Abastecimiento de aguas de León : observaciones

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

The cooling, mass and radius of the neutron star in EXO 0748-676 in quiescence with XMM-Newton

We analyse four XMM-Newton observations of the neutron-star low-mass X-ray binary EXO 0748$-$676 in quiescence. We fit the spectra with an absorbed neutron-star atmosphere model, without the need for a high-energy (power-law) component; with a 95 per cent confidence the power-law contributes less than 1 per cent to the total flux of the source in $0.5-10.0$ keV. The fits show significant residuals at around 0.5 keV which can be explained by either a hot gas component around the neutron star or a moderately broad emission line from a residual accretion disc. The temperature of the neutron-star has decreased significantly compared to the previous observation, from 124 eV to 105 eV, with the cooling curve being consistent with either an exponential decay plus a constant or a (broken) power law. The best-fitting neutron-star mass and radius can be better constrained if we extend the fits down to the lowest possible energy available. For an assumed distance of 7.1 kpc, the best-fitting neutron-star mass and radius are $2.00_{-0.24}^{+0.07}~M_\odot$ and $11.3_{-1.0}^{+1.3}$ km if we fit the spectrum over the $0.3-10$ keV range, but $1.50_{-1.0}^{+0.4}~M_\odot$ and $12.2_{-3.6}^{+0.8}$ km if we restrict the fits to the $0.5-10$ keV range. We finally discuss the effect of the assumed distance to the source upon the best-fitting neutron-star mass and radius. As systematic uncertainties in the deduced mass and radius depending on the distance are much larger than the statistical errors, it would be disingenuous to take these results at face value.Comment: 12 pages, 6 figure

Ultrafast Dynamics of Folded Acoustic Phonons from Semiconductor Superlattices.

There is great interest in the coherent control of short-wavelength acoustic phonons using ultrafast laser pulses for applications such as imaging and energy transport. Metallic layers have been used extensively as optical transducers for generation and measurement of strain pulses. This approach is usually limited to a few hundred GHz. The folding of the acoustic branches in periodic superlattices provides an alternative way to couple light pulses with high-frequency (1 THz) crystal vibrations. This dissertation reports on novel studies of laser-generated folded acoustic phonons in semiconductor superlattices. Through ultrafast laser and x-ray experiments, important aspects of the generation, propagation and detection of these modes are obtained. Also, detailed simulations and new theoretical considerations provide insights into the fundamental physics of folded acoustic phonons. Coherent folded acoustic phonons are studied using pump-probe experiments with ultrashort laser and X-ray pulses. A scheme to study the propagation of folded acoustic phonons is introduced that uses two superlattices as acoustic transducers. The folded phonons are generated in one superlattice and detected on a second superlattice 1.2um apart. A solution of the wave equation in terms of eigenmodes accounts for the observed features in the reflectivity spectrum. The model predicts that eigenmodes with frequencies near the acoustic gaps avoid the boundaries and exhibit confinement in the superlattice. The experimental observations confirm the presence of a long lived acoustic mode in the superlattice which lies near the first zone-center folded acoustic gap. This surface-avoiding behavior is shown to ocurr in general for any wave under a periodic perturbation. Short X-ray pulses from the Advanced Photon Source are used to probe the folded acoustic phonons as they propagate from the superlattice into the substrate. Experiments show that a bulk excitation at a wavevector 2pi/D, where D is the superlattice period, is launched from the superlattice into the substrate and propagates at the speed of sound. Results are supported by calculations of the time-resolved diffraction under the presence of strain. This observation demonstrates the capabilities of ultrafast X-ray diffraction for measuring high-wavevector excitations and holds promise for studying dynamical processes in crystals throughout the full Brillouin zone.Ph.D.Applied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58481/1/mtrigo_1.pd

The persistence of memory in ionic conduction probed by nonlinear optics

Predicting practical rates of transport in condensed phases enables the rational design of materials, devices and processes. This is especially critical to developing low-carbon energy technologies such as rechargeable batteries1,2,3. For ionic conduction, the collective mechanisms4,5, variation of conductivity with timescales6,7,8 and confinement9,10, and ambiguity in the phononic origin of translation11,12, call for a direct probe of the fundamental steps of ionic diffusion: ion hops. However, such hops are rare-event large-amplitude translations, and are challenging to excite and detect. Here we use single-cycle terahertz pumps to impulsively trigger ionic hopping in battery solid electrolytes. This is visualized by an induced transient birefringence, enabling direct probing of anisotropy in ionic hopping on the picosecond timescale. The relaxation of the transient signal measures the decay of orientational memory, and the production of entropy in diffusion. We extend experimental results using in silico transient birefringence to identify vibrational attempt frequencies for ion hopping. Using nonlinear optical methods, we probe ion transport at its fastest limit, distinguish correlated conduction mechanisms from a true random walk at the atomic scale, and demonstrate the connection between activated transport and the thermodynamics of information

Population structure and gene flow of Geoffroy's cat (Leopardus geoffroyi) in the Uruguayan Savanna ecoregion

Felids are among the species most threatened by habitat fragmentation resulting from land-use change. In the Uruguayan Savanna ecoregion, about 30% of natural habitats have been lost, large felids have been eradicated from most of the region, and the impact of anthropogenic threats over the smaller species that remain is unknown. To develop management strategies, it is important to enhance knowledge about species population structure and landscape connectivity, particularly when land-use change will continue and intensify in the next years. In this study, we evaluate the population structure and gene flow of Geoffroy's cat in the Uruguayan Savanna ecoregion. We generated a matrix of 11 microsatellite loci for 70 individuals. Based on Bayesian approaches we found that within the Uruguayan Savanna, Geoffroy's cat shows high levels of genetic variability and no population structure. However, we observed genetic differences between individuals from the Uruguayan Savanna and those from the contiguous ecoregion, the Argentinian Humid Pampa. Four first-generation migrants from Humid Pampa were identified in the Uruguayan Savanna, suggesting a stronger gene flow in the west-east direction. We detected a past bottleneck followed by a subsequent recovery in Geoffroy's cat populations in both ecoregions. These results lay the groundwork to understand the population dynamics and conservation status of Geoffroy's cat in the Uruguayan Savanna ecoregion, and provide baseline data to establish population monitoring.Fil: Bou, Nadia. Ministerio de Educacion y Cultura.; UruguayFil: Soutullo, Álvaro. Universidad de la Republica; UruguayFil: Hernández, Daniel. Laboratorio de Control Ambiental; UruguayFil: Mannise, Natalia. Ministerio de Educacion y Cultura.; UruguayFil: González, Susana. Ministerio de Educacion y Cultura.; UruguayFil: Bartesaghi, Lucía. Ministerio de Educacion y Cultura.; UruguayFil: Pereira, Javier Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Merino, Mariano Lisandro. Universidad Nacional del Noroeste de la Provincia de Buenos Aires. Centro de Bioinvestigaciones (Sede Junín); ArgentinaFil: Espinosa, Caroline. Universidade Federal do Rio Grande do Sul; BrasilFil: Trigo, Tatiane C.. Museu de Ciencias Naturais; ArgentinaFil: Cosse, Mariana. Ministerio de Educacion y Cultura.; Urugua

All-optical seeding of a light-induced phase transition with correlated disorder

Ultrafast manipulation of vibrational coherence is an emergent route to control the structure of solids. However, this strategy can only induce long-range correlations and cannot modify atomic structure locally, which is required in many technologically-relevant phase transitions. Here, we demonstrate that ultrafast lasers can generate incoherent structural fluctuations which are more efficient for material control than coherent vibrations, extending optical control to a wider range of materials. We observe that local, non-equilibrium lattice distortions generated by a weak laser pulse reduce the energy barrier to switch between insulating and metallic states in vanadium dioxide by 6%. Seeding inhomogeneous structural-fluctuations presents an alternative, more energy efficient, route for controlling materials that may be applicable to all solids, including those used in data and energy storage devices

Ultrafast disordering of vanadium dimers in photoexcited VO2

Time-resolved x-ray scattering can be used to investigate the dynamics of materials during the switch from one structural phase to another. So far, methods provide an ensemble average and may miss crucial aspects of the detailed mechanisms at play. Wall et al. used a total-scattering technique to probe the dynamics of the ultrafast insulator-to-metal transition of vanadium dioxide (VO2) (see the Perspective by Cavalleri). Femtosecond x-ray pulses provide access to the time- and momentum-resolved dynamics of the structural transition. Their results show that the photoinduced transition is of the order-disorder type, driven by an ultrafast change in the lattice potential that suddenly unlocks the vanadium atoms and yields large-amplitude uncorrelated motions, rather than occurring through a coherent displacive mechanism.Peer ReviewedPostprint (author's final draft

Outflow Legacy Accretion Survey: unveiling the wind driving mechanism in BHXRBs

Transient black-hole X-ray binaries viewed at high inclinations display blue-shifted absorption lines in their X-ray spectra. These features are the signatures of powerful, hot and equatorial accretion disk winds being driven from these systems in their luminous soft states. Remarkably, blue-shifted absorption lines have recently also been discovered in optical and NIR recombination lines and ultraviolet resonance features. These features must also be produced in an outflow, but the physical conditions traced by these outflows are different. Despite this, the characteristic Doppler velocities of all three types of signatures are comparable, yet they have never been observed simultaneously. It is therefore completely unclear if they are associated with distinct outflows (e.g. driven by different mechanisms) or simply with different regions/phases within the same outflow. Here, we propose to answer this question by carrying out simultaneous time-resolved spectroscopy of a high-inclination system in the X-ray, ultraviolet and optical bands, in its two distinct physical configurations (hard- and soft-states). This will allow us to test if the three types of wind features are present simultaneously, and, if so, whether they display correlated variability and/or velocity structure