1,678 research outputs found
Observability of intermittent radio sources in galaxy groups and clusters
22 pages, 24 figures. This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We have carried out numerical hydrodynamic simulations of radio jets from active galactic nuclei using the PLUTO simulation code, with the aim of investigating the effect of different environments and intermittency of energy injection on the resulting dynamics and observable properties of the jet-inflated lobes. Initially conical jets are simulated in poor group and cluster environments. We show that the environment into which a radio jet is propagating plays a large role in the resulting morphology, dynamics and observable properties of the radio source. The same jet collimates much later in a poor group compared to a cluster, which leads to pronounced differences in radio morphology. The intermittency of the jet also affects the observable properties of the radio source, and multiple hotspots are present for multiple outburst jets in the cluster environment. We quantify the detectability of active and quiescent phases, and find this to be strongly environment-dependent. We conclude that the dynamics and observational properties of jets depend strongly on the details of energy injection and environment.Peer reviewedFinal Accepted Versio
Evolution of HII regions in hierarchically structured molecular clouds
We present observations of the H91 recombination line emission
towards a sample of nine HII regions associated with 6.7-GHz methanol masers,
and report arcsecond-scale emission around compact cores. We derive physical
parameters for our sources, and find that although simple hydrostatic models of
region evolution reproduce the observed region sizes, they significantly
underestimate emission measures. We argue that these findings are consistent
with young source ages in our sample, and can be explained by existence of
density gradients in the ionised gas.Comment: 11 pages, 6 figures; accepted for publication in MNRA
Ecophysiology of halophytes: questions and challenges
Halophytes are able to tolerate and even benefit from salt concentrations that kill most other plant species and, at the very least, may provide genes that allow transgenic conference of salinity tolerance to crops. In addition, some halophytes have already been tested as vegetable, forage and oilseed crops. However, physiological mechanisms behind the remarkable ability of halophytes to live in highly saline environment are not fully understood. This talk highlights some unanswered questions and challenges in understanding halophyte physiology, with a specific emphasis on complexity of plant-environmental interaction
Magnetic fields in galaxies: I. Radio disks in local late-type galaxies
We develop an analytical model to follow the cosmological evolution of
magnetic fields in disk galaxies. Our assumption is that fields are amplified
from a small seed field via magnetohydrodynamical (MHD) turbulence. We further
assume that this process is fast compared to other relevant timescales, and
occurs principally in the cold disk gas. We follow the turbulent energy density
using the Shabala & Alexander (2009) galaxy formation and evolution model.
Three processes are important to the turbulent energy budget: infall of cool
gas onto the disk and supernova feedback increase the turbulence; while star
formation removes gas and hence turbulent energy from the cold gas. Finally, we
assume that field energy is continuously transferred from the incoherent random
field into an ordered field by differential galactic rotation. Model
predictions are compared with observations of local late type galaxies by Fitt
& Alexander (1993) and Shabala et al. (2008). The model reproduces observed
magnetic field strengths and luminosities in low and intermediate-mass
galaxies. These quantities are overpredicted in the most massive hosts,
suggesting that inclusion of gas ejection by powerful AGNs is necessary in
order to quench gas cooling and reconcile the predicted and observed magnetic
field strengths.Comment: 10 pages, 8 figures; MNRAS in pres
Difference in root K+ retention ability and reduced sensitivity of K+ -permeable channels to reactive oxygen species confer differential salt tolerance in three Brassica species
Brassica species are known to possess significant inter and intraspecies variability in salinity stress tolerance, but the cell-specific mechanisms conferring this difference remain elusive. In this work, the role and relative contribution of several key plasma membrane transporters to salinity stress tolerance were evaluated in three Brassica species (B.
napus, B. juncea, and B. oleracea) using a range of electrophysiological assays. Initial root growth assay and viability staining revealed that B. napus was most tolerant amongst the three species, followed by B. juncea and B. oleracea. At the mechanistic level, this difference was conferred by at least three complementary physiological mechanisms: (i) higher Na+ extrusion ability from roots resulting from increased expression and activity of plasma membrane SOS1-like Na+/H+ exchangers; (ii) better root K+ retention ability resulting from stress-inducible activation of H+-ATPase and ability to maintain more negative membrane potential under saline conditions; and (iii) reduced sensitivity of B. napus root K+ -permeable channels to reactive oxygen species (ROS). The last two mechanisms played the dominant role and conferred most of the differential salt sensitivity between species. Brassica napus plants were also more efficient in preventing the stress-induced increase in GORK transcript levels and up-regulation of expression of AKT1, HAK5, and HKT1 transporter genes. Taken together, our data provide the mechanistic explanation for differential salt stress
sensitivity amongst these species and shed light on transcriptional and post-translational regulation of key ion transport systems involved in the maintenance of the root plasma membrane potential and cytosolic K/Na ratio as a key attribute for salt tolerance in Brassica species
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