强流脉冲电子束作用下钽金属靶膨胀的轴向约束

研究了强流脉冲电子束与钽金属靶相互作用后靶材流体动力学膨胀的轴向约束问题。由于电子束在金属钛和钽内的能量沉积存在差异,未完全气化的钛箔对气化膨胀的钽材能够起到约束作用,并且可以通过吸收钽的能量来降低钽的膨胀速度。通过分析比较电子束在靶上形成孔洞的形貌以及高速相机拍摄得到的不同时刻靶材喷射的图像,证实了钛箔能够对钽金属靶的轴向膨胀起到一定的约束作用。尤其是电子束打靶过后1μs内的初始阶段,约束效果比较明显。     

Cr(Ⅵ)吸附剂研究进展

重金属污染不仅威胁着自然环境的持续发展,也对人类健康提出了严峻的考验。其中,六价铬因为环境污染持续久,危害大,更是得到各国研究者的重视。各种吸附材料对于六价铬的移除能力以及移除机理不尽相同。本文主要介绍了Cr(Ⅵ)吸附材料分类及其特点,重点分析了聚合物吸附材料在吸附和分离Cr(Ⅵ)方面的应用进展,并简要介绍了Cr(Ⅵ)吸附过程中的吸附动力学模型和等温方程式,以Langmuir和Freundlich模型等为例加以说明,为解决重金属铬离子引起的环境污染尤其水污染问题提供借鉴。     

富氮空心蠕虫状碳材料的合成及其苯甲醇非金属选择性催化氧化的高活性

Carbon materials have become one of the research hotspots in the field of catalysis as a typical representative of non-metallic catalytic materials. Herein, a facile synthetic strategy is developed to fabricate a series of hollow carbon nanoworms (h-NCNWs) that contain nitrogen up to 9.83 wt% by employing graphitic carbon nitride (g-C₃N₄) as the sacrificing template and solid nitrogen source. The h-NCNWs catalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), N₂ adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric (TG), Raman spectra, and X-ray photoelectron spectroscopies (XPS). The catalytic activities of the h-NCNWs catalysts for selective oxidation of benzyl alcohol with O₂ were also evaluated. The characterization results revealed that the h-NCNWs catalysts displayed a unique hollow worm-like nanostructure with turbostratic carbon shells. The nitrogen content and shell thickness can be tuned by varying the relative ratio of resorcinol to g-C₃N₄ during the preparation process. Furthermore, nitrogen is incorporated to the carbon network in the form of graphite (predominantly) and pyridine, which is critical for the enhancement of the catalytic activity of carbon catalysts for the selective oxidation of benzyl alcohol. At a reaction temperature of 120 ℃, a 24.9% conversion of benzyl alcohol with > 99% selectivity to benzaldehyde can be achieved on the h-NCNWs catalyst prepared with a mass ratio of resorcinol to g-C₃N₄ of 0.5. However, the catalytic activities of the h-NCNWs catalysts were dependent on the amount of N dopants, in particular graphitic nitrogen species. The conversion of benzyl alcohol markedly decreased to 13.1% on the h-NCNWs catalyst prepared with a mass ratio of resorcinol to g-C₃N₄ of 1.5. Moreover, the h-NCNWs catalyst showed excellent stability during the reaction process. The conversion of benzyl alcohol and the high selectivity to aldehyde can be kept within five catalytic runs over the h-NCNWs0.5 catalyst. These results indicate that rationally designed carbon materials have great potential as highly efficient heterogeneous catalysts for oxidation reactions.     

10MeVLIA强流电子束的输运

介绍了１０ＭｅＶ直线感应加速器（ＬＩＡ）束输运系统布局及实验的调试规律。分析了束横向运动对束稳定输运的影响，理论分析和实验调试的结果表明，抑制束稳定输运的主要障碍来自束的横向运动。当束稳定输运时，可获得束能１０．４ＭｅＶ，束流强度２．６ｋＡ，束半高宽约１００ｎｓ的强流脉冲电子束。     

聚甲基异丙烯基酮和聚异亚丙基丙酮的不对称硅氢化反应

光活性高分子的合成具有重要意义，它在生物活性高分子、用于不对称合成的高分子试剂或催化剂以及不对称选择性色谱柱填料等领域具有潜在的应用价值．研究表明，不对称选择性聚合反应难以获得高光学活性的高分子［１］，而手性过渡金属络合物催化的高分子不对称反应是获得...     

聚甲基乙烯基酮的不对称还原反应

聚甲基乙烯基酮的不对称还原反应李弘姚金水何炳林（吸附与分离功能高分子材料国家重点实验室南开大学高分子化学研究所天津３０００７１）关键词对称硅氢化，聚甲基乙烯基酮，手性噻唑烷，铑近年来手性过渡金属络合物催化的前手性酮和烯的不对称硅氢化反应已在国际上受...     

噻唑烷类手性配体在不对称硅氢化反应中的应用(Ⅱ)

噻唑烷类手性配体在不对称硅氢化反应中的应用（Ⅱ）＊李弘姚金水何炳林（南开大学高分子化学研究所吸附与分离功能高分子材料国家重点实验室，天津３０００７１）关键词手性配体，铑络合物，噻唑烷，苯乙酮，不对称硅氢化自８０年代末期以来，合成了许多高活性、高选择性...     

Spectrofluorimetric Assay of Cationic Surfactants by Fluorescence Quenching of 9-Anthracenecarboxylic Acid

A new simple, selective and sensitive fluorescence quenching method was developed to determine cationic surfactants with the 9-anthracenecarboxylic acid (ACA). The fluorescence intensity of ACA was decreased by addition of trace amounts of cationic surfactants. Under optimum conditions, the ratio of fluorescence intensity in the absence and presence of cationic surfactants was proportional to the concentration of cationic surfactants over the range of 0.3–4.5 × 10⁻⁵ mol L⁻¹ for cetylpyridinium chloride (CPC) and 0.4–6.0 × 10⁻⁵ mol L⁻¹ for cetyl trimethyl-ammonium bromide (CTAB). The detection limits are 1.0 × 10⁻⁶ mol L⁻¹ for CPC and 1.2 × 10⁻⁶ mol L⁻¹ for CTAB, respectively. Based on this approach, this paper presents a new quantitative method for cationic surfactants assay.     

On the selective local stabilization of the mixed Q1–P0 element

In this paper we study the stability and performance of the quadrilateral finite element ??₁–??₀ (bili‐ near/constant) for the Stokes equations. We set up a framework to show the stability of the element for a wide range of meshes with macroelement patches. We apply the new theory to show the stability of ??₁–??₀ elements on some previously studied meshes and on some newly suggested meshes. Nevertheless such earlier and newly suggested meshes are not effective in practice, compared to the traditional unstable meshes for the ??₁–??₀ element. The new theory leads naturally to a general idea in treating instability of square ??₁–??₀ elements by the local stabilization on macroelement patches of larger, but fixed sizes. The good performance of the traditional ??₁–??₀ square elements with filtering can be kept in some cases after the local stabilization. Some numerical tests are provided to support the theory and to show the performance of stabilized ??₁–??₀ elements. Copyright © 2007 John Wiley & Sons, Ltd.