17,454 research outputs found
Testing of silver cadmium cells Final report
Life cycle tests to determine silver cadmium cell capabilit
Development of a nickel cadmium storage cell immune to damage from overdischarge and overcharge
Nickel-cadmium battery immune to damage from overcharge and overdischarg
Non-Abelian quantized Hall states of electrons at filling factors 12/5 and 13/5 in the first excited Landau level
We present results of extensive numerical calculations on the ground state of
electrons in the first excited (n=1) Landau level with Coulomb interactions,
and including non-zero thickness effects, for filling factors 12/5 and 13/5 in
the torus geometry. In a region that includes these experimentally-relevant
values, we find that the energy spectrum and the overlaps with the trial states
support the previous hypothesis that the system is in the non-Abelian k = 3
liquid phase we introduced in a previous paper.Comment: 5 pages (Revtex4), 7 figure
The X-ray properties of the merging galaxy pair NGC 4038/9 - the Antennae
We report the results of an X-ray spectral imaging observation of the
Antennae with the ROSAT PSPC. 55% of the soft X-ray flux from the system is
resolved into discrete sources, including components identified with the
galactic nuclei and large HII regions, whilst the remainder appears to be
predominantly genuinely diffuse emission from gas at a temperature ~4x10^6 K.
The morphology of the emission is unusual, combining a halo which envelopes the
galactic discs, with what appears to be a distorted, but well-collimated
bipolar outflow. We derive physical parameters for the hot gas in both diffuse
components, which are of some interest, given that the Antennae probably
represents an elliptical galaxy in the making.Comment: 15 pages plus 9 figures, uuencoded encapsulated postscript file.
Accepted for publication in MNRA
The XMM-Newton slew survey in the 2-10 keV band
The XMM-Newton Slew Survey (XSS) covers a significant fraction of the sky in
a broad X-ray bandpass. Although shallow by contemporary standards, in the
`classical' 2-10 keV band of X-ray astronomy, the XSS provides significantly
better sensitivity than any currently available all-sky survey. We investigate
the source content of the XSS, focussing on detections in the 2-10 keV band
down to a very low threshold (> 4 counts net of background). At the faint end,
the survey reaches a flux sensitivity of roughly 3e-12 erg/cm2/s (2-10 keV).
Our starting point was a sample of 487 sources detected in the XMMSL1d2 XSS at
high galactic latitude in the hard band. Through cross-correlation with
published source catalogues from surveys spanning the electromagnetic spectrum
from radio to gamma-rays, we find that 45% of the sources have likely
identifications with normal/active galaxies, 18% are associated with other
classes of X-ray object (nearby coronally active stars, accreting binaries,
clusters of galaxies), leaving 37% of the XSS sources with no current
identification. We go on to define an XSS extragalactic hard band sample
comprised of 219 galaxies and active galaxies. We investigate the properties of
this extragalactic sample including its X-ray logN-logS distribution. We find
that in the low-count limit, the XSS is strongly affected by Eddington bias.
There is also a very strong bias in the XSS against the detection of extended
sources, most notably clusters of galaxies. A significant fraction of the
detections at and around the low-count limit may be spurious. Nevertheless, it
is possible to use the XSS to extract a reasonably robust sample of
extragalactic sources, excluding galaxy clusters. The differential logN-logS
relation of these extragalactic sources matches very well to the HEAO-1 A2
all-sky survey measurements at bright fluxes and to the 2XMM source counts at
the faint end.Comment: 16 pages, 13 figures, FITS table of XSS extragalactic sample
available from http://www.star.le.ac.uk/~amr30/Slew
When is general wariness favored in avoiding multiple predator types?
Free access to article and electronic appendices via DOI.Adaptive responses to predation are generally studied assuming only one predator type exists, but most prey species are depredated by multiple types. When multiple types occur, the optimal antipredator response level may be determined solely by the probability of attack by the relevant predator: "specific responsiveness." Conversely, an increase in the probability of attack by one predator type might increase responsiveness to an alternative predator type: "general wariness." We formulate a mathematical model in which a prey animal perceives a cue providing information on the probability of two predator types being present. It can perform one of two evasive behaviors that vary in their suitability as a response to the "wrong" predator type. We show that general wariness is optimal when incorrect behavioral decisions have differential fitness costs. Counterintuitively, difficulty in discriminating between predator types does not favor general wariness. We predict that where responses to predator types are mutually exclusive (e.g., referential alarm-calling), specific responsiveness will occur; we suggest that prey generalize their defensive responses based on cue similarity due to an assumption of response utility; and we predict, with relevance to conservation, that habituation to human disturbance should generalize only to predators that elicit the same antipredator response as humans
The XMM-Newton Slew Survey: Towards The Whole X-ray Sky and the Rarest X-ray Events
The data collected by XMM-Newton as it slews between pointings currently
cover almost half the entire sky, and many familiar features and new sources
are visible. The soft-band sensitivity limit of the Slew is close to that of
the RASS, and a large-area Slew-RASS comparison now provides the best
opportunity for discovering extremely rare high-variability objects.Comment: To appear in Proceedings of "X-ray Astronomy 2009: Present Status,
Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September
7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin
The XMM-Newton Slew Survey: towards the XMMSL1 catalogue
The XMM-Newton satellite is the most sensitive X-ray observatory flown to
date due to the great collecting area of its mirrors coupled with the high
quantum efficiency of the EPIC detectors. It performs slewing manoeuvers
between observation targets tracking almost circular orbits through the
ecliptic poles due to the Sun constraint. Slews are made with the EPIC cameras
open and the other instruments closed, operating with the observing mode set to
the one of the previous pointed observation and the medium filter in place.
Slew observations from the EPIC-pn camera in FF, eFF and LW modes provide
data, resulting in a maximum of 15 seconds of on-source time. These data can be
used to give a uniform survey of the X-ray sky, at great sensitivity in the
hard band compared with other X-ray all-sky surveys.Comment: 2 pages, 2 figures, to appear in the proceedings of "The X-ray
Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200
The XMM-Newton Slew Survey
XMM-Newton, with the huge collecting area of its mirrors and the high quantum
efficiency of its EPIC detectors, is the most sensitive X-ray observatory ever
flown. This is strikingly evident during slew exposures, which, while yielding
only at most 14 seconds of on-source exposure time, actually constitute a 2-10
keV survey ten times deeper than all other "all-sky" surveys. The current
(April 2005) XMM archive contains 374 slew exposures which give a uniform
coverage over around 10,000 square degrees (approx. 25% of the sky). Here we
describe the results of pilot studies, the current status of the XMM-Newton
Slew Survey, up-to-date results and our progress towards constructing a
catalogue of slew detections in the full 0.2-12 keV energy band.Comment: 3 pages, 4 figures, XMM-Newton EPIC Consortium Meeting, Schloss
Ringberg, Germany, April 2005, to appear in MPE Repor
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