An autonomous valve stiction detection system based on data characterization

This paper proposes a valve stiction detection system which selects valve stiction detection algorithms based on characterizations of the data. For this purpose, novel data feature indexes are proposed, which quantify the presence of oscillations, mean-nonstationarity, noise and nonlinearities in a given data sequence. The selection is then performed according to the conditions on the index values in which each method can be applied successfully. Finally, the stiction detection decision is given by combining the detection decisions made by the selected methods. The paper ends demonstrating the effectiveness of the proposed valve stiction detection system with benchmark industrial data.     

Nonlinear control for reactive navigation of a nonholonomic robot for environmental nongradient‐based extremum seeking in maze‐like scenes

A single Dubins car‐like mobile robot travels with a constant speed in a planar workspace cluttered with arbitrarily complex obstacles, possibly maze‐like ones. An unknown scalar field is defined on the plane. The sensors supply the robot with the field value at its current location and its distance to the nearest obstacle. We present a new control law that drives the robot to the location where the field attains its maximum, while avoiding collisions with the obstacles. This is justified by a mathematically rigorous global convergence result and is confirmed via computer simulations. The proposed algorithm does not use gradient estimation and is nondemanding with respect to computation and motion. Copyright © 2017 John Wiley & Sons, Ltd.     

Electroreduction of oxygen over iron macrocyclic catalysts for DMFC applications

The performance of macrocyclic catalysts in oxygen reduction was investigated for a direct methanol fuel cell. The dependence of catalytic activity on different factors was determined for two classes of precursors; namely, iron porphyrin (Fe-PC) and iron phthalocyanine (Fe-TPP). It was found that there was an optimal heat-treating temperature for each precursor. Heat-treated Fe-TPP shows maximum activity at 750 °C, while the highest performance in the case of Fe-PC is observed at 500 °C. It was shown that oxygen reduction activity is affected by the number of nitrogen bonds formed with iron, particle size, and formation of carbon layers.     

Review of Anisotropic Terahertz Material Response

Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials. In response to an electromagnetic wave, anisotropic absorptive and refractive properties result in dichroic and birefringent optical phenomena both in the linear and nonlinear optics regimes. Such material properties have led to a diverse array of useful polarization components in the visible and near-infrared, but mature technology is non-existent in the terahertz (THz). Here, we review several novel types of anisotropic material responses observed in the THz frequency range, including both linear and circular anisotropy, which have long-term implications for the development of THz polarization optics. We start with the extreme linear anisotropy of macroscopically aligned carbon nanotubes, arising from their intrinsically anisotropic dynamic conductivity. Magnetically induced anisotropy will then be reviewed, including the giant Faraday effects observed in semiconductors, semimetals, and two-dimensional electron systems.     

Formation mechanism and packing options in tubular anodic titania films

Titania nanotube arrays were synthesized via anodic oxidation of titanium foils in glycerol electrolyte containing NH₄F at anodization voltage ranging from 10 V to 30 V. The structural parameters of self-organized periodic arrays of titania nanotubes were determined by small-angle neutron scattering and scanning electron microscopy techniques. Transmission electron microscopy and electron diffraction studies of single-standing nanotubes revealed the presence of nanocrystalline titanium oxide phases with oxidation states lower than +4 (TiO, Ti₂O₃). Several assumptions on growth and self-organization mechanism of nanotube arrays have been made.     

Sorting of neural spikes: When wavelet based methods outperform principal component analysis

Sorting of the extracellularly recorded spikes is a basic prerequisite for analysis of the cooperative neural behavior and neural code. Fundamentally the sorting performance is defined by the quality of discriminative features extracted from spike waveforms. Here we discuss two features extraction approaches: principal component analysis (PCA), and wavelet transform (WT). We show that only when properly tuned to the data, the WT technique may outperform PCA. We present a novel method for extraction of spike features based on a combination of PCA and continuous WT. The method automatically tunes its WT part to the data structure making use of knowledge obtained by PCA. We demonstrate the method on simulated and experimental data sets.     

Anomalous peculiarity of coolant temperature feedback in PWRs

According to conventional thinking on power regulation in a reactor with a negative feedback, the power change has the same sign as the introduced reactivity causing it. In this study we consider the opposite situation, which is anomalous in the sense of the usual power behavior. This anomaly connects with spatial peculiarity of coolant temperature reactivity effect and predisposition to it is inherited for reactors, which are sufficiently large in the direction of the coolant flow. The analysis is performed using simplified one-dimensional reactor models with one feedback on the coolant temperature. In the perpendicular (radial) direction reactor is assumed to be uniform and infinite.     

New approach to the problem of globally convergent frequency estimator

This note proposes a solution to the problem of real‐time globally convergent estimation of the frequency of a bias sinusoid signal. The method is an alternative to known approaches. The new frequency estimator is a fourth‐order system for the case of bias sinusoidal signals and has significant advantages over prior methods. Copyright © 2007 John Wiley & Sons, Ltd.