1,556 research outputs found
INTEGRAL observations of the Large Magellanic Cloud region
We present the preliminary results of the INTEGRAL survey of the Large
Magellanic Cloud. The observations have been carried out in January 2003 (about
10^6 s) and January 2004 (about 4x10^5 s). Here we concentrate on the bright
sources LMC X-1, LMC X-2, LMC X-3 located in our satellite galaxy, and on the
serendipitous detections of the Galactic Low Mass X-ray Binary EXO 0748-676 and
of the Seyfert 2 galaxy IRAS 04575-7537.Comment: 4 pages, 7 figures. To be published in the Proceedings of the 5th
INTEGRAL Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munic
The Nature of the Compact Supernova Remnants in Starburst Galaxies
Radio observations of starburst regions in galaxies have revealed groups of
compact nonthermal sources that may be radiative supernova remnants expanding
in the interclump medium of molecular clouds. Because of the high pressure in
starburst regions, the interclump medium may have a density ~ 10^3 H atoms
cm^{-3} in a starburst nucleus like M82 and ~ 10^4 H atoms cm^{-3} in an
ultraluminous galaxy like Arp 220. In M82, our model can account for the sizes,
the slow evolution, the high radio luminosities, and the low X-ray luminosities
of the sources. We predict expansion velocities ~ 500 km/s, which is slower
than the one case measured by VLBI techniques. Although we predict the remnants
to be radiative, the expected radiation is difficult to detect because it is at
infrared wavelengths and the starburst is itself very luminous; one detection
possibility is broad [OI] 63 micron line emission at the positions of the radio
remnants. The more luminous and compact remnants in Arp 220 can be accounted
for by the higher molecular cloud density. In our model, the observed remnants
lose most of the supernova energy to radiation. Other explosions in a lower
density medium may directly heat a hot, low density interstellar component,
leading to the superwinds that are associated with starburst regions.Comment: 11 pages, 1 figure, ApJ submitte
The Large-scale Bipolar Wind in the Galactic Center
During a 9-month campaign (1996--1997), the Midcourse Space Experiment (MSX)
satellite mapped the Galactic Plane at mid-infrared wavelengths (4.3--21.3um).
Here we report evidence for a spectacular limb- brightened, bipolar structure
at the Galactic Center extending more than a degree (170 pc at 8.0 kpc) on
either side of the plane. The 8.3um emission shows a tight correlation with the
3, 6 and 11 cm continuum structure over the same scales. Dense gas and dust are
being entrained in a large-scale bipolar wind powered by a central starburst.
The inferred energy injection at the source is ~10^54/kappa erg for which
\kappa is the covering fraction of the dusty shell (kappa <= 0.1).
There is observational evidence for a galactic wind on much larger scales,
presumably from the same central source which produced the bipolar shell seen
by MSX. Sofue has argued that the North Polar Spur -- a thermal x-ray/radio
loop which extends from the Galactic Plane to b = +80 deg -- was powered by a
nuclear explosion (1-30 x 10^55 erg) roughly 15 Myr ago. We demonstrate that an
open-ended bipolar wind (~10^55 erg), when viewed in near-field projection,
provides the most natural explanation for the observed loop structure. The
ROSAT 1.5 keV diffuse x-ray map over the inner 45 deg provides compelling
evidence for this interpretation. Since the faint bipolar emission would be
very difficult to detect beyond the Galaxy, the phenomenon of large-scale
galactic winds may be far more common than has been observed to date.Comment: 24 pages, 6 figures, aastex. High resolution figures are available at
ftp://www.aao.gov.au/pub/local/jbh/astro-ph/GC/. Astrophysical Journal,
accepte
Generation and quality control of lipidomics data for the alzheimers disease neuroimaging initiative cohort.
Alzheimers disease (AD) is a major public health priority with a large socioeconomic burden and complex etiology. The Alzheimer Disease Metabolomics Consortium (ADMC) and the Alzheimer Disease Neuroimaging Initiative (ADNI) aim to gain new biological insights in the disease etiology. We report here an untargeted lipidomics of serum specimens of 806 subjects within the ADNI1 cohort (188 AD, 392 mild cognitive impairment and 226 cognitively normal subjects) along with 83 quality control samples. Lipids were detected and measured using an ultra-high-performance liquid chromatography quadruple/time-of-flight mass spectrometry (UHPLC-QTOF MS) instrument operated in both negative and positive electrospray ionization modes. The dataset includes a total 513 unique lipid species out of which 341 are known lipids. For over 95% of the detected lipids, a relative standard deviation of better than 20% was achieved in the quality control samples, indicating high technical reproducibility. Association modeling of this dataset and available clinical, metabolomics and drug-use data will provide novel insights into the AD etiology. These datasets are available at the ADNI repository at http://adni.loni.usc.edu/
Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes
Quantum dots defined in carbon nanotubes are a platform for both basic
scientific studies and research into new device applications. In particular,
they have unique properties that make them attractive for studying the coherent
properties of single electron spins. To perform such experiments it is
necessary to confine a single electron in a quantum dot with highly tunable
barriers, but disorder has until now prevented tunable nanotube-based
quantum-dot devices from reaching the single-electron regime. Here, we use
local gate voltages applied to an ultra-clean suspended nanotube to confine a
single electron in both a single quantum dot and, for the first time, in a
tunable double quantum dot. This tunability is limited by a novel type of
tunnelling that is analogous to that in the Klein paradox of relativistic
quantum mechanics.Comment: 21 pages including supplementary informatio
New possibilities for research on reef fish across the continental shelf of South Africa
[From introduction] Subtidal research presents numerous challenges that restrict the ability to answer fundamental ecological questions related to reef systems. These challenges are closely associated with traditional monitoring methods and include depth restrictions (e.g. safe diving depths for underwater visual census), habitat destruction (e.g. trawling), mortality of target species (e.g. controlled angling and fish traps), and high operating costs (e.g. remotely operated vehicles
and large research vessels. Whereas many of these challenges do not apply or are avoidable in the shallow subtidal environment, the difficulties grow as one attempts to sample deeper benthic habitats. This situation has resulted in a paucity of knowledge on the structure and ecology of deep water reef habitats around the coast of South Africa and in most marine areas around the world. Furthermore, the inability to effectively survey deep water benthic environments has limited the capacity of researchers to investigate connectivity between shallow and deep water habitats in a standardised and comparable fashio
Secret Symmetries in AdS/CFT
We discuss special quantum group (secret) symmetries of the integrable system
associated to the AdS/CFT correspondence. These symmetries have by now been
observed in a variety of forms, including the spectral problem, the boundary
scattering problem, n-point amplitudes, the pure-spinor formulation and quantum
affine deformations.Comment: 20 pages, pdfLaTeX; Submitted to the Proceedings of the Nordita
program `Exact Results in Gauge-String Dualities'; Based on the talk
presented by A.T., Nordita, 15 February 201
The Nature of Starburst Activity in M82
We present new evolutionary synthesis models of M82 based mainly on
observations consisting of near-infrared integral field spectroscopy and
mid-infrared spectroscopy. The models incorporate stellar evolution, spectral
synthesis, and photoionization modeling, and are optimized for 1-45 micron
observations of starburst galaxies. The data allow us to model the starburst
regions on scales as small as 25 pc. We investigate the initial mass function
(IMF) of the stars and constrain quantitatively the spatial and temporal
evolution of starburst activity in M82. We find a typical decay timescale for
individual burst sites of a few million years. The data are consistent with the
formation of very massive stars (> 50-100 Msun) and require a flattening of the
starburst IMF below a few solar masses assuming a Salpeter slope at higher
masses. Our results are well matched by a scenario in which the global
starburst activity in M82 occurred in two successive episodes each lasting a
few million years, peaking about 10 and 5 Myr ago. The first episode took place
throughout the central regions of M82 and was particularly intense at the
nucleus while the second episode occurred predominantly in a circumnuclear ring
and along the stellar bar. We interpret this sequence as resulting from the
gravitational interaction M82 and its neighbour M81, and subsequent bar-driven
evolution. The short burst duration on all spatial scales indicates strong
negative feedback effects of starburst activity, both locally and globally.
Simple energetics considerations suggest the collective mechanical energy
released by massive stars was able to rapidly inhibit star formation after the
onset of each episode.Comment: 48 pages, incl. 16 Postscript figures; accepted for publication in
the Astrophysical Journa
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