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This thesis focuses on the study of hybrid perovskites properties for the purposes of photovoltaic applications. During the almost four years PhD project that has lead to this thesis the record photovoltaic efficiency for this technology has in- creased from 10.9% to 22.1%. Such a significant pace of development can be com- pared with few other materials. It is for this reason that hybrid perovsites have at- tracted impressive research efforts. We approached the study of such unique ma- terials using computational ab-initio techniques, and in particular Density Func- tional Theory. We considered different materials, but most of the attention was concentrated on MAPI (CH 3 NH 3 PbI 3 ). The results are divided in three chapters, each exploring a different material prop- erty. The first chapter reports the electronic structure of the material bulk, sur- faces, and other electronic-related properties such as the rotation barrier for the organic component and the Berry phase polarization. The second chapter focuses on the vibrational properties primary employing the harmonic approximation but also extends to the quasi-harmonic approximation. The outcome of these calculations permitted us to calculate theoretical IR and Ra- man spectra which are in good agreement with different experimental measure- ments. The quasi-harmonic approximation was used to calculate temperature dependent properties, such as the Grüneisen parameter, the thermal dependence of heat capacity and the thermal volumetric expansion. The third and last chapter reviews the thermodynamic properties of binary halide compounds. The cobination of ab-initio calculations with the generalised quasi- chemical approximation has allowed to study the stability of mixed composition perovskites. The results certified a set of stable structures that could stand at the base of observed phenomena of photo-degradation of hybrid perovskite based devices. All three chapters have been written to understand the chemical and physical behaviour of hybrid perovskites and to extended and contribute to the under- standing of experimental work.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Sadegh, Nader; Committee Member: Chen, Xu-Yan; Committee Member: Chen, Ye-Hwa. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This thesis is a project of intellectual history which focuses on the development of notions of power and the nation-state in realist thought. The main aim of the thesis is to offer a comprehensive account of how different conceptions of power in the work of various realist thinkers influence their perceptions of the nation-state. Although both power and the state are considered as central to realism, their connection has not been adequately discussed and remains largely implicit. The thesis aims at illuminating such a connection. The authors under examination are both key realist thinkers and representative of the diversity of realist thought as well as of the development from classical to structural realism. As such, the thesis focuses on the works of E.H. Carr, H. Morgenthau (as classical realists), J. Herz (as a transitional figure) and J. Mearsheimer (as a structural realist). The thesis engages with each realist’s theory in a three-step process. First, it analyses their conceptualisation of power and the role it plays in their ontological and epistemological assumptions. Then, using that conceptualisation of power as a starting point, it discusses its impact on the way the realist under examination understood the nation-state. Finally, the way the aforementioned realists engaged with the foreign policies of given nation-states is employed as an illustration of their theoretical framework. The thesis identifies a close interplay between power and the nation-state in all realists examined. Power plays a central role in each realist’s ontology and as such influences profoundly the way they conceptualised the nation-state. The latter can thus be approached as a manifestation of power which is unfixed in time. The realists examined approach the state as a historically conditioned entity. As such, it is argued that it is power that constitutes the core analytical category of realism rather than the state whose very conception is dependent upon that of power. In terms of the development of realism, a process of gradual narrowing down of the concept of power from classical to structural approaches is observed. The multifaceted conception of power advanced by early realists is abandoned in favour of an approach which understands power as material capabilities. While this approach is compatible with a scientific vision of politics as manifested after the second debate it reduces significantly realism’s analytical purchase both in understanding power and the nation-state. This is evident in the precarious balance that neorealists have to attain when theorising nationalism, the ideological corollary of the nation-state, which can more fully be accounted for by classical realists. Finally, by removing power from the field of epistemology, structural variants of realism lack the reflexivity of earlier realists and as such find it difficult to engage in foreign policy debates without compromising the core assumptions of their theory. The thesis is structured as follows: In the introduction, the thesis is put in the context of existing literature on realism and the way questions of power and the nation-state have been addressed in the past. Questions of methodology and selection of authors are also addressed in the introduction. The following four chapters are dedicated to analysing the theories of the selected realists. The concluding section summarises the findings and main argument of the thesis.

O controle de constitucionalidade de leis sempre foi objeto de desconfiança da teoria democrática. Sob qual justificativa juízes não eleitos podem ter a última palavra sobre o significado de direitos fundamentais? É assim que a questão costumou ser formulada pela tradição. Alguns a responderam em favor desse arranjo, outros em defesa da supremacia do parlamento. Essa seria uma encruzilhada da separação de poderes e as teorias da última palavra se enfrentam nesses termos. A tese investiga uma saída alternativa para esse dilema, oferecida pelas teorias do diálogo institucional. Segundo essa corrente, a última palavra, na democracia, não existe. O trabalho defende que ambas as perspectivas, última palavra e diálogo, têm papel analítico importante a cumprir. Propõe que uma interação de caráter deliberativo, e não somente adversarial, entre os poderes, tem maiores possibilidades de, ao longo do tempo, produzir boas respostas sobre os direitos fundamentais. Torna a separação de poderes sensível ao bom argumento / The judicial review of legislation has always been under the distrust of democratic theory. Under what justification can unelected judges have the last word upon fundamental rights? Thats the way the question has been formulated by the tradition. Some are favourable to this institutional arrangement, whereas others defend the supremacy of parliament. This would be the crossroads of the separation of powers and theories of last word face the dispute under these terms. The thesis investigates an alternative response to this dilemma, offered by theories of institutional dialogue. According to it, there is no last word in a democracy. The dissertation defends that both perspectives last word and dialogue have an important analytical role to play. Is proposes that an interaction of a deliberative kind rather than adversarial is more likely, in the long term, to produce better answers about rights. It turns separation of powers sensitive to the quality of argument

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Based on a multi-mode multi-level Jaynes-Cummings model and multi-photon resonance theory, a set of universal two-qubit and three-qubit gates has been realized where dual-rail qubits are encoded in cavities. In this way, the information has been stored in cavities and the off-resonant levels have been eliminated by the theory of an effective two-level Hamiltonian. A further model, namely the spin-J model, has been introduced so that a complete population inversion for levels of interest has been achieved and periodic multilevel multi-photon models have been performed. The combination of the two models has been employed to address two-level, three-level, four-level, and even five-level configurations. Considering the present cavity-QED experiments, several numerical simulations have been designed in order to check the robustness of the logic gates to variations in experimentally important parameters including the coupling constants and the detunings. Finally, based on Liouville's equation, and the wave-function treatments, the impact of decoherence processes on the fidelity of the qubit states in the iSWAP and the Fredkin gates has been studied. This thesis may have applications to quantum information processing, involving logic with simple quantum bits, with the possible application to the building of a quantum computer.

This thesis studies three aspects of gravity in quantum field theory. First quantum gravity effects are investigated using effective field theory techniques. In particular, we consider quantum gravity effects in grand unified theory and study their effects on the unification of the masses in such models. We find that the fermion masses unification conditions receive a sizeable correction from the quantum gravitational effects and one thus cannot predict the high energy unification only by the extrapolation from low energy physics without the understanding of gravitational effect in high energy. Secondly we study quantum field theory in curved spacetime in order to understand further about some of the properties of gravity. Keeping gravity as background field we discuss modified gravity theories in different set of parameters called frames; they are the Jordan frame and the Einstein frame respectively. We show how to map gravitational theories at the quantum field theoretical level. The key observation is that there is a non-trivial Jacobian. It can be interpreted as boundary term. Finally we investigate a new canonical quantisation paradigm. In that framework, quantum gravity is power counting renormalisable. Furthermore, the theory is unitary and the problem of time is solved. We use this framework to calculate the solution for the quantum wave function and the semiclassical Hamilton-Jacob function. We study the Hawking-Bekenstein entropy in the spherical symmetric mini-superspace for Schwarzschild black hole, and find that it can be produced naturally from first principles. Importantly it is accompanied naturally by non-thermal quantum correction terms which is generally believed to restore the information loss.

In this thesis we study several topics within the subject of extra dimensions and composite Higgs models. We first look at a scenario with a warped extra dimension known as the Randall-Sundrum (RS) model, and put all Standard Model fields in the bulk. We investigate various aspects of the model and argue that the presence of higher dimensional operators in the 5D bulk has a non-negligible effect on the electroweak precision observables, meaning that current electroweak constraints on non-custodial warped models could be weaker than previously thought. Then, using holographic techniques, we study correlations between the top partner masses and the Higgs potential in composite Higgs models. It is known that a light Higgs (~ 125 GeV) generally requires light top partners at around 700-800 GeV. However in these calculations the 5D volume is always fixed such that the 5D cutoff is around ~ MPl. The effect of lowering this 5D cutoff has been studied previously in bulk RS models as a way of reducing constraints from some flavour and electroweak precision observables, these models were dubbed "Little Randall-Sundrum models". Here we consider a similar setup in the context of holographic composite Higgs models and show that reducing the 5D cutoff leads to a lighter Higgs without a lowering of the top partner masses or an increase in fine-tuning. We find that the model is perfectly consistent with a 125 GeV Higgs and top partners above 1 TeV. This reduced 5D cutoff implies an intermediate scale between the electroweak scale and the Planck scale. Lastly we consider a similar warped model with a low 5D cutoff, except this time our goal is to study diphoton signals from Kaluza-Klein gravitons in a warped extra dimension. With a KK graviton of mass 750 GeV and spin-1 states at ~ 2:5 TeV, we show that having a low 5D cutoff increases the diphoton signal and the decay to gluons. With this model we show that we can explain the recently observed diphoton excess in terms of a Kaluza-Klein graviton from a holographic composite Higgs model, while keeping other decay channels within the relevant experimental bounds.