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101.
102.
航天反射镜材料SiC 总被引:1,自引:0,他引:1
航天反射镜材料的一些优选性质包括密度低、弹性模量高、热膨胀系数低及热传导率高。与传统光学材料相比,碳化硅(SiC)具有优异的机械和热性能,被认为是引入注目的反射镜材料。本文概述了SiC的基体成形工艺和机械精加工工艺,讨论了其优缺点,并概述了国内外的发展现状。 相似文献
103.
用化学气相淀积(CVD)的方法, 在6H-SiC衬底上同质外延生长SiC层, 继而外延生长了Si1-yCy合金薄膜, 用X射线衍射(XRD)、扫描电子显微镜(SEM)、拉曼散射等方法对所得的样品进行了表征测量, 着重研究了生长得到的Si1-yCy合金的晶体结构。SEM结果显示6H-SiC外延层上生长的Si1-yCy合金薄膜表面平整, 晶粒大小均匀; XRD衍射谱仅显示单一的特征衍射峰(2θ约为28.5°), 表明得到的合金薄膜晶体取向单一, 其晶体类型为4H型; 粗略估算, 合金薄膜中C含量约为3.7%。拉曼谱显示:随生长气源中的C/Si比的增加, Si1-yCy合金薄膜中替位式C含量逐渐增大, 当C/Si比达到一定值时, 合金薄膜中有间隙式C出现, 造成晶体缺陷, Si1-yCy合金薄膜晶体质量下降。 相似文献
104.
Stella Vallejos Polona Umek Toni Stoycheva Fatima Annanouch Eduard Llobet Xavier Correig Patrizia De Marco Carla Bittencourt Chris Blackman 《Advanced functional materials》2013,23(10):1313-1322
Tungsten oxide nanostructures functionalized with gold or platinum NPs are synthesized and integrated, using a single‐step method via aerosol‐assisted chemical vapour deposition, onto micro‐electromechanical system (MEMS)‐based gas‐sensor platforms. This co‐deposition method is demonstrated to be an effective route to incorporate metal nanoparticles (NP) or combinations of metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides (MOX). The results show variations in electronic and sensing properties of tungsten oxide according to the metal NPs introduced, which are used to discriminate effectively analytes (C2H5OH, H2, and CO) that are present in proton‐exchange fuel cells. Improved sensing characteristics, in particular to H2, are observed at 250 °C with Pt‐functionalized tungsten oxide films, whereas non‐functionalized tungsten oxide films show responses to low concentrations of CO at low temperatures. Differences in the sensing characteristics of these films are attributed to the different reactivities of metal NPs (Au and Pt), and to the degree of electronic interaction at the MOX/metal NP interface. The method presented in this work has advantages over other methods of integrating nanomaterials and devices, of having fewer processing steps, relatively low processing temperature, and no requirement for substrate pre‐treatment. 相似文献
105.
热铁盘法抛光CVD金刚石需要在800℃以上的真空环境下进行,抛光过程中金刚石的固定,常采用陶瓷胶粘结的方法,该法在实际使过程中经常出现陶瓷胶粘结不牢而导致金刚石脱落.据此设计出一套高温真空环境下使用的金刚石夹具,在抛光厚度0.7 mm的金刚石时,将其装夹在0.4 mm深的凹槽内,留出0.3 mm左右的高度以供抛光.加载方式可以实现加热过程中无载荷,抛光过程中施加载荷.实验表明,该夹具在抛光过程中,可以实现金刚石的完全固定,并能在273 mm/s的抛光速度条件下稳定工作.在温度800℃,速度273 mm/s,载荷2.54 kg,抛光30 min的条件下,金刚石表面粗糙度可由原始的Ra9.6 μm抛光至Ra0.16 μm. 相似文献
106.
微/纳米复合多层金刚石自支撑膜的制备及应力研究 总被引:1,自引:0,他引:1
利用大功率DC Arc Plasma Jet CVD装置,采用Ar-H2-CH4混合气体为气源,通过优化工艺参数,在多晶钼衬底上制备出了多层复合金刚石自支撑膜.利用扫描电镜(SEM)、X射线衍射(XRD)、激光拉曼谱(Raman)对膜体进行表征,结果显示,多层膜体的组织结构体现了微米金刚石与纳米金刚石的典型特征;复合金刚石自支撑膜具有光滑的表面,微米层与纳米层间呈相互嵌套式的界面;此外,利用激光拉曼谱分析了多层膜中的内应力状态,研究发现,多层膜中各层膜体具有不同的内应力状态,内应力沿膜体生长方向有明显变化,呈现出从压应力到拉应力的变化过程. 相似文献
107.
Extreme ambient temperature has been associated with increased daily mortality across the world. We describe the ambient temperature-mortality association for four capital cities in East Asia, Seoul, Beijing, Tokyo, and Taipei, and identify a threshold temperature for each city and the percent increase in mortality. We adapted generalized linear modeling with natural cubic splines (GLM + NS) to examine the association between daily mean apparent temperature (AT) and total mortality, as well as mortality due to respiratory (RD) and cardiovascular (CVD) causes in a threshold model. We conducted a time-series analysis adjusting for day of the week and long-term time trend. The study period differed by city. The threshold temperature for all seasons was estimated to be 30.1-33.5 °C, 31.3-32.3 °C, 29.4-30.8 °C, and 25.2°-31.5 °C for Seoul, Beijing, Tokyo, and Taipei, respectively, on the same day. For the mean daily AT increase of 1 °C above the thresholds in Seoul, Tokyo, and Taipei, estimated percentage increases in daily total mortality were 2.7 (95% confidence interval (CI) = 2.2-3.1), 1.7 (95% CI = 1.5-2.0), and 4.3 (95% CI = 2.9-5.7), respectively. Beijing provided no total mortality counts. Estimated percentage increases were 2.7-10.5 for RD mortality, 1.1-9.3 for CVD mortality in 4 cities. This study identified increased mortality due to exposure to elevated AT. The importance of effects of AT and city-specific threshold temperatures suggests that analyses of the impact of climate change should take regional differences into consideration. 相似文献
108.
Imad Ibrahim Yang Zhang Alexey Popov Lothar Dunsch Bernd Büchner Gianaurelio Cuniberti Mark H Rümmeli 《Nanoscale research letters》2013,8(1):265
All-carbon single-walled carbon nanotubes (SWCNTs) were successfully synthesized, nucleated using a fullerene derivative. A systematic investigation into the initial preparation of C60 fullerenes as growth nucleators for the SWCNTs was conducted. Enhancement in the yield of the produced SWCNT has been achieved with exploring different dispersing media for the fullerenes, the period, and environment of the initial thermal treatment of the fullerenes in addition to the use of different fullerene-based structures. The systematic studies significantly advance our understanding of the growth of the all-carbon catalyst-free single-walled carbon nanotubes. Field-effect transistors were fabricated using the catalyst-free SWCNT and then electrically characterized, showing current capacity as high as the well-studied catalyst-assisted nanotubes. 相似文献
109.
Barbara Fruci Stefania Giuliano Angela Mazza Roberta Malaguarnera Antonino Belfiore 《International journal of molecular sciences》2013,14(11):22933-22966
Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder worldwide. Several lines of evidence have indicated a pathogenic role of insulin resistance, and a strong association with type 2 diabetes (T2MD) and metabolic syndrome. Importantly, NAFLD appears to enhance the risk for T2MD, as well as worsen glycemic control and cardiovascular disease in diabetic patients. In turn, T2MD may promote NAFLD progression. The opportunity to take into account NAFLD in T2MD prevention and care has stimulated several clinical studies in which antidiabetic drugs, such as metformin, thiazolidinediones, GLP-1 analogues and DPP-4 inhibitors have been evaluated in NAFLD patients. In this review, we provide an overview of preclinical and clinical evidences on the possible efficacy of antidiabetic drugs in NAFLD treatment. Overall, available data suggest that metformin has beneficial effects on body weight reduction and metabolic parameters, with uncertain effects on liver histology, while pioglitazone may improve liver histology. Few data, mostly preclinical, are available on DPP4 inhibitors and GLP-1 analogues. The heterogeneity of these studies and the small number of patients do not allow for firm conclusions about treatment guidelines, and further randomized, controlled studies are needed. 相似文献
110.
A. K. M. Fazle Kibria Young Hwan Mo Min Hee Yun Moon J. Kim Kee Suk Nahm 《Korean Journal of Chemical Engineering》2001,18(2):208-214
Multi-wall carbon nanotubes (MWNTs) were synthesized by catalytic decomposition of acetylene over Fe, Ni and Fe-Ni bimetallic
catalysts supported on alumina under various controlled conditions. The growth density and diameter of CNTs were markedly
dependent on the activation time of catalysts in H2 atmosphere, reaction time, reaction temperature, flow rate of acetylene, and catalyst composition. Bimetallic catalysts were
apt to produce narrower diameter of CNTs than single metal catalysts. For the growth of CNTs at 600 ‡C under 10/100 seem flow
of C2H2/H2 mixture, the narrowest diameter about 20 nm was observed at the reaction time of 1 h for 20Fe : 20Ni : 60Al2O3 catalyst, but at that of 1.5 h for 10Fe : 30Ni : 60Al2O3 catalyst. It was considered that the diameter and density of CNTs decreased with the increase of the growth time mainly due
to hydrogen etching. The growth of CNTs followed the tip growth mode. 相似文献