Ion migration in nepheline: a dielectric spectroscopy and computer modelling study

 Using a combination of dielectric spectroscopy and atomistic computer simulation techniques, the dynamical behaviour of the loosely bound (Na⁺ and K⁺) channel ions in nepheline has been investigated. The low-frequency dielectric properties of a natural Bancroft nepheline have been studied from room temperature to 1100 K. At each temperature, the dielectric constant, conductivity and dielectric loss were determined over a range of frequencies from 100 Hz to 10 MHz. At high temperatures a distinct Debye-type relaxation in the dielectric loss spectrum was observed; the activation energy for this process was determined to be 1.38 ± 0.02 eV. Atomistic simulation techniques were used to elucidate the mechanism and energetics of cation migration. A mechanism involving the hopping of Na⁺ ions between oval sites and partially occupied hexagonal (K⁺) sites, via a bottleneck consisting of a distorted sixfold ring of (Al,Si)O₄ tetrahedra, was found to give a calculated energy barrier in very good agreement with the experimentally determined activation energy. These results confirm the nature of the process responsible for the observed dielectric behaviour. Overall, this study demonstrates the intrinsic, microscopic control of cation diffusion processes in rock-forming minerals. Identifying specific energy barriers and preferred diffusion pathways is fundamental to the prediction of diffusion energetics. Received: 8 May 2000 / Accepted: 21 July 2000     

WISE USE OF WETLAND FOR SUSTAINABLE LIVELIHOOD THROUGH PARTICIPATORY APPROACH： A CASE OF ADAPTING TO CLIMATE CHANGE

1INTRODUCTION Hydroponics(aGreekword,hydromeanswater andponos,labour),asoil-lessagriculture,isa termtobedescribedinseveralwaysinwhichplants cangrowwithoutsoil,byuseofaninertmedium whereplantcantakeupessentialnutrients,either fromwaterinwhichanutrientsolutionisaddedor fromorganicmaterialsthatexistsinthemedium.Thesemediacanbegravel,sand,peat,vermiculate,prelite,sawdustorotherplantmatters(organiccom ponents).Therefore,theprocessinwhichaquatic weedsaredumpedonwatertoconstructfloatingbed orart…     

Palaeoweathering characteristics of an intrabasaltic red bole of the Deccan Flood Basalts near Shrivardhan of western coast of India

An intrabasaltic red bole horizon is studied for its weathering characteristics with respect to the underlying and overlying basalts. The study indicates that all the three units have been considerably weathered; the red bole unit, however shows some distinctive characteristics. The red boles show a higher cation exchange capacity (CEC) and lower sodium adsorption ratio (SAR) and organic carbon (OC) as compared to the weathered basalts. The lower values of Al₂O₃, TiO₂ and Fe₂O₃(T) in red boles indicate their lesser weathering than the underlying and overlying basalts, which is further corroborated by the weathering intensity measured by the indices like chemical index of alteration (CIA) and statistical empirical index of chemical weathering (W). It is also evident that the red bole samples show more retention of original mafic and felsic components. While K₂O exhibits an erratic behaviour, the MgO and CaO do not show much leaching in red boles. Lesser leaching and salinity in the red boles is indicated by the higher values of calcification and lower values of salinization. The SiO₂–Al₂O₃–Fe₂O₃ plot indicates that red bole samples are close to the basalt field, while the weathered upper basalt is more kaolinized than the weathered lower basalt. These observations reveal that the post-formational weathering processes have least affected the original palaeoweathering characters of the red bole horizon and hence the intrabasaltic palaeosols (weathering horizons) can effectively be used to constrain the palaeoweathering and palaeoclimates during the continental flood basalt episodes in the geologic past.     

Spawning of major carps in the lower Halda River,Bangladesh

Spawning biology and spawn fishery of three valuable species of Indian major carps,Catla catla, Labeo rohita andCirrhinus mrigala, in the lower Halda River, Bangladesh, were studied in 1978. The major carps spawned only in the Sonairchar oxbow-bend from April to June on or near the dates of the full moon and the new moon. The tide was then at its highest level, and there was heavy flood water runoff from the hill region with sharp increases in water level, turbidity and current velocity, as well as decreases in water temperature, dissolved oxygen, and hydrogen ion concentration. These three heterogeneric species, as a result of parallelism or convergence in evolution, overlap in their environmental requirements for spawning. The nursery ground of the major carp fry spawned in the Halda River was found to be in the Bay of Bengal. The brood stock origin is suspected to be at the Shankha River, 40 miles south of the Karnafuli River. The spawn fishery in the Halda River was intensive but inefficient. Engineering works and water management schemes are threatening the spawning habitat.     

Social capital, community based management, and fishers’ livelihood in Bangladesh

This paper examines the impact of Community Based Fisheries Management (CBFM) on fishing households’ welfare in Bangladesh. It analyses how the various types of livelihood assets contribute to fishers’ household incomes. The study found that fishers in CBFM project areas have improved their access to different assets including social, human, physical, financial and natural capitals. The regression results show that social capital contributed significantly to household income, indicating that social factors play very important roles in poverty alleviation in Bangladesh. Future poverty alleviation policy options need to give priority to investments in human, physical and natural capital assets.     

Flood susceptibility modelling using advanced ensemble machine learning models

Floods are one of nature's most destructive disasters because of the immense damage to land, buildings, and human fatalities.It is difficult to forecast the areas that are vulnerable to flash flooding due to the dynamic and complex nature of the flash floods.Therefore, earlier identification of flash flood susceptible sites can be performed using advanced machine learning models for managing flood disasters.In this study, we applied and assessed two new hybrid ensemble models, namely Dagging and Random Subspace(RS) coupled with Artificial Neural Network(ANN), Random Forest(RF), and Support Vector Machine(SVM) which are the other three state-of-the-art machine learning models for modelling flood susceptibility maps at the Teesta River basin, the northern region of Bangladesh.The application of these models includes twelve flood influencing factors with 413 current and former flooding points, which were transferred in a GIS environment.The information gain ratio, the multicollinearity diagnostics tests were employed to determine the association between the occurrences and flood influential factors.For the validation and the comparison of these models, for the ability to predict the statistical appraisal measures such as Freidman, Wilcoxon signed-rank, and t-paired tests and Receiver Operating Characteristic Curve(ROC) were employed.The value of the Area Under the Curve(AUC) of ROC was above 0.80 for all models.For flood susceptibility modelling, the Dagging model performs superior, followed by RF,the ANN, the SVM, and the RS, then the several benchmark models.The approach and solution-oriented outcomes outlined in this paper will assist state and local authorities as well as policy makers in reducing flood-related threats and will also assist in the implementation of effective mitigation strategies to mitigate future damage.     

Pan-African Magmatism, and Sedimentation in the NW Himalaya

Correlation of early Palaeozoic, Pan-African (500 ± 50 Ma) granites that intruded the Chail, Salkhala, Haimanta Formations in the Lesser Himalaya, Zanskar crystallines, and Lower Taglang La of Tso-Morari crystallines in the northwestern Himalaya, is based on the field relationship, tectonic setting, mineralogical, and geochemical characteristics, and isotope dating of the granites. These granite plutons exhibit identical petrographical, and geochemical character. The mineralogical composition of the granites is quite similar, consisting of quartz, K-feldspar, plagioclase feldspar, biotite, muscovite, garnet, tourmaline, ± cordierite, andalusite, and sillimanite fibrolite. The granite which are massive, and inequigranular in the core of the plutons, show strongly foliated character indicating development of ductile shear zone at the margins. These are peraluminous S-type granites having high A/CNK value (> 1). Presence of normative corundum, rounded shape of zircon, and high initial Sr ratio suggest crustal source of the granites. Mantle normalized spider-diagram exhibits similar characters for all these granitoids. The intrusion of the Pan-African granites mark an abrupt end of the sedimentation that continued virtually uninterrupted from Palaeoproterozoic. The sudden break in sedimentation towards the terminal phases of the Lower Cambrian has been observed in almost all parts in Lesser as well as the Tethys Himalaya. Occurrences of large number of plutons along different tectonic belts of northwestern Himalaya are indicative of widespread tectono-thermal event during early Palaeozoic (500 ± 50 Ma). The bracketing of the two features like, the break in sedimentation during post-Late Cambrian, and the intrusion of granites around 500 ± 50 Ma, is considered to be the result of a strong diastrophic orogenic event correlatable to the late phases of the Pan-African Orogeny in Africa.     

Climatology of landfalling tropical cyclones in Bangladesh 1877–2003

Bangladesh is highly susceptible to tropical cyclones. Unfortunately, there is a dearth of climatological studies on the tropical cyclones of Bangladesh. The Global Tropical Cyclone Climatic Atlas (GTCCA) lists historical storm track information for all the seven tropical cyclone ocean basins including the North Indian Ocean. Using GIS, tropical cyclones that made landfall in Bangladesh during 1877–2003 are identified and examined from the climatological perspective. For the convenience of study, the coast of Bangladesh is divided into five segments and comparisons are made among the coastal segments in terms of cyclone landfall and vulnerability. There is a large variability in the year-to-year occurrence of landfalling tropical cyclones in Bangladesh. Most of the tropical cyclones (70%) hit in the months of May–June and October–November generally show the well-known pattern of pre- and post-monsoon cyclone seasons in that region.     

Frontal recession of Parkachik Glacier between 1971-2015, Zanskar Himalaya using remote sensing and field data

Parkachik Glacier is located in the Suru sub-basin of the Upper Indus River, Zanskar Himalaya. The Glacier has been analysed using Corona KH-4B (1971), Landsat-TM (1999), field survey (2015), Google Earth^TM (2015) and ASTER GDEM (2015) for frontal recession and area changes. Overall, from 1971 to 2015, the Glacier has retreated by 127 ± 0.09 m i.e. (0.75 ± 0.07%) at a rate of 2.9 ± 0.004 ma^?1 with a simultaneous decrease in area from 49.5 to 48.8 km² i.e. 740 ± 0.7 m² (1.5 ± 0.09%) at a rate of 74 ± 0.7 m²a^?1. However, during recent decade (1999–2015), the rate of glacier recession of 3.9 ± 0.004 ma^?1 with a corresponding area loss of 500 ± 0.74m² (1 ± 0.1%) was higher than the retreat rate of 2.3 ± 0.001 ma^?1 and an area loss of 240 ± 0.02m² (0.48 ± 0.08%) during 1971–1999. In the field, the evidences of glacier recession are present in the form of separated dead ice blocks from the main Glacier, recessional dumps/moraines, active ice calving activity and a small proglacial pond/lake at the terminus/snout of the Glacier. However, the recession over the studied period has been very slow and is controlled by its topographic configuration, particularly the large altitudinal range (6030–3620 m), almost northerly aspect and steep slope (average ~ 30°).