812 research outputs found
MageCometâweb application for harmonizing existing large-scale experiment descriptions
Motivation: Meta-analysis of large gene expression datasets obtained from public repositories requires consistently annotated data. Curation of such experiments, however, is an expert activity which involves repetitive manipulation of text. Existing tools for automated curation are few, which bottleneck the analysis pipeline
Nature of bonding and electronic structure in MgB2, a boron intercalation superconductor
Chemical bonding and electronic structure of MgB2, a boron-based newly
discovered superconductor, is studied using self-consistent band structure
techniques. Analysis of the transformation of the band structure for the
hypothetical series of graphite - primitive graphite - primitive graphite-like
boron - intercalated boron, shows that the band structure of MgB2 is
graphite-like, with pi-bands falling deeper than in ordinary graphite. These
bands possess a typically delocalized and metallic, as opposed to covalent,
character. The in-plane sigma-bands retain their 2D covalent character, but
exhibit a metallic hole-type conductivity. The coexistence of 2D covalent
in-plane and 3D metallic-type interlayer conducting bands is a peculiar feature
of MgB2. We analyze the 2D and 3D features of the band structure of MgB2 and
related compounds, and their contributions to conductivity.Comment: 4 pages in revtex, 3 figures in 4 separate EPS file
Superconductivity of metallic boron in MgB_2
Boron in MgB_2 forms layers of honeycomb lattices with magnesium as a space
filler. Band structure calculations indicate that Mg is substantially ionized,
and the bands at the Fermi level derive mainly from B orbitals. Strong bonding
with an ionic component and considerable metallic density of states yield a
sizeable electron-phonon coupling. Using the rigid atomic sphere approximation
and an analogy to Al, we estimate the coupling constant lambda to be of order
1. Together with high phonon frequencies, which we estimate via zone-center
frozen phonon calculations to be between 300 and 700 cm^-1, this produces a
high critical temperature, consistent with recent experiments reporting Tc=39 K
(J. Akimitsu et al., to be published). Thus MgB_2 can be viewed as an analog of
the long sought, but still hypothetical, superconducting metallic hydrogen.Comment: several typos corrected, most importantly, units in the tables fixed
and a missing zero in the expression for the resistivity restore
Impact of paternal deployment to the conflicts in Iraq and Afghanistan and paternal post-traumatic stress disorder on the children of military fathers
Background
Little is known about the social and emotional well-being of children
whose fathers have been deployed to the conflicts in Iraq/
Afghanistan or who have post-traumatic stress disorder (PTSD).
Aims
To examine the emotional and behavioural well-being of children
whose fathers are or have been in the UK armed forces, in particular
the effects of paternal deployment to the conflicts in Iraq
or Afghanistan and paternal PTSD.
Method
Fathers who had taken part in a large tri-service cohort and had
children aged 3â16 years were asked about the emotional and
behavioural well-being of their child(ren) and assessed for
symptoms of PTSD via online questionnaires and telephone
interview.
Results
In total, 621 (67%) fathers participated, providing data on
1044 children. Paternal deployment to Iraq or Afghanistan was
not associated with childhood emotional and behavioural
difficulties. Paternal probable PTSD were associated with child
hyperactivity. This finding was limited to boys and those under
11 years of age.
Conclusions
This study showed that adverse childhood emotional and
behavioural well-being was not associated with paternal
deployment but was associated with paternal probable PTSD
Search for TeV Gamma-Rays from Shell-Type Supernova Remnants
If cosmic rays with energies <100 TeV originate in the galaxy and are
accelerated in shock waves in shell-type supernova remnants (SNRs), gamma-rays
will be produced as the result of proton and electron interactions with the
local interstellar medium, and by inverse Compton emission from electrons
scattering soft photon fields. We report on observations of two supernova
remnants with the Whipple Observatory's 10 m gamma-ray telescope. No
significant detections have been made and upper limits on the >500 GeV flux are
reported. Non-thermal X-ray emission detected from one of these remnants
(Cassiopeia A) has been interpreted as synchrotron emission from electrons in
the ambient magnetic fields. Gamma-ray emission detected from the
Monoceros/Rosette Nebula region has been interpreted as evidence of cosmic-ray
acceleration. We interpret our results in the context of these observations.Comment: 4 pages, 2 figures, to appear in the proceedings of 26th
International Cosmic Ray Conference (Salt Lake City, 1999
The Flux Variability of Markarian 501 in Very High Energy Gamma Rays
The BL Lacertae object Markarian 501 was identified as a source of gamma-ray
emission at the Whipple Observatory in March 1995. Here we present a flux
variability analysis on several times-scales of the 233 hour data set
accumulated over 213 nights (from March 1995 to July 1998) with the Whipple
Observatory 10 m atmospheric Cherenkov imaging telescope. In 1995, with the
exception of a single night, the flux from Markarian 501 was constant on daily
and monthly time-scales and had an average flux of only 10% that of the Crab
Nebula, making it the weakest VHE source detected to date. In 1996, the average
flux was approximately twice the 1995 flux and showed significant
month-to-month variability. No significant day-scale variations were detected.
The average gamma-ray flux above ~350 GeV in the 1997 observing season rose to
1.4 times that of the Crab Nebula -- 14 times the 1995 discovery level --
allowing a search for variability on time-scales shorter than one day.
Significant hour-scale variability was present in the 1997 data, with the
shortest, observed on MJD 50607, having a doubling time of ~2 hours. In 1998
the average emission level decreased considerably from that of 1997 (to ~20% of
the Crab Nebula flux) but two significant flaring events were observed. Thus,
the emission from Markarian 501 shows large amplitude and rapid flux
variability at very high energies as does Markarian 421. It also shows large
mean flux level variations on year-to-year time-scales, behaviour which has not
been seen from Markarian 421 so far.Comment: 19 pages, 3 figures, to appear in ApJ, June 20, 1999, Vol. 518 #
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