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

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

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

Análise comparativa de resultados de espetrometria gama portátil em afloramentos rochosos

São comparadas estimativas de elementos obtidas por espetrometria gama portátil em afloramentos de rochas metamórficas e ígneas, assim como medições de campo e análises laboratoriais para uma das rochas ígneas consideradas, tendo em vista contribuir para a discussão da utilidade da espetrometria portátil técnica na avaliação dos ma teriaisEste 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

Algumas considerações sobre o estudo estatístico de medições de dose em grãos de argamassas por luminescência estimulada opticamente

Fundação das Universidades PortuguesasMinisterio de Ciencia e Innovación (Espanha)Fundação para a Ciência e a Tecnologia (FCT)Ação Integrada E-141”(Fundação das Universidades Portuguesas)/“Acción Integrada PT2009-0077” (Ministerio de Ciencia e Innovación)/PEst-OE/CTE/UI0697/201

Three-Body Dynamics and Self-Powering of an Electrodynamic Tether in a Plasmasphere

The dynamics of an electrodynamic tether in a three-body gravitational environment are investigated. In the classical two-body scenario the extraction of power is at the expense of orbital kinetic energy. As a result of power extraction, an electrodynamic tether satellite system loses altitude and deorbits. This concept has been proposed and well investigated in the past, for example for orbital debris mitigation and spent stages reentry. On the other hand, in the three-body scenario an electrodynamic tether can be placed in an equilibrium position fixed with respect to the two primary bodies without deorbiting, and at the same time generate power for onboard use. The appearance of new equilibrium positions in the perturbed three-body problem allow this to happen as the electrical power is extracted at the expenses of the plasma corotating with the primary body. Fundamental differences between the classical twobody dynamics and the new phenomena appearing in the circular restricted three-body problem perturbed by the electrodynamic force of the electrodynamic tether are shown in the paper. An interesting application of an electrodynamic tether placed in the Jupiter plasma torus is then considered, in which the electrodynamic tether generates useful electrical power of about 1 kW with a 20-km-long electrodynamic tether from the environmental plasma without losing orbital energy

Microscopy studies in support of dating of mortars of historical buildings

Fundação das Universidades PortuguesasMinisterio de Ciencia e InnovaciónFundação para a Ciência e a Tecnologia (FCT

An Analysis of Open Innovation Strategies in Firms in Low and Medium Technology Industries

Open innovation (OI) has been mainly associated with high-technology firms. This paper aims to analyze how firms in low and medium technology industries implement their OI strategy. In doing so, we explore common patterns in OI strategies by considering inbound, outbound, and coupled OI practices. We also examine whether there are differences in innovation performance among companies adopting a specific OI strategy. The study is carried out on a sample of 242 Spanish innovating companies. Based on the relevance of the different OI practices, we identify three types of OI firms: advanced open innovators, intermediate open innovators, and incipient open innovators. Our results reveal that advanced open innovators have a higher performance in product innovation, and that there are no differences among groups in process and organizational innovation

Geological materials and external gamma radiation

A diretiva 2013/59/EURATOM pretende fixar normas de segurança para a exposição a radiações ionizantes (como a radiação gama), incluindo a regulação da comercialização de materiais de construção, podendo ter efeitos restritivos no aproveitamento económico destes. Esta diretiva define um limite para a contribuição dos materiais de construção (incluindo os materiais geológicos) para a radiação gama externa (contribuição avaliada por um índice baseado em estimativas das concentrações de átomos que emitem radiação gama). São revistos os fatores que influenciam a contribuição dos materiais geológicos para a radiação gama externa de espaços interiores, em termos gerais e no caso de estudo de um granito alterado. Os resultados são confrontados com os critérios da diretiva referida, concluindo-se que a mesma poderá ser excessivamente restritiva para os usos atualmente mais comuns da pedra natural (utilização parcial de revestimentos finos). Em situações envolvendo uma maior aplicação de material (e.g. algumas construções históricas), a perigosidade de atingir níveis de radiação acima do valor de referência indicado na diretiva é maior mas é necessário considerar fatores como o tempo de exposição e o uso de revestimentos com nível de radiação inferior ao do material considerado (com implicações em termos de valorização de materiais e opções construtivas).The directive 2013/59 / EURATOM intends to establish safety standards for exposure to ionizing radiation (such as gamma radiation), including the regulation of building materials trade (it could, hence, have restrictive effects on the economic exploitation of this materials). This directive sets a limit on the contribution of building materials (including geological materials) for external gamma radiation (contribution assessed by an index based on quantitative estimations of atoms that emit gamma radiation). The factors that influence the contribution of geological materials for external gamma radiation in interior spaces are reviewed for the general case and for the case of a weathered granite from Braga. Results are compared with the criteria of the considered directive, concluding that this directive could be excessively restrictive for the currently most common uses of natural stone (partial cladding). In situations involving the use of larger amounts of stone (e.g. some historical buildings), the hazard of reaching a radiation level above the reference level proposed in the directive are higher but one needs to consider factors such as exposure time and the use of coatings with radiation level lower than that of the considered material (this could have implications in terms of materials valorisation and constructive options).Este 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. O grupo de investigação CULXEO de que faz parte J. Sanjurjo-Sánchez é financiado pela Xunta de Galicia através do programa “Consolidación e estructuración de unidades de investigación competitivas — Grupo de potencial de crecimiento” (GPC2015/024).info:eu-repo/semantics/publishedVersio