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排序方式: 共有207条查询结果,搜索用时 286 毫秒
91.
Oxidation ofR,R,R-α-tocopherol (vitamin E; TH) by peroxyl radicals generated from the azo initiator azobis(2,4-dimethylvaleronitrile) in acetonitrile, hexane, or in phospholipid liposomes yields 8a-(alkyldioxy)tocopherone adducts,
8a-(hydroxy)tocopherone, and their hydrolysis product α-tocopherolquinone TH oxidation also yields 4a,5-epoxy- and 7,8-epoxy-8a-(hydroperoxy)tocopherones
and their respective hydrolysis products 2,3-epoxy-α-tocopherolquinone and 5,6-epoxy-α-tocopherolquinone. Previous work indicates
that the distribution of TH oxidation products varies with reaction environment. We investigated the dependence of antioxidant
stoichiometry on TH oxidation product distribution for reactions in hexane, acetonitrile, and in phosphatidylcholine liposomes.
Yields of 8a-substituted tocopherones were highest in hexane and lowest in phosphatidylcholine liposomes. In contrast, yields
of epoxide products were highest in the liposome system and lowest in hexane. Yields of α-tocopherolquinone were similar in
all three systems. Antioxidant stoichiometry, measured by the inhibited autoxidation method, was approximately 2.0 peroxyl
radicals trapped per TH consumed in acetonitrile and in liposomes. In hexane, a slightly larger stoichiometric factor of approximately
2.5 was measured. This may, in part, reflect the generation of more reactive alkoxyl radicals in hexane. The reaction environment
thus markedly affects the balance between competing TH oxidation pathways but produces comparatively little effect on antioxidant
stoichiometry. These results imply that competing reaction pathways contribute similarly to the antioxidant chemistry of TH. 相似文献
92.
93.
M Heitkemper RL Burr M Jarrett V Hertig MK Lustyk EF Bond 《Canadian Metallurgical Quarterly》1998,43(9):2093-2098
Autonomic nervous system function was assessed in women with and without irritable bowel syndrome using frequency domain measures of heart rate variability. Women were interviewed and placed into the irritable bowel syndrome (N = 25) group based on history of diagnosis and self-report of current gastrointestinal symptoms. Women in the control group denied a history of chronic gastrointestinal symptoms (N = 15). Women were followed for one menstrual cycle with a symptom diary, and during mid-luteal phase they wore a Holter 24-hr electrocardiograph monitor. Women with irritable bowel syndrome demonstrated significantly lower vagal tone as measured by the high frequency spectrum relative to control women. In addition, women with irritable bowel syndrome had a flattened 24-hr pattern of heart rate variability, with significantly lower levels of vagal tone during sleep. These results suggest that systemic sympathovagal balance may be shifted in a subset of women with irritable bowel syndrome. 相似文献
94.
J.R. Stegeman A.L. Kyle B.L. Burr H.B. Jemison R.R. Davison C.J. Glover J.A. Bullin 《Petroleum Science and Technology》1992,10(4):767-794
Supercritical extraction with n-pentane was used to separate asphalt into distinct fractions having different physical and compositional properties. A pilot-scale supercritical unit capable of processing thirty kilograms of asphalt per day was designed and fabricated specifically for asphalt fractionation. The operation and design of the unit is similar to the ROSE (Residuum Oil Supercritical Extraction) process of Keer-McGee. This unit was used to separate asphalt into five different fractions ranging from soft greases to asphaltene-like solids. Supplemental room-temperature solvent fractionation of the hardest of these five using binary pentane/cyclohexane mixtures produces, a total of eight fractions. A variety of analyses provide chemical and physical ctauracterization of the fractions. These include: (1) Corbett Fractionation, (2) FT-IR spectroscopy, (3) size exclusion chromatography, (4) nickel and vanadium atomic absorption, and (5) viscosity 相似文献
95.
Given a real valued function f(X,Y), a box region B0⊆R2 and ε>0, we want to compute an ε-isotopic polygonal approximation to the restriction of the curve S=f−1(0)={p∈R2:f(p)=0} to B0. We focus on subdivision algorithms because of their adaptive complexity and ease of implementation. Plantinga & Vegter gave a numerical subdivision algorithm that is exact when the curve S is bounded and non-singular. They used a computational model that relied only on function evaluation and interval arithmetic. We generalize their algorithm to any bounded (but possibly non-simply connected) region that does not contain singularities of S. With this generalization as a subroutine, we provide a method to detect isolated algebraic singularities and their branching degree. This appears to be the first complete purely numerical method to compute isotopic approximations of algebraic curves with isolated singularities. 相似文献
96.
Faulwetter JL Burr MD Cunningham AB Stewart FM Camper AK Stein OR 《Water science and technology》2011,64(10):2089-2095
Floating islands are a form of treatment wetland characterized by a mat of synthetic matrix at the water surface into which macrophytes can be planted and through which water passes. We evaluated two matrix materials for treating domestic wastewater, recycled plastic and recycled carpet fibers, for chemical oxygen demand (COD) and nitrogen removal. These materials were compared to pea gravel or open water (control). Experiments were conducted in laboratory scale columns fed with synthetic wastewater containing COD, organic and inorganic nitrogen, and mineral salts. Columns were unplanted, naturally inoculated, and operated in batch mode with continuous recirculation and aeration. COD was efficiently removed in all systems examined (>90% removal). Ammonia was efficiently removed by nitrification. Removal of total dissolved N was ~50% by day 28, by which time most remaining nitrogen was present as NO(3)-N. Complete removal of NO(3)-N by denitrification was accomplished by dosing columns with molasses. Microbial communities of interest were visualized with denaturing gradient gel electrophoresis (DGGE) by targeting specific functional genes. Shifts in the denitrifying community were observed post-molasses addition, when nitrate levels decreased. The conditioning time for reliable nitrification was determined to be approximately three months. These results suggest that floating treatment wetlands are a viable alternative for domestic wastewater treatment. 相似文献
97.
Christine M. Anderson‐Cook Michael S. Hamada Tom Burr 《Quality and Reliability Engineering International》2016,32(7):2415-2433
This article considers the analysis of designed experiments when there is measurement error in the true response or so‐called response measurement error. We consider both additive and multiplicative response measurement errors. Through a simulation study, we investigate the impact of ignoring the response measurement error in the analysis, that is, by using a standard analysis based on t‐tests. In addition, we examine the role of repeat measurements in improving the quality of estimation and prediction in the presence of response measurement error. We also study a Bayesian approach that accounts for the response measurement error directly through the specification of the model, and allows including additional information about variability in the analysis. We consider the impact on power, prediction, and optimization. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
98.
A case of spontaneous colocutaneous fistula arising from the transverse colon is reported and the literature is reviewed. 相似文献
99.
J. P. Kass W. O. Lundberg G. O. Burr 《Journal of the American Oil Chemists' Society》1940,17(3):50-53
The linoleic acid content of a series of seed fats was determined by the thiocyanometric and the tetrabromide-precipitation
methods in a search for isomeric linoleic acids. The results indicated the presence of only one form of linoleic acid. The
tetrabromide number was shown to be affected by the pronounced solubility of alpha tetrabromostearic acid in the other bromides
and in the solid acids, its determination therefore being of only limited value. The thiocyanogen numbers of pure linoleic
and linolenic acids were found to be empirical values differing markedly from the theoretical constants, requiring a revision
of the accepted equations for the calculation of the per cent concentration of the unsaturated acids in oils and mixed fatty
acids.
Aided by grants from the National Livestock and Meat Board and the Graduate School of the University. Presented before the
13th convention of the American Oil Chemists’ Society in Chicago, October 6, 1939. Assistance in the preparation of these
materials was furnished by the personnel of Work Projects Administration, Official Project No. 65-1-71-140, Sub-project No.
325. 相似文献
100.
An experimental procedure for determining the relation between the number of stored holograms and the raw bit-error rate (BER) (the BER before error correction) of a holographic storage system is described. Compared with conventional recording schedules that equalize the diffraction efficiency, scheduling of recording exposures to achieve a uniform raw BER is shown to improve capacity. The experimentally obtained capacity versus the raw-BER scaling is used to study the effects of modulation and error-correction coding in holographic storage. The use of coding is shown to increase the number of holograms that can be stored; however, the redundancy associated with coding incurs a capacity cost per hologram. This trade-off is quantified, and an optimal working point for the overall system is identified. This procedure makes it possible to compare, under realistic conditions, system choices whose impact cannot be fully analyzed or simulated. Using LiNbO(3) in the 90 degrees geometry, we implement this capacity-estimation procedure and compare several block-based modulation codes and thresholding techniques on the basis of total user capacity. 相似文献