5,339 research outputs found
Alien Registration- Cowan, Lee D. (Blaine, Aroostook County)
https://digitalmaine.com/alien_docs/27365/thumbnail.jp
Supernovae versus Neutron Star Mergers as the Major r-Process Sources
I show that recent observations of r-process abundances in metal-poor stars
are difficult to explain if neutron star mergers (NSMs) are the major r-process
sources. In contrast, such observations and meteoritic data on Hf182 and I129
in the early solar system support a self-consistent picture of r-process
enrichment by supernovae (SNe). While further theoretical studies of r-process
production and enrichment are needed for both SNe and NSMs, I emphasize two
possible direct observational tests of the SN r-process model: gamma rays from
decay of r-process nuclei in SN remnants and surface contamination of the
companion by SN r-process ejecta in binaries.Comment: 5 pages, to appear in ApJ
Three-dimensional dielectric photonic crystal structures for laser-driven acceleration
We present the design and simulation of a three-dimensional photonic crystal
waveguide for linear laser-driven acceleration in vacuum. The structure
confines a synchronous speed-of-light accelerating mode in both transverse
dimensions. We report the properties of this mode, including sustainable
gradient and optical-to-beam efficiency. We present a novel method for
confining a particle beam using optical fields as focusing elements. This
technique, combined with careful structure design, is shown to have a large
dynamic aperture and minimal emittance growth, even over millions of optical
wavelengths
Larkin-Ovchinnikov-Fulde-Ferrell phase in the superconductor (TMTSF)2ClO4: Theory versus experiment
We consider a formation of the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase
in a quasi-one-dimensional (Q1D) conductor in a magnetic field, parallel to its
conducting chains, where we take into account both the paramagnetic
spin-splitting and orbital destructive effects against superconductivity. We
show that, due to a relative weakness of the orbital effects in a Q1D case, the
LOFF phase appears in (TMTSF)ClO superconductor for real values of its
Q1D band parameters. We compare our theoretical calculations with the recent
experimental data by Y. Maeno's group [S. Yonezawa et al., Phys. Rev. Lett.
\textbf{100}, 117002 (2008)] and show that there is a good qualitative and
quantitative agreement between the theory and experimental data.Comment: 4 pages, 1 figur
The effects of r-process heating on fall-back accretion in compact object mergers
We explore the effects of r-process nucleosynthesis on fall-back accretion in
neutron star(NS)-NS and black hole-NS mergers, and the resulting implications
for short-duration gamma-ray bursts (GRBs). Though dynamically important, the
energy released during the r-process is not yet taken into account in merger
simulations. We use a nuclear reaction network to calculate the heating (due to
beta-decays and nuclear fission) experienced by material on the
marginally-bound orbits nominally responsible for late-time fall-back. Since
matter with longer orbital periods t_orb experiences lower densities, for
longer periods of time, the total r-process heating rises rapidly with t_orb,
such that material with t_orb > 1 seconds can become completely unbound. Thus,
r-process heating fundamentally changes the canonical prediction of an
uninterrupted power-law decline in the fall-back rate dM/dt at late times. When
the timescale for r-process to complete is > 1 second, the heating produces a
complete cut-off in fall-back accretion after ~ 1 second; if robust, this would
imply that fall-back accretion cannot explain the late-time X-ray flaring
observed following some short GRBs. However, for a narrow, but physically
plausible, range of parameters, fall-back accretion can resume after ~ 10 s,
despite having been strongly suppressed for ~ 1-10 s after the merger. This
suggests the intriguing possibility that the gap observed between the prompt
and extended emission in short GRBs is a manifestation of r-process heating.Comment: 7 pages; 4 figures; submitted to MNRA
Monetary impact of Taenia solium cysticercosis in four countries
The societal monetary burden of cysticercosis in the Eastern Cape Province, South Africa, Honduras, India and the United States of America were estimated. Data on the frequency of infection and on associated morbidity in both human and pig populations and their costs were collected. Decision trees were used to assess the frequency of medical care and loss of value of pigs with their monetary impact
Accuracy of Serological Testing for the Diagnosis of Prevalent Neurocysticercosis in Outpatients with Epilepsy, Eastern Cape Province, South Africa
Epilepsy is a significant contributor to morbidity world-wide in persons of all ages. Little is known, however, about its causes. In the developing world, parasitic infections of the brain, in particular Taenia solium neurocysticercosis (NCC) are thought to be important factors. Determining whether or not there is infection in the brain is difficult since to be certain, specialized imaging studies, such as CT scans, are required. These are expensive and not widely available. In addition, they are not appropriate for use in large, population-based studies. Thus, blood tests for evidence of infection with T. solium are often done instead to estimate the presence of NCC. In this study's population of persons with epilepsy being seen at a hospital out-patient clinic in South Africa, 37% had CT evidence of NCC, a percentage similar to that reported in other developing countries. The study also found that blood tests were not generally useful compared to CT for correctly identifying those persons who did or did not have NCC, and thus, they cannot be relied upon for field studies of NCC
Effective connectivity reveals strategy differences in an expert calculator
Mathematical reasoning is a core component of cognition and the study of experts defines the upper limits of human cognitive abilities, which is why we are fascinated by peak performers, such as chess masters and mental calculators. Here, we investigated the neural bases of calendrical skills, i.e. the ability to rapidly identify the weekday of a particular date, in a gifted mental calculator who does not fall in the autistic spectrum, using functional MRI. Graph-based mapping of effective connectivity, but not univariate analysis, revealed distinct anatomical location of “cortical hubs” supporting the processing of well-practiced close dates and less-practiced remote dates: the former engaged predominantly occipital and medial temporal areas, whereas the latter were associated mainly with prefrontal, orbitofrontal and anterior cingulate connectivity. These results point to the effect of extensive practice on the development of expertise and long term working memory, and demonstrate the role of frontal networks in supporting performance on less practiced calculations, which incur additional processing demands. Through the example of calendrical skills, our results demonstrate that the ability to perform complex calculations is initially supported by extensive attentional and strategic resources, which, as expertise develops, are gradually replaced by access to long term working memory for familiar material
Spin density wave dislocation in chromium probed by coherent x-ray diffraction
We report on the study of a magnetic dislocation in pure chromium. Coherent
x-ray diffraction profiles obtained on the incommensurate Spin Density Wave
(SDW) reflection are consistent with the presence of a dislocation of the
magnetic order, embedded at a few micrometers from the surface of the sample.
Beyond the specific case of magnetic dislocations in chromium, this work may
open up a new method for the study of magnetic defects embedded in the bulk.Comment: 8 pages, 7 figure
LEP Limits on CP-Violating Non-Minimal Higgs Sectors
We derive a sum rule which shows how to extend LEP limits on the masses of
the lightest CP-even and CP-odd Higgs bosons of a CP-conserving
two-Higgs-doublet model to any two Higgs bosons of a general CP-violating
two-Higgs-doublet model. We generalize the analysis to a Higgs sector
consisting of an arbitrary number of Higgs doublets and singlets, giving
explicit limits for the CP-conserving and CP-violating two-doublet plus
one-singlet Higgs sectors.Comment: 9 pages, full postscript file is available via anonymous ftp at
ftp://ucdhep.ucdavis.edu/gunion/lepcpv.p
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