102 research outputs found
Electron Cloud Buildup Characterization Using Shielded Pickup Measurements and Custom Modeling Code at CESRTA
The Cornell Electron Storage Ring Test Accelerator experimental program
includes investigations into electron cloud buildup, applying various
mitigation techniques in custom vacuum chambers. Among these are two 1.1-m-long
sections located symmetrically in the east and west arc regions. These chambers
are equipped with pickup detectors shielded against the direct beam-induced
signal. They detect cloud electrons migrating through an 18-mm-diameter pattern
of small holes in the top of the chamber. A digitizing oscilloscope is used to
record the signals, providing time-resolved information on cloud development.
Carbon-coated, TiN-coated and uncoated aluminum chambers have been tested.
Electron and positron beams of 2.1, 4.0 and 5.3 GeV with a variety of bunch
populations and spacings in steps of 4 and 14 ns have been used. Here we report
on results from the ECLOUD modeling code which highlight the sensitivity of
these measurements to the physical phenomena determining cloud buildup such as
the photoelectron production azimuthal and energy distributions, and the
secondary yield parameters including the true secondary, re-diffused, and
elastic yield values.Comment: Presented at ECLOUD'12: Joint INFN-CERN-EuCARD-AccNet Workshop on
Electron-Cloud Effects, La Biodola, Isola d'Elba, Italy, 5-9 June 2012;
CERN-2013-002, pp. 241-25
Imprint of DES superstructures on the cosmic microwave background
Small temperature anisotropies in the cosmic microwave background (CMB) can be sourced by density perturbations via the late-time integrated Sachs-Wolfe (ISW) effect. Large voids and superclusters are excellent environments to make a localized measurement of this tiny imprint. In some cases excess signals have been reported. We probed these claims with an independent data set, using the first year data of the Dark Energy Survey (DES) in a different footprint, and using a different superstructure finding strategy. We identified 52 large voids and 102 superclusters at redshifts 0.2 < z < 0.65. We used the Jubilee simulation to a priori evaluate the optimal ISW measurement configuration for our compensated top-hat filtering technique, and then performed a stacking measurement of the CMB temperature field based on the DES data. For optimal configurations, we detected a cumulative cold imprint of voids with DeltaTf ≈ -5.0 ± 3.7 muK and a hot imprint of superclusters DeltaTf ≈ 5.1 ± 3.2 muK; this is ˜1.2sigma higher than the expected |DeltaTf| ≈ 0.6 muK imprint of such superstructures in Lambda cold dark matter (LambdaCDM). If we instead use an a posteriori selected filter size (R/Rv = 0.6), we can find a temperature decrement as large as DeltaTf ≈ -9.8 ± 4.7 muK for voids, which is ˜2sigma above LambdaCDM expectations and is comparable to previous measurements made using Sloan Digital Sky Survey superstructure data
CMB lensing tomography with the DES Science Verification galaxies
We measure the cross-correlation between the galaxy density in the Dark Energy Survey (DES) Science Verification data and the lensing of the cosmic microwave background (CMB) as reconstructed with the Planck satellite and the South Pole Telescope (SPT). When using the DES main galaxy sample over the full redshift range 0.2 2sigma) detections in all bins. Comparing to the fiducial Planck cosmology, we find the redshift evolution of the signal matches expectations, although the amplitude is consistently lower than predicted across redshift bins. We test for possible systematics that could affect our result and find no evidence for significant contamination. Finally, we demonstrate how these measurements can be used to constrain the growth of structure across cosmic time. We find the data are fit by a model in which the amplitude of structure in the z< 1.2 universe is 0.73 ± 0.16 times as large as predicted in the Lambda cold dark matter Planck cosmology, a 1.7sigma deviation
Reconstructing the Inflaton Potential --- an Overview
We review the relation between the inflationary potential and the spectra of
density (scalar) perturbations and gravitational waves (tensor perturbations)
produced, with particular emphasis on the possibility of reconstructing the
inflaton potential from observations. The spectra provide a potentially
powerful test of the inflationary hypothesis; they are not independent but
instead are linked by consistency relations reflecting their origin from a
single inflationary potential. To lowest-order in a perturbation expansion
there is a single, now familiar, relation between the tensor spectral index and
the relative amplitude of the spectra. We demonstrate that there is an infinite
hierarchy of such consistency equations, though observational difficulties
suggest only the first is ever likely to be useful. We also note that since
observations are expected to yield much better information on the scalars than
on the tensors, it is likely to be the next-order version of this consistency
equation which will be appropriate, not the lowest-order one. If inflation
passes the consistency test, one can then confidently use the remaining
observational information to constrain the inflationary potential, and we
survey the general perturbative scheme for carrying out this procedure.
Explicit expressions valid to next-lowest order in the expansion are presented.
We then briefly assess the prospects for future observations reaching the
quality required, and consider a simulated data set that is motivated by this
outlook.Comment: 69 pages standard LaTeX plus 4 postscript figures. Postscript version
of text in landscape format (35 pages) available at
http://star-www.maps.susx.ac.uk/papers/infcos_papers.html Modifications are a
variety of updates to discussion and reference
Gut microbiome composition is linked to whole grain-induced immunological improvements
The involvement of the gut microbiota in metabolic disorders, and the ability of whole grains to affect both host metabolism and gut microbial ecology, suggest that some benefits of whole grains are mediated through their effects on the gut microbiome. Nutritional studies that assess the effect of whole grains on both the gut microbiome and human physiology are needed. We conducted a randomized cross-over trial with four-week treatments in which 28 healthy humans consumed a daily dose of 60 g of whole-grain barley (WGB), brown rice (BR), or an equal mixture of the two (BR+WGB), and characterized their impact on fecal microbial ecology and blood markers of inflammation, glucose and lipid metabolism. All treatments increased microbial diversity, the Firmicutes/Bacteroidetes ratio, and the abundance of the genus Blautia in fecal samples. The inclusion of WGB enriched the genera Roseburia, Bifidobacterium and Dialister, and the species Eubacterium rectale, Roseburia faecis and Roseburia intestinalis. Whole grains, and especially the BR+WGB treatment, reduced plasma interleukin-6 (IL-6) and peak postprandial glucose. Shifts in the abundance of Eubacterium rectale were associated with changes in the glucose and insulin postprandial response. Interestingly, subjects with greater improvements in IL-6 levels harbored significantly higher proportions of Dialister and lower abundance of Coriobacteriaceae. In conclusion, this study revealed that a short-term intake of whole grains induced compositional alterations of the gut microbiota that coincided with improvements in host physiological measures related to metabolic dysfunctions in humans
Dark Energy Survey Year 1 results: cosmological constraints from galaxy clustering and weak lensing
We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg 2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). We combine three two-point functions: (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, we use independent pairs of galaxy shape, photometric redshift estimation and validation, and likelihood analysis pipelines. To prevent confirmation bias, the bulk of the analysis was carried out while blind to the true results; we describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat Λ CDM and w CDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for Λ CDM) or 7 (for w CDM) cosmological parameters including the neutrino mass density and including the 457 × 457 element analytic covariance matrix. We find consistent cosmological results from these three two-point functions, and from their combination obtain S 8 ≡σ 8 (Ω m /0.3) 0.5 =0.783 +0.021 −0.025 and Ω m =0.264 +0.032 −0.019 for Λ CDM for w CDM, we find S 8 =0.794 +0.029 −0.027, Ω m =0.279 +0.043 −0.022, and w=−0.80 +0.20 −0.22 at 68% CL. The precision of these DES Y1 results rivals that from the Planck cosmic microwave background measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for S 8 and Ω m are lower than the central values from Planck
Imprint of DES super-structures on the Cosmic Microwave Background
Small temperature anisotropies in the Cosmic Microwave Background can be sourced by density perturbations via the late-time integrated Sachs-Wolfe effect. Large voids and superclusters are excellent environments to make a localized measurement of this tiny imprint. In some cases excess signals have been reported. We probed these claims with an independent data set, using the first year data of the Dark Energy Survey in a different footprint, and using a different super-structure finding strategy. We identified 52 large voids and 102 superclusters at redshifts . We used the Jubilee simulation to a priori evaluate the optimal ISW measurement configuration for our compensated top-hat filtering technique, and then performed a stacking measurement of the CMB temperature field based on the DES data. For optimal configurations, we detected a cumulative cold imprint of voids with and a hot imprint of superclusters ; this is higher than the expected imprint of such super-structures in CDM. If we instead use an a posteriori selected filter size (), we can find a temperature decrement as large as for voids, which is above CDM expectations and is comparable to previous measurements made using SDSS super-structure data
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