1,632 research outputs found
On the population of remnant FRII radio galaxies and implications for radio source dynamics
The purpose of this work is two-fold: (1) to quantify the occurrence of
ultra-steep spectrum remnant FRII radio galaxies in a 74 MHz flux limited
sample, and (2) perform Monte-Carlo simulations of the population of active and
remnant FRII radio galaxies to confront models of remnant lobe evolution, and
provide guidance for further investigation of remnant radio galaxies. We find
that fewer than 2 of FRII radio galaxies with S Jy are
candidate ultra-steep spectrum remnants, where we define ultra-steep spectrum
as . Our Monte-Carlo simulations
demonstrate that models involving Sedov-like expansion in the remnant phase,
resulting in rapid adiabatic energy losses, are consistent with this upper
limit, and predict the existence of nearly twice as many remnants with normal
(not ultra-steep) spectra in the observed frequency range as there are
ultra-steep spectrum remnants. This model also predicts an ultra-steep remnant
fraction approaching 10 at redshifts . Importantly, this model
implies the lobes remain over-pressured with respect to the ambient medium well
after their active lifetime, in contrast with existing observational evidence
that many FRII radio galaxy lobes reach pressure equilibrium with the external
medium whilst still in the active phase. The predicted age distribution of
remnants is a steeply decreasing function of age. In other words young remnants
are expected to be much more common than old remnants in flux limited samples.
For this reason, incorporating higher frequency data GHz will be of
great benefit to future studies of the remnant population.Comment: 19 pages, 8 figures, 4 table
The LOFAR view of massive early-type galaxies: Transition from radio AGN to host emission
We extend the study of the radio emission in early-type galaxies (ETGs) in
the nearby Universe (recession velocity <7,500 km/s) as seen by the 150 MHz
Low-Frequency ARray (LOFAR) observations and extend the sample from giant ETGs
to massive (~6x10^10 - 3x10^11 solar masses) ETGs (mETGS) with -25 < MK <
-23.5. Images from the second data release of the LOFAR Two-metre Sky Survey
were available for 432 mETGs, 48% of which are detected above a typical
luminosity of ~3x10^20 W/Hz. Most (85%) of the detected sources are compact,
with sizes <4 kpc. The radio emission of 31 mETGs is extended on scales ranging
from 2 to 180 kpc (median 12 kpc). In several cases, it is aligned with the
host galaxy. We set a limit of ~1% to the fraction of remnant or restarted
objects, which is ~16% of the extended sources.
We found that the properties of the radio sources are connected with the
stellar mass of the ETGs (the median radio power, the fraction of extended
radio sources, and the link with the large-scale environment). However, these
results only describe statistical trends because the radio properties of
sources of similar stellar mass and environment show a large spread of radio
properties. These trends break at the lowest host luminosities (MK>-24.5). This
effect is strengthened by the analysis of even less massive ETGs, with -23.5 <
MK < -21.5. This suggests that at a mass of ~2x10^11 solar masses, a general
transition occurs from radio emission produced from radio-loud active galactic
nuclei (AGN) to processes related to the host galaxy and (or) radio quiet AGN.
At this luminosity, a transition in the stellar surface brightness profile also
occurs from Sersic galaxies to those with a depleted stellar core, the
so-called core galaxies. This finding is in line with previous results that
indicated that only core galaxies host radio-loud AGN.Comment: Pre-proofs version - Accepted for publication in A&
Respostas morfofisiológicas de plantas de açacu (Hura crepitans L.) provenientes de várzeas do Rio Amazonas: efeito da anoxia do solo.
Neste trabalho foram avaliadas as respostas morfofisiológicas de plantas de açacu (Hura crepitans) sob a anoxia do solo com diferentes idades (90 e 120 dias) e períodos de inundação (0, 10, 20 e 30 dias). O estudo identificou que as plantas desenvolveram mecanismos adaptativos (estruturas morfológicas como lenticelas hipertróficas e raízes adventícias) e apresentaram comportamento fisiológico que lhes propiciaram tolerância à anoxia. As respostas das plantas ao excesso de água no solo incluíram inibição do crescimento vegetativo, clorose e senescência foliar. O estresse hídrico por anoxia comprometeu a viabilidade das plantas de 90 dias de idade, enquanto as plantas de açacu de 120 dias de idade mostraram-se tolerantes ao alagamento
Perioperative hemodynamic goal-directed therapy and mortality: a systematic review and meta-analysis with meta-regression
INTRODUCTION: Recent data found that perioperative goal directed therapy (GDT) was effective only in higher control mortality rates (> 20%) with a relatively high heterogeneity that limited the strength of evidence. The aim of the present meta-analysis was to clearly understand which high risk patients may benefit of GDT.EVIDENCE ACQUISITION: Systematic review of randomized controlled trials with meta-analyses, including a meta-regression technique. MEDLINE, EMBASE, and The Cochrane Library databases were searched (1980-January 2015). Trials enrolling adult surgical patients and comparing the effects of GDT versus standard hemodynamic therapy were considered. The primary outcome measure was mortality. Data synthesis was obtained by using Odds Ratio (OR) with 95% confidence interval (CI) by random-effects model.EVIDENCE SYNTHESIS: Fifty eight studies met the inclusion criteria (8171 participants). Pooled OR for mortality was 0.70 (95% CI 0.56-0.88, P= 0.002, no statistical heterogeneity). GDT significantly reduced mortality when it is > 10% in control group (OR 0.43, 95% CI 0.30-0.61, P< 0.00001). The meta-regression model showed that the cut off of 10% of mortality rate in control group significantly differentiates 43 studies from the other 15, with a regression coefficient b of -0.033 and a P value of 0.0001. The significant effect of GDT was driven by high risk of bias studies (OR 0.48, 95% CI 0.34-0.67, P< 0.0001).CONCLUSIONS: The present meta-analysis, adopting the meta-regression technique, suggests that GDT significantly reduces mortality even when the event control rate is > 10%
Seleção de ideótipos de espécies florestais de múltiplo uso em planícies fluviais do Baixo Amazonas, Pará.
A pesquisa objetivou selecionar ideótipos arbóreos de múltiplo uso, baseado em informações etnobotânicas de comunidades ribeirinhas de planícies fluviais do Baixo Amazonas, Pará, para uso em sistemas silvipastoris. Como essas áreas foram antropizadas pela agricultura seguida da pecuária, esses sistemas são considerados alternativas viáveis para sua recuperação. Por meio de pesquisa participativa junto aos ribeirinhos, foi utilizado um questionário semi-estruturado para determinar as espécies arbóreas de maior importância para essas populações, enfocando sua finalidade e formas de uso, consumidor destino e a abundância nas comunidades estudadas. As espécies florestais de interesse dos ribeirinhos concentraram-se nas frutíferas, para alimentação humana e animal, seguidas daquelas com função madeireira. Em sua grande maioria, essas espécies são utilizadas internamente na propriedade, não gerando produtos excedentes e foram consideradas, pelos entrevistados como de ?grande" abundância na região
Enriching fallow vegetation in the eastern Amazon of Brazil: towards improving land-use.
Editado por Reinhard Lieberei, Helmut Bianchi, Vera Boehm, Christoph Reisdorff
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