Concentration profile of glass fiber bundles in epoxy‐based gradient composites during centrifugation

The short fiber bundles separated from the machining waste of a printed circuit board (PCB) manufacturing plant were used in preparing functionally graded composites using polysulfide‐modified epoxy resin. The graded material was developed using centrifugation technique. The centrifugation time was varied to obtain different gradient profiles. The concentration profile was then compared with the theoretical HD model (Hashmi‐Dwivedi model), which was modified to accommodate the changes in the shape of suspending particles. A shape factor was introduced in terminal velocity estimation. The simulated results are in agreement with the experimental trends. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Storage space estimation for videos using fading channels

In this paper, we propose a model for estimating the buffer storage for providing continuous delivery of the video data to users. The model incorporates the jitter delay, which is a switching delay between two consecutive video segments being transmitted through a logical channel. The jitter delay is assumed to be Rayleigh distributed as it characterizes the channel fading.     

Review Carbon fibers for composites

An attempt has been made to review and analyze the developments made during last few decades in the field of high performance carbon fibers. The focus is primarily on high technology sector, which includes aerospace and nuclear engineering or other areas, where the large scale use of carbon fibers is driven by maximum performance and not by cost factors. We have identified and suggested some specific areas for future research in order to minimize the gap between theoretical and practically realized tensile strengths and other mechanical properties of carbon fibers.     

Development and electrical characterization of carbon soot filled polyester graded composites

In this paper a novel method to develop carbon soot filled polyester graded composites has been reported. Dielectric measurements were conducted on these graded composites in the temperature range from 30 to 150 °C and in the frequency range 1–10 kHz to study and analyse the effect of temperature and frequency variation on dielectric constant (ε′) and dielectric dissipation factor (tan δ). It was observed that an increase of carbon soot content increased the dielectric constant gradually, which established the formation of a graded structure. Dielectric data were analysed using existing theoretical models. It was observed that Maxwell–Garnett model fits best for the dielectric data obtained experimentally for these graded composites. Compensation law confirmed the semi conducting behaviour of the composites. Cole–Cole plot for graded composites showed dielectric relaxation probably due to dipolar groups of polyester and interfacial polarization that occurred in the composites.     

Ethanol and LPG sensing characteristics of SnO<Subscript>2</Subscript> activated Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> thick film sensor

The sensing response of pure and SnO₂ activated Cr₂O₃ to ethanol vapours and liquefied petroleum gas (LPG) has been investigated. Fine particles of commercial chromium oxide powder were selected and deposited as thick film to act as a gas sensor. The sensor surface has been activated by tin dioxide, on surface oxidation of tin chloride. The concentration of tin chloride solution, used as activator, was varied from 0 to 5% and its effect on gas response, selectivity and operating temperature has been studied. It was found that response to ethanol vapours significantly improved, whereas response to LPG remained unaffected. Moreover, operating temperature remains unchanged both for LPG and ethanol vapours.     

Preparation and charge transport studies of chemically synthesized polyaniline

Polyaniline doped with p-toluenesulfonic acid was synthesized using in situ chemical oxidation method for optimization of synthesis parameters. For p-toluenesulfonic acid/aniline molar ratio of 5, the obtained polymer exhibits highest value of the electrical conductivity. The electrical conductivity of polyaniline doped with p-toluenesulfonic acid was measured in the temperature range of 30–300 K. The conductivity of polyaniline was found to increase with rise in the temperature. The measured conductivity versus temperature data was fitted with Arrhenius model, variable range hopping (VRH) model and Kivelson model in order to investigate the charge transfer mechanism in polyaniline. It is shown that conductivity observed over wide temperature range of 30–300 K follows Kivelson model obeying power law behavior.     

Oxygen index: Correlations to other fire tests

An investigation has been carried out of the limiting oxygen index (LOI) test. A review of the literature shows that, although there is abundant information on the test, it is not clear that its results correlate well with those of any other test, or indeed with those of real fires. Theoretical considerations indicate that the test could be improved by using it with bottom ignition rather than with the standard top ignition. A number of materials were tested in the cone calorimeter and in the LOI, and various correlations were attempted. In general, correlations between some of the cone calorimeter properties measured and the inverse of the LOI made sense. These correlations were not, however, sufficiently sensitive, even when investigating small effects on a single base polymer system, to justify using the LOI as a proxy for the cone in any way. The LOI is likely to continue to be used extensively. This work suggests that quality control and, possibly, mechanistic or other flame-retardant additive studies, are its only applications where the results can be justified.