Aspects of reproduction of the brown mussel Perna perna at the Iture rocky beach near Cape Coast,Ghana

Aspects of the reproductive biology of the brown mussel Perna perna at the Iture rocky beach near Cape Coast, Ghana, were studied from September 2014 to August 2015. The current study was aimed at providing information useful for managing the mussel fishery in this locality and also that would form the basis for designing appropriate culture methods for the species. Microscopic examination of fresh smears of gonadal material, as well as histological preparations of the gonad, were used to study the sexuality and breeding pattern of the species. Monthly gonadal and condition indices were also determined. Perna perna exhibited gonochoristic sexuality with a sex ratio of approximately 1:1 throughout the study period. Sexes were identifiable at shell lengths of 15.0–19.9 mm. Five stages of gonadal development were identified in both sexes. Gametogenic activity was continuous throughout the year, with two major spawning activities, from April to June and from August to December. These periods coincided with the major and minor rainy seasons, respectively, as well as the major upwelling period in August. Condition indices suggest that the mussels were in better condition for harvesting in March and August prior to the major spawning events.     

Application of Remote Sensing and Geographic Information System in infrastructure development

Road transportation network development is a vital component of infrastructure development. Absence of database on roads of Trivandrum district was felt as a major hindrance in prioritizing improvement/development/repair of the roads for better traffic efficacy. High resolution PAN imagery (IRS-IC, September-December 1999, 1:25,000 scale) was visually interpreted to decipher road net work for preparing an elaborate database for Kerala Highway. The data were incorporated on 1:25,000 scale SOI base maps. Field verification was carried out to identify and categorize the PWD roads as per their administrative sections. Final maps were digitized in ARC/INFO environment. Information about terrain conditions was also generated using satellite remote sensing images and aerial photographs. Incorporating the height source and elevation data in the value field and taking mass points as input, a TIN (Triangulated Irregular Network) model of a sample area near Vellanad, 22 km east of Trivandrum city was created to analyse the terrain-road network interrelationship. Our case study involving draping of road network on TIN model as well as on geomorphology map established that this methodology could be used to define alternative and efficient route corridors, with particular emphasis on selection of the least-cost route and prioritization of repair.     

Impact of lead contamination on the engineering properties of clayey soil

Clay liners are widely used as barriers to arrest the migration of pollutants. These liners are subjected to leaching of various chemicals and hazardous wastes. Migration of heavy metals through the liner material may lead to changes in the soil properties and this, in turn, may affect the performance of liners. In this paper, the change in index and engineering properties of clayey soil due to migration of lead is presented. Pronounced changes in soil properties are noticed when the soil is contaminated with high concentrations of lead. The findings from the present study are important while designing liners in landfills used for containment of pollution due to heavy metals and hazardous wastes.     

Keni — the Vanishing Wonder Well

This paper discusses the ancient perennial water abstraction structures—Keni—developed by the tribal communities in Wayanad district, Kerala, southwest coast of India. Keni is shallow wooden abstraction structure built in the soil zone where the water table is near or above the ground level. These traditional water abstraction structures are perfect example of water harvesting and water purification. As a preliminary assessment, a detailed survey of the Keni in the district is conducted and the result of the chemical analysis of water from the Keni is presented in this paper. Water from Kenis meet the drinking water quality standards prescribed by the BIS.     

Stable isotope characteristics of precipitation of Pamba River basin,Kerala, India

Stable isotope composition of precipitation from Pamba River basin, Kerala, India, is evaluated to understand the role of spatial and temporal variations on rainwater isotope characteristics. Physiographically different locations in the basin showed strong spatial and temporal variations. δ ¹⁸O varied from ?7.63 to ?1.75 ‰ in the lowlands; from ?9.32 to ?1.94 ‰ in the midlands and from ?11.6 to ?4.00 ‰ in the highlands. Local Meteoric Water Lines (LMWL) for the three regions were determined separately and an overall LMWL for the whole of the basin was found to be δ ²H = 6.6 (±0.4) δ ¹⁸ O+10.4 (±2.0). Altitude effect was evident for the basin (0.1 ‰ for δ ¹⁸O and 0.8 ‰ for δ ²H per 100 m elevation), while the amount effect was weak. The precipitation formed from the marine moisture supplied at a steady rate, without much isotopic evolution in this period may have masked the possible depletion of heavier isotopes with increasing rainfall. Consistently high d-excess values showed the influence of recycled vapour, despite the prevailing high relative humidity. The oceanic and continental vapour source origins for the south-west and north-east monsoons were clearly noted in the precipitation in the basin. Rayleigh distillation model showed about 30% rainout of the monsoon vapour mass in the basin.     

Hard electron energy distribution in the relativistic shocks of gamma-ray burst afterglows

Particle acceleration in relativistic shocks is not a very well understood subject. Owing to that difficulty, radiation spectra from relativistic shocks, such as those in gamma-ray burst (GRB) afterglows, have been often modelled by making assumptions about the underlying electron distribution. One such assumption is a relatively soft distribution of the particle energy, which need not be true always, as is obvious from observations of several GRB afterglows. In this paper, we describe modifications to the afterglow standard model to accommodate energy spectra which are 'hard'. We calculate the overall evolution of the synchrotron and Compton flux arising from such a distribution. We also model two afterglows, GRB010222 and GRB020813, under this assumption and estimate the physical parameters.     

Explosive and Radio-Selected Transients: Transient Astronomy with Square Kilometre Array and its Precursors

With the high sensitivity and wide-field coverage of the Square Kilometre Array (SKA), large samples of explosive transients are expected to be discovered. Radio wavelengths, especially in commensal survey mode, are particularly well-suited for uncovering the complex transient phenomena. This is because observations at radio wavelengths may suffer less obscuration than in other bands (e.g. optical/IR or X-rays) due to dust absorption. At the same time, multiwaveband information often provides critical source classification rapidly than possible with only radio band data. Therefore, multiwaveband observational efforts with wide fields of view will be the key to progress of transients astronomy from the middle 2020s offering unprecedented deep images and high spatial and spectral resolutions. Radio observations of Gamma Ray Bursts (GRBs) with SKA will uncover not only much fainter bursts and verifying claims of sensitivity-limited population versus intrinsically dim GRBs, they will also unravel the enigmatic population of orphan afterglows. The supernova rate problem caused by dust extinction in optical bands is expected to be lifted in the SKA era. In addition, the debate of single degenerate scenario versus double degenerate scenario will be put to rest for the progenitors of thermonuclear supernovae, since highly sensitive measurements will lead to very accurate mass loss estimation in these supernovae. One also expects to detect gravitationally lensed supernovae in far away Universe in the SKA bands. Radio counterparts of the gravitational waves are likely to become a reality once SKA comes online. In addition, SKA is likely to discover various new kinds of transients.     

Key morphological changes and their linkages with stream power and land-use changes in the Upper Tapi River basin,India

Knowledge on spatio-temporal variations in planform, hydraulic geometry, and bed-level variations of alluvial streams is required for planning and development of hydraulic structures and bank protection works. In the current study, a Geographic Information System (GIS) has been used to analyze topographical maps, multi-temporal remotely sensed imagery, and hydrologic and hydraulic data to extract the morphological parameters of the Upper Tapi River, India. The river has been found to have consistent migration towards the northern direction, with erosion/deposition on right/left banks. The river has not experienced any major meander except in the lower reaches of the Upper Tapi Gorge and minor braiding conditions at the location where the river emerges from mountainous topography to the plain region. The analyzed river cross sections were found to be depth dominated, and contain large flows within the channel banks. The cross-sections exhibited moderate channel bed adjustments in 1994, 2006, and 2007 wherein excessive sediment flux and stream power were capable of causing morphological changes in the river. High intensity rainfall in the subcatchment resulted in high sediment flux into the river during 1994, which was reported to cause significant aggradation at the downgauging station. The analysis of sediment flux into the river in conjunction with decadal land use land cover, revealed that sediment yield from the catchment was reduced during 2000–2010 due to an increase in water bodies in the form of minor hydraulic structures. The entry of comparatively less sediment laden water into the river, resulted in moderate bed degradation especially in 2006 and 2007 as observed at the downstream station. The methodology applied in the current study is generic in nature and can be applied to other rivers to identify their morphological issues.