Dissertations / Theses: 'Theory of materials'

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Taga, Adrian. "Materials Engineering Using Density Functional Theory." Doctoral thesis, KTH, Materials Science and Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3809.

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This doctoral thesis presents density functionalcalculations applied in several domains of interest in solidstate physics and materials science. Non-collinear magnetismhas been studied both in an artificial multi-layer structure,which could have technological relevance as a magnetic sensordevice, and as excitations in 3d ferromagnets. The intricatebulk crystal structure of γ-alumina has been investigated.An improved embedded cluster method is developed and applied tostudy the geometric and electronic structures and opticalabsorption energies of neutral and positively charged oxygenvacancies in α-quartz. Ab initio total energycalculations, based on the EMTO theory, have been used todetermine the elastic properties of Al_1-xLi_xrandom alloys in the face-centered cubiccrystallographic phase. The obtained overall good agreementwith experiment demonstrates the applicability of the quantummechanics formulated within the framework of the DensityFunctional Theory for mapping the structural and mechanicalproperties of random alloys against chemical composition.

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Kocevski, Vancho. "Theory and Modelling of Functional Materials." Doctoral thesis, Uppsala universitet, Materialteori, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-248513.

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The diverse field of material research has been steadily expanding with a great help from computational physics, especially in the investigation of the fundamental properties of materials. This has driven the computational physics to become one of the main branches of physics, allowing for density functional theory (DFT) to develop as one of the cornerstones of material research. Nowdays, DFT is the method of choice in a great variety of studies, from fundamental properties, to materials modelling and searching for new materials. In this thesis, DFT is employed for the study of a small part of this vast pool of applications. Specifically, the microscopic characteristics of Zn1-xCdxS alloys are studied by looking into the evolution of the local structure. In addition, the way to model the growth of graphene on Fe(110) surface is discussed. The structural stability of silicon nanocrystals with various shapes is analysed in detail, as well. DFT is further used in studying different properties of semiconductor nanocrystals. The size evolution of the character of the band gap in silicon nanocrystals is investigated in terms of changes in the character of the states around the band gap. The influence of various surface impurities on the band gap, as well as on the electronic and optical properties of silicon nanocrystals is further studied. In addition, the future use of silicon nanocrystals in photovoltaic devices is examined by studying the band alignment and the charge densities of silicon nanocrystals embedded in a silicon carbide matrix. Furthermore, the electronic and optical properties of different semiconductor nanocrystals is also investigated. In the case of the CdSe/CdS and CdS/ZnS core-shell nanocrystals the influence of the nanocrystal size and different structural models on their properties is analysed. For silicon nanocrystal capped with organic ligands, the changes in the optical properties and lifetimes is thoroughly examined with changes in the type of organic ligand.

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Prasai, Binay K. "Theory and Experiment of Chalcogenide Materials." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1374002400.

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Osorio, Guillén Jorge Mario. "Density Functional Theory in Computational Materials Science." Doctoral thesis, Uppsala University, Department of Physics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4496.

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The present thesis is concerned to the application of first-principles self-consistent total-energy calculations within the density functional theory on different topics in materials science.

Crystallographic phase-transitions under high-pressure has been study for TiO2, FeI2, Fe3O4, Ti, the heavy alkali metals Cs and Rb, and C3N4. A new high-pressure polymorph of TiO2 has been discovered, this new polymorph has an orthorhombic OI (Pbca) crystal structure, which is predicted theoretically for the pressure range 50 to 100 GPa. Also, the crystal structures of Cs and Rb metals have been studied under high compressions. Our results confirm the recent high-pressure experimental observations of new complex crystal structures for the Cs-III and Rb-III phases. Thus, it is now certain that the famous isostructural phase transition in Cs is rather a new crystallographic phase transition.

The elastic properties of the new superconductor MgB2 and Al-doped MgB2 have been investigated. Values of all independent elastic constants (c11, c12, c13, c33, and c55) as well as bulk moduli in the a and c directions (Ba and Bc respectively) are predicted. Our analysis suggests that the high anisotropy of the calculated elastic moduli is a strong indication that MgB2 should be rather brittle. Al doping decreases the elastic anisotropy of MgB2 in the a and c directions, but, it will not change the brittle behaviour of the material considerably.

The three most relevant battery properties, namely average voltage, energy density and specific energy, as well as the electronic structure of the Li/LixMPO4 systems, where M is either Fe, Mn, or Co have been calculated. The mixing between Fe and Mn in these materials is also examined. Our calculated values for these properties are in good agreement with recent experimental values. Further insight is gained from the electronic density of states of these materials, through which conclusions about the physical properties of the various phases are made.

The electronic and magnetic properties of the dilute magnetic semiconductor Mn-doped ZnO has been calculated. We have found that for an Mn concentration of 5.6%, the ferromagnetic configuration is energetically stable in comparison to the antiferromgnetic one. A half-metallic electronic structure is calculated by the GGA approximation, where Mn ions are in a divalent state leading to a total magnetic moment of 5 μB per Mn atom.

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Osorio, Guillén Jorge Mario. "Density functional theory in computational materials science /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4496.

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Conroy, Michael W. "Density Functional Theory Studies of Energetic Materials." Scholar Commons, 2009. http://scholarcommons.usf.edu/etd/3691.

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First-principles calculations employing density functional theory (DFT) were performed on the energetic materials PETN, HMX, RDX, nitromethane, and a recently discovered material, nitrate ester 1 (NEST-1). The aims of the study were to accurately predict the isothermal equation of state for each material, improve the description of these molecular crystals in DFT by introducing a correction for dispersion interactions, and perform uniaxial compressions to investigate physical properties that might contribute to anisotropic sensitivity. For each system, hydrostatic-compression simulations were performed. Important properties calculated from the simulations such as the equilibrium structure, isothermal equation of state, and bulk moduli were compared with available experimental data to assess the agreement of the calculation method. The largest contribution to the error was believed to be caused by a poor description of van der Waals (vdW) interactions within the DFT formalism. An empirical van der Waals correction to DFT was added to VASP to increase agreement with experiment. The average agreement of the calculated unit-cell volumes for six energetic crystals improved from approximately 9% to 2%, and the isothermal EOS showed improvement for PETN, HMX, RDX, and nitromethane. A comparison was made between DFT results with and without the vdW correction to identify possible advantages and limitations. Uniaxial compressions perpendicular to seven low-index crystallographic planes were performed on PETN, HMX, RDX, nitromethane, and NEST-1. The principal stresses, shear stresses, and band gaps for each direction were compared with available experimental information on shock-induced sensitivity to determine possible correlations between physical properties and sensitivity. The results for PETN, the only system for which the anisotropic sensitivity has been thoroughly investigated by experiment, indicated a possible correlation between maximum shear stress and sensitivity. The uniaxial compressions that corresponded to the greatest maximum shear stresses in HMX, RDX, solid nitromethane, and NEST-1 were identified and predicted as directions with possibly greater sensitivity. Experimental data is anticipated for comparison with the predictions.

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Woods, Matthew. "Relativistic theory of photoemission for magnetic materials." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325858.

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Tsamados, Michel. "Mechanical response of glassy materials : theory and simulation." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00466081.

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Il est bien établi que les propriétés mécaniques et rhéologiques d'une large classe de matériaux vitreux amorphes met en jeu - contrairement aux dislocations dans les cristaux - des rearrangements structuraux localisés formant par un processus de cascade des bandes de cisaillements. Cette localisation de la déformation est observée dans divers systèmes vitreux ainsi que dans des simulations numériques. Cette réponse mécanique complexe reste mal comprise à une échelle microscopique et il n'est pas clair si l'écoulement plastique peut être associé à une origine structurale locale ou à des processus purement dynamiques.Dans cette thèse nous envisageons ces problématiques à l'aide de simulations atomiques athermales sur un système Lennard-Jones modèle. Nous calculons le tenseur élastique moyenné localement sur une échelle nanométrique. A cette échelle, le verre est assimilable à un matériau composite comprenant un échafaudage rigide et des zones fragiles. L'étude détaillée de la déformation plastique à différents taux de cisaillement met en évidence divers régimes d'écoulement. En dessous d'un taux de cisaillement critique dépendant de la taille du système, la réponse mécanique atteind une limite quasistatique (effets de taille fini, cascades d'événements plastiques, contrainte seuil) alors que pour des taux de cisaillement plus importants les propriétés rhéologiques sont fixées par le taux de cisaillement imposé. Dans ce régime nous mettons en évidence la croissance d'une longueur de coopérativité dynamique et discutons de sa dépendance avec le taux de cisaillements.

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Iusan, Diana Mihaela. "Density Functional Theory Applied to Materials for Spintronics." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-119887.

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The properties of dilute magnetic semiconductors have been studied by combined ab initio, Monte Carlo, and experimental techniques. This class of materials could be very important for future spintronic devices, that offer enriched functionality by making use of both the spin and the charge of the electrons. The main part of the thesis concerns the transition metal doped ZnO. The role of defects on the magnetic interactions in Mn-doped ZnO was investigated. In the presence of acceptor defects such as zinc vacancies and oxygen substitution by nitrogen, the magnetic interactions are ferromagnetic. For dilute concentrations of Mn (~ 5%) the ordering temperature of the system is low, due to the short ranged character of the exchange interactions and disorder effects. The clustering tendency of the Co atoms in a ZnO matrix was also studied. The electronic structure, and in turn the magnetic interactions among the Co atoms, is strongly dependent on the exchange-correlation functional used. It is found that Co impurities tend to form nanoclusters and that the interactions among these atoms are antiferromagnetic within the local spin density approximation + Hubbard U approach. The electronic structure, as well as the chemical and magnetic interactions in Co and (Co,Al)-doped ZnO, was investigated by joined experimental and theoretical techniques. For a good agreement between the two, approximations beyond the local density approximation must be used. It is found that the Co atoms prefer to cluster within the semiconducting matrix, a tendency which is increased with Al co-doping. We envision that it is best to describe the system as superparamagnetic due to the formation of Co nanoclusters within which the interactions are antiferromagnetic. The magnetic anisotropy and evolution of magnetic domains in Fe81Ni19/Co(001) superlattices were investigated both experimentally, as well as using model spin dynamics. A magnetic reorientation transition was found.

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Larsson, Ashley Ian. "Mathematical aspects of wave theory for inhomogeneous materials /." Title page, table of contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phl334.pdf.

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Elmzughi, Farag Gema. "Theory of polaritons in semiconductor and magnetic materials." Thesis, University of Essex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295600.

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Naeem, Majid. "Theory, modelling, and applications of advanced electromagnetic materials." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/31858.

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A multitude of recent work predicts many novel concepts based on the availability of non-natural materials; some prominent examples include transformation optics (TO) and perfect lens. The interest in this eld has grown dramatically due to spec- ulated possibility to allow for continuously varying material properties to steer the incident wave at will, such as for the TO. The posed challenges for their realisation include the limitations of numerical modelling and manufacturing techniques. A de- sign scheme has been proposed, in this thesis, for composite materials: the desired electromagnetic properties of composites can be engineered by judiciously varying the volume fraction of the inclusion-to-host materials, by manipulating the geomet- ric arrangement of inclusions, or by altering their dielectric contrast. The analysis of the homogenised response of the designed materials at macro-scale requires effective medium modelling techniques. The existing effective medium approximation tech- niques have been discussed, and their pros and cons outlined. A homogenization scheme has been introduced that is based on the interaction of the incident wave and the nanoparticles at the micro-scale, which further requires efficient electromagnetic modelling. The conventional nanoparticle modelling techniques, as well as the state of the art, have been reviewed and a dipole-moment-based method to efficiently solve modern nanoparticle-based electromagnetic problems has been outlined. The appli- cability of the proposed scheme has been demonstrated by employing it to design various EM devices. An improved permittivity extraction scheme has been proposed for the homogenization of composites. Unlike classical homogenization schemes, the extracted parameters, using the proposed technique, follow the relation between the real and imaginary parts, that is, Kramers-Kronig relations. Several random and periodic structures have been simulated for the purpose of extracting the ef- fective electromagnetic properties and interpreting the results so as to establish a connection between them.

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Gillespie, Peter N. O. "Theory of charge transfer in solar energy materials." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/22771/.

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Ghaderi, Ali. "A mathematical theory for mixing of particulate materials." Thesis, University of Surrey, 2006. http://epubs.surrey.ac.uk/844427/.

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A theoretical framework for sampling theory is developed. In this relation, concepts like mixture heterogeneity and representative samples are mathematically defined. Further, the relation between Gy's concepts of accuracy and reproducibility with mixture quality and the entropy of the sample distribution is established. Moreover, it is shown that within the developed homework, Lacey's conjecture is mathematically consistent. It is also shown that a consequence of the theory is the prediction of the number of key components of given size in random binary closed batch systems. It is also shown that this estimate is a function of microstructural properties of the mixture under study. Furthermore, this theory is used to develop a unifying approach to description of RTD of continuous systems. These results are further used to develop a model for RTD of a commercial twin screw extruder. A new theoretical approach to the dynamics of the mixing processes is developed. In this context, the concept of heterogeneity landscape is introduced. It is argued that the valleys in the heterogeneity landscape correspond to different equilibrium states of the mixture. Further, it is shown that the valleys in the heterogeneity landscape can mathematically be described by heterogeneity equation and this would allow for classification of all the valleys. The characteristic function of the general solution to the heterogeneity equation is also determined. Moreover, it is shown that based on the mathematical model for the valleys, one can deduce that in the case of insufficient information about the mixture structure, the normal distribution, up to the second order; is the best distribution in describing the mixture structure.

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Vogl, Gregory William. "Comprehensive Theory of Heat Transfer in Heterogeneous Materials." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/30881.

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For over forty years, researchers have attempted to refine the Fourier heat equation to model heat transfer in engineering materials. The equation cannot accurately predict temperatures in some applications, such as during transients in microscale (< 10^-12 s) situations. However, even in situations where the time duration is relatively large, the Fourier heat equation might fail to predict observed non-Fourier behavior. Therefore, non-Fourier models must be created for certain engineering applications, in which accurate temperature modeling is necessary for design purposes. In this thesis, we use the Fourier heat equation to create a general non-Fourier, but diffusive, equation that governs the matrix temperature in a composite material. The composite is composed of a matrix with embedded particles. We let the composite materials be governed by Fourier's law and let the heat transfer between the matrix and particles be governed by contact conductance. After we make certain assumptions, we derive a general integro-differential equation governing the matrix temperature. We then non-dimensionalize the general equation and show that our model reduces to that used by other researchers under a special limit of a non-dimensional parameter. We formulate an initial-boundary-value problem in order to study the behavior of the general matrix temperature equation. We show that the thermalization time governs the transition of the general equation from its small-time limit to its large-time limit, which are both Fourier heat equations. We also conclude that our general model cannot accurately describe temperature changes in an experimental sand composite.
Master of Science

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Gochan, Matthew. "Fermi Liquid Properties of Dirac Materials:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:108726.

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Thesis advisor: Kevin S. Bedell
One of the many achievements of renowned physicist L.D. Landau was the formulation of Fermi Liquid Theory (FLT). Originally debuted in the 1950s, FLT has seen abundant success in understanding degenerate Fermi systems and is still used today when trying to understand the physics of a new interacting Fermi system. Of its many advantages, FLT excels in explaining why interacting Fermi systems behave like their non-interacting counterparts, and understanding transport phenomena without cumbersome and confusing mathematics. In this work, FLT is applied to systems whose low energy excitations obey the massless Dirac equation; i.e. the energy dispersion is linear in momentum, ε α ρ, as opposed to the normal quadratic, ε α ρ². Such behavior is seen in numerous, seemingly unrelated, materials including graphene, high T[subscript]c superconductors, Weyl semimetals, etc. While each of these materials possesses its own unique properties, it is their low energy behavior that provides the justification for their grouping into one family of materials called Dirac materials (DM). As will be shown, the linear spectrum and massless behavior leads to profound differences from the normal Fermi liquid behavior in both equilibrium and transport phenomena. For example, with mass having no meaning, we see the usual effective mass relation from FLT being replaced by an effective velocity ratio. Additionally, as FLT in d=2 has been poorly studied in the past, and since the most famous DM in graphene is a d=2 system, a thorough analysis of FLT in d=2 is presented. This reduced dimensionality leads to substantial differences including undamped collective modes and altered quasiparticle lifetime. In chapter 3, we apply the Virial theorem to DM and obtain an expression for the total average ground state energy $E=\frac{B}{r_s}$ where $B$ is a constant independent of density and $r_s$ is a dimensionless parameter related to the density of the system: the interparticle spacing $r$ is related to $r_s$ through $r=ar_s$ where $a$ is a characterstic length of the system (for example, in graphene, $a=1.42$ \AA). The expression derived for $E$ is unusual in that it's typically impossible to obtain a closed form for the energy with all interactions included. Additionally, the result allows for easy calculation of various thermodynamic quantities such as the compressibility and chemical potential. From there, we use the Fermi liquid results from the previous chapter and obtain an expression for $B$ in terms of constants and Fermi liquid parameters $F_0^s$ and $F_1^s$. When combined with experimental results for the compressibility, we find that the Fermi liquid parameters are density independent implying a unitary like behavior for DM. In chapter 4, we discuss the alleged universal KSS lower bound in DM. The bound, $\frac{\eta}{s}\geq\frac{\hbar}{4\pi k_B}$, was derived from high energy/string theory considerations and was conjectured to be obeyed by all quantum liquids regardless of density. The bound provides information on the interactions in the quantum liquid being studied and equality indicates a nearly perfect quantum fluid. Since its birth, the bound has been highly studied in various systems, mathematically broken, and poorly experimented on due to the difficult nature of measuring viscosity. First, we provide the first physical example of violation by showing $\frac{\eta}{s}\rightarrow 0$ as $T\rightarrow T_c$ in a unitary Fermi gas. Next, we determine the bound in DM in d=2,3 and show unusual behavior that isn't seen when the bound is calculated for normal Fermi systems. Finally we conclude in chapter 5 and discuss the outlook and other avenues to explore in DM. Specifically, it must be pointed out that the physics of what happens near charge neutrality in DM is still poorly understood. Our work in understanding the Fermi liquid state in DM is necessary in understanding DM as a whole. Such a task is crucial when we consider the potential in DM, experimentally, technologically, and purely for our understanding
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics

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Schenck, David Robert. "Some Formation Problems for Linear Elastic Materials." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28608.

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Some equations of linear elasticity are developed, including those specific to certain actuator structures considered in formation theory. The invariance of the strain-energy under the transformation from rectangular to spherical coordinates is then established for use in two specific formation problems. The first problem, involving an elastic structure with a cylindrical equilibrium configuration, is formulated in two dimensions using polar coordinates. It is shown that $L^2$ controls suffice to obtain boundary displacements in $H^{1/2}$. The second problem has a spherical equilibrium configuration and utilizes the elastic equations in spherical coordinates. Results similar to those obtained in the two dimensional case are indicated for the three dimensional problem.
Ph. D.

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Chimata, Raghuveer. "Optical Properties of Materials Calculated from First Principles Theory." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132195.

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In this project work, we performed ab-inito calculations for 20 different non-magnetic materials (band gap ranging between 0.5 eV to 13 eV ) and three different magnetic materials such as NiO, EuO and GdN using density functional theory (DFT). Generalized gradient approximation (PBE) and hybrid functional (HSE06, PBE0) within projector-augmented wave (PAW) methodology were adopted to investigate the electronic properties, whereas only PBE approximation was used to study optical properties of these materials. Furthermore, for magnetic materials, PBE+U method was employed to treat the strongly correlated d and f electrons. Subtle difference in f electron state at the Fermi level in EuO and GdN for different approximations was thoroughly evaluated here. Using HSE06 we have showed that for non-magnetic materials the band-gap values were comparable with the experimental values. ForEuO we have observed a band-gap of 0.8 eV by using PBE+U approximation. However, in the HSE06 approximation, no band-gap was observed at Fermi level. The optical properties for non-magnetic systems were evaluated by calculating the dynamic dielectric functions such as absorption, reflection and energy-loss spectroscopy with the help of self-developed numerical codes. The static dielectric matrices of materials were calculated using density functional perturbation theory. The static dielectric constant values were calculated by different approaches: i) by including local field effects in both DFT and random phase approximations (RPA) and ii) excluding local field effects and including local field effects in DFT. The static constant values of the materials including local field effects for RPA approximation yielded better results than other methods.

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Monson, Peter A. "Dynamic mean field theory for fluids in mesoporous materials." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184643.

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Martinez, Irene Suarez. "Theory of diffusion and plasticity in layered carbon materials." Thesis, University of Sussex, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439023.

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Hull, Brian David. "Mathematical theory of flow processes of fibre-reinforced materials." Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335766.

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Belof, Jonathan L. "Theory and simulation of metal-organic materials and biomolecules." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0003272.

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Grant, Carl L. "Sunday school curriculum materials development blending theory and technology /." Theological Research Exchange Network (TREN), 1993. http://www.tren.com.

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Minahen, Timothy M. Knowles James K. Knauss Wolfgang Gustav. "Structural instabilities involving time dependent materials : theory and experiment /." Diss., Pasadena, Calif. : California Institute of Technology, 1992. http://resolver.caltech.edu/CaltechETD:etd-08082007-100442.

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SANTOS, JOSE CARLOS LEITE DOS. "A MATHEMATICAL FORMULATION OF THE THEORY OF GRANULAR MATERIALS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1987. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33274@1.

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O propósito deste trabalho é propor um modelo teórico axiomático, que descreva o comportamento termomecânico de materiais granulares, fundamentado em uma descrição física simples, do que entende-se por material granular. No capítulo I, faz-se uma revisão bibliográfica, objetivando uma visão geral do estado da arte e delinear a importância do estudo de materiais granulares. No capítulo II, utiliza-se um método axiomático estabelecendo-se as equações de balanço que descrevem o comportamento termodinâmico de materiais granulares. No capítulo III, utilizando-se um outro método axiomático, analisa-se algumas condições de contorno para materiais granulares. No capítulo IV, estuda-se restrições internas em materiais granulares, exemplificando-se algumas. Finalmente no capítulo V, aplica-se o embasamento teórico dos capítulos anteriores, na solução do problema de escoamento de um material granular entre placas paralelas.
The aim of this work is to establish an axiomatic theoretical model, for description of the thermomechanical behavior of granular materials, based on a simple physical description of what mean granular materials. On the first chapter, it s make an overview of the acctual state of the arte, giving the real importance of the study of granular materials. On the second chapter, by using an axiomatic method, the balances equations for thermomechanical behavior of granular materials, was established. On the the III, by using another axiomatic method, some boundary condictions for granular materials, was analysed. On the chapter IV, by using a coceptual model for internal constraints, some internal constraints for granular materials, was exemplified. At least, on chapter V, the theoretical backgoung established in the previous chapter, is applied to solve the problem of granular flow between two parallel plates.

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Monson, Peter A. "Dynamic mean field theory for fluids in mesoporous materials." Diffusion fundamentals 16 (2011) 13, S. 1-2, 2011. https://ul.qucosa.de/id/qucosa%3A13742.

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Jain, Anubhav Ph D. Massachusetts Institute of Technology. "The Materials genome : rapid materials screening for renewable energy using high-throughput density functional theory." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69789.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 204-211).
This thesis relates to the emerging field of high-throughput density functional theory (DFT) computation for materials design and optimization. Although highthroughput DFT is a promising new method for materials discovery, its practical implementation can be difficult. This thesis describes in detail a software infrastructure used to perform over 80,000 DFT computations. Accurately calculating total energies of diverse chemistries is an ongoing effort in the electronic structure community. We describe a method of mixing total energy calculations from different energy functionals (e.g., GGA and GGA+U) so that highthroughput calculations can be more accurately applied over a wide chemical space. Having described methods to perform accurate and rapid DFT calculations, we move next to applications. A first application relates to finding sorbents for Hg gas removal for Integrated Gas Combined Cycle (IGCC) power plants. We demonstrate that rapid computations of amalgamation and oxidation energies can identify the most promising metal sorbents from a candidate list. In the future, more extensive candidate lists might be tested. A second application relates to the design and understanding of Li ion battery cathodes. We compute some properties of about 15,000 virtual cathode materials to identify a new cathode chemistry, Li₉V₃(P₂O₇)₃(PO₄)₂ . This mixed diphosphate-phosphate material was recently synthesized by both our research group and by an outside group. We perform an in-depth computational study of Li₉V₃(P₂O₇)₃(PO₄)₂ and suggest Mo doping as an avenue for its improvement. A major concern for Li ion battery cathodes is safety with respect to 02 release. By examining our large data set of computations on cathode materials, we show that i) safety roughly decreases with increasing voltage and ii) for a given redox couple, polyanion groups reduce safety. These results suggest important limitations for researchers designing high-voltage cathodes. Finally, this thesis describes the beginnings of a highly collaborative 'Materials Genome' web resource to share our calculated results with the general materials community. Through the Materials Genome, we expect that the work presented in this thesis will not only contribute to the applications discussed herein, but help make high-throughput computations accessible to the broader materials community.
by Anubhav Jain.
Ph.D.

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Östlin, Andreas. "Electronic structure studies and method development for complex materials." Doctoral thesis, KTH, Tillämpad materialfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-167109.

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Over the years electronic structure theory has proven to be a powerful method with which one can probe the behaviour of materials, making it possible to describe and predict material properties. The numerical tools needed for these methods are always in need of development, since the desire to calculate more complex materials pushes this field forward. This thesis contains work on both this implementational and developmental aspects. It begins by reviewing density functional theory and dynamical mean field theory, with the aim of merging these two methods. We point out theoretical and technical issues that may occur while doing this. One issue is the Padé approximant, which is used for analytical continuation. We assess the approximant and point out difficulties that can occur, and propose and evaluate methods for their solution. The virial theorem is assessed within the framework of density functional theory merged with many-body methods. We find that the virial theorem is extended from its usual form, and confirm this by performing practical calculations. The unified theory of crystal structure for transition metals has been established a long time ago using early electronic structure calculations. Here we implement the first- principles exact muffin-tin orbitals method to investigate the structural properties of the 6d transition metals. The goal of our study is to verify the existing theory for the mostly unknown 6d series and the performance of the current state-of-the art in the case of heavy d metals. It is found that these elements behave similarly to their lighter counterparts, except for a few deviations. In these cases we argue that it is relativistic effects that cause this anomalous behaviour. Palladium is then studied, taking many-body effects into account. We find that we can reproduce experimental photoemission spectra by these methods, as well as the Fermi surface. The thesis ends with an investigation of the stacking fault energies of the strongly correlated metal cerium. In addition to providing the first ab-initio stacking fault data for the two cubic phases of Ce, we discuss how these results could have an impact on the interpretation of the phase diagram of cerium

QC 20150522

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29

Gokay, Kemal. "Contact Mechanics Of Graded Materials With Two Dimensional Material Property Variations." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606527/index.pdf.

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ABSTRACT CONTACT MECHANICS OF GRADED MATERIALS WITH TWODIMENSIONAL MATERIAL PROPERTY VARIATIONS Gö
kay, Kemal M.S., Department of Mechanical Engineering Supervisor: Asst. Prof. Dr. Serkan Dag September 2005, 62 pages Ceramic layers used as protective coatings in tribological applications are known to be prone to cracking and debonding due to their brittle nature. Recent experiments with functionally graded ceramics however show that these material systems are particularly useful in enhancing the resistance of a surface to tribological damage. This improved behavior is attributed to the influence of the material property gradation on the stress distribution that develops at the contacting surfaces. The main interest in the present study is in the contact mechanics of a functionally graded surface with a two &ndash
dimensional spatial variation in the modulus of elasticity. Poisson&rsquo
s ratio is assumed to be constant due to its insignificant effect on the contact stress distribution [30]. In the formulation of the problem it is assumed that the functionally graded surface is in frictional sliding contact with a rigid flat stamp. Using elasticity theory and semi-infinite plane approximation for the graded medium, the problem is reduced to a singular integral equation of the second kind. Integral equation is solved numerically by expanding the unknown contact stress distribution into a series of Jacobi polynomials and using suitable collocation points. The developed method is validated by providing comparisons to a closed form solution derived for homogeneous materials. Main numerical results consist of the effects of the material nonhomogeneity parameters, coefficient of friction and stamp size and location on the contact stress distribution.

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30

Garred, Jason. "Trade in raw materials and economic development." Thesis, London School of Economics and Political Science (University of London), 2015. http://etheses.lse.ac.uk/3092/.

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This thesis considers three cases in which trade in natural resources and other raw materials can inform us about wider questions of economic development. The first chapter, “Capturing the Value Chain: The Persistence of Trade Policy in China After WTO Accession”, considers whether in the GATT/WTO era, developing countries are still able to actively conduct trade policy. In this study, I show that after China’s entry into WTO, required import tariff reductions on downstream sectors have been partly offset by an alternative policy with similar effects: export restrictions on raw materials. I also find that larger rises in Chinese raw materials export taxes after WTO accession have been associated with greater downstream export growth. The second chapter, “Winners and Losers from a Commodities-for-Manufactures Trade Boom”, examines two contrasting outcomes of the ‘de-industrialization’ associated with rising trade between China and other developing countries. In particular, this chapter compares changes in labour market outcomes in Brazilian regions stimulated by rising demand from China for raw materials, with Brazilian regions whose manufacturing sectors have been harmed by Chinese import competition. While there was slower growth in manufacturing wages and greater rises in local wage inequality in ‘loser’ regions between 2000 and 2010, ‘winner’ regions experienced higher wage growth, lower takeup of cash transfers and positive effects on job quality. The third chapter,“Access to Raw Materials and Local Comparative Advantage: The Effects of India’s Freight Equalization Policy”, considers the importance of access to raw materials for industrial development. It does so by looking at the effects of a Indian policy that aimed to remove regional comparative advantages associated with proximity to raw materials, by equalizing prices of steel across India. The results suggest that in practice, this policy may have had only a limited effect on access to raw materials across Indian states.

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31

Motteram, Gary. "Crossing material boundaries : a cultural-historical case study of e-learning materials development in China." Thesis, University of Manchester, 2007. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:147344.

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This thesis makes use of activity theory as a lens to explore how professionals learn. The study focuses initially on my professional understandings arising from the application of Cultural Historical Activity Theory (CHAT) to the eChina-UK project funded by HEFCE in the UK, an attempt to develop collaborative elearning projects in British and Chinese universities, and secondly on purposeful interviews with project staff about their professional learning in the project. The thesis begins by setting the scene for the project showing how it came about. The literature review explores CHAT and allied issues of Adult Education considering how adults may learn in both formal and informal contexts. It also contextualises the project by giving background on Higher Education, China and distance/e-learning. The research questions that it addresses are: 1. What roles do artefacts have in mediating collaborative working on elearning materials? 2. How do boundary crossers/brokers impact on a project of this type? 3. How do different cultural histories have an impact on the disposition that the ‘developers’ have to artefacts and materials? 4. What and how do the subjects of the activity systems learn? What role, if any, do artefacts play? What role, if any, do the brokers play in the learning? This practitioner case study makes use of a variety of data. The initial data consisted of field notes which were part of the project process. Theoretically driven hunches that surfaced from these data led to further purposeful data collection via interviews investigating the following: Virtual Learning Environments (VLEs), a materials design template and pilots; and boundary crossers. Also considered is the nature of the professional learning that occurred for eight core participants in the project. The thesis in addition explores the constructs of transfer, transformation and expansive learning. The study proposes a refinement of our understanding of these constructs. It also demonstrates how important and significant boundary objects are to successful international project work along with the boundary crossers who support the development of the artefacts. In addition, it shows how an engagement with transfer, transformation and expansive learning contributes to the professional development of the subjects in their respective activity systems.

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32

Dziekan, Thomas. "Electronic Transport in Strained Materials." Doctoral thesis, Uppsala University, Department of Physics and Materials Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8471.

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In this thesis the conductivity of strained materials has been investigated using density functional theory and a semiclassical transport theory based on the Boltzmann equation.

In transition metals trends are reproduced without adjustable parameters. The introduction of one temperature dependent cross section allowed the reproduction of resistivity trends between 10 and 1000K.

The effect of strain on transition metals in bcc and fcc structure was studied deforming the unit cell along the tetragonal deformation path. The anisotropy of the conductivity varied on wide range of the c/a-ratio. The orbitals at the Fermi level determined the principal behavior. Pairs of elements with permutated number of electrons and holes in the 4d band showed similar behavior. The concept of the tetragonal deformation was also applied on semiconductors.

The deformation of Vanadium in X/V superlattices (X=Cr,~Fe,~Mo) due to Hydrogen loading depends on the properties of X. It was found that counteracting effects due to the presence of Hydrogen influence the conductivity.

It is shown that a small magnetic moment of the V host reduces the hydrogen solubility. Depending on the magnitude of the tetragonal distortion of V, the hydrogen dissolution becomes favored for larger moments.

Finally, extra charge filling of the bandstructure of Cr and Mo decreases the Fermi velocity and increases the density of states at the Fermi energy.

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33

Jakel, Roland. "Analysis of Hyperelastic Materials with Mechanica - Theory and Application Examples." Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-201000705.

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Part 1: Theoretic background information - Review of Hooke’s law for linear elastic materials - The strain energy density of linear elastic materials - Hyperelastic material - Material laws for hyperelastic materials - About selecting the material model and performing tests - Implementation of hyperelastic material laws in Mechanica - Defining hyperelastic material parameters in Mechanica - Test set-ups and specimen shapes of the supported material tests - The uniaxial compression test - Stress and strain definitions in the Mechanica LDA analysis Part 2: Application examples - A test specimen subjected to uniaxial loading - A volumetric compression test - A planar test - Influence of the material law Appendix - PTC Simulation Services Introduction - Dictionary Technical English-German
Teil 1: Theoretische Hintergrundinformation - Das Hookesche Gesetz für linear-elastische Werkstoffe - Die Dehnungsenergiedichte für linear-elastische Materialien - Hyperelastisches Material - Materialgesetze für Hyperelastizität - Auswählen des Materialgesetzes und Testdurchführung - Implementierung der hyperelastischen Materialgesetze in Mechanica - Definieren der hyperelastischen Materialparameter in Mechanica - Testaufbauten und Prüfkörper der unterstützten Materialtests - Der einachsige Druckversuch - Spannungs- und Dehnungsdefinition in der Mechanica-Analyse mit großen Verformungen Teil 2: Anwendungsbeispiele - Ein einachsig beanspruchter Prüfkörper - Ein volumetrischer Drucktest - Ein planarer Test - Einfluss des Materialgesetzes Anhang: - Kurzvorstellung der PTC Simulationsdienstleistungen - Wörterbuch technisches Englisch-Deutsch

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34

Schaarschmidt, Martin. "Theory of light propagation in nano-structured materials and semiconductors." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980074541.

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35

Colizzi, G. "Theory of hydrogen bonded ferroelectric materials : the case of KDP." Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419559.

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36

Finot, Marc A. "Deformation of multi-layered and graded materials : theory and experiments." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10599.

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37

Ledoux, Antoine M. Eng Massachusetts Institute of Technology. "Theory of piezoelectric materials and their applications in civil engineering." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66839.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 39).
The goal of this thesis is to explore ways of harvesting energy from a building. To be more specific, the conversion of mechanical energy into electrical energy using piezoelectric materials is studied. Applications of piezoelectric materials as actuators are also explored, with particular interest in the question: what is the maximum moment that an actuator, whose energy comes from piezoelectricity, can develop when attached to a beam. As a piezoelectric material cannot generate much energy, and often requires amplification, the goal is to optimize the circuit linked to the piezoelectric material to obtain as much power as possible.
by Antoine Ledoux.
M.Eng.

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38

Dhindsa, Manjeet S. "Advanced Theory, Materials and Applications for Electrowetting on Structured Surfaces." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1299009714.

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39

Evans, Sarah Margaret Mary. "The theory of mixed valent and Kondo systems." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236121.

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40

Saluja, Navtej Singh 1965. "Electromagnetic stirring of metallic melts : theory and experiments." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13709.

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41

Frary, Megan. "Crystallographically consistent percolation theory for grain boundary networks." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33402.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.
Includes bibliographical references (p. 127-134).
Grain boundaries are known to play a role in many important material properties including creep resistance, ductility and cracking resistance. Although the structure and properties of individual boundaries are important, the overall behavior of the material is determined largely by the connectivity of grain boundaries in the microstructure. Grain boundary networks may be studied in the framework of percolation theory by classifying boundaries as special or general to the property of interest. In standard percolation theory, boundaries are randomly assigned as special or general; however, this approach is invalid in realistic grain boundary networks due to the requirement for crystallographic consistency around any closed circuit in the microstructure. The goal of this work is to understand the effects of these local constraints on the connectivity and percolation behavior of crystallographically consistent grain boundary networks. Using computer simulations and analytical models, the behavior of crystallographically consistent networks is compared to that of randomly-assembled networks at several different length scales. At the most local level, triple junctions and quadruple nodes are found to be preferentially coordinated by special and general boundaries, leading to nonrandom network topologies that are quantified using topological parameters.
(cont.) Although the properties of the simulated microstructures, including connectivity length and average cluster radius of gyration, are described by the same scaling exponents as in standard percolation theory, the amplitude prefactors in the scaling relationships are changed as a result of the crystallographic constraint. The percolation threshold, an important parameter in microstructural design, is also found to differ from that of standard percolation theory by as much as ±0.05. Although all of the simulated grain boundary networks studied here are distinctly nonrandom, no two cases have the same behavior, the details of which depend strongly on the specific microstructural model. Therefore, a unified approach for locally correlated percolation problems is developed that allows the effects of the requirement for crystallographic consistency to be compared directly from system to system. This new approach can be extended beyond the study of grain boundary networks to include other locally-correlated percolation problems.
by Megan E. Frary.
Ph.D.

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42

Zhou, Aiguo Barsoum M. W. Barsoum M. W. Kalidindi Surya. "Kinking nonlinear elastic solids : theory and experiments /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2804.

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43

Guáqueta, R. Camilo (Richard Camilo) 1981. "Computer simulations for a scholastic theory of granular drainage." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17613.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2003.
"June 2003."
Includes bibliographical references (leaf 44).
There is a surprising lack of good models for granular flow. In 2002, Bazant proposed a new stochastic kinematic model of granular drainage from a silo. The new model rests on the notion that flow in the silo is caused by the migration of extended regions of excess interstitial space upward from the orifice at the bottom. An implementation of this model with the purpose of simulating the behavior of particles in the silo was developed by the author, and several results were obtained using simulations carried out with this implementation. As regards particle streamlines, average velocity profiles, predictions of particle mixing and of particle diffusivity, it was found that qualitative and quantitative agreement with experiments was excellent, in particular for a specific version of the implementation. This version uses a self-correlated random walk to describe the motion of the excess interstitial space through the silo. The model can also be used to make predictions about many other features of the granular flow (such as granular temperature), that are not as accessible through experiment's, and for which empirical behavior is not well known. In particular, the implementation of the model developed in this work can be used to simulate three dimensional flow, whereas existing experimental techniques are limited to observing two dimensions.
R. Camilo Guáqueta.
S.B.

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44

Lee, Jeong-Won. "Novel terahertz and nanophotonic lasers : theory, design, and fabrication." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98165.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 101-106).
In this thesis, we will explore numerical modeling and fabrication of laser sources. First, we demonstrate and distinguish experimentally the existence of special type of Fano resonances at k~~0 in a macroscopic two-dimensional photonic crystal slab. We fabricate a square lattice array of holes in silicon nitride layer and perform an angular resolved spectral analysis of the various Fano resonances. We elucidate their radiation behavior using temporal coupled-mode theory and symmetry considerations. The unique simplicity of this system whereby an ultra-long lifetime delocalized electromagnetic field can exist above the surface and consequently easily interact with added matter, provides exciting new opportunities for the study of light and matter interaction. However, we confirmed that achievable quality factor (Q) is limited by fabrication imperfection. Therefore, in the second part, we present an extensive fabrication optimization process, through which we established improved Q by a factor of three. Lastly, we report a comprehensive theoretical analysis and new experimental data of high-pressure (> 1 Torr) lasing action in optically-pumped far-infrared (OPFIR) lasers. No previous models could satisfactorily capture high-pressure operation because of the growing role of excited vibrational levels. Without these additional excited vibrational levels, molecules are artificially trapped in lower energy vibrational levels. This, in turn, prematurely triggers the so-called vibrational bottleneck and quenches the lasing action at low pressures in the previous models. Even though the high-pressure behavior can be more realistically modeled by including numerous excited vibrational levels, it would dramatically increase the computation time, and more importantly, the rate constants connecting all these levels are unknown. We propose a new model with an expandable pool which embodies 120 excited vibrational levels. Moreover, the knowledge of state-to-state rates among the excited vibrational levels is unnecessary in the proposed new model since the net rate related to the expandable level can be found by equilibrium conditions. Together with a detailed calculation of the pump rate and the wall collision rate, our model qualitatively and quantitatively reproduces experimentally measured high-pressure behavior. The model can be universally used for any OPFIR gas laser system. Thus, our work puts forward a theoretical formalism that could enable the advancement of compact terahertz radiation sources.
by Jeongwon Lee.
Ph. D.

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45

Hiremath, Mahantesh S. "A dynamical theory of deformable fluid-saturated porous solids /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487331541711205.

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46

Fullager, Daniel B. "Theory, Characterization and Applications of Infrared Hyperbolic Metamaterials." Thesis, The University of North Carolina at Charlotte, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10267303.

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Hyperbolic Metamaterials (HMMs) are engineered structures capable of supporting lightmatter interactions that are not normally observed in naturally occuring material systems. These unusual responses are enabled by an enhancement of the photonic density of states (PDOS) in the material. The PDOS enhancement is a result of deliberately introduced anisotropy via a permittivity sign-change in HMM structures which increases the number and frequency spread of possible wave vectors that propagate in the material. Subwavelength structural features allow effective medium theories to be invoked to construct the k-space isofrequency quadratic curves that, for HMMs, result in the k-space isofrequency contour transitioning from being a bounded surface to an unbounded one. Since the PDOS is the integral of the differential volume between k-space contours, unbounded manifolds lead to the implication of an infinite or otherwise drastically enhanced PDOS. Since stored heat can be thought of as a set of non-radiative electromagnetic modes, in this dissertation we demonstrate that HMMs provide an ideal platform to attempt to modify the thermal/IR emissivity of a material. We also show that HMMs provide a platform for broadband plasmonic sensing. The advent of commercial two photon polymerization tools has enabled the rapid production of nano- and microstructures which can be used as scaffolds for directive infrared scatterers. We describe how such directive components can be used to address thermal management needs in vacuum environments in order to maximize radiative thermal transfer. In this context, the fundamental limitations of enhanced spon- taneous emission due to conjugate impedance matched scatterers are also explored. The HMM/conjugate scatterer system’s performance is strongly correlated with the dielectric function of the negative permittivity component of the HMM. In order to fully understand the significance of these engineered materials, we examine in detail the electromagnetic response of one ternary material system, aluminium-doped zinc oxide (AZO), whose tuneable plasma frequency makes it ideal for HMM and thermal transfer applications. This study draws upon first principle calculations from the open literature utilizing a Hubbard-U corrected model for the non-local interaction of charge carriers in AZO crystalline systems. We present the first complete dielectric function of industrially produced AZO samples from DC to 30,000 cm^–1 and conclude with an assessment of this material’s suitability fo the applications described.

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47

Damewood, Liam James. "Theoretical Models of Spintronic Materials." Thesis, University of California, Davis, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3602035.

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In the past three decades, spintronic devices have played an important technological role. Half-metallic alloys have drawn much attention due to their special properties and promised spintronic applications. This dissertation describes some theoretical techniques used in first-principal calculations of alloys that may be useful for spintronic device applications with an emphasis on half-metallic ferromagnets. I consider three types of simple spintronic materials using a wide range of theoretical techniques. They are (a) transition metal based half-Heusler alloys, like CrMnSb, where the ordering of the two transition metal elements within the unit cell can cause the material to be ferromagnetic semiconductors or semiconductors with zero net magnetic moment, (b) half-Heusler alloys involving Li, like LiMnSi, where the Li stabilizes the structure and increases the magnetic moment of zinc blende half-metals by one Bohr magneton per formula unit, and (c) zinc blende alloys, like CrAs, where many-body techniques improve the fundamental gap by considering the physical effects of the local field. Also, I provide a survey of the theoretical models and numerical methods used to treat the above systems.

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48

Guo, Dandan. "Theory of optical nonlinearity in pi-conjugated polymers and related materials." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186192.

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Within the framework of interacting-electron models, the optical nonlinearity in π-conjugated polymers is investigated theoretically. A complete microscopic many-body theory is developed for the mechanism of the third order nonlinearity in these materials. The universality and the predictability of the theory are well established. It is found that the bulk of the optical nonlinearity in conjugated polymers is determined by four essential states although all the excited states are involved. It is also found that electron-electron Coulomb interactions in one-dimensional systems play key roles in the nonlinear optical processes and are responsible for the observed spectroscopic features. The theoretical results are compared with experiments in wide variety of materials and excellent agreements between theory and experiments are obtained. With the essential-state theory, various experiments are explained within a single unified theory for the first time, and many controversies are resolved.

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49

Kilic, Bahattin. "Peridynamic Theory for Progressive Failure Prediction in Homogeneous and Heterogeneous Materials." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/193658.

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The classical continuum theory is not capable of predicting failure without an external crack growth criteria and treats the interface having zero thickness. Alternatively, a nonlocal continuum theory referred to as peridynamic theory eliminates these shortcomings by utilizing formulation that uses displacements, rather than derivatives of displacements, and including material failure in its constitutive relations through the response functions. This study presents a new response function as part of the peridynamic theory to include thermal loading. Furthermore, an efficient numerical algorithm is presented for solution of peridynamic equations. Solution method relies on the discretization of peridynamic equations at collocation points resulting in a set of ordinary differential equations with respect to time. These differential equations are then integrated using explicit methods. In order to improve numerical efficiency of the computations, spatial partitioning is introduced through uniform grids as arrays of linked lists. Furthermore, the domain of interest is divided into subunits each of which is assigned to a specific processor to utilize parallel processing using OpenMP. In order to obtain the static solutions, the adaptive dynamic relaxation method is developed for the solution of peridynamic equations. Furthermore, an approach to couple peridynamic theory and finite element analysis is introduced to take advantage of their salient features. The regions in which failure is expected are modeled using peridynamics while the remaining regions are modeled utilizing finite element method. Finally, the present solution method is utilized for damage prediction of many problems subjected to mechanical, thermal and buckling loads.

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50

Kiang, Ching-Hwa Goddard William A. Goddard William A. "Physics and chemistry of advanced nanoscale materials : experiment, simulation, and theory /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10162007-105256.

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Dissertations / Theses on the topic 'Theory of materials'

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