Short directed cycles in bipartite digraphs

The Caccetta-H\"aggkvist conjecture implies that for every integer $k\ge 1$, if $G$ is a bipartite digraph, with $n$ vertices in each part, and every vertex has out-degree more than $n/(k+1)$, then $G$ has a directed cycle of length at most $2k$. If true this is best possible, and we prove this for $k = 1,2,3,4,6$ and all $k\ge 224,539$. More generally, we conjecture that for every integer $k\ge 1$, and every pair of reals $\alpha, \beta> 0$ with $k\alpha +\beta>1$, if $G$ is a bipartite digraph with bipartition $(A,B)$, where every vertex in $A$ has out-degree at least $\beta|B|$, and every vertex in $B$ has out-degree at least $\alpha|A|$, then $G$ has a directed cycle of length at most $2k$. This implies the Caccetta-H\"aggkvist conjecture (set $\beta>0$ and very small), and again is best possible for infinitely many pairs $(\alpha,\beta)$. We prove this for $k = 1,2$, and prove a weaker statement (that $\alpha+\beta>2/(k+1)$ suffices) for $k=3,4$

Costs and Benefits of Preventing Workplace Accidents: The Case of Participatory Ergonomics

This paper provides a cost-benefit analysis of a participatory ergonomics program conducted at the beginning of the 1990s to reduce back-related disorders among packers at a warehouse of the Société des Alcools du Québec in Quebec City. After evaluating the costs of the program, we present a rigorous econometric analysis to assess how many accidents have been prevented by the program so as to compute the direct and indirects costs avoided as a result of such accident reduction. We show that the program has indeed been profitable for the firm. Les auteurs de cet article ont effectué l'analyse coûts-avantages d'un programme ergonomique mis en oeuvre en 1990 pour diminuer, avec la participation des intéressés, les problèmes liés aux maux de dos chez les manutentionnaires d'un entrepôt de la Société des Alcools du Québec situé dans la ville de Québec. Après avoir estimé les coûts du programme, ils ont conduit une analyse économétrique rigoureuse pour déterminer le nombre d'accidents évités grâce au programme. Ils ont pu ainsi calculer les coûts directs et indirects qui n'auront pas à être subis à cause de la réduction du nombre des accidents. Ils en concluent que le programme a réellement été rentable pour la S.A.Q.

Rcapture: Loglinear Models for Capture-Recapture in R

This article introduces Rcapture, an R package for capture-recapture experiments. The data for analysis consists of the frequencies of the observable capture histories over the t capture occasions of the experiment. A capture history is a vector of zeros and ones where one stands for a capture and zero for a miss. Rcapture can fit three types of models. With a closed population model, the goal of the analysis is to estimate the size N of the population which is assumed to be constant throughout the experiment. The estimator depends on the way in which the capture probabilities of the animals vary. Rcapture features several models for these capture probabilities that lead to different estimators for N. In an open population model, immigration and death occur between sampling periods. The estimation of survival rates is of primary interest. Rcapture can fit the basic Cormack-Jolly-Seber and Jolly-Seber model to such data. The third type of models fitted by Rcapture are robust design models. It features two levels of sampling; closed population models apply within primary periods and an open population model applies between periods. Most models in Rcapture have a loglinear form; they are fitted by carrying out a Poisson regression with the R function glm. Estimates of the demographic parameters of interest are derived from the loglinear parameter estimates; their variances are obtained by linearization. The novel feature of this package is the provision of several new options for modeling capture probabilities heterogeneity between animals in both closed population models and the primary periods of a robust design. It also implements many of the techniques developed by R. M. Cormack for open population models.

Why Is it so Difficult to Know if National Pride Leads the Way to European Identity or Prevents it ?

For a long time, support for European integration could be analysed without much reference tothe attachments of European citizens to their nations. Beyond the recurring acknowledgement of thestrong social determination of attitudes towards Europe, analysts did observe important differences insupport between European countries, but these were considered as encompassing all sorts ofdifferences between these countries; there was no need to infer major differences in the ways differentpeoples of Europe relate to their own country.Nowadays, most analysts of European Union consider that the growing process of Europeanintegration has changed the very nature of attitudes towards Europe. Since 1994 and the setting up ofEuropean citizenship, support for the European Union should no longer be analysed as tolerantattitudes towards a remote and foreign object, and might be addressed as a European identity buildingprocess. Hence, the question of the relationship between the support for the European Union and thecommitment of European citizens to their own country should not be avoided anymore (Diez Medrano2003). This article will examine over time the relationship between national and Europeancommitments, which we will apprehend through the notion of national and European identifications.European identity; identity; Europeanization; Europeanization

Pure pairs. I. Trees and linear anticomplete pairs

The Erdos-Hajnal Conjecture asserts that for every graph H there is a constant c > 0 such that every graph G that does not contain H as an induced subgraph has a clique or stable set of cardinality at least |G|^c. In this paper, we prove a conjecture of Liebenau and Pilipczuk, that for every forest H there exists c > 0, such that every graph G contains either an induced copy of H, or a vertex of degree at least c|G|, or two disjoint sets of at least c|G| vertices with no edges between them. It follows that for every forest H there is c > 0 so that if G contains neither H nor its complement as an induced subgraph then there is a clique or stable set of cardinality at least |G|^c

Classification of Southern Ocean krill and icefish echoes using random forests

Acknowledgements The authors thank the crews, fishers, and scientists who conducted the various surveys from which data were obtained. This work was supported by the Government of South Georgia and South Sandwich Islands. Additional logistical support provided by The South Atlantic Environmental Research Institute, with thanks to Paul Brickle. PF receives funding from the MASTS pooling initiative (TheMarine Alliance for Science and Technology for Scotland), and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. SF is funded by the Natural Environment Research Council, and data were provided from the British Antarctic Survey Ecosystems Long-term Monitoring and Surveys programme as part of the BAS Polar Science for Planet Earth Programme. The authors also thank the anonymous referees for their helpful suggestions on an earlier version of this manuscript.Peer reviewedPostprin

Velocimetry of red blood cells in microvessels by the dual-slit method: Effect of velocity gradients

The dual-slit is a photometric technique used for the measurement of red blood cell (RBC) velocity in microvessels. Two photometric windows (slits) are positioned along the vessel. Because the light is modulated by the RBCs flowing through the microvessel, a time dependent signal is captured for each window. A time delay between the two signals is obtained by temporal cross correlation, and is used to deduce a velocity, knowing the distance between the two slits. Despite its wide use in the field of microvascular research, the velocity actually measured by this technique has not yet been unambiguously related to a relevant velocity scale of the flow (e.g. mean or maximal velocity) or to the blood flow rate. This is due to a lack of fundamental understanding of the measurement and also because such a relationship is crucially dependent on the non-uniform velocity distribution of RBCs in the direction parallel to the light beam, which is generally unknown. The aim of the present work is to clarify the physical significance of the velocity measured by the dual-slit technique. For that purpose, dual-slit measurements were performed on computer-generated image sequences of RBCs flowing in microvessels, which allowed all the parameters related to this technique to be precisely controlled. A parametric study determined the range of optimal parameters for the implementation of the dual-slit technique. In this range, it was shown that, whatever the parameters governing the flow, the measured velocity was the maximal RBC velocity found in the direction parallel to the light beam. This finding was then verified by working with image sequences of flowing RBCs acquired in PDMS micro-systems in vitro. Besides confirming the results and physical understanding gained from the study with computer generated images, this in vitro study showed that the profile of RBC maximal velocity across the channel was blunter than a parabolic profile, and exhibited a non-zero sliding velocity at the channel walls. Overall, the present work demonstrates the robustness and high accuracy of the optimized dual-slit technique in various flow conditions, especially at high hematocrit, and discusses its potential for applications in vivo