Parametric attosecond pulse amplification far from the ionization threshold from high order harmonic generation in He+^+

Parametric amplification of attosecond coherent pulses around 100 eV at the single-atom level is demonstrated for the first time by using the 3D time-dependent Schr{\"o}dinger equation in high-harmonic generation processes from excited states of He$^+$. We present the attosecond dynamics of the amplification process far from the ionization threshold and resolve the physics behind it. The amplification of a particular central photon energy requires the seed XUV pulses to be perfectly synchronized in time with the driving laser field for stimulated recombination to the He$^+$ ground state and is only produced in a few specific laser cycles in agreement with the experimental measurements. Our simulations show that the amplified photon energy region can be controlled by varying the peak intensity of the laser field. Our results pave the way to the realization of compact attosecond pulse intense XUV lasers with broad applications

Mathematical e-Learning: state of the art and experiences at the Open University of Catalonia

In this article we present a review of the state of the art in mathematical e-learning and some personal experiences on this area developed during the last eleven years at the Open University of Catalonia (UOC), a completely online university located in Spain. The article discusses important aspects related to online mathematics courses offered in higher education programs, including: benefits and challenges, universities offering this type of education, methodological considerations, emergent technologies, learning projects and environments, etc. Also, key aspects of the UOC mathematical e-learning model and its historical evolution are described and analysed. Special attention is paid to mathematical curricula in computer sciences degrees, where a lot of work needs to be done in order to adapt mathematics courses to the continuously changing educational necessities of students. A curricula design proposal, based on a top-down approach, is presented as a best practice. Finally, some trends and future perspectives on the subject are suggested

Environmental factors influencing butterfly abundance after a severe wildfire in Mediterranean vegetation

Factores ambientales que influyen en la abundancia de mariposas después de un gran incendio forestal en la vegetación mediterráneaA pesar de la atención prestada a la ecología de los lepidópteros, en la región mediterránea poco se sabe acerca de las respuestas de sus comunidades a los incendios forestales. Aquí, evaluamos la comunidad de mariposas dos años después de un gran incendio forestal que afectó 13.000 ha en Cataluña (NE de España) en relación con el hábitat circundante no quemado, mediante transectos para censos visuales. Se examinaron varios parámetros de la comunidad, como la abundancia, la diversidad, la riqueza de especies y equitatividad, comparando las áreas quemadas y no quemadas. Se utilizó el análisis de correspondencias para analizar la composición específica y abundancia relativa de las especies en la comunidad. La influencia de las variables ambientales sobre la abundancia de algunas especies comunes se analizó con modelos mixtos lineales generalizados, teniendo en cuenta los efectos espaciales. No se encontraron diferencias significativas entre los tratamientos en los parámetros de la comunidad y no se detectó dominancia en la zona quemada. La estructura de la vegetación y la distribución geográfica de los transectos influyó en la ordenación de las especies y los transectos en el análisis de correpondencias, peró no se encontró ningún efecto evidente del fuego. Los resultados de los modelos lineales generalizados mixtos (GLMM) señalaron la importancia de la disponibilidad de néctar, el fuego y estructura de la vegetación para explicar la abundancia poblacional de la mayoría de las especies modelizadas.Despite the attention given to the ecology of butterflies, little is known about their community response to wildfires in the Mediterranean region. Here, we evaluated the butterfly assemblage two years after a severe, 13,000 ha wildfire in Catalonia (NE Spain) in relation to the surrounding unburned habitat. Using visual transect censuses we assessed community parameters such as abundance, diversity, species richness and equitability in burned and unburned areas. Correspondence analysis was used to analyse specific composition and relative abundance of species in the community. The influence of environmental variables on the abundance of some common species was analysed using generalized linear mixed models, taking spatial effects into account. No significant differences were found between areas for any of the community parameters, and no dominance was detected in the burned area. The structure of the vegetation and the geographical distribution of transects influenced the ordination of species and transects on the correspondence analysis plot. Generalized linear mixed models (GLMM) results underscored the role of nectar availability, fire and vegetation structure on the abundance of most species studied.Factores ambientales que influyen en la abundancia de mariposas después de un gran incendio forestal en la vegetación mediterráneaA pesar de la atención prestada a la ecología de los lepidópteros, en la región mediterránea poco se sabe acerca de las respuestas de sus comunidades a los incendios forestales. Aquí, evaluamos la comunidad de mariposas dos años después de un gran incendio forestal que afectó 13.000 ha en Cataluña (NE de España) en relación con el hábitat circundante no quemado, mediante transectos para censos visuales. Se examinaron varios parámetros de la comunidad, como la abundancia, la diversidad, la riqueza de especies y equitatividad, comparando las áreas quemadas y no quemadas. Se utilizó el análisis de correspondencias para analizar la composición específica y abundancia relativa de las especies en la comunidad. La influencia de las variables ambientales sobre la abundancia de algunas especies comunes se analizó con modelos mixtos lineales generalizados, teniendo en cuenta los efectos espaciales. No se encontraron diferencias significativas entre los tratamientos en los parámetros de la comunidad y no se detectó dominancia en la zona quemada. La estructura de la vegetación y la distribución geográfica de los transectos influyó en la ordenación de las especies y los transectos en el análisis de correpondencias, peró no se encontró ningún efecto evidente del fuego. Los resultados de los modelos lineales generalizados mixtos (GLMM) señalaron la importancia de la disponibilidad de néctar, el fuego y estructura de la vegetación para explicar la abundancia poblacional de la mayoría de las especies modelizadas

A Potential Route to Reduce Ischemia/Reperfusion Injury in Organ Preservation

The pathophysiological process of ischemia and reperfusion injury (IRI), an inevitable step in organ transplantation, causes important biochemical and structural changes that can result in serious organ damage. IRI is relevant for early graft dysfunction and graft survival. Today, in a global context of organ shortages, most organs come from extended criteria donors (ECDs), which are more sensitive to IRI. The main objective of organ preservation solutions is to protect against IRI through the application of specific, nonphysiological components, under conditions of no blood or oxygen, and then under conditions of metabolic reduction by hypothermia. The composition of hypothermic solutions includes osmotic and oncotic buffering components, and they are intracellular (rich in potassium) or extracellular (rich in sodium). However, above all, they all contain the same type of components intended to protect against IRI, such as glutathione, adenosine and allopurinol. These components have not changed for more than 30 years, even though our knowledge of IRI, and much of the relevant literature, questions their stability or efficacy. In addition, several pharmacological molecules have been the subjects of preclinical studies to optimize this protection. Among them, trimetazidine, tacrolimus and carvedilol have shown the most benefits. In fact, these drugs are already in clinical use, and it is a question of repositioning them for this novel use, without additional risk. This new strategy of including them would allow us to shift from cold storage solutions to cold preservation solutions including multitarget pharmacological components, offering protection against IRI and thus protecting today's more vulnerable organs

All-solid-state VUV frequency comb at 160 nm using high-harmonic generation in nonlinear femtosecond enhancement cavity

© 2019 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.We realized a solid-state-based vacuum ultraviolet frequency comb by harmonics generation in an external enhancement cavity. Optical conversions were so far reported by only using gaseous media. We present a theory that allows the most suited solid generation medium to be selected for specific target harmonics by adapting the material’s bandgap. We experimentally use a thin AlN film grown on a sapphire substrate to realize a compact frequency comb high-harmonic source in the Deep Ultraviolet (DUV)/Vacuum Ultraviolet/Deep Ultraviolet (VUV) spectral range. By extending our earlier VUV source [Opt. Express 26, 21900 (2018)] with the enhancement cavity, a sub-Watt level Ti:sapphire femtosecond frequency comb is enhanced to 24 W stored average power, its 3rd, 5th, and 7th harmonics are generated, and the targeted 5th harmonic’s power at 160 nm increased by two orders of magnitude. The emerging nonlinear effects in the solid medium, together with suitable intra-cavity dispersion management, support optimal enhancement and stable locking. To demonstrate the realized frequency comb’s spectroscopic ability, we report on the beat measurement between the 3rd harmonic beam and a 266 nm CW laser reaching about 1 MHz accuracy.Peer ReviewedPostprint (published version

Ultrashort pulse control of space-dependent excitations in a three-level system

Coherent control of regions with spatial excitation of populations and coherence between two lower states in three-level Λ-type quantum systems mediated by the self-induced transparency (SIT) phenomenon is theoretically investigated with one- and two-color ultrashort pulses and with pulse sequences beyond the slowly varying envelope (SVEA) and rotating wave (RWA) approximations. The effects of different parameters characterizing the pulses and the medium on the location as well as the width of such excited regions have been studied numerically by means of the finite-difference time-domain (FDTD) method. It has been determined that with a scheme of two-pulse excitation one can effectively control the position at which the region is written and its width. In particular, the position of the excited region can be controlled by the area of the pulses. We find that the maximum value of the population transferred to the lower excited state depends on the detuning of the pulses with respect to the one-photon resonances, and that both position and width of the region also depend on the temporal duration of the pulses. We show how after the excited region is written, its position can be shifted by additional pulses. On the basis of numerical results, scaling laws are formulated for the reported phenomena. With such control, the width of the region excited inside the medium can be reduced to the order of the wavelength of the light