X-ray Outflows in the Swift Burst Alert Detected Seyfert 1s

Previous surveys of outflows in low-redshift active galactic nuclei (AGN) have relied on the analysis of sources selected primarily for their optical/X-ray brightness, and are therefore biased. Towards determining the outflow properties of local AGN, we detect warm absorption signatures of O VII and O VIII absorption edges in the available Suzaku/XMM-Newton CCD spectra of an unbiased sample of 44 Seyfert 1-1.5 sources selected in the very hard X-rays (14-195 keV) with the Swift Burst Alert Telescope. From our analysis, we find that O VII and O VIII absorption edges are present in 41% of the sample. This fraction is dependent on luminosity, with outflow detections in 60% of low luminosity and 30% of high luminosity sources. However, grating spectroscopy of the highest luminosity sources reveals that ~ 80% of these sources have ionized absorbers, but that the ionization states are higher/lower than produces the O VII and O VIII edges. This suggests that ionized absorption may be present in all local Seyfert 1s.Comment: 13 pages, 2 figures, accepted in ApJ

Light gage steel connections with high-strength, high-torqued bolts

The usual methods for designing bolted connections of conventional steel structures must be modified for application to thin-walled, light-gage steel construction. This is so because the ratios of bolt diameter to steel thickness in light-gage construction are generally much larger than those customary in conventional construction. In a previous paper [1] the writer has published the results of 547 tests of light-gage steel connections with ordinary black bolts. The results could be expressed in four simple equations for determining failure loads which, when used with an appropriate factor of safety, can serve as a safe basis for design. It is the purpose of the present paper to report and evaluate the results of 476 additional tests made on similar connections, but with high-strength, high-torqued bolts of the kind which has come into use in the U. S. A. during the last five years. These tests were undertaken in order to investigate in what manner such connections would perform differently from those made with ordinary bolts, and what possible advantage could be gained from using these special bolts in light-gage, thin-walled steel construction

Transient nuclear criticality analysis of aqueous fissile solutions using point nuclear reactor kinetics and phenomenological thermal-hydraulic feedback models

This thesis presents a range of mathematical and computational models for use in transient nuclear criticality safety assessment. A mathematical model for quantifying the uncertainty in the wait-time probability distributions of criticality excursions initiated in the presence of weak intrinsic neutron sources is presented. This model is used to demonstrate the potential influence of parametric uncertainty on the wait-time probability distributions of the 1958 Y-12 criticality accident and experiments on the Caliban reactor. Also presented in this thesis is a new mathematical and computational model of radiolytic gas production and evolution in fissile liquids. This model has been validated against nuclear criticality safety benchmark experiments on fissile solution reactors and has been shown to accurately predict features of the fission power profiles related to the appearance and advection of radiolytic gas voids in the solution. The model has also demonstrated efficacy in predicting the timing and magnitude of secondary peaks in the fission power output. The purpose of this new mathematical and computational radiolytic gas model was to improve the simulation of fissile liquid criticality transients while removing the need for the adjustable heuristic parameters used by existing fissile liquid simulation codes. These parameters, which must be appropriately adjusted to criticality safety benchmark experiments, are dependent on the geometry and composition of the system being analysed. The need for these heuristic parameters therefore precludes the use of these codes as predictive modelling and simulation tools. The new mathematical and computational model, presented in this thesis, offers valuable insights into the behaviour of radiolytic gas in fissile liquid systems.Open Acces

Stress distribution in and equivalent width of flanges of wide, thin-wall steel beams

The use of different forms of wide-flange, thin-wall steel beams is becoming increasingly widespread. Part of the information necessary for a national design of such members is the knowledge of the stress distribution in and the equivalent width of the flanges of such beams. This problem is analyzed in this paper on the basis of the theory of plane stress. As a result, tables and curves are given from which the equivalent width of any given beam can be read directly for use in practical design. An investigation is given of the limitations of this analysis due to the fact that extremely wide and thin flanges tend to curve out of their plane toward the neutral axis. A summary of test data confirms very satisfactorily the analytical results