美国电子束焊接技术

本文介绍了过去五十年美国电子束焊接历程材料加工首次采用电子束（EB）始于20世纪初,用于在真空条件下熔化耐火材料。此后,随着电子束两个主要支撑技术（真空工程及电子光学）水平的提高,应用电子束加工其它类型的材料逐步增加,电子束技术不断进步与成熟。目前电子束的应用见附表,从附表中可以看出,电子束应用范围从低功率密度（窄,表层型）到高功率密度（深,渗入型）的变化过程。     

Occurrence of perfluoroalkyl compounds in surface waters from the North Pacific to the Arctic Ocean

Perfluoroalkyl compounds (PFCs) were determined in 22 surface water samples (39-76°N) and three sea ice core and snow samples (77-87°N) collected from North Pacific to the Arctic Ocean during the fourth Chinese Arctic Expedition in 2010. Geographically, the average concentration of ∑PFC in surface water samples were 560 ± 170 pg L(-1) for the Northwest Pacific Ocean, 500 ± 170 pg L(-1) for the Arctic Ocean, and 340 ± 130 pg L(-1) for the Bering Sea, respectively. The perfluoroalkyl carboxylates (PFCAs) were the dominant PFC class in the water samples, however, the spatial pattern of PFCs varied. The C(5), C(7) and C(8) PFCAs (i.e., perfluoropentanoate (PFPA), perfluoroheptanoate (PFHpA), and perfluorooctanoate (PFOA)) were the dominant PFCs in the Northwest Pacific Ocean while in the Bering Sea the PFPA dominated. The changing in the pattern and concentrations in Pacific Ocean indicate that the PFCs in surface water were influenced by sources from the East-Asian (such as Japan and China) and North American coast, and dilution effect during their transport to the Arctic. The presence of PFCs in the snow and ice core samples indicates an atmospheric deposition of PFCs in the Arctic. The elevated PFC concentration in the Arctic Ocean shows that the ice melting had an impact on the PFC levels and distribution. In addition, the C(4) and C(5) PFCAs (i.e., perfluorobutanoate (PFBA), PFPA) became the dominant PFCs in the Arctic Ocean indicating that PFBA is a marker for sea ice melting as the source of exposure.     

经典纽约下午茶点

坐在“天词廊”的丝绒布沙发上。窗户外面的水波纹路．时隐时现地折射到桌子边上。冬日下午温暖的阳光．透过落地玻璃照进来,令周围充盈着浪漫的金色氛围。大厅中飘荡着优雅的钢琴声。醇厚的咖啡。或是一壶红茶。配上精致的茶点。午后的心情也慵懒写意起来。     

4-氯吡咯[2,3-d]嘧啶的合成

以氰乙酸乙酯和溴乙醛缩二乙醇为起始原料合成了标题化合物,与文献相比,产物处理简单,反应收率高,总收率达42.3%,含量≥98.5%.通过元素分析、IR、1HNMRT产品进行了表征.     

别嘌呤醇合成方法的改进

以氰乙酸乙酯和原甲酸三乙酯为起始原料,合成了标题化合物。经改进的方法与文献相比,产物处理简单,反应产率高,总收率达53.7%,含量≥99.5%。     

减小页岩气开发的负面影响

中国可能是全世界页岩气资源潜力最高的国家,据估测,总可开采储量高达25万亿～36万亿立方米。2012年3月,中国能源局推出了雄心勃勃的计划,提出页岩气产量存2015年将达到65亿立方米,到2020年的产量高达600亿～1000亿立方米。     

少根根霉γ-亚麻酸高产菌株选育

以少根根霉(Rhizopus arrhizus)R0为出发菌株,利用紫外诱变结合失水苹果酰肼筛选的方法,选育出突变株R4,摇瓶培养菌体油脂含量35.55%,其中GLA占油脂的12.5%,比原始菌株油脂含量提高了93.94%,GLA提高了276.5%.经传代培养证明,选到的突变株产γ-亚麻酸性能稳定.     

如何投资进口葡萄酒

基于世界人口第一大国消费人群的基数以及正在上升的经济发展水平,中国的酒业市场也随之成为一个巨大的市场,投资酒业也已经成为一种新的投资时尚。但是,酒业中又有国产酒与进口酒之分,即使是国产酒又同样有许多细分市场。     

普罗旺斯 生活梦想家的艺术盛宴

法国南部的7月是薰衣草和向日葵盛开的季节,这里大片紫色和大片金黄恐怕是地球上最难一遇的自然色版了,只有在这个地域在这个时节可以一见,喜欢摄影的人会抓住清晨与夕阳下最好的光线,捕捉最迷人的色彩。