Seismic site characterization and site response study of Nirsa (India)

Natural Hazards - The Nirsa block, a coal mining area, and an industrial town lies in the southern part of Dhanbad district, at the border between the Indian states of Jharkhand and West Bengal....     

Automated star–galaxy segregation using spectral and integrated band data for TAUVEX/ASTROSAT satellite data pipeline

We employ an Artificial Neural Network (ANN) based technique to develop a pipeline for automated segregation of stars from the galaxies to be observed by Tel-Aviv University Ultra-Violet Experiment (TAUVEX). We use synthetic spectra of stars from UVBLUE library and selected International Ultraviolet Explorer (IUE) low-resolution spectra for galaxies in the ultraviolet (UV) region from 1250 to 3220 Å as the training set and IUE low-resolution spectra for both the stars and the galaxies as the test set. All the data sets have been pre-processed to get band integrated fluxes so as to mimic the observations of the TAUVEX UV imager. We also perform the ANN based segregation scheme using the full length spectral features (which will also be useful for the ASTROSAT mission). Our results suggest that, in the case of the non-availability of full spectral features, the limited band integrated features can be used to segregate the two classes of objects; although the band data classification is less accurate than the full spectral data classification.     

High-Speed Solar Wind Streams during 1996 – 2007: Sources,Statistical Distribution,and Plasma/Field Properties

We present a catalog of high-speed streams, along with their solar sources for solar cycle 23. We study their distribution during different years and different phases of solar cycle after classifying them into different groups based on their source(s), duration, and speed. We also study the average plasma/field properties of streams after dividing them into suitable groups on the basis of their source(s), duration and speed. It is expected that the catalog and statistical results presented in this work will further stimulate the space weather and solar-terrestrial studies involving high-speed streams.     

Controlled Blasting for Removal of Concrete Plugs in Draft Tube Tunnels at Sardar Sarovar Project

During construction of the Sardar Sarovar (Narmada) Hydro Electric Project in India, an unprecedented flood entered the power house cavern through draft tube tunnels and caused damage to underground structures. After this incident, these draft tubes were plugged with concrete/reinforced concrete to prevent future flooding. After heavy gates were erected at the exit end of the draft tube tunnels, these plugs had to be removed by drilling and blasting without causing any damage to the concrete lining and the ribs erected in the tunnels. Controlled blasting was designed and executed successfully for removal of the plugs in the same manner as for tunnel blasting. This paper describes the details of concrete plugs, details of drilling and blasting adopted, and some interesting observations in respect of drilling and blasting in the concrete plugs. A seismic method based on the measurement of P-wave velocity in the concrete lining before and after blasting was used to quantify the changes (damage) to concrete lining.     

A reappraisal of polymetamorphism in the Eastern Ghats belt — A view from north of the Godavari rift

Evidence collated from different parts of the Eastern Ghats belt north of the Godavari rift (barring the “Western Charnockite Zone” ) indicates that this sector evolved through a series of compressive structures (F₁ to F₃), with prolific migmatization in quartzofeldspathic and metapelitic gneisses synchronous with F₁ shortening, as was the syn-F₁ emplacement of profuse megacrystic K-feldspar-bearing granitoid bodies. Thereafter, melt productivity of the rocks (synchronous withF ₂– F₃ folding) sharply decreased. Mineral parageneses stable in the S₁, S₂ and S₃ fabrics indicate persistence of granulite facies conditions. P-T estimates on orthopyroxene + garnet + plagioclase + quartz assemblages anchored to recrystallized mosaic that overgrow all penetrative fabric elements in mafic granulites, granitoids and quartzofeldspathic gneisses are in the range of 900‡-950‡C and P≅ 8–9 kbar. This estimate is comparable to those retrieved from sapphirine-bearing paragenesis in Mg-Al metapelites that appear to be diachronous in relation to the fabric elements, and arguably disrupt the granoblastic mosaic. These facets in the northern sector of the orogenic belt are compatible with either a single cycle of tectonic events (i.e., F₁, F₂ and F₃ in continuum), or temporally-separate thermo-tectonic events, with the peak of earlier metamorphism (pre- to syn-F₁) at lower temperature (in the granulite facies) in comparison to the record of high post-F₃-T_max values. It is suggested on the basis of the above evidence that the late Proterozoic/Pan-African granulites in the Eastern Ghats belt north of the Godavari rift, are unlikely to be reworked equivalents of any older granulitic crust, such as the ∼1.6 Ga granulites south of the rift. Instead, the temporally disparate sectors may represent different crustal segments with unconnected pre-amalgamation tectonic history. However, if the ∼ 1.6 Ga granulites of the Western Charnockite Zone continue northwards across the rift, as suggested by recent isotope data, there are serious doubts as to the validity of a north-south division within the Eastern Ghats belt.     

Long term ionospheric electron content variations over Delhi

Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91E; dip Latitude 24.8°N), India, for the period 1975/80 and 1986/89 belonging to an ascending phase of solar activity during first halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IEC_max (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IEC_max shows positive correlation with F_10.7 up to about 200 flux units at equinox and 240 units both in winter and summer; for greater F_10.7 values, IEC_max is substantially constant in all the seasons. IECmax and magnetic activity (A_p) are found to be positively correlated in summer in high solar activity. Winter IEC_max shows positive correlation with A_p in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IEC_max is independent of A_p in both solar cycles in low solar activity. A study of day-to-day variations in IEC_max shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation.