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国际化学奥林匹克竞赛(IChO)在其创办以来,随着她日益增长的声望,已经发展成为一个真正的世界范围的竞赛。来自各国在化学上最有才能的青年的每年聚会,对这些学生来说是一件大事和激励人心的经历。陪同学生的教师,在某种程度上代表着各国的中学化学教育,他们也喜爱这种定期和直接交流信息的极难得的机会。然而,IChO 的发展,已经产生了与组织工作和竞赛内容有关的许多问题。近来谈论最多的是国际奥林匹克竞赛参加者人数的增长问题。1986年在荷兰莱顿所举行的第十八届IChO,参加者已有来自三大洲22个国家之多,并且还有十多个国家(包括澳大利亚及亚洲、非洲、和南美的一些国家)表示对这种竞赛感兴趣。 相似文献
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Fengkun GUO 《原子核物理评论》2020,37(3):406-413
对强子谱的研究有助于加深量子色动力学中色禁闭现象的理解。强子谱中存在诸多疑难问题,特别是2003年以来各高能物理实验上发现了很多难以理解的新的强子共振结构,其中大量是在重夸克偶素质量区间发现的,它们被统称为$XYZ$ 结构。强子共振态对应于$S$ 矩阵的极点。除此之外,$S$ 矩阵还具有其它类型的奇点,比如由于三个中间态粒子同时在 壳导致的三角奇点。本文中,我们将讨论三角奇点在$XYZ$ 物理中的实现,注重于构造可以用来分析 其对$e^+e^-\to\psi\pi^+\pi^-$ 反应的$\psi\pi$ 不变质量谱中的带电$Z_c$ 结构的影响的振幅。 相似文献
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文中对R116跨临界热泵循环进行了理论分析,分别计算了压缩机最优排气压力和回热器对系统性能的影响。计算结果表明,系统存在最优排气压力,最优排气压力与制冷剂气冷器出口温度、蒸发温度以及过热度都有关系,利用多项式函数对最优排气压力进行了拟合,拟合的最大相对误差为-5.92%,平均相对偏差为1.77%;在蒸发温度-5℃、0℃、5℃,过热度5℃、10℃、15℃,气冷器出口温度25℃—70℃的情况下,分别对系统回热循环性能进行了分析计算,结果表明回热循环性能较无回热循环有大幅的改善,改善幅度介于12—95%之间。文中结果可以为R116跨临界热泵系统的设计和控制提供理论参考。 相似文献
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Yuki Morimoto Dr. Fengkun Chen Yusuke Matsuo Koki Kise Dr. Takayuki Tanaka Prof. Dr. Atsuhiro Osuka 《化学:亚洲杂志》2021,16(6):648-655
Hetero[8]circulenes have emerged as novel functionalized heteronanographenes that show various promising functions such as bright fluorescence, charge transporting, and redox reactivities. One of the effective synthetic strategy is the fold-in type oxidative fusion reaction of ortho-phenylene-bridged cyclic tetrapyrroles, whose construction, however, is not well-sophisticated in terms of reproducibility and possibility for versatile derivatization. In this paper, a “reverse” coupling strategy has been developed, which enabled synthesis of opp-type low symmetric analogues of cyclic tetrapyrroles. Oxidative fusion reaction conditions to afford tetraaza[8]circulenes have also been reinvestigated and improved. Substituent effects of cyclic tetrapyrroles and tetrabenzotetraaza[8]circulenes are studied for solid-state structures and packing structures, redox potentials, and optical properties. 相似文献
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采用CO_2天然混合制冷剂的制冷系统热力学分析 总被引:1,自引:1,他引:0
受工况条件的限制,CO2制冷系统在实际应用中往往需要采用跨临界循环,高压侧压力高达10MPa及以上。高的运行压力对系统各部件、设备的安全运行均提出更高要求,从而造成初投资增大。采用CO2混合工质,可以有效地改善纯的CO2系统存在的不足。针对三组CO2天然混合工质——R744/R290、R744/R600、R744/R600 a,在特定的工况条件下,对制冷系统进行了热力学理论分析和计算。探讨了混合工质中CO2不同质量配比、不同蒸发器出口制冷剂温度对系统制冷量、COP和冷凝压力的影响。结果表明:在相同工况下,R744/R290的冷凝压力比R744R/600高12~23%,比R744/R600 a高19~24%;R744/R290的COP值比R744/R600高33~41%,比R744/R600 a高25~32%。 相似文献
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Fengkun Chen Dr. Jie Zhang Prof. Xinhua Wan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(15):4558-4567
Computational analysis predicts that intramolecular charge transfer (ICT) exists in anthraquinone imide (AQI) derivatives with electron‐donating substituents at the 6‐position, such as 4‐methoxylphenyl, 4‐N,N‐dimethylaminophenyl, and thiophene. However, for those with electron‐withdrawing ones, no clear ICT interaction could be observed. We predicted, on the basis of the simulation results, that AQI derivatives with electron‐donating substituents would be piezochromic. To verify this hypothesis, the corresponding AQI derivatives with various substituents were synthesized. Absorption spectra recorded with a diffuse reflectance method on powders revealed that 4‐methoxylphenyl‐, 4‐N,N‐dimethylaminophenyl‐, and thiophene‐substituted AQI exhibited piezochromism, but not 4‐nitrophenyl‐substituted AQI, which is in good agreement with the simulation results. Interestingly, redshifts of both the lower and higher energy absorption bands were observed along with redshifts of the emission spectra. However, XRD patterns before and after being pressed presented no significant changes, which was different from known piezochromic molecules described in the literature. An unprecedented mechanism in which enhanced ICT from better conjugation between the donor and acceptor segments induced by the decrease of θ under pressure could be responsible for the piezochromism of aryl‐substituted AQIs is proposed. 相似文献