Experimental study of the brittle–ductile transition in hot cutting of SG iron specimens

http://www.sciencedirect.com/science/article/pii/S0924013612002579The present paper investigates the brittle-ductile transition (BDT) of the primary shear zone during cutting of spheroidal graphite (SG) iron in the austenitization temperature range (around 1000 °C). The experimental tests were performed using a cutting test bench in the cutting speed range of 0.8 to 1.6m.s-1. The cut surfaces were studied using optical microscopy and Scanning Electron Microscope (SEM) analysis techniques. The obtained results revealed either consequent deep fractured regions governed by a brittle-cracking regime (BCR) or a crack-free cut surface governed by a ductile-shear regime (DSR) with large plastic deformations. When cutting data were discussed with respect to the influences of cutting parameters and obtained cut surface, the correlation is significantly rich. Both cut surface integrity, cutting force curves and metallographic results show a BDT indicating a change in the dominating hot cutting process mechanism. Such a transition is associated with the dynamic recrystallization promoting strain softening and hot cutting by ductile shearing

Digital image correlation as a usefful tool of analysis of hot cutting process

This study deals with the use of Digital Image Correlation (DIC) to investigate the physical phenomena taking place during the orthogonal cutting of a SG iron specimen at high temperature (around 1,000 °C). After h aving recalled the scientific and industrial context, the experimental procedure developed to record the pictures of the tool covered with a speckle pattern at a frequency of 10,000 Hz (thanks to a high speed camera) is explained. The quantitative exploitation of these recordings is leading to a first set of results showing how the cutting speed and the rake angle of the tool have an influence on the physics of the cutting operation.Arts et Métiers ParisTech - DGAR

Trapping efficiency of plastic bottle "wickertraps" for population assessment of river Macrobrachium (Crustacea : Decapoda)

Small wickertraps made from plastic bottles are used to sample #Macrobrachium communities (#Crustacea Decapoda) in the rivers of Nuku-Hiva (Marquesas Islands, French Polynesia). Relations are established between sampling effort (number of traps per m2), number of crustacea caught, and surface of the pool. Catch per trap decreased with increasing trap density up to a threshold of about 8 traps per m2. Escape measurements, in a river and in the laboratory, help to describe the behaviour of the shrimps towards the traps. Escape was greater at night than during the day. The number of shrimps entering the traps was inversely proportional to the number of shrimps already in the traps. Sampling efficiency of the traps was estimated, in a single trial, at 40-47% for a trap density of 8.3 traps per m2. (Résumé d'auteur

Competition and facilitation between the marine nitrogen-fixing <i>cyanobacterium</i> Cyanothece and its associated bacterial community

N2-fixing cyanobacteria represent a major source of new nitrogen and carbon for marine microbial communities, but little is known about their ecological interactions with associated microbiota. In this study we investigated the interactions between the unicellular N2-fixing cyanobacterium Cyanothece sp. Miami BG043511 and its associated free-living chemotrophic bacteria at different concentrations of nitrate and dissolved organic carbon and different temperatures. High temperature strongly stimulated the growth of Cyanothece, but had less effect on the growth and community composition of the chemotrophic bacteria. Conversely, nitrate and carbon addition did not significantly increase the abundance of Cyanothece, but strongly affected the abundance and species composition of the associated chemotrophic bacteria. In nitrate-free medium the associated bacterial community was co-dominated by the putative diazotroph Mesorhizobium and the putative aerobic anoxygenic phototroph Erythrobacter and after addition of organic carbon also by the Flavobacterium Muricauda. Addition of nitrate shifted the composition toward co-dominance by Erythrobacter and the Gammaproteobacterium Marinobacter. Our results indicate that Cyanothece modified the species composition of its associated bacteria through a combination of competition and facilitation. Furthermore, within the bacterial community, niche differentiation appeared to play an important role, contributing to the coexistence of a variety of different functional groups. An important implication of these findings is that changes in nitrogen and carbon availability due to, e.g., eutrophication and climate change are likely to have a major impact on the species composition of the bacterial community associated with N2-fixing cyanobacteria

Assessment of bacterial dependence on marine primary production along a northern latitudinal gradient

Recent observations in polar marine waters have shown that a large fraction of primary production may be lost to respiration by planktonic bacteria due to very low bacterial growth efficiencies in cold waters. Here we report that sea temperature may be a key factor influencing the interaction between bacteria and primary production in North Atlantic and Arctic waters, suggesting that low primary production rates could not sustain bacterial carbon demand in the coldest Arctic waters. The use of freshly produced phytoplankton exudate by bacteria in early- and mid-summer was assessed, together with the bacterial uptake of dissolved inorganic nitrogen (DIN = nitrate and ammonium), in surface waters along a latitudinal gradient from the North Sea to the Arctic sea ice. Bacterial production was independent of the low primary production measured in the coldest waters. Under these conditions, heterotrophic bacteria can consume a large fraction of DIN and N-rich organic matter, making them strong contributors to N fluxes in these waters

Etude d'une méthode d'échantillonnage des populations de chevrettes (Macrobrachium lar. et M. australe) des rivières de Nuku Hiva (Marquises, Polynésie française)

Une méthode d'échantillonnage des #Macrobrachium, macrocrustacés dulçaquicoles, est étudiée dans le cadre d'un suivi de la faune non cible aux traitements des rivières de l'île de Nuku-Hiva (Marquises) visant l'éradication du "nono noir des vallées" (#Simulim buissoni). Plusieurs engins de pêche ont été étudiés dont de petites nasses fabriquées à l'aide de bouteilles plastiques. Le "comportement" de ces bouteilles en regard des captures échantillonnées est abordé par comparaison avec les captures d'autres types de pièges (grandes nasses et pêche électrique), divers types de bouteilles (appâtées, colorées), et différentes orientations des bouteilles dans la rivière. L'abondance des captures est analysée en fonction de l'échappement et des fluctuations de l'effort d'échantillonnage (nombre de bouteilles/unité de surface). L'efficacité des bouteilles transparentes quant à l'abondance des prises est étudiée après des estimations du nombre total de chevrettes dans le milieu résultant d'opérations de marquage-recapture et de comptages visuels de nuit. Enfin, une interprétation de l'abondance et de la densité des chevrettes par des variables écologiques descriptives du milieu est proposée. (Résumé d'auteur

Enhancing Graph Neural Networks with Quantum Computed Encodings

Transformers are increasingly employed for graph data, demonstrating competitive performance in diverse tasks. To incorporate graph information into these models, it is essential to enhance node and edge features with positional encodings. In this work, we propose novel families of positional encodings tailored for graph transformers. These encodings leverage the long-range correlations inherent in quantum systems, which arise from mapping the topology of a graph onto interactions between qubits in a quantum computer. Our inspiration stems from the recent advancements in quantum processing units, which offer computational capabilities beyond the reach of classical hardware. We prove that some of these quantum features are theoretically more expressive for certain graphs than the commonly used relative random walk probabilities. Empirically, we show that the performance of state-of-the-art models can be improved on standard benchmarks and large-scale datasets by computing tractable versions of quantum features. Our findings highlight the potential of leveraging quantum computing capabilities to potentially enhance the performance of transformers in handling graph data.Comment: arXiv admin note: text overlap with arXiv:2210.1061

Weak interpolation in Banach spaces

1. Trait-based approaches predict ecosystem functioning under environmental change by relating traits predicting changes in species densities (response traits) to traits driving ecosystem functioning (effect traits). Stressors can however affect ecosystem functioning not only by altering species densities, but also by directly changing species effect traits. 2. We first identified the response traits predicting the cell density of 18 marine benthic diatom strains along gradients of two chemical stressors (a pesticide and a metal, atrazine and copper). We then tested if response traits could predict stressor-induced changes in ecosystem functioning, i.e. changes in the effect traits driving the diatoms’ potential contribution to primary production, sediment stabilization and energy content in intertidal systems. Finally, we examined if changes in density and changes in ecosystem functioning were correlated, to assess whether species capable of growing under stressful conditions could maintain their contribution to ecosystem functioning. 3. The relationship between response traits and stressor-induced changes in density and ecosystem functioning was different depending on stressor type: a set of intercorrelated morphological traits predicted changes in both density and ecosystem functioning under metal stress, with large cells being more stress-resistant. Changes in density and changes in ecosystem functioning were positively related: diatoms whose density was least affected by the metal were also able to sustain functioning under metal exposure. 4. In contrast, the capacity for mixotrophic growth predicted changes in density, but not changes in ecosystem functioning under pesticide stress. Pesticide effects on density and on ecosystem functioning were negatively related for energy content and sediment stabilization, indicating a limited capacity of pesticide-tolerant diatoms to maintain their contribution to ecosystem functioning. Synthesis. Ecosystem functioning under stress can depend on whether response traits driving changes in density also predict direct stress effects on the species’ contribution to ecosystem functioning. Based on our results, we expect a disproportionate loss of functioning when traits driving species densities do not allow to maintain ecosystem functioning under stress

Développement d'une méthode de mesure de champs cinématiques pour étudier la coupe à chaud

Ce travail se concentre sur le développement d'une technique de mesure de champs cinématiques pour l'étude des phénomènes se déroulant lors de la découpe à chaud d'alliages métalliques. Le développement d'une méthode de mesure permettant d'observer le comportement mécanique à ces températures élevées (environ 1000 °C) reste un challenge. Ce travail se propose de relever ce défi. Des cartes de déformations et de vitesses de déformation ont été obtenues grace à l'élaboration d'un mouchetis résistant à la température couplé avec un système d'observation ad hoc pour permettre une étude cinématique locale lors de la découpe à chaud de la pièce à l'aide de la corrélation d'images numériques

Effect of Si, Cu and processing parameters on Al-Si-Cu HPDC castings

Chemical composition of secondary Al-Si-Cu alloys and working variables of high-pressure die casting process (HPDC) may change for the same casting parts from one country to another in the world. They can even sometimes vary from one manufacturing site to another within the same country. An experimental study on the influence of alloying elements contents (Si and Cu), casting temperature and injection pressure on mechanical properties of die cast aluminum alloys was carried out to support the automotive industry suppliers in designing their cast parts. The microstructural features and the porosity level were also investigated and assessed. The primary objective is to highlight the modification mechanisms of the achieved properties using tensile tests, hardness measurements and microstructural observations performed on a HPDC casting parts. Low pressure and low temperature increase the rate of porosity, promote the formation of coarse Fe-rich intermetallic compounds and change the morphology of α-Al phases. These in turn deteriorate mechanical tensile properties. However, variation of alloying elements contents modifies the optimum properties achieved when part is made at constant casting processing parameters. Finally, the interactions between the studied parameters of HPDC and the chemical alloying elements show also a significant influence on the tensile properties