288 research outputs found
Sky Variability in the y Band at the LSST Site
We have measured spatial and temporal variability in the y band sky
brightness over the course of four nights above Cerro Tololo near Cerro Pachon,
Chile, the planned site for the Large Synoptic Survey Telescope (LSST). Our
wide-angle camera lens provided a 41 deg field of view and a 145 arcsec pixel
scale. We minimized potential system throughput differences by deploying a deep
depletion CCD and a filter that matches the proposed LSST y_3 band (970 nm-1030
nm). Images of the sky exhibited coherent wave structure, attributable to
atmospheric gravity waves at 90 km altitude, creating 3%-4% rms spatial sky
flux variability on scales of about 2 degrees and larger. Over the course of a
full night the y_3 band additionally showed highly coherent temporal
variability of up to a factor of 2 in flux. We estimate the mean absolute sky
level to be approximately y_3 = 17.8 mag (Vega), or y_3 = 18.3 mag (AB). While
our observations were made through a y_3 filter, the relative sky brightness
variability should hold for all proposed y bands, whereas the absolute levels
should more strongly depend on spectral response. The spatial variability
presents a challenge to wide-field cameras that require illumination correction
strategies that make use of stacked sky flats. The temporal variability may
warrant an adaptive y band imaging strategy for LSST, to take advantage of
times when the sky is darkest.Comment: 8 pages, 5 figures, accepted to PASP. Minor changes from referee
report and editor's revisions
Novel Algorithms Reveal Streptococcal Transcriptomes and Clues about Undefined Genes
Bacteria–host interactions are dynamic processes, and understanding transcriptional responses that directly or indirectly regulate the expression of genes involved in initial infection stages would illuminate the molecular events that result in host colonization. We used oligonucleotide microarrays to monitor (in vitro) differential gene expression in group A streptococci during pharyngeal cell adherence, the first overt infection stage. We present neighbor clustering, a new computational method for further analyzing bacterial microarray data that combines two informative characteristics of bacterial genes that share common function or regulation: (1) similar gene expression profiles (i.e., co-expression); and (2) physical proximity of genes on the chromosome. This method identifies statistically significant clusters of co-expressed gene neighbors that potentially share common function or regulation by coupling statistically analyzed gene expression profiles with the chromosomal position of genes. We applied this method to our own data and to those of others, and we show that it identified a greater number of differentially expressed genes, facilitating the reconstruction of more multimeric proteins and complete metabolic pathways than would have been possible without its application. We assessed the biological significance of two identified genes by assaying deletion mutants for adherence in vitro and show that neighbor clustering indeed provides biologically relevant data. Neighbor clustering provides a more comprehensive view of the molecular responses of streptococci during pharyngeal cell adherence
Dietary fat and carbohydrates differentially alter insulin sensitivity during caloric restriction
BACKGROUND AND AIMS: We determined the effects of acute and chronic calorie restriction with either a low-fat, high-carbohydrate diet or a low-carbohydrate diet on hepatic and skeletal muscle insulin sensitivity. METHODS: Twenty-two obese subjects (body-mass index, 36.5±0.8kg/m(2)) were randomized to a high-carbohydrate (>180g/d) or low-carbohydrate (<60g/d) energy-deficit diet. A euglycemic–hyperinsulinemic clamp, muscle biopsies, and magnetic resonance spectroscopy were used to determine insulin action, cellular insulin signaling and intrahepatic triglyceride content before, after 48 h, and after ~11 wks (7% weight loss) of diet therapy. RESULTS: At 48 h, intrahepatic triglyceride content decreased more in the low-carbohydrate than the high-carbohydrate diet group (29.6±4.8% vs. 8.9±1.4%; P<0.05), but was similar in both groups after 7% weight loss (low-carbohydrate diet, 38.0±4.5% vs. high-carbohydrate diet, 44.5±13.5%). Basal glucose production rate decreased more in the low-carbohydrate than the high-carbohydrate diet group at 48 h (23.4±2.2% vs. 7.2±1.4%, P<0.05) and after 7% weight loss (20.0±2.4% vs. 7.9±1.2%, P<0.05). Insulin-mediated glucose uptake did not change at 48 h, but increased similarly in both groups after 7% weight loss (48.4±14.3%, P<0.05). In both groups, insulin-stimulated phosphorylation of Jun N-terminal kinase decreased by 29±13% and phosphorylation of Akt and insulin receptor substrate -1 increased by 35±9% and 36±9%, respectively, after 7% weight loss (all p<0.05). CONCLUSION: Moderate calorie restriction causes temporal changes in liver and skeletal muscle metabolism; 48 h of calorie restriction affects the liver (intrahepatic triglyceride content, hepatic insulin sensitivity, and glucose production), whereas moderate weight loss affects muscle (insulin-mediated glucose uptake and insulin signaling)
Cryogenic Optical Performance of a Lightweighted Mirror Assembly for Future Space Astronomical Telescopes: Correlating Optical Test Results and Thermal Optical Model
A 43cm diameter stacked core mirror demonstrator was interferometrically tested at room temperature down to 250 degrees Kelvin for thermal deformation. The 2.5m radius of curvature spherical mirror assembly was constructed by low temperature fusing three abrasive waterjet core sections between two CNC pocket milled face sheets. The 93% lightweighted Corning ULE mirror assembly represents the current state of the art for future UV, optical, near IR space telescopes. During the multiple thermal test cycles, test results of interferometric test, thermal IR images of the front face were recorded in order to validate thermal optical model
An inter-laboratory comparison of urinary 3-hydroxypropylmercapturic acid measurement demonstrates good reproducibility between laboratories
<p>Abstract</p> <p>Background</p> <p>Biomarkers have been used extensively in clinical studies to assess toxicant exposure in smokers and non-smokers and have recently been used in the evaluation of novel tobacco products. The urinary metabolite 3-HPMA, a metabolite of the major tobacco smoke toxicity contributor acrolein, is one example of a biomarker used to measure exposure to tobacco smoke. A number of laboratories have developed liquid chromatography with tandem mass spectrometry (LC-MS/MS) based methods to measure urinary 3-HPMA; however, it is unclear to what extent the data obtained by these different laboratories are comparable.</p> <p>Findings</p> <p>This report describes an inter-laboratory comparison carried out to evaluate the comparability of 3-HPMA measurement between four laboratories. A common set of spiked and authentic smoker and non-smoker urine samples were used. Each laboratory used their in-house LC-MS/MS method and a common internal standard. A comparison of the repeatability ('r'), reproducibility ('R'), and coefficient of variation for 3-HPMA demonstrated that within-laboratory variation was consistently lower than between-laboratory variation. The average inter-laboratory coefficient of variation was 7% for fortified urine samples and 16.2% for authentic urine samples. Together, this represents an inter-laboratory variation of 12.2%.</p> <p>Conclusion</p> <p>The results from this first inter-laboratory comparison for the measurement of 3-HPMA in urine demonstrate a reasonably good consensus between laboratories. However, some consistent measurement biases were still observed between laboratories, suggesting that additional work may be required to further reduce the inter-laboratory coefficient of variation.</p
Herschel Exploitation of Local Galaxy Andromeda (HELGA) III: The Star Formation Law in M31
We present a detailed study of how the Star Formation Rate (SFR) relates to
the interstellar medium (ISM) of M31 at ~140pc scales. The SFR is calculated
using the far-ultraviolet and 24um emission, corrected for the old stellar
population in M31. We find a global value for the SFR of 0.25+/-0.05Msun/yr and
compare this with the SFR found using the total far-infrared (FIR) luminosity.
There is general agreement in regions where young stars dominate the dust
heating. Atomic hydrogen (HI) and molecular gas (traced by carbon monoxide, CO)
or the dust mass is used to trace the total gas in the ISM. We show that the
global surface densities of SFR and gas mass place M31 amongst a set of low-SFR
galaxies in the plot of Kennicutt (1998b). The relationship between SFR and gas
surface density is tested in six radial annuli across M31, assuming a power law
relationship with index, N. The star formation law using total gas traced by HI
and CO gives a global index of N=2.03+/-0.04, with a significant variation with
radius; the highest values are observed in the 10kpc ring. We suggest that this
slope is due to HI turning molecular at ~10Msun/pc2. When looking at H2
regions, we measure a higher mean SFR suggesting a better spatial correlation
between H2 and SF. We find N~0.6 with consistent results throughout the disk -
this is at the low end of values found in previous work and argues against a
superlinear SF law on small scales.Comment: 12 pages, 10 figure
Kepler eclipsing binary stars. VII. the catalogue of eclipsing binaries found in the entire Kepler data set
The primary Kepler Mission provided nearly continuous monitoring of ~200,000 objects with unprecedented photometric precision. We present the final catalog of eclipsing binary systems within the 105 deg2 Kepler field of view. This release incorporates the full extent of the data from the primary mission (Q0-Q17 Data Release). As a result, new systems have been added, additional false positives have been removed, ephemerides and principal parameters have been recomputed, classifications have been revised to rely on analytical models, and eclipse timing variations have been computed for each system. We identify several classes of systems including those that exhibit tertiary eclipse events, systems that show clear evidence of additional bodies, heartbeat systems, systems with changing eclipse depths, and systems exhibiting only one eclipse event over the duration of the mission. We have updated the period and galactic latitude distribution diagrams and included a catalog completeness evaluation. The total number of identified eclipsing and ellipsoidal binary systems in the Kepler field of view has increased to 2878, 1.3% of all observed Kepler targets
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
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