Nitrogen Use Efficiency in Durum Wheat (Triticum durum Desf.) Grown under Semiarid Conditions in Algeria

The proper and sustainable management of nitrogen fertilization is one of the most common problems of cereal cultivation in semiarid regions, which are characterized by a wide variability in climatic conditions. The current work was conducted to evaluate the effects of nitrogen fertilization on the agronomic and economic aspects of durum wheat cultivated under rainfed semiarid conditions in Algeria and to determine the most efficient nitrogen use efficiency (NUE) among four genotypes that are widespread in the country (tall and short, old and modern genotypes). The four genotypes, Bousselam, MBB, Megress, and GTAdur, were investigated under four nitrogen rates from 0 to 120 kg N ha−1 during three cropping seasons (2016 to 2018). The results indicate that the total nitrogen uptake at maturity (NM), nitrogen uptake by grain (NG), nitrogen harvest index (NHI), NUE and its components, such as nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE), were significantly affected by year, genotype, and nitrogen level. From this study, it appears that higher nitrogen rates improved NM and NG. However, no effects on either grain yield or marginal net return (MNR) were observed; conversely, increased nitrogen levels produced a 13% reduction in the economic return. In other words, in the North African environment, the response to nitrogen is more evident in quality than in yield, which in turn is dependent on the yearly weather conditions and cultivated genotypes. Moreover, nitrogen negatively affected NUE and its components (NUpE, NUtE). On average, NUE displayed low values (14.77 kg kg−1), mostly irregular and highly dependent on weather conditions; in the best year, it did not exceed 60% (19.87 kg kg−1) of the global average value of 33 kg kg−1. Moreover, the modern genotypes Megress (tall) and GTAdur (short) showed the best capacity to tolerate different nitrogen conditions and water shortages, providing relatively superior yields, as well as more effective N use from fertilizers and the soil than the other two genotypes

Mechanics of Reversible Unzipping

We study the mechanics of a reversible decohesion (unzipping) of an elastic layer subjected to quasi-static end-point loading. At the micro level the system is simulated by an elastic chain of particles interacting with a rigid foundation through breakable springs. Such system can be viewed as prototypical for the description of a wide range of phenomena from peeling of polymeric tapes, to rolling of cells, working of gecko's fibrillar structures and denaturation of DNA. We construct a rigorous continuum limit of the discrete model which captures both stable and metastable configurations and present a detailed parametric study of the interplay between elastic and cohesive interactions. We show that the model reproduces the experimentally observed abrupt transition from an incremental evolution of the adhesion front to a sudden complete decohesion of a macroscopic segment of the adhesion layer. As the microscopic parameters vary the macroscopic response changes from quasi-ductile to quasi-brittle, with corresponding decrease in the size of the adhesion hysteresis. At the micro-scale this corresponds to a transition from a `localized' to a `diffuse' structure of the decohesion front (domain wall). We obtain an explicit expression for the critical debonding threshold in the limit when the internal length scales are much smaller than the size of the system. The achieved parametric control of the microscopic mechanism can be used in the design of new biological inspired adhesion devices and machines

A 3D modelling of the protrusion and retraction of a single cell during the motiliy and the rolling

The rolling is an important kind of cell adhesion, especially in the case of the immune mechanism, due to the leukocyte action, which is strongly influenced by molecular affinity [1]. Our purpose, in this paper, is the presentation of a 3D theorical model which describes the behaviour of the contact interface cell-wall during the rolling and the cell deformation. The first point concerns the modelling of the contact interface, which is assimilated to a circular plate, linked to the wall (e.g vein) by elastic springs. The second point concerns the modelling of the active deformation due to the change of the cytoskeleton structure during the cell motility

Influence of the mechanical damping on the rolling of a single biological cell: A stochastic approach

The rolling is an important kind of cell adhesion, especially in the case of the immune mechanism, due to the leukocyte action, which is strongly influenced by molecular affinity [1].
Our purpose, in this paper, is the presentation of a 2D model which describes the behaviour of the contact interface cell-wall during the rolling. The cell membrane and the wall are assimilated to two rectilinear elastic beams, linked by elastic springs in the case of undamped connections [2] or viscoelastic element in the case of a dissipative behavior. As a first step, the motion of the interface is analyzed, under the external actions of the dynamical fluid pressure, the Van der Waals (attractive forces) and electrostatic effects (repulsive). The second point corresponds to the combination of the vibration of the contact zone and the rupture of the existing connections under a pulling effort. The last step concerns the description of the kinetic of junction between the free ligands and receptors, which constitutes the new connections.
The numerical simulations show the rolling phenomenon, the influence of the mechanical damping on the behavior of the contact interface and the kinetics of junctions between the adhesion free molecules