Singular perturbations of some nonlinear problems

We deal with singular perturbations of nonlinear problems depending on a small parameter ε > 0. First we consider the abstract theory of singular perturbations of variational inequalities involving some nonlinear operators, defined in Banach spaces, and describe the asymptotic behavior of these solutions as ε → 0. Then these abstract results are applied to some boundary value problems. Bibliography: 15 title

Singular perturbations of some nonlinear problems

We deal with singular perturbations of nonlinear problems depending on a small parameter ε > 0. First we consider the abstract theory of singular perturbations of variational inequalities involving some nonlinear operators, defined in Banach spaces, and describe the asymptotic behavior of these solutions as ε → 0. Then these abstract results are applied to some boundary value problems. Bibliography: 15 title

Numerical Simulation of the Type Inversion in n+-p-p+ Si Solar Cells, Used for Space Applications, under 1 MeV Electron Irradiation

AbstractSolar cells, used for space applications, are exposed to energetic particles such as protons and electrons. The energetic particles create defects in the active region of the solar cell and the latter performance can be severely degraded. One of the phenomenons observed in Silicon solar cells exposed to 1 MeV electron irradiation is type inversion of its active region. This behaviour is numerically simulated using the SCAPS software. The current-voltage characteristics of a Si n+-p-p+ structure are calculated under AM0 for different fluences of 1MeV electrons. It was found that, amongst the many defects created, only one of them is responsible for type inversion. It is a minority trap that is an electron trap in the p-type base of the n+-p-p+ solar cell

The effect of structural characteristics of ZnO and NiO thin films on the performance of NiO/ZnO photodetectors

Material properties play an important role in the fabrication of optoelectronic devices such as photodetectors because it is ultimately reflected in their efficiency and performance. To fabricate a NiO/ZnO heterojunction with better structural properties using a low-cost and uncomplicated deposition process, we studied the influence of NiO and ZnO thickness by taking different volumes of spray solution (5, 10, and 15 ml) on the structural and morphological properties that were investigated using the spray pyrolysis technique. When the films' thickness increased, the crystalline structure of both films improved. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002). The NiO X-ray diffraction patterns showed that the films were in cubic phase with orientation (111) and the peak density increased with the film thickness. According to our experimental conditions and XRD results, we suggest that thicker NiO and ZnO are the optimal films to fabricate a NiO/ZnO heterostructure. It is found that Raman and XRD results confirm the formation of NiO/ZnO heterostructure. The morphology of NiO/ZnO is smooth and completely covers the substrate without any pinholes. The further investigation related to the effect of NiO and ZnO thin films' structural properties on NiO/ZnO heterostructure photodetector performance is presented using the simulations. It is worth mentioning that based on the suggested transport models, the results confirm that the origin of the dark current has been attributed to the tunneling and thermionic emission at the interface while bulk defects, leading to the increase Shockley-Read-Hall recombination and generation, control the carrier transport. Furthermore, we studied the effect of Gaussian and tail acceptor/donor defects on the current-voltage (J-V) characteristics and responsivity. The obtained results showed that increasing NiO tail states cause an increase in tunneling current. In contrast, the deep defects density in both ZnO and NiO affects the photodetection characteristics, resulting in a decrease in responsivity and photocurrent when these defects increase

SIRR-MOD—A Decision Support System for Identifying Optimal Irrigation Water Needs at Field and District Scale

SIRR-MOD is a DSS integrating two numerical modules: (1) A agro-hydrological model (named FLOWS-HAGES) for simulating flow of water and solutes in heterogeneous agri-environmental systems; (2) A model for simulating the hydraulics of the irrigation network (named COPAM). FLOW-HAGES provides a daily list of hydrants opening based on water or crop criteria. Then, an optimal sequence of hydrants may be established by passing the volumes to be delivered to a model (COPAM) for simulating the hydraulics of the irrigation network, in order to guarantee that the discharges flowing inside the distribution pipes network are delivered under optimal pressure head distribution. In this paper, we only illustrated the potential of FLOWS-HAGES model in simulating the daily evolution of: soil water contents and pressure heads in the soil profile; water uptake; stress periods for each crop; return fluxes to the groundwater under pressurized irrigation systems and climatic conditions at district level. This methodology has been applied to establish irrigation scheduling over the irrigation season for sector 6 of the Irrigation District 10 in the “Sinistra Ofanto” irrigation system. Irrigation water volumes calculated by FLOWS-HAGES model were compared to the volumes delivered by farmers, showing irrigation simulated by the model more frequent than those supplied by the farmers and with lower irrigation volumes

A bimodal extension of the ARYA&PARIS approach for predicting hydraulic properties of structured soils

The main purpose of this paper is to develop a bimodal pedotransfer function to obtain soil water retention (WRC) and hydraulic conductivity (HCC) curves. The proposed pedo-transfer function (PTF) extends the Arya and Paris (AP) approach, which is based on particle size distribution (PSD), by incorporating aggregate-size distribution (ASD) into the PTF to obtain the bimodal WRC. A bimodal porosity approach was developed to quantify the fraction of each of the porous systems (matrix and macropores) in overall soil porosity. Saturated hydraulic conductivity, K 0 , was obtained from WRC using the Kozeny-Carman equation, whose parameters were inferred from the behaviour of the bimodal WRC close to saturation. Finally, the Mualem model was applied to obtain the HCC. In order to calibrate the PTF, measured soil physical and hydraulic properties data were used, coming from field infiltration experiments from an irrigation sector of 140 ha area in the “Sinistra Ofanto” irrigation system in Apulia, southern Italy. The infiltration data were fitted by using both bimodal and unimodal hydraulic properties by an inverse solution of the Richards equation. The bimodal “measured” hydraulic properties were then used to calibrate the scaling parameter (α AP ) of the proposed bimodal AP ( bimAP ) PTF. Similarly, for the sake f comparison with the bimodal results, the unimodal hydraulic properties were used to calibrate the α AP of the classical unimodal AP ( unimAP ) PTF. Compared to the unimAP PTF, the proposed bimAP significantly improves the predictions of the mean WRC parameters and K 0 , as well as the prediction of the shape of the whole HCC. Moreover, compared to the unimodal approach, it also allows keeping the hydraulic parameters’ spatial variability observed in the calibration dataset. Multiple linear regression (MLR) was also applied to analyse the sensitivity of the bimodal α AP parameter to textural and structural features, confirming significant predictive effects of soil structure

Effect of the source solution quantity on optical characteristics of ZnO and NiO thin films grown by spray pyrolysis for the design NiO/ZnO photodetectors

Zinc Oxide (ZnO) and Nickel Oxide (NiO) thin films were prepared using the spray pyrolysis technique using three different quantities of solution 5, 10, and 15 ml, to modify their optical properties. Optical characterization of the obtained thin films showed that the bandgap and the transparency of NiO and ZnO decrease with increasing solution quantity. The films are highly transparent making them suitable for optoelectronic applications. It is worth noting that NiO has a low growth rate compared to ZnO due to its larger bandgap. The different parameters obtained for both films are then used to simulate the electrical characteristics and the responsivity of a NiO/ZnO heterojunction based PN photodiode. Both the electrical characteristics and the responsivity improve with increasing quantities of solution. These findings may help to find an optimal design for photodiode fabrication