Tidal influence on suspended sediment distribution and dispersal in the northern Andaman Sea and Gulf of Martaban

Surface and water column profiles of suspended matter collected during April-May 2002, and satellite images were used to study factors influencing suspended sediment concentrations (SSCs) and dispersal in the northern Andaman Sea and Gulf of Martaban, one of the largest highly turbid areas of the world's oceans. Perennial high SSC in the Gulf of Martaban is due to a combination of factors including resuspension of sediments by strong tidal currents, shallow bathymetry and seasonal sediment influx from rivers. From satellite images, it was observed that in the central portion of the Gulf of Martaban, the turbidity front oscillates about 150 km in phase with spring-neap tidal cycles and the area covered by the turbid zone (SSC>15 mg l⁻¹) increases from less than 15 000 km² during neap tide to more than 45 000 km² during spring tide. The sediment discharged by the Ayeyarwady River is transported mainly eastward, along the coast, into the Gulf of Martaban. Occasionally, during the winter monsoon period, sediment plumes are seen heading westward into the Bay of Bengal. Turbidity profiles show that bottom nepheloid layers are actively transporting some of the sediments into the deep Andaman Sea via the Martaban canyon.     

Influence of Frequency on the Behaviour of Plate Anchors Subjected to Cyclic Loading

This article reports the response of embedded circular plate anchors to varying frequencies of cyclic loading. The effects of time period of loading cycles and pre-loading on movement of anchors and post-cyclic monotonic pullout behavior are studied using a model circular (80 mm diameter) plate anchor, buried at embedment ratio of six in a soft saturated clay. The frequencies of loading cycles have showed considerable effect on movement of anchors. For given duration of loading, higher frequency cycles cause more movement of anchor than lower frequency cycles. Pre-loading reduces the movement of anchors in subsequent loading stages. When anchors are recycled at a load ratio level less than the pre-cycling load, the movement of anchor in recycling phase are very much reduced, but if the recycling is done at a higher load ratio level, the effect is not that much pronounced and the anchors behave as if they were not subjected to any cycling load in the past. Anchor subjected to cyclic loading and then monotonic pullout shows an increase in initial stiffness, whereas the peak pullout load was found to decrease marginally over that of an anchor not subjected to any cyclic loading. For the present test conditions, the relative post-cyclic stiffness of anchors is found to vary from 1.169 to 1.327.     

Record of carbonate preservation and the Mid‐Brunhes climatic shift from a seamount top with low sedimentation rates in the Central Indian Basin

In the present investigation, an age model of carbonate‐rich cores from a seamount top in the Central Indian Basin (CIB) was constructed using both isotopic (²³⁰Th_excess, AMS ¹⁴C, oxygen isotopes) and biostratigraphic methods. The chronologies using the two methods are in good agreement, yielding a record of the late Middle Pleistocene to the Pleistocene–Holocene transition (550 to 11.5 ka). The first appearance datum (FAD) of the radiolarian Buccinosphaera invaginata (180 ka) and coccolith Emiliania huxleyi (268 ka) and the last appearance datum (LAD) of the radiolarian Stylatractus universus (425 ka) were used. A monsoon‐induced productivity increase was inferred from carbonate, organic carbon and δ¹³C records in response to the Mid‐Brunhes Climatic Shift (MBCS), consistent with an increased global productivity. While the coccolith diversity increased, a decrease in coccolith productivity was found during the MBCS. At nearly the same time period, earlier records from the equatorial Indian Ocean, western Indian Ocean and eastern Africa have shown an increased productivity in response to the influence of westerlies and increased monsoon. The influence of easterlies from Australia and the intensification of aridity are evidenced by increased kaolinite content and clay‐sized sediments in response to the MBCS. An increased abundance of Globorotalia menardii and other resistant species beginning from marine isotope stage (MIS) 11 and the proliferation of coccolith Gephyrocapsa spp. indicate increased dissolution, which is consistent with the widespread global carbonate dissolution during this period. The relatively high carbonate dissolution during the transition period of MIS 3/2 and glacial to interglacial periods (MIS 6, 7 and 8) may be due to the enhanced flow of corrosive Antarctic Bottom Water (AABW) into the CIB.     

Magnetic studies on charnockites of Palni Hills

The magnetic properties like coercive force, mean mass susceptibility and relative remanence of some charnockites of Palni Hills, South India collected at different altitudes were measured.     

Environmental evaluation of medchal taluk,Andhra Pradesh using aerial photographs

The human interaction with nature in the form of improper exploitation and unplanned utilisation of natural resources has caused a lot of environmental imbalance in nature. The aerial photographs and other repetitive orbital remote sensing data provide valuable information in identification and surveying of such environmentally imbalanced zones. In this study the aerial photographs were used in identifying such vulnerable areas and some remedial measures are suggested for the planned exploitation of natural resources without damaging the environment.     

Palaeomagnetic study of some charnockites of the Palni Hills

The intensity of natural remanence magnetisation (NRM) is measured along the three mutually-perpendicular directions using an astatic magnetometer. The intensity of induced magnetisation is measured using an apparatus fabricated in the laboratory. The Koenigsberger ratio has been calculated for all the samples and the ratio has been used to test the stability of NRM in the samples. The mean direction of magnetisation is determined from the three components of the NRM intensity. The palaeomagnetic pole position of the samples is determined using the direction of magnetisation and the site location. An attempt has been made to fix the geological age of the charnockites using palaeomagnetic methods.     

Multiobjective optimal FLC driven hybrid mass damper system for torsionally coupled,seismically excited structures

In most of the research work on structural vibration control only two‐dimensional plane structural modelling has been considered, although only a few practical building structures can be modelled as planar structures. Therefore, these methods are not directly applicable to the majority of the practical building structures. This paper discusses the design of a multiobjective optimal fuzzy logic controller (FLC) driven hybrid mass damper (HMD) system for seismically excited torsionally coupled building structures. Floor acceleration and velocity information have been used as feedback to the fuzzy logic controller. A three branch tournament Genetic Algorithm has been used for the multiobjective optimal design of the FLC driven HMD system, where the minimization of the non‐dimensionalized peak displacement, acceleration and rotation of the structure about its vertical axis, have been as the three objective functions. The proposed multiobjective optimal fuzzy logic controller has been verified for an example problem reported in the literature. This HMD system consists of four HMDs arranged in such a way that the system can control the torsional mode of vibration effectively in addition to the flexure modes of vibration. Copyright © 2002 John Wiley & Sons, Ltd.     

An analogue model study of electromagnetic induction for island-continent ocean channels for the H polarization

Using an electromagnetic analogue model, the behavior of time-varying electromagnetic fields for an island near a continental coastline is examined for the H-polarization case, in which the electric field of the inducing source is perpendicular to the continental coastline. A study of the effect of the shape of the island, using square- and circular-island models, indicates that over the island, anomalies in the field components are confined to a smaller area for the circular island than for the square island. A study of the effect of ocean-channel width between the island and continent shows that, as the channel width decreases, anomalies in the magnetic field components over the island decrease. The anomaly in the electric field at the continental coastline first increases and then decreases with decreasing channel width.     

On the comparison of laboratory electromagnetic analogue model measurements and finite-difference numerical calculations

This work compares experimental analogue model measurements and finite-difference numerical calculations of the electric and magnetic fields for the cases of induction in a highly conducting plate and wedge embedded in a poorly conducting host earth. The results indicate very good agreement between the experimental and theoretical results and confirm the validity of the analogue and numerical methods for studying complex induction problems.     

Estimation of Cd,Pb and flame retardants in electric mosquito bat using EDXRF,ICP-OES,AAS and GC–MS

In the present study, investigated the concentrations of hazardous substances such as Pb, Cd and polybrominated flame retardants present in an electric mosquito bats, which are used for trapping the mosquitoes in the domestic areas. China has captured a big share of mosquito bat market in India and penetrated deep into rural areas also. The presence of hazardous substances is fatal to environment and human beings. Hence, the concentrations of hazardous substances present in the bats need to be estimated accurately. The dismantled homogeneous samples were subjected to estimate the toxic metals like cadmium and lead by using energy-dispersive X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectroscopy and atomic absorption spectroscopy for comparison. The flame brominated retardants were tested using gas chromatography–mass spectrometer. The analytical data obtained from the power supply wires of the bat suggest that the concentration levels of cadmium found to be below the detection limits. Whereas the lead content has higher in the range of 3574–7575 ppm than the permissible limits set by the e-waste rule, i.e. 1000 ppm. Moreover, the high amount of lead (>80,000 ppm) was obtained in the printed circuit board apart from power supply wires of mosquito bat. The content of brominated flame retardants in mosquito bat was estimated to be within the limits of e-waste rule. Considering their significant high hazardous metals content, coupled with their large quantities of mosquito bats used in the country, there is a need to control the hazardous waste of mosquito bats.