Characterization of solar-grade silicon produced by the SiF4-Na process

A process was developed for producing low cost solar grade silicon by the reaction between SiF4 gas and sodium metal. The results of the characterization of the silicon are presented. These results include impurity levels, electronic properties of the silicon after crystal growth, and the performance of solar photovoltaic cells fabricated from wafers of the single crystals. The efficiency of the solar cells fabricated from semiconductor silicon and SiF4-Na silicon was the same

A Conley index study of the evolution of the Lorenz strange set

In this paper we study the Lorenz equations using the perspective of the Conley index theory. More specifically, we examine the evolution of the strange set that these equations posses throughout the different values of the parameter. We also analyze some natural Morse decompositions of the global attractor of the system and the role of the strange set in these decompositions. We calculate the corresponding Morse equations and study their change along the successive bifurcations. In addition, we formulate and prove some theorems which are applicable in more general situations. These theorems refer to Poincar\'{e}-Andronov-Hopf bifurcations of arbitrary codimension, bifurcations with two homoclinic loops and a study of the role of the travelling repellers in the transformation of repeller-attractor pairs into attractor-repeller ones.Comment: 22 pages, 1 figur

Advances in materials science and engineering assessment of gamma radiation hazards related to geologic materials: comparison of results by field gamma spectrometry and laboratory methods

Geologic materials are a potential source of external gamma radiation in buildings due to the presence of radioisotopes (K-40 and isotopes from U and Th decay families). The contents of these radioisotopes can be evaluated by laboratory analyses that require the extraction of samples, with associated financial and time constraints, and it is also difficult to perform on materials already applied in existing structures. In this work, portable gamma spectrometry results are compared with laboratory analyses in terms of radioisotopes estimations, and the activity concentration index is calculated from them (which assess the conjoint contribution of the different radioisotopes to the external gamma radiation). The studied objects are rocks and their "in situ" weathering products. The results obtained indicate that despite several problems posed by field measurements with portable gamma spectrometry, namely, in terms of the geometric characteristics of the objects measured, this technique has the potential to identify materials with different hazard levels related to external gamma radiation.The Lab2PT-Landscapes, Heritage and Territory laboratory-AUR/04509 is supported by the Portuguese "Fundacao para a Ciencia e a Tecnologia" (Portuguese funds and where applicable the FEDER co-financing, in the aim of the new partnership agreement PT2020 and COMPETE2020-POCI 01 0145 FEDER 007528). The University Institute of Geology of the University of A Coruna (Spain) received support from Xunta de Galicia with funds from "Consolidacion y estructuracion de unidades de investigacion competitivas-Grupo de potencial de crecimiento" (GPC2015/024). The authors would like to thank A. Pinto, F. Dias, M. Cunha, and P. Pereira for help during the field work

Dados de espetrometria gama portátil e tipologia de espaços interiores

Versão dos autoresNeste trabalho são discutidos resultados de análise multivariada de estimativas obtidas por espectrometria gama portátil em espaços interiores de construções na cidade de Braga, com diferentes proporções de granito, para avaliar uma proposta de tipologia dos mesmosEste trabalho foi desenvolvido no âmbito das atividades do Lab2PT- Laboratório de Paisagens, Património e Território (AUR/04509) financiado pela FCT através de fundos nacionais e quando aplicável do cofinanciamento do FEDER, no âmbito dos novos acordos de parceria PT2020 e COMPETE 2020 – POCI-01-0145-FEDER-007528.info:eu-repo/semantics/publishedVersio

Shape index, Brouwer degree and Poincaré-Hopf theorem

In this paper we study the relationship of the Brouwer degree of a vector field with the dynamics of the induced flow. Analogous relations are studied for the index of a vector field. We obtain new forms of the Poincaré-Hopf theorem and of the Borsuk and Hirsch antipodal theorems. As an application, we calculate the Brouwer degree of the vector field of the Lorenz equations in isolating blocks of the Lorenz strange set.Depto. de Álgebra, Geometría y TopologíaFac. de Ciencias MatemáticasFALSEMinisterio de Ciencia, Innovación y Universidadesunpu

Novel duplex vapor electrochemical method for silicon solar cells

Progress in the development of low-cost solar arrays is reported. Topics covered include: (1) development of a simplified feed system for the Na used in the Na-SiF4 reactor; (2) production of high purity silicon through the reduction of sodium fluosilicate with sodium metal; (3) the leaching process for recovering silicon from the reaction products of the SiF4-Na reaction; and (4) silicon separation by the melting of the reaction product