2,205 research outputs found
Yarkovsky Drift Detections for 247 Near-Earth Asteroids
The Yarkovsky effect is a thermal process acting upon the orbits of small
celestial bodies, which can cause these orbits to slowly expand or contract
with time. The effect is subtle (da/dt ~ 10^-4 au/My for a 1 km diameter
object) and is thus generally difficult to measure. We analyzed both optical
and radar astrometry for 600 near-Earth asteroids (NEAs) for the purpose of
detecting and quantifying the Yarkovsky effect. We present 247 NEAs with
measured drift rates, which is the largest published set of Yarkovsky
detections. This large sample size provides an opportunity to examine the
Yarkovsky effect in a statistical manner. In particular, we describe two
independent population-based tests that verify the measurement of Yarkovsky
orbital drift. First, we provide observational confirmation for the Yarkovsky
effect's theoretical size dependence of 1/D, where D is diameter. Second, we
find that the observed ratio of negative to positive drift rates in our sample
is 2.34, which, accounting for bias and sampling uncertainty, implies an actual
ratio of . This ratio has a vanishingly small probability of
occurring due to chance or statistical noise. The observed ratio of retrograde
to prograde rotators is two times lower than the ratio expected from numerical
predictions from NEA population studies and traditional assumptions about the
sense of rotation of NEAs originating from various main belt escape routes. We
also examine the efficiency with which solar energy is converted into orbital
energy and find a median efficiency in our sample of 12%. We interpret this
efficiency in terms of NEA spin and thermal properties.Comment: 27 pages, 9 figures, published in the Astronomical Journal, 159, 92,
202
Sleep Disturbances and Glucose Metabolism in Older Adults: The Cardiovascular Health Study.
ObjectiveWe examined the associations of symptoms of sleep-disordered breathing (SDB), which was defined as loud snoring, stopping breathing for a while during sleep, and daytime sleepiness, and insomnia with glucose metabolism and incident type 2 diabetes in older adults.Research design and methodsBetween 1989 and 1993, the Cardiovascular Health Study recruited 5,888 participants ≥65 years of age from four U.S. communities. Participants reported SDB and insomnia symptoms yearly through 1989-1994. In 1989-1990, participants underwent an oral glucose tolerance test, from which insulin secretion and insulin sensitivity were estimated. Fasting glucose levels were measured in 1989-1990 and again in 1992-1993, 1994-1995, 1996-1997, and 1998-1999, and medication use was ascertained yearly. We determined the cross-sectional associations of sleep symptoms with fasting glucose levels, 2-h glucose levels, insulin sensitivity, and insulin secretion using generalized estimated equations and linear regression models. We determined the associations of updated and averaged sleep symptoms with incident diabetes in Cox proportional hazards models. We adjusted for sociodemographics, lifestyle factors, and medical history.ResultsObserved apnea, snoring, and daytime sleepiness were associated with higher fasting glucose levels, higher 2-h glucose levels, lower insulin sensitivity, and higher insulin secretion. The risk of the development of type 2 diabetes was positively associated with observed apnea (hazard ratio [HR] 1.84 [95% CI 1.19-2.86]), snoring (HR 1.27 [95% CI 0.95-1.71]), and daytime sleepiness (HR 1.54 [95% CI 1.13-2.12]). In contrast, we did not find consistent associations between insomnia symptoms and glucose metabolism or incident type 2 diabetes.ConclusionsEasily collected symptoms of SDB are strongly associated with insulin resistance and the incidence of type 2 diabetes in older adults. Monitoring glucose metabolism in such patients may prove useful in identifying candidates for lifestyle or pharmacological therapy. Further studies are needed to determine whether insomnia symptoms affect the risk of diabetes in younger adults
Binaries in the Kuiper Belt
Binaries have played a crucial role many times in the history of modern
astronomy and are doing so again in the rapidly evolving exploration of the
Kuiper Belt. The large fraction of transneptunian objects that are binary or
multiple, 48 such systems are now known, has been an unanticipated windfall.
Separations and relative magnitudes measured in discovery images give important
information on the statistical properties of the binary population that can be
related to competing models of binary formation. Orbits, derived for 13
systems, provide a determination of the system mass. Masses can be used to
derive densities and albedos when an independent size measurement is available.
Angular momenta and relative sizes of the majority of binaries are consistent
with formation by dynamical capture. The small satellites of the largest
transneptunian objects, in contrast, are more likely formed from collisions.
Correlations of the fraction of binaries with different dynamical populations
or with other physical variables have the potential to constrain models of the
origin and evolution of the transneptunian population as a whole. Other means
of studying binaries have only begun to be exploited, including lightcurve,
color, and spectral data. Because of the several channels for obtaining unique
physical information, it is already clear that binaries will emerge as one of
the most useful tools for unraveling the many complexities of transneptunian
space.Comment: Accepted for inclusion in "The Kuiper Belt", University of Arizona
Press, Space Science Series Corrected references in Table
On the Evolution of the Velocity-Mass-Size Relations of Disk-Dominated Galaxies over the Past 10 Billion Years
We study the evolution of the scaling relations between maximum circular
velocity, stellar mass and optical half-light radius of star-forming
disk-dominated galaxies in the context of LCDM-based galaxy formation models.
Using data from the literature combined with new data from the DEEP2 and AEGIS
surveys we show that there is a consistent observational and theoretical
picture for the evolution of these scaling relations from z\sim 2 to z=0. The
evolution of the observed stellar scaling relations is weaker than that of the
virial scaling relations of dark matter haloes, which can be reproduced, both
qualitatively and quantitatively, with a simple, cosmologically-motivated model
for disk evolution inside growing NFW dark matter haloes. In this model optical
half-light radii are smaller, both at fixed stellar mass and maximum circular
velocity, at higher redshifts. This model also predicts that the scaling
relations between baryonic quantities evolve even more weakly than the
corresponding stellar relations. We emphasize, though, that this weak evolution
does not imply that individual galaxies evolve weakly. On the contrary,
individual galaxies grow strongly in mass, size and velocity, but in such a way
that they move largely along the scaling relations. Finally, recent
observations have claimed surprisingly large sizes for a number of star-forming
disk galaxies at z \sim 2, which has caused some authors to suggest that high
redshift disk galaxies have abnormally high spin parameters. However, we argue
that the disk scale lengths in question have been systematically overestimated
by a factor \sim 2, and that there is an offset of a factor \sim 1.4 between
H\alpha sizes and optical sizes. Taking these effects into account, there is no
indication that star forming galaxies at high redshifts (z\sim 2) have
abnormally high spin parameters.Comment: 19 pages, 10 figures, accepted to MNRAS, minor changes to previous
versio
Про один підхід до ідентифікації особи за контуром профілю носа
У статті розглядається підхід для ідентифікації особи за контуром профілю носа. Для знаходження простору ознак пропонується використовувати апроксимацію за допомогою B-сплайнів. Алгоритмічна реалізація підходу використовує моделювання структури бази даних у вигляді n- вимірного куба.В статье рассматривается подход для идентификации личности по контуру носа. Для нахождения пространства признаков предлагается использовать аппроксимацию с помощью B-сплайнов. Алгоритмическая реализация подхода использует моделирование структуры базы данных в виде n-мерного куба.An approach of human identification by the nose contour profile is researched in the paper. B-splines approximation is suggested for determining the feature space. Algorithmic implementation of the approach uses database structure in the form of n-dimensional cube
Chronic urban hotspots and agricultural drainage drive microbial pollution of karst water resources in rural developing regions
Contamination of surface and groundwater systems with human and animal faecal matter leads to exposure of reliant populations to disease causing micro-organisms. This exposure route remains a major cause of infection and mortality in developing countries, particularly rural regions. To meet the UN's sustainable development goal 6: Ensure availability and sustainable management of water and sanitation for all, we need to identify the key controls on faecal contamination across relevant settings. We conducted a high-resolution spatial study of E. coli concentration in catchment drainage waters over 6 months in a mixed land-use catchment in the extensive karst region extending across impoverished southwest China. Using a mixed effects modelling framework, we tested how land-use, karst hydrology, antecedent meteorological conditions, agricultural cycles, hydrochemistry, and position in the catchment system affected E. coli concentrations. Land-use was the best predictor of faecal contamination levels. Sites in urban areas were chronically highly contaminated, but water draining from agricultural land was also consistently contaminated and there was a catchment wide pulse of higher E. coli concentrations, turbidity, and discharge during paddy field drainage. E. coli concentration increased with increasing antecedent rainfall across all land-use types and compartments of the karst hydrological system (underground and surface waters), but decreased with increasing pH. This is interpreted to be a result of processes affecting pH, such as water residence time, rather than the direct effect of pH on E. coli survival. Improved containment and treatment of human waste in areas of higher population density would likely reduce contamination hotspots, and further research is needed to identify the nature and distribution of sources in agricultural land
Causality and the semantics of provenance
Provenance, or information about the sources, derivation, custody or history
of data, has been studied recently in a number of contexts, including
databases, scientific workflows and the Semantic Web. Many provenance
mechanisms have been developed, motivated by informal notions such as
influence, dependence, explanation and causality. However, there has been
little study of whether these mechanisms formally satisfy appropriate policies
or even how to formalize relevant motivating concepts such as causality. We
contend that mathematical models of these concepts are needed to justify and
compare provenance techniques. In this paper we review a theory of causality
based on structural models that has been developed in artificial intelligence,
and describe work in progress on a causal semantics for provenance graphs.Comment: Workshop submissio
Morally Respectful Listening and its Epistemic Consequences
What does it mean to listen to someone respectfully, that is, insofar as they are due recognition respect? This paper addresses that question and gives the following answer: it is to listen in such a way that you are open to being surprised. A specific interpretation of this openness to surprise is then defended
Addressing human resources for health needs to support HIV epidemic control: prioritizing site-level interventions in Democratic Republic of the Congo, 2018-2020
Introduction: The United States President's Emergency Plan for AIDS Relief (PEPFAR) in Democratic Republic of the Congo (DRC) continues to fund programs aimed at achieving epidemic control in three provinces where 30 percent of people living with HIV/AIDS in the country reside. Challenges around human resources for health impede the delivery of quality HIV/AIDS services in DRC. Methods: In partnership with the United States Health Resources and Services Administration (HRSA), PEPFAR, and DRC Ministry of Health (MoH), Columbia University's International Center for AIDS Prevention (ICAP at Columbia University) worked with 16 PEPFAR-identified high-priority health facilities and developed specific interventions to address challenges in achieving PEPFAR 95-95-95 targets. Once interventions were selected and prioritized using a collaborative, criteria-driven approach, implementation of these human resources for health improvements began alongside care and treatment efforts already underway. This study began in October 2018, and high-priority interventions were launched in July 2019. Monthly reporting of key PEPFAR metrics continues for evaluation purposes. Results: All 16 high-priority health facilities participated fully. Of several hypothesized interventions, 12 were selected as highest priority, and budgets and task plans were developed for each. The interventions were launched for implementation and evaluation within six months of Ministry of Health approval. Conclusion: This assessment delineated necessary interventions to address site-specific human resources for health challenges/deficiencies. Downstream reporting of key PEPFAR 95-95-95 metrics, including Monitoring, Evaluation, and Reporting indicators, will allow intervention teams to conduct program evaluations and their impacts on targets
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