Efficient improvement of laser beam quality by coherent combining in an improved Michelson cavity

The efficient improvement of laser beam quality is demonstrated by coherent combining of two Nd:YVO4 lasers in an improved Michelson cavity. When the two lasers are separately operated with beam qualities of M(x)2 = 1.74 and M(y)2 = 1.34 for laser 1 and M(x)2 = 1.53 and M(y)2 = 1.39 for laser 2, by coherent combining of the two lasers, a single beam output exceeding 2 W with a nearly perfect TEM00 mode (M(x)2 = 1.08, M(y)2 = 1.04) is obtained. Moreover, it can withstand environmental perturbations with no change in beam quality or output power and has the potential for scaling to much higher output power with high beam quality by coherent addition of multiple lasers in this configuration.     

与交通安全有关的几道物理题

在人的生命越来越得到重视的今天,安全教育已经成为学校教育的重要任务之一．面对每年10万多人的死伤,更觉得加强对安全意识比较薄弱的中学生进行安全教育的必要．据报道：分析全国道路交通事故情况,主要原因有超速行驶、酒后驾驶、疲劳驾驶,恶劣天气导致的事故,特别是全国雨、雪、雾等恶劣天气条件下发生道路交通事故;还有低驾龄驾驶人肇事等．     

1,2,6,7-四氢-8H-茚并[5,4-b]呋喃-8-酮的合成新方法

发展了一条1,2,6,7-四氢-8H-茚并[5,4-b]呋喃-8-酮的新合成方法,以价廉、易得的对溴苯酚为原料,在无水碳酸钾作用下与2-溴乙醛缩二乙醇缩合后用多聚磷酸(PPA)环合得5-溴苯并呋喃,该中间体与丙烯酸甲酯在Pd(OAc)2催化下,经Heck偶合反应得3-(苯并呋喃-5-基)丙酸甲酯,在氢氧化钠水溶液中经Raney Ni催化氢化和水解一锅反应得3-(2,3-二氢苯并呋喃-5-基)丙酸,再经二溴代、Friedel-Crafts酰化反应和氢解脱溴,得1,2,6,7-四氢-8H-茚并[5,4-b]呋喃-8-酮,7步反应总收率49.9%.该方法原料易得、反应条件温和、操作简便、产物分离纯化容易,收率良好,适合大规模制备1,2,6,7-四氢-8H-茚并[5,4-b]呋喃-8-酮.     

掠夺与归还：西方争议性遗产的伦理困境

殖民地文物归还事件引发的争议揭示了去殖民化进程的困境。“归还”被期待生成新的关系伦理,但其认知与行动都基于以所有权为核心的物权伦理,未能关照殖民主义文物占有的神话学经验,遮蔽了物伦理的政治性与异质性;而将物权伦理作为“普世伦理”正是资本主义全球扩张的结果。维护物权伦理的物的知识巩固了对文物的祛魅与分裂,使文物即便归还,也仍需“神圣”博物馆赋能,有悖于“恢复原状”的假设。以物为主体/物质化的伦理考察有助于突破物权伦理的普世意识,建立起对普遍困境的反身性思考。作为争议性文化遗产的殖民地文物及其归还事件应作为生产性的实践,激发去殖民化的知识反思。     

Solid-phase microextraction under controlled agitation conditions for rapid on-site sampling of organic pollutants in water

An electric drill coupled with a solid-phase microextraction (SPME) polydimethylsiloxane (PDMS) fiber or a PDMS thin film was used for rapid sampling of polycyclic aromatic hydrocarbons (PAHs) in aqueous samples. Laboratory experiments demonstrated that the sampling rates of SPME fiber and thin film can be predicted theoretically. Compared with the SPME fiber, the PDMS thin film active sampler exhibited a higher sampling rate and much better sensitivity due to its higher surface-to-volume ratio and its larger extraction phase volume. The amount of the analytes extracted by the thin film was around 100 times higher than those obtained by fiber, for both 5 min rapid sampling and equilibrium extraction. A new thin film active sampler was then developed for rapid on-site water sampling. The sampling kit included a portable electric drill, a copper mesh pocket, a piece of thin film, and a liner. Laboratory experiments indicated that the sampling remained in the linear uptake phase with this sampler to 8 min for the PAHs. Field test illustrated that this novel sampler was excellent for rapid on-site water sampling due to its short sampling period, high sampling efficiency and durability The thin film sampling kit facilitates on-site sampling, sample preparation, storage and transport. This new sampler is more user-friendly and easier to commercialize than previous samplers.     

Field sampling with a polydimethylsiloxane thin-film

In this research, field samplers are developed using polydimethylsiloxane (PDMS) thin-film as the extraction phase. This technique is based on a similar theory, the solid-phase microextraction (SPME) technique. More specifically, the development of the field sampler involves cutting a section of PDMS thin-film into a specific size and shape, and mounting it onto a stainless steel wire (the handle). The thin-film is then placed into a protective copper cage prior to deployment to prevent biofouling. Kinetic calibration or equilibrium calibration with the standards in the extraction phase is used to introduce an isotopically labeled internal standard for on-site calibration. The initial loading of the standard onto the thin-film and the amount of standard remaining on the thin-film are determined using gas chromatography-mass spectrometry and subsequently used to estimate the concentration of the target analytes. In addition, the field samplers are deployed in the field at two locations (the Meuse River in Eijsden, The Netherlands from April to May, 2005 and Hamilton Harbour located at the western tip of Lake Ontario, ON, Canada from September to December, 2006). Polycyclic aromatic hydrocarbons are identified, and concentrations of fluoranthene and pyrene are estimated in the low ng/L range. The results from both sampling sites are within the expected ranges for environmental samples. This polymeric extraction phase has a high surface-to-volume ratio compared with SPME, which results in higher sensitivity and mass uptake, leading to the detection of lower levels of analytes that many other techniques are unable to achieve.     

Antiangiogenic phenylpropanoid glycosides from Gynura cusimbua

A new phenylpropanoid glycoside, named α-L-rhamnopyranosyl-(1?2)-β-D-[4″-(8E)-7-(3,4-dihydroxyphenyl)-8-propenoate, 1″-O-(7S)-7-(3,4-dihydroxyphenyl)-7-methoxy-ethyl]-glucopyranoside (1), together with nine known compounds (2–10) were isolated from the active fraction (n-Butanol fraction) of Gynura cusimbua for the first time. The known compounds (2–10) were identified as phenylpropanoid glycosides on the basis of extensive spectral data and references. The antiangiogenic activities of compounds (1–10) were evaluated by MTT assay on HUVECs and wild-type zebrafish in vivo model assay. As a result, compounds 1, 6, 7, 8 and 10 exhibited certain antiangiogenic activities.     

Synthesis, characterization, antibacterial and antifungal evaluation of novel monosaccharide esters

A novel series of 3-(2-furyl)acrylate monosaccharide esters Ia–f and menthyloxycarbonyl monosaccharide esters IIa–f were designed and synthesized. The chemical structures of the target compounds were confirmed by IR, 1H- and 13C-NMR and ESI-MS, and the target compounds were investigated for their in vitro antibacterial and antifungal activities. The antibacterial screening results showed that the 3-(2-furyl)acrylate monosaccharide ester derivatives Ia–f were either inactive or only weakly active against the three Gram-positive bacterial strains tested, whereas the menthyloxycarbonyl monosaccharide ester derivatives IIa–f exhibited higher levels of activity, with compound IIe being especially potent. The results of the antifungal screening revealed that compounds Ib, Ie, IIb and IIc displayed potent in vitro activities, whereas If and IIf showed promising activities against all of the microorganisms tested, with If exhibiting levels of activity deserving of further investigation.