Spatial and time variations in critical frequencies of the ionospheric <Emphasis Type="Italic">F</Emphasis> region above the zone of equatorial earthquake preparation

Spatial and time variations in the critical frequencies foF2 before the strong earthquake of August 15, 1963, with the magnitude M = 7.75 are analyzed. The epicenter of the earthquake was located in the vicinity of the magnetic equator in the American longitudinal sector. The data of the topside ionosonde on board Alouette-1 and of the series of ground-based ionosondes has been used for this purpose. The ground-based ionosondes made it possible to detect an insignificant anomalous decrease in foF2 within the zone of earthquake preparation a few days prior to the earthquake. This result confirms the conclusion drawn earlier on the basis of the satellite data. The modification of the ionosphere at the F-region level is more evident in the satellite than in the ground-based data. It is also noted that the character of the time variations in foF2 a day before the earthquake is similar to the so called “quiet time” Q-disturbances in the ionosphere, when the electron concentration at the F region maximum differs from the median values by more than 20% under undisturbed geophysical conditions.     

A new class of bulk viscous cosmological models in a scale covariant theory of gravitation

Field equations of cosmological models with bulk viscosity are constructed in the scale covariant theory of gravitation. A new class of solutions for the model is found by applying a variable deceleration parameter. Some physical implications of these solutions are briefly discussed.     

Particle creation with time dependent gravitational and cosmological constants

The effect of particle creation on the evolution of FRW cosmological model has been studied. The universe has been considered as an open thermodynamic system when particle creation leads to supplementary negative creation pressure in addition to the thermodynamic pressure. Dynamical behaviors of the cosmological solutions have been studied.     

Anisotropic universe with cosmic strings and bulk viscosity in a scalar–tensor theory of gravitation

A spatially homogeneous and anisotropic Bianchi type-I cosmological model is obtained in a scalar–tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. Some physical and kinematical properties of the model are discussed. It is observed that the bulk viscosity has a greater role in getting an accelerated expansion of the universe in this theory.     

Trace element and isotopic studies of Permo-Carboniferous carbonate nodules from Talchir sediments of peninsular India: Environmental and provenance implications

Syngenetic carbonate nodules constitute an interesting feature of the glaciogene sediments of various Talchir basins in peninsular India. Petrographic, cathodoluminescence and sedimentary results suggest that many of these nodules contain primary carbonate precipitates whose geochemical signatures can be used for determining environment of deposition and provenance of the sediments and drainage source. Several nodules were collected from Gondwana basins of east-central India and analyzed for stable carbon and oxygen isotope ratios, REE and trace element composition, and Sr isotope ratio. The mean δ¹⁸O and δ¹³C values of the calcites in the nodules are — 19.5% and-9.7% (w.r.t. PDB) respectively suggesting a freshwater environment (probably lacustrine) for formation of these objects. Trace element ratios (Eu/Eu * and La/Yb) of the nodule samples show that the source of the sediments in the Damodar valley basin was the granites, gneisses and intrusives in the Chotanagpur region. The sediments in the Mahanadi valley were derived from granulites, charnockites and granites of the eastern ghat region. The Sr concentration of the carbonate phase of the nodules is low, ranging from 10–60 ng/g. The⁸⁷Sr/⁸⁶Sr ratios of the samples from the west Bokaro basin and Ramgarh basin vary from 0.735 to 0.748 (mean: 0.739) and from 0.726 to 0.733 (mean: 0.730) respectively. These values are consistent with our proposition that water of these basins drained through the granitic rocks of the Chotanagpur region. In contrast, the⁸⁷Sr/⁸⁶Sr ratios of the samples from the Talchir basin (Type area) of Mahanadi valley vary from 0.718 to 0.723 (mean: 0.719). These⁸⁷Sr/⁸⁶Sr ratios are close to those of the granulites in the adjoining eastern ghat belt suggesting that area as the drainage source.     

The new intermediate polar RX J1238 − 38: a system below the period gap?

We present optical observations of the recently discovered ROSAT source RX J1238 − 38, which is a new member of the intermediate polar class of asynchronous magnetic cataclysmic variables (CVs). Optical photometry reveals two coherent periodicities at 1860 and 2147 s respectively, with similar amplitudes of ∼ 8 per cent. Infrared ( J -band) intensity variations are detected only at the 1860-s period, at an amplitude of ∼ 15 per cent. The initial hypothesis, that these two periods were the spin and synodic (i.e., beat) period respectively, appears not to be supported by the spectroscopic data. The emission lines vary on the longer photometric period, and radial velocity variations are detected at this period and at a longer period of ∼ 5300 s, which we identify as the spin and orbital periods respectively. The most likely explanation for the 1860-s period is that it is the first harmonic of the ω − Ω sideband, leading to an improved determination of the orbital period as 5077 s (= 84 min). If this interpretation is correct, RX J1238 − 38 joins EX Hya as the only other intermediate polar below the 2–3 h period gap, and with an orbital period close to the minimum for CVs with non-degenerate secondaries. The spin-modulated emission-line radial velocities and widths appear to be anticorrelated, with maximum width occurring at maximum blueshift. Such an anticorrelation is expected for aspect changes of accretion curtains. Polarimetric observations of RX J1238 − 38 were inconclusive, although we can put a limit of 0.4 per cent on any variability on the circular polarization, and certainly there is no indication of variations at the photometric or spectroscopic periods.