Finite-size left-passage probability in percolation

We obtain an exact finite-size expression for the probability that a percolation hull will touch the boundary, on a strip of finite width. Our calculation is based on the q-deformed Knizhnik--Zamolodchikov approach, and the results are expressed in terms of symplectic characters. In the large size limit, we recover the scaling behaviour predicted by Schramm's left-passage formula. We also derive a general relation between the left-passage probability in the Fortuin--Kasteleyn cluster model and the magnetisation profile in the open XXZ chain with diagonal, complex boundary terms.Comment: 21 pages, 8 figure

A numerical adaptation of SAW identities from the honeycomb to other 2D lattices

Recently, Duminil-Copin and Smirnov proved a long-standing conjecture by Nienhuis that the connective constant of self-avoiding walks on the honeycomb lattice is $\sqrt{2+\sqrt{2}}.$ A key identity used in that proof depends on the existence of a parafermionic observable for self-avoiding walks on the honeycomb lattice. Despite the absence of a corresponding observable for SAW on the square and triangular lattices, we show that in the limit of large lattices, some of the consequences observed on the honeycomb lattice persist on other lattices. This permits the accurate estimation, though not an exact evaluation, of certain critical amplitudes, as well as critical points, for these lattices. For the honeycomb lattice an exact amplitude for loops is proved.Comment: 21 pages, 7 figures. Changes in v2: Improved numerical analysis, giving greater precision. Explanation of why we observe what we do. Extra reference

Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model studies

It has been assumed until very recently that all long-range correlations are screened in three-dimensional melts of linear homopolymers on distances beyond the correlation length $\xi$ characterizing the decay of the density fluctuations. Summarizing simulation results obtained by means of a variant of the bond-fluctuation model with finite monomer excluded volume interactions and topology violating local and global Monte Carlo moves, we show that due to an interplay of the chain connectivity and the incompressibility constraint, both static and dynamical correlations arise on distances $r \gg \xi$. These correlations are scale-free and, surprisingly, do not depend explicitly on the compressibility of the solution. Both monodisperse and (essentially) Flory-distributed equilibrium polymers are considered.Comment: 60 pages, 49 figure

Evaluation de l’action publique et déterminants fonciers. Analyse de deux projets de lutte contre la désertification au Sud-Algérien et au Nord-Cameroun

International audienceDesertification is the land loss of productive capacities due to the combination of climate variability and human pressure. It is understood both as a global environmental and a rural development issue. In this paper, the authors show how projects to combat desertification can create new land tenure during the time they are implemented and how these temporary changes can lead to some definitive transformation of both the concerned resources and the way they are appropriated. The two cases analyzed deal with pastoral projects to reverse desertification trend in arid areas of Algeria (2004-2008) and North-Cameroon (1978-1983). Ex post assessments show how these two projects have led to both the transformation of pastoral resources and their tenure, exacerbating local inequalities.La désertification, entendue comme la perte de capacités productives de terres liée à la combinaison de variations climatiques et d'activités humaines (CNULCD, 1994) est reconnue comme un problème d'environnement mondial et de développement rural. Dans cet article, les auteurs montrent comment les projets de lutte contre la désertification (LCD) engendrent la création d'espaces fonciers de transition, le temps de leur mise en oeuvre. Les deux cas présentés concernent des projets pastoraux de LCD, l'un en Algérie (2004-2008) et l'autre au nord-Cameroun (1978-1983). L'évaluation ex post des deux projets montre que ces processus transitoires de transformation du foncier pastoral conduisent à une transformation radicale de la ressource considérée ainsi que de ses modes d'appropriation

Evaluation de l’action publique et déterminants fonciers. Analyse de deux projets de lutte contre la désertification au Sud-Algérien et au Nord-Cameroun

International audienceDesertification is the land loss of productive capacities due to the combination of climate variability and human pressure. It is understood both as a global environmental and a rural development issue. In this paper, the authors show how projects to combat desertification can create new land tenure during the time they are implemented and how these temporary changes can lead to some definitive transformation of both the concerned resources and the way they are appropriated. The two cases analyzed deal with pastoral projects to reverse desertification trend in arid areas of Algeria (2004-2008) and North-Cameroon (1978-1983). Ex post assessments show how these two projects have led to both the transformation of pastoral resources and their tenure, exacerbating local inequalities.La désertification, entendue comme la perte de capacités productives de terres liée à la combinaison de variations climatiques et d'activités humaines (CNULCD, 1994) est reconnue comme un problème d'environnement mondial et de développement rural. Dans cet article, les auteurs montrent comment les projets de lutte contre la désertification (LCD) engendrent la création d'espaces fonciers de transition, le temps de leur mise en oeuvre. Les deux cas présentés concernent des projets pastoraux de LCD, l'un en Algérie (2004-2008) et l'autre au nord-Cameroun (1978-1983). L'évaluation ex post des deux projets montre que ces processus transitoires de transformation du foncier pastoral conduisent à une transformation radicale de la ressource considérée ainsi que de ses modes d'appropriation

Achievable Rate Region of the Bidirectional Buffer-Aided Relay Channel With Block Fading

The bidirectional relay channel, in which two users communicate with each other through a relay node, is a simple but fundamental and practical network architecture. In this paper, we consider the block fading bidirectional relay channel and propose efficient transmission strategies that exploit the block fading property of the channel. Thereby, we consider a decode-and-forward relay and assume that a direct link between the two users is not present. Our aim is to characterize the long-term achievable rate region and to develop protocols which achieve all points of the obtained rate region. Specifically, in the bidirectional relay channel, there exist six possible transmission modes: four point-to-point modes (user 1-to-relay, user 2-to-relay, relay-to-user 1, relay-to-user 2), a multiple-access mode (both users to the relay), and a broadcast mode (the relay to both users). Most existing protocols assume a fixed schedule for using a subset of the aforementioned transmission modes. Motivated by this limitation, we develop protocols which are not restricted to adhere to a predefined schedule for using the transmission modes. In fact, based on the instantaneous channel state information (CSI) of the involved links, the proposed protocol selects the optimal transmission mode in each time slot to maximize the long-term achievable rate region. Thereby, we consider two different types of transmit power constraints: 1) a joint long-term power constraint for all nodes, and 2) a fixed transmit power for each node. Furthermore, to enable the use of a non-predefined schedule for transmission mode selection, the relay has to be equipped with two buffers for storage of the information received from both users. As data buffering increases the end-to-end delay, we consider both delay-unconstrained and delay-constrained transmission in the paper.Comment: submitted to IEEE Transaction on Information Theor

Nonlinear compressible magnetohydrodynamic flows modeling of a process ICP torch

Magnetohydrodynamics (MHD) describes the physical behavior of inductively coupled plasma (ICP). The goal of this paper is to provide a physical understanding of a process ICP torch using a resistive MHD model. This includes a basic description and derivation of the fluid model. Inductive plasma is treated as a continuous, conducting fluid that satisfies the classical laws of motion and thermodynamics. This model combines fluid equations, similar to those used in fluid dynamics, with Maxwell’s equations. Steady fluid flow and temperature equations are simultaneously solved (direct method) using a finite elements method (FEM). The electromagnetic field equations are formulated in terms of potential vector with applied voltage source, so this model is physically more consistent, a more accurate and a faster simulation. The governing resistive MHD equations for an inductive plasma flow under local thermodynamic equilibrium (LTE) and laminar flow are presented, with appropriate boundary conditions. The model enabled to obtain the electromagnetic fields, temperature and flow velocity distributions also allows the determination of the electric parameters such as impedance of the plasma torch, total power, eddy losses, etc