In situ electrochemical characterization of natural pyrite as a galvanic catalyst using single-particle microelectrode technique in ferric sulfate solutions

Ferric reduction on the surface of pyrite, a major factor governing the overall kinetics of pyrite-assisted leaching of chalcopyrite in sulfate solutions, is investigated. In order to study the effect of pyrite on chalcopyrite leaching, four different pyrite samples were used in the leaching process. A single-particle microelectrode technique was employed to investigate the electrochemical and semiconducting properties of different pyrite samples by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy, and Mott–Schottky methods in a solution containing 0.5 mol/L sulfuric acid, 0.005 mol/L ferric sulfate, and 0.005 mol/L ferrous sulfate. During leaching, differences were observed in the behavior of different pyrite samples. CV showed a difference in the magnitude of the ferric reduction reaction peaks. An equivalent analog circuit was used to model the impedance spectra, which led to the conclusion that pyrite samples with lower charge transfer resistance are better catalysts for ferric reduction. Mott–Schottky analysis was used to quantify variations in some semiconductive and electrical properties of pyrite samples from different geographical locations.     

A theoretical study on surface modification of a nanosized BC3 tube using C2H4 and its derivatives

Chemical functionalization of a BC₃ nanotube (BC₃NT) with C₂X₄ (X = –H, –F, –CH₂F, –CN, –NH₂, –NO₂, –CH₃, and –OCH₃) was investigated by density functional theory calculations. It was found that C₂H₄ prefers to be added to a B–C bond of the tube wall. The interaction energies are calculated to be ranging from ?0.03 to ?40.32 kcal/mol, and their relative magnitude order is found to be as follows: C₂F₄ > C₂(NH₂)₄ > C₂H₄ > C₂(NO₂)₄ > C₂(OCH₃)₄ > C₂(CN₄)₂ > C₂(CH₃)₄ > C₂(CH₂F)₄. For chemically modified BC₃NTs with various functional groups, the functionalization energy can be correlated with the trend of relative electron-withdrawing or electron-donating capability of the adsorbates. The calculated density of states shows that the functionalization of BC₃NT with these functional groups (except C₂(NO₂)₄) can be generally classified as a certain type of “electronically harmless modification”. We believe that the preservation of electronic properties of BC₃NTs coupled with the enhancement of solubility may render the chemical modification to be an effective way for the purification of BC₃NTs. The insight provided by this theoretical study may also assist future development of BC₃NTs with targeted chemoselectivity through chemical functionalization.     

Personalized PageRank Clustering: A graph clustering algorithm based on random walks

Graph clustering has been an essential part in many methods and thus its accuracy has a significant effect on many applications. In addition, exponential growth of real-world graphs such as social networks, biological networks and electrical circuits demands clustering algorithms with nearly-linear time and space complexity. In this paper we propose Personalized PageRank Clustering (PPC) that employs the inherent cluster exploratory property of random walks to reveal the clusters of a given graph. We combine random walks and modularity to precisely and efficiently reveal the clusters of a graph. PPC is a top-down algorithm so it can reveal inherent clusters of a graph more accurately than other nearly-linear approaches that are mainly bottom-up. It also gives a hierarchy of clusters that is useful in many applications. PPC has a linear time and space complexity and has been superior to most of the available clustering algorithms on many datasets. Furthermore, its top-down approach makes it a flexible solution for clustering problems with different requirements.     

Ferrofluidic Open Loop Pulsating Heat Pipes: Efficient Candidates for Thermal Management Of Electronics

Thermal management of electronic devices is presently a serious concern. This article investigates the thermal performance of a five-turn open-loop pulsating heat pipe in both start-up and steady thermal conditions. The effects of working fluid, namely water and ferrofluid, heat input, charging ratio, ferrofluid concentration, orientation, as well as application of magnetic field, are explored. Experimental results show that using ferrofluid enhances the thermal performance in comparison with the case of distilled water under certain conditions. In addition, applying a magnetic field on the open-loop pulsating heat pipe charged with ferrofluid improves its thermal performance. Charging ratios that lead to lower thermal are mentioned. Optimum concentration of ferrofluid in steady-state performance is 2.5 g/L. This study helps to design electronic cooling devices more efficiently.     

Low threshold gain metal coated laser nanoresonators

We introduce a low refractive index layer between the metal and the gain medium in metal-coated laser resonators and demonstrate that it can significantly reduce the dissipation losses. Analysis of a gain medium waveguide shows that for a given waveguide radius, the low index layer has an optimal thickness for which the lasing threshold gain is minimal. The waveguide analysis is used for the design of a novel three-dimensional cylindrical resonator that is smaller than the vacuum wavelength in all three dimensions and exhibits a low enough threshold gain to lase at room temperature.     

Flow-induced crystallization of high-density polyethylene: the effects of shear and uniaxial extension

The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of high-density polyethylene (a metallocene and a ZN-HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed at temperatures below and well above the peak melting point of the polyethylenes in order to characterize their flow-induced crystallization behavior at rates relevant to processing (elongational rates up to 30 s^− 1 and shear rates 1 to 1,000 s^− 1 depending on the application). Generally, strain and strain rate found to enhance crystallization in both shear and elongation. In particular, extensional flow was found to be a much stronger stimulus for polymer crystallization compared to shear. At temperatures well above the melting peak point (up to 25°C), polymer crystallized under elongational flow, while there was no sign of crystallization under simple shear. A modified Kolmogorov crystallization model (Kolmogorov, Bull Akad Sci USSR, Class Sci, Math Nat 1:355–359, 1937) proposed by Tanner and Qi (Chem Eng Sci 64:4576–4579, 2009) was used to describe the crystallization kinetics under both shear and elongational flow at different temperatures.     

On Indefinite Quadratic Optimization over the Intersection of Balls and Linear Constraints

Journal of Optimization Theory and Applications - In this paper, we study the minimization of an indefinite quadratic function over the intersection of balls and linear inequality constraints...