13,037 research outputs found
Simlandscape: serious gaming in participatory spatial
In an attempt to improve support for contemporary spatial planning practice, Simlandscape has been developed. In this document the development of Simlandscape as ¿serious game¿ in digital form is described. In its current state, Simlandscape exists in two methodological forms; as an analogue game and as a planning support system using GIS for research and design. The game focuses on simulation of plan processes and on the resulting transformation of areas involved. Players interact with an analogue area model. The planning support system focuses on design and evaluation of plan scenarios and the data handling and presentation accompanying this process. A major challenge now is to integrate, upgrade and digitize components of the analogous game with the planning support system. Several interesting components (practical and scientific) of this project are identified and are discussed
Modification of the simple mass balance equation for calculation of critical loads of acidity.
Over the last few years, the simple mass balance equation for the calculation of critical loads of acidity has been gradually modified as the underlying critical load concepts have developed and as problems with particular forms of the equation have been identified, through application in particular countries. The first major update of the equation took place following a workshop held in Vienna, Austria (Hojesky et al. 1993). The workshop was held to discuss problems which had been identified when the then current form of the equation was applied in countries with high rainfall. The problems had largely arisen because of simplifications and assumptions incorporated into the early formulation of the equation. The equation was reformulated to overcome the problems identified at the workshop. However, further problems were identified when the reformulated equation was applied in the UK in situations with a combination of high rainfall, large marine inputs and widespread occurrence of organic soils. A small workshop was, therefore held in Grange-over-Sands, UK in late 1993 to dicuss the problems and to further re-evaluate the equation. The problems had arisen in the UK because of simplifications and assumptions made in the formulation concerning, in particular, cation leaching and uptake. As a result, a more rigorous treatment of these variables was incorporated into the equation. The reformulation of the equation, as derived at the September 1993 workshop is described below
Micron-sized forsterite grains in the pre-planetary nebula of IRAS 17150-3224 - Searching for clues on the mysterious evolution of massive AGB stars
We study the grain properties and location of the forsterite crystals in the
circumstellar environment of the pre-planetary nebula (PPN) IRAS 17150-3224 in
order to learn more about the as yet poorly understood evolutionary phase prior
to the PPN. We use the best-fit model for IRAS 17150-3224 of Meixner et al.
(2002) and add forsterite to this model. We investigate different spatial
distributions and grain sizes of the forsterite crystals in the circumstellar
environment. We compare the spectral bands of forsterite in the mid-infrared
and at 69 micrometre in radiative transport models to those in ISO-SWS and
Herschel/PACS observations. We can reproduce the non-detection of the
mid-infrared bands and the detection of the 69 micrometre feature with models
where the forsterite is distributed in the whole outflow, in the superwind
region, or in the AGB-wind region emitted previous to the superwind, but we
cannot discriminate between these three models. To reproduce the observed
spectral bands with these three models, the forsterite crystals need to be
dominated by a grain size population of 2 micrometre up to 6 micrometre. We
hypothesise that the large forsterite crystals were formed after the superwind
phase of IRAS 17150-3224, where the star developed an as yet unknown hyperwind
with an extremely high mass-loss rate (10^-3 Msol/yr). The high densities of
such a hyperwind could be responsible for the efficient grain growth of both
amorphous and crystalline dust in the outflow. Several mechanisms are discussed
that might explain the lower-limit of 2 micrometre found for the forsterite
grains, but none are satisfactory. Among the mechanisms explored is a possible
selection effect due to radiation pressure based on photon scattering on
micron-sized grains.Comment: Accepted by A&
Dusty wind of W Hya. Multi-wavelength modelling of the present-day and recent mass-loss
Low- and intermediate-mass stars go through a period of intense mass-loss at
the end of their lives in a phase known as the asymptotic giant branch (AGB).
During the AGB a significant fraction of their initial mass is expelled in a
stellar wind. This process controls the final stages of their evolution and
contributes to the chemical evolution of galaxies. However, the wind-driving
mechanism of AGB stars is not yet well understood, especially so for
oxygen-rich sources. Characterizing both the present-day mass-loss and wind
structure and the evolution of the mass-loss rate of such stars is paramount to
advancing our understanding of this processes. We modelled the dust envelope of
W Hya using an advanced radiative transfer code. The dust model was analysed in
the light of a previously calculated gas-phase wind model and compared to
measurements available in the literature, such as infrared spectra, infrared
images, and optical scattered light fractions. We find that the dust spectrum
of W Hya can partly be explained by a gravitationally bound dust shell that
probably is responsible for most of the amorphous AlO emission. The
composition of the large (\,0.3\,m) grains needed to explain the
scattered light cannot be constrained, but probably is dominated by silicates.
Silicate emission in the thermal infrared was found to originate from beyond 40
AU from the star and we find that they need to have substantial near-infrared
opacities to be visible at such large distances. The increase in near-infrared
opacity of the dust at these distances roughly coincides with a sudden increase
in expansion velocity as deduced from the gas-phase CO lines. Finally, the
recent mass loss of W Hya is confirmed to be highly variable and we identify a
strong peak in the mass-loss rate that occurred about 3500 years ago and lasted
for a few hundred years.Comment: 15 pages, 13 figure
Tortuous ways to the extraction of neutron observables from inclusive lepton scattering
We analyze new JLAB data for inclusive electron scattering on various
targets. Computed and measured total inclusive cross sections in the range
show on a logarithmic scale reasonable agreement
for all targets. However, closer inspection of the Quasi-Elastic components
bares serious discrepancies. EMC ratios which may contain less systematic
errors fare the same. The above observations for the new data do not enable the
extraction of the magnetic form factor (FF) and the Structure Function
(SFs) of the neutron, although the application of exactly the same
analysis to older data had been successful. We add to the above analysis older
CLAS collaboration on . Removing some scattered points, it appears
possible to obtain the above mentioned neutron information. We compare our
results with others from alternative sources. Particular attention is paid to
the A=3 iso-doublet. Present data exist only for He, but the available
input and charge symmetry also enable computations for H. Their average is
the computed iso-scalar part and is compared with the empirical modification of
He towards a fictitious A=3 iso-singlet.Comment: 27 pages, 30 figure
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