Improved imaging of a karst aquifer using focused source electromagnetic and differentially normalized method: a qualitative analysis

Geophysical investigations using conventional techniques applied to groundwater exploration can often present strong limitations involving high financial costs, complex acquisition logistics and high ambiguity in results. Dispersion of the electric current flow, induced polarization) effects, cultural noises and shallow lateral heterogeneities represent the main problems faced by geoelectric methods in these types of surveys. Moreover, elements such as intrusions and mineralization at different depths may be responsible for signal attenuation as well as high resistivity in unsaturated zones and complex three-dimensional formations or clayey zones cause variations in the electric current. The focused source electromagnetic and differentially normalized method approaches can help to solve some these issues. Aiming at a higher signal-to-noise ratio, the focused source electromagnetic method and approaches of the differentially normalized method, first applied to petroleum exploration, are tested on a groundwater target, in a karst environment sectioned by a diabase dyke. We performed the processing and analysis on real IP resistivity profiling data acquired with two-way dipole-dipole array, guided by magnetic data acquired on the same profile, mapping a diabase dyke. The inversion of focused source electromagnetic method/differentially normalized method was not performed, instead that we converted the induced polarization–resistivity data to a differential signal to qualitatively prove the presence of aquifer. Joint interpretation of focused source electromagnetic method curves and inverted two-dimensional induced polarization–resistivity sections allowed for precise delineation of a conductive zone associated with the karst aquifer, le magnetics allowed for the definition of a neighbour dyke. The techniques have great potential in the aid of groundwater exploration, contributing substantially to the reduction of interpretation ambiguity. Focused source electromagnetic method/differentially normalized method/ approaches show that a simple linear combination of the conventional geoelectric data is able to remove the geological noise and provide the vertical focusing of the electric current.     

Is the propagation of electromagnetic radiation in cosmological background in agreement with the standard model?

We have found the conditions which a background metric must obey in order that Maxwell equations have a solution depending harmonically on time in it. In particular, for the standard model, these solutions do not exist.     

Artificial neural networks applied to mineral potential mapping for copper-gold mineralizations in the Carajás Mineral Province, Brazil

Motivated by recent successful results of artificial neural network modelling in a variety of problems related to the geosciences, we have applied a radial basis functional link net to a regional-scale mapping of the potential for Cu-Au mineralizations in the Carajás Mineral Province, northern Brazil. To derive the input feature vectors, we have used geological and both radiometric and magnetic geophysical data. A k -fold cross-validation method was employed in order to tune the parameters of the network and to select the best radial basis functional link net model amongst several others. Subsets of the available data set were used for training and validation and the estimated overall accuracy of the selected model is 91.7%. The plotting of a cumulative area versus favourability curve allowed us to define favourability zones of occurrences of Cu-Au mineralizations and to assess the efficiency and the predictive power of the model. A binary map showing high and low favourability sectors was produced for the study area as an end product that can be used to guide and support more detailed exploration efforts. Our results show that 4.18% of the study area has an extremely high potential to contain Cu-Au mineralizations, especially those of iron-oxide Cu-Au type, which are related to volcanic rocks and hydrothermal alteration.     

Classification of marine bioregions on the east coast of South Africa

Marine bioregional planning requires a meaningful classification and spatial delineation of the ocean environment using biological and physical characteristics. The relative inaccessibility of much of the ocean and the paucity of directly measured data spanning entire planning regions mean that surrogate data, such as satellite imagery, are frequently used to develop spatial classifications. However, due to a lack of appropriate biological data, these classifications often rely on abiotic variables, which act as surrogates for biodiversity. The aim of this study was to produce a fine-scale bioregional classification, using multivariate clustering, for the inshore and offshore marine environment off the east coast of South Africa, adjacent to the province of KwaZulu-Natal and out to the boundary of the exclusive economic zone (EEZ), 200 nautical miles offshore. We used remotely sensed data of sea surface temperature, chlorophyll a and turbidity, together with interpolated bathymetry and continental-slope data, as well as additional inshore data on sediments, seabed oxygen and bottom temperature. A multivariate k-means analysis was used to produce a fine-scale marine bioregionalisation, with three bioregions subdivided into 12 biozones. The offshore classification was primarily a pelagic bioregionalisation, whereas the inshore classification (on the continental shelf) was a coupled benthopelagic bioregionalisation, owing to the availability of benthic data for this area. The resulting classification was used as a base layer for a systematic conservation plan developed for the province, and provided the methods for subsequent planning conducted for the entire South African EEZ. Validation of the classification is currently being conducted in marine research programmes that are sampling benthic biota and habitats in a sampling design stratified according to the biozones delineated in this study.     

The future of informal settlements: lessons in the legalization of disputed urban land in Recife, Brazil

The aim of this paper is to explore the relationship between legalization of land tenure and people's capacity to compete for and sustain their stake in the urban land market. Two aspects of land regularization are taken into account: the benefits of land regularization (as collateral for investments); and the perverse aspects of disputes over improved land (due to increased scarcity of illegal, but affordable housing land). Most research on illegal urban land has systematically investigated how to legalize illegal settlements to improve the effectiveness of service provision, whilst attracting public investments. But, few understand the underlying factors motivating people to improve and consolidate their houses where no legal tenure exists. The absence of substantial understanding about people's perceptions of their tenure security has encouraged most research to conclude that improving tenure security leads to higher levels of housing consolidation. What this paper shows is that the relationship between people's perceptions of land tenure security and housing consolidation is much more malleable and complex than conventionally assumed. The subtle difference between tenure of the land and tenure of the house indicates that people are willing to invest in their housing conditions almost irrespectively of their land tenure situation. This finding challenges the orthodox views of the property rights school of thought. In addition, this paper contends that what legalization is really doing is to reduce the available land stock for the poorest families, because legalization decreases the amount of illegal land (illegal land is undesirable, but affordable for the poor). The orthodox legal system needs to be revised to include the poorest families in the urban society of the new millennium.     

Estimates of Reynolds stress in a highly energetic shelf sea

In recent years the use of Acoustic Doppler Current Profilers (ADCPs) to estimate Reynolds stresses, using the so-called variance method, has become popular; and although there was great effort in studying the uncertainties on this technique, there were no reports in the main literature of its validity using independent measurements. This work reports on the comparison of ADCP and Acoustic Current Velocimeter (ADV) estimates of Reynolds stresses. The comparison of the ADCP and ADV is encouraging during periods when no strong waves were present with both the explained variance of 0.8 and the slope of the regression being 0.97. Nevertheless, when strong waves are present the method breaks down and the comparison between ADCP and ADV is very poor with R² =0.04.     

Numerical self correction of non-homogeneous behaviour of data in linear wave propagation

Summary An attempt is made to construct a scheme of numerical integration for the wave operator that can detect which kind of non-homogeneous term has acted over the data and later use this knowledge to integrate the operator in time. Data is generated with a wave initially at rest, and a scheme is presented to detect these functions and study how these values can be extrapolated in time to be used. The use of known functions to generate data is required only to check the effectiveness of the numerical device.     

Toward an early warning system for dengue prevention: modeling climate impact on dengue transmission

Dengue fever is the most prevalent mosquito-borne viral disease of humans in tropical lands. As an efficient vaccine is not yet available, the only means to prevent epidemics is to control mosquito populations. These are influenced by human behavior and climatic conditions and thus, need constant effort and are very expansive. Examples of succeeded prevention are rare because of the continuous reintroduction of virus or vector from outside, or growing resistance of mosquito populations to insecticides. Climate variability and global warming are other factors which may favour epidemics of dengue. During a pilot study in Claris EC project, a model for the transmission of dengue was built, to serve as a tool for estimating the risk of epidemic transmission and eventually forecasting the risk under climatic change scenarios. An ultimate objective would be to use the model as an early warning system with meteorological forecasts as input, thus allowing better decision making and prevention.