Evaluation of epifluorescence image analysis of biofilm growth on stainless steel surfaces

Biofilm growth of Bacillus subtilis, Pseudomonas fragi, Pediococcus inopinatus and Listeria monocytogenes was studied on stainless steel surfaces at room and low temperatures to evaluate the results of traditional hygiene measures. The results were compared with those of image analysis of stainless steel surfaces in an epifluorescence microscope. Statistical analyses were carried out to determine the variations between the conventional cultivation swab method, the glycocalyx amount obtained using swabbing, and the values of the areas of the biofilm, slime and cells. As a general rule, old biofilms showed total counts at approximately the same levels as the young biofilm. The results showed that temperature affected the results for all strains except B. subtilis. The strains of Pe. inopinatus and Ps. fragi showed increased attachment at 6°C and L. monocytogenes at 25°C. The biofilm slime was more easily detached than the cells. The results indicated that the traditional swab method is not reliable for the measurement of biofilm formation on surfaces.     

用于荧光光谱测定的微量固体粉末样品制样优化*

为满足微量固体粉末荧光检测要求,采用薄层制样法,改变黏结剂种类、黏结剂的用量、涂层厚度以及后处理方法来进行其制样工艺优化。 结果表明:以聚乙烯醇做黏结剂、1∶5的固液比、在50 ℃烘干30 min、涂片次数3层的薄层制样优化工艺可满足荧光固体测样的要求。采用t检验比较固体样品池装样和薄层制样法的荧光检测结果发现两者无显著性差异,薄层制样优化工艺的需样量较样品池减少90%。     

Distinguishing between Decaffeinated and Regular Coffee by HS-SPME-GC×GC-TOFMS,Chemometrics, and Machine Learning

Coffee, one of the most popular beverages in the world, attracts consumers by its rich aroma and the stimulating effect of caffeine. Increasing consumers prefer decaffeinated coffee to regular coffee due to health concerns. There are some main decaffeination methods commonly used by commercial coffee producers for decades. However, a certain amount of the aroma precursors can be removed together with caffeine, which could cause a thin taste of decaffeinated coffee. To understand the difference between regular and decaffeinated coffee from the volatile composition point of view, headspace solid-phase microextraction two-dimensional gas chromatography time-of-flight mass spectrometry (HS-SPME-GC×GC-TOFMS) was employed to examine the headspace volatiles of eight pairs of regular and decaffeinated coffees in this study. Using the key aroma-related volatiles, decaffeinated coffee was significantly separated from regular coffee by principal component analysis (PCA). Using feature-selection tools (univariate analysis: t-test and multivariate analysis: partial least squares-discriminant analysis (PLS-DA)), a group of pyrazines was observed to be significantly different between regular coffee and decaffeinated coffee. Pyrazines were more enriched in the regular coffee, which was due to the reduction of sucrose during the decaffeination process. The reduction of pyrazines led to a lack of nutty, roasted, chocolate, earthy, and musty aroma in the decaffeinated coffee. For the non-targeted analysis, the random forest (RF) classification algorithm was used to select the most important features that could enable a distinct classification between the two coffee types. In total, 20 discriminatory features were identified. The results suggested that pyrazine-derived compounds were a strong marker for the regular coffee group whereas furan-derived compounds were a strong marker for the decaffeinated coffee samples.     

电子监控探测人物身高的分析

依据重庆市公安局刑警大队提供的监控数据,分析监控器摄象时影响身高的因素,利用多元回归的原理建立了三个预测身高的回归模型,并对其作出了优劣评价,最终确定出犯罪嫌疑人实际身高与其在照片上的像高、电子监控器距地面的高度、人与监控器的垂直和偏离距离四个因素的最优回归模型.该最优模型的可决系数R2=0.9931,预测身高与实际身高有97.89%的误差点在±0.02m范围内,73.09%在±0.01m范围内.并对最优模型中的预测身高与实际身高进行配对样本的t检验,两者间无显著性差异.     

关于“t,F显著性检验应用中的一个问题”之我见

在应用ｔ、Ｆ检验时，要严格地区分方差齐性与方差非齐性两种不同的情况。在两种不同的情况下，计算总方差与自由度所用的公式是不同的。     

硫代硫酸钠标准溶液配制中标定基准物质的优化选择

对硫代硫酸钠标准溶液配制实验中不同基准物质的标定效果进行了对比研究,结合试剂用量、反应时间、显著性检验等分析说明不同基准物质所产生的结果:重铬酸钾、碘酸钾、溴酸钾均可实现对硫代硫酸钠溶液的标定。其中溴酸钾作为标定的基准物质时,试剂用量少,反应时间短,实验费用低且终点易于观察。双侧t检验符合统计学要求,更适用于硫代硫酸钠溶液标定,有望引入学生实验。     

化学探头法与荧光光谱法测定水中溶解氧量

探讨了化学探头法和荧光光谱法测定水中溶解氧的关系。分别用F检验和t检验对两组数据进行了比较,结果表明两组数据的精密度和系统误差都没有显著差异,两种方法测定溶解氧的相对标准偏差(RSD,n=9)分别为0.35%,0.33%。进而又探讨了溶解氧与NaCl含量、温度之间的关系,结果表明溶解氧含量随NaCl含量的增加、温度的升高而逐渐降低。     

广东省3G业务潜在用户群调查分析

本文对广东省广州,深圳,中山三市3G潜在用户群问卷调查的数据进行统计分析,了解其现有手机消费习惯,以及对3G业务的认识,取向.研究结果有助于运行商及政策制定者了解3G潜在用户群对3G业务的态度及期望,从而制定符合消费者需求的3G业务开发策略,保证3G业务运营的成功开发。     

环保型酸式自动滴定管的研制与应用

介绍了一种环保型酸式自动滴定管的结构、特点及使用方法。这种滴定管节省试剂,废液排放量极小,操作简单、省时,克服了常规微量滴定管精密度差、装液难、零点和滴定终点不易控制的缺点。通过数理统计方法,将环保型酸式自动滴定管与标称容量为50mL的常规酸式滴定管平行测定结果进行了比较,试验证明,该滴定分析的精密度、准确度不仅与50mL常规酸式滴定管相当,而且操作性还优于50mL常规酸式滴定管。     

碰撞打靶实验中的能量损失及不确定度估算

对碰撞打靶实验中的能量损失,先作理论估算,再通过实验验证.讨论二者不一致时如何获得修正值以及测量值的显著性检验问题.还讨论了实验的不确定度估算问题.得出的结论是碰撞打靶实验过程中的能量损失大部分源于非弹性碰撞,其余主要来自空气阻力.