NOPR Collection:

The design and performance characteristics of a 40 kHz mini pinger transducer for marine applications

Tue, 01 Dec 1992 00:00:00 GMT

Title: The design and performance characteristics of a 40 kHz mini pinger transducer for marine applications Authors: Saksena, T K; Jain, S K; Gupta, Reeta Abstract: A mini pinger transducer using radial mode tubular piezoceramic elements of frequency 40 kHz has been developed for intended applications in tracking of small submerged objects. The design criteria to achieve the desired frequency and directional responses for the transducer is discussed. Its performance characteristics such as the source level. transmitting sensitivity and directional response are reported. Electrical impedance characteristics of the transducer and the electro acoustical efficiency obtained are also given. The range of the device activated using 3V battery is estimated to be 50 m. Page(s): 303-305

Distribution of clay minerals in sediments of Vellar river environment, east coast of India

Tue, 01 Dec 1992 00:00:00 GMT

Title: Distribution of clay minerals in sediments of Vellar river environment, east coast of India Authors: Mohan, P M; Damodaran, K T Abstract: X-ray diffraction study of the < 2 mum clay fraction of 18 surface sediment samples from Vellar river and its surrounding environments (estuary, tidal channel and nearshore marine) indicates that montmorillonite is the most dominant clay mineral followed by kaolinite + chlorite. Illite is present only in the southern and central sectors, of the nearshore marine environment. The percentage of montmorillonite is comparatively higher in the river, estuary and tidal channel than the nearshore marine environment. Kaolinite + chlorite and illite percentages show higher amounts in nearshore than in other environments. From the analyses of various factors, it is concluded that selective transportational and depositional processes govern the distribution of clay minerals. Page(s): 300-302

Unusual thickening of collarette in Sagitta bedoti (Chaetognatha) from the polluted environments of Bombay coast

Tue, 01 Dec 1992 00:00:00 GMT

Title: Unusual thickening of collarette in Sagitta bedoti (Chaetognatha) from the polluted environments of Bombay coast Authors: Nair, Vijayalakshmi R; Nagasawa, Sachiko; Ramaiah, Neelam; Nemoto, Takahisa Abstract: Sagitta bedoti dominated the chaetognath fauna of the nearshore waters of Bombay. S. bedoti from the polluted creek environments developed an unusually bulky collarette which extended from the neck to the seminal vesicles. Such extensive development of epidermal thickening probably serves as a protective sheath to withstand the unfavourable water quality. Page(s): 296-299

Pollution assessment through trace metal analysis of sediments of four tributary rivers of Pakistan draining into the Arabian Sea

Tue, 01 Dec 1992 00:00:00 GMT

Title: Pollution assessment through trace metal analysis of sediments of four tributary rivers of Pakistan draining into the Arabian Sea Authors: Ashraf, M; Tariq, Jaleel; Jaffar, M Abstract: Concentrations of metals (Ag, As, Cd, Cr, Cu, Fe., Mn, Ni, Pb, Zn and Hg) in the bottom surfacial sediments both from the mouth of four contributory rivers draining into the Arabian Sea, Pakistan, and the adjoining coastal area are reported. No strong metal concentration variation was observed suggesting an almost identical enrichment of the metals at the sites. The sediments from the area showed maximum levels of Fe (8.47%), Mn (240 mug.g-1), Ni (128.7 mug.g-1), Pb (18.7 mug.g-1), Zn (146.2 mug.g-1) and Hg (4.10 mug.g-1) while the minimum levels found were of As (0.13 mug.g-1) and Hg (0.12 mug.g-1). The study indicated the existence of a metal pollution stress in that a large flux of heavy metals was being brought into the sea by the Hub and the Malir rivers. Page(s): 292-295