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1
Diat, Olivier. "Effet du cisaillement sur des phases lyotropes : phase lamellaire et phase éponge." Bordeaux 1, 1992. http://www.theses.fr/1992BOR10611.
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Les phases de membranes ont ete depuis longtemps l'objet de nombreuses etudes, quant a leurs proprietes statiques. Dans cette these, nous etudions leur dynamique et plus specifiquement, l'effet d'un cisaillement. Par differentes techniques de mesure (conoscopie, diffusion de lumiere, de neutrons ou de rayons x, microscopie, rheologie), nous presentons, et analysons les differents etats d'orientation d'une phase lamellaire lyotrope dans un systeme quaternaire eau-dodecane-sds-pentanol; un etat de vesicules multi-lamellaires de taille controlee par le cisaillement existe quel que soit le systeme lamellaire etudie. Une etude parallele concerne l'effet du cisaillement sur une phase eponge et semble indiquer une transition vers une phase lamellaire
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Butler, Jonny. "Phase structure, phrase structure, and quantification." Thesis, University of York, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415175.
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Auguste, Frédéric. "Flexibilité et structure de deux phases lyotropes : phase lamellaire et phase de vésicules." Bordeaux 1, 1993. http://www.theses.fr/1993BOR10587.
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Sang, Yan. "Phases and Phase Transitions in Quantum Ferromagnets." Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/18716.
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In this dissertation we study the phases and phase transition properties of
quantum ferromagnets and related magnetic materials. We first investigate the effects of an external magnetic field on the Goldstone mode of a helical magnet, such as MnSi. The field introduces a qualitatively new term into the dispersion relation of the Goldstone mode, which in turn changes the temperature dependences of the contributions of the Goldstone mode to thermodynamic and transport properties. We then study how the phase transition properties of quantum ferromagnets evolve with increasing quenched disorder. We find that there are three distinct regimes for different amounts of disorder. When the disorder is small enough, the quantum ferromagnetic phase transitions is generically of first order. If the disorder is in an intermediate region, the ferromagnetic phase transition is of second order and effectively characterized by mean-field critical exponents. If the disorder is strong enough the ferromagnetic phase transitions are continuous and are characterized by non-mean-field critical exponents.
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Ran, Ying. "Spin liquids, exotic phases and phase transitions." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/45404.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.<br>Includes bibliographical references (p. 135-139).<br>Spin liquid, or featureless Mott-Insulator, is a theoretical state of matter firstly motivated from study on High-Tc superconductor. The most striking property of spin liquids is that they do not break any physical symmetry, yet there are many types of them, meaning a phase transition is necessary from one spin liquid to another. It was a long debate about whether these exotic states can serve as the ground states in real materials or even models. In this thesis I firstly discuss a large-N model, where we show the spin liquid states can be the ground states. Because the spin liquid phases cannot be characterized by symmetry breaking, the phase transitions associated with them are naturally beyond the traditional Laudau's paradigm. I discuss a few scenarios of these exotic phase transitions to show a general picture about what can happen for such exotic transitions. Those exotic phase transitions can actually serve as a way to detect these exotic phases. Then I move to a much more realistic model: spin-1/2 Kagome lattice, where we propose a U(1)-Dirac spin liquid as the ground state. The implications on the recent material ZnCu3(OH)6C12 are discussed. Finally, I come back to the high-Tc problem. A doped spin liquid can naturally be superconducting whose many properties have already been confirmed by experiments. Here I particularly study one experimental puzzle: the nodal-antinodal dichotomy in underdoped High-Tc material. This used to be one difficulty of the doped spin liquid theory. We show that a doped spin liquid can naturally has nodal-antinodal dichotomy due to further neighbor hoppings (t' and t").<br>by Ying Ran.<br>Ph.D.
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Xu, Jian. "X-Band Phase Shifters for Phased Array." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1196888776.
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Zetterling, Fredrik. "Phase Transformations in Computer Simulated Icosahedrally Ordered Phases." Doctoral thesis, KTH, Numerical Analysis and Computer Science, NADA, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3570.
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<p>Computer simulations play a profound and fundamental role inmodern theoretical physics, chemistry and materials science. Tounderstand the complex physics of metally liquids, metals,quasicrystals and metally glasses a working model imposing thelocal and global order is needed. Experiments and theory havepredicted the local order in liquid metals to beicosahedral.</p><p>The current work has been done using molecular dynamicscomputer simulations of a monatomic system using a simplepair-potential for the interactions. Two new pair-potentialshas been developed, the Zetterling-1(Z1) and Zetterling-2(Z2)potentials. They are specifically modeled to impose icosahedralorder. The basis for the development of the potentials was theold Dzugutov potential which is known to freeze into adodecagonal quasicrystal. The new Zetterling potentials have alonger interaction range and a narrower first minimum. The morenarrow first minimum will enhance the local icosahedralordering and the longer interaction range was introduced toincorporate a second maximum in the potential mimicing theFriedel oscillations found in metallic systems. These Friedeloscillations are due to the singularity which arises at theFermi surface due to the screening of the positive charge bythe electron gas.</p><p>Five papers are included in the study. The first two papersare studies of icosahedral clustering in the liquid andsupercooled liquid. The simulations in Paper I was done usingthe old Dzugutov potential while the new potentials were usedin Paper II using both molecular dynamics and the Basin Hoppingalgorithm presented in Chapter 5. Paper III considers theconcept of dynamical ergodicity in the context of thesuper-cooled liquid behaviour. The simulations were made usingthe old Dzugutov potential. Paper IVr eports a moleculardynamics simulation using the Dzugutov potential undersuper-cooling. A formation of icosahedrally structured domainswith distinctly slow diffusion which grows with cooling in alow-dimensional manner and percolate around Tc, the criticaltemperature of the mode-coupling theory. A sharp slowing downof the structural relaxation relative to diffusion is observed.It is concluded that this effect cannot be accounted for by thespatial variation in atomic mobility. The low-dimensionalclustering is discussed as a possible mechanism of fragility.Paper Vin vestigates the crystallization of a simple monatomicliquid model which utilizes the Zetterling-1 potential. Thesystem forms a thermodynamically stable solid phase exhibitingcubic symmetry. Its diffraction pattern is identified as thatof γ-brass, a tetrahedrally packed crystalline structurewith 52 atoms in the unit cell.</p><p><b>Keywords:</b>simple liquids, molecular dynamics, pairpotential, icosahedral cluster.</p>
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Knott, Michael. "Phases and phase transitions in charged colloidal suspensions." Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270941.
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Zhao, Qing. "Pseudostationary Phase for Solid Phase Extraction." TopSCHOLAR®, 2006. http://digitalcommons.wku.edu/theses/988.
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A unique pseudostationary phase for Solid Phase Extraction is presented. This pseudostationary phase consists of surfactant, which is initially immobilized onto hydrophilic cation exchange resin. The surfactant chain through hydrophobic interactions extracts hydrophobic analytes in the same manner as conventional bonded alkyl moieties on silica based non-polar sorbents. Although hydrophobic analytes can be efficiently trapped on commercially available non-polar sorbents (i.e. Ci8 silica), organic solvents that are necessary to break strong hydrophobic interactions between the analytes and the sorbent are harmful. They are also incompatible for direct introduction into a reversed phase liquid chromatographic set up. In the presented approach, the entire pseudostationary phase may be removed via ion exchange in very mild aqueous solutions, resulting in very efficient elutions with a final extract that is mild and reversed phase liquid chromatographic compatible. Rinse solution parameters were optimized and various cationic surfactants attached to cation exchangeable silica including silica modified with sulfopropyl groups and unmodified silica were investigated to reach sufficient sorbent hydrophobicity to capture EPA 16 priority polycyclic aromatic hydrocarbons (PAHs). PAHs were preconcentrated from river water and were determined using fluorescence detector coupled to high performance liquid chromatography (HPLC). Detections limits for all PAHs examined were lower than EPA's maximum contaminant level.
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Ghaemi, Mohammadi Pouyan. "Phases and phase transitions of strongly correlated electron systems." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45456.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.<br>Includes bibliographical references (leaves 169-174).<br>Different experiments on strongly correlated materials have shown phenomena which are not consistent with our conventional understandings. We still do not have a general framework to explain these properties. Developing such a general framework is much beyond the scope of this thesis, but here we try to address some of challenges in simpler models that are more tractable. In correlated metals it appears as strong correlations have different effect on different parts of fermi surface. Perhaps most striking example of this is normal state of optimally doped cuprates; the quasiparticle peaks on the nominal fermi surface do not appear uniformly. We try to track such phenomena in heavy fermion systems, which are correlated fermi liquids. In these systems, a lattice of localized electrons in f or d orbitals is coupled to the conduction electrons through an antiferromagnetic coupling. Singlets are formed between localized and conduction electrons. This singlet naturally have non-zero internal angular momentum. This nontrivial structure leads to anisotropic effect of strong correlations. Internal structure of Kondo singlet can also lead to quantum Hall effect in Kondo insulator, and formation of isolated points on the fermi surface with fractionalized quasiparticles. In the second part we study a phase transition in Heisenberg model between two insulating phases, Neel ordered and certain spin liquid state, popular in theories of the cuprates. The existence of such a transition has a number of interesting implications for spin liquid based approaches to the underdoped cuprates and clarifies existing ideas for incorporating antiferromagnetic long range order into such a spin liquid based approach. This transition might also be enlightening, despite fundamental differences, for the heavy fermion critical points where a second order transition between the heavy fermion phase and a metallic phase with magnetic antiferromagnetic order is observed.<br>by Pouyan Ghaemi Mohammadi.<br>Ph.D.
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Sanyal, Alarka. "CMOS Phase Shifter for Conformal Phased Array Beamformer Applications." Thesis, North Dakota State University, 2015. https://hdl.handle.net/10365/27697.
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A vector modulator based phase shifter is developed using 0.18um CMOS process at S-band frequency to be integrated into a conformal phased array antenna to recover the desired radiation pattern in the entire 360? range. The phase shifter has a variable gain amplifier integrated into the circuit in order to vary gain along with phase for precise control to correct the degraded radiation pattern due to the conformal shaping. The results show state-of-the-art performances including more than 7dB conversion gain with variable feature, a continuous phase rotation of 360? with steps as low as 11.25? and very low power consumption of 17mW, for the first time to the best of the authors? knowledge. The chip size including all pads is 1.5mm X 0.75mm.<br>ND NASA EPSCoR (Agreement FAR0020852)
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Magozore, Caxton. "DSP phase angle controlled three phase to single phase uninterruptible power supply." Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/5177.
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Kunda, Wilkinson. "Two phase problems and two phase flow." Thesis, University of Hull, 1986. http://hydra.hull.ac.uk/resources/hull:5902.
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In section 1 of this thesis a two-dimensional mathematical model is used to investigate the circulation in a gas-bubble agitation system of a cylindrical vessel for the case of an orifice located at the centre of the base. The two-phase (liquid/gas) region is assumed to be confined to a cone-shaped region and is investigated using Wallis' Drift Flux Model. In the single-phase (liquid) region the turbulent Navier-Stokes equations, written in terms of the stream function, are used for the mathematical model. The analysis in the two-phase region yields the boundary conditions on the two-phase/single-phase boundary. The velocity field in the two-phase region is solved analytically giving results in closed form. A numerical algorithm is developed for calculating liquid flow in the single phase region, and numerical results are presented graphically in terms of the stream function. In section 2 two moving interface problems are investigated. Small time analytic solutions are found for three-dimensional inward solidification of a half space initially at fusion temperature in the first problem. In the second problem, perturbation solutions for melting of a cylindrical annulus with constant heat flux on inner surface are given. In both problems the interface immobilization technique is used. Interface locations at various times are calculated for the inward solidification problem and the results shown in three-dimensional graphs. First and second perturbation terms for the interface location are given for the second problem and graphs of each are presented for a particular case.
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Gurunlu, Cemil. "Single-phase operations of three-phase generators." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/32922.
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The ever-increasing demand for power, and the correspondingly greater complexity of power systems, is leading to more severe problems of system reliability. Modern society is so dependent on the usage of electrical power that even a short interruption of service can cause serious problems. A public utility cannot be expected to provide a perfect power supply, since many of the possible causes of a power disturbance are beyond its control. The windings of small diesel-driven three-phase generator sets are often capable of being connected in either a zig-zag or an Edison-delta arrangement, to provide a single-phase supply for standby or emergency purposes. Although many of these generators are genuinely on standby (i.e. they are brought into operation only as a result of a system failure), many others operate continuously in situations where no mains supply is available. The thesis aims to investigate both the steady-state and the dynamic performance of a three-phase salient-pole generator, when reconnected in either a zig-zag or an Edison-delta configuration, and to provide a performance comparison with the more familiar modes of single-phase operation involving line-to-line and line-to-neutral loading. Symmetrical components are used to investigate the steady-state performance and a phase model is used to determine both the steady state and transient performance. Analytical expressions are obtained for the short-circuit currents for various generator connections by utilizing the modified Clarke transformation. The theoretical results from various models are compared with experimental results on a test machine. Losses, efficiency and voltage waveforms for various generator connections are experimentally obtained for the test machine. Results are discussed and suggestions for future research are included.
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Li, Yichen. "Phase-field Modeling of Phase Change Phenomena." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99148.
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The phase-field method has become a popular numerical tool for moving boundary problems in recent years. In this method, the interface is intrinsically diffuse and stores a mixing energy that is equivalent to surface tension. The major advantage of this method is its energy formulation which makes it easy to incorporate different physics. Meanwhile, the energy decay property can be used to guide the design of energy stable numerical schemes.
In this dissertation, we investigate the application of the Allen-Cahn model, a member of the phase-field family, in the simulation of phase change problems. Because phase change is usually accompanied with latent heat, heat transfer also needs to be considered. Firstly, we go through different theoretical aspects of the Allen-Cahn model for nonconserved interfacial dynamics. We derive the equilibrium interface profile and the connection between surface tension and mixing energy. We also discuss the well-known convex splitting algorithm, which is linear and unconditionally energy stable. Secondly, by modifying the free energy functional, we give the Allen-Cahn model for isothermal phase transformation. In particular, we explain how the Gibbs-Thomson effect and the kinetic effect are recovered. Thirdly, we couple the Allen-Chan and heat transfer equations in a way that the whole system has the energy decay property. We also propose a convex-splitting-based numerical scheme that satisfies a similar discrete energy law. The equations are solved by a finite-element method using the deal.ii library. Finally, we present numerical results on the evolution of a liquid drop in isothermal and non-isothermal settings. The numerical results agree well with theoretical analysis.<br>Master of Science<br>Phase change phenomena, such as freezing and melting, are ubiquitous in our everyday life. Mathematically, this is a moving boundary problem where the phase front evolves based on the local temperature. The phase change is usually accompanied with the release or absorption of latent heat, which in turn affects the temperature. In this work, we develop a phase-field model, where the phase front is treated as a diffuse interface, to simulate the liquid-solid transition. This model is consistent with the second law of thermodynamics. Our finite-element simulations successfully capture the solidification and melting processes including the interesting phenomenon of recalescence.
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Lei, Siu Long. "Phase-field simulations of two-phase flows /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MATH%202009%20LEI.
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Kim, Sunghwan. "Phase shifter approaches for compact low-power phased array transmitters." Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3398530.
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Thesis (Ph. D.)--University of California, San Diego, 2010.<br>Title from first page of PDF file (viewed May 5, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 103-109).
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Tweedlie-Yuill, Tracey. "Characterisation of cyanopropyl stationary phases for reserved phase liquid chromatography." Thesis, University of Strathclyde, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488857.
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The current study has demonstrated that CN phases have poor stability and should not be operated above pH 5.7. Nonetheless, a number of protocols have been developed for the characterization of CN phases that include a measurement of silanophilic interaction determined in mobile phases with pH > 5.7. The aim of this study was to perform the chromatographic characterization of commercially available CN phases using two distinct approaches.
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Waichigo, Martin M. "Alkylammonium Carboxylates as Mobile Phases for Reversed-Phase Liquid Chromatography." Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1134142423.
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Loginova, Irina. "Phase-field modeling of diffusion controlled phase transformations." Doctoral thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3626.
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<p>Diffusion controlled phase transformations are studied bymeans of the phase-field method. Morphological evolution ofdendrites, grains and Widmanst\"atten plates is modeled andsimulated.</p><p>Growth of dendrites into highly supersaturated liquids ismodeled for binary alloy solidification. Phase-field equationsthat involve both temperature and solute redistribution areformulated. It is demonstrated that while at low undercoolingheat diffusion does not affect the growth of dendrites, i.e.solidification is nearly isothermal, at high cooling rates thesupersaturation is replaced by the thermal undercooling as thedriving force for growth.</p><p>In experiments many crystals with different orientationsnucleate. The growth of randomly oriented dendrites, theirsubsequent impingement ant formation of grain boundaries arestudied in two dimensions using the FEM on adaptive grids.</p><p>The structure of dendrites is determined by growthconditions and physical parameters of the solidifying material.Effects of the undercooling and anisotropic surface energy onthe crystal morphology are investigated. Transition betweenseaweeds, doublons and dendrites solidifying out of puresubstance is studied and compared to experimental data. Two-and three-dimensional simulations are performed in parallel onadaptive and uniform meshes.</p><p>A phase-field method based on the Gibbs energy functional isformulated for ferrite to austenite phase transformation inFe-C. In combination with the solute drag model, transitionbetween diffusion controlled and massive transformations as afunction of C concentration and temperature is established byperforming a large number of one dimensional calculations withreal physical parameters. In two dimensions, growth ofWidmanstaetten plates is governed by the highly anisotropicsurface energy. It is found that the plate tip can beapproximated as sharp, in agreement with experiments.</p><p><b>Keywords:</b>heat and solute diffusion, solidification,solid-solid phase transformation, microstructure, crystalgrowth, dendrite, grain boundary, Widmanstaetten plate,phase-field, adaptive mesh generation, FEM.</p>
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Whitaker, T. S. "Measurement of two-phase flows by phase separation." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240831.
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Ai, Chiayu. "Phase measurement accuracy limitation in phase shifting interferometry." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184252.
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In phase shift interferometry (PSI), several factors affect measurement accuracy, such as piezoelectric transducer (PZT) calibration (i.e. PZT slope error) and PZT nonlinearity, vibration, spurious reflection, source bandwidth, detector nonlinearity, and detector noise. The effects of these error sources on several algorithms to solve the phase of the wavefront are studied. When the simple arctangent formula is used, if the PZT slope is properly adjusted, the error due to the PZT quadratic nonlinearity can be tremendously reduced. An exact solution is derived to remove the error when the PZT quadratic nonlinearity is large. Although Carre's formula is insensitive to PZT slope, this formula is more sensitive to the detector nonlinearity than the simple arctangent formula. For most error sources, the error of the phase solved has a double-frequency characteristic. Thus, averaging two measured phases of two runs, which have a ninety degree phase shift related to each other, can effectively reduce the error. For a small vibration, the phase error has a very simple relation to the vibration amplitude, and a very complex relation to the vibration frequency. Although the error caused by vibration has this double-frequency characteristic, the averaging technique does not apply. The error caused by spurious reflection does not have such a characteristic. A new algorithm is proposed to eliminate the phase error caused by certain types of spurious reflection. When detector noise is concerned, the phase error is inversely proportional to the modulation of the intensity times the square root of the number of steps/buckets. For the shot noise, the phase error is inversely proportional to the fringe contrast times the square root of the total number of photons. In practice, the shot noise is very much smaller than the detector noise. In a practical environment, PZT calibration, vibration, and spurious reflection have much more prominent effects on the PSI than the source bandwidth, detector nonlinearity, and detector noise. When spurious reflection and vibration are under control, and the signal-to-noise ratio is about 20, the PSI has an accuracy of 2 degrees, i.e. 3.3nm at 633nm. Because vibration and detector noise are random error sources, the errors caused by them can be reduced by averaging many measurements. However, the error caused by the other discussed sources cannot be reduced by averaging many measurements.
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Bitteur, Sylvaine. "Etude, par chromatographie en phase liquide, du partage de composes d'arôme entre une phase aqueuse et des phases stationnaires hydrophobes." Paris 6, 1986. http://www.theses.fr/1986PA066449.
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Ce travail a consisté à étudier dans quelle mesure la chromatographie en phase liquide permet d'extraire les composes d'arôme présents en très faible concentration dans les effluents aqueux des industries agro-alimentaires. Les rendements d'extraction accessibles par enrichissement de traces étant directement lies aux facteurs de capacité des solutés d'intérêt, l'étude proposée se ramenait à celle du partage de composes d'arôme entre une phase aqueuse et des phases stationnaires hydrophobes. La première partie détaille les divers paramètres susceptibles de modifier les rendements d'extraction par les principaux types de supports apolaires de la chromatographie en phase liquide et met en évidence le caractère indispensable d'une étude systématique préalable. Une telle étude, menée à l'aide de composes modèles d'arôme et de supports chromatographiques choisis fait l'objet de la seconde partie. L'ensemble des résultats obtenus au terme de cette études systématique est finalement teste dans le cas concret d'un effluent aqueux industriel contenant des composes d'arôme de cassis à l'état de traces.
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Bitteur, Sylvaine. "Etude par chromatographie en phase liquide, du partage de composés d'arome entre une phase aqueuse et des phases stationnaires hydrophobes." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb375960653.
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Pollock, Asher W. "Phase Shift." Ohio University Honors Tutorial College / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1492781853322151.
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Debray, Jean-Christophe. "Elaboration de phases stationnaires originales pour la chromatographie en phase gazeuse." Rouen, 2014. http://www.theses.fr/2014ROUES048.
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Scobie, Hugh Alistair. "Dietary hydroxycinnamic acids, phase I and Phase II metabolism." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0018/MQ54178.pdf.
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Xu, Hui. "Phase structure and phase transitions in semicrystalline isotactic polystyrene /." Thesis, Connect to Dissertations & Theses @ Tufts University, 2005.
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Thesis (Ph.D.)--Tufts University, 2005.<br>Adviser: Peggy Cebe. Submitted to the Dept. of Physics. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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McBride, Roy. "Phase measurement and phase control in fibre-optic interferometers." Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/1219.
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Simpkin, Neil John. "Solution behaviour and phase-phase diffusion of microbial lipases." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387207.
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Uzunoglu, Vasil, and Ann B. Maiorano. "PHASE CORRECTION AND PHASE CANCELLING NETWORKS IN QPSK MODEMS." International Foundation for Telemetering, 1985. http://hdl.handle.net/10150/615732.
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International Telemetering Conference Proceedings / October 28-31, 1985 / Riviera Hotel, Las Vegas, Nevada<br>At bit rates lower than 100Mbit/s, the Synchronous Oscillator (SO) [1-4] has substantial tracking band combined with steep skirt selectivity to satisfy all the requirements of a carrier recovery network without the need for a phase correction network. At higher bit rates however, there is a need for a phase correction or phase cancelling network, if the BER variations with respect to hard wired case must be confined to less than 0.2dB with IF offsets of ±30kHz. At bit rates higher than 100Mbit/s, the multiply by four process in a QPSK modem deteriorates the signal-to-noise ratio by more than 15 dB (18dB at Eb/No = 6.4 dB) and the synchronization signal-to-noise ratio at the input to the SO drops below 0dB (!5dB at Eb/No = 6.4dB). This reduction in the signal-to-noise ratio reduces the tracking band of the SO which in turn increases the phase shift per unit frequency offset.
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Powanwe, Arthur Sadrack. "Brain Rhythm Fluctuations: Envelope-Phase Modeling and Phase Synchronization." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42116.
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Fast neural oscillations known as beta (12-30Hz) and gamma (30-100Hz) rhythms are recorded across several brain areas of various species. They have been linked to diverse functions like perception, attention, cognition, or interareal brain communication.
The majority of the tasks performed by the brain involves communication between brain areas. To efficiently perform communication, mathematical models of brain activity require representing neural oscillations as sustained and coherent rhythms. However, some recordings show that fast oscillations are not sustained or coherent. Rather they are noisy and appear as short and random epochs of sustained activity called bursts.
Therefore, modeling such noisy oscillations and investigating their ability to show interareal coherence and phase synchronization are important questions that need to be addressed.
In this thesis, we propose theoretical models of noisy oscillations in the gamma and beta bands with the same properties as those observed in in \textit{vivo}. Such models should exhibit dynamic and statistical features of the data and support dynamic phase synchronization. We consider networks composed of excitatory and inhibitory populations.
Noise is the result of the finite size effect of the system or the synaptic inputs. The associated dynamics of the Local Field Potentials (LFPs) are modeled as linear equations, sustained by additive and/or multiplicative noises. Such oscillatory LFPs are also known as noise-induced or quasi-cycles oscillations.
The LFPs are better described using the envelope-phase representation. In this framework, a burst is defined as an epoch during which the envelope magnitude exceeds a given threshold. Fortunately, to the lowest order, the envelope dynamics are uncoupled from the phase dynamics for both additive and multiplicative noises. For additive noise, we derive the mean burst duration via a mean first passage time approach and uncover an optimal range of parameters for healthy rhythms. Multiplicative noise is shown theoretically to further synchronize neural activities and better explain pathologies with an excess of neural synchronization. We used the stochastic averaging method (SAM) as a theoretical tool to derive the envelope-phase equations. The SAM is extended to extract the envelope-phase equations of two coupled brain areas. The goal is to tackle the question of phase synchronization of noise-induced oscillations with application to interareal brain communication. The results show that noise and propagation delay are essential ingredients for dynamic phase synchronization of quasi-cycles. This suggests that the noisy oscillations recorded in \textit{vivo} and modeled here as quasi-cycles are good candidates for such neural communication. We further extend the use of the SAM to describe several coupled networks subject to white and colored noises across the Hopf bifurcation ie in both quasi-cycle and limit cycle regimes. This allows the description of multiple brain areas in the envelope-phase framework.
The SAM constitutes an appropriate and flexible theoretical tool to describe a large class of stochastic oscillatory phenomena through the envelope-phase framework.
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Agrawal, Vaibhav. "Multiscale Phase-field Model for Phase Transformation and Fracture." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/850.
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We address two problems in this thesis. First, a phase-field model for structural phase transformations in solids and second, a model for dynamic fracture. The existing approaches for both phase transformations and fracture can be grouped into two categories. Sharp-interface models, where interfaces are singular surfaces; and regularized-interface models, such as phase-field models, where interfaces are smeared out. The former are challenging for numerical solutions because the interfaces or crack needs to be explicitly tracked, but have the advantage that the kinetics of existing interfaces or cracks and the nucleation of new interfaces can be transparently and precisely prescribed. The diffused interface models such as phasefield models do not require explicit tracking of interfaces and makes them computationally attractive. However, the specification of kinetics and nucleation is both restrictive and extremely opaque in such models. This prevents straightforward calibration of phase-field models to experiment and/or molecular simulations, and breaks the multiscale hierarchy of passing information from atomic to continuum. Consequently, phase-field models cannot be confidently used in dynamic settings. We present a model which has all the advantages of existing phase-field models but also allows us to prescribe kinetics and nucleation criteria. We present a number of examples to characterize and demonstrate the features of the model. We also extend it to the case of multiple phases where preserving kinetics of each kind of interface is more complex. We use the phase transformation model with certain changes to model dynamic fracture. We achieve the advantage of prescribing nucleation and kinetics independent of each other. We demonstrate examples of anisotropic crack propagation and crack propagation on an interface in a composite material. We also report some limitations of phase-field models for fracture which have not been mentioned in the existing literature. These limitations include dependence of effective crack width and hence the effective surface energy on the crack speed, lack of a reasonable approximation for the mechanical response of cracked region and inability to model large deformations.
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Beck, Markus. "Boron in Palladium: interaction, phase formation and phase transformation." [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9556602.
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Kokel, Samuel John. "Retrodirective phase-lock loop controlled phased array antenna for a solar power satellite system." Texas A&M University, 2004. http://hdl.handle.net/1969.1/3047.
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This thesis proposes a novel technique using a phase-lock loop (PLL) style phase control loop to achieve retrodirective phased array antenna steering. This novel approach introduces the concept of phase scaling and frequency translation. It releases the retrodirective transmit-receive frequency ratio from integer constraints and avoids steering approximation errors.
The concept was developed to achieve automatic and precise beam steering for the solar power satellite (SPS). The testing was performed using a transceiver converting a pair of received 2.9 GHz signals down to 10 MHz, and up converting two 10 MHz signals to 5.8 GHz. Phase scaling and conjugation was performed at the 10 MHz IF using linear XOR phase detectors and a PLL loop to synthesize a 10 MHz signal with conjugate phase.
A phase control loop design is presented using PLL design theory achieving a full 2π steering range. The concept of retrodirective beam steering is also presented in detail. Operational theory and techniques of the proposed method are presented. The prototype circuit is built and the fabrication details are presented. Measured performance is presented along with measurement techniques. Pilot phase detectors and PCL achieve good linearity as required. The achieved performance is benchmarked with standards derived from likely performance requirements of the SPS and beam steering of small versus large arrays are considered.
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Apte, Pankaj A. "Phase equilibria and nucleation in condensed phases a statistical mechanical study /." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1135876018.
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Baumann, Wolfgang [Verfasser]. "Phase-transformation kinetics of TiCr2 laves phases / vorgelegt von Wolfgang Baumann." Stuttgart : Max-Planck-Inst. für Metallforschung, 2010. http://d-nb.info/1007316489/34.
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Charles, Cameron T. "A calibrated phase and amplitude control system for phased-array transmitters /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/5911.
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Khong, Teck Meng. "Heterogeneous gas phase reactions for the production of chemically bonded phases." Thesis, Birkbeck (University of London), 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246077.
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Grover, Tarun Ph D. Massachusetts Institute of Technology. "Applied fractionalization : quantum phases and phase transitions of strongly interacting systems." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/68973.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 131-136).<br>Strongly correlated systems present interesting challenges in condensed matter physics. On the one hand, the theoretical work in the last two decades suggests that strong interactions may lead to new phases and phase transitions of matter that don't fit paradigms such as Fermi liquid theory or Landau's theory of phase transitions. On the other hand, there are actual materials which are undoubtedly governed by strong interactions and indeed do not fit the conventional paradigms but whose behavior often doesn't quite match our theoretical expectations. This gap between theory and experiments is slowly narrowing owing to the discovery of new materials and recent advances in numerical simulations. As an example, the material K - (ET)2Cu 2(CN) 3 exhibits metallic specific heat in its insulating phase. This is indicative of the theoretically proposed phenomena of 'fractionalization' where elementary excitations in a phase carry quantum numbers that are fractions of that corresponding to an electron. Similarly, there is growing numerical evidence of the theoretical phenomena of 'deconfined quantum criticality', where quantum Berry phases lead to emergence of fractionalized particles right at the phase transition. In this thesis we study phenomena where the concept of fractionalization is a useful tool to explore new phases and phase transitions. Most of our examples are in the context of frustrated quantum magnets. Along the way, we also explore topics such as quantum numbers of topological defects and non-abelian phases of matter. Whenever possible, we compare theoretical predictions with experimental and numerical data. We also discuss deconfined quantum criticality in the context of metallic systems where it opens the route to phase transitions very different from the conventional spin-density wave instability of Fermi surface.<br>by Tarun Grover.<br>Ph.D.
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Lienne, Michelle. "Separation d'enantiomeres par chromatographie en phase liquide sur phases stationnaires chirales." Paris 6, 1989. http://www.theses.fr/1989PA066318.
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La separation directe d'enantiomeres par chromatographie en phase liquide sur phases stationnaires chirales (psc) repose sur la difference de stabilite des complexes diastereoisomeres formes transitoirement entre les enantiomeres du solute et les entites chirales de la psc. La premiere partie de ce memoire est consacree a l'etude de psc de type pirkle synthetisees a partir d'oxydes de phosphines chiraux ou de derives n-dinitro-3,5-benzoyle (dnb) d'acides amines. Des mecanismes bimoleculaires de reconnaissance chirale sont discutes et les parametres qui les affectent sont evalues. La seconde partie rassemble trois exemples de strategies de separations enantiomeriques concernant des composes appartenant a des familles therapeutiques variees: butyrolactones et butyrolactames (cytotoxiques), sulfoxides derives du benzimidazole (anthelminthiques) et esters de l'acide (thienyl-3)-2-cyclohexyl-2-glycolique (anticholinergiques)
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Huang, Tsang-Min. "Phase Equilibria of Binary Liquid Crystal Mixtures Involving Induced Ordered Phases." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1284381816.
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Apte, Pankaj A. "Phase equilibria and nucleation in condensed phases: a statistical mechanical study." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1135876018.
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Torrellas-Hidalgo, Luzmila. "EFFECTS OF ETHANOL/WATER MOBILE PHASES ON REVERSED-PHASE LIQUID CHROMATOGRAPHY." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275466.
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Ye, Bing. "Unconventional Quantum Phases in Strongly Correlated Systems." Thesis, Boston College, 2016. http://hdl.handle.net/2345/bc-ir:106990.
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Thesis advisor: Ying Ran<br>In this thesis, I investigated and implemented various numerical and simulation methods, including mean field theory, functional renormalization group method (fRG), density matrix renormalization group (DMRG) method etc., to find different quantum phases and quantum phase diagrams on models of correlated electronic systems. I found different phase diagrams with phases such as magnetism, superconductivity. By summarizing the strength and limitations of these methods, I investigated the projected entangled paired states (PEPS) with symmetry quantum number to sharply distinguish phases into crude classes and applied a variation of fast full update (FFU) prototype[58] to simulate different phases numerically. This method provides a promising, powerful and efficient way to simulate unconventional quantum phases and quantum phase diagrams in correlated electronic systems<br>Thesis (PhD) — Boston College, 2016<br>Submitted to: Boston College. Graduate School of Arts and Sciences<br>Discipline: Physics
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Azevedo, Cesar R. de Farias. "Phase diagram and phase transformations in Ti-Al-Si system." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/1278.
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Wang, Junjia. "Phase information and phase modulated signals in fibre optical communications." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107763.
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In future telecommunication networks, a wide range of pulse durations 0.1–100 ps, duty cycles from less than 1% to 99%, and different modulation formats, such as on-off-keying (OOK) and binary or differential phase-shift-keying (BPSK or DPSK) will be selected, depending on the network size and the bit rate. A transparent all-optical format conversion between OOK and DPSK is highly demanded to connect cost effective OOK based metropolitan area networks (MAN) to robust PSK-based long‐haul backbone networks. Moreover, for such complex optical transmission systems, the information on the phase and amplitude of the pulses is required for predicting the effects of chromatic dispersion and various optical nonlinearities. A temporal resolution of 1 ps and a sensitivity of less than 0.1 mW are required for an ideal characterization of optical pulses used in optical communications systems.In this thesis, we simulate the simple method of pulse characterization using sinusoidal optical phase modulation proposed by Kang and Dorrer using OptiSystem™ and MATLAB™. We also experimentally verify this method. A detailed characterization of all optical OOK to DPSK format conversion is presented by comparing simulation and experimental results for the receiver sensitivity (i.e., received power to have a BER of 〖10〗^(-9)) on the important properties of the input signal. By knowing the optimum configuration of the single channel OOK to DPSK format conversion, we then perform an OOK to DPSK format conversion with wavelength multicasting, which can operate simultaneously at four different wavelengths.<br>Les réseaux de communications optiques de l'avenir sont plus complexes : la durée des impulsions varie entre 0.1 ps et 100 ps, les rapports cycliques peuvent s'étendre entre 1% et 100% et il y aura différents formats de modulation. Par exemple, le choix entre la modulation à tout ou rien (OOK) et la modulation par excursion différentielle (DPSK) se fait en fonction de l'étendue du réseau et le débit binaire. Un format de conversion entre OOK et DPSK qui est intégralement optique est requis pour connecter les MAN basées sur le format OOK, qui est rentable, et DPSK, qui est très utile pour l'infrastructure des réseaux à longues distances. Pour les systèmes de transmission optique complexe comme ceux-ci, les informations sur la phase et l'amplitude des impulsions sont requises pour prédire les effets de la dispersion chromatique et des diverses non linéarités optiques. Une résolution de 1 ps et une sensibilité plus basse que 0.1 mW sont nécessaires pour caractériser les impulsions idéales utilisées dans les systèmes de communications optiques. Dans cette thèse, nous avons utilisé OptiSystem™ et MATLAB™ pour simuler une méthode simple pour caractériser les formats de modulations optiques de phases sinusoïdales proposées par Inuk Kang et Christophe Dorrer. Nous avons aussi prouvé la méthode expérimentalement. Une caractérisation détaillée des formats de conversion de OOK a DPSK est présentée en faisant la comparaison des simulations et des résultats expérimentaux pour vérifier l'influence de la puissance reçue, qui doit avoir un BER de〖10〗^(-9), sur les propriétés importantes du signal d'entré. L'optimisation de la configuration des formats de conversion de OOK à DPSK pour un seul canal nous a permis de concevoir la conversion multipoint de OOK à DPSK pour l'opération simultanée de quatre longueurs d'ondes différentes.
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Davis, Kyle. "Radio frequency photonic in-phase and quadrature-phase vector modulation." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50354.
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The focus of this thesis is to investigate the implementation of Radio Frequency (RF) In-Phase and Quadrature-Phase (I/Q) vector modulation through the use of modern photonic components and sub-systems which offer extremely wide RF intrinsic bandwidths. All-electronic vector modulators suffer from frequency coverage limitations and amplitude and phase instability due to components such as phase shifters and variable gain controllers operating at or near 100\% bandwidth. In stark contrast, once an RF signal has been modulated onto an optical carrier, the percent bandwidth of the RF to carrier is typically less than 0.01\% percent.
The fundamental mechanisms and basic electronic and photonic components needed to achieve vector modulation is introduced first. The primary electrical component required in most architectures is the 90° RF hybrid coupler, which is required to generate the RF I and Q terms. The two primary photonic building blocks, aside from the laser, electro-optic modulator and demodulator, are Mach-Zehnder Modulators (MZM) and Variable Optical Attenuators (VOA). Through the utilization of these components, multiple past architectures are explored and multiple new architectures are designed simulated.
For each architecture, there is a discussion on the practical implementation. Considerations such as system complexity, integration, and sensitivity to unwanted environmental stimuli are taken into account with potential solutions to alleviate these risks. In closing, the noise figure and its impact on Spur-Free Dynamic Range (SFDR) for a basic RF photonic link is derived to provide a system-level figure of merit that can be used, in most RF applications, to determine the overall performance utility current and future designs.
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Thein, Ferdinand [Verfasser]. "Results for two phase flows with phase transition / Ferdinand Thein." Magdeburg : Universitätsbibliothek, 2018. http://d-nb.info/1165650487/34.
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Garber, Edward Martin. "Surface acoustic wave single-phase unidirectional transducers and phase weighting." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15225.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985.<br>MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.<br>Bibliography: leaves 245-253.<br>by Edward Martin Garber.<br>Ph.D.