The Himalayan foreland basin crust and upper mantle

Modeling of multimode surface wave group velocity dispersion data sampling the eastern and the western Ganga basins, reveals a three layer crust with an average V_s of 3.7 km s^?1, draped by ～2.5 km foreland sediments. The Moho is at a depth of 43 ± 2 km and 41 ± 2 km beneath the eastern and the western Ganga basins respectively. Crustal V_p/V_s shows a felsic upper and middle crust beneath the eastern Ganga basin (1.70) compared to a more mafic western Ganga basin crust (1.77). Due to higher radiogenic heat production in felsic than mafic rocks, a lateral thermal heterogeneity will be present in the foreland basin crust. This heterogeneity had been previously observed in the north Indian Shield immediately south of the foreland basin and must also continue northward below the Himalaya. The high heat producing felsic crust, underthrust below the Himalayas could be an important cause for melting of midcrustal rocks and emplacement of leucogranites. This is a plausible explanation for abundance of leucogranites in the east-central Himalaya compared to the west. The uppermost mantle V_s is also significantly lower beneath the eastern Ganga basin (4.30 km s^?1) compared to the west (4.44 km s^?1).     

Productivity Analysis of Draglines Operating in Horizontal and Vertical Tandem Mode of Operation in a Coal Mine—A Case Study

The tandem operation of draglines is in use in some of the major Indian opencast coalmines owing to the favourable geo-mining conditions, technical suitability, efficiency and economic viability. In view of the importance of tandem operation, the present study has been undertaken in a large Indian opencast coalmine in order to critically investigate the horizontal and vertical tandem operation of draglines on moderately strong and high sandstone benches (35–42 m), overlying a 15–18 m thick coal seam. The study has revealed that although the preparation of balancing diagram for planning of dragline operations is the first and the most important step, its actual implementation is equally important. Marked discrepancies in the productivity parameters as envisaged by the balancing diagram and as observed in the field studies, have been investigated and reported. The study also propounds the importance of appraisal of dragline productivity parameters, such as, cycle time, swing angle, seating position, availability, utilization, etc., in the field scale. Irrespective of the mode of operation (horizontal or vertical tandem), the study moots the concept of computation of the weighted cycle time and overall cycle time vis-à-vis swing angle variation for the draglines operating in field. The results drawn from the case study have been discussed in terms of cycle time computations, annual output computation and evaluation of earthmoving efficiency for the horizontal and vertical tandem modes of operation.     

X-ray crystallography and mineral chemistry of bastnaesite from Kanigiri granite,Prakasam district,Andhra Pradesh,India

The authors report the results of X-ray diffraction (XRD) and geochemical studies on bastnaesites (lanthanum cerium fluoro-carbonate) hosted in alkali Kanigiri Granite of the Prakasam district in Andhra Pradesh, India. The XRD pattern of the investigated bastnaesite displays sharply-defined reflections. The observed d-spacings of the bastnaesite are in very close agreement with those published for bastnaesite standard in International Centre for Diffraction Data (ICDD) Card No. 11–340. The calculated unit cell parameters (a _o ; c _o ) and unit cell volume (V) of the studied bastnaesite (a _o 7.1301–7.1413 Å, c _o 9.7643–9.7902Å and V 429.8940–432.3875 ų) are almost equal to values published for bastnaesite standard (c _o 7.1290 Å, c _o 9.7744 Å and V 430.19 ų) in the relevant data card. Geochemical data of bastnaesite reveals high content of Ce (mean 27.22%) followed by La (mean 16.82%), Nd (mean 6.12%) and Pr (mean 1.91%). Compared to light REE (LREE) content (mean 437165 ppm), heavy REE (HREE) content (mean 5867 ppm) is drastically low, with unusually high LREE/HREE ratio (mean 80). The chondrite-normalised plot also exhibits drastic enrichment of LREE relative to HREE with pronounced negative Euanomaly (mean Eu/Eu* = 0.15). High (LREE) _N / (HREE) _N , (La/Lu) _N , (La/Yb) _N and (Ce/Yb) _N ratios reveal higher fractionation of LREE relative to HREE. The rare earth element (REE) contents of the studied bastnaesite are very close to REE contents of bastnaesite hosted in alkali syenite from Madagascar. The presence of bastnaesite in Kanigiri Granite and soils derived from it enhances the scope of further exploration for bastnaesite in several bodies of alkaline rocks and alkali granitoids present along the eastern margins of the Cuddapah basin, Andhra Pradesh.     

On the out of phase appearance of large-scale diffuse magnetic field of the Sun with respect to sunspots

We assume the large-scale diffuse magnetic field of the Sun to originate from the poloidal component of a dynamo operating at the base of the convection zone, whereas the sunspots are due to the toroidal component. The evolution of the poloidal component is studied to model the poleward migration of the diffuse field seen on the solar surface and the polar reversal at the time of sunspots maxima (Dikpati and Choudhuri 1994, 1995).     

Solar activity forecast with a dynamo model

Although systematic measurements of the Sun's polar magnetic field exist only from mid-1970s, other proxies can be used to infer the polar field at earlier times. The observational data indicate a strong correlation between the polar field at a sunspot minimum and the strength of the next cycle, although the strength of the cycle is not correlated well with the polar field produced at its end. This suggests that the Babcock–Leighton mechanism of poloidal field generation from decaying sunspots involves randomness, whereas the other aspects of the dynamo process must be reasonably ordered and deterministic. Only if the magnetic diffusivity within the convection zone is assumed to be high (of order  10¹² cm² s⁻¹  ), we can explain the correlation between the polar field at a minimum and the next cycle. We give several independent arguments that the diffusivity must be of this order. In a dynamo model with diffusivity like this, the poloidal field generated at the mid-latitudes is advected toward the poles by the meridional circulation and simultaneously diffuses towards the tachocline, where the toroidal field for the next cycle is produced. To model actual solar cycles with a dynamo model having such high diffusivity, we have to feed the observational data of the poloidal field at the minimum into the theoretical model. We develop a method of doing this in a systematic way. Our model predicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry of solar activity is also calculated with our model and compared with observational data.     

Weak waves in radiating gases

The propagation of weak waves has been studied by taking into account the influence of thermal radiative field. The singular surface theory is used to determine the modes of wave propagation and to evaluate the behaviour at the wave head. The effects of thermal radiation, conduction and the initial wave front curvature on the nonlinear breaking of weak waves are discussed. It is concluded that, under the thermal radiation effects, the shock wave formation is either disallowed or delayed. On the other hand, the thermal conduction effects destabilize the waves.     

Sensitivity Analysis of Internal Dragline Dump stability: Finite Element Analysis

The stability of mine waste dump is of paramount importance from economic and safety point of view. The present paper deals with the stability analysis of an internal dragline dump of an opencast coal mine by finite element method to classify input parameters in terms of sensitivity. Sensitivity analysis has been carried out for geometrical and geotechnical parameters of dump slope. It has been concluded from the results that ??friction angle?? is a more sensitive parameter as compared to the cohesion of dump material. The geometrical parameters of ??slope angle?? and ??height of dragline dump?? are classified as very high sensitive. The ??height of main dump?? could be classified as least sensitive, whereas, ??gradient of the seam?? and ??thickness of coal rib?? as medium sensitive parameters.     

On the Connection Between Mean Field Dynamo Theory and Flux Tubes

Mean field dynamo theory deals with various mean quantities and does not directly throw any light on the question of existence of flux tubes. We can, however, draw important conclusions about flux tubes in the interior of the Sun by combining additional arguments with the insights gained from solar dynamo solutions. The polar magnetic field of the Sun is of order 10 G, whereas the toroidal magnetic field at the bottom of the convection zone has been estimated to be 100000 G. Simple order-of-magnitude estimates show that the shear in the tachocline is not sufficient to stretch a 10 G mean radial field into a 100000 G mean toroidal field. We argue that the polar field of the Sun must get concentrated into intermittent flux tubes before it is advected to the tachocline. We estimate the strengths and filling factors of these flux tubes. Stretching by shear in the tachocline is then expected to produce a highly intermittent magnetic configuration at the bottom of the convection zone. The meridional flow at the bottom of the convection zone should be able to carry this intermittent magnetic field equatorward, as suggested recently by Nandy and Choudhuri (2002). When a flux tube from the bottom of the convection zone rises to a region of pre-existing poloidal field at the surface, we point out that it picks up a twist in accordance with the observations of current helicities at the solar surface.