44,510 research outputs found
Engineering study for a mass memory system for advanced spacecrafts Final report, 1 Dec. 1969 - 1 Jul. 1970
Mass memory system for advanced spacecraf
A prototype system for detecting the radio-frequency pulse associated with cosmic ray air showers
The development of a system to detect the radio-frequency (RF) pulse
associated with extensive air showers of cosmic rays is described. This work
was performed at the CASA/MIA array in Utah, with the intention of designing
equipment that can be used in conjunction with the Auger Giant Array. A small
subset of data (less than 40 out of a total of 600 hours of running time),
taken under low-noise conditions, permitted upper limits to be placed on the
rate for pulses accompanying showers of energies around eV.Comment: 53 pages, LaTeX, 19 figures, published in Nuclear Instruments and
Methods. Revised version; some references update
Visualising and quantifying 'excess deaths' in Scotland compared with the rest of the UK and the rest of Western Europe
BACKGROUND: Scotland has higher mortality rates than the rest of Western Europe (rWE), with more cardiovascular disease and cancer among older adults; and alcohol-related and drug-related deaths, suicide and violence among younger adults. METHODS: We obtained sex, age-specific and year-specific all-cause mortality rates for Scotland and other populations, and explored differences in mortality both visually and numerically. RESULTS: Scotland's age-specific mortality was higher than the rest of the UK (rUK) since 1950, and has increased. Between the 1950s and 2000s, 'excess deaths' by age 80 per 100 000 population associated with living in Scotland grew from 4341 to 7203 compared with rUK, and from 4132 to 8828 compared with rWE. UK-wide mortality risk compared with rWE also increased, from 240 'excess deaths' in the 1950s to 2320 in the 2000s. Cohorts born in the 1940s and 1950s throughout the UK including Scotland had lower mortality risk than comparable rWE populations, especially for males. Mortality rates were higher in Scotland than rUK and rWE among younger adults from the 1990s onwards suggesting an age-period interaction. CONCLUSIONS: Worsening mortality among young adults in the past 30 years reversed a relative advantage evident for those born between 1950 and 1960. Compared with rWE, Scotland and rUK have followed similar trends but Scotland has started from a worse position and had worse working age-period effects in the 1990s and 2000s
High-field noise in metallic diffusive conductors
We analyze high-field current fluctuations in degenerate conductors by
mapping the electronic Fermi-liquid correlations at equilibrium to their
semiclassical non-equilibrium form. Our resulting Boltzmann description is
applicable to diffusive mesoscopic wires. We derive a non-equilibrium
connection between thermal fluctuations of the current and resistive
dissipation. In the weak-field limit this is the canonical fluctuation-
dissipation theorem. Away from equilibrium, the connection enables explicit
calculation of the excess ``hot-electron'' contribution to the thermal
spectrum. We show that excess thermal noise is strongly inhibited by Pauli
exclusion. This behaviour is generic to the semiclassical metallic regime.Comment: 13 pp, one fig. Companion paper to cond-mat/9911251. Final version,
to appear in J. Phys.: Cond. Ma
Proceedings of the 1st Space Plasma Computer Analysis Network (SCAN) Workshop
The purpose of the workshop was to identify specific cooperative scientific study topics within the discipline of Ionosphere Magnetosphere Coupling processes and to develop methods and procedures to accomplish this cooperative research using SCAN facilities. Cooperative scientific research was initiated in the areas of polar cusp composition, O+ polar outflow, and magnetospheric boundary morphology studies and an approach using a common metafile structure was adopted to facilitate the exchange of data and plots between the various workshop participants. The advantages of in person versus remote workshops were discussed also
Remarks on the Classical Size of D-Branes
We discuss different criteria for `classical size' of extremal Dirichlet
p-branes in type-II supergravity. Using strong-weak coupling duality, we find
that the size of the strong-coupling region at the core of the (p<3)-branes, is
always given by the asymptotic string scale, if measured in the weakly coupled
dual string metric. We also point out how the eleven-dimensional Planck scale
arises in the classical 0-brane solution, as well as the ten-dimensional Planck
scale in the D-instanton solution.Comment: 8 pp, harvma
Effect of positron-atom interactions on the annihilation gamma spectra of molecules
Calculations of gamma spectra for positron annihilation on a selection of
molecules, including methane and its fluoro-substitutes, ethane, propane,
butane and benzene are presented. The annihilation gamma spectra characterise
the momentum distribution of the electron-positron pair at the instant of
annihilation. The contribution to the gamma spectra from individual molecular
orbitals is obtained from electron momentum densities calculated using modern
computational quantum chemistry density functional theory tools. The
calculation, in its simplest form, effectively treats the low-energy
(thermalised, room-temperature) positron as a plane wave and gives annihilation
gamma spectra that are about 40% broader than experiment, although the main
chemical trends are reproduced. We show that this effective "narrowing" of the
experimental spectra is due to the action of the molecular potential on the
positron, chiefly, due to the positron repulsion from the nuclei. It leads to a
suppression of the contribution of small positron-nuclear separations where the
electron momentum is large. To investigate the effect of the nuclear repulsion,
as well as that of short-range electron-positron and positron-molecule
correlations, a linear combination of atomic orbital description of the
molecular orbitals is employed. It facilitates the incorporation of correction
factors which can be calculated from atomic many-body theory and account for
the repulsion and correlations. Their inclusion in the calculation gives gamma
spectrum linewidths that are in much better agreement with experiment.
Furthermore, it is shown that the effective distortion of the electron momentum
density, when it is observed through positron annihilation gamma spectra, can
be approximated by a relatively simple scaling factor.Comment: 26 pages, 12 figure
Evaluation of the application of ERTS-1 data to the regional land use planning process
The author has identified the following significant results. Employing simple and economical extraction methods, ERTS can provide valuable data to the planners at the state or regional level with a frequency never before possible. Interactive computer methods of working directly with ERTS digital information show much promise for providing land use information at a more specific level, since the data format production rate of ERTS justifies improved methods of analysis
Compact Nuclei in Galaxies at Moderate Redshift:II. Their Nature and Implications for the AGN Luminosity Function
This study explores the space density and properties of active galaxies to
z=0.8. We have investigated the frequency and nature of unresolved nuclei in
galaxies at moderate redshift as indicators of nuclear activity such as Active
Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged
galaxies with multi-component models using maximum likelihood estimate
techniques to determine the best model fit. We select those galaxies requiring
an unresolved point-source component in the galaxy nucleus, in addition to a
disk and/or bulge component, to adequately model the galaxy light. We have
searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies
containing compact nuclei. In our survey of 1033 galaxies, the fraction
containing an unresolved nuclear component greater than 5% of the total galaxy
light is 9+/-1% corrected for incompleteness. In this second of two papers in
this series, we discuss the nature of the compact nuclei and their hosts.
We present the upper limit luminosity function (LF) for low-luminosity AGN
(LLAGN) in two redshift bins to z=0.8. Mild number density evolution is
detected for nuclei at -18 -16
and this flatness, combined with the increase in number density, is
inconsistent with pure luminosity evolution. Based on the amount of density
evolution observed for these objects, we find that almost all present-day
spiral galaxies could have hosted a LLAGN at some point in their lives. We also
comment on the likely contribution of these compact nuclei to the soft X-ray
background.Comment: 50 pages, 14 figures, to appear in ApJ, April 199
Discovery of a Galaxy Cluster in the Foreground of the Wide-Separation Quasar Pair UM425
We report the discovery of a cluster of galaxies in the field of UM425, a
pair of quasars separated by 6.5arcsec. Based on this finding, we revisit the
long-standing question of whether this quasar pair is a binary quasar or a
wide-separation lens. Previous work has shown that both quasars are at z=1.465
and show broad absorption lines. No evidence for a lensing galaxy has been
found between the quasars, but there were two hints of a foreground cluster:
diffuse X-ray emission observed with Chandra, and an excess of faint galaxies
observed with the Hubble Space Telescope. Here we show, via VLT spectroscopy,
that there is a spike in the redshift histogram of galaxies at z=0.77. We
estimate the chance of finding a random velocity structure of such significance
to be about 5%, and thereby interpret the diffuse X-ray emission as originating
from z=0.77, rather than the quasar redshift. The mass of the cluster, as
estimated from either the velocity dispersion of the z=0.77 galaxies or the
X-ray luminosity of the diffuse emission, would be consistent with the
theoretical mass required for gravitational lensing. The positional offset
between the X-ray centroid and the expected location of the mass centroid is
about 40kpc, which is not too different from offsets observed in lower redshift
clusters. However, UM425 would be an unusual gravitational lens, by virtue of
the absence of a bright primary lensing galaxy. Unless the mass-to-light ratio
of the galaxy is at least 80 times larger than usual, the lensing hypothesis
requires that the galaxy group or cluster plays a uniquely important role in
producing the observed deflections.
Based on observations performed with the Very Large Telescope at the European
Southern Observatory, Paranal, Chile.Comment: 12 pages, accepted by ApJ 2005, May 1
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