Estimation of the dynamics and yields of cereals in a semi-arid area using remote sensing and the SAFY growth model

In semi-arid areas, a strongly variable climate represents a major risk for food safety. An operational grain yield forecasting system, which could help decision-makers to make early assessments and plan annual imports, is thus needed. It can be challenging to monitor the crop canopy and production capacity of plants, especially cereals. In this context, the aim of the present study is to analyse the characteristics of two types of irrigated and non-irrigated cereals: barley and wheat. Through the use of a rich database, acquired over a period of two years for more than 30 test fields, and from 20 optical satellite SPOT/HRV images, two research approaches are considered. First, statistical analysis is used to characterize the vegetation’s dynamics and grain yield, based on remotely sensed (satellite) normalized difference vegetation index (NDVI) measurements. A relationship is established between the NDVI and LAI (leaf area index). Different robust relationships (exponential or linear) are established between the satellite NDVI index acquired from SPOT/HRV images, just before the time of maximum growth (April), and grain and straw, for barley and wheat vegetation covers. Following validation of the proposed empirical approaches, yield maps are produced for the studied site. The second approach is based on the application of a Simple Algorithm for Yield Estimation (SAFY) growth model, developed to simulate the dynamics of the LAI and the grain yield. An inter-comparison between ground yield measurements and SAFY model simulations reveals that yields are underestimated by this model. Finally, the combination of multi-temporal satellite measurements with the SAFY model estimations is also proposed for the purposes of yield mapping. Although the results produced by the SAFY model are found to be reasonably well correlated with those determined by satellite measurements (NDVI), the grain yields are nevertheless underestimated.     

Development of Turbulent Wakes Evolving from Asymmetric Shear Layers

ABSTRACT

This paper reports an experimental investigation on the response of a turbulent wake past an elongated flat plate to various upstream flow conditions Different tripping wires were placed on the upper side of the plate downstream the leading edge resulting in asymmetric shear layers evolving from the trailing edges. Mean flow and turbulent fields of the asymmetric wakes were compared to their symmetrical counterpart. The symmetrical wake was found to attain a self-similar state whereas asymmetric wakes continued to slowly evolve towards an expected asymptotic behavior at a rate that strongly depends on the imposed initial conditions.     

Improving the adhesion strength of polymers: effect of surface treatments

Abstract

To improve their adhesion strength, polymeric surfaces are usually modified through different treatments. This study investigates the effect of mechanical, chemical, and energetic treatments on the bonding strength of ethylene propylene diene methylene (EPDM), polyvinyl chloride (PVC), and acrylonitrile butadiene styrene (ABS) materials. Three adhesives based on different chemical compositions, namely silicone, polyurethane, and modified-silane (MS) polymer, were considered. Results show that the effect of the applied treatments on the adhesion strength of EPDM surfaces is insignificant. Only a slight improvement is obtained in the case of polyurethane-based adhesive, while the failure modes remained adhesive. As for PVC, most treatments were effective in the case of the silicone-based adhesive, especially grit blasting, primer, and UV/ozone treatments. Only UV/ozone treatment improved the adhesion strength and altered the failure mechanisms of this material when polyurethane and MS-based adhesives are used. The adhesion of ABS increased and the failure modes changed from adhesive to cohesive for most treatments. Particularly, a significant improvement is obtained when primer coating and UV/ozone radiation are applied. This comparative study paves the way for the design of polymeric joints with highly enhanced adhesion performance.     

Purification of silicon powder by the formation of thin porous layer followed by photo-thermal annealing

ABSTRACT: Porous silicon has been prepared using a vapor-etching based technique on a commercial silicon powder. Strong visible emission was observed in all samples. Obtained silicon powder with a thin porous layer at the surface was subjected to a photo-thermal annealing at different temperatures under oxygen atmosphere followed by a chemical treatment. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) results indicate that silicon purity is im-proved from 99.1 to 99.994 % after annealing at 900 degreesC.     

Evaluation of machining process by integrating 3D manufacturing dispersions,functional constraints,and the concept of small displacement torsors

This paper presents a 3D formalization of manufacturing tolerancing which associates the concept of small displacements, the functional constraints, and manufacturing process capability. This approach would make it possible to establish relations which limit the surface variations of the production mechanism by the functional specifications. These relations have a number of requirements imposed by designer and are sufficient to evaluate the manufacturing process. The variations of the manufacturing process are defined in relation to variations measured by 3D measuring.