Microstructural and electrical properties of varistors prepared from coated ZnO nanopowders

This paper describes a solution-based technique for fabrication of varistor grade composite nanopowders. The method consists of coating major varistor dopants on the surface of the ZnO nanoparticles. As a result, a homogenous mixture of dopants and ZnO nanoparticles will be achieved. TEM results indicated that a composite layer of dopants with the average particle size of 9 nm on the surface of ZnO nanoparticles has been successfully prepared. Sintering of the coated powders was performed in temperatures as low as 850 °C and final specimens with average particle size of 900 nm and density of 98.5% were achieved. In comparison to conventional mixing, varistors prepared from coated nanopowders exhibited superior electrical properties and microstructure homogeneity. The improvement of electrical properties can be attributed to small grain size, homogenous distribution of dopants and elimination of large Bi-Pockets. In addition, the processing route of schottky barrier formation is quite different from what is generally considered as the method of barrier formation in ZnO grain boundaries.     

An adaptive latency mitigation scheme for massively multiuser virtual environments

As massively multiuser virtual environments (MMVEs) expand in terms of size and user population, they tend toward using P2P architectures as a way to provide scalability without the need for large centralized resources. Distributed hash table (DHT)-based networks have been introduced as a promising option for overlay-based distributed massively multiuser virtual environment applications. However, overlay latency stretch seriously affects MMVE performance where QoS is crucial for real-time user collaboration. This work includes a series of efforts in the alleviation of such undesired latency. Our approach to latency mitigation consists of two phases. First, we propose a position-based ID assignment approach to minimize message hop-count by exploiting the clustered pattern of traffic exchange among MMVE users. Second, we introduce a new ant-based distributed neighbor selection scheme that can be used by MMVE users to select the best neighbors within their areas of interest. In order to evaluate the performance of this heuristic approach, we model the neighbor selection problem in the form of a network flow problem and use its solution as an optimality bound to compare the results. Simulation results demonstrate that the proposed algorithms will compensate for DHT latency stretch to a high extent and the performance of the resulting system would closely follow the optimal bound while communication overhead is negligible.     

Supertough (Polyamide 6)/(acrylonitrile butadiene rubber) nano alloy through in situ polymerization of caprolactam in the presence of acrylonitrile butadiene rubber nanophase

In this work, polymerization of caprolactam (CL) was carried out in the presence of acrylonitrile butadiene rubber (NBR) during the reactive melt‐mixing process. During shear mixing, NBR particles swelled and dissolved in the molten CL, which led to separation and distribution of rubber particles to nanoscale in the dissolution stage. Then, in an internal mixer, supertough Polyamide 6 was prepared via melt polymerization of CL/NBR mixture, sodium caprolactam as a catalyst, and hexamethylene diisocyanate as an activator. The effects of various concentrations of catalyst and activator on the initiation time of the reaction were determined. Physical and mechanical properties of different formulations prepared via reactive melt blending were determined by tensile and impact measurements, differential scanning calorimetry, Fourier‐transform infrared spectroscopy, X‐ray scattering techniques, transmission electron microscopy, and dynamic mechanical thermal analysis. Experimental results showed that a recipe with 3% nitrile rubber in a CL/NBR mixture enhances the physical and mechanical properties the best, compared with other formulations. This condition led to the formation of NBR nanospheres during melt polymerization of Polyamide 6 as well. J. VINYL ADDIT. TECHNOL., 21:116–121, 2015. © 2014 Society of Plastics Engineers     

Study of photochemical and sonochemical processes efficiency for degradation of dyes in aqueous solution

The degradation of two commercially available dyestuffs (C.I. Reactive Black 5 and C.I. Disperse Orange 25) by ultraviolet radiation (UV), ultrasonic irradiation (US), UV/H₂O₂ and US/H₂O₂ processes was investigated in a laboratory-scale batch photoreactor equipped with a 55 W immersed-type low-pressure mercury vapor lamp and a sonoreactor with low frequency (42 kHz) plate type transducer at 170 W of acoustic power. The toxicity was also evaluated in acute toxicity studies using Daphnia magna. Results showed that color removal efficiencies by US and US/H₂O₂ processes were negligible for both dyes. Almost complete disappearance of Reactive Black 5 (97.9%) in UV/H₂O₂ process was possible after 5 min of irradiation. The maximum color removal efficiency of Disperse Orange 25 after 10 min of irradiation, however, was only 9.2% and reached a maximum value of 41% after 120 min of irradiation. Pseudo-first order kinetics with respect to dyestuffs concentrations was found to fit all the experimental data. The results clearly showed that both dyes examined were toxic to D. magna and resulted in quite low LC₅₀ values.     

Production and quality of fish fingers from different fish species

Abstract Production of fish fingers was achieved by using fish species such as sardine (Sardina pilchardus, Walbaum, 1792), whiting (Merlangius merlangus, Linnaeus, 1758) and pike perch (Sander lucioperca, Linnaeus, 1758). Quality changes of battered fish patties during a period of 8 months at –18 °C were investigated. According to the results of microbiological and chemical analysis, fish fingers were found to be within acceptable limits during frozen storage for 8 months. However, sensory analysis showed that, at the end of the frozen storage, fish fingers made from sardine could not be consumed because of rancidity.     

Enzymatic treatment of peanut kernels to reduce allergen levels

This study investigated the use of enzymatic treatment to reduce peanut allergens in peanut kernels as affected by processing conditions. Two major peanut allergens, Ara h 1 and Ara h 2, were used as indicators of process effectiveness. Enzymatic treatment effectively reduced Ara h 1 and Ara h 2 in roasted peanut kernels by up to 100% under optimal conditions. For instance, treatment of roasted peanut kernels with α-chymotrypsin and trypsin for 1–3 h significantly increased the solubility of peanut protein while reducing Ara h 1 and Ara h 2 in peanut kernel extracts by 100% and 98%, respectively, based on ELISA readings. Ara h 1 and Ara h 2 levels in peanut protein extracts were inversely correlated with protein solubility in roasted peanut. Blanching of kernels enhanced the effectiveness of enzyme treatment in roasted peanuts but not in raw peanuts. The optimal concentration of enzyme was determined by response surface to be in the range of 0.1–0.2%. No consistent results were obtained for raw peanut kernels since Ara h 1 and Ara h 2 increased in peanut protein extracts under some treatment conditions and decreased in others.     

Dynamical and structural behavior of hydroxyethylcellulose hydrogels obtained by chemical gelation

Rheological, dynamical, de‐swelling, turbidity, and structural features during gelation with a chemical cross‐linking agent of semi‐dilute aqueous solutions of hydroxyethylcellulose (HEC) were investigated at different cross‐linker concentrations. A higher level of cross‐linker leads to faster gelation and stronger incipient hydrogel. The rheological results favor the percolation model. The cross‐linking reaction proceeds over a long time in the post‐gel region, and this produces gels with a solid‐like response. Dynamic light‐scattering experiments reveal a fast and a slow relaxation mode. The slow relaxation time increases and the sample becomes more heterogeneous in the course of gelation. In the post‐gel region, the gels shrink during a long period of time and this phenomenon is accompanied by strong turbidity enhancement. Small‐angle neutron scattering results from samples quenched at a certain stage in the post‐gel regime disclose growth of heterogeneity in the gel with increasing level of cross‐linker addition. At smaller length scales, no effect of cross‐linker addition could be detected on the structural organization, and scattered intensity in this domain suggests that the HEC chains are locally stretched. Copyright © 2006 Society of Chemical Industry     

Pilot study of pathophysiology of constipation among community diabetics

We aimed to compare gastrointestinal transit and defecatory function in a random sample of people with or without diabetes mellitus in a US community who reported constipation or laxative use. In this pilot study we measured: gastric, small bowel, and colonic transit by scintigraphy; vector manometry of anal sphincters at rest and during squeeze; defecatory dynamics by balloon expulsion test; and scintigraphic measurement of anorectal angle at rest and during defecation. Autonomic function tests were performed in diabetics. Diabetics with constipation had a higher prevalence of abnormal evacuation or prolonged colonic transit during the first 24 hr than controls (P = 0.07): three had prolonged 24-hr colonic transit, and three abnormal evacuation. Among constipated controls, only one had anismus. Overall, diabetics had slower colonic transit during the first 24 hr than nondiabetics (P < 0.05). Community diabetics who experience constipation or use laxatives have a greater prevalence of delayed 24-hr colonic transit or evacuatory dysfunction than community controls.     

A novel 2-D programmable photonic time-delay device formillimeter-wave signal processing applications

We describe a novel programmable photonic true time-delay device that has the properties of low loss, inherent two dimensionality with a packing density exceeding 25 lines/cm², virtually infinite bandwidth, and is easy to manufacture. The delay resolution of the device is on the order of femtoseconds (microns in space) and the total delay exceeds one nanosecond (30 cm in space)