Sensitivity of the r-process to nuclear masses

The rapid neutron capture process (r-process) is thought to be responsible for the creation of more than half of all elements beyond iron. The scientific challenges to understanding the origin of the heavy elements beyond iron lie in both the uncertainties associated with astrophysical conditions that are needed to allow an r-process to occur and a vast lack of knowledge about the properties of nuclei far from stability. There is great global competition to access and measure the most exotic nuclei that existing facilities can reach, while simultaneously building new, more powerful accelerators to make even more exotic nuclei. This work is an attempt to determine the most crucial nuclear masses to measure using an r-process simulation code and several mass models (FRDM, Duflo-Zuker, and HFB-21). The most important nuclear masses to measure are determined by the changes in the resulting r-process abundances. Nuclei around the closed shells near N=50, 82, and 126 have the largest impact on r-process abundances irrespective of the mass models used.Comment: 5 pages, 4 figures, accepted in European Physical Journal

An Investigation of Shock Wave Physics via Hybrid CFD-BGK Solution Methods for Nonequilibrium Flows

The Unified Flow Solver, a hybrid continuum-rarefied code, is used to investigate the internal structure of a normal shock wave for a Mach range of 1.55 to 9.0 for Argon, and 1.53 to 3.8 for diatomic Nitrogen. Reciprocal shock thickness, density, temperature, heat flux, and the velocity distribution function are calculated for a one-dimensional shock wave and compared with experimental data from Alsmeyer and DSMC results from Bird. Using the Euler, Navier-Stokes, BGK model, and Three-Temperature BGK model schemes, results from UFS compare well with experiment and DSMC. The Euler scheme shows atypical results, possibly resulting from modifications made to include internal energies. An entropy spot is introduced into a two-dimensional domain to investigate entropy-shock interactions over a range of Knudsen numbers (Kn=0.01, 0.1, and 1.0) for Mach 2.0 in Argon. Previous work on entropy-shock interactions has only been performed using an Euler scheme. Here, results are presented in Argon using coupled BGK and Navier-Stokes solvers. Density, pressure, and temperature profiles, as well as the profiles of their gradients, are reported at certain times after the entropy spot convects through the shock

Scattering, Adsorption, and Langmuir-Hinshelwood Desorption Models for Physisorptive and Chemisorptive Gas-Surface Systems

Surface effects limit the performance of hypersonic vehicles, micro-electro-mechanical devices, and directed energy systems. This research develops methods to predict adsorption, scattering, and thermal desorption of molecules on a surface. These methods apply to physisorptive (adsorption and scattering) and chemisorptive (thermal desorption) gas-surface systems, and are developed under the Direct Simulation Monte Carlo construct. The novel adsorption and scattering contribution, the Modified Kisliuk with Scattering method, predicts angular and energy distributions, and adsorption probabilities. These results agree more closely with experiment than the state-of-the-art Cercignani-Lampis-Lord scattering kernel. Super-elastic scattering is predicted. Gas-adlayer interactions are included for the first time. The new thermal desorption model accurately predicts angular and energy distributions. The equations of motion are non-dimensionalized. Accurate timing is included. Initial conditions are chosen from a new truncated Maxwell- Boltzmann distribution. The absorption energy barrier is shown to significantly contribute only to translational energy

Sensitivity studies for r-process nucleosynthesis in three astrophysical scenarios

In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are built up via a sequence of neutron captures and beta decays that involves thousands of nuclei far from stability. Though we understand the basics of how the r-process proceeds, its astrophysical site is still not conclusively known. The nuclear network simulations we use to test potential astrophysical scenarios require nuclear physics data (masses, beta decay lifetimes, neutron capture rates, fission probabilities) for all of the nuclei on the neutron-rich side of the nuclear chart, from the valley of stability to the neutron drip line. Here we discuss recent sensitivity studies that aim to determine which individual pieces of nuclear data are the most crucial for r-process calculations. We consider three types of astrophysical scenarios: a traditional hot r-process, a cold r-process in which the temperature and density drop rapidly, and a neutron star merger trajectory.Comment: 8 pages, 4 figures, submitted to the Proceedings of the International Nuclear Physics Conference (INPC) 201

A critical approach to the development of a framework to support the evaluation of information strategies in UK Higher Education Institutions

A thesis submitted for the degree of Doctor of Philosophy to the University of LutonThe objective of this thesis has been to develop a framework to support the evaluation of information strategies of UK higher education institutions (REIs). For this study the theoretical and empirical literature was extensively reviewed and four substantial pieces of empirical research were conducted. These included action research CAR), two pieces of ethnographic research, and a case study. The AR analysed problems encountered with a Student Records System at a UK university and identified both immediate and deeper causes for these problems. Ethnography I involved the researcher's participation in the information strategy development process at the same university: This included consideration of the development processes adopted and also the way that decisions were taken. Ethnography II consisted of participant observation at a range of workshops and conferences organised by the Joint Information Systems Committee on information strategy development at UK REIs. These provided a broad picture of information strategy development procedures being adopted across these HEls. The case study investigated in detail the implementation of an information strategy at a university different from that examined in AR and Ethnography I. These empirical investigations all included in-depth interviews. In total 117 people of various levels and backgrounds involved in information strategies and associated information systems within UK HEIs were interviewed. Key findings from the empirical research were: Many HErs in the process of developing an information strate!:,,),, or about to do so, were not fully sure how this should be achieved nor the extent of the likely benefits. Most HEIs implementing information strategies were using top-down directed system approaches, leaving little room for more inclusive bottom-up emergent planning. Information strategies need to be developed and evaluated using strongly human-centred methods, primarily because it became apparent that the successful functioning of such a strategy is dependent on the motivation and competencies of the people who create and use the information. Investigations into aspects of information strategy development and implementation need to focus on people's perceptions of the situation rather than seeking an objective truth independent of the participants. This reflects a Kantian perspective of knowledge. Overall, the empirical findings supported the use of a Critical Systems Thinking approach in the evaluation of information strategies at higher education institutions. The development of the evaluative framework, the main objective of the thesis, took place in two phases: developing the framework based on the literature review and revising the framework from the empirical research investigations involving a process of critical iteration. The first phase identified a range of elements associated with an HErs information strategy, and for each element highlighted the relevant theoretical andlor empirical literature that bears on the issues being addressed. In particular, the framework is strongly influenced by insights drawn from the work of three key social theorists: Kant, Habermas and Foucault. In addition, the framework includes 'guidelines for evaluation', where these are more practical questions to ask and areas to investigate when evaluating a given element ofthe strategy. The second phase took the framework through a series of reflections and revisions based on the findings from the empirical investigations. In each case, insights were gained that related to the use or applicability ofthe framework. By combining the findings from the theoretical and empirical literature with those from the empirical research, the final framework, which is believed to have filled a gap in the theoretical literature, aims to encompass the complexity of information strategy development and implementation within HEIs. The framework reflects a human-centred and Critical Systems Thinking approach, and is designed to allow potential evaluators to identify underlying causes for the success or failure of an information strategy that is implemented at an HEI

Measurements and Monte-Carlo simulations of the particle self-shielding effect of B4C grains in neutron shielding concrete

A combined measurement and Monte-Carlo simulation study was carried out in order to characterize the particle self-shielding effect of B4C grains in neutron shielding concrete. Several batches of a specialized neutron shielding concrete, with varying B4C grain sizes, were exposed to a 2 {\AA} neutron beam at the R2D2 test beamline at the Institute for Energy Technology located in Kjeller, Norway. The direct and scattered neutrons were detected with a neutron detector placed behind the concrete blocks and the results were compared to Geant4 simulations. The particle self-shielding effect was included in the Geant4 simulations by calculating effective neutron cross-sections during the Monte-Carlo simulation process. It is shown that this method well reproduces the measured results. Our results show that shielding calculations for low-energy neutrons using such materials would lead to an underestimate of the shielding required for a certain design scenario if the particle self-shielding effect is not included in the calculations.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0