155 research outputs found
Stable Motions of Vehicle Formations
We investigate stable maneuvers for a group of autonomous vehicles while moving in formation. The allowed decentralized feeback laws are factored through the Laplacian matrix of the communication graph. We show that such laws allow for stable circular or elliptical motions for certain vehicle dynamics. We find necessary and sufficient conditions on the feedback gains and the dynamic parameters for convergence to formation. In particular, we prove that for undirected graphs there exist feedback gains that stabilize rotational (or elliptical) motions of arbitrary radius (or eceentricity). In the directed graph case we provide necessary and sufficient conditions on the curvature that guarantee stability for a given choice of feedback gains. We also investigate stable motions involving reorientation of the formation along the direction of motion
Buried Black Hole Growth in IR-selected Mergers: New Results from Chandra
Observations and theoretical simulations suggest that a significant fraction
of merger-triggered accretion onto supermassive black holes is highly obscured,
particularly in late-stage galaxy mergers, when the black hole is expected to
grow most rapidly. Starting with the Wide-Field Infrared Survey Explorer
all-sky survey, we identified a population of galaxies whose morphologies
suggest ongoing interaction and which exhibit red mid-infrared colors often
associated with powerful active galactic nuclei (AGNs). In a follow-up to our
pilot study, we now present Chandra/ACIS and XMM-Newton X-ray observations for
the full sample of the brightest 15 IR-preselected mergers. All mergers reveal
at least one nuclear X-ray source, with 8 out of 15 systems exhibiting dual
nuclear X-ray sources, highly suggestive of single and dual AGNs. Combining
these X-ray results with optical line ratios and with near-IR coronal emission
line diagnostics, obtained with the near-IR spectrographs on the Large
Binocular Telescope, we confirm that 13 out of the 15 mergers host AGNs, two of
which host dual AGNs. Several of these AGNs are not detected in the optical.
All X-ray sources appear X-ray weak relative to their mid-infrared continuum,
and of the nine X-ray sources with sufficient counts for spectral analysis,
eight reveal strong evidence of high absorption with column densities of
~cm. These observations demonstrate that a
significant population of single and dual AGNs are missed by optical studies,
due to high absorption, adding to the growing body of evidence that the epoch
of peak black hole growth in mergers occurs in a highly obscured phase.Comment: 29 pages, 22 figures; (Main text: 17 pages, 4 figures
Impact of Ammonium on Syntrophic Organohalide-Respiring and Fermenting Microbial Communities
Citation: Delgado, A. G., Fajardo-Williams, D., Kegerreis, K. L., Parameswaran, P., & Krajmalnik-Brown, R. (2016). Impact of Ammonium on Syntrophic Organohalide-Respiring and Fermenting Microbial Communities. Msphere, 1(2), 10. doi:10.1128/mSphere.00053-16Syntrophic interactions between organohalide-respiring and fermentative microorganisms are critical for effective bioremediation of halogenated compounds. This work investigated the effect of ammonium concentration (up to 4 g liter(-1) NH4+-N) on trichloroethene-reducing Dehalococcoides mccartyi and Geobacteraceae in microbial communities fed lactate and methanol. We found that production of ethene by D. mccartyi occurred in mineral medium containing = 1 g liter(-1) NH4+-N, organohalide-respiring dynamics shifted from D. mccartyi and Geobacteraceae to mainly D. mccartyi. An increasing concentration of ammonium was coupled to lower metabolic rates, longer lag times, and lower gene abundances for all microbial processes studied. The methanol fermentation pathway to acetate and H-2 was conserved, regardless of the ammonium concentration provided. However, lactate fermentation shifted from propionic to acetogenic at concentrations of >= 2 g liter(-1) NH4+-N. Our study findings strongly support a tolerance of D. mccartyi to high ammonium concentrations, highlighting the feasibility of organohalide respiration in ammonium-contaminated subsurface environments. IMPORTANCE Contamination with ammonium and chlorinated solvents has been reported in numerous subsurface environments, and these chemicals bring significant challenges for in situ bioremediation. Dehalococcoides mccartyi is able to reduce the chlorinated solvent trichloroethene to the nontoxic end product ethene. Fermentative bacteria are of central importance for organohalide respiration and bioremediation to provide D. mccartyi with H2, their electron donor, acetate, their carbon source, and other micronutrients. In this study, we found that high concentrations of ammonium negatively correlated with rates of trichloroethene reductive dehalogenation and fermentation. However, detoxification of trichloroethene to nontoxic ethene occurred even at ammonium concentrations typical of those found in animal waste (up to >= 2 g liter(-1) NH4+-N). To date, hundreds of subsurface environments have been bioremediated through the unique metabolic capability of D. mccartyi. These findings extend our knowledge of D. mccartyi and provide insight for bioremediation of sites contaminated with chlorinated solvents and ammonium
Dietary acid load and chronic kidney disease among adults in the United States
Abstract
Background
Diet can markedly affect acid-base status and it significantly influences chronic kidney disease (CKD) and its progression. The relationship of dietary acid load (DAL) and CKD has not been assessed on a population level. We examined the association of estimated net acid excretion (NAEes) with CKD; and socio-demographic and clinical correlates of NAEes.
Methods
Among 12,293 U.S. adult participants aged >20 years in the National Health and Nutrition Examination Survey 1999–2004, we assessed dietary acid by estimating NAEes from nutrient intake and body surface area; kidney damage by albuminuria; and kidney dysfunction by eGFR < 60 ml/min/1.73m2 using the MDRD equation. We tested the association of NAEes with participant characteristics using median regression; while for albuminuria, eGFR, and stages of CKD we used logistic regression.
Results
Median regression results (β per quintile) indicated that adults aged 40–60 years (β [95% CI] = 3.1 [0.3–5.8]), poverty (β [95% CI] = 7.1 [4.01–10.22]), black race (β [95% CI] = 13.8 [10.8–16.8]), and male sex (β [95% CI] = 3.0 [0.7- 5.2]) were significantly associated with an increasing level of NAEes. Higher levels of NAEes compared with lower levels were associated with greater odds of albuminuria (OR [95% CI] = 1.57 [1.20–2.05]). We observed a trend toward greater NAEes being associated with higher risk of low eGFR, which persisted after adjustment for confounders.
Conclusion
Higher NAEes is associated with albuminuria and low eGFR, and socio-demographic risk factors for CKD are associated with higher levels of NAEes. DAL may be an important target for future interventions in populations at high risk for CKD.http://deepblue.lib.umich.edu/bitstream/2027.42/109474/1/12882_2014_Article_829.pd
Validation of the Oncomineâ„¢ Focus Panel for Next Generation Sequencing of clinical tumour samples
The clinical utility of next-generation sequencing (NGS) for a diverse range of targets is expanding, increasing the need for multiplexed analysis of both DNA and RNA. However, translation into daily use requires a rigorous and comprehensive validation strategy. The aim of this clinical validation was to assess the performance of the Ion Torrent Personal Genome Machine (IonPGM™) and validate the Oncomine™ Focus DNA and RNA Fusion panels for clinical application in solid tumour testing of formalin-fixed, paraffin-embedded (FFPE) tissue. Using a mixture of routine FFPE and reference material across a variety of tissue and specimen types, we sequenced 86 and 31 samples on the Oncomine™ Focus DNA and RNA Fusion assays, respectively. This validation considered a number of parameters including the clinical robustness of the bioinformatics pipeline for variant detection and interpretation. The Oncomine™ Focus DNA assay had a sample and variant-based sensitivity of 99.1 and 97.1%, respectively, and an assay specificity of 100%. The Oncomine™ Focus Fusion panel had a good sensitivity and specificity based upon the samples assessed, however requires further validation to confirm findings due to limited sample numbers. We observed a good sequencing performance based upon amplicon, gene (hotspot variants within gene) and sample specific analysis with 92% of clinical samples obtaining an average amplicon coverage above 500X. Detection of some indels was challenging for the routine IonReporter™ workflow; however, the addition of NextGENe® software improved indel identification demonstrating the importance of both bench and bioinformatic validation. With an increasing number of clinically actionable targets requiring a variety of methodologies, NGS provides a cost-effective and time-saving methodology to assess multiple targets across different modalities. We suggest the use of multiple analysis software to ensure identification of clinically applicable variants.Publisher PDFPeer reviewe
Estimating the glutamate transporter surface density in distinct sub-cellular compartments of mouse hippocampal astrocytes
Glutamate transporters preserve the spatial specificity of synaptic transmission by limiting glutamate diffusion away from the synaptic cleft, and prevent excitotoxicity by keeping the extracellular concentration of glutamate at low nanomolar levels. Glutamate transporters are abundantly expressed in astrocytes, and previous estimates have been obtained about their surface expression in astrocytes of the rat hippocampus and cerebellum. Analogous estimates for the mouse hippocampus are currently not available. In this work, we derive the surface density of astrocytic glutamate transporters in mice of different ages via quantitative dot blot. We find that the surface density of glial glutamate transporters is similar in 7-8 week old mice and rats. In mice, the levels of glutamate transporters increase until about 6 months of age and then begin to decline slowly. Our data, obtained from a combination of experimental and modeling approaches, point to the existence of stark differences in the density of expression of glutamate transporters across different sub-cellular compartments, indicating that the extent to which astrocytes limit extrasynaptic glutamate diffusion depends not only on their level of synaptic coverage, but also on the identity of the astrocyte compartment in contact with the synapse. Together, these findings provide information on how heterogeneity in the spatial distribution of glutamate transporters in the plasma membrane of hippocampal astrocytes my alter glutamate receptor activation out of the synaptic cleft
Probing the Balance of AGN and Star-Forming Activity in the Local Universe with ChaMP
The combination of the SDSS and the Chandra Multiwavelength Project (ChaMP)
currently offers the largest and most homogeneously selected sample of nearby
galaxies for investigating the relation between X-ray nuclear emission, nebular
line-emission, black hole masses, and properties of the associated stellar
populations. We present here novel constraints that both X-ray luminosity Lx
and X-ray spectral energy distribution bring to the galaxy evolutionary
sequence H II -> Seyfert/Transition Object -> LINER -> Passive suggested by
optical data. In particular, we show that both Lx and Gamma, the slope of the
power-law that best fits the 0.5 - 8 keV spectra, are consistent with a clear
decline in the accretion power along the sequence, corresponding to a softening
of their spectra. This implies that, at z ~ 0, or at low luminosity AGN levels,
there is an anti-correlation between Gamma and L/Ledd, opposite to the trend
exhibited by high z AGN (quasars). The turning point in the Gamma -L/Ledd LLAGN
+ quasars relation occurs near Gamma ~ 1.5 and L/Ledd ~ 0.01. Interestingly,
this is identical to what stellar mass X-ray binaries exhibit, indicating that
we have probably found the first empirical evidence for an intrinsic switch in
the accretion mode, from advection-dominated flows to standard (disk/corona)
accretion modes in supermassive black hole accretors, similar to what has been
seen and proposed to happen in stellar mass black hole systems. The
anti-correlation we find between Gamma and L/Ledd may instead indicate that
stronger accretion correlates with greater absorption. Therefore the trend for
softer spectra toward more luminous, high redshift, and strongly accreting
AGN/quasars could simply be the result of strong selection biases reflected in
the dearth of type 2 quasar detections.Comment: 23 pages, 8 figures, 1 long (3 page) table, to appear in Ap
Mechanisms explaining transitions between tonic and phasic firing in neuronal populations as predicted by a low dimensional firing rate model
Several firing patterns experimentally observed in neural populations have
been successfully correlated to animal behavior. Population bursting, hereby
regarded as a period of high firing rate followed by a period of quiescence, is
typically observed in groups of neurons during behavior. Biophysical
membrane-potential models of single cell bursting involve at least three
equations. Extending such models to study the collective behavior of neural
populations involves thousands of equations and can be very expensive
computationally. For this reason, low dimensional population models that
capture biophysical aspects of networks are needed.
\noindent The present paper uses a firing-rate model to study mechanisms that
trigger and stop transitions between tonic and phasic population firing. These
mechanisms are captured through a two-dimensional system, which can potentially
be extended to include interactions between different areas of the nervous
system with a small number of equations. The typical behavior of midbrain
dopaminergic neurons in the rodent is used as an example to illustrate and
interpret our results.
\noindent The model presented here can be used as a building block to study
interactions between networks of neurons. This theoretical approach may help
contextualize and understand the factors involved in regulating burst firing in
populations and how it may modulate distinct aspects of behavior.Comment: 25 pages (including references and appendices); 12 figures uploaded
as separate file
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