聚乙烯纤维加强聚甲基丙烯酸甲酯的机械性能测试

目的　观察聚乙烯纤维对聚甲基丙烯酸甲酯是否有加强作用。方法　采用自制模具,制作化学固化聚甲基丙烯酸甲酯(PMMA)组、化学固化PMMA加0·25 mm结扎丝组、化学固化PMMA加Ribbond聚乙烯纤维组3组试样,共28个。用万能材料实验机进行三点弯曲实验,记录试样的弯曲强度和弹性模量值,并进行统计分析。结果　化学固化PMMA组的弯曲强度为(51·383±2·761)MPa,弹性模量为(179 1·2±113·760)MPa。化学固化PMMA加 0·25 mm结扎丝组的弯曲强度为(58·725±1·218)MPa,弹性模量为(209 2·76±120·280)MPa。Ribbond聚乙烯纤维加强组的弯曲强度为(80·975±2·580)MPa,弹性模量为(286 6·53±107·510)MPa。经单因素方差分析各组之间皆有显著性差异(P<0·001)。Newman-Keuls法检测各组之间均有显著性差异(P<0·05)。结论　Ribbond聚乙烯纤维加强能显著提高聚甲基丙烯酸甲酯的弯曲强度和弹性模量。     

预浸润玻璃纤维强化复合树脂的力学性能

大学口腔医院　修复科;2.北京大学口腔医院　材料教研室,北京100081) [摘要]　目的　研究预浸润玻璃纤维对不同复合树脂的强化效果。方法　制作Sinfony和belleGlass两种复合树脂的加入和不加预浸润玻璃纤维的标准试件(25 mm×2 mm×2 mm),于(37±1)℃的蒸馏水环境中保存24 h后,在万能力学试验机上测试弯曲强度和弹性模量。结果　Sinfony复合树脂加入纤维后弯曲强度和弹性模量显著提高,分别为(555·76±67·31)MPa和(12·59±3·06)GPa,较不加玻璃纤维试件平均提高了4·9和2·5倍(P=0);belleGlass复合树脂加入纤维后弹性模量有提高,为(14·10±2·88)Gpa,较不加玻璃纤维试件平均提高了0·9倍(P=0),而弯曲强度提高不明显。结论　预浸润玻璃纤维可以显著提高复合树脂的力学性能,但对不同复合树脂的强化效果有明显差别。     

Crystalline Structure and Viscoelastic Behavior in Composites of a Metallocenic Ethylene‐1‐octene Copolymer and Glass Fiber

Several composites with short glass fiber of a copolymer of ethylene and 1‐octene, synthesized with a metallocene catalyst, have been prepared, up to a fiber content of 40 wt.‐%. The effect of the fiber on the crystalline structure and on the viscoelastic response are analyzed. The role of glass fiber incorporation on crystallite development is discussed based on real‐time variable‐temperature WAXS and SAXS experiments. The viscoelastic behavior is considerably modified by incorporation of the glass fiber when compared with the plain copolymer. Thus, both the intensity and location of the γ and β relaxations are dependent on the fiber content. Moreover, the stiffness is considerably increased in the composites, allowing the analysis of the viscoelastic behavior up to temperatures well inside the melting region of the copolymer crystals, and thus enlarging substantially the service temperature of these composites. The β relaxation is assigned to the glass transition temperature, in agreement with the calorimetric results (DSC and MDSC) in these composites.     

Comparative Life Cycle Assessment of Asphalt Mixtures Using Composite Admixtures of Lignin and Glass Fibers

Lignin and glass fiber were used as additives to improve the quality of road pavements and minimize moisture damage and cracking at low temperatures on asphalt pavement, according to a previous laboratory study. The aim of this paper is to make a significant contribution to the environmental assessment of the construction of road pavements using four types of asphalt mixtures based on the life cycle assessment (LCA) methodology according to the requirements of ISO 14040, considering the impact of raw material extraction, asphalt mixture manufacturing, transportation, and wearing surface construction. The results of the environmental assessment showed that all studied asphalt mixtures do not offer any improvement in all impact categories, and three modified asphalt mixtures have a slight negative effect in all impact categories. The composite mixture has the highest negative effect of the studied three modified asphalt mixtures in all categories except in the marine aquatic ecotoxicity potential category and freshwater aquatic ecotoxicity potential category, where the lignin modified asphalt mixture has the highest negative effect in these two categories but has the best environmental impacts on most of other impact categories. Furthermore, the negative effect caused by composite asphalt mixtures is minimal and thus can be used to improve the overall performance of asphalt pavement.     

Research on Damage and Deterioration of Fiber Concrete under Acid Rain Environment Based on GM(1,1)-Markov

With steel fiber and basalt fiber volume dosing serving as variation parameters, a total of 200 d cycles of acid rain corrosion cycle tests were conducted on fiber concrete in this study. We selected three durability evaluation parameters to assess the degree of damage deterioration on fiber concrete, used scanning electron microscopy, mercury intrusion porosimetry, and a dimensional microhardness meter to analyze the concrete micromorphology, and established a GM(1,1)-Markov model for life prediction of its durability. Results reveal that the acid rain environment is the most sensitive to the influence of the relative dynamic elastic modulus evaluation parameter, and concrete has specimens that show failure damage under this parameter evaluation. Incorporation of fibers can reduce the amount of corrosion products inside the concrete, decrease the proportion of harmful pores, optimize the mean pore-size, and significantly improve the resistance to acid rain attack. Concrete with 2% steel fiber and 0.1% basalt fiber by volume has the least change in durability damage, and the predicted service life by GM(1,1)-Markov model is 322 d.     

阻塞性睡眠呼吸暂停患者的视网膜神经纤维层厚度变化：meta分析

目的:评估阻塞性睡眠呼吸暂停(OSA)患者视网膜神经纤维层(RNFL)厚度变化。方法:制定文献检索策略,计算机检索PubMed、Embase、万方科技期刊全文及硕士论文数据库(Wanfang data)及中国学术期刊全文数据库(CNKI),按纳入和排除标准选择文献,结局指标是RNFL厚度。采用STATA(MP VER....     

Up‐regulation of novel intermediate filament proteins in primary fiber cells: An indicator of all vertebrate lens fiber differentiation?

The early embryonic development and expression patterns of the eye lens specific cytoskeletal proteins, CP49 and CP95, were determined for the chick and were found to be similar in both human and mouse. These proteins, as well as their homologs in other species, are obligate polymerization partners which form unique filamentous structures termed “beaded filaments.” CP49 and CP95 appeared as protein products after 3 days of embryonic development in the chick during the elongation of primary fiber cells. Although limited data were obtained for human embryos at these early developmental timepoints, they were consistent with the interpretation that the up‐regulation of these lens specific proteins began only after the initiation of lens vesicle closure. In situ hybridization with the mouse lens confirmed that message levels for beaded filament proteins were greatly elevated in differentiating primary fiber cells. Nuclease protection assays established that mRNA levels for CP49 remained relatively constant while CP95 mRNA levels increased once the process of secondary fiber formation was under way. Although present in relatively low abundance, the mRNA for a unique splice variant of CP49, CP49_INS, was also detected early in embryonic development and into adulthood. Peptide‐specific antibodies directed against unique predicted sequences were able to confirm the protein expression of CP49_INS in both embryonic and adult chick lens cells. These data present the first detailed study of the expression of CP49 and CP95 during early lens development. They suggest that the up‐regulated expression of CP49 and CP95 could serve as pan‐specific markers for all vertebrate lens fiber development. Anat Rec 258:25–33, 2000. © 2000 Wiley‐Liss, Inc.     

香烟烟雾对小鼠视网膜组织病理学结构的影响

目的　探讨香烟烟雾对小鼠视网膜组织病理学结构的影响。方法　选取12只C57BL雄性小鼠,随机分为对照组（6只）及实验组（6只）。对照组不做特殊处理,实验组小鼠暴露于香烟烟雾中,每天2次,每次30 min,持续暴露12周后处死。取两组小鼠左眼分别行HE染色、免疫荧光染色及TUNEL染色观察视网膜各层结构的变化、三级β-微管蛋白（class III β-tubulin,Tuj1）的表达及视网膜内细胞凋亡情况;两组小鼠右眼在透射电子显微镜下观察视网膜色素上皮（retinal pigment epithelium,RPE）细胞超微结构的改变。结果　对照组及实验组小鼠视网膜全层厚度分别为（216.53±7.43）μm和（182.27±4.98）μm,视网膜神经纤维层厚度分别为（11.49±0.56）μm和（4.62±1.07）μm,内网状层厚度分别为（52.08±3.17）μm和（37.28±2.86）μm,两组相比差异均有统计学意义（均为P＜0.05）。对照组和实验组视网膜神经节细胞层内细胞数分别为（389.72±4.56）个和（378.71±2.16）个,差异无统计学意义（P＞0.05）。与对照组比较,实验组神经节细胞的细胞核部分形状不规则,排列疏密不均,局部可见细胞核缺失,Tuj1免疫荧光染色的荧光强度实验组较对照组减弱。TUNEL染色结果显示,两组视网膜各层均未见明确阳性染色。透射电子显微镜下观察,实验组RPE细胞内细胞基底部褶皱数量明显减少、局部有缺失。结论　香烟烟雾对小鼠视网膜神经层的组织病理学结构及RPE细胞的超微结构均有一定影响。     

基于弥散张量成像的脑白质微结构分析方法在视路损伤中的应用进展

视觉通路包括视神经、视交叉、视束、视放射及视皮质.常规磁共振检查技术难以发现视路损伤后白质纤维微结构改变,眼科学检查也存在一定的局限性及主观性,且不能探测后视路的变化.弥散张量成像(diffusion tensor imaging,DTI)作为一种新兴的磁共振成像技术,通过各种后处理分析方法 结合不同的参数进行分析,可...     

Current concepts of climbing fiber function

This review examines several of the current postulates regarding the function of one of the most intriguing afferent systems in the brain, the climbing fiber system. The fact that these afferents are activated under a variety of conditions has contributed substantially to the diversity of postulates that have been proposed. In part because of the unique anatomical relationship between individual climbing fibers and the dendritic tree of Purkinje cells, these afferents have been proposed as a key input in establishing long-term plastic changes in the cerebellar cortex. This concept is contrasted with other postulates proposing that the heterosynaptic action of this system produces a short-lasting enhancement rather than a long-term depression of Purkinje cell responsiveness. Although a generally accepted view regarding climbing fiber function does not exist, this review emphasizes the extensive functional insights that have been reported and supports the notion that progress toward a complete understanding of these afferents will require an integration of their morphological characteristics with the fundamental physiological properties of their responses assessed in a variety of contexts and conditions. Anat. Rec. (New Anat.) 253:118–126, 1998. © 1998 Wiley-Liss, Inc.