909 research outputs found
Investigation into the variations of moisture content of two buildings constructed with light earth walls
This paper briefly describes the background to light earth buildings and details a series of moisture measurements undertaken upon the clay and straw, (light earth) constructed walls of two UK based buildings. The methodology of measurement that was based upon previous studies undertaken on walls made from straw bales is described. A novel âin-wallâ wet heating system used in one of the two buildings allows the investigation of the effects of direct wall heating upon the distribution of moisture in the walls. The influence of exterior and interior temperature and humidity are described as are the variations in moisture migration introduced by the in-wall heating system. It was concluded that both buildings have exterior wall moisture content readings that indicate little risk of degradation due to interior wall moisture levels (although the Studio walls do exhibit higher and if suffered over long time periods, dangerous moisture readings for part of the measurement period)
Compact Nuclei in Galaxies at Moderate Redshift: I. Imaging and Spectroscopy
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 3% of the total galaxy
light is 16+/-3% corrected for incompleteness and 9+/-1% for nuclei greater
than 5% of the galaxy light. Spectroscopic redshifts have been obtained for 35
of our AGN/starburst candidates and photometric redshifts are estimated to an
accuracy of sigma_z=0.1 for the remaining sample. In this paper, the first of
two in this series, we present the selected HST imaged galaxies having
unresolved nuclei and discuss the selection procedure. We also present the
ground-based spectroscopy for these galaxies as well as the photometric
redshifts estimated for those galaxies without spectra.Comment: 56 pages, 22 figures, to appear in ApJ Supplement Series, April 199
Compact Nuclei in Moderately Redshifted Galaxies
The Hubble Space Telescope WFPC2 is being used to obtain high-resolution
images in the V and I bands for several thousand distant galaxies as part of
the Medium Deep Survey (MDS). An important scientific aim of the MDS is to
identify possible AGN candidates from these images in order to measure the
faint end of the AGN luminosity function as well as to study the host galaxies
of AGNs and nuclear starburst systems. We are able to identify candidate
objects based on morphology. Candidates are selected by fitting bulge+disk
models and bulge+disk+point source nuclei models to HST imaged galaxies and
determining the best model fit to the galaxy light profile. We present results
from a sample of MDS galaxies with I less than 21.5 mag that have been searched
for AGN/starburst nuclei in this manner. We identify 84 candidates with
unresolved nuclei in a sample of 825 galaxies. For the expected range of galaxy
redshifts, all normal bulges are resolved. Most of the candidates are found in
galaxies displaying exponential disks with some containing an additional bulge
component. 5% of the hosts are dominated by an r^-1/4 bulge. The V-I color
distribution of the nuclei is consistent with a dominant population of
Seyfert-type nuclei combined with an additional population of starbursts. Our
results suggest that 10% +/- 1% of field galaxies at z less than 0.6 may
contain AGN/starburst nuclei that are 1 to 5 magnitudes fainter than the host
galaxies.Comment: 12 pages AASTeX manuscript, 3 separate Postscript figures, to be
published in ApJ Letter
The Morphologically Divided Redshift Distribution of Faint Galaxies
We have constructed a morphologically divided redshift distribution of faint
field galaxies using a statistically unbiased sample of 196 galaxies brighter
than I = 21.5 for which detailed morphological information (from the Hubble
Space Telescope) as well as ground-based spectroscopic redshifts are available.
Galaxies are classified into 3 rough morphological types according to their
visual appearance (E/S0s, Spirals, Sdm/dE/Irr/Pec's), and redshift
distributions are constructed for each type. The most striking feature is the
abundance of low to moderate redshift Sdm/dE/Irr/Pec's at I < 19.5. This
confirms that the faint end slope of the luminosity function (LF) is steep
(alpha < -1.4) for these objects. We also find that Sdm/dE/Irr/Pec's are fairly
abundant at moderate redshifts, and this can be explained by strong luminosity
evolution. However, the normalization factor (or the number density) of the LF
of Sdm/dE/Irr/Pec's is not much higher than that of the local LF of
Sdm/dE/Irr/Pec's. Furthermore, as we go to fainter magnitudes, the abundance of
moderate to high redshift Irr/Pec's increases considerably. This cannot be
explained by strong luminosity evolution of the dwarf galaxy populations alone:
these Irr/Pec's are probably the progenitors of present day ellipticals and
spiral galaxies which are undergoing rapid star formation or merging with their
neighbors. On the other hand, the redshift distributions of E/S0s and spirals
are fairly consistent those expected from passive luminosity evolution, and are
only in slight disagreement with the non-evolving model.Comment: 11 pages, 4 figures (published in ApJ
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
ASCA Observations of the Starburst-Driven Superwind Galaxy NGC 2146: Broad Band (0.6 - 9 keV) Spectral Properties
We report ASCA GIS and SIS observations of the nearby (D = 11.6 Mpc), nearly
edge-on, starburst galaxy NGC 2146. These X-ray spectral data complement ROSAT
PSPC and HRI imaging discussed by Armus et al., 1995. The broad band (0.6-9
keV) X-ray spectrum of NGC 2146 is best described by a two component model: the
soft X-ray emission with a Raymond-Smith thermal plasma model having a
temperature of kT keV; the hard X-ray emission with a thermal plasma
model having kT keV or a power-law model having a photon index of
. We do not find compelling evidence of substantial excess absorption
above the Galactic value. The soft (hard) thermal component provides about 30%
(70%) of the total luminosity in the 0.5 - 2.0 keV energy band, while in the
2-10 keV energy range only the hard component plays a major role. The spectral
results allow us to set tighter constraints on the starburst-driven superwind
model, which we show can satisfactorily account for the luminosity, mass, and
energy content represented by the soft X-ray spectral component. We estimate
that the mass outflow rate ( 9 M per year) is about an order of
magnitude greater than the predicted rate at which supernovae and stellar winds
return mass into the interstellar medium and, therefore, argue that the flow is
strongly "mass-loaded" with material in and around the starburst. The estimated
outflow velocity of the hot gas is close to the escape velocity from the
galaxy, so the fate of the gas is not clear. We suggest that the hard X-ray
spectral component is due to the combined emission of X-ray binaries and/or
young supernovae remnants associated with the starburst.Comment: 26 pages plus 4 figures, LaTex manuscript, Accepted for publication
in the Astrophysical Journa
Use of detailed kinetic mechanisms for the prediction of autoignitions
This paper describes how automatically generated detailed kinetic mechanisms
are obtained for the oxidation of alkanes and how these models could lead to a
better understanding of autoignition and cool flame risks at elevated
conditions. Examples of prediction of the occurrence of different autoignition
phenomena, such as cool flames or two-stage ignitions are presented depending
on the condition of pressure, temperature and mixture composition. Three
compounds are treated, a light alkane, propane, and two heavier ones, n-heptane
and n-decane
Investigation of Gravitational Lens Mass Models
We have previously reported the discovery of strong gravitational lensing by
faint elliptical galaxies using the WFPC2 on HST and here we investigate their
potential usefulness in putting constraints on lens mass models. We compare
various ellipsoidal surface mass distributions, including those with and
without a core radius, as well as models in which the mass distributions are
assumed to have the same axis ratio and orientation as the galaxy light. We
also study models which use a spherical mass distribution having various
profiles, both empirical and following those predicted by CDM simulations.
These models also include a gravitational shear term. The model parameters and
associated errors have been derived by 2-dimensional analysis of the observed
HST WFPC2 images. The maximum likelihood procedure iteratively converges
simultaneously on the model for the lensing elliptical galaxy and the lensed
image components. The motivation for this study was to distinguish between
these mass models with this technique. However, we find that, despite using the
full image data rather than just locations and integrated magnitudes, the
lenses are fit equally well with several of the mass models. Each of the mass
models generates a similar configuration but with a different magnification and
cross-sectional area within the caustic, and both of these latter quantities
govern the discovery probability of lensing in the survey. These differences
contribute to considerable cosmic scatter in any estimate of the cosmological
constant using gravitational lenses.Comment: 10 pages with 6 embedded figures, tentatively scheduled to be
published in the July 2001 issue of The Astronomical Journal. For additional
information see http://mds.phys.cmu.edu/lense
Warm season cloud-to-ground lightningâprecipitation relationships
ABSTRACT This study examines the relationship between cloud-to-ground (CG) lightning and surface precipitation using observations from six regions (each on the order of 10 000 km 2 ), April through October (1989-93), in the southcentral United States. The relationship is evaluated using two different methods. First, regression equations are fit to the data, initially for only the CG lightning flash density and precipitation, and then with additional atmospheric and lightning parameters. Second, days are categorized according to differences in the precipitationto-CG lightning ratio; the same additional parameters are then examined for differences occurring within each category. Results show that the relationship between CG lightning and surface precipitation is highly variable; r 2 coefficients range from 0.121 in Baton Rouge to 0.601 in Dallas. A measure of the positive CG lightning flash density is the best addition to the model, statistically significant in all regions. When days are categorized, the percentage of lightning that is positive shows the most significant differences between categories, ranging from Ϝ4% on days with a ''low'' precipitation-to-CG lightning ratio, to 12%-36% on days with a ''high'' ratio. Other lightning parameters give less significant results; however, three atmospheric parameters (CAPE, lifted index, and Showalter index) do show a significant trend suggesting that there is much less instability in the atmosphere on ''high'' ratio days than on ''low'' ratio days
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