Bianchi type-I cosmological models with time dependent q and Λ-term in general relativity

On getting motivation from increasing evidence for the need of a geometry that resembles Bianchi morphology to explain the observed anisotropy in the WMAP data, Einstein’s field equations with variable cosmological “constant” are considered in presence of perfect fluid for a homogeneous and anisotropic Bianchi type-I space-time. Einstein’s field equations are solved by considering a time dependent deceleration parameter which affords a late time acceleration in the universe. The cosmological constant Λ is found to be a decreasing function of time and it approaches a small positive value at the present epoch which is corroborated by consequences from recent supernovae Ia observations. From recently developed Statefinder pair, the behavior of different stages of the evolution of the universe has been studied. The physical significance of the cosmological models have also been discussed.     

Appropriate viscous damping for nonlinear time‐history analysis of base‐isolated reinforced concrete buildings

There is no consensus at the present time regarding an appropriate approach to model viscous damping in nonlinear time‐history analysis of base‐isolated buildings because of uncertainties associated with quantification of energy dissipation. Therefore, in this study, the effects of modeling viscous damping on the response of base‐isolated reinforced concrete buildings subjected to earthquake ground motions are investigated. The test results of a reduced‐scale three‐story building previously tested on a shaking table are compared with three‐dimensional finite element simulation results. The study is primarily focused on nonlinear direct‐integration time‐history analysis, where many different approaches of modeling viscous damping, developed within the framework of Rayleigh damping are considered. Nonlinear direct‐integration time‐history analysis results reveal that the damping ratio as well as the approach used to model damping has significant effects on the response, and quite importantly, a damping ratio of 1% is more appropriate in simulating the response than a damping ratio of 5%. It is shown that stiffness‐proportional damping, where the coefficient multiplying the stiffness matrix is calculated from the frequency of the base‐isolated building with the post‐elastic stiffness of the isolation system, provides reasonable estimates of the peak response indicators, in addition to being able to capture the frequency content of the response very well. Furthermore, nonlinear modal time‐history analyses using constant as well as frequency‐dependent modal damping are also performed for comparison purposes. It was found that for nonlinear modal time‐history analysis, frequency‐dependent damping, where zero damping is assigned to the frequencies below the fundamental frequency of the superstructure for a fixed‐base condition and 5% damping is assigned to all other frequencies, is more appropriate, than 5% constant damping. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of secondary compression on undrained strength of soft kaolinites

Soft kaolinite deposits of marine origin are encountered as foundation soils in many parts of the world. The well-developed flocculated structure of kaolinite-bearing marine deposits is amenable to alterations from leaching of pore solution salts, loss of overburden, and secondary compression. Secondary compression causes densification of microstructure that may impact the viscous resistance, soil stiffness, and undrained shear strength of kaolinite-bearing marine deposits. This study examines the influence of secondary compression on viscous resistance and constrained stress–strain modulus of soft kaolinites prepared in synthetic seawater and sodium chloride solutions. The impact of secondary compression on undrained shear strength is interpreted from changes in microstructure, percent monovalent cation concentration, viscous resistance, and constrained stress–strain modulus. Kaolinite specimens experience reduction in void space during secondary compression. Breakdown of edge–face (E–F) and edge–edge (E–E) contacts of kaolinite particles during secondary compression and creation of interlocking zones is observed from scanning electron micrograph studies. Breakdown of E–F and E–E contacts is considered responsible for reduction in constrained stress–strain modulus during secondary compression. Concomitant, creation of interlocking zones at particle contacts increases the viscous resistance of microstructure that enhances the undrained shear strength of soft kaolinites.     

Assessing anthropogenic pressure and its impact on Hippophae salicifolia pockets in Central Himalaya, Uttarakhand

Natural habitat of Hippophae salicifolia in Central Himalaya is continuously being degraded due to habitat destruction and harvesting.Although logging is prohibited,habitat destruction has increased because of regular road construction,repairing and broadening activities.In addition,Hippophae resources are continuously being harvested by lopping(both partial and complete) for fuelwood,fodder and fruits in higher Himalayan region.This paper presents a detailed analysis of relationship between density,demographic structure,and harvesting of H.salicifolia growing pockets in the five major valleys(Gangotri,Yamunotri,Niti,Mana and Bhyundhar) of Uttarakhand in Central Himalaya,India.A total of 120 quadrats were laid randomly to study population structure,regeneration,sex ratio and lopping using quadrats of 100 m 2(24 in each valley) in Hippophae growing patches.Our study shows that the density,size distribution,and regeneration of Hippophae vary considerably among the major valleys.Trees in the Yamunotri valley have the highest density of large trees but the lowest density of seedlings.In contrast,there are few large trees but many seedlings in the Mana valley.The number and size of lopped trees also varied among the valleys.Lopping was greatest in Bhyundhar(11.4%) and Yamunotri(19.7%) and least in Niti(3.9%).The size of lopped trees differed substantially as well.In Bhyundhar,the largest trees were taken while saplings were taken in Yamunotri.Our study revealed that unsustainable harvesting from plants for fuel,fencing and fruits along with road broadening activities in Central Himalaya are the main cause of habitat destruction.Our research highlights the urgent need for in-situ and ex-situ conservation of Hippophae salicifolia so that it’s potential can be harnessed sustainably by rural hill societies for their socio-economic development.     

Structural performance of a base-isolated reinforced concrete building subjected to seismic pounding

The effects of seismic pounding on the structural performance of a base-isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four-story base-isolated RC building with retaining walls at the base and with a four-story fixed-base RC building is studied. Three-dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base-isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base-isolated building is substantially influenced by the pounding. The investigated base-isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.     

Trends in reference evapotranspiration in the humid region of northeast India

In the present study, the trends in the reference evapotranspiration (ET_O) estimated through the Penman‐Monteith method were investigated over the humid region of northeast (NE) India by using the Mann‐Kendall (MK) test after removing the effect of significant lag‐1 serial correlation from the time series of ET_O by pre‐whitening. During the last 22 years, ET_O has been found to decrease significantly at annual and seasonal time scales for 6 sites in NE India and NE India as a whole. The seasonal decreases in ET_O have, however, been more significant in the pre‐monsoon season, indicating the presence of an element of a seasonal cycle. The decreases in ET_O are mainly attributed to the net radiation and wind speed, which are also corroborated by the observed trends in these two parameters at almost all the times scales over most of the sites in NE India. The steady decrease in wind speed and decline in net radiation not only balanced the impact of the temperature increases on ET_O, but may have actually caused the decreases in ET_O over the humid region of northeast India. Copyright © 2011 John Wiley & Sons, Ltd.     

Indicative proxy evidences of the changing monsoonal precipitation during the last millennium over central west coast of India: A possible link to solar variability

Proxy records of paleomonsoonal variations were obtained, utilizing foraminiferal tracers in two shallow water sediment cores collected from the inner shelf region off Karwar, central west coast of India. The preliminary results record the average signature of relatively better monsoonal precipitation at around 1400?C1410, 1575?C1590 and 1750 AD with intermittent dry phases from around (1290?C1355 AD), (1425?C1535 AD) and (1600?C1665 AD) due to general reduction in the intensity of the rainfall. A comparison with the solar variability (Wolf, Sporer and Maunder sun spot minima) during the last thousand years suggests a possible linkage between the rainfall pattern and solar variability. The presented results though preliminary in nature due to limited dating of the sediments put forth only a possibility of inter-correspondence between solar variability and rainfall intensity. To further augment the reasoning, a number of sediment cores with close spaced dating control need to be studied from geographically distinct regions.     

Do changes in coiling directions in planktonic foraminifera correspond to dimorphic reproduction?

A total of 25 surface sediment samples, collected along a North-South transect (from 9.69° N to 55.01° S and from 80° E and 40° E) in the south western Indian Ocean, were used to study the coiling direction patterns in foraminifera planktonic species Neogloboquadrina pachyderma, Globigerinita glutinata and Globigerina bulloides. Comparison between the coiling direction and mean proloculus size (MPS) revealed that all these profiles along N-S transect were not in tandem and thus indicated non-existence of any relationship between the coiling direction and reproductive modes expressed in terms of mean proloculus size.