Teaching durability in automotive applications using a reliability approach

Fatigue phenomena, which appear generally below the yield stress, is the cause of more than 80 % of in-service mechanical failures. However, the optimization of the weight and cost when designing mechanical components or structures, linked to improved performance, leads to increasingly stressed components. Therefore a fatigue design approach must be done by the engineer. This paper shows the experience gained over five academic years of teaching fatigue the assessment of automotive components using a reliability approach to predict probability of failure, in the engineering school, Arts et Métiers ParisTech, in France. The choice was made to present a comprehensive fatigue assessment approach using a method, initially developed in the automotive industry and since extended to the aeronautical and mechanical industries. This method is known as the “Stress-Strength interference analysis”. The “Stress” represents the distribution of the driver severity, and the “Strength” represents the distribution of the fatigue strength of all the components. A suspension arm is used to illustrate the approach. The Dang Van multiaxial fatigue criterion is implemented in a Finite Elements Code and a danger coefficient is visualized on the meshed structure. The fatigue analysis is interpreted with respect to the target reliability sought by the car- manufacturer

Statistical Estimation of Mechanical Parameters of Clarinet Reeds Using Experimental and Numerical Approaches

A set of 55 clarinet reeds is observed by holography, collecting 2 series of measurements made under 2 different moisture contents, from which the resonance frequencies of the 15 first modes are deduced. A statistical analysis of the results reveals good correlations, but also significant differences between both series. Within a given series, flexural modes are not strongly correlated. A Principal Component Analysis (PCA) shows that the measurements of each series can be described with 3 factors capturing more than $90\%$ of the variance: the first is linked with transverse modes, the second with flexural modes of high order and the third with the first flexural mode. A forth factor is necessary to take into account the individual sensitivity to moisture content. Numerical 3D simulations are conducted by Finite Element Method, based on a given reed shape and an orthotropic model. A sensitivity analysis revels that, besides the density, the theoretical frequencies depend mainly on 2 parameters: $E_L$ and $G_{LT}$. An approximate analytical formula is proposed to calculate the resonance frequencies as a function of these 2 parameters. The discrepancy between the observed frequencies and those calculated with the analytical formula suggests that the elastic moduli of the measured reeds are frequency dependent. A viscoelastic model is then developed, whose parameters are computed as a linear combination from 4 orthogonal components, using a standard least squares fitting procedure and leading to an objective characterization of the material properties of the cane \textit{Arundo donax}

Natural Cognitive Foundations of Teacher Knowledge: An Evolutionary and Cognitive Load Account

International audienceInstructional process management (encompassing instructional design and classroom management) is known to be very complex, mainly due to its context and the large and diverse amount of knowledge driving it: content knowledge, pedagogical knowledge (PK), curriculum knowledge, knowledge of learners and their characteristics, knowledge of educational contexts, pedagogical content knowledge, and knowledge of educational ends (Shulman, 1987). This complexity makes researchers unable to detect well-defined practices, and a knowledge base leading to efficient teaching with low training cost is missing (Koedinger, Booth, & Klahr, 2013). The attempts so far to investigate these pieces of knowledge can be categorised in two paths. The first path considers novice vs. expert knowledge comparisons to model knowledge growth across experience (Hogan, Rabinowitz, & Craven, 2003). The second path considers knowledge bases every teacher needs in order to work efficiently. These two paths both have some concerns. Teachers' expertise is not so clear-cut and the way teachers develop it through experience is difficult to model and diagnose. Further, specifying a comprehensive knowledge base about teaching is often externally-driven (Hattie, 2009; Wang, Haertel, & Walberg, 1993), listing a superficial knowledge base of 'what works', often unrelated to teachers' beliefs and knowledge and/or their cognitive abilities. Pedagogical Content Knowledge (PCK), as Shulman (1987, p. 8) argued, is " that special amalgam of content and pedagogy that is uniquely the province of teachers, their own special form of special understanding ". This proposition, as well as Shulman's professional knowledge development model, has become widespread in the educational sciences research field. However, some problems can be raised, notwithstanding its vagueness (" special amalgam " , also see Kind, 2015). First, teaching is mainly seen as a " learned profession " (see Shulman, 1987, p. 9), while the social and informal facet of this activity, relying on mainly innate abilities, remains unaddressed. Second, we refer to van Driel et al.'s (2001) definition of PCK: " the knowledge the teachers must have in order to teach science " (emphasis added) to highlight that the orientation of such a knowledge base is highly prescriptive in nature: it states appropriate knowledge so that anyone having it can be a good teacher, and many research lines have been oriented to differentiating novices from experts with regard to PCK. Third, this model emphasises a unidirectional way in which teachers' beliefs and knowledge 2 influence his or her social behaviour, whereas bidirectional ways are more likely to occur (Rimm-Kaufman & Hamre, 2010). The aim of this paper is to explore a cognitive way to define teachers' professional knowledge (TPK), arguing that some 'natural' knowledge, stemming from several human social abilities – and, for many of them, animal – is thus engaged in teaching as well. The actions grounded on such knowledge are undertaken automatically or at a low cognitive load due to the nature of the latter. Some theoretical views on teaching include such an assumption (Csibra, 2007; Csibra & Gergely, 2011; Strauss, 2005; Strauss & Ziv, 2012), but so far, little research has investigated teachers' cognitive processes in relation to both natural cognition and Cognitive Load Theory (CLT) (see however Feldon, 2007; Moos & Pitton, 2013). The remainder of this paper seeks firstly to consider teachers' actions through the lens of natural cognition and pedagogy, then to set up a framework for teacher cognition and knowledge, showing that several social abilities and knowledge can be used for teaching purposes, and with a low cognitive load. Then, we describe the abilities for teaching as primary vs. secondary knowledge. Eventually, we use this framework to assess or predict which cognitive load is in relation with teachers' performances according to the CLASS, a renowned classroom observation system

Probabilistic life of DA 718 for aircraft engine disks

International audienceThe micro-mechanisms of crack initiation and propagation identified for DA 718, as well as the competition between initiation site types and locations, cannot be accurately accounted for by current certified methods used to establish aircraft engine disks life,essentially phenomenological. Once identified, these micro-mechanisms have been modelized by mesoscopic models using very few parameters and depending strongly on material mechanical behavior. LCF data scatter was mainly attributed to probabilistic nature of particle presence in a given volume, and probability of fracture at the first LCF cycle. In order to describe these effects and develop a model able to account for LCF scatter by the only means of physical mechanisms description, a global macroscopic and probabilistic model has been proposed. This model can be used as a post-processing routine of a finite element analysis. Confrontation of the global probabilistic model to experimental data gathered on notched samples gives good results, and the proposed method shows more realistic than the standard one on the cases exposed. Contrary to the standard method, it allows in addition to determine the predominant initiation site as a function of loading, material behavior and microstructure inherited from forging process, giving way to possible material and forging route optimisation at the design stage, to fulfill given structural life objectives

Improving MANET routing with satellite out-of-band signaling

International audienceRouting in mobile ad hoc networks is a complex task due to the mobility of the nodes and the constraints linked to a wireless multihop network (e.g., limited bandwidth, collisions, and bit errors). These adverse conditions impair not only data traffic but also routing signaling traffic, which feeds route computation. In this contribution, we propose to use satellite communications to help in the distribution of mobile ad hoc network routing signaling. The optimized link-state routing (OLSR) is chosen among several routing protocols to be extended with satellite-based signaling, yielding a version we call OLSR hybrid signaling (OLSR-H). This new scheme is evaluated through simulations and yields improvements of approximately 10% in the data delivery ratio compared with a regular OLSR. This evaluation is conducted using two different network topology models, one being fit for representing forest firefighting operations

Methodical advances in reproducibility research : A proof of concept qualitative comparative analysis of reproducing animal data in humans

Background: While the term reproducibility crisis mainly reflects reproducibility of experiments between laboratories, reproducibility between species also remains problematic. We previously summarised the published reproducibility between animal and human studies; i.e. the translational success rates, which varied from 0% to 100%. Based on analyses of individual factors, we could not predict reproducibility. Several potential analyses can assess effect of combinations of predictors on an outcome. Regression analysis (RGA) is common, but not ideal to analyse multiple interactions and specific configurations (≈ combinations) of variables, which could be highly relevant to reproducibility. Qualitative comparative analysis (QCA) is based on set theory and Boolean algebra, and was successfully used in other fields. We reanalysed the data from our preceding review with QCA. Results: This QCA resulted in the following preliminary formula for successful translation: ∼Old*∼Intervention*∼Large*MultSpec*Quantitative Which means that within the analysed dataset, the combination of relative recency (∼ means not; >1999), analyses at event or study level (not at intervention level), n 85%). Other combinations of factors showed less consistent or negative results. An RGA on the same data did not identify any of the included variables as significant contributors. Conclusions: While these data were not collected with the QCA in mind, they illustrate that the approach is viable and relevant for this research field. The QCA seems a highly promising approach to furthering our knowledge on between-species reproducibility

Two mycoheterotrophic orchids from Thailand tropical dipterocarpacean forests associate with a broad diversity of ectomycorrhizal fungi

<p>Abstract</p> <p>Background</p> <p>Mycoheterotrophic plants are considered to associate very specifically with fungi. Mycoheterotrophic orchids are mostly associated with ectomycorrhizal fungi in temperate regions, or with saprobes or parasites in tropical regions. Although most mycoheterotrophic orchids occur in the tropics, few studies have been devoted to them, and the main conclusions about their specificity have hitherto been drawn from their association with ectomycorrhizal fungi in temperate regions.</p> <p>Results</p> <p>We investigated three Asiatic Neottieae species from ectomycorrhizal forests in Thailand. We found that all were associated with ectomycorrhizal fungi, such as Thelephoraceae, Russulaceae and Sebacinales. Based on ¹³C enrichment of their biomass, they probably received their organic carbon from these fungi, as do mycoheterotrophic Neottieae from temperate regions. Moreover, ¹³C enrichment suggested that some nearby green orchids received part of their carbon from fungi too. Nevertheless, two of the three orchids presented a unique feature for mycoheterotrophic plants: they were not specifically associated with a narrow clade of fungi. Some orchid individuals were even associated with up to nine different fungi.</p> <p>Conclusion</p> <p>Our results demonstrate that some green and mycoheterotrophic orchids in tropical regions can receive carbon from ectomycorrhizal fungi, and thus from trees. Our results reveal the absence of specificity in two mycoheterotrophic orchid-fungus associations in tropical regions, in contrast to most previous studies of mycoheterotrophic plants, which have been mainly focused on temperate orchids.</p

Radiofrequency conical emission from femtosecond filaments in air

International audienceWe show that the broadband conical emission associated with filaments in air extends down to the radiofrequency region. This rf emission which originates from the longitudinal oscillation of charged ions formed during filamentation is strongly enhanced by the presence of a longitudinal static electric field