Evolution of vinyl chloride conversion below critical micelle concentration: A response surface analysis

Utilizing response surface methodology, the conversion of vinyl chloride monomer (VCM) was monitored when the polymerization temperature, the type of surfactant, and the weight ratio of water‐to‐monomer (W/M) were taken as the emulsion polymerization variables. Because the homogeneous nucleation was found to be the dominant mechanism in VCM emulsion polymerization, irrespective of the surfactant concentration, the whole experiments have been carried out below critical micelle concentration of the used surfactants. Among all the studied variables, the polymerization temperature appeared as the most effective parameter; moreover, its interactive effect with W/M caused different trends in the alteration of final conversion being observed. Also, depending on the reaction temperature, the VCM conversion would be affected by the type of the surfactant used. Contrarily, simultaneous change in the type of surfactant and W/M revealed an insignificant effect on the evolution of VCM conversion. The optimization of final conversion of VCM was also accessible through contour plots of response surface methodology. It is worth noting that, taking a conventional approach into consideration, the alteration of VCM conversion seemed to be a monotonic function of temperature. J. VINYL ADDIT. TECHNOL., 21:157–165, 2015. © 2014 Society of Plastics Engineers     

FQL‐RED: an adaptive scalable schema for active queue management

In a potentially congested network, random early detection (RED) active queue management (AQM) proved effective in improving throughput and average queuing delay. The main disadvantage of RED is its sensitive parameters that are impossible to estimate perfectly and adjust manually because of the dynamic nature of the network. For this reason, RED performs differently during different phases of a scenario and there is no guarantee that it will have optimal performance. Giving adaptability to RED has been the subject of broad research studies ever since RED was proposed. After a substantial study of AQM schemes and presenting a novel categorization for so‐called modern approaches utilizing artificial intelligence tools to improve AQM, this paper proposes an algorithm enhancing RED as an add‐on patch that makes minimal changes to the original RED. Being built on the basis of AQM schemes like ARED and Fuzzy‐RED, this algorithm inherits adaptability and is able to adjust RED inaccurate parameters regarding network traffic status, trying to optimize throughput and average queuing delay in a scenario. This algorithm is a Q‐learning method enhanced with a fuzzy inference system to provide RED with self‐adaptation and improved performance as a result. Given the name of FQL‐RED, this algorithm outperformed RED, ARED, and Fuzzy‐RED, as the OPNET simulations show. Copyright © 2010 John Wiley & Sons, Ltd.     

A collective and abridged lexical query for delineation of nanotechnology publications

In order to monitor articles/patents in nanotechnology, there is little agreement on a universal lexical query or even an explicit definition of nanotechnology. Here in the light of a proposed definition, a set of case studies has been conducted to remove keywords which are not exclusive to nanotechnology. This resulted in a collective and abridged lexical query (CALQ) for nanotechnology delineation. Through bibliometric quantification of already-proposed as well as the novel keywords, it was shown that all keywords included in CALQ have considerable exclusive retrieval and precision, while the removed keywords do not satisfy either of these numerical thresholds. This approach may also be applied for the future updating of CALQ.     

Parametric study of a 2-d model of the nip region in a counter-rotating,non-intermeshing twin screw extruder

Within the polymer processing industry, the demand for more efficient mixing within the existing mixer geometries and keeping a tighter control over increasingly difficult applications calls for a quantitative understanding of the role of the mixer geometry on the mixing performance. An important extruder geometry to consider is the Counter-Rotating, Non-Intermeshing Twin Screw Extruder (CRTSE). Recent studies suggest that the greater than linear mixing performance in this geometry may be attributed to the flow in the nip region. Solution of the fluid dynamic equations for a 2-D model of the nip region was found in order to quantify mixing using a FEM software called FIDAP which was available to us on the CRAY X-MP supercomputer at San Diego Supercomputer Center. In order to study the effects of design parameters in the nip region, an arbitrary interface was placed in the entrance of the region. A program called “LINE” tracks the path and growth of the interface through the region. Measures of mixing are computed and compared. Effect of several design parameters on mixing performance are studied. Conclusions are presented as to the relative effect of various design parameters. Discussions regarding the measures of mixing and mixing efficiency are presented.     

Unique microstructure analysis of ethylene-propylene copolymer synthesized using catalytic system based on α-diimine nickel complexes: a comparative study by 13C NMR technique

The microstructure of rubber-like ethylene-propylene copolymer (MN4) produced by a mixed nickel-based system (MN) containing catalysts of dibromo[N,N′-bis(2,6-diisopropylphenyl)-2,3-butanediimine]nickel(II) n1 and dibromo[N,N′-(phenanthrene-9,10-diylidene)bis(2,6-diisopropylaniline)]nickel(II) n2 was determined by ¹³C NMR technique. Sequences distribution of ethylene (E), propylene (P), EP, inverted propylene and uninterrupted methylene and also methylene number-average sequence lengths for the copolymer (MN4) were estimated. The results obtained from the MN4 EP copolymer were compared with reported copolymers which had been synthesized using constrained geometry catalyst (CGC) and vanadium-based Ziegler-Natta catalyst. The results demonstrated that the MN4 EP copolymer had fewer alternating comonomer sequences than ethylene-propylene elastomers obtained by CGC and vanadium-based (V) catalysts. A large number of the inversion structures (66 %) and high mole percent of sequences containing a long branch (3.2 mol%) were also observed in unique microstructure of the copolymer (MN4).     

Non-Intrusive Online Quality of Experience Assessment for Voice Communications

Recently user quality of experience (QoE) is employed in evaluating end user satisfaction in communications systems. Generally, current approaches for QoE assessment are obtrusive, laboratory based and offline. Estimation of user satisfaction in static manner based on mean opinion score is not directly related to instantaneous individual end user contentment. In this paper, based on correlations between user’s physiological signals and her/his feelings about the service quality, a non-intrusive and user centric QoE assessment system for voice communications is developed. The findings of this study indicate that the emotional patterns in response to the changes in channel quality can be adapted to estimate the level of satisfaction in a QoE assessment system in a live manner. Based on experimental results, two categories of users are identified: sensitive and insensitive towards quality degradations. The results indicate that for the sensitive users, our non-intrusive subjective quality assessment method outperforms ITU-T P.563 standard with respect to root mean square error; while, the results are much better among the insensitive users.     

Numerical investigation of the mechanism behind the deflagration to detonation transition in homogeneous and inhomogeneous mixtures of H2-air in an obstructed channel

The accidental release of hydrogen into enclosures can result in a flammable mixture with concentration gradients and possible deflagration-to-detonation transition (DDT). This numerical study aims to investigate the effect of obstacle spacing and mixture concentration on the DDT in a homogeneous and inhomogeneous hydrogen-air mixture. The paper focuses on the mechanisms behind the DDT in two mixtures with an average hydrogen concentration of 15% and 30%. Unlike the near-stoichiometric mixture, in the lean mixture, DDT only occurs in the inhomogeneous mixture. Depending on obstacle spacing, three different regimes of DDT were observed in the near-stoichiometric inhomogeneous mixture: i) Detonation was ignited when a strong Mach stem formed and propagated between the obstacles; ii) two explosion centers appeared when incident shock and Mach stem reflected from upper and lower obstacles, respectively; iii) Mach stem did not form but DDT occurred behind the flame front at the top of the obstacle.     

Analysis of nonpremixed multiregion laminar flames through biofuel porous particles considering the effect of heat recirculation

In this study, a comprehensive analysis is conducted to evaluate the effects of heat recirculation and particle porosity on combustion characteristics of multizone counterflow nonpremixed flames fed with porous biofuel particles. For this purpose, the structure of flame contains preheat, postvaporization, and oxidizer zones. Additionally, Lycopodium is considered as the volatile biofuel, especially due to its appreciable flammability and dispensability. Dimensionalized and nondimensionalized forms of mass and energy conservation equations are scrutinized in each zone. To explore of the thermal recirculation effect, a specific term is included in the energy conservation equation. The variation of several parameters, including flame temperature, particle radius, mass fraction of the gaseous fuel and oxidizer, mass particle content, equivalence ratio, and particle porosity, is studied in this work considering and ignoring the thermal recirculation impact. As a result, increasing heat recirculation coefficient from $k=0$ to 1 will rise the flame temperature and shift the flame position to the left side (fuel nozzle). Furthermore, consideration of the thermal heat recirculation will improve the gaseous fuel production in the preheat and postvaporization zones. Additionally, an increase in mass concentration and reduction of particles radius and porosity would lead to a rise in the flame temperature.     

Comparison of sorption behavior of Th(IV) and U(VI) on modified impregnated resin containing quinizarin with that conventional prepared impregnated resin

This paper reports the results obtained by studying the ion-exchange properties of a new solvent impregnated resin (SIR), which was prepared by impregnation of quinizarin (1,4-dihydroxyanthraquinone, QNZ) on Amberlite XAD-16 after nitration of the benzene rings present in its structure. The sorption behavior of Th(IV) and U(VI) on/in the modified SIR was compared with that of the SIR prepared via the conventional method. It was observed that sorption capacity and sorption rate of the modified SIR are significantly greater than the conventional one. The modified SIR was then applied to the extraction of Th(IV) and U(VI) ions at the presence of many co-existence metal ions. The results obtained denote on successful application of this new SIR to analysis of natural water samples spiked to Th(IV) and U(VI) ions.