Influence of density on the electrical behaviour of a steel metallic wool

Le but de ce papier est de présenter l'influence de la densité sur le comportement électrique d'une laine d'acier. Les courbes conductivité électrique – densité relative sont bien décrites par une loi puissance. L'exposant de cette loi varie entre 2.3 et 3.5 avec la densité initiale. Cette évolution est corrélée avec l'exposant des lois puissances décrivant les courbes contrainte – densité

Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest

Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2&thinsp;min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100&thinsp;% and 98.5&thinsp;% of fluxes were above minimum detectable flux – MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25&thinsp;min was more appropriate for reliable estimation of most N2O fluxes (85.6&thinsp;% of measured fluxes are above MDF&thinsp;±&thinsp;0.002&thinsp;nmol&thinsp;m−2&thinsp;s−1). Our study highlights the importance of adjusted closure time for each gas.</p

Pinning of a solid--liquid--vapour interface by stripes of obstacles

We use a macroscopic Hamiltonian approach to study the pinning of a solid--liquid--vapour contact line on an array of equidistant stripes of obstacles perpendicular to the liquid. We propose an estimate of the density of pinning stripes for which collective pinning of the contact line happens. This estimate is shown to be in good agreement with Langevin equation simulation of the macroscopic Hamiltonian. Finally we introduce a 2--dimensional mean field theory which for small strength of the pinning stripes and for small capillary length gives an excellent description of the averaged height of the contact line.Comment: Plain tex, 12 pages, 3 figures available upon reques

Atmospheric deposition of elements and its relevance for nutrient budgets of tropical forests

Atmospheric deposition is an important component of the nutrient cycles of terrestrial ecosystems, but field measurements are especially scarce in tropical regions. In this study we analysed 15 months of precipitation chemistry collected in an old growth tropical forest located in French Guiana. We measured nutrient inputs via bulk precipitation and throughfall and used the canopy budget model to estimate nutrient fluxes via canopy exchange and dry deposition. Based on this method we quantified net fluxes of macronutrients and compared their contribution to internal cycling rates via litterfall. Our results suggest that while atmospheric deposition of nitrogen was relatively high (13 kg ha−1 year−1), and mainly in organic forms, the N inputs via litterfall were an order of magnitude higher. In contrast to nitrogen, we found that atmospheric deposition of phosphorus (0.5 kg ha−1 year−1) supplied up to one third of the annual litterfall input to the forest floor. Most strikingly, combined annual inputs of potassium via atmospheric deposition (14 kg ha−1 year−1) and canopy leaching (22 kg ha−1 year−1) were three times larger than internal nutrient recycling via litterfall (11 kg ha−1 year−1). We conclude that atmospheric deposition of phosphorus and especially potassium may play an important role in sustaining the productivity of this old-growth tropical rainforest

Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest

Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above minimum detectable flux - MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 min was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of adjusted closure time for each gas

On the critical nature of plastic flow: one and two dimensional models

Steady state plastic flows have been compared to developed turbulence because the two phenomena share the inherent complexity of particle trajectories, the scale free spatial patterns and the power law statistics of fluctuations. The origin of the apparently chaotic and at the same time highly correlated microscopic response in plasticity remains hidden behind conventional engineering models which are based on smooth fitting functions. To regain access to fluctuations, we study in this paper a minimal mesoscopic model whose goal is to elucidate the origin of scale free behavior in plasticity. We limit our description to fcc type crystals and leave out both temperature and rate effects. We provide simple illustrations of the fact that complexity in rate independent athermal plastic flows is due to marginal stability of the underlying elastic system. Our conclusions are based on a reduction of an over-damped visco-elasticity problem for a system with a rugged elastic energy landscape to an integer valued automaton. We start with an overdamped one dimensional model and show that it reproduces the main macroscopic phenomenology of rate independent plastic behavior but falls short of generating self similar structure of fluctuations. We then provide evidence that a two dimensional model is already adequate for describing power law statistics of avalanches and fractal character of dislocation patterning. In addition to capturing experimentally measured critical exponents, the proposed minimal model shows finite size scaling collapse and generates realistic shape functions in the scaling laws.Comment: 72 pages, 40 Figures, International Journal of Engineering Science for the special issue in honor of Victor Berdichevsky, 201

Impacts of changed litter inputs on soil CO2 efflux in three forest types in central south China

We have defined Neutrosophic Over-/Under-/Off-Set and Logic for the first time in 1995 and published in 2007. During 1995-2016 we presented them to various national and international conferences and seminars. These new notions are totally different from other sets/logics/probabilities. We extended the neutrosophic set respectively to Neutrosophic Overset {when some neutrosophic component is > 1}, to Neutrosophic Underset {when some neutrosophic component is < 0}, and to Neutrosophic Offset {when some neutrosophic components are off the interval [0, 1], i.e. some neutrosophic component > 1 and other neutrosophic component < 0}. This is no surprise since our real-world has numerous examples and applications of over-/under-/off-neutrosophic components

Après une décennie de « buzz » : quelle pertinence pour le concept de modèle d’affaires en stratégie?

Une dizaine d’années après la renaissance manifeste de l’intérêt des praticiens, puis des chercheurs, pour le concept de modèle d’affaires (business model), la question de sa pertinence au regard des concepts et des outils existants en stratégie persiste. Concept polysémique? Concept « valise »? Concept utile? Concept durable? Autant de questions qui, au-delà de la popularité du concept, nous invitent à porter un regard à la fois critique et constructif sur le modèle d’affaires dans le champ du management stratégique.Alors que notre pratique d’enseignement de la stratégie et d’accompagnement de projets d’innovation nous amenait à questionner la pertinence du concept/outil du modèle d’affaires, il nous sembla qu’un tour de table s’imposait pour tenter de répondre aux questions soulevées. Ce tour de table s’est tenu le 8 juin 2011 lors de la XXe conférence de l’Association Internationale de Management Stratégique (AIMS) à Nantes. Ce petit ouvrage a pour but de faire partager au lecteur l’intégralité des propos échangés ce jour-là