4,102 research outputs found
Vela, its X-ray nebula, and the polarization of pulsar radiation
The recent identification of the perpendicular mode of radio polarization as
the primary one in the Vela pulsar by Lai et al. (2001) is interpreted in terms
of the maser mechanism proposed by Luo & Melrose (1995). We suggest that such a
mechanism may also be operative for the parallel mode which opens up the
possibility of accounting for all types of polarization observed in pulsars. We
propose an alternative interpretation of the arcs in the nebular X-radiation
observed by Pavlov et al.(2000) & Helfand et al. (2001) with the Chandra
Observatory, and interpreted by the latter as an equatorial wind. We interpret
the arcs as traces of the particle beams from the two magnetic poles at the
shock front. We also propose that the alignment with the rotation axis of the
jet-like feature bisecting the arcs is an effect of projection on the sky plane
and that there is no physical jet along the axis of rotation.Comment: 7 pages, 3 figures; version 2; accepted for publication in A&
The observational evidence pertinent to possible kick mechanisms in neutron stars
We examine available observations on pulsars for evidence pertaining to
mechanisms proposed to explain the origin of their velocities. We find that
mechanisms predicting a correlation between the rotation axis and the pulsar
velocity are ruled out. Also, that there is no significant correlation between
pulsar magnetic field strengths and velocities. With respect to recent
suggestions postulating asymmetric impulses at birth being solely responsible
for both the spins and velocities of pulsars, single impulses of any duration
and multiple extended duration impulses appear ruled out.Comment: 7 pages. Accepted for publication in Astronomy & Astrophysic
Considerations concerning fatigue life of metal matrix composites
Since metal matrix composites (MMC) are composed from two very distinct materials each having their own physical and mechanical properties, it is feasible that the fatigue resistance depends on the strength of the weaker constituent. Based on this assumption, isothermal fatigue lives of several MMC's were analyzed utilizing a fatigue life diagram approach. For each MMC, the fatigue life diagram was quantified using the mechanical properties of its constituents. The fatigue life regions controlled by fiber fracture and matrix were also quantitatively defined
Status of crustacean fishery resources -Winter School on Impact of Climate Change on Indian Marine Fisheries held at CMFRI, Cochin 18.1.2008 to 7.2.2008
From the economic and industrial point of view, edible marine crustaceans consisting of shrimps,
lobsters are the most important constituents of the commercial fish landings in the country. Major portion
of the landings was exported in various product forms. Investigations on resources and biology of shrimps,
lobsters and other important crustaceans were initiated at the CMFRI in 1947 and since then, valuable data
had been collected. Information on catch and effort, composition of landings, species-wise details on age
and growth, food and feeding, maturation and spawning, migration and population characteristics for shrimps,
lobsters and crabs were collected from fish landing centers along the Indian coast. This voluminous database
has provided a strong foundation for assessment of edible crustacean stock, so as to suggest appropriate
regulatory measures for effective management of these resources. A comprehensive account on the fishery
and biological characteristics on edible crustaceans, and management options for their optimum exploitation
based on the research carried out by CMFRI is presented here
Commercial prospects for farming spiny lobsters
Tropical spiny lobsters are fast growing and highly adaptable to captive condition
Lobster farming in India
Spiny or rock lobsters are low volume and
high value fisheries which support some of the
most valuable marine resource worldwide. India,
earns an approximate US $ 15 million each year
through export of lobsters, mostly to Southeast
Asian countries and Japan, although less than,
3,000 tonnes is landed annually. The potential for
increasing the yield from the wild fisheries is
limited, as the stock is subjected to extreme fishing
pressure and is nearing their long term equilibrium
yield. Hence, the most imaginative management
strategy seems to be increasing the production
through population enhancement and aquaculture.
Recent success in rearing the phyllosoma larvae,
has significantly improved the chances of captive
breeding and seed production in spiny lobsters
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