220 research outputs found
Really Social Syndication: A Conceptual View on Microblogging
This working paper presents a formal comparison of microblogging and the traditional blogging stack facilitating RSS. The aim is to provide a better understanding of the differences and similarities of these two technologies. Our findings suggest that they use the same concepts (channels and items) but differ in the support of interaction between them. However, we argue that the foundation for the richer interaction experience of microblogging is its lack of interoperability and its centralistic approach. Therefore, future research should focus on combining the advantages of both RSS technology and microblogging
Technological Change in Economic Models of Environmental Policy: A Survey
This paper provides an overview of the treatment of technological change in economic models of environmental policy. Numerous economic modeling studies have confirmed the sensitivity of mid- and long-run climate change mitigation cost and benefit projections to assumptions about technology costs. In general, technical progress is considered to be a noneconomic, exogenous variable in global climate change modeling. However, there is overwhelming evidence that technological change is not an exogenous variable but to an important degree endogenous, induced by needs and pressures. Hence, some environmenteconomy models treat technological change as endogenous, responding to socio-economic variables. Three main elements in models of technological innovation are: (i) corporate investment in research and development, (ii) spillovers from R&D, and (iii) technology learning, especially learning-by-doing. The incorporation of induced technological change in different types of environmental-economic models tends to reduce the costs of environmental policy, accelerates abatement and may lead to positive spillover and negative leakage
WIATEC: A World Integrated Assessment Model of Global Trade Environment and Climate Change
XMM-LSS discovery of a z=1.22 galaxy cluster
We present details of the discovery of XLSSJ022303.0-043622, a z=1.2 cluster
of galaxies. This cluster was identified from its X-ray properties and selected
as a z>1 candidate from its optical/near-IR characteristics in the XMM
Large-Scale Structure Survey (XMM-LSS). It is the most distant system
discovered in the survey to date. We present ground-based optical and near IR
observations of the system carried out as part of the XMM-LSS survey. The
cluster has a bolometric X-ray luminosity of 1.1 +/- 0.7 x 10^44 erg/s, fainter
than most other known z>1 X-ray selected clusters. In the optical it has a
remarkably compact core, with at least a dozen galaxies inside a 125 kpc radius
circle centred on the X-ray position. Most of the galaxies within the core, and
those spectroscopically confirmed to be cluster members, have stellar masses
similar to those of massive cluster galaxies at low redshift. They have colours
comparable to those of galaxies in other z>1 clusters, consistent with showing
little sign of strong ongoing star formation. The bulk of the star formation
within the galaxies appears to have ceased at least 1.5 Gyr before the observed
epoch. Our results are consistent with massive cluster galaxies forming at z>1
and passively evolving thereafter. We also show that the system is
straightforwardly identified in Spitzer/IRAC 3.6 and 4.5 micron data obtained
by the SWIRE survey emphasising the power and utility of joint XMM and Spitzer
searches for the most distant clusters.Comment: 8 pages, 6 figures, MNRAS accepte
Constraints on modified gravity from the observed X-ray luminosity function of galaxy clusters
We use measurements of the growth of cosmic structure, as inferred from the
observed evolution of the X-ray luminosity function (XLF) of galaxy clusters,
to constrain departures from General Relativity (GR) on cosmological scales. We
employ the popular growth rate parameterization, Omega_m(z)^gamma, for which GR
predicts a growth index gamma~0.55. We use observations of the cosmic microwave
background (CMB), type Ia supernovae (SNIa), and X-ray cluster gas-mass
fractions (fgas), to simultaneously constrain the expansion history and energy
content of the Universe, as described by the background model parameters:
Omega_m, w, and Omega_k, i.e., the mean matter density, the dark energy
equation of state parameter, and the mean curvature, respectively. Using
conservative allowances for systematic uncertainties, in particular for the
evolution of the mass-luminosity scaling relation in the XLF analysis, we find
gamma=0.51+0.16-0.15 and Omega_m=0.27+-0.02 (68.3 per cent confidence limits),
for a flat cosmological constant (LCDM) background model. Allowing w to be a
free parameter, we find gamma=0.44+0.17-0.15. Relaxing the flatness prior in
the LCDM model, we obtain gamma=0.51+0.19-0.16. When in addition to the XLF
data we use the CMB data to constrain gamma through the ISW effect, we obtain a
combined constraint of gamma=0.45+0.14-0.12 for the flat LCDM model. Our
analysis provides the tightest constraints to date on the growth index. We find
no evidence for departures from General Relativity on cosmological scales.Comment: 7 pages, 2 figures, 1 table. Accepted for publication in MNRAS. Minor
improvements. Conclusions unchange
Moral Concerns on Tradable Pollution Permits in International Environmental Agreements
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