Effects of convective available potential energy,temperature and humidity on the variability of thunderstorm frequency over Bangladesh

Theoretical and Applied Climatology - The present study examines the effects of convective available potential energy (CAPE), temperature and humidity on the spatiotemporal variation of...     

Rare earth element distribution in some hydrothermal minerals: evidence for crystallographic control

Rare earth element (REE) abundances were measured by neutron activation analysis in anhydrite (CaSO₄), barite (BaSO₄), siderite (FeCO₃) and galena (PbS). A simple crystal-chemical model qualitatively describes the relative affinities for REE substitution in anhydrite, barite, and siderite. When normalized to ‘crustal’ abundances (as an approximation to the hydrothermal fluid REE pattern), log REE abundance is a surprisingly linear function of (ionic radius of major cation—ionic radius of REE)² for the three hydrothermal minerals, individually and collectively. An important exception, however, is Eu, which is anomalously enriched in barite and depleted in siderite relative to REE of neighboring atomic number and trivalent ionic radius. In principle, REE analyses of suitable pairs of co-existing hydrothermal minerals, combined with appropriate experimental data, could yield both the REE content and the temperature of the parental hydrothermal fluid.The REE have only very weak chalcophilic tendencies, and this is reflected by the very low abundances in galena—La, 0.6 ppb; Sm, 0.06 ppb; the remainder are below detection limits.     

Grid resolution study of ground water flow and transport

Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution.     

Finite-difference migration of the field of refracted waves in studies of the deep structure of the Earth’s crust and the upper mantle based on the DSS (on the example of the <Emphasis Type="Italic">DOBRE</Emphasis> profile)

The main results of deep seismic sounding (DSS) are usually presented in the form of high-velocity models of the medium. Some model examples and the international DOBRE profile have shown that the informativeness of the data obtained can be significantly enhanced by the construction of wave images of the Earth’s crust, based on the migration of refracted and wide-angle reflected waves. The Donets Basin Refraction/Reflection Experiment (DOBRE) profile crosses the Dnieper-Donets paleorift zone in the Donbas region. Along the profile, refracted waves from the basement and the upper mantle and the reflections from the crust basement (the M boundary) are reliably traced. This wave migration has been used to construct a wave image of the structure of the Earth’s crust. As a result, a clear seismic image of the basement surface, whose depth changes along the profile from 0 to 20 km, was obtained. In near-slope parts of the basin, several major faults were identified that had not been identified previously during standard kinematic data processing. It is shown that the crust-upper mantle transition zone is a clearly reflective horizon only within the crystalline massifs; under a depression, it is represented by a lens-shaped highly-heterogeneous area. As shown in the model examples, the images obtained using such a migration accurately reflect the structural features of the medium, in spite of its complicated structure.     

Reconstruction of Holocene paleohydrological and sedimentological characteristics of Umm Ar-Rimam basin (northern Kuwait)

The paleohydrological and sedimentological characteristics of a playa lake in northern Kuwait (Arabian Gulf) are reconstructed using sedimentological, geochemical, and isotopic techniques. The sequence consists of up to 8 cycles of S-poor, alluvial sediments capped by a thin organic soil interbedded with gravity-fall calcrete sediments. The succession is locally derived from mainly Quaternary sediments and is regressive with upsection filling of the subsiding basin by cycles of sheetwash flow in response to climatic change. There is no natural, open-water lake water as indicated by low total organic carbon (TOC) data, but the presence of incised calcrete yardangs suggests that more extensive open-water conditions were operative in the past. Stable isotope (δ¹⁸O‰ and δ¹³C‰) values of the authigenic carbonates indicate the following three distinct processes: evaporation, meteoric fluid infiltration, and rapid per-descensum flow (rapid downward movement of water and playa sediment through pipes) through a porous, clastic sequence. Because evaporites are scarce, other factors besides evaporation action control chemical and isotopic compositions of the per-decensum lake fluids. Consequently, the isotopic composition cannot be interpreted exclusively as an indicator of salinity or evaporation ratio. The degassing of CO₂ during groundwater discharge may explain the enriched carbon isotope values for the authigenic carbonates precipitated in the sediments. Hydrologically closed lake water bodies tend to show low negative carbonate oxygen and carbon isotopic signatures. Isotopically negative δ¹³C values imply a strong input of soil-zone carbon to the groundwater of the top 60 cm of the sediment. Lakes that are hydrologically closed and evaporate or equilibrate with atmospheric CO₂ will tend to have low negative δ¹⁸O and δ¹³C values in the carbonates as reported by Talbot (Chem Geol: Isotope Geosci Sect 80(4):261–279, 1990). Biologically active lakes will tend toward lower δ¹³C of dissolved carbon due to the photosynthetic effects of ¹²C withdrawal as reported by Dunagan and Driese (J Sed Res 69:772–783, 1999). Increased biological activity during sedimentation may account for low carbon isotope values where plants were abundant, but in shrinkage-dominated systems (those of clay-rich soil subjecting to wet-dry conditions), carbon isotopes will be largely inherited from the calcretic limestones in the land extending landward of the coast and not influenced by coastal processes (known as hinterland), such as Umm Ar-Rimam depression. This basin does not fit the classic shallow playa-type basins of the Arabian Peninsula but rather the recharge playas of the southwestern USA.     

Surface water quality evaluation in Odukpani, Calabar Flank, south-eastern Nigeria

 The present article is the second in a series of baseline water quality evaluation studies in parts of south-eastern Nigeria. Study results indicate that the water samples from the study are generally acidic, soft and fresh in addition to low sodium and salinity hazard. Regression equations indicate a good positive correlation between conductivity and Na, Ca, Mg and SO₄. Ca-SO₄ and Ca-Cl constitute the major facies in the area. Generally the waters in the area are good for most domestic and agricultural purposes. Received: 14 April 1997 · Accepted: 3 February 1998     

On mass transport in deep water waves

Summary Various formulations of the mass-transport problem are compared for progressive waves in deep water. In order to calculate the mass-transport velocity as a function of depth in the main body of the fluid, it is necessary to include the effect of viscous wave attenuation. It is shown that the usual assumptions of periodicity in distance and attenuation with time or periodicity in time and attenuation with distance, are both physically unsatisfactory. The first does not specify a unique solution, and the second is incompatible with the assumption of zero surface stress. A certain critical constant tangential wind stress will maintain strictly time-periodic deep water waves. The corresponding attenuation with distance is then calculated to order ³. A constant tangential stress greater or less than the critical causes waves, necessarily decaying with distance, to grow or decay with time.     

Use of Carbonatites in the Production of Precipitated Calcium Carbonate: A Case Study from Eppawala,Sri Lanka

The study investigates the possibility of using carbonatite in the production of precipitated calcium carbonate (PCC). We made use of fresh apatite-rich carbonatites found at the phosphate mining sites at Eppawala, Sri Lanka. Analyses of the fresh carbonatite were performed with the aid of optical microscopy, powder X-ray diffraction (XRD), atomic absorption spectrophotometry (AAS), UV/visible spectrophotometry (UVVS), and thermo gravimetric analysis (TGA). Quicklime obtained from calcinations of carbonatites was used in synthesizing PCC via a lime-soda process. The end product was analyzed with XRD, TGA, AAS, and UVVS. Results revealed that the most common CO₃ ^2? phase available in fresh carbonatites is calcite (>65%). The Ca-rich CO₃ ^2? phase can be distinguished easily from other available minerals because its mode of occurrence in carbonatite matrix is different to that of other minerals. The results of TGA show that the decomposition of CO₃ ^2? phase initiates at about 340°C, which leads to lower energy consumption during calcinations. Post-magmatic hydrothermal process may have been the cause of the formation of thermally unstable CO₃ ^2? phases. Hydration of quicklime from the carbonatite yields much higher Ca²⁺ in the solution than from marble under the same experimental conditions. The synthesized PCC particles are in the calcite polymorphic form. The purity of PCC varies from 96 to 98 wt%. The maximum precipitable CaCO₃ from 1 g of quicklime is about 1.1 g. Hence, fresh carbonatites has great economic potential for the production of PCC.     

Urban Slum Detection Approaches from High-Resolution Satellite Data Using Statistical and Spectral Based Approaches

This paper proposes a new technique to detect the urban slums from urban buildings using very high resolution data. Many cities in the Global South are facing the development and growth of highly dynamic slum areas, but often lack detailed spatial information. Unlike buildings, vegetation and other features, urban slums lack in their unique spectral signatures. Thus, accurate detection of slums using remote sensing data poses real challenge to researchers and decision-makers. In this work, gray-level co-occurrence matrix, Tamura-based statistical feature extraction and wavelet frame transform-based spectral feature extraction techniques are proposed for detecting the urban slums from urban buildings. The very high resolution data of Madurai city, South India, acquired by Worldview-2 sensor (1.84 m) proved the ability of the proposed approaches to identify urban slums from urban buildings. Experimental results demonstrate that the proposed wavelet frame transform-based approach can generate higher classification accuracy than other approaches.