An analytic approach to probability tables for the unresolved resonance region

The Unresolved Resonance Region (URR) connects the fast neutron region with the Resolved Resonance Region (RRR). The URR is problematic since resonances are not resolvable experimentally yet the fluctuations in the neutron cross sections play a discernible and technologically important role: the URR in a typical nucleus is in the 100 keV – 2 MeV window where the typical fission spectrum peaks. The URR also represents the transition between R-matrix theory used to described isolated resonances and Hauser-Feshbach theory which accurately describes the average cross sections. In practice, only average or systematic features of the resonances in the URR are known and are tabulated in evaluations in a nuclear data library such as ENDF/B-VII.1. Codes such as AMPX and NJOY can compute the probability distribution of the cross section in the URR under some assumptions using Monte Carlo realizations of sets of resonances. These probability distributions are stored in the so-called PURR tables. In our work, we begin to develop a scheme for computing the covariance of the cross section probability distribution analytically. Our approach offers the possibility of defining the limits of applicability of Hauser-Feshbach theory and suggests a way to calculate PURR tables directly from systematics for nuclei whose RRR is unknown, provided one makes appropriate assumptions about the shape of the cross section probability distribution

Theoretical Evaluation of the Reaction Rates for 26Al(n,p)26Mg and 26Al(n,a)23Na

The reactions that destroy 26Al in massive stars have significance in a number of astrophysical contexts. We evaluate the reaction rates of 26Al(n,p)26Mg and 26Al(n,a)23Na using cross sections obtained from the codes EMPIRE and TALYS. These have been compared to the published rates obtained from the non-smoker code and to some experimental data. We show that the results obtained from EMPIRE and TALYS are comparable to those from non-smoker. We also show how the theoretical results vary with respect to changes in the input parameters. Finally, we present recommended rates for these reactions using the available experimental data and our new theoretical results

Gamma-gamma angular-correlation measurements in the 44Ca(n, γ)45Ca reaction

Angular correlation measurements of γ-radiation following thermal neutron capture in 44Ca have been performed with a combination of Ge(Li) and NaI detectors. Spins could be assigned to the following 45Ca levels (Ex in MeV): Jπ(0.17) = , , and assignment is consistent with recent shell-model calculations. Some E2/M1 mixing ratios of transitions between bound states of 45Ca have been determined

Measuring and modeling the role of time margins on drivers’ pedal control inputs during cornering speed adaptation

Reducing conflicts between drivers and assistance systems has become an important issue in recent times, resulting in a need for a better understanding of how humans drive. Current models of driver speed choice on curved roads do not model accelerator and brake pedal deflections, and consequently do not account for the fact that deceleration usually occurs in two distinct phases. The contribution of this work lies in the combination of studies of driver’s visual fixations during curve driving with research on how drivers use time thresholds as safety margins, resulting in a more realistic computational driver model that uses thresholds on a single visual perceptual variable to trigger the release of the accelerator and the application of the brakes. A simulator experiment showed that, after individualization of the thresholds using a binary classification method, the model is capable of accurately capturing the speed adaptation of 15 human drivers on single lane roads with multiple curves.Aerospace Engineering | Control & Simulatio

Fatigue behavior of welded T-joints by FSW in the AA5083 alloy

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbr