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1
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.Includes bibliographical references (p. 135-139).
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").
by Ying Ran.
Ph.D.
3
Freyssingeas, Eric. "Diffusion du rayonnement par des phases de membranes : phases lamellaires, phases éponges." Bordeaux 1, 1994. http://www.theses.fr/1994BOR10526.
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Nous etudions par diffusion du rayonnement les proprietes statiques et dynamiques de bicouches de tensioactifs en solution, organisees en phases lamellaires et en phases eponges. Le travail realise peut etre divise en deux grandes parties: i) l'etude, par diffusion statique de la lumiere et diffusion des rayons x, des consequences des fluctuations des membranes sur la structure des phases lamellaires et des phases eponges, permettant ainsi la mesure du module d'elasticite de courbure d'une membrane. Ii) l'etude de la dynamique des phases lamellaires et des phases eponges par diffusion quasi elastique de la lumiere. Tout d'abord dans le regime hydrodynamique quand la longueur d'onde des fluctuations est grande devant la taille du systeme etudie. Puis hors regime hydrodynamique, quand la longueur d'onde de fluctuations est petite devant la taille du systeme etudie
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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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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.
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.
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.
Keywords:simple liquids, molecular dynamics, pairpotential, icosahedral cluster.
5
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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Boullay, P. "Caractérisations structurales, phases modulées et transitions de phases: le cas des phases d'Aurivillius." Habilitation à diriger des recherches, Université de Caen, 2008. http://tel.archives-ouvertes.fr/tel-00522718.
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Bien que mon activité de recherche a été principalement axée sur la caractérisation structurale des phases d'Aurivillius en relation avec leurs propriétés ferroélectriques, je me suis aussi intéréssé à divers aspects liés à la synthèse de ces phases que ce soit sous forme de monocristaux, de poudres ou encore de films (voie chimique). Une première section consacrée à la synthèse ouvrira donc cette deuxième partie. Dès mon arrivée au SPCTS, une part importante de mon activité a été consacrée à l'étude des intercroissances à longues périodes qui ont pu être observées dans divers systèmes mais dont les caractéristiques structurales restaient inconnues. Sur la base de nos observations expérimentales, un modèle cristallographique généralisé utilisant le formalisme des groupes de super-espace a été développé pour les stuctures de type Aurivillius. Ce travail est issu d'une collaboration étroite avec l'équipe du Prof. J.M. Perez-Mato de l'Université de Bilbao. Cette nouvelle approche cristallographique et son utilisation constitueront la deuxième section. L'étude des relations structure/propriétés dans ces composés a constitué une autre part importante de mes recherches au SPCTS avec, notamment, le co-encadrement de la thèse de Jenny Tellier. Les divers aspects de la transition ferroélectrique-paraélectrique (FE-PE) rencontrés dans les composés de type Aurivillius ont été abordés que ce soit dans le cas des termes simples, des composés d'intercroissances que dans le cas, moins classique, des composés présentant un comportement ressemblant à celui de "relaxeurs" tel que Pb(Mg1/3Nb2/3)O3. Ce travail visant à décrire les mécanismes structuraux associés à la transition FE-PE fera l'objet de la troisième et dernière section.
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Heinisch, Sabine. "Optimisation des phases mobiles binaires et ternaires en chromatographie en phase liquide à polarité de phases inversée." Lyon 1, 1993. http://www.theses.fr/1993LYO10116.
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Le but de ce travail est de developper une methode d'optimisation rapide et fiable pour etablir les conditions d'elution optimales en chromatographie en phase liquide a polarite de phases inversee. Nous avons tente, par cette methode, de resoudre un grand nombre des problemes auxquels le chromatographiste peut se trouver confronte: optimisation en gradient d'elution, prise en compte des hauteurs relatives et asymetries des pics, selection de modificateurs organiques. Les performances de cette methode ainsi que ces limites sont discutees dans ce travail et illustrees par differentes applications
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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 RanIn 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
Thesis (PhD) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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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.Includes bibliographical references (leaves 169-174).
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.
by Pouyan Ghaemi Mohammadi.
Ph.D.
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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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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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Tellier, Jenny. "Sur les phases d'Aurivillius : études structurales et transitions de phases." Limoges, 2006. https://aurore.unilim.fr/theses/nxfile/default/dd157e3d-cbb2-4ec9-95b3-2e5100ed9b30/blobholder:0/2006LIMO0019.pdf.
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Les phases d'Aurivillius (Bi2O2)2+(Am-1BmO3m+l)2- sont des composés ferroélectriques, orthorhombiques à température ambiante et tétragonaux à haute température. Une étude à l'ambiante de composés dits relaxeurs montre que ces derniers sont caractérisés par une structure moyenne très peu déformée proche de la structure prototype avec un affaiblissement des liaisons Bi-O entre le bloc perovskite et la couche (Bi2O2)2+. Des cations autres que Bi3+ apparaissent présents dans cette couche. Microstructuralement, il existe des désordres impliquant des fluctuations locales de composition pouvant être à l'origine du comportement relaxeur. Une étude en température combinant plusieurs techniques permet d'obtenir des informations sur la transition de phase FE-PE et montre une grande diversité de comportement. Plus particulièrement, des monocristaux des composés SrBi2Ta2O9, SrBi2Nb2O9 et Bi4Ti2,8Cr0,2O12 sont étudiés par DRX et microcopie optique. L'utilité de ces deux techniques est discutéeAurivillius phases, with general formula (Bi2O2)2+(Am-1BmO3m+l)2- can be ferroelectric or relaxor materials. They display orthorhombic symmetry at room temperature and tetragonal at high temperature. Structural study of ferroelectric and relaxor compounds at room temperature show that relaxors' structure is legs distorted than that of ferroelectrics. Their fluorite slabs are independent and contain non-bismuth cations. Disorder in relax ors is showed using TEM analysis. It leads to local variations of structure which can be responsible for relaxor behaviour. Phase transition study cannot be carried out systematically for such compounds. The case of SrBi2Ta2O9, SrBi2Nb2O9 and Bi4Ti2,8Cr0,2O12 is considered, and additional information is given about other Aurivillius phases
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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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Kerkau, Alexander. "Disorder in Laves Phases." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-109917.
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Intermetallic compounds are solid phases containing two or more metallic elements, whose crystal structure differs from that of its constituents [1]. The largest group among these compounds with more than 1400 binary and ternary representatives are the so-called Laves phases. The classification of an intermetallic compound as a Laves phase is solely based on the atomic configuration and the component ratio in the crystal structure. With the ideal composition AB2, the Laves phases crystallize in three closely related structure types which are named after their representatives, MgCu2 (C15, cubic), MgZn2 (C14, hexagonal) and MgNi2 (C36, hexagonal). Laves phases are built by almost all metals of the periodic system of the elements. A significant feature of many of these is the formation of broad homogeneity ranges by mutual substitution of atoms in combination with composition or temperature dependent phase transformations between the different Laves phase polytypes. Laves phases have received considerable attention in recent years as potential structural and functional materials. They combine high melting points with considerable creep resistance, high strength and fracture toughness and good corrosion and oxidation resistance. Some Laves phases like NbFe2 [2] or TaFe2 [3] show intriguing magnetic and electronic properties which provide a deeper inside into phenomenons like quantum criticality. Especially transition-metal based Laves phases like NbCr2 [4] and ZrCr2 [5] are promising candidates for the development of new high-temperature structural materials. The major drawback of the Laves phases, however, is their low-temperature brittleness. Many experimental and theoretical investigations have shown, that the low-temperature ductility can be improved by controlling the crystal structure with the help of phase transformations, by mechanical twinning or the addition of third elements.
The addition of ternary alloying elements can alter the physical and electronic properties of the Laves phases and plays an important role in the composition dependent stability of the different polytypes. Some ternary Laves phases show an interesting phenomenon called site occupation reversal. It describes a composition dependent behavior of the alloying elements which prefer to occupy different crystallographic sites at different concentrations. The understanding of the point defect structure/mechanism and the site occupation of the alloying elements is thus of critical importance for the proper description of phase stability. The basis for the broad application of any metallic material is the knowledge of the corresponding phase diagram. The experimental determination of phase diagrams however, is tedious, time consuming and expensive work and the huge abundance of Laves phase makes this an impractical task. Thus, the time it takes to discover new advanced materials and to move them from the laboratory to the commercial market place is fairly long today. A cheap and fast enhancement for the development of new materials is the calculation of phase diagrams and physical properties using techniques like CALPHAD (CALculation of PHAse Diagrams) and DFT (Density Functional Theory).
Very recently the Office of Science and Technology Policy of the United States White House announced to provide a budget of $100 million to launch the Materials Genome Initiative [6, 7]. The aim of this initiative is to provide the infrastructure and training needed to discover, develop, manufacture, and deploy advanced materials in a more expeditious and economical way [8]. One of the project’s three supporting legs is the calculation and prediction of crystal structures and physical properties using advanced Computational tools. "An early benchmark will be the ability to incorporate improved predictive modeling algorithms of materials behavior into existing product design tools. For example, the crystal structure and physical properties of the materials [. . . ]." [8]. Their computational tools of choice are the same as used in this work to predict crystal structures and site occupation factors. Contents of this work is the investigation of the substitutional disorder in binary and ternary Laves phases. This includes the experimental determination of the composition dependent stability of the Laves phase polytypes and the distribution of the substitution atoms in the crystal lattice of the respective phases, i.e., the site occupation factors (s.o.f.). For this purpose, detailed experimental studies on the two systems Cr–Co–Nb and Fe–Ta–V were performed and the Laves phase polytypes, their homogeneity ranges, the lattice parameters and the site occupation factors were determined. The experimental results are compared with the results obtained from quantum mechanical calculations. DFT is used to determine the composition dependent enthalpies of formation which serve as a measure for the stability of the different Laves phase polytypes. Additionally, the applicability of various approximations and their influence on the results has been checked.
This study is thus also supposed to develop and improve the tools necessary for the calculation of phase stability and homogeneity ranges in ternary phases. Chapter two in the first part of this work describes the crystal structures of the Laves phases in detail with focus on the polytype stability, the site occupation and the c/a-ratio of hexagonal C14 Laves phases. Subsequently, the phase diagrams of the investigated systems and the occurring Laves phases are discussed. Chapter three briefly describes the experimental and theoretical methods used in this work. The last section of part one gives a detailed explanation of how the phase stability, the lattice parameters and the site occupation factors are calculated. The second part "Results and discussion" contains the discussion of the experimental and theoretical results for the intensively investigated systems Co–Cr–Nb (chapter five) and Fe–Ta–V (chapter six). Several other ternary C14 Laves phases and their site occupation behavior are studied in chapter seven. The thesis is concluded with a summary in chapter eight. Several additional information is contained in the appendix.
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Constantin, Doru. "Phases lamellaires dopées." Habilitation à diriger des recherches, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00667450.
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Cet ouvrage représente un résumé partiel de mes travaux depuis l'arrivée au Laboratoire de Physique des Solides en octobre 2005, en tant que chargé de recherches au CNRS. Le projet que j'avais présenté à l'époque portait principalement sur la formulation et l'étude par des techniques de diffusion du rayonnement de phases lamellaires de tensioactifs dopées avec des inclusions inorganiques, sphériques ou anisotropes. Un deuxième sujet de recherche (dans la même mouvance que le premier) envisageait la mesure de l'interaction entre des peptides insérés dans des membranes de lipides. Finalement, un troisième sujet assez distinct des deux précédents était l'étude de la dynamique de particules colloïdales par la diffusion dynamique des rayons X (XPCS, selon l'acronyme anglais).
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Ramos, Laurence. "Phases hexagonales dopees." Paris 6, 1997. http://www.theses.fr/1997PA066711.
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La phase hexagonale dopee est la combinaison d'une suspension colloidale de particules magnetiques et d'une phase hexagonale lyotrope. La matrice hexagonale est un arrangement bidimensionnel de cylindres liquides apolaires dans un solvant aqueux. Nous montrons que le controle de la courbure spontanee de la monocouche via la force ionique de l'eau permet d'acceder a une tres large gamme de variation pour le diametre des cylindres. Des particules solides de taille nanometrique peuvent alors etre incorporees dans les cylindres des phases les plus gonflees. Nous avons explore les proprietes structurales, magnetiques et elastiques des phases hexagonales dopees. L'etude de la structure par diffusion des rayons x aux petits angles montre que la presence du colloide solide ne perturbe pas l'ordre cristallin du reseau bidimensionnel de cylindres. Les spectres montrent par ailleurs que les particules sont depletees des parois des cylindres. La repartition spatiale fortement anisotrope des grains magnetiques induit des comportements specifiques lorsqu'ils sont soumis a un champ magnetique : des instabilites de type cristal liquide sont observees a tres bas champ. Elles traduisent une reorientation des cylindres le long du champ et sont la signature d'un couplage fort entre les particules et la matrice lyotrope. Enfin nous explorons les proprietes elastiques des phases hexagonales dopees par des methodes statiques et dynamiques. L'analyse des textures observees en microscopie optique polarisante permet d'acceder a une longueur caracteristique de l'elasticite et montre que la presence du colloide durcit la phase hexagonale. D'autre part, les experiences de diffusion quasi-elastique de la lumiere effectuees sur des echantillons hexagonaux orientes montrent un couplage entre la diffusion brownienne des particules et un mode de relaxation des fluctuations de concentration en cylindres ; un modele hydrodynamique est propose qui rend compte de l'ensemble des resultats.
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Henry, Louis-Paul. "Glace bidimensionnelle classique et quantique : phases de Coulomb et phases ordonnées." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00932367.
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La frustration - c'est-à-dire la présence d'interactions de nature compétitive - donne lieu à des effets de grande complexité en physique. La glace - aussi bien la phase bien connue de l'eau, que ses analogues magnétiques, dites " glaces de spin " - en offre un exemple remarquable. Pour des interactions à courte portée et des degrés de liberté classiques, son état fondamental est infiniment dégénéré, et comporte en outre des corrélations à longue portée induites par une contrainte locale, caractéristiques de la phase dite de Coulomb. Ses excitations élémentaires correspondent au retournement d'un dipôle qui se " fractionnalise " en deux monopôles. Dans cette thèse nous nous intéressons à la stabilité de cette phase de Coulomb dans la glace bidimensionnelle - réalisée aussi bien comme glace de protons dans des composés organiques, que comme glace de spin dans des systèmes nanomagnétiques. Dans le cas classique, les interactions dipolaires - présentes dans les systèmes expérimentaux - déstabilisent la phase de Coulomb dans son état fondamental. Cependant, une déformation de la simple géométrie planaire permet de récupérer cette phase dans un régime où différents états ordonnés entrent en compétition. Dans le cas quantique, les fluctuations dues à un champ magnétique transverse induisent une brisure de symétrie dans l'état fondamental qui, à basse température, cède la place à une phase de Coulomb quantique, réalisant un liquide de spin quantique avec excitations fractionnalisées. Nos résultats sont obtenus à l'aide de méthodes analytiques (analyse harmonique classique et quantique et théorie de perturbations) aussi bien que numériques (Monte Carlo) fondées sur des algorithmes originaux.
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Chatchawalsaisin, Jittima, John Kendrick, S. C. Tuble, and Jamshed Anwar. "An optimized force field for crystalline phases of resorcinol." Royal Society of Chemistry, 2008. http://hdl.handle.net/10454/4733.
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noThe two known crystalline phases of resorcinol and their phase transitions are of considerable interest. The crystals exhibit pyro- and piezo-electricity and, remarkably, the higher temperature phase is the denser phase. Furthermore, crystals of the phase, by virtue of having a polar axis, have played a crucial role in investigating fundamental issues of crystal growth. We report an optimized force field for the molecular simulation of crystalline phases of resorcinol. The hydroxyl groups of the resorcinol molecule have a torsional degree of freedom and the molecule adopts a different conformation in each of the two phases of resorcinol. The torsional barrier, therefore, was considered to be critical and has been characterized using ab initio methods. Although the atomic partial charges showed some dependence on the molecular conformation, a single set of partial charges was found to be sufficient in describing the electrostatic potential for all conformations. The parameters for the van der Waals interactions were optimized using sensitivity analysis. The proposed force field reproduces not only the static structures but also the stability of the crystalline phases in extended molecular dynamics simulations.
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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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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.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 131-136).
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.
by Tarun Grover.
Ph.D.
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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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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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Kemiklioglu, Emine. "Polymer Stabilized and Dispersed Blue Phases." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1409153158.
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Gendron, François-Xavier. "Contribution à la discrimination chirale à l'état solide et accès aux énantiomères pures par cristallisation." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMR032/document.
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Le besoin d’accès aux énantiomères purs a largement augmenté depuis les années 90. Les procédés ayant recours à la cristallisation sont souvent moins cher mais tout aussi efficace que les autres procédés. Deux études ont été réalisées dans cette thèse : -La première concerne l’amélioration d’un procédé déjà établi. En effet, l’efficacité de la Cristallisation Préférentielle (PC) de conglomérat est connue. Néanmoins, son application à des solutions solides images l’une de l’autre dans un miroir est plus complexe. Est présenté le premier exemple de PC réalisée sur un système à solution solide complète démixant à basse température : le sel d’hydrogénomaléate de baclofène (un API). De plus, il s’agit de la première preuve expérimentale d’un tel équilibre de phases et de PC de solutions solides dont les résultats sont comparables à la cristallisation préférentielle traditionnelle. -Le second sujet ne traite pas directement de la séparation d’énantiomère mais de prometteuses discriminations chirales ont été obtenues. Le diagramme d’équilibre de phases entre les compositions racémiques de deux couples d’atropoisomères a été étudié. Deux résultats en lien avec la discrimination chirale ont été établis : le premier est la possibilité de déracémiser un composé A initialement non-discriminé (composé racémique) à l’intérieur de la matrice d’un composé B discriminé (conglomérat). Le second est l’observation d’un nouveau type de chiralité : Chiralité Induite par Dissymmétrie de Distribution (CIDD)The need for access to pure enantiomers has largely increased since the nineties. Processes using crystallization are often cheaper and as efficient as other processes. Thus, the improvement of existing techniques and the need for new processes are attractive for scientist and industry. Two studies have been performed in this thesis:The first one concerns the improvement of an existing technique. Indeed, conglomerate Preferential Crystallization efficiency is well known. Nonetheless, its application to mirror image partial solid solutions is more difficult. Here is presented the first example of PC performed on a complete solid solution at high temperature which shows a solid solutions demixion at low temperature: the baclofen hydrogenomaleate salt (an API). Moreover, it is the first experimental observation of such phase equilibria and PC of mirror image solid solutions whose results are comparable to classical PC. -The second topic did not involve directly enantiomer separation but promising chiral discriminations have been obtained. The phase diagram between the racemic composition of two couples of atropisomers has been defined. Beside multiples equilibria observed, two results concerning the chiral discrimination can be highlighted: the first one is the possibility to deracemize a compound A initially not discriminated (racemic compound) inside the matrix of a compound B (which forms a stable conglomerate). The second is the observation of a new kind of chirality: Chirality Induced by Dissymmetric Distribution (CIDD)
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Humphrey, Caroline. "Deformation in MAX phases." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610553.
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Liu, Tianhan. "Strongly Correlated Topological Phases." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066403.
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Cette thèse porte principalement sur l'étude de modèles de fermions en interactions contenant un couplage spin-orbite. Ces modèles (i) peuvent décrire une classe de matériaux composés d'iridates sur le réseau en nid d'abeille ou (ii) pourraient être réalisés artificiellement dans des systèmes d’atomes froids. Nous avons étudié, dans un premier temps, le système à demi-remplissage avec l'interaction de Hubbard et un couplage spin-orbite anisotrope. Nous avons trouvé plusieurs phases: la phase isolant topologique pour de faibles corrélations, et deux phases avec des ordres magnétiques frustrés, l'ordre de Néel et l'ordre spiral, dans la limite de très fortes corrélations. La transition entre les régimes de faibles et de fortes corrélations est une transition de Mott dans laquelle les excitations électroniques se fractionnent en excitations de charge et de spin. Les charges sont localisées par l'interaction. Le secteur de spin présente de fortes fluctuations qui sont modélisées par un gaz d’instantons. Nous avons ensuite exploré la physique d'un système régi au demi-remplissage par le modèle de Kitaev-Heisenberg, qui présente une phase magnétique de type zig-zag. En dopant le système, autour du quart remplissage, la structure de bande présente de nouveaux centres de symétrie en plus de la symétrie d'inversion. Le couplage de spin de Kitaev-Heisenberg favorise alors la formation de paires de Cooper dans un état triplet autour de ces centres de symétrie. La condensation de ces paires de Cooper autour de ces vecteurs d'onde non triviaux se manifeste par une modulation spatiale du paramètre d'ordre supraconducteur, comme dans la supraconductivité de Fulde–Ferrell–Larkin–Ovchinnikov (FFLO). La dernière partie de la thèse propose et étudie une implémentation des phases topologiques dite de Haldane et de Kane-Mele dans un système avec deux espèces de fermions sur le réseau en nid d'abeille, stabilisée grâce à l’interaction RKKY médiée par l’espèce rapide et qui agit sur l’espèce lenteThis thesis is dedicated largely to the study of theoretical models describing interacting fermions with a spin-orbit coupling. These models (i) can describe a class of 2D iridate materials on the honeycomb lattice or (ii) could be realized artificially in ultra-cold gases in optical lattices. We have studied, in the first part, the half-filled honeycomb lattice model with on-site Hubbard interaction and anisotropic spin-orbit coupling. We find several different phases: the topological insulator phase at weak coupling, and two frustrated magnetic phases, the Néel order and spiral order, in the limit of strong correlations. The transition between the weak and strong correlation regimes is a Mott transition, through which electrons are fractionalized into spins and charges. Charges are localized by the interactions. The spin sector exhibits strong fluctuations which are modeled by an instanton gas. Then, we have explored a system described by the Kitaev-Heisenberg spin Hamiltonian at half-filling, which exhibits a zig-zag magnetic order. While doping the system around the quarter filling, the band structure presents novel symmetry centers apart from the inversion symmetry point. The Kitaev-Heisenberg coupling favors the formation of triplet Cooper pairs around these new symmetry centers. The condensation of these pairs around these non-trivial wave vectors is manifested by the spatial modulation of the superconducting order parameter, by analogy to the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) superconductivity. The last part of the thesis is dedicated to an implementation of the Haldane and Kane-Mele topological phases in a system composed of two fermionic species on the honeycomb lattice. The driving mechanism is the RKKY interaction induced by the fast fermion species on the slower one
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Ghetta, Véronique. "Cristallochimie des phases ternaires." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37605409s.
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Aufrecht, Jochen Marc [Verfasser]. "Phase transformations of the NbCr2 and HfCr2 Laves phases / Jochen Marc Aufrecht." Stuttgart : Max-Planck-Inst. für Metallforschung, 2010. http://d-nb.info/1010529943/34.
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Watson, Richard Charles. "Studies of reversed phase high performance liquid chromatography (RP-HPLC) stationary phases." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338492.
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Li, Hongxing. "Mechanical Properties of Dual Phase Alloys Composed of Soft and Hard Phases." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215959.
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Speybrouck, David. "Impact de l'additif en chromatographie en phase supercritique sur phases stationnaires énantiosélectives." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMR052/document.
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Le développement de molécules chirales est devenu un enjeu majeur pour l’industrie pharmaceutique. Lors de la mise au point d’un nouveau principe actif, la chromatographie en phase supercritique (CPS) sur phases stationnaires énantiosélectives, est devenue une méthode incontournable pour l’analyse ou la purification d’énantiomères. Il n’en demeure pas moins que certains composés tels que les composés basiques restent délicats à analyser par cette technique et que l’ajout d’un additif basique dans la phase mobile est très souvent nécessaire. La quantité d’additif ajoutée dans la phase mobile est souvent choisie de manière arbitraire en se basant sur les spécifications des fournisseurs de phases stationnaires et sur les travaux publiés dans le domaine, sans se soucier de l’effet potentiel sur la résolution d’une modification de sa concentration. Ce travail de thèse a démontré l’importance de la concentration en additif dans la phase mobile lors de l’analyse de mélanges d’énantiomères par CPS, avec notamment des effets significatifs sur l’énantiosélectivité allant jusqu’à une inversion de leur ordre d’élution selon la concentration en additif. Dans un deuxième temps cette étude a consisté en une amélioration de notre compréhension des modes d’actions de l’additif, sur la phase stationnaire et sur la phase mobile permettant de poser des hypothèses sur les effets observés lors de la séparation d’énantiomères. La dernière partie est consacrée à la présentation de différents exemples, justifiant l’intérêt de moduler la concentration en additif lors de séparations d’énantiomèresNowadays, the development of chiral molecule is a strategic issue for the pharmaceutical industry. During the development of a new molecular entity, supercritical fluid chromatography using enantioselective stationary phases is essential for the analysis or the purification of racemates. Despite the advantages of SFC, the analysis of some compounds like basic compounds may still be a challenge. Their analysis most of the time, requires an additive in the mobile phase. In many cases additives concentration is chosen arbitrarily, based on the columns supplier guidelines and work already published, regardless of the impact of the additive concentration on the resolution. This work has shown the impact of the additives concentration for the analysis of enantiomers by SFC, in particular a significative impact on the enantioselectivity of chiral stationary phases, with for some of them a reversal elution order depending on the additive concentration. The second objective is to improve our knowledge on the mechanism of action of the additive both on the stationary phase and the mobile phase. The last part is dedicated to the presentation of a few examples highlighting the positive impact of the variation of the additives concentration for enantiomer separation
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Ficheux, Marie-Françoise. "Etude de systèmes mixtes polymère / tensioactif en phases organisées : diagrammes de phases et interactions." Bordeaux 1, 1995. http://www.theses.fr/1995BOR10624.
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Des systemes mixtes ou un tensio-actif et un polymere sont simultanement presents en solution aqueuse sont l'objet de cette etude pour l'essentiel experimentale. Les tensio-actifs, anioniques, peuvent former des structures lamellaires (cristal liquide smectique a) ou hexagonales (cristal liquide colonnaire). Les polymeres, hydrosolubles et non-ioniques, sont inseres dans ces structures. Le diagramme de phases de tels systemes est etabli. On remarque dans certains cas la presence d'une separation de phase entre deux phases lamellaires pour des teneurs intermediaires en tensio-actif et en polymere. La contribution attractive aux interactions entre bicouches en phase lamellaire due a la presence du polymere, est etudiee quantitativement par des experiences de diffusion de la lumiere et des neutrons. Les resultats suggerent la presence ou la proximite d'un point critique lamellaire-lamellaire
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Terescenco, Daria. "Evaluation et compréhension de la structure de l’émulsifiant et son impact sur les propriétés physiques, physico-chimiques et sensorielles d’émulsions cosmétiques." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMLH05/document.
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L’émulsifiant est une matière première largement utilisée dans les systèmes formulés de type émulsion. Grâce à sa structure chimique amphiphile, cette molécule diminue la tension interfaciale entre les deux liquides non miscibles qui composent une émulsion, ce qui augmente la stabilité du système dans le temps. En plus, à cause de sa structure, il peut former des cristaux liquides dans les systèmes formulés, ce qui impacte considérablement les propriétés physico-chimiques et applicatives des émulsions. Ce projet vise l’étude d’un tensioactif mixte naturel alkyl polyglucoside/alcool gras. Les propriétés de celui-ci ont été d’abord investiguées via la construction du diagramme de phase. Ainsi, il a été démontré que la variation de la concentration et du ratio alkyl polyglucoside/alcool gras dans l’émulsifiant mixte favorise le passage de solutions micellaires vers les cristaux liquides de types lamellaire ou hexagonale dans les systèmes étudiés. La maitrise des propriétés des systèmes binaires a permis, par la suite, de comprendre les métamorphoses subies par le système lorsqu’une phase grasse est incorporée. La structure chimique des émollients (présence des hétéroatomes) affecte l’organisation des cristaux liquides formés par les molécules amphiphiles. Par conséquent, en fonction de l’émollient utilisé, les propriétés microscopiques et macroscopiques des systèmes changent (taille et distribution des gouttelettes, profil rhéologique, thermique et de texture). Finalement, les propriétés applicatives des émulsions sont aussi affectées, comme cela a été montré via l’analyse sensorielle et les mesures biométriques in-vivoEmulsifier is a raw material widely used in formulated systems of emulsion type. Due to its amphiphilic chemical structure, this molecule decreases the interfacial tension between two immiscible liquids that form an emulsion, which increases the stability of the system over time. In addition, it can form liquid crystals in the formulated systems because of its structure and this has a considerable impact on the physicochemical and applicative properties of emulsions. The objective of this project is to study a natural alkyl polyglucoside/fatty alcohol mixed surfactant. Its properties were first investigated via the construction of the phase diagram. Thus, it has been shown that the variation of the concentration and of the ratio of alkyl polyglucoside/fatty alcohol in the mixed emulsifier favors the transition between the micellar solutions towards liquid crystals of lamellar or hexagonal type in the studied systems. Next, the mastering of the binary systems properties allowed understanding the metamorphoses undergone by the system when an oil phase is incorporated into it. The chemical structure of emollients (presence of heteroatoms) affects the organization of liquid crystals formed by the amphiphilic molecules. Therefore, depending on the emollient type, the microscopic and macroscopic properties of the systems change (droplet sizes and distribution, rheological, thermal and texture profile). Finally, the applicative properties of emulsions are also affected, as shown by sensory analysis and in-vivo biometric measurements
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Gray, Sarah Jane. "Dissipative particle dynamics simulations of surfactant systems : phase diagrams, phases and self-assembly." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12641/.
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Surfactants, as lyotropic liquid crystals, exhibit a whole host of ordered liquid phases, as a function of surfactant concentration, solvent identity, and any additives present. These ordered phases confer properties to the solution on a macroscopic level, and so understanding ordered phase formation is critical in predicting the physical behaviours of surfactant--containing mixtures. Typically, household cleaning products contain sufficiently low surfactant concentrations that micellar solutions form, resulting in isotropic, low viscosity liquids. However, in recent years ``single unit dose'' (SUD) products have became increasing popular. The formulation of SUDs results in high concentrations of surfactant, which can result in undesirable properties such as excessively high viscosity, turbidity, and poor product dispersal. This work aims to elucidate the nature of the ordered structures that form in these products, and understand the molecular driving factors that result in their formation. To gain an understanding of the molecular--level interactions involved in these liquid mixtures, we applied the Dissipative Particle Dynamics (DPD) simulation method. DPD is the ideal technique to study mesophase formation of these mixtures as it is exceptionally fast, allowing one to simulate on the mesoscale (the pertinent length scale for mesophase studies) while retaining detail on the order of molecular fragments. The main body of this work has been dedicated to investigating the parameterisation of DPD models in a tractable manner. We have developed a highly transferable DPD model of the most common anionic surfactants: sodium dodecylsulphate, linear alkylbenzene sulphonate, and alkylether sulphate. Our model reproduces the phase behaviour of both individual isomers and isomeric mixtures, across entire phase diagrams (with respect to concentration). Although there are some difficulties in producing chemically tractable models with DPD, once developed these models are an incredibly powerful tool in studying phase behaviour from a molecular perspective.
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Impéror-Clerc, Marianne. "Étude de transition de phase vers les phases cubiques des systèmes eau/surfactant." Paris 11, 1992. https://tel.archives-ouvertes.fr/tel-01989797.
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Les phases cubiques des systèmes binaires eau/surfactant sont un cas d'organisation liquide-cristalline de la matière très surprenant. Leur structure allie, a un ordre local liquide, une périodicité tridimensionnelle à l'échelle mésoscopique, qui en fait de véritables cristaux de films fluides. Elle se caractérise également par une topologie bicontinue tout à fait remarquable. Partant de l'observation de la croissance en épitaxie d'une phase cubique (de groupe d'espace Ia3d, le plus fréquent) à partir des mésophases lamellaire et hexagonale, nous nous sommes attaches à décrire comment, d'un point de vue purement structural, il est possible de déduire la structure cubique de celles, plus simples, de ces autres mésophases. Tout d'abord, la croissance en épitaxie de la phase cubique a été observée en diffusion des rayons X sur des échantillons monocristallins, ainsi qu'au microscope polarisant. Des désordres caractéristiques de chacune des mésophases, liés à leur nature liquide cristalline, ont également été mis en évidence grâce aux clichés de diffraction X et analyses. Nous avons ensuite utilisé des modèles géométriques récents, pour poser le problème du passage d'une phase à l'autre en termes purement topologiques de transformations de surfaces. Des intermédiaires possibles pour les deux transitions ont été conçus : les surfaces tours pour la transition hexagonale/cubique et les tunnels entre plans pour la transition lamellaire/cubique, expliquant notamment l'apparition de la topologie bicontinue de la phase cubique.
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Liu, Kun. "Polymeric Monolithic Stationary Phases for Capillary Reversed-phase Liquid Chromatography of Small Molecules." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/3843.
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Highly cross-linked monoliths prepared from single cross-linking monomers were found to increase surface area and stability. Therefore, seven cross-linking monomers, i.e., 1,3-butanediol dimethacrylate (1,3-BDDMA), 1,4-butanediol dimethacrylate (1,4-BDDMA), neopentyl glycol dimethacrylate (NPGDMA), 1,5-pentanediol dimethacrylate (1,5-PDDMA), 1,6-hexanediol dimethacrylate (1,6-HDDMA), 1,10-decanediol dimethacrylate (1,10-DDDMA), and 1,12-dodecanediol dimethacrylate (1,12-DoDDMA), were used to synthesize highly cross-linked monolithic columns in 75-µm i.d. capillaries by one-step UV-initiated polymerization using dodecanol and methanol as porogens for reversed-phase liquid chromatography (RPLC) of small molecules. Selection of porogen type and concentration was investigated in detail. Isocratic elution of alkylbenzenes at a flow rate of 300 nL/min was conducted for all of the monoliths. Gradient elution of alkylbenzenes and alkylparabens provided high resolution separations. Several of the monoliths demonstrated column efficiencies in excess of 50,000 plates/m. Monoliths with longer alkyl-bridging chains showed very little shrinking or swelling in solvents of different polarities. In addition, highly cross-linked monolithic capillary columns poly(1,6-HDDMA), poly(cyclohexanediol dimethacrylate) [poly(CHDDMA)] and poly(1,4-phenylene diacrylate) [poly(PHDA)], were synthesized and compared for RPLC of small molecules. Isocratic elution of alkylbenzenes was performed using 1,6-HDDMA and CHDDMA monolithic columns. Gradient elution of alkylbenzenes using all three monolithic columns showed good separations. Monolithic columns formed from 1,6-HDDMA, which had a linear alkyl-bridging chain structure, exhibited the highest column efficiencies (86,000 plates/m). Optimized columns showed high permeability and high run-to-run and column-to-column reproducibilities. Monoliths prepared from controlled/living polymerization was demonstrated exhibiting narrower molecular weight distribution and more homogeneous cross-linked structures due to the reversible character of this polymerization method. Thus, monolithic columns were developed from three cross-linking monomers, i.e., 1, 12-DoDDMA, trimethylolpropane trimethacrylate (TMPTMA) and pentaerythritol tetraacrylate (PETA) using organotellurium-mediated living radical polymerization (TERP) in 150-µm i.d. capillaries for RPLC of small molecules. Selection of the polymerization conditions for the 1,12-DoDDMA monolirh was investigated in detail. Isocratic elution of alkylbenzenes was achieved with good efficiency (47,700 to 64,200 plates/m for uracil) using all monolithic columns prepared using TERP.
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Ghelli, Greta. "Topological phases in spin ladders." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17050/.
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Questa tesi si occupa di approfondire lo studio di possibili fasi topologiche in un sistema costituito da due catene di spin caratterizzate entrambe da un'interazione alternata forte e debole. Infatti è interessante capire se questo tipo di interazione può portare a termini topologici non nulli nella funzione di partizione, termini che invece sono assenti per due catene accoppiate quando l'interazione tra spin vicini è sempre la stessa.
Quello che si scopre dal punto di vista analitico è che, quando l'interazione su una catena è traslata di un sito rispetto a quella sull'altra catena, il nostro modello, nel limite del continuo, si può mappare nel modello sigma non lineare più un termine topologico diverso da zero. In corrispondenza di un certo valore critico del termine topologico si ha una transizione di fase tra due fasi isolanti differenti. Tale valore critico corrisponde a un certo valore critico del parametro che caratterizza l'interazione alternata sulle catene.
L'analisi numerica, basata sul metodo DMRG, conferma questa previsione teorica. Inoltre, dal confronto tra i risultati numerici per i livelli energetici ottenuti con condizioni al contorno aperte e chiuse, si può già notare che una delle due fasi sembra avere proprietà topologiche non triviali.
E' dunque molto interessante chiedersi se queste fasi siano caratterizzate da un qualche tipo di ordine topologico, rilevabile attraverso parametri d'ordine non locali. Le simulazioni numeriche confermano questa ipotesi: il parametro d'ordine non locale di stringa è non nullo nella fase caratterizzata da proprietà topologiche non triviali, che è dunque identificata come un isolante di Haldane, e il parametro d'ordine non locale di parità è non nullo nella fase topologicamente triviale, che è dunque identificata come un isolante di Mott. Si ha dunque una transizione di fase tra l'isolante di Mott e l'isolante di Haldane.
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Deger, Sinan. "Geometrical Phases And Magnetic Monopoles." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12612989/index.pdf.
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In this thesis, we study the subject of geometrical phases in detail by considering its various forms. We focus primarily on the relation between quantum geometrical phases and magnetic monopoles, and study how one can make use of the concepts of geometrical phases to define magnetic monopoles.
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Dahl, Anders. "Persistence of Microcredit Market Phases." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for industriell økonomi og teknologiledelse, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15047.
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I formulate a phase theory of microcredit market dynamics. The theory is developed and validated using an in-depth multiple case study examining three mature microfinance markets: Bolivia, Bosnia and Herzegovina, and Morocco. I present a specific case study framework that is used to analyze each of the three markets separately. This framework combines qualitative and quantitative empirical analysis through the evaluation of 12 specific indicators. These indicators are chosen to represent four different market dynamics that are believed to affect microfinance institutions and their performance.A cross-case analysis is conducted to detect similar patterns across the three mature markets, and the findings are summarized into the phase theory. I present a theory of six different phases that a microfinance market goes through from its emergence until the crisis is resolved. Some of the important findings across the three cases are rapid growth, increased bargaining power of consumers and excessive funding to the microfinance institutions, all in the time period leading up to the repayment crisis.In essence, the phase theory predicts that a market that grows beyond what is sustainable and controllable will eventually crash when macroeconomic instability occurs. To make sure a market maintains a sustainable growth, it’s important for the microfinance institutions to focus on long-term profitability over short-term growth. Mechanisms for information sharing are also essential to eliminate the new information asymmetries that arise from introducing competition in microcredit markets.I also examine a microfinance market that is under development: Cambodia. This market has not yet experienced a repayment crisis, and I apply the phase theory on this case market to assess how likely it is that it will.
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Gooblar, David. "Philip Roth : the major phases." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1444184/.
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This thesis is a study of the major phases of the career of Philip Roth. In the nearly fifty years since his first book, Roth has published close to thirty works, creating a body of work now as large and as varied as any twentieth century writer. In an attempt to chart the progression of this career, I break down Roth's oeuvre into six chronological phases, beginning in the late 50s and ending at the start of the new century. Having carried out extensive research into Roth's archive in the Library of Congress, contemporary reception of the books, and a variety of often overlooked cultural contexts, I have attempted to offer a new and original take on Roth's most interesting and distinctive preoccupations. Beginning with Goodbye, Columbus, Roth's first book, I examine the author's complicated relationship with, and treatment of, the idea of Jewish community in America. The second chapter follows Roth's vexed pursuit of, and eventual rejection of, an ideal of literary seriousness in the 1960s, especially in relation to the example of the New York Intellectuals. Chapter 3 looks at Roth's preoccupation with two figures from twentieth century European Jewish history, Franz Kafka and Anne Frank, who figure in a number of Roth's books during the 1970s. Chapter 4 examines the important role that psychoanalysis plays in Roth's books, from the burlesque of an analytic session of Portnoy's Complaint, to an apparent break with psychoanalytic thinking in 1986's The Counterlife. The next phase is Roth's "autobiographical" period of 1988 to 1993, during which he produced four books each at a different point along a continuum between autobiography and fiction. In these works, Roth comes to grips with the ethical issues that his fiction had played with for so long. Finally, the last chapter looks at Roth's final books of the century, investigating how his assessment of three periods of twentieth century American history shows a fascination with individuals who attempt to break free from the forces of determination. Rather than, as is commonly espoused, a break with his earlier work, I argue that the "American Trilogy" continues concerns that have preoccupied Roth from the very start of his career.
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Schofield, Andrew John. "Flux phases for correlated fermions." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282101.
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Calderón, Krejci Juan Enrique. "Rabi hamiltonian and geometric phases." Master's thesis, Pontificia Universidad Católica del Perú, 2016. http://tesis.pucp.edu.pe/repositorio/handle/123456789/6889.
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Esta tesis estudia fases geométricas que aparecen cuando un átomo de dos niveles interacciona con un campo electromagnético monomodal cuantizado, un modelo descrito por el Hamiltoniano de Rabi (HR). Como se conoce, el HR no tiene una solución cerrada; no obstante, cuando el acoplamiento entre el átomo y campo es débil, la aproximación de onda rotante (RWA) puede ser aplicada. Esto resulta en el Hamiltoniano de Jaynes-Cummings (HJC), el cual es una útil solución analítica aproximada del primero. Cuando la RWA puede ser aplicada, fenómenos físicos predichos en el modelo de Rabi deben también aparecer en el modelo de Jaynes-Cummings; caso contario, la aproximación será físicamente inconsistente. Esto último generó una controversia después de una reciente afirmación sobre fases de Berry en el HR. De acuerdo a ésta, la RWA no es válida para ningún valor del acoplamiento entre el átomo y campo. Los resultados de esta investigación, cálculos numéricos de la fase de Berry en el HR, muestran que este no es el caso y que afirmaciones contrarias son inconsistentes con un argumento analítico que concierne al modelo de Rabi. Adicionalmente, se muestra que estos resultados convergen a los respectivos para el HJC, concluyendo as__ que la RWA es consistente al aplicarse a fases de Berry, como era de esperarse. Finalmente, se discute que la aparición de fases de Berry no depende de la condición adiabática; por lo tanto, el marco de estudio apropiado es el cinemático, el cual contiene a la fase de Berry como un caso particular de la fase geométrica. También se discute que el Hamiltoniano no desempeña un rol importante, salvo de proveedor de los autovectores usados en el cálculo de la fase geométrica. Esto manifiesta la característica esencial de la cual depende la fase geométrica, que es la geometría del espacio de rayos. Este espacio depende de los tipos de evolución que sean considerados. Este punto es ilustrado estudiando una diferente transformación unitaria en el modelo de Schwinger.Tesis
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Markwick, Phineus R. L. "Reorientation dynamics in condensed phases." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/15267.
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Using Raman lineshape analysis and dielectric relaxation techniques, the reorientation dynamics of single molecules in partially disordered phases is studied. Reorientation correlation functions for a prototypical isotropic liquid CS2 are presented over a broad temperature range. Calculated values of the integrated correlation time, rms intermolecular torque and collision frequency suggest the onset of substancial local structuring in the liquid phase on cooling to below 220K. An ab initio DFT computer simulation shows that the intermolecular torque arises from a strong dipole moment interaction created by the bending mode vibration of CS2 and by a weaker dipole moment interaction which oscillates on a much faster time-scale due to the anti-symmetric stretch vibrational mode. A solvation dynamics study of CS2 in cyclohexane provides the first observation of the free-volume effect occurring at the isotropic-plastic crystal phase transition. Reorientation correlation functions are presented for various members of the nCB [4-n-Alkyl-4'-Cyanobiphenyl] homologous series in the isotropic phase. Two distinct relaxation processes are observed; A very fast intra-molecular relaxation mechanism assigned to the flexibility of the anisotropic molecules, and a slow exponentially-decaying rotational-translational relaxation process with a complex temperature dependence. The results of dielectric relaxation studies under high pressure of two liquid crystals (6PCH [4-trans-4-n-Hexyl-Cyclohexyl-Benzonitrile] and 8CB) are presented. The extraction of reorientational activation parameters in the isotropic, nematic and smectic A phase allows the formulation of a reorientational model. Steric effects determine the predominant relaxation process. Increasing the molecular alignment, reduces the steric interaction and facilitates molecular reorientation about the short-molecular axes, though molecular flexibility and dipole-dipole interactions also play a role. The order parameter in the nematic phase is seen to be strongly dependent on the rigidity of the constituent molecules.
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Lu, Fuyan. "Topological Phases with Crystalline Symmetries." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524790822570583.
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