534 research outputs found
Advanced electro-optical imaging techniques
The papers presented at the symposium are given which deal with the present state of sensors, as may be applicable to the Large Space Telescope (LST) program. Several aspects of sensors are covered including a discussion of the properties of photocathodes and the operational imaging camera tubes
Luminosity calibration of low redshift quasars
European (SERC) were combined with U.S. shifts on the IUE in order to obtain the long integration times required to record spectra of faint quasars. LWR spectra of the nearby giant radio galaxy Centarus A(NGC 5548) was attempted in an effort to determine the chemical composition and stellar populations in this unusual galaxy. The IUE results from the low redshift quasar study, combined with the data from an extensive ground based survey, are described
Spectrophotometry of 2 complete samples of flat radio spectrum quasars
Spectrophotometry of two complete samples of flat-spectrum radio quasars show that for these objects there is a strong correlation between the equivalent width of the CIV wavelength 1550 emission line and the luminosity of the underlying continuum. Assuming Friedmann cosmologies, the scatter in this correlation is a minimum for q (sub o) is approximately 1. Alternatively, luminosity evolution can be invoked to give compact distributions for q (sub o) is approximately 0 models. A sample of Seyfert galaxies observed with IUE shows that despite some dispersion the average equivalent width of CIV wavelength 1550 in Seyfert galaxies is independent of the underlying continuum luminosity. New redshifts for 4 quasars are given
An assay for argininosuccinate synthetase in Neurospora
An assay for argininosuccinate synthetase in Neurospor
Evaluation of Hand-Dug Wells in Rural Haiti
Water resources, especially safe, potable water, are limited for many Haitians. In areas where shallow groundwater is available, many household water needs such as laundry, bathing, and cooking are supplied by hand–dug wells. In order to better understand the water quality and prevalence of these household wells, 35 hand–dug wells were surveyed and sampled near the Hôpital Albert Schweitzer in Deschapelles, Haiti. Water samples were collected and tested for fecal coliform and Escherichia coli using the IDEXX Colilert–18 method. Of the samples collected, 89 percent were determined unsafe to use as a drinking water source based on the World Health Organization standard of 1.0 colony–forming unit (cfu) E. coli per 100 mL. Sixty–six percent of the wells exceeded recreational/body contact standards for the state of Michigan (130 cfu/100 mL). Some of these wells were deemed suitable for conversion to a new well type called in situ filtration (ISF) wells. In situ filtration wells are installed with an internal sand filter pack, PVC casing, pump, and cap which seals the well from surface contamination and provides additional water treatment as water is pumped. Previous ISF installations have reduced E. coli to safe drinking water levels within 90 day
Do Quasars Lens Quasars?
If the unexpectedly high frequency of quasar pairs with very different
component redshifts is due to the lensing of a population of background quasars
by the foreground quasar, typical lens masses must be \sim10^{12}M_{\sun} and
the sum of all such quasar lenses would have to contain times the
closure density of the Universe. It then seems plausible that a very high
fraction of all \sim10^{12} M_{\sun} gravitational lenses with redshifts
contain quasars. Here I propose that these systems have evolved to
form the present population of massive galaxies with M and M
>5\times10^{11} M_{\sun}.Comment: 6 pages, aas style, ams symbols, ApJL (accepted
Geomorphic History of the Grand River and Grand River Valley: Natural and Anthropomorphic Hydraulic Controls
Preliminary investigation into the feasibility and benefits of removing 5 low head dams located on the Grand River, in the city of Grand Rapids, Michigan, is currently underway. The anthropomorphic hydraulic controls (dams), constructed in the late 1800’s, were built at the location of several bedrock exposures which served as natural hydraulic controls. Prior to dam construction, an abrupt change in river gradient at these exposures resulted in the rapids for which Grand Rapids is named. Evaluation of several alternatives for restoring more natural flow and sediment dynamics in the Grand Rapids reach is part of the removal effort.
This study provides a detailed explanation of the geomorphic setting and history of the entire Grand River, including new mapping and sediment data for five natural hydraulic controls that were identified during preliminary investigation of the region. These controls were confirmed through bathymetric mapping of a ~13 kilometer reach upstream of Grand Rapids between Ada and Lowell, Michigan. A 135 meter long and roughly 30 meter wide exposure of boulder-rich fluvial sediment was identified 5 kilometers upstream of Ada, Michigan. The exposure trends generally N-S and contains fine sand to large boulders. The surface of the exposure possesses a D50 of 87.6 mm and a D10 and D90 of and 12.2 mm and 1,302 mm, respectively. The subsurface of this deposit has a D50 of 14.8 mm and a D10 and D90 of 7.3 mm and 95.5 mm, respectively. The top of the deposit is not flat. Surveying indicates the elevation of the top of the deposit varies by up to a meter. This exposure provides unique substrate and habitat uncommon in the Grand River, which is primarily a sand and silt dominated river. Further mapping and sampling of this exposure may provide data which will allow this reach to be used as an analogue for restoration efforts in Grand Rapids.
The Grand River Valley (GRV), through which the lower Grand River flows, is significantly larger than the modern floodplain. Previous research has suggested that the GRV was formed, since the last glacial maximum (LGM), by glacial outwash travelling from the Huron Basin to Glacial Lake Chicago (in the Lake Michigan Basin). Mapping and analysis of approximately 40,000 water wells adjacent to the Grand River Valley revealed: 1) a bedrock channel, presumably occupied by the ancestral Grand River; 2) evidence for a Grand River outlet north of the modern location which predates the LGM; and 3) a N-S trending area of thick alluvium and boulder occurrence which may represent valley fill of the pre-LGM bedrock valley
The metal absorption systems of the Hubble Deep Field South QSO
The Hubble Deep Field South (HDFS) has been recently selected and the
observations are planned for October 1998. We present a high resolution (FWHM
\kms) spectrum of the quasar J2233--606 () which
is located 5.1 arcmin East of the HDFS. The spectrum obtained with the New
Technology Telescope redward of the Lyman-- emission line covers the
spectral range 4386--8270 \AA. This range corresponds to redshift intervals for
CIV and MgII intervening systems of and
respectively. The data reveal the presence of two complex intervening CIV
systems at redshift and and two complex associated
() systems. Other two CIV systems at and
, suggested by the presence of strong Lyman-- lines in low
resolution ground based and Hubble Space Telescope (HST) STIS observations
(Sealey et al. 1998) have been identified. The system at is also
responsible for the Lyman limit absorption seen in the HST/STIS spectrum. The
main goal of the present work is to provide astronomers interested in the
Hubble Deep Field South program with information related to absorbing
structures at high redshift, which are distributed along the nearby QSO line of
sight. For this purpose, the reduced spectrum, obtained from three hours of
integration time, has been released to the astronomical community.Comment: revisited version accepted for publication by Astronomical Journal;
minor changes; typographical errors corrected; results and discussion
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