Large scale model testing to investigate the influence of granular cushion layer on the performance of disconnected piled raft system

Acta Geotechnica - This paper presents the results of 1g model tests performed on instrumented model foundations, i.e., unpiled raft, single piled raft, single disconnected piled raft (DPR) and...     

Rhyolites in continental mafic Large Igneous Provinces: Petrology,geochemistry and petrogenesis

We present a detailed review of the petrological and geochemical aspects of rhyolite and associated silicic volcanic rocks(up to 20 vol%of all rocks)reported to date from twelve well known Phanerozoic continental mafic Large Igneous Provinces(LIPs).These typically spread over<104 km^2(rarely 105 km^2 for Parana-Etendeka)area and comprise<10~4 km^3 of extrusive silicic rocks,erupted either during or after the main basaltic eruption within<5 Myr,with some eruption(s)continuing for≤30 Myr.These rhyolites and associated silicic volcanic rocks(60-81 wt.%of SiO2)are mostly metaluminous to peraluminous and are formed via(ⅰ)fractional crystallization of parental mafic magma with negligible crustal contamination,and(ⅱ)melting of continental crust or assimilation and fractional crystallization(AFC)of mafic magma with significant crustal contribution.Rhyolites formed by extensive fractional crystallization are characterized by the presence of clinopyroxene phenocrysts,exhibit steep negative slopes in bivariate major oxides plots and weak to no Nb-Ta anomaly;these typically have temperature>900℃.Rhyolites formed by significant crustal contribution are characterized by strong negative Nb-Ta anomalies,absence of clinopyroxene phenocrysts,and are likely to have a magma temperature<900℃.Geochemical signatures suggest rhyolite melt generation in the plagioclase stability field with a minor fraction originating from lower crustal depths.A large part of the compositional variability in rhyolites,particularly the SrNd-Pb-O isotope ratios,suggests a significant role of continental crust(upper crustal melting or AFC)in the evolution of these silicic rocks in the continental mafic LIPs.     

Control of climate and Tethyan legacy on distribution of Paleocene–Eocene gastropods and establishment of the Northern Tropical Realm

Palaeobiogeographical distribution of gastropod genera from the Paleocene and the Eocene has been analysed. Based on this distribution, formal palaeobiogeographical provinces have been established and their relationships are sought. It has been found that the provinces were largely restricted to the palaeo-tropics and subtropics mainly of the northern hemisphere and they share a large proportion of their generic composition. The Northern Tropical Realm has been established to include these provinces. The distribution evinces presence of ocean surface currents in the tropics across longitudes. The possible currents moved through the relict Tethys Ocean, across the Atlantic Ocean and perhaps also across the Pacific. However, planktotrophic larvae of these benthic molluscs could not cross the deep ocean barrier that lay between the Northern Tropical Realm and the Austro-New Zealand Province of the southern hemisphere. The gastropod fauna in the latter province evolved independently. Distribution of all the provinces within palaeo-tropics and subtropics indicates strong control of temperature over it. Paleocene–Eocene Thermal Maximum appears to be responsible for extinction and range contraction of high latitude faunas. Low latitude faunas also suffered significant extinction. However, large diversification in the Eocene was a response to widespread transgression that coincided with the thermal event.     

Groundwater resources management through flow modeling in lower part of Bhagirathi — Jalangi interfluve,Nadia, West Bengal

Groundwater utilization in Nadia district, West Bengal has been subjected to rapid exploitation in the wake of increasing urbanization and production of agricultural commodities. It is, therefore, necessary to evaluate the existing trend and availability of groundwater in time and space and its movement for proper planning in future. In the present study, an attempt has been made develop a groundwater management model using Visual MODFLOW software. The groundwater flow model for the study area was formulated by using input hydrogeological data and appropriate boundary conditions. The groundwater flow pattern of the study area indicates the occurrence of base flow which feed both the Rivers Bhagirathi and Jalangi throughout the year. The computed hydraulic heads were calibrated by comparing with observed groundwater level data for years 2004 to 2006 and were verified with the data of 2007. The outcome of modeling shows that this model can be used for prediction purpose in the future by updating input boundary conditions and hydrologic stresses during the preceding year. The model optimized unit draft for deep tube well as 556.5 m³/day and the same for shallow tube well as 41 m³/day keeping the existing tube well structures in running condition and maintaining the present and recent past trends of groundwater level. The model can be further improved if more spatial and temporal input parameters are available and can be incorporated into the model for more realistic characterization of groundwater flow.     

A framework for risk-based assessment of urban floods in coastal cities

Natural Hazards - Many coastal cities in developing countries are at the risk of flooding due to a progressive increase in the built-up areas and poor management of storm water. The flooding...     

Tuned liquid dampers for controlling earthquake response of structures

Numerical simulations of a single‐degree‐of‐freedom (SDOF) structure, rigidly supporting a tuned liquid damper (TLD) and subjected to both real and artificially generated earthquake ground motions, show that a properly designed TLD can significantly reduce the structure's response to these motions. The TLD is a rigid, rectangular tank with shallow water in it. Its fundamental linear sloshing frequency is tuned to the structure's natural frequency. The TLD is more effective in reducing structural response as the ground excitation level increases. This is because it then dissipates more energy due to sloshing and wave breaking. A larger water‐depth to tank‐length ratio than previous studies suggested, which still falls within the constraint of shallow water theory, is shown to be more suitable for excitation levels expected in strong earthquake motions. A larger water‐mass to structure‐mass ratio is shown to be required for a TLD to remain equally effective as structural damping increases. Furthermore, the reduction in response is seen to be fairly insensitive to the bandwidth of the ground motion but is dependent on the structure's natural frequency relative to the significant ground frequencies. Finally, a practical approach is suggested for the design of a TLD to control earthquake response. Copyright © 2000 John Wiley & Sons, Ltd.     

El Niño Modoki connection to extremely-low streamflow of the Paranaíba River in Brazil

Extremely-low discharge events of the Paranaíba River basin during the austral summer season (December–February, DJF), are found to be associated with the Pacific sea surface temperature anomalies resembling the recently identified El Niño Modoki phenomenon. Extreme discharge events are identified based on their persistent flow for 7 days and more after taking retention time into consideration. Ninety percent of the extremely low discharge events during peak streamflow seasons of DJF, are found to occur during the El Niño Modoki years. A diagnostics study of atmospheric anomalies has shown a clear connection between the modified Walker circulation, associated with the El Niño Modoki, and the precipitation anomalies over the Paranaíba River basin. The climate variations have direct relationship with the rainfall. Streamflow variations are considered as the surrogates to rainfalls. Thus, El Niño Modoki phase is important component to understand and predict the streamflow variations in the Paranaíba River basin.     

Assessment of future climate variability and potential adaptation strategies on yield of peanut and Kharif rice in eastern India

Theoretical and Applied Climatology - Temperature and CO2 are the two most important climate parameters that affect crop yield directly. In this study, the impact of these two parameters on the...     

Evolution of narrow-band spectrum of two random Stokes wavetrains in deep water

Ocean Dynamics - Fourth-order nonlinear evolution equation (NLEE), which is an excellent starting point for the analysis of nonlinear deep water surface waves, are used here to investigate the...