Development of an artificial neural network based multi-model ensemble to estimate the northeast monsoon rainfall over south peninsular India: an application of extreme learning machine

The south peninsular part of India gets maximum amount of rainfall during the northeast monsoon (NEM) season [October to November (OND)] which is the primary source of water for the agricultural activities in this region. A nonlinear method viz., Extreme learning machine (ELM) has been employed on general circulation model (GCM) products to make the multi-model ensemble (MME) based estimation of NEM rainfall (NEMR). The ELM is basically is an improved learning algorithm for the single feed-forward neural network (SLFN) architecture. The 27 year (1982–2008) lead-1 (using initial conditions of September for forecasting the mean rainfall of OND) hindcast runs (1982–2008) from seven GCM has been used to make MME. The improvement of the proposed method with respect to other regular MME (simple arithmetic mean of GCMs (EM) and singular value decomposition based multiple linear regressions based MME) has been assessed through several skill metrics like Spread distribution, multiplicative bias, prediction errors, the yield of prediction, Pearson’s and Kendal’s correlation coefficient and Wilmort’s index of agreement. The efficiency of ELM estimated rainfall is established by all the stated skill scores. The performance of ELM in extreme NEMR years, out of which 4 years are characterized by deficit rainfall and 5 years are identified as excess, is also examined. It is found that the ELM could expeditiously capture these extremes reasonably well as compared to the other MME approaches.     

Mapping of magnetic basement in Central India from aeromagnetic data for scaling geology

The Central Indian region has a complex geology covering the Godavari Graben, the Bastar Craton (including the Chhattisgarh Basin), the Eastern Ghat Mobile Belt, the Mahanadi Graben and some part of the Deccan Trap, the northern Singhbhum Orogen and the eastern Dharwar Craton. The region is well covered by reconnaissance‐scale aeromagnetic data, analysed for the estimation of basement and shallow anomalous magnetic sources depth using scaling spectral method. The shallow magnetic anomalies are found to vary from 1 to 3 km, whereas magnetic basement depth values are found to vary from 2 to 7 km. The shallowest basement depth of 2 km corresponds to the Kanker granites, a part of the Bastar Craton, whereas the deepest basement depth of 7 km is for the Godavari Basin and the southeastern part of the Eastern Ghat Mobile Belt near the Parvatipuram Bobbili fault. The estimated basement depth values correlate well with the values found from earlier geophysical studies. The earlier geophysical studies are limited to few tectonic units, whereas our estimation provides detailed magnetic basement mapping in the region. The magnetic basement and shallow depth values in the region indicate complex tectonic, heterogeneity, and intrusive bodies at different depths, which can be attributed to different thermo‐tectonic processes since Precambrian.     

Petrogenesis of lunar meteorite EET 96008

Lunar meteorite EET 96008 is a fragmental breccia that predominantly consists of basaltic mineral clasts (0.5-2 mm), along with minor lithic fragments and breccia clasts. The matrix consists mainly of smaller mineral fragments (<0.5 mm), bound by glassy cement, the majority of which are pyroxene and plagioclase. The pyroxene possesses extensive exsolution lamellae. These lamellae, up to 1 μm in width, are atypical for mare-basalts. One of the distinguishing textures of EET 96008 is the presence of small pockets (∼400 × 500 μm) of mesostasis areas consisting of coarse (∼20 μm) intergrowths of ferroaugite, fayalite and Si-rich glass. Laths of ilmenite, armalcolite, apatite and whitlockite are also distributed in these areas. Ilmenite grains are abundant and dispersed throughout the thin sections. Chromite and ulvöspinel are present but in minor abundance. Troilite, generally rare in this rock, occurs as several grains in one pyroxene crystal. FeNi metal is conspicuously absent from this meteorite.The molar Fe/Mn ratio in olivines and pyroxenes and the age of the meteorite are evidence for a lunar origin. The mineralogy of EET 96008 shows close affinity to a mare-basalt source, albeit with possible minor highland/non-mare components. The bulk-rock, major-, trace- and rare-earth-element (REE) contents are similar to that of very low-titanium (VLT) basalts, which have experienced extreme fractional crystallization to the point of silicate liquid immiscibility. Mineralogical and textural features of this sample suggest that at least some of the breccia components were derived from a slow-cooled magma. The mineralogy and petrology of EET 96008 is strikingly similar to the lunar meteorite EET 87521, and we support the conclusion that EET 96008 and EET 87521 should be paired.Isochron ages of 3530 ± 270 Ma for apatite and 3519 ± 100 Ma for whitlockite of this rock are consistent with derivation from a mare-basalt precursor. These ages are within error of the low-Ti basalts, dated from the Apollo 12 and 15 sites. The whole-rock, platinum-group-element (PGE) contents of EET 96008 overlap with pristine low-Ti mare basalts, suggesting the presence of only a minimal extraterrestrial component.     

Aeromagnetic signatures of Precambrian shield and suture zones of Peninsular India

In many Precambrian provinces the understanding of the tectonic history is constrained by limited exposure and aeromagnetic data provide information below the surface cover of sediments,water,etc.and help build a tectonic model of the region.The advantage of using the aeromagnetic data is that the data set has uniform coverage and is independent of the accessibility of the region.In the present study,available reconnaissance scale aeromagnetic data over Peninsular India are analyzed to understand the magnetic signatures of the Precambrian shield and suture zones thereby throwing light on the tectonics of the region.Utilizing a combination of differential reduction to pole map,analytic signal,vertical and tilt derivative and upward continuation maps we are able to identify magnetic source distribution,tectonic elements,terrane boundaries,suture zones and metamorphic history of the region.The magnetic sources in the region are mainly related to charnockites,iron ore and alkaline intrusives.Our analysis suggests that the Chitradurga boundary shear and Sileru shear are terrane boundaries while we interpret the signatures of Palghat Cauvery and Achankovil shears to represent suture zones.Processes like metamorphism leave their signatures on the magnetic data:prograde granulites(charnockites)and retrograde eclogites are known to have high susceptibility.We fnd that charnockites intruded by alkali plutons have higher magnetization compared to the retrogressed charnockites.We interpret that the Dharwar craton to the north of isograd representing greenschist to amphibolite facies transition,has been subjected to metamorphism under low geothermal conditions.Some recent studies suggest a plate tectonic model of subductionecollisioneaccretion tectonics around the Palghat Cauvery shear zone(PCSZ).Our analysis is able to identify several west to east trending high amplitude magnetic anomalies with deep sources in the region from Palghat Cauvery shear to Achankovil shear.The magnetic high associated with PCSZ may represent the extruded high pressureeultra high temperature metamorphic belt(granulites at shallow levels and retrogressed eclogites at deeper levels)formed as a result of subduction process.The EW highs within the Madurai block can be related to the metamorphosed clastic sediments,BIF and mafc/ultramafc bodies resulting from the process of accretion.     

ANALYSIS OF ROCKBOLT REINFORCEMENT USING BEAM-COLUMN THEORY

A simple analytical procedure that applies classical beam-column theory for evaluating passive rockbolt roof reinforcement is presented in this paper. The analytical model is derived from first principles and is capable of modelling any number of reinforcing bolts. Each rockbolt is modelled as a linear spring and the model allows for non-uniform bolt spacing. In this study the rock beam is assumed to be isotropic and linearly elastic for the sake of simplicity. However, the analytical model can be extended to include anisotropic rockmass as well as inelastic material behaviour. The solution to the coupled set of governing equations is obtained by using a simple numerical solution procedure. The results from the analytical model indicate that the critical buckling load of a rock beam is strongly influenced by the ambient rock modulus. For salt-rock excavations the rock modulus typically declines with time due to various phenomena, and a diminished modulus could seriously compromise roof stability. The other main conclusion of this study is that rockbolts loose their effectiveness in restraining a roof beam once its critical buckling load is approached. In such a situation, increasing bolt stiffness does not improve its reinforcing action on a roof beam but it enhances the possibility of bolt failure due to anchor pull-out. © 1997 by John Wiley & Sons, Ltd. Int. J. Numer. Anal. Meth. Geomech., vol. 21, 241–253 (1997)     

Evaluation of vertical impact factor coefficients for continuous and integral railway bridges under high-speed moving loads

In the railway bridge analysis and design method,dynamic train loads are regarded as static loads enhanced by an impact factor(IF).The IF coefficients for various railway bridges have been reported as a function of span length or frequency of the bridges in Eurocode(2003).However,these IF coefficient values neglect the effects of very high speeds(>200 km/h)and soil-structure interaction(SSI).In this work,a comprehensive study to assess the impact factor coefficients of mid-span vertical displacements for continuous and integral railway bridges subjected to high-speed moving loads is reported.Three different configurations,each for the three-dimensional(3D)continuous and integral bridge,are considered.Also,single-track(1-T)and two-track(2-T)“real train”loading cases for both these bridge types are considered.Subsequently,finite element analysis of the full-scale 3D bridge models,to identify their IF values,considering the effects of SSI for three different soil conditions,is conducted.The IF values obtained from the study for both bridge types are comparable and are greater than the values recommended by Eurocode(2003).The results reveal that with a loss of soil stiffness,the IF value reduces;thus,it confirms the importance of SSI analysis.     

A seismic study to investigate the prospect of gas hydrate in Mahanadi deep water basin,northeastern continental margin of India

The presence of gas hydrates, one of the new alternative energy resources for the future, along the Indian continental margins has been inferred mainly from bottom simulating reflectors (BSR) and the gas stability zone thickness mapping. Gas hydrate reserves in Krishna Godawari Basin have been established with the help of gas-hydrate related proxies inferred from multidisciplinary investigations. In the present study, an analysis of 3D seismic data of nearly 3,420 km² area of Mahanadi deep water basin was performed in search of seismic proxies related with the existence of natural gas hydrate in the region. Analysis depicts the presence of BSR-like features over a large areal extent of nearly 250 km² in the central western part of the basin, which exhibit all characteristics of a classical BSR associated with gas hydrate accumulation in a region. The observed BSR is present in a specific area restricted to a structural low at the Neogene level. The coherency inversion of pre-stack time migration (PSTM) gathers shows definite inversion of interval velocity across the BSR interface which indicates hydrate bearing sediments overlying the free gas bearing sediments. The amplitude versus offset analysis of PSTM gathers shows increase of amplitude with offset, a common trend as observed in BSR associated with gas hydrate accumulation. Results suggest the possibility of gas hydrate accumulation in the central part of the basin specifically in the area of structural low at the Neogene level. These results would serve as preliminary information for selecting prospective gas hydrate accumulation areas for further integrated or individual study from geophysical, geological, geochemical and microbiological perspectives for confirmation of gas hydrate reserves in the area. Further, on the basis of these results it is envisaged that biogenic gas might have been generated in the region which under suitable temperature and pressure conditions might have been transformed into the gas hydrates, and therefore, an integrated study comprising geophysical, geological, geochemical and microbiological data is suggested to establish the gas hydrate reserves in Mahanadi deep water basin.     

On the RH relations across weak and strong shocks in van der Waals gases

The Rankine–Hugoniot (RH) jump relations for normal shock waves in van der Waals fluids have been studied in order to improve a theoretical understanding of those shock related phenomena as observed in a real atmosphere which cannot be accounted for by the ideal gas model. The RH jump relations for the pressure, density, particle velocity, temperature, speed of sound, adiabatic compressibility and change-in-entropy across the shock front have been analysed in terms of the non-idealness parameter of the gas, downstream Mach number and adiabatic index of the gas. Further, as the strength of shock waves may range from weak to strong, the convenient forms of RH jump relations for weak and strong shock waves have been discussed, simultaneously. Finally, the effects on the flow-field behind the shock front have been explored due to the non-idealness parameter of the gas, downstream Mach number and adiabatic index of the gas.     

The formation and aqueous alteration of CM2 chondrites and their relationship to CO3 chondrites: A fresh isotopic (O,Cd, Cr,Si, Te,Ti, and Zn) perspective from the Winchcombe CM2 fall

As part of an integrated consortium study, we have undertaken O, Cd, Cr, Si, Te, Ti, and Zn whole rock isotopic measurements of the Winchcombe CM2 meteorite. δ⁶⁶Zn values determined for two Winchcombe aliquots are +0.29 ± 0.05‰ (2SD) and +0.45 ± 0.05‰ (2SD). The difference between these analyses likely reflects sample heterogeneity. Zn isotope compositions for Winchcombe show excellent agreement with published CM2 data. δ¹¹⁴Cd for a single Winchcombe aliquot is +0.29 ± 0.04‰ (2SD), which is close to a previous result for Murchison. δ¹³⁰Te values for three aliquots gave indistinguishable results, with a mean value of +0.62 ± 0.01‰ (2SD) and are essentially identical to published values for CM2s. ε⁵³Cr and ε⁵⁴Cr for Winchcombe are 0.319 ± 0.029 (2SE) and 0.775 ± 0.067 (2SE), respectively. Based on its Cr isotopic composition, Winchcombe plots close to other CM2 chondrites. ε⁵⁰Ti and ε⁴⁶Ti values for Winchcombe are 3.21 ± 0.09 (2SE) and 0.46 ± 0.08 (2SE), respectively, and are in line with recently published data for CM2s. The δ³⁰Si composition of Winchcombe is −0.50 ± 0.06‰ (2SD, n = 11) and is essentially indistinguishable from measurements obtained on other CM2 chondrites. In conformity with petrographic observations, oxygen isotope analyses of both bulk and micromilled fractions from Winchcombe clearly demonstrate that its parent body experienced extensive aqueous alteration. The style of alteration exhibited by Winchcombe is consistent with relatively closed system processes. Analysis of different fractions within Winchcombe broadly support the view that, while different lithologies within an individual CM2 meteorite can be highly variable, each meteorite is characterized by a predominant alteration type. Mixing of different lithologies within a regolith environment to form cataclastic matrix is supported by oxygen isotope analysis of micromilled fractions from Winchcombe. Previously unpublished bulk oxygen isotope data for 12 CM2 chondrites, when combined with published data, define a well-constrained regression line with a slope of 0.77. Winchcombe analyses define a more limited linear trend at the isotopically heavy, more aqueously altered, end of the slope 0.77 CM2 array. The CM2 slope 0.77 array intersects the oxygen isotope field of CO3 falls, indicating that the unaltered precursor material to the CMs was essentially identical in oxygen isotope composition to the CO3 falls. Our data are consistent with earlier suggestions that the main differences between the CO3s and CM2s reflect differing amounts of water ice that co-accreted into their respective parent bodies, being high in the case of CM2s and low in the case of CO3s. The small difference in Si isotope compositions between the CM and CO meteorites can be explained by different proportions of matrix versus refractory silicates. CMs and COs may also be indistinguishable with respect to Ti and Cr isotopes; however, further analysis is required to test this possibility. The close relationship between CO3 and CM2 chondrites revealed by our data supports the emerging view that the snow line within protoplanetary disks marks an important zone of planetesimal accretion.