Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 142-145).

Thesis--New York University. / Bibliography: p. [124]-125.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Gerald W. Hoffmann and C. Fred Moore. Vita. "Center of mass energy" written as symbols in title. Includes bibliographical references. Also available from UMI.

Th.--Sci. phys.--Paris 13--Bobigny, 1981. / Rés.

Ship collision accidents are rare events but pose huge threat to human lives, assets, and the environment. Collision resistance of ships is usually assessed in terms of ship structural response such as member displacement, energy dissipation and the extent of damage. Many researchers have sought for effective models that compute ship stochastic response during collisions by considering the variability of collision scenario parameters. However, the models were limited by the capability of the collision computational models and did not completely capture collision scenario, and material and geometric uncertainties. In addition, the simplified models capturing the input-response relationships of the ship structural impact mechanics are in implicit forms which makes them unsuitable for assessing the performance of structural design specifications in collisions. Furthermore, with increasing ship passages in the Arctic region, the probabilities of ship-iceberg interactions are increasing, highlighting the need to focus on risk based ship designs. In this research, a conceptual stochastic modelling framework is developed for performance characterisation and quantitative risk assessment of ship-ship and ship-iceberg collisions. In this direction, an interface for automated stochastic finite element computations was developed to model ship structural resistance in reference collision scenarios. The stochastic structural response was characterised based on the onset of the ship structural failure. The focus was initially on ship-ship collisions to quantify the uncertainties experimentally and to characterise the performance for a variety of striking ships. The framework was then extended to consider probabilistic performance measures in ship-iceberg collisions. The computationally intensive collision response models were captured with efficient surrogate representations so that the performance measures can be obtained with gradient based reliability approaches. The most probable input design sets for the response distribution were sampled with Latin Hypercube models. The probabilistic performance measures were also combined with available collision frequency models from literature for risk computations and to demonstrate the risk tolerance measures. The framework underlines the significance of different risk components, providing valuable guidance for improving risk-based ship designs. Although, a double-hull crude oil carrier is presented as the struck ship, the approach can be readily extended to characterise the performance and risk of other ship structures in collisions.

abstract: 3D models of white dwarf collisions are used to assess the likelihood of double-degenerate mergers as progenitors for Type Ia supernovae (henceforth SNIa) and to identify observational signatures of double-degenerate collisions. Observations of individual SNIa, SNIa rates in different galaxy types, and double white dwarf binary systems suggest that mergers or collisions between two white dwarfs play a role in the overall SNIa population. Given the possibility of two progenitor systems (single-degenerate and double-degenerate), the sample of SNIa used in cosmological calcula- tions needs to be carefully examined. To improve calculations of cosmological parameters, the development of calibrated diagnostics for double-degenerate progenitor SNIa is essential. Head-on white dwarf collision simulations are used to provide an upper limit on the Ni-56 production in white dwarf collisions. In chapter II, I explore zero impact parameter collisions of white dwarfs using the Eulerian grid code FLASH. The initial 1D white dwarf profiles are created assuming hydrostatic equilibrium and a uniform composition of 50% C-12 and 50% O-16. The masses range from 0.64 to 0.81 solar masses and have an isothermal temperature of 10^7 K. I map these 1D models onto a 3D grid, where the dimensions of the grid are each eight times the white dwarf radius, and the dwarfs are initially placed four white dwarf radii apart (center to center). To provide insight into a larger range of physical possibilities, I also model non-zero impact parameter white dwarf collisions (Chapter III). Although head-on white dwarf collisions provide an upper limit on Ni-56 production, non-zero impact parameter collisions provide insight into a wider range of physical scenarios. The initial conditions (box size, initial separation, composition, and initial temperature) are identical to those used for the head-on collisions (Chapter II) for the same range of masses. For each mass pair- ing, collision simulations are carried out at impact parameters b=1 and b=2 (grazing). Finally, I will address future work to be performed (Chapter IV). / Dissertation/Thesis / Ph.D. Astrophysics 2012

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The reaction D(p, γ )He³ was studied at incident proton energies of less than 50 kev. The method was to bombard heavy ice targets with the proton beam from the 50 kv accelerator. This machine develops an intense beam of 60 to 80 microamps which is necessary to produce a substantial yield despite the low reaction cross section. The angular distribution of the γ-rays was found to follow a (sin²θ +B) pattern as expected from earlier work carried out at higher energies. In the neighborhood of 35 kev the value of B was found, by measurements of the yield at 90° and at 0° to the incident beam direction, to be .283± .110. The total cross section was found to take on the following values: [In column] E(kev), 29.1, 37.5 44.0 ; [In column] σ(cm² ) x 10⁻³², 4.87 ± 1.05, 11.2 ± 2.8, 12.0 ± 4.0 / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An expression for the spin-lattice relaxation time, T₁, of a dilute monatomic gas can be derived starting from the quantum-mechanical Boltzmann equation. The real difficulty in calculating the relaxation time for a particular system lies in the evaluation of the transition operator which appears in the expression for T₁ˉ¹. In this thesis, the relevant part of the transition operator, t₁, is estimated by a distorted-wave Born approximation (DWBA). The monatomic gas is approximated by a specific model. In this model the collisions described by t₁ are governed by two potentials: one, the isotropic rigid sphere potential, V₀, and the other, the anisotropic dipole-dipole nuclear spin interaction potential, V₁. The latter interaction describes the coupling between the degenerate nuclear spin states of the atoms and the translational degrees of freedom in the gas. The former (isotropic) potential governs the explicit form of the rigid sphere distorted wave. After the DWBA transition operator is substituted into the equation for the relaxation time, the expression for T₁ˉ¹ breaks up into two terms, the "diagonal" and "non-diagonal" contributions. At this stage the explicit expression for T₁ˉ is sufficiently complicated that, in order to finish the calculation, analytical approximations to the diagonal and non-diagonal terms are made. These approximations may be succinctly described by stating that they result in two separate evaluations, a linear and a quadratic one, for the overall relaxation time. The magnitude of a small parameter c² , which appears in the exponential term of T₁ˉ¹ , is used as the basis for neglecting certain contributions to the integrals which arise in estimating T₁ˉ¹. The linear and quadratic approximations yield numerical factors of 3,50 and 2.56 respectively, in the expression for the relaxation time. These values are to be compared with the factor of 2 obtained elsewhere. / Science, Faculty of / Chemistry, Department of / Graduate