107,556 research outputs found

    Agassiz, Garman, Albatross, and the Collection of Deep-sea Fishes

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    The first of Alexander Agassiz’ voyages on the U.S. Fish Commission steamer Albatross in 1891 yielded significant scientific results. This paper reviews the background of the voyage, including the career path that led Agassiz to the back deck of the Albatross. We also give a brief account of the life and work of Samuel Garman. Garman wrote up the ichthyological material from this Albatross voyage in a magnificent book on deep-sea fishes published in 1899. This book was exceptional in its coverage, anatomical detail, and recognition of phylogenetically important morphology

    The Short Rotation Period of Nereid

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    We determine the period, p = 11.52 \pm 0.14 h, and a light curve peak-to-peak amplitude, a = 0.029 \pm 0.003 magnitudes, of the Neptunian irregular satellite Nereid. If the light curve variation is due to albedo variations across the surface, rather than solely to the shape of Nereid variations, the rotation period would be a factor of two shorter. In either case, such a rotation period and light curve amplitude, together with Nereid's orbital period, p=360.14 days, imply that Nereid is almost certainly in a regular rotation state, rather than the chaotic rotation state suggested by Schaefer and Schaefer (1988,2000) and Dobrovolskis (1995). Assuming that Nereid is perfectly spherical, the albedo variation is 3% across the observed surface. Assuming a uniform geometric albedo, the observed cross sectional area varies by 3%. We caution that the lightcurve found in this paper only sets limits on the combination of albedo and physical irregularity and that we cannot determine the orientation of Nereid's spin axis from our data.Comment: Accepted by ApJ Letters, 11 pages (incl. 1 figure

    Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies

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    Dynamical models for 17 Coma early-type galaxies are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between M=-18.79 and M=-22.56. Kinematical long-slit observations cover at least the major and minor axis and extend to 1-4 effective radii. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy models with a dark matter halo match the data better than models without. The statistical significance is over 95 percent for 8 galaxies, around 90 percent for 5 galaxies and for four galaxies it is not significant. For the highly significant cases systematic deviations between observed and modelled kinematics are clearly seen; for the remaining galaxies differences are more statistical in nature. Best-fit models contain 10-50 percent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density. The central phase-space density of dark matter is often orders of magnitude lower than in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss-Hermite coefficient H4. Changing the balance between data-fit and regularisation constraints does not change the reconstructed mass structure significantly. Model anisotropies tend to strengthen if the weight on regularisation is reduced, but the general property of a galaxy to be radially or tangentially anisotropic, respectively, does not change. (abridged)Comment: 31 pages, 34 figures; accepted for publication in MNRA

    Photodynamic Therapy of Necrobiosis Lipoidica - A Multicenter Study of 18 Patients

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    Background: Necrobiosis lipoidica (NL) is a granulomatous skin disease of unknown origin, and no reliably effective treatment option exists to handle this often disfiguring disease. Recently, a patient with long-lasting NL was reported to be cured by topical photodynamic therapy (PDT). Objective: To evaluate the overall potential of PDT in the treatment of NL on the lower legs. Methods: Retrospective study of 18 patients (aged 16 - 62 years) from 3 European university departments of dermatology treated with PDT for NL. Methyl aminolevulinate or 5-aminolevulinic acid were used as topically applied photosensitizers. Illumination followed with red light-emitting diode light. Results: Complete response was seen in 1/18 patients after 9 PDT cycles, and partial response in 6/18 patients (2 - 14 PDT cycles) giving an overall response rate of 39% (7/18). Conclusion: Although almost 40% of the cases showed some degree of response, PDT cannot currently be recommended as first-line therapy of NL. Subpopulations of therapy-resistant NL patients may, however, benefit from PDT. Copyright (C) 2008 S. Karger AG, Base

    Sustainable urban development in practice:the SAVE concept

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    The need for sustainable development of the urban environment presents the research community with a number of challenges and opportunities. A considerable volume of research has been undertaken into the constituent parts of this complex problem and a number of tool kits and methodologies have been developed to enable and encourage the application of specific aspects of research in practice. However, there is limited evidence of the holistic integration of the body of knowledge arising from the research within real-life decision-making practices. In this paper we present an overview of the existing body of knowledge relating to sustainable development of the urban environment and propose a generic framework for its integration within current practices. This framework recognises the need to: understand social, economic, and environmental issues; understand the decision-making processes; provide a means of measurement, assessment, or valuation of the issues; provide analytical methods for the comparative assessment of complex data to enable an evaluation of strategies and design options and to communicate effectively throughout the process with a wide range of stakeholders. The components of a novel sustainability assessment, visualisation and enhancement (SAVE) framework, developed by the authors to ‘operationalise’ the body of knowledge are presented and justified. These include: decision-mapping methods to identify points of intervention; indicator identification and measurement approaches; appropriate mathematical and analytical tools and an interactive simulation and visualisation platform which integrates and communicates complex multivariate information to diverse stakeholder groups. We report on the application of the SAVE framework to a major urban development project and reflect on its current and potential impact on the development. Conclusions are also drawn about its general applicability

    Particle-particle and quasiparticle random phase approximations: Connections to coupled cluster theory

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    We establish a formal connection between the particle-particle (pp) random phase approximation (RPA) and the ladder channel of the coupled cluster doubles (CCD) equations. The relationship between RPA and CCD is best understood within a Bogoliubov quasiparticle (qp) RPA formalism. This work is a follow-up to our previous formal proof on the connection between particle-hole (ph) RPA and ring-CCD. Whereas RPA is a quasibosonic approximation, CC theory is a correct bosonization in the sense that the wavefunction and Hilbert space are exactly fermionic. Coupled cluster theory achieves this goal by interacting the ph (ring) and pp (ladder) diagrams via a third channel that we here call "crossed-ring" whose presence allows for full fermionic antisymmetry. Additionally, coupled cluster incorporates what we call "mosaic" terms which can be absorbed into defining a new effective one-body Hamiltonian. The inclusion of these mosaic terms seems to be quite important. The pp-RPA an d qp-RPA equations are textbook material in nuclear structure physics but are largely unknown in quantum chemistry, where particle number fluctuations and Bogoliubov determinants are rarely used. We believe that the ideas and connections discussed in this paper may help design improved ways of incorporating RPA correlation into density functionals based on a CC perspective

    Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations

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    We analyse the performance of twelve different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and disc stability. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in the Hernquist and Katz (1989) algorithm. For all tests we find that the artificial viscosity is the most important factor distinguishing the results from the various implementations. The second most important factor is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included has comparatively little effect on the results. Combining the equation of motion presented in Thomas and Couchman (1992) with a modification of the Monaghan and Gingold (1983) artificial viscosity leads to an SPH scheme that is both fast and reliable.Comment: 30 pages, 26 figures and 9 tables included. Submitted to MNRAS. Postscript version available at ftp://phobos.astro.uwo.ca/pub/etittley/papers/sphtest.ps.g

    Tailoring symmetry groups using external alternate fields

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    Macroscopic systems with continuous symmetries subjected to oscillatory fields have phases and transitions that are qualitatively different from their equilibrium ones. Depending on the amplitude and frequency of the fields applied, Heisenberg ferromagnets can become XY or Ising-like -or, conversely, anisotropies can be compensated -thus changing the nature of the ordered phase and the topology of defects. The phenomena can be viewed as a dynamic form of "order by disorder".Comment: 4 pages, 2 figures finite dimension and selection mechanism clarifie

    Chandra Detection of Massive Black Holes in Galactic Cooling Flows

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    Anticipating forthcoming observations with the Chandra X-ray telescope, we describe the continuation of interstellar cooling flows deep into the cores of elliptical galaxies. Interstellar gas within about r = 50 parsecs from the massive black hole is heated to T > 1 keV and should be visible unless thermal heating is diluted by non-thermal pressure. Since our flows are subsonic near the massive black holes, distributed cooling continues within 300 pc from the center. Dark, low mass stars formed in this region may be responsible for some of the mass attributed to central black holes.Comment: 6 pages with 3 figures; accepted by Astrophysical Journal Letter
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