Temperature-Dependent As K-Edge EXAFS Studies of LaFe <Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>AsO (<Emphasis Type="Italic">x</Emphasis> = 0.0 and 0.11) Single Crystals

We report the experimental results of temperature-dependent polarized As K-edge extended X-ray absorption fine structure (EXAFS) of LaFe_1?x Co _x AsO (x = 0.0 and 0.11) single crystals. By aligning the Fe–As bond direction in the direction of the X-ray beam polarization, we have been able to identify an anomaly in the Fe–As bond correlations at the tetragonal to orthorhombic transition at 150 K, while previous investigations with standard unpolarized EXAFS of undoped LaFeAsO powder samples were not able to detect any such anomaly. Using our approach, we have been able to identify in the superconducting doped sample, LaFe_0.89Co_0.11AsO, a broad anomaly around 60 K. The low-temperature anomaly has good correlations with the temperature dependence of several properties like resistivity, magnetic susceptibility and linear thermal expansion, indicating the emergence of the dynamical oscillations of the Fe–As pairs.     

Alternative Local Melting-Solidification of Suspended Nanoparticles for Heterostructure Formation Enabled by Pulsed Laser Irradiation

Phase formation by pulsed laser irradiation of suspended nanoparticles has recently been introduced as a promising synthesis technique for heterostructures. The main challenge still lingers regarding the exact mechanism of particle formation due to the non-equilibrium kinetic by-products resulting from the localized alternative, fast, high-temperature nature of the process. Here, the authors analyze the bond breaking/formation of copper or copper (II) interfaces with ethanol during the absorption of pulses for Cu-CuO-Cu₂O formation applicable as an electrocatalyst in ethanol oxidation fuel cells. This study includes but is not limited to, a comprehensive discussion of the interaction between nano-laser pulses and suspension for practical control of the synthesis process. The observed exponential and logarithmic changes in the content of heterostructures for the CuO-ethanol and Cu-ethanol samples irradiated with different fluences are interpreted as the dominant role of physical and chemical reactions, respectively, during the pulsed laser irradiation of suspensions synthesis. It is also shown that the local interface between dissociated ethanol and the molten sphere is responsible for the oxidative/reductive interactions resulting in the formation of catalytic-augmented Cu³⁺ by-product, thanks to the reactive bond force field molecular dynamics studies confirmed by ab-initio calculations and experimental observations.     

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.     

RbfA Is Involved in Two Important Stages of 30S Subunit Assembly: Formation of the Central Pseudoknot and Docking of Helix 44 to the Decoding Center

Ribosome biogenesis is a highly coordinated and complex process that requires numerous assembly factors that ensure prompt and flawless maturation of ribosomal subunits. Despite the increasing amount of data collected, the exact role of most assembly factors and mechanistic details of their operation remain unclear, mainly due to the shortage of high-resolution structural information. Here, using cryo-electron microscopy, we characterized 30S ribosomal particles isolated from an Escherichia coli strain with a deleted gene for the RbfA factor. The cryo-EM maps for pre-30S subunits were divided into six classes corresponding to consecutive assembly intermediates: from the particles with a completely unresolved head domain and unfolded central pseudoknot to almost mature 30S subunits with well-resolved body, platform, and head domains and partially distorted helix 44. The structures of two predominant 30S intermediates belonging to most populated classes obtained at 2.7 Å resolutions indicate that RbfA acts at two distinctive 30S assembly stages: early formation of the central pseudoknot including folding of the head, and positioning of helix 44 in the decoding center at a later stage. Additionally, it was shown that the formation of the central pseudoknot may promote stabilization of the head domain, likely through the RbfA-dependent maturation of the neck helix 28. An update to the model of factor-dependent 30S maturation is proposed, suggesting that RfbA is involved in most of the subunit assembly process.     

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.