4,739 research outputs found
CdS solar cell development Final report
Plastic substrate, cadmium sulfide thin film solor cel
Near-infrared adaptive optics imaging of high redshift quasars
The properties of high redshift quasar host galaxies are studied, in order to
investigate the connection between galaxy evolution, nuclear activity, and the
formation of supermassive black holes. We combine new near-infrared
observations of three high redshift quasars (2 < z < 3), obtained at the ESO
Very Large Telescope equipped with adaptive optics, with selected data from the
literature. For the three new objects we were able to detect and characterize
the properties of the host galaxy, found to be consistent with those of massive
elliptical galaxies of M(R) ~ -24.7 for the one radio loud quasar, and M(R) ~
-23.8 for the two radio quiet quasars. When combined with existing data at
lower redshift, these new observations depict a scenario where the host
galaxies of radio loud quasars are seen to follow the expected trend of
luminous (~5L*) elliptical galaxies undergoing passive evolution. This trend is
remarkably similar to that followed by radio galaxies at z > 1.5. Radio quiet
quasars hosts also follow a similar trend but at a lower average luminosity
(~0.5 mag dimmer). The data indicate that quasar host galaxies are already
fully formed at epochs as early as ~2 Gyr after the Big Bang and then passively
fade in luminosity to the present epoch.Comment: Accepted for publication in ApJ, 24 pages, 10 figure
Aerosol particles in the Mexican East Pacific <BR> Part I: processing and vertical redistribution by clouds
International audienceAirborne measurements of aerosol particle size distributions were made in the Mexican Intertropical Convergence Zone. The volume concentrations of submicron and super micron particles at cloud base were compared with those in near-cloud regions over a range of altitudes. Of 78 near-cloud regions analyzed, 68% and 45% had enhanced volumes of submicron particles and supermicron particles, respectively. In addition, 35% of these regions had supermicron particles removed, presumably by precipitation. In 61% of the cases the enhancement in volume occurred over the size range from 0.1 to 50 ?m whereas only submicron volumes were enhanced in 35% of the cases. In regions near clouds that were formed in air of maritime origin the frequency of volume enhancement decreased with increasing altitude and was twice as frequent on the dissipating side of clouds compared to the growing side. No such differences were found in the regions near clouds formed in air originating from the land. The frequency and average magnitude of volume enhancement are in qualitative and quantitative agreement with previous observational and theoretical studies that relate enhancements in particle mass to the uptake by cloud droplets of SO2 accompanied by additional growth by droplet coalescence
On Dwarf Galaxies as the Source of Intracluster Gas
Recent observational evidence for steep dwarf galaxy luminosity functions in
several rich clusters has led to speculation that their precursors may be the
source of the majority of gas and metals inferred from intracluster medium
(ICM) x-ray observations. Their deposition into the ICM is presumed to occur
through early supernovae-driven winds, the resultant systems reflecting the
photometric and chemical properties of the low luminosity dwarf spheroidals and
ellipticals we observe locally. We consider this scenario, utilising a
self-consistent model for spheroidal photo-chemical evolution and gas ejection
via galactic superwinds. Insisting that post-wind dwarfs obey the observed
colour-luminosity-metallicity relations, we conclude that the bulk of the ICM
gas and metals does not originate within their precursors.Comment: 43 pages, 8 figures, LaTeX, also available at
http://msowww.anu.edu.au/~gibson/publications.html, to appear in ApJ, Vol
473, 1997, in pres
A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree Survey
We have measured the surface density of galaxies toward 14 X-ray-selected
cluster candidates at redshifts greater than z=0.46, and we show that they are
associated with rich galaxy concentrations. We find that the clusters range
between Abell richness classes 0-2, and have a most probable richness class of
one. We compare the richness distribution of our distant clusters to those for
three samples of nearby clusters with similar X-ray luminosities. We find that
the nearby and distant samples have similar richness distributions, which shows
that clusters have apparently not evolved substantially in richness since
redshift z =0.5. We compare the distribution of distant X-ray clusters in the
L_x--richness plane to the distribution of optically-selected clusters from the
Palomar Distant Cluster Survey. The optically-selected clusters appear overly
rich for their X-ray luminosities when compared to X-ray-selected clusters.
Apparently, X-ray and optical surveys do not necessarily sample identical mass
concentrations at large redshifts. This may indicate the existence of a
population of optically rich clusters with anomalously low X-ray emission. More
likely, however, it reflects the tendency for optical surveys to select
unvirialized mass concentrations, as might be expected when peering along
large-scale filaments.Comment: The abstract has been abridged. Accepted for publication in the
Astrophysical Journa
A Forward-Design Approach to Increase the Production of Poly-3-Hydroxybutyrate in Genetically Engineered Escherichia coli
Biopolymers, such as poly-3-hydroxybutyrate (P(3HB)) are produced as a carbon store in an array of organisms and exhibit characteristics which are similar to oil-derived plastics, yet have the added advantages of biodegradability and biocompatibility. Despite these advantages, P(3HB) production is currently more expensive than the production of oil-derived plastics, and therefore, more efficient P(3HB) production processes would be desirable. In this study, we describe the model-guided design and experimental validation of several engineered P(3HB) producing operons. In particular, we describe the characterization of a hybrid phaCAB operon that consists of a dual promoter (native and J23104) and RBS (native and B0034) design. P(3HB) production at 24 h was around six-fold higher in hybrid phaCAB engineered Escherichia coli in comparison to E. coli engineered with the native phaCAB operon from Ralstonia eutropha H16. Additionally, we describe the utilization of non-recyclable waste as a low-cost carbon source for the production of P(3HB)
Virgo cluster early-type dwarf galaxies with the Sloan Digital Sky Survey. IV. The color-magnitude relation
We present an analysis of the optical colors of 413 Virgo cluster early-type
dwarf galaxies (dEs), based on Sloan Digital Sky Survey imaging data. Our study
comprises (1) a comparison of the color-magnitude relation (CMR) of the
different dE subclasses that we identified in Paper III of this series, (2) a
comparison of the shape of the CMR in low and high-density regions, (3) an
analysis of the scatter of the CMR, and (4) an interpretation of the observed
colors with ages and metallicities from population synthesis models. We find
that the CMRs of nucleated (dE(N)) and non-nucleated dEs (dE(nN)) are
significantly different from each other, with similar colors at fainter
magnitudes (r > 17 mag), but increasingly redder colors of the dE(N)s at
brighter magnitudes. We interpret this with older ages and/or higher
metallicities of the brighter dE(N)s. The dEs with disk features have similar
colors as the dE(N)s and seem to be only slightly younger and/or less
metal-rich on average. Furthermore, we find a small but significant dependence
of the CMR on local projected galaxy number density, consistently seen in all
of u-r, g-r, and g-i, and weakly i-z. We deduce that a significant intrinsic
color scatter of the CMR is present, even when allowing for a distance spread
of our galaxies. No increase of the CMR scatter at fainter magnitudes is
observed down to r = 17 mag (Mr = -14 mag). The color residuals, i.e., the
offsets of the data points from the linear fit to the CMR, are clearly
correlated with each other in all colors for the dE(N)s and for the full dE
sample. We conclude that there must be at least two different formation
channels for early-type dwarfs in order to explain the heterogeneity of this
class of galaxy. (Abridged)Comment: 17 pages + 12 figures. Accepted for publication in A
Hydrodynamical description of a hadron-quark first-order phase transition
Solutions of hydrodynamical equations are presented for the equation of state
of the Var der Waals type allowing for the first order phase transition.
Attention is focused on description of the hadron-quark phase transition in
heavy ion collisions. It is shown that fluctuations dissolve and grow as if the
fluid is effectively very viscous. Even in spinodal region germs are growing
slowly due to viscosity and critical slowing down. This prevents enhancement of
fluctuations in the near-critical region, which is frequently considered as a
signal of the critical point in heavy ion collisions.Comment: 4 pages, 4 figure
Hubble Space Telescope Observations of the Oldest Star Clusters in the LMC
We present V, V-I color-magnitude diagrams (CMDs) for three old star clusters
in the Large Magellanic Cloud (LMC): NGC 1466, NGC 2257 and Hodge 11. Our data
extend about 3 magnitudes below the main-sequence turnoff, allowing us to
determine accurate relative ages and the blue straggler frequencies. Based on a
differential comparison of the CMDs, any age difference between the three LMC
clusters is less than 1.5 Gyr. Comparing their CMDs to those of M 92 and M 3,
the LMC clusters, unless their published metallicities are significantly in
error, are the same age as the old Galactic globulars. The similar ages to
Galactic globulars are shown to be consistent with hierarchial clustering
models of galaxy formation. The blue straggler frequencies are also similar to
those of Galactic globular clusters. We derive a true distance modulus to the
LMC of (m-M)=18.46 +/- 0.09 (assuming (m-M)=14.61 for M 92) using these three
LMC clusters.Comment: 22 pages; to be published in Ap
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