用密度泛函和XANES计算研究Zn2+在水锰矿表面的吸附和沉淀

用密度泛函理论(density function theory, DFT)和X射线近边结构(X-ray absorption near edge structure, XANES)模拟计算了不同酸度(pH = 7.0, 7.5 和 8.0)下Zn(II)在水锰矿表面的吸附. 优化的几何结构表明, 只有双边吸附方式的水解簇既能解释H+ 释放机制, 又能与扩展X射线吸收精细结构(extended X-ray absorption fine structure, EXAFS)实验键长值相吻合. 吸附能计算表明, 各种吸附方式的稳定性双边(DE)>双角(DC)>B型单边(SE-B)>A型单边(SE-A)；水解能计算表明各种吸附态Zn2+ 均比溶液中水合锌离子易水解. 各种吸附簇模型的XANES计算谱未能与实验谱吻合, 即, 表面发生的并不是简单的吸附. pH=7.5和pH=8.0吸附样品的XANES实验谱与Zn5(OH)6(CO3)2的实验谱非常接近, 因此认为pH=7.5和pH=8.0下Zn(II)在水锰矿表面发生沉淀, Zn(II)是Zn—O八面体和Zn—O四面体的混合, 它们按类似Zn5(OH)6(CO3)2结构中的八面体和四面体排列方式排列. pH=7.0时, Zn(II)在水锰矿表面发生的主要是边连接方式的吸附.     

Mutual functionalization of dinitrogen and methane mediated by heteronuclear metal cluster anions CoTaC2−

The direct coupling of dinitrogen (N₂) and methane (CH₄) to construct the N–C bond is a fascinating but challenging approach for the energy-saving synthesis of N-containing organic compounds. Herein we identified a likely reaction pathway for N–C coupling from N₂ and CH₄ mediated by heteronuclear metal cluster anions CoTaC₂⁻, which starts with the dissociative adsorption of N₂ on CoTaC₂⁻ to generate a Ta^δ+–N_t^δ− (terminal-nitrogen) Lewis acid–base pair (LABP), followed by the further activation of CH₄ by CoTaC₂N₂⁻ to construct the N–C bond. The N N cleavage by CoTaC₂⁻ affording two N atoms with strong charge buffering ability plays a key part, which facilitates the H₃C–H cleavage via the LABP mechanism and the N–C formation via a CH₃ migration mechanism. A novel N_t triggering strategy to couple N₂ and CH₄ molecules using metal clusters was accordingly proposed, which provides a new idea for the direct synthesis of N-containing compounds.

A possible N–C bond formation directly from N₂ and CH₄ mediated by heteronuclear metal cluster anions CoTaC₂⁻ at room temperature was identified.     

Entanglement for a Bimodal Cavity Field Interacting with a Two-Level Atom

Negativity has been adopted to investigate the entanglement in a system composed of a two-level atom and a two-mode cavity field. Effects of Kerr-like medium and the number of photon inside the cavity on the entanglement are studied. Our results show that atomic initial state must be superposed, so that the two cavity field modes can be entangled. Moreover, we also conclude that the number of photon in the two cavity mode should be equal. The interaction between modes, namely, the Kerr effect, has a significant negative contribution. Note that the atom frequency and the cavity frequency have an indistinguishable effect, so a corresponding approximation has been made in this article. These results may be useful for quantum information in optics systems.     

Low-cost synthesis of flowerlike α-Fe2O3 nanostructures for heavy metal ion removal: adsorption property and mechanism

Flowerlike α-Fe(2)O(3) nanostructures were synthesized via a template-free microwave-assisted solvothermal method. All chemicals used were low-cost compounds and environmentally benign. These flowerlike α-Fe(2)O(3) nanostructures had high surface area and abundant hydroxyl on their surface. When tested as an adsorbent for arsenic and chromium removal, the flowerlike α-Fe(2)O(3) nanostructures showed excellent adsorption properties. The adsorption mechanism for As(V) and Cr(VI) onto flowerlike α-Fe(2)O(3) nanostructures was elucidated by X-ray photoelectron spectroscopy and synchrotron-based X-ray absorption near edge structure analysis. The results suggested that ion exchange between surface hydroxyl groups and As(V) or Cr(VI) species was accounted for by the adsorption. With maximum capacities of 51 and 30 mg g(-1) for As(V) and Cr(VI), respectively, these low-cost flowerlike α-Fe(2)O(3) nanostructures are an attractive adsorbent for the removal of As(V) and Cr(VI) from water.     

Dissociations of O2 molecules on ultrathin Pb(111) films: first-principles plane wave calculations

Using first-principles calculations, we systematically study the dissociations of O₂ molecules on different ultrathin Pb(111) films. According to our previous work revealing the molecular adsorption precursor states for O₂, we further explore why there are two nearly degenerate adsorption states on Pb(111) ultrathin films, but no precursor adsorption states existing at all on Mg(0001) and Al(111) surfaces. The reason is concluded to be the different surface electronic structures. For the O₂ dissociation, we consider both the reaction channels from gas-like and molecularly adsorbed O₂ molecules. We find that the energy barrier for O₂ dissociation from the molecular adsorption precursor states is always smaller than that from O₂ gas. The most energetically favorable dissociation process is found to be the same on different Pb(111) films, and the energy barriers are found to be influenced by the quantum size effects of Pb(111) films.     

Dissociations of O2 molecules on ultrathin Pb（111） films： first-principles plane wave calculations

Using first-principles calculations,we systematically study the dissociations of O₂ molecules on different ultrathin Pb（111） films.According to our previous work revealing the molecular adsorption precursor states for O₂,we further explore why there are two nearly degenerate adsorption states on Pb（111） ultrathin films,but no precursor adsorption states existing at all on Mg（0001） and Al（111） surfaces.The reason is concluded to be the different surface electronic structures.For the O₂ dissociation,we consider both the reaction channels from gas-like and molecularly adsorbed O₂ molecules.We find that the energy barrier for O₂ dissociation from the molecular adsorption precursor states is always smaller than that from O₂ gas.The most energetically favorable dissociation process is found to be the same on different Pb（111） films,and the energy barriers are found to be influenced by the quantum size effects of Pb（111） films.     

Biopreparation of an anti-inflammatory agent,diarctigenin, from arctiin isolated from Arctium lappa by Rhizoctonia solani AG-4

In the preliminary screening for the plant-derived pesticides against Rhizoctonia solani Kühn AG-4 (RS AG-4), the indicator compounds arctiin (1) and arctigenin (2) in methanol extracts of Arctium lappa L. were consumed and transformed to other compounds. Thus, in the present study RS AG-4 was used as a biocatalyst and the biotransformation of arctiin (1) was investigated. Conversion of arctiin (1) to arctigenin (2) was achieved by the enzymatic hydrolysis of sugar moiety. In addition, an anti-inflammatory lignan dimer reported from the Arctium species, diarctigenin (3) was afforded in good yields. The HPLC monitoring of the biotransformation process indicated the possible mechanism. It would be an excellent method to produce a large scale of diarctigenin (3) for the successive medicinal examinations.     

BEPC电子直线加速器束流线改进和e,π试验束

在BEPC电子直线加速器上建立起了E1,E2,E3试验束,其中E1初级束专门提供给强流慢正电子装置应用,E2束是初级正/负电子束,E3为次级高能e±,π±和质子等单粒子试验束,其动量连续可调.粒子定位误差0.2—0.4mm,混合负粒子计数率3—4Hz.已成功地为BESⅢ的TOF探测器模型测试提供试验束流.     

基于模态分解的扩散火焰动态响应特性分析

针对扩散火焰燃烧不稳定性,以钝体扰流扩散火焰为对象,研究不同频率声波激励下火焰动态响应特性,通过傅里叶变换(FFT)与本征正交分解法(POD)分析火焰的图像的空间分布的频谱特性.结果 表明,火焰振荡的主要模态为火焰整体的横向振荡、尾流区的频闪振荡与纵向振荡,当外加声波激励频率与火焰自身不稳定频率接近时会增强火焰的频闪振荡与纵向振荡幅值.在高频声波激励条件下,火焰整体积分值的傅立叶变换分析无法获得激励频率的响应,而通过POD方法对火焰空间结构动态变化的分析可以得到激励频率的响应,对于分布式扩散火焰,POD方法能获得更多火焰动态变化特征.     

核物质中五夸克重子态(θ) +的有效质量

在相对论平均场框架下,根据夸克介子耦合模型思想引入密度相关的标量耦合系数gNσ ,计算了密度相关耦合系数下,核物质标量密度、五夸克重子态(θ) 有效质量随核物质密度的变化情况,并与不变耦合系数下情况相比较.发现在低密度区域,密度相关的耦合系数对其影响很小,但在高密区域影响明显.表明,在密度相关的耦合系数影响下,标量介子与重子的相互作用在高密度区域被削弱.