A technique for improving the accuracy of quadrangular mixed finite elements for Darcy’s flow on heterogeneous domains

The mixed hybrid finite element (MHFE) method is well suited for the resolution of the Darcy’s flow on anisotropic and heterogeneous domains. However, the accuracy of the method can be altered for highly distorted meshes with non-convex quadrangles. Moreover, the standard quadrangular MHFE method can lead to non-physical oscillations for transient simulations since it does not respect the maximum principle.In this work, we derive a new realization of the MHFE method on general convex or non-convex quadrangular elements. Each element is fictitiously divided into triangles. The mass balance and flux law are then discretized over each triangle and aggregated to eliminate interior degrees of freedom at the quadrangular element level. The method is combined with the mass lumping procedure for triangles to improve the monotonicity of the discretization. The material properties as well as the pressure and the divergence of the flux are allowed to vary inside the quadrangular element to better describe heterogeneous domains.The obtained matrix is symmetric and positive definite and has the same stencil than the standard approach. The numerical experiments show the performances of this formulation compared to the standard one for heterogeneous domains and non-convex elements. An example is also provided for transient flow simulations where the unphysical oscillations are avoided with the new approach.     

Aerobic decolourization of the indigo dye-containing textile wastewater using continuous combined bioreactors

An aerobic bioprocess was applied to Indigo dye-containing textile wastewater treatment aiming at the colour elimination and biodegradation. A combined aerobic system using continuous stirred tank reactor (CSTR) and fixed film bioreactor (FFB) was continuously operated at constant temperature and fed with the textile wastewater (pH: 7.5 and total chemical oxygen demand (COD): 1185 mg l(-1)). The CSTR is a 1l continuous flow stirred tank reactor with a 700 ml working volume, and operated with a variable wastewater loading rate (WLR) from 0.92 to 3.7 g l(-1) d(-1). The FFB is a 1.5l continuous flow with three compartments packed with a rippled cylindrical polyethylene support, operated with a variable WLR between 0.09 and 0.73 g l(-1) d(-1). The combined two bioreactors were inoculated by an acclimated microbial consortium and continuously operated with four total WLR. This system presented high COD elimination and colour removal efficiencies of 97.5% and 97.3%, respectively, obtained with a total hydraulic retention time (HRT) of 4 days and total WLR of 0.29 g l(-1) d(-1). The effects of WLR on absorption phenomena on the yield of conversion of substrate on biomass (R(TSS/COD)) and on the yield of conversion of substrate on active biomass (R(VVS/COD)) are discussed. The increase of WLR and the decrease of HRT diminished the performances of this system in terms of decolourization and COD removal explained by the sloughing of biofilm, and the washout phenomena.     

Synthesis of polypyrrole/Fe-kanemite nanocomposite through in situ polymerization: effect of iron exchange,acid treatment,and CO<Subscript>2</Subscript> adsorption properties

This paper focuses on the synthesis of polypyrrole/Fe-kanemite nanocomposites by in situ polymerization of pyrrole. Different percentages of PPy/Fe-kan have been prepared and tested for the CO₂ adsorption. Fe-exchanged kanemite was prepared using various iron contents and used as an oxidant for the preparation of PPy/Fe-kan nanocomposite. The obtained materials were characterized using various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, ultraviolet–visible (UV–vis), thermogravimetric analysis TGA, energy dispersive X-ray analysis, scanning and transmission electronic microscopy (SEM, TEM). Based on the XRD and UV–vis analysis, the exchange process leads to the formation of various iron species on the external and internal surface. The thermal stability of PPy/Fe-kan was improved and increased in the following order PPy/Fe-kan (1%) > PPy/Fe-kan (3%) > PPy/Fe-kan (5%) > PPy/Fe-kan (10%) > PPy. SEM and TEM analysis show that the nanocomposite particles have spherical morphology with a high dispersion of the Fe-kanemite in the polymer matrix. CO₂ adsorption at 0 and 15 °C was carried using a volumetric method, and the recorded isotherm indicated that the CO₂ adsorption capacity of PPy/Fe-kan can be enhanced through modification by polypyrrole. The unmodified Na-kanemite has low CO₂ adsorption capacity around 0.05 mmol g^?1 at 15 °C, while the PPy/Fe-kan (5%) nanocomposite presented the best CO₂ adsorption capacity around 1.7 mmol g^?1 at 0 °C under low pressure that is mainly attributable to physical adsorption.     

Characterization of Two Nanofiltration Membranes for the Separation of Ions from Acid Mine Water

We evaluated nanofiltration for separation of ions from acid mine drainage (AMD), using two composite nanofiltration membranes (Nano-Pro-3012 and NF90) as examples of the polyamide class of acid-stable membranes. The structure of the NF membranes was characterized by scanning electron and atomic force microscopy. The NF90 displayed a higher permeate flux than Nano-Pro-3012, with higher relative roughness at both pH values. Both membranes suitably rejected most of the metals found in the AMD, but the Nano-Pro-3012 membrane proved unsuitable for sulphate removal.     

Assessing the Effect of Damaged and Fractured Concrete Cutoff Wall on the Dynamics of Seawater Intrusion

Water Resources Management - The physical cutoff barrier is one of the best known techniques to control seawater intrusion in a coastal aquifer. This method is widely used in many sites worldwide,...     

Sol–gel synthesis and sintering of submicronic copper molybdate (α-CuMoO4) powders

A sol–gel method was proposed to prepare copper II molybdate α-CuMoO₄ powders. A gel was first obtained via the polymerizable complex method, using citric acid as complexing and polymerizing agent, dried at 120 °C and decomposed at 300 °C. A calcination in the temperature range 400–500 °C for 2 h led to the pure phase α-CuMoO₄. The different powders obtained were characterized by X ray diffraction analysis and by transmission (TEM) and scanning (SEM) electron microscopies.     

Laryngocele as an etiology of respiratory distress

Laryngocele is usually benign affection of the larynx. But serious forms of clinical emergency necessitating tracheotomy are possible. We reported 3 cases. New methods of treatment are presented endoscopic resection and laser marsupialization.     

The Effect of Defects on the Mobility of HEMT Transistors Based on AIGaN/GaN

A phenomenological low-filed mobility model is developed to describe the dependence ot the carrier molgmty on me gate to source bias applied for AIGaN/GaN high electron mobility transistor. The results show excellent agreement with experimental data, when compared thereby proving the validity of the model. In the proposed work the temporal evolution of the mobility degradation shows a sharp decline in emission rates below 456 s-1. We also note a sharp decline for large defects densities.     

Investigating the Effect of Process Parameter on the Properties of Rf Sputtered pSi Thin Film by Taguchi and ANOVA Analysis

Silicon - Boron doped pSi was deposited on Si substrate in the RF magnetron sputtering system by varying three process parameters, namely-sputtering power, working pressure, and Ar gas flow rate....     

Cation–dipole interaction that creates ordered ion channels in an anion exchange membrane for fast OH− conduction

Precise control over polyelectrolyte architecture, engineered for self-assembly of ion-conducting channels, is of fundamental and technological importance to many fields, for example, fuel cells and redox flow batteries and electrodialysis. Building on recent advances with the supramolecular chemistry, we introduce inter/intra-molecular cation–dipole interactions between pendent quaternary ammoniums cations and polar polyethylene glycol grafts in an anion-exchange membrane (AEM). Such interactions lead to desirable, ordered ion-conducting pathways when in the membrane form. Comparison of the results of molecular dynamics simulation with ¹H NMR and nano-scale microscopy analyses show that the cation–dipole interactions enhance self-assembly and the formation of interconnected ionic network domains, providing three-dimensional pathways for both water and ion transport. The resultant AEM exhibits high OH⁻ conductivity (49 mS cm⁻¹ at 30°C) and a completive peak power density of 622 mW cm⁻² at 70°C when tested in a H₂/O₂ single-cell alkaline membrane fuel cell.