Assessing the effect of foam layers on transport phenomena is of significant interest in many industries, so a method for predicting foam layer properties has been developed. A model of the propagation of radiation from an amplitude-modulated laser beam through a non-absorbing foam layer has been developed using diffusion theory. Measurements predicted by diffusion theory were compared to results generated using Monte Carlo methods for a variety of foam layer properties in both the time-domain and the frequency-domain. The properties that were varied include the layer thickness, the scattering coefficient, and the asymmetry parameter. Layer thicknesses between 8.5 mm and 18 cm were considered. Values of the scattering coefficient ranged from about 600 m-1 to 14000 m-1, while the asymmetry parameter varied between 0 and 1. A conjugate-gradient algorithm was used to minimize the difference between simulated Monte Carlo measurements and diffusion theory predicted measurements. A large set of simulated measurements, calculated at various source-detector separations and three discrete frequencies were used to predict the layer properties. Ten blind cases were considered and property predictions were made for each. The predicted properties were within approximately 10% of the actual values, and on average the errors were approximately 4%. Predictions of the reduced scattering coefficient were all within approximately 5% with the majority being within 3%. Predictions of L were all within approximately 10% with the majority being within 7%. Attempts to separate g from the reduced scattering coefficient were unsuccessful, and it was determined that implementation of different source models might make such attempts possible. It was shown that with a large number of measurements, properties could be accurately predicted. A method for reducing the number of measurements needed for accurate property estimation was developed. Starting with a single measurement location, property predictions were made. An approach for updating the optimal detector location, based on the current estimate of the properties, was developed and applied to three cases. Property predictions for the three cases were made to within 10% of the actual values. A maximum of three measurement locations were necessary to obtain such predictions, a significant reduction as compared to the previously illustrated method.

Climate change-related hazards negatively impact ecosystems, economies, and quality of life. Significant resources have been invested in data collection and research with the goal of enhanced understanding and capacity to predict future conditions in order to mitigate or adapt to intensifying hazard risk. The expansive production of climate science has generated a necessary complimentary enterprise dedicated to enhancing decision-makers’ understanding of and access to climate science as it is essential for future societal and ecological well-being. Though the aim of these many tools is to support resilient decision-making in the face of climate change, professionals report an underutilization of climate resilience tools. It has been suggested that stakeholder engagement during climate resilience tool development will improve the rates of use; however, there have been no studies to explore if the findings from tool diffusion and adoption studies in other sectors translate to climate resilience tools. An end-user engagement process for the development of a climate resilience tool was established and implemented. The process itself and the outcomes of the process, in this case an online climate decision-support tool called Gulf TREE (www.GulfTREE.org), were studied. Findings included documenting that end-user engagement during climate resilience tool development, while more costly and time intensive, does lead to increased rates of diffusion and adoption of a climate resilience tool through both direct and indirect means. This work demonstrated that pre-development engagement to scope tool development is critical for maximizing relative benefit of a climate resilience tool. Additionally, all phases of engagement are necessary for both a useable and useful tool because each phase contributes to different attributes of the tool. Further research areas identified include understanding how much and what kind of stakeholder engagement is necessary to support continued diffusion and adoption after a tool is released, the role that mandates in climate resilience has on the adoption and diffusion of climate resilience tools, and how to define if a climate resilience tool has been successful.

This study examines the deployment of Wireless E9-1-1 Phase One and Wireless E9-1-1 Phase Two as a diffusion of innovation. The research method used in this study is a cross-sectional study employing secondary data in a discriminant function analysis. The study population is Virginia units of local governments (95 counties and 39 cities) that had not deployed Wireless E9-1-1 Phase One or Wireless E9-1-1 Phase Two as of January 1, 2001. The period of time included in this study is from 2001 to 2006. The purpose of the study is to assess the overall accuracy of the three principle theories of policy innovation adoption: diffusion, internal determinants, and unified theory, which are variations of the fundamental diffusion theory, in predicting the deployment of wireless E9-1-1 by Virginia units of local government. This assessment was conducted by identifying Virginia specific variables from models associated with these policy innovation theories to determine the best performing model for the deployment of Wireless E9-1-1 throughout the Commonwealth of Virginia. The Virginia specific variables utilized in this study are: Wealth, Population, Fiscal Health, Dedicated Funding, Financial Dependency, Urbanization, Regionalism, and Proximity to Interstate. Dedicated Funding and Regionalism had the largest absolute size of correlation among the predictor variables for the deployment of Wireless E9-1-1 Phase One and Wireless E9-1-1 Phase Two, thus generating the best performing model. This information will provide the basis from which to develop a statewide comprehensive policy and plan for Next Generation 9-1-1 and will help provide an answer to the question of when and how governments get involved in designing and implementing a 9-1-1 emergency service network.

The remarkable spread of the Internet has generated new opportunities for companies to promote themselves and communicate with their customers. The most used Internet service of finding information today is search engines (e.g. Google, Bing, Yahoo) were almost three million searches are preformed every minute worldwide. This trend has led to an importance for companies having their websites visible on these search engines. In addition, people tend to be more and more on the go and are searching with their smartphones instead of traditional personal computer (PC). Meaning that companies’ websites can be available for customers 24 hour a day, 7 days a week, independent on customers location. Consequently, companies have the possibilities to reach the attention of customers when they actually search for a product/service and are therefore most likely to purchase.   In this thesis a marketing strategy has been developed for managers regarding how to master this new communication tool, in order to reach success and competitive advantage. This strategy was developed by investigate in what characteristics and functions users desire when searching with their smartphone. Together with three hypotheses tested if the perceived user-friendliness, relative advantage and compatibility within mobile search have a positive affect on the intention of use this new technology.   In this bachelor thesis a survey was conducted among people in generation C living in Sweden, which resulted in 397 completed responses. The hypotheses were tested with use of a regression analysis and the findings were that the relative advantage and compatibility in mobile search has a positive affect on the intention of use. Therefore, this thesis suggests companies to develop their mobile search engine marketing strategy with the aim of delivering value and satisfying the customer. Moreover, this thesis recommend managers to keep their mobile website quick, relevant and making sure having valuable and informative information about their business in the description text visible to users in the search engine hit list.   Finally, the majority of the population does already act on this new market and it is therefore of great importance for companies satisfying these users in order to stay competitive.

The advection-diffusion equation has been extensively used in air pollution models to simulate mean contaminant concentrations in the planetary boundary layer (PBL). Therefore, in a Eulerian framework, it is possible to theoretically model the dispersion from a continuous point source, given adequate boundary and initial conditions and the knowledge of the mean wind velocity and turbulent concentration fluxes. The choice of an appropriate parameterization for such fluxes plays an important role in the performance of air quality dispersion models based on the advection-diffusion equation. As a consequence, much of the turbulent dispersion research is associated with the specification of these fluxes. The most commonly used approximation for closing the advection-diffusion equation is to relate the turbulent concentration fluxes to mean concentration gradients through the use of eddy diffusivities, which carry within them the physical structure of the turbulent transport phenomenon. For a continuous point source the eddy diffusivities may vary spatially and temporally along the contaminant travel time. Taylor s statistical diffusion theory (1921) determines that the turbulent dispersion depends on the distance from a continuous point source. In the proximity of the source, the fluid particles tend to preserve the memory from their initial turbulent environment. For long travel times, this memory is lost, and the motion of the particles depends only on the local turbulence properties (BATCHELOR, 1949).The aim of the present study is to present a new formulation for the eddy diffusivities in terms of the distance from the source in an inhomogeneous, shear-generated turbulence. The proposition is based on expressions for the turbulent velocity spectra and the statistical diffusion theory. These eddy diffusivities, derived for neutral conditions are described by a complex integral formulation that must be numerically solved. An additional aim of this work is to obtain a simple algebraic expression for the eddy diffusivities in a neutral PBL as a function of the turbulence properties (inhomogeneous turbulence) and the distance from the source. Therefore, the hypothesis to be tested in this study is whether the complex integral formulation for eddy diffusivities can be expressed (substituted) by a simpler algebraic expression. Finally, to investigate the influence of the memory effect in the turbulent dispersion process, a vertical eddy diffusivity is evaluated as a function of the distance from the source against its asymptotic limit employing an Eulerian air pollution model and atmospheric dispersion experiments that were carried out in strong wind conditions. / A equação de difusão-advecção tem sido amplamente utilizada em modelos de poluição do ar para simular as concentrações médias de contaminantes na camada limite planetária (CLP). Portanto, seguindo uma formulação Euleriana, é possível construir um modelo teórico de dispersão de uma fonte pontual contínua a partir de um limite adequado, de condições iniciais e do conhecimento da velocidade média do vento e dos fluxos turbulentos de concentração. A escolha de uma parametrização apropriada para estes fluxos desempenha um papel importante em modelos de dispersão e de qualidade do ar que se baseiam na equação de difusão-advecção. Como consequência, muitas das pesquisas em dispersão turbulenta estão relacionadas com a especificação destes fluxos. A aproximação mais comumente usada para fechar a equação de difusão-advecção relaciona os fluxos turbulentos de concentração com os gradientes de concentração média através do uso de coeficientes de difusão. Estes carregam em si a estrutura física do fenômeno de transporte turbulento. Para uma fonte pontual contínua, tais coeficientes podem variar espacialmente e temporalmente ao longo da viagem dos contaminantes. A teoria de difusão estatística de Taylor (1921) determina que a dispersão turbulenta dependa da distancia de uma fonte pontual continua. Na proximidade da fonte, as partículas de fluído mantêm a memória do seu ambiente inicial turbulento. Para longos tempos de viagem, essa memória se perde, e o movimento das partículas segue apenas as propriedades locais de turbulência (BATCHELOR, 1949). O objetivo deste estudo é apresentar uma nova formulação para os coeficientes de difusão assintóticos e em função da distância da fonte para turbulência não-homogênea. A proposição se baseia em expressões dos espectros de energia cinética turbulenta e na teoria da difusão estatística. Estes coeficientes de difusão função da posição, derivados de condições neutras, são descritos por uma formulação complexa integral que deve ser resolvida numericamente. Um objetivo adicional neste trabalho é a derivação de uma expressão algébrica simples para os coeficientes de difusão, em função das propriedades da turbulência (turbulência não-homogênea) e da distância da fonte. A hipótese a ser testada neste estudo é se a formulação complexa integral para os coeficientes de difusão pode ser substituída por uma simples solução algébrica. Para investigar a influência do efeito de memória no processo de dispersão turbulenta, a difusividade vertical é avaliada em função da distância da fonte contra o seu limite assintótico. Para tanto, se utiliza um modelo Euleriano de poluição do ar cujos resultados são comparados com experimentos de dispersão atmosférica que foram realizados em condições de vento forte.

Made available in DSpace on 2015-04-16T14:48:37Z (GMT). No. of bitstreams: 1 arquivototal1.pdf: 1798793 bytes, checksum: a622918fa2dff41a673786c6c71acfcb (MD5) Previous issue date: 2011-02-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this study, the research model based on the technology acceptance model (TAM) (DAVIS et al., 1989) and innovation diffusion theory (IDT) (ROGERS, 2003) was used to analyze the relation between the characteristics of innovation and teacher s behavior in the process of adoption and use of Moodle in the undergraduate courses at distance. Survey was applied with 162 teachers at distance of Universidade Federal da Paraíba Virtual, issue focusing on the perceived characteristics of innovation, attitude and intention about the use of Moodle. Multivariate statistical techniques were performed: 1) content-vality to analyze the complete structure of scale for relevance and representativeness of items and to verify which items refer to construct in question; 2) exploratory factory analysis to know the structure of interrelationship of the original variables of IDT; 3) confirmatory factor analysis to guarantee conceptual validity for the pattern observed; 4) coefficient alpha to verify the homogeneity of set of items; 5) ANOVA to verify the likely differences between the groups of respondents; and 6) multiple regression analysis to analyze the relation between constructs. Results showed that not all factors of IDT had effect on attitude and intention. Only three constructs had significant effect on attitude and/or intention: relative advantage+compatibility for work style (β = 0,792), visibility (β = 0,166) and result demonstrability (β = 0,152). Moreover, teachers had a positive attitude in relation to use of Moodle and a positive intention in relation to use in the future. It was not possible to confirm all the relation of TAM, probably this verification was been compromised for some problems in the measurement process, thus, the only unsupported relationship of TAM was the effect of complexity on attitude. An academic contribution was that although some constructs of IDT did not show effect on the constructs of TAM, the model provided evidence of appropriated application of constructs of TAM with IDT to measure attitude and intention of use of Moodle. A management contribution was the understanding and prediction the teacher s behavior in relation to adoption and use process of Moodle, being possible to verify the effectiveness of innovative project of distance learning in the UFPB Virtual. / Nesse estudo, o modelo de pesquisa baseado no modelo de aceitação da tecnologia (Technology Acceptance Model - TAM) (DAVIS et al., 1989) e na teoria da difusão da inovação (Innovation Diffusion Theory - IDT) (ROGERS, 2003) foi usado para analisar a relação entre as características de inovação e o comportamento dos docentes no processo de adoção e de uso do Moodle em cursos de graduação a distância. Foi utilizada uma estratégia de levantamento (survey) aplicado a 162 docentes a distância da Universidade Federal da Paraíba Virtual, focando questão sobre as características percebidas de inovação, atitude e intenção em torno do uso do Moodle. Foram realizadas técnicas estatísticas multivariadas: 1) validação de translação para analisar a estrutura completa das escalas em relação à pertinência e representatividade dos itens e a verificação de que os itens propostos remetem ao construto em questão; 2) análise fatorial exploratória para conhecer a estrutura das inter-relações das variáveis originais da IDT; 3) análise fatorial confirmatória para garantir a validade conceitual para os padrões observados; 4) alpha de Cronbach para verificar a homogeneidade do conjunto de itens das escalas; 5) ANOVA para verificar as possíveis diferenças entre os grupos de respondentes; e 6) análise de regressão múltipla para analisar a relação entre os construtos. Os resultados revelaram que nem todos os fatores da IDT tiveram efeito sobre atitude e intenção. Apenas três construtos apresentaram efeito significativo sobre a atitude e/ou intenção: avanço relativo+compatibilidade por estilo de trabalho (β = 0,792), visibilidade (β = 0,166) e demonstrabilidade de resultado (β = 0,152). Além disso, os docentes tiveram uma atitude positiva em relação ao uso do Moodle bem como uma intenção positiva em relação ao seu uso futuro. Não foi possível confirmar todos os relacionamentos do TAM, provavelmente essa verificação foi comprometida por alguns problemas no processo de mensuração das escalas, sendo assim, o único relacionamento do TAM não suportado foi o efeito de complexidade sobre atitude. Uma contribuição acadêmica foi que apesar de alguns construtos da IDT não terem apresentado efeito sobre os construtos do TAM, o modelo forneceu evidência de aplicação apropriada dos construtos do TAM com os da IDT para medir a atitude e intenção de uso do Moodle. Uma contribuição gerencial foi a compreensão e previsão do comportamento dos docentes EaD em relação ao processo de adoção e uso do Moodle, possibilitando verificar a efetividade do projeto inovador de EaD na UFPB Virtual.

Electric vehicle adoption is one of the most prominent discussions currently facing the automotive industry, as this is an inevitable change towards a more sustainable future of transportation. Traditionally, car manufacturers adapt to consumer needs changing, thus prompting high relevance for understanding the consumer perspective and purchasing influences. This study aims to build a deeper understanding of the importance of internal and external factors on the EV consumer decision-making process, as well as to explore how the perception of such factors change upon adoption of electric vehicles. The study follows a positivism approach by conducting deductive research. A conceptual framework is developed based on review of research literature of rational choice theory, the consumer decision-making model, and factors impacting EV consumers, and constructing a model from the findings. Quantitative survey data is then collected following the model presented, and results are obtained using SPSS. Finally, the analysis applies the social identity theory, innovation diffusion theory, and theory of planned behavior for further evaluative discussions. The findings show that internal factors such as environmental awareness and fears and anxieties have a vital impact on consumers’ decisions of EV adoption and evaluation of EV alternatives, while social influences have a relatively small impact on the decision. The findings suggest a link between the theory of planned behavior and changing perceptions upon adoption of EV, in which factors relating to attitudes and perceived behavioral control are more susceptible to changing, while factors relating to subjective norms are not.

<p>A wide variety of phase evolution phenomena observed in solids such as intermetallic growth at the junction between two metals subjected to high temperature, growth of oxide on metal surfaces due to atmospheric exposure and void evolution induced by electromigration in microelectronic devices for example, can be classified as being driven by reaction-diffusion processes. These phase evolution phenomena have a significant impact on material reliability for critical applications, and therefore, there is a requirement for modeling such reaction-diffusion driven phase evolution phenomena. It is difficult to analyze these due to the complexity of modeling the evolving interface between solid phases. Additional complexity is  due to the multi-physics nature of the diffusive and reactive processes. Diffusion in solids is driven by a variety of stimuli such as current, temperature and stress, in addition to the chemical potential. Therefore, there is a need for a model that accounts for the influence of such factors on phase evolution. In this thesis,  a generalized continuum based reaction-diffusion theory for phase and void evolution in solid state is developed. The derivation starts off with generalized interface balance laws for mass, momentum and energy. The thermodynamic entropy inequality for irreversible phase growth is derived for arbitrary anisotropic and inhomogeneous surface stress. These interface relations are combined with governing relations in the material bulk for the temperature, stress, electrical and concentration fields, to develop a general model capable of analyzing and describing phase evolution in solids. This theory is then applied to a variety of intermetallic phase and void evolution phenomena observed in microelectronics.</p> <p><br></p> <p>Electromigration induced voiding in thin metal films is an example of phase evolution that is an important reliability concern in microelectronics. Studies have reported that the electromigration induced void growth rate is inversely related to the adhesion of metal thin films with the base and capping layers. Electromigration experiments are performed on fabricated test devices with Cu thin films with SiNx and TiN capping layers. The observations from electromigration experiments on thin Cu metal films at a range of temperatures indicate that the contribution of interface adhesion strength to electromigration resistance decreases with an increase in temperature. The generalized reaction-diffusion theory developed here is modified to develop an expression to account for the effect of base and passivation layer adhesion and temperature on electromigration resistance of metal thin films. The void growth rates measured in the experiments are analyzed with the expression for void growth rate to estimate the interface adhesion strength for the Cu-TiN and Cu-SiNx interfaces. </p> <p><br></p> <p>Demand for increased bandwidth, power efficiency and performance requirements have resulted in a trend of reduction in size and pitch of Cu pillar-Solder micro-bump interconnects used in heterogeneously integrated packages. As the size of micro-bumps reduce, reliability challenges due to voiding in the solder joint and the growth of Cu-Sn intermetallics are observed. The underlying reaction-diffusion mechanisms responsible for Cu-Sn intermetallic growth and voiding in solder joints are unclear at this stage and require further investigation. The current practice of material characterization in micro-bumps involve destructive cross-sectioning and polishing of the micro-bumps after testing. These processes result in loss of continuity in the samples used for the experiments, and material removal due to abrasive polishing might result in a loss of critical information. Therefore, a novel test device capable of non-destructive characterization of Cu-Sn intermetallic growth and voiding in sub-30 micron size micro-bumps is designed and fabricated in this work. The fabricated test devices are subjected to thermal aging for over 1000 h and the underlying reaction-diffusion mechanisms behind the intermetallic phase and void evolution are investigated. </p> <p><br></p> <p>A reaction-diffusion mechanism is proposed explaining the evolution of  various Cu-Sn intermetallic phases and solder joint void observed from experiments. Using the reaction-diffusion mechanism inferred from the thermal aging experiments and the generalized reaction-diffusion theory for phase evolution developed in this thesis, a sharp interface model is developed for the evolution of Cu-Sn intermetallic phases and solder joint void. The diffuse interface phase field equivalent equations for the sharp interface model governing equations are developed using matched formal asymptotic analysis. The evolution of Cu-Sn intermetallic phase and voids in the solder joint are simulated for different temperatures and current density to demonstrate the validity of the phase field and sharp interface models.  </p> <p><br></p>

No description available.

Diffusion plays an important role in a number of processes like heterogeneous catalysis, corrosion, separation and purification of chemicals of industrial importance, steel hardening, fuel cells, and solid electrolytes for batteries. It also plays a vital role in several biological processes like transport across biomembranes, nerve impulse, flow of blood and permeation of ingested drug. The elementary process of diffusion in solids is quite different from those in liquids. Similarly, the mode of diffusion in porous solid where different regimes such Knudsen regime exists bears little similarity to those in a dense close-packed crystalline solid. Chapter 1 provides a brief introduction to basics of diffusion in different phases of condensed matter. Among the various phases discussed are liquids, close-packed crystalline solids (e.g., body-centered cubic solids), amorphous solids (e.g. glasses) and microporous crystalline solids (e.g., zeolites). Diffusion in these widely differing phases often bears no resemblance to each other; the rate of diffusion in these phases varies over many orders of magnitude and the elementary step and mechanism in the diffusion process are very different. Brief introduction to theories for diffusion in these phases is provided. Various experimental techniques to measure diffusivities are discussed. Different microscopic models to explain the Quasi Elastic Neutron Scattering (QENS) spectra of these phases yield an insight into the elementary step of the diffusion process. Notwithstanding the fact that completely different models are invoked to explain diffusion in different phases, there are certain underlying generic behaviour across these widely differing phases as the recent work on size dependence of diffusion in these phases demonstrate. Diffusion of a molecule or species (in the context of diffusion within condensed phases) without loss of generality may be said to occur in a medium. A universal behaviour observed is that self diffusivity exhibits a maximum as a function of the size of the diffusant when the diffusant is confined to a medium, as a result of what is known as the Levitation Effect. Such a maximum in self diffusivity has been seen in widely differing medium: microporous solids, dense liquids, ions in polar solvents, etc. The aim of the thesis is to investigate and further explore such universal behaviour and demonstrate for the first time the existence of common trends across different condensed phases in spite of difference in the detail at the microscopic level. In Chapter 2, we report a molecular dynamics study of diffusion of diatomic species AB within zeolite Y. The bond length of A-B as well as the interaction of A and B with the host zeolite atoms are varied. The results demonstrate that for the symmetric case (when A=B or AA), there exists a preferred bond length (determined by the bottleneck or window diameter) when the diffusivity is maximum. This is in agreement with previous results on monatomic species which also exhibit a similar diffusivity maximum. More importantly, no such maximum is seen when the interaction asymmetric is introduced in AB. Slight asymmetry in the interaction gives rise to a weak maximum while large asymmetry in interaction obliterates the diffusivity maximum. These results suggest that the importance of interaction between the diffusant and the medium in Levitation Effect or size-dependent diffusivity maximum. Further, it also demonstrates for the first time the close association between an inversion centre (in a statistical sense and not in the crystallographic sense) and the Levitation Effect. In Chapter 3, a study of size dependence of solutes in a Lennard-Jones liquid is reported. Einstein and others derived the reciprocal dependence of the self-diffusivity D on the solute radius ru for large solutes based on kinetic theory. We examine here (a) the range of ru over which Stokes-Einstein (SE) dependence is valid and (b) the precise dependence for small solutes outside of the SE regime. We show through molecular dynamics simulations that there are two distinct regimes for smaller solutes: (i) the interaction or Levitation Effect (LE) regime for solutes of intermediate sizes and (ii) the D 1/ru2 for still smaller solutes. We show that as the solute-solvent size ratio decreases, the breakdown in the Stokes-Einstein relationship leading to the LE regime has its origin in dispersion interaction between the solute and the solvent. These results explain reports of enhanced solute diffusion in solvents existing in the literature seen for small solutes for which no explanation exists. Several properties have been computed to understand the nature of solute motion in different regimes. We investigate in Chapter 4, the dependence of self diffusivity on the size of the diffusant in a disordered medium with the objective of understanding the experimentally observed correlation between self diffusivity and activation energy seen in a wide variety of glasses. Typically, it is found in many ionic glasses that a higher conductivity is associated with lower activation energy and vice versa. Our understanding of transport in glasses as provided by existing theories does not offer an explanation of this correlation. We have carried out molecular dynamics simulation as a function of the size of the impurity atom or diffusant (both neutral and charged) in a model host amorphous matrix. We find that there is a maximum in self diffusivity as a function of the size of the impurity atom suggesting that there is an appropriate size for which the diffusivity is maximum. The activation energy is found to be the lowest for this size of the impurity. A similar maximum has previously been found in other condensed phases such as confined fluids and dense liquids and has its origin in the Levitation Effect. The implications of this result for understanding ionic conductivity in glasses are discussed. Our result suggests that there is a relation between microscopic structure of the amorphous solid, diffusivity or conductivity and activation energy. The nature of this relationship is discussed in terms of the Levitation parameter showing that diffusivity is maximum when the size of the neck or doorway radius is comparable with the size of the diffusant. Our computational results here are in excellent agreement with independent experimental results which show that structural features of the glass are important in determining the ionic conductivity. In Chapter 5, we report results of molecular dynamics investigations into neutral impurity diffusing within an amorphous solid as a function of the size of the diffusant and density of the host amorphous matrix. We find that self diffusivity exhibits an anomalous maximum as a function of the size of the impurity species. An analysis of properties of the impurity atom with maximum diffusivity shows that it is associated with lower mean square force, reduced backscattering of velocity autocorrelation function, near-exponential decay of the intermediate scattering function (as compared to stretched-exponential decay for other sizes of the impurity species) and lower activation energy. These results demonstrate the existence of well known size-dependent diffusivity maximum in disordered solids. Further, we show that the diffusivity maximum is observed at lower impurity diameters with increase in density. This is explained in terms of the levitation parameter and the void structure of the amorphous solid. We demonstrate that these results imply contrasting dependence of self diffusivity (D) on the density of the amorphous matrix, . D increases with  for small sizes of the impurity but shows an increase followed by a decrease for intermediate sizes of the impurity atom. For large sizes of the impurity atom, D decreases with increase in . These contrasting dependence arises naturally from the existence of Levitation Effect. In Chapter 6, we discuss size dependence of impurity diffusion in an ordered system. We report molecular dynamics simulation studies to understand the role of impurity size and impurity-host interaction on impurity diffusivity in a body centered cubic solid. The simulation studies have been performed for a set of impurity-host interaction parameter ih (i=impurity, h=host atom) for a range of impurity sizes in rigid and flexible bcc solids. A double maximum is seen corresponding to two different sizes of the impurity species. Anomalous maximum is seen for a larger size of the impurity species in the case of the rigid host as compared to flexible host. The second anomalous diffusivity disappears with decrease in ih in flexible bcc solid. For one of the ih where double diffusivity maxima are observed, various properties are analysed to understand the anomalous diffusion behaviour. The impurity with anomalous diffusion has lower activation energy as compared to other impurities. Among the two anomalous impurities, the impurity with higher diffusivity has lower activation energy. The anomalous regime impurities as associated with velocity autocorrelation function with little or no backscattering, minimum average mean square force due to host atoms, lower activation energy. The self intermediate scattering function shows faster decay and a single relaxation time for anomalous regime impurity and two relaxation times for other impurity sizes. The wavenumber dependence of diffusivity of impurities shows oscillatory behaviour except for the anomalous regime impurities which show monotonic dependence on wavenumber. Chapter 7 discusses the influence of temperature induced solid-liquid phase transition on the size-dependent diffusivity. We report results for two distinct cases: (a) when the phase change is associated with corresponding changes in density and (b) when the phase change occurs at constant density. The latter is carried out so as to obtain the influence of disorder on the size-dependent diffusion or Levitation Effect. Studies with variable density are useful to understand the effect of disorder as well as change in density on size-dependent diffusivity. Two diffusivity maxima in the solid face-centred cubic phase is seen when the impurity-medium interaction is sufficiently large. One of these diffusivity maximum disappears with decrease in h. The impurities near the diffusivity maximum show velocity autocorrelation function with little backscattering, minimum in the average mean square force, lower activation energy, faster decay of self intermediate scattering function with a single relaxation time and a monotonic decay in wavevector dependence of diffusivity. Chapter 8 reports molecular dynamics simulations of a model guest tetrahedral molecule AX4 with differing bond lengths lAX have been carried out in a sphere with different surface roughness. The rotational-diffusion coefficient Dr shows a maximum for a particular value of lAX. This corresponds to the distance at which the interaction of the guest with the atoms of the host is most favourable. Although, the intensity of the maximum decreases with increase in the roughness of the confining surface, it is seen that the maximum exists even for a reasonably high degree of roughness. The observed maximum arises from the minimum in the torque on the tetrahedral molecule from its interaction with the confining medium due to mutual cancellation of forces. Activation energy for rotation is seen to be also a minimum for the bond length for which Dr is a maximum. These results suggest that there is a maximum in the rotational-diffusion coefficient when the rotating molecule is confined to a sphere of comparable size similar to the maximum in translational diffusion coefficient seen in porous solids and known as the Levitation Effect. On increase in the roughness of the sphere surface, the value of lAX at which the maximum in Dr is seen decreases. This is similar to the shift seen in the size of the diffusant corresponding to maximum diffusivity in the case of translational diffusivity. In Chapter 9 possible extensions to the work reported in the previous chapters and the directions to take are discussed. Symmetry plays an important role in size dependent diffusivity maximum in microporous crystalline solids; it would be interesting to investigate if similar role of symmetry exists in case of liquids and other disordered solids. Previous work from this laboratory on ions in water has shown the importance of electrostatic interactions. In the light of this, it would be interesting to see the influence of long-range interactions in breakdown of Stokes-Einstein relationship in liquids. Effect of density of the medium on impurity diffusion can be studied over a wide range of densities in case of supercritical fluids such as ions in water (where electrostatic interactions are present) and these can provide greater insight into dependence of diffusion on density. The origin of two diffusivity maxima in case of body-centered and face-centred cubic solids needs a detailed investigation to understand its origin. Quantification of disorder and its effect on size dependence of diffusion would be of interest. A detailed comparison with experimental data of matrix isolated molecules to understand and verify the dependence of rotational diffusivity on the size of the molecule as well as the cavity radius would be instructive.