1,018,525 research outputs found

    Triplets of galaxies: Their dynamics, evolution, and the origin of chaos in them

    Get PDF
    Recently Karachentsev's group at The Smithsonian Astrophysical Observatory (SAO) (6-meter Telescope Observatory) published a list of 84 triple systems of galaxies with their distances, radial (line of sight) velocities, and angular sizes (Karachentseva et al., 1988). This gives a new ground for studies of the dark matter problem which fills the gap between the large cosmic scales (White, 1987; Dekel and Rees, 1987, and Einasto et al., 1977) and the scale of individual galaxies (Erickson et al., 1987). The data on the typical velocity dispersions and linear dimension of the triplets indicate that they contain considerable amounts of dark matter (see also earlier work of Karachentseva et al., 1979). Numerical simulations show that the statistical characteristics of the Karachentsev triplets can be imitated by model ensembles of triple systems with dark matter masses M sub d = (1-3 x 10(exp 12) M sub O, which is almost ten times greater than the typical mass of stellar galaxies estimated by the standard mass-to-luminosity ration (Kiseleva and Chernin, 1988). Here, the authors report that important information can be drawn from the data on the visible configurations of these systems. The statistics of configurations provide an independent evidence for dark matter in the triplets; moreover, it enables one to argue that dark matter seems to be distributed over the whole volume of the typical triplet forming its common corona rather than concentrated within individual coronae (or haloes) of the member galaxies

    A Comparison of Information Systems Coverage in the CPA, CIA and CMA Examinations for the Period 1987-1991

    Get PDF
    In recent years, three major accounting professional organizations, the American Institute of Certified Public Accountants (AICPA), Institute of Management Accountants (IMA) and Internal Auditors Institute (IIA) have considered and issued statements on the body of knowledge deemed necessary for practice as a Certified Public Accountant, Certified Management Accountant and Certified Internal Auditor. In each instance, knowledge and skills in information systems technology were included. This is not surprising, in view of the fact that changes in technology have dramatically altered the way in which accounting data is gathered, processed, stored, accessed and reported. Each of these professional organizations also requires or recommends the passing of an organization-sponsored certification examination for entry into or recognition within the various practice areas. While the examinations are not the only means of assessing the knowledge and skills necessary for certification, they are an important tool in evaluating the extent of the qualifications presented by a candidate. In view of the above, one may postulate that the certification examination, in each instance, would include coverage of the areas of knowledge included in the prerequisite body of knowledge. In particular, since each of the professional groups cite information systems (IS) knowledge as an important knowledge component, one would expect to observe test items addressing current IS in each exam

    Integrating case study and survey research methods: An example in information systems

    Get PDF
    The case for combining research methods generally, and more specifically that for combining qualitative and quantitative methods, is strong. Yet, research designs that extensively integrate both fieldwork (e.g. case studies) and survey research are rare. More¬over, some journals tend tacitly to specialize by methodology thereby encouraging purity of method. The multi-method model of research while not new, has not been appreciated. In this respect it is useful to articulate and describe its usage through example. By reference to a recently completed study of IS consultant engagement success factors this paper presents an analysis of the benefits of integrating case study and survey research methods. The emphasis is on the qualitative case study method and how it can compliment more quantitative survey research. Benefits are demonstrated through specific examples from the reference study.</i

    Analysis of the Brinkman equation as a model for flow in porous media

    Get PDF
    The fundamental solution or Green's function for flow in porous media is determined using Stokesian dynamics, a molecular-dynamics-like simulation method capable of describing the motions and forces of hydrodynamically interacting particles in Stokes flow. By evaluating the velocity disturbance caused by a source particle on field particles located throughout a monodisperse porous medium at a given value of volume fraction of solids ø, and by considering many such realizations of the (random) porous medium, the fundamental solution is determined. Comparison of this fundamental solution with the Green's function of the Brinkman equation shows that the Brinkman equation accurately describes the flow in porous media for volume fractions below 0.05. For larger volume fractions significant differences between the two exist, indicating that the Brinkman equation has lost detailed predictive value, although it still describes qualitatively the behavior in moderately concentrated porous media. At low ø where the Brinkman equation is known to be valid, the agreement between the simulation results and the Brinkman equation demonstrates that the Stokesian dynamics method correctly captures the screening characteristic of porous media. The simulation results for ø ≥ 0.05 may be useful as a basis of comparison for future theoretical work

    Adaptive optical networks using photorefractive crystals

    Get PDF
    The capabilities of photorefractive crystals as media for holographic interconnections in neural networks are examined. Limitations on the density of interconnections and the number of holographic associations which can be stored in photorefractive crystals are derived. Optical architectures for implementing various neural schemes are described. Experimental results are presented for one of these architectures

    Developments in getting GIS technologies into classrooms

    Get PDF
    The paper maps progress in the adoption of GIS in secondary education over more than 15 years, As it explores the incentives and impediments in the adoption of GlS in secondary schools, it notes the rich technology base in North America, and benefits of national geography curriculum and support structures in Britain

    Technology@Utopia

    Get PDF

    The environment of HII galaxies

    Get PDF
    Recent morphological studies (Telles \& Terlevich 1994) of HII galaxies, i.e. dwarf galaxies dominated by a very luminous starburst, have indicated that luminous HII galaxies tend to show distorted morphology suggestive of tidal interactions triggering the present starburst while low luminosity HII galaxies tend to be instead symmetric and regular. To check the tidal origin of the starburst in HII galaxies, we have searched for companions in the neighbourhood of a sample of 51 HII galaxies. We found that only 12 HII galaxies have a neighbour within a projected distance of 1 Mpc and 250 \kmsec~ in velocity difference, and of these 12, only 4 have a luminous (MB<_B < --19) neighbour. Surprisingly, isolated HII galaxies tend to be of high luminosity and disturbed morphology while HII galaxies with neighbours tend to be low luminosity regular HII galaxies. Furthermore, the metal abundance and the equivalent width of the emission lines in HII galaxies do not depend on the presence of a companion. These results are opposed to simple expectations if interaction with a bright companion is the main mechanism triggering the starbursts. We have also found a loose group of HII galaxies with no luminous companion. For this, there is the additional difficulty of understanding how these starbursts are synchronized on time scales of less than 10710^7 yrs in systems separated by \sim 1-2 Mpc.Comment: 7 pages, uuencoded, compressed, postscript file. (three figures included). Also available via anonymous ftp from ftp://cast0.ast.cam.ac.uk/pub/etelles/environ.ps.

    Review of research in feature-based design

    Get PDF
    Research in feature-based design is reviewed. Feature-based design is regarded as a key factor towards CAD/CAPP integration from a process planning point of view. From a design point of view, feature-based design offers possibilities for supporting the design process better than current CAD systems do. The evolution of feature definitions is briefly discussed. Features and their role in the design process and as representatives of design-objects and design-object knowledge are discussed. The main research issues related to feature-based design are outlined. These are: feature representation, features and tolerances, feature validation, multiple viewpoints towards features, features and standardization, and features and languages. An overview of some academic feature-based design systems is provided. Future research issues in feature-based design are outlined. The conclusion is that feature-based design is still in its infancy, and that more research is needed for a better support of the design process and better integration with manufacturing, although major advances have already been made
    corecore