326 research outputs found
Constraints on Cosmology and Gravity from the Dynamics of Voids
The Universe is mostly composed of large and relatively empty domains known
as cosmic voids, whereas its matter content is predominantly distributed along
their boundaries. The remaining material inside them, either dark or luminous
matter, is attracted to these boundaries and causes voids to expand faster and
to grow emptier over time. Using the distribution of galaxies centered on voids
identified in the Sloan Digital Sky Survey and adopting minimal assumptions on
the statistical motion of these galaxies, we constrain the average matter
content in the Universe today, as well as the
linear growth rate of structure at median redshift
, where is the galaxy bias ( C.L.). These values
originate from a percent-level measurement of the anisotropic distortion in the
void-galaxy cross-correlation function, , and are
robust to consistency tests with bootstraps of the data and simulated mock
catalogs within an additional systematic uncertainty of half that size. They
surpass (and are complementary to) existing constraints by unlocking
cosmological information on smaller scales through an accurate model of
nonlinear clustering and dynamics in void environments. As such, our analysis
furnishes a powerful probe of deviations from Einstein's general relativity in
the low-density regime which has largely remained untested so far. We find no
evidence for such deviations in the data at hand.Comment: 11 pages, 7 figures. Reflects published version in PRL including
Supplemental Materia
Estimation of fiber diameters in the spinal dorsal columns from clinical data
Lack of human morphometric data regarding the largest nerve fibers in the dorsal columns (DCs) of the spinal cord has lead to the estimation of the diameters of these fibers from clinical data retrieved from patients with a new spinal cord stimulation (SCS) system. These patients indicated the perception threshold of stimulation induced paresthesia in various body segments, while the stimulation amplitude was increased. The fiber diameters were calculated with a computer model, developed to calculate the effects of SCS on spinal nerve fibers. This computer model consists of two parts: (1) a three-dimensional (3-D) volume conductor model of a spinal cord segment in which the potential distribution due to electrical stimulation is calculated and (2) an electrical equivalent cable model of myelinated nerve fiber, which uses the calculated potential field to determine the threshold stimulus needed for activation. It is shown that the largest fibers in the medial DCs are significantly smaller than the largest fibers in the lateral parts. This finding is in accordance with the fiber distribution in cat, derived from the corresponding propagation velocities. Moreover, it is shown that the mediolateral increase in fiber diameter is mainly confined to the lateral parts of the DCs. Implementation of this mediolateral fiber diameter distribution of the DCs in the computer model enables the prediction of the recruitment order of dermatomal paresthesias following increasing electrical stimulation amplitud
Aqueous Processes and Microbial Habitability of Gale Crater Sediments from the Blunts Point to the Glenn Torridon Clay Unit
A driving factor for sending the Mars Science Laboratory, Curiosity rover to Gale Crater was the orbital detection of clay minerals in the Glen Torridon (GT) clay unit. Clay mineral detections in GT suggested a past aqueous environment that was habitable, and could contain organic evidence of past microbiology. The mission of the Sample Analysis at Mars (SAM) instrument onboard Curiosity was to detect organic evidence of past microbiology and to detect volatile bearing mineralogy that can inform on whether past geochemical conditions would have supported microbiological activity. The objective of this work was to 1) evaluate the depositional/alteration conditions of Blunts Point (BP) to GT sediments 2) search for evidence of organics, and 3) evaluate microbial habitability in the BP, Vera Rubin Ridge (VRR), and GT sedimentary rock
A first estimate of radio halo statistics from large-scale cosmological simulation
We present a first estimate based on a cosmological gasdynamics simulation of
galaxy cluster radio halo counts to be expected in forthcoming low-frequency
radio surveys. Our estimate is based on a FLASH simulation of the LCDM model
for which we have assigned radio power to clusters via a model that relates
radio emissivity to cluster magnetic field strength, intracluster turbulence,
and density. We vary several free parameters of this model and find that radio
halo number counts vary by up to a factor of two for average magnetic fields
ranging from 0.2 to 3.1 uG. However, we predict significantly fewer
low-frequency radio halos than expected from previous semi-analytic estimates,
although this discrepancy could be explained by frequency-dependent radio halo
probabilities as predicted in reacceleration models. We find that upcoming
surveys will have difficulty in distinguishing models because of large
uncertainties and low number counts. Additionally, according to our modeling we
find that expected number counts can be degenerate with both reacceleration and
hadronic secondary models of cosmic ray generation. We find that relations
between radio power and mass and X-ray luminosity may be used to distinguish
models, and by building mock radio sky maps we demonstrate that surveys such as
LOFAR may have sufficient resolution and sensitivity to break this model
degeneracy by imaging many individual clusters.Comment: 18 pages, 14 figures, revised from referee comments, ApJ accepted,
public catalog available at
http://sipapu.astro.illinois.edu/http://sipapu.astro.illinois.edu/foswiki/bin/view/Main/RadioHaloMap
Reduction in Unnecessary Clinical Laboratory Testing Through Utilization Management at a US Government Veterans Affairs Hospital
Objectives: To implement an electronic laboratory utilization management system (laboratory expert system [LES]) to provide safe and effective reductions in unnecessary clinical laboratory testing.
Methods: The LES is a set of frequency filter subroutines within the Veterans Affairs hospital and laboratory information system that was formulated by an interdisciplinary medical team.Results: Since implementing the LES, total test volume has decreased by a mean of 11.18% per year compared with our pre-LES test volume. This change was not attributable to fluctuations in outpatient visits or inpatient days of care. Laboratory cost savings were estimated at 163,751 for 2012 and 2013, respectively. A significant portion of these cost savings was attributable to reductions in high-volume, large panel testing. No adverse effects on patient care were reported, and mean length of stay for patients remained unchanged.
Conclusions: Electronic laboratory utilization systems can effectively reduce unnecessary laboratory testing without compromising patient care
Maximum likelihood analysis of systematic errors in interferometric observations of the cosmic microwave background
We investigate the impact of instrumental systematic errors in
interferometric measurements of the cosmic microwave background (CMB)
temperature and polarization power spectra. We simulate interferometric CMB
observations to generate mock visibilities and estimate power spectra using the
statistically optimal maximum likelihood technique. We define a quadratic error
measure to determine allowable levels of systematic error that do not induce
power spectrum errors beyond a given tolerance. As an example, in this study we
focus on differential pointing errors. The effects of other systematics can be
simulated by this pipeline in a straightforward manner. We find that, in order
to accurately recover the underlying B-modes for r=0.01 at 28<l<384,
Gaussian-distributed pointing errors must be controlled to 0.7^\circ rms for an
interferometer with an antenna configuration similar to QUBIC, in agreement
with analytical estimates. Only the statistical uncertainty for 28<l<88 would
be changed at ~10% level. With the same instrumental configuration, we find the
pointing errors would slightly bias the 2-\sigma upper limit of the
tensor-to-scalar ratio r by ~10%. We also show that the impact of pointing
errors on the TB and EB measurements is negligibly small.Comment: 10 pages, 4 figures, accepted for publication in ApJS. Includes
improvements in clarity of presentation and Fig.4 added, in response to
refere
Perturbative calculation of the scaled factorial moments in second-order quark-hadron phase transition within the Ginzburg-Landau description
The scaled factorial moments are studied for a second-order
quark-hadron phase transition within the Ginzburg-Landau description. The role
played by the ground state of the system under low temperature is emphasized.
After a local shift of the order parameter the fluctuations are around the
ground state, and a perturbative calculation for can be carried out.
Power scaling between 's is shown, and a universal scaling exponent
is given for the case with weak correlations and weak
self-interactions.Comment: 12 pages in RevTeX, 12 eps figure
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