Palaeoecological implications of corallinacean red algae and halimedacean green algae from the prang formation of south shillong plateau, meghalaya

The southwestern part of south Shillong plateau (Meghalaya, N-E India), designated as Sylhet Limestone Group is sub-divided into three lithounits i.e., Lakadong, Umlatdoh and Prang formations in ascending order. The Prang Formation is the youngest lithostratigraphic unit of the Sylhet Limestone Group and has been dated as Middle to early Upper Eocene based on the benthic foraminifera studies. Thin section analysis of carbonate rocks from Prang Formation, exposed in the Bholaganj limestone quarry yielded a rich assemblage of calcareous algae. The coralline algal assemblage comprises both non-geniculate and geniculate forms. The green algae are represented by species of Halimeda belonging to the family Halimedaceae. Palaeoecological interpretation based on diversity, growth-form analysis and taphonomic aspects of the algal assemblage indicate that in all probabilities the deposition of Prang Formation occurred in shallow, warm, shelf environment of normal salinity within the transgressive phase.     

A study of generalized second law of thermodynamics in modified f(R) Horava–Lifshitz gravity

This work investigates the validity of the generalized second law of thermodynamics in modified f(R) Horava–Lifshitz gravity proposed by Chaichian et al. (Class. Quantum Grav. 27: 185021, 2010), which is invariant under foliation-preserving diffeomorphisms. It has been observed that the equation of state parameter behaves like quintessence (w>−1). We study the thermodynamics of the apparent, event and particle horizons in this modified gravity. We observe that under this gravity, the time derivative of total entropy stays at positive level and hence the generalized second law is validated.     

Rotation and strain of linear and planar structures in three-dimensional progressive deformation

Rotation and progressive strain have been studied for a sheet embedded in a matrix which undergoes rotational three-dimensional strain under constant volume conditions. The mathematics gives explicit information on the following features:

1. (1) The length and position (relative to a defined coordinate system) of the principal axes of the strain ellipsoid at any stage of the progressive deformation.

2. (2) The position and length of the principal axes in any plane intersecting the strain ellipsoid, also at any stage of the deformation.

3. (3) The position and length of passive markers which initially coincided with the principal axes in an intersecting plane. This is of consequence for the distinction between passively rotating structures and actively forming structures.

4. (4) The shear strain parallel to an intersecting plane or sheet, as indicated by the angular difference between the normal to an intersecting plane at any time and the marker at the same time which initially, however, was parallel to the normal. This layer-parallel shear causes boudins to rotate and the axial plane of buckles to tilt.

The relationships have been expressed quantitatively in the bulk of the paper and illustrated in diagrams. The analysis presented is basic for the study of the deformational behavior of competent sheets of rocks embedded in less competent ones.     

Structural and metamorphic evolution of the rocks of the Jutogh Group, Chur half-klippe, Himachal Himalayas: A summary and comparison with the Simla area

The rocks of the Jutogh Group in the Himachal Himalayas and their equivalents elsewhere are now considered to represent a several km thick crustal scale ductile shear zone, the so called Main Central Thrust Zone. In this article we present a summary of structural and metamorphic evolution of the Jutogh Group of rocks in the Chur half-klippe and compare our results with those of Naha and Ray (1972) who worked in the adjacent Simla klippe. The deformational history of the Jutogh Group of rocks in the area around the Chur-peak, as deduced from small-scale structures, can be segmented into: (1) an early event giving rise to two sets of very tight to isoclinal and coaxial folds with gentle dip of axial planes and easterly or westerly trend of axes, (2) an event of superimposed progressive ductile shearing during which a plethora of small-scale structures have developed which includes successive generations of strongly non-cylindrical folds, several generations of mylonitic foliation, extensional structures and late-stage small-scale thrusts, and (3) a last stage deformation during which a set of open and upright folds developed, but these are regionally unimportant. The structure in the largest scale (tens of km) can be best described in terms of stacked up thin thrust sheets. Km-scale asymmetric recumbent folds with strongly non-cylindrical hinge lines, developed as a consequence of ductile shearing, are present in one of these thrust sheets. The ductile shearing, large-scale folding and thrusting can be related to the development of the Main Central Thrust Zone. The microstructural relations show that the main phase of regional low-to medium-grade metamorphism (T ≈ 430–600°C andP ≈ 4.5–8.5 kbar) is pre-kinematic with respect to the formation of the Main Central Thrust Zone. Growth zoned garnets with typical bell-shaped Mn profiles and compensating bowl-shaped Fe profiles are compatible with this phase of metamorphism. Some of the larger garnet grains, however, show flat compositional profiles; if they represent homogenization of growth zoning, it would be a possible evidence of a relict high-grade metamorphism. The ductile shearing was accompanied by a low-greenschist facies metamorphism during which mainly chlorite and occasionally biotite porphyroblasts crystallized.     

Tropical cyclone: expressions for velocity components and stability parameter

Tropical cyclones are the most devastating natural calamity forming in the ocean bed and die out in land. The life cycle of a tropical cyclone is mainly classified into four stages: (a) formation or genesis stage, (b) intensification stage, (c) mature stage and (d) decay stage. The intensification and mature stages are also known as tropical storm and cyclone (hurricane) stage, respectively. To develop the model of tropical cyclone we have taken the momentum conservation equation, equation of continuity and equation of hydrostatic balance in cylindrical coordinate system. Also the equation of state and the equation relating the velocity component and stream function are taken into account. We have assumed a suitable analytic form of the radial component of velocity as a function of radial distance (r) from the axis of the cyclone and vertical distance (z) from the sea bed. So in our model we have taken a cyclone as a rotating cylinder. With the use of the expression of the radial component velocity we have solved the governing nonlinear equation in the cylindrical coordinate system of a cyclone using ‘Wentzel–Kramers–Brillouin approximation’ and estimated the transverse velocity on the sea bed and in the vicinity of the eye wall of the cyclone. From the results we also get a path to generalize the tropical cyclone model as a vortex which is a generating curve of a cyclone. We also determine the vertical component of velocity of the cyclone. In this work we define a new parameter called the cyclone stability parameter (CSP). The CSP helps to determine the stability of a tropical cyclone from its genesis.     

Camouflage Detection Using MWIR Hyperspectral Images

Mid Wave Infra Red (MWIR) region of the electromagnetic spectrum is a key region that is exploited for long range infrared reconnaissance and surveillance applications. Detecting enemy targets and being undetectable is the prime requirement of the modern warfare. In the present study MWIR hyperspectral imaging has been exploited for detection of camouflaged targets in the scene. Detection methodology has been developed using unsupervised target detection algorithms (Reed Xiaoli, K-Means and ISODATA). Methodology has been successfully tested in extracting camouflaged targets from the background. Performance results have been compared. The proposed methodology may in future be applied in detection and identification of gases and minerals in the field.     

Chromian spinel-rich black sands from eastern shoreline of Andaman Island,India: Implication for source characteristics

Black sands rich in chromian spinel commonly occur in pockets along the eastern shoreline of Andaman Island where various types of peridotites and volcanics belonging to the Andaman ophiolite suite are exposed in close vicinity. The chemistry of these detrital chromian spinels has been extensively used here in identifying the source rocks vis-à-vis deciphering the source characteristics. The composition of the chromian spinels (Cr#: 0.20–0.88, Mg#: 0.26–0.77, Al ₂ O ₃: 5.04–48.21 wt.%, TiO ₂: up to 1.39 wt.% and Fe ²⁺/Fe ³⁺: 1.73–9.12) varies widely signifying multiple sources, of which mantle peridotites and volcanic rocks are relevant in an ophiolitic terrain. The volcanic chromian spinels are relatively fresh, commonly euhedral, sometimes with compositional variations, and contain inclusions in contrast to the mantle peridotitic chromian spinels which are rounded, extensively fractured, and altered. We used a number of geochemical bivariate plots in order to know the provenance protoliths. The volcanic chromian spinels show geochemical characters of MORB, related to spreading centers (either MOR or back-arc) and also boninites/arc-tholeiites, related to active subduction. On the other hand, the peridotitic spinels indicate partially depleted lherzolite and depleted harzburgite source of the ophiolite suite.