7,873 research outputs found
Ionizing radiation from hydrogen recombination strongly suppresses the lithium scattering signature in the CMB
It has been suggested that secondary CMB anisotropies generated by neutral lithium could open a new observational window into the universe around the redshift z~400, and permit a determination of the primordial lithium abundance. The effect is due to resonant scattering in the allowed Li i doublet (2s2S1/2-2p2P1/2,3/2), so its observability depends on the formation history of neutral lithium. Here we show that the ultraviolet photons produced during hydrogen recombination are sufficient to keep lithium in the Li ii ionization stage in the relevant redshift range and suppress the neutral fraction by ~3 orders of magnitude from previous calculations, making the lithium signature unobservable
Transparency of 0.2% GdCl3 Doped Water in a Stainless Steel Test Environment
The possibility of neutron and neutrino detection using water Cerenkov
detectors doped with gadolinium holds the promise of constructing very large
high-efficiency detectors with wide-ranging application in basic science and
national security. This study addressed a major concern regarding the
feasibility of such detectors: the transparency of the doped water to the
ultraviolet Cerenkov light. We report on experiments conducted using a 19-meter
water transparency measuring instrument and associated materials test tank.
Sensitive measurements of the transparency of water doped with 0.2% GdCl3 at
337nm, 400nm and 420nm were made using this instrument. These measurements
indicate that GdCl3 is not an appropriate dopant in stainless steel constructed
water Cerenkov detectors.Comment: 17 pages, 11 figures, corrects typos, changes formatting, adds error
bars to figure
Interloper bias in future large-scale structure surveys
Next-generation spectroscopic surveys will map the large-scale structure of
the observable universe, using emission line galaxies as tracers. While each
survey will map the sky with a specific emission line, interloping emission
lines can masquerade as the survey's intended emission line at different
redshifts. Interloping lines from galaxies that are not removed can contaminate
the power spectrum measurement, mixing correlations from various redshifts and
diluting the true signal. We assess the potential for power spectrum
contamination, finding that an interloper fraction worse than 0.2% could bias
power spectrum measurements for future surveys by more than 10% of statistical
errors, while also biasing power spectrum inferences. We also construct a
formalism for predicting cosmological parameter bias, demonstrating that a
0.15%-0.3% interloper fraction could bias the growth rate by more than 10% of
the error, which can affect constraints on gravity upcoming surveys. We use the
COSMOS Mock Catalog (CMC), with the emission lines re-scaled to better
reproduce recent data, to predict potential interloper fractions for the Prime
Focus Spectrograph (PFS) and the Wide-Field InfraRed Survey Telescope (WFIRST).
We find that secondary line identification, or confirming galaxy redshifts by
finding correlated emission lines, can remove interlopers for PFS. For WFIRST,
we use the CMC to predict that the 0.2% target can be reached for the WFIRST
H survey, but sensitive optical and near-infrared photometry will be
required. For the WFIRST [OIII] survey, the predicted interloper fractions
reach several percent and their effects will have to be estimated and removed
statistically (e.g. with deep training samples). (Abridged)Comment: Matches version accepted by PAS
Detection of large scale intrinsic ellipticity-density correlation from the Sloan Digital Sky Survey and implications for weak lensing surveys
The power spectrum of weak lensing shear caused by large-scale structure is
an emerging tool for precision cosmology, in particular for measuring the
effects of dark energy on the growth of structure at low redshift. One
potential source of systematic error is intrinsic alignments of ellipticities
of neighbouring galaxies (II correlation) that could mimic the correlations due
to lensing. A related possibility pointed out by Hirata and Seljak (2004) is
correlation between the intrinsic ellipticities of galaxies and the density
field responsible for gravitational lensing shear (GI correlation). We present
constraints on both the II and GI correlations using 265 908 spectroscopic
galaxies from the SDSS, and using galaxies as tracers of the mass in the case
of the GI analysis. The availability of redshifts in the SDSS allows us to
select galaxies at small radial separations, which both reduces noise in the
intrinsic alignment measurement and suppresses galaxy- galaxy lensing (which
otherwise swamps the GI correlation). While we find no detection of the II
correlation, our results are nonetheless statistically consistent with recent
detections found using the SuperCOSMOS survey. In contrast, we have a clear
detection of GI correlation in galaxies brighter than L* that persists to the
largest scales probed (60 Mpc/h) and with a sign predicted by theoretical
models. This correlation could cause the existing lensing surveys at z~1 to
underestimate the linear amplitude of fluctuations by as much as 20% depending
on the source sample used, while for surveys at z~0.5 the underestimation may
reach 30%. (Abridged.)Comment: 16 pages, matches version published in MNRAS (only minor changes in
presentation from original version
Trunk muscle activity during drop jump performance in adolescent athletes with back pain
It was with great interest we read the recently published article “Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain.” Investigating back pain (BP) in adolescents is commendable as there is growing evidence that for many, an experience of BP as early as 14 years of age may relate to ongoing pain in adulthood (Coenen et al., 2017). Indeed, the conventional narrative is changing as individual physical factors such as posture, use of schoolbags, and hypermobility are only weakly associated with adolescent BP. Rather, factors which predict BP at a young age are considered to be multi-dimensional and include gender, negative BP beliefs and poor mental health (O\u27Sullivan et al., 2017; Smith et al., 2017). Mueller et al. (2017) have focused on a single physical factor (trunk muscle activation patterns) drawing inferences regarding BP prevention and treatment. This article prompts consideration of three essential aspects regarding research design and interpretation of findings:
1. Interpreting results from cross-sectional designs
2. Interpreting pain-related differences in motor behavior
3. Translating and conveying scientific results to the end-user (patients, healthcare professionals and policy makers)
Calculated Electron Fluxes at Airplane Altitudes
A precision measurement of atmospheric electron fluxes has been performed on
a Japanese commercial airliner (Enomoto, {\it et al.}, 1991). We have performed
a monte carlo calculation of the cosmic ray secondary electron fluxes expected
in this experiment. The monte carlo uses the hadronic portion of our neutrino
flux cascade program combined with the electromagnetic cascade portion of the
CERN library program GEANT. Our results give good agreement with the data,
provided we boost the overall normalization of the primary cosmic ray flux by
12\% over the normalization used in the neutrino flux calculation.Comment: in REVTEX, 12 pages + 4 figures available upon reques
Molecular Density Functional Theory for water with liquid-gas coexistence and correct pressure
The solvation of hydrophobic solutes in water is special because liquid and
gas are almost at coexistence. In the common hypernetted chain approximation to
integral equations, or equivalently in the homogenous reference fluid of
molecular density functional theory, coexistence is not taken into account.
Hydration structures and energies of nanometer-scale hydrophobic solutes are
thus incorrect. In this article, we propose a bridge functional that corrects
this thermodynamic inconsistency by introducing a metastable gas phase for the
homogeneous solvent. We show how this can be done by a third order expansion of
the functional around the bulk liquid density that imposes the right pressure
and the correct second order derivatives. Although this theory is not limited
to water, we apply it to study hydrophobic solvation in water at room
temperature and pressure and compare the results to all-atom simulations. With
this correction, molecular density functional theory gives, at a modest
computational cost, quantitative hydration free energies and structures of
small molecular solutes like n-alkanes, and of hard sphere solutes whose radii
range from angstroms to nanometers. The macroscopic liquid-gas surface tension
predicted by the theory is comparable to experiments. This theory gives an
alternative to the empirical hard sphere bridge correction used so far by
several authors.Comment: 18 pages, 6 figure
Superconductivity in metal rich Li-Pd-B ternary Boride
8K superconductivity was observed in the metal rich Li-Pd-B ternary system.
Structural, microstructural, electrical and magnetic investigations for various
compositions proved that Li2Pd3B compound, which has a cubic structure composed
of distorted Pd6B octahedrons, is responsible for the superconductivity. This
is the first observation of superconductivity in metal rich ternary borides
containing alkaline metal and Pd as a late transition metal. The compound
prepared by arc melting has high density, is stable in the air and has an upper
critical field, Hc2(0), of 6T.Comment: 4 pages, 5 figur
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