7,295 research outputs found
Affine Solitons: A Relation Between Tau Functions, Dressing and B\"acklund Transformations
We reconsider the construction of solitons by dressing transformations in the
sine-Gordon model. We show that the -soliton solutions are in the orbit of
the vacuum, and we identify the elements in the dressing group which allow us
to built the -soliton solutions from the vacuum solution. The dressed
-functions can be computed in two different ways~: either using adjoint
actions in the affine Lie algebra , and this gives the relation
with the B\"acklund transformations, or using the level one representations of
the affine Lie algebra , and this directly gives the formulae
for the -functions in terms of vertex operators.Comment: 33 pages. SPhT-92-055; LPTHE-92-1
Sahara or Sahel? The fuzzy geography of terrorism in West Africa
Since the mid-2000s, terrorism has pushed the peripheries of West Africa into the news and the public eye. While the political implications of this phenomenon have been extensively documented, most commentators have adopted a zonal approach to terrorism in which the Sahel and the Sahara are usually confused. This paper assumes that this confusion dramatically highlights the failure of academic and common geography to think beyond territories in West Africa, and to move away from a ?sedentary? vision of West African societies. The paper contributes to an understanding of the geographical locations of terrorism in West Africa by showing, firstly, what the main reasons behind the current confusion between the Sahel and Sahara are. Secondly, we show that this confusion arose from a territorial vision of space, which has important implications not only for local economic activities, but also for our own understanding of the spatiality of networks in West Africa.terrorism; space; networks; Social Network Analysis (SNA); Sahel; Sahara; West Africa
Clarification and complement to "Mean-field description and propagation of chaos in networks of Hodgkin-Huxley and FitzHugh-Nagumo neurons"
In this note, we clarify the well-posedness of the limit equations to the
mean-field -neuron models proposed in Baladron et al. and we prove the
associated propagation of chaos property. We also complete the modeling issue
in Baladron et al. by discussing the well-posedness of the stochastic
differential equations which govern the behavior of the ion channels and the
amount of available neurotransmitters
Enabling computation of correlation bounds for finite-dimensional quantum systems via symmetrisation
We present a technique for reducing the computational requirements by several
orders of magnitude in the evaluation of semidefinite relaxations for bounding
the set of quantum correlations arising from finite-dimensional Hilbert spaces.
The technique, which we make publicly available through a user-friendly
software package, relies on the exploitation of symmetries present in the
optimisation problem to reduce the number of variables and the block sizes in
semidefinite relaxations. It is widely applicable in problems encountered in
quantum information theory and enables computations that were previously too
demanding. We demonstrate its advantages and general applicability in several
physical problems. In particular, we use it to robustly certify the
non-projectiveness of high-dimensional measurements in a black-box scenario
based on self-tests of -dimensional symmetric informationally complete
POVMs.Comment: A. T. and D. R. contributed equally for this projec
Viscoroute 2.0: a tool for the simulation of moving load effects on asphalt pavement
As shown by strains measured on full scale experimental aircraft structures,
traffic of slow-moving multiple loads leads to asymmetric transverse strains
that can be higher than longitudinal strains at the bottom of asphalt pavement
layers. To analyze this effect, a model and a software called ViscoRoute have
been developed. In these tools, the structure is represented by a multilayered
half-space, the thermo-viscoelastic behaviour of asphalt layers is accounted by
the Huet-Sayegh rheological law and loads are assumed to move at constant
speed. First, the paper presents a comparison of results obtained with
ViscoRoute to results stemming from the specialized literature. For thick
asphalt pavement and several configurations of moving loads, other ViscoRoute
simulations confirm that it is necessary to incorporate viscoelastic effects in
the modelling to well predict the pavement behaviour and to anticipate possible
damages in the structure.Comment: 27 pages
Water temperature modeling in the Garonne River (France)
Stream water temperature is one of the most important parameters for water quality and ecosystem studies. Temperature can influence many chemical and biological processes and therefore impacts on the living conditions and distribution of aquatic ecosystems. Simplified models such as statistical models can be very useful for practitioners and water resource management. The present study assessed two statistical models â an equilibrium-based model and stochastic autoregressive model with exogenous inputs â in modeling daily mean water temperatures in the Garonne River from 1988 to 2005. The equilibrium temperature-based model is an approach where net heat flux at the water surface is expressed as a simpler form than in traditional deterministic models. The stochastic autoregressive model with exogenous inputs consists of decomposing the water temperature time series into a seasonal component and a short-term component (residual component). The seasonal component was modeled by Fourier series and residuals by a second-order autoregressive process (Markov chain) with use of short-term air temperatures as exogenous input. The models were calibrated using data of the first half of the period 1988â2005 and validated on the second half. Calibration of the models was done using temperatures above 20 âŠC only to ensure better prediction of high temperatures that are currently at stake for the aquatic conditions of the Garonne River, and particularly for freshwater migrating fishes such as Atlantic Salmon (Salmo salar L.). The results obtained for both approaches indicated that both models performed well with an average root mean square error for observed temperatures above 20 âŠC that varied on an annual basis from 0.55 âŠC to 1.72 âŠC on validation, and good predictions of temporal occurrences and durations of three temperature threshold crossings linked to the conditions of migration and survival of Atlantic Salmon
Spectro-interferometric observations of interacting massive stars with VEGA/CHARA
We obtained spectro-interferometric observations in the visible of
Lyrae and Sgr using the instrument VEGA of the CHARA interferometric
array. For Lyrae, the dispersed fringe visibilities and differential
phases were obtained in spectral regions containing the H and HeI 6678
lines and the H and HeI 4921 lines. Whereas the source is unresolved in
the continuum, the source of the emission lines is resolved and the photocenter
of the bulk of the H emission exhibits offsets correlated with the
orbital phase. For Sgr, both the continuum and H sources are
resolved, but no clear binary signal is detected. The differential phase shift
across the line reveals that the bulk of the H emission is clearly
offset from the primary
Phase-space methods in nuclear reactions around the Fermi energy
Some prescriptions for in-medium complex particle production in nuclear
reactions are proposed. They have been implemented in two models to simulate
nucleon-nucleus (nIPSE) and nucleus-nucleus (HIPSE) reactions around the Fermi
energy \cite{Lac04,Lac05}. Our work emphasizes the effect of randomness in
cluster formation, the importance of the nucleonic Fermi motion as well as the
role of conservation laws. The key role of the phase-space exploration before
and after secondary decay is underlined. This is illustrated in the case of two
debated issues: the memory loss of the entrance channel in central collisions
and the partitions after the pre-equilibrium stage.Comment: Proceedings of the IWM2005 workshop, Catane (Italy), Nov. 2005.
DOWNLOAD HIPSE program at:
http://caeinfo.in2p3.fr/theorie/theory_lacroix.htm
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