4,349 research outputs found
The Service Sojourn: Conceptualizing the College Student Volunteer Experience
Despite the increasing popularity of volunteerism in student activities and service-learning courses on college campuses, little is known about the experience of volunteers. This study examines the experience of 16 students from the University of Utah who t participated in community service. The qualitative investigation is based on 54 interviews regarding student descriptions of their experience. What common events occurred? How did they make sense of their experience? What, really, did they learn? Ethnographic interviews and a naturalistic approach were used to identify patterns and analyze the data. Grounded in reoccurring themes such as leaving familiar surroundings. the shock of a new environment, and efforts to adjust, the concept of a sojourn was used to interpret students\u27 experience. This interpretive metaphor not only provided a framework for conceptualizing common aspects of volunteer experience, but it also highlighted the cross-cultural nature of these encounters. Students who ventured on these sojourns in service reported positive outcomes such as a better understanding of others, a matured sense of identity, a more complex view of the world, and an enhanced sense of personal efficacy
Providing the Third Dimension: High-resolution Multibeam Sonar as a Tool for Archaeological Investigations - An Example from the D-day Beaches of Normandy
In general, marine archaeological investigations begin in the archives, using historic maps, coast surveys, and other materials, to define submerged areas suspected to contain potentially significant historical sites. Following this research phase, a typical archaeological survey uses sidescan sonar and marine magnetometers as initial search tools. Targets are then examined through direct observation by divers, video, or photographs. Magnetometers can demonstrate the presence, absence, and relative susceptibility of ferrous objects but provide little indication of the nature of the target. Sidescan sonar can present a clear image of the overall nature of a target and its surrounding environment, but the sidescan image is often distorted and contains little information about the true 3-D shape of the object. Optical techniques allow precise identification of objects but suffer from very limited range, even in the best of situations. Modern high-resolution multibeam sonar offers an opportunity to cover a relatively large area from a safe distance above the target, while resolving the true three-dimensional (3-D) shape of the object with centimeter-level resolution. A clear demonstration of the applicability of highresolution multibeam sonar to wreck and artifact investigations occurred this summer when the Naval Historical Center (NHC), the Center for Coastal and Ocean Mapping (CCOM) at the University of New Hampshire, and Reson Inc., collaborated to explore the state of preservation and impact on the surrounding environment of a series of wrecks located off the coast of Normandy, France, adjacent to the American landing sectors The survey augmented previously collected magnetometer and high-resolution sidescan sonar data using a Reson 8125 high-resolution focused multibeam sonar with 240, 0.5° (at nadir) beams distributed over a 120° swath. The team investigated 21 areas in water depths ranging from about three -to 30 meters (m); some areas contained individual targets such as landing craft, barges, a destroyer, troop carrier, etc., while others contained multiple smaller targets such as tanks and trucks. Of particular interest were the well-preserved caissons and blockships of the artificial Mulberry Harbor deployed off Omaha Beach. The near-field beam-forming capability of the Reson 8125 combined with 3-D visualization techniques provided an unprecedented level of detail including the ability to recognize individual components of the wrecks (ramps, gun turrets, hatches, etc.), the state of preservation of the wrecks, and the impact of the wrecks on the surrounding seafloor
SarS, a SarA Homolog Repressible by agr, Is an Activator of Protein A Synthesis in Staphylococcus aureus
The expression of protein A (spa) is repressed by global regulatory loci sarA and agr. Although SarA may directly bind to the spa promoter to downregulate spa expression, the mechanism by which agr represses spa expression is not clearly understood. In searching for SarA homologs in the partially released genome, we found a SarA homolog, encoding a 250-amino-acid protein designated SarS, upstream of the spa gene. The expression of sarS was almost undetectable in parental strain RN6390 but was highly expressed in agr and sarA mutants, strains normally expressing high level of protein A. Interestingly, protein A expression was decreased in a sarS mutant as detected in an immunoblot but returned to near-parental levels in a complemented sarS mutant. Transcriptional fusion studies with a 158- and a 491-bp spa promoter fragment linked to the xylE reporter gene disclosed that the transcription of the spa promoter was also downregulated in the sarS mutant compared with the parental strain. Interestingly, the enhancement in spa expression in an agr mutant returned to a near-parental level in the agr sarS double mutant but not in the sarA sarS double mutant. Correlating with this divergent finding is the observation that enhanced sarS expression in an agr mutant was repressed by the sarA locus supplied in trans but not in a sarA mutant expressing RNAIII from a plasmid. Gel shift studies also revealed the specific binding of SarS to the 158-bp spa promoter. Taken together, these data indicated that the agr locus probably mediates spa repression by suppressing the transcription of sarS, an activator of spa expression. However, the pathway by which the sarA locus downregulates spa expression is sarS independent
SN~1991T: Reflections of Past Glory
We have obtained photometry and spectra of SN~1991T which extend more than
1000 days past maximum light, by far the longest a SN~Ia has been followed.
Although SN~1991T exhibited nearly normal photometric behavior in the first 400
days following maximum, by 600 days its decline had slowed, and by 950~days the
supernova brightness was consistent with a constant apparent magnitude of
. Spectra near maximum showed minor variations on the SN~Ia theme
which grew less conspicuous during the exponential decline. At 270 days the
nebular spectrum was composed of Fe and Co lines common to SNe~Ia. However, by
750 days past maximum light, these lines had shifted in wavelength, and were
superimposed on a strong blue continuum. The luminosity of SN~1991T at 950 days
is more than ~ergs~s with a rate of
decline of less than mags/100~days. We show that this emission is likely
to be light that was emitted by SN~1991T near maximum light which has reflected
from foreground dust, much like the light echos observed around SN~1987A.Comment: 15 pages (includes figures and tables) uuencoded compressed
postscript, CfA Preprint - To Appear in ApJ
Automated Reasoning for Multi-step Feature Model Configuration Problems
The increasing complexity and cost of software-intensive
systems has led developers to seek ways of increasing software
reusability. One software reuse approach is to develop
a Software Product-line (SPL), which is a reconfigurable
software architecture that can be reused across projects.
Creating configurations of the SPL that meets arbitrary requirements
is hard.
Existing research has focused on techniques that produce
a configuration of the SPL in a single step. This paper
provides three contributions to the study of multi-step configuration
for SPLs. First, we present a formal model of
multi-step SPL configuration and map this model to constraint
satisfaction problems (CSPs). Second, we show how
solutions to these CSP configuration problem CSPs can be
derived automatically with a constraint solver. Third, we
present empirical results demonstrating that our CSP-based
technique can solve multi-step configuration problems involving
hundreds of features in seconds.Comisión Interministerial de Ciencia y Tecnología TIN2006-00472Junta de Andalucía TIC-253
The Mount Stromlo Abell Cluster Supernova Search
We have initiated a three-year project to find supernovae (SNe) in a
well-defined sample of high-density southern Abell clusters with redshifts
. These observations will provide a volume-limited sample of SNe Ia
to more than a magnitude below their peak brightness, and will enable us to:
(1) measure the luminosity function of SNe, (2) further explore the correlation
of light curve shape with the absolute luminosity of SNe Ia to better
understand SNe Ia as distance indicators, (3) measure SN rates, (4) measure the
bulk motion of the Local Group using SNe Ia, and (5) directly compare SN Ia
distances to brightest cluster galaxy distances. We use the MaCHO wide-field
2-color imager on the 1.3m telescope at Mount Stromlo to routinely monitor
clusters per week. We describe our technique for target selection and
scheduling search observations, and for finding and identifying SN candidates.
We also describe the results from the first year of our program, including the
detection of 19 SNe, several RR-Lyrae variables, and hundreds of asteroids.Comment: 20 pages, 10 figures, 3 tables. Accepted for publication in AJ, Jan.
1998 issu
SN1997cy/GRB970514 - A New Piece in the GRB Puzzle?
We present observations of SN1997cy, a supernova discovered as part of the
Mount Stromlo Abell Cluster SN Search, which does not easily fit into the
traditional classification scheme for supernovae. This object's extraordinary
optical properties and coincidence with GRB970514, a short duration gamma ray
burst, suggest a second case, after SN1998bw/GRB980425, for a SN-GRB
association. SN1997cy is among the most luminous SNe yet discovered and has a
peculiar spectrum. We present evidence that SN1997cy ejected approximately 2
solar masses of 56Ni, supported by its late-time light curve, and FeII/[FeIII]
lines in its spectrum, although it is possible that both these observations can
be explained via circumstellar interaction. While SN1998bw and SN1997cy appear
to be very different objects with respect to both their gamma ray and optical
properties, SN1997cy and the optical transient associated with GRB970508 have
roughly similar late-time optical behavior. This similarity may indicate that
the late-time optical output of these two intrinsically bright transient events
have a common physical process. Although the connection between GRB970514 and
SN1997cy is suggestive, it is not conclusive. However, if this association is
real, followup of short duration GRBs detected with BATSE or HETE2 should
reveal objects similar to SN1997cy.Comment: 26 pages including 6 postscript figures and 3 tables. Submitted to
ApJ. Re-calibrated photometry - objects are about 0.3mags brighter than in
original versio
Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization
Within one billion years of the Big Bang, intergalactic hydrogen was ionized
by sources emitting ultraviolet and higher energy photons. This was the final
phenomenon to globally affect all the baryons (visible matter) in the Universe.
It is referred to as cosmic reionization and is an integral component of
cosmology. It is broadly expected that intrinsically faint galaxies were the
primary ionizing sources due to their abundance in this epoch. However, at the
highest redshifts (; lookback time 13.1 Gyr), all galaxies with
spectroscopic confirmations to date are intrinsically bright and, therefore,
not necessarily representative of the general population. Here, we report the
unequivocal spectroscopic detection of a low luminosity galaxy at . We
detected the Lyman- emission line at {\AA} in two separate
observations with MOSFIRE on the Keck I Telescope and independently with the
Hubble Space Telescope's slit-less grism spectrograph, implying a source
redshift of . The galaxy is gravitationally magnified by
the massive galaxy cluster MACS J1423.8+2404 (), with an estimated
intrinsic luminosity of mag and a stellar mass of
solar masses. Both are an order of
magnitude lower than the four other Lyman- emitters currently known at
, making it probably the most distant representative source of
reionization found to date
Generating high quality libraries for DIA MS with empirically corrected peptide predictions.
Data-independent acquisition approaches typically rely on experiment-specific spectrum libraries, requiring offline fractionation and tens to hundreds of injections. We demonstrate a library generation workflow that leverages fragmentation and retention time prediction to build libraries containing every peptide in a proteome, and then refines those libraries with empirical data. Our method specifically enables rapid, experiment-specific library generation for non-model organisms, which we demonstrate using the malaria parasite Plasmodium falciparum, and non-canonical databases, which we show by detecting missense variants in HeLa
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