2,117 research outputs found
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
Hablamos Juntos (Together We Speak): Interpreters, Provider Communication, and Satisfaction with Care
The Hablamos Juntos—Together We Speak (HJ)—national demonstration project targeted the improvement of language access for Spanish-speaking Latinos in areas with rapidly growing Latino populations. The objective of HJ was to improve doctor-patient communication by increasing access to and quality of interpreter services for Spanish-speaking patients.
To investigate how access to interpreters for adult Spanish-speaking Latinos is associated with ratings of doctor/office staff communication and satisfaction with care.
Cross-sectional cohort study.
A total of 1,590 Spanish-speaking Latino adults from eight sites across the United States who participated in the outpatient HJ evaluation.
We analyzed two multi-item measures of doctor communication (4 items) and office staff helpfulness (2 items), and one global item of satisfaction with care by interpreter use. We performed regression analyses to control for patient sociodemographic characteristics, survey year, and clustering at the site of care.
Ninety-five percent of participants were born outside the US, 81% were females, and survey response rates ranged from 45% to 85% across sites. In this cohort of Spanish-speaking patients, those who needed and always used interpreters reported better experiences with care than their counterparts who needed but had interpreters unavailable. Patients who always used an interpreter had better adjusted ratings of doctor communication [effect size (ES = 0.51)], office staff helpfulness (ES = 0.37), and satisfaction with care (ES = 0.37) than patients who needed but did not always use an interpreter. Patients who needed and always used interpreters also reported better experiences with care in all three domains measured [doctor communication (ES = 0.30), office staff helpfulness (ES = 0.21), and satisfaction with care (ES = 0.23)] than patients who did not need interpreters.
Among adult Spanish-speaking Latinos, interpreter use is independently associated with higher satisfaction with doctor communication, office staff helpfulness, and ambulatory care. Increased attention to the need for effective interpreter services is warranted in areas with rapidly growing Spanish-speaking populations
Supersymmetric AdS_4 black holes and attractors
Using the general recipe given in arXiv:0804.0009, where all timelike
supersymmetric solutions of N=2, D=4 gauged supergravity coupled to abelian
vector multiplets were classified, we construct the first examples of genuine
supersymmetric black holes in AdS_4 with nonconstant scalar fields. This is
done for various choices of the prepotential, amongst others for the STU model.
These solutions permit to study the BPS attractor flow in AdS. We also
determine the most general supersymmetric static near-horizon geometry and
obtain the attractor equations in gauged supergravity. As a general feature we
find the presence of flat directions in the black hole potential, i.e.,
generically the values of the moduli on the horizon are not completely
specified by the charges. For one of the considered prepotentials, the
resulting moduli space is determined explicitely. Still, in all cases, we find
that the black hole entropy depends only on the charges, in agreement with the
attractor mechanism.Comment: 25 pages, uses JHEP3.cl
A procedure for the change point problem in parametric models based on phi-divergence test-statistics
This paper studies the change point problem for a general parametric,
univariate or multivariate family of distributions. An information theoretic
procedure is developed which is based on general divergence measures for
testing the hypothesis of the existence of a change. For comparing the accuracy
of the new test-statistic a simulation study is performed for the special case
of a univariate discrete model. Finally, the procedure proposed in this paper
is illustrated through a classical change-point example
Introduction to Configuration Path Integral Monte Carlo
In low-temperature high-density plasmas quantum effects of the electrons are
becoming increasingly important. This requires the development of new
theoretical and computational tools. Quantum Monte Carlo methods are among the
most successful approaches to first-principle simulations of many-body quantum
systems. In this chapter we present a recently developed method---the
configuration path integral Monte Carlo (CPIMC) method for moderately coupled,
highly degenerate fermions at finite temperatures. It is based on the second
quantization representation of the -particle density operator in a basis of
(anti-)symmetrized -particle states (configurations of occupation numbers)
and allows to tread arbitrary pair interactions in a continuous space.
We give a detailed description of the method and discuss the application to
electrons or, more generally, Coulomb-interacting fermions. As a test case we
consider a few quantum particles in a one-dimensional harmonic trap. Depending
on the coupling parameter (ratio of the interaction energy to kinetic energy),
the method strongly reduces the sign problem as compared to direct path
integral Monte Carlo (DPIMC) simulations in the regime of strong degeneracy
which is of particular importance for dense matter in laser plasmas or compact
stars. In order to provide a self-contained introduction, the chapter includes
a short introduction to Metropolis Monte Carlo methods and the second
quantization of quantum mechanics.Comment: chapter in book "Introduction to Complex Plasmas: Scientific
Challenges and Technological Opportunities", Michael Bonitz, K. Becker, J.
Lopez and H. Thomsen (Eds.) Springer Series "Atomic, Optical and Plasma
Physics", vol. 82, Springer 2014, pp. 153-194 ISBN: 978-3-319-05436-0 (Print)
978-3-319-05437-7 (Online
Insights from Amphioxus into the Evolution of Vertebrate Cartilage
Central to the story of vertebrate evolution is the origin of the vertebrate head, a problem difficult to approach using paleontology and comparative morphology due to a lack of unambiguous intermediate forms. Embryologically, much of the vertebrate head is derived from two ectodermal tissues, the neural crest and cranial placodes. Recent work in protochordates suggests the first chordates possessed migratory neural tube cells with some features of neural crest cells. However, it is unclear how and when these cells acquired the ability to form cellular cartilage, a cell type unique to vertebrates. It has been variously proposed that the neural crest acquired chondrogenic ability by recruiting proto-chondrogenic gene programs deployed in the neural tube, pharynx, and notochord. To test these hypotheses we examined the expression of 11 amphioxus orthologs of genes involved in neural crest chondrogenesis. Consistent with cellular cartilage as a vertebrate novelty, we find that no single amphioxus tissue co-expresses all or most of these genes. However, most are variously co-expressed in mesodermal derivatives. Our results suggest that neural crest-derived cartilage evolved by serial cooption of genes which functioned primitively in mesoderm
Nel positively regulates the genesis of retinal ganglion cells by promoting their differentiation and survival during development
Peer reviewedPublisher PD
Impacts of organic and conventional crop management on diversity and activity of free-living nitrogen fixing bacteria and total bacteria are subsidiary to temporal effects
A three year field study (2007-2009) of the diversity and numbers of the total and metabolically active free-living diazotophic bacteria and total bacterial communities in organic and conventionally managed agricultural soil was conducted at the Nafferton Factorial Systems Comparison (NFSC) study, in northeast England. The result demonstrated that there was no consistent effect of either organic or conventional soil management across the three years on the diversity or quantity of either diazotrophic or total bacterial communities. However, ordination analyses carried out on data from each individual year showed that factors associated with the different fertility management measures including availability of nitrogen species, organic carbon and pH, did exert significant effects on the structure of both diazotrophic and total bacterial communities. It appeared that the dominant drivers of qualitative and quantitative changes in both communities were annual and seasonal effects. Moreover, regression analyses showed activity of both communities was significantly affected by soil temperature and climatic conditions. The diazotrophic community showed no significant change in diversity across the three years, however, the total bacterial community significantly increased in diversity year on year. Diversity was always greatest during March for both diazotrophic and total bacterial communities. Quantitative analyses using qPCR of each community indicated that metabolically active diazotrophs were highest in year 1 but the population significantly declined in year 2 before recovering somewhat in the final year. The total bacterial population in contrast increased significantly each year. Seasonal effects were less consistent in this quantitative study
Kretzoiarctos gen. nov., the Oldest Member of the Giant Panda Clade
The phylogenetic position of the giant panda, Ailuropoda melanoleuca (Carnivora: Ursidae: Ailuropodinae), has been one of the most hotly debated topics by mammalian biologists and paleontologists during the last century. Based on molecular data, it is currently recognized as a true ursid, sister-taxon of the remaining extant bears, from which it would have diverged by the Early Miocene. However, from a paleobiogeographic and chronological perspective, the origin of the giant panda lineage has remained elusive due to the scarcity of the available Miocene fossil record. Until recently, the genus Ailurarctos from the Late Miocene of China (ca. 8–7 mya) was recognized as the oldest undoubted member of the Ailuropodinae, suggesting that the panda lineage might have originated from an Ursavus ancestor. The role of the purported ailuropodine Agriarctos, from the Miocene of Europe, in the origins of this clade has been generally dismissed due to the paucity of the available material. Here, we describe a new ailuropodine genus, Kretzoiarctos gen. nov., based on remains from two Middle Miocene (ca. 12–11 Ma) Spanish localities. A cladistic analysis of fossil and extant members of the Ursoidea confirms the inclusion of the new genus into the Ailuropodinae. Moreover, Kretzoiarctos precedes in time the previously-known, Late Miocene members of the giant panda clade from Eurasia (Agriarctos and Ailurarctos). The former can be therefore considered the oldest recorded member of the giant panda lineage, which has significant implications for understanding the origins of this clade from a paleobiogeographic viewpoint
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