107,556 research outputs found
Agassiz, Garman, Albatross, and the Collection of Deep-sea Fishes
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
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
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
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
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
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Internalisation of membrane progesterone receptor-α after treatment with progesterone: Potential involvement of a clathrin-dependent pathway
This article has been made available through the Brunel Open Access Publishing Fund.Internalisation and recycling of seven trans-membrane domain receptors is a critical regulatory event for their signalling. The mechanism(s) by which membrane progesterone receptor-α (mPRα) number is regulated on the cell surface is unclear. In this study, we investigated the cellular distribution of mPRα and mechanisms of mPRα trafficking using a cell line derived from a primary culture of human myometrial cells (M11) as an experimental model. RT-PCR and immunofluorescent analysis demonstrated expression of mPRα in M11 cells with mPRα primarily distributed on the cell surface under basal conditions. For the first time, plasma membrane localisation of mPRα was confirmed using immuno-gold transmission electron microscopy. Stimulation of M11 cells with progesterone (P4, 100 nM) resulted in internalisation of mPRα from the plasma membrane to the cytoplasm (10 min) and subsequent partial translocation back to the cell surface (20 min). We investigated potential endocytotic pathways involved in trafficking of mPRα after its internalisation. Partial co-localisation of clathrin with mPRα was obvious after 10 min of P4 treatment. Of note, chlorpromazine (inhibitor of clathrin-mediated pathway) inhibited the endocytosis of mPRα, whereas treatment with nystatin (inhibitor of caveolae-mediated pathway) did not affect internalisation. Collectively, these data suggest that mPRα is expressed on the cell surface of M11 cells and undergoes endocytosis after P4 stimulation primarily via a clathrin-mediated pathway.This article is available through the Brunel Open Access Publishing Fun
Particle-particle and quasiparticle random phase approximations: Connections to coupled cluster theory
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
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
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
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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