Characteristics of Radium Desorption from Sediments in the Salt Water Environment

海底沉积物向上覆水体扩散的镭是海洋水体中镭同位素的重要来源之一。为了研究沉积物中镭同位素的解吸和扩散特点,进行了不同盐度和不同粒度条件下224rA和226rA解吸的模拟实验,并通过多个时间段的沉积物培养实验获取224rA和226rA的扩散通量。实验结果表明:随着水体盐度增大,沉积物中224rA、226rA的解吸量随之增加,在盐度为25时,解吸量基本达到最大值;在同一咸水环境条件下,4个粒级(2000~1000μM、1000~500μM、500~250μM、250~125μM)的沉积物的224rA、226rA解吸量比较接近,粒级>2000μM的224rA、226rA解吸量略高于上述4个粒级,而粒级<125μM的224rA、226rA解吸量远大于上述5个粒级;胶州湾沉积物中224rA和226rA的平均扩散通量分别为0.85 bQ·M–2·d–1和0.022 bQ·M–2·d–1。Radium diffusion from sediments to overlying water is one of the important sources of radium isotopes in ocean water.A series of laboratory desorption/diffusion experiments were conducted to help elucidate the characteristics of sediments on 224 Ra and 226 Ra desorption and diffusion,which included 1) 224 Ra and 226 Ra desorption from sediments in water of different salinities,2) 224 Ra and 226 Ra desorption from sediments of different grain sizes in water of the same salinity,3) 224 Ra and 226 Ra diffusive fluxes by observing Ra enrichment with time in the overlying water of incubated sediments.The experimental results show that there is an increase in the amount of 224 Ra and 226 Ra with the increase of salinity from 5 to 30,and Ra desorption is strongest at the salinity of 25.Under the same salt water condition,224 Ra and 226 Ra desorption activities of the four grain sizes(2000~1000 μm,1000~500 μm,500~250 μm and 250~125 μm) of sediments are very close to each other.When the grain sizes of sediments are larger than 2000μm,the 224 Ra and 226 Ra desorption activities are slightly higher than those of the sediments of the above-mentioned four grain sizes.When the grain sizes of sediments are less than 125 μm,the 224 Ra and 226 Ra desorption activities are much larger than those of the above-mentioned five grain sizes.The average diffusive fluxes of 224 Ra and 226 Ra of sediments from Jiaozhou Bay are 0.85 Bq·m-2·d-1 and 0.022 Bq·m-2·d-1,respectively.国家自然科学基金项目(编号:41072174)资

Real-space imaging with pattern recognition of a ligand-protected Ag374 nanocluster at sub-molecular resolution

厦门大学化学化工学院郑南峰教授团队长期致力于研究固体功能材料的表界面化学行为，在分子水平上实现对固体功能材料的化学性能的调控与优化。得益于固体表面物理化学国家重点实验室的多学科合作以及能源材料化学协同创新中心的多单位优势互补，郑南峰教授课题组通过与校内外多个课题组的密切合作，近期在功能材料的可控制备、复杂表界面结构的高分辨表征和表界面过程分子机制的深入理解等方面取得系列重要进展，相关成果近期均在Nature Communications发表。 针对纳米颗粒表面配体难被高分辨直接成像的特点，与厦门大学郑兰荪、谢兆雄等教授以及中科院大连化物所杨学明研究员、马志博副研究员和芬兰于韦斯屈莱大学HannuHäkkinen教授等多个团队紧密合作，在利用扫描隧道显微镜表征金属纳米团簇的表面配体层结构方面取得重要进展。以原子结构精确的 Ag374纳米团簇为研究对象，利用超高真空扫描隧道显微镜分别在液氦及液氮温度下获得了单个团簇亚分子高分辨率的拓扑图像。【Abstract】High-resolution real-space imaging of nanoparticle surfaces is desirable for better understanding of surface composition and morphology, molecular interactions at the surface, and nanoparticle chemical functionality in its environment. However, achieving molecular or sub-molecular resolution has proven to be very challenging, due to highly curved nanoparticle surfaces and often insufficient knowledge of the monolayer composition. Here, we demonstrate sub-molecular resolution in scanning tunneling microscopy imaging of thiol monolayer of a 5 nm nanoparticle Ag374 protected by tert-butyl benzene thiol. The experimental data is confirmed by comparisons through a pattern recognition algorithm to simulated topography images from density functional theory using the known total structure of the Ag374 nanocluster. Our work demonstrates a working methodology for investigations of structure and composition of organic monolayers on curved nanoparticle surfaces, which helps designing functionalities for nanoparticle-based applications.The experimental work done in Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences, was supported both by Xiamen University (The National Key R&D Program of China grant 2017YFA0207302, National Natural Science Foundation of China, grant 21731005, 21420102001 and 21721001 the National Key R&D Program of China grant 2017YFA0207302) and DICP (National Natural Science Foundation of China grant 21688102, the Strategic Priority Research Program of Chinese Academy of Science, grant XDB17000000, the National Key Research and Development Program of the MOST of China, grant 2016YFA0200603 and the open fund of the state key laboratory of molecular reaction dynamics in DICP, CAS, grant SKLMRD-K201707). Q.Z. thanks Dr. Huayan Yang for providing the samples for STM imaging. S.M. and H.H. thank T. Kärkkäinen and P. Nieminen for discussions on pattern recognition algorithms. The theoretical and computational work in the University of Jyväskylä was funded by the Academy of Finland (grants 294217, 315549, AIPSE program, and H.H.’s Academy Professorship). H.H. acknowledges the support from China’s National Innovation and Intelligence Introduction Base visitor program. S.K. thanks the Vilho, Yrjö, and Kalle Väisälä Foundation for the grant for doctoral studies. The DFT simulations were done at the Finnish national supercomputing center CSC and at the Barcelona Supercomputing Center (PRACE project “NANOMETALS”). 研究工作得到了科技部、国家自然科学基金委和教育部，中科院先导项目，国家重点研发计划，分子反应动力学国家重点实验室开放课题基金等项目的资助

2-SPR/（U+UPR）P（vA）可重构并联机构的运动学与工作空间研究

提出了一种含可重构运动副的2-SPR/（U+UPR）P（vA）冗余并联机构，可应用于并联操作平台。首先，建立了2-SPR/（U+UPR）P（vA）并联机构的螺旋矩阵，求解机构在R相和U相下的自由度，并应用修正的Kutzbach-Grübler公式对机构的自由度进行了验证；其次，应用闭环矢量法求解机构的两组运动学逆解并验证、应用粒子群优化算法研究建立机构在R相下的正解模型并验证；最后，联合使用SolidWorks和Matlab软件求解了机构在R相下的可达工作空间和U相下的平动工作空间。研究结果为该机构的进一步优化和实际应用提供了理论支持

并联MZI型IQ调制器的直流偏置特性实验研究

相干光通信下的PDM-QPSK（双偏振复用正交相位键控）技术是光通信网络扩容的有效方式,因而被广泛研究。文章针对MZI（马赫曾德干涉型）IQ（正交）调制器的调制过程建立数学模型,分析了偏置电压及相位条件对调制信号的影响,总结出针对IQ调制器直流偏置特性的快速测试方法及算法思想。实际工程应用表明,该方法快速简单且准确性高

A multiplicative maximin-based evaluation approach for evolutionary many-objective optimization

This paper presents a new fitness evaluation approach based on aggregated pairwise comparisons (APC), i.e., a multiplicative maximin fitness ranking indicator with norm-p (M2F-p), for solving multi/many-objective problems. The M2F-p uses an adjustable aggregation of pairwise comparisons induced by p to alleviate the incomparability of solutions in terms of Pareto dominance when the number of objectives increases. We analyze the search ability of M2F-p under different p values. It is shown that the p values can control the shape of contour lines (i.e., a set of equal M2F-p values), which can affect the convergence and uniformity of solutions. Then, we illustrate that the M2F-p offers a set of promising properties that can enhance the discriminability of solutions. Further, we develop an efficient algorithm based on M2F-p by using an adaptive p-selection strategy and a diversity-maintenance mechanism. We conduct experiments on a suit of test problems with up to 10 objectives. The experimental results validate the effectiveness of the proposed algorithm on both multi-objective problems and many-objective problems.</p

堇青石基体化学气相沉积碳化硅薄膜及其性能表征

采用等温等压化学气相沉积技术，分别以CH3SiCl3-H2和SiCl4-CH4-H2为气源，在沉积温度1100和1000℃、压力101kPa条件下，制备了SiC薄膜．利用SEM和XRD、显微拉曼光谱、EDAX元素分析、HRTEM等测试技术对沉积薄膜的结构和组成进行了表征．结果表明，1100℃时，以CH3SiCl3-H2为气源沉积得到纯净的SiC薄膜，以β-SiC（111）面择优定向生长，由微米级的金字塔锥形结构组成，硅含量随着沉积温度降低而增加；以SiCl-CH4-H2为气源沉积得到非晶态碳掺杂的SiC薄膜，碳含量随着沉积温度降低而增加．此外，以CH3SiCl3-H2为气源沉积的SiC颗粒平均粒径均比以SiCl4-CHa-H2为气源的粒径大．前者SiC薄膜的方块电阻在kΩ级以上，且随着沉积温度的下降急剧升高；后者1100℃时制备的薄膜的方块电阻在kΩ级以上，且随着沉积温度的降低而急剧下降，1000℃时降低到Ω级