1,352 research outputs found
Millimeter-wave aperture synthesis radiometry for snow and ice mapping
An outline design for a dual-band mm-wave polarimetric SAIR has been presented and is considered to be tractable. The envisaged application is for snow and ice mapping and ocean wind vector measurement. The vastly increased complexity of the high-frequency waveband may not be justified by the scientific benefit and operation at an additional lower frequency such as 18 GHz may give improved classification, though with reduced spatial resolution. The authors describe the outline design for a polarimetric, mm-wave SAIR. One-dimensional aperture synthesis employs a hybrid technique in which a long linear array of real-aperture stick antennas form over-lapping fan beams on the ground and aperture synthesis within the fan beams enables synthesis of the mm-wave image. Critical aspects for building a high-resolution, mm-wave ESTAR are system calibration and the construction of stick antennas that will be 3 m long and about half a wavelength wide.Peer ReviewedPostprint (published version
Rabdomiólisis tras la práctica de spinning: una asociación peculiar
ResumenLa rabdomiólisis de esfuerzo es una entidad clínica con unas características especiales. Se describe un cuadro de rabdomiólisis en un varón joven y sano, tras la práctica de una única sesión de spinning y se compara con otros descritos en la literatura. El objetivo es exponer las peculiaridades de la asociación del spinning con la rabdomiólisis por esfuerzo y conocer el riesgo de esta patología, aun en personas sanas, en relación con esta práctica deportiva. La contracción muscular que se produce en este ejercicio y la percepción disminuida del esfuerzo, al ser una actividad realizada en grupo, estimulada ambientalmente y alentada por un monitor, pueden contribuir a esta asociación.AbstractExertional rhabdomyolysis is a distinct entity with special characteristics. We present a case report, and literature review, of rhabdomyolysis in a young healthy male adult after practicing a single spinning session. The objective is to explain the peculiarities of the association spinning and exertional rhabdomyolysis and determine the risk of this disease, even in healthy people, concerning this sport. Muscular contraction during this exercise and the diminished perception of effort, due to being a group activity encouraged by a monitor, may contribute to its association
Confusing the extragalactic neutrino flux limit with a neutrino propagation limit
We study the possible suppression of the extragalactic neutrino flux due to a
nonstandard interaction during its propagation. In particular, we study
neutrino interaction with an ultra-light scalar field dark matter. It is shown
that the extragalactic neutrino flux may be suppressed by such an interaction,
leading to a new mechanism to reduce the ultra-high energy neutrino flux. We
study both the cases of non-self-conjugate as well as self-conjugate dark
matter. In the first case, the suppression is independent of the neutrino and
dark matter masses. We conclude that care must be taken when explaining limits
on the neutrino flux through source acceleration mechanisms only, since there
could be other mechanisms for the reduction of the neutrino flux.Comment: 15 pages, 4 figures. Important changes implemented. Abstract
modified. Conclusions remain. To be published in JCA
Added and Free Sugars: review in the literature of estimated intakes and its main food sources
Semiquantitative theory of electronic Raman scattering from medium-size quantum dots
A consistent semiquantitative theoretical analysis of electronic Raman
scattering from many-electron quantum dots under resonance excitation
conditions has been performed. The theory is based on
random-phase-approximation-like wave functions, with the Coulomb interactions
treated exactly, and hole valence-band mixing accounted for within the
Kohn-Luttinger Hamiltonian framework. The widths of intermediate and final
states in the scattering process, although treated phenomenologically, play a
significant role in the calculations, particularly for well above band gap
excitation. The calculated polarized and unpolarized Raman spectra reveal a
great complexity of features and details when the incident light energy is
swept from below, through, and above the quantum dot band gap. Incoming and
outgoing resonances dramatically modify the Raman intensities of the single
particle, charge density, and spin density excitations. The theoretical results
are presented in detail and discussed with regard to experimental observations.Comment: Submitted to Phys. Rev.
Total and free sugar estimated intake and main dietary sources in the portuguese population: the national food, nutrition and physical activity survey (ian-af 2015-2016)
Late-time cosmology in (phantom) scalar-tensor theory: dark energy and the cosmic speed-up
We consider late-time cosmology in a (phantom) scalar-tensor theory with an
exponential potential, as a dark energy model with equation of state parameter
close to -1 (a bit above or below this value). Scalar (and also other kinds of)
matter can be easily taken into account. An exact spatially-flat FRW cosmology
is constructed for such theory, which admits (eternal or transient)
acceleration phases for the current universe, in correspondence with
observational results. Some remarks on the possible origin of the phantom,
starting from a more fundamental theory, are also made. It is shown that
quantum gravity effects may prevent (or, at least, delay or soften) the cosmic
doomsday catastrophe associated with the phantom, i.e. the otherwise
unavoidable finite-time future singularity (Big Rip). A novel dark energy model
(higher-derivative scalar-tensor theory) is introduced and it is shown to admit
an effective phantom/quintessence description with a transient acceleration
phase. In this case, gravity favors that an initially insignificant portion of
dark energy becomes dominant over the standard matter/radiation components in
the evolution process.Comment: LaTeX file, 48 pages, discussion of Big Rip is enlarged, a reference
is adde
Density functional method for nonequilibrium electron transport
We describe an ab initio method for calculating the electronic structure,
electronic transport, and forces acting on the atoms, for atomic scale systems
connected to semi-infinite electrodes and with an applied voltage bias. Our
method is based on the density functional theory (DFT) as implemented in the
well tested Siesta approach (which uses non-local norm-conserving
pseudopotentials to describe the effect of the core electrons, and linear
combination of finite-range numerical atomic orbitals to describe the valence
states). We fully deal with the atomistic structure of the whole system,
treating both the contact and the electrodes on the same footing. The effect of
the finite bias (including selfconsistency and the solution of the
electrostatic problem) is taken into account using nonequilibrium Green's
functions. We relate the nonequilibrium Green's function expressions to the
more transparent scheme involving the scattering states. As an illustration,
the method is applied to three systems where we are able to compare our results
to earlier ab initio DFT calculations or experiments, and we point out
differences between this method and existing schemes. The systems considered
are: (1) single atom carbon wires connected to aluminum electrodes with
extended or finite cross section, (2) single atom gold wires, and finally (3)
large carbon nanotube systems with point defects.Comment: 18 pages, 23 figure
Circumstellar interaction in supernovae in dense environments - an observational perspective
In a supernova explosion, the ejecta interacting with the surrounding
circumstellar medium (CSM) give rise to variety of radiation. Since CSM is
created from the mass lost from the progenitor star, it carries footprints of
the late time evolution of the star. This is one of the unique ways to get a
handle on the nature of the progenitor star system. Here, I will focus mainly
on the supernovae (SNe) exploding in dense environments, a.k.a. Type IIn SNe.
Radio and X-ray emission from this class of SNe have revealed important
modifications in their radiation properties, due to the presence of high
density CSM. Forward shock dominance of the X-ray emission, internal free-free
absorption of the radio emission, episodic or non-steady mass loss rate,
asymmetry in the explosion seem to be common properties of this class of SNe.Comment: Fixed minor typos. 31 pages, 9 figures, accepted for publication in
Space Science Reviews. Chapter in International Space Science Institute
(ISSI) Book on "Supernovae" to be published in Space Science Reviews by
Springe
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201
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