Dissertations / Theses: 'Afterglow (Physics) – Mathematical models'

1

Kowalewski, Jacob. "Mathematical Models in Cellular Biophysics." Licentiate thesis, KTH, Applied Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4361.

Full text

Abstract:

Cellular biophysics deals with, among other things, transport processes within cells. This thesis presents two studies where mathematical models have been used to explain how two of these processes occur.

Cellular membranes separate cells from their exterior environment and also divide a cell into several subcellular regions. Since the 1970s lateral diffusion in these membranes has been studied, one the most important experimental techniques in these studies is fluorescence recovery after photobleach (FRAP). A mathematical model developed in this thesis describes how dopamine 1 receptors (D1R) diffuse in a neuronal dendritic membrane. Analytical and numerical methods have been used to solve the partial differential equations that are expressed in the model. The choice of method depends mostly on the complexity of the geometry in the model.

Calcium ions (Ca²⁺) are known to be involved in several intracellular signaling mechanisms. One interesting concept within this field is a signaling microdomain where the inositol 1,4,5-triphosphate receptor (IP₃R) in the endoplasmic reticulum (ER) membrane physically interacts with plasma membrane proteins. This microdomain has been shown to cause the intracellular Ca²⁺ level to oscillate. The second model in this thesis describes a signaling network involving both ER membrane bound and plasma membrane Ca²⁺ channels and pumps, among them store-operated Ca²⁺ (SOC) channels. A MATLAB^® toolbox was developed to implement the signaling networks and simulate its properties. This model was also implemented using Virtual cell.

The results show a high resemblance between the mathematical model and FRAP data in the D1R study. The model shows a distinct difference in recovery characteristics of simulated FRAP experiments on whole dendrites and dendritic spines, due to differences in geometry. The model can also explain trapping of D1R in dendritic spines.

The results of the Ca²⁺ signaling model show that stimulation of IP3R can cause Ca²⁺ oscillations in the same frequency range as has been seen in experiments. The removing of SOC channels from the model can alter the characteristics as well as qualitative appearance of Ca²⁺ oscillations.

Cellulär biofysik behandlar bland annat transportprocesser i celler. I denna avhandling presenteras två studier där matematiska modeller har använts för att förklara hur två av dess processer uppkommer.

Cellmembran separerar celler från deras yttre miljö och delar även upp en cell i flera subcellulära regioner. Sedan 1970-talet har lateral diffusion i dessa membran studerats, en av de viktigaste experimentella metoderna i dessa studier är fluorescence recovery after photobleach (FRAP). En matematisk modell utvecklad i denna avhandling beskriver hur dopamin 1-receptorer (D1R) diffunderar i en neural dendrits membran. Analytiska och numeriska metoder har använts för att lösa de partiella differentialekvationer som uttrycks i modellen. Valet av metod beror främst på komplexiteten hos geometrin i modellen.

Kalciumjoner (Ca2+) är kända för att ingå i flera intracellulära signalmekanismer. Ett intressant koncept inom detta fält är en signalerande mikrodomän där inositol 1,4,5-trifosfatreceptorn (IP3R) i endoplasmatiska nätverksmembranet (ER-membranet) fysiskt interagerar med proteiner i plasmamembranet. Denna mikrodomän har visats vara orsak till oscillationer i den intracellulära Ca2+-nivån. Den andra modellen i denna avhandling beskriver ett signalerande nätverk där både Ca2+-kanaler och pumpar bundna i ER-membranet och i plasmamembranet, däribland store-operated Ca2+(SOC)-kanaler, ingår. Ett MATLAB®-verktyg utvecklades för att implementera signalnätverket och simulera dess egenskaper. Denna modell implementerades även i Virtual cell.

Resultaten visar en stark likhet mellan den matematiska modellen och FRAP-datat i D1R-studien. Modellen visar en distinkt skillnad i återhämtningsegenskaper hos simulerade FRAP-experiment på hela dendriter och dendritiska spines, beroende på skillnader i geometri. Modellen kan även förklara infångning av D1R i dendritiska spines.

Resultaten från Ca2+-signaleringmodellen visar att stimulering av IP3R kan orsaka Ca2+-oscillationer inom samma frekvensområde som tidigare setts i experiment. Att ta bort SOC-kanaler från modellen kan ändra karaktär hos, såväl som den kvalitativa uppkomsten av Ca2+-oscillationer.

APA, Harvard, Vancouver, ISO, and other styles

2

Burnham, Christian James. "Structural and dynamical properties of mathematical water models." Thesis, University of Salford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299208.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Zhu, Dewei. "Development and validation of mathematical models for chemical vapor deposition processes /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487686243822723.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Bougenaya, Yamina. "Fermion models on the lattice and in field theory." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7080/.

Full text

Abstract:

The first part deals with lattice approach to field theories. The fermion doubling problems are described. This doubling can be removed if a dual lattice is introduced, as first pointed out by Stacey. His method is developed and in the process a formalism for the construction of a covariant difference lattice operator and thus of a gauge invariant action, is exhibited. It is shown how this formalism relates to the work of Wilson. Problems of gauge invariance can be traced back to the absence of the Leibnitz rule on the lattice. To circumvent this failure the usual notion of the product is replaced by a convolution. The solutions display a complementarity : the more localised the product the more extended is the approximation to the derivative and vice-versa. It is found that the form of the difference operator in the continuous limit dictates the formulation of the full two-dimensional supersymmetric algebra. The construction of the fields necessary to form the Wess-Zumino model follows from the requirement of anticommutativity of the supersymmetric charges. In the second part, the Skyrme model is reviewed and Bogomolnyi conditions are defined and discussed. It appears that while the Skyrme model has many satisfactory features, it fails to describe the interactions between nucleons correctly. These problems are brought out and the available solutions reviewed.

APA, Harvard, Vancouver, ISO, and other styles

5

Li, Hongjie. "Mathematical study on plasmon materials and their applications." HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/642.

Full text

Abstract:

This thesis is concerned with the mathematical analysis of plasmon materials and their applications, including the cloaking effect and the super-resolution in imaging induced by plasmon resonances. We consider these phenomena in two regimes, namely, the quasi-static regime and the finite-frequency regime beyond the quasi-static approximation. In the quasi-static regime, we first show that the plasmon resonance could occur for the elastic system in both two and three dimensions. By establishing the primal and dual variational principles and constructing the perfect plasmon waves, we prove that the plasmon resonance can occur for a delicate plasmonic configuration with appropriately choosing Lame parameters. We also apply the spectral method to show the phenomenon of cloaking due to anomalous localized resonance (CALR) through analyzing the spectral system of the Neumann-Poincare (N-P) operator. Moreover, based on the obtained spectral properties of the N-P operator, we strictly verify the plasmon resonance in the quasi-static approximation and construct a general and novel class of plasmonic configurations to ensure the occurrence of the CALR, which significantly generalizes the existing research on plasmon resonances in the literature. Finally, we derive the perturbed displacement field associated with a given elastic source field with the presence of nanoparticles. By analyzing the spectral properties of the associated Neumann-Poincare operator, the leading-order term of the perturbed elastic wave field is determined, which could help to achieve the super-resolution in the elastic imaging. For the case beyond the quasi-static approximation, we develop two approaches to achieve the plasmon resonance. The first one is achieved by the explicit construction, though it is very delicate and subtle. We first show that the cloaking due to anomalous localized resonance could occur for the Helmholtz system within finite frequencies beyond the quasi-static approximation. More precisely, by investigating the spectral system of the corresponding Neumann-Poincare operator within finite frequencies, we include the plasmon parameters, the shape of the plasmonic inclusion and the source term as a whole system to achieve the phenomenon of the cloaking due to anomalous localized resonance. Furthermore, we show that the surface plasmon resonance and the cloaking effect can occur for the Maxwell system beyond the quasi-static approximation by calculating the spectral system of the matrix-valued integral operator. The other one is achieved via the localization and geometrization. Through the investigation on the eigenfunctions of the corresponding Neumann-Poincare operator, we show that the plasmon resonance occurs locally near the high-curvature point of the plasmonic inclusion. It is worth mentioning that we present the first investigation in the literature on the geometric structures of the Neumann-Poincare eigenfunctions.

APA, Harvard, Vancouver, ISO, and other styles

6

Oh, Joung Hoon. "Behavior of an ion in a bubble in the ground state." PDXScholar, 1991. https://pdxscholar.library.pdx.edu/open_access_etds/4193.

Full text

Abstract:

Deuterons might be trapped in a bubble embryo which occur s due to statistical fluctuation in heavy water. The size of the bubble embryo is expected to be an order of a small molecule. The ground state energy level which the deuteron may occupy in the bubble is calculated by solving the Schroedinger equation, and by considering the interaction between the trapped deuteron by a spherical bubble and the surrounding polarized liquid medium (heavy water). From the dependence of the energy eigenvalue of the ground state on the bubble radius, the pressure exerted on the bubble wall is obtained. It is found that the pressure is negatively very large if the bubble radius is about the molecular size (3 to 7 Å). From extrapolating this result to larger sizes, we expect that a bubble would quickly collapse if enough energy is supplied and never grows to a stable bubble when the deuteron is trapped in the ground state.

APA, Harvard, Vancouver, ISO, and other styles

7

Beylin, Andrey V. "Supersymmetric Landau Models." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/624.

Full text

Abstract:

This work is focused on the different supersymmetric extensions of the Landau model. We aim to fully solve each model and describe its energy levels, wavefunctions, Hilbert space and define a norm on it, as well as find symmetry generators and transformations with respect to them. Several possible generalizations were considered before. It was found for Landau model on the so called Superflag manifold as well as planar Superflag and Superplane Landau models that standard norm on the Hilbert space is not positive definite. Later for planar cases it was found that it is possible to fix this by introducing a new norm which will be invariant and positive definite. Surprisingly this procedure brings up "hidden" symmetries for the known super Landau models. In the dissertation we apply the same procedure for Landau model on superpshere and Superflag manifolds. It turns out that superpsherical Landau model is equivalent to the Superflag model with one of the parameters fixed. Because the model on superpshere can be recovered from the Superflag we will do calculations of corrected norm only for the Superflag. After this we develop a different generalization of the Superplane Landau model. Starting with Lagrangian in a superfield form we introduce two arbitrary functions of superfields K(Φ) and V(Φ) into the Lagrangian. We follow with the component form of Lagrangian. The quantization of the model is possible, and we will show that there is a reparametrization which turn equation of motion of the first scheme into the second set. Standard metric is again non-positive definite and we apply already known procedure to correct it. It will not be possible to solve Schrodinger equations in general with undefined K and V, so we consider one specific case which give us Landau model on a sphere with N = 2 supersymmetry, which put it apart from the superspherical Landau model, which have a superpshere for a target space but do not possess supersymmetry.

APA, Harvard, Vancouver, ISO, and other styles

8

Rosado, Linares Jesús. "Analysis of some diffusive and kinetic models in mathematical biology and physics." Doctoral thesis, Universitat Autònoma de Barcelona, 2010. http://hdl.handle.net/10803/3113.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Myers, Cliff. "A fractal analysis of diffusion limited aggregation." PDXScholar, 1988. https://pdxscholar.library.pdx.edu/open_access_etds/4047.

Full text

Abstract:

A modified Witten-Sander algorithm was devised for the diffusion-limited aggregation process. The simulation and analysis were performed on a personal computer. The fractal dimension was determined by using various forms of a two-point density correlation function and by the radius of gyration. The results of computing the correlation function with square and circular windows were analyzed. The correlation function was further modified to include the edge from analysis and those results were compared to the fractal dimensions obtained from the whole aggregate. The fractal dimensions of 1.67 ± .01 and 1.75 ± .08 agree with the accepted values. Animation of the aggregation process elucidated the limited penetration into the interior and the zone of most active deposition at the exterior of the aggregate.

APA, Harvard, Vancouver, ISO, and other styles

10

Schmidtt, David Marmolejo. "Two loop super-WZNW model with reductions to supersymmetric and fermionic integrable models/." São Paulo, 2009. http://hdl.handle.net/11449/132737.

Full text

Abstract:

Orientador: José Francisco Gomes
Banca: Luiz Agostinho Ferreira
Banca: Francesco Toppan
Banca: Marco Aurélio Cattacin Kneipp
Banca: Clisthenis Ponce Constantinidis
Resumo: Nessa tese se constrói o funcional de ação dos modelos de Toda supersimétricos afins e se deduzem as transformações de supersimétria dos modelos desde o ponto de vista de fluxos de simetria Fermionicos. A integrabilidade é definida em termos de um problema de fatorização de Riemann-Hilbert estendido que unifica parâmetros de evolução Abelianos e não Abelianos. Se introduzem modelos integráveis puramente Fermionicos definidos em supercosets onde toda a parte Bosonica é completamente eliminada. Vários exemplos são considerados
Abstract: In this thesis we construct the action functional for the supersymmetric affine Toda models and deduce the supersymmetry transformations of the models from the point of view of Fermionic symmetry flows. The underlying Integrability is defined in terms of an extended Riemann-Hilbert factorization problem which unifies Abelian and non-Abelian evolution parameters. We also introduce purely Fermionic Integrable models defined on supercosets where the Bosonic part is completely eliminated. Several examples are consider
Doutor

APA, Harvard, Vancouver, ISO, and other styles

11

Yu, Shaning. "Particle collection in a flotation column." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66002.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Muir, Stuart. "A relativisitic, 3-dimensional smoothed particle hydrodynamics (SPH) algorithm and its applications." Monash University, School of Mathematical Sciences, 2003. http://arrow.monash.edu.au/hdl/1959.1/9513.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Chen, Chen, and 陈晨. "Numerical studies of phase fluctuations in cuprate superconductors." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46482623.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

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 text

Abstract:

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.

APA, Harvard, Vancouver, ISO, and other styles

15

趙學安 and Xuean Zhao. "Electrochemical capacitance in a mesoscopic structure." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31239778.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Schmidt, Piet O. "Origins of Effective Charge of Multivalent Ions at a Membrane/Water Interface and Distribution of 2,3,4,5-Tetrachlorophenol in a Membrane Model System." PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/5049.

Full text

Abstract:

Biological cells and subcellular organelles are surrounded by membranes to form compartments performing specialized functions. Adsorption or partitioning of biologically active compounds into the membrane is the first step in the process of modification of cell function. This work is concerned with the problem of distribution of charged molecules between water and electrically charged membrane surface and between water and octanol. Part I of this thesis is focused on the electrostatic interactions taking place between charges on the membrane and ions present in the aqueous region of the membrane/water interface. The objective was to explore theoretically the origin of anomalous behavior of Ruthenium Red (RuR), a positively charged hexavalent ion. It was discovered in studies of RuR adsorption to negatively charged membranes that within the framework of the Gouy-Chapman theory of the membrane/water interface, RuR behaves as an ion with effective charge less than its physical charge. Moreover, the effective charge was found to be dependent on the density of electric charge at the membrane surface. Two theoretical models of the interfacial region were examined: the Rod Model and the Maximum Density Model. The Rod Model takes into account steric constraints imposed on RuR at the vicinity of the membrane surface. The Maximum Density Model attempts to account for non-ideal behavior by including repulsive interactions. These theoretical studies illustrate the consequences of finite size and ion-ion interactions of adsorption of large molecular ions to electrically charged membrane surfaces. Part II is an experimental study whose objective was to determine the partition coefficient of the negatively charged 2,3,4,5-tetrachlorophenol (TeCP) between water and octanol. The study was based on spectrophotometric measurements of the equilibrium concentrations of TeCP in water and octanol as a function of pH. The octanol/water partition coefficient for both the non-ionized and ionized species of TeCP were determined. It was found that the partition coefficient of ionized TeCP to lipid membrane is about 400 times greater than that for octanol. This result supports the hypothesis that the octanol/water partition coefficient of ionized chlorophenols cannot be used for predicting their distribution between water and lipid-bilayercontaining elements of the environment.

APA, Harvard, Vancouver, ISO, and other styles

17

洪觀宇 and Roy Hung. "Time domain analysis and synthesis of cello tones based on perceptual quality and playing gestures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31215348.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Movahedi-Lankarani, Hamid. "Canonical equations of motion and estimation of parameters in the analysis of impact problems." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184490.

Full text

Abstract:

The transient dynamic analysis of constrained mechanical systems may require the solution of a mixed set of algebraic and differential equations of motion. The usual formulation of these equations is expressed in terms of the accelerations of the system components. A canonical form of the equations of motion in terms of the system velocities and the time derivative of the system momenta may be used instead. This is a natural form of the equations in which all the state variables are explicitly expressed, and have the same physical importance. The numerical solution obtained from the canonical equations shows more accuracy and stability, specifically for systems with large and fluctuating forces. For the mechanical systems that undergo an impact, the usual numerical solution of the equations of motion is not valid. Two different methods of analysis of impact problems are presented. In one method, the variations of the impulsive force during the contact period are directly added to the vector of forces in the canonical equations of motion. In the second method, based on the assumption of instantaneous nature of impact, a set of momentum balance-impulse equations is derived by explicitly integrating the canonical equations. These equations are solved at the time of impact for the jump in the system momenta right after impact. Necessary parameters are evaluated for the performance of the two methods of analysis. These parameters include the maximum relative indentation, the maximum contact force, and the coefficient of restitution. The parameters are determined for the collision between two bodies in a system with any general geometric or material properties. The influence of friction modeling in the magnitude and the direction of the total force at the contact surfaces is discussed. The dynamics of a vehicle collision is studied in order to illustrate the efficiency of obtaining a solution to the canonical equations, the simplicity of solving the momentum balance-impulse equations.

APA, Harvard, Vancouver, ISO, and other styles

19

Lau, Wai-ping, and 劉偉平. "Minimising the calculation time of the cluster program by choosing theminimum convergent cluster size and the best relaxation factor." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B29760392.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Takizawa, Michiru Clara. "The ladder operator approach to constructing conserved operators in integrable one-dimensional lattice models /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18577.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Alvarez, Benjamin. "Scattering Theory for Mathematical Models of the Weak Interaction." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0227.

Full text

Abstract:

Dans ce travail nous considérons d'abord un modèle mathématique de la désintégration des bosons W en leptons. L'hamiltonien d'énergie libre est perturbé par un terme d'interaction issu du modèle standard de la physique des particules. Après avoir introduit des coupures en hautes énergies ainsi qu'en espace, nous démontrons que l'Hamiltonien est un opérateur auto-adjoint sur un produit tensoriel d'espaces de Fock. Nous en étudions la théorie de la diffusion. D'abord, nous supposons que les neutrinos ont une masse non nulle et la complétude asymptotique est vérifiée pour une valeur quelconque de la constante de couplage. Dans un deuxième temps, nous considérons des neutrinos non massifs dans un modèle simplifié. Nous démontrons alors la complétude asymptotique en supposant que la constante de couplage est suffisamment petite, en utilisant une théorie de Mourre singulière, des estimations de propagation adaptées ainsi que la conservation d'une certaine combinaison linéaire d'opérateurs de nombre de particules. Nous étudions par ailleurs des modèles de théorie des champs pour un nombre fini mais quelconque de fermions de spin 1/2. Le terme d'interaction est obtenu en considérant toutes les combinaisons possibles pour les opérateurs de création et d'annihilation. Les différents champs peuvent être massifs comme non massifs et le noyau d'interaction doit vérifier des hypothèses de régularité en espace comme en moment. L'hamiltonien est alors un opérateur auto-adjoint, quelque soit l'intensité de l'interaction, sur un produit tensoriel d'espaces de Fock. Nous démontrons par ailleurs l'existence d'un état fondamental. Nos résultats s'appuient sur une interpolation d'estimation en Nτ et peuvent intervenir dans la modélisation de processus d'interaction faible dans la théorie de Fermi. Nous présenterons enfin une façon de retirer la troncature en espace sur des modèles jouets anfin de définir un modèle invariant par translation
In this work, we consider, first, mathematical models of the weak decay of the vector bosons W into leptons. The free quantum field Hamiltonian is perturbed by an interaction term from the standard model of particle physics. After the introduction of high energy and spatial cut-offs, the total quantum Hamiltonian defines a self-adjoint operator on a tensor product of Fock spaces. We study the scattering theory for such models. First, the masses of the neutrinos are supposed to be positive: for all values of the coupling constant, we prove asymptotic completeness of the wave operators. In a second model, neutrinos are treated as massless particles and we consider a simpler interaction Hamiltonian: for small enough values of the coupling constant, we prove again asymptotic completeness, using singular Mourre's theory, suitable propagation estimates and the conservation of the difference of some number operators. We moreover study Hamiltonian models representing an arbitrary number of spin 1/2 fermion quantum fields interacting through arbitrary processes of creation or annihilation of particles. The fields may be massive or massless. The interaction form factors are supposed to satisfy some regularity conditions in both position and momentum space. Without any restriction on the strength of the interaction, we prove that the Hamiltonian identifies to a self-adjoint operator on a tensor product of anti-symmetric Fock spaces and we establish the existence of a ground state. Our results rely on novel interpolated Nτ estimates. They apply to models arising from the Fermi theory of weak interactions, with ultraviolet and spatial cut-offs. Finally, the removal of spatial cut-off to define translation invariant toy models will be quickly discussed in the last chapter

APA, Harvard, Vancouver, ISO, and other styles

22

Bradley, Frank Mitchell. "Transport imaging for the study of quantum scattering phenomena in next generation Semiconductor devices /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FBradley.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Kapp, David Anthony. "Effect of correlation between shadowing and shadowed points in rough surface scattering." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06302009-040300/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Schafer, Kenneth Joseph. "The development of time-dependent mean-field theory for ion-metal interactions." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184786.

Full text

Abstract:

The development of time-dependent mean-field theory (TDMF) for the treatment of ion-metal interactions is detailed. By allowing for the time-dependent, nonlinear response of the conduction electrons, TDMF provides a self-consistent description that is free of the adiabatic and linear response approximations that have conventionally been used to treat dynamical processes in simple metals. We present the first results of three-dimensional simulations of a bare proton passing through a thin metallic foil. The nonlinear-induced electron density, dynamical screening potential, and electronic stopping power are all displayed as functions of time for several proton velocities ranging from one-half to eight times the Fermi velocity of a simple metal (sodium). We find that a sizable induced density forms behind the proton and that this density is carried along in the wake of the proton with very little dispersion as it traverses the foil. At proton velocities comparable to or above the Fermi velocity, these wake-riding electrons are shaken off as the proton passes through the rear surface of the foil. We find no evidence that the proton forms a stable hydrogen atom as it traverses the foil. At the velocities studied, the conduction electrons provide a weak, asymmetric screening of the proton, with some regions behind the proton actually being overscreened at the higher velocities. A comparison of our results with a standard linear response treatment of the problem reveals both qualitative and quantitative differences in the calculated time-dependent electron density and screening length. We find that the basic assumption underlying the linear response approximation is not justified in this case, due to the strongly nonlinear nature of the conduction electrons' response. These results are illustrative of the kinds of calculations that can be carried out with the simulation package that we have developed and we describe several applications that are planned for the near future. Several innovations in numerical technique, developed in the course of this work, are also detailed.

APA, Harvard, Vancouver, ISO, and other styles

25

Chow, Fung-kiu, and 鄒鳳嬌. "Modeling the minority-seeking behavior in complex adaptive systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B29367487.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Spies, Ruben Daniel. "Mathematical modelling, finite dimensional approximations and sensitivity analysis for phase transitions in shape memory alloys." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-165948/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Jones, William Raymond. "Mathematical models for the cure and viscosity characteristics of an epoxy resin and their applications in computer simulations of composite material manufacturing processes." Thesis, University of Salford, 1988. http://usir.salford.ac.uk/14708/.

Full text

Abstract:

Aspects that affect the manufacture of aeroengine components in carbon fibre reinforced epoxy resin composite material are described and in particular. factors influencing the process of consolidation of preimpregnated material laminates to final component form are critically assessed. Attention is drawn to the need both to acquire a full understanding of the physics of the consolidation process and to obtain quantitative process control data for efficient development and subsequent production of new components. All the variables associated with the process of laminate consolidation are dependent on basic matrix resin characteristics especially its cure advancement and the consequent effect on the resin viscosity at all stages of a moulding cycle. To quantify the matrix resin chernorheological behaviour, methods for the generation of mathematical models for the cure and viscosity changes undergone by a dicyandiamide (DICY) cured epoxy resin system are described. By the use of these mathematical models a program for use on a personal computer has been written by means of which the cure,exotherTnic heat generation and viscosity of the resin may be simulated under both isothermal and linear temperature ramp conditions. Examples are included of the application of the models in the solution of problems encountered in the autoclave process for composoite material components.

APA, Harvard, Vancouver, ISO, and other styles

28

Hudson, Austin Scott. "Applications of Remote Sensing to the Study of Estuarine Physics: Suspended Sediment Dynamics in the Columbia River Estuary." PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/2093.

Full text

Abstract:

Estuarine circulation and its associated transport processes drive the environmental integrity of many near-shore habitats (the coastal ocean, rivers, estuaries and emergent wetlands). A thorough understanding and consideration of this circulation is, therefore, vital in the proper management of these habitats. The aim of this study is to bring together theory and new satellite observations in the Columbia River Estuary to increase our understanding of estuarine circulation and transport. Surface reflectance measurements gathered by the Moderate Imaging Spectroradiometer (MODIS) are first compared to in situ observations to develop an empirical model for remotely derived surface turbidity. Results indicate that MODIS data significantly correlate with in situ measurements of turbidity throughout the CRE (R2 = 0.96). Remote estimates of turbidity are then used to explore the physical processes that drive their spatial distribution. Although the response to different hydrodynamic conditions varies throughout the system, global levels of turbidity are most sensitive to fluvial and tidal inputs and increase during spring tides and high river flow. As a result, the turbidity field has temporal cycles that are consistent with the frequency of these processes. The location of the estuarine turbidity maximum (ETM) is highly dynamic and typically migrates downstream as the tidal velocity or river flow increases. The ETM becomes trapped near the Megler Bridge (river kilometer 20), however, and the presence of strong topography in this region suggests there exists an interaction between bottom topography and sediment transport. A 2-D semi-analytical model, developed herein from the simplified Navier-Stokes equations, confirms that topographic features exhibit substantial influence on longitudinal turbidity distributions. The model considers the coupled, tidally-averaged velocity (composed of gravitational circulation, internal tidal asymmetry, and river flow) and salinity fields and assumes a condition of morphodynamic equilibrium to estimate the distribution of sediment for arbitrary channel configurations. Model simulations demonstrate that topographic highs tend to increase local seaward sediment fluxes, and that topographic lows increase local landward sediment fluxes. Sediment flux convergence near topographic highs compresses the local turbidity distribution, whereas flux divergence near topographic lows dilates the distribution and, under appropriate conditions, produces multiple ETMs. In summary a combination of the model and satellite data has given valuable new insights into the sediment dynamics of estuarine environments; in particular, both show that turbidity distribution and ETM location vary considerably with tidal and river flow conditions, fluctuating on a variety of timescales, and are heavily influenced by bottom topography.

APA, Harvard, Vancouver, ISO, and other styles

29

Elsden, Tom. "Numerical modelling of ultra low frequency waves in Earth's magnetosphere." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/15663.

Full text

Abstract:

Ultra Low Frequency (ULF) waves are a ubiquitous feature of Earth's outer atmosphere, known as the magnetosphere, having been observed on the ground for almost two centuries, and in space over the last 50 years. These waves represent small oscillations in Earth's magnetic field, most often as a response to the external influence of the solar wind. They are important for the transfer of energy throughout the magnetosphere and for coupling different regions together. In this thesis, various features of these oscillations are considered. A detailed background on the history and previous study of ULF waves relevant to our work is given in the introductory chapter. In the following chapters, we predominantly use numerical methods to model ULF waves, which are carefully developed and thoroughly tested. We consider the application of these methods to reports on ground and spaced based observations, which allows a more in depth study of the data. In one case, the simulation results provide evidence for an alternative explanation of the data to the original report, which displays the power of theoretical modelling. An analytical model is also constructed, which is tested on simulation data, to identify the incidence and reflection of a class of ULF wave in the flank magnetosphere. This technique is developed with the aim of future applications to satellite data. Further to this, we develop models both in Cartesian and dipole geometries to investigate some of the theoretical aspects of the coupling between various waves modes. New light is shed on the coupling of compressional (fast) and transverse (Alfvén) magnetohydrodynamic (MHD) wave modes in a 3D dipole geometry. Overall, this thesis aims to develop useful numerical models, which can be used to aid in the interpretation of ULF wave observations, as well as probing new aspects of the existing wave theory.

APA, Harvard, Vancouver, ISO, and other styles

30

Dunn, Patrick. "Binary mixtures near surfaces." PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/4216.

Full text

Abstract:

This paper presents an approach to modeling a binary mixture near a surf ace. The approach used is based on statistical mechanics. The Cluster Variation (CV) method is used to solve an Ising-like model with a cluster size of two (neighboring lattice points). The free energy of the system is expressed in terms of the probabilities of occurrences of particular clusters. The CV method is first developed for a homogeneous system which leads to a set of three non-linear partial differential equations. The surface boundary is then introduced and the CV method is developed for this system which leads to a set of seven non-linear partial differential equations for each layer. In the calculations, the Natural Iteration (NI) method is introduced as a method of solving these non-linear partial differential equations. The steps involved in implementing the NI method are outlined. The number of layers is chosen to be 32. Concentration profiles are calculated for the binary system using the NI method and the results are discussed.

APA, Harvard, Vancouver, ISO, and other styles

31

黃新祥 and Sun-cheung Wong. "Ab initio calculations of silicon clusters." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B3122197X.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Newkirk, Michael Hayes. "An altimeter waveform model for combined surface and volume scattering." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40170.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Moller, Karl. "Dynamics of an active crosslinker on a chain and aspects of the dynamics of polymer networks." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/18001.

Full text

Abstract:

Thesis (MSc)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: Active materials are a subset of soft matter that is constantly being driven out of an equilibrium state due to the energy input from internal processes such as the hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP), as found in biological systems. Firstly, we construct and study a simple model of a flexible filament with an active crosslinker/molecular motor. We treat the system on a mesoscopic scale using a Langevin equation approach, which we analyse via a functional integral approach using the Martin-Siggia-Rose formalism. We characterise the steady state behaviour of the system up to first order in the motor force and also the autocorrelation of fluctuations of the position of the active crosslink on the filament. We find that this autocorrelation function does not depend on the motor force up to first order for the case where the crosslinker is located in the middle of the contour length of the filament. Properties that characterise the elastic response of the system are studied and found to scale with the autocorrelation of fluctuations of the active crosslink position. Secondly, we give a brief overview of the current state of dynamical polymer network theory and then propose two dynamical network models based on a Cayley-tree topology. Our first model takes a renormalisation approach and derive recurrence relations for the coupling constants of the system. The second model builds on the ideas of an Edwards type network theory where Wick’s theorem is employed to enforce the constraint conditions. Both models are examined using a functional integral approach.
AFRIKAANSE OPSOMMING: Aktiewe stelsels is ’n subveld van sagte materie fisika wat handel oor sisteme wat uit ekwilibruim gedryf word deur middel van interne prossesse, soos wat gevind word in biologiese stelsels. Eerstens konstruëer en bestudeer ons ’n model vir ’n buigbare filament met ’n aktiewe kruisskakelaar of molekulêre motor. Ons formuleer die stelsel op ’n mesoskopiese skaal deur gebruik te maak van ’n Langevin vergelyking formalisme en bestudeer die stelsel deur gebruik te maak van funksionaal integraal metodes deur middel van die Martin-Siggia-Rose formalisme. Dit laat ons in staat om die tydonafhankle gedrag van die stelsel te bestudeer tot op eerste orde in die motorkrag. Ons is ook in staat om die outokorrelasie fluktuasies van die posisie van die aktiewe kruisskakelaar te karakteriseer. Ons vind dat die outokorrelasie onafhanklink is van die motorkrag tot eerste orde in die geval waar die kruisskakelaar in die middel van die filament geleë is. Die elastiese eienksappe van die sisteem word ook ondersoek en gevind dat die skaleer soos die outokorrelasie van die fluktuasies van die aktiewe kruisskakelaar posisie. Tweedens gee ons ’n vlugtige oorsig van die huidige toestand van dinamiese polimeer netwerk teorie en stel dan ons eie twee modelle voor wat gebasseer is op ’n Caylee-boom topologie. Ons eerste model maak gebruik van ’n hernormering beginsel en dit laat ons toe om rekurrensierelasies vir die koppelingskonstates te verkry. Die tweede model bou op idees van ’n Edwards tipe netwerk teorie waar Wick se teorema ingespan word om die beperkingskondisies af te dwing. Beide modelle word met funksionaal integraal metodes bestudeer.

APA, Harvard, Vancouver, ISO, and other styles

34

Thomas, Kuryan. "A statistical theory of the epilepsies." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/87673.

Full text

Abstract:

A new physical and mathematical model for the epilepsies is proposed, based on the theory of bond percolation on finite lattices. Within this model, the onset of seizures in the brain is identified with the appearance of spanning clusters of neurons engaged in the spurious and uncontrollable electrical activity characteristic of seizures. It is proposed that the fraction of excitatory to inhibitory synapses can be identified with a bond probability, and that the bond probability is a randomly varying quantity displaying Gaussian statistics. The consequences of the proposed model to the treatment of the epilepsies is explored. The nature of the data on the epilepsies which can be acquired in a clinical setting is described. It is shown that such data can be analyzed to provide preliminary support for the bond percolation hypothesis, and to quantify the efficacy of anti-epileptic drugs in a treatment program. The results of a battery of statistical tests on seizure distributions are discussed. The physical theory of the electroencephalogram (EEG) is described, and extant models of the electrical activity measured by the EEG are discussed, with an emphasis on their physical behavior. A proposal is made to explain the difference between the power spectra of electrical activity measured with cranial probes and with the EEG. Statistical tests on the characteristic EEG manifestations of epileptic activity are conducted, and their results described. Computer simulations of a correlated bond percolating system are constructed. It is shown that the statistical properties of the results of such a simulation are strongly suggestive of the statistical properties of clinical data. The study finds no contradictions between the predictions of the bond percolation model and the observed properties of the available data. Suggestions are made for further research and for techniques based on the proposed model which may be used for tuning the effects of anti-epileptic drugs.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

35

Ho, Yanfang. "Group theoretical analysis of in-shell interaction in atoms." Scholarly Commons, 1985. https://scholarlycommons.pacific.edu/uop_etds/487.

Full text

Abstract:

A group theoretic approach to Layzer's 1/2 expansion method is explored. In part this builds on earlier work of Wulfman(2), of Moshinsky et al(l4), and of Sinanoglu, Herrick(lS), and Kellman (16) on second row atoms. I investigate atoms with electrons in the 3s-3p-3d shell and find: 1. Wulfman's constant of motion accurately predicts configuration mixing for systems with two to eight electrons in the 3s-3p subshell. 2. The same constant of motion accurately predicts configuration mixing for systems with two electrons in the 3s-3p-3d shell. 3. It accurately predicts configuration mixing in systems of high angular momentum L and of high spin angular momentum S containing three electrons in the 3s-3p-3d shell, but gives less accurate results when L and S are both small. I also show how effective nuclear charges may be calculated by a group theoretical approach. In addition I explore several new methods for expressing electron repulsion operators in terms of operators of the 80(4,2) dynamical group of one - electron atoms.

APA, Harvard, Vancouver, ISO, and other styles

36

Lundholm, Douglas. "Zero-energy states in supersymmetric matrix models." Doctoral thesis, KTH, Matematik (Avd.), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12846.

Full text

Abstract:

The work of this Ph.D. thesis in mathematics concerns the problem of determining existence, uniqueness, and structure of zero-energy states in supersymmetric matrix models, which arise from a quantum mechanical description of the physics of relativistic membranes, reduced Yang-Mills gauge theory, and of nonperturbative features of string theory, respectively M-theory. Several new approaches to this problem are introduced and considered in the course of seven scientific papers, including: construction by recursive methods (Papers A and D), deformations and alternative models (Papers B and C), averaging with respect to symmetries (Paper E), and weighted supersymmetry and index theory (Papers F and G). The mathematical tools used and developed for these approaches include Clifford algebras and associated representation theory, structure of supersymmetric quantum mechanics, as well as spectral theory of (matrix-) Schrödinger operators.
QC20100629

APA, Harvard, Vancouver, ISO, and other styles

37

Luo, Xianghui 1983. "Symmetries of Cauchy Horizons and Global Stability of Cosmological Models." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11543.

Full text

Abstract:

ix, 111 p.
This dissertation contains the results obtained from a study of two subjects in mathematical general relativity. The first part of this dissertation is about the existence of Killing symmetries in spacetimes containing a compact Cauchy horizon. We prove the existence of a nontrivial Killing symmetry in a large class of analytic cosmological spacetimes with a compact Cauchy horizon for any spacetime dimension. In doing so, we also remove the restrictive analyticity condition and obtain a generalization to the smooth case. The second part of the dissertation presents our results on the global stability problem for a class of cosmological models. We investigate the power law inflating cosmological models in the presence of electromagnetic fields. A stability result for such cosmological spacetimes is proved. This dissertation includes unpublished co-authored material.
Committee in charge: James Brau, Chair; James Isenberg, Advisor; Paul Csonka, Member; John Toner, Member; Peng Lu, Outside Member

APA, Harvard, Vancouver, ISO, and other styles

38

Ndayishimye, Joram. "Alpha cluster structure and scattering in 20Ne, 44Ti, 94Mo, 136Te and 212Po." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6484.

Full text

Abstract:

Thesis (MSc)--University of Stellenbosch, 2011.
ENGLISH ABSTRACT: We investigate the nuclei 20Ne, 44Ti, 94Mo, 136Te and 212Po using a model of an α-cluster orbiting a closed shell core. A purely phenomenological cluster-core potential is found to provide a successful description of the spectra, B(E2↓) transition strengths, and α-decay rates of the low-lying positive parity states of these nuclei. We then use the same potential as the real part of an optical model potential to describe the α elastic scattering by 16O, 40Ca, 90Zr and 208Pb. The experimental differential cross-section data are reasonably well reproduced with the imaginary potential depth as the only free parameter. The special case of the 8Be system is also analysed.
AFRIKAANSE OPSOMMING: Ons ondersoek die kerne 20Ne, 44Ti, 94Mo, 136Te en 212Po deur gebruik te maak van ’n model waar ’n α-bondel om ’n kern met ’n geslote skil wentel. ’n Suiwer fenomenologiese bondelkern potentiaal is gevind wat die energie spektra, B(E2 ↓) oorgangs sterktes, en α-verval tempo vir laagliggende positiewe pariteitstoestande vir hierdie kerne beskryf. Ons gebruik dieselfde potentiaal as die reele deel van die optiese potentiaal om die alpha elastiese verstrooiing deur die kerne 16O, 40Ca, 90Zr en 208Pb te beskryf. Die eksperimentele differensiele kansvlak data word redelik goed gereprodukseer met slegs die imaginere potensiaal diepte as die enigste vrye parameter. Die spesiale geval van 8Be is ook ondersoek.

APA, Harvard, Vancouver, ISO, and other styles

39

Monette, Liza. "Numerical simulations of nucleation and growth phenomena." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64053.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Munoz, Esparza Domingo. "Multiscale modelling of atmospheric flows: towards improving the representation of boundary layer physics." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209363.

Full text

Abstract:

Atmospheric boundary layer flows are characterized by the coexistence of a broad range of scales. These scales cover from synoptic- (100-5000 km) and meso-scales (1-100 km) up to three-dimensional micro-scale turbulence (less than a few kilometers). This multiscale nature inherent to atmospheric flows clearly determines the behaviour of the atmospheric boundary layer, whose structure and evolution are of major importance for the wind energy community. This PhD thesis is focused on the development of a numerical methodology that allows to include contribution from all the above mentioned scales, with the purpose of improving the representation of boundary layer processes. The multiscale numerical methodology is developed based on a numerical weather prediction (NWP) model, the Weather Research and Forecasting (WRF) model.

Prior to the development of the multiscale numerical methodology, one-year of sonic anemometer and wind LiDAR measurements from the FINO1 offshore platform are analyzed. A comprehensive database of offshore measurements in the lowest 250 m of the boundary layer is developed after quality data check and correction for flow distortion effects by the measurement mast, allowing the characterization of the offshore conditions at FINO1. Spectral analysis of high frequency sonic anemometer measurements is used to estimate a robust averaing time for the turbulent fluxes that minimizes non-universal contributions from mesoscale structures but captures the contribution from boundary layer turbulence, employing the Ogive function concept. A stability classification of the measurements is carried out based on the Obukhov length. Results compare well to other surface layer observational studies while vertical wind speed profiles exhibit the expected stability-dependency.

Although NWP models have been extensively used for weather forecasting purposes, a comprehensive analysis of its suitability to meet the wind energy requirements needs to be carried out. The applicability of the WRF mesoscale model to reproduce offshore boundary layer characteristics is evaluated and validated against field measurements from FINO1. The ability of six planetary boundary layer (PBL) parameterizations to account for stability effects is analyzed. Overall, PBL parameterizations are rather accurate in reproducing the vertical structure of the boundary layer for convective and neutral stabilities. However, difficulties are found under stable stratifications, due to the general tendency of PBL formulations to be overdiffusive and therefore, not capable to develope the strong vertical gradients found in the observations. A low-level jet and a very shallow boundary layer cases are simulated to provide further insights into the limits of the parameterizations.

Large-eddy simulations (LES) based on averaged conditions from a convective episode at FINO1 are conducted to understand the mechanisms of transition and equilibration that occur in turbulent one-way nested simulations. The nonlinear backscatter and anisotropy subgrid scale model with a prognostic turbulent kinetic energy equation is found to be capable of providing similar results when performing one-way nested large-eddy simulations to a reference stand-alone domain using periodic lateral boundary conditions. A good agreement is obtained in terms of velocity shear and turbulent fluxes of heat and momentum, while velocity variances are overestimated. A considerable streamwise fetch is needed following each domain transition for appropriate energy levels to be reached at high wavelengths and for the solution to reach quasi-stationary results. A pile-up of energy is observed at low wavelengths on the first nested domain, mitigated by the inclusion of a second nested domain with higher resolution that allows the development of an appropriate turbulent energy cascade.

As the final step towards developing the multiscale capabilities of WRF, the specific problem of the transition from meso- to micro-scales in atmospheric models is addressed. The challenge is to generate turbulence on inner LES domain from smooth mesoscale inflow. Several new methods are proposed to trigger the development of turbulent features. The inclusion of adequate potential temperature perturbations near the inflow boundaries of the LES domain results in a very good agreement of mean velocity profiles, variances and turbulent fluxes, as well as velocity spectra, when compared to periodic stand-alone simulations. This perturbation method allows an efficient generation of fully developed turbulence and is tested under a broad range of atmospheric stabilities: convective, neutral and stable conditions, showing successful results in all the regimes.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

APA, Harvard, Vancouver, ISO, and other styles

41

Mateyisi, Mohau Jacob. "Polymer networks with mobile force-applying crosslinks." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6759.

Full text

Abstract:

Thesis (MSc)--University of Stellenbosch, 2011.
ENGLISH ABSTRACT: We construct and study a simple model for an active gel of exible polymer filaments crosslinked by a molecular motor cluster that perform reversible work while translating along the filaments. The filament end points are crosslinked to an elastic background. In this sense we employ a simplified model for motor clusters that act as slipping links that exert force while moving along the strands. Using the framework of replica theory, quenched averages are taken over the disorder which originates from permanent random crosslinking of network end points to the background. We investigate how a small motor force contributes to the elastic properties of the network. We learn that in addition to the normal elastic response for the network there is an extra contribution to the network elasticity from the motor activity. This depends on the ratio of the entropic spring constant for the linked bio-polymerchain to the spring constant of the tether of the motor.
AFRIKAANSE OPSOMMING: Ons konstrueer en bestudeer 'n eenvoudige model vir 'n aktiewe netwerk van eksieble polimeerfilamente wat deur grosse van molekulere motors aan mekaar verbind word wat omkeerbare werk doen terwyl dit langs die filamente transleer. Die eindpunte van die filamente is aan 'n elastiese agtergrond verbind. In hierdie sin benut ons 'n eenvoudige model vir motorclusters wat as verskuifbare verbindings krag op die filamente tydens beweging kan uitoefen. Nie-termiese wanorde gemiddeldes word geneem oor die wanorde wat deur die lukrake permanente verbindings van netwerk eindpunte aan die agtergrond veroorsaak word. Ons ondersoek hoe 'n klein motorkrag tot die elastiese eienskappe van die netwerk bydra. Ons leer dat daar bo en behalwe die gewone elastiese respons vir die netwerk 'n elastiese bydrae as gevolg van die motors se aktiwiteit voorkom. Dit hang af van die verhouding van die entropiese veerkonstante van die biopolimerketting tot die veerkonstante van die anker van die motor.

APA, Harvard, Vancouver, ISO, and other styles

42

Powell, James Eckhardt. "Building a Multivariable Linear Regression Model of On-road Traffic for Creation of High Resolution Emission Inventories." PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3415.

Full text

Abstract:

Emissions inventories are an important tool, often built by governments, and used to manage emissions. To build an inventory of urban CO2 emissions and other fossil fuel combustion products in the urban atmosphere, an inventory of on-road traffic is required. In particular, a high resolution inventory is necessary to capture the local characteristics of transport emissions. These emissions vary widely due to the local nature of the fleet, fuel, and roads. Here we show a new model of ADT for the Portland, OR metropolitan region. The backbone is traffic counter recordings made by the Portland Bureau of Transportation at 7,767 sites over 21 years (1986-2006), augmented with PORTAL (The Portland Regional Transportation Archive Listing) freeway traffic count data. We constructed a regression model to fill in traffic network gaps using GIS data such as road class and population density. An EPA-supplied emissions factor was used to estimate transportation CO2 emissions, which is compared to several other estimates for the city's CO2 footprint.

APA, Harvard, Vancouver, ISO, and other styles

43

Johnson, Jared Drew. "An Algebra Isomorphism for the Landau-Ginzburg Mirror Symmetry Conjecture." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2793.

Full text

Abstract:

Landau-Ginzburg mirror symmetry takes place in the context of affine singularities in CN. Given such a singularity defined by a quasihomogeneous polynomial W and an appropriate group of symmetries G, one can construct the FJRW theory (see [3]). This construction fills the role of the A-model in a mirror symmetry proposal of Berglund and H ubsch [1]. The conjecture is that the A-model of W and G should match the B-model of a dual singularity and dual group (which we denote by WT and GT). The B-model construction is based on the Milnor ring, or local algebra, of the singularity. We verify this conjecture for a wide class of singularities on the level of Frobenius algebras, generalizing work of Krawitz [10]. We also review the relevant parts of the constructions.

APA, Harvard, Vancouver, ISO, and other styles

44

Bajodah, Abdulrahman H. "Acceleration constraints in modeling and control of nonholonomic systems." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04072004-180000/unrestricted/bajodah%5Fabdulrahman%5Fh%5F200312%5Fphd.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

McCorkle, Tricia Dawn. "Math, music, and membranes: A historical survey of the question "can one hear the shape of a drum"?" CSUSB ScholarWorks, 2005. https://scholarworks.lib.csusb.edu/etd-project/2933.

Full text

Abstract:

In 1966 Mark Kac posed an interesting question regarding vibrating membranes and the sounds they make. His article entitled "Can One Hear the Shape of a Drum?", which appeared in The American Mathematical Monthly, generated much interest and scholarly debate. The evolution of Kac's intriguing question will be the subject of this project.

APA, Harvard, Vancouver, ISO, and other styles

46

Bruna, Maria. "Excluded-volume effects in stochastic models of diffusion." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:020c2d3e-5fef-478c-9861-553cd310daf5.

Full text

Abstract:

Stochastic models describing how interacting individuals give rise to collective behaviour have become a widely used tool across disciplines—ranging from biology to physics to social sciences. Continuum population-level models based on partial differential equations for the population density can be a very useful tool (when, for large systems, particle-based models become computationally intractable), but the challenge is to predict the correct macroscopic description of the key attributes at the particle level (such as interactions between individuals and evolution rules). In this thesis we consider the simple class of models consisting of diffusive particles with short-range interactions. It is relevant to many applications, such as colloidal systems and granular gases, and also for more complex systems such as diffusion through ion channels, biological cell populations and animal swarms. To derive the macroscopic model of such systems, previous studies have used ad hoc closure approximations, often generating errors. Instead, we provide a new systematic method based on matched asymptotic expansions to establish the link between the individual- and the population-level models. We begin by deriving the population-level model of a system of identical Brownian hard spheres. The result is a nonlinear diffusion equation for the one-particle density function with excluded-volume effects enhancing the overall collective diffusion rate. We then expand this core problem in several directions. First, for a system with two types of particles (two species) we obtain a nonlinear cross-diffusion model. This model captures both alternative notions of diffusion, the collective diffusion and the self-diffusion, and can be used to study diffusion through obstacles. Second, we study the diffusion of finite-size particles through confined domains such as a narrow channel or a Hele–Shaw cell. In this case the macroscopic model depends on a confinement parameter and interpolates between severe confinement (e.g., a single- file diffusion in the narrow channel case) and an unconfined situation. Finally, the analysis for diffusive soft spheres, particles with soft-core repulsive potentials, yields an interaction-dependent non-linear term in the diffusion equation.

APA, Harvard, Vancouver, ISO, and other styles

47

Blok, Hendrik J. "On the nature of the stock market : simulations and experiments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ56507.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Macnamara, Cicely K. "The period ratio P₁/2P₂ in coronal waves." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2101.

Full text

Abstract:

Increasing observational evidence of wave modes brings us to a closer understanding of the solar corona. Coronal seismology allows us to combine wave observations and theory to determine otherwise unknown parameters. The period ratio, P₁/2P₂, between the period P₁ of the fundamental mode and the period P₂ of its first overtone is one such tool of coronal seismology and its departure from unity provides information about the structure of the corona. In this thesis we consider the period ratio P₁/2P₂ of coronal loops from a theoretical standpoint. Previous theory and observations indicate that the period ratio is likely to be less than unity for oscillations of coronal loops. We consider the role of damping and density structuring on the period ratio. In Chapter 2 we consider analytically the one-dimensional wave equation with the inclusion of a generic damping term for both uniform and non-uniform media. Results suggest that the period ratio is dominated by longitudinal structuring rather than damping. In Chapter 3 we consider analytically the effects of thermal conduction and compressive viscosity on the period ratio for a longitudinally propagating sound wave. We find that damping by either thermal conduction or compressive viscosity typically has a small effect on the period ratio. For coronal values of thermal conduction the effect on the period ratio is negligible. For compressive viscosity the effect on the period ratio may become important for some short hot loops. In Chapter 4 we extend the analysis of Chapter 3 to include radiative cooling and find that it too has a negligible effect on the period ratio for typical coronal values. As an extension to the investigation, damping rates are considered for thermal conduction, compressive viscosity and radiative cooling. The damping time is found to be optimal for each mechanism in a different temperature range, namely below 1 MK for radiative cooling, 2 − 6 MK for thermal conduction and above 6 MK for compressive viscosity. In Chapter 5 we consider analytically the period ratio for the fast kink, sausage and n = N modes of a magnetic slab, discussing both an Epstein density profile and a simple step function profile. We find that transverse density structuring in the form of an Epstein profile or a step function profile may contribute to the shift of the period ratio for long thin slab-like structures. The similarity in the behaviour of the period ratio for both profiles means either can be used as a robust model. We consider also other profiles numerically for the kink mode, which are found to be either slab-like or Epstein-like suggesting again that it is not necessary to distinguish the nature of the density profile when considering the period ratio.

APA, Harvard, Vancouver, ISO, and other styles

49

Lee, Graham Kim Huat. "Glass rain : modelling the formation, dynamics and radiative-transport of cloud particles in hot Jupiter exoplanet atmospheres." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/11740.

Full text

Abstract:

The atmospheres of exoplanets are being characterised in increasing detail by observational facilities and will be examined with even greater clarity with upcoming space based missions such as the James Webb Space Telescope (JWST) and the Wide Field InfraRed Survey Telescope (WFIRST). A major component of exoplanet atmospheres is the presence of cloud particles which produce characteristic observational signatures in transit spectra and influence the geometric albedo of exoplanets. Despite a decade of observational evidence, the formation, dynamics and radiative-transport of exoplanet atmospheric cloud particles remains an open question in the exoplanet community. In this thesis, we investigate the kinetic chemistry of cloud formation in hot Jupiter exoplanets, their effect on the atmospheric dynamics and observable properties. We use a static 1D cloud formation code to investigate the cloud formation properties of the hot Jupiter HD 189733b. We couple a time-dependent kinetic cloud formation to a 3D radiative-hydrodynamic simulation of the atmosphere of HD 189733b and investigate the dynamical properties of cloud particles in the atmosphere. We develop a 3D multiple-scattering Monte Carlo radiative-transfer code to post-process the results of the cloudy HD 189733b RHD simulation and compare the results to observational results. We find that the cloud structures of the hot Jupiter HD 189733b are likely to be highly inhomogeneous, with differences in cloud particle sizes, number density and composition with longitude, latitude and depth. Cloud structures are most divergent between the dayside and nightside faces of the planet due to the instability of silicate materials on the hotter dayside. We find that the HD 189733b simulation in post-processing is consistent with geometric albedo observations of the planet. Due to the scattering properties of the cloud particles we predict that HD 189733b will be brighter in the upcoming space missions CHaracterising ExOPlanet Satellite (CHEOPS) bandpass compared to the Transiting Exoplanet Space Survey (TESS) bandpass.

APA, Harvard, Vancouver, ISO, and other styles

50

Lacroix, Sylvain. "Modèles intégrables avec fonction twist et modèles de Gaudin affines." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN014/document.

Full text

Abstract:

Cette thèse a pour sujet une classe de théories des champs intégrables appelées modèles avec fonction twist. Les principaux exemples de tels modèles sont les modèles sigma non-linéaires intégrables, tel le Modèle Principal Chiral, et leurs déformations. Un premier résultat obtenu est la preuve que le modèle dit de Bi-Yang-Baxter, qui est une déformation à deux paramètres du Modèle Principal Chiral, est lui aussi un modèle avec fonction twist. Il est ensuite montré que les déformations de type Yang-Baxter modifient certaines symétries globales du modèle non déformé en symétries de Poisson-Lie. Un autre chapitre concerne la construction d'une infinité de charges locales en involution pour tous les modèles sigma intégrables et leurs déformations : ce résultat repose sur le formalisme général partagé par tous ces modèles en tant que théories des champs avec fonction twist.La seconde partie de la thèse a pour sujet les modèles de Gaudin. Ceux-ci sont des modèles intégrables associés à des algèbres de Lie. En particulier, les théories des champs avec fonction twist sont liées aux modèles de Gaudin associés à des algèbres de Lie affines. Une approche standard pour l'étude du spectre des modèles de Gaudin quantiques sur des algèbres finies est celle de Feigin-Frenkel-Reshetikhin. Dans cette thèse, des généralisations de cette approche sont conjecturées, motivées et testées. L'une d'elles concerne les modèles de Gaudin finis dits cyclotomiques. La seconde porte sur les modèles de Gaudin associés à des algèbres affines
This thesis deals with a class of integrable field theories called models with twist function. The main examples of such models are integrable non-linear sigma models, such as the Principal Chiral Model, and their deformations. A first obtained result is the proof that the so-called Bi-Yang-Baxter model, which is a two-parameter deformation of the Principal Chiral Model, is also a model with twist function. It is then shown that Yang-Baxter type deformations modify certain global symmetries of the undeformed model into Poisson-Lie symmetries. Another chapter concerns the construction of an infinite number of local charges in involution for all integrable sigma models and their deformations: this result is based on the general formalism shared by all these models as field theories with twist function.The second part of the thesis concerns Gaudin models. These are integrable models associated with Lie algebras. In particular, field theories with twist function are related to Gaudin models associated with affine Lie algebras. A standard approach for studying the spectrum of quantum Gaudin models over finite algebras is the one of Feigin-Frenkel-Reshetikhin. In this thesis, generalisations of this approach are conjectured, motivated and tested. One of them deals with the so-called cyclotomic finite Gaudin models. The second one concerns the Gaudin models associated with affine Lie algebras

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Afterglow (Physics) – Mathematical models'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles