4,417 research outputs found
Local solutions in Sobolev spaces with negative indices for the "good" Boussinesq equation
We study the local well-posedness of the initial-value problem for the
nonlinear "good" Boussinesq equation with data in Sobolev spaces \textit{}
for negative indices of .Comment: Referee comments incorporate
Perceptions of the impact of the COVID-19 pandemic on the work of science journalists: global perspectives
The article presents the results of a survey of science journalists from six world regions about their work during the COVID-19 pandemic. The responses show perception of increasing workload for most participants. Local scientists and peer-reviewed articles are the main sources. According to the respondents, scientists have become more available during the pandemic. The use of preprint articles was a frequent practice, but a considerable proportion declared they did not adopt different procedures when reporting them. Most also said they take fake news into account when writing their stories.info:eu-repo/semantics/publishedVersio
Cluster vs. Field Elliptical Galaxies and Clues on their Formation
Using new observations for a sample of 931 early-type galaxies we investigate
whether the \mg2--\so relation shows any dependence on the local environment.
The galaxies have been assigned to three different environments depending on
the local overdensity: clusters, groups, and field, having used our
completeredshift database to guide the assignment of galaxies. It is found that
cluster, group and field early-type galaxies follow almost identical \mg2--\so\
relations, with the largest \mg2 zero-point difference (clusters minus field)
being only mag. No correlation of the residuals is found with
the morphological type or the bulge to disk ratio. Using stellar population
models in a differential fashion, this small zero-point difference implies a
luminosity-weighted age difference of only Gyr between the
corresponding stellar populations, with field galaxies being younger. The
mass-weighted age difference could be significantly smaller, if minor events of
late star formation took place preferentially in field galaxies. We combine
these results with the existing evidence for the bulk of stars in cluster
early-type galaxies having formed at very high redshift, and conclude that the
bulk of stars in galactic spheroids had to form at high redshifts (z\gsim 3),
no matter whether such spheroids now reside in low or high density regions. The
cosmological implications of these findings are briefly discussed.Comment: 16 pages, 2 figures, accepted for publication in the ApJ.
The Negative Dimensional Oscillator at Finite Temperature
We study the thermal behavior of the negative dimensional harmonic oscillator
of Dunne and Halliday that at zero temperature, due to a hidden BRST symmetry
of the classical harmonic oscillator, is shown to be equivalent to the
Grassmann oscillator of Finkelstein and Villasante. At finite temperature we
verify that although being described by Grassmann numbers the thermal behavior
of the negative dimensional oscillator is quite different from a Fermi system.Comment: 8 pages, IF/UFRJ/93/0
On the physical interpretation of effective actions using Schwinger's formula
We show explicitly that Schwinger's formula for one-loop effective actions
corresponds to the summation of energies associated with the zero-point
oscillations of the fields. We begin with a formal proof, and after that we
confirm it using a regularization prescription.Comment: 5 p., REVTEX, IF-UFRJ-9
Sistema para estimação de área plantada por amostragem - SEARA - proposta de delineamento amostral para café em São Paulo e para grãos em Minas Gerais.
A informação precisa e atualizada referente à produção agrícola brasileira é importante e estratégica, tanto do ponto de vista econômico como da segurança alimentar. O aumento da disponibilidade de imagens de sensoriamento remoto, bem como outros avanços tecnológicos recentes, como os sistemas de informação geográfica (SIGs) e os aparelhos de posicionamento global (GPS), podem facilitar a obtenção de estimativas de área plantada, um componente fundamental da previsão de safras, e permitir o acesso a uma informação essencial em aplicações ambientais: a localização espacial dos cultivos. Embora a previsão oficial de safras no Brasil ainda seja realizada de forma subjetiva, existe um esforço da Companhia Nacional de Abastecimento (CONAB) para o aperfeiçoamento metodológico do sistema de previsão, que inclui o Projeto GeoSafras. A presente pesquisa, que pretende contribuir para esse esforço, é baseada numa abordagem que associa a amostragem estatística, imagens de satélite, SIG e GPS, e que foi desenvolvida preliminarmente pela Embrapa Meio Ambiente para estimar, de forma objetiva e probabilística, a área plantada com determinada cultura em um Município.bitstream/CNPMA/6300/1/documentos_49.pd
The Motions of Clusters of Galaxies and the Dipoles of the Peculiar Velocity Field
In preceding papers of this series, TF relations for galaxies in 24 clusters
with radial velocities between 1000 and 9200 km/s (SCI sample) were obtained, a
Tully-Fisher (TF) template relation was constructed and mean offsets of each
cluster with respect to the template obtained. Here, an estimate of the
line-of-sight peculiar velocities of the clusters and their associated errors
are given. It is found that cluster peculiar velocities in the Cosmic Microwave
Background reference frame do not exceed 600 k/ms and that their distribution
has a line-of-sight dispersion of 300 k/ms, suggesting a more quiescent cluster
peculiar velocity field than previously reported. When measured in a reference
frame in which the Local Group is at rest, the set of clusters at cz > 3000
km/s exhibits a dipole moment in agreement with that of the CMB, both in
amplitude and apex direction. It is estimated that the bulk flow of a sphere of
6000 km/s radius in the CMB reference frame is between 140 and 320 km/s. These
results are in agreement with those obtained from an independent sample of
field galaxies (Giovanelli et al. 1998; see astro-ph/9807274)Comment: 9 pages, 2 tables, 7 figures, uses AAS LaTex; to appear in A
Using Lean to Counteract Complexity
Based on a literature review and drawing from the experience of lean implementation in multipleconstruction projects, this paper explores the notion that simplicity and integrality might be crucial for anyproduction system seeking to develop competences against variations derived from both internal andexternal sources. A discussion using different systems thinking approaches is conducted to provide a betterunderstanding of the volatile behaviour of complex organizations. The aim is to encourage initiatives thataddress organizational simplicity and integrality in construction projects and, more important, to highlightthe important role of lean tools and principles for this endeavour
Agreement between BMI and body fat obesity definitions in a physically active population
Body mass index (BMI) is a widely used proxy of body composition (BC). Concerns exist regarding possible BMI misclassification among active populations. We compared the prevalence of obesity as categorized by BMI or by skinfold estimates of body fat percentage (BF%) in a physically active population. Subjects and methods 3,822 military firefighters underwent a physical fitness evaluation including cardiorespiratory fitness (CRF) by the 12 min-Cooper test, abdominal strength by sit-up test (SUT) and body composition (BC) by BF% (as the reference), as well as BMI. Obesity was defined by BF% > 25% and BMI ≥ 30 kg/m2. Agreement was evaluated by sensitivity and specificity of BMI, positive and negative predictive values (PPV/NPV), positive and negative likelihood (LR+/LR-), receiver operating characteristic (ROC) curves and also across age, CRF and SUT subgroups. Results The prevalence of obesity estimated by BMI (13.3%) was similar to BF% (15.9%). Overall agreement was high (85.8%) and varied in different subgroups (75.3-94.5%). BMI underestimated the prevalence of obesity in all categories with high specificity (≥ 81.2%) and low sensitivity (≤ 67.0). All indices were affected by CRF, age and SUT, with better sensitivity, NPV and LR- in the less fit and older groups; and higher specificity, PPV and LR+ among the fittest and youngest groups. ROC curves showed high area under the curve (≥ 0.77) except for subjects with CRF ≥ 14 METs (= 0.46). Conclusion Both measures yielded similar obesity prevalences, with high agreement. BMI did not overestimate obesity prevalence. BMI ≥ 30 was highly specific to exclude obesity. Because of systematic under estimation, a lower BMI cut-off point might be considered in this population
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