Computational modelling of void growth in swelled hydrogels

The nature and the large notable distinguishing features of polymeric gels explain their pervasive use as biomaterials in both regenerative medicine and tissue engineering. With regard to their biocompatibility, their ability to withstand large deformation and their significant capacity of solvent absorption, these biomaterials are often selected owing to their versatile mechanical properties and especially the closeness to soft biological tissues, amongst others. A finite-strain theory for the study of the overall behaviour of a porous polymeric gel where microvoids are present is presented. The swollen polymeric gel is modeled as a two-component body composed of two incompressible components, namely, an elastic porous polymer imbibed with a solvant. The chemical equilibrium is assumed to be preponderate at the interface between the porous polymer and the environment where the chemical potential of the solvent is fixed. The initially dry porous polymer undergoes large deformation induced by absorption of a solvent from the environment and mechanical loading. In this paper an attempt is made towards obtaining an estimation of the macroscopic responses of the swollen porous polymer to prescribed proportional loadings. To this end, a two-level representation of the material at hand for which the Representative Volume Element (RVE) imbibed with a solvent is a simple axisymmetric cylinder composed of a homogeneous matrix surrounding a spherical void, is considered. The computational study addresses the situation where the RVE is subjected to prescribed axial and lateral overall stresses under conditions of constant overall stress triaxiality. For fixed values of the Flory-Huggins parameter and the nominal concentration of the solvent, the overall stress-strain behaviour of the RVE model, the influence of the initial porosity, and the prescribed stress triaxiality ratio have been outlined

La "responsabilité de protéger" et le recours à la force : leçons libyennes

Cet article tente de définir la "responsabilité de protéger" (R2P) comme une norme émergente, dont l’existence normative n’est plus à démontrer, mais qui peine à trouver une légitimité devant tous les acteurs internationaux. Le paradoxe naît de la stratégie française de vouloir en faire un des principes directeurs de sa politique étrangère, comme le préconise le nouveau Livre blanc sur la défense et la sécurité nationale, malgré le dissensus qui s’exprime sur la R2P. L’analyse se résume en trois hypothèses : • Le contexte international dans la période post-bipolaire se caractérise par une fragmentation de la "communauté internationale" et une redéfinition de la notion de "guerre" ; • Le Sommet mondial de 2005, signant "l’Onuisation" du concept de la R2P, a préservé le souverainisme du système international ; • L’intervention en Libye a servi le dissensus sur la R2P en colorant le concept d’impérialisme occidental.The Responsiblity to Protect (R2P) and the use of force: lessons from Lybia - This paper attempts to define the ‘Responsibility to Protect’ as an emerging norm: while its normative existence is not questioned, the concept has yet to find legitimacy in the eyes of all international actors. Nevertheless, French strategic thinking has sought to make R2P a fundamental principle of its foreign policy with respect to national defense, creating a normative discrepancy. The analysis can be summed up in the three following hypotheses: • The international context in the post-bipolar period is characterized by a fragmentation of the so-called ‘international community’ and a redefinition of the concept of “war” ; • The 2005 World Summit made R2P a UN tool but essentially recalled the principle of state sovereignty ; • The 2011 intervention in Libya served to fuel dissensus further on R2P through identification of the concept with Western imperialism

Nonlinear Control of an AC-connected DC MicroGrid

New connection constraints for the power network (Grid Codes) require more flexible and reliable systems, with robust solutions to cope with uncertainties and intermittence from renewable energy sources (renewables), such as photovoltaic arrays. A solution for interconnecting such renewables to the main grid is to use storage systems and a Direct Current (DC) MicroGrid. A "Plug and Play" approach based on the "System of Systems" philosophy using distributed control methodologies is developed in the present work. This approach allows to interconnect a number of elements to a DC MicroGrid as power sources like photovoltaic arrays, storage systems in different time scales like batteries and supercapacitors, and loads like electric vehicles and the main AC grid. The proposed scheme can easily be scalable to a much larger number of elements.Comment: IEEE IECON 2016, the 42nd Annual Conference of IEEE Industrial Electronics Society, October 24-27, 201

Nonlinear Control of a DC MicroGrid for the Integration of Photovoltaic Panels

New connection constraints for the power network (Grid Codes) require more flexible and reliable systems, with robust solutions to cope with uncertainties and intermittence from renewable energy sources (renewables), such as photovoltaic arrays. The interconnection of such renewables with storage systems through a Direct Current (DC) MicroGrid can fulfill these requirements. A "Plug and Play" approach based on the "System of Systems" philosophy using distributed control methodologies is developed in the present work. This approach allows to interconnect a number of elements to a DC MicroGrid as power sources like photovoltaic arrays, storage systems in different time scales like batteries and supercapacitors, and loads like electric vehicles and the main AC grid. The proposed scheme can easily be scalable to a much larger number of elements.Comment: arXiv admin note: text overlap with arXiv:1607.0848

Les modalités d'intensification raisonnées des systèmes agropastoraux en territoires steppiques aux ressources altérées

Contexte et objectifs : les aléas météorologiques et le changement du régime climatique conjoints aux changements socioculturels obligent les éleveurs à trouver des stratégies pour maintenir leurs activités. Ils doivent trouver de nouvelles pratiques, notamment en matière alimentaire. L'apport des besoins des animaux était auparavant assuré essentiellement par les parcours. A présent ils couvrent moins de 40 %. En conséquence, il s'agit pour les éleveurs d'explorer des modes de conduites plus intensif. Cette orientation peut amoindrir la vulnérabilité des systèmes d'élevage vis-à-vis du manque de pluies et donc de fourrages dans les pâtures. En revanche, cela rend les éleveurs dépendant en approvisionnement en compléments. Le questionnement de notre étude porte sur les diverses pratiques mises en oeuvre par les éleveurs et connaitre la situation actuelle de leurs systèmes et de leur productivité animale. Matériel et méthodes : pour se faire, nous avons réalisé 80 entretiens au niveau de la willaya de Tébessa. Le recueil de données fiables en milieu semi arides dans les différents élevages est un travail délicat. Les données issues de 80 enquêtes/entretiens et observations auprès des troupeaux de la région agropastorale font ressortir des caractéristiques marquées des exploitations enquêtées. Résultats et discussion : l'analyse structurale des troupeaux affirme que la taille des troupeaux varie dans le temps et dans l'espace sous l'influence des aléas climatiques, de leurs stratégies et pratiques. Il apparait dans une première perception : un groupe des éleveurs ont recours à l'intensification qui utilise les concentrés comme une principale alimentation, un groupe des agropasteurs, autre groupe qui comprend les éleveurs non détenteurs de terrains agricoles mais pour le maintien des troupeaux existant font le pâturage et le recours à l'alimentation concentrés comme complémentation. Conclusion : ces formes sont des solutions récentes pour le maintien de leurs troupeaux. L'intensification d'élevage augmente la taille du troupeau, cependant il transforme les prairies en terres cultivées avec l'abandon de terres difficiles et peu productives, destruction et fragmentation des habitats naturels perte de connectivité du paysage

Global Timing Optimization in Chip Design

In this thesis, we aim at solving the interconnect optimization problem comprehensively. By balancing global timing, routing, placement, and power constraints in a global model, we obtain solutions which outperform the classic approach in both resource usage and timing quality. For the time-cost tradeoff problem in chip design, we present a new implementation of a primal-dual optimization algorithm. Instead of requiring separable delay constraints as in previous approaches, it only has mild assumptions on the delay model. The approach allows us to achieve leakage reductions of up to 8% on netlists that were pre-optimized by one of the most successful algorithms. The Vt assignment problem with separable delays directly corresponds to the discrete time-cost tradeoff problem in directed graphs. If d is the maximum number of vertices in any path, our practical algorithm yields a d approximation. Previously, Svensson showed that for general instances with unbounded values of d no constant factor approximation exists if we assume P≠NP and the Unique Games Conjecture holds. For the discrete time-cost tradeoff problem, we devise an improved algorithm with a guarantee of d/2. We achieve this by reformulating the problem to a vertex cover problem in d-partite hypergraphs. For this more general problem, the approximation ratio of our new algorithm is slightly better than d/2, which is asymptotically best possible under the Unique Games Conjecture and P≠NP. We also study the inapproximability of the time-cost tradeoff problem and show that no better approximation ratio than (d+2)/4 is possible, again assuming the Unique Games Conjecture and P≠NP. Therefore, we settle the approximability of this problem up to a factor of less than 2. We then focus on the gate sizing problem. It is similar to the time-cost tradeoff problem but optimizes a more involved timing function, which is not linear but only posynomial. Schorr presented a resource-sharing formulation for the gate sizing problem in her dissertation. We give a new runtime analysis for the resource sharing algorithm applied to gate sizing, resolving small inaccuracies in the previous proof. Finally, we consider the buffering problem. In this problem the interconnect for all nets should be computed. Simultaneously, repeating gates need to be inserted to strengthen electrical signals. We build on the resource sharing formulation for this problem given by Rotter and his initial implementation. On the theoretic side, we modify the model by using a path based formulation for timing proposed by Hähnle. The new implementation is now robust enough to be used in an industrial environment. It outperforms a state-of-the-art design flow in almost all metrics, including netlength, power, congestion and timing. We also implement speedups that reduce the runtime by up to 70%

Monogenic fields with odd class number Part I: odd degree

We bound the average number of $2$-torsion elements in the class group of monogenised fields of odd degree (and compute it precisely conditional on a tail estimate) using an orbit parametrisation of Wood. Curiously, we find that the average number of non-trivial $2$-torsion elements in the class group of monogenised fields of any given odd degree is twice the value predicted for the full family of fields of that degree by the Cohen-Lenstra-Martinet-Malle heuristic! We also find that monogenicity has an increasing effect on the average number of non-trivial $2$-torsion elements in the narrow class group. In addition, we obtain unconditional statements for monogenised rings of odd degree. For an order $\mathcal{O}$, denote by $\mathcal{I}_2(\mathcal{O})$ the group of $2$-torsion ideals of $\mathcal{O}$. We show that the average value of the difference $\left|{\rm Cl_2}(\mathcal{O})\right|-2^{1-r_1-r_2}\left| \mathcal{I}_2(\mathcal{O}) \right|$ over all monogenised orders $\mathcal{O}$ of fixed signature $(r_1,r_2)$ is $1+2^{1-r_1-r_2}$. For $3$-torsion in quadratic orders, $2$-torsion in cubic orders, and $2$-torsion in orders arising from odd degree binary forms, work of Bhargava-Varma and Ho-Shankar-Varma shows that the corresponding difference averaged over the full family of orders is equal to $1$. This shows that monogenicity has an increasing effect not only on the class group of fields, but also on the class group of orders. Our method gives a dual proof of a result of Bhargava-Hanke-Shankar in the cubic case, reveals an interesting structure underpinning the deviation of these averages from those expected for the full families, and extends to the case of monogenised rings and fields of even degree at least $4$.Comment: 48 pages, 2 figure

Testing for Nonlinear Dynamics in the Stock Exchange of Thailand (SET)

Understanding stock market price fluctuations plays an important role in economic policy and in corporate investment and financing strategies. In recent years, Khantavit and others have investigated the proposition that nonlinear processes studied in Chaos theory play an important role in these fluctuations. This study provides a detailed examination of this hypothesis using data from the Stock Exchange of Thailand (SET) from 1975 to 1999. The study finds that the distribution of the daily return on the SET index is nonnormal and leptokurtic. The results of the study also suggest that non-linear processes play a significant role in stock market behavio