1,562 research outputs found
Optimization of MLS receivers for multipath environments
Optimal design studies of MLS angle-receivers and a theoretical design-study of MLS DME-receivers are reported. The angle-receiver results include an integration of the scan data processor and tracking filter components of the optimal receiver into a unified structure. An extensive simulation study comparing the performance of the optimal and threshold receivers in a wide variety of representative dynamical interference environments was made. The optimal receiver was generally superior. A simulation of the performance of the threshold and delay-and-compare receivers in various signal environments was performed. An analysis of combined errors due to lateral reflections from vertical structures with small differential path delays, specular ground reflections with neglible differential path delays, and thermal noise in the receivers is provided
Cirrhosis of the Liver: A Clinical Study of 100 Cases in Glasgow, 1946-1957
Abstract Not Provided
The Likelihood Ratio as a tool for Radio Continuum Surveys with SKA precursor telescopes
In this paper we investigate the performance of the likelihood ratio method
as a tool for identifying optical and infrared counterparts to proposed radio
continuum surveys with SKA precursor and pathfinder telescopes. We present a
comparison of the infrared counterparts identified by the likelihood ratio in
the VISTA Deep Extragalactic Observations (VIDEO) survey to radio observations
with 6, 10 and 15 arcsec resolution. We cross-match a deep radio catalogue
consisting of radio sources with peak flux density 60 Jy with deep
near-infrared data limited to 22.6. Comparing the
infrared counterparts from this procedure to those obtained when cross-matching
a set of simulated lower resolution radio catalogues indicates that degrading
the resolution from 6 arcsec to 10 and 15 arcsec decreases the completeness of
the cross-matched catalogue by approximately 3 and 7 percent respectively. When
matching against shallower infrared data, comparable to that achieved by the
VISTA Hemisphere Survey, the fraction of radio sources with reliably identified
counterparts drops from 89%, at 22.6, to 47% with
20.0. Decreasing the resolution at this shallower
infrared limit does not result in any further decrease in the completeness
produced by the likelihood ratio matching procedure. However, we note that
radio continuum surveys with the MeerKAT and eventually the SKA, will require
long baselines in order to ensure that the resulting maps are not limited by
instrumental confusion noise.Comment: 10 pages, 7 figures, accepted for publication in mnra
Optimization of MLS receivers for multipath environments
A receiver is designed for aircraft (A/C), which, as a component of the proposed Microwave Landing System (MLS), is capable of optimal performance in the multipath environments found in air terminal areas. Topics discussed include: the angle-tracking problem of the MLS receiver; signal modeling; preliminary approaches to optimal design; suboptimal design; and simulation study
SNOWBOARDER'S FRACTURE: CHANGING JOINT MECHANICS BY FOOT POSITION DURING A SIMULATED LANDING TASK
A high proportion of fractures to the lateral process of the talus (LPT) has been reported in snowboarding, which accounted for 34% of all ankle fractures (Kirkpatrick et al., 1998). A fracture to the LPT is an injury unique to snowboarders and is often misdiagnosed by physicians as an anterolateral ankle sprain. LPT fractures often involve the articular surface of the subtalar joint and it has been shown that misdiagnosis may lead to severe degeneration of the ankle joint and long term morbidity (Boon et aI., 1999). The mechanism of this injury has been studied intensively. LPT fractures are high impact injuries, landing after aerial manoeuvres is thought to be the major cause of LPT fractures (Boon et aI., 1999). In a cadaver study no fractures to the LPT were recorded under purely dorsalflexed conditions but in six of the eight specimens fractures occurred with the addition of 20° external rotation. An axial load of 2200 -8900 N was required to produce a fracture (LPT) in this position. It was proposed by Boon and colleagues tr.at the subsequent 'opening' of the ankle joint seen with heel inversion and external rotation of the talus results in the lateral process shifting upwards on the posterior articular process of the calcaneus. The purpose of this study was to simulate a snowboard landing in the laboratory with using an inverse dynamics approach to calculate effective joint loading for different binding alignments. It was hypothesised that the 'stance' chosen will affect loading and that an optimum foot alignment will help to minimise joint load
On faint companions in the close environment of star-forming dwarf galaxies. Possible external star formation triggers ?
We have searched for companion galaxies in the close environment of 98
star-forming dwarf galaxies (SFDGs) from field and low density environments,
using the NASA Extragalactic Database. Most of the companions are dwarf
galaxies which due to observational selection effects were previously
disregarded in environmental studies of SFDGs. A subsample at low redshift,
cz<2000 km/s, was chosen to partially eliminate the observational bias against
distant dwarf companions. We find companion candidates for approximately 30% of
the objects within a projected linear separation s_p<100 kpc and a redshift
difference (Delta cz)<500 km/s. The limited completeness of the available data
sets, together with the non-negligible frequency of HI clouds in the vicinity
of SFDGs indicated by recent radio surveys, suggest that a considerably larger
fraction of these galaxies may be accompanied by low-mass systems. This casts
doubt on the hypothesis that the majority of them can be considered truly
isolated. The velocity differences between companion candidates and sample
SFDGs amount typically to (Delta cz)<250 km/s, and show a rising distribution
towards lower (Delta cz). This is similarly found for dwarf satellites of
spiral galaxies, suggesting a physical association between the companion
candidates and the sample SFDGs. SFDGs with a close companion do not show
significant differences in their Hbeta equivalent widths and B-V colours as
compared to isolated ones. However, the available data do not allow us to rule
out that interactions with close dwarf companions can influence the star
formation activity in SFDGs.Comment: 9 pages, 5 figures, to appear in A&A; also available at
http://www.uni-sw.gwdg.de/~knoeske/PUB_LIST/sfdg_comps.ps.g
Optimization of MLS receivers for multipath environments
The angle tracking problems in microwave landing system receivers along with a receiver design capable of optimal performance in the multipath environments found in air terminal areas were studied. Included were various theoretical and evaluative studies like: (1) signal model development; (2) derivation of optimal receiver structures; and (3) development and use of computer simulations for receiver algorithm evaluation. The development of an experimental receiver for flight testing is presented. An overview of the work and summary of principal results and conclusions are reported
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