Survey on the chemical composition of several tropical wood species

Variability in the chemical composition of 614 species is described in a database containing measurements of wood polymers (cellulose, lignin and pentosan), as well as overall extraneous components (ethanol-benzene, or hot water extracts and ash, with a focus on silica content). These measurements were taken between 1945 and 1990 using the same standard protocol. In all, 1,194 trees belonging to 614 species, 358 genera and 89 families were measured. At species level, variability (quantified by the coefficient of variation) was rather high for density (27%), much lower for lignin and cellulose (14% and 10%) and much higher for ethanol/benzene extractives, hot water extractives and ash content (81%, 60% and 76%). Considering trees with at least five different specimens, and species with at least 10 different trees, it was possible to investigate within-tree and withinspecies variability. Large differences were found between trees of a given species for extraneous components, and more than one tree should be needed per species. For density, lignin, pentosan and cellulose, the distribution of values was nearly symmetrical, with mean values of 720 kg/m3 for density, 29.1% for lignin, 15.8% for pentosan, and 42.4% for cellulose. There were clear differences between species for lignin content. For extraneous components, the distribution was very dissymmetrical, with a minority of woods rich in this component composing the high value tail. A high value for any extraneous component, even in only one tree, is sufficient to classify the species in respect of that component. Siliceous woods identified by silica bodies in anatomy have a very high silica content and only those species deserve a silica study

Creep behaviour of as received, aged and cold worked INCONEL 617 at 850 °C and 950 °C

The effect of initial microstructure on alloy 617 creep behaviour has been investigated at 850 °C and 950 °C. The solution treated material shows non-classical creep behaviour at both temperatures with a strain rate drop at the beginning of the tests followed by a creep rate increase to a plateau before the onset of the tertiary creep. The intragranular secondary carbides which precipitate early at test temperature are responsible of the strong initial hardening effect by pinning the dislocations. This effect is overpassed during the thermo mechanical ageing of the alloy which induces growth of these carbides. Prior 1000 h thermal ageing at the temperature test totally removes the strain rate drop and reduces the lifetime. The intragranular microstructure has evolved thanks to the prior thermal ageing before the creep tests. Microstructural examinations also show the presence of grain boundary migration and recrystallization in the material during creep tests of the as received and aged materials. Preliminary cold work treatment highly reduces the strain rate of Inconel 617 and enhances the lifetime at 850 °C while the opposite is observed at 950 °C

Isospin breaking in pion and Ke4K_{e4} form factors

Isospin breaking in the $K_{\ell 4}$ form factors induced by the difference between charged and neutral pion masses is discussed within a framework built on suitably subtracted dispersion representations. The $K_{\ell 4}$ form factors are constructed in an iterative way up to two loops in the low-energy expansion by implementing analyticity, crossing, and unitarity due to two-meson intermediate states. Analytical expressions for the phases of the two-loop form factors of the $K^\pm\to\pi^+\pi^- e^\pm \nu_e$ channel are presented, allowing one to connect the difference of form-factor phase shifts measured experimentally (out of the isospin limit) and the difference of $S$- and $P$-wave $\pi\pi$ phase shifts studied theoretically (in the isospin limit). The dependence with respect to the two $S$-wave scattering lengths $a_0^0$ and $a_0^2$ in the isospin limit is worked out in a general way, in contrast to previous analyses based on one-loop chiral perturbation theory. The results on the phases of the $K^\pm\to\pi^+\pi^- e^\pm \nu_e$ form factors obtained by the NA48/2 collaboration at the CERN SPS are reanalysed including isospin-breaking correction to extract values for the scattering lengths $a_0^0$ and $a_0^2$.Comment: 15 pages, 3 figures, prepared for the proceedings of the XIth Confinement and Hadron Spectrum Conference, Saint-Petersburg, Sept. 8-12, 201

Short-distance QCD corrections to K0Kˉ0K^0\bar{K}^0 mixing at next-to-leading order in Left-Right models

Left-Right (LR) models are extensions of the Standard Model where left-right symmetry is restored at high energies, and which are strongly constrained by kaon mixing described in the framework of the $|\Delta S|=2$ effective Hamiltonian. We consider the short-distance QCD corrections to this Hamiltonian both in the Standard Model (SM) and in LR models. The leading logarithms occurring in these short-distance corrections can be resummed within a rigourous Effective Field Theory (EFT) approach integrating out heavy degrees of freedom progressively, or using an approximate simpler method of regions identifying the ranges of loop momentum generating large logarithms in the relevant two-loop diagrams. We compare the two approaches in the SM at next-to-leading order, finding a very good agreement when one scale dominates the problem, but only a fair agreement in the presence of a large logarithm at leading order. We compute the short-distance QCD corrections for LR models at next-to-leading order using the method of regions, and we compare the results with the EFT approach for the $WW'$ box with two charm quarks (together with additional diagrams forming a gauge-invariant combination), where a large logarithm occurs already at leading order. We conclude by providing next-to-leading-order estimates for $cc$, $ct$ and $tt$ boxes in LR models.Comment: Accepted for publication in JHE

Bounds for self-stabilization in unidirectional networks

A distributed algorithm is self-stabilizing if after faults and attacks hit the system and place it in some arbitrary global state, the systems recovers from this catastrophic situation without external intervention in finite time. Unidirectional networks preclude many common techniques in self-stabilization from being used, such as preserving local predicates. In this paper, we investigate the intrinsic complexity of achieving self-stabilization in unidirectional networks, and focus on the classical vertex coloring problem. When deterministic solutions are considered, we prove a lower bound of $n$ states per process (where $n$ is the network size) and a recovery time of at least $n(n-1)/2$ actions in total. We present a deterministic algorithm with matching upper bounds that performs in arbitrary graphs. When probabilistic solutions are considered, we observe that at least $\Delta + 1$ states per process and a recovery time of $\Omega(n)$ actions in total are required (where $\Delta$ denotes the maximal degree of the underlying simple undirected graph). We present a probabilistically self-stabilizing algorithm that uses $\mathtt{k}$ states per process, where $\mathtt{k}$ is a parameter of the algorithm. When $\mathtt{k}=\Delta+1$, the algorithm recovers in expected $O(\Delta n)$ actions. When $\mathtt{k}$ may grow arbitrarily, the algorithm recovers in expected O(n) actions in total. Thus, our algorithm can be made optimal with respect to space or time complexity

Towards Industrialized Conception and Production of Serious Games

Serious Games (SGs) have experienced a tremendous outburst these last years. Video game companies have been producing fun, user-friendly SGs, but their educational value has yet to be proven. Meanwhile, cognition research scientist have been developing SGs in such a way as to guarantee an educational gain, but the fun and attractive characteristics featured often would not meet the public's expectations. The ideal SG must combine these two aspects while still being economically viable. In this article, we propose a production chain model to efficiently conceive and produce SGs that are certified for their educational gain and fun qualities. Each step of this chain will be described along with the human actors, the tools and the documents that intervene

L'évaluation d'opérations locales de maîtrise de l'énergie : un domaine privilégié d'approches pluridisciplinaires

International audienceLa maîtrise de l'énergie s'est imposée comme une priorité dans un contexte de croissance de la demande en services énergétiques, d'épuisement des ressources et de réduction des émissions polluantes. En parallèle, les échelons locaux prennent une importance croissante dans la mise en œuvre des politiques de développement durable. Les agendas 21 se déclinent en local et les Plans Climats en territorial. Les acteurs impliqués dans ces opérations ont des expériences et compétences variées, et recherchent des conseils et expertises complémentaires pour les accompagner dans leurs projets. Cette demande est renforcée par un contexte en pleine évolution : ouverture des marchés de l'énergie à la concurrence, nouveaux instruments d'intervention, nouvelle répartition des rôles entre les acteurs. Elle est aussi suscitée par une volonté de développer des approches territoriales transversales. L'évaluation répond à ces besoins, aussi bien pour rendre compte des résultats atteints, que pour comprendre comment assurer le succès des futures actions ou encore pour former les acteurs à des nouvelles problématiques. Ces objectifs d'évaluation font appel à des ressources dans différents domaines : énergétique, sciences économiques, sociologie, etc. Cet article présente une revue de travaux sur les actions d'efficacité énergétique dans différentes disciplines, pour faire ressortir quels pourraient être les apports d'une approche d'évaluation pluridisciplinaire. Un rapprochement est alors envisagé entre cet aspect pluridisciplinaire de l'évaluation et l'essor des démarches territoriales au niveau local, qui apparaît ainsi comme un lieu privilégié de nouvelles approches expérimentales d'évaluation