Simple Electrical Logging Technique for Base Metal Exploration

—It is well known that electrical logs of boreholes can play a signi|fi|cant role in base metal exploration in identifying mineralised zones, especially when there is core loss or the borehole diameter is small or if drilling is by percussion. However, electrical logging is not widely utilised because of the additional burden on finances and time.¶A simple electrical logging technique, based on a pole-pole (hole-to-surface) configuration with one borehole electrode and nearly akin to the single point method, for S.P., resistivity and I.P. parameters, is presented. It is shown that it has the resolution of the single point method and the penetration of a very long normal sonde which is helpful for detection. Besides these features, the main advantage of this technique is that it can be easily carried out using ground I.P. (time domain) equipment.¶The electrical logs obtained in different base metal belts in Rajasthan, India, employing this technique and using ground I.P. equipment in connection with mise-à-la-masse surveys, illustrate the above features. A comparison with logs recorded by means of multi-electrode drill hole I.P. equipment of Scintrex, Canada, substantiates the same.     

Design and Optimization of a Ground Water Monitoring System Using GIS and Multicriteria Decision Analysis

A GIS-based methodology has been developed to design a ground water monitoring system and implemented for a selected area in Mae-Klong River Basin, Thailand. A multicriteria decision-making analysis has been performed to optimize the network system based on major criteria which govern the monitoring network design such as minimization of cost of construction, reduction of kriging standard deviations, etc. The methodology developed in this study is a new approach to designing monitoring networks which can be used for any site considering site-specific aspects. It makes it possible to choose the best monitoring network from various alternatives based on the prioritization of decision factors.     

Inversion of GDS data of northwest Himalaya using EM2INV

This paper reviews the validity of earlier models obtained after quantitative interpretation of GDS data and presents a fresh model using the inversion scheme EM2INV. The 2-D inversion of data is more objective than the earlier interpretation performed by using trial and error method. The inversion results indicate that the present model differs from the earlier ones. The reason could be that available GDS data are sufficient only for deriving the horizontal variation of subsurface resistivity. In order to study the vertical resistivity variation additional MT sounding data would be required. It would therefore be desirable to carry out MT survey in the specified area. A more comprehensive/appropriate model could be derived from joint inversion of GDS and MT data.     

Effect of overtaking disturbances on a strong cylindrical hydromagnetic shock wave in a self-gravitating gas

The effect of overtaking disturbances upon the free propagation of strong cylindrical hydromagnetic shock through a self-gravitating gas has been studied by an approximating technique developed by Yadav. Assuming an initial density distribution law as ₀=r^–w, where is the density at the axis of symmetry and is a constant, the analytical relation for shock velocity and shock strength modified by overtaking waves has been obtained under two conditions: viz., (i) when the applied axial magnetic field is strong and (ii) when the field is weak. The results obtained here are compared with those for a freely propagating shock. The conclusions arrived at agreed with experimental results.It is shown that the applications of the CCW method and the neglect of overtaking disturbances are equivalent.     

Nitrogen and phosphorus budgets in the Baltic Sea

The paper reports the budgets of inorganic and total nitrogen and phosphorus based on a recalculation of the existing water balance. The nitrogen budgets indicate that humus carried by river runoff probably dominates in the sedimentation of nitrogenous organic matter, while the excess transferred to the layer below the halocline is controlled by the amounts added by river runoff and waste disposal. The budgets appear to be considerably influenced by eutrophication and human activity. The phosphorus budget indicates that the supply of organic phosphorus and oxygen in the layers below the halocline are in a precarious balance with each other. Phosphorus and nitrogen compounds appear to sediment in almost the same proportions as their concentrations in the bottom water.     

Fatigue damage in randomly vibrating jack-up platforms under non-Gaussian loads

The problem of fatigue damage estimation of ageing jack-up platforms is considered, using theories of random processes. The sea-wave excitations are modelled as stationary, Gaussian random processes, with specified power spectral density function. The loads acting on the structure due to the sea waves is calculated using Morison’s equation and are therefore non-Gaussian whose probabilistic properties are not available in explicit form. Assuming linear structure behaviour, the probabilistic properties of the structure response are determined using theories of random vibrations. The simple peak counting method is adopted for estimating the mean fatigue damage. This requires knowledge of the joint probability density function of the structure response and its first and second time derivatives, at the same time instant. A methodology has been presented for developing analytical expressions for this joint pdf. This requires evaluation of multidimensional integrals. A recently developed computational algorithm is presented to deal with integrals for which derivation of closed form analytical expressions may not be feasible. The methodology proposed in this paper provides an alternative and computationally cheaper technique for estimating the fatigue damage in comparison to the Monte Carlo simulation procedure. Numerical results have been presented for illustration of the proposed methodology.     

The application of low-rank and sparse decomposition method in the field of climatology

Theoretical and Applied Climatology - The present study reports a low-rank and sparse decomposition method that separates the mean and the variability of a climate data field. Until now, the...     

Feature preserving speckle filtering of the SAR images by wavelet transform

Synthetic Aperture Radar (SAR) images are corrupted by speckle noise due to random interference of electromagnetic waves. The speckle degrades the quality of the image and makes it difficult to interpret, analyse and classify. This paper proposes a method that reduces the speckle and preserves the features by using scale-space correlation between the scales. The results show that the proposed method is better than the widely used filters based on the spatial domain, such as Lee, Kuan, Frost, Ehfrost, Median, Gamma filters in terms of feature preservation. Moreover the proposed method achieves a wide range of balances between speckle reduction and feature preservation, and thus is applicable in different applications such as road detection, detection/ identification of bridge, and ribbon like structures. Furthermore, the proposed method does not require prior modeling of either the image or noise statistics. It uses the variance of the detail wavelets coefficients to estimate noise variance.     

Growth of monodisperse,submicron aerosol particles exposed to SO2, H2O2, and NH3

The growth of monodisperse particles (0.07 to 0.5 µm) exposed to SO₂ (0–860 ppb), H₂O₂ (0–150 ppb) and sometimes NH₃ (0–550 ppb) in purified air at 22 °C at relative humidities ranging from 25 to 75% were measured using the Tandem Differential Mobility Analyzer technique. The experiments were performed in a flow reactor with aqueous (NH₄)₂SO₄ and Na₂SO₄ droplets. For (NH₄)₂SO₄ droplets the fractional diameter growth was independent of size above 0.3 µm but decreased with decreasing size below that. When NH₃ was added the fractional growth increased with decreasing size. Measurements were compared with predictions of a model that accounts for solubility of the reactive gases, the liquid phase oxidation of SO₂ by H₂O₂, and ionic equilibria. Agreement between measured and predicted droplet growth is reasonable when the ionic strength effects are included. Theory and experiments suggest that NH₃ evaporation is responsible for the decrease in relative growth rates for small aqueous ammonium sulfate particles. The observed droplet growth rates are too slow to explain observed growth rates of secondary atmospheric sulfate particles.     

A probabilistic assessment of seismic damage in ductile structures

The current practices in ductility-based earthquake design ignore the damage caused by the repeated random inelastic excursions. A ductile structure may however suffer different degrees of damage depending on the number and amplitudes of these inelastic excursions. The information about the largest response peak as available from the response spectra may not thus be enough as the higher-order peaks are likely to play an important role in the progressing damage. A probabilistic model is proposed here to estimate the damage in a structure with a given amount of ductility by using the order statistics of the higher-order peaks. The proposed formulation relates damage to the entire response process, not just to the largest response. It thus accounts for the different roles played by the total number of peaks in the process, the relative amplitudes and number of excursions, and frequency content of the response process.