High-energy radiation-resistant vulcanizates. II. EPDM

In this article, Part II of the series, we report a detail study on stabilization of EPDM vulcanizates in γ-radiation environment. The special additives (antirads), namely pyrene (Py), brominated acenaphthene (BrAc), poly(acenaphthene sulfide) (PAcSu) and poly(pyrene sulfide) (PPySu) were used for the stabilization studies. The efficiency of these antirads for EPDM had been monitored by the means of electrical resistivity, wide-angle X-ray diffraction, and mechanical properties. The stabilization of EPDM to withstand 200 Mrads of γ radiation in air environment is achieved. © 1994 John Wiley & Sons, Inc.     

High-energy radiation-resistant elastomeric vulcanizates. I. Chlorosulfonated polyethylene

In this article, a detailed study on the stabilization of chlorosulfonated polyethylene (CSP) vulcanizates in γ radiation is reported. The special additives (antirads) for the stabilization are synthesized from polynuclear aromatics and formulated in the laboratory. The effect of these antirad formulations on the physicochemical structure and performance properties of these materials is studied by monitoring the degradation in γ radiation using resistivity, wide-angle X-ray diffraction, and mechanical properties. Antirad formulations to stabilize CSP against a total dosage of 200 Mrads of γ radiation have been achieved. © 1994 John Wiley & Sons, Inc.     

Decentralized semaphore support in a virtual shared-memory system

Distributed shared memory has increasingly become a desirable programming model on which to program multicomputer systems. Such systems strike a balance between the performance attainable in distributed-memory multiprocessors and the ease of programming on shared-memory systems. In shared-memory systems, concurrent tasks communicate through shared variables, and synchronization of access to shared data is an important issue. Semaphores have been traditionally used to provide this synchronization. In this paper we propose a decentralized scheme to support semaphores in a virtual shared-memory system. Our method of grouping semaphores into semaphore pages and caching a semaphore at a processor on demand eliminates the reliability problems and bottlenecks associated with centralized schemes. We compare the performance of our scheme with a centralized implementation of semaphores and conclude that our system performs better under high semaphore access rates as well as larger numbers of processors.     

Isotopic zoning and origin of the aquifers in the discharge area of the geothermal fields of ahuachapán and Chipilapa, El Salvador

The northern discharge areas of the Ahuachapán, and Chipilapa geothermal fields can be subdivided into four different zones based on their structural position, and the isotopic and chemical composition of their waters. In general, the contribution of geothermal waters from these two fields was estimated to be less than 10%. Elevation effects are of little importance, whereas a slight trend towards higher isotopic values with increasing water temperatures may exist.The NNW-SSE-trending Escalante and Agua Caliente faults represent lateral groundwater barriers, and provide vertical conduits for the ascending geothermal waters. The western discharge areas seem to be more influenced by the Ahuachapán, geothermal field, whereas those to the east are more influenced by the Chipilapa field.Groundwaters in the Northern Plain are mainly from shallow northward-flowing aquifers. These waters show temperature effects, mixing with geothermal waters and are affected by the geology of the area. However, none of these factors alone can explain the isotopic variations observed in the waters of the northern discharge areas.     

Finger Forwarding Scheme to Reduce Lookup Cost in Structured P2P Networks

Wireless Personal Communications - Peer-to-peer (P2P) networks are distributed systems where each user shares his resources and cooperates with other users. These networks are designed over...     

Production,stabilisation and characterisation of silver nanoparticles coated with bioactive polymers pluronic F68, PVP and PVA

The increasing and alarming panorama of bacterial infections and associated morbidities that occur during medical and hospital procedures makes the development of technologies that aid in controlling such bacterial infections of utmost importance. Recent studies have shown that formulations with metal nanoparticles exhibit good antibacterial properties against a broad spectrum of microorganisms. Moreover, it was demonstrated that some biologically active polymeric materials, when applied in combination with chemical antimicrobial agents, enhance the therapeutic action of the latter. The research effort entertained herein aimed at the physico‐chemical characterisation of silver nanoparticles obtained by chemical reduction, stabilised by bioactive polymers polyvinyl alcohol and polyvinylpyrrolidone, and further co‐stabilised by pluronic F68. Scanning electron microscopy images of the nanoparticles produced, coated with different stabilisers, have shown that the chemical nature of the stabilisation effect promoted incorporation of pluronic in the nanoparticles and was closely related to an increase in the silver concentration in the nanoparticle samples obtained via energy‐dispersive X‐ray spectroscopy. The study described herein also shows that the nature of the stabiliser favours the interaction of pluronic F68 with samples containing silver nanoparticles.Inspec keywords: silver, nanoparticles, polymer films, coatings, nanocomposites, nanofabrication, microorganisms, biomedical materials, nanomedicine, antibacterial activity, reduction (chemical), scanning electron microscopy, X‐ray chemical analysisOther keywords: bioactive polymers pluronic F68 coated silver nanoparticles, PVP coated silver nanoparticles, PVA coated silver nanoparticles, bacterial infections, associated morbidities, medical procedures, hospital procedures, antibacterial properties, microorganisms, biologically active polymeric materials, chemical antimicrobial agents, therapeutic action, physicochemical characterisation, chemical reduction, bioactive polymers polyvinyl alcohol, polyvinylpyrrolidone, scanning electron microscopy, stabilisation effect, energy‐dispersive X‐ray spectroscopy, Ag     

Biogenic fabrication of CuNPs,Cu bioconjugates and in vitro assessment of antimicrobial and antioxidant activity

In the present study, the authors synthesised copper nanoparticles (CuNPs) by using extract of Zingiber officinale (ginger) and later the NPs were bioconjugated with nisin, which shows antimicrobial activity against food spoilage microorganisms. CuNPs and its bioconjugate were characterised by ultraviolet–vis spectroscopy, NP tracking analysis, Zetasizer, transmission electron microscopy analysis, X‐ray diffraction and Fourier transform infra‐red (FTIR) spectroscopy. Zeta potential of CuNPs and its bioconjugate were found to be very stable. They evaluated in vitro efficacy of CuNPs and its bioconjugate against selected food spoilage bacteria: namely, Staphylococcus aureus, Pseudomonas fluorescens, Listeria monocytogenes and fungi including Fusarium moniliforme and Aspergillus niger. Antimicrobial activity of CuNPs was found to be maximum against F. moniliforme (18 mm) and the least activity was noted against L. monocytogenes (13 mm). Antioxidant activity of CuNPs and ginger extract was performed by various methods such as total antioxidant capacity reducing power assay, 1‐1‐diphenyl‐2‐picryl‐hydrazyl free radical scavenging assay and hydrogen peroxide assay. Antioxidant activity of CuNPs was higher as compared with ginger extract. Hence, CuNPs and its bioconjugate can be used against food spoilage microorganisms.Inspec keywords: antibacterial activity, biomedical materials, copper, nanoparticles, nanofabrication, nanomedicine, microorganisms, ultraviolet spectra, visible spectra, electrokinetic effects, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectra, free radical reactions, food technologyOther keywords: biogenic fabrication, Cu bioconjugates, in vitro assessment, antimicrobial activity, antioxidant activity, copper nanoparticles, Zingiber officinale, ultraviolet‐visible spectroscopy, NP tracking analysis, Zetasizer, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, FTIR, zeta‐potential, food spoilage bacteria, Staphylococcus aureus, Pseudomonas fluorescens, Listeria monocytogenes, fungi, Fusarium moniliforme, Aspergillus niger, F. moniliforme, L. monocytogenes, ginger extract, total antioxidant capacity, power assay, 1‐1‐diphenyl‐2‐picryl‐hydrazyl free radical scavenging assay, hydrogen peroxide assay, food spoilage microorganisms, Cu     

Degradation and cross-linking of ethylene-propylene copolymer rubber on reaction with maleic anhydride and/or peroxides

The reaction of EPR with dicumyl peroxide at 180°C or t-butyl perbenzoate at 140°C resulted in the formation of a fraction insoluble in cyclohexane at 22°C. The presence of maleic anhydride (MAH) in the EPR-peroxide reaction mixture increased the amount of insoluble polymer, whose concentration decreased as the peroxide concentration increased. The [η] of the cyclohexane-soluble polymer decreased and the MAH content increased as the peroxide concentration increased at constant MAH concentration. The [η] and the MAH content of the soluble polymer increased as the MAH concentration increased at constant peroxide concentration. The EPR-peroxide and EPR-MAH-peroxide reaction products were soluble in refluxing xylene and could be fractionated by precipitation with acetone. The presence of stearamide in the EPR-MAH-peroxide reaction mixture decreased the amount of cyclohexane-insoluble polymer, indicative of decreased cross-linking, but the [η] of the soluble EPR-g-MAH increased, indicative of decreased degradation, analogous to the effect of stearamide in the MAH-peroxide reactions with LDPE and PP, respectively.     

NO2-initiated polymerization of acrylonitrile

The polymerization of acrylonitrile initiated with NO₂ in dimethyl sulfoxide has been studied. The kinetics of polymerization was followed gravimetrically. The effect of monomer, initiator, and temperature on the rate of polymerization has been given. The overall activation energy was found to be 18.06 kcal.mol^?1. The polymerization with NO₂ appears to be initiated by a free-radical mechanism.