Shape-changing Collisions of Coupled Bright Solitons in Birefringent Optical Fibers

Wecritically review the recent progress in understanding soliton propagation in birefringent optical fibers.By constructing the most general bright two-soliton solution of the integrable coupled nonlinear Schroedinger equation (Manakov model) we point out that solitons in birefringent fibers can in general change their shape after interaction due to a change in the intensity distribution among the modes even though the total energy is conserved. However, the standard shape-preserving collision (elastic collision) property of the (1+1)-dimensional solitons is recovered when restrictions are imposed on some of the soliton parameters. As a consequence the following further properties can be deduced using this shape-changing collision. (i) The exciting possibility of switching of solitons between orthogonally polarized modes of the birefringent fiber exists. (ii) When additional effects due to periodic rotation of birefringence axes are considered, the shape changing collision can be used as a switch to suppress or to enhance the periodic intensity exchange between the orthogonally polarized modes. (iii) For ultra short optical soliton pulse propagation in non-Kerr media, from the governing equation an integrable system of coupled nonlinear Schroedinger equation with cubic-quintic terms is identified. It admits a nonlocal Poisson bracket structure. (iv) If we take the higher-order terms in the coupled nonlinear Schroedinger equation into account then their effect on the shape-changing collision of solitons, during optical pulse propagation, can be studied by using a direct perturbational approach.Comment: 14 pages, ROMP31, 4 EPS figure

Self-consistency of relativistic observables with general relativity in the white dwarf-neutron star binary pulsar PSR J1141-6545

Here we report timing measurements of the relativistic binary pulsar PSR J1141-6545 that constrain the component masses and demonstrate that the orbital period derivative \dot Pb = (-4+/-1)x10^-13 is consistent with gravitational wave emission as described by the general theory of relativity. The mass of the neutron star and its companion are 1.30+/-0.02 Mo and 0.986+/-0.020 Mo respectively, suggesting a white dwarf companion, and extending the range of systems for which general relativity provides a correct description. On evolutionary grounds, the progenitor mass of PSR J1141-6545 should be near the minimum for neutron star production. Its mass is two standard deviations below the mean of the other neutron stars, suggesting a relationship between progenitor and remnant masses.Comment: 10 pages, 2 figures, revised version to Ap J Letter

The resources of the Indian mackerel - characteristics, exploitation and future prospects

The Indian mackerel contributed to an annual average (1993-'99) catch of 2.17 lakh tonnes (t). The west coast landed about 80% of its total catch and remaining by the east coast. The resource is rich in upwelling areas of the west coast with a catch contribution of 38.68% from Kerala followed by Kamataka and Maharashtra. The fishery is characterized by annual fluctuations in the catch ranging from 0.14 lakh t in 1968 to 2.9 lakh t in 1989. The annual fluctuations do not show any pattern; whereas the decade! trends show a cyclic pattern of ups and downs. The fluctuations are more pronounced along the upwelling areas of the west coast. In 1990s, there was a quantum leap in the annual catch chiefly due to the introduction of large seine nets and motorization of country crafts. The increase was maximum in Kerala, moderate in Maharashtra and poor in Kamataka. Along the east coast also fishery showed considerable improvement. Of late, the role of trawl net in the mackerel fishery is gaining importance. The surface fishery using large seines along the upwelling areas seems to depend very much on the intensity and duration of upwelling which is perhaps causing the fluctuations in catch rather than the variations in the abundance of the resource. The behaviour of the fish to ascend with upwelling and spreading to deeper waters with sitiking of thermocline seem to control exploitation and protect the resilience of the stocks. Perhaps the richness of the resource is much stronger than hitherto believed. With proper management the production can reach further heights

Influence of process variables on precursor and carbon fibres

Special grade acrylic fibres have been developed from PAN-co-methyl acrylate. The effect of molecular weight and distribution have heen studied in relation to precursor and carbon fibre propcrties. The influence of process variables such as coagulation bath temperature, stretching, etc. on strength and modulus of fibres have been studied

Transient radio emisison from SAX J1808.4-3658

We report on the detection of radio emission from the accretion-powered X-ray millisecond pulsar SAX J1808.4-3658, using the Australia Telescope Compact Array. We detected a ~0.8 mJy source at the position of SAX J1808.4-3658 on 1998 April 27, approximately one day after the onset of a rapid decline in the X-ray flux; no such source was seen on the previous day. We consider this emission to be related to the radio emission from other X-ray binaries, and is most likely associated with an ejection of material from the system. No radio emission was detected at later epochs, indicating that if SAX J1808.4-3658 is a radio pulsar during X-ray quiescence then its monochromatic luminosity must be less than L(1.4 GHz) ~6 mJy/kpc^2.Comment: 6 pages, uses emulateapj.sty, one embedded PS figure. Accepted to ApJ Letter

Screening, production, and characterization of biologically active secondary metabolite(s) from marine Streptomyces sp. PA9 for antimicrobial, antioxidant, and mosquito larvicidal activity

1319-1326Bioprospecting of actinobacteria from understudied ecosystems is a promising source for extracting novel bioactive metabolites. A study was undertaken to characterize and analyze the bio-efficacy of actinobacterial extract for antimicrobial, larvicidal, and antioxidant activities. Seven morphologically different actinobacterial cultures isolated from mangrove rhizosphere sediment near Parangipettai, South India, were tested for antimicrobial activity. Bioactive metabolites from one potential strain PA9 were produced by submerged fermentation. The selected Streptomyces sp. PA9 was subjected to the production of crude extract for antimicrobial, larvicidal, and antioxidant activity. The actinobacterial compound was characterized by Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography–mass spectrometry (GC–MS). The PA9 actinobacterial crude extract showed best antimicrobial activity against clinical bacteria, Salmonella typhi (21.6 ± 0.88 mm) and fungi, Candida albicans (26.6 ± 0.88 mm). The PA9 extract showed significant larvicidal activity against Culex quinquefasciatus with LC50=173.21 µg/ml and r2=0.841. The PA9 extract also exhibited antioxidant activity from DPPH (72%) and nitric oxide free radicals (85%). The characterization of the PA9 extract by FTIR analysis showed the presence of possible functional groups. Active compounds were isolated by HPLC and GC–MS with major and minor peaks observed on the basis of retention time. The bio-efficacy of PA9 has warranted further studies to develop a baseline for the drug development

Exact soliton solutions of coupled nonlinear Schr\"odinger equations: Shape changing collisions, logic gates and partially coherent solitons

The novel dynamical features underlying soliton interactions in coupled nonlinear Schr{\"o}dinger equations, which model multimode wave propagation under varied physical situations in nonlinear optics, are studied. In this paper, by explicitly constructing multisoliton solutions (upto four-soliton solutions) for two coupled and arbitrary $N$-coupled nonlinear Schr{\"o}dinger equations using the Hirota bilinearization method, we bring out clearly the various features underlying the fascinating shape changing (intensity redistribution) collisions of solitons, including changes in amplitudes, phases and relative separation distances, and the very many possibilities of energy redistributions among the modes of solitons. However in this multisoliton collision process the pair-wise collision nature is shown to be preserved in spite of the changes in the amplitudes and phases of the solitons. Detailed asymptotic analysis also shows that when solitons undergo multiple collisions, there exists the exciting possibility of shape restoration of atleast one soliton during interactions of more than two solitons represented by three and higher order soliton solutions. From application point of view, we have shown from the asymptotic expressions how the amplitude (intensity) redistribution can be written as a generalized linear fractional transformation for the $N$-component case. Also we indicate how the multisolitons can be reinterpreted as various logic gates for suitable choices of the soliton parameters, leading to possible multistate logic. In addition, we point out that the various recently studied partially coherent solitons are just special cases of the bright soliton solutions exhibiting shape changing collisions, thereby explaining their variable profile and shape variation in collision process.Comment: 50 Pages, 13 .jpg figures. To appear in PR

Pulsar Radio Emission Altitude from Curvature Radiation

We assume that the relativistic sources moving along the dipolar magnetic field lines emit curvature radiation. The beamed emission occurs in the direction of tangents to the field lines, and to receive it, the sight line must align with the tangent within the beaming angle 1/gamma, where gamma is the particle Lorentz factor. By solving the viewing geometry in an inclined and rotating dipole magnetic field, we show that, at any given pulse phase, observer tends to receive radiation only from the specific heights allowed by the geometry. We find outer conal components are emitted at higher altitudes compared to inner components including the core. At any pulse phase, low frequency emission comes from higher altitudes than high frequency emission. We have modeled the emission heights of pulse components of PSR B0329+54, and estimated field line curvature radii and particle Lorentz factors in the emission regions.Comment: 14 pages, 3 figures. Accepted for Astrophysical Journal, 200