Petrography and chemistry of SiO2 filling phases in the amethyst geodes from the Serra Geral Formation deposit,Rio Grande do Sul,Brazil

The filling process of amethyst-bearing geodes from Serra Geral Formation basalts, Brazil, is investigated by different methods performed on the SiO₂ filling phases. Image analysis of quartz–amethyst deposits suggests a single growing mechanism ruled by geometric selection of randomly oriented crystals. Microthermometry of fluid inclusions reveals formation temperature lower than 100 °C, probably lower than 50 °C, and fluid salinity as high as 3 mass% NaCl eq. Composition in REE and trace-elements measured by ICP-MS on acid-digested or laser-ablated samples indicates a common genesis for amethyst, quartz and chalcedony, as well as the absence of significant variations from one geode to another. ⁸⁷Sr/⁸⁶Sr data on chalcedony shows that both the host basalt or the Botucatu sandstone are possible silica sources. These data, combined with thermo-kinetic considerations, permit us to discuss the filling process. We argue in favor of the contribution of a mineralized fluid of hydrothermal origin producing a regional silica source which decreased with time. The observed mineral sequence is related to the depletion of silica in the solution.     

3D Seismic survey design using mixed-radix based algorithm inversion

The determination of three-dimensional geometry and acquisition parameters, the seismic acquisition survey design, is constantly subject of studies in obtaining data with the highest seismic quality, operational efficiency and cost minimization. In this paper, we propose a methodology for inverting geometry parameters of three-dimensional orthogonal land seismic surveys based on a direct search method using a mixed-radix based algorithm. In this algorithm, the search space is discretized on a mixed-radix base, which depends on the extreme values and the search resolution of each parameter. We will show how to reparametrize the orthogonal acquisition geometry elements in order to obtain the independents and integers parameters that are necessary to construct the mixed-radix base. For the optimization purpose, we define an objective function to contemplate target parameters associated with the elements of the acquisition geometry directly related to the geophysical and operational constraints. Taking in account that the mathematical functions and the objective function we define for the problem have no significant computational cost, all model space parameters are fast and efficiently tested. We applied the algorithm, using as input data, provided by a one-line roll orthogonal reference geometry, assuming a pair of geological objectives as shallow and deep targets. All selected models that meet both the proposed objectives and the constraints are organized by decreasing order of fitness so that with the mixed-radix inversion algorithm we found not only the best model, but also a set of suitable models. Likewise, with the best set of geometries, it is possible to establish a direct comparison between them, analysing their adherence to the technical and operational requirements according to the availability and degree of detail of each one. We show the top 10 best results as a table, allowing a direct comparison between all aspects of these geometries, and we summarize the results showing graphically the fitness of all selected geometries and the inverted geometry elements for the 1000 best geometries. These graphical displays provide a direct way to understand how each model behaves as the fitness decreases. The algorithm is very flexible and its application can be extended to any environment and type of acquisition geometry, and in any phase study of an area be it regional, exploratory or development.     

Spectral classification of water masses under the influence of the Amazon River plume

The large amount of dissolved and particulate material discharged by the Amazon River into the Equatorial Atlantic Ocean cause distinct spectral response of its waters as compared to the nearby ocean waters. This paper shows the application of K-means clustering algorithm for classifying water masses in the region under the Amazon River plume influence according to their spectral behavior. Salinity and temperature data from 67 oceanographic stations were related to Sea-viewing Wide Field-of-view Sensor (SeaWiFS) remote sensing reflectances values and the following bio-optical products:(i) chlorophyll-a concentration, (ii) water attenuation coefficient and (iii) absorption coefficient for dissolved and detrital material. Four different water masses were identified such as:(1) oceanic water, (2) intermediate oceanic water, (3) intermediate river plume water and (4) Amazon River plume water. The spectral behavior of these water masses allowed concluding that the main active optical component of the waters in the region is the colored dissolved organic matter originated mostly from the Amazon River.     

Variation of Plasma Pressure at the Auroral Oval Latitudes before,during, and after the Isolated Geomagnetic Substorm on December 22, 2008

Geomagnetism and Aeronomy - The change in plasma pressure at the latitudes of the auroral oval before, during, and after the isolated geomagnetic substorm on December 22, 2008, were studied using...     

Forest‐Cover Change from Labor‐ and Capital‐Intensive Commercial Logging in the Southern Chocó Rainforests*

This article examines two key aspects of land‐cover change in the south of the Chocó region. First, it assesses and compares the local impact on forest condition of labor‐intensive and capital‐intensive commercial logging. Second, it assesses the regional significance and permanency of these changes. Studies of land‐cover change associated with commercial logging have focused almost exclusively on capital‐intensive extraction and have assumed that after logging, degraded forests are transformed into agricultural cover. This study shows that both capital‐ and labor‐intensive logging result in similar land‐cover changes (i.e., forest degradation) if the timber sought is the same. However, labor‐intensive loggers also seek timber species not sought by capital‐intensive loggers, and this impact is statistically different from the impact of the extraction of the first group of species. Results also show that only a small fraction (20–30 percent) of the area logged is later converted to agricultural cover types. The persistence of logged forests means that up to 20 percent of the remaining forest cover could correspond to forests with significant and lasting levels of degradation. Furthermore, the different production requirements for each group of species also mean that there is a spatial differentiation in the impact of logging in the region. Logged forests are arranged into two consecutive corridors on each side of access routes (e.g., rivers). The first corridor corresponds to a narrow (approximately 1‐km) band of high‐intensity degradation. The second, broader (approximately 2‐km) forest band, with lower levels of degradation, extends inland along first‐tier corridors. A key factor determining the permanency of this land‐cover pattern is the strong control local communities have over the land in the region. This limits the spread of patterns observed in other frontier areas, especially the conversion of logged forests into agricultural cover.     

The resurgence of Malaria in India 1965–76

Summary and Tentative Conclusion The eradication campaign faltered, for historical reasons some of which are tentatively suggested above and which would be worthy of fuller study as an important part of recent medical history; it is one of those historical topics so intertwined with political and social history that an interdisciplinary approach would be fruitful — if the necessary documents could be made accessible, in India and perhaps in international organisations and subscribing government archives too.Once the campaign faltered malaria seems to have diffused from the four foci suggested, the Kutch saltmarsh area and the hill-forest tracts of Madhya, Orissa and Assam. The role of wet years in areas normally arid, semi-arid or only moderately humid seems crucial in the diffusion process, and if the gaps in the rainfall anomaly maps can be filled we shall try to provide a more rigorous analysis of this relationship. Some humid and perhumid areas of high agricultural development, and dense or very dense rural populations, and one or two areas of considerable industrial and urban development like Greater Calcutta and nearby towns, seem so far to be happily little affected by the diffusion of malaria, even though as late as 1948 some including much of West Bengal were hyperendemic areas. It remains to be established by detailed studies if these areas are better prepared in some way — natural immunity must have faded especially in the considerable proportion of young people who have been born since malaria eradication was almost within grasp; or are they so far comparatively fortunate through some chances of the diffusion pattern?Urban malaria, and one might say Anopheles stephensi malaria, is probably more widespread and more significant as an important public health problem than in former times. Once more the need for detailed local studies is clear.It is important to re-read the introductory paragraph of this paper. The fiftyfold increase from 100000 to 5 million cases represents a sharp resurgence but the 5 million cases of 1975 and 1976, and few scores of recorded deaths, still represent a remarkable achievement as compared with the 75 million cases and 800,000 deaths a year at the time of Independence. From over 5 million in 1976 to 10 million in the first nine months of 1977, however, is a quite disquieting increase. If complacence did indeed play a part in the crucial years of resurgence in the late 1960s, it is unlikely to continue today in medical circles. One can only hope that politicians will take the issue seriously. Studies of the economic, educational and demographic impact of the resurgence may help them to do so.     

Determination of the strain ellipsoid from measurements on any three sections

An ellipsoid is defined by, and may be re-constructed from, any three sections through it. In the field, calculation of the strain ellipsoid from general sections (two-dimensional strain ellipses determined from measured strain markers) is complicated by the fact that, due to experimental error and/or strain inhomogeneity, the three ellipses may not come from the same ellipsoid. The ellipses must first be adjusted to make them compatible. A method is suggested by which an adjustment ellipse is determined analytically for each of the three sections. Application of these adjustment ellipses makes the three sections compatible, and the strain ellipsoid may be determined. The principal axes of the ellipsoid are derived from the ellipsoid matrix by eigenvector analysis. Examples are given of practical applications of this method.     

A genetic algorithm for filter design to enhance features in seismic images

We present a novel method to enhance seismic data for manual and automatic interpretation. We use a genetic algorithm to optimize a kernel that, when convolved with the seismic image, appears to enhance the internal characteristics of salt bodies and the sub‐salt stratigraphy. The performance of the genetic algorithm was validated by the use of test images prior to its application on the seismic data. We present the evolution of the resulting kernel and its convolved image. This image was analysed by a seismic interpreter, highlighting possible advantages over the original one. The effects of the kernel were also subject to an automatic interpretation technique based on principal component analysis. Statistical comparison of these results with those from the original image, by means of the Mann‐Whitney U‐test, proved the convolved image to be more appropriate for automatic interpretation.