Carbon/ceramics composites — Preparation and properties

Fabrication methods for carbon/ceramics composites were established by using two different processes of hot-pressing and pressureless sintering without any binder phase. In the hot pressing method, some boron compounds were found to be an effective aid for sintering and graphitization of coke powder above 2000°C under some pressure. When the content of boron compound such as B₄C was high, graphite/B₄C composites could be fabricated. If some other ceramic powder such as NbC, TiC or TaC was mixed in addition to the B₄C, three component composites with graphite matrix could be obtained. In pressureless sintering method, raw coke carbon powder was ground for a long time to be transformed in to a sinterable and non-graphitizing-type carbon powder. From a mix of ceramic powders such as SiC or B₄C with the ground coke powder, the composites of carbon/SiC or carbon/SiC/B₄C systems could be fabricated by heat-treatment under normal pressure.Some properties of the graphite samples and carbon/ceramic composites were investigated. It was found that their mechanical properties were much better than those of conventional graphite samples and the resistance to oxidation and corrosion was also excellent. It is suggested that the composites could be applied as bearing or mechanical seals both for use in high temperature environments and as machine parts in contact with some molten metals.     

Biomimetic Glucose Trigger-Insulin Release System Based on Hydrogel Loading Bidentate β-Cyclodextrin

Initiated by the specific binding between D-glucose and biological receptors, the human body has a delicate metabolic system to regulate blood D-glucose levels, but failing to release insulin would induce hyperglycemia or type I diabetes. While insulin delivery is an effective form of hyperglycemia therapy, the self-regulated triggering of insulin release for on-demand supplementation remains inadequate. Here, a biomimetic glucose trigger-insulin release system, that is, a bidentate β-cyclodextrin-based hydrogel with preloaded insulin is presented; the dual self-regulated system shows a specific D-glucose response to realize accurate monitoring and simultaneous on-demand trigger insulin release. The specific binding between D-glucose and the bidentate β-cyclodextrin induces the release of protons, causing macroscopic swelling of the hydrogel, subsequently triggering the on-demand and long-term supplementation of insulin. On the contrary, isomers of D-glucose, such as D-fructose and D-galactose, cause shrinking of the hydrogel, and retard insulin release. In-vivo studies in type I diabetic mice model ascertain that although the bidentate β-CD hydrogel is preloaded with short-activity insulin, it exerts long-activity control of blood glucose level over 12 h.     

Vinylation of phenol by acetaldehyde: A new reaction for the synthesis of o-vinylphenol

A new catalytic reaction for the single-step synthesis of o-vinylphenol from phenol and acetaldehyde in the gas phase is investigated in this work. A search for an efficient catalyst was made. The best results were obtained with a modified Cr₂O₃ catalyst supported on γ-Al₂O₃. The effect of content of Cr₂O₃ and potassium as a modifying additive was studied. It was shown that the catalyst containing 13% Cr₂O₃ and 1% K makes it possible to obtain o-vinylphenol with a selectivity of 100% referred to phenol and up to 87% referred to acetaldehyde. The influence of reaction conditions on the activity, selectivity and stability of catalyst operation was elucidated.     

Fire modeling of an emerging fire suppression system

Self-contained fire extinguishers are a robust, reliable and minimally invasive means of fire suppression for gloveboxes. Test methodology has been developed (experiments and computations) to predict fire induced tube wall failure in small scale compartments such as gloveboxes. A small scale test apparatus has been developed to characterize tube wall temperature and breakage properties. Computational tools have been used to better understand experiments. The heat release rate and heat flux have been accurately predicted because the forward predicted temperatures closely matched the experimentally measured values. Data generated from computational modeling of fire phenomena helps to identify the limitations of self-contained fire extinguishers.     

高氯酸盐在食品中的暴露情况及检测技术的研究进展

环境污染物高氯酸盐对食品安全和人体健康存在巨大威胁,近年来在食品和健康领域引起了人们的广泛关注。本文介绍了高氯酸盐对人体的危害,总结了高氯酸盐在国内茶叶、蔬菜、乳粉和水等食品中的暴露情况和欧盟等国家或组织对食品中高氯酸盐含量的限定,重点评述了高氯酸盐的8种检测方法,展望了未来的研究方向,以期为以后高氯酸盐的快速检测、标准制定和食品中的含量限定提供借鉴。     

亚麻籽油在煎炸过程中的品质变化

本文研究了常规煎炸条件下,经过不同煎炸时间的亚麻籽油营养成分、理化指标及有害物质含量,并通过主成分分析对其煎炸性能进行了综合评价。结果表明:未经煎炸的亚麻籽油不饱和度达81.77%,其α-亚麻酸的含量为47.50%,是一种富含多不饱和脂肪酸、高营养价值的食用油。亚麻籽油在170 ℃连续煎炸60 h（5 d）过程中,亚麻籽油的色泽、酸价、过氧化值、折光指数、羰基价、极性组分、生育酚含量、脂肪酸组成均有显著（P<0.05） 变化,煎炸全程没有产生苯并（α）芘;5种主要脂肪酸（α-亚麻酸、油酸、亚油酸、棕榈酸、硬脂酸）含量均呈下降趋势,C17:0以下的五种饱和脂肪酸（辛酸、癸酸、月桂酸、肉豆蔻酸、棕榈酸）含量均呈逐渐升高的趋势,其余脂肪酸呈下降趋势。通过煎炸性能分析,煎炸35 h后的亚麻籽油的酸价超过国家限量,其他项目均在国家限量范围以内,经综合评估30 h基本到达亚麻籽的煎炸使用极限,在30 h的煎炸时间内是一种健康良好的煎炸用油。     

甘草、黄芪、党参中27种重金属及微量元素含量变化的研究

目的研究甘草、黄芪、党参原药材及饮片中27种重金属及微量元素的含量变化。方法样品采用湿法消解后,经电感耦合等离子体质谱法测定,并采用PASW Statistics 18.0软件进行聚类分析。结果27种重金属及微量元素线性关系良好,线性范围为0~200μg/L(r≥0.9978),检出限为0.00147~6.252 mg/kg,精密度值在0.3%~0.7%范围内,稳定性相对标准偏差值在1.6%~5.6%范围内。9批甘草、黄芪、党参原药材及饮片中27种元素树状聚类分析可以将样本分为4类。结论该方法操作简便、分析快速、灵敏度高,适用于甘草、黄芪、党参原药材和饮片中重金属及微量元素的测定。     

膨化食品中菌落总数测定结果的不确定度评定

目的对膨化食品中菌落总数检测结果进行不确定度评定,确保检测结果的准确可靠。方法根据GB 4789.2-2016《食品安全国家标准食品微生物学检验菌落总数测定》、SN/T 4091-2015《食品微生物学测量不确定度评估指南》和JJF1059.1-2012《测量不确定度评定与表示》,对膨化食品中的菌落总数进行测定,对产生不确定度的来源进行分析,并对其不确定度进行评定。结果对不确定度的分量进行量化和合成,合成不确定度为0.0295,扩展不确定度为0.0617。该批样品菌落总数的置信区间范围为1.1×10~4≤X≤1.4×10~4 CFU/g。结论影响膨化食品中菌落总数不确定度的主要因素是样品重复测量引入的不确定度。     

气相色谱串联质谱法测定白酒中的甲醇含量

利用气相色谱串联质谱（GC-MS/MS）技术,建立白酒中的甲醇的定性定量检测方法。样品无需前处理直接进样,采用Agilent DB-FFAP毛细管柱（30 m×2.5 mm,2.5 μm）,柱温采用程序升温,电子电离源（EI）为离子源,分流比为40∶1,质谱离子源温度230 ℃,四极杆温度为150 ℃,多反应监测（MRM）模式进行定量分析。经检测,甲醇在0.2～200.0 mg/L质量浓度范围内线性关系良好,相关系数R2均＞0.995,方法检出限为0.1 mg/L,定量限为0.5 mg/L,加标回收率为89.17%～98.52%,精密度试验结果相对标准偏差（RSD）为1.5%～4.2%。与国标方法相比,该方法简单、快速、准确、灵敏度高,可以应用于白酒中甲醇含量的定性定量测定,适用于白酒监督检测及质量控制。     

三七药材中微生物污染的研究

目的:对三七药材微生物污染情况进行分析和研究,探讨三七药材微生物污染的主要种类,为灭菌工艺的进一步研究提供理论支撑。 方法: 参照2015年版《中国药典》四部通则1105、1106的方法,并结合传统生化和基质辅助激光解吸电离飞行时间质谱(MALDI-TOF-MS)对纯化的菌落进行鉴定。最后,运用SPSS 18.0软件对数据进行进一步地统计和分析。 结果: 三七药材在经过100℃、30min热处理后,需氧菌总数呈现均匀性地下降,芽孢杆菌属、水生拉恩菌为三七药材污染概率较高的菌。结论: 在三七药材灭菌工艺的考察中,应该着重杀灭芽孢杆菌,为确保安全和药效,需要结合多种灭菌方法。