16,973 research outputs found
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.
Bulk Viscosity of Interacting Hadrons
We show that first approximations to the bulk viscosity are
expressible in terms of factors that depend on the sound speed , the
enthalpy, and the interaction (elastic and inelastic) cross section. The
explicit dependence of on the factor is
demonstrated in the Chapman-Enskog approximation as well as the variational and
relaxation time approaches. The interesting feature of bulk viscosity is that
the dominant contributions at a given temperature arise from particles which
are neither extremely nonrelativistic nor extremely relativistic. Numerical
results for a model binary mixture are reported.Comment: 4 pages, 1 figure, Contribution to Quark Matter 2009, Knoxville,
Tennessee, US
Skating on slippery ice
The friction of a stationary moving skate on smooth ice is investigated, in
particular in relation to the formation of a thin layer of water between skate
and ice. It is found that the combination of ploughing and sliding gives a
friction force that is rather insensitive for parameters such as velocity and
temperature. The weak dependence originates from the pressure adjustment inside
the water layer. For instance, high velocities, which would give rise to high
friction, also lead to large pressures, which, in turn, decrease the contact
zone and so lower the friction. The theory is a combination and completion of
two existing but conflicting theories on the formation of the water layer.Comment: 26 pages, 8 figures Posted at SciPos
Reptation in the Rubinstein-Duke model: the influence of end-reptons dynamics
We investigate the Rubinstein-Duke model for polymer reptation by means of
density-matrix renormalization group techniques both in absence and presence of
a driving field. In the former case the renewal time \tau and the diffusion
coefficient D are calculated for chains up to N=150 reptons and their scaling
behavior in N is analyzed. Both quantities scale as powers of N: and with the asymptotic exponents z=3 and x=2, in agreement
with the reptation theory. For an intermediate range of lengths, however, the
data are well-fitted by some effective exponents whose values are quite
sensitive to the dynamics of the end reptons. We find 2.7 <z< 3.3 and 1.8 <x<
2.1 for the range of parameters considered and we suggest how to influence the
end reptons dynamics in order to bring out such a behavior. At finite and not
too small driving field, we observe the onset of the so-called band inversion
phenomenon according to which long polymers migrate faster than shorter ones as
opposed to the small field dynamics. For chains in the range of 20 reptons we
present detailed shapes of the reptating chain as function of the driving field
and the end repton dynamics.Comment: RevTeX 12 Pages and 14 figure
Probing the basins of attraction of a recurrent neural network
A recurrent neural network is considered that can retrieve a collection of
patterns, as well as slightly perturbed versions of this `pure' set of patterns
via fixed points of its dynamics. By replacing the set of dynamical
constraints, i.e., the fixed point equations, by an extended collection of
fixed-point-like equations, analytical expressions are found for the weights
w_ij(b) of the net, which depend on a certain parameter b. This so-called basin
parameter b is such that for b=0 there are, a priori, no perturbed patterns to
be recognized by the net. It is shown by a numerical study, via probing sets,
that a net constructed to recognize perturbed patterns, i.e., with values of
the connections w_ij(b) with b unequal zero, possesses larger basins of
attraction than a net made with the help of a pure set of patterns, i.e., with
connections w_ij(b=0). The mathematical results obtained can, in principle, be
realized by an actual, biological neural net.Comment: 17 pages, LaTeX, 2 figure
- …