Study of the Development of Positive Streamers Along an Ice Surface

This paper presents the results of fundamental investigations on the inception and propagation of corona discharge on an ice surface stressed with a standard lightning impulse voltage. High-speed photography and photomultiplier techniques were used to observe and record the propagation of the streamers. The effects of several experimental parameters such as freezing water conductivity and HV rod electrode radius on the streamer inception parameters were investigated. Moreover, time to first streamer, inception voltage and corresponding field, as well as streamer propagation velocity and charge deposited by a streamer on ice surface were measured. The results are discussed and emphases are laid on the main factors influencing the development of positive streamers on ice surface.     

Analysis of chitin particle size on maximum power generation, power longevity, and Coulombic efficiency in solid-substrate microbial fuel cells

Microbial fuel cells (MFCs) produce bioelectricity from a wide variety of organic and inorganic substrates. Chitin can be used as a slowly degrading substrate in MFCs and thus as a long-term fuel to sustain power by these devices in remote locations. However, little is known about the effects of particle size on power density and length of the power cycle (longevity). We therefore examined power generation from chitin particles sieved to produce three average particle sizes (0.28, 0.46 and 0.78 mm). The longevity increased from 9 to 33 days with an increase in the particle diameter from 0.28 to 0.78 mm. Coulombic efficiency also increased with particle size from 18% to 56%. The maximum power density was lower for the largest (0.78 mm) particles (176 mW m⁻²), with higher power densities for the 0.28 mm (272 mW m⁻²) and 0.46 mm (252 mW m⁻²) particle sizes. The measured lifetimes of these particles scaled with particle diameter to the 1.3 power. Application of a fractal dissolution model indicates chitin particles had a three-dimensional fractal dimension between 2 and 2.3. These results demonstrate particles can be used as a sustainable fuel in MFCs, but that particle sizes will need to be controlled to achieve desired power levels.     

A general unified treatment of lamellar inhomogeneities

Consider a lamellar inhomogeneity embedded in an unbounded isotropic elastic medium. When the elastic moduli of the lamellar inhomogeneity are zero it is a crack, if its elastic moduli are infinite it is an anticrack, and when its elastic moduli are finite it is called a quasicrack. Based on the Eshelby’s equivalent inclusion method (EIM), the present paper develops a unified approach for determination of the exact closed-form expressions for modes I, II, and III stress intensity factors (SIFs) at the tips of lamellar inhomogeneities under a remote applied polynomial loading.     

Production of superhydrophobic polymer fibers with embedded particles using the electrospinning technique

Superhydrophobic materials are currently used for their water‐repelling, self‐cleaning and anti‐fouling properties but are also potentially attractive to prevent snow or ice accumulation on exposed structures. Using the electrospinning technique, polymer mats made of polystyrene and poly[tetrafluoroethylene‐co‐(vinylidene fluoride)‐co‐propylene] (PTVFP) were prepared. They were found to show highly hydrophobic properties, water contact angle (CA) between 130 and 150°, when a dual fiber–bead microstructure was observed. Superhydrophobicity, CA > 150°, was reached when PTVFP mats were electrospun from a polymer solution containing dispersed polytetrafluoroethylene (PTFE) nanoparticles. Using atomic force microscopy imaging, protruding nanosized asperities on fiber and bead surfaces were observed and this structure led to superhydrophobic properties. Materials prepared from a high‐viscosity PTVFP/ethyl acetate solution with PTFE particles, 200 nm diameter and 8% (w/w), showed an 11.2% improvement in hydrophobicity, CA = 161°, compared to the materials obtained from a particle‐free polymer solution (CA = 143°). Copyright © 2007 Society of Chemical Industry     

Magnetically Recyclable Cufe2o4 Nanoparticles as an Efficient and Reusable Catalyst for the Green Synthesis of 2,4,6,8,10,12-Hexabenzyl-2,4,6,8,10,12-hexaazaisowurtzitane as CL-20 Explosive Precursor

Magnetic nanoparticles of copper ferrite (CuFe₂O₄ MNPs) have been simply prepared and applied as an efficient recyclable and reusable catalyst for the green synthesis of 2,4,6,8,10,12-hexabenzyl-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0^5,9.0^3,11]dodecane (HBIW). The structure of the synthesized pure HBIW (recrystallization from ethanol) was confirmed by using various spectral techniques like infrared (IR), ¹H-NMR, ¹³C-NMR and some of its physical properties. The prepared catalyst was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). In addition, CuFe₂O₄ MNPs could be reused up to seven runs without any significant loss of activity. Finally, the remarkable advantages of this method are the simple experimental procedure, shorter reaction times, simple workup, and green aspects by avoiding toxic catalysts and high yield of product.     

Morphological investigation of synthetic poly(amic acid)/cerium oxide nanostructures

A new kind of intermediate hybrid nanocomposites (NCs) composed of poly(amic acid) (PAA) and surface modified ceria nanoparticles (NP)s had been prepared by sonochemical assisted synthesis. The PAA containing pendent benzamide units had been synthesized by the reaction of 3,5‐diamino‐N‐(4‐hydroxyphenyl) benzamide and benzene‐1,2,4,5‐tetracarboxylic dianhydride through polycondensation reaction. The structure of the prepared PAA was studied by spectroscopic techniques. The surface modifications of ceria NPs were achieved by using hexadecyltrimethoxysilane. Results of FTIR analysis demonstrated that the aliphatic chains have been covalently bonded to the surface of the CeO₂ NPs. PAA/CeO₂ NCs with different contents including 4, 8, and 12 wt% of CeO₂ NPs was prepared by using sonochemical method. Characterization with FTIR, powder X‐ray diffraction, field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) confirmed the success in synthesis of NCs with well dispersion properties. XRD analysis results showed that the obtained NCs displayed the crystalline nature of ceria NPs and the amorphous character of PAA matrix. The particles size of ceria NPs in NCs are about 50–70 nm as characterized by FE‐SEM, TEM, and AFM analyses. This work demonstrates the application of intermediates as new matrices for preparation of hybrid nanostructures. POLYM. ENG. SCI., 55:2339–2348, 2015. © 2015 Society of Plastics Engineers     

Effect of electron beam irradiation dose on the rheology,morphology, and thermal properties of branched polypropylene/polybutene‐1 blend

The aim of this work is to study the influence of electron beam irradiation on the structure of polypropylene (PP)/polybutene‐1 (PB‐1) blend in the branching process. The blend with 10 wt% of PB‐1 and 0.5 wt% trimethylolpropane trimethacrylate monomer is prepared and irradiated at different doses. The rheological properties of the melts in shear and extensional mode were evaluated, and their thermal behavior, crystalline structure, and morphology are studied by differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electron microscopy. The presence of long chain branched structure is approved by higher zero‐shear viscosity (η₀), longer relaxation time and pronounced strain‐hardening behavior in the within the range of dose tested. By increasing the irradiation dose and enhancing chain scission in the backbone and long chain branches, the decline in melting temperature, duplication of melting peak, and the decrease in zero‐shear viscosity were observed. The morphological study of the blends before and after irradiation revealed no considerable change in PB‐1 droplet size and their distribution in the PP matrix. The emulsion theoretical models could predict well the rheological behavior of all samples and no significant change was observed on the interfacial interaction of PP and PB‐1. POLYM. ENG. SCI., 54:1747–1756, 2014. © 2013 Society of Plastics Engineers     

Magnetic molecularly imprinted polymer nanoparticles coupled with high performance liquid chromatography for solid‐phase extraction of carvedilol in serum samples

Herein, we report a magnetic molecularly imprinted polymers (m‐MIPs) using Fe₃O₄ as a magnetic component, carvedilol as a template molecule for the solid‐phase extraction (MISPE) as the sample clean‐up technique combined with high‐performance liquid chromatography (HPLC) and for the controlled release of carvedilol at different pH values of 1.0 (simulated gastric fluid), 6.8 (simulated intestinal fluid), and 7.4 (simulated biological fluid). The adsorption kinetics was modeled with the pseudo‐first‐order and pseudo‐second‐order kinetics, and the adsorption isotherms were fitted with Langmuir and Freundlich models. The performance of the m‐MIPs for the controlled release of carvedilol was assessed and results indicated that the magnetic MIPs also have potential applications in controlled drug release. Furthermore, the m‐MIPs were applied to the extraction of carvedilol from human blood plasma samples. Carvedilol can be quantified by this method in the 2–350 μg L^?1 concentration range. The limit of detection and limit of quantification in plasma samples are 0.13 and 0.45 μg L^?1. The results from HPLC showed good precision (3.5% for 50.0 μg L^?1) and recoveries (between 85 and 93) using m‐MIP from human plasma samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41209.     

Detection of broken rotor bars in induction motors using nonlinear Kalman filters

This paper presents a model-based fault detection approach for induction motors. A new filtering technique using Unscented Kalman Filter (UKF) and Extended Kalman Filter (EKF) is utilized as a state estimation tool for on-line detection of broken bars in induction motors based on rotor parameter value estimation from stator current and voltage processing. The hypothesis on which the detection is based is that the failure events are detected by jumps in the estimated parameter values of the model. Both UKF and EKF are used to estimate the value of rotor resistance. Upon breaking a bar the estimated rotor resistance is increased instantly, thus providing two values of resistance after and before bar breakage. In order to compare the estimation performance of the EKF and UKF, both observers are designed for the same motor model and run with the same covariance matrices under the same conditions. Computer simulations are carried out for a squirrel cage induction motor. The results show the superiority of UKF over EKF in nonlinear system (such as induction motors) as it provides better estimates for rotor fault detection.