排序方式: 共有74条查询结果,搜索用时 0 毫秒
71.
针对柴油机气门故障的诊断样本少和非线性数据特征等问题,最小二乘法的支持向量机(LSSVM)能够较好地进行诊断研究,但由于惩罚因子[C]和内核参数[σ]的选取对诊断结果影响较大,有必要对其进行参数优化,因此提出了基于二进制微分进化算法(BDE)的最小二乘法支持向量机算法。利用柴油机气门振动信号作为数据,经小波变换作为模型特征,建立了基于BDE-LSSVM故障诊断模型,并与基于遗传和基于粒子群算法的LSSVM模型进行柴油机气门故障诊断的性能对比。比较结果证明,基于BDE优化的LSSVM模型在故障特征选取前后具有更好的适应度值和稳定度,故障分类准确性高且运算速度更快。 相似文献
72.
Patrick Trouillas Philippe Marsal Didier Siri Roberto Lazzaroni Jean-Luc Duroux 《Food chemistry》2006
Over the past decade, the chemical behaviour of flavonoids as antioxidants has become the subject of intense experimental research. In this paper, we use a quantum-chemical approach to shed light on the reactivity of two flavonoids, quercetin and taxifolin. We particularly focus on the 3-OH site and the role played by the 2,3-double bond in the reactivity of that site. In order to establish the most efficient theoretical methodology, different methods, either Hartree–Fock-based or derived from density functional theory, and different basis sets (from 6-311G(d) to 6-311++G(2d,p)) were tested on phenol and catechol, for which experimental bond dissociation enthalpy (BDE) values are available. It appears that (U)B3P86/6-311+G(d,p) is the most relevant method for BDE prediction of these phenolic compounds and it has, therefore, been used for an extensive study of the two flavonoids. 相似文献
73.
Zimmer KE Montaño M Olsaker I Dahl E Berg V Karlsson C Murk AJ Skaare JU Ropstad E Verhaegen S 《The Science of the total environment》2011,409(11):2040-2048
This study investigated the effects of two mixtures of persistent organic pollutants (POPs) on steroidogenesis in the H295R cell line. The two mixtures were obtained from the livers of burbot (Lota lota) caught in two Norwegian lakes (Mjøsa and Losna) with different contaminant profiles. Steroid hormone levels in the cell culture medium and mRNA levels of 16 genes involved in steroidogenesis were investigated. The crude Lake Mjøsa extract had to be diluted ten times more than the Lake Losna extract in order to prevent cytotoxicity. The ten times diluted Lake Mjøsa mixture had higher levels of DDT and derivates (∑ DDTs, 1.7 times) and brominated flame retardants (∑ BDEs and HBCD, 15-25 times) than the Lake Losna mixture, which, on the other hand, had higher concentrations of ∑ PCBs (1.5 times higher) and also of HCB, ∑ HCH isomers and ∑ chlordane isomers (5-20 times higher).In the cell culture media, only cortisol levels were increased at the highest exposure concentration to the Lake Mjøsa mixture, while both cortisol and estradiol levels were increased following exposure to the two highest Lake Losna mixture exposure concentrations. Testosterone levels decreased only at the highest exposure concentration of the Lake Losna mixture. Multivariate models suggested that ∑ PCBs, and to a lesser extent ∑ DDTs, were responsible for the cortisol responses, while estradiol and testosterone alterations were best explained by HCB and ∑ PCBs, respectively. Exposure to the mixtures generally increased mRNA levels, with smaller effects exerted by the Lake Mjøsa mixture than the Lake Losna mixture. It was concluded that both mixtures affected steroidogenesis in the H295R cells. Small differences in mixture composition, rather than the high content of brominated flame retardants in the Lake Mjøsa mixture, were suggested to be the most probable reason for the apparent differences in potencies of the two mixtures. 相似文献
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