Pt/NbPWO双功能催化剂的制备及氢解碱木质素制备芳香单体

木质素是一种天然芳香族聚合物,约占木质纤维素的30%,是唯一通过裂解C―O醚键和C―C键生产芳香族化学品或液体燃料的可再生芳香族资源。迄今为止,对木质素氢解制备有价值化合物的研究主要集中在相对不稳定的C―O键的裂解上,这限制了木质素氢解的效率。采用水热法和湿浸渍法制备了多功能Pt/NbPWO催化剂。通过破坏碱木质素中的C―O键和C―C键,可以得到产率为18.02%的芳香族单体。该反应不仅可以断裂木质素聚合物中醚键,同时也可以断裂部分关键的C―C键。其氢解机理可能是丰富的Brønsted酸和Lewis酸位点参与了C―C的活化。此外,重点分析载体和Pt物种在Pt/NbPWO催化剂中的协同作用。     

Removal of Cu(II) Contamination from Aqueous Solution by Ethylenediamine@β-Zeolite Composite

The low cost β-zeolite and ethylenediamine modified β-zeolite (EDA@β-zeolite) were prepared by self-assembly method and used for Cu(II) removal from contaminated aqueous solution. Removal ability of β-zeolite toward Cu(II) was greatly improved after ethylenediamine (EDA) modification, the removal performance was greatly affected by environmental conditions. XPS results illustrated that the amide group played important role in the removal process by forming complexes with Cu(II). The EDA@β-zeolite showed desirable recycling ability. The finding herein suggested that the proposed composite is a promising and suitable candidate for the removal of Cu(II) from contaminated natural wastewater and aquifer.     

Cylindrical invisibility cloak with simplified material parameters is inherently visible

It was proposed that perfect invisibility cloaks can be constructed for hiding objects from electromagnetic illumination [J. B. Pendry, D. Schurig, and D. R. Smith, Science 312, 1780 (2006)10.1126/science.1125907]. The cylindrical cloaks experimentally demonstrated [D. Schurig, Science 314, 977 (2006)10.1126/science.1133628] and theoretically proposed [W. Cai, Nat. Photon. 1, 224 (2007)10.1038/nphoton.2007.28] have however simplified material parameters in order to facilitate easier realization as well as to avoid infinities in optical constants. Here we show that the cylindrical cloaks with simplified material parameters inherently allow the zeroth-order cylindrical wave to pass through the cloak as if the cloak is made of a homogeneous isotropic medium, and thus visible. To all high-order cylindrical waves, our numerical simulation suggests that the simplified cloak inherits some properties of the ideal cloak, but finite scatterings exist.     

Ideal cylindrical cloak: perfect but sensitive to tiny perturbations

A cylindrical wave expansion method is developed to obtain the scattering field for an ideal two-dimensional cylindrical invisibility cloak. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary of the cloak shell. We confirm that a cloak with the ideal material parameters is a perfect invisibility cloak by systematically studying the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering and penetration.     

基于语义的软件服务故障自动诊断模型

模仿学习是机器人仿生机制研究的主要内容之一,即通过观察、理解、学习、模仿示教行为实现机器人的仿生特性。基于高斯过程分别表达采集离散示教信号所构成的示教轨迹和含有未知参数策略的模仿轨迹,构建模仿学习方法框架,将概率模型匹配引入到模仿学习中,以KL散度为代价函数比较两种轨迹的概率分布,运用梯度下降法寻求使KL散度最小的最优模仿控制策略,将策略应用于模仿机器人以完成与示教相同的模仿任务。以关节型机器人的机械臂摆动行为模仿为学习任务进行仿真,结果表明基于概率轨迹匹配的模仿学习方法能够实现机械臂摆动行为模仿,学习过程较传统方法简易且学习效果较好。     

Rapid analysis of aflatoxins B1, B2, and ochratoxin A in rice samples using dispersive liquid–liquid microextraction combined with HPLC

A novel, simple, and rapid method is presented for the analysis of aflatoxin B₁, aflatoxin B₂, and ochratoxin A in rice samples by dispersive liquid–liquid microextraction combined with LC and fluorescence detection. After extraction of the rice samples with a mixture of acetonitrile/water/acetic acid, mycotoxins were rapidly partitioned into a small volume of organic solvent (chloroform) by dispersive liquid–liquid microextraction. The three mycotoxins were simultaneously determined by LC with fluorescence detection after precolumn derivatization for aflatoxin B₁ and B₂. Parameters affecting both extraction and dispersive liquid–liquid microextraction procedures, including the extraction solvent, the type and volume of extractant, the volume of dispersive solvent, the addition of salt, the pH and the extraction time, were optimized. The optimized protocol provided an enrichment factor of approximately 1.25 and with detection of limits (0.06–0.5 μg/kg) below the maximum levels imposed by current regulations for aflatoxins and ochratoxin A. The mean recovery of three mycotoxins ranged from 82.9–112%, with a RSD less than 7.9% in all cases. The method was successfully applied to measure mycotoxins in commercial rice samples collected from local supermarkets in China.     

Recent advances of ambient ionization mass spectrometry imaging in clinical research

The structural information and spatial distribution of molecules in biological tissues are closely related to the potential molecular mechanisms of disease origin, transfer, and classification. Ambient ionization mass spectrometry imaging is an effective tool that provides molecular images while describing in situ information of biomolecules in complex samples, in which ionization occurs at atmospheric pressure with the samples being analyzed in the native state. Ambient ionization mass spectrometry imaging can directly analyze tissue samples at a fairly high resolution to obtain molecules in situ information on the tissue surface to identify pathological features associated with a disease, resulting in the wide applications in pharmacy, food science, botanical research, and especially clinical research. Herein, novel ambient ionization techniques, such as techniques based on spray and solid‐liquid extraction, techniques based on plasma desorption, techniques based on laser desorption ablation, and techniques based on acoustic desorption were introduced, and the data processing of ambient ionization mass spectrometry imaging was briefly reviewed. Besides, we also highlight recent applications of this imaging technology in clinical researches and discuss the challenges in this imaging technology and the perspectives on the future of the clinical research.     

Seeking magneto-structural correlations in easily tailored pentagonal bipyramid Dy(III) single-ion magnets

Science China Chemistry - Controlling molecular magnetic anisotropy via structural engineering is delicate and fascinating, especially for single-molecule magnets (SMMs). Herein a family of...     

La1/3Sr2/3Fe1-xCoxO3体系中的Co替代效应研究

本文通过对La1/3Sr2/3Fe1-xCoxO3系列样品进行X射线衍射(XRD)和变温电阻率(p～T)、比热(C～T)、磁化率(M～T)等测试,研究了Co掺杂对该系列样品的晶体结构和电热磁性质的影响.结果表明,随着Co掺杂量的增加,晶胞体积单调减小;电阻中电荷有序(charge ordering,CO)的特征逐渐消失.Co含量低的样品随着温度降低发生顺磁-反铁磁(PM-AFM)转变和金属-绝缘体(M-I)转变;Co含量高的样品则在磁转变温度以下表现出团簇玻璃型短程铁磁有序行为,并且在整个测量温区内具有金属导电特性.这些证明Co掺杂引起电子的局域化效应是导致体系电磁和输运行为发生变化的主要原因.