5,747 research outputs found
Stationary waves and slowly moving features in the night upper clouds of Venus
At the cloud top level of Venus (65-70 km altitude) the atmosphere rotates 60
times faster than the underlying surface, a phenomenon known as superrotation.
Whereas on Venus's dayside the cloud top motions are well determined and Venus
general circulation models predict a mean zonal flow at the upper clouds
similar on both day and nightside, the nightside circulation remains poorly
studied except for the polar region. Here we report global measurements of the
nightside circulation at the upper cloud level. We tracked individual features
in thermal emission images at 3.8 and 5.0 obtained between
2006 and 2008 by the Visible and Infrared Thermal Imaging Spectrometer
(VIRTIS-M) onboard Venus Express and in 2015 by ground-based measurements with
the Medium-Resolution 0.8-5.5 Micron Spectrograph and Imager (SpeX) at the
National Aeronautics and Space Administration Infrared Telescope Facility
(NASA/IRTF). The zonal motions range from -110 to -60 m s, consistent
with those found for the dayside but with larger dispersion. Slow motions (-50
to -20 m s) were also found and remain unexplained. In addition,
abundant stationary wave patterns with zonal speeds from -10 to +10 m s
dominate the night upper clouds and concentrate over the regions of higher
surface elevation.Comment: 15 pages, 4 figures, 6 supplementary figure
The dependence of oxygen and nitrogen abundances on stellar mass from the CALIFA survey
We analysed the optical spectra of HII regions extracted from a sample of 350
galaxies of the CALIFA survey. We calculated total O/H abundances and, for the
first time, N/O ratios using the semi-empirical routine HII-CHI-mistry, which,
according to P\'erez-Montero (2014), is consistent with the direct method and
reduces the uncertainty in the O/H derivation using [NII] lines owing to the
dispersion in the O/H-N/O relation. Then we performed linear fittings to the
abundances as a function of the de-projected galactocentric distances. The
analysis of the radial distribution both for O/H and N/O in the non-interacting
galaxies reveals that both average slopes are negative, but a non-negligible
fraction of objects have a flat or even a positive gradient (at least 10\% for
O/H and 4\% for N/O). The slopes normalised to the effective radius appear to
have a slight dependence on the total stellar mass and the morphological type,
as late low-mass objects tend to have flatter slopes. No clear relation is
found, however, to explain the presence of inverted gradients in this sample,
and there is no dependence between the average slopes and the presence of a
bar. The relation between the resulting O/H and N/O linear fittings at the
effective radius is much tighter (correlation coefficient = 0.80) than
between O/H and N/O slopes ( = 0.39) or for O/H and N/O in the
individual \hii\ regions ( = 0.37). These O/H and N/O values at the
effective radius also correlate very tightly (less than 0.03 dex of dispersion)
with total luminosity and stellar mass. The relation with other integrated
properties, such as star formation rate, colour, or morphology, can be
understood only in light of the found relation with mass.Comment: Accepted for publication in A&A. 20 pages, 19 figure
Rare Events and Scale--Invariant Dynamics of Perturbations in Delayed Dynamical Systems
We study the dynamics of perturbations in time delayed dynamical systems.
Using a suitable space-time coordinate transformation, we find that the time
evolution of the linearized perturbations (Lyapunov vector) can be mapped to
the linear Zhang surface growth model [Y.-C. Zhang, J. Phys. France {\bf 51},
2129 (1990)], which is known to describe surface roughening driven by power-law
distributed noise. As a consequence, Lyapunov vector dynamics is dominated by
rare random events that lead to non-Gaussian fluctuations and multiscaling
properties.Comment: Final version to appear in Phys. Rev. Lett., 4 pages, 3 eps fig
Analysis of the wave propagation properties of a periodic array of rigid cylinders perpendicular to a finite impedance surface
The effect of the presence of a finite impedance surface on the wave
propagation properties of a two-dimensional periodic array of rigid cylinders
with their axes perpendicular to the surface is both numerically and
experimentally analyzed in this work. In this realistic situation both the
incident and the scattered waves interact with these two elements, the surface
and the array. The interaction between the excess attenuation effect, due to
the destructive interference produced by the superposition of the incident wave
and the reflected one by the surface, and the bandgap, due to the periodicity
of the array, is fundamental for the design of devices to control the
transmission of waves based on periodic arrays. The most obvious application is
perhaps the design of Sonic Crystals Noise Barriers. Two different finite
impedance surfaces have been analyzed in the work in order to observe the
dependence of the wave propagation properties on the impedance of the surface
The action of obestatin in skeletal muscle repair: stem cell expansion, muscle growth, and microenvironment remodeling
The development of therapeutic strategies for skeletal muscle diseases, such as physical injuries and myopathies, depends on the knowledge of regulatory signals that control the myogenic process. The obestatin/GPR39 system operates as an autocrine signal in the regulation of skeletal myogenesis. Using a mouse model of skeletal muscle regeneration after injury and several cellular strategies, we explored the potential use of obestatin as a therapeutic agent for the treatment of trauma-induced muscle injuries. Our results evidenced that the overexpression of the preproghrelin, and thus obestatin, and GPR39 in skeletal muscle increased regeneration after muscle injury. More importantly, the intramuscular injection of
obestatin significantly enhanced muscle regeneration by simulating satellite stem cell expansion as well as myofiber hypertrophy through a kinase hierarchy. Added to the myogenic action, the obestatin administration resulted in an increased expression of VEGF/VEGFR2 and the consequent microvascularization, with no effect on collagen deposition in skeletal muscle. Furthermore, the potential inhibition of myostatin during obestatin treatment might contribute to its myogenic action improving muscle growth and regeneration. Taken together, our data demonstrate successful improvement of muscle regeneration, indicating obestatin is a potential therapeutic agent for skeletal muscle injury and would
benefit other myopathies related to muscle regeneration
Propagating and evanescent properties of duble-point defect in sonic crystals
Complex band structures and multiple scattering theory have been
used in this paper to analyze the overlapping of the evanescent waves localized
in point defects in sonic crystals (SCs). The extended plane wave expansion
(EPWE) with supercell approximation gives the imaginary part of the Bloch
vectors that produces the decay of the localized modes inside the periodic
system. Double cavities can present a coupling between the evanescent modes
localized in the defect, showing a symmetric or antisymmetric mode. When point
defects are close, the complex band structures reveal a splitting of the frequencies
of the localized modes. Both the real part and the imaginary values of k of
the localized modes in the cavities present different values for each localized
mode, which gives different properties for each mode. The novel measurements,
in very good agreement with analytical data, show experimental evidence of
the symmetric and antisymmetric localized modes for a double-point defect in
SCs. The investigation of the localization phenomena and the coupling between
defects in periodic systems has fundamental importance in both pure and applied
physics.This work was supported by MEC (the Spanish Government) and FEDER funds through grants MAT2009-09438 and MTM2009-14483-C02-02.Romero García, V.; Sánchez Pérez, JV.; García-Raffi, LM. (2010). Propagating and evanescent properties of duble-point defect in sonic crystals. New Journal of Physics. 12:1-14. doi:10.1088/1367-2630/12/8/083024S1141
Stiff monatomic gold wires with a spinning zigzag geometry
Using first principles density functional calculations, gold monatomic wires
are found to exhibit a zigzag shape which remains under tension, becoming
linear just before breaking. At room temperature they are found to spin, what
explains the extremely long apparent interatomic distances shown by electron
microscopy.The zigzag structure is stable if the tension is relieved, the wire
holding its chainlike shape even as a free-standing cluster. This unexpected
metallic-wire stiffness stems from the transverse quantization in the wire, as
shown in a simple free electron model.Comment: 4 pages, latex, 5 figures, submitted to PR
Magnetic equilibrium design for the SMART tokamak
The SMall Aspect Ratio Tokamak (SMART) device is a new compact (plasma major radius R≥0.40 m, minor radius a≥0.20 m, aspect ratio A≥1.7) spherical tokamak, currently in development at the University of Seville. The SMART device has been designed to achieve a magnetic field at the plasma center of up to B=1.0 T with plasma currents up to I=500 kA and a pulse length up to τ=500 ms. A wide range of plasma shaping configurations are envisaged, including triangularities between −0.50≤δ≤0.50 and elongations of κ≤2.25. Control of plasma shaping is achieved through four axially variable poloidal field coils (PF), and four fixed divertor (Div) coils, nominally allowing operation in lower-single null, upper-single null and double-null configurations. This work examines phase 2 of the SMART device, presenting a baseline reference equilibrium and two highly-shaped triangular equilibria. The relevant PF and Div coil current waveforms are also presented. Equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents.The authors would like to thank the VEST team for their technical and engineering support. This work received funding from the Fondo Europeo de Desarollo Regional (FEDER) by the European Commission under grant agreement numbers IE17-5670 and US-15570. In addition support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 805162) is gratefully acknowledged
A genetic approach for long term virtual organization distribution
Electronic versíon of an article published as International Journal on Artificial Intelligent Tools, Volume 20, issue 2, 2011. 10.1142/S0218213011000152. © World Scientific Publishing Company[EN] An agent-based Virtual Organization is a complex entity where dynamic collections of agents agree to share resources in order to accomplish a global goal or offer a complex service. An important problem for the performance of the Virtual Organization is the distribution of the agents across the computational resources. The final distribution should provide a good load balancing for the organization. In this article, a genetic algorithm is applied to calculate a proper distribution across hosts in an agent-based Virtual Organization. Additionally, an abstract multi-agent system architecture which provides infrastructure for Virtual Organization distribution is introduced. The developed genetic solution employs an elitist crossover operator where one of the children inherits the most promising genetic material from the parents with higher probability. In order to validate the genetic proposal, the designed genetic algorithm has been successfully compared to several heuristics in different scenarios. © 2011 World Scientific Publishing Company.This work is supported by TIN2008-04446, TIN2009-13839-C03-01, CSD2007-00022 and FPU grant AP2008-00600 of the Spanish government, and PROMETEO 2008/051 of the Generalitat Valenciana.Sánchez Anguix, V.; Valero Cubas, S.; García Fornes, AM. (2011). A genetic approach for long term virtual organization distribution. International Journal on Artificial Intelligence Tools. 20(2):271-295. https://doi.org/10.1142/S0218213011000152S27129520
- …