42,563 research outputs found
Validation of the new Hipparcos reduction
Context.A new reduction of the astrometric data as produced by the Hipparcos
mission has been published, claiming accuracies for nearly all stars brighter
than magnitude Hp = 8 to be better, by up to a factor 4, than in the original
catalogue. Aims.The new Hipparcos astrometric catalogue is checked for the
quality of the data and the consistency of the formal errors as well as the
possible presence of error correlations. The differences with the earlier
publication are explained. Methods. The internal errors are followed through
the reduction process, and the external errors are investigated on the basis of
a comparison with radio observations of a small selection of stars, and the
distribution of negative parallaxes. Error correlation levels are investigated
and the reduction by more than a factor 10 as obtained in the new catalogue is
explained. Results.The formal errors on the parallaxes for the new catalogue
are confirmed. The presence of a small amount of additional noise, though
unlikely, cannot be ruled out. Conclusions. The new reduction of the Hipparcos
astrometric data provides an improvement by a factor 2.2 in the total weight
compared to the catalogue published in 1997, and provides much improved data
for a wide range of studies on stellar luminosities and local galactic
kinematics.Comment: 12 pages, 19 figures, accepted for publication by Astronomy and
Astrophysic
Imagining the Great Lakes Region: discourses and practices of civil society regional approaches for peacebuilding in Rwanda, Burundi and DR Congo
The idea has gained ground in recent years that, as conflicts in the countries of the Great Lakes Region are strongly interlinked, regional approaches are necessary to resolve them. This interest in regional dimensions of conflict and peacebuilding also gains currency in other parts of the world. Attention to regional approaches is reflected in the efforts of international organisations and donors to promote civil society peacebuilding. They assume that regional cooperation and exchange between civil society organisations contribute to peace, and provide an alternative to single-country interventions or regional diplomatic initiatives. This paper explores how such assumptions work out in practice. Experiences in the Great Lakes Region show that local and international organisations have difficulty in analysing the regional character of conflict and arriving at collaborative regional strategies. Moreover, local civil society organisations are deeply embedded in the politics of regional conflict. Consequently, the shift to regional peacebuilding approaches remains more theoretical than practical. This paper suggests that international supporting organisations need to adjust their ambitions in regional peacebuilding, but nonetheless have roles in fostering regional identification among civil society organisations
Energy Dependence of Particle Production in nucleus-nucleus collisions at the CERN SPS
New preliminary results on kaon and pion production in central 30AGeV Pb+Pb
collisions are presented. The data are compared to data at lower and higher
energies to examine the energy dependence of the kaon to pion ratios and the
inverse slope parameters of kaons. The results are compared to expectations
from models with and without a phase transition to the Quark Gluon Plasma.Comment: 4 pages, 5 figures, presented at XXXVIIIth Rencontres de Moriond, QCD
and High Energy Hadronic Interactions sessio
Comparing energy loss phenomenology
High-pT particle production is suppressed in heavy ion collisions due to
parton energy loss in dense QCD matter. Here we present a systematic comparison
of two different theoretical approximations to parton energy loss calculations:
the opacity expansion and the multiple-soft scattering approximation for the
simple case of a quark traversing a homogeneous piece of matter with fixed
length (the TECHQM 'brick problem'), with focus on the range of parameters that
is relevant for interpreting RHIC measurements of high-pT hadron suppression.Comment: Proceedings for workshop 'High-pt at the LHC 09', Prague, submitted
to Proceedings of Science. 8 pages, 3 figures Update v2: fix typos in Eq 1.
Two paradigms for religious representation: The physicist and the playground
In an earlier issue, I argue (2014) that psychology and epistemology should distinguish religious credence from factual belief. These are distinct cognitive attitudes. Levy (2017) rejects this distinction, arguing that both religious and factual “beliefs” are subject to “shifting” on the basis of fluency and “intuitiveness.” Levy’s theory, however, (1) is out of keeping with much research in cognitive science of religion and (2) misrepresents the notion of factual belief employed in my theory. So his claims don’t undermine my distinction. I conclude by suggesting some approaches to empirically testing our views
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