The study is focused on the thermal entanglement of spin chains. Chains consisting of two and three qubits are considered. These chains are considered open because they are coupled to bosonic baths at different temperatures. The baths represent the environment. The dynamics of these open systems are examined as are the effects of different parameters - such as bath temperature - on the entanglement of the spins. The measure of entanglement used in these cases is the concurrence. Comparisons are made between a model that assumes a strong spinspin interaction and one that assumes a weak one. In all these cases, analytical solutions for the system dynamics are presented. It is found that at large times, all systems converge to a state that depends only on bath temperature. It is also found that increases in bath temperatures diminish the entanglement between spins and that at high enough temperatures the entanglement vanishes altogether. The time and temperature dependence of the entanglement is different for the two models that are studied. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

No description available.

Chemical reactions usually involve the conversion of reactants to products by overcoming an energetic barrier. Most commonly, this process can be assisted by adding energy through heat (thermochemistry), light (photochemistry) or electric current (electrochemistry). The fourth option is to overcome the reaction barrier through application of mechanical work, termed mechanochemistry. This method has received much attention from the scientific community in the last decade. Both theoretical and experimental studies have been performed, demonstrating the ability of mechanochemistry to activate reactions, with a strong focus on ringopening reactions. The vast majority of studies have focused on unimolecular reactions involving bond-rupture, which is very intuitively activated by the application of tensile stress. However, bimolecular reactions, which often involve bond formation as well as rupture, have received much less attention. In this thesis, we seek to change this by undertaking an in-depth study of mechanochemical activation of addition reactions to carbon-carbon double bonds, which involve the formation of two single bonds while the double bond becomes a single bond. We observe that large barrier changes can be induced by applying external force to reactions of this type, and the magnitude of these changes can be controlled by the choice of alkene substrate. By studying the changes induced in the geometry of the substrate, we are able to begin explaining the origins of the barrier reduction effect. In addition, by studying the contributions to the barrier change from mechanical work and the contributions from geometry changes, we discover that steric hindrance to a reaction can play a very significant role in the mechanochemical activation of the reaction. / Thesis (Master, Chemistry) -- Queen's University, 2010-11-29 10:43:04.945

Spin-orbit coupling and the related effects of A-doubling and spin-splitting have been well known to spectroscopists for some considerable time. The importance of these phenomena stems from the advent of radioastronomy and the study of the interstellar medium. Identification of the molecules, and the molecular transitions, in the interstellar dust clouds is necessary for an understanding of the cooling process by which these clouds can contract to form new stars.

This thesis presents time-dependent density functional theory studies on electronic and vibronically resolved linear and nonlinear optical absorption and dichroism spectra of organic molecules. Special attention has been paid to the influence of solvent environment and molecular vibrations on one-, two- and three-photon absorption and one- and two-photon circular dichroism. It is found that dielectric medium as described by polarizable continuum model can enhance remarkably three-photon absorption cross section of a highly conjugated fluorene derivative, for which the simplified two-state model is shown to be largely inadequate. Origin-invariant density functional calculations on one- and two-photon circular dichroisms of a chiral molecule confirm that the recently developed CAMB3LYP functional performs better than the popular B3LYP functional for Rydberg-states. The first experimental measurement of TPCD spectra is performed on an axial chiral system in tetrahydrofunan, where the double L-scan technique is applied. Theoretical calculations well reproduce the experimental profiles when both the electron correlation and the solvent effect are taken into account. Vibronically resolved one- and two-photon absorption spectra of charge-transfer molecules have been obtained using a Linear Coupling model, where the 'borrowing mechanism' for the so-called Herzberg-Teller contribution is analyzed in detail. It is shown that Herzberg-Teller contribution can introduce a change of sign to the chiral responses of a molecule without the involvement of different electronic states, which has important consequences for the assignment of absolute configurations of chiral molecules. Adiabatic harmonic Franck-Condon model is also applied to simulate vibronically resolved one- and two-photon circular dichroism spectra of the same chiral system, where the sign-inversion and the interference between Franck-Condon and Herzberg-Teller contributions are also observed. / QC 20100727

Thesis (Ph.D.)--McMaster University (Canada), 1990. / Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0301. Supervisor: R. F. W. Bader.

Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009. / Committee Chair: Landman, Uzi; Committee Member: Barnett, Robert; Committee Member: Chou, Meiyin; Committee Member: El-Sayed, Mostafa; Committee Member: Yannouleas, Constantine.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Thesis (Ph.D.) -- McMaster University, 2001. / Includes bibliographical references (leaves 170-174).

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