Full two-photon downconversion of just a single photon

We demonstrate, both numerically and analytically, that it is possible to generate two photons from one and only one photon. We characterize the output two photon field and make our calculations close to reality by including losses. Our proposal relies on real or artificial three-level atoms with a cyclic transition strongly coupled to a one-dimensional waveguide. We show that close to perfect downconversion with efficiency over 99% is reachable using state-of-the-art Waveguide QED architectures such as photonic crystals or superconducting circuits. In particular, we sketch an implementation in circuit QED, where the three level atom is a transmon

Cyttaria hariotii E.Fisch. as a promising source of pullulan and Mn(II)-pullulan complexes for Mn-deficiency remediation in winter cereals

Pullulan, a water-soluble polysaccharide consisting of maltotriose units used in the preparation of edible films and drug delivery, is generally produced from starch by Aureobasidium pullulans (de Bary & Löwenthal) G.Arnaud fungus. In this article, the characterisation of an alternative pullulan source - the stromata of Cyttaria hariotii E.Fisch. fungus - by elemental analysis, infrared spectroscopy and thermal analysis techniques is reported. With a view to a possible valorisation of this pullulan and its derivatives as bioactive formulations in agriculture, low-molecular-weight pullulan (<7 kDa) complexes with Mn(II), suitable for the remediation of Mn-deficiencies in winter cereal by foliar application, were synthesised and characterised by mass spectrometry

Search for the sub-stellar lithium depletion boundary in the open star cluster Coma Berenices

We mainly aim to search for the lithium depletion boundary (LDB) among the sub-stellar population of the open star cluster Coma Berenices. We carried out a search for brown dwarf (BD) candidates using colour-magnitude diagrams combining optical and infrared photometry from the latest public releases of the following large-scale surveys: UKIRT/UKIDSS, Pan-STARRS, SDSS, and AllWISE. We checked astrometric consistency with cluster membership using $Gaia$ DR2. A couple dozen new candidate BDs located inside the tidal radius of Coma Ber are reported, but none of these are significantly fainter and cooler than previously known members. A search for Li in three new and five previously known BD candidate cluster members was performed via spectroscopic observations using the OSIRIS instrument at the 10.4-m GTC. No LiI resonance doublet at 6707.8 A was detected in any of eight Coma Ber targets in the magnitude range J=15--19 and G=20--23 observed with the GTC. Spectral types and radial velocities were derived from the GTC spectra. These values confirm the cluster membership of four L2--L2.5 dwarfs, two of which are new in the literature. The large Li depletion factors found among the four bona fide BD members in Coma Ber implies that the LDB must be located at spectral type later than L2.5 in this cluster. Using the latest evolutionary models for BDs, a lower limit of 550 Myr on the cluster age is set. This constraint has been combined with other dating methods to obtain an updated age estimate of 780$\pm$230 Myr for the Coma Ber open cluster. Identification of significantly cooler sub-stellar cluster members in Coma Ber awaits the advent of the Euclid wide survey, which should reach a depth of about J=23; this superb sensitivity will make it possible to determine the precise location of the sub-stellar LDB in this cluster and to carry out a complete census of its sub-stellar population.Comment: 10 pages, 7 figures, accepted for publication in A&

Experiencia educativa para fomentar el aprendizaje autónomo a través de preguntas tipo test generadas por los alumnos

Describimos en este artículo una experiencia docente que trata de incentivar el proceso de aprendizaje autónomo del alumno mediante la realización de tests con preguntas generadas por ellos. La idea es que el alumno perciba que participa de una manera directa en su calificación, ya que sus preguntas pasarán a formar parte del examen. Un conjunto de herramientas permite la interacción alumno-profesor y alumno-alumno a través del campus virtual. En este sentido, profesores y alumnos pueden ver todas las preguntas formuladas por los otros compañeros. De esta manera incentivamos el análisis crítico (comprender la calidad de las preguntas ajenas). Hemos comprobado, comparando los resultados académicos de distintos años, que el 88% de los alumnos que han incorporado a su metodología de estudio estas estrategias más activas y participativas han conseguido aprobar la asignatura.In this paper we describe a teaching experience that tries to motivate students following an autonomous learning process. To this end, we conduct tests with questions created by the students. The idea is that students perceive that they participate in their rating in a direct way, because their questions will become part of the final test. A set of tools allows us interaction student-teacher and student-student through the virtual campus. In this way, students and teachers can see all the generated questions. Thus, we motivate the critical analysis (how to undertand the quality of questions). We found, comparing to academic results of different academic years, that the 88% of the studens that have included to their learning methodology these active and participative strategies, have been able to pass the course.Peer Reviewe

Implementation of a resistance training on young football players

El objetivo de este estudio, es comprobar el efecto de un programa de 20 sesiones de entrenamiento específico de fuerza en futbolistas jóvenes Participaron 38 sujetos en el estudio, divididos en un grupo experimental (GE) y un grupo control (GC). Al GE se le administró un entrenamiento de fútbol y un trabajo específico de fuerza; mientras el GC sólo efectuó práctica de fútbol. Ambos fueron evaluados al inicio y al final del programa, con el objetivo de conocer su fuerza dinámica máxima en los flexores y extensores de la rodilla; su masa muscular en las extremidades inferiores; el porcentaje de grasa; y, por último, la velocidad en las pruebas de 10 y 20 metros. Únicamente el GE mejora de forma muy significativa la fuerza dinámica máxima (p<0,01). No se encuentran diferencias en la masa muscular, ni en la velocidad. El GE y el GC incrementan el porcentaje de grasa corporalThe aim of this study is to check the effect of a specific training strength program on young footballers. 38 players took place in the study; they were divided into an experimental group (EG) and a control group (CG). The EG added a specific strength work to their football workout, whereas the CG just practised football. Both of them were assessed at the beginning and at the end of the program to know their maximum dynamic strength in their flexor and extensor muscles of their knees; their muscle mass in their lower extremities; their body mass and fat percentage; and their speed in the 10 and 20 metres trials. Just the EG improves remarkably their maximum dynamic strength … No differences in their muscle mass or in their movement strength are found. The EG and the CG increase their MBRate and their body fa

Physicochemical characterization and antimicrobial activity against Erwinia amylovora, Erwinia vitivora, and Diplodia seriata of a light purple Hibiscus syriacus L. Cultivar

Phytochemicals are essential raw materials for the production of formulations that can be helpful in crop protection. In particular, Hibiscus spp., which are often used in traditional medicine, are rich in potential bioactive molecules. This study presents an analysis of the thermal, vibrational, and phytochemical characteristics of a light purple variety of Hibiscus syriacus, using thermal gravimetric and differential scanning calorimetry, Fourier-transform infrared spectroscopy, and gas chromatography-mass spectroscopy techniques. Further, with a view to its valorization, the antimicrobial activity of its extracts has been investigated in vitro against Erwinia amylovora (the phytopathogen responsible for fire blight in apples, pears, and some other members of the family Rosaceae), Erwinia vitivora (the causal agent of the “maladie d’Oléron” in grapevines), and Diplodia seriata (responsible for “Bot canker”). Higher heating values and thermal features showed similarities with kenaf biomass. The main compounds identified in the hydro-methanolic extracts were: in flowers, 1-heptacosanol, heptacosane, 1-tetracosanol, hexadecenoic acid, 9,12,15-octadecatrienoic acid, and 9,12-octadecadienoic acid; and in leaves, the coumarin derivative 4,4,6,8-tetramethyl-2-chromanone, vitamin E, phytol, and sitosterol. MIC values of 500 and 375 μg·mL−1 were obtained against E. amylovora for flower and leaf extracts, respectively, upon conjugation with chitosan oligomers (to improve solubility and bioavailability). In the case of E. vitivora, MIC values of 250 and 500 μg·mL−1, respectively, were registered. Regarding the antifungal activity, EC90 values of 975.8 and 603.5 μg·mL−1, respectively, were found. These findings suggest that H. syriacus (cv. ‘Mathilde’) may be a promising source of antimicrobials for agriculture

Form invariance symmetry generates a large set of FRW cosmologies

We show that Einstein's field equations for spatially flat Friedmann-Robertson-Walker (FRW) space times have a form invariance symmetry (FIS) realized by the form invariance transformations (FIT) which are indeed generated by an invertible function of the source energy density. These transformations act on the Hubble expansion rate, the energy density, and pressure of the cosmic fluid; likewise such transformations are endowed with a Lie group structure. Each representation of this group is associated with a particular fluid and consequently a determined cosmology, so that, the FIS defines a set of equivalent cosmological models. We focus our seek in the FIT generated by a linear function because it provides a natural framework to express the duality and also produces a large sets of cosmologies, starting from a seed one, in several contexts as for instance in the cases of a perfect fluid source and a scalar field driven by a potential depending linearly on the scalar field kinetic energy density.Comment: 11 pages, 3 figures. Accepted for publication in Modern Physics Letters A (2012