1,976 research outputs found
Wide Binary Effects on Asymmetries in Asymptotic Giant Branch Circumstellar Envelopes
Observations of increasingly higher spatial resolution reveal the existence
of asymmetries in the circumstellar envelopes of a small fraction of asymptotic
giant branch (AGB) stars. Although there is no general consensus for their
origin, a binary companion star may be responsible. Within this framework, we
investigate the gravitational effects associated with a sufficiently wide
binary system, where Roche lobe overflow is unimportant, on the outflowing
envelopes of AGB stars using three dimensional hydrodynamic simulations. The
effects due to individual binary components are separately studied, enabling
investigation of the stellar and circumstellar characteristics in detail. The
reflex motion of the AGB star alters the wind velocity distribution, thereby,
determining the overall shape of the outflowing envelope. On the other hand,
the interaction of the companion with the envelope produces a gravitational
wake, which exhibits a vertically thinner shape. The two patterns overlap and
form clumpy structures. To illustrate the diversity of shapes, we present the
numerical results as a function of inclination angle. Not only is spiral
structure produced by the binary interaction, but arc patterns are also found
that represent the former structure when viewed at different inclinations. The
arcs reveal a systematic shift of their centers of curvature for cases when the
orbital speed of the AGB star is comparable to its wind speed. They take on the
shape of a peanut for inclinations nearly edge-on. In the limit of slow orbital
motion of the AGB star relative to the wind speed, the arc pattern becomes
nearly spherically symmetric. We find that the aspect ratio of the overall
oblate shape of the pattern is an important diagnostic probe of the binary as
it can be used to constrain the orbital velocity of the AGB star, and moreover
the binary mass ratio.Comment: 33 pages, 11 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Rindler horizon entropy from nonstationarity
Finite entropy and energy are obtained for the horizon of a Rindler observer
on the grounds of the nonstatic character of the geometry beyond the horizon.
Edery - Constantineau prescription is used to find the dynamical phase space of
this particular spacetime. The number of microstates rooted from the ignorance
of a Rindler observer of the parameter from the nonstationary region is
calculated.
We suggest that the gravitational energy density constructed by means of the
horizon energy and using the Holographic Principle is proportional to ,
similar with a result recently obtained by Padmanabhan and with the energy
density of the electromagnetic field.Comment: 8 pages, no figures, version published in PLB 703(5),(2011) pp.
641-644, DOI: 10.1016/j.physletb.2011.08.06
A Deep 150 MHz GMRT Survey in Eridanus
We present results of a 150 MHz survey of a field centered on Epsilon
Eridani, undertaken with the Giant Metrewave Radio Telescope (GMRT). The survey
covers an area with a diameter of 2 deg, has a spatial resolution of 30" and a
noise level of 3.1 mJy at the pointing centre. These observations provide a
deeper and higher resolution view of the 150 MHz radio sky than the 7C survey
(although the 7C survey covers a much larger area). A total of 113 sources were
detected, most are point-like, but 20 are extended. We present an analysis of
these sources, in conjunction with the NVSS (at 1.4 GHz) and VLSS (at 74 MHz).
This process allowed us to identify 5 Ultra Steep Spectrum (USS) radio sources
that are candidate high redshift radio galaxies (HzRGs). In addition, we have
derived the dN/dS distribution for these observations and compare our results
with other low frequency radio surveys.Comment: 12 pages, 11 figures, 3 tables, accepted for publication in MNRA
The desiccation-tolerant vascular plants' paradox: the role of environmental constraints on the diversity and distribution of plants able to resurrect from dryness
The desiccation-tolerant vascular plants (DT plants) are often perceived as plants able to deal with environmental harshness and paradigms concerning ecological aspects of desiccation tolerance have been developed. Here, we discuss the ecology of DT plants, testing untested paradigms and fulfilling knowledge gaps regarding their ecology and conservation by combining biogeographical and functional approaches from a taxonomic, phylogenetic, and conservation perspective.Die austrocknungstoleranten Gefäßpflanzen (AT-Pflanzen) werden oft als Pflanzen angesehen, die in der Lage sind, mit Umweltrauheiten umzugehen, und es wurden Paradigmen bezüglich ökologischer Aspekte der Austrocknungstoleranz entwickelt. Hier wurde die Ökologie von AT-Pflanzen diskutiert, ungetestete Paradigmen getestet und Wissenslücken bezüglich ihrer Ökologie und Erhaltung geschlossen
Rotation of the Solar System planets and the origin of the Moon in the context of the tidal downsizing hypothesis
It has been proposed recently that the first step in the formation of both
rocky and gas giant planets is dust sedimentation into a solid core inside a
gas clump (giant planet embryo). The clumps are then assumed to migrate closer
to the star where their metal poor envelopes are sheared away by the tidal
forces or by an irradiation-driven mass loss. We consider the implications of
this hypothesis for natal rotation rates of both terrestrial and gas giant
planets. It is found that both types of planets may rotate near their break up
angular frequencies at birth. The direction of the spin should coincide with
that of the parent disc and the star, except in cases of embryos that had close
interactions or mergers with other embryos in the past. Furthermore, the large
repository of specific angular momentum at birth also allows formation of close
binary rocky planets inside the same embryos. We compare these predictions with
rotation rates of planets in the Solar System and also question whether the
Earth-Moon pair could have been formed within the same giant planet embryo.Comment: latex typo corrected -- Fig2a and Fig3a were switched by error in the
previous versio
Enterocin 416K1, an antilisterial bacteriocin produced by Enterococcus casseliflavus IM 416K1 isolated from Italian sausages.
Enterococci (118) from Italian sausages were tested for the production of antimicrobial substances. Of these, 7.6\% showed antibacterial activity against one or several closely related microorganisms used as indicators. Enterococcus casseliflavus IM 416K1 in particular produced a bacteriocin (Enterocin 416K1) with strong anti-listerial antagonistic activity. The bacteriocin withstood heating at 90 degrees C for 120 min and storage at 4 degrees C for 6 months. The mode of action was identified as bactericidal. The crude activity of Enterocin 416K1 was linked to a molecule with an apparent molecular weight smaller than 5 kDa. Plasmid analysis of E. casseliflavus IM 416K1 revealed the presence of four plasmids with different molecular weights (34, 11, 7 and 3.3 MDa). All the Bac- variants produced by curing experiments showed loss of the single plasmid of 34 MDa. Bacteriocin activity and immunity production may be linked to genes located on that same plasmid
Inhibition of Multidrug-Resistant Gram-Positive and Gram-Negative Bacteria by a Photoactivated Porphyrin
The authors studied the in vitro antibacterial activity of the photo-activated porphyrin meso-tri(N-methyl-pyridyl), mono(N-tetradecyl-pyridyl)porphine (C14) against four multidrug-resistant bacteria: Staphylococcus aureus, Enterococcus faecalis (Gram-positive), Escherichia coli, Pseudomonas aeruginosa (Gram-negative). Using 10 g/ml of porphyrin and 60 sec irradiation we observed the remarkable susceptibility of S. aureus and E. faecalis to treatment while, under the same conditions, E. coli and P. aeruginosa showed very low susceptibility. In a later stage, suspensions of Gram-negative bacteria were processed with EDTA before photo-activation, obtaining a significant decrease in viable counts. In view of the results, if the combination of low porphyrin concentrations and short irradiation times will be effective in vivo also, this approach could be a possible alternative to antibiotics, in particular against localized infections due to multidrug-resistant microorganisms
AGN in deep radio/X-ray surveys: hunting the earliest massive galaxies
Despite the plethora of deep (sub-mJy) radio surveys there remains
considerable doubt as to the exact nature of the galaxies contributing to the
source counts. Current evidence suggests that starformation in moderately
luminous 'normal' galaxies is responsible for the bulk of the emission below
1mJy. However given the sensitivities of these surveys we would expect a
fraction of these sources to be distant radio galaxies. Using deep VLA and GMRT
data we have found ~20 high-z candidate radio galaxies in two fields using the
classical ultra-steep radio spectrum technique (De Breuck et al., 2000) and
selecting galaxies with faint (i'>25) optical counterparts. Several of these
sources have X-ray detections in our deep XMM/Chandra observations and have
fluxes high enough to put them in the quasar regime if they lie above redshift
3. Recently performed Spitzer GTO observations and upcoming near-infrared
observations will help reveal the nature of these sources.Comment: 4 pages, 5 figures, "Granada Workshop on High Redshift Radiogalaxies
Study of five penicillinase producing Neisseria gonorrhoeae isolated in Italy.
Five penicillinase producing Neisseria gonorrhoeae (PPNG) were isolated from urethral specimens of men admitted to the "Santa Chiara" Hospital (Trento, Italy). All strains proved to be resistant to penicillin and ampicillin, and sensitive to cefuroxime, erythromycin, tetracycline, spectinomycin, nalidixic acid and ciprofloxacin. PPNG plasmid profiles showed that four of the isolates carried the 3.2 MDa "Africa" plasmid and one the 4.5 MDa "Asia" plasmid, the two well-known phenotypes reported in the USA and Europe as well as in Asian and African countries. Membrane matings were performed using N. gonorrhoeae carrying the 24.5 MDa conjugative plasmid as donors and E. coli K12 J 53 as recipient. The transfer of beta-lactamic antibiotic resistance was supported by the presence of 4.5 or 3.2 MDa plasmid bands and by beta-lactamase production in the transconjugants. Restriction analysis of Asian and African plasmids is reported
Study of two bacteriocins produced by Enterococcus casseliflavus and Ent. faecalis.
The antimicrobial activity of two plasmid-borne bacteriocins produced by Enterococcus casseliflavus IM 416K1 and Ent. faecalis IM 388C and their mating transferability were studied.Both bacteriocins showed antibacterial activity against taxonomically related micro-organisms and Listeria monocytogenes but differ for heat sensitivity, antimicrobial titre, molecular size and class of affiliation. The transferability by mating of the antibacterial properties from producers to Enterococcus faecalis JH2-2 revealed that the bacteriocin-phenotype was linked in both strains to genes located on a 34 MDa plasmid. This result was confirmed by loss of antibacterial activity and immunity after curing treatment.Restriction analysis has shown a different profile of the two conjugative plasmids. Enterocin 416K1 and Enterocin 388C could represent natural antilisterial agents to use in food technology.The transferability of the 34 MDa conjugative plasmids might be considered a possibility for the study of bacteriocins expression in bacterial hosts different from the native strains
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