A preliminary account and review of the simple methods for determining the operational parameters of fishing gear, underwater, with notes on its application

An account and review of the simple methods for determining the operational parameters of fishing gear, underwater, such a tilt of otter boards (outwards or inwards, forwards or afterwards), vertical height of net, its horizontal spread, angle of divergence at bosom, spread between wing tips, angle of inclination of danlenos, butterfly, slope of legs and sweep-line has been given. The relationship of distance between the otter boards spread and the vertical height of net has been obtained as generally linear. The possibilities of regulating the vertical height of net (dependent variate) and spread of otter boards (independent variate) for increasing the fishing efficiency has been discussed. The angle of attack of oval shaped otter boards used during the operations still remain undetermined, however, it has been explained how the best angle of attack for increasing the efficiency of gear can be obtained by regulating the ratio of depth to warp for a given net. The inadequacy of the mere indices of catch per hour of trawling in comparing the relative efficiency of trawls in gear research studies has been indicated. The importance of estimating the operational parameters and its application to commercial fisheries depending upon the distribution pattern of fish and in gear research has been discussed. The efficiency of the jelly bottle method has been compared statistically with the observations made on the trawl gear underwater with instruments.

On the relative utility of different methods to increase the vertical height in an otter trawl

Comparative fishing experiments to study the relative utility of different methods for increased vertical spread of bottom trawl and the availability of off bottom fishes in the region were made using gussets, kite, separate float line and side panels on a two seam net. The catch rates as well as composition of fish were studied. The opening of the trawl mouth, both horizontally and vertically, under different operating gears and towing tension on warps were measured and estimated for comparison purposes. Better catch rate with good quality fishes was obtained with the gear operated with separate float line. With kite, the vertical spread was increased with less catch indicating poor concentration of off bottom fishes.

Articulated wooden blades for a horizontal-axis wind turbine. Design, construction and testing.

A pair of blades were constructed following a Tapered Chord, Zero Twist pattern after Anderson. The construction uses the Wood Epoxy Saturation Technique, with a solid Beech main spar and leading edge joined together with laminated veneers of beech forming a D-section; the trailing edge is formed from millimetre ply skins, foam filled to resist compressive loads. This construction leads to an extremely light, flexible blade, with the centres of gravity and torsion well forward, giving good stability. Each blade has three built-in strain gauges, alowing flapwise bending to be measured. Stiffness, and natural frequencies, were measured, to input to a numerical computer model to calculate blade deformation during operation, and to determine stability boundaries of the blade. Preliminary aerodynamic performance measurements are presented and close agreement is found with theory.

ANALYSIS OF A PROBLEM INVOLVING RADIAL CONSOLIDATION.

An analytical solution is presented for the vertical consolidation of a cylindrical annulus of clay with horizontal drainage occurring to concentric internal and external drainage boundaries. Numerical results are given for various ratios of internal and external radii and it is shown that solutions for conventional one-dimensional consolidation, and for consolidation of a cylindrical block of clay with drainage only to the outer cylindrical boundary form extremes to the analysis presented here. An application of the solution to the estimation of horizontal permeability of clay is briefly described.

Vertical distribution of molluscs in the intertidal area in and around Mumbai, India

Vertical distribution of intertidal molluscs in and around Mumbai had been studied. Each species has an upper and lower limit of distribution along the vertical intertidal gradient and are concentrated at particular levels or zones where they find optimum living conditions. Zonation of the intertidal area with reference to molluscs at rocky shores of TIFR, Bandstand and NCPA has similarities. However, there is no similarity in zonation among rocky, sandy and muddy shores. Rocky intertidal zones are more diverse and dense in terms of molluscs. The mid and lower littoral zones have rich diversity. The upper littoral zone at some sites, especially Girgaon chowpatty is totally devoid of molluscs due to anthropogenic activities. Gafrarium divaricatum, Nerita oryzarum, N. polita and Neritina crepidularia have established themselves in all three marked zones, indicating their power to adjust with the wide fluctuations in surrounding environmental conditions.

SOME MEASUREMENTS OF THE PERMEABILITY OF KAOLIN.

This paper reports an experimental investigation of the vertical and horizontal permeabilities of speswhite kaolin clay. The permeabilities were measured using falling head permeability tests. A modification to a conventional oedometer was devised so that either vertical or horizontal permeabilities could be determined. It was found that the vertical and horizontal permeabilities of the clay slurry were similar, but that as the clay was consolidated one dimensionally the anisotropy of the clay fabric resulted in a greater horizontal permeability than the vertical permeability at any void ratio. Both permeabilities were uniquely related to the void ratio.

Post-processing of vertical-cavity surface-emitting lasers for transverse mode and polarization control

The operation on how high quality single-mode operation can be readily attained on etching circles in multimode devices is discussed. Arrays of such spots can also be envisaged. Control of the polarization state is also achieved by use of deep line etches. The output filaments and beam shapes of the conventional multimode vertical cavity surface emitting lasers (VCSEL) is shown to be engineered in terms of their positions, widths, and polarizations by use of focused ion beam etching (FIBE). Several GaAs quantum well top-emitting devices with cavity diameters of 10 μm and 18 μm were investigated.

Mode control in vertical-cavity surface-emitting lasers by post-processing using focused ion-beaih etching

Single-mode emission is achieved in previously multimode gain-guided vertical-cavity surface-emitting lasers (VCSEL's) by localized modification of the mirror reflectivity using focused ion-beam etching. Reflectivity engineering is also demonstrated to suppress transverse mode emission in an oxide-confined device, reducing the spectral width from 1.2 nm to less than 0.5 nm.

Mode-controlled vertical cavity surface emitting lasers for bandwidth enhancement of multimode fibre links

A GaAs Vertical Cavity Surface Emitting Laser (VCSEL) that generates controlled modes offset from the center is described. The device is modulated with a 27-1 pseudo-random bit sequence and its output is transmitted along a 1 km length of multimode fiber (MMF). Open eyes are obtained for data rates as high as 1.4Gb/s. The transmission bandwidth increases by a factor of 4 over over-filled launch (OFL). This enhancement is stable against environment influences on the fiber.

High bandwidth multimode fiber links using subcarrier multiplexing in vertical-cavity surface-emitting lasers

The usage of subcarrier multiplexing (SCM) techniques to allow link transmission in excess of the specified fiber bandwidth is described. A series of 200-Mbit/s channels with carrier frequencies of up to more than twenty times the 3-dB fiber bandwidth have been successfully used, the maximum being limited by the available electronics. To assess the transmission of the fiber, digitally modulated channels are placed on high frequency carrier signals and then used to modulate a vertical-cavity surface-emitting lasers (VCSEL).

Mechanism of polarization pinning in vertical cavity surface emitting lasers using focused ion beam etching

Photoluminescence experiments have identified strain as the origin for polarization pinning in vertical cavity surface emitting lasers post-processed by focused ion beam etching. Theoretical models were applied to deduce the strain in devices. Post-annealing was used to optimize polarization pinning.

Spatial emission control of vertical cavity surface emitting lasers to provide bandwidth gain in multimode fibre links using a simple alignment technique

Etched VCSEL sources are reported which avoid bandwidth collapse in multimode fibre using a simple coupling technique to control the launch. These devices have allowed better than over-filled launch bandwidth for alignment tolerances of ±7 microns.