Magnetotelluric studies from two contrasting Brazilian basins: a reassessment of old data

Before the mid-1980s large numbers of magnetotelluric (MT) data were collected and interpreted without addressing the possible effects of near-surface (e.g. static) distortion contributions. In the intervening time, modelling and interpretation techniques have improved. There are many instances where extensive, processed tensor survey data of reasonable quality exist on various back-up media. Before any complete reanalysis of these often large data sets, it is useful to investigate the degree of the distortion effects and the approximate degree of resolution of the data. Such assessment should help to clarify whether a full tensorial reanalysis is worthwhile. The present study provides contrasting examples of the reappraisal of old data sets collected in two Brazilian basins, both with associated seismic reflection profiles and deep exploration well-logs. Both examples use 'simplified' data consisting of only the off-diagonal tensor elements. These data are used in a limited way to assess static distortion and their intrinsic resolution capabilities. In the first example, from the basalt-covered Parana basin, a very high degree of static distortion is displayed. The application of simple distortion correction techniques allow the data to define the main (vertical) geoelectric units of the basin. In the second example, from the Solimoes basin in northern Brazil, static distortion, although less severe, can be readily identified. In this complex petroleum province the resolution of structure, both vertical and lateral, is of very low order. The MT data appear 'blind' to the detail of the Palaeozoic sedimentary rocks, and more detailed reanalysis is probably not warranted

Magnetotelluric imaging of basalt-covered sediments

The magnetotelluric (MT) technique has evolved as a tool in difficult exploration problems such as seismic poor record areas (Orange 1989) and in frontier basin regions (Christopherson 1991). Since it is a deep-probing wavefield technique, MT can assist in confirming the presence of deep sedimentary rocks and in providing estimates of the thickness of surface formations and the broad structural features of both sediments and basement

How Football Players’ Age Affect Passing Patterns of Play According to Field Location

This study aimed to characterize the passing patterns that support collective tactical behaviour in football players of different ages (U15, U17, and U19) in different field zones. Two hundred and twenty-eight male players, divided into U15, U17, and U19, participated in the study. Cluster analysis was used to group the passes into three sizes (short, medium, and long). The chi-square test was used to analyse the effect of player age on game-passing patterns in each field zone. The results revealed that long and medium passes were used more in areas close to the goals and short passes in the middle area of the field, concerning all ages (p < 0.001). Furthermore, the analysis of the relative distance between the ball carrier and the receiver indicated that older players (U17 and U19) used more distant players to pass the ball in medium and long passes. These results can help coaches design small-sided games according to the players’ ages and adjust to the field’s space and the numerical relationship, thus creating a greater transfer from training to competition.info:eu-repo/semantics/publishedVersio

A study of static shift removal from magnetotelluric data

Near-surface inhomogeneities can distort magnetotelluric (MT) data, thereby limiting interpretational accuracy. In the specific case of near-surface galvanic distortion the resulting frequency independent shift in apparent resistivity sounding curves can be most readily identified in data which are predominantly one-dimensional (1D). We here consider data from a detailed grid survey which are thoroughly contaminated by parallel offsets. The data were collected over a limited portion of the basalt-covered Paranfi basin in Brazil. The data appear largely lD over a three decade bandwidth down to a low frequency limit of about 0.1 Hz. A realistic conceptua! model consists of a variable thin-sheet over a basin in which the layer parameters vary sufficiently slowly (laterally) that a 1D interpretation of the static corrected data is valid down to some maximum depth (in this case basement). We consider the performance of three methods which attempt to remove static offsets and provide assessments of the configuration of the geoelectric units of the basin. The three methods consist of curve shifting, statistical/spatial averaging, and the application of parameter constraints. The unambiguous removal of static offsets undoubtedly requires one or more independent constraints at each measurement location. In the absence of such control the three methods are necessarily statistical and each must supply a constraint that has least conflict with the data characteristics. Simple spatial averaging of our data proves effective but the degree of success is generally not known. Parametric constraints, applied as uniform layer resistivities, allow phase-only (non-distorted) data inversion. Inverse models obtained from this approach are found to provide accurate estimates of the depth to the main resistivity interface, the base of the basalt cover, in the vicinity of a control well

Distortions of magnetotelluric sounding curves due to a slope

This study considers a particular case of 2D modeling, namely the topographic effect on MT data. A simple way to remove topographic effects is to incorporate surface elevations, or depres­sions, into the forward model. In cases where a 2D approximation is valid, any 2D algorithm may be used for the calculations. Such a scheme allows model results and observations to be compared along a profile. This approach, however, does not necessarily provide useful answers since the topography may, and in fact nearly always does, couple with the geoelectric structure and/or varies on a more rapid scale than the observations. In order to understand the effect of topography on MT data the degree and characteristics of the distortion introduced by a simple slope are consid­ered. The slope model constitutes a general result with distortion characteristics that can be ex­tended to other features such as a depression or a hill. The introduction of additional features such as a superimposed geoelectric structure would greatly complicate the problem due to electro­magnetic coupling effects which would necessarily be a function of frequency. The single slope, or half-graben, is probably the simplest class of general near-surface distortions that affect MT data. The period range used is from 0.02 s (50 Hz) to 100 s (0.01 Hz), i.e. both audio and magneto­telluric observations are considered. The elevation of the slope is fixed at a 'throw' of 1 km and slope angles range from 0° to 90°. The spatial and frequency distortions due to the slope are considered in detail. At a particular location the distorting effect of the slope introduces a false gradient into an otherwise lD sounding curve. The topographic distortion introduced is investi­gated by applying a lD inverse procedure to the obtained results. The way in which false layers may be introduced into the geoelectric section is illustrated. An analytical solution to a purely DC topographic problem is also considered. The analytical results are compared with the correspond­ing low frequency results obtained with the numerical models of the present study

Magnetotelluric data processing: a case study

Magnetotelluric (MT) data collected simultaneously at one or more sites may be processed by a number of different methods. Such methods attempt to remove or suppress the effect of noise on the data channels. The desired results are accurate, unbiased and repeatable estimates of the impedance tensor as a function of frequency and location. In this study we perform an investigation of the analysis of an MT data set sampled at 5 s. Both single-site (SS) and remote-reference (RR) techniques are employed to estimate the impedance tensor Z. Two biased SS estimates of Z are used to compare the performance of five coherence­ based acceptance criteria. It is demonstrated that the RR predicted coherence between local fields can be used for selecting data windows, and provides a necessary assessment of the reliability of a given RR estimate. It is demonstrated that the variance of an RR estimate depends strongly on the local signal-to-noise ratios (as monitored by the local predicted coherence) and depends weakly on the number of data windows, as long as coherences are above a moderate threshold. Although, for our data, an estimate of Z obtained using a remote electric field is grossly inaccurate, its associated predicted coherence is as efficient in selecting low-noise-level data windows as its counterpart obtained using a remote magnetic field. The relation between SS and RR predicted coherences, the latter estimated using both electric and magnetic fields, is investigated. A hybrid selection technique that uses a remote electric field is suggested

LUCIS:a learning experience to improve lifetime and operating strategies in low power PEM fuel cells

LUCIS, a demonstration project co-financed by the Innovation Agency in Portugal (AdI), was carried out in the framework of the DEMTEC Programme (Incentives to Technologically Innovative Pilot Systems). Its main goals were: Validate the reliability of proton exchange membrane fuel cells (PEMFC) when used in practical situations and the competitive advantages that these solutions can represent compared to conventional solutions; Evaluate impacts associated with the use of hydrogen and the benefits to business competitiveness. This project allowed a learning experience in real applications of low power PEMFC. Demonstrations were grouped in two large categories that covered several applications of PEMFC. The prototypes used were produced by SRE (Portugal) and were specifically designed to be used in small power applications, portable, traction or stationary. In this work, the technological validation was carried out for different stacks with power from 10 to 100W. Hydrogen was supplied by compressed gas bottles and metallic hydrides. All the fuel cells were previously characterized in specialized laboratories. Recommendations were drawn for every application in order to improve fuel cell lifetime and operating strategies

Produção de serviços e qualidade da assistência hospitalar no Estado do Rio de Janeiro, Brasil - 1992 a 1995

INTRODUCTION: Recent trends in hospital care in the Stade of Rio de Janeiro, Brazil, are analysed. The data are taken from the Unified Health Care System (SUS) and cover monthly obsevations between January 1992 and October 1995 for the public, teaching and private hospital subsectors. METHODOLOGY: The data entries are based on hospital declarations on the AIH form, processed by the National Inpatient Information System (SIH-SUS). When comparing the three subsectors, production of services and outcome were examined particularly closely. Comparisons are made using structural models for time series based on the break-down of a time series into components of interest, such as trend, seasonal variation and irregularity. RESULTS: The analysis shows a significant downward trend in the frequency of hospital admissions in the State of Rio de Janeiro, probably reflecting the deliberate withdraw of financial investments in this sector, which began in 1993. This reduction was selective with regard to age group distribution - being greater in the adult and elderly groups. The analysis has also shown that the teaching sector has steadilly raised its admissions. The quality of care was analysed through the sentinel event approach. For the State of Rio de Janeiro as a whole, the occurrence of avoidable deaths during the hospital admission process shows a weak overall tendency to decline as detected by the reduction of this kind of death in the private sub-sector. In public and teaching hospitals the frequency of avoidable deaths has remained stable. The frequency of maternal deaths has remained high and stable, while the number of caesarean sections shows a significant increase, despite the high figures observed at the beginning of the period. CONCLUSIONS: The results of this study indicate an overall decline in the quality of health care offered by the SUS within the Rio de Janeiro State. Regardless of the existing limitations in SIH-SUS, this study has shown this to be a useful instrument for monitoring hospital care services.INTRODUÇÃO: Objetivou-se analisar as tendência recentes na assistência hospitalar no Estado do Rio de Janeiro. Os dados originam-se da prestação mensal de serviços dos subsetores, universitários e privado, credenciados ao Sistema Único de Saúde (SUS), entre janeiro de 1992 e outubro de 1995. METODOLOGIA: Foram utilizadas as informações registradas nos formulários de Autorização de Internação Hospitalar, processadas pelo Sistema de Informações Hospitalares do SUS (SIH-SUS). A análise comparativa dos três subsetores centrou-se na produção dos serviços e resultados. Tais comparações foram realizadas utilizando-se modelos estruturais de séries temporais, que se baseiam na decomposição de componentes de interesse, como tendência, sazonalidade e irregularidade. RESULTADOS: A freqüência de internações no Estado tendeu ao declínio, em decorrência especialmente da retração do subsetor público a partir de 1993. Essa redução foi seletiva &#151; no que se refere à distribuição por faixas etárias &#151; concentrando-se nos adultos e idosos. Somente o subsetor universitário aumentou gradativamente o volume de admissões. A qualidade da assistência foi avaliada por meio da abordagem de eventos-sentinelas. A ocorrência de óbitos evitáveis nas internações no Estado apresentou discreta tendência ao declínio, detectada pela sua redução no subsetor privado. Nos subsetores público e universitário, a freqüência dos óbitos evitáveis manteve-se estável. A ocorrência de óbitos maternos no Estado permaneceu alta e estável, enquanto os índices de cesárea revelaram significativo crescimento, apesar de já ter sido observado, desde o início do período, valores bastante altos. CONCLUSÕES: Há problemas sérios na qualidade da atenção hospitalar prestada pelo SUS, no Estado, os quais, a julgar pela situação apresentada nos indicadores utilizados, vêm se agravado. Embora exiba limitações, o banco de dados do SIH-SUS mostrou ser instrumento útil para o monitoramento dos serviços hospitalares