‘Thermohaline front’ off the east coast of India and its generating mechanism

Physical oceanography measurements reveal a strong salinity (0.18 psu km⁻¹) and temperature (0.07 °C km⁻¹) front off the east coast of India in December 1997. T–S diagrams suggest lateral mixing between the fresh water at the coast and the ambient warmer, saltier water. This front seems to be the result of southward advection of fresh and cool water, formed in the northern Bay of Bengal during the monsoon, by the East Indian Coastal Current, as suggested by the large-scale salinity structure in the SODA re-analysis and the anti-cyclonic gyre in the northwestern Bay of Bengal during winter. The data further reveals an offshore front in January, which appears to be the result of a meso-scale re-circulation around an eddy, bringing cold and freshwater from the northern Bay of Bengal further away from the shore. Our cruise data hence illustrates that very strong salinity fronts can appear in the Bay of Bengal after the monsoon, as a result of intense coastal circulation and stirring by eddies.

     

Theoretical and experimental analysis of tethered buoy instability in gravity waves

The motion of a tethered spherical buoy subjected to incident regular waves was measured in a wave tank. Transverse instability was observed when the period of the wave generated was close to one-half of the natural period of the buoy. The transverse instability confirmed as Mathieu type was predominant at the surface but diminished with increase in the depth of submergence. The stable and unstable zones were determined on the Mathieu's instability diagram. Experimental results were in agreement with the predicted zone of instability for a two degree of freedom oscillation problem of Mathieu type which has a periodically varying spring constant.     

Studying Land Use Travel Demand Interaction Using 3S Technology for Tiruchirappalli City

This paper gives an overview of a major application of modern geospatial tools such as remote sensing, GIS and GPS, i.e., 3S technology in estimating travel demand along Indian roads by considering the study area, Tiruchirappalli urban city in Tamil Nadu. In the study, an attempt was made to estimate travel demand based on the current land-use classification as the pattern of travel depends on the type of land use activity in a zone. IRS high resolution image Cartosat-1 of year 2009 was used to extract the land-use information required. The travel demand model developed was validated with the field obtained OD-matrix to understand the accuracy of the method considered.     

Pulsar observations at 34.5 MHz using the Gauribidanur Telescope: I

The behaviour of pulsars at low radio-frequencies (below ≈ 50 MHz) remains poorly understood mainly due to very limited observational data on pulsars at these frequencies. We report here our measurements of pulse profiles at 34.5 MHz of 8 pulsars using the Gauribidanur Radio Telescope. None of the 8 pulsars show any significant interpulse emission at this frequency which conflicts with an earlier claim from 25 MHz observations. With the exception of one pulsar (PSR 0943 + 10) all the observed pulsars show turnovers at frequencies above 35 MHz in their spectra. We also report our attempts to study the short and long term variations in the pulsar signals at this low frequency.     

Seasonal variation of Caligus rotundigenitalis infestation on the host fish Etroplus suratensis from the Cochin Backwaters,southwest coast of India

Investigation of four edible fishes(Etroplus suratensis, Oreochromis mossambicus, Lates calcarifer, Chanos chanos)collected from a fish landing center along Cochin Backwaters has done for caligid infestation. Of these, caligids were detected only from Etroplus suratensis and was identified to be Caligus rotundigenitalis. Parasites were attached to the inner side of operculum of host which indicates strong site preference. The annual observation of prevalence, mean intensity and abundance were fo...     

Photometric and spectroscopic study of R CMa

UBV light curves and spectrograms of R CMa obtained with the 48-inch telescope of Japal-Rangapur Observatory during 1980–82 have been used for deriving the eclipse and orbital elements as well as the absolute dimensions of the components. The primary is found to be a Main-Sequence F2V star of mass 1.52M and the secondary a subgiant star of spectral type G8 and mass 0.20M which fills its Roche lobe, in agreement with Kopal and Shapley (1956) results, Kopal (1959), or Sahade's (1963) results. From a consideration of the possible evolution of this system it is concluded that a large fraction of the original mass of the secondary is lost from the system. A study of the period changes indicates the possible presence of a third component of mass of about 0.5M which is most likely to be anM dwarf.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Segmentation of well logs by maximum-likelihood estimation

A maximum-likelihood procedure for segmenting digital well-log data is presented. The method is based on a univariate state variable model in which an observed log is treated as a time-series consisting of two terms: a Gauss-Markov signal remaining constant over a segment, and an additive Gaussian, but not necessarily stationary, noise. The signal jumps by a random amount at a segment boundary. The inverse problem of log segmentation consists of detecting the segment boundaries from a given log. The problem is solved using a Bayesian approach in which the unknown parameters, the locations of segment boundaries and the jumps in the signal value, are estimated by maximizing the likelihood function for the observed data. An algorithm based on Kalman smoothing and single most likelihood replacement (SMLR) procedure is proposed. The performance of the method is illustrated with a case study comprising of multisuite log data from an exploratory well. The method is found to be rapid and robust. The resulting segments are found to be geologically consistent.     

‘Thermohaline front’ off the east coast of India and its generating mechanism

Physical oceanography measurements reveal a strong salinity (0.18 psu km^?1) and temperature (0.07 °C km^?1) front off the east coast of India in December 1997. T–S diagrams suggest lateral mixing between the fresh water at the coast and the ambient warmer, saltier water. This front seems to be the result of southward advection of fresh and cool water, formed in the northern Bay of Bengal during the monsoon, by the East Indian Coastal Current, as suggested by the large-scale salinity structure in the SODA re-analysis and the anti-cyclonic gyre in the northwestern Bay of Bengal during winter. The data further reveals an offshore front in January, which appears to be the result of a meso-scale re-circulation around an eddy, bringing cold and freshwater from the northern Bay of Bengal further away from the shore. Our cruise data hence illustrates that very strong salinity fronts can appear in the Bay of Bengal after the monsoon, as a result of intense coastal circulation and stirring by eddies.