5,569 research outputs found
Keck Spectroscopy of Gravitationally Lensed z=4 Galaxies: Improved Constraints on the Escape Fraction of Ionizing Photons
The fraction of ionizing photons that escape from young star-forming galaxies
is one of the largest uncertainties in determining the role of galaxies in
cosmic reionization. Yet traditional techniques for measuring this fraction are
inapplicable at the redshifts of interest due to foreground screening by the
Lyman alpha forest. In an earlier study, we demonstrated a reduction in the
equivalent width of low-ionization absorption lines in composite spectra of
Lyman break galaxies at z=4 compared to similar measures at z=3. This might
imply a lower covering fraction of neutral gas and hence an increase with
redshift in the escape fraction of ionizing photons. However, our spectral
resolution was inadequate to differentiate between several alternative
explanations, including changes with redshift in the outflow kinematics. Here
we present higher quality spectra of 3 gravitationally lensed Lyman break
galaxies at z=4 with a spectral resolution sufficient to break this degeneracy
of interpretation. We present a method for deriving the covering fraction of
low-ionization gas as a function of outflow velocity and compare the results
with similar quality data taken for galaxies at lower redshift. We find a
significant trend of lower covering fractions of low-ionization gas for
galaxies with strong \Lya emission. In combination with the demographic trends
of \Lya emission with redshift from our earlier work, our results provide new
evidence for a reduction in the average H I covering fraction, and hence an
increase in the escape fraction of ionizing radiation from Lyman break
galaxies, with redshift.Comment: submitted to Ap
Cholesterol dependence of HTLV-I infection
Cholesterol-rich plasma membrane microdomains are important for entry of many viruses, including retro-viruses. Depletion of cholesterol with 2-hydroxypropyl-β-cyclodextrin inhibits entry of human T cell leukemia virus type I (HTLV-1) and HTLV-I envelope pseudotyped lentivirus particles. Using a soluble fusion protein of the HTLV-I surface envelope protein with the immunoglobulin Fc domain, the HTLV-I receptor was found to colocalize with a raft-associated marker and to cluster in specific plasma membrane microdomains. Depletion of cholesterol did not alter receptor binding activity, suggesting a requirement for cholesterol in a postbinding virus entry step
Towards global data products of Essential Biodiversity Variables on species traits
Essential Biodiversity Variables (EBVs) allow observation and reporting of global biodiversity change, but a detailed framework for the empirical derivation of specific EBVs has yet to be developed. Here, we re-examine and refine the previous candidate set of species traits EBVs and show how traits related to phenology, morphology, reproduction, physiology and movement can contribute to EBV operationalization. The selected EBVs express intra-specific trait variation and allow monitoring of how organisms respond to global change. We evaluate the societal relevance of species traits EBVs for policy targets and demonstrate how open, interoperable and machine-readable trait data enable the building of EBV data products. We outline collection methods, meta(data) standardization, reproducible workflows, semantic tools and licence requirements for producing species traits EBVs. An operationalization is critical for assessing progress towards biodiversity conservation and sustainable development goals and has wide implications for data-intensive science in ecology, biogeography, conservation and Earth observation
A spectrum of physics-informed Gaussian processes for regression in engineering
Despite the growing availability of sensing and data in general, we remain
unable to fully characterise many in-service engineering systems and structures
from a purely data-driven approach. The vast data and resources available to
capture human activity are unmatched in our engineered world, and, even in
cases where data could be referred to as ``big,'' they will rarely hold
information across operational windows or life spans. This paper pursues the
combination of machine learning technology and physics-based reasoning to
enhance our ability to make predictive models with limited data. By explicitly
linking the physics-based view of stochastic processes with a data-based
regression approach, a spectrum of possible Gaussian process models are
introduced that enable the incorporation of different levels of expert
knowledge of a system. Examples illustrate how these approaches can
significantly reduce reliance on data collection whilst also increasing the
interpretability of the model, another important consideration in this context
Intra-Rater and Inter-Rater Reliability of Pressure Pain Algometry of the Sural and Tibial Nerves in Asymptomatic Elite Youth Footballers
Ankle injuries are highly prevalent in elite youth footballers and increase the mechanosensitivity of the local neural tissue, which may predispose athletes to re-injury and prolong rehabilitation periods. Increased neural mechanosensitivity presents clinically as altered pain pressure thresholds (PPTs) which are measured with pressure algometry. The purpose of this study was to determine the intra-rater and inter-rater reliability of PPTs of the ankle neural tissue in asymptomatic elite youth football players. Three raters utilised a digital algometer to evaluate the PPTs of the Sural and Tibial nervous tissue at the ankle of elite youth male footballers. Intraclass correlation coefficients (ICCs) with 95% confidence intervals (CI) were calculated to assess intra-rater and inter-rater reliability and Bland–Altman figures were plotted to enable visual evaluation of measurement error with a significance level of p < 0.05. Thirty-four players (16–18 years old) were assessed. Excellent intra-rater (Tibial ICC 0.88 (0.76–0.94); Sural ICC 0.89 (0.79–0.95)) and good inter-rater reliability (Tibial ICC 0.66 (0.40–0.82); Sural 0.71 (0.50–0.85)) was demonstrated. Bland–Altman plots demonstrated low levels of measurement error. Pressure algometry can be utilised clinically to accurately evaluate the PPTs of the Tibial and Sural nervous tissue at the ankle in asymptomatic elite male youth footballers
Radiocarbon age-offsets in an arctic lake reveal the long-term response of permafrost carbon to climate change
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 119 (2014): 1630–1651, doi:10.1002/2014JG002688.Continued warming of the Arctic may cause permafrost to thaw and speed the decomposition of large stores of soil organic carbon (OC), thereby accentuating global warming. However, it is unclear if recent warming has raised the current rates of permafrost OC release to anomalous levels or to what extent soil carbon release is sensitive to climate forcing. Here we use a time series of radiocarbon age-offsets (14C) between the bulk lake sediment and plant macrofossils deposited in an arctic lake as an archive for soil and permafrost OC release over the last 14,500 years. The lake traps and archives OC imported from the watershed and allows us to test whether prior warming events stimulated old carbon release and heightened age-offsets. Today, the age-offset (2 ka; thousand of calibrated years before A.D. 1950) and the depositional rate of ancient OC from the watershed into the lake are relatively low and similar to those during the Younger Dryas cold interval (occurring 12.9–11.7 ka). In contrast, age-offsets were higher (3.0–5.0 ka) when summer air temperatures were warmer than present during the Holocene Thermal Maximum (11.7–9.0 ka) and Bølling-Allerød periods (14.5–12.9 ka). During these warm times, permafrost thaw contributed to ancient OC depositional rates that were ~10 times greater than today. Although permafrost OC was vulnerable to climate warming in the past, we suggest surface soil organic horizons and peat are presently limiting summer thaw and carbon release. As a result, the temperature threshold to trigger widespread permafrost OC release is higher than during previous warming events.National Science Foundation. Grant Number: ARC-09021692015-02-2
anti-Tricyclo[4.2.1.12,5]deca-3,7-diene-9,10-dione
The title compound, C10H8O2, is a precursor to an unusual bis-homoaromatic dication and to heterodiamantanes and other oxa-cage compounds. Two independent molecules, each of which is situated on a center of symmetry, comprise the unit cell. Both molecules are in nearly identical chair conformations
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