26,262 research outputs found
Sub-arcsecond Morphology of Planetary Nebulae
Planetary nebulae (PNe) can be roughly categorized into several broad
morphological classes. The high quality images of PNe acquired in recent years,
however, have revealed a wealth of fine structures that preclude simplistic
models for their formation. Here we present narrow-band, sub-arcsecond images
of a sample of relatively large PNe that illustrate the complexity and variety
of small-scale structures. This is especially true for bipolar PNe, for which
the images reveal multi-polar ejections and, in some cases, suggest turbulent
gas motions. Our images also reveal the presence or signs of jet-like outflows
in several objects in which this kind of component has not been previously
reported.Comment: 7 pages, 7 figures, Accepted for publication in PAS
An updated catalog of OH-maser-emitting planetary nebulae
Aims. We studied the characteristics of planetary nebulae (PNe) that show
both OH maser and radio continuum emission (hereafter OHPNe). These have been
proposed to be very young PNe, and therefore, they could be key objects for
understanding the formation and evolution of PNe. Methods. We consulted the
literature searching for interferometric observations of radio continuum and OH
masers toward evolved stars, including the information from several surveys. We
also processed radio continuum and OH maser observations toward PNe in the Very
Large Array data archive. The high positional accuracy provided by
interferometric observations allow us to confirm or reject the association
between OH maser and radio continuum emission. Results. We found a total of six
PNe that present both OH maser and radio continuum emissions, as confirmed with
radio interferometric observations. These are bona fide OHPNe. The confirmed
OHPNe present a bipolar morphology in resolved images of their ionized emission
at different wavelengths, suggesting that the OH maser emission in PNe is
related to nonspherical mass-loss phenomena. The OH maser spectra in PNe
present a clear asymmetry, tending to show blueshifted emission with respect to
the systemic velocity. Their infrared colors suggest that most of these objects
are very young PNe. OHPNe do not form a homogeneous group, and seem to
represent a variety of different evolutionary stages. We suggest that OH masers
pumped in the AGB phase may disappear during the post-AGB phase, but reappear
once the source becomes a PN and its radio continuum emission is amplified by
the OH molecules. Therefore, OH maser emission could last significantly longer
than the previously assumed 1000 yr after the end of the AGB phase. This maser
lifetime may be longer in PNe with more massive central stars, which ionize a
larger amount of gas in the envelope.Comment: 16 pages, 5 figures, 4 tables. Accepted for publication by Astronomy
& Astrophysic
On-off intermittency and amplitude-phase synchronization in Keplerian shear flows
We study the development of coherent structures in local simulations of the
magnetorotational instability in accretion discs in regimes of on-off
intermittency. In a previous paper [Chian et al., Phys. Rev. Lett. 104, 254102
(2010)], we have shown that the laminar and bursty states due to the on-off
spatiotemporal intermittency in a one-dimensional model of nonlinear waves
correspond, respectively, to nonattracting coherent structures with higher and
lower degrees of amplitude-phase synchronization. In this paper we extend these
results to a three-dimensional model of magnetized Keplerian shear flows.
Keeping the kinetic Reynolds number and the magnetic Prandtl number fixed, we
investigate two different intermittent regimes by varying the plasma beta
parameter. The first regime is characterized by turbulent patterns interrupted
by the recurrent emergence of a large-scale coherent structure known as
two-channel flow, where the state of the system can be described by a single
Fourier mode. The second regime is dominated by the turbulence with sporadic
emergence of coherent structures with shapes that are reminiscent of a
perturbed channel flow. By computing the Fourier power and phase spectral
entropies in three-dimensions, we show that the large-scale coherent structures
are characterized by a high degree of amplitude-phase synchronization.Comment: 17 pages, 10 figure
Emergent SU(3) symmetry in random spin-1 chains
We show that generic SU(2)-invariant random spin-1 chains have phases with an
emergent SU(3) symmetry. We map out the full zero-temperature phase diagram and
identify two different phases: (i) a conventional random singlet phase (RSP) of
strongly bound spin pairs (SU(3) "mesons") and (ii) an unconventional RSP of
bound SU(3) "baryons", which are formed, in the great majority, by spin trios
located at random positions. The emergent SU(3) symmetry dictates that
susceptibilities and correlation functions of both dipolar and quadrupolar spin
operators have the same asymptotic behavior.Comment: 5 pages plus 3-page Supplemental Material, 5 figures; published
versio
The importance of community development for health and well-being
Public health - Economic aspects
Impact of acute and long-term exposure to oxybenzone on the Caenorhabditis elegans life history
UV-filters are the active ingredients providing weatherproofing to industrial products and UV-light protection in personal care products such as sun-tan lotions. Sun-tan lotions products are commonly recommended to protect the skin from the sun’s damaging rays however their increasing prevalence in drinking water and aquatic
environments has raised concern regarding their effect on both human and environmental health. The common UV-filter Oxybenzone (BP-3) has been highlighted as a compound of particular concern due to its high prevalence, its known toxicity in aquatic species and its ability to accumulate in the active sludge of waste-water treatment plants. Here, we investigate for the first time the effect of BP-3 on the
fecundity and growth of the terrestrial nematode Caenorhabditis elegans and develop a novel method of modelling the UV-filter pollution associated with the use of UV-filter contaminated active sludge as fertilizer. Our results show that four hour BP-3 exposure did not affect reproductive health at environmentally relevant concentrations (experimental concentrations of 50, 100, 250 and 500 μg/L) however, two of three replicates demonstrated a significant effect of BP-3 (experimental concentrations of
500, 1000, 1500, 2000 μg/L) on total C. elegans fecundity. One replicate also demonstrated that nematodes acutely exposed to 500 μg/L of BP-3 were significantly larger than those measured before the experiment, potentially suggesting an effect on the nematodes ability to control osmolarity. It was found that BP-3 did not influence the growth of C.elegans, which contradicts previous research. This highlights the need for further investigation into BP-3 toxicity. Finally, it was found that in one of the replicates, the nematodes exposed to E. coli contaminated with 1500 μg/L BP-3 were significantly smaller than those exposed to E. coli contaminated with 1000 μg/L BP-3,suggesting the need for further investigation into the potential environmental risks associated with UV-filter pollution originating from active sludge. In conclusion the
research conducted in this project provides a novel insight into BP-3 toxicity and the development of a universal toxicity model, which could provide reasoning for the
implementation of restrictions on dangerous UV-filters both in localised areas but also internationally
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