Evaluation of a self-equilibrium cutting strategy for the contour method of residual stress measurement

An assessment of cutting-induced plasticity (CIP) is performed, by finite element (FE) prediction of the plastic strain accumulation along the cut tip when the EDM wire sections the NeT TG4 weld benchmark specimen along two cutting directions. The first direction corresponds to a conventional (C) cutting strategy, whereby the EDM wire cuts through the thickness of the weld specimen and travels in a direction transverse to the weld. The second direction corresponds to a self-equilibrating cutting (SE) strategy, whereby the EDM wire cuts across the transverse direction of the weld specimens and travels through the thickness of the plate. The cutting thus progresses simultaneously through the compression-tension-compression regions of present weld residual stress (WRS) field. This type of cutting strategy is believed to minimize the CIP by minimising residual stress redistribution during cutting, due to stress equilibration across the sectioned material. The simulated cutting procedures are conducted under a range of clamping conditions to assess whether mechanical restraint has a primary or secondary influence on CIP accumulation. Both predictions of CIP and the resultant back-calculated WRS demonstrate that (i) mechanical restraint is the primary variable influencing CIP development, and (ii) under no circumstance does a self-equilibrating cutting strategy perform significantly better than a conventional cutting approach. The reason that self-equilibrating cuts are not effective is illustrated by calculating the Mode I (KI) stress intensity factor (SIF) along the cut tip, and correlating trends in KI to CIP development

Laue Lens Development for Hard X-rays (>60 keV)

Results of reflectivity measurements of mosaic crystal samples of Cu (111) are reported. These tests were performed in the context of a feasibility study of a hard X-ray focusing telescope for space astronomy with energy passband from 60 to 600 keV. The technique envisaged is that of using mosaic crystals in transmission configuration that diffract X-rays for Bragg diffraction (Laue lens). The Laue lens assumed has a spherical shape with focal length $f$. It is made of flat mosaic crystal tiles suitably positioned in the lens. The samples were grown and worked for this project at the Institute Laue-Langevin (ILL) in Grenoble (France), while the reflectivity tests were performed at the X-ray facility of the Physics Department of the University of Ferrara.Comment: 6 pages, 12 figures, accepted for publication in IEEE Transactions on Nuclear Scienc

Reduction of Dilute Ising Spin Glasses

The recently proposed reduction method for diluted spin glasses is investigated in depth. In particular, the Edwards-Anderson model with \pm J and Gaussian bond disorder on hyper-cubic lattices in d=2, 3, and 4 is studied for a range of bond dilutions. The results demonstrate the effectiveness of using bond dilution to elucidate low-temperature properties of Ising spin glasses, and provide a starting point to enhance the methods used in reduction. Based on that, a greedy heuristic call ``Dominant Bond Reduction'' is introduced and explored.Comment: 10 pages, revtex, final version, find related material at http://www.physics.emory.edu/faculty/boettcher

The entropy of randomized network ensembles

Randomized network ensembles are the null models of real networks and are extensivelly used to compare a real system to a null hypothesis. In this paper we study network ensembles with the same degree distribution, the same degree-correlations or the same community structure of any given real network. We characterize these randomized network ensembles by their entropy, i.e. the normalized logarithm of the total number of networks which are part of these ensembles. We estimate the entropy of randomized ensembles starting from a large set of real directed and undirected networks. We propose entropy as an indicator to assess the role of each structural feature in a given real network.We observe that the ensembles with fixed scale-free degree distribution have smaller entropy than the ensembles with homogeneous degree distribution indicating a higher level of order in scale-free networks.Comment: (6 pages,1 figure,2 tables

Singularities in ternary mixtures of k-core percolation

Heterogeneous k-core percolation is an extension of a percolation model which has interesting applications to the resilience of networks under random damage. In this model, the notion of node robustness is local, instead of global as in uniform k-core percolation. One of the advantages of k-core percolation models is the validity of an analytical mathematical framework for a large class of network topologies. We study ternary mixtures of node types in random networks and show the presence of a new type of critical phenomenon. This scenario may have useful applications in the stability of large scale infrastructures and the description of glass-forming systems.Comment: To appear in Complex Networks, Studies in Computational Intelligence, Proceedings of CompleNet 201

Importance de l’intéraction entre les cultivars de blé et les souches du Fusarium graminearum dans l’évaluation de la résistance à la fusariose de l’épi

Des expériences factorielles ont été réalisées au champ à deux stations, le campus de l'Université Laval en 1991 et 1992 et la ferme de Saint-Louis-de-Pintendre en 1992 et 1993, pour préciser si le développement de la fusariose de l'épi du blé est influencé par l'interaction entre les cultivars et les souches du Fusarium graminearum. Neuf souches du F. graminearum ont été inoculées à onze cultivars de blé (Triticum aestivum) et un cultivar de triticale (x Triticosecale) représentatifs de la gamme de sensibilité à cette maladie au Québec. L'analyse de la variance combinée a mis en évidence des interactions significatives entre les cultivars, les souches et les environnements. Les interactions cultivars x souches et cultivars x environnements expliquent une faible proportion de la somme des carrés totale et n'entraînent pas de modifications majeures dans le classement moyen de la sensibilité des cultivars. Concernant l'interaction cultivars x souches, le classement moyen de la sensibilité des cultivars, notamment Casavant et Concorde, variait avec les souches. Cette recherche contre pour la première fois que l'importance relative des différentes interactions entre les souches, les cultivars et les environnements est comparable dans l'évaluation de la résistance à la fusariose de l'épi du blé.Factorial experiments were carried out in the field at the campus of Universite Laval in 1991 and 1992, and Saint-Louis-de-Pintendre station in 1992 and 1993. The objective was to specify if wheat scab development caused by Fusarium graminearum is significantly affected by cultivar x strain interactions. Eleven wheat (Triticum aestivum) cultivars and one triticale (x Triticosecale) cultivar representing the range of sensitivity to this disease in Quebec were inoculated with nine strains of F. graminearum. Significant interactions between cultivars, strains and environments were shown by the results of a combined analysis of variance. Cultivar x strain and cultivar x environment interactions explained a small proportion of the total sum of squares and did not have a strong impact on cultivar average ranking by environment or strain. However, the examination of cultivar x strain interactions revealed that the rank of cultivars such as Casavant and Concorde changed when different strains were compared. This research shows for the first time that all interactions involving cultivars, strains and environments have a similar impact on wheat scab resistance screening

Soil Microbial Community Changes in Wooded Mountain Pastures due to Simulated Effects of Cattle Grazing

The effect of cattle activity on pastures can be subdivided into three categories of disturbances: herbage removal, dunging and trampling. The objective of this study was to assess separately or in combination the effect of these factors on the potential activities of soil microbial communities and to compare these effects with those of soil properties and plant composition or biomass. Controlled treatments simulating the three factors were applied in a fenced area including a light gradient (sunny and shady situation): (i) repeated mowing; (ii) trampling; (iii) fertilizing with a liquid mixture of dung and urine. In the third year of the experiment, community level physiological profiles (CLPP) (Biolog Ecoplates™) were measured for each plots. Furthermore soil chemical properties (pH, total organic carbon, total nitrogen and total phosphorus), plant species composition and plant biomass were also assessed. Despite differences in plant communities and soil properties, the metabolic potential of the microbial community in the sunny and in the shady situations were similar. Effects of treatments on microbial communities were more pronounced in the sunny than in the shady situation. In both cases, repeated mowing was the first factor retained for explaining functional variations. In contrast, fertilizing was not a significant factor. The vegetation explained a high proportion of variation of the microbial community descriptors in the sunny situation, while no significant variation appeared under shady condition. The three components of cattle activities influenced differently the soil microbial communities and this depended on the light conditions within the wooded pasture. Cattle activities may also change spatially at a fine scale and short-term and induce changes in the microbial community structure. Thus, the shifting mosaic that has been described for the vegetation of pastures may also apply for below-ground microbial communitie

Frequency and Diversity of Nitrate Reductase Genes among Nitrate-Dissimilating Pseudomonas in the Rhizosphere of Perennial Grasses Grown in Field Conditions

A total of 1246 Pseudomonas strains were isolated from the rhizosphere of two perennial grasses (Lolium perenne and Molinia coerulea) with different nitrogen requirements. The plants were grown in their native soil under ambient and elevated atmospheric CO2 content (pCO2) at the Swiss FACE (Free Air CO2 Enrichment) facility. Root-, rhizosphere-, and non-rhizospheric soil-associated strains were characterized in terms of their ability to reduce nitrate during an in vitro assay and with respect to the genes encoding the membrane-bound (named NAR) and periplasmic (NAP) nitrate reductases so far described in the genus Pseudomonas. The diversity of corresponding genes was assessed by PCR-RFLP on narG and napA genes, which encode the catalytic subunit of nitrate reductases. The frequency of nitrate-dissimilating strains decreased with root proximity for both plants and was enhanced under elevated pCO2 in the rhizosphere of L. perenne. NAR (54% of strains) as well as NAP (49%) forms were present in nitrate-reducing strains, 15.5% of the 439 strains tested harbouring both genes. The relative proportions of narG and napA detected in Pseudomonas strains were different according to root proximity and for both pCO2 treatments: the NAR form was more abundant close to the root surface and for plants grown under elevated pCO2. Putative denitrifiers harbored mainly the membrane-bound (NAR) form of nitrate reductase. Finally, both narG and napA sequences displayed a high level of diversity. Anyway, this diversity was correlated neither with the root proximity nor with the pCO2 treatmen

Importance de l’intéraction entre les cultivars de blé et les souches du Fusarium graminearum dans l’évaluation de la résistance à la fusariose de l’épi

Des expériences factorielles ont été réalisées au champ à deux stations, le campus de l'Université Laval en 1991 et 1992 et la ferme de Saint-Louis-de-Pintendre en 1992 et 1993, pour préciser si le développement de la fusariose de l'épi du blé est influencé par l'interaction entre les cultivars et les souches du Fusarium graminearum. Neuf souches du F. graminearum ont été inoculées à onze cultivars de blé (Triticum aestivum) et un cultivar de triticale (x Triticosecale) représentatifs de la gamme de sensibilité à cette maladie au Québec. L'analyse de la variance combinée a mis en évidence des interactions significatives entre les cultivars, les souches et les environnements. Les interactions cultivars x souches et cultivars x environnements expliquent une faible proportion de la somme des carrés totale et n'entraînent pas de modifications majeures dans le classement moyen de la sensibilité des cultivars. Concernant l'interaction cultivars x souches, le classement moyen de la sensibilité des cultivars, notamment Casavant et Concorde, variait avec les souches. Cette recherche contre pour la première fois que l'importance relative des différentes interactions entre les souches, les cultivars et les environnements est comparable dans l'évaluation de la résistance à la fusariose de l'épi du blé.Factorial experiments were carried out in the field at the campus of Universite Laval in 1991 and 1992, and Saint-Louis-de-Pintendre station in 1992 and 1993. The objective was to specify if wheat scab development caused by Fusarium graminearum is significantly affected by cultivar x strain interactions. Eleven wheat (Triticum aestivum) cultivars and one triticale (x Triticosecale) cultivar representing the range of sensitivity to this disease in Quebec were inoculated with nine strains of F. graminearum. Significant interactions between cultivars, strains and environments were shown by the results of a combined analysis of variance. Cultivar x strain and cultivar x environment interactions explained a small proportion of the total sum of squares and did not have a strong impact on cultivar average ranking by environment or strain. However, the examination of cultivar x strain interactions revealed that the rank of cultivars such as Casavant and Concorde changed when different strains were compared. This research shows for the first time that all interactions involving cultivars, strains and environments have a similar impact on wheat scab resistance screening