Direct transition metal-free C-S bond formation: synthesis of 2-aminobenzothiazole derivatives via base-mediated approach

A general, efficient, and more practical protocol for the base-mediated intermolecular or intramolecular S-arylation leading to the 2-aminobenzothiazole derivatives is reported. Remarkably, all reactions were carried out under transition-metal-free conditions with good to excellent yields, rendering the methodology presented herein highly valuable from both environmental and economic points of view.     

Copper‐catalyzed Clauson–Kass pyrroles synthesis in aqueous media

An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Discontinuous crack-bridging model for fracture toughness analysis of nacre

Studying the structure–property relation of biological materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of advanced biomimetic materials. In this paper, we present a microstructure-based fracture mechanics model to investigate the toughening effect due to the crack-bridging mechanism of platelets. Our theoretical analysis demonstrates the crucial contribution of this mechanism to the high toughness of nacre. It is found that the fracture toughness of nacre exhibits distinct dependence on the sizes of platelets, and the optimized ranges for the thickness and length of platelets required to achieve higher fracture toughness are given. In addition, the effects of such factors as the mechanical properties of the organic phase (or interfaces), the effective elastic modulus of nacre, and the stacking pattern of platelets are also examined. Finally, some guidelines for the biomimetic design of novel materials are proposed based on our theoretical analysis.     

无人机视角下的林木爆燃火特性研究

森林火灾“爆燃”现象的特征是突然发生的高强度、高蔓延速度的燃烧。目前为止,关于“爆燃火”的原因还没有达成共识。以无人机视角下对林木爆燃火特性研究,以四川木里特大森林火灾为研究对象,通过分析凉山州某森林扑火部队3月31日木里森林火灾当天KWT（科卫泰）无人机航拍火场画面,结合无人机实时影像及实地调研数据,分析了峡谷地形林火蔓延时空特征,探讨了峡谷中风向风速变化时空分布规律,研究了地形变化条件下,不同海拔高度风速特征,建立了无人机倾角测量风速模型（其中为风速m·s-1,为无人机倾角°）。结果表明,高山峻岭特殊地形环境下每天4:00—12:00时间段为静风期,为峡谷林火扑救最佳时期;午后15:00—17:00和晚上20:00—22:00为山谷地形风速活跃期;仿真软件数据显示山顶、谷底与山腰不同海拔位置的风速风向不统一,谷底会产生乱流现象,且风速与海拔不存在正相关关系,小气候在复杂地形中占主导影响地位;在谷口至山谷深处的中间位置会出现气流速度的波峰状态,并易形成乱流,为爆燃火发生提供了客观必要条件。该研究可为复杂地形环境下,森林草原火灾扑救安全提供数据和技术支撑。     

恒星对增长螺旋引力扰动的非线性响应及其对增长模式的致稳作用*

本文计算了在增长的螺旋扰动引力场中恒星响应的非线性效应.结果表明,这一非线性效应会导致Q值的增加,从而降低增长率.对于振幅很小,增长率也较小的螺旋形模式,Q值增加较慢;对于振幅较大或增民率较大的模式,Q值也增加较快,从而有效地抑正振幅的增长.这一调节机制是使得由线性理论所得出的增长模式最终达到准稳状态的原因之一。     

Studies on self-pumped phase conjugation in Cu-doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 crystals

The use of Cu-doped (K_0.5Na_0.5)_0.2(Sr_0.61Ba_0.39)_0.9Nb₂O₆ as self-pumped phase conjugators using internal reflection is reported. Reflectivities as high as 63% at 5145.5 nm and 60% at 632.8 nm were realized. It was found that the photorefractive response changes significantly at different doping concentration. The responses of the crystals to the laser wavelength, incident angle and dopant concentration are studied.     

电感耦合等离子体原子发射光谱分析中光谱干扰校正卡尔曼滤波法研究

本文利用电感耦合等离子体原子发射光谱多色仪的扫描功能,用卡尔曼滤波法对各种光谱干扰进行校正。结果表明,该法能处理各种类型光谱干扰,不需要样品基体匹配,其测定回收率明显优于在峰法和离峰法,具有简便、准确等优点。     

质子交换光波导生长动力学研究

分析了质子交换光波导的生长动力学并给出了波导层厚度与生长时间的计算公式。     

标度系统一致性矩阵容量的计算方法

本文研究正互反矩阵的变换性质 ,提出一种保持正互反矩阵一致性程度的等价分类 ,为计算各种标度系统下的一致矩阵容量提供了计算方法