Field-scale analysis of water and nutrient use efficiency for vegetable production in a West African urban agricultural system

Urban agriculture increasingly supplies food and non-food services to the rapidly growing West African cities. However, with its typically heavy use of fertilizers and uncontrolled use of water, it bears severe risks of soil and groundwater pollution. This study was carried out in Bobo Dioulasso (Burkina Faso, West Africa) at two commercial gardening sites. It aimed at performing a detailed characterization of farmer’s water and nutrient management strategies. Four vegetable crops were monitored (tomato, cabbage, carrot and lettuce). Water inputs (rainfall and irrigation), nutrient inputs (organic and mineral fertilizers and nutrients in irrigation water) and crop uptake were monitored over a 1–2-year period. In addition, pan lysimeters allowed monitoring drainage. Depending on the site, 3–8% of the input water was lost by drainage, i.e., as much as 293 mm/year at one of the sites. During the dry season, when the farmer has full control over the water supply, water application exceeded plant requirements by as much as 40%, which reveals inefficient water use. Up to 800 kg N ha⁻¹, 140 kg P ha⁻¹ and 500 kg K ha⁻¹ were applied for a single crop cycle. With few exceptions, crops tended to be strongly over-fertilized, except for K at one of the two sites. Nutrient supply exceeded crop requirements by 109 to 2,012 kg N, 66 to 450 kg P and 0 to 393 kg K per year. These results, in combination with the large observed rates of drainage, are indicative of a high risk of nutrient leaching and groundwater contamination. The partial factor productivity of nutrients tended to be low. These results therefore suggested that there is scope to substantially reduce nutrient application rates in these systems without adverse effects on yields, which would be beneficial for groundwater resources and improve the economic returns.     

Tribological behaviour of Pearlitic and Bainitic steel grades under various sliding conditions

Railway systems have to cope with increasing and heavier traffic conditions. New rail steel grades are designed to extend rail life and to prevent rail defects. The tribological response of such steel grades under wheel-rail contact conditions needs to be studied before its use on real track. Tests on reduced-scale simulator, i.e. roller-on-plate tribometer with wheel-rail contact like conditions, have been performed on three rail steel grades: the Pearlitic, the heat-treated Pearlitic and the Bainitic. Results show a difference in both sensitivity and mechanism of particle detachment with the steel grade microstructure, but no difference in friction coefficient evolution.     

High-resolution full-field optical coherence tomography with a Linnik microscope

We describe an original microscope for high-resolution optical coherence tomography applications. Our system is based on a Linnik interference microscope with high-numerical-aperture objectives. Lock-in detection of the interference signal is achieved in parallel on a CCD by use of a photoelastic birefringence modulator and full-field stroboscopic illumination with an infrared LED. Transverse cross-section (en-face, or XY) images can be obtained in real time with better than 1-microm axial (Z) resolution and 0.5-microm transverse (XY) resolution. A sensitivity of approximately 80 dB is reached at a 1-image/s acquisition rate, which allows tomography in scattering media such as biological tissues.     

Aequorin-based functional assays for G-protein-coupled receptors,ion channels,and tyrosine kinase receptors

Aequorin is a photoprotein originating from jellyfish, whose luminescent activity is dependent on the concentration of calcium ions. Due to the high sensitivity and low background linked to luminescent assays, as well as to its absence of toxicity and its large linear dynamic range, aequorin has been used as an intracellular calcium indicator since its discovery in the early 1960s. The first applications of aequorin involved its microinjection in cells. The cloning of its gene in 1985 opened the way to the stable expression of aequorin in cell lines or even entire organisms. Here we present the validation of aequorin as a functional assay for the screening of G-protein-coupled receptors, ion channels, and tyrosine kinase receptors, as well as for their pharmacological characterization in agonist and antagonist detection assays. We optimized our cell suspension-based assay and determined that the most sensitive assay was performed at room temperature, with mitochondrially expressed aequorin and using coelenterazine derivative h for reconstitution of aequorin. The robustness of the assay and the current availability of luminometers with integrated injectors allow aequorin to fit perfectly with high throughput functional assays requirements.     

Population computation of vectorial transformations

Many neurons of the central nervous system are broadly tuned to some sensory or motor variables. This property allows one to assign to each neuron a preferred attribute (PA). The width of tuning curves and the distribution of PAs in a population of neurons tuned to a given variable define the collective behavior of the population. In this article, we study the relationship of the nature of the tuning curves, the distribution of PAs, and computational properties of linear neuronal populations. We show that noise-resistant distributed linear algebraic processing and learning can be implemented by a population of cosine tuned neurons assuming a nonuniform but regular distribution of PAs. We extend these results analytically to the noncosine tuning and uniform distribution case and show with a numerical simulation that the results remain valid for a nonuniform regular distribution of PAs for broad noncosine tuning curves. These observations provide a theoretical basis for modeling general nonlinear sensorimotor transformations as sets of local linearized representations.     

A Unifying and Rigorous Shape from Shading Method Adapted to Realistic Data and Applications

We propose a new method for the Lambertian Shape From Shading (SFS) problem based on the notion of Crandall-Lions viscosity solution. This method has the advantage of requiring the knowledge of the solution (the surface to be reconstructed) only on some part of the boundary and/or of the singular set (the set of the points at maximal intensity). Moreover it unifies in an unique mathematical formulation the works of Rouy et al. [34, 50], Falcone et al. [21], Prados et al. [46, 48, 49], based on the notion of viscosity solutions and the work of Dupuis and Oliensis [17] dealing with classical solutions and value functions. Also, it allows to generalize their results to the “perspective SFS” problem recently simultaneously introduced in [13,46,55]. While the theoretical part has been developed in [44], in this paper we give some stability results and we describe numerical schemes for the SFS based on this method. We construct provably convergent and robust algorithms. Finally, we apply our SFS method to real images and we suggest some real-life applications.