Organocatalytic stereoselective cationic polymerization of vinyl ethers by employing a confined BrΦnsted acid as the catalyst

The properties of poly(vinyl ether)s(PVEs)are highly dependent on their tacticity,and the appealing thermoplastics features of isotactic PVEs have drawn considerable efforts to develop stereoselective cationic polymerization methods to access this class of polymers.However,reported methods that could achieve a high degree of tacticity control are limited to process employing metal-based Lewis acids,and with various limitations on catalyst loading,monomer scope,etc.Here,we introduce a metal-free stereoselective cationic polymerization of vinyl ethers by employing a class of chiral confined Br?nsted acids,imidodiphosphorimidates(IDPis),as the catalyst.This organocatalytic approach features its metal-free conditions,high efficiency,high stereoselectivity,single catalyst system,operation simplicity,etc.     

一种混沌伪随机序列复杂度分析法

分析了已有的序列线性复杂度分析方法，提出了用近似熵算法计算混沌运动的测度熵，作为衡量混沌伪随机序列复杂度的标准.理论研究表明，利用较短的观察序列，该方法能够准确地反映混沌系统和混沌伪随机序列复杂度的大小，可以作为判断利用混沌系统产生的伪随机序列的复杂度准则.实验结果表明该方法的有效性和理论结果的正确性. 关键词： 混沌 伪随机序列 熵     

Characteristics of a 4-fold segmented clover detectore

Four high-purity germanium 4-fold segmented Clover detectors have been applied in the experiment of neutron-rich nucleus 21N. The performance of those four Clovers have been tested with radioactive sources and in-beam experiments, and the main results including energy resolution, peak-to-total ratios, the variation of the hit pattern distribution in different crystals of one Clover detector with the energy of γ ray, and absolute full energy peak detection effciency curve, were presented.     

Three new eudesmane sesquiterpenes from Artemisia vestita

Three eudesmane sesquiterpene lactones,namely artemivestinolides A–C(1–3),along with three known 11-epimeric lactones(4–6),were isolated from the aerial parts of Artemisia vestita.Their structures were elucidated on the basis of extensive spectroscopic analyses(IR,HR-ESIMS,1D NMR and 2D NMR),and the absolute confgurations were determined by single-crystal X-ray diffraction(with copper radiation).Furthermore,in an in vitro assay,the three new compounds exhibited a moderate inhibition of the lipopolysaccharide(LPS)-induced nitric oxide(NO)production in BV-2 microglial cells.     

Asymptotically optimal staffing of service systems with joint QoS constraints

We consider the problem of staffing large-scale service systems with multiple customer classes and multiple dedicated server pools under joint quality-of-service (QoS) constraints. We first analyze the case in which arrival rates are deterministic and the QoS metric is the probability a customer is queued, given by the Erlang-C formula. We use the Janssen–Van Leeuwaarden–Zwart bounds to obtain asymptotically optimal solutions to this problem. The second model considered is one in which the arrival rates are not completely known in advance (before the server staffing levels are chosen), but rather are known via a probability distribution. In this case, we provide asymptotically optimal solutions to the resulting stochastic integer program, leveraging results obtained for the case of deterministic arrivals.     

A novel ion-pairing chromatographic method for the simultaneous determination of both nicarbazin components in feed additives: chemometric tools for improving the optimization and validation

The development, optimization and validation of an ion-pairing high performance liquid chromatography method for the simultaneous determination of both nicarbazin (NIC) components: 4,4′-dinitrocarbanilide (DNC) and 2-hydroxy-4,6-dimethylpyrimidine (HDP) in bulk materials and feed additives are described. An experimental design was used for the optimization of the chromatographic system. Four variables, including mobile phase composition and oven temperature, were analyzed through a central composite design exploring their contribution to analyte separation. Five responses: peak resolutions, HDP capacity factor, HDP tailing and analysis time, were modelled by using the response surface methodology and were optimized simultaneously by implementing the desirability function. The optimum conditions resulted in a mobile phase consisting of 10.0 mmol L⁻¹ of 1-heptanesulfonate, 20.0 mmol L⁻¹ of sodium acetate, pH = 3.30 buffer and acetonitrile in a gradient system at a flow rate of 1.00 mL min⁻¹. Column was an INERSTIL ODS-3 (4.6 mm × 150 mm, 5 μm particle size) at 40.0 °C. Detection was performed at 300 nm by a diode array detector. The validation results of the method indicated a high selectivity and good precision characteristics, with RSD less than 1.0% for both components, both in intra and inter-assay precision studies. Linearity was proved for a range of 32.0-50.0 μg mL⁻¹ of NIC in sample solution. The recovery, studied at three different fortification levels, varied from 98.0 to 101.4 for HDP and from 99.1 to 100.2 for DNC. The applicability of the method was demonstrated by determining DNC and HDP content in raw materials and commercial formulations used for coccidiosis prevention. Assays results on real samples showed that considerable differences in molecular ratio DNC:HDP exist among them.     

基于近红外光谱法的沉积物间隙水化学组分快速测量

通过对巢湖柱状沉积物剖面间.隙水样品的近红外光谱(NIR)分析,采用OSC+WC和WC+OSC光谱预处理方法,结合偏最小二乘法(PLS)回归,建立了分层沉积物间隙水中TN,NH3-N,PO33-,TOC和SiO3的校正模型,该模型的TN,NH3-N,PO33-,TOC和SiO-3的预测值与实测值的校正相关系数分别为0....     

Electrospinning preparation and mechanical properties of PVA/HNTs composite nanofibers

In this paper, the PVA/HNTs composite nanofibers with well‐enhanced mechanical properties were successfully prepared by electrospinning technique. The structure and properties of the composite nanofibers were characterized by TEM, XRD, FT‐IR, and DSC. The results indicated that the highly oriented and dispersed HNTs wrapped in polymer matrix were achieved by inducing function during electrospinning processing. The mechanical properties of the PVA/HNTs composite nanofibers depended on HNTs content were investigated, which showed 72.4% increase in tensile strength at optimal filling content. Copyright © 2016 John Wiley & Sons, Ltd.     

International nanotechnology development in 2003: Country,institution, and technology field analysis based on USPTO patent database

Nanoscale science and engineering (NSE) have seen rapid growth and expansion in new areas in recent years. This paper provides an international patent analysis using the U.S. Patent and Trademark Office (USPTO) data searched by keywords of the entire text: title, abstract, claims, and specifications. A fraction of these patents fully satisfy the National Nanotechnology Initiative definition of nanotechnology (which requires exploiting specific phenomena and direct manipulation at the nanoscale), while others only make use of NSE tools and methods of investigation. In previous work we proposed an integrated patent analysis and visualization framework of patent content mapping for the NSE field and of knowledge flow pattern identification until 2002. In this paper, the results are updated for 2003, and the new trends are presented.     

The nature of synergistic effects in transition metal oxides/in-situ intermediate-hydroxides for enhanced oxygen evolution reaction

Oxygen evolution reaction is highly important for hydrogen production via water splitting but requires ～0.22 V onset overpotential, resulting in at least 15% extra energy consumption even utilized with the benchmark hetero-doped transition-metal hydroxide catalysts. The lack of fundamental understanding on catalyst behaviour and on synergistic mechanisms limit the breakthrough for material design. Here, we systematically summarise a variety of investigations and arguments on the mechanism from the microscale (optimal octahedral intermediate with six M?O coordination) to atomic scale (the active site behaviour). The electron–orbital scale (e_g) is further described for the intrinsic OER activity. The synergistic effect may also lead to a short-cut pathway of lattice-oxygen-mediated mechanism to achieve a smaller overpotential. This review provides a theoretical reference for the design of advanced catalysts.