10,621 research outputs found
Scattering of low-energy electrons and positrons by atomic beryllium: Ramsauer-Townsend effect
Total cross sections for the scattering of low-energy electrons and positrons
by atomic beryllium in the energy range below the first inelastic thresholds
are calculated. A Ramsauer-Townsend minimum is seen in the electron scattering
cross sections, while no such effect is found in the case of positron
scattering. A minimum total cross section of 0.016 a.u. at 0.0029 eV is
observed for the electron case. In the limit of zero energy, the cross sections
yield a scattering length of -0.61 a.u. for electron and +13.8 a.u. for
positron scattering
Benthic Macrofauna of the New York Bight, 1979-89
The benthic macrofauna of the New York Bight has been monitored extensively, primarily to determine trends over space and time in biological effects of waste inputs. In
the present study, from 44 to 48 stations were sampled each summer from 1980-1985. Data from other Bight benthic studies are included to· extend the temporal coverage
from 1979 to 1989. Numbers of species and amphipods per sample, taken as relatively sensitive indicators of environmental stress, showed consistent spatial patterns. Lowest values were found in the Christiaensen Basin and other inshore areas, and numbers increased toward the outermost shelf and Hudson Shelf Valley stations. There were
statistically significant decreases in species and amphipods at most stations from 1980 to 1985. (Preliminary data from a more recent study suggest numbers of species increased again between 1986 and 1989.) Cluster analysis of 1980-85 data indicated several distinct assemblages-sewage sludge dumpsite, sludge accumulation area, inner Shelf Valley, outer Shelf Valley, outer shelf-with little change over time. The "enriched" and "highly altered" assemblages in the Basin appear similar to those reported since sampling began there in 1968. No consistently defaunated areas have been found in any sampling programs over the past 20 years. On a gross level, therefore, recent faunal responses to any environmental changes are not evident, but the more sensitive measures used, i.e. numbers of species and amphipods, do indicate widespread recent effects. Causes of the faunal changes are not obvious; some possibilities, including increasing effects of sewage
sludge or other waste inputs, natural factors, and sampling artifacts, are discussed. (PDF file contains 54 pages.
Intermediate- to high-energy positrons scattered by alkali-metal atoms
We present calculations of the differential, integrated elastic, and total cross sections for positrons scattered from alkali-metal atoms. The energy of the positrons ranges from 10 eV to 1000 eV. In the calculations we use parameter-free model potentials for the correlation-polarization and absorption interactions. The absorption potential used for positron scattering is based on a quasifree model that we recently proposed and tested for the noble-gas targets. For positron–alkali-metal scattering the model potentials have produced reliable scattering cross sections over the extended range of impact energies when compared against the available experimental data
Low-energy differential scattering of electrons and positrons from noble gases
Calculations of cross sections for electron (e−) and positron (e+) scattering from ground-state He, Ne, Ar, Kr, and Xe at projectile energies below the lowest inelastic thresholds are presented. The main focus in the present work is on the differential cross sections, since angular distributions depend sensitively on the choice of interaction potentials used in the calculations. A part of the interaction potential used in the calculations includes a parameter-free correlation-polarization potential which is (a) based on physical ideas of what a correlation-polarization potential should be, (b) different for various target gases, and (c) distinct for electron and positron scattering. The present calculations of differential cross sections predict the locations of the principal maxima and minima with good accuracy and the shapes of the calculated differential cross-section curves compare quite well with available experimental cross sections
Flux calibration of the AAO/UKST SuperCOSMOS H-alpha Survey
The AAO/UKST SuperCOSMOS H Survey (SHS) was, when completed in 2003,
a powerful addition to extant wide-field surveys. The combination of areal
coverage, spatial resolution and sensitivity in a narrow imaging band, still
marks it out today as an excellent resource for the astronomical community. The
233 separate fields are available online in digital form, with each field
covering 25 square degrees. The SHS has been the motivation for equivalent
surveys in the north, and new digital H surveys now beginning in the
south such as VPHAS+. It has been the foundation of many important discovery
projects with the Macquarie/AAO/Strasbourg H planetary nebula project
being a particularly successful example. However, the full potential of the SHS
has been hampered by lack of a clear route to acceptable flux calibration from
the base photographic data. We have determined the calibration factors for 170
individual SHS fields, and present a direct pathway to the measurement of
integrated H fluxes and surface brightnesses for resolved nebulae
detected in the SHS. We also include a catalogue of integrated H fluxes
for 100 planetary and other nebulae measured from the SHS, and use these
data to show that fluxes, accurate to 0.10 - 0.14 dex (25-35 per
cent), can be obtained from these fields. For the remaining 63 fields, a mean
calibration factor of 12.0 counts pix R can be used, allowing the
determination of reasonable integrated fluxes accurate to better than 0.2
dex (50 per cent). We outline the procedures involved and the caveats
that need to be appreciated in achieving such flux measurements. This paper
forms a handy reference source that will significantly increase the scientific
utility of the SHS.Comment: 14 pages, 12 figures, 2 tables (plus 7 pp. of supplementary online
information). Version to appear in MNRA
Seasonal Variation in 25(OH)D at Aberdeen (57°N) and Bone Health Indicators- Could Holidays in the Sun and Cod Liver Oil Supplements Alleviate Deficiency?
Vitamin D has been linked with many health outcomes. The aim of this longitudinal study, was to assess predictors of seasonal variation of 25-hydroxy-vitamin D (25(OH)D) (including use of supplements and holidays in sunny destinations) at a northerly latitude in the UK (57°N) in relation to bone health indicators. 365 healthy postmenopausal women (mean age 62.0 y (SD 1.4)) had 25(OH)D measurements by immunoassay, serum C-telopeptide (CTX), estimates of sunlight exposure (badges of polysulphone film), information regarding holidays in sunny destinations, and diet (from food diaries, including use of supplements such as cod liver oil (CLO)) at fixed 3-monthly intervals over 15 months (subject retention 88%) with an additional 25(OH)D assessment in spring 2008. Bone mineral density (BMD) at the lumbar spine (LS) and dual hip was measured in autumn 2006 and spring 2007 (Lunar I-DXA). Deficiency prevalence (25(OH)
Towards ecological sustainability: observations on the role of the arts
This paper describes how the arts shape environmental behaviour of individuals and society and is a synthesis arising from a program of previous publication. The literature suggests that the arts may have a role in shaping environmental behaviour but it is not clear how or in what circumstances this might occur. Hence we set out to describe ways in which the arts shape environmental behaviour at the individual level and, through the accumulated actions of individuals, at the societal level. Through this examination we aim to explain the role of the arts in moving society towards ecological sustainability. Our research drew on interviews with 96 key informants working in the arts and in the natural resource management sectors, combined with a mix of empirical, experimental and post hoc studies of eight community-based art and environment events. On the basis of this research, a model was developed to describe how the arts can shape environmental behaviour. Three pathways are proposed: communicating information in an engaging form; creating empathy towards the natural environment; and embedding the arts in ecologically sustainable development
Commentary: The History of Neurosurgery at Albany Medical College and Albany Medical Center Hospital, Albany, New York.
The origins of the Department of Neurosurgery at Albany Medical College closely parallel the development of early America and the establishment of modern health care.The tales of Washington Irving, the works of the Hudson River School of painters, and summers in the Catskill Mountains or Adirondacks are the stories that color the history of Upstate New York (Figure1). As a social, industrial, and political hub of the American colonies, New England’s need for centers providing structured medicine led to the creation of Albany Medical College in1839, one of the earliest such institutions in the young nation.1 Rapid progress in nearly every other realm of life required medical advancements as well, prompting subspecialization and the development of neurosurgery in the region
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