电力变压器的动稳定

在变压器短路电动力的计算中,目前是以静态力代替动态力的方法来进行的。这不能适应变压器机械强度的要求。针对此问题,从电动力的基本理论出发,建立起变压器的动态数学模型,对变压器在短路电流作用下线圈产生的动态力进行了理论分析和计算,对在短路电流作用下的变压器线圈(器身)绝缘结构进行了初步研究,提出了动稳定的计算方法。     

Development of methods for the determination of vitamins A, E and β-carotene in processed foods based on supercritical fluid extraction: a collaborative study

New methodologies based on supercritical fluid extraction (SFE) have been developed for the determination of fat-soluble vitamins in processed foods. The results obtained so far indicate that SFE is well suited to extraction of fat-soluble vitamins from food products, although validation work is required to establish accuracy and precision. The vitamins investigated were A, E and β-carotene, and the processed foods were UHT milk, milk powder, minced meat, liver paste, infant formula, canned baby food and margarine. Extraction equipment employed analyte collection on either a solid-phase trap or in a solvent. After extraction, the samples were saponified and the vitamins determined using reversed-phase liquid chromatography with ultraviolet or fluorescence detection. Sample throughput was at least 12 samples day -1 , i.e. at least twice the number achievable with a conventional extraction methodology. The detection limits for the vitamins in different processed foods were well below 0.1 µg g -1 . Recoveries (in comparison with vitamin levels obtained using conventional solvent extraction) were close to 100% for experienced personal with access to modern automatic equipment. To reach this level, it was necessary to protect the vitamins with an antioxidant during the different steps of the analysis procedure, to add methanol or ethanol to the extraction cell to facilitate the analyte extraction from the food matrix, and when using a solid-phase trap, to employ a fractionated extraction-elution procedure to prevent breakthrough losses. The developed methods were tested in a validation exercise between five laboratories, which had taken part in the method development, and in an intercomparison between 10 laboratories including laboratories with less experience of vitamin determination. The within-laboratory RSD was generally ≤11%. The average of the between-laboratory relative standard deviation (RSD) was about 23% in the validation, and increased to about 40% in the intercomparison. Ruggedness tests performed at different steps of the project showed that different types and models of equipment did not give large differences in recoveries. Thus, the increasing RSD can largely be ascribed to differences in experience in vitamin analysis of the participants.     

Analysis of trans fatty acids in deep frying oils by three different approaches

Simulated frying experiments were performed on three different types of oils with French fries as the fried food. Comparison of frying oil samples was then made with their control counterparts (i.e. oil samples heated without food). Three different methods, gas chromatography (GC), attenuated total reflection (ATR) AOCS method Cd 14d-99 and attenuated total reflection negative second derivative absorbance (−2D ATR), were applied to quantify total trans fats. The total trans fats were found to be higher in the frying oil samples as compared to the control samples, which might be due to the presence of a high amount of trans fats in the pre-fried and frozen French fries. In general, the ATR AOCS method Cd 14d-99 produced lower amounts of trans fatty acids and the −2D ATR absorbance method produced higher amounts when compared with those obtained by gas chromatography.     

Fatty Acid Composition and Trans Fatty Acids in Crisps and Cakes in Turkey's Markets

In this study, trans fatty acid and fatty acid composition of 57 crisps and 50 cakes sold in the markets in Turkey were determined. C 18:1, oleic acid, was the major fatty acid in all crisps and cake samples. The percentages of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) ranged between 27.98–46.57, 35.73–47.57, and 9.86–35.90 g/100 g fatty acids in crisps and 35.41–54.03, 25.89–44.87, and 10.52–26.97 g/100 g fatty acids in cakes, respectively. Total trans fatty acids ranged from 0.02 to 1.35 g/100 g fatty acids in crisps and 0.00 to 5.05 g/100 g fatty acids in cakes, respectively.     

Colour research with architectural relevance: How can different approaches gain from each other?

Colour research from different scientific traditions start from different basic questions and use different methods and concepts. This makes it difficult to communicate and to judge result relevance in a wider perspective. Here we start from architects' need of colour knowledge and discuss recent studies of colour appearance and colour emotion, with and without explicit connection to architecture. We stress the need for further development and clarification of concepts and conclude that the multitude of studies with different approaches can be seen as cases, jointly adding to a widened and deepened understanding of colour. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Effect of Substitution of High Stearic Low Linolenic Acid Soybean Oil for Hydrogenated Soybean Oil on Fatty Acid Intake

High stearic, low α-linolenic acid soybean oil (HSLL) has been developed via traditional breeding to serve as a substitute for partially hydrogenated soybean oils used in food manufacturing. The purpose of this study was to estimate the impact on fatty acid intake in the United States if HSLL were substituted for partially hydrogenated soybean oils used in several food categories, including baked goods, shortenings, fried foods, and margarines. Using National Health and Nutrition Examination Survey (NHANES) data (1999–2002), baseline intakes of five fatty acids and trans fatty acids (TFA) were determined at the mean and 90th percentile of fat consumption. Then intakes of these fatty acids were determined after HSLL was substituted for 100% of the partially hydrogenated soybean oils used in these four food categories. The results show that baseline intake of stearic acid is 3.0% energy at the mean and 3.3% energy at the 90th percentile. Use of HSLL could increase stearic acid intake to about 4–5% energy. Mean intakes of TFA could decrease from 2.5 to 0.9% energy, and intake of palmitic acid would remain unchanged. Use of HSLL as a substitute for partially hydrogenated soybean oils would result in changes in the fatty acid composition of the US diet consistent with current dietary recommendations.