Resonant tunneling through protected quantum dots at phosphorene edges

We theoretically investigate phosphorene zigzag nanorribons as a platform for constriction engineering. In the presence of a constriction at the upper edge, quantum confinement of edge protected states reveals resonant tunnelling Breit-Wigner transmission peaks, if the upper edge is uncoupled to the lower edge. Coupling between edges in thin constrictions gives rise to Fano-like and anti-resonances in the transmission spectrum of the system.Comment: 8 pages,7 figure

Lucky Spectroscopy, an equivalent technique to Lucky Imaging. Spatially resolved spectroscopy of massive close visual binaries using the William Herschel Telescope

CONTEXT: Many massive stars have nearby companions whose presence hamper their characterization through spectroscopy. AIMS: We want to obtain spatially resolved spectroscopy of close massive visual binaries to derive their spectral types. METHODS: We obtain a large number of short long-slit spectroscopic exposures of five close binaries under good seeing conditions, select those with the best characteristics, extract the spectra using multiple-profile fitting, and combine the results to derive spatially separated spectra. RESULTS: We demonstrate the usefulness of Lucky Spectroscopy by presenting the spatially resolved spectra of the components of each system, in two cases with separations of only ~0.3". Those are delta Ori Aa+Ab (resolved in the optical for the first time) and sigma Ori AaAb+B (first time ever resolved). We also spatially resolve 15 Mon AaAb+B, zeta Ori AaAb+B (both previously resolved with GOSSS, the Galactic O-Star Spectroscopic Survey), and eta Ori AaAb+B, a system with two spectroscopic B+B binaries and a fifth visual component. The systems have in common that they are composed of an inner pair of slow rotators orbited by one or more fast rotators, a characteristic that could have consequences for the theories of massive star formation.Comment: Accepted for publication in A&A, 7 page

Utilización de aditivos para mejorar la sensibilidad de las mezclas bituminosas al calentamiento con microondas

This study examines the potential of adding electric arc furnace slag to bituminous mixtures to be heated by microwaves. The susceptibility of bituminous mixtures to microwave energy is limited and so, in order to improve the energy performance of the heating process, it is necessary to incorporate additives or components to the mixture so as to improve the capacity for microwave heating. The article presents the results of adding various components, (steel wool, scrap tire wire, silicon carbide, iron filings) and an alternative aggregate: electric arc furnace slag. According to the results obtained in the laboratory, slag addition of at least 5% by weight of the bituminous mixture represents the best option for both technical and economic reasons. The results may promote the valorization of this steel industry residue in bituminous mixtures by improving microwave heating response.El presente trabajo examina el potencial de añadir escorias siderúrgicas de horno de arco eléctrico en mezclas bituminosas cuando se calientan con energía de microondas. La susceptibilidad de las mezclas bituminosas a las microondas es limitada y con el objetivo de incrementarla es necesario incorporar aditivos o componentes que sí son susceptibles. El artículo presenta los resultados obtenidos con varios aditivos (lana de acero, alambre metálico reciclado de neumáticos fuera de uso, carburo de silíceo y limaduras de hierro) y un árido alternativo: escorias de horno de arco eléctrico. De acuerdo con los resultados obtenidos en el estudio, la incorporación de escorias en al menos un 5% en masa de la mezcla bituminosa representa la mejor opción por motivos técnicos y económicos. Este resultado puede potenciar la valorización de este residuo de la industria del acero en mezclas bituminosas para mejorar su respuesta al calentamiento con energía microondas

Preyssler Heteropolyacids in the Self-Etherification of 5-Hydroxymethylfurfural to 5,5′-[Oxybis(methylene)]bis-2-furfural Under Mild Reaction Conditions

The synthesis of 5,5′-[oxybis(methylene)]bis-2-furfural (OBMF) from 5-hydroxymethylfurfural (5-HMF) was studied using bulk and alumina-supported Preyssler heteropolyacids (HPAs). The formation of OBMF was related to the amount of Brønsted acid sites, and the lowest yield of OBMF was obtained with supported HPAs. However, the Lewis acidity of the HPA supported on Al2O3 favored the formation of 2,5-dimethylfurane. The effects of solvent, catalyst loading, temperature, and reaction time on the selectivity to OBMF from 5-HMF were studied to optimize OBMF production using bulk Preyssler HPAs; a yield of 84 % to OBMF was obtained at 5 h and 343 K. These results demonstrate that bulk Preyssler HPA is a good candidate for OBMF synthesis under mild reaction conditions.Fil: Páez, Alexander. Universidad Pedagógica y Tecnológica de Colombia; ColombiaFil: Rojas, Hugo A.. Universidad Pedagógica y Tecnológica de Colombia;Fil: Portilla Zúñiga, Omar Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; ArgentinaFil: Sathicq, Angel Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; ArgentinaFil: Afonso, Carlos A. M.. Universidade de Lisboa; PortugalFil: Romanelli, Gustavo Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; ArgentinaFil: Martínez, José J.. Universidad Pedagógica y Tecnológica de Colombia; Colombi

Robust signatures in the current-voltage characteristics of DNA molecules oriented between two graphene nanoribbon electrodes

In this work we numerically calculate the electric current through three kinds of DNA sequences (telomeric, \lambda-DNA, and p53-DNA) described by different heuristic models. A bias voltage is applied between two zig-zag edged graphene contacts attached to the DNA segments, while a gate terminal modulates the conductance of the molecule. The calculation of current is performed by integrating the transmission function (calculated using the lattice Green's function) over the range of energies allowed by the chemical potentials. We show that a telomeric DNA sequence, when treated as a quantum wire in the fully coherent low-temperature regime, works as an excellent semiconductor. Clear steps are apparent in the current-voltage curves of telomeric sequences and are present independent of lengths and sequence initialisation at the contacts. The current-voltage curves suggest the existence of stepped structures independent of length and sequencing initialisation at the contacts. We also find that the molecule-electrode coupling can drastically influence the magnitude of the current. The difference between telomeric DNA and other DNA, such as \lambda-DNA and DNA for the tumour suppressor p53, is particularly visible in the length dependence of the current

Propagación del desgarro de tejido biológico empleado en la construcción de bioprótesis cardíacas en función de la forma y el tipo de sutura

En este trabajo hemos estudiado la fuerza necesaria para propagar un desgarro en un tejido de pericardio de avestruz, tejido alternativo y en estudio para la fabricación de bioprótesis cardiacas. Se analiza la influencia de dos de las suturas más empleadas en cirugía cardiovascular: Prolene® y Gore-Tex®, en este comportamiento mecánico. El tejido se suturó de dos formas distintas borde-borde y en solapa. Para los ensayos se utilizó un péndulo Elmendorf capaz de medir, la fuerza necesaria para propagar el desgarro de un tejido. Se analizaron 106 ensayos, tras aplicar criterios de selección morfológica habituales en estos ensayos y que homogenizaron las muestras por su espesor y las hicieron comparables. La serie de control, no suturada, necesitó 24 N, como valor medio, para propagar el desgarro en 1 cm, mientras que las series suturadas borde con borde, con Gore-Tex® y con Prolene®, necesitaron, para la misma propagación del d-esga-rro, 12.69 N (p=0.001) y 16.18 N respectivamente. Esta pérdida de resistencia no se observó en las series suturadas con solape de 1 cm de longitud, 29.73 N, como valor medio, en la serie suturada con Gore-Tex® y 42.56 N, como valor medio, en la serie suturada con Prolene® (p=0.000). La sutura de Prolene® mostró una mayor resistencia a la propagación del desgarro que la sutura de Gore-Tex®. Una sutura protegida, mediante una zona previa no rasgada, dificulta la propagación del desgarro y puede tener interés desde un punto de vista constructivo en el diseño de las formas de sutura de implantes o bioprótesis

A note on the SG(m) test

López et al. (Reg Sci Urban Econ 40(2–3):106–115, 2010) introduce a nonparametric test of spatial dependence, called SG(m). The test is claimed to be consistent and asymptotically Chi-square distributed. Elsinger (Reg Sci Urban Econ 43(5):838–840, 2013) raises doubts about the two properties. Using a particular counterexample, he shows that the asymptotic distribution of the SG(m) test may be far from the Chi-square family; the property of consistency is also questioned. In this note, the authors want to clarify the properties of the SG(m) test. We argue that the cause of the conflict is in the specification of the symbolization map. The discrepancies can be solved by adjusting some of the definitions made in the original paper. Moreover, we introduce a permutational bootstrapped version of the SG(m) test, which is powerful and robust to the underlying statistical assumptions. This bootstrapped version may be very useful in an applied context

CCD Photometry of Trapezia Stars I

We present photometric CCD observations of stars in four stellar trapezia ADS 15184, ADS 4728, ADS 2843, and ADS 16795. This study is performed on images obtained at the Observatorio Astron\'omico Nacional at San Pedro M\'artir (OAN), Baja California, M\'exico. In this work we utilise aperture photometry to measure the $U$, $B$, $V$, $R$ and $I$ magnitudes of some of the stars in these dynamically unstable stellar clusters (trapezia). Using the $Q=(U-B)-0.72(B-V)$ parameter we obtained the spectral type of the studied stars as well as their distance to the Sun and their reddening. Slight differences between the $Q$-derived Spectral types and those listed in SIMBAD might be due to a different value, from $0.72$, for the slope of the reddening line on the two-colour diagram.Comment: 34 pages, 12 figures, 31 tables, accepted for publication in RevMexAA, vol. 60, num. 1, April 2