Enhanced Antibacterial Activity of Nanocrystalline ZnO Due to Increased ROS‐Mediated Cell Injury

An innovative study aimed at understanding the influence of the particle size of ZnO (from the microscale down to the nanoscale) on its antibacterial effect is reported herein. The antibacterial activity of ZnO has been found to be due to a reaction of the ZnO surface with water. Electron‐spin resonance measurements reveal that aqueous suspensions of small nanoparticles of ZnO produce increased levels of reactive oxygen species, namely hydroxyl radicals. Interestingly, a remarkable enhancement of the oxidative stress, beyond the level yielded by the ZnO itself, is detected following the antibacterial treatment. Likewise, an exposure of bacteria to the small ZnO nanoparticles results in an increased cellular internalization of the nanoparticles and bacterial cell damage. An examination of the antibacterial effect is performed on two bacterial species: Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive). The nanocrystalline particles of ZnO are synthesized using ultrasonic irradiation, and the particle sizes are controlled using different solvents during the sonication process. Taken as a whole, it is apparent that the unique properties (i.e., small size and corresponding large specific surface area) of small nanometer‐scale ZnO particles impose several effects that govern its antibacterial action. These effects are size dependent and do not exist in the range of microscale particles.     

Sonochemical deposition of silver nanoparticles on wool fibers

Silver nanoparticles were deposited on the surface of natural wool with the aid of powered ultrasound. The average particle size was 5–10 nm, but larger aggregates of 50–100 nm were also observed. The sonochemical irradiation of a slurry containing wool fibers, silver nitrate, and ammonia in an aqueous medium for 120 min under an argon atmosphere yielded a silver–wool nanocomposite. By varying the gas and reaction conditions, we could achieve control over the deposition of the metallic silver particles on the surface of the wool fibers. The resulting silver‐deposited wool samples were characterized with X‐ray diffraction, transmission electron microscopy, high‐resolution transmission electron microscopy, high‐resolution scanning electron microscopy, electron‐dispersive X‐ray analysis, Brunauer, Emmett, and Teller physical adsorption method, X‐ray photoelectron spectroscopy, and Raman and diffused reflection optical spectroscopy. The results showed that the strong adhesion of the silver to the wool was a result of the adsorption and interaction of silver with sulfur moieties related to the cysteine group. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1732–1737, 2007     

Treatment of high-strength dairy wastewater in an anaerobic deep reservoir: analysis of the methanogenic fermentation pathway and the rate-limiting step

The wastewater of the largest dairy factory in Israel (Tnuva, Tel-Yosef), discharging approximately 6000 tons BOD per year, is treated in two serial, deep reservoirs (anaerobic/facultative). In this study, which focused on the anaerobic reservoir, we combined in situ measurements (over 18 months) and supporting lab experiments, in order to evaluate its efficiency and to identify the rate-limiting step of the methanogenic fermentation pathway. The anaerobic reservoir could remove above 75% of the BOD and COD all year round, but this was not enough to prevent malodors during the winter. Acetate and propionate, products of lactose fermentation, were the predominant intermediate metabolites in the reservoir and their concentrations were strongly dependent on the temperature and the organic load. The combined effects of colder winter temperatures and seasonal increase of organic load, resulted in a decreased rate of propionate oxidation and a consequent accumulation of soluble BOD and COD. Laboratory batch experiments, conducted during this season, found propionate oxidation to be the rate-limiting step in the process, characterized by a lag period preceding its degradation.     

Nitrogen-14 NMR of Solutes in Liquid Crystals: NH4NO3 and (CH3)4N NO3 in the DSCG–Water System

Measurements of the nitrogen-14 and deuterium quadrupolar splittings in NH₄NO₃ and (CH₃)₄ N NO₃ dissolved in the disodiumcromoglycate–water liquid crystalline system are presented. Nitrogen-14 T₁ values in aqueous solutions for these salts are also given. The results are discussed and compared with similar studies on solutes containing ¹⁴N in ordered media.     

Torsion of perforated cores: Planar formulation

A planar finite element approximate solution for the torsional analysis of symmetric perforated cores is given. The solution involves neglecting the out-of-plane stiffness of the walls of the core. Only one-quarter of the core is analyzed, using super elements assembled from high order plane stress finite elements. The results of the analysis are compared with the results from three-dimensional finite element analysis. It is observed that for almost all realistic designs the planar approximation is justified. The solution is very close with significant reduction in computation time and data preparation effort.     

Rapid deposition of transparent super-hydrophobic layers on various surfaces using microwave plasma

We report herein on a very fast and simple process for the fabrication of transparent superhydrophobic surfaces by using microwave (MW) plasma. It was found that the reaction of various organic liquids in MW argon plasma yields hydrophobic polymeric layers on a large assortment of surfaces, including glass, polymeric surfaces, ceramics, metals, and even paper. In most cases, these polymers are deposited as a rough layer composed of 10-15 nm nanoparticles (NPs). This roughness, together with the chemical hydrophobic nature of the coated materials, is responsible for the superhydrophobic nature of the surface. The typical reaction time of the coating procedure was 1-10 s. The stability of these superhydrophobic surfaces was examined outdoors, and was found to last 2-5 days under direct exposure to the environment and to last 2 months when the sample was protected by a quartz cover. A detailed characterization study of the chemical composition of the layers followed using XPS, solid-state NMR, and IR measurements. Modifications were introduced in the products leading to a substantial improvement in the stability of the products outdoors.     

Theoretical model for non-intermeshing twin screw extruders

A simple theoretical model for flow in nonintermeshing twin screw extruders has been derived. The assumptions which in single screw extruders result in the “two parallel plates” model, in twin screw extruders result in the “three parallel plates” model. The flow rate equation can be expressed, for Newtonian fluids, in terms of drag and pressure flow terms, as in single screw extrusion theory, but each term is multiplied by a geometrical factor. This factor incorporates the effect of one screw on the drag and pressure flow terms of the other. The theoretical model was experimentally verified on a 1 inch diameter Bausano twin screw extruder.     

The bulk photovoltaic effect in photorefractive K1-xLixTa1-yNbyO3 crystals

Experimental evidence of the bulk photovoltaic effect in photorefractive K_1-xLi_xTa_1-xNb_yO₃ (KLTN) crystals is shown. The dependence of the bulk photovoltaic effect on the pbotorefractive impurities type is presented. The current voltage characteristic is presented for different temperatures. It was found that, in Fe-doped KLTN crystals at low temperature, the bulk photovoltaic effect is the dominant transport mechanism contributing to the photorefractive process.