IGU Commission on Health and Developement     

Helen Roy  Eric Wajnberg 《GeoJournal》1989,18(4):451-451

The International Geographical Union Reports

IGU Commission on Population Geography  相似文献   

Occurrence of thorite and radioactive zircon in syenite pegmatite,North of Ashwaraopet,Khammam district,Andhra Pradesh,India     

K. Surya Prakash Rao  R. S. N. Sastry  Gautam Roy 《Journal of Earth System Science》1989,98(2):183-187

This paper reports the occurrence of thorite and confirms the earlier find of radioactive zircon by Subbarao, Murali and others from syenite pegmatite in the Vinayakapuram-Kunavaram alkaline belt in the Khammam district of Andhra Pradesh, India. Thorite has also been found as residual concentrations in soil overlying the pegmatite.  相似文献   

Etude de la couche limite de surface sahelienne — Experience Yantala     

Jean-Pierre Pagès  Jean-Pierre Frangi  Pierre Durand  Claude Estournel  Aimé Druilhet 《Boundary-Layer Meteorology》1988,43(1-2):183-203

This paper presents data concerning the energy budget in the surface layer in the Sahel region (a semi-desert area). The results are drawn from a measurement campaign made in the Niamey region in the Niger, in April–May 1984 (the Yantala Campaign). The sensible heat flux is computed with the profile method, the ground heat flux is deduced from measurement of the temperature field, and the radiative net flux is measured directly with a balancemeter. The latent heat flux, which is deduced from the energy budget balance is very weak and within the accuracy limit of the method. The diurnal variation of the net flux is symmetrical, with a maximum at noon. On the other hand, the sensible heat flux variation is asymmetrical, with an afternoon decrease much slower than the morning increase. After 3.30 pm, it becomes higher than the net flux. This is compensated for by the sign change of the ground heat flux, whose maximum is found in the morning at 11 am. The second part of this paper shows the importance of one term in the surface-layer energy budget: the long-wave radiative divergence between the ground and the top of the surface layer in high superadiabatic conditions. We show, with a radiative model on the one hand and direct measurement of the radiative divergence on the other hand, that this term reaches several tens of W m^-2 in the superadiabatic conditions found in the Sahel region.   相似文献   

Description de deux nouvelles Cyclotelles (Bacillariophyceae) de milieux alcalins et eutrophes:Cyclotella costei nov. sp. etCyclotella wuethrichiana nov. sp.     

Jean Claude Druart  François Straub 《Aquatic Sciences - Research Across Boundaries》1988,50(2):182-188

Two new species of the genus Cyclotella are presented which have been discovered during ecological and paleoecological research studies in the littoral zone of two small alkaline eutrophic lakes in France (Lake Paladru) and in Switzerland (Lake Le Loclat). These new species are namedCyclotella costei nov. sp. andCyclotella wuethrichiana nov. sp.  相似文献   

A simplified computational approach for prediction of transient climatic conditions in underground mine airways     

T. R. Roy 《Geotechnical and Geological Engineering》1993,11(1):15-23

Summary A simplified approach for prediction of transient climatic conditions in an underground airway os presented. The dry surface temperature of the airway is calculated using a finite difference scheme, whereas the wet surface temperature is determined following the concept of pseudo-base-temperature of air and using the value of thermal gradient at the dry surface as obtained from the finite difference solution of the temperature profile in the dry rock. The air-current temperatures are regularly evaluated after a suitable time span so as to simulate a real-case situation, and the re-evaluated air-current temperatures are used for further calculations. For increasing age of the airway the wet surface temperature obtained by the finite difference scheme, with an appropriate value of thermal diffusivity, is compared with its value determined by the pseudo-base-temperature approach.  相似文献   

A three dimensional perspective on the evolution of Archaean crust: LITHOPROBE seismic reflection images in the southwestern Superior province     

John Ludden  Claude Hubert  Arthur Barnes  Bernd Milkereit  Edward Sawyer 《Lithos》1993,30(3-4):357-372

15011993

Abstract

In 1990–1991 the LITHOPROBE project completed 450 km of seismic reflection profiles across the late Archaean crust of the southwestern Superior province. The results define a broad three-fold division of crust: upper crust in the Abitibi greenstone belt is non-reflective and is a 6–8 km veneer of volcanic and plutonic supracrustal rocks, whereas, in the sediment-gneiss dominated Pontiac subprovince, upper crust comprises shallow northwest-dipping turbidite sequences; mid-crust, in both the Abitibi and the Pontiac subprovinces, is interpreted as imbricate sequences of metasedimentary and metaplutonic rocks; lower crust in both subprovinces has a horizontal layer parallel strycture which may represent interleaved mafic-intermediate gneisses. The seismic signature of the northern Abitibi greenstone belt may be represented in an exposed 25 km crustal section in the Kapuskasing stuctural zone.

Preliminary tectonic models based on the seismic data are consistent with a plate-tectonic scenario involving oblique subduction and imbrication of sedimentary, plutonic and volcanic sequences. The northern Abitibi supracrustal sequences either represent an allochthon, or overlie an allochthonous underthrust metasedimentary and plutonic sequence which may be equivalent to a metasedimentary subprovince such as the Pontiac or Quetico.

Seismic velocities have yet to be defined. However, crustal thicknesses are relatively constant at 35–40 km. The thinnest crust is adjacent to the Grenville Front where Moho is very well defined.  相似文献   

Characterisation of ecological parameters in tropical forest community—A remote sensing approach     

P S Roy  Sarnam Singh  M C Porwal 《Journal of the Indian Society of Remote Sensing》1993,21(3):127-149

Satellite Remote Sensing data has been used for vegetation mapping, initial stratification, distribution of sample plots and for calculating the area under different vegetation types. Primary and secondary analyses of vegetation has been done using phytosociological ground data collected from sample piots to assess the ecological importance of different species. Interrelationships among different communities have been evaluated through various available indices. The spatial distribution and vegetation analysis indicate that commercial extraction of natural forests of Andaman has set in retrogression. The evergreen forests subjected to shorter rotation of commercial exploitation are being invaded with seral deciduous species. The study highlights the status of forests (spatial and community) and stresses the need to conserve germplasm present in the natural evergreen forests.  相似文献   

Factors Affecting Efficient Aquifer Restoration at In Situ Uranium Mine Sites     

James L. Osiensky  Roy E. Williams 《Ground Water Monitoring & Remediation》1990,10(2):107-112

In situ mining of uranium typically requires the injection of a reactive leaching solution (lixiviant) such as sodium carbonate/bicarbonate, ammonium carbonate/bicarbonate, or sulfuric acid, and an oxidant such as hydrogen peroxide or oxygen into an ore-bearing, confined aquifer. It also requires the environmental restoration of the source aquifer. The stratigraphy of sandstone uranium deposits typically consists of interbedded layers of poorly consolidated sands and clays and gravels deposited in fluvial or coastal environments. The parameters that influence the migration of lixiviant during mining and restoration in these environments include induced hydraulic gradients, hydrodynamic dispersion, heterogeneity, anisotropy, physicochemical reactions, leakage into and/or through confining layers, and convergence of flow lines due to partial well penetration.
The effectiveness of the various methods of aquifer restoration is sit -specific and is dependent upon the site hydrogeology and hydrogeochemistry, and the chemistry of the lixiviant. Each method of aquifer restoration has advantages and disadvantages. Selection of the most effective and economically feasible method requires detailed knowledge of the site-specific hydrogeologic conditions.  相似文献   

Fuzzy factorial analysis of snow avalanches     

Claude Jaccard 《Natural Hazards》1990,3(4):329-340

The mutual influence of 21 factors pertaining to terrain, weather, forest and snowpack have been discussed by 10 experts. The semantic (nil, weak, medium, high) evaluations are translated as membership degrees of fuzzy sets, and averaged between the experts by taking their fuzzy expectation value, yielding a 21 × 21 fuzzy matrix for direct interactions. Fuzzy successive multiplications and additions of the matrix give the indirect interactions. The activity and the passivity of the factors with respect to avalanches is represented by directed weighted graphs, and the average semantic values by a 4 × 4 matrix: the activity (passivity) is weak (strong) for tree damage; medium (nil) for altitude; medium (weak) for ground shape; medium (medium) for vegetation, soil, wind, microclimate, tree type, vertical distribution and mechanics of trees, snowpack distribution and snow gliding; strong (nil) for ground inclination and exposition, weather; strong (medium) for heat, precipitation, horizontal distribution of trees, snowpack constitution and stability.  相似文献   

Convective instabilities in a variable viscosity fluid cooled from above     

Claude Jaupart  Barry Parsons 《Physics of the Earth and Planetary Interiors》1985,39(1):14-32

Whether in the mantle or in magma chambers, convective flows are characterized by large variations of viscosity. We study the influence of the viscosity structure on the development of convective instabilities in a viscous fluid which is cooled from above. The upper and lower boundaries of the fluid are stress-free. A viscosity dependence with depth of the form ν₀ + ν₁ exp(?γ.z) is assumed. After the temperature of the top boundary is lowered, velocity and temperature perturbations are followed numerically until convective breakdown occurs. Viscosity contrasts of up to 10⁷ and Rayleigh numbers of up to 10⁸ are studied.For intermediate viscosity contrasts (around 10³), convective breakdown is characterized by the almost simultaneous appearance of two modes of instability. One involves the whole fluid layer, has a large horizontal wavelength (several times the layer depth) and exhibits plate-like behaviour. The other mode has a much smaller wavelength and develops below a rigid lid. The “whole layer” mode dominates for small viscosity contrasts but is suppressed by viscous dissipation at large viscosity contrasts.For the “rigid lid” mode, we emphasize that it is the form of the viscosity variation which determines the instability. For steep viscosity profiles, convective flow does not penetrate deeply in the viscous region and only weak convection develops. We propose a simple method to define the rigid lid thickness. We are thus able to compute the true depth extent and the effective driving temperature difference of convective flow. Because viscosity contrasts in the convecting region do not exceed 100, simple scaling arguments are sufficient to describe the instability. The critical wavelength is proportional to the thickness of the thermal boundary layer below the rigid lid. Convection occurs when a Rayleigh number defined locally exceeds a critical value of 160–200. Finally, we show that a local Rayleigh number can be computed at any depth in the fluid and that convection develops below depth z_r (the rigid lid thickness) such that this number is maximum.The simple similarity laws are applied to the upper mantle beneath oceans and yield estimates of 5 × 10¹⁵?5 × 10¹⁶ m² s^?1 for viscosity in the thermal boundary layer below the plate.  相似文献