872 research outputs found
The effects of regional insolation differences upon advanced solar thermal electric power plant performance and energy costs
The performance and cost of the 10 MWe advanced solar thermal electric power plants sited in various regions of the continental United States were determined. The regional insolation data base is discussed. A range for the forecast cost of conventional electricity by region and nationally over the next several cades are presented
The effects of regional insolation differences upon advanced solar thermal electric power plant performance and energy costs
The performance and cost of four 10 MWe advanced solar thermal electric power plants sited in various regions of the continental United States was studied. Each region has different insolation characteristics which result in varying collector field areas, plant performance, capital costs and energy costs. The regional variation in solar plant performance was assessed in relation to the expected rise in the future cost of residential and commercial electricity supplied by conventional utility power systems in the same regions. A discussion of the regional insolation data base is presented along with a description of the solar systems performance and costs. A range for the forecast cost of conventional electricity by region and nationally over the next several decades is given
Extreme Ultraviolet Emission in the Fornax Cluster of Galaxies
We present studies of the Extreme Ultraviolet (EUV) emission in the Fornax
cluster of galaxies; a relatively nearby well-studied cluster with X-ray
emitting cluster gas and a very large radio source. We examine both the
large-scale (~size of the X-ray emitting cluster gas), and the small-scale
(<arcmin) emission.
We find that this cluster has large-scale diffuse EUV emission. However, at
the sensitivity level of the existing EUVE data, this emission is due entirely
to the low energy tail of the X-ray emitting gas. We have also examined
small-scale structures in raw EUVE images of this cluster. We find that
small-scale irregularities are present in all raw Deep Survey images as a
result of small-scale detector effects. These effects can be removed by
appropriate flat-fielding. After flat-fielding, the Fornax cluster still shows
a few significant regions of small-scale EUV enhancement. We find that these
are emission from stars and galaxies in the field. We find that at existing
levels of sensitivity, there is no excess EUV emission in the cluster on either
large or small scales.Comment: 6 pages, 3 eps figures, aastex5, Accepted to ApJ
The H_2O Jet Target
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Evidence Against the Sciama Model of Radiative Decay of Massive Neutrinos
We report on spectral observations of the night sky in the band around 900
angstroms where the emission line in the Sciama model of radiatively decaying
massive neutrinos would be present. The data were obtained with a high
resolution, high sensitivity spectrometer flown on the Spanish MINISAT
satellite. The observed emission is far less intense than that expected in the
Sciama model.Comment: 9 pages, accepted to Ap
Towards Autopoietic Computing
A key challenge in modern computing is to develop systems that address
complex, dynamic problems in a scalable and efficient way, because the
increasing complexity of software makes designing and maintaining efficient and
flexible systems increasingly difficult. Biological systems are thought to
possess robust, scalable processing paradigms that can automatically manage
complex, dynamic problem spaces, possessing several properties that may be
useful in computer systems. The biological properties of self-organisation,
self-replication, self-management, and scalability are addressed in an
interesting way by autopoiesis, a descriptive theory of the cell founded on the
concept of a system's circular organisation to define its boundary with its
environment. In this paper, therefore, we review the main concepts of
autopoiesis and then discuss how they could be related to fundamental concepts
and theories of computation. The paper is conceptual in nature and the emphasis
is on the review of other people's work in this area as part of a longer-term
strategy to develop a formal theory of autopoietic computing.Comment: 10 Pages, 3 figure
Recommended from our members
Validation of the cognitive recovery assessments with the Postoperative Quality of Recovery Scale in patients with low-baseline cognition
Patients with pre-surgery cognitive impairment cannot currently be assessed for cognitive recovery after surgery using the Postoperative Quality of Recovery Scale (PostopQRS),as they would mathematically be scored as recovered. The group nonetheless represent a frail cohort at high risk of recovering poorly. We aimed to validate a novel method to score cognitive recovery in patients with low baseline cognition, using the number of low-score tests rather than their numerical values. Face validity was demonstrated in 86 participants in whom both PostopQRS and an 11-item neuropsychological battery were performed. The PostopQRS agreed with neuropsychological categorization of low versus normal cognition 74% of the time, with all but 5 incorrectly coded participants deviating by only 1 neurocognitive test. Cognitive recovery over time was comparable for groups with differing baseline cognitive function, irrespective of whether PostopQRS or neuropsychological methods were used. Discriminant validation was demonstrated in a post hoc analysis of the Steroids in Cardiac Surgery (SIRS) substudy by allocating groups to normal (n=246) or low baseline cognition (n=231) stratified by cognitive recovery on day 1. Recovery was similar for participants with low and normal baseline cognition. Postoperative length of stay was longer in patients with failed cognitive recovery whether they had normal (10.4±10.0 vs. 8.0±5.9 days, P=0.02) or low baseline cognition (12.0±11.1 vs. 8.2±4.7 days, P<0.01). Overall quality of recovery, as well as cognitive, emotive, and physiological recovery in those who recovered was independent of baseline cognition. The modified scoring method for the PostopQRS cognitive domain therefore demonstrates acceptable face and discriminant validity
Unveiling the Active Nucleus of Centaurus A
We report new HST WFPC2 and NICMOS observations of the center of the nearest
radio galaxy Centaurus A (NGC 5128) and discuss their implications for our
understanding of the active nucleus and jet. We detect the active nucleus in
the near-IR (K and H) and, for the first time, in the optical (I and V),
deriving the spectral energy distribution of the nucleus from the radio to
X-rays. The optical and part of the near-IR emission can be explained by the
extrapolation of the X-ray power law reddened by A_V~14mag, a value consistent
with other independent estimates.
The 20pc-scale nuclear disk discovered by Schreier et al. (1998) is detected
in the [FeII] 1.64mic line and presents a morphology similar to that observed
in Pa alpha with a [FeII]/Pa alpha ratio typical of low ionization Seyfert
galaxies and LINERs. NICMOS 3 Pa alpha observations in a 50"x50" circumnuclear
region suggest enhanced star formation (~0.3Msun/yr) at the edges of the
putative bar seen with ISO, perhaps due to shocks driven into the gas.
The light profile, reconstructed from V, H and K observations, shows that
Centaurus A has a core profile with a resolved break at ~4" and suggests a
black--hole mass of ~10^9 Msun. A linear blue structure aligned with the
radio/X-ray jet may indicate a channel of relatively low reddening in which
dust has been swept away by the jet.Comment: 19 pages, 13 figures, Astrophysical Journal, in press. High quality
figures available at http://www.arcetri.astro.it/~marconi/colpic.htm
Coma revealed as an extended hard X-rays source by INTEGRAL IBIS/ISGRI
Aims. We report the INTEGRAL/IBIS observations of the Coma Cluster in the
hard X-ray/soft-ray domain. Methods. Since the Coma Cluster appears as an
extended source, its global intensity and significance cannot be directly
extracted with standard coded mask analysis. We used the method of imaging the
extended sources with a coded mask telescope developed by Renaud et al. (2006).
Results. The imaging capabilities and the sensitivity of the IBIS/ISGRI coded
mask instrument allows us to identify for the first time the site of the
emission above ~ 15 keV. We have studied the Coma Cluster morphology in the
18-30keV band and found that it follows the prediction based on X-ray
observations.We also bring constraints on the non-thermal mechanism
contribution at higher energies.Comment: 4 pages, 4 figures, Accepted for publication in A&A Letter
UV and EUV Instruments
We describe telescopes and instruments that were developed and used for
astronomical research in the ultraviolet (UV) and extreme ultraviolet (EUV)
regions of the electromagnetic spectrum. The wavelength ranges covered by these
bands are not uniquely defined. We use the following convention here: The EUV
and UV span the regions ~100-912 and 912-3000 Angstroem respectively. The
limitation between both ranges is a natural choice, because the hydrogen Lyman
absorption edge is located at 912 Angstroem. At smaller wavelengths,
astronomical sources are strongly absorbed by the interstellar medium. It also
marks a technical limit, because telescopes and instruments are of different
design. In the EUV range, the technology is strongly related to that utilized
in X-ray astronomy, while in the UV range the instruments in many cases have
their roots in optical astronomy. We will, therefore, describe the UV and EUV
instruments in appropriate conciseness and refer to the respective chapters of
this volume for more technical details.Comment: To appear in: Landolt-Boernstein, New Series VI/4A, Astronomy,
Astrophysics, and Cosmology; Instruments and Methods, ed. J.E. Truemper,
Springer-Verlag, Berlin, 201
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