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991.
In order to demonstrate compliance with the overall migration limit given in amended EC Directive 90/128/EEC, overall migration tests are usually performed on the finished food packaging with food stimulants. For packaging converters, in particular, who thermoform a wide range of containers from an extruded sheet, the cost of testing for compliance can be prohibitive. However, the Directive also allows compliance to be demonstrated by use of a ‘more severe test’. In this study a ‘more severe test’ has been developed for PVC and VC/VA co-polymer materials involving extraction with methanol or a methanol/water mixture and evaporation to dryness. This procedure has been optimised so that it is simple and rapid to perform and gives slightly higher results for the extruded sheet compared to overall migration tests conducted with fatty and aqueous food simulants. Results are presented demonstrating the rapid extraction test to be a ‘more severe test’ and that it could be used by converters in conjunction with good manufacturing practice (GMP) to demonstrate compliance with the overall migration limit in a cost-effective way. © 1997 John Wiley & Sons, Ltd.  相似文献   
992.
While high-performance architectures have included some Instruction-Level Parallelism (ILP) for at least 25 years, recent computer designs have exploited ILP to a significant degree. Although a local scheduler is not sufficient for generation of excellent ILP code, it is necessary as many global scheduling and software pipelining techniques rely on a local scheduler. Global scheduling techniques are well-documented, yet practical discussions of local schedulers are notable in their absence. This paper strives to remedy that disparity by describing a list scheduling framework and several important practical details that, taken together, allow implementation of an efficient local instruction scheduler that is easily retargetable for ILP architectures. The foundation of our machine-independent instruction scheduler is a timing model that allows easy retargetability to a wide range of architectures. In addition to describing how a general list-scheduler can be implemented within the framework of our timing model, experimental results indicate that lookahead scheduling can profoundly improve a scheduler's ability to produce a legal schedule. Further experimental data shows that deciding to schedule a data dependence DAG (DDD) in forward or reverse order depends significantly upon that target architecture, suggesting the possibility of scheduling in each direction and using the best of the two schedules. In contrast, experiments demonstrate little difference in code quality for schedules generated by either instruction-driven or operation-driven schedulers. Thus, the inherent flexibility of operation-driven methods suggests including that approach in a retargetable instruction scheduler. List scheduling is, of course, a heuristic scheduling method. A variety of scheduling heuristics are presented. In addition, the paper describes a method, using a genetic algorithm search, to ‘fine-tune’ the weights of twenty-four individual heuristics to form a DDD-node heuristic tuned to a specific architecture. © 1998 John Wiley & Sons, Ltd.  相似文献   
993.
Transient gasification rates and fluid temperatures were measured for polydimethylsiloxane fluids ranging in viscosity from 0.65 cS to 60 000 cS in a nitrogen atmosphere at external radiant fluxes from 20 kW/m2 to 70 kW/m2. A detailed energy balance for each fluid sample was conducted to determine its global heat of vaporization. Two major energy loss corrections were identified and quantified. The absorption of incident radiation by the volatile products from short chain oligomers was measured and found to substantially reduce the incident flux to the sample surface; the energy loss due to re-radiation was determined to be a substantial factor in reducing the net heat flux to the sample for long chain length fluids. Other energy losses, e.g. heat loss to the substrate, were observed but were less significant. The average gasification rate for each fluid increased linearly with increasing external radiant flux. The global heat of gasification increases with an increase in the chain length (molecular weight) for the siloxane oligomers. These agreed well with calculated values. The global heat of gasification for 50 cS fluid is about 1200 kJ/kg and its value remains nearly constant for all higher molecular weight dimethylsiloxanes. Pyrolysis rates for siloxane fluids are very sensitive to trace catalysts. Measurements of the global heat of gasification for ultra-clean polymers resulted in significantly higher values (3000 kJ/kg). The gasification of siloxanes occurs via two modes or combinations thereof: (1) volatilization of molecular species native to the polymer, and (2) volatilization of thermal degradation products. The former process dominates for low molecular weight siloxanes (η<10 cS) and the latter process dominates for high molecular weight siloxanes (η>1000 cS). For the intermediate molecular weight siloxanes, both volatilization and degradation processes occur. © 1998 John Wiley & Sons, Ltd.  相似文献   
994.
The use of porous materials for the removal of traces of hydrogen sulphide from gas streams was investigated in this study. It was found that microporous carbons had the highest removal efficiency. This was due to the fact that carbons have extra potential for the oxidation of hydrogen sulphide while other sorbents remove the gas only by adsorption. The oxidative removal efficiency of microporous carbons was found to be a function of water vapour pressure, oxygen concentration and temperature. The mechanism of the reaction is discussed. © 1997 SCI.  相似文献   
995.
996.
The vital lipophilic dye N‐(3‐triethylammoniumpropyl)‐4‐[6‐(4‐(diethylamino)phenyl]hexatrienyl) pyridinium dibromide (FM 4‐64) was used to study the effect of ethanol stress and heat shock on endocytosis in the yeast Saccharomyces cerevisiae. Yeast cells stained with FM 4‐64 were placed in a culture chamber and the internalization of the dye was monitored by fluorescence microscopy during perfusion of the cells with fresh growth medium. In the absence of ethanol in the perfusion medium, the internalization of FM 4‐64 from the plasma membrane to the vacuolar membrane by yeast cells harvested from the exponential phase of growth was completed in 30 min. The presence of 6% (v/v) ethanol in the perfusion medium had no obvious effect on the internalization of FM 4‐64 from the plasma membrane, but did lead to an accumulation of the dye in endocytic intermediates. Consequently, vacuolar membrane staining was delayed. Cells stained with FM 4‐64 and subjected to heat shock displayed a similar effect, with endocytic intermediates becoming more prominent with the severity of the heat shock. For both ethanol stress and heat shock, vacuolar morphology altered from segregated structures to a single, large organelle. The findings of this study reinforce previous observations that ethanol stress and heat shock induce similar responses in yeast. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   
997.
998.
Triphenyl tetrazolium chloride (TTC) staining of individual isolated barley aleurone layers was carried out under aseptic conditions and the amount of formazan generated under a standardized incubation period was quantified. The nature of the tests minimized or excluded the influences of grain damage, ageing or contaminating microorganisms. Embryos from selected Triumph barley grains, having intensely or poorly staining aleurone layers, were grown on to maturity. Collected grain was analysed and embryos from the highest‐staining progeny from the high‐staining aleurone line and the lowest‐staining progeny of the low‐staining aleurone line were grown on to yield grain of the second selected generations. Aleurone layers of the high‐staining line continued to stain intensely, respired strongly, and generated large amounts of α‐amylase in response to gibberellic acid and embryos from these grains respired and grew vigorously, as did whole grains. In contrast, the aleurone layers of grains from the low‐staining line continued to stain poorly and respired weakly, generated little α‐amylase in response to gibberellic acid, the embryos respired slowly and lacked vigour and, like the whole grains, grew poorly. It is proposed that these results are the consequence of the selection procedure separating lines with superior and inferior mitochondria. If this apparently novel approach using TTC staining is confirmed as being valid, it opens a new way for plant breeders to select for more vigorous cereal lines.  相似文献   
999.
Macrophages and lymphocytes demonstrate metabolic plasticity, which is dependent partly on their state of activation and partly on the availability of various energy yielding and biosynthetic substrates (fatty acids, glucose, and amino acids). These substrates are essential to fuel-based metabolic reprogramming that supports optimal immune function, including the inflammatory response. In this review, we will focus on metabolism in macrophages and lymphocytes and discuss the role of fatty acids in governing the phenotype, activation, and functional status of these important cells. We summarize the current understanding of the pathways of fatty acid metabolism and related mechanisms of action and also explore possible new perspectives in this exciting area of research.  相似文献   
1000.
The headspace solid-phase microextraction (HS-SPME) technique combined with GC–MS was evaluated to study 33 selected flavour compounds released from chewing gum. The operating conditions of SPME were optimised, including different fibres (PDMS, DVB/CAR/PDMS, PA and PDMS/DVB), sample size, extraction time and temperature. The results indicated that while HS-SPME was a rapid and valuable technique, poor reproducibility occurred under all conditions. It was found that this deficiency could be alleviated by utilising mathematical modelling techniques, an approach which had not been previously used in the analysis of flavour compounds in chewing gum by HS-SPME. Compared to the instrumental analysis data themselves, the models provided more insights to the release behaviour of flavour compounds from chewing gum and the more reproducible kinetic rate constants might be used for comparing the release of different compounds or the same compound under different conditions.  相似文献   
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