Variations of the chemical composition of clonal black tea (Camellia sinensis) due to delayed withering

The chemical composition of black teas (Camellia sinensis L) varies when the green leaf from which they are manufactured is withered physically to the same degree but for different periods. Caffeine contents progressively increase with prolonged withering time whereas theaflavins decrease due to prolonged withering. Although the sums of group I and group II volatile flavour compounds (VFC) decrease with prolonged withering time, the flavour index (expressed as group II VFC/group I VFC) increases due to prolonged withering. No significant changes were noted in the thearubigin levels with variation in withering time, but the tasters' evaluations were at a maximum for teas withered for 14 h. Subsequently the evaluation decreased with longer withering times.     

Variations in the leaf standard,chemical composition and quality of black tea (Camellia sinensis) due to plucking intervals

Green leaf standard, chemical composition and quality of black tea (Camellia sinensis (L) O Kuntze) change with plucking intervals. Long plucking intervals lead to poor leaf standard with a lot of mature leaves and lower theaflavins, the sum of volatile flavour compounds imparting a sweet flowery aroma (group II volatile flavour compounds), caffeine contents and tasters' evaluations of black tea. The sum of volatile flavour compounds imparting inferior, grassy, green flavour (group I volatile flavour compounds) to tea, however, increases with long plucking intervals.     

地市级地面数字电视发射机常见故障分析

随着中国加快推进地面数字电视（DTMB）无线覆盖工程的建设,提高技术人员对地面数字电视发射系统设备的维护维修水平、故障判断排除能力刻不容缓。本文结合由包头市微波总站建设的市级地面数字电视单频网项目,对其运行中常见的发射机故障进行了分析和总结。     

网络攻防模拟实验平台的设计与实现

针对网络攻防环境难以构建的难题,提出了基于虚拟环境的网络攻防模拟实验平台,给出了模拟实验平台的组成结构,分析了在该平台上开展网络攻防模拟实验过程和系统运行机制。分别对网络攻击子系统和网络防护子系统进行了详细设计,研究了两个子系统中采用的关键技术及实现方法。通过采用虚拟机技术,在服务器上虚拟出网络攻击和网络防护子系统,能够实现当前绝大多数的网路攻击操作以及网络防护的配置管理,能够为用户提供功能更为全面、性能更为优越、仿真程度更为逼真的网络攻防实验训练环境。     

变压器型式试验的样品组成和样品数量的确定(上)

研究和讨论了GB 19212.1-2003,5.2和附录B分别规定的单规格变压器的试验规则和"系列变压器的试验"规则,提出了确定变压器型式试验的样品组成和样品数量的一种可操作的方案.     

基于PUFS的不经意传输协议

不经意传输(OT, oblivious transfer）协议是密码学中的一个基本协议。基于物理不可克隆函数（PUF, physical unclonable function）给出物理不可克隆函数系统（PUFS, physical unclonable function system）的概念,并在此基础上提出一个新的不经意传输协议（POT, PUFS based OT）,最后在通用可组合（UC, universal composition）框架内给出POT协议抵抗静态敌手的安全性证明。相比于传统基于公钥加密的OT方案,POT协议不使用任何可计算的假设,而是基于PUFS的安全属性实现,因此在很大程度上减小了计算和通信开销。     

含油页岩不同极性试剂连续抽提物饱和烃组成特征

页岩中不同赋存状态原油的分离成为当前较为关注的问题。采用极性逐渐增强的正己烷、二氯甲烷和三氯甲烷对祁连山木里煤田钻孔的含油页岩样品进行连续抽提,对各抽提物分别做族组分和定量色谱—质谱分析。研究结果表明:正己烷冷浸泡抽提物主要为页岩内自由态烃类,以饱和烃为主;而三氯甲烷索氏抽提物则主要为吸附态烃类,其中极性组分含量高,且碳数较高的正构烷烃丰度高;随溶剂极性的增加,连续抽提物生标参数C_(29)ααα甾烷20S/(20S+20R)与C_(24)四环萜烷/C_(26)三环萜烷比值逐渐增加,而C_(21)/C_(23)三环萜烷比值逐渐减小,但C_(23)三环萜烷/C_(30)藿烷和C_(31)升藿烷22S/(22S+22R)比值基本保持不变,另外部分参数比值则表现为无规律性的变化;尽管各种抽提物烃类组成和分子参数存在一定的差异,但各类化合物分布模式和部分参数值差异很小,表明3种连续抽提物(不同赋存状态的烃类)均为页岩内本源烃,而非外来烃。     

M6断块中低孔隙度渗透率砂岩储层饱和度模型优选方法

通过M6断块19块中低孔隙度渗透率砂岩样品的岩电实验结果得出,地层因素和孔隙度总体表现出非阿尔奇关系的特征,直接沿用Archie公式计算含水饱和度不准确。在Archie公式的基础上,分析了岩电参数m、n的变化规律,当n为定值时,认为m是影响饱和度精度的关键参数,在实验结果中归纳出m受无效导电孔隙(有效孔隙与有效导电孔隙的差值)的影响较大,提出利用无效孔隙求取m,进而提高Archie公式求取饱和度的精度。基于等效岩石组分理论对岩石导电性的影响,利用遗传算法求解方程组中每块样品的比例系数k和临界饱和度Swc,总结出变化规律,依据EREM模型采用迭代法得到相应的饱和度。通过对比3种方法求取的结果,结合试油层段的束缚水饱和度,表明EREM模型得到的含水饱和度最接近实际地层情况,而变参数Archie公式计算的结果次之。研究认为EREM模型更适合于中低孔隙度渗透率砂岩储层的饱和度计算。     

常减压原油混炼装置的多目标协同优化

本文基于遗传算法开发了一套多目标协同优化策略,用以优化运行中的常减压原油混炼装置,同步优化了其经济效益、加热炉能耗和二氧化碳排放量三个目标函数,并且研究了三个目标函数之间的相互关系。本次研究通过软件集成实现优化算法的运行,当计算出最大经济效益、最小加热炉能耗和最小二氧化碳排放量时,即获得了Pareto解集,从而解决了炼厂的实际问题。优化结果表明,在维持现有加热炉负荷和二氧化碳排放量的基础上,通过调节原油混炼比,经济效益仍有较大的增长趋势。     

Antimicrobial effects of cinnamon bark oil on microbial composition and quality of grass carp (Ctenopharyngodon idellus) fillets during chilled storage

In this study, 11 essential oils were initially screened for antimicrobial activity against Aeromonas veronii, Acinetobacter johnsonii, Shewanella putrefaciens, and Pseudomonas jessenii. Cinnamon bark oil exhibited the highest antimicrobial activity and was used as a natural preservative in grass carp fillets stored at 4 ± 1 °C. Sensory assessment, total volatile basic nitrogen (TVB-N), color, biogenic amines, adenosine triphosphate (ATP)-related compounds, K-value, and presence of microbiota were analyzed during storage. Cinnamon bark oil treatment was found to be effective in enhancing organoleptic quality, inhibiting microbial growth, and delaying the increase of TVB-N, putrescine, cadaverine and K-value. Based on sensory analysis, shelf-life of grass carp fillets was 8 days for the control and 12 days for the treatment group. According to high-throughput sequencing, Aeromonas and Pseudomonas were the predominant microbiota in fresh grass carp. As storage time progressed, the microbial composition of both control and treatment samples became less diverse. Pseudomonas followed by Aeromonas were dominant in spoiled control samples. However, there were significant differences in microbial composition between control and treatment samples at the end of storage. Cinnamon bark oil treatment inhibited the growth of Aeromonas and Shewanella, and Pseudomonas was the only predominant microbiota found in spoiled treatment samples.