Several organic reactions that could potentially involve coarctate transition states were investigated by a combination of experimental and theoretical studies. In the thermal fragmentation of ∆-1,3,4-oxadiazolines, the mechanism supported by kinetic isotope effects and theoretical calculations is a three-step process that does not demonstrate any special stabilization in coarctate transition states. Rather than undergoing a direct coarctate conversion to product, the mechanism avoids coarctate steps. The last step is a concerted coarctate reaction, but being concerted may be viewed as being enforced by the necessity to avoid high-energy intermediates. In the deoxygenation of epoxides with dichlorocarbene, the stabilization from the transition state aromaticity is not great enough to compete with the preference for asynchronous bonding changes. KIEs and calculations suggested that the reaction occurs in a concerted manner but with a highly asynchronous early transition state with much more Cα-O bond breaking than Cβ-O bond breaking. In the Shi epoxidation, a large β-olefinic 13C isotope effect and small α-carbon isotope effect indicated an asynchronous transition state with more advanced formation of the C-O bond to the β-olefinic carbon. The calculated lowest-energy transition structures are generally those in which the differential formation of the incipient C-O bonds, the "asynchronicity," resembles that of an unhindered model, and the imposition of greater or less asynchronicity leads to higher barriers. In reactions of cis-disubstituted and terminal alkenes using Shi's oxazolidinone catalyst, the asynchronicity of the epoxidation transition state leads to increased steric interaction with the oxazolidinone when a π-conjugating substituent is distal to the oxazolidinone but decreased steric interaction when the π-conjugating substituent is proximal to the oxazolidinone. Dynamic effects were studied in Diels-Alder reaction between acrolein and methyl vinyl ketone. This reaction yields two products in a ratio of 3.0 ± 0.5. Theoretical studies shows that only one transition structure is involved in the formation of both. Quasiclassical trajectory calculations on an MP2 surface give a prediction of a product ratio of 45:14 (3.2:1), which is in good agreement with the experimental observation.

This dissertation analyzes the optimal mix of direct and indirect taxes in an economy with multiple tax collecting authorities when both the taxes are subject to evasion and to what extent the tax compliance behavior of individuals in the United States are persistent and spatially dependent. Essay I derives and provides an intuitive interpretation of: (i) impact of the changes in the government instruments on tax evasion by firms, the expected prices they charge, and the expected tax rates they face; (ii) a generalized version of Ramsey rule for optimal commodity taxation which accounts for income tax evasion from either or both the tax authorities; (iii) generalized formulae for the optimal income tax rate for each of the tax authorities; and (iv) the tradeoff between optimal tax rates and audit probabilities for each of the tax authorities. It also re-examines controversies surrounding the uniform income taxes and the differentiated commodity taxes, and investigates how income tax evasion affects the progressivity of the income tax rates. It concludes that whether or not tax evasion calls for reductions in the optimal income tax rates hinges on how tax evasion and the associated concealment costs vary across individual taxpayers. Essay II introduces the twin issues of spatiality and persistence in the individual income tax evasion. While the issue of persistence arises through accumulated learning over time, spatiality arises for several reasons. Some these include the exchange of information between taxpayers; the social norm of tax compliance: an individual would comply if everybody in the society complies and vice versa; individuals faced with dynamic stochastic decision problems that pose immense computational challenges may simply look to others to infer satisfactory policies and interpersonal dependence works through learning by imitating rather than learning by doing. State-level annual per return evasion of individual income tax and related data were used to examine the above hypotheses and found supports for both of them in the individual income tax evasion in the United States.

The mechanism of three important aldol reactions and a biomimetic transamination is investigated using a combination of experimental kinetic isotope effects (KIEs), standard theoretical calculations and dynamics trajectory simulations. This powerful mechanistic probe is found to be invaluable in understanding intricate details of the mechanism of these reactions. The successful application of variational transition state theory including multidimensional tunneling to theoretically predict isotope effects, described in this dissertation, represents a significant advance in our research methodology. The role of dynamic effects in aldol reactions is examined in great detail. The study of the proline catalyzed aldol reaction has revealed an intriguing new dynamic effect - quasiclassical corner cutting - where reactive trajectories cut the corner between reactant and product valleys and avoid the saddle point. This phenomenon affects the KIEs observed in this reaction in a way that is not predictable by transition state theory. The study of the Roush allylboration of aldehydes presents an example where recrossing affects experimental observations. The comparative study of the allylboration of two electronically different aldehydes, which are predicted to have different amounts of recrossing, suggests a complex interplay of tunneling and recrossing affecting the observed KIEs. The Mukaiyama aldol reaction has been investigated and the results unequivocally rule out the key carbon-carbon bond forming step as rate-limiting. This raises several interesting mechanistic scenarios - an electron transfer mechanism with two different rate-limiting steps for the two components, emerges as the most probable possibility. Finally, labeling studies of the base catalyzed 1,3- proton transfer reaction of fluorinated imines point to a stepwise process involving an azomethine ylide intermediate. It is found that dynamic effects play a role in determining the product ratio in this reaction.

Statistical models like Transition State Theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) Theory have generally been successful in predicting the rates and selectivities of chemical reactions. However, these statistical models can fail to explain experimental results of ordinary organic reactions. For these reactions, consideration of nonstatistical dynamic effects or the detailed motion and momenta of the atoms is necessary to account for the experimental observations. Dynamic effects have been found to be important in a growing number of reactions and the nature of these effects can be varied. One of the most interesting reactions investigated is the ozonolysis of vinyl ethers. Ozonolysis of a homologous series of vinyl ethers in solution exhibit experimental product ratios wherein the selectivity among cleavage pathways increases with the size of the alkyl group to an extent that is far less than RRKM theory would predict. Trajectory studies account for the observed selectivities and support a mechanism involving a competition between cleavage of the primary ozonide and intramolecular vibrational energy redistribution. A recent theoretical study from our group predicted that a highly asynchronous organocatalytic Diels-Alder (DA) reaction, which is concerted in the potential energy surface, is stepwise in the free energy surface. Kinetic isotope effects (KIEs) were measured for three DA reactions. We envision that the entropic barrier may have several experimental consequences such as unusual isotope effects due to extensive recrossing. Preliminary results for the organocatalytic reaction show an intramolecular KIE close to unity that cannot be reconciled with statistical theories. This is in contrast with Lewis-acid catalyzed and thermal DA reactions, which exhibit substantial "normal" intramolecular KIEs that are in accord with TST predictions. Finally, the Baeyer-Villiger oxidation of cylohexanone in water was investigated. KIEs were measured for the oxidation of cyclohexanone with peracetic acid and trifluoroperacetic acid. When using peracetic acid as the oxidant, the alkyl migration was determined to be the rate-determining step based on significant intermolecular KIEs on the carbonyl and alpha-methylene carbons. A change in the rate-determining step is seen when trifluoroperacetic acid is used. Only the carbonyl carbon exhibits a significant isotope effect. Theoretical predictions provide an experimental picture of the transition states and qualitatively support these conclusions.

Nos últimos anos cresceu o interesse por construir edifícios cada vez mais altos, os quais estampam o poderio tecnológico e econômico das nações. Concomitantemente as estruturas se tornaram mais esbeltas e flexíveis e os fenômenos dinâmicos oriundos da ação do vento, que em edificações baixas não representam grande relevância no carregamento, começam a surgir e apresentar seus efeitos. Desta maneira, é importante conhecer como se desenvolve o escoamento do ar e a distribuição das pressões no entorno destas estruturas. Neste trabalho, caracteriza-se aerodinamicamente, através de dados oriundos de ensaios em túnel de vento, dois empreendimentos reais e presentes na engenharia nacional. Os carregamentos foram gerados através da integração simultânea de pressões e transformados em espectros de força, os quais auxiliam na visualização da energia cinética contida nas rajadas, na ocorrência de desprendimento cadenciado de vórtices, martelamento e na influência que as edificações vizinhas apresentam no escoamento. A análise é realizada local e globalmente, possibilitando verificar em que “zona”, ou faixa de altura, é mais significante para o carregamento da estrutura como um todo. O fenômeno de desprendimento de vórtices é caracterizado por um pico no espectro transversal à incidência do vento. Quando existem edificações ou obstáculos na região a barlavento, a estrutura pode ser martelada até a altura média destes obstáculos. Por fim, os resultados aqui apresentados podem servir de auxílio no pré-dimensionamento de estruturas com configurações similares, como comparativo e validação para pesquisas futuras e como referencial na elaboração de códigos normativos referentes ao tema. Destaca-se a importância de ensaios em túnel de vento, principalmente quando a estrutura a ser analisada possui um detalhamento arquitetônico complexo. Estes ensaios permitem ao projetista simular todos os casos de carregamento e os efeitos de vizinhança com maior confiabilidade e precisão em relação a métodos simplificados contidos, atualmente, em códigos e normas. / In recent years many high-rise buildings have been built, which are a way to represent the economic and technological power of nations. Concomitantly, the structures have become slender and more flexible, and the dynamic phenomena of wind, which in low buildings do not represent a great relevance in the loading, start to show their effects. In this way, it is extremely important to know how the wind flow and the pressure distribution occur around these structures. In this research, two real projects, present in the national engineering, are characterized aerodynamically through data from wind tunnel tests. The loadings were processed through the simultaneous integration of pressures and transformed into force spectra, which aid in the visualization of the kinetic energy contained in the bursts, in the occurrence of vortex shedding, buffeting and the influence of the neighboring buildings on the wind flow. The analysis is performed locally and globally, making it possible to verify which "zone", or height range, is more significant to the loading of the structure as a whole. It can be seen that the phenomenon of vortex shedding is characterized by a peak in the crosswind spectrum and the buffeting phenomenon appears when there are buildings or obstacles in the windward region. Finally, the results presented here can be helpful in the pre-design of structures with similar configurations, in the comparison and validation for future researches and as a reference in the review of normative codes. Emphasis is given to the importance of wind tunnel testing, which allows the designer to simulate all loading cases and neighborhood effects with greater precision compared to simplified methods currently contained in codes and standards.

<p>Creating three dimensional hair is still one of the hardest elements when creating characters. Problems occur because of the constant changes in the software every few years. A major goal is to create as realistic hair as possible in Autodesk Maya and to supply this detailed information on to other 3D artist. Techniques are researched and reviewed on how different hair systems are created, as well as how dynamic effects react on the moving hair.</p>

Nos últimos anos cresceu o interesse por construir edifícios cada vez mais altos, os quais estampam o poderio tecnológico e econômico das nações. Concomitantemente as estruturas se tornaram mais esbeltas e flexíveis e os fenômenos dinâmicos oriundos da ação do vento, que em edificações baixas não representam grande relevância no carregamento, começam a surgir e apresentar seus efeitos. Desta maneira, é importante conhecer como se desenvolve o escoamento do ar e a distribuição das pressões no entorno destas estruturas. Neste trabalho, caracteriza-se aerodinamicamente, através de dados oriundos de ensaios em túnel de vento, dois empreendimentos reais e presentes na engenharia nacional. Os carregamentos foram gerados através da integração simultânea de pressões e transformados em espectros de força, os quais auxiliam na visualização da energia cinética contida nas rajadas, na ocorrência de desprendimento cadenciado de vórtices, martelamento e na influência que as edificações vizinhas apresentam no escoamento. A análise é realizada local e globalmente, possibilitando verificar em que “zona”, ou faixa de altura, é mais significante para o carregamento da estrutura como um todo. O fenômeno de desprendimento de vórtices é caracterizado por um pico no espectro transversal à incidência do vento. Quando existem edificações ou obstáculos na região a barlavento, a estrutura pode ser martelada até a altura média destes obstáculos. Por fim, os resultados aqui apresentados podem servir de auxílio no pré-dimensionamento de estruturas com configurações similares, como comparativo e validação para pesquisas futuras e como referencial na elaboração de códigos normativos referentes ao tema. Destaca-se a importância de ensaios em túnel de vento, principalmente quando a estrutura a ser analisada possui um detalhamento arquitetônico complexo. Estes ensaios permitem ao projetista simular todos os casos de carregamento e os efeitos de vizinhança com maior confiabilidade e precisão em relação a métodos simplificados contidos, atualmente, em códigos e normas. / In recent years many high-rise buildings have been built, which are a way to represent the economic and technological power of nations. Concomitantly, the structures have become slender and more flexible, and the dynamic phenomena of wind, which in low buildings do not represent a great relevance in the loading, start to show their effects. In this way, it is extremely important to know how the wind flow and the pressure distribution occur around these structures. In this research, two real projects, present in the national engineering, are characterized aerodynamically through data from wind tunnel tests. The loadings were processed through the simultaneous integration of pressures and transformed into force spectra, which aid in the visualization of the kinetic energy contained in the bursts, in the occurrence of vortex shedding, buffeting and the influence of the neighboring buildings on the wind flow. The analysis is performed locally and globally, making it possible to verify which "zone", or height range, is more significant to the loading of the structure as a whole. It can be seen that the phenomenon of vortex shedding is characterized by a peak in the crosswind spectrum and the buffeting phenomenon appears when there are buildings or obstacles in the windward region. Finally, the results presented here can be helpful in the pre-design of structures with similar configurations, in the comparison and validation for future researches and as a reference in the review of normative codes. Emphasis is given to the importance of wind tunnel testing, which allows the designer to simulate all loading cases and neighborhood effects with greater precision compared to simplified methods currently contained in codes and standards.

Nos últimos anos cresceu o interesse por construir edifícios cada vez mais altos, os quais estampam o poderio tecnológico e econômico das nações. Concomitantemente as estruturas se tornaram mais esbeltas e flexíveis e os fenômenos dinâmicos oriundos da ação do vento, que em edificações baixas não representam grande relevância no carregamento, começam a surgir e apresentar seus efeitos. Desta maneira, é importante conhecer como se desenvolve o escoamento do ar e a distribuição das pressões no entorno destas estruturas. Neste trabalho, caracteriza-se aerodinamicamente, através de dados oriundos de ensaios em túnel de vento, dois empreendimentos reais e presentes na engenharia nacional. Os carregamentos foram gerados através da integração simultânea de pressões e transformados em espectros de força, os quais auxiliam na visualização da energia cinética contida nas rajadas, na ocorrência de desprendimento cadenciado de vórtices, martelamento e na influência que as edificações vizinhas apresentam no escoamento. A análise é realizada local e globalmente, possibilitando verificar em que “zona”, ou faixa de altura, é mais significante para o carregamento da estrutura como um todo. O fenômeno de desprendimento de vórtices é caracterizado por um pico no espectro transversal à incidência do vento. Quando existem edificações ou obstáculos na região a barlavento, a estrutura pode ser martelada até a altura média destes obstáculos. Por fim, os resultados aqui apresentados podem servir de auxílio no pré-dimensionamento de estruturas com configurações similares, como comparativo e validação para pesquisas futuras e como referencial na elaboração de códigos normativos referentes ao tema. Destaca-se a importância de ensaios em túnel de vento, principalmente quando a estrutura a ser analisada possui um detalhamento arquitetônico complexo. Estes ensaios permitem ao projetista simular todos os casos de carregamento e os efeitos de vizinhança com maior confiabilidade e precisão em relação a métodos simplificados contidos, atualmente, em códigos e normas. / In recent years many high-rise buildings have been built, which are a way to represent the economic and technological power of nations. Concomitantly, the structures have become slender and more flexible, and the dynamic phenomena of wind, which in low buildings do not represent a great relevance in the loading, start to show their effects. In this way, it is extremely important to know how the wind flow and the pressure distribution occur around these structures. In this research, two real projects, present in the national engineering, are characterized aerodynamically through data from wind tunnel tests. The loadings were processed through the simultaneous integration of pressures and transformed into force spectra, which aid in the visualization of the kinetic energy contained in the bursts, in the occurrence of vortex shedding, buffeting and the influence of the neighboring buildings on the wind flow. The analysis is performed locally and globally, making it possible to verify which "zone", or height range, is more significant to the loading of the structure as a whole. It can be seen that the phenomenon of vortex shedding is characterized by a peak in the crosswind spectrum and the buffeting phenomenon appears when there are buildings or obstacles in the windward region. Finally, the results presented here can be helpful in the pre-design of structures with similar configurations, in the comparison and validation for future researches and as a reference in the review of normative codes. Emphasis is given to the importance of wind tunnel testing, which allows the designer to simulate all loading cases and neighborhood effects with greater precision compared to simplified methods currently contained in codes and standards.

The behaviour of concrete structures subjected to high impulsive loading such as blast involves complex responses at the constituent material as well as local to global structural levels. To fully describe the processes involved, detailed numerical simulation is generally required and it is in fact commonly employed nowadays in this field of investigations. However, the demands on a rigorous computational model with the capability to represent different regimes of responses throughout the entire process, namely the stress wave stage under the immediate impulsive (blast) loading, the development of local composite mechanism (such as shear), and finally the global bending / residual structural state, have not been established nor thoroughly investigated in the literature. This thesis aims to fill in this gap and develop an effective and efficient modelling framework for reinforced concrete (RC) structures under impulsive loading, with a particular focus on the analysis of complex dynamic shear mechanisms and the residual structural capacities. This thesis uses a benchmark RC slab as a testbed to firstly examine the validity of commonly applied finite element setup and typical material models for the analysis of the structural response into the global deformation phase and the residual state. This is followed by a detailed scrutiny of the demands on the concrete material model in terms of preserving a realistic representation of the tension/shear behaviour and the significance of such features in simulating realistically the structural response in a reinforced concrete environment. Deficiencies of a widely used concrete material model, namely the Karagozian and Case concrete (KCC) model, in this respect are investigated and a modification scheme to the relevant aspects of the material model is proposed. The modification is demonstrated to result in satisfactory improvement in terms of ensuring more robust simulation of reinforced concrete response to blast loading. To deal with the inevitable modelling uncertainties in the part of concrete surrounding reinforcing bars in a numerical model, an equivalent transitional layer model is proposed for use in finite element modelling of RC structures subjected to impulsive loading. The main objectives of the equivalent transitional layer are to achieve a consist transfer of stress between rebar to concrete outside the transitional zone, and to maintain a realistic relative “sliding” displacement between the outer edge of the transitional layer and the rebar, while the inner edge of the transitional layer is perfectly bonded (with node-sharing) to the rebar. With appropriate descriptions of the softening and failure of the material for the transitional layer, the deformation profile and the strength can be reasonably represented in a consistent manner using the perfect-bond scheme which is commonly adopted in this field of applications. The transitional layer also incorporates features to ensure mesh-independent bond strength. Validation of proposed transitional layer model is carried out against results from RC pullout and beam experiments. The above modelling framework is subsequently employed to investigate the dynamic shear resistance of RC beam/slab under impulsive loading, recognising that the information on the dynamic shear strength in very scarce in the literature. The influence of loading rate on the change of shear span, which alters the shear resistance mechanism and generally results in an increase of the shear capacity, is discussed. The influence of the strain rate enhancement of the material strength on the dynamic shear capacity is also evaluated.

Creating three dimensional hair is still one of the hardest elements when creating characters. Problems occur because of the constant changes in the software every few years. A major goal is to create as realistic hair as possible in Autodesk Maya and to supply this detailed information on to other 3D artist. Techniques are researched and reviewed on how different hair systems are created, as well as how dynamic effects react on the moving hair.