The effect of photo-oxidation on thermal and fire retardancy of polypropylene nanocomposites

Nanocomposites of polypropylene-graft-maleic anhydride/clay were prepared by melt blending in an extruder mixer. The nanoscale dispersion of the clay in the polymer was analysed by wide-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of XRD and TEM showed that the nanocomposites obtained were a kind of intercalated-delaminated structures side by side with different dominant states, depending on the clay used and on the processing conditions. The consequences of photo-oxidation on the thermal stability and fire retardant properties of the nanocomposites were investigated using thermogravimetric analysis and cone calorimetry tests. It appeared that this degradation dramatically affected the important properties of the nanocomposites. A loss of thermal stability and fire retardant performance was observed. This was ascribed to scission reactions that occurred during the oxidative degradation prior to thermal and fire tests.     

Analysis of protein adsorption and binding at biosensor polymer interfaces using X-ray photon spectroscopy and scanning electrochemical microscopy

We describe a method, based on X-ray photoelectron spectroscopy (XPS) measurements, to assess the extent of protein adsorption or binding on a variety of different muTAS and biosensor interfaces. Underpinning this method is the labeling of protein molecules with either iodine- or bromine-containing motifs by using protocols previously developed for radiotracer studies. Using this method, we have examined the adsorption and binding properties of a variety of modified electrodeposited polymer interfaces as well as other materials used in muTAS device fabrication. Using polymer interfaces modified with poly(propylene glycol) (PPG) chains, our results indicate that a chain of at least approximately 30 monomer units is required to inhibit nonspecific adsorption from concentrated protein solutions. The XPS methodology was also used to probe specific binding of avidins and enzyme conjugates thereof to biotinylated and mixed biotin/PPG-modified polymer interfaces. In one example, using competitive binding, it was established that the mode of binding of a peroxidase-streptavidin conjugate to a biotinylated modified polymer interface was primarily via the streptavidin moiety (as opposed to nonspecific binding via the enzyme conjugate). XPS evaluation of nonspecific and specific peroxidase-streptavidin immobilization on various functionalized polymers has guided the design and fabrication of functionalized interdigitated electrodes in a biosensing muTAS device. Subsequent characterization of this device using scanning electrochemical microscopy (SECM) corroborated the adsorption and binding previously inferred from XPS measurements on macroscale electrodes.     

Metabolic efficiency during arm and leg exercise at the same relative intensities

This study was conducted to compare gross efficiency (GE), net efficiency (NE), work efficiency (WE), and delta efficiency (DE) between arm crank and cycle exercise at the same relative intensities. Eight college-aged males underwent two experimental trials presented in a randomized counterbalanced order. During each trial subjects performed three intermittent 7-min exercise bouts separated by 10-min rest intervals on an arm or semirecumbent leg ergometer. The power outputs for the three bouts of arm crank or cycle exercise corresponded to 50, 60, and 70% of the mode-specific VO2peak. GE, NE, and WE were determined as the ratio of Kcal.min-1 equivalent of power output to Kcal.min-1 of total energy expended, energy expended above rest and energy expended above unloaded exercise, respectively. DE was determined as the ratio of the increment of Kcal.min-1 of power output above the previous lower intensity to the increment of kcal.min-1 of total energy expended above the previous lower intensity. GE and NE did not differ between arm crank and cycle exercises. However, WE was lower (P < 0.05) during arm crank than cycle exercise at 50, 60, and 70% VO2peak. DE was also lower (P < 0.05) during arm crank than cycle exercise at delta 50-60 and at delta 60-70% VO2peak. It is concluded metabolic efficiency as determined by work and delta efficiency indices was lower during arm crank compared with cycle exercise at the same relative intensities. These findings add to the understanding of the difference in metabolic efficiency between upper and lower body exercise.     

Cognitive networks: adaptation and learning to achieve end-to-end performance objectives

In this article we advance the idea of a cognitive network, capable of perceiving current network conditions and then planning, learning, and acting according to end-to-end goals. Cognitive networks are motivated by the complexity, heterogeneity, and reliability requirements of tomorrow's networks, which are increasingly expected to self-organize to meet user and application objectives. We compare and contrast cognitive networks with related research on cognitive radios and cross-layer design. By defining cognitive networks, examining their relationship to other technologies, discussing critical design issues, and providing a framework for implementation, we aim to establish a foundation for further research and discussion     

Choline,ergosterol and tocopherol content of some norwegian lichens

21 species of common Norwegian lichens were investigated for their content of choline, ergosterol and tocopherols. The choline content varied 20-fold between species, but most lichens were good sources of choline. Law but significant concentrations of ergosterol were found in many of the samples, indicating the value of these plants as a reserve of vitamin D. a-Tocopherol was the only member of the vitamin E group detected in the lichens. The contents were higher than those found in blue-green algae, the phycobionts of many lichens. A new technique for the determination of ergosterol, based on chromatography on alumina-containing paper, was developed.     

Diversity of the heterotrophic microbial populations for distinguishing natural mineral waters

In the recent years the consumption of natural mineral waters has risen all over the world, becoming a usual alternative for tap water and other beverages. Natural mineral waters are complex environments containing a high diversity of autochthonous microbiota. The identification and characterization of this indigenous microbiota may help to detect changes occurring in the different steps of the bottling process and take preventive measures before the bottled water arrives to the consumer. The aims of this study were to describe the bacterial heterotrophic populations in natural mineral waters with a cultivation-dependent method and determine whether their autochthonous microbiota were specific enough to be clearly distinguished from that of other natural mineral waters with a phenotypic-based method. For this purpose, water from three independent Spanish springs was sampled in two seasons (winter and summer) and heterotrophic aerobic bacterial strains were isolated at two temperatures (22 ± 2°C and 36 ± 2°C) on R2A agar. Isolates were phenotyped biochemically with Php-48 plates (Bactus AB, Sweden), and the indexes of diversity and similarity between populations were calculated. The 16S rRNA gene of the most representative strains of each biochemical cluster was sequenced for its identification. Finally, a ten-fold cross-validation method was assayed for the identification of the origin of a natural mineral water when phenotyping a set of isolates. High levels of diversity were found at all sites. One of the sources was found to present less diversity due to a confirmed contamination with Pseudomonas aeruginosa. The study of the similarities showed that growing temperatures and seasons caused significant differences in structures and composition at the sources. In addition, several bacterial species were isolated and identified, some of them rarely isolated in natural mineral waters, revealing the complexity and lack of knowledge of these ecosystems. Consequently, the applied phenotypic methodology was found to be feasible for differential identification of microbiota in these environments. Moreover, the experimental model assayed was strong enough to identify the origin of a natural mineral water. It may thus be possible to confirm that the evaluation of diversity of heterotrophic aerobic bacterial populations could be applied to identify bottled water sources.     

Enumeration of bifidobacterial populations with selective media to determine the source of waterborne fecal pollution

Bifidobacteria are one of the main groups of bacteria found in the intestine of humans and other animals. They have been proposed as indicators to identify the source of fecal pollution, since certain Bifidobacterium spp. are found only in humans. However, species identification remains difficult, and has limited their practical application. In this study, a simple assay based on the ratio of sorbitol-fermenting bifidobacteria to total colony forming units on Human Bifido Sorbitol Agar (HBSA) medium was developed. Ratios greater than 0.2 were indicative of human fecal pollution while animal-derived slaughterhouse effluent had a ratio less than 0.05. This is a low-cost, easily implemented approach which may have wide applicability when characterizing recent and high concentrated fecal pollution.     

Comparative photo‐oxidation under natural and accelerated conditions of polypropylene nanocomposites produced by extrusion and injection molding

The photo‐oxidation behavior under natural and accelerated conditions of polypropylene/layered silicate nanocomposite is studied in this article. The nanocomposites are prepared via simple melt mixing (extrusion and injection molding). The structure obtained is very dependent on the preparation mode and the modified clay used; mostly, exfoliation structure is produced. The nanocomposites start their photo‐degradation earlier than the control samples polypropylene and polypropylene‐graft‐maleic anhydride with a higher oxidation rate for specimen produced by injection molding. This is explained by the presence of organiphilic‐modified montmorillonite layers that trap the oxygen, increasing the oxygen pressure in the bulk and leading to a decrease of the induction period. Contrary to the control samples that display auto acceleration in their oxidation kinetics, the nanocomposites show a slight tendency to a plateau indicating a slowing down of the photo‐oxidation process. This is ascribed to oxygen starvation that occurs in the nanocomposite. The acceleration factor is found to be higher for the nanocomposite comparatively of the control samples. With the aid of SF₄ and NO treatments, the mechanism of photo degradation was found to be similar in PPgMA and its nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007