27,061 research outputs found
Electrical system/environment interactions on the planet Mars
The Martian environment is a diverse environment with which systems will interact in numerous ways. Preliminary thoughts on electrical system/environment interactions which might be of interest to system designers at all stages of system design are presented. These interactions are primarily related to electrical charging, contamination, and Martian surface sand and dust
Visual Search for Galaxies near the Northern Crossing of the Supergalactic plane by the Milky Way
We have visually examined twelve Palomar red Plates for galaxies at low
Galactic latitude b, where the Supergalactic Plane (SGP) is crossed by the
Galactic Plane (GP), at Galactic longitude l ~135 degrees. The catalogue
consists of 2575 galaxy candidates, of which 462 have major axis diameters d >=
0.8 arc min (uncorrected for extinction). Galaxy candidates can be identified
down to |b| ~ 0 degrees. One of our galaxy candidates (J24 = Dwingeloo 1) has
recently been discovered independently in 21cm by Kraan-Korteweg et al. (1994)
as a nearby galaxy. Comparisons with the structures seen in the IRAS and UGC
catalogues are made. We compare the success rate of identifying galaxies using
the IRAS Point Source Catalogue under different colour selection criteria. The
criteria that require both the 60 micron and 100 micron fluxes to be of high
quality, have the highest probability of selecting a galaxy (with d >= 0.6 arc
min), but at the expense of selecting a smaller number of galaxies in total.Comment: uuencoded compressed postscript, without figures. The figures are
available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Electric field induced charge noise in doped silicon: ionization of phosphorus donors
We report low frequency charge noise measurement on silicon substrates with
different phosphorus doping densities. The measurements are performed with
aluminum single electron transistors (SETs) at millikelvin temperatures where
the substrates are in the insulating regime. By measuring the SET Coulomb
oscillations, we find a gate voltage dependent charge noise on the more heavily
doped substrate. This charge noise, which is seen to have a 1/f spectrum, is
attributed to the electric field induced tunneling of electrons from their
phosphorus donor potentials.Comment: 4 page, 3 figure
Hydrogen bonding in C-methylated nitroanilines : the three-dimensional framework structure of 2-methyl-4-nitroaniline
Peer reviewedPublisher PD
MGGPOD: a Monte Carlo Suite for Modeling Instrumental Line and Continuum Backgrounds in Gamma-Ray Astronomy
Intense and complex instrumental backgrounds, against which the much smaller
signals from celestial sources have to be discerned, are a notorious problem
for low and intermediate energy gamma-ray astronomy (~50 keV - 10 MeV).
Therefore a detailed qualitative and quantitative understanding of instrumental
line and continuum backgrounds is crucial for most stages of gamma-ray
astronomy missions, ranging from the design and development of new
instrumentation through performance prediction to data reduction. We have
developed MGGPOD, a user-friendly suite of Monte Carlo codes built around the
widely used GEANT (Version 3.21) package, to simulate ab initio the physical
processes relevant for the production of instrumental backgrounds. These
include the build-up and delayed decay of radioactive isotopes as well as the
prompt de-excitation of excited nuclei, both of which give rise to a plethora
of instrumental gamma-ray background lines in addition to continuum
backgrounds. The MGGPOD package and documentation are publicly available for
download from http://sigma-2.cesr.fr/spi/MGGPOD/.
We demonstrate the capabilities of the MGGPOD suite by modeling high
resolution gamma-ray spectra recorded by the Transient Gamma-Ray Spectrometer
(TGRS) on board Wind during 1995. The TGRS is a Ge spectrometer operating in
the 40 keV to 8 MeV range. Due to its fine energy resolution, these spectra
reveal the complex instrumental background in formidable detail, particularly
the many prompt and delayed gamma-ray lines. We evaluate the successes and
failures of the MGGPOD package in reproducing TGRS data, and provide
identifications for the numerous instrumental lines.Comment: 60 pages, 13 figures, 7 tables, accepted for publication in ApJ
Offside goals and induced breaches of contract
An analysis of Global Resources Group Ltd v Mackay which explores the possibility of building links between the offside goals rule and nominate delict of inducing breach of contract
Counts and Sizes of Galaxies in the Hubble Deep Field - South: Implications for the Next Generation Space Telescope
Science objectives for the Next Generation Space Telescope (NGST) include a
large component of galaxy surveys, both imaging and spectroscopy. The Hubble
Deep Field datasets include the deepest observations ever made in the
ultraviolet, optical and near infrared, reaching depths comparable to that
expected for NGST spectroscopy. We present the source counts, galaxy sizes and
isophotal filling factors of the HDF-South images. The observed integrated
galaxy counts reach >500 galaxies per square arcminute at AB<30. We extend
these counts to faint levels in the infrared using models. The trend previously
seen that fainter galaxies are smaller, continues to AB=29 in the high
resolution HDF-S STIS image, where galaxies have a typical half-light radius of
0.1 arcseconds. Extensive Monte Carlo simulations show that the small measured
sizes are not due to selection effects until >29mag. Using the HDF-S NICMOS
image, we show that galaxies are smaller in the near infrared than they are in
the optical. We analyze the isophotal filling factor of the HDF-S STIS image,
and show that this image is mostly empty sky even at the limits of galaxy
detection, a conclusion we expect to hold true for NGST spectroscopy. At the
surface brightness limits expected for NGST imaging, however, about a quarter
of the sky is occupied by the outer isophotes of AB<30 galaxies. We discuss the
implications of these data on several design concepts of the NGST near-infrared
spectrograph. We compare the effects of resolution and the confusion limit of
various designs, as well as the multiplexing advantages of either multi-object
or full-field spectroscopy. We argue that the optimal choice for NGST
spectroscopy of high redshift galaxies is a multi-object spectrograph (MOS)
with target selection by a micro electro mechanical system (MEMS) device.Comment: 27 pages including 10 figures, accepted for publication in the
Astronomical Journal, June 2000, abridged abstrac
NGC 3312: A victim of ram pressure sweeping
Researchers are undertaking a volume limited survey of the Hydra I cluster in neutral hydrogen using the National Radio Astronomy Observatory's Very Large Array (VLA). The main purpose is to study the effects of a dense environment on the gaseous component of the galaxies. Observational evidence has been accumulating recently that ram pressure sweeping does occur in the centers of clusters, but it is possible that tidal interactions play a role as well. Results of high resolution HI imaging of NGC 3312, the large peculiar spiral near the cluster center are presented. Hydra I (= A1060) is the nearest rich cluster beyond Virgo and, as such, presents a unique opportunity to do a complete survey of a cluster. It is similar to the Virgo cluster in many of its general physical characteristics, such as size, x ray luminosity, velocity dispersion, and galaxy content (high spiral fraction). However, Hydra I appears to be more regular and relaxed. This is evident in the x ray distribution in its central region, which is radially symmetric and centered on the dominant galaxy, NGC 3311, a cD-like elliptical. The observed x ray luminosity implies a central gas density of 4.5 x 10 to the 3rd power cm(-3). Gallagher (1978) argued from optical images of NGC 3312 that this galaxy might be an ideal candidate to directly study effects of the ram pressure process; it might currently be undergoing stripping of its interstellar medium. The researchers' data are consistent with this suggestion, but other origins of the peculiar appearance cannot yet be ruled out
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