1,397 research outputs found
SN 2011hw: Helium-Rich Circumstellar Gas and the Luminous Blue Variable to Wolf-Rayet Transition in Supernova Progenitors
We present optical photometry and spectroscopy of the peculiar Type IIn/Ibn
supernova SN2011hw. Its light curve exhibits a slower decline rate than normal
SNeIbc, with a peak absolute magnitude of -19.5 (unfiltered) and a secondary
peak of -18.3 mag (R). Spectra of SN2011hw are unusual compared to normal SN
types, most closely resembling the spectra of SNeIbn. We center our analysis on
comparing SN 2011hw to the well-studied TypeIbn SN2006jc. While the two SNe
have many important similarities, the differences are quite telling: compared
to SN2006jc, SN2011hw has weaker HeI and CaII lines and relatively stronger H
lines, its light curve has a higher luminosity and slower decline rate, and
emission lines associated with the progenitor's CSM are narrower. One can
reproduce the unusual continuum shape of SN2011hw with equal contributions of a
6000K blackbody and a spectrum of SN2006jc. We attribute this emission
component and many other differences between the two SNe to extra opacity from
a small amount of additional H in SN2011hw, analogous to the small H mass that
makes SNeIIb differ from SNeIb. Slower speeds in the CSM and elevated H content
suggest a connection between the progenitor of SN2011hw and the class of
Ofpe/WN9 stars, which have been associated with LBVs in their hot quiescent
phases between outbursts, and are H-poor - but not H-free like classical
Wolf-Rayet (WR) stars. We conclude that the similarities and differences
between SN2011hw and SN2006jc can be largely understood if their progenitors
exploded at different points in the transitional evolution from an LBV to a WR
star.Comment: 11 pages, 7 figures, submitted to MNRA
FLUORESCENCE STUDIES ON PHOTOSYNTHETIC PIGMENT DEVELOPMENT IN RHODOPSEUDOMONAS SPHEROIDES * , â€
When bleached, aerobically grown cells of Rhodopseudomonas spheroides are transferred to semi-aerobic conditions to induce bacteriochlorophyll synthesis, a new fluorescence band, with a maximum at 790 nm, is observed in addition to the 885 nm emission maximum normally seen in pigmented cells. The 790 nm fluorescence may be due to bacterio-chlorophyll which has not been bound into the chromatophore membrane. The quantum yield of the 885 nm fluorescence is at first relatively high and then, about 1 hour after transfer, drops to the level found in pigmented photosynthetic cells. The coupling to the rest of the photo-synthetic apparatus, as indicated by the effect of dithionite on the fluorescence, also seems to occur during the first hour of pigment development, which suggests that the onset of fluorescence quenching is due at least in part to the synthesis of photochemical reaction centers. Continuation of these studies should provide new information on the formation, structure and molecular interactions of the pigments and the photosynthetic membranes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73322/1/j.1751-1097.1968.tb08021.x.pd
Dust Production and Particle Acceleration in Supernova 1987A Revealed with ALMA
Supernova (SN) explosions are crucial engines driving the evolution of
galaxies by shock heating gas, increasing the metallicity, creating dust, and
accelerating energetic particles. In 2012 we used the Atacama Large
Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed
supernovae since the invention of the telescope. We present spatially resolved
images at 450um, 870um, 1.4mm, and 2.8mm, an important transition wavelength
range. Longer wavelength emission is dominated by synchrotron radiation from
shock-accelerated particles, shorter wavelengths by emission from the largest
mass of dust measured in a supernova remnant (>0.2Msun). For the first time we
show unambiguously that this dust has formed in the inner ejecta (the cold
remnants of the exploded star's core). The dust emission is concentrated to the
center of the remnant, so the dust has not yet been affected by the shocks. If
a significant fraction survives, and if SN 1987A is typical, supernovae are
important cosmological dust producers.Comment: ApJL accepte
Reaction rate uncertainties and 26Al in AGB silicon carbide stardust
Stardust is a class of presolar grains each of which presents an ideally
uncontaminated stellar sample. Mainstream silicon carbide (SiC) stardust formed
in the extended envelopes of carbon-rich asymptotic giant branch (AGB) stars
and incorporated the radioactive nucleus 26Al as a trace element. The aim of
this paper is to analyse in detail the effect of nuclear uncertainties, in
particular the large uncertainties of up to four orders of magnitude related to
the 26Al_g+(p,gamma)27Si reaction rate, on the production of 26Al in AGB stars
and compare model predictions to data obtained from laboratory analysis of SiC
stardust grains. Stellar uncertainties are also briefly discussed. We use a
detailed nucleosynthesis postprocessing code to calculate the 26Al/27Al ratios
at the surface of AGB stars of different masses (M = 1.75, 3, and 5 M_sun) and
metallicities (Z = 0.02, 0.012, and 0.008). For the lower limit and recommended
value of the 26Al_g(p,gamma)27Si reaction rate, the predicted 26Al/27Al ratios
replicate the upper values of the range of the 26Al/27Al ratios measured in SiC
grains. For the upper limit of the 26Al_g(p,gamma)27Si reaction rate, instead,
the predicted 26Al/27Al ratios are approximately 100 times lower and lie below
the range observed in SiC grains. When considering models of different masses
and metallicities, the spread of more than an order of magnitude in the
26Al/27Al ratios measured in stellar SiC grains is not reproduced. We propose
two scenarios to explain the spread of the 26Al/27Al ratios observed in
mainstream SiC, depending on the choice of the 26Al_g+p reaction rate. One
involves different times of stardust formation, the other involves extra-mixing
processes. Stronger conclusions will be possible after more information is
available from future nuclear experiments on the 26Al_g+p reaction.Comment: 6 pages, 5 Postscript figures, accepted for publication in Astronomy
and Astrophysic
On the asymptotic giant branch star origin of peculiar spinel grain OC2
Microscopic presolar grains extracted from primitive meteorites have
extremely anomalous isotopic compositions revealing the stellar origin of these
grains. The composition of presolar spinel grain OC2 is different from that of
all other presolar spinel grains. Large excesses of the heavy Mg isotopes are
present and thus an origin from an intermediate-mass (IM) asymptotic giant
branch (AGB) star was previously proposed for this grain. We discuss the
isotopic compositions of presolar spinel grain OC2 and compare them to
theoretical predictions. We show that the isotopic composition of O, Mg and Al
in OC2 could be the signature of an AGB star of IM and metallicity close to
solar experiencing hot bottom burning, or of an AGB star of low mass (LM) and
low metallicity suffering very efficient cool bottom processing. Large
measurement uncertainty in the Fe isotopic composition prevents us from
discriminating which model better represents the parent star of OC2. However,
the Cr isotopic composition of the grain favors an origin in an IM-AGB star of
metallicity close to solar. Our IM-AGB models produce a self-consistent
solution to match the composition of OC2 within the uncertainties related to
reaction rates. Within this solution we predict that the 16O(p,g)17F and the
17O(p,a)14N reaction rates should be close to their lower and upper limits,
respectively. By finding more grains like OC2 and by precisely measuring their
Fe and Cr isotopic compositions, it may be possible in the future to derive
constraints on massive AGB models from the study of presolar grains.Comment: 10 pages, 8 figures, accepted for publication on Astronomy &
Astrophysic
Empathy, engagement, entrainment: the interaction dynamics of aesthetic experience
A recent version of the view that aesthetic experience is based in empathy as inner
imitation explains aesthetic experience as the automatic simulation of actions,
emotions, and bodily sensations depicted in an artwork by motor neurons in the brain. Criticizing the simulation theory for committing to an erroneous concept of empathy and failing to distinguish regular from aesthetic experiences of art, I advance an alternative, dynamic approach and claim that aesthetic experience is enacted and skillful, based in the recognition of others’ experiences as distinct from one’s own. In combining insights from mainly psychology, phenomenology, and cognitive science, the dynamic approach aims to explain the emergence of aesthetic experience in terms of the reciprocal interaction between viewer and artwork. I argue that aesthetic experience emerges by participatory sense-making and revolves around movement as a means for creating meaning. While entrainment merely plays a preparatory part in this, aesthetic engagement constitutes the phenomenological side of coupling to an artwork and provides the context for exploration, and eventually for moving, seeing, and feeling with art. I submit that aesthetic experience emerges from bodily and emotional engagement with works of art via the complementary processes of the perception–action and motion–emotion loops. The former involves the embodied
visual exploration of an artwork in physical space, and progressively structures and organizes visual experience by way of perceptual feedback from body movements made in response to the artwork. The latter concerns the movement qualities and shapes of implicit and explicit bodily responses to an artwork that cue emotion and thereby modulate over-all affect and attitude. The two processes cause the viewer to bodily and emotionally move with and be moved by individual works of art, and consequently to recognize another psychological orientation than her own, which explains how art can cause feelings of insight or awe and disclose aspects of life that are unfamiliar or novel to the viewer
A view through a window: Social relations, material objects and locality
In this article the authors ask what it would mean to think sociologically about the window as a specific material and symbolic object. Drawing on qualitative analysis of a series of comparative interviews with residents in three different streets in a diverse local area of Glasgow, they explore what the use and experience of windows tells us about their respondents’ very different relationships to the places where they live. On the one hand, the window, as a material feature of the home, helps us grasp the lived reality of class inequality and how such inequality shapes people’s day-to-day experience. On the other hand, windows are symbolically charged objects, existing at the border of the domestic and public world. For this reason, they feature in important ways in local debates over the appearance, ownership and conservation of the built environment. The article explores these struggles, and shows what they reveal about the construction of belonging in the neighbourhood, a process which is both classed and racialised at one and the same time.ESR
A Minimal Model of Metabolism Based Chemotaxis
Since the pioneering work by Julius Adler in the 1960's, bacterial chemotaxis has been predominantly studied as metabolism-independent. All available simulation models of bacterial chemotaxis endorse this assumption. Recent studies have shown, however, that many metabolism-dependent chemotactic patterns occur in bacteria. We hereby present the simplest artificial protocell model capable of performing metabolism-based chemotaxis. The model serves as a proof of concept to show how even the simplest metabolism can sustain chemotactic patterns of varying sophistication. It also reproduces a set of phenomena that have recently attracted attention on bacterial chemotaxis and provides insights about alternative mechanisms that could instantiate them. We conclude that relaxing the metabolism-independent assumption provides important theoretical advances, forces us to rethink some established pre-conceptions and may help us better understand unexplored and poorly understood aspects of bacterial chemotaxis
Delineation of Cohen Syndrome Following a Large-Scale Genotype-Phenotype Screen
Cohen syndrome is an autosomal recessive condition associated with developmental delay, facial dysmorphism, pigmentary retinopathy, and neutropenia. The pleiotropic phenotype, combined with insufficient clinical data, often leads to an erroneous diagnosis and has led to confusion in the literature. Here, we report the results of a comprehensive genotype-phenotype study on the largest cohort of patients with Cohen syndrome assembled to date. We found 22 different COH1 mutations, of which 19 are novel, in probands identified by our diagnostic criteria. In addition, we identified another three novel mutations in patients with incomplete clinical data. By contrast, no COH1 mutations were found in patients with a provisional diagnosis of Cohen syndrome who did not fulfill the diagnostic criteria (“Cohen-like” syndrome). This study provides a molecular confirmation of the clinical phenotype associated with Cohen syndrome and provides a basis for laboratory screening that will be valuable in its diagnosis
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