In vivo Visualization of the Process of Hg2+ Bioaccumulation in Water Flea Daphnia carinata by a Novel Aggregation‐Induced Emission Fluorogen

This paper employs a specially designed aggregation‐induced emission fluorogen (AIEgen) to in vivo visualize the process of Hg²⁺ bioaccumulation in a common species of freshwater zooplankton Daphnia carinata (D. carinata) by two methods, direct Hg²⁺ absorption and ingestion of Hg²⁺ contaminated food. We analysed the relevance between photoluminescence (PL, I₅₉₅/I₄₈₀) ratios and Hg²⁺ (C_Hg2+) and developed the master curve for Hg²⁺ determination based on measuring the PL intensity of the solution. Meanwhile, fluorescent image analysis showed that the major recipient organs of Hg²⁺ in D. carinata were the compound eyes and carapace, followed by the intestine and shell gland, but not the brain or heart. The response of D. carinata to Hg²⁺ via uptake from surrounding water differed distinctly from that through food intake of the algae (Euglena gracilis) contaminated by mercury. When Hg²⁺ was encapsulated by algae membrane, no fluorescence was detected, and the carapace morphology remained intact after ingesting algae for 80 min, in contrast to the rapid carapace deformation by direct Hg²⁺ absorption. The D. carinata showed higher mortality by direct Hg²⁺ immersion than via food ingestion. The reason for the high mortality after Hg²⁺ immersion was possibly due to carapace deformity after chemical reaction between chitin and mercury, but the biochemical pathway leading to morality needs further study.     

Oxidation of Reduced Ceria by Incorporation of Hydrogen

The interaction of hydrogen with reduced ceria (CeO_2?x) powders and CeO_2?x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce³⁺ species to hydrogen, which results in the formation of Ce⁴⁺, and thus in oxidation of ceria.     

硬X光光电成像系统面密度分辨能力

 针对基于将X光转换成可见光接收的硬X光光电成像系统,研究了系统面密度分辨能力的理论模型,获得了系统面密度分辨能力的上下限的表达式;建立了对硬X光成像系统对面密度分辨能力的测量方法。利用自制面密度分辨率板,实验测量了由射频X光机、转换屏、光纤锥耦合和CCD相机组成的硬X光光电成像系统在不同照射量下的面密度极限分辨能力的上下限值。实验结果与理论分析模型分析趋势一致,在未饱和条件下面密度分辨力上限随着照射量的增加而不断增加,而面密度分辨力下限随着照射量的增加将减小。     

Γ-环及其矩阵环的QN-根和K-根

文中研究了Γ－环Ｍ与其矩阵环Γ_ｎ，ｍ－环Ｍ_ｍ，ｎ根的关系，得到了：ＱＮ（Ｍ_ｍ，ｎ）(?)（ＱＮ（Ｍ））_ｍ，ｎ；Ｋ（Ｍ_ｍ，ｎ）(?)（Ｋ（Ｍ））_ｍ，ｎ．这里ＱＮ－根是Γ－环元素的强幂零性所确定的根，Ｋ－根是诣零根     

有幺单Γ－环类所确定的上根

结合环根论中由具有单位元的单环类所确定的上根就是Ｂｒｏｗｎ－ＭｃＣｏｙ根．本文指出在Γ－环中，鉴于Γ－环单位元的复杂性质使得有幺单Γ－环类确定的上根演变成８个，进而研究了这些根之间及这些根与Γ－环其它根之间的大小关系．     

PVP封端剂对Pd纳米晶电催化氧化甲醇和乙醇性能的影响

Direct alcohol fuel cells (DAFCs) have attracted considerable research interest because of their potential application as alternative power sources for automotive systems and portable electronics. Pd-based catalysts represent one of the most popular catalysts for DAFCs due to their excellent electrocatalytic activities in alkaline electrolytes. Thus, it is of great importance to understand the structure-activity relationship of Pd electrocatalysts for alcohol electrocatalysis. Recently, size- and shape- controlled Pd nanocrystals have been successfully synthesized and subsequently used to study the size and shape effects of Pd electrocatalysts on alcohol electrocatalysis, in which the Pd (100) facet exhibited higher electrocatalytic oxidation activity for small alcohol molecules than the Pd (111) and (110) facets. Although it is well known that capping ligands, which are widely used in wet chemistry for the size- and shape-controlled synthesis of metal nanocrystals, likely chemisorb onto the surfaces of the resulting metal nanocrystals and influence their surface structure and surface-mediated properties, such as catalysis, this issue was not considered in previous studies of Pd nanocrystal electrocatalysts for electrocatalytic oxidation of small alcohol molecules. In this study, we prepared polyvinylpyrrolidone (PVP)-capped Pd nanocrystals with different morphologies and sizes and comparatively studied their electrocatalytic activities for methanol and ethanol oxidation in alkaline solutions. The chemisorbed PVP molecules transferred charge to the Pd nanocrystals, and the finer Pd nanocrystals had a higher coverage of chemisorbed PVP, and thus exposed fewer accessible surface sites, experienced more extensive PVP-to-Pd charge transfer, and were more negatively charged. The intrinsic electrocatalytic activity, represented by the electrochemical surface area (ECSA)-normalized electrocatalytic activity, of Pd nanocubes with exposed (100) facets increases with the particle size, indicating that the more negatively-charged Pd surface is less electrocatalytically active. The Pd nanocubes with average sizes between 12 and 19 nm are intrinsically more electrocatalytically active than commercial Pd black electrocatalysts, while the activity of Pd nanocubes with an averages size of 8 nm is less. This suggests that the enhancement effect of the exposed (100) facets surpasses the deteriorative effect of the negatively charged Pd surface for the Pd nanocubes with average sizes between 12 and 19 nm, whereas the deteriorative effect of the negatively charged Pd surface surpasses the enhancement effect of the exposed (100) facets for the Pd nanocubes with average sizes of 8 nm due to the extensive PVP-to-Pd charge transfer. Moreover, the Pd nanocubes with average sizes of 8 nm exhibit similar intrinsic electrocatalytic activity to the Pd nanooctahedra with (111) facets exposed and average sizes of 7 nm, indicating that the electronic structure of Pd electrocatalysts plays a more important role in influencing the electrocatalytic activity than the exposed facet. Since the chemisorbed PVP molecules block the surface sites on Pd nanocrystals that are accessible to the reactants, all Pd nanocrystals exhibit lower mass-normalized electrocatalytic activity than the Pd black electrocatalysts, and the mass-normalized electrocatalytic activity increases with the ECSA. These results clearly demonstrate that the size- and shape-dependent electrocatalytic activity of Pd nanocrystals capped with PVP for methanol and ethanol oxidation should be attributed to both the exposed facets of the Pd nanocrystals and the size-dependent electronic structures of the Pd nanocrystals resulting from the size-dependent PVP coverage and PVP-to-Pd charge transfer. Therefore, capping ligands on capped metal nanocrystals inevitably influence their surface structures and surface-mediated properties, which must be considered for a comprehensive understanding of the structure-activity relationship of capped metal nanocrystals.     

Statistical inference for the nonparametric and semiparametric hidden Markov model via the composite likelihood approach

Science China Mathematics - In this paper, we propose a new estimation method for a nonparametric hidden Markov model (HMM), in which both the emission model and the transition matrix are...     

TiO2/Cu2O Core/Ultrathin Shell Nanorods as Efficient and Stable Photocatalysts for Water Reduction

P‐type Cu₂O has been long considered as an attractive photocatalyst for photocatalytic water reduction, but few successful examples has been reported. Here, we report the synthesis of TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods by a redox reaction between Cu²⁺ and in‐situ generated Ti³⁺ when Cu²⁺‐exchanged H‐titanate nanotubes are calcined in air. Owing to the strong TiO₂‐Cu₂O interfacial interaction, TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods are highly active and stable in photocatalytic water reduction. The TiO₂ core and Cu₂O ultrathin film shell respectively act as the photosensitizer and cocatalyst, and both the photoexcited electrons in the conduction band and the holes in the valence band of TiO₂ respectively transfer to the conduction band and valence band of the Cu₂O ultrathin film shell. Our results unambiguously show that Cu₂O itself can act as the highly active and stable cocatalyst for photocatalytic water reduction.     

From superhydrophilicity to superhydrophobicity: the wetting behavior of a methylsilicone/phenolic resin/silica composite surface

A methylsilicone/phenolic resin/silica composite surface was prepared by a casting method. The wetting behavior of the surface was investigated. It was found that the as-prepared surface can be varied from superhydrophilicity to superhydrophobicity as the drying temperature increased. Methylsilicone/silica and phenolic resin/silica composite surfaces were also prepared as comparisons. Both of them cannot achieve superhydrophobicity. A mechanism was proposed to explain this phenomenon.     

环范畴和广义Г-环范畴间的关系

以R表示具有乘法单位元的结合环范畴,这里obR是结合环类,态射是保持单位元的环同态。以GΓR表示具有乘法单位元的广义Γ-环范畴,这里obGΓR是广义Γ-环类,态射是保持单位元的广义Γ-环同态。本文证明了:R和GΓR是等价的。