ESR study and copolymer analysis of acrylamide-methacrylamide solid solutions

When acrylamide-methacrylamide mixed crystals are irradiated by ultraviolet (UV) rays, a copolymeric sample is obtained containing both monomeric constituents. For identification and quantitative analysis of these copolymers, a modified form of UV spectroscopy was used. The greatest advantage of UV spectroscopy for copolymer analysis lies in its rapid application. A comparison of the spectrum of the unknown compositions with spectra of known systems by using a calibration curve and the shifts in absorption maxima in different concentrations are valuable aids in establishing the composition. Electron spin resonance (ESR) provides a correlation between the obtained copolymer composition and the shape of the signal of the responsible radical. ESR spectra obtained for UV-irradiated acrylamide-methacrylamide mixed crystals reveal that during polymerization both radicals are present. As methacrylamide percentage increases in the mixture, the signal becomes similar to the 9-line spectrum of pure methacrylamide. When there is 90% methacrylamide present in the original mixture, a 5-line signal is observed, with even-numbered peaks in the methacrylamide signal appearing now as shoulders. When the methacrylamide percentage is about 16%, a characteristic 3-line signal of acrylamide is dominant. As the methacrylamide percentage increases in the original mixture of the copolymers, ESR signals indicate a decrease in the rate constant values for second-order decay at 60°C. The stability of the formed radicals was studied by admitting oxygen to the copolymeric samples as well as to the homopolymeric systems. Since the peroxidic radicals are more active in the hydrogen abstraction process, they decay more rapidly than the macro radical itself by a bimolecular termination reaction. As the methacrylamide percentage increases in the copolymeric mixtures, the peroxide radical formation becomes more difficult. This indicates that polymethacrylamide brings more stability in copolymerization reactions with acrylamide. The polymerization rate of both monomers and their mixed crystals were enhanced by adding chlorine gas before irradiation. Chlorine acts as an agent for slowing down the radical decay as well as accelerating the radical initiation reactions.     

Effect of the surface roughness and construction material on wall slip in the flow of concentrated suspensions

Recent studies on polyethylene, elastomers, and thermoplastics have revealed that the construction material and surface roughness are two important factors affecting wall slip. In this study, to determine the true rheological behavior of model concentrated suspensions, a multiple‐gap separation method was used in a parallel disk rheometer. The model suspensions studied were poly (methyl methacrylate) particles with an average particle size of 121.2 μm in hydroxyl‐terminated polybutadiene. The aim of this study was to investigate the effect of disk R_a in the range of 0.49–1.51 μm and disk construction material on the wall slip and the true viscosity of the model concentrated suspensions. The wall slip velocity and the viscosity were found to be independent of R_a for particle size‐to‐disk R_a ratios of 80–247. Also, the true viscosity was found not to be affected by the rheometer surface construction material. Glass surfaces resulted in the highest slip velocity, whereas aluminum surfaces resulted in the lowest slip velocity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3341–3347, 2007     

Monomer reactivity ratios in UV-initiated free-radical copolymerization reactions

The homopolymers of styrene (S) and vinyl acetate (VA) and their copolymers were prepared in bulk by ultraviolet (UV)-radiation-initiated free-radical polymerization with azobisisobutyronitrile (AIBN) as an initiator. The reacitivity ratios for these copolymerizations were determined by analyzing the monomer content in the copolymers by UV spectroscopy. The same method was extended to other copolymers of styrene such as styrene–methyl methacrylate and styrene–ethyl acrylate. A new analysis method was developed to measure reactivity ratios. For this purpose, UV light was used as a photochemical initiator and UV absorption spectroscopy was used for the determination of the instantaneous composition of copolymers. Nuclear magnetic resonance (NMR) was used to calculate percent conversion. © 1995 John Wiley & Sons, Inc.     

A DFT Study of Ethylene Hydrogenation Reaction Mechanisms on Ni13 Nanocluster

Metal nanoclusters can potentially exhibit high catalytic activity and selectivity due to not only a high number of exposed surface atoms but also active sites with different coordination numbers as compared to bulk catalyst surface. In this study ethylene hydrogenation was used as a model reaction in an effort to elaborate reactivity of small Ni nanoclusters and the ethylene hydrogenation reaction mechanism. Two mechanistic pathways; representing Eley–Rideal and Horiuti–Polanyi type of mechanism for ethylene hydrogenation reaction are studied. It has been concluded that Horiuti–Polanyi type is more favorable when compared to Eley–Rideal type.     

The architectural colour design process: An evaluation of sequential media via semantic ratings

In recent studies, contextual situations of applied colours are compared to colours presented as samples or chips. Findings of such studies point out different results in terms of similarities or differences between the evaluations of isolated/abstract colours and contextualized situations. Architectural and spatial contexts have their own characteristics regarding colouring criteria, so it is of great importance to examine the architectural/spatial colouring process from this point of view. This study explores this process by investigating the consistency of semantic ratings of four sequential stages of the architectural colour design process, namely, colour chips/samples, abstract compositions, perspective drawings and 3D models. The architectural context for the study was a simple interior space. Fifteen different colour schemes were applied on the four media representing the stages. Subjects rated the 15 sets against seven bipolar, five‐step semantic differential scales. The scales consisted of harmonious‐discord, pleasant‐unpleasant, comfortable‐uncomfortable, spacious‐confined, static‐dynamic, exciting‐calming and extroverted‐introverted. Findings indicated that there are significant associations between the evaluations of the abstract compositions, the perspective drawings and the 3D models; however, the evaluations of colour chips are significantly different than the others. The medium effect observed mostly between abstract and contextualized media. Additionally, factor analysis showed that pleasantness, harmony, spaciousness and comfort are connected in the evaluations of contextual situations, while pleasantness and harmony differ from spaciousness and comfort in the evaluations of colour chips and abstract compositions. The factor of activity (arousal) (dynamism, excitement, and extroversion) stays the same for all four media. It is also found that different colour characteristics are determinative over different media. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Maximum‐likelihood maximum‐entropy constrained probability density function estimation for prediction of rare events

This work addresses the problem of estimating complete probability density functions (PDFs) from historical process data that are incomplete (lack information on rare events), in the framework of Bayesian networks. In particular, this article presents a method of estimating the probabilities of events for which historical process data have no record. The rare‐event prediction problem becomes more difficult and interesting, when an accurate first‐principles model of the process is not available. To address this problem, a novel method of estimating complete multivariate PDFs is proposed. This method uses the maximum entropy and maximum likelihood principles. It is tested on mathematical and process examples, and the application and satisfactory performance of the method in risk assessment and fault detection are shown. Also, the proposed method is compared with a few copula methods and a nonparametric kernel method, in terms of performance, flexibility, interpretability, and rate of convergence. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1013–1026, 2014     

Use of Fenton oxidation to improve the biodegradability of a pharmaceutical wastewater

The applicability of Fenton's oxidation to improve the biodegradability of a pharmaceutical wastewater to be treated biologically was investigated. The wastewater was originated from a factory producing a variety of pharmaceutical chemicals. Treatability studies were conducted under laboratory conditions with all chemicals (having COD varying from 900 to 7000 mg/L) produced in the factory in order to determine the operational conditions to utilize in the full-scale treatment plant. Optimum pH was determined as 3.5 and 7.0 for the first (oxidation) and second stage (coagulation) of the Fenton process, respectively. For all chemicals, COD removal efficiency was highest when the molar ratio of H(2)O(2)/Fe(2+) was 150-250. At H(2)O(2)/Fe(2+) ratio of 155, 0.3M H(2)O(2) and 0.002 M Fe(2+), provided 45-65% COD removal. The wastewater treatment plant that employs Fenton oxidation followed by aerobic degradation in sequencing batch reactors (SBR), built after these treatability studies provided an overall COD removal efficiency of 98%, and compliance with the discharge limits. The efficiency of the Fenton's oxidation was around 45-50% and the efficiency in the SBR system which has two reactors each having a volume of 8m(3) and operated with a total cycle time of 1 day, was around 98%, regarding the COD removal.     

An investigation of heavy metal biosorption in relation to C/N ratio of activated sludge

The effect of C/N ratio of activated sludge on heavy metal biosorption was investigated. Three sets of semi-continuous reactors with different feed C/N ratios (9, 21 and 43 mg COD/mg TKN) were set up. Sorption equilibrium tests have indicated that the biosorptive capacity of activated sludge was highly dependent on metal species and the C/N ratio. The increase in C/N ratio resulted in an increase in the Cd(II) sorption capacity of activated sludge whereas it decreased the Cu(II) sorption capacity. As for Zn(II), a different behavior was observed such that, the highest and lowest capacities have occurred at C/N ratio of 21 and 43, respectively. For Ni(II) biosorption, isotherm tests produced greatly scattered data; so, it was not possible to obtain any plausible result to indicate the relationship between maximum adsorptive capacity and C/N ratio. The accompanying release of Ca(II) and Mg(II) ions and also carbohydrates into the solution during biosorption have indicated that ion exchange mechanism was involved however, was not the only mechanism during the sorption process.     

Maxim GMSL SerDes器件的预加重和均衡

发送端的预加重和接收端的均衡能够使串行器/解串器(SerDes)采用廉价的电缆传输数据或延长数据传输距离。本文介绍了电缆对信号传输的影响,以及如何补偿。此外,文章介绍了使用有损电缆时,如何利用Maxim的多媒体串行链路(GMSL)产品构建可靠链路。本文还简要介绍了线路均衡技术。     

Analytical Evaluation of Transient Magnetic Fields Due to RWG Current Bases

A new analytical approach for obtaining the time samples of the magnetic field intensity due to an impulsively excited Rao-Wilton-Glisson (RWG) basis function is presented. The approach is formulated directly in the time domain. It is shown that the magnetic field is related to the arc segments formed by the intersection of the triangular patch of the RWG basis with the sphere that is centered at the observation point and that has a radius of , where is the speed of light. In particular, the magnetic field can be expressed as the variations of two quantities with respect to . The first quantity is the arc segment length, and the second quantity is the bisecting vector of the arc segment. Analytical representations of these quantities are presented. Contrary to previous studies, these representations do not require the calculation of the intersection points of the sphere with the boundaries of the bases. The validity of the obtained time domain formulae is demonstrated through comparison of the results with those obtained in the frequency domain by using numerical quadrature. Finally, it is demonstrated that the derived formulae yield closed-form expressions when convolved with piecewise polynomial temporal basis functions.