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21.
Cun Feng Fan David A. Waldman Shaw Ling Hsu 《Journal of Polymer Science.Polymer Physics》1991,29(2):235-246
Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface. 相似文献
22.
苦丁茶与常用茶中微量元素分析 总被引:4,自引:0,他引:4
苦丁茶又称苦丁、苦簦、皋卢等 ,是我国南方和东南亚地区常饮的代用茶 .几千年民间饮用和现代医学验证苦丁茶具有清热解毒、杀菌消炎、活血脉、降血脂、降胆固醇等功效 .近 10年来 ,科技人员对苦丁茶的化学成分进行了多方面的研究 ,确定其中含有化学成分达 2 0 0多种[1] ,一部分与普通茶叶相同 ,如咖啡碱、多酚类、儿茶素、氨基酸等 ,但含量比普通茶叶低[2 ] ,此外 ,苦丁茶还含有熊果酸 (Ursolic acid)、β 香树脂醇 (β Amyrin)、蛇麻脂醇 (Lupeol)、熊果醇 (Uvaol)和 β 谷甾醇 (β Sisterol)等 .但… 相似文献
23.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
24.
M. Sperling Xuefeng Yin B. Welz 《Spectrochimica Acta Part B: Atomic Spectroscopy》1991,46(14):1789-1801
Arsenic(III) can be quantitatively extracted using sodium diethyldithiocarbamate (NaDDTC) as the complexing agent and C18 reversed phase packing as the column material for solid phase extraction. Arsenic(V) must be reduced to its trivalent oxidation state prior to extraction. A mixture of sodium sulphite, hydrochloric acid, sodium thiosulphate and potassium iodide was found to be optimum for on-line reduction. When the sorbent extraction is carried out without and with the addition of the reduction mixture, arsenic(III) and total arsenic can be determined sequentially by graphite furnace atomic absorption spectrometry with detection limits (3 σ) of 0.32 ng for As(III) and 0.43 ng for total arsenic. A 7.6-fold enhancement in peak area compared to direct injection of 40 μl samples was obtained after 60 s preconcentration. Results obtained for sea water standard reference materials, using aqueous standards for calibration, agree well with certified values. A precision of 5.5% RSD was obtained for total arsenic in a sea water sample (1.65
As). Results obtained for synthetic mixtures of trivalent and pentavalent arsenic agreed well with expected values. 相似文献
25.
A graph G is 3‐domination critical if its domination number γ is 3 and the addition of any edge decreases γ by 1. Let G be a 3‐connected 3‐domination critical graph of order n. In this paper, we show that there is a path of length at least n?2 between any two distinct vertices in G and the lower bound is sharp. © 2002 John Wiley & Sons, Inc. J Graph Theory 39: 76–85, 2002 相似文献
26.
27.
殷志云 《中南大学学报(自然科学版)》1993,(6)
本文讨论了一般结合环与(左)S-单式周期环在一定条件下的结构问题,得出它们分别是局部交换环与诣零交换环,或为局部交换环的亚直和。同时,推广和改进了文献[l]的结果。 相似文献
28.
冯有纲 《贵州工业大学学报(自然科学版)》1988,(2)
本文阐述了 QSTEM 技术中获得的晶面夹角值与晶面指数之间的位相关系,提出了测量值与理论值的隶属度,建立了测量值与晶面指数之间的模糊关系——矩阵 A,通过两个例子,说明了模糊逼近的具体方法以及参数 T、m 和算子 H 等的具体意义。 相似文献
29.
本文设计了一个测量圆电流平面内磁场分布的实验,实验结果与理论计算能很好地吻合。从而证明该实验设计是可行的。 相似文献
30.
Intramammary expression and therapeutic effect of a human lysozyme-expressing vector for treating bovine mastitis 总被引:2,自引:0,他引:2 下载免费PDF全文
Huai-Chang Sun Fang-Ming Xue Ke Qian Hao-Xia Fang Hua-Lei Qiu Xin-Yu Zhang Zhao-Hua Yin 《浙江大学学报(自然科学英文版)》2006,7(4):324-330
To develop a gene therapy strategy for treating bovine mastitis, a new mammary-specific vector containing human lysozyme (hLYZ) cDNA and kanamycin resistance gene was constructed for intramammary expression and clinical studies. After one time acupuncture or intracisternal infusion of healthy cows with 400 μg of the p215C3LYZ vector, over 2.0 μg/ml of rhLYZ could be detected by enzymatic assay for about 3 weeks in the milk samples. Western blotting showed that rhLYZ secreted into milk samples from the vector-injected cows had molecular weight similar to that of the natural hLYZ in human colostrums. Twenty days after the primary injection, the quarters were re-injected with the same vector by quarter acupuncture and even higher concentrations of rhLYZ could be detected. Indirect competitive ELISA of milk samples showed that the vector injection did not induce detectable humoral immune response against hLYZ. Clinical studies showed that twice acupuncture of quarters with the p215C3LYZ vector had overt therapeutic effect on clinical and subclinical mastitis previously treated with antibiotics, including disappearance of clinical symptoms and relatively high microbiological cure rates. These data provide a solid rationale for using the vector to develop gene therapy for treating bovine mastitis. 相似文献