Acceleration of the universe in f(R) gravity models

A general formalism for the investigation of the late time dynamics of the universe for any analytic f(R) gravity model, along with a cold dark matter, has been discussed in the present work. The formalism is then elucidated with two examples. The values of the parameters of the models are chosen in such a way that they are consistent with the basic observational requirement.     

Five Dimensional Magnetic Universe

Possibility of a persistent structure of source free pure magnetic field contained by the curvature of a static cylindrically symmetric space-time associated with its own strength of energy density in five dimensional Kaluza-Klein space-time is investigated. It may be considered as the generalization of Melvin's 4D ‘magnetic universe’ in five dimensional K-K space-time. Time like and null geodesics are studied in order to investigate the nature of gravitation produced by it and are found not to deviate much from those noted in Melvin's spacetime. It is further interesting to note that near the axis of symmetry our 5D space-time exhibits the conical defect similar to that in the case of a string. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analytic hierarchy process and information value method-based landslide susceptibility mapping and vehicle vulnerability assessment along a highway in Sikkim Himalaya

In hilly areas, highway projects can be a cause of landslides as well as an element of vulnerability due to landslides. Hence, landslide susceptibility mapping of highway corridors can substantially mitigate loss of life and property. For this, a Landslide Susceptibility Assessment Model (LSAM) was developed for a corridor of 27 km along NH 10 in the East Sikkim. Landslide inducing factors viz. Aspect, Distance from Fault, Distance from Road, Drainage Density, Land use and Land cover, Lithology, Plan Curvature, Rainfall, Slope, Soil Depth, and Soil Texture were considered for the study. Results show that areas in proximity to the highway and areas with steeper slope had a higher landslide susceptibility than otherwise. Spatial explicit sensitivity analysis indicated that LSAM was sensitive to distance from the highway and slope. Vehicle vulnerability assessment of base year and horizon years showed that vulnerability increased through time. LSAM is appropriate for hazard mitigation for areas with poor historical data on landslides.     

Gravitational field of a stationary circular cosmic string loop

Gravitational field of a stationary circular cosmic string loop has been studied in the context of full nonlinear Einstein's theory of gravity. It has been assumed that the radial and tangential stresses of the loop are equal to the energy density of the string loop. An exact solution for the system has been presented which has a singularity at a finite distance from the axis, but is regular for any other distances from the axis of the loop. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution pattern and morphochemical relationships of manganese nodules from the Central Indian Basin

In the Central Indian Basin manganese nodule abundance was variable in all sediment types. Mean abundance varied from 1.5 in calcareous ooze to 10.2 kg/m² in terrigenous-siliceous ooze sediments. Nodule grade and growth rates are positively correlated only up to 10 mm/My (million years), and grade shows no distinct relationship with abundance. Relationships between the morphochemical characteristics of the nodules and host sediment types are subtle. Both hydrogenetic and diagenetic nodules (with smooth and rough surfaces respectively) occur on almost all sediments, but in variable proportions. Thus, the overall distribution pattern shows that small nodules (<4-cm diameters) of lower grade (average value Ni+Cu+Co=1.21%) with smooth surfaces are more common on red clay, terrigenous, and terrigenous-siliceous ooze transition-zone sediments. By contrast, large nodules (>4-cm diameters) of higher grade (average value Ni+Cu+Co=1.80%) with rough surfaces are more prevalent on siliceous ooze, siliceous ooze-red clay, and calcareous ooze-red clay transition-zone sediments. This implies an enhanced supply of trace metals from pore waters to rough-surface nodules during early diagenesis.     

Determination of seismic wave attenuation in Delhi,India, towards quantification of regional seismic hazard

Natural Hazards - National capital of India, Delhi is under moderate to high seismic hazard due to active regional faults such as the Mahendragarh fault, the Delhi Haridwar fault, the Sohna fault,...     

Insights on the process of two-stage coronae formation at olivine-plagioclase contact in mafic dyke from Palghat Cauvery Shear Zone,southern India

Mineralogy and Petrology - Coronae between olivine and plagioclase are a common replacement texture in mafic rocks by magmatic and metamorphic processes. Mafic dykes from Palghat Cauvery Shear Zone...     

A Kaapvaal craton debate: Nucleus of an early small supercontinent or affected by an enhanced accretion event?

Incorporation of the Kaapvaal craton within a speculative Neoarchaean–Palaeoproterozoic supercontinent has long been debated, and this idea provides a potential solution to solving the apparently enigmatic provenance of the huge quantities of gold within the famous Witwatersrand auriferous deposits of Kaapvaal. Within a framework of a postulated Neoarchaean “Kenorland” (“northern”; present-day reference) supercontinent, we examine possible “southern” cratons that may have been contiguous with Kaapvaal: Pilbara, Zimbabwe, Dharwar, São Francisco, Amazon, Congo. Brief reviews of their basic geology and inferred evolution in syn-Witwatersrand basin times (c. 3.1–2.8 Ga) show no obvious support for any such supercontinental amalgamations. An alternative idea to explain a measure of gross similarity amongst several Neoarchaean cratons is through global events, such as a c. 3125–3000 Ma cratonic-scale erosive event interpreted for both Pilbara and Kaapvaal, and a much more widespread magmatic event at c. 2760–2680 Ma. We postulate that a global superplume event at c. 3.0 Ga included a plume beneath the Kaapvaal cratonic nucleus, thus halting any subduction around that terrane due to the thermal anomaly. Such a speculative global magmatic event is assumed to have enhanced production of juvenile oceanic crust at mid-ocean ridges, including those “offshore” of the thermally elevated Kaapvaal nucleus. Intra-oceanic obduction complexes may have built up fairly rapidly under such conditions, globally, and once the plume event had abated, “normal” plate tectonics would have resulted in composite (greenstone-tonalite, possibly also including granite) terranes accreting with nuclei such as Kaapvaal. This enhanced plume-related cratonic growth can be seen as a rapid accretion event. Formation of the envisaged ophiolite complexes possibly encompassed deformation-related first-order concentration of gold, and once accretion occurred around Kaapvaal's nucleus, from north and west (present-day frame of reference), a second-order (deformation-related) gold concentration may have resulted. The third order of gold concentration would logically have occurred once placer systems reworked detritus derived from the orogens along the N and W margins of Kaapvaal. Such conditions and placer gold deposits are known from many Neoarchaean cratons. The initial source of gold was presumably from the much hotter Mesoarchaean mantle and may have been related to major changes in Earth's tectonic regime at c. 3.0 Ga. The unique nature of Kaapvaal is probably its early stabilization, enabling formation of a complex flexural foreland basin system, in which vast quantities of placer sediments and heavy minerals could be deposited, and preserved from younger denudation through a unique post-Witwatersrand history.     

Strong ground motion parameters of the 18 September 2011 Sikkim Earthquake Mw = 6.9 and its analysis: a recent seismic hazard scenario

Natural Hazards - The 18 September 2011 earthquake in Sikkim was one the most devastating earthquake in Sikkim Himalaya in India–Asia collision boundary. The source characteristic of this...