545 research outputs found
Some Two-Loop Corrections to the Finite Temperature Effective Potential in the Electroweak Theory
Perturbation theory at finite temperature suffers from well-known infrared
problems. In the standard model, as a result, one cannot calculate the
effective potential for arbitrarily small values of , the Higgs
expectation value. Because the Higgs field is now known not to be extremely
light, it is necessary to determine whether perturbation theory is a reliable
guide to properties of the weak phase transition. In this note, we evaluate the
most singular contributions to the potential at two loops as well as the
leading strong interaction contributions. Above the critical temperature, the
strong interaction corrections are reasonably small, while the weak corrections
are about 10\%, even for rather small values of the Higgs field. At the
critical temperature, the weak corrections have a more substantial effect,
rendering the transition significantly more first order, but not significantly
changing the upper bound on the Higgs mass required for baryogenesis.Comment: 13 pages, figures available on request, SCIPP 92/4
Three-Dimensional Computed Tomography as a Method for Finding Die Attach Voids in Diodes
NASA analyzes electrical, electronic, and electromechanical (EEE) parts used in space vehicles to understand failure modes of these components. The diode is an EEE part critical to NASA missions that can fail due to excessive voiding in the die attach. Metallography, one established method for studying the die attach, is a time-intensive, destructive, and equivocal process whereby mechanical grinding of the diodes is performed to reveal voiding in the die attach. Problems such as die attach pull-out tend to complicate results and can lead to erroneous conclusions. The objective of this study is to determine if three-dimensional computed tomography (3DCT), a nondestructive technique, is a viable alternative to metallography for detecting die attach voiding. The die attach voiding in two- dimensional planes created from 3DCT scans was compared to several physical cross sections of the same diode to determine if the 3DCT scan accurately recreates die attach volumetric variabilit
Early optical spectra of nova V1369 Cen show presence of Lithium
We present early high resolution spectroscopic observations of the nova V1369
Cen. We have detected an absorption feature at 6695.6 \AA\, that we have
identified as blue--shifted Li I 6708 \AA. The absorption line,
moving at -550 km/s, was observed in five high-resolution spectra of the nova
obtained at different epochs. On the basis of the intensity of this absorption
line we infer that a single nova outburst can inject in the Galaxy
0.3 - 4.8 M. Given the current estimates of
Galactic nova rate, this amount is sufficient to explain the puzzling origin of
the overabundance of Lithium observed in young star populations.Comment: 6 pages, 5 figures, accepted for publication in ApJLetter
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