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[reaction: see text] The synthesis of allocyathin B(3) from an advanced intermediate possessing the ring system and relative stereochemistry but lacking the isopropyl and hydroxymethyl groups is reported. The isopropyl group was introduced by radical cyclization of a methyl propargyl acetal of an alpha-bromo ketone, and the hydroxymethyl group was generated by Pd-catalyzed carbonylation of a vinyl triflate. The route provides functionalized intermediates that could allow access to more complex members of the cyathin family of diterpenes. 相似文献
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Small world effects in the harmonious unifying hybrid preferential model (HUHPM) networks are studied both numerically and analytically. The idea and method of the HUHPM is applied to three typical examples of unweighted BA model, weighted BBV model, and the TDE model, so-called HUHPM-BA, HUHPM-BBV and HUHPM-TDE networks. Comparing the HUHPM with current typical models above, it is found that the HUHPM networks has the smallest average path length and the biggest average clustering coefficient. The results demonstrate that the HUHPM is more suitable not only for the un-weighted models but also for the weighted models. 相似文献
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Fei Ye Xiaoyan Qiao Anhui Gui Panpan Liu Shengpeng Wang Xueping Wang Jin Teng Lin Zheng Lin Feng Hanshan Han Binghua Zhang Xun Chen Zhiming Gao Shiwei Gao Pengcheng Zheng 《Molecules (Basel, Switzerland)》2022,27(13)
Roasting is crucial for producing Yuan An yellow tea (YAYT) as it substantially affects sensory quality. However, the effect of roasting time on YAYT flavor quality is not clear. To investigate the effect of roasting time on the sensory qualities, chemical components, odor profiles, and metabolic profile of YAYTs produced with 13 min roasting, 16 min roasting, 19 min roasting, 22 min roasting, and 25 min roasting were determined. The YAYTs roasted for 22 min got higher sensory scores and better chemical qualities, such as the content of gallocatechin (GC), gallocatechin gallate (GCG), free amino acids, solutable sugar, meanwhile the lightness decreased, the hue of tea brew color (b) increased, which meant the tea brew got darker and yellower. YAYTs roasted for 22 min also increased the contents of key odorants, such as benzaldehyde, nonanal, β-cyclocitral, linalool, nerol, α-cedrol, β-ionone, limonene, 2-methylfuran, indole, and longiborneol. Moreover, non-targeted metabolomics identified up to 14 differentially expressed metabolites through pair-wise comparisons, such as flavonoids, phenolic acids, sucrose, and critical metabolites, which were the main components corresponding to YAYT roasted for 22 min. In summary, the current results provide scientific guidance for the production of high quality YAYT. 相似文献
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The determination of 241Am in the environment is of importance in monitoring its release and assessing its environmental impact and radiological risk. This paper aims to give an overview about the recent developments and the state-of-art analytical methods for 241Am determination in environmental samples. Thorough discussions are given in this paper covering a wide range of aspects, including sample pre-treatment and pre-concentration methods, chemical separation techniques, source preparation, radiometric and mass spectrometric measurement techniques, speciation analyses, and tracer applications. The paper focuses on some hyphenated separation methods based on different chromatographic resins, which have been developed to achieve high analytical efficiency and sample throughput for the determination of 241Am. The performances of different radiometric and mass spectrometric measurement techniques for 241Am are evaluated and compared. Tracer applications of 241Am in the environment, including speciation analyses of 241Am, and applications in nuclear forensics are also discussed. 相似文献
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台风对沿海地区气溶胶光学特性的影响分析 总被引:3,自引:0,他引:3
利用CE317太阳辐射计对2005年第19号台风登陆前后期问(9月29 H至10月6日)进行观测实验,采用Langley法分析台风对中国大陆沿海地区气溶胶光学特性的影响.指出台风过后气溶胶光学特性明显发生改变,气溶胶大粒子数增多,小粒子数减小.气溶胶光学厚度、Angstr(o)m波长指数α和大气混浊度系数β为测量期间最低分别为0.132(550 nm处),0.861和0.079.同时利用实验期间APS3321空气动力学粒度仪分析的气溶胶单位体积数粗细质粒所占比重、气溶胶粒子尺度谱分布和实测的日际气溶胶粒子数浓度对实验分析结果.α,β进行对比,发现它们之间的一致性很好. 相似文献
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A novel all-fiber temperature-calibrated refractometer based on a compact fiber Bragg grating(FBG) single-multi-single(SMS)structure is proposed and experimentally demonstrated.The sensor head is composed of a FBG combined with a SMS structure,in which the middle multimode fiber(MMF)section is etched by a time-controlled hydrofluoric.The transmission dip of SMS is extremely sensitive to ambient refractive index(RI)variation,whereas the upstream FBG provides the necessary temperature information for RI calibration.All aforementioned functions are performed via a compact FBG-SMS structure not longer than 25 mm.The proposed sensing device provides a linear RI sensitivity over water or waterbased solutions(RI values near 1.33 at optical wavelengths for most biological and many environmental applications),and has temperature-calibration capability.Hence,the said refractometer is a good candidate for sensing in chemical and biological applications. 相似文献
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Xiangli Qian Huiying Sun Tianlu Chen Danzengluobu Youliang Feng Qi Gao Quanbu Gou Yiqing Guo Hongbo Hu Mingming Kang Haijin Li Cheng Liu Maoyuan Liu Wei Liu Bingqiang Qiao Xu Wang Zhen Wang Guangguang Xin Yuhua Yao Qiang Yuan Yi Zhang 《Frontiers of Physics》2022,17(6):64602
The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energy γ-rays and cosmic rays. With the advantages of a large field-of-view (FOV) and low energy threshold, the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources. This study presents the prospects of using the HADAR experiment for the sky survey of TeV γ-ray sources from TeVCat and provids a one-year survey of statistical significance. Results from the simulation show that a total of 23 galactic point sources, including five supernova remnant sources and superbubbles, four pulsar wind nebula sources, and 14 unidentified sources, were detected in the HADAR FOV with a significance greater than 5 standard deviations (σ). The statistical significance for the Crab Nebula during one year of operation reached 346.0 σ and the one-year integral sensitivity of HADAR above 1 TeV was ~1.3%–2.4% of the flux from the Crab Nebula. 相似文献
20.
基于工频或高频磁化条件下磁芯的测试数据不能准确反映磁芯在单次脉冲磁化下的性能,给出了一种脉冲磁化条件下磁芯性能的测试方法和数据处理方法,实验研究了快脉冲磁化条件下非晶态合金磁芯的损耗特性,磁芯最短饱和时间67 ns,最大磁化速率达到40 T/s。通过数据处理,给出了磁芯损耗与磁化速率的关系曲线,获得了不同磁化速率下磁芯的损耗数据。分析了脉冲磁化条件下涡流损耗和磁滞损耗所占的比例。研究结果表明:脉冲磁化条件下非晶态合金磁芯损耗与磁化速率关系符合饱和波模型,磁芯损耗随磁化速率增大而线性增大。 相似文献