1,078 research outputs found
The VLTI/MIDI view on the inner mass loss of evolved stars from the Herschel MESS sample
The mass-loss process from evolved stars is a key ingredient for our
understanding of many fields of astrophysics, including stellar evolution and
the chemical enrichment of the interstellar medium via stellar yields. One the
main unsolved questions is the geometry of the mass-loss process. Taking
advantage of the results from the Herschel Mass loss of Evolved StarS (MESS)
programme, we initiated a coordinated effort to characterise the geometry of
mass loss from evolved red giants at various spatial scales. For this purpose
we used the MID-infrared interferometric Instrument (MIDI) to resolve the inner
envelope of 14 asymptotic giant branch stars (AGBs) in the MESS sample. In this
contribution we present an overview of the interferometric data collected
within the frame of our Large Programme, and we also add archive data for
completeness. We studied the geometry of the inner atmosphere by comparing the
observations with predictions from different geometric models. Asymmetries are
detected for five O-rich and S-type, suggesting that asymmetries in the N band
are more common among stars with such chemistry. We speculate that this fact is
related to the characteristics of the dust grains. Except for one star, no
interferometric variability is detected, i.e. the changes in size of the shells
of non-mira stars correspond to changes of the visibility of less than 10%. The
observed spectral variability confirms previous findings from the literature.
The detection of dust in our sample follows the location of the AGBs in the
IRAS colour-colour diagram: more dust is detected around oxygen-rich stars in
region II and in the carbon stars in region VII. The SiC dust feature does not
appear in the visibility spectrum of UAnt and SSct, which are two carbon stars
with detached shells. This finding has implications for the theory of SiC dust
formation.Comment: 43 pages, 31 figures; accepted for publication in Astronomy &
Astrophysics. Abstract shortened for compilation reasons. Metadata correcte
Sigurðar saga fóts (The Saga of Sigurðr Foot): A Translation
This is the first English translation of the short Icelandic romance Sigurðar saga fóts, with an introduction presenting the evidence for its dating and immediate literary context. Like most Icelandic romances, Sigurðar saga is a bridal-quest story; the support of a foster-brother is key to the hero winning the bride; and the foster-brothers start out as opponents before recognising their mutual excellence and swearing foster-brotherhood. Uniquely, however, the men who become foster-brothers begin by competing for the same bride (Signý): the eponymous Sigurðr fótr wins Signý only because Ásmundr gives her to him in exchange for foster-brotherhood. Ásmundr’s decision can be read as demonstrating with unusual starkness the superior importance in much Icelandic romance of homosocial relationships over heterosexual ones, giving the saga a certain paradigmatic status. Translating the saga in an open-access forum and reconstructing its literary context will, we hope, encourage further analyses
Sigurðar saga fóts (The Saga of Sigurðr Foot): A Translation
This is the first English translation of the short Icelandic romance Sigurðar saga fóts, with an introduction presenting the evidence for its dating and immediate literary context. Like most Icelandic romances, Sigurðar saga is a bridal-quest story; the support of a foster-brother is key to the hero winning the bride; and the foster-brothers start out as opponents before recognising their mutual excellence and swearing foster-brotherhood. Uniquely, however, the men who become foster-brothers begin by competing for the same bride (Signý): the eponymous Sigurðr fótr wins Signý only because Ásmundr gives her to him in exchange for foster-brotherhood. Ásmundr’s decision can be read as demonstrating with unusual starkness the superior importance in much Icelandic romance of homosocial relationships over heterosexual ones, giving the saga a certain paradigmatic status. Translating the saga in an open-access forum and reconstructing its literary context will, we hope, encourage further analyses
Crushing singularities in spacetimes with spherical, plane and hyperbolic symmetry
It is shown that the initial singularities in spatially compact spacetimes
with spherical, plane or hyperbolic symmetry admitting a compact constant mean
curvature hypersurface are crushing singularities when the matter content of
spacetime is described by the Vlasov equation (collisionless matter) or the
wave equation (massless scalar field). In the spherically symmetric case it is
further shown that if the spacetime admits a maximal slice then there are
crushing singularities both in the past and in the future. The essential
properties of the matter models chosen are that their energy-momentum tensors
satisfy certain inequalities and that they do not develop singularities in a
given regular background spacetime.Comment: 19 page
Absolutely continuous multilinear operators
We introduce the new class of the (p;p1,...,pm; s)-absolutely continuous operators, that is defined using a summability property that provides the multilinear version of the (p, s)-absolutely continuous operators. We give an analogue of the Pietsch domination theorem and a multilinear version of the associated factorization theorem that holds for (p, s)-absolutely continuous operators, obtaining in this way a rich factorization theory. We present also a tensor norm which represents this multi-ideal by trace duality.
As an application, we show that (p; p1, . . . , pm; s)-absolutely continuous multilinear
operators are compact under some requirements. Applications to factorization of linear
maps on Banach function spaces through interpolation spaces are also given.EL-Hadj Dahia acknowledges with thanks the support of the Ministere de l'Enseignament Superieur et de la Recherche Scientifique (Algeria) under grant 555/PGRS/C.U.K.M. (2011) for a short term stage. D. Achour acknowledges with thanks the support of the Ministere de l'Enseignament Superieur et de la Recherche Scientifique (Algeria) under project PNR 8-U28-6543. E.A. Sanchez acknowledges with thanks the support of the Ministerio de Economia y Connpetitividad (Spain) under project #MTM2009-14483-C02-02.Dahia, E.; Achour, D.; Sánchez Pérez, EA. (2013). Absolutely continuous multilinear operators. Journal of Mathematical Analysis and Applications. 397:205-224. https://doi.org/10.1016/j.jmaa.2012.07.034S20522439
ABCC1: a gateway for pharmacological compounds to the ischaemic brain
By preventing access of drugs to the CNS, the blood-brain barrier hampers developments in brain pharmacotherapy. Strong efforts are currently being made to identify drugs that accumulate more efficaciously in ischaemic brain tissue. We identified an ATP-binding cassette (ABC) transporter, ABCC1, which is expressed on the abluminal surface of the brain capillary endothelium and mildly downregulated in response to focal cerebral ischaemia, induced by intraluminal middle cerebral artery occlusion. In biodistribution studies we show that ABCC1 promotes the accumulation of known neuroprotective and neurotoxic compounds in the ischaemic and non-ischaemic brain, ABCC1 deactivation reducing tissue concentrations by up to two orders of magnitude. As such, ABCC1's expression and functionality in the brain differs from the liver, spleen and testis, where ABCC1 is strongly expressed on parenchymal cells, resulting -- in case of liver and testis -- in directed transport from the tissue into the blood. After focal cerebral ischaemia, ABCC1 deactivation abolished the efficacy of both neuroprotective and neurotoxic compounds. Our data indicate that ABCC1 acts as gateway for pharmacological compounds to the stroke brain. We suggest that the tailoring of compounds binding to abluminal but not luminal ABC transporters may facilitate stroke pharmacotherap
Familial Transmission of a Serious Disease—Producing Group A Streptococcus Clone: Case Reports and Review
Invasive group A streptococcus (GAS) infections are emerging diseases; however, person-to-person transmission of invasive GAS producing life-threatening infection has been observed rarely. We report a small intrafamilial cluster of life-threatening GAS infections. A previously healthy 47-year-old father developed necrotizing fasciitis of the neck. Two days later, his 16-year-old daughter developed streptococcal angina, pneumonia, and pleural empyema. Both patients had signs of streptococcal toxic shock syndrome. Pulsed field gel electrophoresis revealed that the M6 strains of GAS isolated from the father and daughter had identical patterns. Cases of person-to-person transmission of invasive GAS infection reported in the literature are also reviewe
The non-convex shape of (234) Barbara, the first Barbarian
Asteroid (234) Barbara is the prototype of a category of asteroids that has
been shown to be extremely rich in refractory inclusions, the oldest material
ever found in the Solar System. It exhibits several peculiar features, most
notably its polarimetric behavior. In recent years other objects sharing the
same property (collectively known as "Barbarians") have been discovered.
Interferometric observations in the mid-infrared with the ESO VLTI suggested
that (234) Barbara might have a bi-lobated shape or even a large companion
satellite. We use a large set of 57 optical lightcurves acquired between 1979
and 2014, together with the timings of two stellar occultations in 2009, to
determine the rotation period, spin-vector coordinates, and 3-D shape of (234)
Barbara, using two different shape reconstruction algorithms. By using the
lightcurves combined to the results obtained from stellar occultations, we are
able to show that the shape of (234) Barbara exhibits large concave areas.
Possible links of the shape to the polarimetric properties and the object
evolution are discussed. We also show that VLTI data can be modeled without the
presence of a satellite.Comment: 10 pages, 6 figure
Improving integrability via absolute summability: a general version of Diestel s Theorem
[EN] A classical result by J. Diestel establishes that the composition of a summing operator with a (strongly measurable) Pettis integrable function gives a Bochner integrable function. In this paper we show that a much more general result is possible regarding the improvement of the integrability of vector valued functions by the summability of the operator. After proving a general result, we center our attention in the particular case given by the -absolutely continuous operators, that allows to prove a lot of special results on integration improvement for selected cases of classical Banach spaces-including C(K), and Hilbert spaces-and operators-p-summing, (q, p)-summing and p-approximable operators.D. Pellegrino acknowledges with thanks the support of CNPq Grant 401735/2013-3 (Brazil). P. Rueda acknowledges with thanks the support of the Ministerio de Economia y Competitividad (Spain) MTM2011-22417. E.A. Sanchez Perez acknowledges with thanks the support of the Ministerio de Economia y Competitividad (Spain) MTM2012-36740-C02-02.Pellegrino, D.; Rueda, P.; Sánchez Pérez, EA. (2016). Improving integrability via absolute summability: a general version of Diestel s Theorem. Positivity. 20(2):369-383. https://doi.org/10.1007/s11117-015-0361-5S369383202Botelho, G., Pellegrino, D., Rueda, P.: A unified Pietsch domination theorem. J. Math. Anal. Appl. 365(1), 269–276 (2010)Defant, A., Floret, K.: Tensor norms and operator ideals. North-Holland, Amsterdam (1992)Diestel, J.: An elementary characterization of absolutely summing operators. Math. Ann. 196, 101–105 (1972)Diestel, J., Jarchow, H., Tonge, A.: Absolutely summing operators. Cambridge University Press, Cambridge (1995)Farmer, J., Johnson, W.B.: Lipschitz p-summing operators. Proc. Amer. Math. Soc. 137, 2989–2995 (2009)Jarchow, H.: Localy convex, spaces. Teubner, Stuttgart (1981)López Molina, J.A., Sánchez Pérez, E.A.: Ideales de operadores absolutamente continuos, Ciencias Exactas, Físicas y Naturales, Madrid. Rev. Real Acad. 87, 349–378 (1993)López Molina, J.A., Sánchez Pérez, E.A.: The associated tensor norm to ( q , p ) -absolutely summing operators on C ( K ) -spaces. Czec. Math. J. 47(4), 627–631 (1997)López, J.A., Molina, Sánchez-Pérez, E.A.: On operator ideals related to ( p , σ ) -absolutely continuous operator. Studia Math. 131(8), 25–40 (2000)Matter, U.: Absolute continuous operators and super-reflexivity. Math. Nachr. 130, 193–216 (1987)Pellegrino, D., Santos, J.: A general Pietsch domination theorem. J. Math. Anal. Appl. 375(1), 371–374 (2011)Pellegrino, D., Santos, J., Seoane-Sepúlveda, J.B.: Some techniques on nonlinear analysis and applications. Adv. Math. 229, 1235–1265 (2012)Pietsch, A.: Operator Ideals. Deutsch. Verlag Wiss., Berlin, 1978; North-Holland, Amsterdam-London-New York-Tokyo (1980)Pisier, G.: Factorization of operators through L p ∞ or L p 1 and noncommutative generalizations. Math. Ann. 276(1), 105–136 (1986)Rodríguez, J.: Absolutely summing operators and integration of vector-valued functions. J. Math. Anal. Appl. 316(2), 579–600 (2006
Quantum gravity and the standard model
We show that a class of background independent models of quantum spacetime
have local excitations that can be mapped to the first generation fermions of
the standard model of particle physics. These states propagate coherently as
they can be shown to be noiseless subsystems of the microscopic quantum
dynamics. These are identified in terms of certain patterns of braiding of
graphs, thus giving a quantum gravitational foundation for the topological
preon model proposed by one of us.
These results apply to a large class of theories in which the Hilbert space
has a basis of states given by ribbon graphs embedded in a three-dimensional
manifold up to diffeomorphisms, and the dynamics is given by local moves on the
graphs, such as arise in the representation theory of quantum groups. For such
models, matter appears to be already included in the microscopic kinematics and
dynamics.Comment: 12 pages, 21 figures, improved presentation, results unchange
- …