Insights into the physico-chemical behavior of CoCl<Subscript>2</Subscript>/polyimide hybrid materials

Hybrid fluorinated polyimide materials have been obtained by incorporation of various quantities of cobalt(II) chloride (CoCl₂) into polyimide matrix. Polycondensation reaction of equimolar amounts of 4,4′-diamino-3′3′-dimethyldiphenylmethane and 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride has been carried out to produce in the first stage a polyamidic acid solution in which CoCl₂?×?6H₂O has been placed. Further thermal treatment of this system led to the corresponding imide structure filled with the halide salt. An exhaustive study was directed to the influence of Co²⁺ ions on the modified polyimide behavior as a function of its surroundings. To survey the functional properties of as-obtained Co²⁺-containing polyimide systems, several techniques such as FTIR, UV-vis and broadband dielectric spectroscopy, differential scanning calorimetry, and thermogravimetric and scanning electron microscopy were employed. A special concern was directed to the study of the optical properties induced by the addition of CoCl₂ into polymer solutions and films. The magnetic response of the polyimide was investigated in correlation with the salt quantity embedded in the PI film. The variation of the real and imaginary parts of the hybrid films’ dielectric permittivity was registered in a broad frequency and temperature range, from 10 to 10⁶ Hz and from ?130 to 230 °C, respectively.     

Encrustation Prevention in PVC Reactors

Poly(vinyl chloride) is one of the world's most important bulk thermoplastics. Approximately 15 million tons are produced annually. About 80% of this is made by the suspension process. Suspension polymerization of vinyl chloride is almost invariably accompanied by the formation of scale on the internal surfaces of the polymerization reactor, including moving surfaces such as those of the impeller. The formation of scale, or deposits of PVC, on the internal surfaces of reactors has always been a problem in the manufacture of PVC because of reduced heat transfer, large alteration of the agitation regime present in the reactor, and broken-off scale fragments that block transfer systems and contaminate the product. Therefore scale must be cleaned periodically. Until the early 1970s these deposits were removed manually; PVC workers were exposed to high levels of VCM and considerable production time was lost. The introduction of large reactors in 1975 made it practical to mechanize the cleaning. High-pressure water sprays are employed for this purpose. However, such devices remove only the slightly adherent sandy deposits. For strongly attached deposits, a thorough manual cleaning is necessary after a series of polymerization batches. Manual cleaning requires extensive safety measures to protect the workers from VCM vapor inside the reactor. In addition, such cleaning is costly and undesirable. In more recent years, methods have been developed to suppress or inhibit the formation of scale on the reactor walls. Proposed solutions in this field are sparese. The patient literature claims many chemical treatments to resuce reactor fouling. Many PVC producers have developed effective buildup-suppressant treatments, which significantly reduce the need for reactior cleaning. They vary from treatments to render the reactor wall hydrophilic and reduce the adsorption of VCM (e.g., application of a sulfonic acid polymer to the reactor surface [1]) to systems containing polymerization inhibitors and radical traps (e.g., organic dyes and phenolic resins). The most successful of these probably work by a combination of both mechanisms. In this paper the soultions are reviewed brifly and emphasis is given to suspension polymerization where the initiator is monomer soluble.     

Influence of Test Conditions on the Lubricated Friction and Wear Behaviour of Al–25Zn–3Cu Alloy

The friction and wear properties of Al–25Zn–3Cu alloy were investigated over a range of oil flow rate, pressure and sliding speed using a pin-on-disc machine, after examining its microstructure and mechanical properties. The results obtained were compared with those of a conventional-bearing material (SAE 65 bronze). It was observed that the microstructure of the Al–25Zn–3Cu alloy consisted of aluminium-rich α, eutectoid α + η and θ phases, while the microstructure of the SAE 65 bronze revealed copper-rich α, and eutectoid α + δ phases. It was found that the friction coefficient, temperature and wear volume of both the alloys decreased sharply with increasing oil flow rate and attained almost constant levels beyond a certain range of oil flow rate. It was also found that the friction coefficient and the wear volume of the alloys decreased with increasing pressure, but was observed to be almost independent of the sliding speed. The Al–25Zn–3Cu alloy exhibited higher wear resistance as compared to that of the bronze under all the test conditions. Smearing type of adhesion appeared to be the most effective wear mechanism for the Al–25Zn–3Cu alloy, while abrasion dominated one for the SAE 65 bronze.     

Modified forward-backward overdetermined Prony method and itsapplication in modelling heart sounds

Prony's method is found to be a very effective method for the analysis-synthesis of transient data. However, straightforward application of this method can lead to poor performance, especially for short and noisy data records. The authors present a new over-determined forward-backward Prony method (MFBPM) and its application to the analysis of the first and second heart sounds. The accuracy of the method is measured using both cross-correlation and the normalised-mean-square-error (NMRSE) between a real signal and a synthetic one. Results from more than 80 different subjects show that the MFBPM is highly stable and gives very good performance with an average cross-correlation coefficient of 99.62%. Comparison of the results based on the NMRSE criterion show that the MFBPM is more precise than the modified backward Prony method (MBPM) with an accuracy improvement of upto 10%, and upto 20%, when compared with the conventional forward-backward Prony method (FBPM). Furthermore, a new method for dynamic estimation of model order is proposed for the case of heart sounds based on a subset of synthesised heart sounds which best approximates the observed data using NMRSE     

Non-identical parallel machine scheduling using genetic algorithm

Most of the scheduling problems are NP-hard. In the literature, several heuristics and dispatching rules are proposed to solve such hard combinatorial optimization problems and genetic algorithm (GA) ranks among the most preferred ones in view of its characteristics such as high adaptability, near optimization and easy realization. But, even though it is a common problem in the industry, only a small number of studies deal with non-identical parallel machines. In this paper, the authors propose a new “crossover operator” and a new “optimality criterion” in order to adapt the GA to non-identical parallel machine scheduling problem. New algorithm is tested on a numerical example by implementing it in a simulation software and computational results are compared to those obtained with LPT (Longest Processing Time) dispatching rule; results were promising. Findings show that, in addition to its high computational speed for larger scale problem, the GA proposed here fits the non-identical parallel machine scheduling problem of minimizing the maximum completion time (makespan).     

The diffusion of water in poly(ditetrahydrofurfuryl itaconate)

The diffusion of water into solid poly(ditetrahydrofurfuryl itaconate) (PDTFI) films and in analogous polymer solutions was measured. Diffusion into solid PDTFI films on a glass support was measured in three solutions of different pH (4, 7 and 10) at 37 and 60 °C during a 90 day period. The uptake was high and was both pH and temperature dependent, ranging from 120 to 2000%. A Fickian mechanism is observed for the initial stages of uptake, whilst a non-Fickian mechanism is present when the equilibrium is approached. The pH 7 samples did not equilibrate at any temperature during the experiment. The FTIR investigations of the films indicated some deesterification took place during the uptake. The diffusion coefficients and diffusion exponents are calculated for the samples. The diffusion of water into PDTFI solution in acetone was measured by PGSE-NMR, showing the expected linear attenuation functions. The diffusion coefficient of water was calculated for polymer concentrations up to 10%.     

The relationship between interpersonal schemas and depressive symptomatology.

Turkish university students (187 men and 191 women), 17–27 years old, participated in this study. They completed the Interpersonal Schema Questionnaire (C. Hill & J. Safran, 1994) and the Beck Depression Inventory (A. Beck, A. Rush, B. Shaw, and G. Emery, 1979). This study extended the research that was conducted by Hill and Safran (1994). The results of this study revealed that individuals in the high-depressive symptomatology group expected less complementary responses from significant others in friendly, dominant, and submissive situations. They expected more complementary responses from them in hostile situations. They also rated their expected responses from others as more undesirable than did individuals in the low-depressive symptomatology group. These findings seem to be congruent with cognitive and interpersonal theories of depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)