28,127 research outputs found

    Convergence properties of simple genetic algorithms

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    The essential parameters determining the behaviour of genetic algorithms were investigated. Computer runs were made while systematically varying the parameter values. Results based on the progress curves obtained from these runs are presented along with results based on the variability of the population as the run progresses

    Shellflow. I. The Convergence of the Velocity Field at 6000 km/s

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    We present the first results from the Shellflow program, an all-sky Tully-Fisher (TF) peculiar velocity survey of 276 Sb-Sc galaxies with redshifts between 4500 and 7000 km/s. Shellflow was designed to minimize systematic errors between observing runs and between telescopes, thereby removing the possibility of a spurious bulk flow caused by data inhomogeneity. A fit to the data yields a bulk flow amplitude V_bulk = 70{+100}{-70} km/s (1 sigma error) with respect to the Cosmic Microwave Background, i.e., consistent with being at rest. At the 95% confidence level, the flow amplitude is < 300 km/s. Our results are insensitive to which Galactic extinction maps we use, and to the parameterization of the TF relation. The larger bulk motion found in analyses of the Mark III peculiar velocity catalog are thus likely to be due to non-uniformities between the subsamples making up Mark III. The absence of bulk flow is consistent with the study of Giovanelli and collaborators and flow field predictions from the observed distribution of IRAS galaxies.Comment: Accepted version for publication in ApJ. Includes an epitaph for Jeffrey Alan Willick (Oct 8, 1959 - Jun 18, 2000

    An HI survey of the Bootes Void. II. The Analysis

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    We discuss the results of a VLA HI survey of the Bootes void and compare the distribution and HI properties of the void galaxies to those of galaxies found in a survey of regions of mean cosmic density. The Bootes survey covers 1100 Mpc3^{3}, or ∌\sim 1\% of the volume of the void and consists of 24 cubes of typically 2 Mpc * 2 Mpc * 1280 km/s, centered on optically known galaxies. Sixteen targets were detected in HI; 18 previously uncataloged objects were discovered directly in HI. The control sample consists of 12 cubes centered on IRAS selected galaxies with FIR luminosities similar to those of the Bootes targets and located in regions of 1 to 2 times the cosmic mean density. In addition to the 12 targets 29 companions were detected in HI. We find that the number of galaxies within 1 Mpc of the targets is the same to within a factor of two for void and control samples, and thus that the small scale clustering of galaxies is the same in regions that differ by a factor of ∌\sim 6 in density on larger scales. A dynamical analysis of the galaxies in the void suggests that on scales of a few Mpc the galaxies are gravitationally bound, forming interacting galaxy pairs, loose pairs and loose groups. One group is compact enough to qualify as a Hickson compact group. The galaxies found in the void are mostly late-type, gas rich systems. A careful scrutiny of their HI and optical properties shows them to be very similar to field galaxies of the same morphological type. This, combined with our finding that the small scale clustering of the galaxies in the void is the same as in the field, suggests that it is the near environment that mostly affects the evolution of galaxies.Comment: Latex file of abstract. The postscript version of the complete paper (0.2 Mb in gzipped format) including all the figures can be retrieved from http://www.astro.rug.nl:80/~secr/ To appear in the February 1996 issue of the Astronomical Journa

    Weak Lensing Determination of the Mass in Galaxy Halos

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    We detect the weak gravitational lensing distortion of 450,000 background galaxies (20<R<23) by 790 foreground galaxies (R<18) selected from the Las Campanas Redshift Survey (LCRS). This is the first detection of weak lensing by field galaxies of known redshift, and as such permits us to reconstruct the shear profile of the typical field galaxy halo in absolute physical units (modulo H_0), and to investigate the dependence of halo mass upon galaxy luminosity. This is also the first galaxy-galaxy lensing study for which the calibration errors are negligible. Within a projected radius of 200 \hkpc, the shear profile is consistent with an isothermal profile with circular velocity 164+-20 km/s for an L* galaxy, consistent with typical disk rotation at this luminosity. This halo mass normalization, combined with the halo profile derived by Fischer et al (2000) from lensing analysis SDSS data, places a lower limit of (2.7+-0.6) x 10^{12}h^{-1} solar masses on the mass of an L* galaxy halo, in good agreement with satellite galaxy studies. Given the known luminosity function of LCRS galaxies, and the assumption that M∝LÎČM\propto L^\beta for galaxies, we determine that the mass within 260\hkpc of normal galaxies contributes Ω=0.16±0.03\Omega=0.16\pm0.03 to the density of the Universe (for ÎČ=1\beta=1) or Ω=0.24±0.06\Omega=0.24\pm0.06 for ÎČ=0.5\beta=0.5. These lensing data suggest that 0.6<ÎČ<2.40.6<\beta<2.4 (95% CL), only marginally in agreement with the usual ÎČ≈0.5\beta\approx0.5 Faber-Jackson or Tully-Fisher scaling. This is the most complete direct inventory of the matter content of the Universe to date.Comment: 18 pages, incl. 3 figures. Submitted to ApJ 6/7/00, still no response from the referee after four months

    Die vakwetenskaplike en wysgerige betekenis van Stoker se konfrontasie met die ‘moderne desendensieleer’

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    In 1926 Stoker wrote an article dealing with the modern biological theory of descent. This contribution endeavours to investigate those arguments and insights which are still valid today. With reference to Von Uexkiill Stoker first of all correctly emphasizes that the Darwinistic theory of descent does not belong within the domain of biology as a special science - it is nothing but a part of philosophy that should be treated within a philosophy of nature. In various contexts Stoker also points out that similarities also presuppose differences something consistently overlooked by Darwinism. The shortcomings in the ‘biogenetic basic law' of Haeckel - which claims that ontogenesis is a recapitulation of phylogenesis as well as of the neglected issue of constancy are lifted out. Stoker in fa d advances a remarkably balanced perspective on the relationship between constancy and dynamics

    Dooyeweerd’s legal and political philosophy: A response to the challenge of historicism

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    A look at the penetrating and encompassing nature of Dooyeweerd’s political and legal philosophy makes it understandable why Georgio Del Vecchio, a reputable Italian philosopher of law, appreciated Dooyeweerd as “the most profound, innovative, and penetrating philosopher since Kant”. Dooyeweerd’s Inaugural address laid the foundation for uncovering the deepest dialectical motivation of modern philosophy, namely the (dialectical) basic motive of nature and freedom (science ideal and personality ideal). Dooyeweerd rejected the idea of a “pure theory of law” because in spite of its uniqueness, the meaning of the jural aspect of reality comes to expression only in its coherence with other irreducible aspects. In opposition to the relativistic claims of historicism, Dooyeweerd emphasises the irreducibility of each aspect of reality. Dooyeweerd exercised immanent criticism on the impasse of a theory of the state without the state and a theory of law without law. Despite his continuing an element of natural law, Dooyeweerd’s approach avoids the antinomous stance of historicism by realising that change can only be established on the basis of constancy. The article concludes with a brief sketch of his systematic programme, as it unfolds in his multi-volume Encyclopaedia of the science of law
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