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排序方式: 共有210条查询结果,搜索用时 15 毫秒
1.
Black W.Z. Woodruff G.W. Kovalchik P.G. Duda F.T. 《Power Delivery, IEEE Transactions on》1994,9(3):1209-1216
This paper presents a mathematical model that is capable of calculating the ampacity of a wide variety of power cable designs consisting of an arbitrary number of layers on a cable reel. The model considers round cables with copper conductors. The validity and accuracy of the ampacity model were verified by comparing the predicted temperature distribution within the reel with measured temperatures collected during an extensive testing program conducted at the US Bureau of Mines (USBM). The mathematical model predicted a temperature distribution within the cable layers that was very close to the measured variation in temperature. The value of the program is illustrated by calculating ampacities for several copper conductor sizes 相似文献
2.
3.
Two high‐head dams on the Elwha River in Washington State (USA) have changed the migratory patterns of resident and anadromous fish, limiting Pacific salmon to the lower 7.9 km of a river that historically supported large Pacific salmon runs. To document the effects of the dams prior to their removal, we measured carbon and nitrogen stable isotope ratios of primary producers, benthic macroinvertebrates, and fish, and water chemistry above, between and below the dams. We found that δ15N was significantly higher in fish, stoneflies, black flies, periphyton and macroalgae where salmon still have access. Fish and chloroperlid stoneflies were enriched in δ13C, but the values were more variable than in δ15N. For some taxa, there were also differences between the two river sections that lack salmon, suggesting that factors other than marine‐derived nutrients are structuring longitudinal isotopic profiles. Consistent with trophic theory, macroalgae had the lowest δ15N, followed by periphyton, macroinvertebrates and fish, with a range of 6.9, 6.2 and 7.7‰ below, between, and above the dams, respectively. Water chemistry analyses confirmed earlier reports that the river is oligotrophic. Phosphorous levels in the Elwha were lower than those found in other regional rivers, with significant differences among regulated, unregulated and reference sections. The removal of these dams, among the largest of such projects ever attempted, is expected to facilitate the return of salmon and their marine‐derived nutrients (MDN) throughout the watershed, possibly altering the food web structure, nutrient levels and stable isotope values that we documented. Published in 2010 by John Wiley & Sons, Ltd. 相似文献
4.
Anna Sowiska-Baranowska Magdalena Maciejewska Paulina Duda 《International journal of molecular sciences》2022,23(14)
The goal of this study was application of corn starch and ground walnut shells in various amounts by weight as biofillers of natural rubber (NR) biocomposites. Additionally, ionic liquid 1-butyl-3-methylimidazolium chloride (BmiCl) and (3-aminopropyl)-triethoxysilane (APTES) were used to increase the activity of biofillers and to improve the curing characteristics of NR composites. The effect of biofillers used and their modification with aminosilane or ionic liquid on the curing characteristics of NR composites and their functional properties, including crosslink density, mechanical properties in static and dynamic conditions, hardness, thermal stability and resistance to thermo-oxidative aging were investigated. Starch and ground walnut shells were classified as inactive fillers, which can be used alternatively to commercial inactive fillers, e.g., chalk. BmiCl and APTES were successfully used to support the vulcanization and to improve the dispersion of biofillers in NR elastomer matrix. Vulcanizates with starch, especially those containing APTES and BmiCl, exhibited improved tensile properties due to the higher crosslink density and homogenous dispersion of starch, which resulted from BmiCl addition. NR filled with ground walnut shells demonstrated improved resistance to thermo-oxidative aging. It resulted from lignin present in walnut shells, the components of which belong to polyphenols, that have an antioxidant activity. 相似文献
5.
M. Tremblay M. Kammer H. Lange S. Plattner C. Baumgartner J.A. Stegeman J. Duda R. Mansfeld D. Döpfer 《Journal of dairy science》2018,101(8):7311-7321
Currently, cows with poor metabolic adaptation during early lactation, or poor metabolic adaptation syndrome (PMAS), are often identified based on detection of hyperketonemia. Unfortunately, elevated blood ketones do not manifest consistently with indications of PMAS. Expected indicators of PMAS include elevated liver enzymes and bilirubin, decreased rumen fill, reduced rumen contractions, and a decrease in milk production. Cows with PMAS typically are higher producing, older cows that are earlier in lactation and have greater body condition score at the start of lactation. It was our aim to evaluate commonly used measures of metabolic health (input variables) that were available [i.e., blood β-hydroxybutyrate acid, milk fat:protein ratio, blood nonesterified fatty acids (NEFA)] to characterize PMAS. Bavarian farms (n = 26) with robotic milking systems were enrolled for weekly visits for an average of 6.7 wk. Physical examinations of the cows (5–50 d in milk) were performed by veterinarians during each visit, and blood and milk samples were collected. Resulting data included 790 observations from 312 cows (309 Simmental, 1 Red Holstein, 2 Holstein). Principal component analysis was conducted on the 3 input variables, followed by K-means cluster analysis of the first 2 orthogonal components. The 5 resulting clusters were then ascribed to low, intermediate, or high PMAS classes based on their degree of agreement with expected PMAS indicators and characteristics in comparison with other clusters. Results revealed that PMAS classes were most significantly associated with blood NEFA levels. Next, we evaluated NEFA values that classify observations into appropriate PMAS classes in this data set, which we called separation values. Our resulting NEFA separation values [<0.39 mmol/L (95% confidence limits = 0.360–0.410) to identify low PMAS observations and ≥0.7 mmol/L (95% confidence limits = 0.650–0.775) to identify high PMAS observations] were similar to values determined for Holsteins in conventional milking settings diagnosed with hyperketonemia and clinical symptoms such as anorexia and a reduction in milk yield, as reported in the literature. Future studies evaluating additional clinical and laboratory data, breeds, and milking systems are needed to validate these finding. The aim of future studies would be to build a PMAS prediction model to alert producers of cows needing attention and help evaluate on-farm metabolic health management at the herd level. 相似文献
6.
Variable temperature 13C nuclear magnetic resonance (NMR) spinlattice (T1) relaxation studies were carried out using pure ethylbenzene, tetrahydrofuran, and methanol samples. Single correlation times, determined from an isotropic rotational diffusion model, were correlated successfully using the free-volume equation. The solvent free-volume parameters estimated in this study were comparable with those determined from viscosity measurements. The solvent free-volume parameters estimated in this study were then used to correlate and predict diffusion behavior of polymer/solvent systems. The results were comparable with those using the parameters from viscometry when the Vrentas–Duda free-volume diffusion model was used. 相似文献
7.
Rémi Nguyen Mathilde Amouroux Alexis Duda Zéphirin Mouloungui 《Journal of the American Oil Chemists' Society》2020,97(7):679-689
The aim of this study was to develop an improved general method for detecting and quantifying mixtures of hydroxy acids and other products of glycerol oxidation in aqueous media, to prevent the confusions that can occur due to similarities and interactions between these compounds depending on media conditions. Standard potential products of glycerol oxidation—glycerol, glyceraldehyde, dihydroxyacetone, glyceric acid, lactic acid, glycolic acid, glyoxylic acid, oxalic acid, tartronic acid, and mesoxalic acid—were analyzed by high-performance liquid chromatography (HPLC) and quantitative 13C nuclear magnetic resonance (NMR), in mixtures of known composition. The results obtained were concordant with the known compositions tested. HPLC was more accurate than quantitative 13C NMR for simple mixtures, but 13C NMR was required for complex mixtures containing dihydroxyacetone and glycerol, oxalic acid and mesoxalic acid, or glyoxylic acid and tartronic acid, pairs of compounds not well separated or detected by HPLC. As proof-of-concept, an unknown mixture generated by glycerol oxidation was analyzed by HPLC and quantitative 13C NMR. The results obtained were concordant and allowed accurate determination of the composition of the sample, which contained mesoxalic acid as the major product, with oxalic acid, tartronic acid, and glyceric acid as by-products. 相似文献
8.
The clinical course was studied as was the condition of cardiohemodynamics in 126 patients with different variants of diphtherial myocarditis (DM) versus 23 patients with unspecific infectious and allergic myocarditis (UIAM). Early DM in the majority of cases runs a moderately severe or severe course because of a stronger--by comparison with late DM and UIAM--predisposition to cardiac insufficiency, sinus bradycardia and heart blocks as well as of a moderately severe systolic dysfunction of the left ventricle (LV), as evidenced by Echo-CG. Late DM runs, on the whole, a mild course, and is associated with minimal LV systolic function inadequacies. 相似文献
9.
The problem of the migration of impurities from plastic containers has been analyzed, and the effect of the outward diffusion of the container contents on the impurity migration has been considered. The system of equations describing the coupled diffusion problem has been solved using finite-difference methods, and an analytical solution has been developed for the initial stages of the mass transfer process. It was found that the outward diffusion of the container contents can exhibit a large effect on the migration of impurity if the ratio of the diffusivity of the container contents to the diffusivity of the impurity exceeds 100. Sufficiently large values of this diffusivity ratio and of the impurity partition coefficient can minimize the buildup of undesirable impurities in the contents of a plastic container. 相似文献
10.