19-去甲类固醇激素检测方法研究进展

综述了19-去甲类固醇激素检测的筛选法、定量法和确证法,探讨了多残留同时检测试纸条和蛋白质芯片等最新技术。     

以甘草为原料的食品天然防腐剂的研制

采用不同的溶剂和提取条件,提取甘草中的抗菌有效成分,然后通过抑菌试验筛选出抗菌力最强的制剂,通过测定该制剂对常见食品污染菌的最小抑菌浓度(MIC),证实该制剂对多种常见的食品污染菌均有较强的抑制作用,保存试验证实本制剂能有效地延长食品的保质期。     

A comparison of 14C, 86Rb,and total excavation for determination of root distributions of individual plants

Individual grass (Bouteloua gracilis) and shrub (Gutierrezia sarothrae) plants were either excavated as monoliths on nail boards, exposed to ¹⁴CO₂, or stem-injected with ⁸⁶Rb to compare the ability of the techniques to determine horizontal and vertical distribution of roots. The vertical distribution or roots directly under plant centers obtained by coring most closely correlated with monolith root length. ¹⁴C activity greatly overestimated near-surface roots and underestimated deep roots. ⁸⁶Rb activity did not follow the pattern of geometric decrease in root biomass with depth. Comparisons of both isotopes with monolith root length, over both horizontal and vertical axes, indicated that ¹⁴C activity was consistently concentrated near the soil surface, and ⁸⁶Rb activity was highly variable and randomly distributed. ¹⁴C may better represent root activity than root mass, and stem-injection methods can result in nonuniform labeling of roots. Caution should be exercised when using tracers to infer root biomass distributions. Resource partitioning between shrubs and grasses is discussed in relation to soil water dynamics in this semiarid grassland.     

A Modification of Stone's Test for Trend for Binary Outcome

Stone (1988) suggested the “first isotonic regression estimator” as a tool for drawing inferences on possibly increased cancer case counts among several subregions around a putative source. He assumed the case counts to be Poisson distributed and therefore introduced a rare disease assumption into his approach. However, when analyzing cross sectional data one would rather refer to prevalence estimates among these subregions around a point risk source (for example the origin of chemical fallout). Therefore we applied antitonic regression estimation in Binomial distributions to derive a test statistic and a p value to test for a possible trend in the observed prevalence data around the putative source. The computation of this p value will be illustrated as well as severe difficulties concerning its interpretation. Further the Maximum Likelihood Ratio approach will be used to derive an alternative test statistic.     

Stretch Coding and Block Coding: Two New Strategies to Represent Questionably Aligned DNA Sequences

Most coding strategies that address the problem of questionable alignment (elision, case sensitive, missing, polymorphic, gaps as presence/absence matrix) conflict with phylogenetic principles, particularly those relating to the concept of homology (shared similiarity explained by common ancestry). In some cases, the test of conjunction is failed. In other cases, characters that are coded ambiguously can lead to character-state optimization in the terminal taxa that conflicts with the original observations. Only data exclusion and contraction avoid these pitfalls. In highly dissimilar sequences additional character states can represent the available information. Two new methods that accomplish this—block and stretch coding—are introduced here. These two new coding strategies are not in conflict with the test of conjunction and do not contradict the original observations. They are comparable to coding practices with morphological data once the intrinsic differences due to character-state identity and topographical identity have been taken into account. It is suggested that, of the three recoding methods, the one is selected that preserves the maximum potential phylogenetic information as measured with the minimum number of steps required for the particular part of the data matrix. Received: 1 August 2000 / Accepted: 10 July 2001