2,181 research outputs found
Direct and Inverse Variational Problems on Time Scales: A Survey
We deal with direct and inverse problems of the calculus of variations on
arbitrary time scales. Firstly, using the Euler-Lagrange equation and the
strengthened Legendre condition, we give a general form for a variational
functional to attain a local minimum at a given point of the vector space.
Furthermore, we provide a necessary condition for a dynamic
integro-differential equation to be an Euler-Lagrange equation (Helmholtz's
problem of the calculus of variations on time scales). New and interesting
results for the discrete and quantum settings are obtained as particular cases.
Finally, we consider very general problems of the calculus of variations given
by the composition of a certain scalar function with delta and nabla integrals
of a vector valued field.Comment: This is a preprint of a paper whose final and definite form will be
published in the Springer Volume 'Modeling, Dynamics, Optimization and
Bioeconomics II', Edited by A. A. Pinto and D. Zilberman (Eds.), Springer
Proceedings in Mathematics & Statistics. Submitted 03/Sept/2014; Accepted,
after a revision, 19/Jan/201
The 492 GHz emission of Sgr A* constrained by ALMA
We report linearly polarized continuum emission properties of Sgr A* at 492 GHz, based on the Atacama Large Millimeter Array (ALMA) observations. We used the observations of the likely unpolarized continuum emission of Titan, and the observations of C\textsc{i} line emission, to gauge the degree of spurious polarization. The Stokes I flux of 3.60.72 Jy during our run is consistent with extrapolations from the previous, lower frequency observations. We found that the continuum emission of Sgr A* at 492 GHz shows large amplitude differences between the XX and the YY correlations. The observed intensity ratio between the XX and YY correlations as a function of parallactic angle may be explained by a constant polarization position angle of 1583. The fitted polarization percentage of Sgr A* during our observational period is 14\%1.2\%. The calibrator quasar J1744-3116 we observed at the same night can be fitted to Stokes I = 252 mJy, with 7.9\%0.9\% polarization in position angle P.A. = 4.14.2. The observed polarization percentage and polarization position angle in the present work appear consistent with those expected from longer wavelength observations in the period of 1999-2005. In particular, the polarization position angle at 492 GHz, expected from the previously fitted 1677 intrinsic polarization position angle and (-5.60.7)10 rotation measure, is 155, which is consistent with our new measurement of polarization position angle within 1. The polarization percentage and the polarization position angle may be varying over the period of our ALMA 12m Array observations, which demands further investigation with future polarization observations
Activation of Ventral Tegmental Area 5-HT2C Receptors Reduces Incentive Motivation
FUNDING AND DISCLOSURE The research was funded by Wellcome Trust (WT098012) to LKH; and National Institute of Health (DK056731) and the Marilyn H. Vincent Foundation to MGM. The University of Michigan Transgenic Core facility is partially supported by the NIH-funded University of Michigan Center for Gastrointestinal Research (DK034933). The remaining authors declare no conflict of interest. ACKNOWLEDGMENTS We thank Dr Celine Cansell, Ms Raffaella Chianese and the staff of the Medical Research Facility for technical assistance. We thank Dr Vladimir Orduña for the scientific advice and technical assistance.Peer reviewedPublisher PD
Exploring common stressors in physical education
Daily stressors, or hassles, refer to the everyday environmental demands that constitute a threat or challenge, or exceed an individual’s biological or psychological capacities (Cohen et al., 1995). Increasing evidence suggests that daily stressors have a significant impact on adolescents’ educational outcomes, for example, performance, wellbeing and negative attitudes toward school, however there is limited research examining the concept of common stressors in PE lessons. As early-adolescence is a developmental period associated with decreased engagement in PE, it is important to identify the environmental stressors that may be associated with increased disengagement. The study comprised 54 secondary school students and six PE teachers from five schools in the English Midlands. Semi-structured focus groups were conducted and a thematic analysis was applied to interview transcripts. Three higher order themes were identified from the data: the social environment, the physical and organisational environment, and the performance environment. Common stressors within the social environment included, interpersonal transactions between peers, differences in effort levels during PE, and working outside one’s peer group. Stressors within the physical and organisational environment consisted of, environmental situations within the changing facilities and the availability of activities. Finally, performance environment stressors included, situations involving the difficult acquisition of physical skills, and situations where physical appearance and physical competencies were exposed. The study extends previous findings by identifying potentially threatening and frustrating, environmental demands that have not been identified in the previous literature. The current study is the first to explore the typical stressors that are experienced by students in PE
Orbital Elements and Stellar Parameters of the Active Binary UX Arietis
This is the final version of the article. Available from American Astronomical Society via the DOI in this record.Stellar activity observed as large surface spots, radio flares, or emission lines is often found in binary systems. UX
Arietis exhibits these signs of activity, originating on the K0 subgiant primary component. Our aim is to resolve the
binary, measure the orbital motion, and provide accurate stellar parameters such as masses and luminosities to aid
in the interpretation of the observed phenomena. Using the CHARA six-telescope optical long-baseline array on
Mount Wilson, California, we obtained amplitudes and phases of the interferometric visibility on baselines up to
330 m in length, resolving the two components of the binary. We reanalyzed archival Center for Astrophysics
spectra to disentangle the binary component spectra and the spectrum of the third component, which was resolved
by speckle interferometry. We also obtained new spectra with the Nordic Optical Telescope, and we present new
photometric data that we use to model stellar surface spot locations. Both interferometric visibilities and
spectroscopic radial velocities are modeled with a spotted primary stellar surface using the Wilson–Devinney code.
We fit the orbital elements to the apparent orbit and radial velocity data to derive the distance (52.1 ± 0.8 pc) and
stellar masses (MP = 1.30 0.06 M, MS = 1.14 0.06 M). The radius of the primary can be determined to be
RP = 5.6 0.1 R and that of the secondary to be RS = 1.6 0.2 R. The equivalent spot coverage of the
primary component was found to be 62% with an effective temperature 20% below that of the unspotted surface.We thank Robert Wilson (University of Florida) for providing a custom version of his code to compute images of spotted stellar surfaces and for his help with using it. This work is based upon observations obtained with the Georgia State University (GSU) Center for High Angular Resolution Astronomy (CHARA) array at Mount Wilson Observatory. The CHARA array is supported by the National Science Foundation under grant numbers AST-1211929 and AST-1411654. Institutional support has been provided by the GSU College of Arts and Sciences and the GSU Office of the Vice President for Research and Economic Development. The MIRC instrument at the CHARA array was funded by the University of Michigan. F.B., R.R., and J.D.M. acknowledge support from NSF-AST 1210972 and 1108963. G.T. acknowledges partial support from NSF grant AST-1509375. S.K. acknowledges support from an STFC Rutherford Fellowship (ST/J004030/1) and ERC Starting Grant (grant agreement no. 639889). This work is also based on observations made with the Nordic Optical Telescope (NOT), operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. This research has made use of the SIMBAD database, operated at the CDS, Strasbourg, France. This research has made use of the Jean-Marie Mariotti Center SearchCal service13 codeveloped by FIZEAU and LAOG/IPAG and of the CDS astronomical databases SIMBAD and VIZIER.14 This research has made use of the Washington Double Star Catalog, maintained at the U.S. Naval Observatory. We thank Nicholas Elias II for discussions. We thank Dimitri Pourbaix for maintaining and providing access to the SB9 database of RV measurements of spectroscopic binaries
MTN-001: Randomized Pharmacokinetic Cross-Over Study Comparing Tenofovir Vaginal Gel and Oral Tablets in Vaginal Tissue and Other Compartments
Background: Oral and vaginal preparations of tenofovir as pre-exposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) infection have demonstrated variable efficacy in men and women prompting assessment of variation in drug concentration as an explanation. Knowledge of tenofovir concentration and its active form, tenofovir diphosphate, at the putative vaginal and rectal site of action and its relationship to concentrations at multiple other anatomic locations may provide key information for both interpreting PrEP study outcomes and planning future PrEP drug development. Objective: MTN-001 was designed to directly compare oral to vaginal steady-state tenofovir pharmacokinetics in blood, vaginal tissue, and vaginal and rectal fluid in a paired cross-over design. Methods and Findings: We enrolled 144 HIV-uninfected women at 4 US and 3 African clinical research sites in an open label, 3-period crossover study of three different daily tenofovir regimens, each for 6 weeks (oral 300 mg tenofovir disoproxil fumarate, vaginal 1% tenofovir gel [40 mg], or both). Serum concentrations after vaginal dosing were 56-fold lower than after oral dosing (p<0.001). Vaginal tissue tenofovir diphosphate was quantifiable in ≥90% of women with vaginal dosing and only 19% of women with oral dosing. Vaginal tissue tenofovir diphosphate was ≥130-fold higher with vaginal compared to oral dosing (p<0.001). Rectal fluid tenofovir concentrations in vaginal dosing periods were higher than concentrations measured in the oral only dosing period (p<0.03). Conclusions: Compared to oral dosing, vaginal dosing achieved much lower serum concentrations and much higher vaginal tissue concentrations. Even allowing for 100-fold concentration differences due to poor adherence or less frequent prescribed dosing, vaginal dosing of tenofovir should provide higher active site concentrations and theoretically greater PrEP efficacy than oral dosing; randomized topical dosing PrEP trials to the contrary indicates that factors beyond tenofovir's antiviral effect substantially influence PrEP efficacy. Trial Registration: ClinicalTrials.gov NCT00592124
Niche as a determinant of word fate in online groups
Patterns of word use both reflect and influence a myriad of human activities
and interactions. Like other entities that are reproduced and evolve, words
rise or decline depending upon a complex interplay between {their intrinsic
properties and the environments in which they function}. Using Internet
discussion communities as model systems, we define the concept of a word niche
as the relationship between the word and the characteristic features of the
environments in which it is used. We develop a method to quantify two important
aspects of the size of the word niche: the range of individuals using the word
and the range of topics it is used to discuss. Controlling for word frequency,
we show that these aspects of the word niche are strong determinants of changes
in word frequency. Previous studies have already indicated that word frequency
itself is a correlate of word success at historical time scales. Our analysis
of changes in word frequencies over time reveals that the relative sizes of
word niches are far more important than word frequencies in the dynamics of the
entire vocabulary at shorter time scales, as the language adapts to new
concepts and social groupings. We also distinguish endogenous versus exogenous
factors as additional contributors to the fates of words, and demonstrate the
force of this distinction in the rise of novel words. Our results indicate that
short-term nonstationarity in word statistics is strongly driven by individual
proclivities, including inclinations to provide novel information and to
project a distinctive social identity.Comment: Supporting Information is available here:
http://www.plosone.org/article/fetchSingleRepresentation.action?uri=info:doi/10.1371/journal.pone.0019009.s00
High energy emission from microquasars
The microquasar phenomenon is associated with the production of jets by X-ray
binaries and, as such, may be associated with the majority of such systems. In
this chapter we briefly outline the associations, definite, probable, possible,
and speculative, between such jets and X-ray, gamma-ray and particle emission.Comment: Contributing chapter to the book Cosmic Gamma-Ray Sources, K.S. Cheng
and G.E. Romero (eds.), to be published by Kluwer Academic Publishers,
Dordrecht, 2004. (19 pages
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