The Supporting Role of the Mangasarian-Fromovitz Constraint Qualification in Calculus of Variations

Journal of Dynamical and Control Systems - The Mangasarian-Fromovitz constraint qualification has played a fundamental role in mathematical programming problems involving inequality constraints. It...     

Short communication: Activity of nisin,lipid bilayer fragments and cationic nisin-lipid nanoparticles against multidrug-resistant Staphylococcus spp. isolated from bovine mastitis

Staphylococci are the main etiological agents of bovine mastitis. Bacteriocins and nanoparticles have emerged as promising alternatives for the future development of antimicrobial agents. This study evaluated the activity of the bacteriocin nisin and bicelles of the synthetic cationic lipid dioctadecyldimethylammonium bromide, alone and in combination, against multidrug-resistant Staphylococcus spp. strains isolated from bovine mastitis. In summary, cationic nisin/dioctadecyldimethylammonium bromide nanoparticles are shown to be a promising alternative for the control of mastitis caused by multidrug-resistant Staphylococcus spp.     

Monodisperse Pd nanoparticles assembled on reduced graphene oxide-Fe3O4 nanocomposites as electrocatalysts for borohydride fuel cells

5 nm palladium nanoparticles (Pd NPs) are synthesized and assembled on reduced graphene oxide-iron oxide nanocomposite (rGO-Fe₃O₄) to be used in oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) studies in alkaline media. The structure and morphology of the resulting Pd/rGO-Fe₃O₄ hybrid material are evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) analyses. The electrochemical behavior of Pd/rGO-Fe₃O₄ hybrid material for the ORR and BOR is investigated by voltammetry with rotating disk and rotating ring disk electrode and electrochemical impedance spectroscopy, enabling evaluation of the number of exchanged electrons, Tafel slope, exchange current density and activation energy. The results reveal that ORR at Pd/rGO-Fe₃O₄ proceeds as a 2-electron process with Tafel slope of 0.133 V dec^?1, while BOR proceeds as a 5.6-electron process with Tafel slope of 0.350 V dec^?1 and exchange current density of 1.38 mA cm^?2. The BOR activation energy was found to be 12.4 kJ mol^?1. Overall, this study demonstrates the good efficiency of Pd/rGO-Fe₃O₄ hybrid material for BOR.     

Energy sector in Ecuador: Current status

This paper describes the current energy sector in Ecuador, its present structure, the oil industry, subsidies, and renewable energy, focusing on the evolution and reform of the electricity sector. Currently, 86% of the primary energy originates from nonrenewable sources. In 2005, the gross electricity generation was 15 127 GWh (45.5% hydropower, 43.11% thermal, and 11.39% imported). Ecuador is the fifth largest oil producer in South America but lacks sufficient oil refining capacity. Reserves of natural gas (NG) are small, and most of NG is produced from oil fields without energy recovery. Several projects are underway to increase the utilization of NG and renewable energies to meet Ecuador commitments to the Kyoto Protocol.     

Technical feasibility assessment of a solar chimney for food drying

Solar dryers use free and renewable energy sources, reduce drying losses (as compared to sun drying) and show lower operational costs than the artificial drying, thus presenting an interesting alternative to conventional dryers. This work proposes to study the feasibility of a solar chimney to dry agricultural products. To assess the technical feasibility of this drying device, a prototype solar chimney, in which the air velocity, temperature and humidity parameters were monitored as a function of the solar incident radiation, was built. Drying tests of food, based on theoretical and experimental studies, assure the technical feasibility of solar chimneys used as solar dryers for agricultural products. The constructed chimney generates a hot airflow with a yearly average rise in temperature (compared to the ambient air temperature) of 13 ± 1 °C. In the prototype, the yearly average mass flow was found to be 1.40 ± 0.08 kg/s, which allowed a drying capacity of approximately 440 kg.