Layer-by-Layer assembled cobalt ferrite nanoparticles for chemical sensing

Ultra-thin (thicknesses of 50-90 nm) nanocomposite films of cobalt ferrite nanoparticles (np-CoFe2O4, 18 nm in diameter) and polyelectrolytes (doped polyaniline-PANI, poly-3,4-ethylenedioxy thiophene: polystyrene sulfonic acid-PEDOT:PSS, and sulfonated lignin-SL) are assembled layer-by-layer onto interdigitated microelectrodes aiming at to create novel nanostructured sensoactive materials for liquid media chemical sensors. The nanocomposites display a distinctive globular morphology with nanoparticles densely-packed while surrounded by polyelectrolytes. Due to the presence of np-CoFe2O4 the nanocomposites display low electrical conductivity according to impedance data. On the other hand, this apparent shortcoming turns such nanocomposites much more sensitive to the presence of ions in solution than films made exclusively of conducting polyelectrolytes. For example, the electrical resistance of np-CoFe2O4/PEDOT:PSS and PANI/SL/np-CoFe2O4/SL architectures has a 10-fold decrease when they are immersed in 20 mmol. L-1 NaCl solution. Impedance spectra fitted with the response of an equivalent circuit model suggest that the interface created between nanoparticles and polyelectrolytes plays a major role on the nanocomposites electrical/dielectrical behavior. Since charge transport is sensitive to nanoparticle-polyelectrolyte interfaces as well as to the physicochemical conditions of the environment, the np-CoFe2O4-based nanocomposites can be used as sensing elements in chemical sensors operated under ac regime and room temperature.

Six-element circuit for maximum power point tracking in photovoltaic-motor systems with variable-frequency drives

A low-cost circuit was developed for stable and efficient maximum power point (MPP) tracking in autonomous photo voltaic-motor systems with variable-frequency drives (VFDs). The circuit is made of two resistors, two capacitors, and two Zener diodes. Its input is the photovoltaic (PV) array voltage and its output feeds the proportional-integral-derivative (PID) controller usually integrated into, the drive. The steady-state frequency-voltage oscillations induced by the circuit were treated in a simplified mathematical model, which was validated by widely characterizing a PV-powered centrifugal pump. General procedures for circuit and controller tuning were recommended based on model equations. The tracking circuit presented here is widely applicable to PV-motor system with VFDs, offering an. efficient open-access technology of unique simplicity. Copyright (C) 2010 John Wiley & Sons, Ltd.

Circuit board accident - organizational dimension hidden by prescribed safety

This study analyzes an accident in which two maintenance workers suffered severe burns while replacing a circuit breaker panel in a steel mill, following model of analysis and prevention of accidents (MAPA) developed with the objective of enlarging the perimeter of interventions and contributing to deconstruction of blame attribution practices. The study was based on materials produced by a health service team in an in-depth analysis of the accident. The analysis shows that decisions related to system modernization were taken without considering their implications in maintenance scheduling and creating conflicts of priorities and of interests between production and safety; and also reveals that the lack of a systemic perspective in safety management was its principal failure. To explain the accident as merely non-fulfillment of idealized formal safety rules feeds practices of blame attribution supported by alibi norms and inhibits possible prevention. In contrast, accident analyses undertaken in worker health surveillance services show potential to reveal origins of these events incubated in the history of the system ignored in practices guided by the traditional paradigm.