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1.
The boundary integral equation (boundary element) method of numerical stress analysis is used to compute stress concentration factors at the intersections between side branches and thick-walled tubes or pressure vessels. Cases of both circular and elliptical side branch cross sections are considered, the effect of the latter being to significantly reduce the maximum stresses generated under internal pressure. For the typical geometries considered, reductions of more than 20% are obtained at optimum ellipse aspect ratios of about 0·8. 相似文献
2.
The boundary integral equation (BIE) method of numerical stress analysis is shown to be a powerful technique for solving axisymmetric fracture mechanics problems of the types encountered in practice in pipes, tubes and pressure vessels. Comparisons with established analytical and finite element solutions for problems involving circumferential and penny-shaped cracks in round bars, spheres and hollow cylinders show that accurate values of stress intensity factors at the tips of cracks can be obtained by this method. The main advantage of the technique over the finite element method is the much reduced amount of labour required to prepare the mesh data, since in the BIE approach only the boundary of an axisymmetric component needs to be discretised into simple and relatively coarse line elements. 相似文献
3.
Squash, like other Cucurbitaceae, have unique sterol profiles that offer an excellent opportunity to examine the relationship
between sterol biosynthesis and plant growth. To determine the effect of sterol biosynthesis inhibition on squash growth,
Cucurbita maxima seedlings with and without cotyledons were subjected to increasing concentrations of the cycloartenol synthase
(EC 5.4.99.8) inhibitor 3β-(2-diethylaminoethoxy) androstenone (U18666A). Inhibition of shoot growth was concentration-dependent
(from 0, 2, 5, 10, and 20 μM); plants with intact cotyledons grew to 26.4, 23.7, 21.6, 20.0, and 15.6 cm, respectively, at
the above inhibitor concentrations, compared to 25.5, 19.4, 17.0, 12.0, and 11 cm for plants with severed cotyledons. In plants
with severed cotyledons, 10 and 20 μM U18666A caused rapid necrosis of the first two, newly emerged, primary leaves, and halted
new leaf formation. Secondary root formation was initially affected at all inhibitor concentrations regardless of whether
cotyledons were present or not. Vegetative tissue showed a decrease in the accumulation of the major squash sterol, 7, 22-stigmastadienol,
accompanied by increased accumulation of minor sterol components. Sterol profiles in cotyledons were unaltered. The data show
that sterols are crucial for maintaining plant growth and viability, but do not address the cotyledonary effect on growth
with respect to sterol biosynthesis.
Based on a paper presented at the Symposium on the “Regulation of Biosynthesis and Function of Isopentenoids”, Atlanta, Georgia,
May 1994. 相似文献
4.
R. F. Wilson W. P. Novitzky G. P. Fenner 《Journal of the American Oil Chemists' Society》1995,72(12):1425-1429
Fungal damage caused by pathogens such asFusarium, Cercospora, andPhomopsis can have a devastating impact on physical quality and farm price of soybeans. In some price-discount schedules, soybeans
may be rejected with as low as 5% fungal damage. Although the severity of this problem varies throughout the United States,
millions of bushels of fungus-damaged soybeans may be destroyed annually due to a lack of markets. The effect of fungal damage
on seed composition was evaluated to assess potential utility of highly damaged soybeans. Graded samples of the cv. Centennial
soybean were dried to 10% moisture and blended on a proportional weight basis to derive a series of treatments from 0 to 80%
fungal damage. A positive correlation was found between fungal damage and both protein and oil concentrations. This condition
was attributed to loss of residual seed mass. As a result, the protein concentration of defatted meal increased from ca. 54
to 66% over the range of 0 to 80% fungal damage. Mycotoxin contamination appeared to be insignificant in these high-protein
meals. Fixed colors in bleached, alkali refined oils were intensified by heat treatment prior to extraction. No significant
differences, however, were noted in total polar lipid content, phospholipid, or tocopherol composition among treatments of
up to 20% fungal damage. Oils from treatments of more than 40% fungal damage were more severely oxidized and could not be
degummed effectively. These data suggest that fungus-damaged soybeans may be blended with high-quality soybeans to alleviate
the chemical symptoms associated with unacceptable product quality. Thus, through various blend ratios, processors may consider
using fungus-damaged soybeans to gain economic advantage, especially when high-quality soybeans have lower protein concentration. 相似文献
5.
6.
International Journal of Fracture - A technique for improving the convergence rate of the Gauss-Seidel iterative procedure for finite element analysis is discussed. It is noted that this technique... 相似文献
7.
Stephen A. Fenner 《Theory of Computing Systems》2003,36(2):199-212
Abstract. We show that the counting classes AWPP and APP [FFKL], [L] are more robust than previously thought. Our results identify a sufficient condition for a language to be low for PP, and we show that this condition is at least as weak as other previously studied criteria. We extend a result of Köbler et al. by proving that all sparse co-C = P languages are in APP, and are thus PP-low. Our results also imply that AWPP ?eq APP, and thus APP contains many other established subclasses of PP-low, thereby reducing several different lowness results to membership in APP. We also show that AWPP and APP are Σ 0 2 -definable classes. Some of our results are reminiscent of amplifying certainty in probabilistic computation. 相似文献
8.
Kern S Singer H Hollender J Schwarzenbach RP Fenner K 《Environmental science & technology》2011,45(7):2833-2841
Transformation products (TPs) of chemicals released to soil, for example, pesticides, are regularly detected in surface and groundwater with some TPs even dominating observed pesticide levels. Given the large number of TPs potentially formed in the environment, straightforward prioritization methods based on available data and simple, evaluative models are required to identify TPs with a high aquatic exposure potential. While different such methods exist, none of them has so far been systematically evaluated against field data. Using a dynamic multimedia, multispecies model for TP prioritization, we compared the predicted relative surface water exposure potential of pesticides and their TPs with experimental data for 16 pesticides and 46 TPs measured in a small river draining a Swiss agricultural catchment. Twenty TPs were determined quantitatively using solid-phase extraction liquid chromatography mass spectrometry (SPE-LC-MS/MS), whereas the remaining 26 TPs could only be detected qualitatively because of the lack of analytical reference standards. Accordingly, the two sets of TPs were used for quantitative and qualitative model evaluation, respectively. Quantitative comparison of predicted with measured surface water exposure ratios for 20 pairs of TPs and parent pesticides indicated agreement within a factor of 10, except for chloridazon-desphenyl and chloridazon-methyl-desphenyl. The latter two TPs were found to be present in elevated concentrations during baseflow conditions and in groundwater samples across Switzerland, pointing toward high concentrations in exfiltrating groundwater. A simple leaching relationship was shown to qualitatively agree with the observed baseflow concentrations and to thus be useful in identifying TPs for which the simple prioritization model might underestimate actual surface water concentrations. Application of the model to the 26 qualitatively analyzed TPs showed that most of those TPs categorized as exhibiting a high aquatic exposure potential could be confirmed to be present in the majority of water samples investigated. On the basis of these results, we propose a generally applicable, model-based approach to identify those TPs of soil-applied organic contaminants that exhibit a high aquatic exposure potential to prioritize them for higher-tier, experimental investigations. 相似文献
9.
Model studies using geometrically similar 300-mm-diameter and 1,600-mm-diameter hydrodynamic separators operating with an underflow have confirmed earlier results indicating that a combination of Froude and Hazen scale laws should be used when predicting prototype separator performance. A hybrid equation is proposed to scale the model inflow rates. This equation provides a good fit to the observed prototype flow versus efficiency data. The need to scale particles using a Hazen scale for settling velocity and a Froude scale for flows is discussed. Treatment factors are calculated for the different particle sizes used, and these confirm the suitability of the device to remove particles with higher settling velocities while passing organic particles with low settling velocities forward to treatment when the device is configured as a grit separator. 相似文献
10.
When micropollutants degrade in the environment, they may form persistent and toxic transformation products, which should be accounted for in the environmental risk assessment of the parent compounds. Transformation products have become a topic of interest not only with regard to their formation in the environment, but also during advanced water treatment processes, where disinfection byproducts can form from benign precursors. In addition, environmental risk assessment of human and veterinary pharmaceuticals requires inclusion of human metabolites as most pharmaceuticals are not excreted into wastewater in their original form, but are extensively metabolized. All three areas have developed their independent approaches to assess the risk associated with transformation product formation including hazard identification, exposure assessment, hazard assessment including dose-response characterization, and risk characterization. This review provides an overview and defines a link among those areas, emphasizing commonalities and encouraging a common approach. We distinguish among approaches to assess transformation products of individual pollutants that are undergoing a particular transformation process, e.g., biotransformation or (photo)oxidation, and approaches with the goal of prioritizing transformation products in terms of their contribution to environmental risk. We classify existing approaches for transformation product assessment in degradation studies as exposure- or effect-driven. In the exposure-driven approach, transformation products are identified and quantified by chemical analysis followed by effect assessment. In the effect-driven approach, a reaction mixture undergoes toxicity testing. If the decrease in toxicity parallels the decrease of parent compound concentration, the transformation products are considered to be irrelevant, and only when toxicity increases or the decrease is not proportional to the parent compound concentration are the TPs identified. For prioritization of transformation products in terms of their contribution to overall environmental risk, we integrate existing research into a coherent model-based, risk-driven framework. In the proposed framework, read-across from data of the parent compound to the transformation products is emphasized, but limitations to this approach are also discussed. Most prominently, we demonstrate how effect data for parent compounds can be used in combination with analysis of toxicophore structures and bioconcentration potential to facilitate transformation product effect assessment. 相似文献