4,552 research outputs found
Vector Correlators in Lattice QCD: methods and applications
We discuss the calculation of the leading hadronic vacuum polarization in
lattice QCD. Exploiting the excellent quality of the compiled experimental data
for the e^+e^- --> hadrons cross-section, we predict the outcome of
large-volume lattice calculations at the physical pion mass, and design
computational strategies for the lattice to have an impact on important
phenomenological quantities such as the leading hadronic contribution to
(g-2)mu and the running of the electromagnetic coupling constant. First, the
R(s) ratio can be calculated directly on the lattice in the threshold region,
and we provide the formulae to do so with twisted boundary conditions. Second,
the current correlator projected onto zero spatial momentum, in a Euclidean
time interval where it can be calculated accurately, provides a potentially
critical test of the experimental R(s) ratio in the region that is most
relevant for (g-2)mu. This observation can also be turned around: the vector
correlator at intermediate distances can be used to determine the lattice
spacing in fm, and we make a concrete proposal in this direction. Finally, we
quantify the finite-size effects on the current correlator coming from
low-energy two-pion states and provide a general parametrization of the vacuum
polarization on the torus.Comment: 16 pages, 9 figure files; corrected a factor 2 in Eq. (7) over the
published versio
A self-consistent theory for graphene transport
We demonstrate theoretically that most of the observed transport properties
of graphene sheets at zero magnetic field can be explained by scattering from
charged impurities. We find that, contrary to common perception, these
properties are not universal but depend on the concentration of charged
impurities . For dirty samples (), the value of the minimum
conductivity at low carrier density is indeed in agreement with early
experiments, with weak dependence on impurity concentration. For cleaner
samples, we predict that the minimum conductivity depends strongly on , increasing to for . A clear strategy to improve graphene mobility is to eliminate
charged impurities or use a substrate with a larger dielectric constant.Comment: To be published in Proc. Natl. Acad. Sci. US
Hash Functions for Episodic Recognition and Retrieval
Episodic memory systems for artificially intelligent agents must cope with an ever-growing episodic memory store. This paper presents an approach for minimizing the size of the store by using specialized hash functions to convert each memory into a relatively short binary code. A set of desiderata for such hash functions are presented including locale sensitivity and reversibility. The paper then introduces multiple approaches for such functions and compares their effectiveness
Genes Involved in Feed Efficiency Identified in a Meta-Analysis of Rumen Tissue from Two Populations of Beef Steers
In cattle, the rumen is an important site for the absorption of feed by-products released by bacterial fermentation, and variation in ruminal function plays a role in cattle feed efficiency. Studies evaluating gene expression in the rumen tissue have been performed prior to this. However, validating the expression of genes identified in additional cattle populations has been challenging. The purpose of this study was to perform a meta-analysis of the ruminal transcriptome of two unrelated populations of animals to identify genes that are involved in feed efficiency across populations. RNAseq data from animals with high and low residual feed intake (RFI) from a United States population of cattle (eight high and eight low RFI) and a Canadian population of cattle (nine high and nine low RFI) were analyzed for differences in gene expression. A total of 83 differentially expressed genes were identified. Some of these genes have been previously identified in other feed efficiency studies. These genes included ATP6AP1, BAG6, RHOG, and YPEL3. Differentially expressed genes involved in the Notch signaling pathway and in protein turnover were also identified. This study, combining two unrelated populations of cattle in a meta-analysis, produced several candidate genes for feed efficiency that may be more robust indicators of feed efficiency than those identified from single populations of animals
Silent Phase of Johne’s Disease in Experimentally Infected Goats – A Study on New and Established Diagnostic Approaches Using Specific and Non-Specific Parameters
The current gold standard diagnostic test for Johne’s disease (JD) is detecting Mycobacterium avium subsp. paratuberculosis (MAP) from fecal samples via culture and/or PCR. Other commercially available JD diagnostic tests focus on the detection of specific antibodies within the serum or milk of infected ruminants. These tests have a high specificity but low their sensitivity and usually fail to diagnose the disease until later stages of the disease. The ideal diagnostic test should detect infected animals already during the silent phase. Here, we evaluate the use of new and established approaches to define the silent phase of JD in experimentally infected goats. None of the established diagnostic tests or new approaches for the detection of humoral and cellular immune responses were positive during the first year of infection. Only the characterization of various subsets of peripheral blood leukocytes and the weight development gave some indication for the presence of a chronic, but silent, infection. Weight differences were present throughout the first year. In addition, some of the subsets of leukocytes (WC1+ T cells, MHC class II+ leukocytes, CD1+ leukocytes, CD14+ granulocytes, and CD14+/MHC class II+ granulocytes) demonstrated significant differences, but only at certain time points
Quantitative Evidence for an Intrinsic Age Spread in the Orion Nebula Cluster
Aims. We present a study of the distribution of stellar ages in the Orion
Nebula Cluster (ONC) based on accurate HST photometry taken from the HST
Treasury Program observations of the ONC utilizing the most recent estimate of
the cluster's distance (Menten et al. 2007). We investigate the presence of an
intrinsic age spread in the region and a possible trend of age with the spatial
distribution. Methods. We estimate the extinction and accretion luminosity
towards each source by performing synthetic photometry on an empirical
calibration of atmospheric models (Da Rio et al. 2010) using the package
Chorizos (Maiz-Apellaniz 2004). The position of the sources in the HR-diagram
is compared with different theoretical isochrones to estimate the mean cluster
age and age dispersion. Through Monte Carlo simulations we quantify the amount
of intrinsic age spread in the region, taking into account uncertainties on the
distance, spectral type, extinction, unresolved binaries, accretion and
photometric variability. Results. According to Siess et al. (2000) evolutionary
models the mean age of the Cluster is 2.2 Myr with a scatter of few Myrs. With
Monte Carlo simulations we find that the observed age spread is inconsistent
with a coeval stellar population, but is in agreement with a star formation
activity between 1.5 and 3.5 Myrs. We also observe light evidence for a trend
of ages with spatial distribution.Comment: 12 pages, 12 figures, Accepted for publication in Astronomy and
Astrophysic
WALLABY Early Science - I. The NGC 7162 Galaxy Group
We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early
science results from the Australian Square Kilometre Array Pathfinder (ASKAP)
observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia
Telescope Compact Array (ATCA) observations of this group to validate the new
ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in
the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership
from four to seven galaxies. Two of the new detections are also the first HI
detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7,
for which we have measured velocities of and km s,
respectively. We confirm that there is extended HI emission around NGC 7162
possibly due to past interactions in the group as indicated by the
offset between the kinematic and morphological major axes for NGC 7162A, and
its HI richness. Taking advantage of the increased resolution (factor of
) of the ASKAP data over archival ATCA observations, we fit a tilted
ring model and use envelope tracing to determine the galaxies' rotation curves.
Using these we estimate the dynamical masses and find, as expected, high dark
matter fractions of for all group members. The
ASKAP data are publicly available.Comment: 20 pages, 11 figures, accepted for publication in MNRA
Data Linkage to Improve Geriatric Oncology Research: A Feasibility Study
Older adults (aged 65 years and older) diagnosed with cancer account for most cancer‐related morbidity and mortality in the United States but are often underrepresented on clinical trials. Recent attention from a variety of professional, research, regulatory, and patient advocacy groups has centered on data linkage and data sharing as a means to capture patient information and outcomes outside of clinical trials to accelerate progress in the fight against cancer. The development of a more robust observational research data infrastructure would help to address gaps in the evidence base regarding optimal approaches to treating cancer among the growing and complex population of older adults. To demonstrate the feasibility of building such a resource, we linked information from a sample of older adults with cancer in North Carolina using three distinct, but complementary, data sources: (a) the Carolina Senior Registry, (b) the North Carolina Central Cancer Registry, and (c) North Carolina fee‐for‐service Medicare claims data. A description of the linkage process, metrics, and characteristics of the final cohort is reported. This study highlights the potential for data linkage to improve the characterization of health status among older adults with cancer and the possibility to conduct passive follow‐up for outcomes of interest over time. Extensions of these linkage efforts in partnership with other institutions will enhance our ability to generate evidence that can inform the management of older adults with cancer
New paradoxical games based on Brownian ratchets
Based on Brownian ratchets, a counter-intuitive phenomenon has recently
emerged -- namely, that two losing games can yield, when combined, a
paradoxical tendency to win. A restriction of this phenomenon is that the rules
depend on the current capital of the player. Here we present new games where
all the rules depend only on the history of the game and not on the capital.
This new history-dependent structure significantly increases the parameter
space for which the effect operates.Comment: 4 pages, 3 eps figures, revte
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