesis está enfocada en el estudio de los efectos de la presión y de la temperatura sobre la dinámica de algunos compuestos puros y mezclas binarias, los cuales forman vidrios estructurales u orientacionales. Se presenta un estudio comparativo entre dos vidrios estructurales (ternidazole y la mezcla de m-fluoroanilina con m-xileno), un cristal plástico binario (formado por neopenthyl alcohol y neopentyl glycol), y dos materiales que presentan desorden estadístico (2-adamantanona y pentacloronitrobenceno). En todos los casos se observa una relajación primaria asociada a los movimientos colectivos de las moléculas y en la mayoría de los casos se observa también relajaciones secundarias. Para cada material se analiza la dependencia de diferentes relajaciones con la temperatura y con la presión y se discute el origen de los procesos secundarios. Uno de los resultados importantes de la tesis es que en sistemas con desorden de baja dimensionalidad, pueden aparecer relajaciones secundarias que obecen a patrones similares a las encontradas en vidrios estructurales
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Colson, Harry George. "Strain relaxation in semiconductor heterostructures." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/843607/.
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The strain relaxation behaviour of and oriented InxGa1-xAs layers grown on GaAs substrates has been investigated using surface profilometry and high resolution X-ray diffraction. The strain relaxation behaviour of single InxGa1-xAs layers (grown by various methods) has been studied using double crystal X-ray diffraction. The layer strain has been shown to be predictable, following the empirical relaxation law given by epsilonr = k/d where epsilonr is the residual strain, d is the layer thickness and k is a constant (= 0.84 nm +/- 0.18 nm). In addition, it is shown, using previously published data, that this law is applicable to other semiconductor alloy systems. Results show that the relaxation behaviour of oriented material is very similar to that of oriented material. However, the critical thickness is 1.23 times that for material in agreement with theory. It is shown that plastic relaxation of good quality epitaxially strained layers is accompanied by roughening of the surface in the form of striations and that the maximum striation height is always less than 20 nm regardless of layer thickness. Measurements of strain relaxation in multi-quantum well type samples show good agreement with a simple geometric theory in which the minimum barrier thickness needed to decouple strained layers of thickness hw is given as 0.62hw.
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Eakin, H. J. W. "Ultrafast relaxation processes in semiconductors." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382634.
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Aldinger, Johannes [Verfasser], and Bernhard [Akademischer Betreuer] Nebel. "Relaxation heuristics for numeric planning." Freiburg : Universität, 2018. http://d-nb.info/1175875155/34.
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Bolldén, Johanna, and Frida Ekdahl. "NOA Relaxation : stressreduktion på flaska?" Thesis, Gymnastik- och idrottshögskolan, GIH, Institutionen för idrotts- och hälsovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:gih:diva-3855.
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Syfte och frågeställningar Syftet med denna studie var att undersöka om den stressreducerande drycken NOA relaxation, innehållande L-theanin och Citronmeliss, har någon fysiologisk samt psykologisk effekt på kvinnliga ishockeyspelare vid konsumtion. Studien undersökte även hur ishockeyspelarnas prestationsförmåga vid kognitiva datortester påverkades vid intag av NOA relaxation. Hypotesen för denna studie är att drycken NOA relaxation har en lugnande, fokusgivande samt stressreducerande effekt både psykologiskt och fysiologiskt på deltagarna. Metod I studien har 7 kvinliga ishockeyspelare deltagit. Deltagarna antingen studerade eller var arbetslösa, åldersspann mellan 17 till 22 år (medelålder 20). Tre stycken testtillfällen utfördes, det första tillfället då deltagarna enbart fick pröva på de kognitiva datortesterna. Dessa datortester kommer från testbatteriet Psychology Experiment Building Language (PEBL) och syftar till att undersöka deltagarens koncentration, minne samt mental flexibilitet. Vid andra och tredje tillfället fick deltagarna konsumera antingen placebo-drycken (FUN light) eller NOA relaxation och sedan utföra datortesterna. Under dessa tillfällen mättes den psykologiska effekten genom enkäten State Trait Anxiety Inventory (STAI) som mäter upplevd ångest, oro och stress. De fysiologiska effekterna mättes med hjälp av blodtryck och puls innan, under och efter utförande av de kognitiva datortesterna. Innan testtillfällena fick deltagarna fylla i en hälsoenkät om deras upplevda hälsa, efter testtillfällena fick de fylla i enkäten STAI. Resultat Resultaten från de kognitiva datortesterna visade inga signifikanta effekter vid konsumtion av NOA relaxation jämfört med placebodrycken. Samma resultat gäller för sammanställningen av poängen från STAI. Ingen signifikans kunde visas gällande lägre puls vid konsumtion av NOA relaxation jämfört med placebodrycken. Samma resultat gäller för det systoliska blodtrycket, dock fann man ett signifikant lägre diastoliskt blodtryck vid konsumtionen av NOA relaxation jämfört med placebodrycken. Slutsats Resultaten från de kognitiva datortesterna samt STAI kunde inte påvisa hypotesen om att NOA relaxation skulle ge en mentalt lugnande samt stressreducerande effekt. Det samma gäller hypotesen om fysiologiskt lugnande samt stressreducerande effekt gällande puls, dock bekräftades hypotesen om ett lägre blodtryck (diastoliskt), detta tyder eventuellt på ett ökat lugn.
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Downes, James R. "Strain relaxation in semiconductor devices." Thesis, University of Surrey, 1995. http://epubs.surrey.ac.uk/773021/.
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Strained layers are incorporated into many electronic devices and particularly into semiconductor lasers. These strained layers can relax, both elastically and plastically, which often impairs the performance of the device. This thesis presents several methods for calculating elastic strain relaxation: a Fourierseries method for stresses imposed on the surfaces of a rectangular block; a Fourier-integral for stress imposed on the surfaces of an infinite layer; and a Green-function method for the stress field about buried inclusions. The methods are used to calculate the strain distributions in a transmission electron microscopy sample, the relaxation at the end facet of a strained-layer laser, and the strain field about a rectangular buried layer. The effects of the strain relaxation on the optical absorption of the laser facet and the zone-centre band structure of the buried layer are discussed. The equilibrium theory of critical thickness is examined in detail and is shown to make unreasonable predictions for highly strained layers; a modification which corrects this behaviour is suggested. The equilibrium theory equates the line tension of a strain relieving dislocation to the strain energy it relieves in the layer. The additional energy corrections which can be included in the line tension are discussed, together with the failure of the equilibrium theories to reliably predict plastic relaxation in all situations.
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Mittendorff, Martin. "Carrier Relaxation Dynamics in Graphene." Forschungszentrum Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-162161.
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Graphene, the two-dimensional lattice of sp2-hybridized carbon atoms, has a great potential for future electronics, in particular for opto-electronic devices. The carrier relaxation dynamics, which is of key importance for such applications, is in the main focus of this thesis. Besides a short introduction into the most prominent material properties of graphene and the experimental techniques, this thesis is divided into three main parts.
The investigation of the carrier relaxation dynamics in the absence of a magnetic field is presented in Chapter 3. In the first experiment, the anisotropy of the carrier excitation and relaxation in momentum space was investigated by pump-probe measurements in the near-infrared range.
While this anisotropy was not considered in all previous experiments, our measurements with a temporal resolution of less than 50 fs revealed the polarization dependence of the carrier excitation and the subsequent relaxation. About 150 fs after the electrons are excited, the carrier distribution in momentum space gets isotropic, caused by electron-phonon scattering. In a second set of two-color pump-probe experiments, the temperature of the hot carrier distribution, which was obtained within the duration of the pump pulse (about 200 fs), could be estimated. Furthermore, a change in sign of the pump-probe signal can be used as an indicator for the Fermi energy of different graphene layers.
Pump-probe experiments in the far-infrared range in reflection and transmission geometry were performed at high pump power. A strong saturation of the pump-induced transmission was found in previous experiments, which was attributed to the pump-induced change in absorption. Our investigation shows the strong influence of pump-induced reflection at long wavelengths, as well as a lot smaller influence of the saturation of the pump-induced change in absorption. At a high pump power, the increase of the reflection exceeds the change in absorption strongly, which leads to negative pump-probe signals in transmission geometry.
In Chapter 4, investigations of the carrier dynamics of graphene in magnetic fields of up to 7T are presented. Even though the optical properties of Landau-quantized graphene are very interesting, the carrier dynamics were nearly unexplored. A low photon energy of 14meV allows the investigation of the intraband Landau-level (LL) transitions. These experiments revealed two main findings: Firstly, the Landau quantization strongly suppresses the carrier relaxation via optical-phonon scattering, resulting in an increased relaxation time.
Secondly, a change in sign of the pump-probe signal can be observed when the magnetic field is varied. This change in sign indicates a hot carrier distribution shortly after the pump pulse, which means that carrier-carrier scattering remains very strong in magnetic fields. In a second set of pump-probe measurements, carried out at a photon energy of 75meV, the relaxation dynamics of interband LL transitions was investigated. In particular, experiments on the two energetically degenerate LL transitions LL(−1)->LL(0) and LL(0)->LL(1) showed the influence of extremely strong Auger processes.
An ultrafast and extremely broadband terahertz detector, based on a graphene flake, is presented in the last chapter of this thesis. To couple the radiation efficiently to the small flake, the inner part of a logarithmic periodic antenna is connected to it. With a rise time of about 50 ps in a wavelength range of 9 μm to 500 μm, this detector is very interesting to obtain the temporal overlap in two-color pump-probe experiments with the free-electron laser FELBE. Furthermore, the importance of the substrate material, in particular for the high-speed performance, is discussed.
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Simnett, Sarah Jacqueline. "Relaxation processes in cardiac muscle." Thesis, University of Oxford, 1993. http://ora.ox.ac.uk/objects/uuid:9b670123-f816-42be-8d74-c37917af200b.
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James, Michael J. "Relaxation of the human detrusor." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284528.
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Usher, Sarah Jane. "Carrier relaxation in semiconductor structures." Thesis, University of Exeter, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385758.
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Ahir, Samit Vallabhbhai. "Nanotube-polymer actuation & relaxation." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612763.
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Vandoolaeghe, Wendy Leigh. "Stress relaxation in polymer networks." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614364.
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Hachiya, Marco Antonio de Oliveira. "Spin relaxation in semiconductor nanostructures." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-13012014-151605/.
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In the research field of spintronics, it is essential to have a deep understanding of the relaxation mechanisms of the spin degree of freedom. To this end, we study the spin relaxation in semiconductor nanostructures with spin-orbit interaction. First we analyze the spin decay and dephasing in graphene quantum dots within the framework of the Bloch-Redfield theory. We consider a gate-tunable circular graphene quantum dot where the intrinsic and Rashba spin-orbit interactions are operative. We derive an effective Hamiltonian via the Schrieffer-Wolff transformation describing the coupling of the electron spin to potential fluctuations generated by the lattice vibrations. The spin relaxation occurs with energy relaxation provided by the electron-phonon coupling and the spin-flip transition assisted by spin-orbit interactions. We predict a minimum of the spin relaxation time T1 as a function of the external magnetic field Bext caused by the Rashba spin-orbit coupling-induced anticrossing of opposite spin states. By constrast, the intrinsic spin-orbit interaction leads to monotonic behavior of T1 with Bext due to direct spin-phonon coupling. We also demonstrate that the spin decoherence time T2 = 2T1 in graphene is dominated by relaxation processes up to leading order in the spin-orbit interaction and the electron-phonon coupling mechanisms. Secondly, we develop a numerical model to account for the D´yakonov-Perel spin relaxation mechanism in multisubband quantum wires. We consider the elastic spin-conserving scattering events in the time-evolution operator and then evaluate the time-dependent expectation value of the spin operators. After averaging these results over an ensemble, we can extract the spin relaxation time as a function of Bext. We observe a non-monotonic behavior for the spin relaxation time with Bext aligned perpendicularly to the quantum wire. This effect is called ballistic spin resonance. In our model, the ballistic spin resonance occurs near the subband anticrossing induced by the subband-spin mixing spin-orbit interaction term. In systems with weak spin-orbit coupling strenghts, no spin resonance is observed when Bext is parallel to the channel. Nevertheless, we also predict the emergence of anomalous resonances plateaus in systems with strong spin-orbit couplings even when Bext is aligned with the quantum wire. Finally, we predict the emergence of a robust spin-density helical crossed pattern in two-dimensional electron gas with Rashba α and Dresselhaus β spin-orbit couplings. This pattern arises in a quantum well with two occupied subbands when the spin-orbit coupling strenghts are tuned to have equal absolute strengths but opposite signs, e.g., α1 = +β1 e α2 = −β2 for the first v = 1 and second v = 2 subbands. We named this novel pattern as crossed persistent spin helices. We analyze the spin-charge coupled diffusion equations in order to investigate the lifetime of the crossed persistent spin helices and the feasibility of probing the crossed persistent spin helix mode. We also study the inteband spin-orbit interaction effects on the crossed persistent spin helices, energy anticrossings and spin textures induced by the interband spin-orbit couplingNo campo de pesquisa denominado spintrônica é de fundamental importância o entendimento dos mecanismos de relaxação de spin. A fim de contribuir com esse objetivo, estudamos a relaxação de spin em nanoestruturas semicondutoras na presença da interação spin-órbita. Primeiramente, analisamos o decaimento e defasamento do spin eletrônico em pontos quânticos formados no grafeno usando a teoria de Bloch-Redfield. Consideramos um ponto quântico circular com as interações spin-órbita intrínseca e de Rashba. A relaxação de spin ocorre via relaxacação de energia pela interação elétron-fônon acompanhado do mecanismo de spin-flip auxiliado pela interação spin-órbita. Previmos a presença de um mínimo no tempo de relaxação de spin T1 em função do campo magnético externo Bext causado pelo acoplamento spin-órbita de Rashba que por sua vez leva a cruzamento evitado de níveis de energia com spins opostos. Em contraste, a interação spin-órbita intrínseca gera um comportamento monotônico de T1 com Bext devido ao acoplamento direto spin-fônon. Demonstramos também que o tempo de decoerência de spin T2 = 2T1 é dominado por contribuições dos mecanismos de relaxação em primeira ordem na interação spin-órbita e na interação elétron-fônon. Desenvolvemos também um modelo numérico que leva em conta o mecanismo de relaxação de spin de D´yakonov-Perel em fios quânticos com múltiplas subbandas. Consideramos espalhamentos elásticos, que conservam a orientação do spin, no operador evolução temporal. Em seguida, calculamos o valor esperado dos operadores de spin dependentes do tempo para um ensemble de elétrons. Por fim, extraímos o tempo de relaxação de spin em função do campo magnético externo Bext. Observamos um comportamento não-monotônico da relaxação de spin para um campo Bext alinhado perpendicularmente ao fio quântico. Em sistemas com acoplamento spin-órbita fracos, nenhuma ressonância de spin é encontrada quando Bext está alinhado paralelamento ao fio quântico. No entanto, previmos o aparecimento de ressonâncias de spin anômalas em sistemas com forte acoplamento spin-órbita mesmo quando Bext está alinhado ao canal balístico. Por fim, estudamos a formação de uma densidade de spin helicoidal cruzada e robusta contra espalhamento por impurezas em um gás bi-dimensional de elétrons na presença das interações spin-órbita de Rashba α and Dresselhaus β. Generalizamos o efeito previsto para um poço quântico com uma subbanda para duas subbandas ocupadas quando as interações spin-órbita assumem o mesmo valor em intensidade mas sinais opostos, e.g., α1 = +β1 e α2 = −β2 para a primeira v = 1 e segunda v = 2 subbandas. Denominamos esse novo padrão de helicóides de spin persistentes e cruzadas. Analisamos as equações de difusão com carga e spin acoplados com o intuito de investigarmos o tempo de vida das densidades de spin helicoidais cruzadas e a possibilidade de medi-las com os experimentos atuais. Estudamos também o efeito da interação spin-órbita interbanda na relaxação dos modos helicoidais de spin, espectro de energia com cruzamentos evitados e texturas de spin
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Griese, Andrew Herman. "Relaxation behavior of dense suspensions." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127924.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 16-17).
Dense suspensions of solid particles in Newtonian fluids exhibit a variety of non-Newtonian behaviors depending on the shear stress applied to the suspension and the particle mass fraction ([mathematical symbol]m). Suspensions at sufficiently high fm shear-thicken dramatically and eventually shear jam, showing behaviors typified by solids. But, little is known about how dense suspensions relax out of this stressed rheological state. To understand the relaxation behavior of a cornstarch/water dense suspension, samples are prepared at different fm, in the range that shows dramatic shear thickening, between 54.5% and 58.5% cornstarch. Each sample is formed into drops and kept in the stressed state through dynamic shearing using a B&K permanent magnet shaker, then allowed to relax. We show that dense suspensions relax with two distinct timescales. A short timescale that is independent of [mathematical symbol]m, denoting the settling of the drop onto the flat surface, and a longer timescale that is governed by the viscosity of the dense suspension and increases as [mathematical symbol]m increases above 55.75%. Our work provides an understanding of how a dense suspension relaxes out of a shear-thickened state.
by Andrew Herman Griese.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Anderson, Curtis James. "Analysis of Controlled Over-Relaxation." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1342456200.
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Paterson, Chris Edward. "Progressive relaxation : a meta-analysis /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487332636477408.
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Anuar, Mohd Shamsul. "The elastic relaxation during tabletting." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5465.
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The process of pharmaceutical tabletting involves the application of stress onto the powdered drug ingredients contained within a rigid die. This compaction process will cause the powder to densify and form a tablet, which is then ejected from the die cavity. In reality, the tablet will incur some elastic strains during the compaction process and the tablet dimensional changes resulted due to the elastic relaxation of the tablet in the subsequent processing stages undermine the final tablet mechanical integrity. The ejection stage, where the tablet is extruded from the die, has not been studied extensively and is an important stage where any tabletting defects are immediately visible. It is then the purpose of this Thesis to experimentally elucidate the behaviour of the tablet elastic relaxation and its influence on the tablet mechanical integrity during the ejection, the final stage of the compaction process. The Thesis starts with highlighting the existence of the tablet elastic relaxation during the ejection stage that has been successfully studied on-line by the novel use of accurate laser sensors to record the tablet dimensional changes, with particular emphasis on the interrelationship of the tablet elastic relaxation with the observed ejection force and the tabletting defects of the Paracetamol tablet. The use of a lubricated die has also been shown to reduce the tablet elastic relaxation and the tabletting defects of the Paracetamol tablets. In terms of the time-dependent nature of the elastic relaxation, subtle time-dependent elastic relaxation behaviour has been observed and eludicated for the chosen time-dependent Starch material. A brief, but detailed and comprehensive material comparison consisting Aspirin, microcrystalline cellulose (Avicel) and Paracetamol is presented in terms of the elastic relaxation during the ejection stage. The observed tablet elastic relaxation is then interrelated with the tablet strength, which is determined by an indirect tensile test (Brazilian) and a direct tensile test. Finally, the presence of a localized elastic relaxation occurring at the interface of an Avicel bilayered tablet has been shown to undermine the strength of the bilayered tablet, where the extent of the interface weaknesses is clearly dependent upon the behaviour of the localized elastic relaxation. In conclusion, the Thesis has successfully demonstrated and elucidated the tablet elastic relaxation behaviour during the ejection stage and the consequences on the final tablet mechanical integrity.
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Vidal, Alexandre. "Relaxation et oscillations en salves." Paris 6, 2007. http://www.theses.fr/2007PA066670.
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Les oscillations en salves apparaissent dans de nombreux systèmes biologiques, physiologiques et écologiques. Elles se caractérisent par l’alternance de phases dites silencieuses ou quiescentes séparées par des phases dites actives ou pulsatiles. Cette thèse est consacrée à l'analyse mathématique des systèmes dynamiques lents-rapides proposés pour la modélisation des oscillations en salves. Grâce à la théorie des bifurcations, la théorie des perturbations singulières et l’utilisation d’éclatements à paramètres, nous caractérisons les différents comportements de tels systèmes. En particulier, nous utilisons des développements asymptotiques pour les applications de transition entre phases d’évolution lentes et rapides. Nous montrons des résultats d’existence d’orbites périodiques non triviales, de convergence d’un continuum d’orbites vers un ensemble limite-périodique et d’apparition de « canards ».
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Alvès, Francisco. "Etude de la relaxation magnétique dans les alliages ferromagnétiques amorphes : corrélations avec la relaxation structurale." Paris 11, 1993. http://www.theses.fr/1993PA112179.
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L'évolution de la structure magnétique a été étudiée par l'intermédiaire de la perméabilité initiale i sur deux alliages ferromagnétiques amorphes, un alliage à base fer (2605 s2) et l'autre à base cobalt (2705 mN) de magnétostriction très différente. L'analyse thermique a été effectuée dans la gamme 20-400c. Les comportements en temps et température ont été étudiés. La construction des variations isochrones permet de mettre en évidence certains spectres de relaxation. Notamment à basse température, la relaxation est liée à des phénomènes de traînage magnétique caractérisés par une décroissance temporelle de i (da). La construction des variations isothermes permet, elle, de décrire le comportement temporel et d'en dégager les temps de relaxation moyens. Cette description a été faite suivant trois approches. Les résultats montrent que les processus de relaxation magnétique dans des matériaux amorphes font intervenir une fonction de distribution des temps de relaxation de type fenêtre très large. Nous avons corrélé ces résultats avec d'autres mesures. La calorimétrie différentielle à balayage permet de déterminer tc ainsi que les énergies associées a la relaxation structurale. Des observations des structures en domaines ont été faites. Des mesures magnétiques, basées sur le relevé du cycle d'hystérésis, nous ont permis de caractériser le ferromagnétisme doux de ces matériaux. Nous avons finalement observé que, dans ce type d'approche de la relaxation magnétique, l'intensité de la da dépend de deux facteurs: La structure en domaines (avec existence éventuelle d'une anisotropie magnétique induite) et les défauts structuraux à l'origine de la da; facteurs qui ont pu être découplés en étudiant le matériau 2705 mN. Les traitements thermiques effectués sur cet alliage, en guérissant les contraintes internes, minimisent les phénomènes de relaxation, d'où une plus grande stabilité thermique et magnétique de la structure
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Mi, Yunping. "Anelastic relaxation of oxygen in YBaCuO /." [S.l.] : [s.n.], 1994. http://library.epfl.ch/theses/?nr=1253.
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Prêtre, Philippe Antoine Prêtre Philippe. "Relaxation mechanisms in nonlinear optical polymers /." [S.l.] : [s.n.], 1995. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=11193.
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Matthews, Jermey N. A. "Thermodynamics and relaxation during actin polymerization." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2346.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Chemical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Gassmann, Alexandra. "Proteinspezifische Dynamik und Relaxation in Myoglobin." [S.l.] : [s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=959786392.
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Hoeppe, Ulrich Ernst Ewald. "Relaxation und Spinwelleninstabilitäten in polykristallinen Ferromagneten." [S.l. : s.n.], 2003. http://elib.tu-darmstadt.de/diss/000332.
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Ulrich, Markus. "Transport und Relaxation in nanokristallinen Materialien." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968640923.
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Bouriquet, Bertrand. "Relaxation en forme et multifragmentation nucléaire." Phd thesis, Université de Caen, 2001. http://tel.archives-ouvertes.fr/tel-00003803.
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Ce travail concerne la caractérisation des réactions de multifragmentation induites dans les collisions centrales de Xe+Sn à 32 MeV /A mesurées avec le détecteur INDRA. Cette caractérisation informe sur le degré d'équilibration. Un aspect crucial pour ces études est la sélection des événements. Dans cette étude deux approches ont été utilisées pour la sélection des collisions d'intérêt. La première approche s'appuie sur des sélecteurs de centralité (angle de flot, angle d'émission du plus gros fragment, multiplicité totale de particules chargées). La seconde approche qui constitue une innovation dans le domaine de la physique nucléaire est l'utilisation des cartes auto-organisées de Kohonen. Cette méthode permet un classement en topologie des événements sans utiliser explicitement des variables reliées à la forme. Les deux méthodes de sélection indiquent la coexistence d'au moins deux niveaux de dissipation dans les collisions les plus centrales. La méthode des cartes auto-organisées permet de déconvoluer ces processus. L'échantillon associé au processus de multifragmentation et à la plus grande conversion de l'énergie initiale représente 5% (250 mb) de la section efficace totale de réaction. Quelle que soit la méthode de sélection la forme moyenne de la source est allongée dans la direction du faisceau. Ce résultat signe une relaxation incomplète du degré de liberté de forme. Les données expérimentales sont comparées avec un modèle de multifragmentation statistique (SMM) incluant la déformation de la source et une énergie collective d'expansion. La caractérisation des réactions de multifragmentation en terme de taille, d'énergie d'excitation d'énergie collective d'expansion et de déformation est indépendante du mode de sélection utilisé. De cette comparaison on déduit que 70% de l'énergie disponible et 83% des nucléons du système initial ont été équilibré durant la réaction.
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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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Hou, Jixuan. "Stress relaxation in entangled polymer melts." Thesis, Lyon, École normale supérieure, 2012. http://www.theses.fr/2012ENSL0733.
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La relation entre les propriétés viscoélastiques complexes de liquides polymères et leur structure microscopique et la dynamique est une question clé dans la science des matériaux et de la biophysique. Les théories modernes de la dynamique des polymères et la rhéologie décrivent les aspects universels du comportement viscoélastique sur la base de l'idée que les enchevêtrements moléculaires confinent filaments individuels à une dimension, la dynamique diffusifs (reptation) dans le tube-comme les régions dans l'espace. Alors que le modèle de tube est validé par son succès, ses éléments constitutifs (les statistiques et la dynamique de l'axe du tube ou des chemins primitifs et de l'confinement "cage" de chaînes voisines) ne sont pas directement observables. (1) Nous présentons un vaste ensemble de résultats de simulation pour la relaxation des contraintes à l'équilibre et l'étape-tendues perles printemps polymères fondus (En collaboration avec: C. Svaneborg et GS Grest). Les données nous permettent d'explorer la dynamique de la chaîne et le module de la relaxation de cisaillement dans le régime plateau pour les chaînes avec Z~40 enchevêtrements et dans le régime de relaxation terminale pour Z~10. Nous avons effectué des tests sans paramètres de plusieurs modèles différents de tubes à l'aide de (Rouse) la mobilité connue des chaînes unentangled et la longueur d'enchevêtrement de fusion déterminé par l'analyse du chemin primitif de l'état microscopique topologique de nos systèmes. (2) Nous présentons une compréhension complète pour la détente des empêtré polymère linéaire fond que les liens de la dynamique et la théorie de Rouse tube par une interprétation dynamique qui s’appellel’analyse du chemin primitive. La chaîne primitive, qui est la moyenne d'ensemble des conformations de la chaîne, se rétrécit strictement d’après la dynamique Rouse jusqu'à ce qu'il renconte les obstacles formés par d'autres chaînes primitives. Le temps d'arrêt de la diminution peut être déterminée par l'argument que la zone balayée par la chaîne primitive sur une longueur de propagation de tension qui est égale à la taille du maille de filet du travail formé par les chaînes de primitives. Le processus physique avant l'heure d'arrêt est assez présenté par l'analyse du chemin primitif. Après le temps d'arrêt, les longueurs primitives seront rétrécites par la reptation et la fluctuation de la longueur de contour .Cette procedure peut être décrite comme la modèle du tube, par exemple, Likhtman-McLeish (LM) la théorie. (3) Nous constatons que la théorie sous-estime la relaxation LM module de cisaillement dû à un double comptage de l'effet de courte longueur d'onde (p> Z) dans les modes partie de relaxation de Rouse et en fonction de la trompe de mémoire μ (t). LM extrapolé μ (t) à la limite du continuum, ce qui entraîne une décroissance sur des échelles de temps inférieur au temps de l'intrication, où le mouvement de la chaîne primitive devrait être négligeable. Pour corriger cela, nous avons retiré de la partie de fluctuation contour longueur de μ (t) la contribution des modes avec un temps de relaxation plus court que le temps d'enchevêtrement. Nous trouvons un excellent accord entre nos données de simulation et la théorie LM modifiée en utilisant l'approximation reptation double pour la libération de contrainte, ce qui démonte que l'analyse du chemin primitif de la structure microscopique apporte du modèle de tube avec une puissance prédictive des processus dynamiques. L'utilisation de systèmes plus complexes pour le traitement de la libération de contrainte devrait conduire à un accord encore mieuxThe relation between the complex viscoelastic properties of polymer liquids and their microscopic structure and dynamics is a key issue in materials science and biophysics. Modern theories of polymer dynamics and rheology describe the universal aspects of the viscoelastic behavior based on the idea that molecular entanglements confine individual filaments to a one-dimensional, diffusive dynamics (reptation) in tube-like regions in space. While the tube model is validated through its success, its constituting elements (the statistics and dynamics of the tube axis or primitive paths and of the confining "cage" of neighboring chains) are not directly observable. (1) We present an extensive set of simulation results for the stress relaxation in equilibrium and step-strained bead-spring polymer melts (In cooperation with: C. Svaneborg and G. S. Grest). The data allow us to explore the chain dynamics and the shear relaxation modulus into the plateau regime for chains with Z~40 entanglements and into the terminal relaxation regime for Z~10. We have performed parameter-free tests of several different tube models by using the known (Rouse) mobility of unentangled chains and the melt entanglement length determined via the primitive path analysis of the microscopic topological state of our systems. (2) We present a full understanding for relaxation of entangled linear polymer melts that links the Rouse dynamics and tube theory via a dynamic interpretation of the so called primitive path analysis. The primitive chain, which is the ensemble average of the chain conformations, shrinks strictly following the Rouse dynamic until it encounters the obstacles formed by other primitive chains. The stop time of the shrinking can be determined by the argument that the area swept by the primitive chain over a tension propagation length is equal to the mesh size of the net work formed by the primitive chains. The physical process before the stop time is fairly presented by primitive path analysis. After the stop time, the primitive length shrinks via reptation and contour length fluctuation, which is well described by the tube theory, e.g. Likhtman-McLeish (LM) theory. (3) We find that the LM theory underestimates the shear relaxation modulus due to a double-counting of the effect of short-wavelength (p>Z) modes in Rouse relaxation part and in tube memory function μ(t). LM extrapolated μ(t) to the continuum limit, resulting a decay on time scales smaller than the entanglement time, where the motion of the primitive chain should be negligible. To correct this, we have removed from the contour length fluctuation part of μ(t) the contribution of modes with a relaxation time shorter than entanglement time. We find excellent agreement between our simulation data and the modified LM theory using the double reptation approximation for constraint release, which demonstrates that the primitive path analysis of the microscopic structure endows the tube model with predictive power for dynamical processes. The use of more elaborate schemes for treating constraint release should lead to even better agreement
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Dotzauer, Erik. "Energy system operation by Lagrangian relaxation /." Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek665s.pdf.
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Zakharov, Dmitry. "Exchange and relaxation in spin chains /." Göttingen : Cuvillier, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016072157&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Chui, Atta Yik Kwan. "Relaxation and excitation : aspects of magnetodynamics." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321451.
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McPherson, Michael. "Irradiated silicon detectors as relaxation devices." Thesis, Lancaster University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246131.
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Hotta, A. "Dynamics and relaxation of anisotropic elastomers." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604251.
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This thesis is concerned with the dynamics and mechanical relaxation properties of three types of anisotropic rubbers. The main part of the work concentrates on Liquid Crystalline Elastomers (LCE). The first type of elastomer is a monodomain LCE synthesised from a route established by Finkelmann et al. The second elastomer is a polydomain LCE. Finally an elastomeric block copolymer is included in the work. A range of mechanical measurements were made to explore the physical properties of the materials over a wide range of temperatures. Stress/Strain, dynamic mechanical data and thermal expansion data are presented for certain materials. In addition, X-ray order parameter data is measured. Key findings from the work include the experimental observations of a reduction in shear modulus of the monodomain LCE at the nematic-isotropic transition and the result was found to be consistent with previously published theoretical modelling. In addition, thermal expansions changes at the nematic-isotropic transition were correlated with X-ray order parameter data and theoretical model. The effect of chain stiffness was systematically explored. Anisotropic elastic properties were established and time-temperature superpositions were explored for all materials. Some of the results presented in this thesis have appeared as publications.
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Lusher, C. P. "Nuclear magnetic relaxation in gaseous helium." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356513.
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Longitudinal relaxation times T1 have been measured in 'He gas, using pulsed NMR, for number densities between 3x 1023 and 6x 102' spins/m' and temperatures between 0.6 and 15K. Relaxation takes place on or near the walls of the pyrex sample cells and measurements of Tl give information about the surface phases. A low temperature amplifier containing GaAs FET devices was developed to improve the spectrometer sensitivity. An amplifier noise temperature of 0.9 ± 0.5K was obtained at 1.16 MHz and an NMR signal was observed at 4.2K with the sensitivity being mainly limited by Johnson noise in the receiver coil. Baking the pyrex cells under vacuum and discharge cleaning the walls before sealing in the sample gas were found to increase the bulk gas Tl's by two or three orders of magnitude. A cryogenic wall coating of solid molecular hydrogen was found to delay the formation of a 'He monolayer on cooling and T, measurements were consistent with a binding energy of %, 13K for a 3He atom to a hydrogen surface. Once a 3He monolayer has formed the dipolar interaction between adsorbed spins is thought to be the dominant source of relaxation in the sealed cells. The presence of "He generally causes T, to rise on cooling below 2K due to preferential adsorption of "He at the surface. However, 'He atoms which dissolve in quasiparticle states in the superfluid helium film can be an extra source of relaxation. In the dirty cells relaxation probably takes place in quasiparticle states at the free surface of the saturated helium film, which are bound with an energy of 5.1 t 0.3K. In a cleaned, sealed cell a T, of ti 8 hours was measured at 7.7 MHz and 0.8K. In this case relaxation is probably occurring 2 or 3 helium layers away from the helium-hydrogen interface