A study on biological clogging of nonwoven geotextiles under leachate flow

This paper presents results of long-term permittivity tests using leachate to evaluate biological clogging of nonwoven geotextiles. Three types of geotextiles with varying masses per unit area were used in the tests. The identification and quantification of microorganisms in the geotextile were carried out as well as microscopic investigations. The accuracies of semi-empirical models to evaluate the kinetics of bacteria growth and to correlate hydraulic properties and microbiological parameters were examined. Permittivity tests under increasing water heads were also performed on the geotextile samples already subjected to long-term leachate flow in order to evaluate the values of water heads required to wash the biofilms out of the geotextile pores. The results of the tests showed the marked reduction of geotextile permeability due to biological clogging and that the results of the predictions by semi-empirical methods were consistent with the biological mechanisms observed.     

Photoelectrochemical reduction of nitrate on p-Si coated with metallic Re thin films

In this study we examined the rhenium electrodeposition process onto p-Si(100) from acidic media. The study was carried out by means of cyclic voltammetry and the potential-steps method from which the corresponding nucleation and growth mechanism were determined. Both methods were performed under illumination using a solar simulator for electron photogeneration. A 3D progressive nucleation, diffusion-controlled growth of rhenium films was found. Likewise, a morphologic analysis was completed for the deposits obtained at different potential values by means of atomic force microscopy. An energetic characterization through capacitance measurements (Mott–Schottky plots and parallel capacitance) of the p-Si/NO₃⁻ and p-Si/Re/NO₃⁻ interfaces was done.The photoelectrochemical reduction of nitrate ions, PERN, on the different p-Si/Re electrode systems synthesized was studied. An overpotential decrease of 0.3 V and a photocurrent increase for the PERN on p-Si(100)/Re electrode systems compared with p-Si(100) and metallic Re was found. Finally, the kinetic parameters of the cathodic reactions in the p-Si and p-Si/Re acidic media were estimated using intensity modulated photocurrent spectroscopy. A brief analysis from this technique was done. According to these results, the p-Si/Re electrode system could be a potential photoelectrocatalyst for the PERN.     

VSS global performance improvement based on AW concepts

The influence of the reaching mode on the global performance of variable structure systems (VSS) undergoing sliding regimes is stressed. A comparative analysis between the behaviour during this reaching mode of operation and the problem of windup is realized. Based on the similarities between both control problems, some tools of the control theory of constrained linear systems are exploited to improve the reaching mode of VSS.     

Chile's national nutritional supplementation program for older people: lessons learned

Demographic changes in developing countries have resulted in rapid increases in the size of the older population. As a result, health-care budgets face increasing costs associated with the declining health and function of older people. Some governments have responded to this situation by designing innovative programs aimed at older people. One such program, implemented by the government of Chile, distributes an instant food mix fortified with vitamins and minerals to all persons over 70 years old who are registered by the national health service. The national health service covers approximately 90% of the older population. The program specifically targets nutritional vulnerability and micronutrient deficiency, which are common among poor older people in Chile. We present here the findings of a one-year investigation into all aspects of Chile's program for the elderly. The research included in-depth interviews with policy makers and program implementers, focus group discussions with user groups, analysis of the micronutrient content of the nutritional supplement, and telephone interviews of a random sample of older people. The results demonstrate that there can be a considerable degree of self-targeting within national programs; programs need to be sufficiently flexible to permit periodic protocol change; user groups must be consulted both before and during program implementation; and the design of an effective program evaluation must be in place before program implementation. It is hoped that these results will be useful to policy makers and implementers planning programs aimed at improving the health and function of older people.     

Microprocessor-based DC motor drive with spillover field weakening

A microprocessor-based speed control scheme for a separately excited DC motor fed from a DC source, which incorporates both armature-voltage control and spillover field weakening to provide smooth and precise control from standstill to speeds well above the base value, is described. Armature-current limitation during transient operation is achieved using an interventionist system external to the microprocessor controller, thereby simplifying considerably the overall system design. Experimental results obtained from a prototype 5 kW drive are presented to illustrate the excellent dynamic behavior of the scheme     

Singular bifurcations in higher index differential-algebraic equations

The present paper extends the singularity induced bifurcation theorem (SIBT) to higher index differential-algebraic equations (DAEs) in Hessenberg form. The SIBT arises in power system theory, and is also significant within the context of electrical circuits. This phenomenon is due to the presence of singularities in parameter-dependent problems, and it was originally proved for semiexplicit index-1 DAEs. We introduce a new proof of a matrix pencil-based version of this result, relying on the spectral features of the linearization of the underlying ordinary differential equation. This approach is then applied to higher index DAEs in Hessenberg form. For these structures, the SIBT is shown to follow from a minimal index change at the singularity. Additionally, we show that a Kronecker index change is also necessary for the existence of a singularity induced bifurcation point in semi-explicit index-1 and Hessenberg DAEs.     

Stress intensity factors in anisotropic plates using singular isoparametric elements

A conformable displacement model is presented for the finite element analysis of stress intensity factors in linear elastic fracture mechanics. The method is an extension to anisotropic materials of the one developed by Benzley for isotropic materials. Very good agreement is shown for the case of inclined cracks in an orthotropic plate between finite element results and those obtained by least squares collocation of stress functions.