BISTABLE PERFORMANCE OF CLOSELY COUPLED TWIN STRIPE LASERS.

Results are given for bistable effects in closely coupled twin stripe lasers. These devices use controlled adjustment of asymmetric transverse optical gain to obtain bistability. Various bistable effects have been observed. Initially the authors reported a large light/current hysteresis loop obtained as the drive current to the laser was raised and lowered. Information concerning the bistable mechanisms was then obtained by applying small current pulses into each stripe. It was thus found that bistability was involved with the switching from one stable laser waveguiding mechanism to another. More recently the experimental measurement system has been much improved. Through the use of computer control of motorised micromovements and computer controlled data management, time resolved near and far field, and charge carrier concentration distribution measurements have been more accurately carried out. The paper will outline briefly this system, and report on how it has helped to reveal new mechanisms of bistability in twin stripe lasers.

Preparation of an extruded fish snack using twin screw extruder and the storage characteristics of the product

A value-added extruded fish product was prepared with corn flour (80%) and fish (sciaenid) powder (20%), using a twin-screw extruder. The effect of different parameters like moisture, temperature, fish powder concentration, speed of the extruder and die-diameter on expansion ratio and crisp texture were studied. The storage characteristics of the final product were studied using three different types of packaging under nitrogen flushing. The study revealed that aluminum foil is the best packaging material to keep the product acceptable for more than three months.

Some socio-economic aspects of the fishermen of twin pronged floodplain wetlands in West Bengal

A socio-economic investigation was carried out in two fishermen cooperative societies namely Purba Helatala Fishermen Co-operative Society (E-1), Barhal Fishermen Co-operative Society (E-2), under Maldah district, West Bengal to which the beels (flood plains) under study belong. A total of 132 member fishermen, which constituted the sample, were personally interviewed. The age group of the fishermen of the sample in E-1 varied between 20 and 66 years whereas in E-2 it was 22 and 61 years. All the members of the sample belonged to Scheduled Caste (SC) community. The primary occupation of all the respondents of both the beels was observed to be fishing (100%). Maximum number of illiterate respondents was observed to 56% in E-2 and 35% in E-1. It has been observed that as many as 38.3% of fishermen were having fishing experience which ranging from 16 to 20 years in E-1 whereas it was 6 - 10 years (36.1%) in E-2. Maximum number of fishermen lived in thatched houses (41.66%) in E-1 whereas in E-2 most of them lived in houses made of corrugated tin/tile shed (41.66%). As many as 41.55% of E-1 and 30.55% of E-2 used dug-out canoes for their fishing. Maximum number of fishermen used cast net with individualistic approach (100%) followed by Gill net (E-1:41.56% and E-2:55.55%). Most of the fishermen of the sample participated in fishing activities for 241 to 270 days (41.66%) in E-2 whereas it was 211 to 240 days (33.33 %) in E-1 in a year. During fishing season as many as 40.0% of the respondents of E-1 earned on an average Rs. 801.00 to Rs. 900.00 per month whereas it was Rs. 901.00 to Rs.1,000.00 (43.05%) in case of E-2. A section of fishermen of the sample borrowed money often (51.6%) E-1 whereas it was most often (27.27%) of E-2. The respondents of E-2 made regular repayment of the loan to the maximum extent (79.48%) whereas it was 57.44% in E-1. Higher fish production vis-a-vis higher income for the fishermen was observed in the beel (E2) having close characteristic.

The effect of a twin tunnel on the propagation of ground-borne vibration from an underground railway

Accurate predictions of ground-borne vibration levels in the vicinity of an underground railway are greatly sought after in modern urban centres. Yet the complexity involved in simulating the underground environment means that it is necessary to make simplifying assumptions about this system. One such commonly made assumption is to ignore the effects of neighbouring tunnels, despite the fact that many underground railway lines consist of twin-bored tunnels, one for the outbound direction and one for the inbound direction. This paper presents a unique model for two tunnels embedded in a homogeneous, elastic fullspace. Each of these tunnels is subject to both known, dynamic train forces and dynamic cavity forces. The net forces acting on the tunnels are written as the sum of those tractions acting on the invert of a single tunnel, and those tractions that represent the motion induced by the neighbouring tunnel. By apportioning the tractions in this way, the vibration response of a two-tunnel system is written as a linear combination of displacement fields produced by a single-tunnel system. Using Fourier decomposition, forces are partitioned into symmetric and antisymmetric modenumber components to minimise computation times. The significance of the interactions between two tunnels is quantified by calculating the insertion gains, in both the vertical and horizontal directions, that result from the existence of a second tunnel. The insertion-gain results are shown to be localised and highly dependent on frequency, tunnel orientation and tunnel thickness. At some locations, the magnitude of these insertion gains is greater than 20 dB. This demonstrates that a high degree of inaccuracy exists in any surface vibration prediction model that includes only one of the two tunnels. This novel two-tunnel solution represents a significant contribution to the existing body of research into vibration from underground railways, as it shows that the second tunnel has a significant influence on the accuracy of vibration predictions for underground railways. © 2011 Elsevier Ltd. All rights reserved.

Parallel twin-body trawl for shrimps, its design and efficiency

Comparative studies with a new 17 m parallel twin-body trawl and a 17 m bulged belly trawl conducted off Cochin during 1974-77 are reported. The parallel twin body trawl showed an increase of 28% in catch over that of bulged belly with a break up of 39.9% and 23.1 % for prawns and fishes respectively. The increase in catch is attributed to the extra wide mouth opening (26.6 %) of the parallel twin-body trawl. Parallel twin-body trawl had 8.96% lesser resistance which resulted in lower utilization of horse power.

Identification of monozygotic twin chimpanzees by microsatellite analysis

Zygosity determination is important for epidemiological, biological, obstetric, and prognostic studies in both human and nonhuman primates. In this study, microsatellite loci were used to screen a pair of chimpanzee (Pan troglodytes) twins and their parents. The twins share identical alleles at all loci tested. The probability of dizygotic origin is estimated to be 2.9 x 10(-11). Even after excluding linkage of loci on the same chromosome, the probability is still low enough (3.7 x 10(-9)) to exclude dizygotic origin. MHC typing was also done on Patr-DRB and Patr-DQB loci and the twins share identical alleles at both loci, consistent with the microsatellite results. Together these results demonstrate a monozygotic origin for the chimp twins. Our results suggest that microsatellite analysis is a powerful method for zygosity determination, which can be screened reliably and efficiently. Am. J. Primatol. 52:101-106, 2000. (C) 2000 Wiley-Liss, Inc.

Twin trawling for shrimp with dummy doors

Twin trawling; a new concept in shrimp trawling is described in this paper. It essentially involves towing of two trawls of equal size connected in sequence at the inner head and foot rope legs and using a pair of outer otter boards and central neutral door or dummy door with triple bridles and single tow warp. A comparative study with conventional stern trawling using a standard 13.7 m four seam shrimp trawl and two 6 8 m standard four seam trawls as twin-rig has shown considerable reduction in the utilization of power (20 %) with better efficiency in shrimp fishing.

Run-up of solitary waves on twin conical islands using a boussinesq model

This paper investigates the interaction of solitary waves (representative of tsunamis) with idealized flat-topped conical islands. The investigation is based on simulations produced by a numerical model that solves the two-dimensional Boussinesq-type equations of Madsen and Sørensen using a total variation diminishing Lax-Wendroff scheme. After verification against published laboratory data on solitary wave run-up at a single island, the numerical model is applied to study the maximum run-up at a pair of identical conical islands located at different spacings apart for various angles of wave attack. The predicted results indicate that the maximum run-up can be attenuated or enhanced according to the position of the second island because of wave refraction, diffraction, and reflection. It is also observed that the local wave height and hence run-up can be amplified at certain gap spacing between the islands, owing to the interference between the incident waves and the reflected waves between islands. © 2012 American Society of Mechanical Engineers.

Adaptive enhancement of multimode fibre bandwidth by twin-spot offset launch

A binary grating on a Spatial Light Modulator generates twin antiphase spots with adjustable positions across the core of a multimode fibre allowing adaptive excitation of antisymmetric mode-groups for improving modal dispersion or modal multiplexing. © 2011 IEEE.

Numerical simulation of long-term twin-tunnel behaviour at St James's park

The twin-tunnel construction of the Jubilee Line Extension tunnels beneath St James's Park was simulated using coupled-consolidation finite-element analyses. The effect of defining different permeabilities for the final consolidation stage was investigated, and the performance of a fissure softening model was also evaluated. The analyses suggested an unexpectedly high permeability anisotropy for soil around the tunnel crown, possibly due to stress-induced permeability changes, or low-permeability laminations. Also, the permeability profile and lining conductivity were found to differ between the tunnels. Inclusion of the fissure model gave a narrower settlement trough, more alike that in the field, by preferentially softening simple shear behaviour. Long-term settlements at the site continue to increase at an unexpectedly high rate, suggesting the possibility of creep or unexpected soil softening during excavation. © 2012 Taylor & Francis Group.