Ce(SO4)2‐Mediated Nitration of N,N‐Dialkylanilines with NaNO2 in Water

Ce(SO₄)₂‐mediated nitration of N,N‐dialkylanilines with NaNO₂ using water as the solvent has been achieved in good to excellent yields. The nitrating reaction proceeded smoothly at ambient temperature.     

Synthetic and mechanistic studies of metal-free transfer hydrogenations applying polarized olefins as hydrogen acceptors and amine borane adducts as hydrogen donors

Metal-free transfer hydrogenation of polarized olefins (RR'C=CEE': R, R' = H or organyl, E, E' = CN or CO(2)Me) using amine borane adducts RR'NH-BH(3) (R = R' = H, AB; R = Me, R' = H, MAB; R = (t)Bu, R' = H, tBAB; R = R' = Me, DMAB) as hydrogen donors, were studied by means of in situ NMR spectroscopy. Deuterium kinetic isotope effects and the traced hydroboration intermediate revealed that the double H transfer process occurred regio-specifically in two steps with hydride before proton transfer characteristics. Studies on substituent effects and Hammett correlation indicated that the rate determining step of the H(N) transfer is in agreement with a concerted transition state. The very reactive intermediate [NH(2)=BH(2)] generated from AB was trapped by addition of cyclohexene into the reaction mixture forming Cy(2)BNH(2). The final product borazine (BHNH)(3) is assumed to be formed by dehydrocoupling of [NH(2)=BH(2)] or its solvent stabilized derivative [NH(2)=BH(2)]-(solvent), rather than by dehydrogenation of cyclotriborazane (BH(2)NH(2))(3) which is the trimerization product of [NH(2)=BH(2)].     

高温超导转变温度电输运测量的影响因素研究

介绍了一种基于小型制冷机的高温超导转变温度测量装置,并且探究了在这套装置基础上进行实验所需要的测试条件。实验包括三项内容:(1)比较了电流换向法、三点Delta法以及偏置欧姆法三种消除热电势的方法,并最终决定采用适合本装置的电流换向法进行测量;(2)对通入样品的测试电流大小对测试的影响进行了研究,进而确定了进行高温超导材料转变温度测试时所通入电流的范围;(3)对钇系和铊系两种高温铜氧化物超导体进行反复测量,确定最大重复性误差小于0.4K。     

Structural investigation of Te-based chalcogenide glasses using Raman spectroscopy

Structural changes of metals (Zn, Sb, In, Ga) and metal halides (AgI, ZnI₂, CdI₂, PbI₂, BiI₃) modified GeTe₄ glasses were investigated with the aid of Raman spectroscopy. The Raman spectra of these glasses in the frequency region between 100 cm^?1 and 300 cm^?1 display four main bands at about 124, 140, 159 and 275 cm^?1 which are contributed by Ge–Te, Te–Te, Te–Te and Ge–Ge vibration modes. The intensity of 159 cm^?1 and 275 cm^?1 bands vary with the addition of different glass modifiers. While the relative intensity of the 124 cm^?1 and 140 cm^?1 bands are insensitive to composition changes. Glass modifiers like Zn, In and Sb act as glass network unstabilizer which will disorganize the glass network by opening up the chain structures of Ge–Te and Te–Te. In the case of Ga and metal halides, Ga can open up Ge–(Te–Te)_4/2 tetrahedra and form Ga–(Te–Te)_3/2 triangle. Iodine can form covalent bonds with tellurium and decrease the tendency of microcrystal formation. Thus both Ga and iodine ultimately act as glass network stabilizer.     

Gene Regulation Network Inference With Joint Sparse Gaussian Graphical Models

Revealing biological networks is one key objective in systems biology. With microarrays, researchers now routinely measure expression profiles at the genome level under various conditions, and such data may be used to statistically infer gene regulation networks. Gaussian graphical models (GGMs) have proven useful for this purpose by modeling the Markovian dependence among genes. However, a single GGM may not be adequate to describe the potentially differing networks across various conditions, and hence it is more natural to infer multiple GGMs from such data. In this article we propose a class of nonconvex penalty functions aiming at the estimation of multiple GGMs with a flexible joint sparsity constraint. We illustrate the property of our proposed nonconvex penalty functions by simulation study. We then apply the method to a gene expression dataset from the GenCord Project, and show that our method can identify prominent pathways across different conditions. Supplementary materials for this article are available online.     

CuCl2-catalyzed one-pot formation of tetrahydroquinolines from N-methyl-N-alkylanilines and vinyl ethers in the presence of t-butylhydroperoxide

Tetrahydroquinoline skeletons can be formed by a CuCl2-catalyzed one-pot reaction of N-methyl-N-alkylanilines and vinyl ethers in the presence of t-butyl-hydroperoxide.     

连续流动化学方法在无机制备科学中的应用

"连续流动化学"方法是无机制备科学中一种极具发展潜力的科学手段。作为一种已发展成熟的过程强化技术,与溶液合成、水热(溶剂热、离子热)等合成方法相比,"连续流动化学"方法具有可精确调控反应速度、缩短反应周期、优化并放大化学反应、提高产率的独特优势。本文总结了当前连续流动化学在无机物的分离和提取,纳米粒子、多金属氧酸盐等无机材料合成等领域的应用,分析了其在无机制备科学中存在的问题并展望了其的发展趋势。     

Entry of online presale of fresh produce: A competitive analysis

The fresh produce market is one of the last unexplored spaces for e-commerce and has attracted the entrance of many e-commerce firms in recent years; these firms are likely to influence the traditional fresh produce sales channels. The online presale of fresh produce can lower the circulation loss rate while traditional sales channels suffer from a huge waste in the circulation. In this paper, we study the online presale model of fresh produce from a competitive perspective. We examine the pricing and order decisions of one online grocery and one physical store. By examining the physical store with and without the online grocery, we investigate the impact of the entry of an online grocery on the physical store. We first identify two pricing strategies, penetration-pricing and skimming-pricing, for the physical store and two pricing strategies for the online grocery, and then identify the conditions under which pricing equilibrium will occur. We find that the store does not necessarily alter its pricing strategy after the online grocery enters the market. When the physical store uses the penetration-pricing strategy to compete with the online grocery for Internet shoppers, it may fail to achieve that goal if the online grocery's delivery cost is low and if the Internet shoppers account for a relatively low proportion of shoppers. Alternatively, the physical store may fail if the online grocery's delivery cost is not high and if the circulation loss rate of fresh produce is high.     

Assembly of Polypyrrole-Graphene Oxide Hydrogel Nanocomposites and Their Swelling Properties

An effective one-step strategy for the static assembly of hydrogels from polypyrrole (PPy) and graphene oxide (GO) is demonstrated. The static polymerization of pyrrole monomer was carried out in the presence of GO nanosheets, leading to the formation of PPy-GO hydrogels. During the static polymerization process, gelation takes place simultaneously by supramolecular interactions. The well-dispersed GO nanosheets in the polymer networks resulted in a significant improvement in water absorbencies. With only a very low loading of GO in the PPy-GO hydrogels, they exhibited significantly larger water uptake compared to a PPy hydrogel. Even in saline solutions, PPy-GO hydrogels also showed obvious water absorbency. Moreover, the PPy-GO hydrogels exhibited a better water retention ability compared with the control under the same conditions. This method is believed to provide possibilities to combine the extraordinary performances of GO with the multifunctional properties of conducting polymers, thus holding great potential for technical applications in the future.     

Surface-initiated Atom-transfer Radical Polymerization from Polyimide Films and Their Anti-fouling Properties

A simple one-step method for the chloromethylation of polyimide (PI) under mild conditions was used to introduce benzyl chloride groups into PI film surface. Covalently tethered hydrophilic polymer brushes of poly(ethylene glycol) monomethacrylate (PEGMA) and glycidyl methacrylate (GMA) were prepared via surface initiated atom-transfer radical polymerization (ATRP) from the chloromethylated PI surfaces using benzyl chloride groups as the active ATRP initiators. A kinetics study indicated that the chain growth from the films was in agreement with a controlled process. The dormant chain ends of the grafted polymer on the PI films could reinitiate the consecutive surface-initiated ATRP to prepare surface-functionalized diblock copolymer brushes on the PI films. The modified surface was characterized by X-ray photoelectron spectroscopy (XPS) after each modification stage. Protein adsorption experiments indicated that the PI-P(PEGMA) membrane exhibited substantially improved anti-fouling properties compared to the pristine PI surface.