Does PCB accumulation affect the lipid metabolism of the reproductively active oyster Crassostrea virginica?

Polychlorinated biphenyls (PCBs) pose a severe ecological risk. They are hydrophobic and are efficiently sequestered in lipid-rich tissues. Lipids function as energy reserves and as membrane components, and are essential for growth and reproductive processes in bivalves. Accumulation of PCBs may affect the mobilization of lipid reserves and membrane lipid composition; thus they may also impair reproductive and developmental processes. To test whether there are any changes in lipid metabolism, the lipid class and fatty acid composition in structural and reserve lipids of visceral mass, gills and mantle, and eggs of reproductively active oysters were examined. Oysters were fed daily with 0.2 g algal paste containing 0, 0.1, or 1.0 μg PCBs for 15 and 30 days. PCBs in the oyster tissues and eggs were also quantified. After 30 days of exposure PCBs were highly accumulated, up to 2635 ng/g in the visceral mass, 1880 ng/g in gill+mantle, and 671 ng/g (dry wt. bases). No significant changes were noted in either lipid class composition or fatty acid composition of structural or reserve lipids from PCB-exposed oyster tissues and eggs.     

Integrating geochronologic and instrumental approaches across the Bengal Basin

Constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins. The geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem, because the viability of methods can be highly influenced by geomorphic attributes. For example, sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating. Similarly, the rate of sediment transport from source to sink may determine the maturity and/or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating. Here, we explore the viability and quirks of dating and instrumental methods that have been applied in the Bengal Basin, and review the records that they have yielded. This immense, dynamic, and spatially variable system hosts the world's most inhabited delta. Outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans, here and in other populated deltas worldwide. Our review covers radiocarbon dating, luminescence dating, archaeological records and historical maps, short-lived radioisotopes, horizon markers and rod surface elevation tables, geodetic observations, and surface instrumentation. Combined, these tools can be used to reconstruct the history of the Bengal Basin from Late Pleistocene to present day. The growing variety and scope of Bengal Basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

A methodology to select seismic coefficients based on upper bound “Newmark” displacements using earthquake records from Turkey

Strong motion records taken during earthquakes in Turkey are used to calculate Newmark displacements in slopes. These displacements are then utilized in developing a novel displacement-based methodology to select the seismic coefficient which is used to calculate pseudostatic safety factor. In the first step of the study, calculated Newmark displacements are evaluated in three different categories which are as follows: using all data, using data for different earthquake magnitude (M) ranges with and without distance constraint and using data for different peak acceleration (a_max) ranges. For all categories, different equations are obtained to assign slope displacements as a function of the ratio of yield acceleration to peak acceleration. The results show that categorization of data is an important issue, because the displacements are earthquake magnitude and peak acceleration dependent. In the second step, equations obtained for different peak acceleration ranges are used to propose charts linking upper bound slope displacements (D), seismic coefficients (k_h) and pseudostatic safety factors (PSF), which are three important parameters of a pseudostatic approach. This enables the k_h values be chosen based on the allowable displacements, instead of the current applications based on judgement and expertise. The results show that k_h values for any allowable displacement should be based on anticipated a_max values, while use of high PSF values results in lower displacements. Extensive comparison with solutions from the literature is also made. The methodology is best suited for earthquake triggered shallow landslides in natural slopes, consisting of materials which do not lose strength during dynamic loading.     

Dynamic subsidence of Eastern Australia during the Cretaceous

During the Early Cretaceous Australia's eastward passage over sinking subducted slabs induced widespread dynamic subsidence and formation of a large epeiric sea in the eastern interior. Despite evidence for convergence between Australia and the paleo-Pacific, the subduction zone location has been poorly constrained. Using coupled plate tectonic–mantle convection models, we test two end-member scenarios, one with subduction directly east of Australia's reconstructed continental margin, and a second with subduction translated ~ 1000 km east, implying the existence of a back-arc basin. Our models incorporate a rheological model for the mantle and lithosphere, plate motions since 140 Ma and evolving plate boundaries. While mantle rheology affects the magnitude of surface vertical motions, timing of uplift and subsidence depends on plate boundary geometries and kinematics. Computations with a proximal subduction zone result in accelerated basin subsidence occurring 20 Myr too early compared with tectonic subsidence calculated from well data. This timing offset is reconciled when subduction is shifted eastward. Comparisons between seismic tomography and model temperature cross-sections, and an absence of subduction zone volcanism in eastern Australia in the Early Cretaceous provide support for the back-arc basin scenario.     

The photometric method of extrasolar planet detection revisited

We investigate the geometry concerning the photometric method of extrasolar planet detection, i.e., the detection of dimunition of a parent star's brightness during a planetary transit. Under the assumption that planetary orbital inclinations can be defined by a Gaussian with a of 10° centered on the parent star's equatorial plane, Monte Carlo simulations suggest that for a given star observed at an inclination of exactly 90°, the probability of at least one Earth-sized or larger planet being suitably placed for transits is approximately 4%. This probability drops to 3% for a star observed at an inclination of 80°, and is still 0.5% for a star observed at an inclination of 60°. If one can select 100 stars with a pre-determined inclination 80°, the probability of at least one planet being suitably configured for transits is 95%. The majority of transit events are due to planets in small-a orbits similar to the Earth and Venus; thus, the photometric method in principle is the method best suited for the detection of Earthlike planets.The photometric method also allows for testing whether or not planets can exist within binary systems. This can be done by selecting binary systems observed at high orbital inclinations, both eclipsing binaries and wider visual binaries. For a real-world example, we look at the Centauri system (i = 79°.2). If we assume that the equatorial planes of both components coincide with the system's orbital plane, Monte Carlo simulations suggest that the probability of at least one planet (of either component) being suitably configured for transits is approximately 8%.In conclusion, we present a non-exhaustive list of solar-type stars, both single and within binary systems, which exhibit a high equatorial inclination. These objects may be considered as preliminary candidates for planetary searches via the photometric method.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Accuracy Assessment of Pleiades-1 Stereo/Tri-stereo Digital Surface Models: A Case-Study for Citrus Trees

In this study, we assess the quality of the digital surface model (DSM) generated from Pleiades-1 tri-stereo images which can potentially contribute to the detection of citrus trees in terms of height information. The methods tested on stereo/tri-stereo images are; (a) local methods (correlation-based and least squares method), (b) semi-global method (semi-global matching (SGM)), and (c) global method (SIFT-flow). DSMs of three sub-regions of Mersin area have been presented for each stereo/tri-stereo matching method; whereas for the SIFT-flow method, we have only depicted the parallax results. Numerical results reveal that the SGM forward-backward stereo combination which has the largest intersection angle provided the best results in 2 out of 3 test areas. However, the results confirm that none of the methods could reach the desired level of performance for the height estimation of citrus trees that can potentially guide the detection step.     

A statistical model for spatial patterns of Buruli ulcer in the Amansie West district,Ghana

Buruli ulcer (BU), a skin ulceration caused by Mycobacterium ulcerans (MU), is the second most widespread mycobacterium infection in Ghana. Its infection pathway is possibly related to the potable and agricultural water supply. This study aims to identify environmental factors that influence infection in a part of Ghana. It examines the significance of contaminated surface drainage channels and groundwater using conditional autoregressive (CAR) statistical modelling. This type of modelling implies that the spatial pattern of BU incidence in one community depends on the influence of the environment in neighbouring communities. Covariates were included to assess the spatial relationship between environmental risk factors and BU incidence in the study area. The study reveals an association between (a) the mean As content of soil and spatial distribution of BU and (b) the distance to sites of gold mining and spatial distribution of BU. We conclude that both arsenic in the natural environment and gold mining influence BU infection.     

Artificial Neural Networks for Mineral-Potential Mapping: A Case Study from Aravalli Province,Western India

This paper describes a GIS-based application of a radial basis functional link net (RBFLN) to map the potential of SEDEX-type base metal deposits in a study area in the Aravalli metallogenic province (western India). Available public domain geodata of the study area were processed to generate evidential maps, which subsequently were encoded and combined to derive a set of input feature vectors. A subset of feature vectors with known targets (i.e., either known mineralized or known barren locations) was extracted and divided into (a) a training data set and (b) a validation data set. A series of RBFLNs were trained to determine the network architecture and estimate parameters that mapped the maximum number of validation vectors correctly to their respective targets. The trained RBFLN that gave the best performance for the validation data set was used for processing all feature vectors. The output for each feature vector is a predictive value between 1 and 0, indicating the extent to which a feature vector belongs to either the mineralized or the barren class. These values were mapped to generate a predictive classification map, which was reclassified into a favorability map showing zones with high, moderate and low favorability for SEDEX-type base metal deposits in the study area. The method demarcates successfully high favorability zones, which occupy 6% of the study area and contain 94% of the known base metal deposits.