1,341 research outputs found
Single Dish Polarization Calibration
Using the formalism of Hamaker et al. (1996), I derive a method for the
polarization calibration of observations made with a single radio telescope.
This method is particularly appropriate for observations of pulsars, where the
sign and magnitude of the circular polarization are useful for understanding
the emission processes at work. I apply the method to observations of PSR
J1359-6038 made using the multibeam receiver on the Parkes radio telescope.Comment: Accepted by PASA. 11 pages. 3 figure
Software Holography: Interferometric Data Analysis for the Challenges of Next Generation Observatories
Next generation radio observatories such as the MWA, LWA, LOFAR, CARMA and
SKA provide a number of challenges for interferometric data analysis. These
challenges include heterogeneous arrays, direction-dependent instrumental gain,
and refractive and scintillating atmospheric conditions. From the analysis
perspective, this means that calibration solutions can not be described using a
single complex gain per antenna. In this paper we use the optimal map-making
formalism developed for CMB analyses to extend traditional interferometric
radio analysis techniques--removing the assumption of a single complex gain per
antenna and allowing more complete descriptions of the instrumental and
atmospheric conditions. Due to the similarity with holographic mapping of radio
antenna surfaces, we call this extended analysis approach software holography.
The resulting analysis algorithms are computationally efficient, unbiased, and
optimally sensitive. We show how software holography can be used to solve some
of the challenges of next generation observations, and how more familiar
analysis techniques can be derived as limiting cases.Comment: in revie
Fast Food - the early years: Geography and the growth of a chain-store in the UK
We examine the development of UK outlets of a major fast food chain, from inauguration in 1974 until 1990, after which industry structure changed somewhat. The chain effectively introduced the counter-service burger concept. Locational spread across local authority district markets is explained by the characteristics of the areas where the outlets are sited. Of special interest is the effect of scale economies, measured by outlet numbers in neighboring districts. Both first and second entry are examined. We find that the hazard of first entry is positively influenced by market size and population density and negatively by distance from company headquarters.fast food, diffusion, regional economic activity, entry
Fast Food - the early years : Geography and the growth of a chain-store in the UK
We examine the development of UK outlets of a major fast food chain, from inauguration in 1974 until 1990, after which industry structure changed somewhat. The chain effectively introduced the counter-service burger concept. Locational spread across local authority district markets is explained by the characteristics of the areas where the outlets are sited. Of special interest is the effect of scale economies, measured by outlet numbers in neighboring districts. Both first and second entry are examined. We find that the hazard of first entry is positively influenced by market size and population density and negatively by distance from company headquarters.Fast food ; Diffusion ; Regional economic activity ; Entry
Empirical Analysis of Aerial Camera Filters for Shoreline Mapping
Accurate, up-to-date national shoreline is critical in defining the territorial limits of the Unites States, updating nautical charts, and managing coastal resources. The National Oceanic and Atmospheric Administration (NOAA) delineates the interpreted shoreline photogrammetrically using tide-coordinated stereo photography acquired with black-and-white infrared emulsion. In this paper, we present the results of a two-phased study aimed at quantifying the effect of camera filter selection on the interpreted shoreline when utilizing this method of shoreline mapping
Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy
In radio astronomy, reference signals from auxiliary antennas that receive
only the radio frequency interference (RFI) can be modified to model the RFI
environment at the astronomy receivers. The RFI can then be canceled from the
astronomy signal paths. However, astronomers typically only require signal
statistics. If the RFI statistics are changing slowly, the cancellation can be
applied to the signal correlations at a much lower rate than is required for
standard adaptive filters. In this paper we describe five canceler setups;
precorrelation and postcorrelation cancelers that use one or two reference
signals in different ways. The theoretical residual RFI and added noise levels
are examined and are demonstrated using microwave television RFI at the
Australia Telescope Compact Array. The RFI is attenuated to below the system
noise, a reduction of at least 20 dB. While dual-reference cancelers add more
reference noise than single-reference cancelers, this noise is zero-mean and
only adds to the system noise, decreasing the sensitivity. The residual RFI
that remains in the output of single-reference cancelers (but not
dual-reference cancelers) sets a nonzero noise floor that does not act like
random system noise and may limit the achievable sensitivity. Thus,
dual-reference cancelers often result in superior cancellation. Dual-reference
precorrelation cancelers require a double-canceler setup to be useful and to
give equivalent results to dual-reference postcorrelation cancelers.Comment: 11 pages created using emulateap
Unveiling the nature of IGR J17177-3656 with X-ray, NIR and Radio observations
We report on the first broad-band (1-200 keV) simultaneous Chandra-INTEGRAL
observations of the recently discovered hard X-ray transient IGR J17177-3656
that took place on 2011, March 22, about two weeks after the source discovery.
The source had an average absorbed 1-200 keV flux of about 8x10^(-10) erg
cm^(-2) s^(-1). We extracted a precise X-ray position of IGR J17177-3656, RA=17
17 42.62, DEC= -36 56 04.5 (90% uncertainty of 0.6"). We also report Swift,
near infrared and quasi simultaneous radio follow-up observations. With the
multi-wavelength information at hand, we propose IGR J17177-3656 is a low-mass
X-ray binary, seen at high inclination, probably hosting a black hole.Comment: 8 pages, 8 figures, accepted for publication in Ap
- …