Amplitude-frequency response of a helically-wound fiber distributed acoustic sensor (DAS)

The goals of this study were to analyze the capabilities of DAS (distributed sensors) in resolving mining problems, compare them with existing seismoacoustic data collection systems, and prepare the basis for conducting seismoacoustic studies with recording by a fiber optic distributed system. This paper considers the capabilities of recording seismoacoustic responses using fiber optic distributed acoustic systems (DAS). Based on physical and geometrical analysis, the amplitude-frequency responses (characteristics) of recorded longitudinal waves for straight and helically-wound fibers were obtained. In the case of helically-wound fiber, the frequency response depends on several key factors: integrating the measured value along the fiber based on the measurement; the angle of incidence on the cable; and the winding angle of the fiber in the cable. An increase in the winding angle increases the uniformity of the amplitude-frequency characteristics of longitudinal waves both in terms of frequencies and angles of incidence. At the same time, helical winding changes the effective response spacing (gauge length). This makes it possible, by summing the responses of the straight and helically-wound fibers due to the overlap of the spectra, to record frequencies that are suppressed in case of separate recording. Based on the study results, a cable design was proposed to record broadband seismoacoustic responses enabling a wide range of mining and engineering problems to be resolved, and for seismic surveys both in wells and on the surface to be carried out

Capital structure: the role of the funding sources on which Brazilian listed companies are based

Este estudo avaliou a estrutura de capital de companhias abertas brasileiras, no período de 2005 a 2012, verificando o papel das fontes de financiamento nas quais tais companhias se baseiam. Para tanto, foi avaliada a proporção das dívidas em 3 fontes distintas: as instituições financeiras, o mercado de capitais e as fontes com taxas de juros subsidiadas, estas últimas representando um fator institucional da economia brasileira. Foi utilizada uma amostra de 95 empresas, dentre as 150 maiores empresas com ações negociadas na Bolsa de Valores, Mercadorias e Futuros de São Paulo (BM&FBOVESPA). Por meio de modelos com dados em painel, os resultados mostram que as fontes de financiamento impactam a formação da estrutura de capital das empresas, exercendo influência tanto na alavancagem quanto na maturidade das dívidas. Em relação à alavancagem, empresas que têm maior proporção de seus recursos captados no mercado de capitais são mais alavancadas. O mesmo não acontece com as empresas que têm maior proporção de recursos subsidiados. Em relação à maturidade das dívidas, recursos de diferentes maturidades são captados em diferentes fontes: os recursos de menores maturidades são captados em instituições financeiras e os recursos de maiores maturidades são captados no mercado de capitais e nas fontes com taxas de juros subsidiadas - leia-se Banco Nacional de Desenvolvimento Econômico e Social (BNDES). Comparando-se os recursos do mercado de capitais com os recursos subsidiados, verifica-se que os primeiros têm maior maturidade. Tal resultado pode ser justificado em virtude do crescimento do mercado de capitais brasileiro nos últimos anos, a partir de 2009, de modo que as companhias estão se baseando no mercado de capitais para seus financiamentos de maior maturidade e nos recursos subsidiados, do BNDES, para seus financiamentos de maturidades intermediárias.This study evaluated the capital structure of Brazilian listed companies, within the period from 2005 to 2012, verifying the role of the funding sources on which such companies are based. To do this, the debt ratio in 3 different sources was evaluated: financial institutions, capital market, and sources with subsidized interest rates, the latter representing an institutional factor of the Brazilian economy. A sample of 95 companies was used, out of the 150 largest companies listed on the São Paulo Securities, Commodities, and Futures Exchange (BM&FBOVESPA). By using models with panel data, the results show that the funding sources impact on the companies' capital structure formation, influencing both in leverage and in debts maturity. Regarding leverage, companies that have a higher proportion of their funds raised in the capital market are more leveraged. The same is not true for companies that have a higher proportion of subsidized resources. Regarding debts maturity, resources of different maturities are obtained from different sources: the resources of lower maturities are obtained from financial institutions and the resources of higher maturities are obtained from the capital market and sources with subsidized interest rates - i.e. the Brazilian National Bank for Economic and Social Development (BNDES). Comparing the resources from the capital market to subsidized resources, it is concluded that the former have higher maturity. Such a result may be explained by the growth of the Brazilian capital market in recent years, since 2009, so that companies have been based on the capital market for their funding with higher maturity and on subsidized resources, from BNDES, for their funding with intermediate maturities

Discovery of the thallium, lead, bismuth, and polonium isotopes

Currently, forty-two thallium, forty-two lead, forty-one bismuth, and forty-two polonium isotopes have so far been observed; the discovery of these isotopes is discussed. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.Comment: to be published in At. Data Nucl. Data Table