Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3

A scheme is proposed to electrically measure the spin-momentum coupling in the topological insulator surface state by injection of spin polarized electrons from silicon. As a first approach, devices were fabricated consisting of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with independent electrical contacts to silicon and Bi2Se3. Analysis of the temperature dependence of thermionic emission in reverse bias indicates a barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky barrier opens the possibility of novel device designs based on sub-band gap internal photoemission from Bi2Se3 into Si

Triple-Star Candidates Among the Kepler Binaries

We present the results of a search through the photometric database of eclipsing Kepler binaries (Prsa et al. 2011; Slawson et al. 2011) looking for evidence of hierarchical triple star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The "calculated" eclipse times, based on a constant period model, are subtracted from those observed. The resulting O-C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the ~1/2-hour Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O-C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called "physical" delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O-C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions.Comment: 19 pages, 13 figures, 3 tables; ApJ, 2013, 768, 33; corrected Fig. 7, updated references, minor fixes to tex

M-Dwarf Fast Rotators and the Detection of Relatively Young Multiple M-Star Systems

We have searched the Kepler light curves of ~3900 M-star targets for evidence of periodicities that indicate, by means of the effects of starspots, rapid stellar rotation. Several analysis techniques, including Fourier transforms, inspection of folded light curves, 'sonograms', and phase tracking of individual modulation cycles, were applied in order to distinguish the periodicities due to rapid rotation from those due to stellar pulsations, eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets with rotation periods, P_rot, of < 2 days, and 110 with P_rot < 1 day. Some 30 of the 178 systems exhibit two or more independent short periods within the same Kepler photometric aperture, while several have three or more short periods. Adaptive optics imaging and modeling of the Kepler pixel response function for a subset of our sample support the conclusion that the targets with multiple periods are highly likely to be relatively young physical binary, triple, and even quadruple M star systems. We explore in detail the one object with four incommensurate periods all less than 1.2 days, and show that two of the periods arise from one of a close pair of stars, while the other two arise from the second star, which itself is probably a visual binary. If most of these M-star systems with multiple periods turn out to be bound M stars, this could prove a valuable way of discovering young hierarchical M-star systems; the same approach may also be applicable to G and K stars. The ~5% occurrence rate of rapid rotation among the ~3900 M star targets is consistent with spin evolution models that include an initial contraction phase followed by magnetic braking, wherein a typical M star can spend several hundred Myr before spinning down to periods longer than 2 days.Comment: 17 pages, 12 figures, 2 tables; accepted for publication in The Astrophysical Journa

Variabilidad en el indumento de Phaseolus vulgaris var. aborigineus (Fabaceae)

The indument of Phaseolus vulgaris L. var. aborigineus (Burkart) Baudet, a native bean from Argentina, potential source for improvement of cultivated varieties, was compared between different genetic lines. Seeds collected from wild, weedy forms and presumptive hybrid individuals in two distant latitudes were sown in two sites of Buenos Aires University Campus (field and greenhouse). Two type of trichomes were found, which differenciate in length and shape. The pubescence density was significantly different between wild specimens from different latitudes and between culture sites for plants of a same procedence. This character could be involved in physical defences of these plants.El indumento de Phaseolus vulgaris L. var. aborigineus (Burkart) Baudet, un poroto nativo de la Argentina, potencial fuente para mejoramiento de variedades cultivadas, se comparó entre diferentes líneas genéticas. Semillas de individuos silvestres, tipos maleza y presuntos híbridos colectadas en dos latitudes distantes fueron sembradas en dos sitios del campus de la Universidad de Buenos Aires (campo e invernáculo). Se encontraron dos tipos de tricomas que se diferencian en longitud y forma. La densidad de la pubescencia fue significativamente distinta entre especímenes silvestres de distintas latitudes y entre sitios de cultivo para plantas de la misma procedencia; este carácter podría estar relacionado con las defensas físicas de estas plantas.Fil: Ojeda, Fabiana S.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología ExperimentalFil: Amela García, María T.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología ExperimentalFil: Hoc, Patricia S.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimenta

Tuning the proximity effect in a superconductor-graphene-superconductor junction

We have tuned in situ the proximity effect in a single graphene layer coupled to two Pt/Ta superconducting electrodes. An annealing current through the device changed the transmission coefficient of the electrode/graphene interface, increasing the probability of multiple Andreev reflections. Repeated annealing steps improved the contact sufficiently for a Josephson current to be induced in graphene.Comment: Accepted for publication in Phys. Rev.

First report of the nesting of the chilean hawk (<i>Accipiter chilensis</i>) in Argentina

Documentamos por primera vez la nidificación del Peuquito (<i>Accipiter chilensis</i>) en Argentina y proporcionamos detalles sobre el comportamiento parental y de los pichones. El nido fue encontrado en un bosque de coihue (<i>Nothofagus dombeyi</i>) en el Parque Nacional Nahuel Huapi, provincia de Río Negro, Argentina. Consistía en una plataforma de ramas construida a 25.3 m en la copa de un coihue. En tres visitas al nido entre enero y febrero de 2004 observamos adultos llevando presas (principalmente aves) a los pichones en el nido.We describe the first documented nest of the Chilean Hawk (<i>Accipiter chilensis</i>) in Argentina, and give details on the nesting behaviour of parents and nestlings during the fledging stage of the nesting cycle. The nest was found in a coihue (<i>Nothofagus dombeyi</i>) forest in the Nahuel Huapi National Park, Río Negro Province, Argentina. The nest structure was a platform of sticks built 25.3 m in the canopy of a coihue tree. On three visits to the nest between January and February 2004, we observed adults bringing avian prey items to the nestlings in the nest

Spanish validation of the revised depression attitude questionnaire (R-daq)

Purpose: The aim of the study was to develop and validate a Spanish version of the Revised Depression Attitude Questionnaire (R-DAQ). Methods: The R-DAQ was used as a baseline for the study. It was translated and tested to ensure the instrument was appropriate for the target population. 537 Ecuadorian healthcare professionals completed the revised Spanish version of the R-DAQ (SR-DAQ). Statistical and exploratory factor analyses were performed to examine construct validity, internal consistency, readability and floor and ceiling effects. Results: Three factors were obtained: “Professional confidence in depression care”; “Therapeutic optimism about depression”; and “Generalist perspective about depression occurrence, recognition, and management”. The internal consistency of the SR-DAQ was determined by means of Cronbach’s α coefficient, with values ranging between 0.61–0.8. The correlations with the English version reflected adequate validity. The model explained 39% of the variance. Subsequent analysis with a sample restricted to those who had received training in depression produced a model that explained 42% of the variance. Conclusion: The SR-DAQ meets the psychometric requirements for measuring depression attitude in a Spanish-speaking population and shows adequate internal consistency and validity