Dissertations / Theses on the topic 'Phase transition'
To see the other types of publications on this topic, follow the link: Phase transition.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Phase transition.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Klintberg, Lena. "Miniature phase-transition actuators/." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2002. http://publications.uu.se/theses/91-554-5345-7/.
Full text
2
Martin, Adrian Peter. "Cosmological phase transition phenomena." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389880.
Full text
3
Haupt, Kerstin Anna. "Phase transitions in transition metal dichalcogenides studied by femtosecond electron diffraction." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85608.
Full textAbstract:
Thesis (PhD)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Low-dimensional materials are known to undergo phase transitions to differently or- dered states, when cooled to lower temperatures. These phases often show a periodic modulation of the charge density (called a charge density wave – CDW) coupled with a periodic perturbation of the crystal lattice (called a periodic lattice distortion – PLD). Although many experiments have been performed and much has been learnt about CDW phases in low-dimensional materials, the reasons for their existence are still not fully understood yet. Many processes, involving either strong electron–electron or electron–lattice coupling, have been observed which all might play a role in explaining the formation of different phases under different conditions. With the availability of femtosecond lasers it has become possible to study materials under highly nonequilibrium conditions. By suddenly introducing a known amount of energy into the system, the equilibrium state is disturbed and the subsequent relax- ation processes are then observed on timescales of structural and electronic responses. These experiments can deliver valuable information about the complex interactions between the different constituents of condensed matter, which would be inaccessible under equilibrium conditions. We use time resolved electron diffraction to investigate the behaviour of a CDW system perturbed by a short laser pulse. From the observed changes in the diffraction patterns we can directly deduce changes in the lattice structure of our sample. A femtosecond electron diffraction setup was developed at the Laser Research In- stitute in Stellenbosch, South Africa. Short laser pulses produce photo electrons which are accelerated to an energy of 30 keV. Despite space charge broadening effects, elec- tron pulses shorter than 500 fs at sample position can be achieved. Technical details of this system and its characterisation as well as sample preparation techniques and analysis methods are described in detail in this work. Measurements on two members of the quasi-two-dimensional transition metal di- chalcogenides, namely 4Hb-TaSe2 and 1T-TaS2, are shown and discussed. Both show fast (subpicosecond) changes due to the suppression of the PLD and a rapid heating of the lattice. When the induced temperature rise heats the sample above a phase tran- sition temperature, a complete transformation into the new phase was observed. For 4Hb-TaSe2 we found that the recovery to the original state is significantly slower if the PLD was completely suppressed compared to only disturbing it. On 1T-TaS2 we could not only study the suppression of the original phase but also the formation of the higher energetic CDW phase. Long (100 ps) time constants were found for the tran- sition between the two phases. These suggest the presence of an energy barrier which has to be overcome in order to change the CDW phase. Pinning of the CDW by de- fects in the crystal structure result in such an energy barrier and consequently lead to a phase of domain growth which is considerably slower than pure electron or lattice dynamics.
AFRIKAANSE OPSOMMING: Dit is bekend dat lae-dimensionele materie fase oorgange ondergaan na anders ge- ori¨enteerde toestande wanneer afgekoel word tot laer temperature. Hierdie fases toon dikwels ’n periodiese modulasie van die elektron digtheid (genoem ’n “charge density wave” – CDW), tesame met ’n periodiese effek op die kristalrooster (genoem ’n “peri- odic lattice distortion” – PLD). Alhoewel baie eksperimente al uitgevoer is en al baie geleer is oor hierdie CDW fase, is die redes vir hul bestaan nog steeds nie ten volle verstaan nie. Baie prosesse, wat of sterk elektron–elektron of elektron–fonon interaksie toon, is al waargeneem en kan ’n rol speel in die verduideliking van die vorming van die verskillende fases onder verskillende omstandighede. Met die beskikbaarheid van femtosekonde lasers is dit nou moontlik om materie onder hoogs nie-ewewig voorwaardes te bestudeer. Deur skielik ’n bekende hoeveel- heid energie in die stelsel in te voer, word die ewewigstaat versteur en word die daar- opvolgende ontspanning prosesse waargeneem op die tydskaal van atomies struktu- rele en elektroniese bewiging. Hierdie eksperimente kan waardevolle inligting lewer oor die komplekse interaksies tussen die verskillende atomiese komponente van ge- kondenseerde materie, wat ontoeganklik sou wees onder ewewig voorwaardes. Ons gebruik elektrondiffraksie met tyd resolusie van onder ’n pikosekonde om die gedrag van ’n CDW stelsel te ondersoek nadat dit versteur is deur ’n kort laser puls. Van die waargenome veranderinge in die diffraksie patrone kan ons direk aflei watse veranderinge die kristalstruktuur van ons monster ondergaan. ’n Femtosekonde elektronendiffraksie opstelling is ontwikkel by die Lasernavors- ingsinstituut in Stellenbosch, Suid-Afrika. Kort laser pulse produseer foto-elektrone wat dan na ’n energie van 30 keV versnel word. Ten spyte van Coulomb afstoting ef- fekte, kan elektron pulse korter as 500 fs by die monster posisie bereik word. Tegniese besonderhede van hierdie opstelling, tegnieke van die voorbereiding van monsters asook analise metodes word volledig in hierdie tesis beskryf. Metings op twee voorbeelde van kwasi-tweedimensionele semi-metale, naamlik 4Hb-TaSe2 en 1T-TaS2, word gewys en bespreek. Beide wys ’n vinnige (subpikosekon- de) verandering as gevolg van die versteuring van die PLD en ’n vinnige verhitting van die kristalrooster. Wanneer die ge¨ınduseerde temperatuur bo die fase oorgang tempe- ratuur styg, is ’n volledige transformasie na die nuwe fase waargeneem. Vir 4Hb-TaSe2 het ons gevind dat die herstelling na die oorspronklike toestand aansienlik stadiger is as die PLD heeltemal viernietig is in vergelyking met as die PLD net versteur is. Met 1T-TaS2 kon ons nie net alleenlik die vernietiging van die oorspronklike fase sien nie, maar ook die vorming van ’n ho¨er energie CDW fase. Lang (100 ps) tydkonstante is gevind vir die oorgang tussen die twee fases. Hierdie dui op die teenwoordigheid van ’n energie-versperring wat eers oorkom moet word om die CDW fase voledig te ver- ander. Vaspenning van die CDW deur defekte in die kristalstruktuur veroorsaak so’n energie versperring en gevolglik lei dit tot ’n fase van groeiende CDW gebiede wat heelwat stadiger as pure elektron of kritalrooster dinamika is.
4
Qasim, Ilyas. "Structural and Electronic Phase Transitions in Mixed Transition Metal Perovskite Oxides." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10029.
Full textAbstract:
The reported multiferroic perovskite series Sr1-xAxTi1/2Mn1/2O3 has been the subject of numerous structural studies, without reaching consensus. In the current work, the cubic Pm3 ̅m is confirmed for end member SrTi1/2Mn1/2O3 in the Sr1-xAxTi1/2Mn1/2O3 ( A= Ca, La; 0 ≤ x ≤ 1) series. The Pm3 ̅m I4/mcm Pbnm structural evolution was observed with increased doping level of Ca. A cubic Pm3 ̅m rhombohedral R3 ̅c transition occurred when La is substituted instead of Ca. Interesting magnetic behaviours were observed and the major contribution to this was concluded to be the mixed Mn4+/Mn3+ ratio. Ru and Ir have almost identical ionic radii and behave similarly in many ways. Remarkably the structure and properties of SrRuO3 and SrIrO3 are different. The current study revealed that the divalent transition metal doped materials of the type SrR1-xMxO3 (R = Ru, Ir, and M = 3d transition metals) are isostructural. This was achieved by the synthesis of a number of new materials of the type SrIr1-xMxO3. Therefore, these two series are comparatively described in the thesis. The structure and physical properties of the iron doped series SrIr1-xFexO3 are found to be different from those of the divalent doped ones, and this was even true for Ru analogues. Therefore, Fe-doped SrRuO3 and SrIrO3, based on the results of the same level doped materials are presented in a separate chapter. In the final chapter, the impact of Cu2+ doping on the structure and electronic properties of LaCrO3 is described. In order to understand structure property relationships, all the materials structurally characterised have had magnetic and resistivity measurements conducted. Special attention is given to realise the correlations between structure, magnetism, and conductivity.
5
Dogbevia, Moses K. "Gas phase transition metal-cluster catalysis /." abstract and full text PDF (free order & download UNR users only), 2005. http://0-wwwlib.umi.com.innopac.library.unr.edu/dissertations/fullcit/3209128.
Full textAbstract:
Thesis (Ph. D.)--University of Nevada, Reno, 2005."August, 2005." Includes bibliographical references. Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2005]. 1 microfilm reel ; 35 mm.
6
Sopena, Miguel. "Hydrodynamics of the electroweak phase transition." Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/45752/.
Full textAbstract:
This work investigates the hydrodynamics of the expansion of the bubbles of the broken symmetry phase during the electroweak phase transition in the early universe, in which SU(2) electroweak symmetry is broken and fundamental particles acquire mass through the Higgs mechanism. The electroweak phase transition has received renewed attention as a viable setting for the production of the matter-antimatter asymmetry of the universe. The relevant mechanisms are strongly dependent on key parameters like the expansion velocity of the walls of bubbles of the new phase. In addition, the key dynamical parameters of the phase transition may generate signatures (like gravitational waves) which may become detectable in the near future. This work builds on existing hydrodynamical studies of the growth of bubbles of the broken symmetry phase and adapts them to novel scenarios, producing predictions of the wall velocity. The early universe at the time of the electroweak phase transition is modelled as a perfect relativistic fluid. A fundamental problem is to account for the interaction between the so-called cosmic 'plasma' and the bubble wall, which may slow down wall propagation and produce a steady state with finite velocity. This 'friction' is accounted for by a separate term in the hydrodynamical equations. This work adapts existing microphysical calculations of the friction to two physical models chosen because of their suitability as regards producing the baryon asymmetry of the universe: 1) An extension of the Standard Model with dimension-6 operators (for which this is the first calculation of the wall velocity ever produced) and 2) The Light Stop Scenario (LSS) of the Minimal Supersymmetric Standard Model (MSSM) (for which this is the first 2-loop calculation). The predicted values of the wall velocity are coherent and consistent with previous studies, confirming, in particular, the prediction of a low wall velocity for the LSS.
7
Wang, Changnan. "Gel phase transition and molecular recognition." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43921.
Full text
8
Furukawa, Akira. "Phase Transition Dynamics of Complex Fluids." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147797.
Full text
9
Thein, Ferdinand [Verfasser]. "Results for two phase flows with phase transition / Ferdinand Thein." Magdeburg : Universitätsbibliothek, 2018. http://d-nb.info/1165650487/34.
Full text
10
Arrachid, Abdessamad. "The phase transition analyzer : a tool to measure thermal transitions of biopolymers?" Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435986.
Full text
11
Eaglesham, D. J. "Charge density waves and their phase transitions in the transition metal chalcogenides." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375017.
Full text
12
Thompson, Ian. "Dynamic phase transitions in biased ensembles of particle systems with repulsive interactions." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665407.
Full textAbstract:
We study dynamic phase transitions in the constant-volume and constant- pressure ensembles of two different systems: a one-dimensional system of diffusive hard particles and a three-dimensional glass-former of nearly-hard repulsive particles. The dynamic transitions are observed using ensembles of trajectories biased with respect to their dynamic activity, biasing to greater or lower activities than equilibrium allows us to sample different dynamic phases. We perform finite-size scaling of the transitions with respect to sys- tem size and observation time, and compare them to first-order phase tran- sitions. The two ensembles are not equivalent in the one-dimensional model. We compare our results to analytic predictions for diffusive systems in both the active and inactive phases, there are structural signatures for both dy- namic regimes. The active phases show hyperuniform ordering and the inac- tive regimes show jamming behaviour, local jamming in the constant-volume ensemble is achieved through phase separation. In the three-dimensional sys- tem we observe a dynamic transition to a glassy inactive phase, there is no obvious structural change and the structural relaxation time increases sig- nificantly. We take configurations from the active and inactive phases and subject them to a jamming protocol in order to compare the final density of the jammed packings. Previous work shows that the inactive phase of glass-forming systems have a different distribution of vibrational modes and a higher compressibility, this suggests that the jamming behaviour should differ between the two phases. We show that jammed packings generated from inactive configurations are denser than those generated from active configurations.
13
Ponton, Alain. "Transition phase micellaire, phase éponge induite par laser dans une microémulsion." Bordeaux 1, 1989. http://www.theses.fr/1989BOR10549.
Full textAbstract:
Il est montre qu'un faisceau laser pouvait piloter un changement de structure dans un melange quaternaire dilue en tensioactif. La transition est induite entre une phase micellaire et une phase birefringente. Elle se traduit par une hysteresis de l'autofocalisation du faisceau traversant le milieu, en fonction de la puissance
14
Lavrskyi, Mykola. "Modélisation en fonctionnelle de la densité atomique des transformations de phases dans le système Fe-C à basse température." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMR003/document.
Full textAbstract:
Cette thèse a été centrée sur l’étude de la formation d’une phase martensitique dans les aciersFe-Ni-C et sur la diffusion des atomes de carbone dans cette phase à basse température. Lamodélisation à l’échelle atomique a été utilisée. Pour décrire ces phénomènes, deux approchesont été développées: un modèle discret basé sur la théorie de la fonction de densité atomique(ADF) et une approche quasiparticulaire basée sur la théorie atomique de Fratons (AFT). Dansun premier temps, pour montrer l’universalité de notre approche, nous avons appliqué l'AFTpour modéliser la cinétique d'auto-assemblage des atomes initialement désordonnés à desstructures ordonnées complexes. Cette approche a ensuite été appliquée à l'étude detransformation austénite/martensite. Il a été montré que le germe de martensite se développecomme agrégat multivariant dans la matrice austénitique. En utilisant des figures de pôles etdes diagrammes de diffraction simulés, ces variants ont été identifiés et comparés aux donnéesexpérimentales. La diffusion du carbone dans la phase de martensite a été étudiée en utilisantla théorie ADF. Deux systèmes avec différentes propriétés élastiques, Fe-C et Fe-Ni-C, ont étéconsidérés. Il a été montré qu’au cours du premier stade de vieillissement, les atomes decarbone subissent une décomposition spinodale sur les interstices octaédriques du réseautétragonal centré de martensite et forment les zones riches en carbone. Ensuite, la morphologie«tweed-like» des zones riches en carbone est développée. Les résultats des simulations sontun bon accord avec les images expérimentales obtenues par sonde atomique tomographique.La relation entre une mise en ordre de Zener et la concentration des zones riches en carbone aété discutéeThis thesis examines the formation of martensite in Fe-Ni-C steels and the diffusion of carbonatoms in this phase at low temperatures. To achieve this goal the atomistic modeling have beenused. To describe these phenomena two different approaches were developed: a discretemodel based on the Atomic Density Function (ADF) theory and the quasiparticle approachesbased on the Atomic Fraton Theory (AFT). First, the AFT was tested to model a self-assemblykinetics of initially disordered systems to three different classes of ordered one: singlecomponent crystals with fcc and diamond structures, two component crystals with zinc-blendstructure, and polymers with single-strand and double-stranded helixes structures. Then thisapproach was applied to model austenite/martensite transformation. It was shown thatmartensite nucleus grows as multivariant aggregate in austenite matrix. Using pole figures andsimulated diffraction patterns these variants were identified and compared with the experimentaldata. The carbon diffusion in martensite phase was studied using ADF theory. Two systemswith the different elastic properties corresponding to the Fe-C and Fe-Ni-C systems wereconsidered. It was shown that during a first stage of aging the carbon atoms undergo a spinodaldecomposition on the octahedral interstices of bcc lattice and form the carbon-rich zones. Then"tweed-like" morphology of carbon-rich zones is developed. The simulations results are a goodagreement with experimental images obtained by atom probe tomography. The relationbetween Zener ordering and the concentration of carbon reach zones is discussed
15
Du, Chengran. "Nonequilibrium phase transition in binary complex plasmas." Diss., lmu, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-152752.
Full text
16
Yamashita, Hiroki 1981. "Electroweak phase transition and singlet Majoron model." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101691.
Full textAbstract:
First, we review the basics of baryogenesis and models for baryogenesis in the early literature. Then, we discuss the main theme in this thesis, electroweak baryogenesis, which utilizes the electroweak phase transition. We present how the phase transition can be used to achieve baryogenesis. Next, we develop our model, which is the Standard Model with a singlet field coupled to the Higgs doublet negatively and to the right-handed neutrinos. It is a simple extension of the singlet Majoron model. We focus on numerical analysis of the model. Parameter space satisfying all the conditions are found and relevant quantities, such as the critical temperature, the Higgs mass, and the mixing angle are found as well. It turns out that LEP bound on the Higgs mass and the mixing angle is a strong constraint, and only a small fraction of parameter space is acceptable for attaining a strong enough phase transition for baryogenesis.
17
Butcher, C. "Gas-phase transition metal carbonyl cluster chemistry." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597163.
Full textAbstract:
The collision-induced dissociation (CID) of transition metal carbonyl clusters have been recorded and presented using the recently developed technique of energy-dependent electrospray ionisation mass spectrometry (EDESI). EDESI has been improved to incorporate breakdown graphs, allowing complete fragmentation data to be presented. EDESI spectra facilitate the assignment of all ligands, and assist in determining the composition of the cluster core. Electron autodetachment was observed upon ligand loss from multiply charged clusters. For certain clusters, a remarkable amount of structural information was extracted. For example, the structure of [{PtRu5C(CO)15}2Pt(CO)2]2- was correctly predicted from the EDESI spectrum. Photoelectron spectroscopy was carried out on three clusters and selected CID products in the gas phase. The photoelectron spectra for each species revealed a high density of electronic states, and a reduction in electron binding energy was observed on removal of CO ligands. For the dianionic clusters, electron binding energy was approximately zero where electron autodetachment was observed in the EDESI spectra. The gas-phase reactivity of a naked metal cluster has been studied with the use of a Fourier transform ion cyclotron resonance mass spectrometer. A novel “top down” approach has been used to form [CoRu3]- in the gas phase, by synthesising [PPN][CoRu3(CO)13] in the condensed phase and using CID in the electrospray ionisation source to strip the cluster of its ligands. The top down approach to gas phase clusters removes the requirement for a custom-built cluster source, and will allow the study of otherwise difficult to produce mixed-metal systems will interstitial ligands. The reactivity of [CoRu3]- with CH4 and H2 has been studied, and with use of tandem mass spectrometry, [CoRuC]- (a product of the reaction between [CoRu3]- and CH4) was isolated and further reacted with CH4.
18
Moon, Chang Man. "Molecular dynamics study of phase transition phenomena." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/12675.
Full textAbstract:
This computer simulation study carried out by classical the molecular dynamics technique (MD) investigates structural phase transitions of various atomic and molecular condensed matter systems. Particularly, our attention is focused on the signals for their observation. Classical nucleation theory is briefly reviewed in relation to the present study. An overall review is made on the methodology of the MD simulation technique such as the integration of the equations of motion, the rotational motion of molecules which is dealt with the four-component quaternion, and other various techniques involved with the simulation of atomic clusters, the simulation of bulk molecular systems using periodic boundary conditions, and isobaric molecular dynamics. There are also reviews on measurements of thermodynamic quantities which are monitored during the simulation including the pressure, the kinetic energy, and the potential energy as well as their corrections due to the spherical cutoff. In addition, various analysis techniques for the observation of the signals of structural phase transitions are discussed. All the potential functions used in this study are of the pairwise additive atom-atom Lennard-Jones interaction for both the atomic and the molecular systems. A small cluster of a binary mixture of krypton and argon atoms is studied by triggered breathing motions to investigate anharmonic motion which involves the structural phase transitions. A small cluster of krypton atoms is also simulated and discussed in detail concerning the very first moment of nucleation in relation to five-fold symmetric structures. In simulations of sulphurhexafluoride molecule systems, artifacts of finite size and periodic boundary conditions are investigated. Freezing the system by MD is investigated since it is known to supercool in computer simulations. Furthermore, accelerating the nucleation process by various methods such as shear flow, accelerated layer, inclusion of defect molecules, and pressure fluctuations is investigated.
19
Bukharaev, A. A., N. I. Nurgazizov, D. A. Biziaev, A. P. Chuklanov, and T. F. Khanipov. "Current-induced Phase Transition in Ni Nanowires." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35343.
Full textAbstract:
The single ferromagnetic Ni nanowires connecting two contact pads on the silicon oxide surface were
fabricated using the scanning probe nanolithography technique based on the nanoindentation of
polymethylmethacrylate resist and lift-off process. Wires with height from 9 to 26 nm, wide from 200 to
500 and length from 5 to 13 m were obtained. The atomic and magnetic force microscopy was used to
study the morphology and domain structure of the obtained nanowires. Multidomain and single-domain
structures depending on the width of the nanowires were observed. Current-induced phase transition from
ferromagnetic to paramagnetic state in the Ni nanowires was observed when studing of current-voltage
characteristics of such nanostructures. This phenomenon is explained by the Joule heating of ferromagnetic
Ni nanowires by the high-density current over Curie temperature.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35343
20
Bentley, Christopher David. "The phase transition of poly(N-isopropylacrylamide)." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539714.
Full text
21
Murray, Ryan. "Some Asymptotic Results For Phase Transition Models." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/824.
Full text
22
Choi, Man Yee. "Hygroscopicity and phase transition of atmospheric aerosols /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CENG%202004%20CHOI.
Full text
23
Grant, Stuart Alexander. "Phase transition behaviour in constraint satisfaction problems." Thesis, University of Leeds, 1997. http://etheses.whiterose.ac.uk/1273/.
Full textAbstract:
Many problems in artificial intelligence and computer science can be formulated as constraint satisfaction problems (CSPs). A CSP consists of a set of variables among which a set of constraints are imposed, with a solution corresponding to an assignment for every variable such that no constraints are violated. Most forms of CSP are NP-complete. Recent research has shown that the CSP exhibits a phase transition as a control parameter is varied. This transition lies between a region where most problems are easy and soluble, and a region where most problems are easy but insoluble. In the intervening phase transition region, the average problem difficulty is greatest. Phase transition behaviour can be exploited to create test beds of hard and easy problems for CSP algorithms. In this thesis, we study the phase transition of the binary CSP and examine various aspects of complete search algorithms for it. The phenomenon of exceptionally hard problems (`ehps') is examined in detail: these are rare searches on easy problems which become exceptionally expensive for a particular complete algorithm following a poor early search move. An explanation for the occurrence of ehps is proposed, and the relative susceptibility of certain algorithms to the phenomenon is explored. We then show that the phase transition paradigm can be applied to two tasks of polynomial cost complexity: attempting to establish arc and path consistency in a CSP. Phase transition behaviour analogous to that found when searching for a solution is demonstrated for these tasks, and the effectiveness and cost of establishing arc and path consistency is examined. The theme of establishing consistency in CSPs is extended by studying an algorithm which maintains arc consistency during search. Its performance is compared with that of an algorithm which maintains a lower level of consistency, and it is shown that the higher level of consistency reduces average search cost and ehp behaviour on many types of CSP. Finally, the subject of dynamically selecting the variable to instantiate at each stage in the search process is considered. We compare a number of heuristics which attempt to select the variable most likely to lead to failure, and show that the supposed principle behind these appears to be fundamentally flawed.
24
Seto, Yusuke. "Composition, symmetry and phase transition of scapolite." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/145099.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(理学)
甲第11333号
理博第2891号
新制||理||1431(附属図書館)
22976
UT51-2005-D84
京都大学大学院理学研究科地球惑星科学専攻
(主査)助教授 下林 典正, 教授 北村 雅夫, 教授 嶋本 利彦
学位規則第4条第1項該当
25
Sarkar, Sudipta Kumar. "Phase transition in Binary Liquid Crystalline Mixtures." Thesis, University of North Bengal, 2017. http://hdl.handle.net/123456789/2674.
Full text
26
Wang, Fang. "Quantum phase transitions and fluctuations in space charge doped one unit-cell Bi2Sr2CaCu2O8+x." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS436.
Full textAbstract:
La transition supraconducteur-isolant en deux dimensions est une transition de phase quantique continue à la température du zéro absolu provoquée par des paramètres externes tels que le désordre, le champ magnétique ou la concentration de porteurs. De telles transitions ont été induites dans une variété de supraconducteurs bidimensionnels en ajustant différents paramètres externes et étudiées avec une analyse de renormalisation de taille finie. Il y a cependant assez peu d'uniformité dans les résultats car à la fois les systèmes supraconducteurs et les paramètres externes sont divers. Dans cette thèse, nous avons d'abord fabriqué des échantillons BSCCO-2212 d'épaisseur d'une cellule unité et de grande qualité avec la technique de collage anodique, une méthode originale d'exfoliation développée dans notre laboratoire pour préparer des cristaux 2D de haute qualité à partir de matériaux lamellaires massifs. Ensuite, nous avons provoqué la transition supraconducteur-isolant dans les échantillons fabriqués de Bi2.1Sr1.9CaCu2O8+x monocouche par dopage par charge d'espace, qui est une technique efficace de dopage électrostatique à effet de champ. Nous avons déterminé les paramètres critiques associés et développé un moyen fiable d'estimer le dopage dans la région non supraconductrice, un problème crucial et central dans ces matériaux. L'analyse par renormalisation de taille finie donne un dopage critique de 0,057 trous/Cu, une résistance critique de ~ 6.85 kOhm et un produit d'exposant critiques νz ~ 1,57. Ces résultats, ainsi que des travaux antérieurs sur d'autres matériaux, fournissent une image cohérente de la transition supraconducteur-isolant et de sa nature bosonique dans le régime sous-dopé de la supraconductivité émergente dans les supraconducteurs à haute température critique. Ensuite, dans la dernière partie de cette thèse, nous avons également étudié les effets de l'inhomogénéité et des fluctuations sur la transition supraconductrice à l'échelle mésoscopique et nanoscopique à la fois avec des simulations et des mesures de transport. L'utilisation d'un échantillon ultra-mince facilite également l'analyse sur deux fronts. Tout d'abord, en deux dimensions, les phénomènes de fluctuation liés à la transition supraconductrice sont exacerbés, facilitant l'analyse des changements de largeurs. Deuxièmement, les aspects liés à la percolation et au clustering peuvent être facilement simulés et comparés à des modèles analytiques. En particulier, les effets des fluctuations sur le côté surdopé et sous-dopé du diagramme de phase d'une monocouche de BSCCO-2212 sont discutés. Nous avons découvert que le régime de fluctuation dans la partie sous-dopée du diagramme de phase est fondamentalement différent de celui dans la partie où p > 0,19. Nous avons discuté du comportement possible des paires de Cooper liées à nos résultats expérimentaux, ainsi que d'une des théories pouvant l'expliquer (transition BEC-BCS)The superconductor-insulator transition in two dimensions is a continuous quantum phase transition at absolute zero temperature driven by external parameters like disorder, magnetic field, or carrier concentration. Such transitions have been induced in a variety of two dimensional superconductors by tuning different external parameters and studied with a finite-size scaling analysis. There is however not much uniformity in the findings as both the superconducting systems and the tuning parameters are diverse. In this thesis, we first fabricated high quality of one unit-cell BSCCO-2212 samples with anodic bonding technique, an original method of exfoliation developed in our laboratory for preparing high quality 2D crystals from layered bulk materials. Then we revealed the superconductor-insulator transition in the fabricated one unit-cell Bi2.1Sr1.9CaCu2O8+x by space charge doping, which in an effective field effect electrostatic doping technique. We determined the related critical parameters and develop a reliable way to estimate doping in the non-superconducting region, a crucial and central problem in these materials. Finite-size scaling analysis yields a critical doping of 0.057 holes/Cu, a critical resistance of ~ 6.85 kΩ and a scaling exponent product νz ~ 1.57. These results, together with earlier work in other materials, provide a coherent picture of the superconductor-insulator transition and its bosonic nature in the underdoped regime of emerging superconductivity in high critical temperature superconductors. Then in the latter part of this thesis, we also investigated the effects of inhomogeneity and fluctuations on superconducting transition on mesoscopic and nanoscopic scale both with simulation and with simulations and with analysis of transport measurements. The use of an ultra-thin sample also facilitates analysis on two fronts. Firstly, in two dimensions fluctuation phenomena related to the superconducting transition are exacerbated, making the analysis of changes in widths easier. Secondly aspects related to percolation and clustering can be easily simulated and compared with analytical models. Especially, the effects of fluctuations on the overdoped and underdoped side of the phase diagram of one unit-cell BSCCO-2212 are discussed. We discovered that the fluctuation regime in the underdoped part of the phase diagram is fundamentally different from that in the part where p > 0.19. We discussed the possible behaviour of cooper pairs related to our experimental results, as well as one existing theoretical explanation (BEC-BCStransition)
27
Mitra, Sunanda. "Chalcogenide of type I-V-VI₂ for thermoelectric applications." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS562/document.
Full textAbstract:
Ce travail de thèse porte sur une série d’échantillons de composition nominale AgBiSe2-xSx (avec x= 0 à 2), appartenant à la famille des chalcogénures ternaires de type I-V-VI₂. Les analyses structurales et thermiques ont mis en évidence une solution solide complète sans gap de miscibilité, et des transitions de phase pour toutes les compositions. Nous avons pu obtenir des composés monophasés à la fois des phases hexagonale et cubique, et notre étude de DRX en température à mis en évidence une phase rhomboédrique pour certaines compositions (x=1 à 2 dans AgBiSexS2-x). Les résultats de DSC ont confirmé la présence de transitions de phase pour toutes les compositions, avec un déplacement des températures de transition en fonction de la fraction de soufre/sélénium. Notre étude de DRX sous pression de l’échantillon AgBiSe₂ a montré une transition de phase induite par la pression d’une phase hexagonale à rhomboédrique puis cubique. Suite à cette observation, l’application d’une pression chimique, par la substitution de 30% du Bi par du Sb a été utilisée avec succès pour stabiliser la phase cubique pour toutes les compositions. Le dopage par Nb des échantillons substitués par l’antimoine l’a pas eu d’influence sur la nature des phases stables à l’ambiante en comparaison aux échantillons non dopés. Nous avons ensuite étudié l’influence du dopage sur les propriétés de transport. Les valeurs négatives de S pour toutes les compositions indiquent un comportement de semi-conducteur de type n dans la gamme (50-300K). Par ailleurs, nos mesures ont montré à a fois de très faibles valeurs de κ mais aussi une décroissance de ∣S∣ et ρ avec l’augmentation de la fraction de Nb. Ces résultats devraient permettre d’optimiser le facteur de puissance pour améliorer les valeurs de ZT. Enfin, une étude en collaboration avec une équipe chinoise a permis d’obtenir une valeur de ZT de 1.3 à 890K dans un composé AgPbmSnSe₂Here, we report on a series of samples with nominal compositions AgBiSe2-xSx (with x= 0 to 2) belonging to the class of ternary chalcogenides of type I-V-VI₂. The structural and thermal analysis result shows a complete solid solution without miscibility gap and phase transitions for all compositions. We have succeeded in obtaining single phase compounds, of both hexagonal and cubic phase, and the high temperature XRD study showed the rhombohedral phase too for selected compositions (x=1 to 2 in AgBiSexS2-x). The DSC results confirmed the presence of the phase transitions for all compositions, with a shift of the temperature of transition as a function of the sulfur/selenium fraction. The high pressure XRD investigation of the compound AgBiSe₂ showed a pressure induced phase transition from hexagonal-to-rhombohedral-to-cubic phase. In this respect, chemical pressure with 30% Sb on the Bi site has been successfully applied to stabilize the cubic phase for all compositions. Nb doping in the Sb-substituted samples does not show any change in the phase behavior at RT in comparison with the undoped samples. The influence of doping on transport properties was analyzed. The negative value of S for all compositions indicates n-type semiconducting behavior over the range (50-300K). Further, the results not only shows very low value of κ but the ∣S∣ and ρ value also decreases for each composition from Nb fraction 0.02 to 0.04. This gives us the opportunity to optimize the power factor in order to improve the ZT value. At last, collaborative study with Chinese team showed that ZT of 1.3 at 890 K can be achieved for AgPbmSnSe2+m (m = 50)
28
Weber, Tobias [Verfasser]. "Dynamics at the Orbital Ordering Phase Transition in MgV2O4 and at the Ferromagnetic Phase Transition in MnSi / Tobias Weber." München : Verlag Dr. Hut, 2017. http://d-nb.info/1135596522/34.
Full text
29
Endo, Tomoki. "Hadron-quark matter phase transition and the mixed phase in hybrid stars." 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144167.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(理学)
甲第12084号
理博第2978号
新制||理||1444(附属図書館)
23920
UT51-2006-J79
京都大学大学院理学研究科物理学・宇宙物理学専攻
(主査)助教授 菅沼 秀夫, 教授 中村 卓史, 教授 畑 浩之
学位規則第4条第1項該当
30
Mouri, Abdelkader. "Optimisation, caractérisation et comportement physico-chimique dans les milieux modèles de nano-objets en phase inverse." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT207.
Full textAbstract:
Le projet de thèse, mené en collaboration avec le laboratoire Medesis Pharma, porte sur la mise au point de deux formulations pharmaceutiques, une microémulsion inverse et un gel colloïdal, à base de Pécéol®, lécithine, éthanol et eau. Le lithium indiqué dans le traitement de maladies neurodégénératives a été utilisé comme un modèle de principe actif hydrophile dans le cadre de ce projet. Ce travail a été initié par l’étude du comportement de phases du mélange quaternaire Pécéol®/lécithine/éthanol/eau, mettant essentiellement l’accent sur les différents paramètres impliqués dans les transitions de phases, dans le but de déterminer le rôle du Pécéol® et de la lécithine dans la structuration du système.- L’étude des propriétés structurales de la microémulsion, dans le domaine riche en Pécéol®, a montré que la structure du système n’est pas cohérente avec un modèle classique de micelles sphériques, l’hypothèse d’une structure localement lamellaire a été proposée. Les propriétés de solubilisation de la microémulsion ont été évaluées par l’élaboration d’une série de diagrammes de phases pseudo-ternaires, en faisant varier le rapport éthanol/lécithine. Une efficacité optimale a été obtenue pour un rapport éthanol/lécithine égal à 40/60. La formulation optimisée est capable d’incorporer efficacement le lithium (Li), à des concentrations acceptables sans altérer la stabilité du système. L’étude des propriétés d’incorporation du Li dans la microémulsion a montré que le mécanisme d’encapsulation est compatible avec un modèle d’interactions de type drug-surfactant. Les résultats des études de stabilité de la microémulsion vide et chargée en Li menées selon les conditions ICH sont satisfaisants.- La structuration du gel clair, dans le domaine riche en lécithine, a été suivie par des analyses de rhéologie et de microscopie en lumière polarisée en fonction du rapport lécithine/Pécéol®. Les résultats ont montré que les propriétés rhéologiques du gel peuvent être modifiées en ajustant le rapport lécithine/Pécéol®. La caractérisation de la structure du gel clair par diffraction de rayons X aux petits angles (SAXS) et cryofracture conjuguée à la microscopie électronique en transmission (FF-TEM) a mis en évidence une structure anisotrope hexagonale H2. Alors que dans le domaine riche en eau, une structure anisotrope hexagonale inverse H2 et lamellaire Lα a été mise en évidence. Les propriétés rhéologiques modulables du gel dans le domaine riche en lécithine ainsi que sa grande capacité de rétention d’eau, sont particulièrement intéressantes pour une application du gel clair dans le domaine de pharmaceutique et/ou cosmétiqueThis thesis project, carried out in collaboration with Medesis Pharma laboratory, is about the development of two pharmaceutical formulations, a reverse microemulsion and a colloidal gel, based on Pécéol®, lécithine, ethanol and water. The indicated lithium in the treatment of neurodegenerative diseases has been used as a hydrophilic principal active model for this project. This work started with the study of the phase behavior of the four component system Pécéol®/lecithin/éthanol/water, focusing primarily on the various parameters involved in phase transitions in order to determine the role of Pécéol® and lecithin in the structuring of the system.- The study of the structural properties of the reverse microemulsion, in the Pécéol® rich domain, showed that the system structure is not coherent with a classical model of spherical micelles, a hypothesis of a local lamellar structure was proposed. The solubilization properties of the microemulsion were evaluated following the development of a series of pseudo-ternary phase diagrams, by varying the ethanol/lecithin ratio. Optimal efficiency was obtained for an ethanol/lecithin ratio of 40/60. The optimized formulation is capable of effectively incorporating lithium (Li) to acceptable concentrations without altering the stability of the system. The study of the incorporation properties of Li in the microemulsion has shown that the encapsulation mechanism is compatible with drug-surfactant binding model. The results of the stability studies of the free and Li loaded microemulsion, conducted according to ICH conditions, are satisfactory.- The gel structuring was followed, in the lecithin rich domain, through rheological and optical microscopy analyses, according to lecithin/Pécéol® ratio. Results showed that the rheological properties of the gel can be modified by adjusting the lecithin/Pécéol® ratio. Moreover, the characterization of the gel structure through Small Angle X-Ray Scattering (SAXS) and Freeze Fracture-Transmission Electron Microscopy (FF-TEM) showed an inverse hexagonal phase H2. While, in the water rich region, an inverse hexagonal H2 and lamellar Lα phases were identified. The adjustable rheological properties of the clear gel, and its great water solubilisation capacity, are particularly interesting for the application of the gel in pharmaceutical and/or cosmetic fields
31
Mouri, Abdelkader. "Optimisation, caractérisation et comportement physico-chimique dans les milieux modèles de nano-objets en phase inverse." Electronic Thesis or Diss., Montpellier, 2016. http://www.theses.fr/2016MONTT207.
Full textAbstract:
Le projet de thèse, mené en collaboration avec le laboratoire Medesis Pharma, porte sur la mise au point de deux formulations pharmaceutiques, une microémulsion inverse et un gel colloïdal, à base de Pécéol®, lécithine, éthanol et eau. Le lithium indiqué dans le traitement de maladies neurodégénératives a été utilisé comme un modèle de principe actif hydrophile dans le cadre de ce projet. Ce travail a été initié par l’étude du comportement de phases du mélange quaternaire Pécéol®/lécithine/éthanol/eau, mettant essentiellement l’accent sur les différents paramètres impliqués dans les transitions de phases, dans le but de déterminer le rôle du Pécéol® et de la lécithine dans la structuration du système.- L’étude des propriétés structurales de la microémulsion, dans le domaine riche en Pécéol®, a montré que la structure du système n’est pas cohérente avec un modèle classique de micelles sphériques, l’hypothèse d’une structure localement lamellaire a été proposée. Les propriétés de solubilisation de la microémulsion ont été évaluées par l’élaboration d’une série de diagrammes de phases pseudo-ternaires, en faisant varier le rapport éthanol/lécithine. Une efficacité optimale a été obtenue pour un rapport éthanol/lécithine égal à 40/60. La formulation optimisée est capable d’incorporer efficacement le lithium (Li), à des concentrations acceptables sans altérer la stabilité du système. L’étude des propriétés d’incorporation du Li dans la microémulsion a montré que le mécanisme d’encapsulation est compatible avec un modèle d’interactions de type drug-surfactant. Les résultats des études de stabilité de la microémulsion vide et chargée en Li menées selon les conditions ICH sont satisfaisants.- La structuration du gel clair, dans le domaine riche en lécithine, a été suivie par des analyses de rhéologie et de microscopie en lumière polarisée en fonction du rapport lécithine/Pécéol®. Les résultats ont montré que les propriétés rhéologiques du gel peuvent être modifiées en ajustant le rapport lécithine/Pécéol®. La caractérisation de la structure du gel clair par diffraction de rayons X aux petits angles (SAXS) et cryofracture conjuguée à la microscopie électronique en transmission (FF-TEM) a mis en évidence une structure anisotrope hexagonale H2. Alors que dans le domaine riche en eau, une structure anisotrope hexagonale inverse H2 et lamellaire Lα a été mise en évidence. Les propriétés rhéologiques modulables du gel dans le domaine riche en lécithine ainsi que sa grande capacité de rétention d’eau, sont particulièrement intéressantes pour une application du gel clair dans le domaine de pharmaceutique et/ou cosmétiqueThis thesis project, carried out in collaboration with Medesis Pharma laboratory, is about the development of two pharmaceutical formulations, a reverse microemulsion and a colloidal gel, based on Pécéol®, lécithine, ethanol and water. The indicated lithium in the treatment of neurodegenerative diseases has been used as a hydrophilic principal active model for this project. This work started with the study of the phase behavior of the four component system Pécéol®/lecithin/éthanol/water, focusing primarily on the various parameters involved in phase transitions in order to determine the role of Pécéol® and lecithin in the structuring of the system.- The study of the structural properties of the reverse microemulsion, in the Pécéol® rich domain, showed that the system structure is not coherent with a classical model of spherical micelles, a hypothesis of a local lamellar structure was proposed. The solubilization properties of the microemulsion were evaluated following the development of a series of pseudo-ternary phase diagrams, by varying the ethanol/lecithin ratio. Optimal efficiency was obtained for an ethanol/lecithin ratio of 40/60. The optimized formulation is capable of effectively incorporating lithium (Li) to acceptable concentrations without altering the stability of the system. The study of the incorporation properties of Li in the microemulsion has shown that the encapsulation mechanism is compatible with drug-surfactant binding model. The results of the stability studies of the free and Li loaded microemulsion, conducted according to ICH conditions, are satisfactory.- The gel structuring was followed, in the lecithin rich domain, through rheological and optical microscopy analyses, according to lecithin/Pécéol® ratio. Results showed that the rheological properties of the gel can be modified by adjusting the lecithin/Pécéol® ratio. Moreover, the characterization of the gel structure through Small Angle X-Ray Scattering (SAXS) and Freeze Fracture-Transmission Electron Microscopy (FF-TEM) showed an inverse hexagonal phase H2. While, in the water rich region, an inverse hexagonal H2 and lamellar Lα phases were identified. The adjustable rheological properties of the clear gel, and its great water solubilisation capacity, are particularly interesting for the application of the gel in pharmaceutical and/or cosmetic fields
32
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.
Full textAbstract:
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.
33
Chu, Fan. "The ferroelectric phase transition in complex perovskite relaxors /." [S.l.] : [s.n.], 1994. http://library.epfl.ch/theses/?nr=1248.
Full text
34
Takahashi, Katsunori. "SWELLING AND VOLUME PHASE TRANSITION OF POLYMER GELS." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150686.
Full text
35
Kamikado, Kazuhiko. "Chiral phase transition in QCD with critical fluctuation." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/175113.
Full text
36
Falicki, Slawomir. "Two-phase system and transition metal catalyzed reactions." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5663.
Full textAbstract:
The first examples of the application of biphasic and phase transfer catalysis to early-transition-metal organometallic chemistry are described. These include very efficient and convenient syntheses of the ($\eta\sp5$-cyclopentadienyl)tricarbonylhydridovanadate anion under remarkably mild biphasic conditions. The latter is capable of effecting, under phase transfer conditions, the reduction of halides, sterically encumbered nitro compounds, and the cyclodehydration of $\alpha,\beta$-unsaturated ketones. The reactions may proceed via electron transfer pathways. The use of nickel cyanide under biphasic or phase transfer conditions converts vinyl epoxides to the unsaturated ketones and/or unsaturated $\delta$-hydroxyacids. These results represent the first examples of the use of transition-metal complexes in catalytic-two-phase isomerization of vinyl epoxides. The key catalytic species is believed to be the cyanocarbonylnickel anion, participation of which has been proposed in the reaction mechanism. O-Benzyl oxime ethers were obtained in modest yields by the exposure of benzylic bromides to nitric oxide, a palladium(0) or ruthenium complex as the catalyst, aqueous sodium hydroxide, benzene as the organic phase and a quarternary ammonium salt as phase transfer agent. This provides the first example of a catalytic reaction of halides which involves free or co-ordinated nitric oxide and is also a novel process in the area of a phase transfer catalysis utilizing nitric oxide as a reactant.
37
Wehbe, Charbel. "Étude asymptotique de modèles en transition de phase." Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2311/document.
Full textAbstract:
Ce rapport de thèse est consacré à l'étude de modèles de champ de phase de type Caginalp. Nous considérons ici, deux parties : la première étant une généralisation du modèle de champ de phase de Caginalp basée sur la loi de Maxwell-Cattaneo et la seconde traite le même modèle dans sa version conservative. L'étude dans les deux parties est faite dans un domaine borné. De plus, dans la première partie on distingue les cas de conditions aux bords de type Dirichlet ainsi que Neumann, tandis que dans la deuxième partie le modèle est étudié uniquement avec les conditions Dirichlet (avec un potentiel régulier puis un potentiel singulier). Tout d'abord, l'existence, l'unicité, et la régularité des solutions sont analysées aux moyens d'arguments classiques. Ensuite, l'existence d'ensembles bornés absorbants est établie. Enfin, dans certains cas, l'existence de l'attracteur global et d'attracteurs exponentiels sont analysésThis thesis report is devoted to the study of Caginalp type phase-field Models. Here, we consider two parts : the first is a generalization of the Caginalp type phase-field model based on a generalization of the Maxwell-Cattaneo law and the second with the same model in its conservative version. The study in the two parts is made in a bounded domain. In addition, in the first part we distinguish cases of boundary conditions of Dirichlet and Neumann, while in the second part the model is studied only with Dirichlet conditions (with a regular potential and a singular potential). First, the existence, uniqueness, and regularity of solutions are analyzed by means of classical arguments. Then, the existence of bounded absorbing sets is established. Finally, in some cases, the existence of the global attractor and exponential attractors are analyzed
38
Wincure, Benjamin 1966. "Computational modeling of a liquid crystal phase transition." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103308.
Full textAbstract:
This thesis numerically solves the tensor order parameter continuum theory equations for nematic liquid crystals to investigate liquid crystal texturing mechanisms during an isotropic to nematic phase transition in a bulk unstable isotropic phase and next to solid surfaces. The Time Dependent Ginsburg Landau equation with a Landau de Gennes Helmholtz free energy density description is used to predict the shapes, textures and defect mechanisms that occur in the expanding droplets and films of a 4'-pentyl-4-cyanobiphenyl (5CB) nematic phase immediately after their nucleation from an unstable isotropic phase, due to a temperature quench. To create a robust simulation method able to tackle high curvature, defect nucleation, heterogeneous substrates and phase ordering interfaces, particular attention was paid to adapting the mathematical model and computational methods to what was previously known about the nucleation and growth events that occur experimentally during a bulk 5CB isotropic to nematic phase transition and next to decorated solid surfaces. The numerical simulations provide detailed predictions about (i) growth rates for different temperature quenches, (ii) structure of the isotropic-nematic interface, (iii) shapes of expanding nano and submicron nematic droplets, (iv) texturing within growing nano and submicron nematic droplets, (v) a new defect formation mechanism called "interfacial defect shedding", and (vi) the effect of contact angle and interface curvature next to a solid surface with anchoring switches. The main contributions of this thesis are its detailed predictions that emerge from the liquid crystal simulation results, the careful adaptation of the mathematical model and numerical method to what is currently known about early stage growth in a nematic liquid crystal phase, and the validation of new theory by the simulation results.
39
Swainson, Ian Peter. "The phase transition and dynamic disorder in cristobalite." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281903.
Full text
40
Storey, Marianne. "Effect of disorder on the melting phase transition." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322000.
Full text
41
甄冠僑 and Koon-kiu Yan. "Phase transition of certain iterative cellular automation models." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B42575382.
Full text
42
Benson, Kevin E. C. "Aspects of the electroweak phase transition and baryogenesis." Thesis, University of Oxford, 1993. http://ora.ox.ac.uk/objects/uuid:27c64513-bbb7-4f94-b385-4e691354a7b5.
Full textAbstract:
In this thesis we study aspects of the cosmological electroweak phase transition which are relevant to the possibility of baryogenesis at this epoch. We focus on two issues: first, requiring that the observed baryon number be of electroweak origin places strong constraints on electroweak physics, and second, baryogenesis at the electroweak scale may be driven by an asymmetry generated at the GUT scale. We use the effective potential at finite temperature as a means of analyzing phase transitions associated with spontaneous symmetry breaking. We develop the theory with two basic examples: the scalar and Abelian Higgs models. Infrared divergences near the phase transition make the one-loop description unreliable, and indeed invalidate conventional perturbation theory. Borrowing a method from studies of QCD at high temperatures, we demonstrate that the summation of ring diagrams cures the leading infrared divergences and achieves a more reliable perturbative expansion. We then apply this formalism to the minimal Standard Model, following previous work, and confirm weak first-order behavior at the phase transition. We show that requiring the baryon number not be erased by sphaleron processes after the phase transition places a stringent bound on the Higgs mass, which is incompatible with experiment. This cosmological bound, however, may be relaxed by extending the scalar sector of the Standard Model. We consider the two simplest such extensions, the addition of a gauge singlet and of a second doublet. We demonstrate that ring-improvement in the singlet extension alters previous arguments at the one-loop level and yields a more restrictive bound on the Higgs mass. While ring-improvement in the two-doublet model, in principle, also reduces the Higgs mass bound found earlier at one loop, the multitude of new couplings in this model does not permit a definitive statement. We then investigate a mechanism for generating the observed baryon asymmetry (nB/S~ 10-10) at the electroweak phase transition from a pre-existing leptonic asymmetry (LT/s~ 10-5) produced at the GUT scale. This mechanism works by charge transport in a strongly first-order phase transition and avoids the need for large CP-violation at the electroweak scale.
43
Goudochnikov, Pavel. "The cubic phase transition in 2:4 perovskites." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417767.
Full text
44
Daniels, Christopher. "On the phase transition in certain percolation models." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687311.
Full textAbstract:
Consider random sequential adsorption on a chequerboard lattice with arrivals at rate 1 on light squares and at rate λ on dark squares. Ultimately, each square is either occupied, or blocked by an occupied neighbour. Colour the occupied dark squares and blocked light sites black, and the remaining squares white. Independently at each meeting-point of four squares, allow diagonal connections between black squares with probability p; otherwise allow diagonal connections between white squares. We show that there is a critical surface of pairs (λ, p), containing the pair (1,0.5), such that for (λ, p) lying above (respectively, below) the critical surface the black (resp. white) phase percolates, and on the critical surface neither phase percolates. We find conditions satisfied by a broad class of essentially planar percolation models such that for a model satisfying the conditions, the presence or absence of percolation is determined by what happens in a collection of finite boxes. This criterion applies to a (non-degenerate) Poisson Boolean model, to the random connection model for some sufficiently high p < 1, and to the model described above. We also find conditions that do not require rotation invariance which produce a comparable result; these conditions seem plausible, but finding non-trivial examples is a matter for further research.
45
Yu, Xiaohong. "Polymer interactions and the phase transition of gels." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12451.
Full text
46
Dunlap, Terrence L. "Nanoscale near-field imaging of VO2 phase transition." Thesis, California State University, Long Beach, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1600042.
Full textAbstract:
A large focus of this thesis was developing the experimental procedures involved in imaging VO2 during the heating process. In order to study light interactions between an induced dipole and a sample surface to collect various data on its topography, amplitude and phase. Data is collected using a near-eld microscope (s-SNOM) and analyzed using various software that, normalize, lter and display the data in false color image. Specically, research behind this thesis, focuses on the phase transition of Vanadium Dioxide (VO2) as it goes from an insulating to fully metallic phase. Using a wavelength of λ = 10:7μm to image the resonant behavior of the sample, the nucleation of VO2 was imaged as the temperature increased.
47
MANDLER, JACQUES. "Sur la transition de phase de 3-sat." Paris 6, 2000. http://www.theses.fr/2000PA066530.
Full textAbstract:
Dans la premiere partie, nous explorons une nouvelle methode pour trouver les valeurs asymptotiques de sommes de nombres complexes du type s n = n k = 0f n (k). Posant f n(x) = f n (nx), nous avons constate empiriquement que souvent, dans des situations ou la methode du col s'applique a i (f n) = 1 0 f n (x) dx, la quantite ni (f n) constitue un equivalent asymptotique, voire exact de s n. Des exemples typiques sont des sommes alternees de nombres reels, et, contrairement a celles jusqu'ici connues, cette procedure semble d'application assez large. Des resultats partiels sont presentes en vue d'une justification theorique, dont l'un au moins semble prometteur. Parmi nos exemples, signalons un calcul par inclusion-exclusion redonnant la borne superieure de 4. 64 pour le seuil de 3-sat obtenue en 1995 par o dubois et y. Boufkhad. La seconde partie introduit un nouvelle idee dans l'etude du probleme k-sat aleatoire, celle de formule booleenne aleatoire typique ; cette notion est ensuite appliquee a la preuve d'une borne superieur de 4. 506 pour le seuil de 3-sat, la meilleure actuellement etablie de facon rigoureuse. Bien qu'on ne puisse donner un definition canonique, une formule aleatoire typique est essentiellement une formule susceptible de sortir effectivement d'un generateur logiciel. Les techniques mises en uvre dans notre preuve proviennent principalement de l'analyse reelle et des probabilites (grandes deviations). Bien qu'il s'agisse de techniques assez repandues, la preuve elle-meme est longue et complexe.
48
Возний, Андрій Андрійович, Андрей Андреевич Возный, Andrii Andriiovych Voznyi, Володимир Володимирович Косяк, Владимир Владимирович Косяк, and Volodymyr Volodymyrovych Kosiak. "Thermally induced phase transition in SnxSy thin films." Thesis, E-MRS (European Materials Research Society), 2016. http://essuir.sumdu.edu.ua/handle/123456789/46278.
Full textAbstract:
Presently, the earth-abundant and non-toxic SnS2 and SnS compounds could be considered as the promising optoelectronic material. This is due the fact that SnS2 has n-type conductivity, high carrier mobility and wide band gap of 2.2 eV. SnS2 films were obtained by the close-spaced vacuum sublimation method.
49
Duflot-Flandrois, Véronique. "Signaux de transition de phase des systèmes finis." Caen, 2001. http://www.theses.fr/2001CAEN2069.
Full textAbstract:
Les transistions de phase sont des phénomènes communs à tous les systèmes en interaction. Pour des systèmes infinis, elles sont bien décrites par la thermodynamique mais celle-ci ne peut plus être utilisée pour des petits systèmes comme le noyau de l'atome. Nous proposons une approche de mécanique statistique, afin d'extraire les caractéristiques thermodynamiques des petits systèmes ouverts et soumis à des forces non saturantes. Nous nous concentrons en particulier sur la définition et la mise en évidence pour de tels systèmes d'une transition de phase de type liquide gaz. Nous définissons des observables théoriques et expérimentales qui permettent de signer sans ambigui͏̈té la présence et l'ordre de la transition. Une observable pertinente et accessible expérimentalement est la fluctuation d'énergie cinétique, pour une valeur fixée de l'énergie totale. Nous vérifions qu'à l'intérieur de la zone de coexistence, ces fluctuations deviennent anormalement grandes et s'accompagnent de comportements pseudo critiques pour la distribution en taille des fragments. Nous obtenons ces résultats dans le cadre du modèle du gaz sur réseau, avec un hamiltonien de plus proches voisins. Afin de compléter cette étude, nous analysons le comportement des observables lorsque les interactions sont à longue portée. Nous nous concentrons sur la problématique nucléaire en considérant l'effet des interactions coulombiennes. Enfin nous abordons en perspectives des points spécifiques à la physique nucléaire : le rôle de l'isospin et des effets quantiques.
50
Yan, Koon-kiu. "Phase transition of certain iterative cellular automation models." Click to view the E-thesis via HKUTO, 1999. http://sunzi.lib.hku.hk/hkuto/record/B42575382.
Full text