34,055 research outputs found
The Doppler Spectra of Medium Grazing Angle Sea Clutter; Part 1: Characterisation
This paper is concerned with the characterisation of Doppler spectra from high range resolution X-band radar sea clutter observed from an airborne platform over the range of grazing angles, 15° to 45°. It is observed that when looking up or down wind there is a strong correlation between mean Doppler shift and local spectrum intensity. When combined with random fluctuations of spectrum width, these characteristics give the spectra a temporal and spatial variability. This behaviour has previously been observed in low grazing angle data and these results confirm the wider applicability of the models developed using that data. The modelling method is also extended here to capture the bimodal behaviour observed with high intensity returns from breaking waves looking up or down-wind
The Tail of the HI Mass Function
The contribution of extragalactic objects with HI masses below
to the HI mass function remains uncertain. Several aspects of the detection of
low-mass sources in HI surveys are not always considered, and as a result
different analysis techniques yield widely different estimates for their number
density. It is suggested at one extreme that the number density of galaxies
follows a shallow Schechter power-law slope, and at the other extreme that it
follows a steep faint-end rise like that found for field optical sources. Here
we examine a variety of selection effects, issues of completeness, and
consequences of LSS. We derive results for the large Arecibo Dual Beam Survey
which indicate that the field mass function does rise steeply, while within the
Virgo Cluster environs, the slope appears to be much shallower. Dependence on
the local density of galaxies may partially explain differences between
surveys.Comment: 8 pages, presented at Mapping the Hidden Universe: The Universe in
HI. eds Kraan-Korteweg, Henning, Andernac
A comparative assessment of solar thermal electric power plants in the 1-10 MWe range
The candidate power system technologies were ranked in terms of the cost of electric energy each system produces. In all cases, it was assumed that development programs would result in mature power plant systems that could be commercially manufactured. The results of the study, a brief description of the systems examined, and the methodologies used are presented
Technological change and productivity growth in the air transport industry
The progress of the civil air transport industry in the United States was examined in the light of a proposal of Enos who, after examining the growth of the petroleum industry, divided that phenomenon into two phases, the alpha and the beta; that is, the invention, first development and production, and the improvement phase. The civil air transport industry developed along similar lines with the technological progress coming in waves; each wave encompassing several new technological advances while retaining the best of the old ones. At the same time the productivity of the transport aircraft as expressed by the product of the aircraft velocity and the passenger capacity increased sufficiently to allow the direct operating cost in cents per passenger mile to continually decrease with each successive aircraft development
Gas and Stars in an HI-Selected Galaxy Sample
We present the results of a J-band study of the HI-selected Arecibo Dual-Beam
Survey and Arecibo Slice Survey galaxy samples using the 2 Micron All-Sky
Survey data. We find that these galaxies span a wide range of stellar and gas
properties. However, despite the diversity within the samples, we find a very
tight correlation between luminosity and size in the J-band, similar to that we
previously found (Rosenberg & Schneider 2003) between the HI mass and size. We
also find that the correlation between the baryonic mass and the J-band
diameter is even tighter than between the baryonic mass and the rotational
velocity.Comment: AJ in press, 17 pages (including tables and figures) + 6 additional
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