Two characterizations of topological spaces with no infinite discrete subspace

We give two characteristic properties of topological spaces with no infinite discrete subspaces. The first one was obtained recently by the first author. The full result extends well-known characterizations of posets with no infinite antichain.Comment: 10 pages, no figures Replace second author by first author in the abstract and in the first line after Theorem

New constructions of CSS codes obtained by moving to higher alphabets

We generalize a construction of non-binary quantum LDPC codes over \F_{2^m} due to \cite{KHIS11a} and apply it in particular to toric codes. We obtain in this way not only codes with better rates than toric codes but also improve dramatically the performance of standard iterative decoding. Moreover, the new codes obtained in this fashion inherit the distance properties of the underlying toric codes and have therefore a minimum distance which grows as the square root of the length of the code for fixed $m$.Comment: 9 pages, 9 figures, full version of a paper submitted to the IEEE Symposium on Information Theor

About Dynamical Systems Appearing in the Microscopic Traffic Modeling

Motivated by microscopic traffic modeling, we analyze dynamical systems which have a piecewise linear concave dynamics not necessarily monotonic. We introduce a deterministic Petri net extension where edges may have negative weights. The dynamics of these Petri nets are well-defined and may be described by a generalized matrix with a submatrix in the standard algebra with possibly negative entries, and another submatrix in the minplus algebra. When the dynamics is additively homogeneous, a generalized additive eigenvalue may be introduced, and the ergodic theory may be used to define a growth rate under additional technical assumptions. In the traffic example of two roads with one junction, we compute explicitly the eigenvalue and we show, by numerical simulations, that these two quantities (the additive eigenvalue and the growth rate) are not equal, but are close to each other. With this result, we are able to extend the well-studied notion of fundamental traffic diagram (the average flow as a function of the car density on a road) to the case of two roads with one junction and give a very simple analytic approximation of this diagram where four phases appear with clear traffic interpretations. Simulations show that the fundamental diagram shape obtained is also valid for systems with many junctions. To simulate these systems, we have to compute their dynamics, which are not quite simple. For building them in a modular way, we introduce generalized parallel, series and feedback compositions of piecewise linear concave dynamics.Comment: PDF 38 page

Imputing Dairy Producers' Quota Discount Rate Using the Individual Export Milk Program in Quebec

Trade liberalization scenarios are often evaluated using sophisticated programming models that rely on a number of assumptions related to demand and supply parameters. One challenge researchers often encounter in the calibration of dairy trade liberalization models is to identify the supply response of producers under production quotas. The existence of production quotas in the Canadian dairy industry implies departures from standard marginal cost pricing. Under traditional net present value models, an assumption about the discount factors attached to production quotas must be made to infer the supply response of Canadian dairy producers following a change in the economic environment (e.g., import tariffs). The Individual Export Milk (IEM) program in Quebec generated an opportunity to estimate dairy producers’ discount factors for production quotas conditional on different assumptions about structural parameters such as producers’ risk preferences and cost efficiency.International Relations/Trade, Productivity Analysis,

Point-record incentives, asymmetric information and dynamic data

Les politiques de sécurité routière utilisent souvent des mécanismes incitatifs basés sur les infractions pour améliorer le comportement des conducteurs. Ces mécanismes sont soit monétaires (amendes, primes d'assurance), soit non monétaires (permis à points). Nous utilisons des données québécoises couvrant une période allant de 1983 à 1996 pour analyser l'efficacité incitative de ces mécanismes. Nous analysons leurs propriétés théoriques par rapport au nombre de points associés aux infractions et par rapport au temps contrat. Ces propriétés sont ensuite testées empiriquement. Nous comparons l'efficacité globale des différents mécanismes incitatifs et nous relions les résultats obtenus avec les propriétés de la relation entre l'effort de conduite prudente et le risque d'infractions. Nous concluons à la présence d'aléa moral dans les données. Par ailleurs, la prime indicée sur les points introduite en 1992 a réduit de 15% la fréquence d'infractions.

The Traffic Phases of Road Networks

We study the relation between the average traffic flow and the vehicle density on road networks that we call 2D-traffic fundamental diagram. We show that this diagram presents mainly four phases. We analyze different cases. First, the case of a junction managed with a priority rule is presented, four traffic phases are identified and described, and a good analytic approximation of the fundamental diagram is obtained by computing a generalized eigenvalue of the dynamics of the system. Then, the model is extended to the case of two junctions, and finally to a regular city. The system still presents mainly four phases. The role of a critical circuit of non-priority roads appears clearly in the two junctions case. In Section 4, we use traffic light controls to improve the traffic diagram. We present the improvements obtained by open-loop, local feedback, and global feedback strategies. A comparison based on the response times to reach the stationary regime is also given. Finally, we show the importance of the design of the junction. It appears that if the junction is enough large, the traffic is almost not slowed down by the junction.Comment: 37 page