Focusing and spatial resolution of electromagnetic three-coil sounders

Doklady Earth Sciences - Distribution density functions for the sensitivity of a three-coil sounder are constructed as the weighted mean rock volume between the in-phase surfaces of running...     

The Karoo Basin of South Africa: type basin for the coal-bearing deposits of southern Africa

The coal-bearing sediments and coal seams of the Karoo Basin, Southern Africa are described and discussed. The Karoo Basin is bounded on its southern margin by the Cape Fold Belt, onlaps onto the Kaapvaal Craton in the north and is classified as a foreland basin. Coal seams are present within the Early Permian Vryheid Formation and the Triassic Molteno Formation.The peats of the Vryheid Formation accumulated within swamps in a cool temperate climatic regime. Lower and upper delta plain, back-barrier and fluvial environments were associated with peat formation. Thick, laterally extensive coal seams have preferentially accumulated in fluvial environments. The coals are in general inertinite-rich and high in ash. However, increasing vitrinite and decreasing ash contents within seams occur from west to east across the coalfields. The Triassic Molteno coal seams accumulated with aerially restricted swamps in fluvial environments. These Molteno coals are thin, laterally impersistent, vitrinite-rich and shaly, and formed under a warm temperate climatic regime.Palaeoclimate, depositional systems, differential subsidence and basin tectonics influence to varying degrees, the maceral content, thickness and lateral extent of coal seams. However, the geographic position of peat-forming swamps within a foreland basin, coupled with basin tectonics and differential subsidence are envisaged as the primary controls on coal parameters. The Permian coals are situated in proximal positions on the passive margin of the foreland basin. Here, subsidence was limited which enhanced oxidation of organic matter and hence the formation of inertinitic coals. The coals in this tectonic setting are thick and laterally extensive. The Triassci coals are situated within the tectonically active foreland basin margin. Rapid subsidence and sedimentation rates occurred during peat formation which resulted in the preservation of thin, laterally impersistent, high ash, vitrinite-rich, shaly coals.     

A robust algorithm for ellipse-based discrete element modelling of granular materials

With recent research indicating the importance of the rolling mechanism of deformation in granular systems consisting of perfectly round particles, it has become popular to use ellipse-shaped particles in the Discrete Element Method (DEM) numerical model. Inherent in this technique is the need for accurately computing ellipse to ellipse intersection, in order to properly detect contact formation and compute relative contact velocities. However, the commonly used algorithms for computing ellipse-ellipse intersection are generally poorly conditioned and can be inaccurate. An alternate method for computing ellipse-ellipse intersection is developed and presented which results in a well-conditioned, stable and accurate contact detection method. These modification are incorporated into the general DEM algorithm.     

Mantle(?) xenoliths in the carbonatites of northern Transbaikalia

The composition and nature of high-Cr minerals in lithic clasts from the carbonatites of the Veseloe occurrence, northern Transbaikalia, were considered. In order to determine their source, the Cr-bearing phases were compared with chromite, magnetite, and rutile from ultrabasic rocks, mantle xenoliths, and eclogites. It was suggested that the xenoclasts studied were formed at great depths, whereas the carbonatites were directly derived from the mantle rather than formed by the crustal differentiation of a silicate-carbonate melt.     

Solubility of alumina in orthopyroxene plus spinel as a geobarometer in complex systems. Applications to spinel-bearing alpine-type peridotites

The addition of Fe and Cr to the simple system MgO-SiO₂-Al₂O₃ markedly affects the activities of phases involved in the equilibrium

Gravity change and land uplift in Fennoscandia 1966–1984

An analysis is made of the results from all repeated gravity measurements of the Fennoscandian land uplift gravity line 63°. The line is, thereby, divided into two separate parts: one part west of the land uplift maximum, and the other part east of the land uplift maximum. A statistically significant change of gravity is found both for the western part and the eastern one. Both parts give a relation between gravity change and land uplift of about ?0.22μgal/mm.     

Meridional transport of sensible heat in contrasting monsoon activity: Spherical harmonic analysis

Spherical harmonic analysis is made of the grid point values of geopotential heights at 700 mb and 300 mb levels for the months April to August for the years 1967 and 1972. The year 1967 is a good monsoon year and 1972 is a bad monsoon year in India. Meridional transport of sensible heat is obtained in wave number domain using spherical harmonic coefficients at 500 mb level form=1 to 10 andn–m=0 to 10, wherem represents the wave number round the globe andn–m gives the numbers of zero points from north pole to south pole excluding the poles themselves.Large northward transports of sensible heat in the month of May and in the monsoon months at the subtropics are characteristic of bad monsoon. Wave 1 transports sensible heat southward (forn–m=0) and wave 2 transports sensible heat northward (forn–m=4). Strengthening of wave 1 is conducive to good monsoon year and strengthening of wave 2 is conducive to bad monsoon year. These are the same features obtained in Fourier analysis. The contrasting features exist in waves 1 and 2 both in good and in bad monsoon and are better defined in the present analysis than in the Fourier analysis of the earlier study. However, waves 1 and 2 reveal clearer contrast in the present analysis than in the Fourier analysis. Bad monsoon activity is associated with large divergence of heart at subtropics and large convergence of heat at extra tropics.     

Rice research for food security and sustainable agricultural development in Asia: Achievements and future challenges

Rice is the major staple food of Asia, and an important source of employment and income in rural areas, particularly in low-income countries. Research has contributed significantly in achieving food security by increasing the yield potential of rice in irrigated systems, reducing the crop maturity period and achieving yield stability by developing resistance against major insects and diseases in the modern high-yielding varieties. Poverty is, however, still extensive in fragile rainfed rice ecosystems where rice yield has remained low, as scientists have yet to develop high-yielding varieties resistant to abiotic stresses and problem soils. Rice production needs to be increased by another 70% over the next 30 years to meet growing food needs. This has to be achieved with less land, less water, and less labor to accommodate the demand for these inputs from the expanding nonagricultural sectors. The challenge to the rice research community is to make further shifts in yield potential of rice for the irrigated systems, to close the yield gaps in the rainfed systems through developing resistance of high yielding varieties to abiotic stresses, and greater understanding of the interactions between genotypes and environment, developing durable resistance against pests and diseases to reduce farmers' dependence on harmful agrochemicals, and to increase efficiency in the use of water, labor and fertilizers. As further intensification of rice cultivation is inevitable, scientists must understand the negative environmental side-effects of increasing rice productivity, to develop appropriate mitigation options.