1,223 research outputs found
Municipal investment in off-road trails and changes in bicycle commuting in Minneapolis, Minnesota over 10Â years: a longitudinal repeated cross-sectional study
Abstract Background We studied the effect of key development and expansion of an off-road multipurpose trail system in Minneapolis, Minnesota between 2000 and 2007 to understand whether infrastructure investments are associated with increases in commuting by bicycle. Methods We used repeated measures regression on tract-level (Nâ=â116 tracts) data to examine changes in bicycle commuting between 2000 and 2008â2012. We investigated: 1) trail proximity measured as distance from the trail system and 2) trail potential use measured as the proportion of commuting trips to destinations that might traverse the trail system. All analyses (performed 2015â2016) adjusted for tract-level sociodemographic covariates and contemporaneous cycling infrastructure changes (e.g., bicycle lanes). Results Tracts that were both closer to the new trail system and had a higher proportion of trips to destinations across the trail system experienced greater 10-year increases in commuting by bicycle. Conclusions Proximity to off-road infrastructure and travel patterns are relevant to increased bicycle commuting, an important contributor to overall physical activity. Municipal investment in bicycle facilities, especially off-road trails that connect a cityâs population and its employment centers, is likely to lead to increases in commuting by bicycle
Quantum error-correcting codes and 4-dimensional arithmetic hyperbolic manifolds
Using 4-dimensional arithmetic hyperbolic manifolds, we construct some new
homological quantum error correcting codes. They are LDPC codes with linear
rate and distance . Their rate is evaluated via Euler
characteristic arguments and their distance using -systolic
geometry. This construction answers a queston of Z\'emor, who asked whether
homological codes with such parameters could exist at all.Comment: 21 page
On the Quantum Computational Complexity of the Ising Spin Glass Partition Function and of Knot Invariants
It is shown that the canonical problem of classical statistical
thermodynamics, the computation of the partition function, is in the case of
+/-J Ising spin glasses a particular instance of certain simple sums known as
quadratically signed weight enumerators (QWGTs). On the other hand it is known
that quantum computing is polynomially equivalent to classical probabilistic
computing with an oracle for estimating QWGTs. This suggests a connection
between the partition function estimation problem for spin glasses and quantum
computation. This connection extends to knots and graph theory via the
equivalence of the Kauffman polynomial and the partition function for the Potts
model.Comment: 8 pages, incl. 2 figures. v2: Substantially rewritte
The Massive Star Clusters in the Dwarf Merger ESO 185-IG13: is the Red Excess Ubiquitous in Starbursts?
We have investigated the starburst properties of the luminous blue compact
galaxy ESO 185-IG13. The galaxy has been imaged with the high resolution
cameras onboard to the Hubble Space Telescope. From the UV to the IR, the data
reveal a system shaped by hundreds of young star clusters, and fine structures,
like a tidal stream and a shell. The presence of numerous clusters and the
perturbed morphology indicate that the galaxy has been involved in a recent
merger event. Using previous simulations of shell formation in galaxy mergers
we constrain potential progenitors of ESO 185-IG13. The analysis of the star
cluster population is used to investigate the properties of the present
starburst and to date the final merger event, which has produced hundreds of
clusters younger than 100 Myr. We have found a peak of cluster formation only
3.5 Myr old. A large fraction of these clusters will not survive after 10-20
Myr, due to the "infant mortality" caused by gas expulsion. However, this
sample of clusters represents an unique chance to investigate the youngest
phases of cluster evolution. As already observed in the analog blue compact
galaxy Haro 11, a fraction of young clusters are affected by a flux excess at
wavelengths longer than 8000 \AA. Ages, masses, and extinctions of clusters
with this NIR excess are estimated from UV and optical data. We discuss
similarities and differences of the observed NIR excess in ESO 185-IG13
clusters with other cases in the literature. The cluster ages and masses are
used to distinguish among the potential causes of the excess. We observe, as in
Haro 11, that the use of the IR and the (commonly used) I band data results in
overestimates of age and mass in clusters affected by the NIR excess. This has
important implications for a number of related studies of star clusters.Comment: 23 pages, 16 figures, accepted for publication in MNRA
Completing the nuclear reaction puzzle of the nucleosynthesis of 92Mo
One of the greatest questions for modern physics to address is how elements
heavier than iron are created in extreme, astrophysical environments. A
particularly challenging part of that question is the creation of the so-called
p-nuclei, which are believed to be mainly produced in some types of supernovae.
The lack of needed nuclear data presents an obstacle in nailing down the
precise site and astrophysical conditions. In this work, we present for the
first time measurements on the nuclear level density and average strength
function of Mo. State-of-the-art p-process calculations systematically
underestimate the observed solar abundance of this isotope. Our data provide
stringent constraints on the NbMo reaction rate,
which is the last unmeasured reaction in the nucleosynthesis puzzle of
Mo. Based on our results, we conclude that the Mo abundance
anomaly is not due to the nuclear physics input to astrophysical model
calculations.Comment: Submitted to PR
Chiral-symmetry restoration in the linear sigma model at nonzero temperature and baryon density
We study the chiral phase transition in the linear sigma model with 2 quark
flavors and colors. One-loop calculations predict a first-order phase
transition at both and . We also discuss the phase diagram
and make a comparison with a thermal parametrization of existing heavy-ion
experimental data.Comment: 12 pages, 6 ps-figures, LaTe
MicrobiotaâDependent Metabolite Trimethylamine NâOxide and Coronary Artery Calcium in the Coronary Artery Risk Development in Young Adults Study (CARDIA)
BACKGROUND: Clinical studies implicate trimethylamine N-oxide (TMAO; a gut microbiota-dependent nutrient metabolite) in cardiovascular disease risk. There is a lack of population-based data on the role of TMAO in advancing early atherosclerotic disease. We tested the prospective associations between TMAO and coronary artery calcium (CAC) and carotid intima-media thickness (cIMT).
METHODS AND RESULTS: Data were from the Coronary Artery Risk Development in Young Adults Study (CARDIA), a biracial cohort of US adults recruited in 1985-1986 (n=5115). We randomly sampled 817 participants (aged 33-55Â years) who attended examinations in 2000-2001, 2005-2006, and 2010-2011, at which CAC was measured by computed tomography and cIMT (2005-2006) by ultrasound. TMAO was quantified using liquid chromotography mass spectrometry on plasma collected in 2000-2001. Outcomes were incident CAC, defined as Agatston units=0 in 2000-2001 and >0 over 10-year follow-up, CAC progression (any increase over 10-year follow-up), and continuous cIMT. Over the study period, 25% (n=184) of those free of CAC in 2000-2001 (n=746) developed detectable CAC. In 2000-2001, median (interquartile range) TMAO was 2.6 (1.8-4.2) ÎŒmol/L. In multivariable-adjusted models, TMAO was not associated with 10-year CAC incidence (rate ratio=1.03; 95% CI: 0.71-1.52) or CAC progression (0.97; 0.68-1.38) in Poisson regression, or cIMT (beta coefficient: -0.009; -0.03 to 0.01) in linear regression, comparing the fourth to the first quartiles of TMAO.
CONCLUSIONS: In this population-based study, TMAO was not associated with measures of atherosclerosis: CAC incidence, CAC progression, or cIMT. These data indicate that TMAO may not contribute significantly to advancing early atherosclerotic disease risk among healthy early-middle-aged adults
Star cluster formation and evolution in Mrk 930: properties of a metal-poor starburst
We present a HST multiband analysis of the large population of star clusters
in the blue compact galaxy (BCG) Mrk 930. We have reconstructed the spectral
energy distributions of the star clusters and estimated age, mass, and
extinction for a representative sample. We observe a very young cluster
population with 70% of the systems formed less than 10 Myr ago. The peak in the
star cluster age distribution at 4 Myr is corroborated by the presence of
Wolf-Rayet spectral features, and by the observed optical and IR lines ratios
[OIII]/H_beta and [NeIII]/[NeII]. The recovered extinction in these very young
clusters shows large variations, with a decrease at older ages. It is likely
that our analysis is limited to the optically brightest objects (i.e. systems
only partially embedded in their natal cocoons). We map the extinction across
the galaxy using low-resolution spectra and the H_alpha/H_beta ratio, as
obtained from ground-based narrow band imaging. We find that the mean optical
extinction derived in the starburst regions is close to the averaged value
observed in the clusters, but locally, do not trace the more extinguished
clusters. Previous HST studies of BCGs have revealed a population of young and
extremely red super star clusters. We detect a considerable fraction of
clusters affected by a red excess also in Mrk 930. The nature of the red
excess, which turns up at near-IR wavelengths remains unknown. We compare the
cluster and the star formation history, the latter derived from the fit of
spectral population synthesis models to the spectra. We find a general
agreement between the two independently estimated quantities. Using the cluster
properties we perform a study of the host environmental properties. We find
that the cluster formation efficiency is significantly higher, suggesting a key
role of the environment for the formation of these massive objects.[Abridged]Comment: 21 pages, 16 figures, accepted for publication in MNRAS. For
high-resolution figures ask the author
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