4,317 research outputs found
Gravitational instability of solar prominence threads I. Curved magnetic fields without dips
Prominence threads are dense and cold structures lying on curved magnetic
fields that can be suspended in the solar atmosphere against gravity. The
gravitational stability of threads, in the absence of non-ideal effects, is
comprehensively investigated in the present work by means of an elementary but
effective model. Based on purely hydrodynamic equations in one spatial
dimension and applying line-tying conditions at the footpoints of the magnetic
field lines, we derive analytical expressions for the different feasible
equilibria and the corresponding frequencies of oscillation. We find that the
system allows for stable and unstable equilibrium solutions subject to the
initial position of the thread, its density contrast and length, and the total
length of the magnetic field lines. The transition between the two types of
solutions is produced at specific bifurcation points that have been determined
analytically in some particular cases. When the thread is initially at the top
of the concave magnetic field, that is at the apex, we find a supercritical
pitchfork bifurcation, while for a shifted initial thread position with respect
to this point the symmetry is broken and the system is characterised by an
S-shaped bifurcation. The plain results presented in this paper shed new light
on the behaviour of threads in curved magnetic fields under the presence of
gravity and help to interpret more complex numerical magnetohydrodynamics (MHD)
simulations about similar structures.Comment: 13 pages, 9 figure
Morphological studies of the Spitzer Wide-Area Infrared Extragalactic survey galaxy population in the UGC 10214 Hubble space telescope/advanced camera for surveys field
We present the results of a morphological analysis of a small subset of the Spitzer Wide-Area Infrared Extragalactic survey (SWIRE) galaxy population. The analysis is based on public Advanced Camera for Surveys (ACS) data taken inside the SWIRE N1 field, which are the deepest optical high-resolution imaging available within the SWIRE fields as of today. Our reference sample includes 156 galaxies detected by both ACS and SWIRE. Among the various galaxy morphologies, we disentangle two main classes, spheroids (or bulge-dominated galaxies) and disc-dominated ones, for which we compute the number counts as a function of flux. We then limit our sample to objects with Infrared Array Camera (IRAC) fluxes brighter than 10 μJy, estimated ~90 per cent completeness limit of the SWIRE catalogues, and compare the observed counts to model predictions. We find that the observed counts of the spheroidal population agree with the expectations of a hierarchical model while a monolithic scenario predicts steeper counts. Both scenarios, however, underpredict the number of late-type galaxies. These observations show that the large majority (close to 80 per cent) of the 3.6- and 4.5-μm galaxy population, even at these moderately faint fluxes, is dominated by spiral and irregular galaxies or mergers
Masseter muscle thickness measured by ultrasound as a possible link with sarcopenia, malnutrition and dependence in nursing homes
Sarcopenia is a progressive and generalized loss of skeletal muscle mass and strength. It is frequently associated with malnutrition and dependence in nursing homes. Masticatory muscle strength could be the link between sarcopenia, malnutrition and dependence. We aimed to study the relation between sarcopenia, malnutrition and dependence with masseter muscle thickness measured by ultrasound. A cross-sectional study was realized, with 464 patients from 3 public nursing homes in Zaragoza (Spain). The diagnosis of sarcopenia was assessed according to the EuropeanWorking Group on Sarcopenia in Older People 2 criteria, malnutrition by the Mini Nutritional Assessment (MNA) and the Global Leadership Initiative on Malnutrition (GLIM) criteria and functional capacity by the Barhel Index and the texture diet. Masseter muscle thickness (MMT) was measured by ultrasound. The median age was 84.7 years, and 70% of the participants were women. Sarcopenia was confirmed in 39.2% of patients, malnutrition in 26.5% (risk 47.8%), total dependence in 37.9% and diet texture was modified in 44.6%. By logistic regression, once the model was adjusted for age, sex, Barthel index and texture diet, our analyses indicated that each 1 mm decrease in MMT increased the risk of sarcopenia by ~57% (OR: 0.43), the risk of malnutrition by MNA by ~63% (OR: 0.37) and the risk of malnutrition by GLIM by ~34% (OR: 0.66). We found that MMT was reduced in sarcopenic, malnourished and dependent patients, and it could be the common point of a vicious cycle between sarcopenia and malnutrition. Further studies are needed to establish causality. © 2021 by the authors
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A 15 µm selected sample of hHigh-z starbursts and AGNs
We report results from our Spitzer GO-1 program on IRS spectroscopy of a large sample of Luminous Infrared Galaxies and quasars selected from the European Large Area ISO Survey (ELAIS). The selected ELAIS sources have a wide multi-wavelength coverage, including ISOCAM, ISOPHOT, IRAC
and MIPS (from SWIRE), and optical photometry. Here we present the sample selection and results from the IRS spectroscopy
Environment of the submillimeter-bright massive starburst HFLS3 at 6.34
We describe the search for Lyman-break galaxies (LBGs) near the
sub-millimeter bright starburst galaxy HFLS3 at 6.34 and a study on the
environment of this massive galaxy during the end of reionization.We performed
two independent selections of LBGs on images obtained with the \textit{Gran
Telescopio Canarias} (GTC) and the \textit{Hubble Space Telescope} (HST) by
combining non-detections in bands blueward of the Lyman-break and color
selection. A total of 10 objects fulfilling the LBG selection criteria at
5.5 were selected over the 4.54 and 55.5 arcmin covered by our HST
and GTC images, respectively. The photometric redshift, UV luminosity, and the
star-formation rate of these sources were estimated with models of their
spectral energy distribution. These 6 candidates have physical
properties and number densities in agreement with previous results. The UV
luminosity function at 6 and a Voronoi tessellation analysis of this
field shows no strong evidence for an overdensity of relatively bright objects
(m25.9) associated with \textit{HFLS3}. However, the over-density
parameter deduced from this field and the surface density of objects can not
excluded definitively the LBG over-density hypothesis. Moreover we identified
three faint objects at less than three arcseconds from \textit{HFLS3} with
color consistent with those expected for 6 galaxies. Deeper data are
needed to confirm their redshifts and to study their association with
\textit{HFLS3} and the galaxy merger that may be responsible for the massive
starburst.Comment: 14 pages, 12 figures, accepted for publication in Ap
Intraply fracture of fiber-reinforced composites: microscopic mechanisms and modeling
The fracture behavior parallel to the fibers of an E-glass/epoxy unidirectional laminate was studied by
means of three-point tests on notched beams. Selected tests were carried out within a scanning electron
microscope to ascertain the damage and fracture micromechanisms upon loading. The mechanical behavior
of the notched beam was simulated within the framework of the embedded cell model, in which the
actual composite microstructure was resolved in front of the notch tip. In addition, matrix and interface
properties were independently measured in situ using a nanoindentor. The numerical simulations very
accurately predicted the macroscopic response of the composite as well as the damage development
and crack growth in front of the notch tip, demonstrating the ability of the embedded cell approach to
simulate the fracture behavior of heterogeneous materials. Finally, this methodology was exploited to
ascertain the influence of matrix and interface properties on the intraply toughness
Enterorragia masiva en paciente con enfermedad de Von Hippel Lindau
The Von Hippel Lindau disease is an autosomic-dominant neoplasia syndrome produced by a delection or mutation of tumor suppressor gene of chromosome 3p25. It was descripted by the German pathologist Arvid Lindau and the ophthalmologist Eugene Von Hippel, and it is considered also one of 7 000 hereditary disorders known up to the present. Our patient was submitted to a genetic study in 1990 to determine, who relatives had suffered this syndrome (by making a genealogical tree). As the antecedent was taking an operation of renal carcinoma made a year before, and this time, the patient is admitted cause presented a massive enterorrhagia, which motivated a research about him and a surgical intervention as well. The histological study demonstrated the existence of a methastasis of Clear-Cell renal carcinoma, which is a characteristic lesion, when Occurs this Syndrome.La enfermedad de Von Hippel Lindau es un síndrome neoplásico autosómico-dominante provocado por la delección o mutación del gen tumor supresor del cromosoma 3p25. Fue descrito por el oftalmólogo alemán Eugen Von Hippel y el patólogo Arvid Lindau y es uno de los 7 000 trastornos hereditarios conocidos en la actualidad. Nuestro paciente fue estudiado genéticamente en el año 1990 para determinar qué familiares padecían el síndrome mediante la confección de un árbol genealógico, el antecedente fue una operación de un carcinoma renal hace un año aproximadamente y en esta oportunidad ingresa por presentar una enterorragia masiva que motivó su estudio y la intervención quirúrgica. El resultado histológico fue una metástasis de un carcinoma renal de células claras, lesión característica de este síndrome
Regional Implementation Plan for Demersal Fisheries from the Balearic Islands (Western Mediterranean)
The Spitzer Extragalactic Representative Volume Survey (SERVS): The Environments of High-z SDSS Quasi-Stellar-Objects
This paper presents a study of the environments of SDSS Quasi-Stellar-Objects
(QSOs) in the Spitzer Extragalactic Representative Volume Survey (SERVS). We
concentrate on the high-redshift QSOs as these have not been studied in large
numbers with data of this depth before. We use the IRAC 3.6-4.5{\mu}m colour of
objects and ancillary r-band data to filter out as much foreground
contamination as possible. This technique allows us to find a significant (>
4-{\sigma}) over-density of galaxies around QSOs in a redshift bin centred on z
~ 2.0 and a (> 2-{\sigma}) over-density of galaxies around QSOs in a redshift
bin centred on z ~ 3.3. We compare our findings to the predictions of a
semi-analytic galaxy formation model, based on the {\Lambda}CDM millennium
simulation, and find for both redshift bins that the model predictions match
well the source-density we have measured from the SERVS data.Comment: 13 pages, 12 figures, Accepted by Ap
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