281 research outputs found
Evidence of convective rolls in a sunspot penumbra
aims: We study the recently discovered twisting motion of bright penumbral
filaments with the aim of constraining their geometry and the associated
magnetic field. methods: A large sunspot located 40\degr from disk center was
observed at high resolution with the 1-m Swedish Solar Telescope. Inversions of
multi-wavelength polarimetric data and speckle reconstructed time series of
continuum images were used to determine proper motions, as well as the velocity
and magnetic structure in penumbral filaments. results: The continuum movie
reveals apparent lateral motions of bright and dark structures inside bright
filaments oriented parallel to the limb, confirming recent Hinode results. In
these filaments we measure upflows of on their
limbward side and weak downflows on their centerward side. The magnetic field
in them is significantly weaker and more horizontal than in the adjacent dark
filaments. conclusions: The data indicate the presence of vigorous convective
rolls in filaments with a nearly horizontal magnetic field. These are separated
by filaments harbouring stronger, more vertical fields. Because of reduced gas
pressure, we see deeper into the latter. When observed near the limb, the
disk-centerward side of the horizontal-field filaments appear bright due to the
\textit{hot wall} effect known from faculae. We estimate that the convective
rolls transport most of the energy needed to explain the penumbral radiative
flux.Comment: 4 pages, 4 figures, letter to Astronomy & Astrophysic
V12 248. Reemplazo de raíz de aorta según técnica de david y de arco aórtico con injerto trifurcado, en un paciente diagnosticado de síndrome de loeys-dietz
IntroducciónSe describe la técnica quirúrgica de un paciente de 24 años de edad con síndrome de Loeys-Dietz. Se trata de una enfermedad hereditaria del tejido conectivo producida por la mutación del gen del receptor del factor de crecimiento transformante (TGF)-β;. Su característica principal y condicionante del pronóstico es la dilatación del sistema vascular, principalmente la aorta.MétodoEl paciente presentaba dilatación aneurismática de la raíz y del arco aórtico, con un diámetro máximo de 50 mm. Tenía además historia familiar de muerte súbita de origen cardíaco en tres familiares de primer grado a edades tempranas. Ante la indicación de tratamiento quirúrgico se procedió a realizar sustitución de los segmentos aneurismáticos. En la raíz aórtica se realizó técnica de preservación valvular (técnica de David, modificación de Miller). La sustitución del arco aórtico se llevó a cabo mediante interposición de injerto trifurcado, en hipotermia moderada y con perfusión cerebral anterógrada.Resultado y conclusionesNo hubo complicaciones postoperatorias. El tratamiento quirúrgico precoz en los pacientes afectos de síndrome de Loeys-Dietz es imprescindible. La experiencia acumulada hasta el momento revela la agresividad de esta enfermedad. Por ello, es necesario un abordaje completo cuando existe afectación a distintos niveles. El empleo de técnicas de preservación valvular permite además disminuir la morbimortalidad asociada a las prótesis valvulares
The Evershed Flow and the Brightness of the Penumbra
The Evershed flow is a systematic motion of gas that occurs in the penumbra
of all sunspots. Discovered in 1909, it still lacks a satisfactory explanation.
We know that the flow is magnetized, often supersonic, and that it shows
conspicuous fine structure on spatial scales of 0.2"-0.3", but its origin
remains unclear. The hope is that a good observational understanding of the
relation between the flow and the penumbral magnetic field will help us
determine its nature. Here I review advances in the characterization of the
Evershed flow and sunspot magnetic fields from high-resolution spectroscopic
and spectropolarimetric measurements. Using this information as input for 2D
heat transfer simulations, it has been demonstrated that hot Evershed upflows
along nearly horizontal field lines are capable of explaining one of the most
intriguing aspects of sunspots: the surplus brightness of the penumbra relative
to the umbra. They also explain the existence of penumbral filaments with dark
cores. These results support the idea that the Evershed flow is largely
responsible for the transport of energy in the penumbra.Comment: 18 pages, to appear in "Magnetic Coupling between the Interior and
the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer, Heidelberg, 200
Magnetic field emergence in mesogranular-sized exploding granules observed with SUNRISE/IMaX data
We report on magnetic field emergences covering significant areas of
exploding granules. The balloon-borne mission SUNRISE provided high spatial and
temporal resolution images of the solar photosphere. Continuum images,
longitudinal and transverse magnetic field maps and Dopplergrams obtained by
IMaX onboard SUNRISE are analyzed by Local Correlation Traking (LCT),
divergence calculation and time slices, Stokes inversions and numerical
simulations are also employed. We characterize two mesogranular-scale exploding
granules where 10 Mx of magnetic flux emerges. The emergence of
weak unipolar longitudinal fields (100 G) start with a single visible
magnetic polarity, occupying their respective granules' top and following the
granular splitting. After a while, mixed polarities start appearing,
concentrated in downflow lanes. The events last around 20 min. LCT analyses
confirm mesogranular scale expansion, displaying a similar pattern for all the
physical properties, and divergence centers match between all of them. We found
a similar behaviour with the emergence events in a numerical MHD simulation.
Granule expansion velocities are around 1 \kms while magnetic patches expand at
0.65 \kms. One of the analyzed events evidences the emergence of a loop-like
structure. Advection of the emerging magnetic flux features is dominated by
convective motion resulting from the exploding granule due to the magnetic
field frozen in the granular plasma. Intensification of the magnetic field
occurs in the intergranular lanes, probably because of being directed by the
downflowing plasma.Comment: 7 pages, 6 figure
Anomalous electronic susceptibility in Bi2Sr2CuO6+d and comparison with other overdoped cuprates
We report magnetic susceptibility performed on overdoped Bi2Sr2CuO6+d powders
as a function of oxygen doping d and temperature T. The decrease of the spin
susceptibility with increasing T is confirmed. At sufficient high temperature,
the spin susceptibility Chi_s presents an unusual linear temperature dependence
Chi_s ~ Chi_s0 -Chi_1 T. Moreover, a linear correlation between Chi_1 and
Chi_s0 for increasing hole concentration is displayed. A temperature Tchi,
independent of hole doping characterizes this scaling. Comparison with other
cuprates of the literature(LSCO, Tl-2201 and Bi-2212), over the same overdoped
range, shows similarities with above results. These non conventional metal
features will be discussed in terms of a singular narrow-band structure.Comment: 16 pages, 4 figure
Sunspots: from small-scale inhomogeneities towards a global theory
The penumbra of a sunspot is a fascinating phenomenon featuring complex
velocity and magnetic fields. It challenges both our understanding of radiative
magneto-convection and our means to measure and derive the actual geometry of
the magnetic and velocity fields. In this contribution we attempt to summarize
the present state-of-the-art from an observational and a theoretical
perspective.Comment: Accepted for publication in Space Science Review
The Imaging Magnetograph eXperiment (IMaX) for the Sunrise balloon-borne solar observatory
The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by
four institutions in Spain that flew on board the Sunrise balloon-borne
telesocope in June 2009 for almost six days over the Arctic Circle. As a
polarimeter IMaX uses fast polarization modulation (based on the use of two
liquid crystal retarders), real-time image accumulation, and dual beam
polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the
instrument uses a LiNbO3 etalon in double pass and a narrow band pre-filter to
achieve a spectral resolution of 85 mAA. IMaX uses the high Zeeman sensitive
line of Fe I at 5250.2 AA and observes all four Stokes parameters at various
points inside the spectral line. This allows vector magnetograms, Dopplergrams,
and intensity frames to be produced that, after reconstruction, reach spatial
resolutions in the 0.15-0.18 arcsec range over a 50x50 arcsec FOV. Time
cadences vary between ten and 33 seconds, although the shortest one only
includes longitudinal polarimetry. The spectral line is sampled in various ways
depending on the applied observing mode, from just two points inside the line
to 11 of them. All observing modes include one extra wavelength point in the
nearby continuum. Gauss equivalent sensitivities are four Gauss for
longitudinal fields and 80 Gauss for transverse fields per wavelength sample.
The LOS velocities are estimated with statistical errors of the order of 5-40
m/s. The design, calibration and integration phases of the instrument, together
with the implemented data reduction scheme are described in some detail.Comment: 17 figure
Endomicroscopic and transcriptomic analysis of impaired barrier function and malabsorption in environmental enteropathy
Introduction: Environmental enteropathy (EE) is associated with growth failure, micronutrient malabsorption and impaired responses to oral vaccines. We set out to define cellular mechanisms of impaired barrier function in EE and explore protective mechanisms. Methods: We studied 49 adults with environmental enteropathy in Lusaka, Zambia using confocal laser endomicroscopy (CLE); histology, immunohistochemistry and mRNA sequencing of small intestinal biopsies; and correlated these with plasma lipopolysaccharide (LPS) and a zinc uptake test. Results: CLE images (median 134 for each study) showed virtually ubiquitous small intestinal damage. Epithelial defects, imaged by histology and claudin 4 immunostaining, were predominantly seen at the tips of villi and corresponded with leakage imaged in vivo by CLE. In multivariate analysis, circulating log-transformed LPS was correlated with cell shedding events (β = 0.83; P = 0.035) and with serum glucagon-like peptide-2 (β = -0.13; P = 0.007). Zinc uptake from a test dose of 25mg was attenuated in 30/47 (64%) individuals and in multivariate analysis was reduced by HIV, but positively correlated with GLP-2 (β = 2.72; P = 0.03). There was a U-shaped relationship between circulating LPS and villus surface area. Transcriptomic analysis identified 23 differentially expressed genes in severe enteropathy, including protective peptides and proteins. Conclusions: Confocal endomicroscopy, claudin 4 immunostaining and histology identify epithelial defects which are probably sites of bacterial translocation, in the presence of which increased epithelial surface area increases the burden of translocation. GLP 2 and other protective peptides may play an important role in mucosal protection in EE
Self-assembly in solution of a reversible comb-shaped supramolecular polymer
We report a single step synthesis of a polyisobutene with a bis-urea moiety
in the middle of the chain. In low polarity solvents, this polymer
self-assembles by hydrogen bonding to form a combshaped polymer with a central
hydrogen bonded backbone and polyisobutene arms. The comb backbone can be
reversibly broken, and consequently, its length can be tuned by changing the
solvent, the concentration or the temperature. Moreover, we have proved that
the bulkiness of the side-chains have a strong influence on both the
self-assembly pattern and the length of the backbone. Finally, the density of
arms can be reduced, by simply mixing with a low molar mass bis-urea
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