Synthesis of new hydrogels based on the macromolecular reaction of citraconic anhydride copolymers with γ‐aminopropyltriethoxysilane (APTS)

This work describes the synthesis and macromolecular reactions of citraconic anhydride (CA)–acrylamide (AAm) binary reactive copolymers with γ‐aminopropyltriethoxysilane (APTS) as a polyfunctional crosslinker. Copolymers with given composition of poly(CA‐alt‐AAm) were synthesized by radical binary copolymerization with benzoyl peroxide (BPO) as an initiator in benzene at 70°C in nitrogen atmosphere with initial monomer ratio 1 : 1. It was shown that the network structure is formed in poly(CA‐alt‐AAm)/APTS in water by intermolecular reactions between the anhydride unit and the amine group, as well as between the ethoxysilyl fragment and free carboxyl groups of the CA unit and amide unit of AAm. Swelling parameters such as beginning time of the hydrogel‐formation, initial rate of the swelling, swelling rate constant, equilibrium swelling and equilibrium water content were determined for the copolymer/APTS/water system with certain (2.75 : 1) copolymer/crosslinker ratio. Formation of a hyperbranched network structure through the fragmentation of side‐chain reactive groups in studied systems was confirmed by Fourier transform infrared spectroscopy (FT‐IR) method. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of rainy weather on traffic accidents of a freeway using cellular automata model

The aim of this work is to investigate the influence of rainy weather on traffic accidents of a freeway. The micro-scale driving behaviors in rainy weather and possible vehicle rear-end and sideslip accidents are analyzed. An improved CA model of two lanes one-way freeway is presented, where some vehicle accidents will occur when the necessary conditions are simultaneously satisfied. The characteristics of traffic flow under different rainfall intensities are discussed and the accident probabilities are analyzed via the simulation experiments by using variable speed limit(VSL) and incoming flow control. The results indicate that the measures are effective especially during heavy rainstorms or short-time heavy rainfall.According to different rainfall intensities, an appropriate strategy should be adopted in order to reduce the probability of vehicle accidents and enhance traffic flux as well.     

Development of a catalytic enantioselective synthesis of the guanacastepene and heptemerone tricyclic core

For nearly two decades, synthetic chemists have been fascinated by the structural complexity and synthetic challenges afforded by the guanacastepene and heptemerone diterpenoids. Numerous synthetic approaches to these compounds have been reported, but to date the application of enantioselective catalysis to this problem has not been realized. Herein we report an enantioselective synthesis of an advanced intermediate corresponding to the tricyclic core common to the guanacastepenes and heptemerones. Highlights of this work include sequential Pd-catalyzed decarboxylative allylic alkylation reactions to generate the two all carbon quaternary stereocenters, the use of ring-closing metathesis to close the A ring in the presence of a distal allyl sidechain, and a regio- and diastereoselective oxidation of a trienol ether to introduce oxygenation on the A ring.     

Ionic conductivity of sodium beta″-alumina

Measurements of the electrical conductivity of Na ß″-alumina show that the low-temperature activation energies are 0.3337 ± 0.0055 eV for MgO stabilized crystals grown at 1700°C, 0.275 ± 0.015 eV for crystals with the same starting composition position grown at 1650°C, and 0.1716 ± 0.0093 eV for crystals stabilized with ZnO and grown at 1700°C. The conductivities of almost all crystals at 500°C were found to be 1.3 ± 0.6 Ω^?1 cm^?1. In addition to the growth conditions, the presence of a dc electric field, the type of electrode material, the type of conducting ion, and the concentration of stabilizing ion are important in determining the electrical conductivity. These factors are believed to affect the nature of the ordering of vacancies in the ß″-aluminas, leading to variations in the activation energy.     

Ilimaquinone,a sesquiterpenoid quinone from a marine sponge

Ilimaquinone (1) is a new sponge metabolite of composition C₂₂H₃₀O₄. Its structure, which was determined by spectral correlations and X-ray crystallography, comprises a rearranged drimane sesquiterpene moiety linked to a 2-hydroxy-5-methoxybenzoquinone at C-3.     

Magnetization transfer MRI of mouse brain reveals areas of high neural density

Extending applications of magnetization transfer contrast (MTC) in magnetic resonance imaging (MRI) of the human central nervous system, this work quantitatively describes MTC of the murine brain. As a novel finding, complementing T₁- and T₂-weighted MRI, MTC allows for the distinction of densely packed gray matter from normal gray and white matter. Examples include the Purkinje cell layer and the granular cell layer in the mouse cerebellum as well as the delineation of the CA3 subfield of the hippocampus relative to surrounding hippocampal gray matter and white matter tracts such as the hippocampal fimbria. Using a kainate lesion model, the CA3 hyperintensities in MTC and T₁-weighted MRI are assigned to the densely packed somata of pyramidal cells.     

Straightforward Regio- and Diastereoselective Synthesis,Molecular Structure,Intermolecular Interactions and Mechanistic Study of Spirooxindole-Engrafted Rhodanine Analogs

Straightforward regio- and diastereoselective synthesis of bi-spirooxindole-engrafted rhodanine analogs 5a–d were achieved by one-pot multicomponent [3 + 2] cycloaddition (32CA) reaction of stabilized azomethine ylide (AYs 3a–d) generated in situ by condensation of L-thioproline and 6-chloro-isatin with (E)-2-(5-(4-chlorobenzylidene)-2,4-dioxothiazolidin-3-yl)-N-(2-morpholinoethyl)acetamide. The bi-spirooxindole-engrafted rhodanine analogs were constructed with excellent diastereo- and regioselectivity along with high chemical yield. X-ray crystallographic investigations for hybrid 5a revealed the presence of four contiguous stereocenters related to C11, C12, C19 and C22 of the spiro structure. Hirshfeld calculations indicated the presence of many short intermolecular contacts such as Cl...C, S...S, S...H, O...H, N...H, H...C, C...C and H...H interactions. These contacts played a very important role in the crystal stability. The polar nature of the 32CA reaction was studied by analysis of the conceptual DFT reactivity indices. Theoretical study of this 32CA reaction indicated that it takes place through a non-concerted two-stage one-step mechanism associated with the nucleophilic attack of AY 3a to the electrophilic ethylene derivative.     

生物膜动力学的研究现状与展望

生物膜法作为一种高效的废水处理工艺已获得到了广泛的工程应用.生物膜的形成、结构 及其动力学特性对废水处理效果至关重要.本文综述了生物膜的形成过程及其动力学模型的 研究进展,阐述了最近十几年来实验研究中的新发现和新方法,最后展望了将来的研究方向.      

结肠镜联合CEA、CA242鉴别结直肠息肉与癌变的效能研究

本文探讨了通过结肠镜评估病灶直径、病灶数量,联合癌胚抗原(CEA)、糖类抗原242(CA242)鉴别结直肠息肉与癌变的效能.选取2018年1月?2020年1月212例结直肠癌患者作为观察组,另选取同期收治的10 0例结直肠息肉患者作为对照组.比较两组患者的临床资料、病灶直径、病灶数量和CEA、CA242表达水平,发现将...