Nature and origin of microphenocrysts in a basalt

In the upper 4 cm of a basaltic lava 2 kilometers from its source there is little or no significant change in the size, shape, number, and volume of plagioclase microphenocrysts. A maximum rate of clongation of 0.04 micrometers per second would be consistent with the data. These facts suggest that the microphenocrysts developed prior to extrusion, probably during ascent and efferveseence.     

A study of secondary cosmic ray flux variation during the annular eclipse of 15 January 2010 at Rameswaram, India

The gamma ray flux was measured during the annular solar eclipse on January 15, 2010 at Rameswaram, India using NaI (Tl) scintillator detectors and the variation in charged particles and gamma rays was monitored using Geiger Mu¨ller (GM) counters. The gamma ray flux variation was studied in energy range of 0.1–3.5 MeV. Weather parameters (temperature and humidity) were continuously recorded throughout the duration of the eclipse at the site and correlation between gamma ray flux and weather parameters was examined. Analysis of the secondary cosmic ray flux using Fast Fourier Transform (FFT) was carried out to study the impact of the eclipse on the flux modulation. An overall decrease in flux was observed by both GM counters and scintillator detectors. A relative enhancement observed for short time during the eclipse which could be associated with the presence of counter electrojet observed at Rameswaram. This is suggestive of an increase in secondary cosmic ray flux at the geomagnetic equator during every counter electrojet due to decrease in geomagnetic rigidity.     

Self-consistent treatment of tidal variations in the geocenter for precise orbit determination

We show that the current levels of accuracy being achieved for the precise orbit determination (POD) of low-Earth orbiters demonstrate the need for the self-consistent treatment of tidal variations in the geocenter. Our study uses as an example the POD of the OSTM/Jason-2 satellite altimeter mission based upon Global Positioning System (GPS) tracking data. Current GPS-based POD solutions are demonstrating root-mean-square (RMS) radial orbit accuracy and precision of \({<}1\)  cm and 1 mm, respectively. Meanwhile, we show that the RMS of three-dimensional tidal geocenter variations is \({<}6\)  mm, but can be as large as 15 mm, with the largest component along the Earth’s spin axis. Our results demonstrate that GPS-based POD of Earth orbiters is best performed using GPS satellite orbit positions that are defined in a reference frame whose origin is at the center of mass of the entire Earth system, including the ocean tides. Errors in the GPS-based POD solutions for OSTM/Jason-2 of \({<}4\)  mm (3D RMS) and \({<}2\)  mm (radial RMS) are introduced when tidal geocenter variations are not treated consistently. Nevertheless, inconsistent treatment is measurable in the OSTM/Jason-2 POD solutions and manifests through degraded post-fit tracking data residuals, orbit precision, and relative orbit accuracy. For the latter metric, sea surface height crossover variance is higher by \(6~\hbox {mm}^{2}\) when tidal geocenter variations are treated inconsistently.     

Procedure,selection and application of plasticity models for a soil

A five-step procedure involving mathematical formulation, identification and determination of parameters and verification is presented for development and selection of appropriate and reliable constitutive law(s) for geologic media. Comprehensive analyses are performed toward determination of an appropriate law for a (artificial) soil. The most suitable model is obtained by critical evaluation of four different plasticity models; here verification and comparisons of predictions with observations from laboratory tests, and with those from two boundary value problems are used as the basis of the selection. The model thus selected is found to be appropriate for applications to relevant practical problems.     

Prediction of dilation and permeability changes in rock salt

A numerical procedure has been developed for predicting dilation (porosity) and gas permeability changes in rock salt. The hierarchical single-surface constitutive model of Desai and co-workers is used a finite element program to calculate the state of stress and strain surrounding excavations in rock salt. The elastoplastic constitutive model accounts for strain hardening, a non-associative volumetric response and stress-path-dependent behaviour. The calculated stress and strain fields are used in a flow model based on the equivalent channel concept to predict permeability. Parameters for both the mechanical and permeability models are developed from laboratory test results. Two field experiments adjacent to underground excavations are modelled. The extent of the dilated rock zone around the excavation is predicted well, but the magnitude of the porosity and gas permeability is underpredicted very near the excavations. This discrepancy is attributed to model parameters derived from loading-only laboratory tests, whereas significant unloading occurs in the field. The shape of the yield surface was found to be an important factor in dilation and permeability predictions. Similar stress, strain and permeability fields were obtained with different model types (plane strain or axisymmetric) and initial stress states, and with instantaneous and progressive excavation.     

Upper Callovian-Middle Oxfordian belemnite assemblage from Jara Dome,Western Kachchh

Belemnites and ammonites were collected from the Dhosa Oolite beds of Jara Dome in Kachchh. The Dhosa Oolite is an important marker of the Mesozoic sediments exposed in the Kachchh Basin. Nine belemnite species are reported belonging to four genera Belemnopsis, Demubelus, Hibolithes and Conodicoelites. These include Belemnopsis cf. moluccana Boehm, B. calloviensis Oppel, Demubelus weberi Stolley, Hibolithes boloides Stolley, H. longiscissus Stolley, H. cf. compressus Stolley, H. jumarensis Waagen, H. budhaichus Stoliczka and Conodicoelites cf. abadi Challinor. Besides the belemnites, diagnostic ammonoid fauna are also recorded from the studied section enabling better controlled stratigraphic resolution and biostratigraphic correlation. Taxonomic studies on the different belemnite species are presented with illustration for reference.