Synergistic effects of multiple carbon fillers on the rheology of liquid crystal polymer based resins

Adding conductive carbon fillers to insulating thermoplastic resin increases composite electrical and thermal conductivity. Often, as much of a single type of carbon filler is added to achieve the desired conductivity, while still allowing the material to be molded into a bipolar plate for a fuel cell. In this study, varying amounts of three different carbons (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid crystal polymer. The rheology of resulting single filler composites was tested. In addition, the rheological properties of composites containing combinations of two different carbon fillers were studied via a factorial design. In all cases, viscosity increased with increasing filler volume fraction for all shear rates. Over the range of shear rates studied, the viscosity followed a shear‐thinning power law model. The factorial design results indicated that each of the single fillers and all of the two filler combinations caused a statistically significant increase in composite viscosity at a shear rate of 1,000 s⁻¹. The composites containing carbon black and synthetic graphite caused the largest increase in viscosity. It is possible that the highly branched, high surface area structure of carbon black ‘links’ with the synthetic graphite particles, which results in increased composite viscosity. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Hundreds of impossibility results for distributed computing

We survey results from distributed computing that show tasks to be impossible, either outright or within given resource bounds, in various models. The parameters of the models considered include synchrony, fault-tolerance, different communication media, and randomization. The resource bounds refer to time, space and message complexity. These results are useful in understanding the inherent difficulty of individual problems and in studying the power of different models of distributed computing. There is a strong emphasis in our presentation on explaining the wide variety of techniques that are used to obtain the results described.Received: September 2001, Accepted: February 2003,     

On the inherent weakness of conditional primitives

Some well-known primitive operations, such as compare-and-swap, can be used, together with read and write, to implement any object in a wait-free manner. However, this paper shows that, for a large class of objects, including counters, queues, stacks, and single-writer snapshots, wait-free implementations using only these primitive operations and a large class of other primitive operations cannot be space efficient: the number of base objects required is at least linear in the number of processes that share the implemented object. The same lower bounds are obtained for implementations of starvation-free mutual exclusion using only primitive operations from this class. For wait-free implementations of a closely related class of one-time objects, lower bounds on the tradeoff between time and space are presented.     

Evidence for flame extinguishment by thermal mechanisms

This paper presents an analysis of experimental flame and detonation extinguishment data published by a number of authors, including those in a companion paper. The maximum effectiveness observed for each of five common dry chemicals at small particle diameters is shown to be related to heat extraction from the flame by active endothermic sinks—heat capacity, fusion, vaporization, and decomposition. Larger particles are more stable in the flame and the reduced level of effectiveness observed is due principally to the only active sink—heat capacity.Evidence is presented to support two propositions: first, that the strong chemical inhibiting effects exhibited by many substances in flame velocity studies are effectively confined to low-concentration regimes; and second, that regardless of chemical effects, diffusion flames of the type studied are largely extinguished by thermal or heat extraction mechanisms at extinguishant concentrations that are quantitatively predicted by a simple heat balance and a predictable limit temperature.     

差异预处理对竹浆纤维分散性能的影响行为研究

纸浆纤维的分散性能直接影响机械法均质制备纳米纤维素的效率。本研究分析了生物酶解预处理、TEMPO氧化预处理和PFI磨浆预处理对竹浆纤维分散性能的影响。通过表征预处理纤维的表面形态和表面电荷,探讨了引起竹浆纤维分散性能差异的原因。结果表明,TEMPO氧化预处理和PFI磨浆预处理的竹浆纤维分散性好,生物酶解预处理的竹浆纤维分散性差;PFI磨浆预处理的纤维表面分丝帚化好;TEMPO氧化预处理的纤维具有较高的羧基含量和Zeta电位绝对值;0.5%CMC分散剂可以显著提高生物酶解预处理纤维的分散性。     

Molecular Markers in Maternal Blood Exosomes Allow Early Detection of Fetal Alcohol Spectrum Disorders

Prenatal alcohol exposure can cause developmental abnormalities (fetal alcohol spectrum disorders; FASD), including small eyes, face and brain, and neurobehavioral deficits. These cannot be detected early in pregnancy with available imaging techniques. Early diagnosis could facilitate development of therapeutic interventions. Banked human fetal brains and eyes at 9–22 weeks’ gestation were paired with maternal blood samples, analyzed for morphometry, protein, and RNA expression, and apoptotic signaling. Alcohol (EtOH)-exposed (maternal self-report) fetuses were compared with unexposed controls matched for fetal age, sex, and maternal race. Fetal brain-derived exosomes (FB-E) were isolated from maternal blood and analyzed for protein, RNA, and apoptotic markers. EtOH use by mothers, assessed by self-report, was associated with reduced fetal eye diameter, brain size, and markers of synaptogenesis. Brain caspase-3 activity was increased. The reduction in eye and brain sizes were highly correlated with amount of EtOH intake and caspase-3 activity. Levels of several biomarkers in FB-E, most strikingly myelin basic protein (MBP; r > 0.9), correlated highly with morphological abnormalities. Reduction in FB-E MBP levels was highly correlated with EtOH exposure (p < 1.0 × 10⁻¹⁰). Although the morphological features of FAS appear long before they can be detected by live imaging, FB-E in the mother’s blood may contain markers, particularly MBP, that predict FASD.     

Climate change,water management and stakeholder analysis in the Dongjiang River basin in South China

This article proposes a systematic analysis of water management and allocation on the scale of a river basin, considering climate impacts and stakeholder networks in the Dongjiang River basin in South China. Specific approaches are integrated to explore various subtopics. Findings indicate a slight increase of precipitation in the basin and strong fluctuations in this century due to climate extremes, which may lead to seasonal or quality-related water shortages. It is highlighted that alternative options for holistic water management are needed in the basin, and participatory water allocation mechanisms and establishment of a basin-wide management framework could be helpful.     

Validation of pepperoni process for control of Shiga toxin-producing Escherichia coli

The objective of this study was to compare the survival of non-O157 Shiga toxin-producing Escherichia coli (STEC) with E. coli O157:H7 during pepperoni production. Pepperoni batter was inoculated with 7 log CFU/g of a seven-strain STEC mixture, including strains of serotypes O26, O45, O103, O111, O121, O145, and O157. Sausages were fermented to pH ≤4.8, heated at 53.3°C for 1 h, and dried for up to 20 days. STEC strains were enumerated at designated intervals on sorbitol MacConkey (SMAC) and Rainbow (RA) agars; enrichments were completed in modified EC (mEC) broth and nonselective tryptic soy broth (TSB). When plated on SMAC, total E. coli populations decreased 2.6 to 3.5 log after the 1-h heating step at 53.3°C, and a 4.9- to 5-log reduction was observed after 7 days of drying. RA was more sensitive in recovering survivors; log reductions on it were 1.9 to 2.6, 3.8 to 4.2, and 4.6 to 5.3 at the end of cook, and at day 7 and day 14 of drying, respectively. When numbers were less than the limit of detection by direct plating on days 14 and 20 of drying (representing a 5-log kill), no more than one of three samples in each experiment was positive by enrichment with mEC broth; however, STEC strains were recovered in TSB enrichment. Freezing the 7-day dried sausage for 2 to 3 weeks generated an additional 1- to 1.5-log kill. Confirmation by PCR revealed that O103 and O157 had the greatest survival during pepperoni productions, but all serotypes except O111 and O121 were occasionally recovered during drying. This study suggests that non-O157 STEC s trains have comparable or less ability than E. coli O157 to survive the processing steps involved in the manufacture of pepperoni. Processes suitable for control of E. coli O157 will similarly inactivate the other STEC strains tested in this study.     

Reduction in resident microflora, and experimentally inoculated Salmonella enterica, on spinach leaves treated with vinegar and canola oil

In this study, we explored the use of vinegar, or vinegar and canola oil as a salad dressing, to reduce bacterial levels on spinach leaves. We found that incubation of spinach leaves with various types of vinegar substantially reduced the predominantly gram-negative microflora. A similar response was observed when spinach leaves were incubated with white vinegar mixed in various proportions with canola oil, as used in salad dressing. We assessed the effects of vinegar, or vinegar and oil, on spinach leaves that had been experimentally inoculated with a cocktail of Salmonella enterica strains. Allowing the mixture to sit at room temperature for at least 20 min resulted in a substantial reduction (up to 2.0 log CFU) in numbers of S. enterica. Vinegar and oil caused a limited reduction in CFU (0.5 log) for spinach leaves experimentally inoculated with a cocktail of Listeria monocytogenes strains. These findings suggest that mixing spinach leaves with vinegar and oil as a salad dressing can reduce the bacterial load associated with the spinach leaves, including Salmonella if it is present.