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.

Influence of polyaniline and phthalocyanine hole-transport layers on the electrical performance of light-emitting diodes using MEH-PPV as emissive material

The influence of layer-by-layer films of polyaniline and Ni-tetrasulfonated phthalocyanine (PANI/Ni-TS-Pc) on the electrical performance of polymeric light-emitting diodes (PLED) made from (poly[2-methoxy-5-(2`-ethyl-hexyloxy)-1,4-phenylene vinylene]) (MEH-PPV) is investigated by using current versus voltage measurements and impedance spectroscopy. The PLED is composed by a thin layer of MEH-PPV sandwiched between indium tin oxide (ITO) and aluminum electrodes, resulting in the device structure ITO/(PANI/Ni-TS-Pc)(n)/MEH-PPV/Al, where n stands for the number of PANI/Ni-TS-Pc bilayers. The deposition of PANI/Ni-TS-Pc leads to a decrease in the driving voltage of the PLEDs, which reaches a minimum when n = 5 bilayers. In addition, impedance spectroscopy data reveal that the PLED impedance decreases as more PANI/Ni-TS-Pc bilayers are deposited. The PLED structure is further described by an equivalent circuit composed by two R-C combinations, one for the bulk and other for the interface components, in series with a resistance originated in the ITO contact. From the impedance curves, the values for each circuit element is determined and it is found that both, bulk and interface resistances are decreased upon PANI/Ni-TS-Pc deposition. The results indicate that PANI/NiTS-Pc films reduce the contact resistance at ITO/MEH-PPV interface, and for that reason improve the hole-injection within the PLED structure. (c) 2007 Elsevier B.V. All rights reserved.

Analytical tools to assess the voltage stability of induction-based distributed generators

The installation of induction distributed generators should be preceded by a careful study in order to determine if the point of common coupling is suitable for transmission of the generated power, keeping acceptable power quality and system stability. In this sense, this paper presents a simple analytical formulation that allows a fast and comprehensive evaluation of the maximum power delivered by the induction generator, without losing voltage stability. Moreover, this formulation can be used to identify voltage stability issues that limit the generator output power. All the formulation is developed by using the equivalent circuit of squirrel-cage induction machine. Simulation results are used to validate the method, which enables the approach to be used as a guide to reduce the simulation efforts necessary to assess the maximum output power and voltage stability of induction generators. (C) 2011 Elsevier Ltd. All rights reserved.

Dielectric properties of cobalt ferrite nanoparticles in ultrathin nanocomposite films

Multilayered nanocomposite films (thickness 50-90 nm) of cobalt ferrite nanoparticles (np-CoFe2O4, 18 nm) were deposited on top of interdigitated microelectrodes by the layer-by-layer technique in order to study their dielectric properties. For that purpose, two different types of nanocomposite films were prepared by assembling np-CoFe2O4 either with poly(3,4-ethylenedioxy thiophene):poly(styrene sulfonic acid) or with polyaniline and sulfonated lignin. Despite the different film architectures, the morphology of both was dominated by densely-packed layers of nanoparticles surrounded by polyelectrolytes. The dominant effect of np-CoFe2O4 was also observed after impedance spectroscopy measurements, which revealed that dielectric behavior of the nanocomposites was largely influenced by the charge transport across nanoparticle-polyelectrolyte interfaces. For example, nanocomposites containing np-CoFe2O4 exhibited a single low-frequency relaxation process, with time constants exceeding 15 ms. At 1 kHz, the dielectric constant and the dissipation factor (tan ᵟ) of these nanocomposites were 15 and 0.15, respectively. These values are substantially inferior to those reported for pressed pellets made exclusively of similar nanoparticles. Impedance data were further fitted with equivalent circuit models from which individual contributions of particle's bulk and interfaces to the charge transport within the nanocomposites could be evaluated. The present study evidences that such nanocomposites display a dielectric behavior dissimilar from that exhibited by their individual counterparts much likely due to enlarged nanoparticle- polyelectrolyte interfaces.

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.

Evaluation of the Inductive Coupling between Equivalent Emission Sources of Components

The electromagnetic interference between electronic systems or between their components influences the overall performance. It is important thus to model these interferences in order to optimize the position of the components of an electronic system. In this paper, a methodology to construct the equivalent model of magnetic field sources is proposed. It is based on the multipole expansion, and it represents the radiated emission of generic structures in a spherical reference frame. Experimental results for different kinds of sources are presented illustrating our method.

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.

Using Equivalent Emission Sources to Evaluate the Coupling Between Components

The electromagnetic interference between the electronic systems or their components influences the performance of the systems. For that reason, it is important to model these interferences in order to optimize the position of the systems or their components. In this paper, a method is proposed to construct the equivalent emission source models of systems. The proposed method is based on the multipolar expansion by representing the radiated emission of generic structures in a spherical reference (r, theta, phi). Some results are presented illustrating our method.

An integrated approach to remanufacturing: model of a remanufacturing system

Remanufacturing is the process of rebuilding used products that ensures that the quality of remanufactured products is equivalent to that of new ones. Although the theme is gaining ground, it is still little explored due to lack of knowledge, the difficulty of visualizing it systemically, and implementing it effectively. Few models treat remanufacturing as a system. Most of the studies still treated remanufacturing as an isolated process, preventing it from being seen in an integrated manner. Therefore, the aim of this work is to organize the knowledge about remanufacturing, offering a vision of remanufacturing system and contributing to an integrated view about the theme. The methodology employed was a literature review, adopting the General Theory of Systems to characterize the remanufacturing system. This work consolidates and organizes the elements of this system, enabling a better understanding of remanufacturing and assisting companies in adopting the concept.

Effect of parametric uncertainties on the performance of a piezoelectric energy harvesting device

The use of piezoelectric materials for the development of electromechanical devices for the harvesting or scavenging of ambient vibrations has been extensively studied over the last decade. The energy conversion from mechanical (vibratory) to electrical energy is provided by the electromechanical coupling between mechanical strains/stresses and electric charges/voltages in the piezoelectric material. The majority of the studies found in the open literature present a tip-mass cantilever piezoelectric device tuned on the operating frequency. Although recent results show that these devices can be quite effective for harvesting small amounts of electrical energy, little has been published on the robustness of these devices or on the effect of parametric uncertainties on the energy harvested. This work focuses on a cantilever plate with bonded piezoelectric patches and a tip-mass serving as an energy harvesting device. The rectifier and storage electric circuit was replaced by a resistive circuit (R). In addition, an alternative to improve the harvesting performance by adding an inductance in series to the harvesting circuit, thus leading to a resonant circuit (RL), is considered. A coupled finite element model leading to mechanical (displacements) and electrical (charges at electrodes) degrees of freedom is considered. An analysis of the effect of parametric uncertainties of the device on the electric output is performed. Piezoelectric and dielectric constants of the piezoelectric active layers and electric circuit equivalent inductance are considered as stochastic parameters. Mean and confidence intervals of the electric output are evaluated.

Loudness scattering due to vibro-acoustic model variability

The use of numerical simulation in the design and evaluation of products performance is ever increasing. To a greater extent, such estimates are needed in a early design stage, when physical prototypes are not available. When dealing with vibro-acoustic models, known to be computationally expensive, a question remains, which is related to the accuracy of such models in view of the well-know variability inherent to the mass manufacturing production techniques. In addition, both academia and industry have recently realized the importance of actually listening to a products sound, either by measurements or by virtual sound synthesis, in order to assess its performance. In this work, the scatter of significant parameter variations on a simplified vehicle vibro-acoustic model is calculated on loudness metrics using Monte Carlo analysis. The mapping from the system parameters to sound quality metric is performed by a fully-coupled vibro-acoustic finite element model. Different loudness metrics are used, including overall sound pressure level expressed in dB and Specific Loudness in Sones. Sound quality equivalent sources are used to excite this model and the sound pressure level at the driver's head position is acquired to be evaluated according to sound quality metrics. No significant variation has been perceived when evaluating the system using regular sound pressure level expressed in in dB and dB(A). This happens because of the third-octave filters that averages the results under some frequency bands. On the other hand, Zwicker Loudness presents important variations, arguably, due to the masking effects.

A Skyrme-like model with an exact BPS bound

We propose a new Skyrme-like model with fields taking values on the sphere S3 or, equivalently, on the group SU(2). The action of the model contains a quadratic kinetic term plus a quartic term which is the same as that of the Skyrme-Faddeev model. The novelty of the model is that it possess a first order Bogomolny type equation whose solutions automatically satisfy the second order Euler-Lagrange equations. It also possesses a lower bound on the static energy which is saturated by the Bogomolny solutions. Such Bogomolny equation is equivalent to the so-called force free equation used in plasma and solar Physics, and which possesses large classes of solutions. An old result due to Chandrasekhar prevents the existence of finite energy solutions for the force free equation on the entire three- dimensional space R3. We construct new exact finite energy solutions to the Bogomolny equations for the case where the space is the three-sphere S3, using toroidal like coordinates.