AN ALGORITHM FOR SOLVING SPACECRAFT REACHABLE DOMAIN WITH SINGLE-IMPULSE MANEUVERING 1)

航天器轨道机动可达域是表征其在未来时间可能到达空间位置集合的有效方式,对维护航天器在轨安全、改善空间态势感知能力具有重要意义.现有关于可达域计算的方法仍然存在模型复杂、初值敏感性高导致计算效果较差等缺点,因此有必要发展更加简洁有效的可达域包络求解算法.本文基于近心点坐标系建立了基于未来可达位置矢量极值求解的可达域求解模型,首先定义任意指向的矢量描述方法并给出未来该指向位置是否可达的判据;其次,设置转移轨道面内机动方位角,将可达域求解问题转化为当前可达位置矢量方向的单变量极值求解问题,利用极值点处可达域包络面函数梯度需为零的条件确定转移轨道面机动方位角的取值,从而确定航天器的轨道机动可达域;此外根据二体轨道动力学特性,利用包络的对称性减少可达域求解计算量;最后通过蒙特卡洛打靶仿真对提出的可达域求解方法进行仿真验证.结果表明,本文方法对航天器单脉冲轨道机动可达域的计算结果与蒙特卡洛打靶仿真吻合良好,模型更加简洁且计算精度优于现有方法.     

1D and 2D supramolecular structures of silver carborane dicyclohexylphosphine complexes constructed by C-H?H-B dihydrogen bonding interactions

Five new carborane dicyclohexylphosphine complexes, [Ag₂(μ-I)₂{1,2-(P Cy₂)₂-1,2-C₂B₁₀H₁₀}₂] (1), [Ag₂(SCN)₂{1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}₂]_n·CH₂Cl₂ (2), [Ag(ClO₄){1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}]·CH₂Cl₂ (3), [Ag₂(μ-NO₃)₂{1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}₂]·CH₂Cl₂ (4) and [Ag(SC₆H₄COOH){1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}₂]·CH₂Cl₂ (5), have been synthesized by the reactions of 1,2-bis(dicyclohexylphosphino)-1,2-dicarba-closo-dodecaborane with AgX (X = I, SCN, ClO_4, NO₃ and SC₆H₄COOH) in CH₂Cl₂. The structures of the five complexes were characterized by elemental analysis, FT-IR, ¹H, ¹³C, ¹¹B and ³¹P NMR spectroscopy. X-ray structure analysis revealed that the structures of the complexes can be classified into three types. Complexes 1 and 4 are di-μ-X-bridged structures and complexes 3 and 5 are mononuclear structures, while complex 2 is a chain-like polymer. Complexes 1 and 2 form 2D supramolecular networks and complexes 3, 4 and 5 form 1D chains via C-H?H-B dihydrogen bonding interactions.     

Synthesis of block polyethers with various structures and their application in dispersing single-walled carbon nanotubes

The block polyethers with different structure and composition were synthesized by anionic polymerization and used to disperse single-walled carbon nanotubes (SWNTs). The block polyethers with the structure of branch or benzene ring had better dispersion ability than the commercial Pluronic block polyethers (L64 and F127). In order to compare the parameters, dispersion limit and efficiency of polyethers for SWNTs were defined. UV?Cvis?Cnear infrared absorbance spectra showed that eight-branch polyether AE82 had much larger dispersion limit and efficiency than five-branch AE52. BPE containing benzene rings in the molecule had a slightly lower dispersion limit but larger dispersion efficiency than AE82. The defect density of SWNTs dispersed in polyether aqueous solutions was investigated by Raman spectroscopy. The polyethers AE83 and BEP with the structure of poly(ethylene oxide)?Cpoly(propylene oxide) dispersed less defective SWNTs than AE82 and BPE, indicating that the variation of polyether structure and composition could influence the defect density of SWNTs besides dispersion limit and efficiency.     

Synthesis of phosphates and phosphates-acetates hybrids of green tea polyphenol (−)-epigallocatechine-3-gallate (EGCG) and its G ring deoxy analogs as potential anticancer prodrugs

A series of phosphate or phosphate-acetate hybrid modified EGCG or EGCG G ring deoxy analogs were synthesized by a convenient semi-synthesis strategy from the abundant natural compound EGCG.     

低价钛试剂促进下2-(2-硝基苯基)咪唑与席夫碱的反应

在低价钛试剂作用下,以四氢呋喃为溶剂,研究了2-(2-硝基苯基)咪唑与席夫碱的分子间还原偶联反应.结果发现席夫碱中C-N键的断裂优于其与硝基的偶联成环,生成了5,6-二氢化咪唑并[1,2-c]喹唑啉.     

螺烯类化合物的合成研究进展

研究发现螺烯类化合物具有优异的光学和电学性质,已经成为有机化学的研究热点之一,综述了近年来螺烯化合物的合成方法研究进展.     

Molecule-substrate interaction channels of metal-phthalocyanines on graphene on Ni(111) surface

Molecule-substrate interaction channels of metal-phthalocyanines (MPcs, including NiPc, CuPc, ZnPc, FePc, and CoPc) on graphene on Ni(111) were investigated by employing high-resolution electron energy loss spectroscopy (HREELS). Except the expected IR-active modes, some Raman-active modes were also observed in all of MPcs, which are considered in this study. From the origination of the Raman-active features, it was deduced that MPcs are coupled with the substrate mainly through their central metal atom. The Raman-active modes appear as symmetric peaks in the HREELS in the case of MPcs with Ni, Cu, and Zn, whereas they are asymmetric and appear as a Fano line shape in the case of MPcs with Fe and Co. This spectroscopic difference indicates that the molecule-substrate coupling is completely different in the two cases mentioned above. The molecule-substrate interaction strength is considerably weak and comparable with the π-π interaction between molecules in the case of MPcs with Ni, Cu, and Zn, whereas it is much stronger in the case of MPcs with Fe and Co. From the HREELS observations, it can be suggested that the whole molecule can be effectively decoupled from the underneath Ni(111) by inserting a single layer of graphene between them in the case of MPcs with Ni, Cu, and Zn, whereas only benzene rings can be completely decoupled in the case of MPcs with Fe and Co.     

A fully automated system with on-line micro solid-phase extraction combined with capillary liquid chromatography-tandem mass spectrometry for high throughput analysis of microcystins and nodularin-R in tap water and lake water

Microcystins and nodularins are cyclic peptide hepatotoxins and tumour promoters from cyanobacteria. The present study describes the development, validation and practical application of a fully automated analytical method based on on-line micro solid-phase extraction-capillary liquid chromatography-tandem mass spectrometry for the simultaneous determination of seven microcystins and nodularin-R in tap water and lake water. Aliquots of just 100 μL of water samples are sufficient for the detection and quantification of all eight toxins. Selected reaction monitoring was used to obtain the highest sensitivity. Good linear calibrations were obtained for microcystins (50-2000ng/L) and nodularin-R (25-1000 ng/L) in spiked tap water and lake water samples. Excellent interday and intraday repeatability were achieved for eight toxins with relative standard deviation less than 15.7% in three different concentrations. Acceptable recoveries were achieved in the three concentrations with both tap water matrix and lake water matrix and no significant matrix effect was found in tap water and lake water except for microcystin-RR. The limits of detection (signal to noise ratio=3) of toxins were lower than 56.6 ng/L which is far below the 1 μg/L defined by the World Health Organization provisional guideline for microcystin-LR. Finally, this method was successfully applied to lake water samples from Tai lake and proved to be useful for water quality monitoring.