1,412 research outputs found
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Optimization of the Spectral Line Inversion Code
The Very Fast Inversion of the Stokes Vector (VFISV) is a Milne-Eddington
spectral line inversion code used to determine the magnetic and thermodynamic
parameters of the solar photosphere from observations of the Stokes vector in
the 6173 A Fe I line by the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO). We report on the modifications made to the
original VFISV inversion code in order to optimize its operation within the HMI
data pipeline and provide the smoothest solution in active regions. The changes
either sped up the computation or reduced the frequency with which the
algorithm failed to converge to a satisfactory solution. Additionally, coding
bugs which were detected and fixed in the original VFISV release, are reported
here.Comment: Accepted for publication in Solar Physic
Colorimetry technique for scalable characterization of suspended graphene
Previous statistical studies on the mechanical properties of
chemical-vapor-deposited (CVD) suspended graphene membranes have been performed
by means of measuring individual devices or with techniques that affect the
material. Here, we present a colorimetry technique as a parallel, non-invasive,
and affordable way of characterizing suspended graphene devices. We exploit
Newton rings interference patterns to study the deformation of a double-layer
graphene drum 13.2 micrometer in diameter when a pressure step is applied. By
studying the time evolution of the deformation, we find that filling the drum
cavity with air is 2-5 times slower than when it is purged
The influence of coronal EUV irradiance on the emission in the He I 10830 A and D3 multiplets
Two of the most attractive spectral windows for spectropolarimetric
investigations of the physical properties of the plasma structures in the solar
chromosphere and corona are the ones provided by the spectral lines of the He I
10830 A and 5876 A (or D3) multiplets, whose polarization signals are sensitive
to the Hanle and Zeeman effects. However, in order to be able to carry out
reliable diagnostics, it is crucial to have a good physical understanding of
the sensitivity of the observed spectral line radiation to the various
competing driving mechanisms. Here we report a series of off-the-limb non-LTE
calculations of the He I D3 and 10830 A emission profiles, focusing our
investigation on their sensitivity to the EUV coronal irradiation and the model
atmosphere used in the calculations. We show in particular that the intensity
ratio of the blue to the red components in the emission profiles of the He I
10830 A multiplet turns out to be a good candidate as a diagnostic tool for the
coronal irradiance. Measurements of this observable as a function of the
distance to the limb and its confrontation with radiative transfer modeling
might give us valuable information on the physical properties of the solar
atmosphere and on the amount of EUV radiation at relevant wavelengths
penetrating the chromosphere from above.Comment: 19 pages, 11 figures (pre-print format). Accepted for publication in
Ap
Channeling 5-min photospheric oscillations into the solar outer atmosphere through small-scale vertical magnetic flux tubes
We report two-dimensional MHD simulations which demonstrate that photospheric
5-min oscillations can leak into the chromosphere inside small-scale vertical
magnetic flux tubes. The results of our numerical experiments are compatible
with those inferred from simultaneous spectropolarimetric observations of the
photosphere and chromosphere obtained with the Tenerife Infrared Polarimeter
(TIP) at 10830 A. We conclude that the efficiency of energy exchange by
radiation in the solar photosphere can lead to a significant reduction of the
cut-off frequency and may allow for the propagation of the 5 minutes waves
vertically into the chromosphere.Comment: accepted by ApJ
All-Dielectric Rod-Type Metamaterials at Optical Frequencies
Light propagation in all-dielectric rod-type metamaterials is studied
theoretically. The electric and magnetic dipole moments of the rods are derived
analytically in the long-wavelength limit. The effective permittivity and
permeability of a square lattice of rods are calculated by homogenizing the
corresponding array of dipoles. The role of dipole resonances in the optical
properties of the rod array is interpreted. This structure is found to exhibit
a true left-handed behavior, confirming previous experiments [L. Peng
\textit{et al.}, Phys. Rev. Lett. \textbf{98}, 157403 (2007)]. A scaling
analysis shows that this effect holds at optical frequencies and can be
obtained by using rods made, for example, of silicon.Comment: 10 pages, 4 figures. The title has been shortened; Figs. 1, 2 and 3
have been modified; Eq. 4 has been corrected (sign error); A few sentences
have been added/rewritte
General unit-disk representation for periodic multilayers
We suggest a geometrical framework to discuss periodic layered structures in
the unit disk. The band gaps appear when the point representing the system
approaches the unit circle. We show that the trace of the matrix describing the
basic period allows for a classification in three families of orbits with quite
different properties. The laws of convergence of the iterates to the unit
circle can be then considered as universal features of the reflection.Comment: 3 pages, 2 eps-figures. To be published in Optics Letter
Graphene mechanical pixels for Interferometric MOdulator Displays (GIMOD)
Graphene, the carbon monolayer and 2D allotrope of graphite, has the
potential to impact technology with a wide range of applications such as
optical modulators for high-speed communications. In contrast to modulation
devices that rely on plasmonic or electronic effects, MEMS-based modulators can
have wider tuning ranges albeit at a lower operating frequency. These
properties make electro-optic mechanical modulators ideal for reflective-type
display technologies as has been demonstrated previously with SiN membranes in
Interferometric MOdulator Displays (IMODs). Despite their low-power consumption
and performance in bright environments, IMODs suffer from low frame rates and
limited color gamut. Double-layer graphene (DLG) membranes grown by chemical
vapor deposition (CVD) can also recreate the interference effect like in IMODs
as proven with drumheads displaying Newton's rings. Here, we report on the
electro-optical response of CVD DLG mechanical pixels by measuring the change
in wavelength-dependent reflectance of a suspended graphene drumhead as a
function of electrical gating. We use a spectrometer to measure the wavelength
spectrum at different voltages, and find a good agreement with a model based on
light interference. Moreover, to verify that gas compression effects do not
play an important role, we use a stroboscopic illumination technique to study
the electro-optic response of these graphene pixels at frequencies up to 400
Hz. Based on these findings, we demonstrate a continuous full-spectrum
reflective-type pixel technology with a Graphene Interferometric MOdulator
Display (GIMOD) prototype of 2500 pixels per inch (ppi) equivalent to more than
12K resolution.Comment: 13 pages, 4 figure
Convexity in partial cubes: the hull number
We prove that the combinatorial optimization problem of determining the hull
number of a partial cube is NP-complete. This makes partial cubes the minimal
graph class for which NP-completeness of this problem is known and improves
some earlier results in the literature.
On the other hand we provide a polynomial-time algorithm to determine the
hull number of planar partial cube quadrangulations.
Instances of the hull number problem for partial cubes described include
poset dimension and hitting sets for interiors of curves in the plane.
To obtain the above results, we investigate convexity in partial cubes and
characterize these graphs in terms of their lattice of convex subgraphs,
improving a theorem of Handa. Furthermore we provide a topological
representation theorem for planar partial cubes, generalizing a result of
Fukuda and Handa about rank three oriented matroids.Comment: 19 pages, 4 figure
CO72 357. Reconstrucción del cuerpo fibroso mitroaórtico: Resultados perioperatorios y supervivencia a largo plazo
ObjetivosDescribir las características clínicas, resultados perioperatorios y supervivencia a largo plazo de pacientes sometidos a sustitución valvular mitral y aórtica con reconstrucción de la fbrosa mitroaórtica según técnica de David.MétodosRevisión retrospectiva de pacientes sometidos a sustitución valvular y reconstrucción de la fibrosa mitroaórtica intervenidos en los últimos 14 años. Se incluyen 27 pacientes, 63% varones, edad 55,3±16,1 años, EuroSCORE 34,4±25,9. El 70,4% de los pacientes presentaban al menos una cirugía previa. La indicación para el procedimiento fue endocarditis infecciosa complicada con absceso de la unión mitroaórtica en el 74,1%; en el restante 25,9% la principal indicación fue la necesidad de ampliación del anillo aórtico en el seno de una valvulopatía mitroaórtica.ResultadosLa supervivencia perioperatoria (30 días) fue del 85,2%. No se observó mortalidad entre los pacientes sin endocarditis. Estancia media: 42,8±42,8 días. Complicaciones perioperatorias: accidente cerebrovascular agudo (ACVA) 3,1% (1), balón de contrapulsación intraaórtica (BCIA) 11,1% (3), insuficiencia renal aguda (IRA) 7,4% (2), infarto agudo de miocardio (IAM) 3,7% (1), reintervención por sangrado 14,8% (4), ventilación mecánica prolongada 11,1% (3), necesidad de marcapasos (MP) definitivo 22,2%. La supervivencia acumulada para los supervivientes a 1, 3 y 5 años fue de 85,9±7,6%, 75,8 ± 9,5% y 45,5 ± 11,1%, respectivamente. No se observó diferencia significativa al comparar la super-vivencia a 1, 3 y 5 años entre los grupos intervenidos por endocarditis y los no endocarditis (log rank 0,146).ConclusionesLa reconstrucción de la fibrosa mitroaórtica mediante técnica de David representa una alternativa terapéutica para el manejo de patología compleja que involucra esta estructura. Hemos observado buenos resultados perioperatorios y a largo plazo teniendo en cuenta el perfil de alto riesgo de los pacientes que requieren este tipo de intervención
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