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According to the characterization of RNA secondary structures, the RNA secondary structures are transformed into elementary
sequences, namely characteristic sequences of RNA secondary structures, by representing A, U, G, C in A-U/ G-C pairs, as A′,
U′, G′, C′. Based on the representation, three recurrences for mapping RNA secondary structures into 1-D graph, 2-D graph
and 3-D graph are given, respectively. Furthermore, a frequency-based method for RNA secondary structures is given in terms
of 1-D graph. 相似文献
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Haoran Dong Dachao Hu Dr. Benke Hong Dr. Jin Wang Prof. Dr. Xiaoguang Lei 《Angewandte Chemie (International ed. in English)》2023,62(20):e202301872
We report herein the first total syntheses of four natural antibiotics, vermisporin, PF1052/AB4015-A, AB4015-L, AB4015-B, and one hydrogenated natural product derivative, AB4015-A2, that all feature a tetramic acid bearing cis-decalin ring. The construction of the functionalized cis-decalin ring was achieved by a diastereoselective intramolecular Diels-Alder (IMDA) reaction, which proceeded via a rare endo-boat transition state. Through an intramolecular neighboring-group-oriented strategy, the sterically hindered epoxy group in vermisporin, PF1052/AB4015-A and AB4015-L was installed efficiently. A one-pot aminolysis/Dieckmann condensation cascade using l -amino acid derivatives afforded the desired tetramic acid structure. The total synthesis led to the unambiguous verification of the absolute configuration of these natural products. 相似文献
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Xiaoqing Zhang Yesim Gozukara Parveen Sangwan Dachao Gao Stuart Bateman 《Polymer Degradation and Stability》2010,95(12):2309-2317
Biodegradation of a series of chemically modified thermally processed wheat gluten (WG)-based natural polymers were examined according to Australian Standard (AS ISO 14855). Most of these materials reached 93-100% biodegradation within 22 days of composting, and the growth of fungi and significant phase deformation were observed during the process. Chemical crosslinking did slow down the rate or reduce the degree of the biodegradation with different behaviours for different modified systems. The segments containing structures derived from the reactions with additives such as tannin or epoxidised soybean oil remained in the degradation residues while the glycidoxypropyl trimethoxysilane agent produced ∼20% un-degraded residues containing silicon-crosslinking structures. The biodegradation rate of each component of the materials was also different with the protein and starch components degraded fast but lipid degraded relatively slowly. 相似文献
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LinKo-Wei[1]提出猜想:如果F是由Bn中固定秩的不同元素生成的序理想,那么F是Sperner系[1],黄国泰就F是由X的子集Y的所有相同秩的元素生成的序理想,证实了上述猜想[2],本文完全证明了该猜想.本文使用的概念,符号见[2].定理设a... 相似文献
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微结构特性的光学测试平台 总被引:10,自引:0,他引:10
微结构是微机电系统的基本元件,其几何尺寸、运动特性、材料及力学特性直接影响微机电系统的整体性能。提出一种将计算机微视觉、米劳显微干涉、频闪成像和激光多普勒测振等技术充分融合的微结构静态和动态特性的光学测试平台,分别对微谐振器的平面和离面周期运动特性和微机械扭转镜的离面瞬时运动特性进行测试研究。实验结果表明,利用计算机微视觉和频闪成像技术能够实观微结构的平面位移、运动相位及喈振频率等周期运动参量的测试.位移的重复精度为30nm;利用显微干涉和频闪成像技术可实现微结构的离面位移及表面扭曲等周期运动参量的测试.位移的重复精度为3nm;激光多普勒测振技术具有在频域上对微结构瞬态运动进行分析的优点.是时域上周期运动测试的重要补充。 相似文献
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Renewable natural polymers wheat starch (WS) and wheat gluten (WG) were successfully processed into plastic bulk materials using back pressure equal channel angular consolidation (BP-ECAC) without using any additional plasticizers at relatively low temperatures. The strong shear deformation occurred during the process caused an effective deformation of WS or WG granular structures and resulted in an efficient gelatinization of starch or plasticization of gluten with the natural moisture content. Sufficient chain entanglement was formed in both WS and WG materials for achieving strong cohesion among the macromolecule matrixes. The mechanical strength of the obtained plastic materials was comparable to that of conventional polymers but stronger than the strength of thermoplastic WS or plasticized WG. The processing temperature played an important role in determination of morphologies and properties of the plastic materials. Increasing processing temperature would cause more effective gelatinization or plasticization of the natural polymers, enhance the interactions among different components in the systems, and form materials with improved mechanical properties. Thermal cross-linking might play a positive role in the improvement of mechanical properties when processing temperature was increased. However, thermal decomposition could also occur under such severe shearing especially at high temperatures. The optimum temperature for conducting such process was around 100-120 °C for WS and WG. The BP-ECAC method provides a potential to manufacture natural polymer based plastic materials efficiently on an industrial scale for various applications. 相似文献
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在ZnS晶体3C⇔2H结构转变的X—射线Laue衍射分析中,为了解释一维无序造成的异常衍射现象,本文推导了Laue衍射图曲线晶带的“奇异点”计算公式。并应用此公式,计算了ZnSLaue衍射照片上数条晶带上的“奇异点”,计算值与实验值完全吻合。另外,本文还对“奇异点”的形成、特点、标定的意义以及计算公式适用范围进行了讨论。 相似文献