1,543 research outputs found
Community water management and agricultural extension services: effects, impacts and perceptions in the coastal zone of Bangladesh
The coastal region of Bangladesh is prone to natural disasters and these events are expected to worsen as a result of climate change. Combined with anthropogenic factors, these events challenge livelihood opportunities, especially crop production. Waterlogging, tidal activity and the lack of proper drainage facilities are major constraints to agricultural production in these areas.
The CGIAR Research Program on Water, Land and Ecosystems (WLE) tested, at pilot scale, the combination of innovative agricultural technologies with improved water management to overcome these challenges.
This report assesses this intervention by observing the effects, measuring the short-term impacts and understanding the perceptions. The results highlight the need to integrate the interventions into the local context, and acknowledge that institutions and markets need to mature to harness the benefits from innovations. It also underlines the potential of multi-scale interventions combining plot-level and farmer-led innovations, community management and rehabilitation of large schemes
Collimation of extragalactic radio jets in compact steep spectrum and larger sources
We study the collimation of radio jets in the high-luminosity Fanaroff-Riley
class II sources by examining the dependence of the sizes of hotspots and knots
in the radio jets on the overall size of the objects for a sample of compact
steep-spectrum or CSS and larger-sized objects. The objects span a wide range
in overall size from about 50 pc to nearly 1 Mpc. The mean size of the hotspots
increases with the source size during the CSS phase, which is typically taken
to be about 20 kpc, and the relationship flattens for the larger sources. The
sizes of the knots in the compact as well as the larger sources are consistent
with this trend. We discuss possible implications of these trends. We find that
the hotspot closer to the nucleus or core component tends to be more compact
for the most asymmetric objects where the ratio of separations of the hotspots
from the nucleus, r_d > 2. These highly asymmetric sources are invariably CSS
objects, and their location in the hotspot size ratio - separation ratio
diagram is possibly due to their evolution in an asymmetric environment. We
also suggest that some soures, especially of lower luminosity, exhibit an
asymmetry in the collimation of the oppositely-directed radio jets.Comment: MNRAS in press, 9 pages and 3 figures, MNRAS LaTe
High sensitivity low frequency radio observations of cD galaxies
We present the GMRT 235 MHz images of three radio galaxies and 610 MHz images
of two sources belonging to a complete sample of cD galaxies in rich and poor
galaxy clusters. The analysis of the spectral properties confirms the presence
of aged radio emission in two of the presented sources.Comment: 3 pages, 2 figures, To appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
Jet propagation and the asymmetries of CSS radio sources
As Compact Steep Spectrum radio sources have been shown to be more
asymmetrical than larger sources of similar powers, there is a high probability
that they interact with an asymmetric medium in the central regions of the host
elliptical galaxy. We consider a simple analytical model of the propagation of
radio jets through a reasonable asymmetric environment and show that they can
yield the range of arm-length and luminosity asymmetries that have been
observed. We then generalize this to allow for the effects of orientation, and
quantify the substantial enhancements of the asymmetries that can be produced
in this fashion. We present two-dimensional and three-dimensional simulations
of jets propagating through multi-phase media and note that the results from
the simulations are also broadly consistent with the observations.Comment: 11 pages, 6 figures, 1 table, accepted for publication in A&
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