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121.
122.
P.M. Phillips I.W.A. Browne N.J. Jackson P.N. Wilkinson S. Mao D. Rusin D.R. Marlow I. Snellen M. Neeser 《Monthly notices of the Royal Astronomical Society》2001,328(4):1001-1015
The Jodrell Bank–VLA Astrometric Survey (JVAS) and the Cosmic Lens All Sky Survey (CLASS) have been systematically searched for multiple gravitational imaging of sources with image separations between 6 arcsec and 15 arcsec, associated with galaxy group and cluster lensing masses. The radio and optical follow-up observations of all candidates are presented. From a total of ∼15 000 sources only one weak candidate remains and this is not contained in the statistically complete sample of flat-spectrum JVAS/CLASS sources of 11 670 sources. A simple Press–Schechter analysis is performed. For singular isothermal sphere lenses the lack of multiple image systems is inconsistent with the currently favoured cosmologies with at the 4.2 σ level. Cored isothermal lenses reduce the expected number of lens systems and we suggest that the most probable interpretation of our results is that the surface mass density of groups and clusters of galaxies is not high enough to cause multiple imaging and the presence of the mass concentrations associated with individual galaxies is required to produce image separations such as those in B0957+561. 相似文献
123.
R. H. Wilkinson 《Geo-Marine Letters》1986,5(4):231-239
Velocity profiles, suspended sand concentration, and ripple shapes were measured over the tidal cycle on a mobile bed. Variations in ripple shape or dimensions, and the effects of mobile sediment could not account for the variations in bed roughness length, which increased systematically during the tide from 0.5 to 1.3 cm. The effects of acceleration could be the cause as they would lead to the same pattern of variation, but existing theory does not give the correct magnitude. 相似文献
124.
P. N. Wilkinson I. W. A. Browne A. R. Patnaik J. M. Wrobel & B. Sorathia 《Monthly notices of the Royal Astronomical Society》1998,300(3):790-816
We present a catalogue of 540 compact radio sources in the declination ranges +20 ≤ δ B1950 ≤ + 35° and +75 ≤ δ B1950 ≤ + 90°, the positions of which have been measured to an rms accuracy of about 55 mas with the Very Large Array (VLA). These sources are primarily intended for use as phase calibration sources for MERLIN. However, they will also be suitable as phase calibrators for the VLA and can be considered as candidate phase calibrators for very long baseline interferometry (VLBI) networks. 相似文献
125.
Boundaries between the various topographic, geologic, and socio-political entities that span the Earths continental surfaces are determined by a myriad of complexly interrelated natural and/or cultural factors. Areas of large river basins, of lithologic units on geologic maps, and of nations exhibit size frequency distributions that are closely approximated by density functions in which diameters of individual areas are distributed exponentially. As such, size distributions of each type of surface unit are closely modeled as randomly delimited areas. In other words, if one were to walk in a straight line across any particular continent, each step along that transect would embody some random continuous probability of passing out of a major drainage basin, or out of an area of more or less homogeneous rock type, or from one country to another. Moreover, this simple truism gives rise to area frequency distributions for large river basin or outcrop or nation area that are primarily dependent on the number of basins or outcrops or countries that exist across that particular landmass. As a consequence, the size frequencies of these areal units can be closely predicted knowing only the total area under consideration and the number of drainage basins, outcrop areas, or nations that exist within the area. The similarity between area frequencies of large river basins and rock types and nations suggests a nontrivial component of geologic influence on the partitioning of continental surfaces into major political divisions, and implies that cultural and economic factors, which serve to divide and unite political entities, do so within a geological framework. 相似文献
126.
R. H. Wilkinson 《Geo-Marine Letters》1983,3(1):49-52
A logarithmic velocity profile is often fitted to velocity data in order to calculate the friction velocity (u *) and typify the surface texture by a roughness length (z o ). A method is given for estimating the errors in these parameters as calculated by this method. An example is given in which the size of the error is compared with the fluctuations that typically occur in the time seriesu *(t) andz o (t). 相似文献
127.
128.
I. A. Bond N. J. Rattenbury J. Skuljan F. Abe R. J. Dodd J. B. Hearnshaw M. Honda J. Jugaku P. M. Kilmartin A. Marles K. Masuda Y. Matsubara Y. Muraki T. Nakamura G. Nankivell S. Noda C. Noguchi K. Ohnishi M. Reid To. Saito H. Sato M. Sekiguchi D. J. Sullivan T. Sumi M. Takeuti Y. Watase S. Wilkinson R. Yamada T. Yanagisawa P. C. M. Yock 《Monthly notices of the Royal Astronomical Society》2002,333(1):71-83
A search for extrasolar planets was carried out in three gravitational microlensing events of high magnification, MACHO 98–BLG–35 , MACHO 99–LMC–2 and OGLE 00–BUL–12 . Photometry was derived from observational images by the MOA and OGLE groups using an image subtraction technique. For MACHO 98–BLG–35 , additional photometry derived from the MPS and PLANET groups was included. Planetary modelling of the three events was carried out in a supercluster computing environment. The estimated probability for explaining the data on MACHO 98–BLG–35 without a planet is <1 per cent. The best planetary model has a planet of mass ∼(0.4–1.5)× M Earth at a projected radius of either ∼1.5 or ∼2.3 au. We show how multiplanet models can be applied to the data. We calculate exclusion regions for the three events and find that Jupiter-mass planets can be excluded with projected radii from as wide as about 30 au to as close as around 0.5 au for MACHO 98–BLG–35 and OGLE 00–BUL–12 . For MACHO 99–LMC–2 , the exclusion region extends out to around 10 au and constitutes the first limit placed on a planetary companion to an extragalactic star. We derive a particularly high peak magnification of ∼160 for OGLE 00–BUL–12 . We discuss the detectability of planets with masses as low as Mercury in this and similar events. 相似文献
129.
I. W. A. Browne P. N. Wilkinson N. J. F. Jackson S. T. Myers C. D. Fassnacht L. V. E. Koopmans D. R. Marlow M. Norbury D. Rusin C. M. Sykes A. D. Biggs R. D. Blandford A. G. de Bruyn K.-H. Chae P. Helbig L. J. King J. P. McKean T. J. Pearson P. M. Phillips A. C. S. Readhead E. Xanthopoulos T. York 《Monthly notices of the Royal Astronomical Society》2003,341(1):13-32
We report the final results of the search for gravitationally lensed flat-spectrum radio sources found in the combination of CLASS (Cosmic Lens All-Sky Survey) and JVAS (Jodrell Bank VLA Astrometric Survey). VLA (Very Large Array) observations of 16 503 sources have been made, resulting in the largest sample of arcsec-scale lens systems available. Contained within the 16 503 sources is a complete sample of 11 685 sources which have two-point spectral indices between 1.4 and 5 GHz flatter than −0.5, and 5-GHz flux densities ≥30 mJy . A subset of 8958 sources form a well-defined statistical sample suitable for analysis of the lens statistics. We describe the systematic process by which 149 candidate lensed sources were picked from the statistical sample on the basis of possessing multiple compact components in the 0.2-arcsec resolution VLA maps. Candidates were followed up with 0.05-arcsec resolution MERLIN and 0.003-arcsec VLBA observations at 5 GHz and rejected as lens systems if they failed well-defined surface brightness and/or morphological tests. To illustrate the candidate elimination process, we show examples of sources representative of particular morphologies that have been ruled out by the follow-up observations. 194 additional candidates, not in the well-defined sample, were also followed up. Maps for all the candidates can be found on the World Wide Web at http://www.jb.man.ac.uk/research/gravlens/index.html . We summarize the properties of each of the 22 gravitational lens systems in JVAS/CLASS. 12 are double-image systems, nine are four-image systems and one is a six-image system. 13 constitute a statistically well-defined sample giving a point-source lensing rate of 1:690 ± 190 . The interpretation of the results in terms of the properties of the lensing galaxy population and cosmological parameters will be published elsewhere. 相似文献
130.
M. K. Argo N. J. Jackson I. W. A. Browne T. York J. P. McKean A. D. Biggs R. D. Blandford A. G. de Bruyn K. H. Chae C. D. Fassnacht L. V. E. Koopmans S. T. Myers M. Norbury T. J. Pearson P. M. Phillips A. C. S. Readhead D. Rusin P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):957-961