A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

[abstract] In the process of nucleation, the decay of a metastable state is initiated by the formation of a spatially localised region called a nucleus of critical size. In many realistic situations nucleation is initiated at an impurity or defect; such as a dust particle, an irregularity in a sample, or a crack in the wall of a container. The aim of this thesis is to identify and understand the fundamental changes different types of defect make to nucleation by studying a one-dimensional continuum model used to describe solitons. A well established theory due to Langer is extended to calculate the rate of decay of a metastable state due to the nucleation of solitons at defects. Results are used to find the rate of thermally activated magnetisation reversal for a ferromagnetic nanowire with defects in the uniaxial anisotropy. Defects which are narrower than the soliton width (point-like defects) and wider than the soliton width (step defects) are both modelled. An attractive defect breaks the translational symmetry of a soliton and leads to pinning. The pinning of solitons is found to reduce the activation energy required for nucleation, reduce the critical field above which a metastable state becomes unstable, alter the mechanism by which a metastable state decays, and modify the prefactor for the rate of decay. Changes to the prefactor are interpreted in terms of entropy and the dynamics of metastable decay when a defect is present.

xix, 141 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / The constant drive to improve material properties has recently led researchers towards metastable nanostructured materials, increasing the need for new synthetic pathways capable of rationally accessing targeted compounds. A method is demonstrated for using physical vapor deposition to create elementally modulated precursors targeting specific compounds. Controlling the modulation length scale of the precursor allows entire families of misfit layered compounds to be synthesized with atomic level control of the structure. Over 100 new misfit layered compounds were synthesized in the [(BiSe) 1.10 ] m (NbSe 2 ) n , [(PbSe) 1.10 ] m (NbSe 2 ) n , [(PbSe) 1.00 ] m (MoSe 2 ) n , and [(SnSe) 1.10 ] m (MoSe 2 ) n , families. The three-dimensional structures of these compounds are examined. These materials are shown to form turbostratically disordered sheets of transition metal dichalcogenide layers interwoven between blocks of rock salt layers. These layers have very small in-plane grain sizes on the order of 10 mn. The interfaces between these layers lack any epitaxial relationship and yet are atomically abrupt and indicate no strain present. The unique metastable structures lead to fascinating properties in these compounds. The turbostratic disorder leads to extremely low thermal conductivity perpendicular to the layering. Thermal conductivities as low as 0.07 W/m/K were measured. Because of the flexible chemistries, a wide range of electrical properties are accessible in these materials, with electrical conductivities ranging from metallic to semiconducting and carrier concentrations ranging from 10 17 to 10 21 cm -3 . Despite the small grain sizes, respectable mobilities have also been measured, up to 21 cm 2 V -1 s -1 . This work consists, in part, of previously published and coauthored material. / Committee in charge: James Hutchison, Chairperson, Chemistry; David Johnson, Advisor, Chemistry; David Tyler, Member, Chemistry; Geraldine Richmond, Member, Chemistry; Richard Taylor, Outside Member, Physics

Estudamos um sistema de dois níveis acoplados como um modelo que imita o comportamento de líquidos super-resfriados. Em equilíbrio o modelo apresenta uma fase líquida e uma fase cristalina com diversos estados fundamentais. O modelo é definido numa rede quadrada e a cada sítio é associada uma variável estocástica de Ising. A característica que torna este modelo particularmente interessante é que ele apresenta estados metaestáveis duráveis que podem desaparecer dentro do tempo acessível para as simulações numéricas. Para imitar o processo de formação dos vidros, realizamos simulações de Monte Carlo a taxas de resfriamento constante. Apresentamos também simulações para resfriamentos súbitos a temperatura abaixo da temperatura de fusão. / We study a coupled two level systems as a model that imitate the behavior of supercooled liquids that become structural glasses under cooling. In the equilibrium the model shows a liquid phase and a crystalline phase with many grouond states. The model is defined on a square lattice and to each site a stochastic Ising variable is associated. The feature that makes this model particularly interesting is that it display durable metastables states which can vanish within the time available for numerical simulations. In order to imitate the glass former process, we perform Monte Carlo simulations at constant cooling rate. We present also simulations for quenchs to temperatures below the melting temperature.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-27T18:11:39Z No. of bitstreams: 1 ritadecassiapolitovitaalessio.pdf: 1515814 bytes, checksum: ec2256bcf074df2e72a53fe6c0a62c6f (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-07T21:06:14Z (GMT) No. of bitstreams: 1 ritadecassiapolitovitaalessio.pdf: 1515814 bytes, checksum: ec2256bcf074df2e72a53fe6c0a62c6f (MD5) / Made available in DSpace on 2017-08-07T21:06:14Z (GMT). No. of bitstreams: 1 ritadecassiapolitovitaalessio.pdf: 1515814 bytes, checksum: ec2256bcf074df2e72a53fe6c0a62c6f (MD5) Previous issue date: 2009-06-09 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo de ressonâncias, através de estados metaestáveis pelo impacto de elétrons, permite observar estruturas bem definidas nos espectros, gerando informações diretas sobre as energias de formação das ressonâncias, bem como suas formas e larguras. A investigação destas ressonâncias é muito importante em vários ramos da ciência, possuindo inúmeras aplicações biológicas e tecnológicas. Um espectrômetro por impacto de elétrons foi construído e implantado no Laboratório de Física Atômica e Molecular, permitindo a obtenção das funções de excitação do Argônio, do Hélio e da molécula de Nitrogênio, sendo esta técnica inédita no Brasil. Neste espectrômetro aplica-se a técnica dos feixes cruzados, que consiste basicamente de um canhão de elétrons monocromatizado, um feixe de gás efusivo, uma gaiola de Faraday para a blindagem da região de colisão, um detector de íons metaestáveis, devidamente posicionado, e um coletor de Faraday. O canhão de elétrons monocromatizado apresenta uma alta eficiência, cobrindo continuamente uma faixa de energia de 7 a 200 eV, com uma resolução em torno de 50 meV. Para a aquisição dos espectros, a energia do canhão foi varrida a partir do limiar de excitação metaestável até uma energia menor que o primeiro potencial de ionização do alvo estudado. / The study of resonances through metastable states of atoms and molecules by electron impact shows spectra with well-defined structures, providing direct information on the energies of resonances formation, as well as its shapes and widths. The investigation of these resonances is important in several branches of science, such as many technological and biological applications. In this work we have assembled at Laboratory of Atomic and Molecular Physics an electron impact spectrometer which allowed us to collect metastables excitations functions of Argon, Helium and the Nitrogen molecules. As far we know, that was the first time that this technique was performed in Brazil. That spectrometer applies the cross beam technique, and consists of a monochromatized electron gun, an effusive gas beam, a cage to shield the collision region, a metastable detector properly positioned and a Faraday cup. The monocromatized electron gun built has a high efficiency, covering continuously the energy range from 7 to 200 eV, with a resolution of about 50 meV. The three spectras recorded in this work cover the energy range from the excitation metastable threshold up to energy lower than the first ionization potential of the targets studied.