LÓPEZ, FERNANDA [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Time-dependent density-functional theory approach to nonlinear particle-solid interactions in comparison with scattering theory

An explicit expression for the quadratic density-response function of a many-electron system is obtained in the framework of the time-dependent density-functional theory, in terms of the linear and quadratic density-response functions of noninteracting Kohn-Sham electrons and functional derivatives of the time-dependent exchange-correlation potential. This is used to evaluate the quadratic stopping power of a homogeneous electron gas for slow ions, which is demonstrated to be equivalent to that obtained up to second order in the ion charge in the framework of a fully nonlinear scattering approach. Numerical calculations are reported, thereby exploring the range of validity of quadratic-response theory.Comment: 14 pages, 3 figures. To appear in Journal of Physics: Condensed Matte

The diverse meteorology of Jezero crater over the first 250 sols of Perseverance on Mars

ASA’s Perseverance rover’s Mars Environmental Dynamics Analyzer is collecting data at Jezero crater, characterizing the physical processes in the lowest layer of the Martian atmosphere. Here we present measurements from the instrument’s first 250 sols of operation, revealing a spatially and temporally variable meteorology at Jezero. We find that temperature measurements at four heights capture the response of the atmospheric surface layer to multiple phenomena. We observe the transition from a stable night-time thermal inversion to a daytime, highly turbulent convective regime, with large vertical thermal gradients. Measurement of multiple daily optical depths suggests aerosol concentrations are higher in the morning than in the afternoon. Measured wind patterns are driven mainly by local topography, with a small contribution from regional winds. Daily and seasonal variability of relative humidity shows a complex hydrologic cycle. These observations suggest that changes in some local surface properties, such as surface albedo and thermal inertia, play an influential role. On a larger scale, surface pressure measurements show typical signatures of gravity waves and baroclinic eddies in a part of the seasonal cycle previously characterized as low wave activity. These observations, both combined and simultaneous, unveil the diversity of processes driving change on today’s Martian surface at Jezero crater

Non-perturbative methods in two-dimensional quantum field theory

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Hazes and clouds in a singular triple vortex in Saturn's atmosphere from HST/WFC3 multispectral imaging

In this paper we present a study of the vertical haze and cloud structure over a triple vortex in Saturn's atmosphere in the planetographic latitude range 55°N-69°N (del Río-Gaztelurrutia et al., 2018) using HST/WFC3 multispectral imaging. The observations were taken during 29–30 June and 1 July 2015 at ten different filters covering spectral range from the 225 nm to 937 nm, including the deep methane band at 889 nm. Absolute reflectivity measurements of this region at all wavelengths and under a number of illumination and observation geometries are fitted with the values produced by a radiative transfer model. Most of the reflectivity variations in this wavelength range can be attributed to changes in the tropospheric haze. The anticyclones are optically thicker (τ ~25 vs ~10), more vertically extended (~3 gas scale heights vs ~2) and their bases are located deeper in the atmosphere (550 mbar vs 500 mbar) than the cyclone

The behaviour of the O(3) sigma model at theta = pi

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Deep winds beneath Saturn's upper clouds from a seasonal long-lived planetary-scale storm.

Convective storms occur regularly in Saturn's atmosphere. Huge storms known as Great White Spots, which are ten times larger than the regular storms, are rarer and occur about once per Saturnian year (29.5 Earth years). Current models propose that the outbreak of a Great White Spot is due to moist convection induced by water. However, the generation of the global disturbance and its effect on Saturn's permanent winds have hitherto been unconstrained by data, because there was insufficient spatial resolution and temporal sampling to infer the dynamics of Saturn's weather layer (the layer in the troposphere where the cloud forms). Theoretically, it has been suggested that this phenomenon is seasonally controlled. Here we report observations of a storm at northern latitudes in the peak of a weak westward jet during the beginning of northern springtime, in accord with the seasonal cycle but earlier than expected. The storm head moved faster than the jet, was active during the two-month observation period, and triggered a planetary-scale disturbance that circled Saturn but did not significantly alter the ambient zonal winds. Numerical simulations of the phenomenon show that, as on Jupiter, Saturn's winds extend without decay deep down into the weather layer, at least to the water-cloud base at pressures of 10-12 bar, which is much deeper than solar radiation penetrates

Observations of the climate near the surface of Jezero over a half Mars year

International audiencePerseverance landed on Jezero with the most complete suite of environmental sensors ever sent to the surface of another planet. It combines the Mars Environmental Dynamics Analyzer (MEDA), the MastCam-Z and Engineering cameras, SuperCam spectrometers and, finally, the several microphones onboard the Mars 2020 rover. The most recent collection of atmospheric observations at Jezero and their interpretation are building an understanding of what physical processes drive the behavior of the Martian atmosphere near the surface of Jezero. We report on the observed Martian cycles of pressure, temperature, dust opacity with their physical aerosol properties, and the hydrological cycle at Jezero. These cycles have shown different behaviors on time scales from diurnal to seasonal and annual to other locations where we landed before. The differences illustrate the range of environmental processes that one can find near the red planet’s surface. We also report on the observed evolution of the near-surface boundary layer thermodynamics during the day and nighttime regimes