Thermal characterization of some products obtained by chemically modified poly(vinyl chloride) with phenol

The chemical modification of poly(vinyl chloride) (PVC) in reaction with phenol, in the absence of a catalyst and at temperatures within the range of 60°C and the boiling temperature of phenol (180°C), led to the reaction products with the general structure of a vinyl chloride–vinyl phenol copolymer. The synthesized polyphenols were thermally characterized using the following experimental techniques: thermo–optical analysis (TOA), thermogravimetry (TG), derivative thermogravimetry (DTG), and pyrolysis in combination with gas chromatography (P–GC). The PVC samples modified with phenol show a thermal stability lower than the original PVC sample. The glass transition temperatures (T_gs) increase with increased degree of chlorine substitution. The main pyrolysis products of the modified PVC samples are hydrocarbons with low boiling points (C₁–C₄), benzene, toluene, naphthalene, indan, and phenol. The semiquantitative estimation of the pyrolysis products of the synthesized samples led to the conclusion that the following structural element types can be present, statistically distributed along the chain: vinyl chloride and vinyl phenol units, acetylenic and ethylenic units, and indan type structures. © 1995 John Wiley & Sons, Inc.     

A buffer-inventory-based dynamic scheduling algorithm for multimedia-on-demand servers

We present a producer-consumer model of multimedia-on-demand (MOD) servers. The producer retrieves media data from a disk and places it into a set of buffers, while the consumer sends out the data in the buffers to the users. We develop for the producer a buffer-inventory-based dynamic scheduling (BIDS) algorithm that guarantees non-zero inventory and non-overflow of data in the buffers to meet the continuity requirement and no-loss of data for each media stream. The algorithm can deal with heterogeneous me dia streams as well as the transient circumstances upon service completions and arrivals of new requests. To smooth out the impact of bursty data of variable-bit-rate media streams and therefore increase the maximum admissible load of requests, we also introduce into the scheduling scheme a time-scale-dependent peak consumption rate and a virtual cycle time. Based on BIDS, an effective admission control mechanism can be easily established by checking two simple conditions respectively on the overall system load and buffer size. Our algorithm is very easy to implement. Experiments carried out with an actual disk system and real video stream data verify that it is more robust compared to static scheduling algorithms previously proposed in the literature, especially when handling variable-bit-rate media streams.     

The exact order of starlikeness of uniformly convex functions

A Briot-Bouquet differential subordination is used to determine the exact order of starlikeness for the class of uniformly convex functions. In the solution we use some integral representations, which offer the possibility of correct estimation.     

Faithful representation of stimuli with a population of integrate-and-fire neurons

We consider a formal model of stimulus encoding with a circuit consisting of a bank of filters and an ensemble of integrate-and-fire neurons. Such models arise in olfactory systems, vision, and hearing. We demonstrate that bandlimited stimuli can be faithfully represented with spike trains generated by the ensemble of neurons. We provide a stimulus reconstruction scheme based on the spike times of the ensemble of neurons and derive conditions for perfect recovery. The key result calls for the spike density of the neural population to be above the Nyquist rate. We also show that recovery is perfect if the number of neurons in the population is larger than a threshold value. Increasing the number of neurons to achieve a faithful representation of the sensory world is consistent with basic neurobiological thought. Finally we demonstrate that in general, the problem of faithful recovery of stimuli from the spike train of single neurons is ill posed. The stimulus can be recovered, however, from the information contained in the spike train of a population of neurons.     

Polyester/lignosulfonate blends with enhanced properties

The compatibility of poly(ethylene terephthalate) and its copolymer containing isophthalate units with epoxy-modified lignin has been studied. The following methods have been used: DSC, thermogravimetry, IR spectroscopy, contact angle measurements and dielectric properties determination. The optimum compatibility ratios and the necessity of a partial crosslinking with 4,4′-diaminodiphenylmethane to obtain a stable morphology have been established.     

Synthesis and adsorption properties of nanocrystalline ferrites for kinetic modeling development

Nanocrystalline ferrites are known to be used in different applications, including industrial wastewater management. For environmental water issues, one of the most widely applied techniques is the adsorption of pollutants. The adsorption capacity of Congo red (CR) dye on different MFe₂O₄ (M = Co²⁺, Mg²⁺, Mn²⁺, Ni²⁺, and Zn²⁺) ferrites, synthesized by coprecipitation method, was determined. Specific isotherms and kinetic models were used to characterize the adsorption process. Interesting results were obtained for MgFe₂O₄ with adsorption capacity ranging from 39% up to 70% dependent on the initial dye concentration. Furthermore, an artificial intelligence model based on neural network was developed in order to model the adsorption rates followed by the generation of 3D adsorption rate models for each type of synthesized ferrite. These models were obtained in order to provide information about the particle-dye system`s kinetics at various initial CR concentration. Specific techniques were used to characterize the functionalized magnetic particles.     

Variational eigenerosion for rate-dependent plasticity in concrete modeling at small strain

In the context of eigenfracture scheme, the work at hand introduces a variational eigenerosion approach for inelastic materials. The theory seizes situations where the material accumulates large amounts of plastic deformations. For these cases, the surface energy entering the energy balance equation is rescaled to favor fracture, thus energy minimization delivers automatically the crack-tracking solution also for inelastic cases. The minimization approach is sound and preserves the mathematical properties necessary for the Γ-limit proof, thus the existence of (local) minimizers is guaranteed by the Γ-convergence theory. Although it is not possible to demonstrate that the obtained minimizers are global, satisfactory results are obtained with the local minimizers provided by the method. Furthermore, with the goal of addressing the constitutive behavior of concrete, a Drucker-Prager viscoplastic consistency model is introduced in the microplane setting. The model delivers a rate-dependent three-surface smooth yield function that requires hardening and hardening-rate parameters. The independent evolution of viscoplasticity in different microplanes induces anisotropy in the mechanical response. The sound performance of the model is illustrated via numerical examples for both rate-independent and rate-dependent plasticity.     

Municipal web sites accessibility and usability for blind users: preliminary results from a pilot study

Despite the existing regulations and standards at national and international level, web content is still difficult to use, if not completely unusable, for visually impaired people. This paper presents the evaluation results for three municipal web sites. A combined method, based on conformance review and expert review, was employed. Overall, the results reveal a low conformance to WCAG2 and many accessibility and usability problems. The content is not properly structured, and this reduces usability even for sighted user. The analysis of the evaluation data suggests that many accessibility barriers could be avoided by adopting a user-centered approach during web design.     

Development of New Cordierite‐Based Refractory Coatings for Casting Applications

In this study, new refractory coatings based on synthesized cordierite for the casting applications were developed. The investigation included starting raw materials characterization, synthesis of the cordierite, design of the refractory coating as final product, and its application testing. The obtained results pointed out that coating suspension sediment stability was crucial quality parameter. Design and optimization of the coatings composition, with controlled rheological properties included, were achieved by application of different coating components, namely different suspension agents and by alteration of the coating production procedure. Cordierite, used as filler, was obtained by means of synthesis in the solid‐state reaction on the basis of talc, kaolin, and alumina. The investigation showed that the application of these particular types of water/alcohol‐based coatings has positive influence on surface quality and structural and mechanical properties of the castings of aluminum alloys obtained by casting into sand molds by means of evaporable models method, that is, evaporate pattern casting process.