6,933 research outputs found
Elastic-Plastic Fracture Mechanics Analysis of Critical Flaw Size in ARES I-X Flange-to-Skin Welds
NASA's Ares 1 Upper Stage Simulator (USS) is being fabricated from welded A516 steel. In order to insure the structural integrity of these welds it is of interest to calculate the critical initial flaw size (CIFS) to establish rational inspection requirements. The CIFS is in turn dependent on the critical final flaw size (CFS), as well as fatigue flaw growth resulting from transportation, handling and service-induced loading. These calculations were made using linear elastic fracture mechanics (LEFM), which are thought to be conservative because they are based on a lower bound, so called elastic, fracture toughness determined from tests that displayed significant plasticity. Nevertheless, there was still concern that the yield magnitude stresses generated in the flange-to-skin weld by the combination of axial stresses due to axial forces, fit-up stresses, and weld residual stresses, could give rise to significant flaw-tip plasticity, which might render the LEFM results to be non-conservative. The objective of the present study was to employ Elastic Plastic Fracture Mechanics (EPFM) to determine CFS values, and then compare these values to CFS values evaluated using LEFM. CFS values were calculated for twelve cases involving surface and embedded flaws, EPFM analyses with and without plastic shakedown of the stresses, LEFM analyses, and various welding residual stress distributions. For the cases examined, the computed CFS values based on elastic analyses were the smallest in all instances where the failures were predicted to be controlled by the fracture toughness. However, in certain cases, the CFS values predicted by the elastic-plastic analyses were smaller than those predicted by the elastic analyses; in these cases the failure criteria were determined by a breakdown in stress intensity factor validity limits for deep flaws (a greater than 0.90t), rather than by the fracture toughness. Plastic relaxation of stresses accompanying shakedown always increases the calculated CFS values compared to the CFS values determined without shakedown. Thus, it is conservative to ignore shakedown effects
Supersymmetric minisuperspace with non-vanishing fermion number
The Lagrangean of supergravity is dimensionally reduced to one
(time-like) dimension assuming spatial homogeneity of any Bianchi type within
class A of the classification of Ellis and McCallum. The algebra of the
supersymmetry generators, the Lorentz generators, the diffeomorphism generators
and the Hamiltonian generator is determined and found to close. In contrast to
earlier work, infinitely many physical states with non-vanishing even fermion
number are found to exist in these models, indicating that minisuperspace
models in supergravity may be just as useful as in pure gravity.Comment: 4 page
Panoramic Views of the Cygnus Loop
We present a complete atlas of the Cygnus Loop supernova remnant in the light
of [O III] (5007), H alpha, and [S II] (6717, 6731). Despite its shell-like
appearance, the Cygnus Loop is not a current example of a Sedov-Taylor blast
wave. Rather, the optical emission traces interactions of the supernova blast
wave with clumps of gas. The surrounding interstellar medium forms the walls of
a cavity through which the blast wave now propagates, including a nearly
complete shell in which non-radiative filaments are detected. The Cygnus Loop
blast wave is not breaking out of a dense cloud, but is instead running into
confining walls. The interstellar medium dominates not only the appearance of
the Cygnus Loop but also the continued evolution of the blast wave. If this is
a typical example of a supernova remnant, then global models of the
interstellar medium must account for such significant blast wave deceleration.Comment: 28 pages AAS Latex, 28 black+white figures, 6 color figures. To be
published in The Astrophysical Journal Supplement Serie
Cosmology with redshift surveys of radio sources
We use the K-z relation for radio galaxies to illustrate why it has proved
difficult to obtain definitive cosmological results from studies based entirely
on catalogues of the brightest radio sources, e.g. 3C. To improve on this
situation we have been undertaking redshift surveys of complete samples drawn
from the fainter 6C and 7C radio catalogues. We describe these surveys, and
illustrate the new studies they are allowing. We also discuss our `filtered' 6C
redshift surveys: these have led to the discovery of a radio galaxy at z=4.4,
and are sensitive to similar objects at higher redshift provided the space
density of these objects is not declining too rapidly with z. There is
currently no direct evidence for a sharp decline in the space density of radio
galaxies for z > 4, a result only barely consistent with the observed decline
of flat-spectrum radio quasars.Comment: 8 pages Latex, To appear in the "Cosmology with the New Radio
Surveys" Conference - Tenerife 13-15 January 199
J D Bernal: philosophy, politics and the science of science
This paper is an examination of the philosophical and political legacy of John Desmond Bernal. It addresses the evidence of an emerging consensus on Bernal based on the recent biography of Bernal by Andrew Brown and the reviews it has received. It takes issue with this view of Bernal, which tends to be admiring of his scientific contribution, bemused by his sexuality, condescending to his philosophy and hostile to his politics. This article is a critical defence of his philosophical and political position
J D Bernal: philosophy, politics and the science of science
This paper is an examination of the philosophical and political legacy of John Desmond Bernal. It addresses the evidence of an emerging consensus on Bernal based on the recent biography of Bernal by Andrew Brown and the reviews it has received. It takes issue with this view of Bernal, which tends to be admiring of his scientific contribution, bemused by his sexuality, condescending to his philosophy and hostile to his politics. This article is a critical defence of his philosophical and political position
Suicide Rates Among Adolescents and Young Adults in the Mountain West
This fact sheet shows data on suicide death rates among adolescents aged 10 to 24 years in the Mountain West:Nevada, New Mexico, Arizona, Colorado, and Utah. This fact sheet includes data from a report published by the Center for Disease Control in the National Vital Statistics Report which examines adolescent suicide in the U.S
Calculating Casimir Energies in Renormalizable Quantum Field Theory
Quantum vacuum energy has been known to have observable consequences since
1948 when Casimir calculated the force of attraction between parallel uncharged
plates, a phenomenon confirmed experimentally with ever increasing precision.
Casimir himself suggested that a similar attractive self-stress existed for a
conducting spherical shell, but Boyer obtained a repulsive stress. Other
geometries and higher dimensions have been considered over the years. Local
effects, and divergences associated with surfaces and edges have been studied
by several authors. Quite recently, Graham et al. have re-examined such
calculations, using conventional techniques of perturbative quantum field
theory to remove divergences, and have suggested that previous self-stress
results may be suspect. Here we show that the examples considered in their work
are misleading; in particular, it is well-known that in two dimensions a
circular boundary has a divergence in the Casimir energy for massless fields,
while for general dimension not equal to an even integer the corresponding
Casimir energy arising from massless fields interior and exterior to a
hyperspherical shell is finite. It has also long been recognized that the
Casimir energy for massive fields is divergent for . These conclusions
are reinforced by a calculation of the relevant leading Feynman diagram in
and three dimensions. There is therefore no doubt of the validity of the
conventional finite Casimir calculations.Comment: 25 pages, REVTeX4, 1 ps figure. Revision includes new subsection 4B
and Appendix, and other minor correction
2023-2024 Median Earnings Four Years After Graduation From UNLV & UNR
This fact sheet presents data from The HEA Group examining 2023-2024 median earnings four years after graduating with a bachelorâs degree from the University of Nevada, Las Vegas (UNLV) and the University of Nevada, Reno (UNR). Median earnings are presented for the following undergraduate areas of study: business; hospitality; fine arts; education; engineering; medical; sciences and mathematics; and social sciences and humanities
Distribution of Federal Expenditures and Receipts in the Mountain West, 2019-2021
This fact sheet presents data on state and federal fiscal relations from 2019 to 2021 in five Mountain West states: Arizona, Colorado, Nevada, New Mexico, and Utah. The original report from The Rockefeller Institute of Government is published each fiscal year and includes information on state and federal government expenditures and the net difference between state and federal spending for all 50 states. The original report sources data from the âBudget of the U.S. Government, Fiscal Year 2023.
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