Hasta nunca, hasta siempre

Boyero, C. (1998). Hasta nunca, hasta siempre. Nosferatu. Revista de cine. (28):80-81. http://hdl.handle.net/10251/41106.80812

Compuestos de alúminamolibdeno obtenidos por SPS mediante polvos activados mecánicamente

In this work, the main purpose is to develop different composites of Al2O3-Mo varying the volume percentage of materials to see their variation of properties and to find the best composition of metal and ceramic in order to get the best results. As a short way to explain the process to develop the composite, we could say that these were the main stages of the production: 1. For obtaining a homogeneous ceramic-metallic mixture of powders we milled alumina and molybdenum powders. 2. The mixture is milled for 15, 30, 60, 90, 120, 180 and 240 minutes. Different samples of the mixture will be taken and analyzed in SEM and XRD. 3. After finding the right milling time, different pieces of the mixtures will be made by sintering by the SPS process. If the pieces are correctly done, we will make some mechanical tests to analyze its properties. 4. An evolution or properties will be made to analyze the consequences of the volume percentage of molybdenum in the composite. 5. Discussion of the results.El presente trabajo se centrará en la obtención del material compuesto metálico-cerámico formado por alúmina y molibdeno, así como su estudio de propiedades y variación de éstas en función de las proporciones de ambos constituyentes. De una manera breve, el proceso llevado a cabo en este proyecto ha sido el siguiente: 1. Molienda de polvos de alúmina y molibdeno en un molino mecánico. 2. Estudio del tiempo óptimo de molienda. 3. Distintas composiciones de polvos compuestos son sinterizados mediante Spark Plasma Sintering en temperaturas y tiempos variables. 4. Estudio de propiedades y análisis de resultados.Ingeniería Industria

Transverse phase matching of high-order harmonic generation in single-layer graphene

[EN]The efficiency of high-harmonic generation (HHG) from a macroscopic sample is strongly linked to the proper phase matching of the contributions from the microscopic emitters. We develop a combined micro+macroscopic theoretical model that allows us to distinguish the relevance of high-order harmonic phase matching in single-layer graphene. For a Gaussian driving beam, our simulations show that the relevant HHG emission is spatially constrained to a phase-matched ring around the beam axis. This remarkable finding is a direct consequence of the non-perturbative behavior of HHG in graphene—whose harmonic efficiency scaling is similar to that already observed in gases— and bridges the gap between the microscopic and macroscopic HHG in single-layer graphene.This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 851201). We thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (FI-2020-3-0013). Junta de Castilla y León and FEDER (SA287P18); European Research Council (851201); Ministerio de Ciencia, Innovación y Universidades (FIS2016-75652-P, RYC-2017-22745, PID2019-106910GB-I00)

High harmonic generation in armchair carbon nanotubes

[EN]We study high-order harmonic generation (HHG) in armchair-type single-wall carbon nanotubes (SWNTs) driven by ultrashort, mid-infrared laser pulses. For a SWNT with chiral indices (n, n), we demonstrate that HHG is dominated by bands |m| = n − 1 and that the cut-off frequency saturates with intensity, as it occurs in the case of single layer graphene. As a consequence, HHG in SWNTs can be described effectively as a one-dimensional periodic system, whose high-frequency emission can be modified through the proper control of the structural parameters. Additionally, we show that the HHG mechanism in nanotubes has some similarities to that previously reported in single layer graphene. However, as a main difference, the electron-hole pair excitation in SWNTs is connected to the non-adiabatic crossing through the first van Hove singularity of the |m| = n − 1 bands, instead of the crossing through the Dirac point that takes place in graphene.Junta de Castilla y León, European Regional Development Fund(SA287P18); Ministerio de Ciencia, Innovación y Universidades (FIS2016-75652-P, RYC-2017-22745, PID2019-106910GB-I00); European Research Council (851201

Optical anisotropy of non-perturbative high-order harmonic generation in gapless graphene

[EN]High harmonic generation in atomic or molecular targets stands as a robust mechanism to produce coherent ultrashort pulses with controllable polarization in the extreme-ultraviolet. However, the production of elliptically or circularly-polarized harmonics is not straightforward, demanding complex combinations of elliptically or circularly-polarized drivers, or the use of molecular alignment techniques. Nevertheless, recent studies show the feasibility of high-harmonic generation in solids. In contrast with atoms and molecules, solids are high-density targets and therefore more efficient radiation sources. Among solid targets, 2D materials are of special interest due to their particular electronic structure, which conveys special optical properties. In this paper, we present theoretical calculations that demonstrate an extraordinary complex light-spin conversion in single-layer graphene irradiated at non perturbative intensities. Linearly-polarized drivings result in the emission of elliptically-polarized harmonics, and elliptically-polarized drivings may result in linearly-polarized or ellipticity-reversed harmonics. In addition, we demonstrate the ultrafast temporal modulation of the harmonic ellipticity.Junta de Castilla y León (SA287P18); Agencia Estatal de Innovación (FIS2016-75652-P, EQC2018-004117-P); Comunidad de Madrid (2017-T1/IND-5432); Agencia Estatal de Investigación (RYC-2017-22745)

Non-classical high harmonic generation in graphene driven by linearly-polarized laser pulses

[EN]Recent studies in high-order harmonic generation (HHG) in solid targets reveal new scenarios of extraordinary rich electronic dynamics, in comparison to the atomic and molecular cases. For the later, the main aspects of the process can be described semiclassically in terms of electrons that recombine when the trajectories revisit the parent ion. HHG in solids has been described by an analogous mechanism, in this case involving electron-hole pair recombinations. However, it has been recently reported that a substantial part of the HHG emission corresponds to situations where the electron and hole trajectories do not overlap in space. According to the present knowledge, HHG from this imperfect recollisions reflects the quantum nature of the process, arising in systems with large Berry curvatures or for elliptically polarized driving fields. In this work, we demonstrate that imperfect recollisions are also relevant in the more general case. We show the signature of such recollisions in the HHG spectrum from monolayer graphene —a system with null Berry curvature— irradiated by linearly polarized driving fields. Our calculations also reveal that imperfect multiple-order recollisions contribute to the harmonic emission when electron-hole excursion times exceed one cycle of the driving field. We believe that our work adds a substantial contribution to the full understanding of the sub-femtosecond dynamics of HHG in solid systems.European Research Council (851201); Ministerio de Educación, Cultura y Deporte (FPU18/03348); FEDER funds (SA287P18); Junta de Castilla y León (SA287P18); Ramón y Cajal (RYC-2017-22745); Ministerio de Ciencia, Innovación y Universidades (PID2019-106910GB-100)

High-order harmonic spectroscopy of polycrystalline graphene

European Research Council (851201); Ministerio de Educación y Formación Profesional (FPU18/03348); Junta de Castilla y León (SA287P18); Ministerio de Ciencia, Innovación y Universidades (PID2019-106910GB-100, RYC-2017-22745).Present mass production of large-area single-layer graphene relies fundamentally on chemical vapor deposition methods. The generation of grain boundaries, which divides the sample into a set of crystalline domains, is inherent to these fabrication methods. Recent studies have demonstrated a strong anisotropy in the ultrafast non-linear response of single-layer graphene when subjected to non-perturbative, intense laser fields below the damage threshold. We propose to exploit this anisotropy to characterize the size distribution of graphene domains in polycrystals via high-order harmonic polarimetry. Our simulation results demonstrate the sensitivity of the harmonic polarization state to details of the polycrystal grain distribution. In particular, we show that the rotation in the polarization tilt of the highest-order harmonics holds information about the grain distribution in the polycrystal. As a proof-of-concept, we propose a method to determine the standard deviation of the grain size distribution from the values of the most frequent grain size and the standard deviation of the harmonic tilt rotation from a set of hypothetical measurements on different polycrystal realizations. Our work reveals the capability of high-order harmonic polarimetry to characterize polycrystalline two-dimensional materials

Relationship between salt use in fish farms and driftof macroinvertebrates in a freshwater stream

In Chile, salt (NaCl) use per salmon fish farm ranges between 20-30 t yr(-1) and is used to prevent and control fungal infections. An increase in salinity in freshwater can have adverse effects on freshwater biodiversity and ecosystem functions and services. We studied the effects of fish-farm effluents on benthic macroinvertebrate communities in a northern Patagonian stream (Chile). Benthic samples were collected at 3 sites near a land-based salmon aquaculture facility (one located 100 m upstream from the fish-farm outlet for effluent, 2 sites located 200 and 400 m downstream from the effluent source). We found changes in benthic macroinvertebrate communities downstream from the effluent, with higher abundances of tolerant taxa and lower abundances of sensitive taxa, which was related to nutrient and salt concentration in the water. We also studied the effects of salinity on macroinvertebrate drift in a mesocosm experiment conducted in recirculating channels, measuring the drift of 2 salt-sensitive macroinvertebrates (Andesiops peruvianus and Smicridea annulicornis), collected from an unpolluted northern Patagonian stream, after exposure to a range of salinity concentration pulses similar to those from fish farms. Our results demonstrate that (1) fish-farm effluent can alter stream macroinvertebrate community composition and dynamics, and (2) such effects are at least partly driven by high salt concentrations in effluent waters.We thank the vice rectory for research and postgraduate studies at the Catholic University of Temuco and project MECESUP UCT 0804. The study was funded by the Fondecyt project 'Tracing organic pollution from land-based aquaculture systems in terms of fluorescence spectroscopy and assessment of ecotoxicological biomarkers in aquatic organisms in Southern Chile' (Ref. 1130132). L.B. was supported by the Spanish Ministry for Science, Innovation and Universities funds (Ref. RTI2018095023-B-I00) and Basque Government funds (Ref. IT95116) to the UPV/EHU Stream Ecology Group. Editoria

Litter Decomposition can be Reduced by Pesticide Effects on Detritivores and Decomposers: Implications for Tropical Stream Functioning

Understanding which factors affect the process of leaf litter decomposition is crucial if we are to predict changes in the functioning of stream ecosystems as a result of human activities. One major activity with known consequences on streams is agriculture, which is of particular concern in tropical regions, where forests are being rapidly replaced by crops. While pesticides are potential drivers of reduced decomposition rates observed in agricultural tropical streams, their specific effects on the performance of decomposers and detritivores are mostly unknown. We used a microcosm experiment to examine the individual and joint effects of an insecticide (chlorpyrifos) and a fungicide (chlorothalonil) on survival and growth of detritivores (Anchytarsus, Hyalella and Lepidostoma), aquatic hyphomycetes (AH) sporulation rate, taxon richness, assemblage structure, and leaf litter decomposition rates. Our results revealed detrimental effects on detritivore survival (which were mostly due to the insecticide and strongest for Hyalella), changes in AH assemblage structure, and reduced sporulation rate, taxon richness and microbial decomposition (mostly in response to the fungicide). Total decomposition was reduced especially when the pesticides were combined, suggesting that they operated differently and their effects were additive. Importantly, effects on decomposition were greater for single-species detritivore treatments than for the 3-species mixture, indicating that detritivore species loss may exacerbate the consequences of pesticides of stream ecosystem functioning.This work was supported by the National Secretariat for Science, Technology and Innovation (SENACYT; project APY-GC-2018B-052; contract no. 259e2018) and the Ministry of Economy and Finance of Panama (MEF; project 019910.001). AC was supported by a fellowship from SENACYT (contract no. 001e2015) and by the National Research System of Panama (SNI; PhD category; contract no. 186e2018). GC was supported by a fellowship from IFARHU- SENACYT (contract no. 270-2018-1011

Topological high-harmonic spectroscopy.

[EN]Linearly polarized vector beams are structured lasers whose topology is characterized by a well-defined Poincar index, which is a topological invariant during high-order harmonic generation. As such, harmonics are produced as extreme-ultraviolet vector beams that inherit the topology of the driver. This holds for isotropic targets such as oble gases, but analogous behaviour in crystalline solids is still open to discussion. Here, we demonstrate that this conservation rule breaks in crystalline solids, in virtue of their anisotropic non-linear susceptibility. We identify the topological properties of the harmonic field as unique probes, sensitive to both the microscopic and macroscopic features of the target’s complex non-linear response. Our simulations, performed in single-layer graphene, show that the harmonic field is split into a multi-beam structure whose topology encodes information about laser-driven electronic dynamics. Our work promotes the topological analysis of the high-order harmonic field as a spectroscopic tool to reveal the nonlinearities in the coupling of light and target symmetries