Application of magnetic susceptibility anisotropy technique to the study of geological structures in the Armorican massif, France

Magnetic susceptibility anisotropy analyses have been carried out on 300 samples of rock from various metamorphosed regions of Normandy and Brittany, within the northern half of the Armorican massif, to test the ability of the magnetic fabric method (in a relatively complex region where structures have been well charted) to delineate regional structures. The two major structural directions to emerge from the study were a ENE—WSW striking magnetic foliation plane, conforming to a Variscan direction of the Bocaine syncline in the Granville region of Normandy and a ESE—WNW striking magnetic foliation plane conforming to the Armorican direction in the Chateaulin syncline region of Brittany. The magnetic fabric of sites elsewhere confirmed localised structures and minor synclinal structures.

The major advantages of the technique of studying magnetic fabric over petrofabric are the speed at which magnetic fabric can be measured (2 minutes per sample compared with up to 24 h using X-ray goniometry techniques) and the sensitivity of the magnetic fabric to very slight stresses.     

Regional character of induced magnetic variations in India

Variations recorded simultaneously at eight Indian stations during a magnetic storm are analysed to obtain the power spectra for each component using the fast Fourier transform. For two selected peaks, observed for H at all stations, at 49.5- and 70-min periods, a complex demodulation is performed for each component. From the variations thus obtained, horizontal polarization ellipses are drawn for four events of 49.5-min period. The variation of the demodulates and polarization ellipses at the stations shows a regional character which coincides with the physiographic grouping of the stations. Anomalously large Z variations are observed at the equatorial stations, which are near the sea. A distinct feature is the suppression of H at Trivandrum where the polarization ellipses confirm the E-W trend of the induced currents in this region. The overall similarity of the horizontal variations is demonstrated by these ellipses. Horizontal disturbance vectors at Annamalainagar, Trivandrum and Sabhawala confirm channelled currents located previously. At Shillong, the induced effects are evident and the currents are deduced to flow eastward, directly beneath the station.The overall regional similarities in variations are clearly manifested.     

Comparison of reconnaissance soil maps prepared by conventional method and landsat imagery interpretation

Landsat images have been used in conjunction with topographical and geological information to prepare soil map of Mudhol taluk in Bijapur district, Karnataka state. The map has been compared with the reconnaisance map prepared by conventional method using 1:63,360 scale Survey of India toposheets. The study reveals that more accurate soil maps in terms of boundary delineation and composition of soil mapping units could be prepared by interpretation of Landsat images with adequate ground data. The method can thus be used in revising and improving many of the existing reconnaissance soil maps prepared by conventional method.     

Characteristics and morphogenesis of salt-affected soils in southeastern arid Rajasthan

Aerial photographs coupled with ground check and laboratory analysis have helped in mapping of four categories of salt affected soils located in the southeastern tract of arid Rajasthan. The categories are (1) Natural saline soils (2) Relict saline soils (3) Secondary salinized soils due to high water table and (4) Secondary salinised soils due to highly saline water use for irrigation Salinity in natural salt affected soils is mostly sodium chloride followed by sodium-calcium chloride and sodium-chloride-sulphate type. The distribution of the natural salt affected soils along the natural drainage or inconspicuous depressional areas suggest that their occurrence is due to insufficient surface drainage. Further, the pattern of distribution indicates that the origin of salt is within the catchment itself. Deep ploughing and application of organic material have reversed the upward flux of salts and improved the soils. This phenomenon also seems to explain the large occurrence of soils of relict salinity.     

An analysis of the Chow-Kulandaiswamy GHS model

The Chow-Kulandaiswamy general hydrologic system (GHS) model is revisited. Based on a mathematical study by Singh and McCann the GHS model is simplified. Explicit solutions are obtained for special cases which can satisfactorily determine watershed surface runoff response due to given rainfall excess. A rational criterion is developed to determine the number of derivative terms to be retained in the model. In order to determine the coefficients in the GHS model the method of moments is proposed. Criteria are developed to determine complex roots and oscillations for these coefficients. By analysing Chow-Kulandaiswamy's results it is found that in a majority of cases which they studied roots are complex. Moreover, for the cases which have complex roots, a majority of the solutions oscillate. A brief sensitivity analysis of the GHS model is performed with regard to: (a) its leading coefficient, and (b) the order of the differential equation. Finally, the peak characteristics are specified for the second order case and their qualitative properties are shown for the third order case.     

Protein Digestibility by Khosti Fish Colisa fasciatus (Pisces,Anabantidae) under the Influence of Certain Factors

Protein digestibility was determined via two feeding trials in glass aquaria by the indicator (Chromium oxide) method using a mixture of shrimp powder with oil cake and wheat bran respectively (1: 1 W/W) as food. Analyses of feed were made to calculate the crude protein, carbohydrate, lipid and ash contents. Feces were analysed to determine their total nitrogen and chromium oxide. Protein digestibility was studied in relation to salinity of the medium size and weight of the fish body. The apparent digestibility of crude protein of a corresponding die has shown that 1st: Younger fish do possess a lower capability of protein digestion than fish having a medium weight and medium size; 2nd: Older fish with a high weight and large size exhibit no improvement in efficiency to digest the food protein, though their weight and size are significantly greater than those of middle weight and medium size fish; 3rd: The replacement of oil cake by wheat bran decreases the protein digestibility of shrimp powder mixture with them; 4th: A salinity (NaCl) of the aquatic medium at or above 3 g/l depletes the protein digestibility when fish of the same size were experimented with; but a salinity up to 2 g/l does not result in a significant decrease in the protein digestion rate.     

Relationships between rainy days,mean daily intensity and seasonal rainfall in normal,flood and drought years over india

There are limitations in using the seasonal rainfall total in studies of Monsoon rainfall climatology. A correlation analysis of the individual station seasonal rainfall with all India seasonal mean rainfall has been made. After taking the significance test (strictly up to 5% level) the stations which are significantly correlated have been considered in this study in normal, flood and drought years respectively. Analysis of seasonal rainfall data of 50 stations spread over a period of 41 years suggests that a linear relationship fits better than the logarithmic relationship when seasonal rain-fall versus number of rainy days is studied. The linear relationship is also found to be better in the case of seasonal rainfall versus mean daily intensity.     

Some unintended features of elastic finite-difference models

While finite-difference methods have been used extensively for many years to model wave propagation in elastic media, some of the more subtle effects observable in such models are very inadequately documented in the geophysical literature, especially in regard to their practical numerical consequences. In addition to the intended travelling waves, and the undesirable exponential instability revealed by the von Neumann test, typical second-order-time finite-difference equations also support drifting linear solutions, as can be verified, both theoretically and by numerical experiment. The necessity of these solutions, and their relationship to the incompleteness of the set of travelling-wave eigenfunctions of the finite-difference operator, can be exposed by a matrix-based analysis, and exact expressions for them can be obtained by using standard algebraic techniques. A further peculiarity of the finite-difference formulation is numerical anisotropy, which emerges in a grid of more than one spatial dimension, even when the modelled medium is intended to be isotropic. This anisotropy can be explained and quantified in terms of the exact eigenfunction solutions to the finite-difference equation, which, it is found, can be obtained in a simple, closed form, for a typical modern 3D staggered scheme.     

Point-block covariance: A general solution for the two-dimensional stationary random functions

The application of the theory of random functions to problems of ore evaluation may involve computations of the covariance between the mean value of a given block and the functional value at a given point. However, an analytical solution for such a covariance does not exist for nonspherical blocks and for commonly applied models of covariance functions. Further, because this covariance is a function of the spatial arrangements of the block and the point, it has to be evaluated numerically each time for given point—block arrangements. This paper presents a readily available general solution to this problem in the form of a series of graduated curves which, together with some geometric manipulations, may be used to compute the covariance between a pointand a two-dimensional block for all possible point—block arrangements. The availability of the graph thus eliminates the necessity of using the time-absorbing programs on computers for such computations. Finally, many of the approximations that are made in order to avoid cumbersome covariance evaluations are no longer necessary due to the ease of such computations with the help of the graph provided.     

Photo-interpetation for erosion assessment in the beas catchment

Panchromatic vertical aerial photographs in the scale of 1: 15,000 were interpreted for assessment of erosion in the Bcas River Valley Project catchment, Himachal Pradesh in terms of the erosion intensity units. The erosion intensity units imply the relative quantum of sediment yield as deduced from the probable interaction of the significant parameters of erosion comprising physiography, slope, soil characteristics, Vegetation, land use and the visible erosion conditions. The procedure of photo-interpretation as also computation of sediment yield index for each of the different watersheds in the Beas RVP catchment is discussed. The survey revealed that out ofa total of 494 watersheds involving an area of 5.5 lakh ha, 132 watersheds comprising an area of 1.55 lakh ha, have silt yield index of over 1150 and need soil conservation measures on priority basis. Application of photo-interpretation has proved 2 times more efficient than the conventionai method that was followed in a piain area of Matatilla RVP catchment. In a more simpler terrain than Beas catchment and with ideal photographic scale of 1:60,000, the efficiency is expected to increase by 2-3 times than was achieved in Beas RVP catchment