3,057 research outputs found
Past and present deepwater contour-current bedforms at the base of the Sigsbee Escarpment, northern Gulf of Mexico
Using a high-resolution deep-towed seismic system, we have discovered a series
of contour-current bedforms at the base of the Sigsbee Escarpment in the Bryant Canyon
region of the northern Gulf of Mexico. We identify a continuum of bedforms that
include furrows, meandering furrows, flutes and fully eroded seafloor. These contourcurrent
bedforms are linked to current velocities ranging from 20 to upwards of 60 cm/s
based on nearby current meter measurements and similar flume generated bedforms
(Allen, 1969). We identify erosion and non-deposition of up to 25 meters of surface
sediment at the base of Sigsbee Escarpment.
Using 3-D and high-resolution seismic data, sediment samples, and submersible
observations from the Green Knoll area, we further define contour-current bedforms
along the Sigsbee Escarpment. The study area is divided into eleven zones based on
bedform morphology, distribution, and formation processes. We identify a contourcurrent
bedform continuum similar to that of the Bryant Canyon region, while the data
reveals additional features that result from the interaction between topography and
contour-currents. Three regional seismic marker horizons are identified, and we establish an age of ~19 kyr on the deepest horizon. The seismic horizons are correlated
with very subtle changes in sediment properties, which in turn define the maximum
depth of erosion for each of the individual bedforms.
Finally, we show for the first time that furrowed horizons can be acoustically
imaged in three dimensions below seafloor. Analysis of imagery of several horizons
obtained from 3-D seismic data from the Green Knoll region establishes the existence of
multiple paleo-furrow events. The contour current pattern preserved by the paleofurrows
is similar to the presently active seafloor furrows. And, based on the
morphology and development that we establish for the active seafloor furrows, we show
that paleo-furrows are likely formed by currents that are in the same range as those
measured today (20-60 cm/s), that erode into sediments with similar physical properties
to the fine-grained hemipelagic sediments of the present-day seafloor. We further
suggest the possibility that furrows are formed during inter-glacial highstands and buried
during glacial lowstands
Cosmological Acceleration Through Transition to Constant Scalar Curvature
As shown by Parker and Raval, quantum field theory in curved spacetime gives
a possible mechanism for explaining the observed recent acceleration of the
universe. This mechanism, which differs in its dynamics from quintessence
models, causes the universe to make a transition to an accelerating expansion
in which the scalar curvature, R, of spacetime remains constant. This
transition occurs despite the fact that we set the renormalized cosmological
constant to zero. We show that this model agrees very well with the current
observed type-Ia supernova (SNe-Ia) data. There are no free parameters in this
fit, as the relevant observables are determined independently by means of the
current cosmic microwave background radiation (CMBR) data. We also give the
predicted curves for number count tests and for the ratio, w(z), of the dark
energy pressure to its density, as well as for dw(z)/dz versus w(z). These
curves differ significantly from those obtained from a cosmological constant,
and will be tested by planned future observations.Comment: 31 pages, 7 figures; to appear in ApJ. Corrected numerical results;
described quantum basis of theory; 18 references added; 2 figures adde
Collaboration as Locus for Information Literacy Teacher Knowledge Development
Research on collaboration in information literacy curriculum has yielded insights into the opportunities and challenges surrounding efforts to establish sustainable teaching models. Few studies, however, have examined the ways in which these teaching partnerships enrich the knowledge base of instruction librarians and faculty. This paper examines the pedagogical knowledge development of two instructional librarians and one composition instructor in the collaborative teaching of information literacy skills in a composition course. The three instructors share ethnographic accounts recounting the iterative process of developing curriculum to meet the needs of their first-year students. The curricular innovations, including online modules, multiple instruction sessions, and student reflective journals, contributed to a richer knowledge base for the instructors as they managed the needs of their students. Through this collaborative process, they discovered gaps in their knowledge of learners and teaching methods
Antimicrobial resistance in community and nosocomial Escherichia coli urinary tract isolates, London 2005 – 2006
<p>Abstract</p> <p>Background</p> <p><it>Escherichia coli </it>is the commonest cause of community and nosocomial urinary tract infection (UTI). Antibiotic treatment is usually empirical relying on susceptibility data from local surveillance studies. We therefore set out to determine levels of resistance to 8 commonly used antimicrobial agents amongst all urinary isolates obtained over a 12 month period.</p> <p>Methods</p> <p>Antimicrobial susceptibility to ampicillin, amoxicillin/clavulanate, cefalexin, ciprofloxacin, gentamicin, nitrofurantoin, trimethoprim and cefpodoxime was determined for 11,865 <it>E. coli </it>urinary isolates obtained from community and hospitalised patients in East London.</p> <p>Results</p> <p>Nitrofurantoin was the most active agent (94% susceptible), followed by gentamicin and cefpodoxime. High rates of resistance to ampicillin (55%) and trimethoprim (40%), often in combination were observed in both sets of isolates. Although isolates exhibiting resistance to multiple drug classes were rare, resistance to cefpodoxime, indicative of Extended spectrum β-lactamase production, was observed in 5.7% of community and 21.6% of nosocomial isolates.</p> <p>Conclusion</p> <p>With the exception of nitrofurantoin, resistance to agents commonly used as empirical oral treatments for UTI was extremely high. Levels of resistance to trimethoprim and ampicillin render them unsuitable for empirical use. Continued surveillance and investigation of other oral agents for treatment of UTI in the community is required.</p
Past and present deepwater contour-current bedforms at the base of the Sigsbee Escarpment, northern Gulf of Mexico
Using a high-resolution deep-towed seismic system, we have discovered a series
of contour-current bedforms at the base of the Sigsbee Escarpment in the Bryant Canyon
region of the northern Gulf of Mexico. We identify a continuum of bedforms that
include furrows, meandering furrows, flutes and fully eroded seafloor. These contourcurrent
bedforms are linked to current velocities ranging from 20 to upwards of 60 cm/s
based on nearby current meter measurements and similar flume generated bedforms
(Allen, 1969). We identify erosion and non-deposition of up to 25 meters of surface
sediment at the base of Sigsbee Escarpment.
Using 3-D and high-resolution seismic data, sediment samples, and submersible
observations from the Green Knoll area, we further define contour-current bedforms
along the Sigsbee Escarpment. The study area is divided into eleven zones based on
bedform morphology, distribution, and formation processes. We identify a contourcurrent
bedform continuum similar to that of the Bryant Canyon region, while the data
reveals additional features that result from the interaction between topography and
contour-currents. Three regional seismic marker horizons are identified, and we establish an age of ~19 kyr on the deepest horizon. The seismic horizons are correlated
with very subtle changes in sediment properties, which in turn define the maximum
depth of erosion for each of the individual bedforms.
Finally, we show for the first time that furrowed horizons can be acoustically
imaged in three dimensions below seafloor. Analysis of imagery of several horizons
obtained from 3-D seismic data from the Green Knoll region establishes the existence of
multiple paleo-furrow events. The contour current pattern preserved by the paleofurrows
is similar to the presently active seafloor furrows. And, based on the
morphology and development that we establish for the active seafloor furrows, we show
that paleo-furrows are likely formed by currents that are in the same range as those
measured today (20-60 cm/s), that erode into sediments with similar physical properties
to the fine-grained hemipelagic sediments of the present-day seafloor. We further
suggest the possibility that furrows are formed during inter-glacial highstands and buried
during glacial lowstands
eleanor: An open-source tool for extracting light curves from the TESS Full-Frame Images
During its two year prime mission the Transiting Exoplanet Survey Satellite
(TESS) will perform a time-series photometric survey covering over 80% of the
sky. This survey comprises observations of 26 24 x 96 degree sectors that are
each monitored continuously for approximately 27 days. The main goal of TESS is
to find transiting planets around 200,000 pre-selected stars for which fixed
aperture photometry is recorded every two minutes. However, TESS is also
recording and delivering Full-Frame Images (FFIs) of each detector at a 30
minute cadence. We have created an open-source tool, eleanor, to produce light
curves for objects in the TESS FFIs. Here, we describe the methods used in
eleanor to produce light curves that are optimized for planet searches. The
tool performs background subtraction, aperture and PSF photometry,
decorrelation of instrument systematics, and cotrending using principal
component analysis. We recover known transiting exoplanets in the FFIs to
validate the pipeline and perform a limited search for new planet candidates in
Sector 1. Our tests indicate that eleanor produces light curves with
significantly less scatter than other tools that have been used in the
literature. Cadence-stacked images, and raw and detrended eleanor light curves
for each analyzed star will be hosted on MAST, with planet candidates on
ExoFOP-TESS as Community TESS Objects of Interest (CTOIs). This work confirms
the promise that the TESS FFIs will enable the detection of thousands of new
exoplanets and a broad range of time domain astrophysics.Comment: 21 pages, 13 figures, 2 tables, Accepted to PAS
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