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排序方式: 共有794条查询结果,搜索用时 31 毫秒
51.
Marcel Karabín Alena Rýparová Lukáš Jelínek Thomas Kunz Philip Wietstock Frank‐Jürgen Methner Pavel Dostálek 《Journal of the Institute of Brewing》2014,120(3):212-219
One of the critical issues regarding the quality of beer is the change in its chemical composition that occurs during storage. Decomposition of iso‐α‐acids results in an undesirable decrease in bitterness as well as a deterioration in the sensory profile of the beer. These changes are caused by the susceptibility of iso‐α‐acids to degradation owing to the influence of reactive oxygen species and light. The aim of this study was to investigate the influence of storage conditions (temperature, light) on the degradation of iso‐α‐acids during aging, with the main focus on monitoring the relationship between the turnover of iso‐α‐acids, the sulphur dioxide content and the antioxidative potential of stored beer as measured by electron spin resonance spectroscopy. In agreement with previous investigations, a significant decrease in the content of bitter compounds (up to 18 % relative to the original level, depending on storage conditions) was observed. A significant decrease in the antioxidant potential of beer was recorded simultaneously and the data confirmed a strong correlation between these parameters. The decline in beer bitterness could become a marker for estimating oxidative damage during storage. Copyright © 2014 The Institute of Brewing & Distilling 相似文献
52.
羟基磷酸钙ESR信号热衰退中的二级动力学过程 总被引:2,自引:1,他引:1
人工合成羟基磷酸钙和牙珐琅化石的等温退火实验表明,它们的ESR信号的热衰退系一级和二级动力学过程的混合效应。二级衰退常数强依赖于温度。粗测其值在280℃时为10^-19g/s量级。二级过程的存在对ESR法测早期古人类遗址动物牙化石年龄的影响需进一步研究。 相似文献
53.
纳米管钛酸的ESR特性及其可见光照的影响 总被引:5,自引:2,他引:3
本报道了纳米管钛酸在真空-0.1MPa、温度100℃的条件下,经过不同时间处理后的ESR特性及其可见光照的影响.发现纳米管钛酸经一定处理后,不经光照即出现g=2.003 ESR信号,该信号是由捕获一个电子的氧空位(Vo)产生的,此信号随着处理时间的延长而增强;在532nm的可见光照射下,随着光照时间的延长信号强度随之增加,达到一定强度值后,不再随光照时间的延长而增加;光源关闭后,信号强度又逐渐减小,但不能恢复到原来信号强度的水平. 相似文献
54.
LDO降压转换器的稳定性分析 总被引:7,自引:4,他引:3
通过对LDO降压转换器的原理分析,并借助频域的傅里叶分析方法,对其稳定性和频率响应进行了深入的理论研究,得到了提高系统稳定性的补偿方法。频率响应和瞬态响应的仿真结果表明,这种方法显著改善了LDO降压转换器的频率响应,并极大地提高了其稳定性。 相似文献
55.
F. Szöcs 《Journal of food science》2002,67(6):2079-2082
ABSTRACT: We used electron spin resonance (ESR) to investigate free radicals in wheat seeds in air or under vacuum in relation to annealing temperature. Annealing in the 100 to 200 °C range resulted in concentration increases of free radicals in samples. A greater increase was observed for experiments carried out in air than for those under vacuum. Most free radicals occurred in the grain surface layer. The bran contained a concentration of free radicals 100 times greater than that of the white grain portion. The reaction of stable free radicals in bran was also studied during thermal decomposition of dibenzoyl peroxide at high pressure. They reacted with shortlived peroxyl radicals in bran to produce a nonradical product. 相似文献
56.
57.
Z. I. Ali 《应用聚合物科学杂志》2007,103(6):3461-3469
Low‐density polyethylene (LDPE) composites modified with a resin based on ethylene/methacrylic acid copolymer (surlyn) and/or citric acid were electron beam‐irradiated and investigated by electron spin resonance (ESR) at room temperature. ESR studies were carried out directly after irradiation and after various time intervals up to 72 h postirradiation. The irradiated samples showed the ESR spectrum of seven lines that was assigned to the formation of allyl radical. The nature and yield of the allyl radical of the different LDPE samples were analyzed as a function of time after irradiation. Also, the radical concentration, decay, decay rate, and kinetics of radical decay were evaluated. Fourier transform infrared (FTIR) analysis at a series of different temperatures upon cooling from room temperature to ?175°C and the reverse heating to +125°C was also carried out. The structural changes while cooling and heating of LDPE samples were investigated using FTIR spectrometry. The results showed that cooling of unirradiated LDPE samples to ?175°C results in a decrease of the intensities of IR bands. However, heating the samples from ?175°C up to +125°C led to a consequence increase in the intensities of the IR bands. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3461–3469, 2007 相似文献
58.
Radicals formed by irradiation by high energy electron in ethylene–propylene–hexadiene terpolymer (EP–HD) have been studied using electron spin resonance (ESR). Two methods were used to analyse the different radicals formed by irradiation: firstly, classical low temperature irradiations were carried out, secondly, rapid quenching in liquid nitrogen of the material after high dose rate irradiation.
The feasibility and the efficiency of the latter method to observe short-lived radicals have been demonstrated. This type of experiment provides unique information concerning the rate of production and the rate of reaction of radicals. 相似文献
59.
60.
M. Houssa G. PourtoisM. Meuris M.M. Heyns V.V. Afanas’evA. Stesmans 《Microelectronic Engineering》2011,88(4):383-387
The identification of a nontrigonal Ge dangling bond at SiO2/Si1−xGex/SiO2 heterostructures and its electrical activity are discussed, both from experimental and theoretical points of view. This dangling bond is observed from multifrequency electron-spin resonance experiments performed at 4.2 K, for typical Ge concentrations in the range 0.4 ≤ x ≤ 0.85. The electrical activity of this defect is revealed from capacitance-voltage characteristics measured at 300 and 77 K, and is found to behave like an acceptor defect. First-principles calculations of the electronic properties of this Ge dangling bond indicate that its energy level approaches the valence band edge of the Si1−xGex layer as the Ge content increases, confirming its acceptor-like nature. 相似文献