2,493 research outputs found
Milky Way Tomography with K and M Dwarf Stars: the Vertical Structure of the Galactic Disk
We use the number density distributions of K and M dwarf stars with vertical
height from the Galactic disk, determined using observations from the Sloan
Digital Sky Survey, to probe the structure of the Milky Way disk across the
survey's footprint. Using photometric parallax as a distance estimator we
analyze a sample of several million disk stars in matching footprints above and
below the Galactic plane, and we determine the location and extent of vertical
asymmetries in the number counts in a variety of thin- and thick-disk
subsamples in regions of some 200 square degrees within 2 kpc in vertical
distance from the Galactic disk. These disk asymmetries present wave-like
features as previously observed on other scales and at other distances from the
Sun. We additionally explore the scale height of the disk and the implied
offset of the Sun from the Galactic plane at different locations, noting that
the scale height of the disk can differ significantly when measured using stars
only above or only below the plane. Moreover, we compare the shape of the
number density distribution in the north for different latitude ranges with a
fixed range in longitude and find the shape to be sensitive to the selected
latitude window. We explain why this may be indicative of a change in stellar
populations in the latitude regions compared, possibly allowing access to the
systematic metallicity difference between thin- and thick-disk populations
through photometry.Comment: 41 pages, 17 figures, accepted for publication in ApJ; published
version [oversight in Fig. 12 fixed
Optimizing the Placement of Numerical Relativity Simulations using a Mismatch Predicting Neural Network
Gravitational wave observations from merging compact objects are becoming
commonplace, and as detectors improve and gravitational wave sources become
more varied, it is increasingly important to have dense and expansive template
banks of predicted gravitational waveforms. Since numerical relativity is the
only way to fully solve the non-linear merger regime of general relativity for
comparably massed systems, numerical relativity simulations are critical for
gravitational wave detection and analysis. These simulations are
computationally expensive, with each simulation placing one point within the
high dimensional parameter space of binary black hole coalescences. This makes
it important to have a method of placing new simulations in ways that use our
computational resources optimally while ensuring sufficient coverage of the
parameter space. Accomplishing this requires predicting the impact of a new set
of parameters before performing the simulation. To this effect, this paper
introduces a neural network to predict the mismatch between the gravitational
waves of two binary systems. Using this network, we then show how we can
propose new numerical relativity simulations that will provide the most
benefit. We also use the network to identify gaps in existing public catalogs
and identify degeneracies in the binary black hole parameter space.Comment: 14 pages, 11 figure
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A guide to a brain-based approach to thematic, interdisciplinary teaching
This project promotes an interdisciplinary approach to classroom instruction as an alternative to sequential instruction typically practiced in public schools. Specifically targeted are thematic, interdisciplinary teaching strategies
Provider-initiated testing and counselling programmes in sub-Saharan Africa: a systematic review of their operational implementation.
OBJECTIVE: The routine offer of an HIV test during patient-provider encounters is gaining momentum within HIV treatment and prevention programmes. This review examined the operational implementation of provider-initiated testing and counselling (PITC) programmes in sub-Saharan Africa. DESIGN AND METHODS: PUBMED, EMBASE, Global Health, COCHRANE Library and JSTOR databases were searched systematically for articles published in English between January 2000 and November 2010. Grey literature was explored through the websites of international and nongovernmental organizations. Eligibility of studies was based on predetermined criteria applied during independent screening by two researchers. RESULTS: We retained 44 studies out of 5088 references screened. PITC polices have been effective at identifying large numbers of previously undiagnosed individuals. However, the translation of policy guidance into practice has had mixed results, and in several studies of routine programmes the proportion of patients offered an HIV test was disappointingly low. There were wide variations in the rates of acceptance of the test and poor linkage of those testing positive to follow-up assessments and antiretroviral treatment. The challenges encountered encompass a range of areas from logistics, to data systems, human resources and management, reflecting some of the weaknesses of health systems in the region. CONCLUSIONS: The widespread adoption of PITC provides an unprecedented opportunity for identifying HIV-positive individuals who are already in contact with health services and should be accompanied by measures aimed at strengthening health systems and fostering the normalization of HIV at community level. The resources and effort needed to do this successfully should not be underestimated
Integrating nursing theory, practice and research through collaborative research
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75657/1/j.1365-2648.1989.tb00912.x.pd
Local brain connectivity and associations with gender and age
ABSTRACTRegional homogeneity measures synchrony of resting-state brain activity in neighboring voxels, or local connectivity. The effects of age and gender on local connectivity in healthy subjects are unknown. We performed regional homogeneity analyses on resting state BOLD time series data acquired from 58 normal, healthy participants, ranging in age from 11 to 35 (mean 18.1±5.0 years, 32 males). Regional homogeneity was found to be highest for gray matter, with brain regions within the default mode network having the highest local connectivity values. There was a general decrease in regional homogeneity with age with the greatest reduction seen in the anterior cingulate and temporal lobe. Greater female local connectivity in the right hippocampus and amygdala was also noted, regardless of age. These findings suggest that local connectivity at the millimeter scale decreases during development as longer connections are formed, and underscores the importance of examining gender differences in imaging studies of healthy and clinical populations
Prediction of Thermal Protection System Material Permeability and Hydraulic Tortuosity Factor Using Direct Simulation Monte Carlo
Carbon preforms used in Thermal Protection System (TPS) materials are 80 to 90% porous, allowing for boundary layer and pyrolysis gases to flow through the porous regions. The bulk material properties such as permeability and hydraulic tortuosity factor affect the transport of the boundary layer gases. The use of Direct Simulation Monte Carlo along with the Klinkenberg permeability formulation allows us to compute the continuum permeability and Knudsen correction factor for flow in the transition regime. In this work, we have computed the permeability for two types of carbon preforms, namely, Morgan Felt and FiberForm, and assessed the effect of orientation on the permeability. Since both the materials are anisotropic, the permeability was found to depend on orientation, wherein, the materials are more permeable in the in-plane orientation than the through-thickness orientation. The through-thickness orientation was also more tortuous compared to the in-plane material orientation. Compared to Morgan Felt, FiberForm is less permeable, in both, through thickness and in-plane directions
3,4,5-Trichloroaniline Nephrotoxicity in Vitro: Potential Role of Free Radicals and Renal Biotransformation
Chloroanilines are widely used in the manufacture of drugs, pesticides and industrial intermediates. Among the trichloroanilines, 3,4,5-trichloroaniline (TCA) is the most potent nephrotoxicant in vivo. The purpose of this study was to examine the nephrotoxic potential of TCA in vitro and to determine if renal biotransformation and/or free radicals contributed to TCA cytotoxicity using isolated renal cortical cells (IRCC) from male Fischer 344 rats as the animal model. IRCC (~4 million cells/mL; 3 mL) were incubated with TCA (0, 0.1, 0.25, 0.5 or 1.0 mM) for 60–120 min. In some experiments, IRCC were pretreated with an antioxidant or a cytochrome P450 (CYP), flavin monooxygenase (FMO), cyclooxygenase or peroxidase inhibitor prior to incubation with dimethyl sulfoxide (control) or TCA (0.5 mM) for 120 min. At 60 min, TCA did not induce cytotoxicity, but induced cytotoxicity as early as 90 min with 0.5 mM or higher TCA and at 120 min with 0.1 mM or higher TCA, as evidenced by increased lactate dehydrogenase (LDH) release. Pretreatment with the CYP inhibitor piperonyl butoxide, the cyclooxygenase inhibitor indomethacin or the peroxidase inhibitor mercaptosuccinate attenuated TCA cytotoxicity, while pretreatment with FMO inhibitors or the CYP inhibitor metyrapone had no effect on TCA nephrotoxicity. Pretreatment with an antioxidant (α-tocopherol, glutathione, ascorbate or N-acetyl-L-cysteine) also reduced or completely blocked TCA cytotoxicity. These results indicate that TCA is directly nephrotoxic to IRCC in a time and concentration dependent manner. Bioactivation of TCA to toxic metabolites by CYP, cyclooxygenase and/or peroxidase contributes to the mechanism of TCA nephrotoxicity. Lastly, free radicals play a role in TCA cytotoxicity, although the exact nature of the origin of these radicals remains to be determined
Vaccination with live attenuated simian immunodeficiency virus causes dynamic changes in intestinal CD4+CCR5+ T cells
<p>Abstract</p> <p>Background</p> <p>Vaccination with live attenuated SIV can protect against detectable infection with wild-type virus. We have investigated whether target cell depletion contributes to the protection observed. Following vaccination with live attenuated SIV the frequency of intestinal CD4+CCR5+ T cells, an early target of wild-type SIV infection and destruction, was determined at days 3, 7, 10, 21 and 125 post inoculation.</p> <p>Results</p> <p>In naive controls, modest frequencies of intestinal CD4+CCR5+ T cells were predominantly found within the LPL T<sub>TrM-1 </sub>and IEL T<sub>TrM-2 </sub>subsets. At day 3, LPL and IEL CD4+CCR5+ T<sub>EM </sub>cells were dramatically increased whilst less differentiated subsets were greatly reduced, consistent with activation-induced maturation. CCR5 expression remained high at day 7, although there was a shift in subset balance from CD4+CCR5+ T<sub>EM </sub>to less differentiated T<sub>TrM-2 </sub>cells. This increase in intestinal CD4+CCR5+ T cells preceded the peak of SIV RNA plasma loads measured at day 10. Greater than 65.9% depletion of intestinal CD4+CCR5+ T cells followed at day 10, but overall CD4+ T cell homeostasis was maintained by increased CD4+CCR5- T cells. At days 21 and 125, high numbers of intestinal CD4+CCR5- naive T<sub>N </sub>cells were detected concurrent with greatly increased CD4+CCR5+ LPL T<sub>TrM-2 </sub>and IEL T<sub>EM </sub>cells at day 125, yet SIV RNA plasma loads remained low.</p> <p>Conclusions</p> <p>This increase in intestinal CD4+CCR5+ T cells, following vaccination with live attenuated SIV, does not correlate with target cell depletion as a mechanism of protection. Instead, increased intestinal CD4+CCR5+ T cells may correlate with or contribute to the protection conferred by vaccination with live attenuated SIV.</p
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