1,669 research outputs found
The mass content of the Sculptor dwarf spheroidal galaxy
We present a new determination of the mass content of the Sculptor dwarf
spheroidal galaxy, based on a novel approach which takes into account the two
distinct stellar populations present in this galaxy. This method helps to
partially break the well-known mass-anisotropy degeneracy present in the
modelling of pressure-supported stellar systems.Comment: 6 pages, 3 figures. To appear in the proceedings of IAU Symposium 254
"The Galaxy disk in a cosmological context", Copenhagen, June 200
Foodborne urinary tract infections: A new paradigm for antimicrobial-resistant foodborne illness
Urinary tract infections (UTIs) are among the most common bacterial infections worldwide. Disproportionately affecting women, UTIs exact a substantial public burden each year in terms of direct medical expenses, decreased quality of life, and lost productivity. Increasing antimicrobial resistance among strains of extraintestinal pathogenic Escherichia colichallenges successful treatment of UTIs. Community-acquired UTIs were long considered sporadic infections, typically caused by the patientsâ native gastrointestinal microbiota; however, the recent recognition of UTI outbreaks with probable foodborne origins has shifted our understanding of UTI epidemiology. Along with this paradigm shift come new opportunities to disrupt the infection process and possibly quell increasing resistance, including the elimination of non-therapeutic antimicrobial use in food-animal production
Microbial controls on net production of nitrous oxide in a denitrifying woodchip bioreactor
Denitrifying woodchip bioreactors are potential low-cost technologies for the removal of nitrate (NO3-) in water through denitrification. However, if environmental conditions do not support microbial communities performing complete denitrification, other N transformation processes will occur, resulting in the export of nitrite (NO2-), nitrous oxide (N2O), or ammonium (NH4+). To identify the factors controlling the relative accumulation of NO2-, N2O, and/or NH4+ in denitrifying woodchip bioreactors, porewater samples were collected over two operational years from a denitrifying woodchip bioreactor designed for removing NO3- from mine water. Woodchip samples were collected at the end of the operational period. Changes in the abundances of functional genes involved in denitrification, N2O reduction, and dissimilatory NO3- reduction to NH4+ were correlated with porewater chemistry and temperature. Temporal changes in the abundance of the denitrification gene nirS were significantly correlated with increases in porewater N2O concentrations and indicated the preferential selection of incomplete denitrifying pathways ending with N2O. Temperature and the total organic carbon/NO3- ratio were strongly correlated with NH4+ concentrations and inversely correlated with the ratio between denitrification genes and the genes indicative of ammonification (sigma nir/nrfA), suggesting an environmental control on NO3- transformations. Overall, our results for a denitrifying woodchip bioreactor operated at hydraulic residence times of 1.0-2.6 d demonstrate the temporal development in the microbial community and indicate an increased potential for N2O emissions with time from the denitrifying woodchip bioreactor
Neural mechanisms underlying target detection in a dragonfly centrifugal neuron
© The Company of Biologists Ltd 2007Visual identification of targets is an important task for many animals searching for prey or conspecifics. Dragonflies utilize specialized optics in the dorsal acute zone, accompanied by higher-order visual neurons in the lobula complex, and descending neural pathways tuned to the motion of small targets. While recent studies describe the physiology of insect small target motion detector (STMD) neurons, little is known about the mechanisms that underlie their exquisite sensitivity to target motion. Lobula plate tangential cells (LPTCs), a group of neurons in dipteran flies selective for wide-field motion, have been shown to take input from local motion detectors consistent with the classic correlation model developed by Hassenstein and Reichardt in the 1950s. We have tested the hypothesis that similar mechanisms underlie the response of dragonfly STMDs. We show that an anatomically characterized centrifugal STMD neuron (CSTMD1) gives responses that depend strongly on target contrast, a clear prediction of the correlation model. Target stimuli are more complex in spatiotemporal terms than the sinusoidal grating patterns used to study LPTCs, so we used a correlation-based computer model to predict response tuning to velocity and width of moving targets. We show that increasing target width in the direction of travel causes a shift in response tuning to higher velocities, consistent with our model. Finally, we show how the morphology of CSTMD1 allows for impressive spatial interactions when more than one target is present in the visual field.Bart R. H. Geurten, Karin Nordström, Jordanna D. H. Sprayberry, Douglas M. Bolzon and David C. O'Carrol
Effect of Al mole fraction on carrier diffusion lengths and lifetimes in AlxGa1âxAs
The ambipolar diffusion length and carrier lifetime are measured in AlxGa1âxAs for several mole fractions in the interval 0<x<0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented
Group infall of substructures on to a Milky Way-like dark halo
We report the discovery that substructures/subhaloes of a galaxy-size halo
tend to fall in together in groups in cosmological simulations, something that
may explain the oddity of the MW satellite distribution. The original
clustering at the time of infall is still discernible in the angular momenta of
the subhaloes even for events which took place up to eight Gyrs ago, . This phenomenon appears to be rather common since at least 1/3 of the
present-day subhaloes have fallen in groups in our simulations. Hence, this may
well explain the Lynden-Bell & Lynden-Bell ghostly streams. We have also found
that the probability of building up a flattened distribution similar to the MW
satellites is as high as if the MW satellites were from only one
group and when five groups are involved. Therefore, we conclude that
the `peculiar' distribution of satellites around the MW can be expected with
the CDM structure formation theory. This non-random assignment of satellites to
subhaloes implies an environmental dependence on whether these low-mass objects
are able to form stars, possibly related to the nature of reionization in the
early Universe.Comment: To appear in the proceedings of IAU Symposium 254 "The Galaxy disk in
a cosmological context", Copenhagen, June 2008, 6 pages, 2 figure
Antibiotic-resistant Escherichia Coli from Retail Poultry Meat with Different Antibiotic Use Claims
Background We sought to determine if the prevalence of antibiotic-resistant Escherichia coli differed across retail poultry products and among major production categories, including organic, âraised without antibioticsâ, and conventional. Results We collected all available brands of retail chicken and turkeyâincluding conventional, âraised without antibioticâ, and organic productsâevery two weeks from January to December 2012. In total, E. coli was recovered from 91% of 546 turkey products tested and 88% of 1367 chicken products tested. The proportion of samples contaminated with E. coli was similar across all three production categories. Resistance prevalence varied by meat type and was highest among E. coli isolates from turkey for the majority of antibiotics tested. In general, production category had little effect on resistance prevalence among E. coli isolates from chicken, although resistance to gentamicin and multidrug resistance did vary. In contrast, resistance prevalence was significantly higher for 6 of the antibiotics testedâand multidrug resistanceâamong isolates from conventional turkey products when compared to those labelled organic or âraised without antibioticsâ. E. coli isolates from chicken varied strongly in resistance prevalence among different brands within each production category. Conclusion The high prevalence of resistance among E. coli isolates from conventionally-raised turkey meat suggests greater antimicrobial use in conventional turkey production as compared to âraised without antibioticsâ and organic systems. However, among E. coli from chicken meat, resistance prevalence was more strongly linked to brand than to production category, which could be caused by brand-level differences during production and/or processing, including variations in antimicrobial use
Spin-dynamic field coupling in strongly THz driven semiconductors : local inversion symmetry breaking
We study theoretically the optics in undoped direct gap semiconductors which
are strongly driven in the THz regime. We calculate the optical sideband
generation due to nonlinear mixing of the THz field and the near infrared
probe. Starting with an inversion symmetric microscopic Hamiltonian we include
the THz field nonperturbatively using non-equilibrium Green function
techniques. We find that a self induced relativistic spin-THz field coupling
locally breaks the inversion symmetry, resulting in the formation of odd
sidebands which otherwise are absent.Comment: 8 pages, 6 figure
A Keck/HIRES Doppler Search for Planets Orbiting Metal-Poor Dwarfs. I. Testing Giant Planet Formation and Migration Scenarios
We describe a high-precision Doppler search for giant planets orbiting a
well-defined sample of metal-poor dwarfs in the field. This experiment
constitutes a fundamental test of theoretical predictions which will help
discriminate between proposed giant planet formation and migration models. We
present here details on the survey as well as an overall assessment of the
quality of our measurements, making use of the results for the stars that show
no significant velocity variation.Comment: 25 pages, 7 figures, accepted for publication in the Astrophysical
Journa
The MAHA clue - A case report
Microangiopathic hemolytic anemia (MAHA), is one of the causes of extra vascular hemolysis. It is seen in settings with pathologically altered small blood vessels. Disseminated carcinomas may rarely present as MAHA. A case of a 28 year old female with carcinoma stomach, who presented with MAHA as a first manifestation is reported. Acute onset of MAHA, may be the first manifestation of malignancy. In the absence of relatively common causes like disseminated intravascular coagulation,/Hemolytic uremic syndrome/thrombotic thrombocytopenic purpura, MAHA warrants extensive rapid investigations including bone marrow aspiration for possible metastatic deposits
- âŠ