The periodic system: The (multiple) values of an icon

The periodic system is an icon of science, with an exceptional level of usage around the world. It is especially celebrated as a source of information and pedagogical tool. Although many publications on the history and philosophy of the system have appeared over the years, few of them deal with its underlying values aside from predictability. In this issue, scholars from different disciplines use the history of the periodic system to discuss what the system signifies and has signified for scientists and teachers, as well as for philosophers and historians. By presenting different layers of underlying values as they appear in the eyes of the users, we aim to provide a richer understanding of the periodic system, past and present.     

Yb2O3 掺杂氮化硅复合材料的高温动态疲劳行为

研究了N2 气氛加压烧结制备的6 wt %Yb₂O₃ 和2 wt %Al₂O₃ 掺杂氮化硅复合材料在高温下的动态疲劳行为。用维氏压痕法在试样上获得规范的预制裂纹。分别在1000 ℃、1200 ℃、1300 ℃、1400 ℃下, 以1 、0. 5 、0. 1 、0. 01 mm/ min 的不同压头速率对试样进行四点弯曲试验。不同温度下疲劳应力2加载速率函数曲线的对比表明, 这种材料在1200 ℃时, 对亚临界裂纹生长具有最高的抵抗力(即具有最大的亚临界裂纹生长指数N) 。XRD、TEM 分析表面晶界相的晶化、裂纹愈合可以提高亚临界裂纹生长指数。EDS 分析表明, 1200 ℃下氮化硅陶瓷断裂面的氧化有助于晶界相的晶化, 但是在更高的温度下, 则会产生不利影响。      

The periodic table as an icon: A perspective from the philosophy of Charles Sanders Peirce

The aim of this essay is to examine the iconic nature of Mendeleev's periodic table in light of the philosophy of the American pragmatist Charles Sanders Peirce. Mendeleev and Peirce lived at approximately the same time during the 19th and early 20th centuries. They both trained as chemists and, in 1869, the year of Mendeleev's first arrangement of the chemical elements, Peirce published his own arrangement, also based on atomic weights. Peirce developed a theory of iconicity as part of his wider semiotics, an important characteristic of an icon being its epistemic fruitfulness. The periodic table proved to be epistemically fruitful in predicting new relations—new knowledge—such as revised atomic weights and novel elements. By viewing the periodic table through the lens of Peirce's iconicity, I will show how Mendeleev was able both to reveal and to make perspicuous the relations between the chemical elements.     

两种先驱体低温裂解制备石英纤维增强氮化硅复合材料

以全氢聚硅氮烷( PHPS) 和聚甲基硅氮烷( PHMS) 为陶瓷先驱体, 通过循环浸渍和600 ℃低温裂解分别制备了三维石英纤维增强氮化硅复合材料, 对比研究了复合材料的力学性能和微观结构。结果表明: 由PHPS 制备的复合材料密度为1. 83 g/ cm3 , 气孔率10 % , 弯曲强度45. 4 MPa , 材料断口平整, 纤维基体界面结合强; 而由PHMS 制备的复合材料密度仅为1. 66 g/ cm3 , 气孔率16 % , 却具有更高的弯曲强度56. 3 MPa , 材料断面较粗糙,界面结合较弱。先驱体活性不同是导致复合材料界面结合强弱及力学性能不同的主要原因。      

偶联剂处理对玻璃纤维/尼龙复合材料力学性能的影响

采用KH-550 和KH-570 两种不同的偶联剂处理玻璃纤维, 得到的玻璃纤维增强铸型(MC) 尼龙复合材料( GFRMCN) 的力学性能差别很大。经过KH-570 处理GFRMCN 力学性能降低, 而经过KH₂550 处理能有效提高其力学性能; KH₂550 质量分数与处理的玻璃纤维质量分数之间符合定量关系式, 含量为0. 2 %时, GFRMCN的弯曲强度提高了35 % , 弯曲模量提高了72 % , 拉伸强度提高了46 % , 弹性模量提高了88 % , 冲击强度提高了41 %。KH-550 偶联剂在玻璃纤维与尼龙基体之间形成良好界面结合, 达到增强效果; 而未经处理的玻璃纤维断裂时从基体中拔出, 玻纤与尼龙界面相当于缺陷, 使MC 尼龙性能下降。      

COVID-19 testing labs standardized

正China Entry-Exit Inspection and Quarantine Association (CIQA) issued China's first general technical specifications for Fangcang (mobile cabin) shelter nucleic acid testing labs (T/CIQA 16-2021) and mobile nucleic acid testing labs (T/CIQA 17-2021) on March 22.The fast-established Fangcang shelter and mobile testing labs were vital to keeping the pandemic under control in China.Such labs can work during extreme weather,for example at above40 degrees Celsius or below minus 50 degrees Celsius.They will provide useful references to the prevention and control of global pandemic.     

Reproducibility of COVID-19 pre-prints

Scientometrics - To examine the reproducibility of COVID-19 research, we create a dataset of pre-prints posted to arXiv, bioRxiv, and medRxiv between 28 January 2020 and 30 June 2021 that are...     

Joint Statement on COVID-19

Advances in engineering and technology have played an indis-pensable role in shaping social and economic development.A host of new global challenges have appear...     

Zn-Ti取代的BaFe12O19铁氧体

采用标准陶瓷工艺,并进行湿压磁场成型和氧气氛烧结制备了高取向度、低介电损耗的各向异性Ｂａ（ＺｎＴｉ）ｘＦｅ１２－２ｘＯ１９多晶六角铁氧体,随着ｘ值增大,磁化强度减小,居里温度下降,磁晶各向异性常数减小。结果可以通过假设Ｚｎ＾２＋取代了四面体４ｆ１次点阵位和六面体２ｂ次点阵位上的ＦｅＴ＾３＋;Ｔｉ＾４＋取代了自旋向上的八面体１２ｋ,２ａ次点阵位上的Ｆｅ６３＋来解释。