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51.
Halichlorine and Pinnaic acid are two novel marine natural products isolated from a Japanese sponge, and an Okinawan bivalve respectively. The unique azaspirl[4.5]decane-core structure prexent in both compounds provides a synthetic challenge, Herein, we describe a synthetic approach to the azaspiro[4.5]decane-core structure through an intramolecular[3+2] cycloaddition followed by an intra-molecular Michael addition and in situ isomerization to afford the azaspirocyclic core structures stereospecifically in 10 steps with 40% overall yield. Alternatively, the same core structure was achieved by tandem cycloaddition and isomerization approach. 相似文献
52.
LEE G. ANDERSON 《Natural Resource Modeling》2000,13(4):435-470
ABSTRACT. This paper investigates the intertemporal effects of introducing Individual Transferable Quota, ITQ, fishery management programs on stock size, fleet size and composition, and returns to quota holders and to vessel operators. Theoretical analysis is conducted using a specific version of a general dynamic model of a regulated fishery. It is demonstrated that the effects will differ depending upon the prevailing regulation program, current stock size, and existing fleet size, composition and mobility and upon how the stock and fleet change over time after the switch to ITQs. The paper expands upon previous works by modeling the dynamics of change in fleet and stock size and by allowing for changes in the TAC as stock size changes, by comparing ITQs to different regulations, and by allowing the status quo before ITQ implementation to be something other than a bioeconomic equilibrium. Specific cases are analyzed using a simulation model. The analysis shows that the annual return per unit harvest to quota owners can increase or decrease over the transition period due to counteracting effects of changes in stock and fleet size. With ITQs denominated as a percentage of the TAC, the current annual value of a quota share depends upon the annual return per unit of harvest and the annual amount of harvest rights. Because the per unit value can increase or decrease over time, it is also possible that the total value can do the same. Distribution effects are also studied and it is shown that while the gains from quota share received are the present value of a potentially infinite stream of returns, potential losses are the present value of a finite stream, the length of which depends upon the remaining life of the vessel and the expected time it will continue to operate. 相似文献
53.
考察了多糖类手性固定相在含有酸性或碱性添加剂的流动相下高效液相色谱法拆分β受体阻滞剂对映体的效果。色谱条件: 流动相为10%~30%(体积分数,下同)乙醇-正己烷(含0.1%三氟乙酸)和10%~30%乙醇-正己烷(含0.1%三乙胺),流速1.0 mL/min,紫外检测波长254 nm。结果表明,在直链淀粉-三(3,5-二甲基苯基氨基甲酸酯)衍生物手性固定相(Chiralpak AD和Chiralpak IA)上拆分β受体阻滞剂对映体,酸性添加剂的流动相体系与碱性添加剂的流动相体系相比,碱性添加剂的流动相的拆分效果比酸性添加剂的流动相要好。而在纤维素-三(3,5-二甲基苯基氨基甲酸酯)衍生物的手性固定相(Chiralcel OD和Chiralpak IB)上分离β受体阻滞剂,比较酸性添加剂的流动相与碱性添加剂的流动相的拆分效果,发现酸性添加剂的流动相条件下对映体的保留减弱,但对映体的选择性增大,特别是在Chiralcel OD上,酸性添加剂的流动相体系对对映体的选择性非常理想,而且随着流动相中酸性添加剂含量的增加,β受体阻滞剂对映体的分离效果更佳。 相似文献
54.
提出了一个考虑背景光光伏效应贡献的光伏孤子理论,它指出在折射率变化为正的晶体中,既可产生光伏亮孤子,也可产生光伏暗孤子.当背景光对信号光的有效Glass系数之比为R小于1时,孤子是亮的;R大于1时,孤子是暗的.对亮孤子而言,R值越大,孤子越宽,而对暗孤子,R值越大,孤子越窄.当R为1时,不能形成光伏孤子.一维暗孤子实验结果与理论一致.
关键词:
光折变空间孤子
光伏孤子
暗孤子
正折射率改变 相似文献
55.
56.
Applied Physics A 53, no. 3 (1991) 相似文献
57.
58.
We optimize the room-temperature etching of InP using Cl2/CH4/H2 and Cl2/N2 inductively coupled plasma reactive ions. A design of experiment is used in the optimization. The results, in terms of etch rate, surface roughness and etched profile, are presented. These Cl2-based recipes do not require substrate heating and thus can be more cost effectively and widely applied. The Cl2/CH4/H2 process is able to give a higher etch rate (about 850 nm/min) and cleaner surface with less polymer formation compared to the conventional CH4/H2 process. The Cl2/N2 process produces even higher etch rate (as high as 2μm/rain), but rougher surface with slight sidewall undercut. The Cl2/N2 process also has no polymer formation due to the absence of methane gas. Both the processes give very good selectivity to the silicon dioxide (SiO2) etch mask. The selectivity of InP to the oxide mask (up to 55:1) for the Cl2/N2 process is one of the highest reported so far. The etched structures possess reasonably good sidewall verticality and surface quality comparable to that obtained under elevated temperature condition (〉 200℃). 相似文献
59.
Applied Physics A 49, no. 2 (1989) 相似文献
60.
The time-averaged spontaneous radiation power and its spectrum are derived analytically. The collective mode is taken to be electron-cyclotron mode driven by the relativistic electron beam existing in the unstable and late phases of plasma focus. The infrared range radiation calculated is in agreement with experimental observation. 相似文献