Average Depth versus Average Strike-Length of Fissure Veins for Specified Geometries: A Quantitative Approach

Fissure veins are very important source of mineral deposits particularly that of hydrothermal deposits. The average depth vs. average strike-length of fissure vein, which is an interesting topic, was discussed in Bateman (1962). Some say that depth is equal to length while others opined that depth may be equal to half the length. Here the question arises whether the ratio depth/ length which is loosely used refers to depth to length at any given point of time or average depth vs. average length on a statistical basis. Infact these are empirical rules. The empirical rules hold good for an average basis only. Such problems are dealt under geometric probability. The ore body is more like a lens. Infact none of these hold good. The authors developed a method statistically for ore bodies of two geometries namely a circle and an ellipse. In the case of ellipse, three cases are considered namely, (i) the major axis of ellipse is horizontal to X–axis (ii) the major axis of ellipse is parallel to Y axis and (iii) the ellipse is inclined and whose major axis makes an angle q with the X–axis. In any case, only circular ore body is considered in Bateman (1962). In the case of circular body it is shown that the ratio is neither equal to one or ½ as pointed in Bateman (1962).     

Microfabric, chemical and mineralogical study of Indian marine clays

Marine clay deposits are encountered in the coastal regions of the world. They are soft in consistency with low shear strength and are highly compressible. The properties of these deposits are complex and diverse, and they mainly depend on the minerals present and microstructural arrangement of constituent particles. In the present investigation, the physico-chemical properties of the sediment samples obtained from marine deposits of east and west metropolitan coastal cities of India are discussed, and the test results obtained are compared with the synthetic samples such as bentonite and kaolinite. Mineralogical and fabric studies were carried out using scanning electron microscopy and x-ray diffraction techniques. Several consolidation and strength tests were carried out to study the engineering behaviour of these deposits. The strength and compressibility (Cc) values of these deposits varies from 27 to 45 kN/m² and 0.37 to 0.81 respectively. XRD studies confirm the presence of highly compressible clay minerals such as smectite, vermiculite, chlorite and traces of the low swelling mineral, kaolinite. The fabric studies indicate that the constituent particles were arranged in an open network, or flocculated structure resulting in a high void ratio.     

Constraints on the mass and abundance of black holes in the Galactic halo: the high-mass limit

We establish constraints on the mass and abundance of black holes in the Galactic halo by determining their impact on globular clusters, which are conventionally considered to be little evolved. Using detailed Monte Carlo simulations and simple evolutionary models, we argue that black holes with masses M _bh≳(1–3)×10⁶ M_⊙ can comprise no more than a fraction f _bh≈0.17 of the total halo density at Galactocentric radius R ≈8 kpc. This bound arises from requiring stability of the cluster mass function. A more restrictive bound may be derived if we demand that the probability of destruction of any given, low-mass M _c≈(2.5–7.5)×10⁴ M_⊙] globular cluster not exceed 50 per cent; this bound is f _bh≲0.025–0.05 at R ≈8 kpc. This constraint improves those based on disc heating and dynamical friction arguments as well as current lensing results. At smaller radius the constraint on f _bh strengthens, while at larger radius an increased fraction of black holes is allowed.     

Digital Signal Processors in GPS Receivers

Unlike the conventional hardware approaches to GPS base band signal processing, a software GPS receiver is extremely flexible as it comes with all the associated advantages of a software solution. With a software solution, the improvements of silicon technology can be easily translated into better performance at smaller form factors and lower power consumption, without a redesign and/or change to the ASIC. A general purpose Digital Signal Processor (DSP) can be used effectively for GPS signal processing. The memory and speed resources available determine the algorithms and applications that can be effectively implemented in the receiver. The performance of software GPS receivers will soon be difficult to be surpassed by the hardware counterparts, as high-performance processors become available at low cost. ? 2000 John Wiley & Sons, Inc.     

Experimental investigation of hydrodynamic force coefficients over AUV hull form

Extensive use of autonomous underwater vehicles (AUVs) in oceanographic applications necessitates investigation into the hydrodynamic forces acting over an AUV hull form operating under deeply submerged condition. This paper presents a towing tank-based experimental study on forces and moment on AUV hull form in the vertical plane. The AUV hull form considered in the present program is a 1:2 model of the standard hull form Afterbody1. The present measurements were carried out at typical speeds of autonomous underwater vehicles (0.4-1.4 m/s) by varying pitch angles (0-15°). The hydrodynamic forces and moment are measured by an internally mounted multi-component strain gauge type balance. The measurements were used to study variation of axial, normal, drag, lift and pitching moment coefficients with Reynolds number (Re) and angle of attack. The measurements have also been used to validate results obtained from a CFD code that uses Reynolds Average Navier-Stokes equations (ANSYS™ Fluent). The axial and normal force coefficients are increased by 18% and 195%; drag, lift and pitching moment coefficients are increased by 90%, 182% and 297% on AUV hull form at α=15° and Re_v=3.65×10⁵. These results can give better idea for the efficient design of guidance and control systems for AUV.     

Ramgarh crater,Rajasthan, India: Study of Multispectral images obtained by Indian remote sensing satellite (IRS‐IA)

Ramgarh Crater, Rajasthan, India is a potential impact crater that has not been studied so far. The proximity of Ramgarh Crater to the Deccan flood basalt terrain makes it important to examine the spatial and temporal relationship of this crater to Deccan Volcanism because recent studies propose a strong link between impact cratering and major flood basalt eruptions. A detailed multidisciplinary study is necessary to evaluate the structure and lithology of Ramgarh Crater and its temporal relationship to the emplacement of Deccan eruptions in India .Application of the IRS‐IA data to study the lithologic/surface characteristics of Ramgarh Crater (attempted for the first time) indicates the potential application of remote sensing data in these studies. The IRS‐IA data are of good quality and resolution. Our preliminary assessment has shown that these data are helpful in generating lithology soil vegetation profiles of Ramgarh Crater region. These “profile maps” would be useful for targeting the specific areas in the region for a closer look and ground truth verification during the field work and sample collection in the region.     

Geochemistry and petrogenesis of ultramafic and mafic plutonic rocks of the Dras ophiolitic melange, Indus suture (northwest Himalaya)

Geochemical data are presented for a suite of ultramafic and related rocks from the Dras ophiolitic melange of the Indus suture zone in the western Himalaya. Harzburgites from the suite have highly refractory chemistry. Lherzolites from the suite represent modified mantle material and are comparable to potential source rocks for MORB and to the lherzolites of the Bay of Islands ophiolites. Cumulus dunite, pyroxenite and gabbro units contain olivine, chromite, clinopyroxene and plagioclase as the major cumulus phases. Orthopyroxene is absent as a cumulus phase and in this respect the Dras ophiolite differs from the Marum, Betts Cove and Troodos ophiolites. However, the Dras cumulates are similar to the Vourinos and Bay of Islands cumulate sequence and are consistent with accumulation of low-pressure liquidus phases of mid-oceanic ridge-type magmas. Magmas parental to the Dras cumulate rocks contained high 100 Mg/(Mg + Fe²⁺) ratios of 77–79, high Ni, Cr and possibly Ca, low Ti and depleted LREE. Parent magmas were probably similar to those of normal MORB formed by two-stage (or dynamic) melting processes in the mantle. Peridotite fabrics suggest high-temperature plastic (mantle) deformation. Disruption, serpentinisation and melange formation were probably produced during emplacement in the Indus suture zone.     

Solar UV variability: Effects on stratospheric ozone,trace constituents and thermal structure

The effect of long-term (11-year solar cycle) solar UV variability on stratospheric chemical and thermal structure has been studied using a time-dependent one-dimensional model. Previous studies have suggested substantial variations in local and total ozone, and in stratospheric thermal structure from solar minimum to solar maximum. It is shown here that significant variations also occur in some of the trace constituents. Members of the HO _x family and N₂O exhibit the largest variations, and these changes, if detected, may provide additional means of verifying the presence of solar UV variability and its effects. Some of the species show large phase differences with the assumed solar flux variation. The role of chemical and transport time constants on the time variations of the trace species is examined. Comparisons with reported ozone and temperature data show reasonable agreement for the period 1960 to 1972.     

Origin of the Deccan Trap flows at Mahabaleshwar inferred from Nd and Sr isotopic and chemical evidence

The Deccan flows at Mahabaleshwar are divisible into a lower and an upper group, based on Nd and Sr isotopic ratios, which define two correlated trends. This distinction is supported by incompatible element ratios and bulk compositions. The data reflect contamination in a dynamic system of magmas from an LIL-depleted,ε_JUV ≥ +8 mantle by two different negative ε_JUV endmembers, one undoubtedly continental crust, the other either continental crust or enriched mantle. The depleted mantle source, anomalously high in (⁸⁷Sr/⁸⁶Sr), may have been in the subcontinental lithosphere or a region of rising Indian Ocean MORB mantle.     

Fabric and mineralogical studies on lime treated marine clays

The use of lime to improve the engineering properties of weak marine clays is a common method from the past. Recent studies indicate that the various foundation problems occurred with passage of time for offshore structures due to hostile wave conditions and adverse climatic conditions. Hence, there is an urgent need to improve the engineering properties of these soft deposits using well established ground improvement techniques. In the present investigation, an attempt has been made on two marine clays to investigate the microchanges that occurred at particulate level due to the addition of lime and sodium hydroxide chemicals. The influence of sodium hydroxide additive on the fabric of lime treated marine clays has also been studied using scanning electron microscopy (SEM) technique. The formation of various new reaction products due to soil-lime reactions and their stability in marine environment were also studied and reported using x-ray diffraction (XRD) technique. The test results indicate that lime stabilization is effective for improving the properties of marine clays and the presence of sea water increases the efficiency of lime stabilization.