Extended Huckel theory for bandstructure, chemistry, and transport. II. Silicon

In this second paper, we develop transferable semi-empirical parameters for the technologically important material, silicon, using Extended Huckel Theory (EHT) to calculate its electronic structure. The EHT-parameters areoptimized to experimental target values of the band dispersion of bulk-silicon. We obtain a very good quantitative match to the bandstructure characteristics such as bandedges and effective masses, which are competitive with the values obtained within an $sp^3 d^5 s^*$ orthogonal-tight binding model for silicon. The transferability of the parameters is investigated applying them to different physical and chemical environments by calculating the bandstructure of two reconstructed surfaces with different orientations: Si(100) (2x1) and Si(111) (2x1). The reproduced $\pi$- and $\pi^*$-surface bands agree in part quantitatively with DFT-GW calculations and PES/IPES experiments demonstrating their robustness to environmental changes. We further apply the silicon parameters to describe the 1D band dispersion of a unrelaxed rectangular silicon nanowire (SiNW) and demonstrate the EHT-approach of surface passivation using hydrogen. Our EHT-parameters thus provide a quantitative model of bulk-silicon and silicon-based materials such as contacts and surfaces, which are essential ingredients towards a quantitative quantum transport simulation through silicon-based heterostructures.Comment: 9 pages, 9 figure

Catalytic oxidation of emissions in combustion systems for forest biomass, using catalysts with TiO2 support

A study was made of the catalytic oxidation of a model mixture of effluents from forest biomass combustion equipment, consisting principally of methane (CH4), naphthalene (C10H8), carbon monoxide (CO) and oxygen-poor air (10% O2, balance N2), in a laboratory reactor, using MeOx/TiO2 catalysts (Me = Fe, Cu or Mn), prepared using incipient wetness impregnation. It was observed that the addition of metal oxides to the TiO2 increases catalytic activity in the combustion of all the contaminants present in the model effluent (CH 4, C10H8 and CO). The catalysts were characterised using the following techniques: SBET, XRD, DTG/DTA and TPD-NH 3; and from these it was observed that the support presented only the anatase phase in all the catalysts, despite having been subjected to temperatures in excess of 1.000 K during combustion. The highest acidity among all the solids tested, measured by TPD-NH3, was obtained for the FeOx/TiO2 catalysts, which were also those which showed the greatest catalytic activity. This high level of activity may be related to the formation of isolated metallic phases; i.e. hematite (Fe2O3), which would be the active phase in the combustion of C10H8 and CH4. On the other hand, with to respect to the 5 % wt. values of Me/TiO2 (Me: Fe, Cu y Mn) catalysts, the CuO/TiO2 catalyst shows greater activity than Fe2O3/TiO2 and MnOx/TiO2 for the oxidation of CO, which would be related to the formation of CuO on the TiO2 surface. The formation of mixed phases between the metals and the TiO2 was not observed. The SBET of the most active catalyst, Fe2O3/TiO2 (where Fe is 5% w/w in value), was not subject to any changes during the reaction

A Nexafs Study of Nitric Oxide Layers Adsorbed from a nitrite Solution onto a Pt(111) Surface

NO molecules adsorbed on a Pt(111) surface from dipping in an acidic nitrite solution are studied by near edge X-ray absorption fine structure spectroscopy (NEXAFS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) techniques. LEED patterns and STM images show that no long range ordered structures are formed after NO adsorption on a Pt(111) surface. Although the total NO coverage is very low, spectroscopic features in N K-edge and O K-edge absorption spectra have been singled out and related to the different species induced by this preparation method. From these measurements it is concluded that the NO molecule is adsorbed trough the N atom in an upright conformation. The maximum saturation coverage is about 0.3 monolayers, and although nitric oxide is the major component, nitrite and nitrogen species are slightly co-adsorbed on the surface. The results obtained from this study are compared with those previously reported in the literature for NO adsorbed on Pt(111) under UHV conditions

An assessment of emerging networks in the fruit sector: The case of Inca berry in Ecuador

The diversification of agri-food products through emerging chains has a fundamental social and economic role in Ecuador. A substantial amount of research focused only on examining critical factors in terms of agronomic and environmental performance. However, there is a shift in the agri-food chain perspective and study towards more sustainable models of production, logistics trade, and consumption. Aspects such as the socio-economic sustainability, level of collaboration between actors, an adequate chain configuration, and the employment of smart governance mechanisms show the weaknesses where stakeholders can propose enhancements. In this respect, socio-economic and productive factors are consequential and still affecting the progress of these chains. Also, the current growth of market opportunities at the local and international level is a driver to support them by setting sustainable strategies. This study aimed to analyze socio-economic and production aspects to understand the dynamic across the emerging Inca berry (Physalis peruviana) chain located in Ecuador and bring forward potential strategies. Thus, chain vertical and horizontal imensioning was introduced to contribute with relevant insights. The framework applied accounts with a revision of primary and support activities, and flows of high and low relevance. The investigation clustered pre-production, production, and post-production tiers. Also, it executed the food chain mapping, the identification of chain actors, and application of surveys at the supply chain levels to identify strengths and weaknesses based on specific socio-economic and productive variables. Results stated several viable long-term strategies. Examples of those strategies are the diversification of marketing channels, the intervention of academic institutions to improve efficiency, productivity, and the associations' empowerment. All of them aimed at circular economic models. The main research contribution is the application of the chain configuration to assess the chain performance comprehensively. Based on the results, our recommendation is incorporating new indicators to analyze the environmental and institutional components profoundly

Faraday waves on a viscoelastic liquid

We investigate Faraday waves on a viscoelastic liquid. Onset measurements and a nonlinear phase diagram for the selected patterns are presented. By virtue of the elasticity of the material a surface resonance synchronous to the external drive competes with the usual subharmonic Faraday instability. Close to the bicriticality the nonlinear wave interaction gives rise to a variety of novel surface states: Localised patches of hexagons, hexagonal superlattices, coexistence of hexagons and lines. Theoretical stability calculations and qualitative resonance arguments support the experimental observations.Comment: 4 pages, 4figure

Limitations on the smooth confinement of an unstretchable manifold

We prove that an m-dimensional unit ball D^m in the Euclidean space {\mathbb R}^m cannot be isometrically embedded into a higher-dimensional Euclidean ball B_r^d \subset {\mathbb R}^d of radius r < 1/2 unless one of two conditions is met -- (1)The embedding manifold has dimension d >= 2m. (2) The embedding is not smooth. The proof uses differential geometry to show that if d<2m and the embedding is smooth and isometric, we can construct a line from the center of D^m to the boundary that is geodesic in both D^m and in the embedding manifold {\mathbb R}^d. Since such a line has length 1, the diameter of the embedding ball must exceed 1.Comment: 20 Pages, 3 Figure

Pharmacogenetics, tobacco, alcohol and its effect on the risk development cancer

Indexación: Scopus; Scielo.Cancer is the second leading cause of death in the world, causing 8.8 million deaths in 2015 according to the World Health Organization (WHO). Risk factors for cancer include smoking and alcohol consumption. In Chile, 33.6% of the population and 21.2% of young people smokes. Alcohol consumption in the Chilean population is 74.5% and 12.2% in young people. Among the physiological factors that influence the development of cancer, the genetic factor plays a relevant role. It has been shown that the presence of genetic polymorphisms that alter the ability of the body to eliminate contaminants increase the risk of developing cancer. The same applies to polymorphisms that prevent DNA repair due to damage caused by environmental pollutants such as cigarette smoke. The objective of this review is to analyze the state of the art of the relationship between pharmacogenetics, smoking, and alcohol consumption as risk factors for the development of cancer. In conclusion, the results suggest that the presence of polymorphisms that alter the function of biotransformation enzymes phase I (CYP1A1, CYP1E1) and phase II (GST), as well as polymorphisms in DNA repair enzymes (ERCC1 / ERCC2), increase the risk of cancer induced by smoking and alcohol consumption. This association is important considering that smoking and drinking alcohol are highly prevalent among the Chilean population. © 2018, Sociedad Chilena de Pediatria. All rights reserved.Cancer is the second leading cause of death in the world, causing 8.8 million deaths in 2015 according to the World Health Organization (WHO). Risk factors for cancer include smoking and alcohol con sumption. In Chile, 33.6% of the population and 21.2% of young people smokes. Alcohol consump tion in the Chilean population is 74.5% and 12.2% in young people. Among the physiological factors that influence the development of cancer, the genetic factor plays a relevant role. It has been shown that the presence of genetic polymorphisms that alter the ability of the body to eliminate contami nants increase the risk of developing cancer. The same applies to polymorphisms that prevent DNA repair due to damage caused by environmental pollutants such as cigarette smoke. The objective of this review is to analyze the state of the art of the relationship between pharmacogenetics, smoking, and alcohol consumption as risk factors for the development of cancer. In conclusion, the results suggest that the presence of polymorphisms that alter the function of biotransformation enzymes phase I (CYP1A1, CYP1E1) and phase II (GST), as well as polymorphisms in DNA repair enzymes (ERCC1 / ERCC2), increase the risk of cancer induced by smoking and alcohol consumption. This association is important considering that smoking and drinking alcohol are highly prevalent among the Chilean population.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0370-41062018005000709&lng=en&nrm=iso&tlng=e

MARTA: A high-energy cosmic-ray detector concept with high-accuracy muon measurement

A new concept for the direct measurement of muons in air showers is presented. The concept is based on resistive plate chambers (RPCs), which can directly measure muons with very good space and time resolution. The muon detector is shielded by placing it under another detector able to absorb and measure the electromagnetic component of the showers such as a water-Cherenkov detector, commonly used in air shower arrays. The combination of the two detectors in a single, compact detector unit provides a unique measurement that opens rich possibilities in the study of air showers.Comment: 11 page

Nearest pattern interaction and global pattern formation

We studied the effect of nearest pattern interaction on a globally pattern formation in a 2-dimensional space, where patterns are to grow initially from a noise in the presence of periodic supply of energy. Although our approach is general, we found that this study is relevant in particular to the pattern formation on a periodically vibrated granular layer, as it gives a unified perspective of the experimentally observed pattern dynamics such as oscillon and stripe formations, skew-varicose and crossroll instabilities, and also a kink formation and decoration

Crumpling a Thin Sheet

Crumpled sheets have a surprisingly large resistance to further compression. We have studied the crumpling of thin sheets of Mylar under different loading conditions. When placed under a fixed compressive force, the size of a crumpled material decreases logarithmically in time for periods up to three weeks. We also find hysteretic behavior when measuring the compression as a function of applied force. By using a pre-treating protocol, we control this hysteresis and find reproducible scaling behavior for the size of the crumpled material as a function of the applied force.Comment: revtex 4 pages, 6 eps figures submitted to Phys Rev. let