Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Tensile properties and fracture mechanisms of SiCf/TC17 composites at room temperature and 773 K were studied. The results show that fiber elastic deformation and matrix yielding contributed to the shapes of the stress-strain curves of SiCf/TC17 composites, which were the bilinear appearance at 298 K and the slight curvature at 773 K. Major fracture mechanism of SiCf/TC17 composites at room temperature were as follows: multiple fractures of the interfacial reaction layer, single fiber fracture, matrix brittle fracture etc.. Typical fracture mechanism of SiCf/TC17 composites at elevated temperature were as follows: multiple fiber fracture, matrix plastic fracture, interface debonding etc.. Fiber cumulating damage theory was proved to be suitable for estimation of the fracture strength of this composite. The calculations of local loading sharing model while taking three or more fibers failure into account and global loading sharing model were close to the experimental values of room temperature and elevated temperature respectively. In addition, according to fracture mechanisms and strength prediction, tensile fracture process of SiCf/TC17 composites at room and elevated temperature were explained in detail. At room temperature, multiple fractures of the interfacial reaction layer started at first, and then the weak fiber fractured gradually and randomly. After critical fiber cluster has been formed by nearby broken fibers, the crack extended into the matrix from these fibers. With the increase of load, the fibers and the matrix at the tip of crack gradually destroyed. At the same time, the cracks from other critical fiber clusters were also expanding and connecting to each other. When the crack area has reached the critical level, the remaining fiber and matrix quickly fractured. However, at elevated temperature the matrix yielded firstly, and then multiple fracture randomly of the interfacial reaction layer and the weak fiber occurred sequentially. The crack from broken fiber deflected at interface between fiber and matrix, caused interface debonding. With the increasing of broken fiber number, the micro- cavities of matrix emerged gradually in the stress concentration area. When the total crack area accumulated by the broken fibers and micro-cavities of matrix has reached the critical level, the remaining fiber and matrix quickly fractured.
Subjects: Medicine, Pharmacy >> Clinical Medicine submitted time 2022-11-23 Cooperative journals: 《中国全科医学》
Abstract：
Background Subjective cognitive decline（SCD） is the target stage of the early prevention for Alzheimer’s disease. It is beneficial to explore the relevant influencing factors, regulate the modifiable factors for slowing the progression of AD. As we all known, multimorbidity is the crucial and modifiable factor for the objective cognitive impairment, while the study about correlation of SCD with multimorbidity is little and no unified conclusion yet. Objective Explore the correlation of SCD with multimorbidity, with the purpose to provide theoretical basis to the early prevention and intervention for AD. Methods From January 2021 to June 2022, a total of 612 elderly aged 60 years old was selected by convenience sampling from communities and nursing homes in Guangzhou as research subjects. A general information questionnaire was used for collecting socio-demographic and health-related data of the elderly. Objective cognition was accessed using the Montreal Cognitive Assessment Basic （MoCA-B）, Clinical Dementia Rating Scale （CDR）, Hachinski Ischemic Scale （HIS） and Activity of Daily Living （ADL）. SCD was accessed using the standard diagnostic framework for SCD and the Subjective Cognitive Decline Questionnaire （SCD-Q9）. The Pittsburgh Sleep Quality Index （PSQI）, General anxiety disorders scale（GAD-7）, Patient Health Questionnaire-9（PHQ-9） were separately used to assess sleep quality, depression and anxiety symptoms. Binary logistic regression analysis was used to explore the correlation between SCD and multimorbidity among elderly. Results Among elderly, there were 250 （40.8%） cases of SCD. 475 cases （77.6%） of multimorbidity were detected, of which 352 （57.5%） cases with low multimorbidity level, and 123 （20.1%） cases with high multimorbidity level. Logistic regression analysis showed that advanced age, poor ADL, poor sleep quality, anxiety symptoms and high multimorbidity level were risk factors for SCD, while years of education was a protective factor for SCD（均P<0.05）. In addition, the risk of SCD with high multimorbidity level was 1.8 times that of non-high multimorbidity level （OR=1.826, 95%CI=1.037-3.216, P<0.05）. Conclusion High multimorbidity level is associated with SCD as well as the independent risk factor of the occurrence of SCD. For the sake of delaying the development of AD in the elderly and promoting healthy aging, community and nursing facility healthcare professionals could incorporate multimorbidity as an assessment indicator of cognitive decline, collaborate to implement management of multimorbidity and related factors as well as actively identify and intervene in SCD.
Subjects: Biology >> Zoology submitted time 2018-12-24 Cooperative journals: 《动物营养学报》
Abstract：本试验旨在研究白藜芦醇（RES）对氧化损伤小鼠睾丸间质细胞TM3的保护作用，并探索其可能的作用机制。首先，用不同浓度（0、150、200、250、300 μmol/L）的过氧化氢（H2O2）处理小鼠睾丸间质细胞TM3 8 h，确定建立氧化损伤细胞模型的适宜H2O2浓度。用适宜浓度的H2O2建立氧化损伤细胞模型；然后，用不同浓度（0、2.5、5.0和10.0 μmol/L）的RES分别处理正常细胞和氧化损伤细胞24 h，确定RES安全浓度；最后，用安全浓度的RES处理氧化损伤细胞24 h。在整个培养过程中采用iCELLigence实时无标记细胞功能分析仪监测细胞的增殖情况；待安全浓度的RES处理氧化损伤细胞结束后采用2',7'-二氯荧光素二乙酸酯（DCFH-DA）探针法检测细胞中活性氧（ROS）的含量，实时荧光定量PCR（RT-qPCR）和蛋白质印迹（Western blotting）法分别检测沉默调节蛋白1(SIRT1)/UCP2信号通路中关键因子SIRT1和UCP2 mRNA和蛋白质的相对表达量。结果表明：1）用浓度为150 μmol/L及以上的H2O2处理细胞8 h后，极显著降低细胞存活率（P0.05）；用2.5、5.0和10.0 μmol/L的RES处理氧化损伤细胞24 h后，细胞存活率均显著提高（P0.05）。因此，选用5.0 μmol/L为RES的安全浓度。3）用5.0 μmol/L的RES处理氧化损伤细胞24 h后，细胞中ROS的含量较极显著降低（P<0.01）；细胞中SIRT1 mRNA和蛋白质的相对表达量极显著增加（P<0.01），而UCP2 mRNA和蛋白质的相对表达量则显著或极显著降低（P<0.01或P<0.05）。由此可见，适宜浓度的RES可激活SIRT1同时抑制UCP2的表达，UCP2通过负反馈调节方式减少细胞内ROS的生成，从而在一定程度上抑制TM3细胞的氧化损伤。
Subjects: Biology >> Zoology submitted time 2018-12-20 Cooperative journals: 《动物营养学报》
Abstract：本试验旨在研究抗菌肽Sublancin灌胃对卵清白蛋白（OVA）免疫小鼠获得性免疫反应的影响。试验选用6周龄雌性BALA/c小鼠60只，随机分为5个组，每组12只小鼠。空白对照组小鼠灌胃生理盐水，阳性对照组小鼠灌胃2.5 mg/kg体重的左旋咪唑溶液，抗菌肽Sublancin组小鼠灌胃0.5、1.0和2.0 mg/kg体重的抗菌肽Sublancin溶液。各组小鼠连续灌胃14 d。在灌胃结束24 h后用模式抗原OVA皮下注射对各组小鼠进行免疫，14 d后加强免疫1次，第2次免疫7 d后采血和取脾脏，用间接酶联免疫吸附测定（ELISA）法对血清OVA特异性免疫球蛋白G（IgG）及其亚类IgG1、IgG2a和细胞因子含量进行检测。结果表明：1）与空白对照组相比，0.5、1.0和2.0 mg/kg抗菌肽Sublancin组和阳性对照组小鼠血清OVA特异性IgG含量均显著或极显著提高（P0.05）。本试验结果表明，抗菌肽Sublancin可以诱导OVA免疫小鼠产生Th1和Th2混合型免疫反应，增强其体液免疫和细胞免疫功能。
Subjects: Biology >> Bioengineering submitted time 2017-07-24 Cooperative journals: 《中国生物工程杂志》
Abstract： Microalgae have been attracted as one of the potential sustainable bioresoucre due to their high photosynthetic efficiency, shorter growth cycle and enrichment of lipids, protein, carbohydrate, carotenoid and so on. Microalgae have high oil yield per unit area compared with other oilseed crops. In recent years, microalgae have been extensively investigated for biodiesel technology and CO2 emission reduction simultaneously. In addition, microalgae rich in a variety of high-value bioactive substances and have been widely applied in food, medicine and feed fields. The microalgal industry and corresponding research call the standard methods to evaluate the cultivated biomass from aspects. In this paper, it have been reviewed that the methods to examine the most interested components in quantification and quality prevail in order to promote the standardization for analysis of microalgal components in microalgal field.
Subjects: Biology >> Bioengineering submitted time 2017-07-24 Cooperative journals: 《中国生物工程杂志》
Abstract：木聚糖酶和甘露聚糖酶是两种主要的半纤维素酶，广泛应用于诸多领域。本研究选择了3种毕赤酵母内源信号肽Scw11、Dse4和Exg1，以α-factor为参照，分别在毕赤酵母X33中用于表达实验室前期获得的耐热木聚糖酶DSB和耐热甘露聚糖酶ManA，选择适合DSB和ManA表达的信号肽以提高胞外酶活水平。结果表明不同信号肽引导的两种半纤维素酶的酶活水平相差较大：对DSB（分子量为23 KDa），α-factor介导的表达效率明显优于其它3种信号肽；但对ManA（分子量为30 KDa），Dse4和α-factor介导的表达效率相当且明显优于Scw11和Exg1。因此在X33中表达DSB时应选用α-factor，而表达ManA时应选用Dse4或α-factor。此外胞内酶活的结果显示α-factor介导的DSB和ManA重组菌胞内滞留酶活明显高于其它信号肽，而分子量为30 KDa的ManA的滞留酶活又明显高于分子量为23 KDa的DSB，因此在表达ManA蛋白时，选用其它的信号肽，如Dse4，会减少外源蛋白在胞内的滞留从而在一定程度上提高外源蛋白的分泌量。本研究为毕赤酵母表达系统鉴定更多可用的信号肽并筛选到针对目的蛋白的最优信号肽奠定了一定的基础。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：本文简述了近年来国内外SiC纤维增强钛基复合材料的发展进程和应用进展情况，从纤维批量化生产、复合材料界面、主要力学性能、无损检测和结构件研制与考核五个方面对该类材料的研究进展进行了回顾。在纤维批量化生产和结构件研制方面，重点介绍了中国科学院金属研究所的研究工作，并对该类复合材料未来的发展趋势进行了展望
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