Analysis of a regional change in the sign of the SAM�Ctemperature relationship in Antarctica

This study examines regional atmospheric circulation changes associated with a reversal in the sign of the relationship between the Southern Annular Mode (SAM) and near-surface temperatures at Halley station, East Antarctica, during the 1980s. We show that the key factor affecting the regional SAM?Ctemperature relationship (STR) is the relative magnitude of two climatological low pressure centres to the west and east of the area, which determines the source region of air masses advected into the locality. The principal difference affecting the STR is shown to be a trend towards a significantly weaker climatological low (higher pressure) at ~20°E during a positive phase of the SAM. Specifically, it is variations in the phase and magnitude of the wave number three patterns of atmospheric circulation, the non-annular component of the SAM, which are the principal factors governing the regional STR. A similar reversal is observed in the sign of the correlation between the SAM and oxygen-isotope values from an ice core located some 1,200?km east of Halley. This relationship is examined throughout the 20th Century, by comparing the isotope data to SAM reconstructions, and demonstrates marked decadal variability. Thus, these data suggest that switches in the STR are more likely to reflect natural variability in the long-wave patterns over the Southern Ocean rather than the influence of an anthropogenic forcing. This finding is important when considering the potential utility of Antarctic isotope data as a proxy for the SAM.     

State-dependent Riccati equation-based robust dive plane control of AUV with control constraints

The paper treats the question of suboptimal dive plane control of autonomous underwater vehicles (AUVs) using the state-dependent Riccati equation (SDRE) technique. The SDRE method provides an effective mean of designing nonlinear control systems for minimum as well as nonminimum phase AUV models. It is assumed that the hydrodynamic parameters of the nonlinear vehicle model are imprecisely known, and in order to obtain a practical design, a hard constraint on control fin deflection is imposed. The problem of depth control is treated as a robust nonlinear output (depth) regulation problem with constant disturbance and reference exogenous signals. As such an internal model of first-order fed by the tracking error is constructed. A quadratic performance index is chosen for optimization and the algebraic Riccati equation is solved to obtain a suboptimal control law for the model with unconstrained input. For the design of model with fin angle constraints, a slack variable is introduced to transform the constrained control input problem into an unconstrained problem, and a suboptimal control law is designed for the augmented system using a modified performance index. Using the center manifold theorem, it is shown that in the closed-loop system, the system trajectories are regulated to a manifold (called output zeroing manifold) on which the depth tracking error is zero and the equilibrium state is asymptotically stable. Simulation results are presented which show that effective depth control is accomplished in spite of the uncertainties in the system parameters and control fin deflection constraints.     

Hydrogeologic framework of the Deccan terrain of the Koyna River basin, India

The Koyna River basin in India drew the attention of geoscientists after an earthquake (magnitude 7) in 1967. Since then, detailed geological, tectonic, and seismic investigations of this river basin have been carried out by several workers. However, very little study has been done on its hydrogeological framework. The present work aims at filling this gap. Basalts, laterites, alluvium, soils, and talus deposits form shallow unconfined aquifers, with transmissivity of 27–135 m²/d and a regional specific yield of 0.012. In shallow basaltic aquifers, the lower part of the highly weathered and highly jointed horizon above, and the poorly weathered and highly jointed horizon below, form the most potential zone for groundwater occurrence. Well yields in the deeper basaltic aquifers are directly related to the occurrence of lineaments, whereas at a shallower level they are related to geomorphic features. Spring discharges are highly dependent on their source aquifers and areas of recharge. They have a mean winter discharge of 46 m³/d and a summer discharge of 28 m³/d. Chemically, groundwaters are dominated by alkaline earths (Ca²⁺, Mg²⁺) and weak acids (HCO₃ ^–, CO₃ ^–); they are calcium-bicarbonate type (53%) and calcium-magnesium-bicarbonate type (27%) at shallower levels; and calcium-magnesium-bicarbonate type (29%), sodium-bicarbonate type (24%), calcium-bicarbonate type (19%), and calcium-magnesium-sodium-bicarbonate type (19%) in deeper aquifers. The Koyna River basin is characterized by both scarcity and abundance of groundwater. In the water-scarce areas in the dissected plateaus, artificial recharge of aquifers through construction of several recharge structures at suitable locations is highly recommended. In the water-abundant areas in the central valley, on the other hand, expanded consumptive use of water resources is encouraged. Electronic Publication     

Photogeological mapping for regional studies of the Vindhyan rocks around Bundi area,Rajasthan

An area of 2300 sq km s has been mapped around Bundi based on aerial photo-interpretation, with selected field checks at key areas. The oldest rocks exposed are Aravallis comprising a thick pile of argillaceous sediments with thin interbeds of quartzite. The Aravalli rocks have been subjected to two phases of folding and have undergone a low grade of metamorphism. The Vindhyan rocks which comprise arenaceons, argillaceous and calcareous sediments constitute the Kaimur, Rewa and Bhander groups. These rocks occur south of the Aravallis with a faulted contact (Great Boundary Fault) for the major part, and also with unconformable contact at places. The upliftment of the Aravallis on the northern side of the Great Boundary Fault might have created the Vindhyan Basin south of it. The movement appears to have been gradual, keeping pace with the Vindhyan sedimentation, and was possibly revived even after the Vindhyan sedimentation as evidenced by the presence of folding and faulting in Vindhyans in the vicinity of the boundary fault. Strike faulting parallel to the boundary fault is very conspicious resulting in the repetition of the Vindhyan strata in the area east of Bundi. The Vindhyans of Bundi area indicate deposition of sediments in shallow water coastal barrier and lagoonal set-up as evidenced by sedimentary features such as tabular current bedding, ripple marks, huge blankets of sandstone, alternation of shale and limestone etc. Geomorphologically the area may be divided into three units namely:-(a) Pediment on Aravallis, (b) Structural hills on Vindhyan, expressing generally as hogback and cuesta ridges and strike valleys, and (c) Piedmont and alluvial plains (Chambal valley). The photo characters of the different litho-units have been described.     

Age of granitic activity associated with copper–molybdenum mineralization at Malanjkhand, Central India

The Malanjkhand copper–molybdenum deposit in the Bhandara Craton, Central India, is hosted by a granite complex which consists of regionally dominant grey granitoid and pink granitoid confined to the mineralized zone. New SHRIMP RG data on zircons from both granite types are inferred to have crystallized during the same magmatic pulse at ca 2.48 Ga. The discrepancy between zircon age and earlier obtained Rb–Sr whole-rock age is attributed to modification of the Rb–Sr system by hydrothermal overprint. Similarity in petrographic features and chemical affinity in combination with identical age strongly indicate that the pink granite is the hydrothermally altered variety (microclinization and silicification) of the grey granite. The spatially associated, main Cu–Mo mineralization event at Malankhand appears to be broadly contemporaneous with and genetically related to the emplacement of the host granitoids at about 2.48 Ga.     

Changes in the source and transport mechanism of terrigenous input to the Indian sector of Southern Ocean during the late Quaternary and its palaeoceanographic implications

Changes in the terrigenous sediment source and transport mechanisms during the late Quaternary have been investigated using four sediment cores within the Indian sector of Southern Ocean, using the magnetic susceptibility (MS) and sedimentological records. Sediments deposited during the Holocene and other interglacial periods were characterised by low MS, low sand content, reduced ice-rafted detritus (IRD) input and increased illite possibly transported via hydrographic advection from the south. The glacial intervals are characterised by high MS, high sand content, increased IRD input and reduced illite clays, derived from both local as well as Antarctic sources. Significant reduction in clay fraction and illite content during glacials suggests that the erosive and transporting capabilities of the deep and bottom waters could have reduced compared to the interglacial times. The changes in terrigenous influx to this region were significantly influenced by the rhythmic glacial-interglacial fluctuations in bottom circulation and the position of the Polar Front.     

Reservoir Impact Assessment on Land Use/Land Cover and Infrastructure—A Case Study on Polavaram Project

The present study aims to estimate the loss of land use/cover and infrastructure facilities due the submergence by constructing the reservoir over the River Godavari at Polavaram Village. Detailed Land use/cover mapping has been carried out using LISS-III sensor data of IRS P6 satellite and linked to socio-economic data to analyze the administrative boundary wise environmental impact assessment in the study area. Land use/cover features are estimated from the Remote Sensing data through visual interpretation. Area covered below the 45.72 m contour above the mean sea level (MSL) is taken as submerged area due to the dam construction. Total area under submergence is estimated to be 58,658 ha, where 159 villages of three districts are affected by the project. The total population to be rehabilitated is about 1.2 lakhs, out of which maximum affected are Scheduled Tribes (58,781). Besides this, about 311 educational institutions, 202 medical institutions, 37 credit institutions and 55 postal institutions will be submerged due to the project. Further, nine mining sites, 24 tourist/historical sites and 78 agro-based industries will be displaced. The total road length of 673 km will go under submergence.     

Fast transition between high-soft and low-soft states in GRS 1915 + 105: Evidence for a critically viscous accretion flow

We present the results of a detailed analysis of RXTE observations of classω (Klein-Woltet al. 2002) which show an unusual state transition between high-soft and low-soft states in the Galactic microquasar GRS 1915 + 105. Out of about 600 pointed RXTE observations, the source was found to exhibit such state transition only on 16 occasions. An examination of the RXTE/ASM data in conjunction with the pointed observations reveals that these events appeared as a series of quasi-regular dips in two stretches of long duration (about 20 days during each occasion) when hard X-ray and radio flux were very low. The X-ray light curve and colour-colour diagram of the source during these observations are found to be different from any reported so far. The duration of these dips is found to be of the order of a few tens of seconds with a repetition time of a few hundred seconds. The transition between these dips and non-dips which differ in intensity by a factor of ∼ 3.5, is observed to be very fast (∼ a few seconds). It is observed that the low-frequency narrow QPOs are absent in the power density spectrum (PDS) of the dip and non-dip regions of classω and the PDS is a power law in the 0.1–10 Hz frequency range. There is a remarkable similarity in the spectral and timing properties of the source during the dip and non-dip regions in this set of observations. These properties of the source are distinctly different from those seen in the observations of other classes. This indicates that the basic accretion disk structure during both dip and non-dip regions of classω is similar, but differ only in intensity. To explain these observations, we invoke a model in which the viscosity is very close to critical viscosity and the shock wave is weak or absent.     

Orbital evolution and orbital phase resolved spectroscopy of the HMXB pulsar 4U 1538-52 with RXTE-PCA and BeppoSAX

We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3–20 keV energy range were fitted ∼6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at ∼6.4 keV in the restricted energy range of 0.3–10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a spherically symmetric stellar wind from the companion star.