ParisTech

About: ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Residual stress & Finite element method. The organization has 1888 authors who have published 1965 publications receiving 55532 citations. The organization is also known as: Paris Institute of Technology & ParisTech Développement.

One channel defect imaging in a reverberating medium

Abstract: This letter presents an acoustic one-channel location system that takes advantage of the multiple reflections occurring in the reverberating medium under investigation. Experimental results are obtained with guided waves propagating in a bounded aluminum plate. The plate is so designed that there is no direct propagation path between the single transducer and the region of interest in the plate. In that manner, the two-dimensional image obtained in the region of interest is only based on the reverberated acoustic field measured with the single fixed transducer. The method is based on the application of topological optimization methods to wave-based location problems and on a preliminary calibration of the whole system. This calibration mainly consists in measuring the impulse response of the transducer in the region of interest before any object or defect is present. The calibration is here performed with a Laser Doppler velocimeter. The experimental results obtained with this one-channel topological imaging method show accurate location of a single small defect and of multiple small defects, with a resolving power below the wavelength.

Low Amplitude Boom-and-Bust Cycles Define the Septoria Nodorum Blotch Interaction

Abstract: Introduction Septoria nodorum blotch (SNB) is a complex fungal disease of wheat caused by the Dothideomycete fungal pathogen Parastagonospora nodorum. The fungus infects through the use of necrotrophic effectors (NEs) that cause necrosis on hosts carrying matching dominant susceptibility genes. The Western Australia (WA) wheatbelt is a SNB "hot spot" and experiences significant under favorable conditions. Consequently, SNB has been a major target for breeders in WA for many years. Materials and methods In this study, we assembled a panel of 155 WA P. nodorum isolates collected over a 44-year period and compared them to 23 isolates from France and the USA using 28 SSR loci. Results The WA P. nodorum population was clustered into five groups with contrasting properties. 80% of the studied isolates were assigned to two core groups found throughout the collection location and time. The other three non-core groups that encompassed transient and emergent populations were found in restricted locations and time. Changes in group genotypes occurred during periods that coincided with the mass adoption of a single or a small group of widely planted wheat cultivars. When introduced, these cultivars had high scores for SNB resistance. However, the field resistance of these new cultivars often declined over subsequent seasons prompting their replacement with new, more resistant varieties. Pathogenicity assays showed that newly emerged isolates non-core are more pathogenic than old isolates. It is likely that the non-core groups were repeatedly selected for increased virulence on the contemporary popular cultivars. Discussion The low level of genetic diversity within the non-core groups, difference in virulence, low abundance, and restriction to limited locations suggest that these populations more vulnerable to a population crash when the cultivar was replaced by one that was genetically different and more resistant. We characterize the observed pattern as a low-amplitude boom-and-bust cycle in contrast with the classical high amplitude boom-and-bust cycles seen for biotrophic pathogens where the contrast between resistance and susceptibility is typically much greater. Implications of the results are discussed relating to breeding strategies for more sustainable SNB resistance and more generally for pathogens with NEs.

When metacognitive prompts help information search in collaborative setting

Abstract: Introduction It is not surprising that information problem solving (IPS) as “metacognitively complex situations” ( Veenman et al., 2004 ) become an interesting area to study ways to foster the metacognitive processing they required, but that are not spontaneously activated. Objective The goal of the present study was to investigate the positive effect of metacognitive incentives, provided as question prompts, on the metacognitive processing required to collaboratively solve the information problem, and on the IPS scores. Method On the basis of the literature, the prompts were embedded in the IPS process and aimed to support three steps of IPS: information search, information classification and information presentation. Such question prompts were expected to positively impact IPS scores related to each step, compared to a condition without prompt. Moreover, we assumed that the positive effects of question prompts would be mediated by the level of metacognitive processing they activated. An experimental study involving IPS partially conducted in dyads was conducted with two conditions (with prompts, n = 12 and without prompts, n = 14). Results Results partially confirmed the direct and mediated effects of question prompts, but only when oriented on the first step of information search. There were no effects of the question prompts orienting on the next steps of information classification and information presentation. Conclusion Results of this study shed light on the role of metacognition in IPS and allowed to suggest some instructional implications of question prompts to support the IPS process.

En-face full-field optical coherence tomography for fast and efficient fingerprints acquisition

Abstract: Optical coherence tomography (OCT) has been recently proposed by a number of laboratories as a promising tool for fingerprints acquisitions and for fakes discrimination. Indeed OCT being a non-contact, non-destructive optical method that virtually sections the volume of biological tissues that strongly scatter light it appears obvious to use it for fingerprints. Nevertheless most of the OCT setups have to go through the long acquisition of a full 3D image to isolate an “en-face” image suitable for fingerprint analysis. A few “en-face” OCT approaches have been proposed that use either a complex 2D scanning setup and image processing, or a full-field illumination using a camera and a spatially coherent source that induces crosstalks and degrades the image quality. We show here that Full Field OCT (FFOCT) using a spatially incoherent source is able to provide “en-face” high quality optical sectioning of the fingers skin. Indeed such approach shows a unique spatial resolution able to reveal a number of morphological details of fingerprints that are not seen with competing OCT setups. In particular the cellular structure of the stratum corneum and the epidermis-dermis interface appear clearly. We describe our high-resolution (1 micrometer, isotropic) setup and show our first design to get a large field of view while keeping a good sectioning ability of about 3 micrometers. We display the results obtained using these two setups for fingerprints examination.