1,439 research outputs found
Proposed Solid Waste System for Rural Areas of Brookings County, South Dakota
The State Department of Environmental Protection has stated that its goal is to have all solid waste generated in the State of South Dakota, stored, collected and disposed of in a manner which does not cause environmental degradation, potential health hazards, or nuisances to the citizens of South Dakota or its visitors(1). It is the intent to provide efficient economical solid waste management systems throughout the entire State. In addition to properly managed solid waste disposal sites, it is also desired that efficient, routine collection systems be provided in all communities wherever the population is sufficient to support such a collection system(1). The objectives of this study are: 1. To define the solid waste problem as it exists in Brookings County; 2. To study the solid waste problem for a rural area; 3. To estimate the quantity of solid waste involved in Brookings County, both urban and rural; 4. To propose a possible solution to the solid waste collection and disposal problem in a rural area, specifically Brookings County; 5. To estimate the cost of a rural solid waste collection system
Generators for the hyperelliptic Torelli group and the kernel of the Burau representation at t = -1
We prove that the hyperelliptic Torelli group is generated by Dehn twists about
separating curves that are preserved by the hyperelliptic involution. This verifies a
conjecture of Hain. The hyperelliptic Torelli group can be identified with the kernel
of the Burau representation evaluated at t = −1 and also the fundamental group of
the branch locus of the period mapping, and so we obtain analogous generating sets
for those. One application is that each component in Torelli space of the locus of
hyperelliptic curves becomes simply connected when curves of compact type are added
X-Ray Searches for Emission from the WHIM in the Galactic Halo and the Intergalactic Medium
At least 50% of the baryons in the local universe are undetected and
predicted to be in a hot dilute phase (1E5-1E7 K) in low and moderate
overdensity environments. We searched for the predicted diffuse faint emission
through shadowing observations whereby cool foreground gas absorbs more distant
diffuse emission. Observations were obtained with Chandra and XMM-Newton. Using
the cold gas in two galaxies, NGC 891 and NGC 5907, shadows were not detected
and a newer observation of NGC 891 fails to confirm a previously reported X-ray
shadow. Our upper limits lie above model predictions. For Local Group studies,
we used a cloud in the Magellanic Stream and a compact high velocity cloud to
search for a shadow. Instead of a shadow, the X-ray emission was brighter
towards the Magellanic Stream cloud and there is a less significant brightness
enhancement toward the other cloud also. The brightness enhancement toward the
Magellanic Stream cloud is probably due to an interaction with a hot ambient
medium that surrounds the Milky Way. We suggest that this interaction drives a
shock into the cloud, heating the gas to X-ray emitting temperatures.Comment: 10 ApJ pages with 10 figure
Diffuse neutral hydrogen in the HI Parkes All Sky Survey
Observations of neutral hydrogen can provide a wealth of information about
the distribution and kinematics of galaxies. To detect HI beyond the ionisation
edge of galaxy disks, column density sensitivities have to be achieved that
probe the regime of Lyman limit systems. Typically HI observations are limited
to a brightness sensitivity of NHI~10^19 cm-2 but this has to be improved by at
least an order of magnitude. In this paper, reprocessed data is presented that
was originally observed for the HI Parkes All Sky Survey (HIPASS). HIPASS
provides complete coverage of the region that has been observed for the
Westerbork Virgo Filament HI Survey (WVFS), presented in accompanying papers,
and thus is an excellent product for data comparison. The region of interest
extends from 8 to 17 hours in right ascension and from -1 to 10 degrees in
declination. Although the original HIPASS product already has good flux
sensitivity, the sensitivity and noise characteristics can be significantly
improved with a different processing method. The newly processed data has an
1sigma RMS flux sensitivity of ~10 mJy beam-1 over 26 km s-1, corresponding to
a column density sensitivity of ~3\cdot10^17 cm-2. While the RMS sensitivity is
improved by only a modest 20%, the more substantial benefit is in the reduction
of spectral artefacts near bright sources by more than an order of magnitude.
In the reprocessed region we confirm all previously catalogued HIPASS sources
and have identified 29 additional sources of which 14 are completely new HI
detections. Extended emission or companions were sought in the nearby
environment of each discrete detection. With the improved sensitivity after
reprocessing and its large sky coverage, the HIPASS data is a valuable resource
for detection of faint HI emission.(Abridged)Comment: 22 pages plus appendix, 6 figures, appendix will only appear in
online format. Accepted for publication in A&
The Metal-Enriched Outer Disk of NGC 2915
We present optical emission-line spectra for outlying HII regions in the
extended neutral gas disk surrounding the blue compact dwarf galaxy NGC 2915.
Using a combination of strong-line R23 and direct oxygen abundance
measurements, we report a flat, possibly increasing, metallicity gradient out
to 1.2 times the Holmberg radius. We find the outer-disk of NGC 2915 to be
enriched to a metallicity of 0.4 Z_solar. An analysis of the metal yields shows
that the outer disk of NGC 2915 is overabundant for its gas fraction, while the
central star-foming core is similarly under-abundant for its gas fraction. Star
formation rates derived from very deep ~14 ks GALEX FUV exposures indicate that
the low-level of star formation observed at large radii is not sufficient to
have produced the measured oxygen abundances at these galactocentric distances.
We consider 3 plausible mechanisms that may explain the metal-enriched outer
gaseous disk of NGC 2915: radial redistribution of centrally generated metals,
strong galactic winds with subsequent fallback, and galaxy accretion. Our
results have implications for the physical origin of the mass-metallicity
relation for gas-rich dwarf galaxies.Comment: 11 pages, 4 figures, accepted to ApJ April 8th, 201
A Precision Angle Sensor using an Optical Lever inside a Sagnac Interferometer
We built an ultra low noise angle sensor by combining a folded optical lever
and a Sagnac interferometer. The instrument has a measured noise floor of 1.3
prad / Hz^(1/2) at 2.4 kHz. We achieve this record angle sensitivity using a
proof-of-concept apparatus with a conservative N=11 bounces in the optical
lever. This technique could be extended to reach sub-picoradian / Hz^(1/2)
sensitivities with an optimized design.Comment: 3 pages, 4 figure
Mapping Hydrogen in the Galaxy, Galactic Halo, and Local Group with ALFA: The GALFA-HI Survey Starting with TOGS
Radio observations of gas in the Milky Way and Local Group are vital for
understanding how galaxies function as systems. The unique sensitivity of
Arecibo's 305m dish, coupled with the 7-beam Arecibo L-Band Feed Array (ALFA),
provides an unparalleled tool for investigating the full range of interstellar
phenomena traced by the HI 21cm line. The GALFA (Galactic ALFA) HI Survey is
mapping the entire Arecibo sky over a velocity range of -700 to +700 km/s with
0.2 km/s velocity channels and an angular resolution of 3.4 arcminutes. We
present highlights from the TOGS (Turn on GALFA Survey) portion of GALFA-HI,
which is covering thousands of square degrees in commensal drift scan
observations with the ALFALFA and AGES extragalactic ALFA surveys. This work is
supported in part by the National Astronomy and Ionosphere Center, operated by
Cornell University under cooperative agreement with the National Science
Foundation.Comment: 3 pages, including 2 figure pages; figure image quality significantly
reduced; for full resolution version, please see
http://www.naic.edu/~gibson/cv/ao08_writeup.pdf ; to be published in AIP
conference proceedings for ``The Evolution of Galaxies through the Neutral
Hydrogen Window'', eds. R. Minchin & E. Momjia
High-velocity clouds as streams of ionized and neutral gas in the halo of the Milky Way
High-velocity clouds (HVC), fast-moving ionized and neutral gas clouds found
at high galactic latitudes, may play an important role in the evolution of the
Milky Way. The extent of this role depends sensitively on their distances and
total sky covering factor. We search for HVC absorption in HST high resolution
ultraviolet spectra of a carefully selected sample of 133 AGN using a range of
atomic species in different ionization stages. This allows us to identify
neutral, weakly ionized, or highly ionized HVCs over several decades in HI
column densities. The sky covering factor of UV-selected HVCs with |v_LSR|>90
km/s is 68%+/-4% for the entire Galactic sky. We show that our survey is
essentially complete, i.e., an undetected population of HVCs with extremely low
N(H) (HI+HII) is unlikely to be important for the HVC mass budget. We confirm
that the predominantly ionized HVCs contain at least as much mass as the
traditional HI HVCs and show that large HI HVC complexes have generally ionized
envelopes extending far from the HI contours. There are also large regions of
the Galactic sky that are covered with ionized high-velocity gas with little HI
emission nearby. We show that the covering factors of HVCs with 90<|v_LSR|<170
km/s drawn from the AGN and stellar samples are similar. This confirms that
these HVCs are within 5-15 kpc of the sun. The covering factor of these HVCs
drops with decreasing vertical height, which is consistent with HVCs being
decelerated or disrupted as they fall to the Milky Way disk. The HVCs with
|v_LSR|>170 km/s are largely associated with the Magellanic Stream at b<0 and
its leading arm at b>0 as well as other large known HI complexes. Therefore
there is no evidence in the Local Group that any galaxy shows a population of
HVCs extending much farther away than 50 kpc from its host, except possibly for
those tracing remnants of galaxy interaction.Comment: Submitted to MNRAS (19 pages, 11 figures). Comments are welcom
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