On the distinction between Penaeus indicus H. Milne Edwards and Penaeus merguiensis De Man (Crustacea : Penaeidae) with special reference to juveniles

Clear-cut differences between the juveniles of Penaeus indicus and Penaeus merguiensis are pointed out in this paper. On the basis of the colour pattern of the antennal flagella, antennular flagella and the pleopods, and the disposition of the rostral teeth it is now possible to identify the juveniles of P. indicus and P. merglliensis with certainty

Cepstrum Analysis: An Advanced Technique in Vibration Analysis of Defects in Rotating Machinery

Conventional frequency analysis in machinery vibration is not adequate to find out accurately defects in gears, bearings, and blades where sidebands and harmonics are present. Also such an approach is dependent on the transmission path. On the other hand, cepstrum analysis accurately identifies harmonics and sideband families and is a better technique available for fault diagnosis in gears, bearings, and turbine blades of ships and submarines. Cepstrum represents the global power content of a whole family of harmonics and sidebands when more than one family of sidebands are presents at the same time. Also it is insensitive to the transmission path effects since source and transmission path effects are additive and can be separated in cepstrum. The concept, underlying theory and the measurement and analysis involved for using the technique are briefly outlined. Two cases were taken to demonstrate advantage of cepstrum technique over the spectrum analysis. An LP compressor was chosen to study the transmission path effects and a marine gearbox having two sets of sideband families was studied to diagnose the problematic sideband and its severity

Isothermal and Near Isothermal Processing of Titanium Alloys

Isothermal and near isothermal forging are specialized metal processing techniques which are used for producing critical aeroengine components out of advanced materials such as titanium alloys. The process can be used to produce net / near net shape components leading to optimum utilization of materials. As titanium alloys are highly sensitive to temperature and strain rate, these processes help to deform them under slow and controlled strain rates.  Further, these processes can be combined with other conventional and non conventional metal forming processes to refine the microstructure. For example, multiaxial isothermal forging coupled with pack rolling can be used to produce thin sheets out of titanium alloys with submicron grain size. The refined structure exhibits superplastic characteristics at low temperatures and high strain rates. This lower temperature superplastic characteristic can be exploited to establish technologies for producing various components. The paper throws light on the capabilities of isothermal forging process and its variants.Defence Science Journal, 2011, 61(1), pp.72-80, DOI:http://dx.doi.org/10.14429/dsj.61.32

Effect of Heat Transfer on Free Surface Flow of a Jeffrey Fluid over a Deformable Permeable Bed

Free surface flow of a conducting Jeffrey fluid in a channel is investigated. The channel is bounded below by a finite deformable porous layer. The governing equations are solved in the free flow region and deformable porous layer. The expressions for the velocity field and solid displacement are obtained. The effects of the Jeffrey parameter, viscosity parameter, the volume fraction component of the fluid on the velocity displacement and mass flux are discussed. It is found that the velocity increases with the increase in the non-Newtonian Jeffrey parameter. Keywords: Free surface flow; Jeffrey fluid; Porous layer; Permeable bed

The crab fishery resources of India

Crabs support a sustenance fishery of appreciable importance, although, its present status is not comparable with that of those major crustacean fisheries such as prawns and lobsters. In addition to the marine fishery, large number of crabs are landed from the estuaries and brackish water lakes adjoining the coastal areas. To meet the increasing demand for frozen crab meat and to develop an organised crab fishing industry, an evaluation of the existing resources is quite essential. The fishery at present is supported mostly by the edible crabs belonging to the family Portunidae and available information on the various aspects of the fishery show that the fishing is restricted to the inshore areas mostly by operations of small indigenous crafts and gears. In most of the places crabs form an ancillary catch along with other crustaceans and fishes, intensive fishing for crabs alone existing only in selected areas. The annual catch which is less than 4,000 tonnes is subject to marked fluctuations. However, the distribution of the species and the trend in production indicate scope for further expansion. An attempt is made here to study the abundance and production of crabs from three general areas, viz., west coast of India, Gulf of Mannar and Palk Bay and the northern part of the east coast from Point Calimere to Sunderbans with a view to understand the crab resources of the country. The estimation of the potential resources of the offshore waters as indicated by the trawler catches is also mide. The need for biological investigattions on factors governing yield and crab population is stressed

Crustacean resources of the Lakshadweep islands

Information on the crustacean resources of Lakshadweep is limited to only a few faunistic reports on crabs, prawns, lobsters and stomatopods (Alcock, 1895, 1896, 1998, 1899, 1900; Borradaile, 19C3a, 1903b, 1903c, 1903d, 19o6a, 1906b; Sankarankutty, 196); Thomas 1970a, 1970b, Meiyappan and Kathirvel, 1978; Piilai era/, 1984 and Shanbhogue, 1986) A total of 132 species of brachyuran crabs mostly belonging to Calappidae, Majidae, Parthenopidae, Portunidae, Xanthidae, Ocypodidae and Grapsidae, 4 species of palinurid lobsters, 2 species of scyllarid lobsters, 6 species of penaeid prawns and 7 species of stomatopods have been recorded so far from these islands

Spawning concentrations of the sardine, Sardinella gibbosa (Bleeker), off the north Andhra Coast in March - April 1969

Adult Sardinella gibbosa in pre-spawning and spawning stages were observed in March 1969 in Waltair - Kakinada region from catches made 15-20 km from shore. Plankton collections made during this period off Kakinada contained eggs which have been assigned to S. gibbosa based on circumstantial evidence and resemblances. Most of the stomachs of 5. ^/'66oM examined during the period were either empty or contained very little food. These indicate that there was extensive spawning of the species off the North Andhra coast in March-April 1969

On the commercial trawl fisheries off Kakinada During 1967-70

Analysis of the trawler landings during 1967-70 showed the existence of rich prawn grounds of Kakinada, particularly in the shallower regions not exceeding 20 m in depth. In the Ashing ground extending in a depth zone, 5-40 m, the important fishery resources were prawns (forming 24% of the total catch), sciaenids (14.8%), Nemtpterus (9.7%), elasmobranchs (7.1%), silverbellies (6.4%), Laclarius laetarius (4,4%), ribbonflsh (4.4%), clupeids (3.8%), eels (2.6%), carangids (2.6%), and other small miscellaneous fishes. Two peaks were observed in the total catch, one in February-April, which is tiie more predominant (HW, and the other in August-November. The catch rates, seasonal fluctuations and detailed species composition are dealt with in the paper

Stock assessment of Penaeus spp. off the east coast of India

Penaeid prawn Sandingi increased from 20 744 tonnes in 1980 to 37 410 tonnes in 1986 and then declined to 31 029 tonnes in 1989 (average 29 642 tonnes), Prawns of the genus Penaeus supported good fishery all along the east coast of India forming 40% of the penaeid prawn landings. lite three commercially important species, viz. Penaeus indicus, P. semisulcatus and P. monodon, contributed 5 849, 4 387 and 639 tonnes, respectively, to the annual penaeid prawn landings of the east coast. Tamil Nadu with annual landings of 7 880 tonnes was the major contributor to the Penaeus landings of the east coast followed by Andhra Pradesh (1 639 tonnes), Orissa (387 tormes), Pondicherry (119 tonnes) and large trawlers (850 tonnes). Past work on biological aspects such as postlarval immigration, juvenile emigration, i'ood and feeding habits and maturation and spawning has been reviewed. Age and growth parameters of P.indicus and P. semisulcatus were estimated by employing ELEFAN I method. Population estimates of P.indicus and P. semisulcatus showed very high fishing mortality and declining yidd while those of P. monodon indicated scope for increasing the landings. HSY estimates for P. indicus, P. semisulcatus and P. monodon are S 961 tonnes, 4 681 tonnes and 652 tonnes respectively. Species-wise and state-wise catch quotas have been suggested based on MSY and the present landings

Magnitude of lobster resources of India

Lobsters inhabit our tropical waters in different concentrations in some parts of our coasts. The average annual catch of lobsters during the 10 year period of 1975-84 was 1763 toni.es forming 0.82% among the crustaceans ano 0.12 % in the total marire fish landings. Of these 73.56 % was from Gujarat and Maharashtra and 19.45 % from Tamil Nadu. Of the 6 species of spiny lobsters recorded, only 3 of them ana one species of slipper lobster support the fishery of this country. The catches of Panulirus polyphagus and Thenus orientalis were substantial forming about 46.71% and 46.44% respectively. The catch of Panulirus homarus was poor contributing to only 5.89% while that of Panulirus ornatus was almost negligible, being 0.96%. The magnitude of the catch for P. homarus and P. ornatus is so small that they should not be exploited more than the existing rate from the present fishing grounds. Either new grounds have to be found or the population should be raised by culture practices to meet the demand of the market