Stiffness pathologies in discrete granular systems: bifurcation, neutral equilibrium, and instability in the presence of kinematic constraints

The paper develops the stiffness relationship between the movements and forces among a system of discrete interacting grains. The approach is similar to that used in structural analysis, but the stiffness matrix of granular material is inherently non-symmetric because of the geometrics of particle interactions and of the frictional behavior of the contacts. Internal geometric constraints are imposed by the particles' shapes, in particular, by the surface curvatures of the particles at their points of contact. Moreover, the stiffness relationship is incrementally non-linear, and even small assemblies require the analysis of multiple stiffness branches, with each branch region being a pointed convex cone in displacement-space. These aspects of the particle-level stiffness relationship gives rise to three types of micro-scale failure: neutral equilibrium, bifurcation and path instability, and instability of equilibrium. These three pathologies are defined in the context of four types of displacement constraints, which can be readily analyzed with certain generalized inverses. That is, instability and non-uniqueness are investigated in the presence of kinematic constraints. Bifurcation paths can be either stable or unstable, as determined with the Hill-Bazant-Petryk criterion. Examples of simple granular systems of three, sixteen, and sixty four disks are analyzed. With each system, multiple contacts were assumed to be at the friction limit. Even with these small systems, micro-scale failure is expressed in many different forms, with some systems having hundreds of micro-scale failure modes. The examples suggest that micro-scale failure is pervasive within granular materials, with particle arrangements being in a nearly continual state of instability

Towards a Principal-Agent Based Typology of Risks in Public-Private Partnerships

There is a strong economic rationale for close cooperation between the public and private sectors. This has resulted in a significant increase in the demand for the provision of public services through instruments combining public and private money such as public-private partnerships (PPPs or P3s). We describe these arrangements and explore how they can be analyzed using standard tools in economics (incentives and principal-agent theory). We discuss the implications of our approach in terms of identifying risks that are often overlooked before turining to the optimal risk-sharing between the public and private partners, in particular with respect to information asymmetries in risk perceptions. This allows us to propose a typology of the risks associated with PPPs, where both internal risks (the risks associated with the contract) and external risks (those associated with the project) are considered.infrastructure financing, public-private partnerships, principal-agent framework, risk classification, transportation infrastructure, value for money

POWER Assurer le bien - être et la résilience des porcs biologiques

Améliorer le bien-être et la santé des animaux ainsi que les performances environnementales et économiques des élevages de porcs biologiques en Europe grâce à l’amélioration de la conduite et du logement

Interacciones entre la gaviota patiamarilla Larus michahellis y la gaviota de Audouin Larus audouinii en la isla de Dragonera

Interacciones entre la gaviota patiamarilla Larus michahellis y la gaviota de Audouin Larus audouinii en la isla de Dragonera. La gaviota patiamatilla Larus michahellis es una espècie superabundante en el Mediterràneo occidental, lo que supone un grave impacto sobre la biodiversidad. En la isla de Dragonera, unas pequeñas colonias de gaviotas de Audouin Larus audouinii nidifican en la proximidad de una macro-colonia de gaviotas patiamatillas. La siguiente nota reporta los resultados de un estudio piloto sobre las interacciones entre ambas especies. El objetivo es determinar en que medida las gaviotas patiamatillas tienen un impacto negativo sobre el éxito reproductor de las colonias de gaviotas de Audouin.Interaccions entre la gavina vulgar Larus michahellis i la gavina de bec vermell Larus audouinii a l'illa de sa Dragonera. La gavina vulgar Larus michahellis és una espècie superabundant en el Mediterrani occidental, la qual cosa suposa un greu impacte sobre la biodiversitat. A l'illa de sa Dragonera, unes petites colònies de gavines de bec vermell Larus audouinii nidifiquen en la proximitat d'una macro-colònia de gavines vulgars. La següent nota reporta els resultats d'un estudi pilot sobre les interaccions entre ambdues espècies. L'objectiu és determinar en quina mesura les gavines vulgars tenen un impacte negatiu sobre l'èxit reproductor de les colònies de gavines de bec vermell.Interaction between Yellow-legged Gull Larus michabellis and Andouin 's Gull Larus audouinii on the island of Dragonera. Yellow-legged Gull Larus michahellis is a superabundant species in the West Occidental Mediterranean. This supposes dramatic impacts on global biodiversity. In Dragonera island, small colonies of Audouin's Gull breed close to a macro-colony of Yellow-legged Gulls. The following note reports the results of a pilot study on interactions between the two gull species. The goal is to determine how Yellowlegged Gulls have a negative impact on the reproductive success of the Audouin's Gulls

Why observers should train clinical scoring

Epidemiological studies often involve clinical scoring of animals by several observers due to the high number of farms to be visited. Detailed written procedures and intensive observer training minimize variation between observers. This, however, is still not common in international cooperation. We present data on clinical assessment of sows from an EU project on organic pig health (COREPIG) to illustrate the consequences. The clinical scoring system was based on procedures from the Welfare Quality ® project and included measures regarding body condition (5-level scale), injuries (number of lesions >3cm on shoulder, side and hindquarters), lameness (3-level scale), dirtiness (3-level scale) and skin problems (3-level scale). Nine observers from 6 EU countries trained clinical scoring during two days in two herds. Of the 9 observers, 4 had no or little, 2 had intermediate and 3 had extensive experience in working with pigs. Four observers each had little or intermediate experience in clinical scoring of sows and only 1 had extensive experience. Training comprised parameter discussions and joint scoring of animals. After training, each observer scored up to 30 pregnant sows per farm in 3 to 20 herds in six European countries as part of a larger epidemiological protocol. After completion of farm visits, observers scored up to 50 sows independently but at the same day and farm in order to assess inter-observer agreement. Parameters were collapsed into binary variables. We calculated Kendall's Coefficient of Concordance (W) across all observers and Prevalence Adjusted Bias Adjusted Kappas (PABAK) for observer pairs as measures of agreement. Agreement across observers was not acceptable for skin problems and lameness (W 0.60 (N = 26 sows for skin problems, and 31 to 34 sows for other parameters). Pairwise agreement was not acceptable for skin problems and dirtiness (mean PABAK <0.41) and acceptable for injuries shoulder and side (mean PABAK between 0.41 and 0.60). Agreement was good for hindquarter injuries and animal too thin (PABAK = 0.66 and 0.65, respectively), while obesity and lameness had mean PABAK of 0.84 and 0.95. Observer pairs scored 40 to 50 sows per parameter except for skin problems (36 to 49 sows). Results for lameness and obesity should be interpreted with care, as average prevalence across observers were only 3 and 8 %, respectively. Determination of whether a sow was too thin was the parameter with best agreement. The poor agreement for skin problems and dirtiness can be explained by misunderstandings regarding the parameter definition (e.g. inclusion of mud soiling). Extensive practical experience with pigs was of highest benefit for inter-observer agreement. Average PABAK was 0.70 (STD = 0.19, N = 24 scorings; 3 observer pairs, 8 parameters) for experienced observers but ranged between 0.49 and 0.56 (STD range 0.32 to 0.40) for all other combinations of experience level. The level of experience with clinical scoring of pigs did not have obvious positive effects. Average PABAK for all experience combinations ranged from 0.51 to 0.61 (STD range 0.32 to 0.40). By way of explanation, general experience with pigs helps to score an animal because observers will know a wider range of possible scenarios. By contrast, scores of observers who have already learned a scoring system will tend to be biased by their experience. As a conclusion, our data emphasize the importance of intensive observer training before data collection and the need for inter-observer agreement tests before and after data collection

Avant-Propos

Cet avant-propos présente un volume qui propose une réflexion sur les relations entre la religion et l'épistolarité en France et en Grande-Bretagne, aux XVIIe et XVIIIe siècles. Douze spécialistes de la période, en histoire, théologie et littérature, s'interrogent sur des correspondances officielles ou clandestines, spirituelles ou pastorales, pour présenter un panorama des rapports entre les correspondances manuscrites ou imprimées et l'orthodoxie ou les hétérodoxies. Outil de communication entre les croyants, les églises et les communautés, mais aussi entre les membres du clergé et les fidèles, la lettre, qu'elle soit ouverte ou secrète, qu'elle appelle une réponse ou le silence, qu'elle soit cachée, codée, interceptée, imprimée ou diffusée, qu'elle soit isolée ou fasse partie d'un corpus plus large, fut le principal moyen d'expression de la piété et du sentiment religieux dans des siècles marqués par de profonds bouleversements épistémologiques. Prises dans leur ensemble, ces contributions constituent la première tentative d'étude croisée du religieux et de l'épistolaire dans l'espace européen entre Réforme et Révolution

Remote Ischemic Conditioning Influences Mitochondrial Dynamics

Remote ischemic preconditioning (RIPC) has emerged as an attractive strategy to protect the heart against ischemia-reperfusion (I/R) injury. The mechanisms by which remote ischemic conditioning (RIC) is protective are to date unknown, yet a well-accepted theory holds that the mitochondria play a central role. Mitochondria are dynamic organelles that undergo fusion and fission. Interventions that decrease mitochondrial fission or increase mitochondrial fusion have been associated with reduced I/R injury. However, whether RIPC influences mitochondrial dynamics or not has yet to be ascertained.We sought to determine the role played by mitochondrial dynamics in RIPC-induced cardioprotection. Male adult rats exposed in vivo to myocardial I/R were assigned to one of two groups, either undergoing 40 min of myocardial ischemia followed by 120 min of reperfusion (MI group) or four 5-min cycles of limb ischemia interspersed by 5 min of limb reperfusion, immediately prior to myocardial ischemia and 120 min of reperfusion (MI+RIPC group). After reperfusion, infarct size was assessed and myocardial tissue was analyzed by Western blot and electron microscopy. RIPC induced smaller infarct size (-28%), increased mitochondrial fusion protein OPA1, and preserved mitochondrial morphology. These findings suggest that mitochondrial dynamics play a role in the mechanisms of RIPC-induced cardioprotection

Organic Pig Production in Europe - Health Management in Common Organic Pig Farming

Organic farmers in Europe have developed different housing systems for pigs based on the availability of land, soil characteristics, climate, tradition and national organic certification schemes. This guide gives an overview of the typical housing systems used for pigs in organic farming. It lists advantages and disadvantages of the different systems and provides relevant recommendations to farmers for health managment