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111.
A sterically controlled transformation of 3-oxo-17β-acetoxy-Δ1?-α-androstene ( 2 ) into 1β,4β-oxido-3-aza-17β-hydroxy-A-homo-5α-androstane ( 16 ) is described. With the exception of two conversions [ 14 → 15 (60%); 15 → 16 (50%)], the yields of the remaining seven steps are higher than 75% each. The reaction sequence will serve as a model for an analogous partial synthesis of samandarine ( 1 ). 相似文献
112.
Pulsed-laser assisted field evaporation of the Rh{001} plane produces a p(2 × 2) structure. This structure can be destroyed by pulsed-laser heating the surface in the absence of an applied field, and can be restored to near perfection if the pulsed-laser heating is done in an applied field of 3 to 4 . The degree of order increases with the applied electric field. The observed p(2 × 2) surface is therefore a field stabilized structure. 相似文献
113.
Using a duality-like finite energy sum rule, we discuss the assumption of having excited fermions at the W scale in a supersymmetric(SUSY) and non-supersymmetric hypercolour theory where quarks and leptons are bound states of fermion and scalar preon constituents. We conclude that a SUSY-like composite model cannot have excited fermions having a mass smaller than 0.5 TeV. A non-SUSY composite model having composite fermions but elementary W bosons can produce an excited fermion mass of the order of MW provided that the scalar vacuum condensate is of the order of the (TeV)2 scale of compositeness. 相似文献
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116.
将矢量衍射数值算法—严格耦合波分析用于精确计算亚波长闪耀光栅的衍射效率,并分析其衍射特性。建立了闪耀光栅的电磁介质模型,并将楔形不规则结构简化为多层矩形光栅结构,通过电磁场的介质分布建立严格耦合波方程。根据边界条件求解出各层的电磁场分布,再通过增透矩阵方法将各层电磁场依次迭代,求解出了整个结构的衍射效率。计算分析显示,对闪耀角为11.3°、周期为500 nm的金属铝闪耀光栅可以得到高于90%的衍射效率和相应的闪耀级次。实验表明这种矢量衍射数值算法具有较高的准确性,可以推广应用于高致密刻线复杂光栅的衍射计算分析。 相似文献
117.
Pelegrin Blas; Fernandez Pascual; Suarez Rafael; Garcia Maria Dolores 《IMA Journal of Management Mathematics》2006,17(4):373-385
** E-mail: pelegrin{at}um.es Firms normally use either a mill price or a delivered pricepolicy, depending on market conditions (type of good, transportationway, customers location, costs, etc). In this paper, the problemof selecting the best location for an entering firm in competitionwith some pre-existing firms, under each price policy, is studiedon a network for the first time. With mill pricing, an equilibriumin price rarely exists and it is assumed that all competingfirms set a common mill price for all customers. With deliveredpricing, there exists a Nash equilibrium in price and it isassumed that the equilibrium price in each area is offered tothe customers in that area. In both cases, we consider thatcustomers buy from the cheapest facility and the same rulesare used for tie breaking in the lowest cost. While the profitmaximization problem for the entering firm always has optimalsolutions under mill pricing, this problem might not have anoptimal solution under delivered pricing. We show some discretizationresults and give procedures to find the full set of optimal,or -optimal, solutions to the problem under the two price policies.A comparison of results with the two price policies is givenby using an illustrative example. 相似文献
118.
Dehydroindigo: a new piece into the Maya Blue puzzle from the voltammetry of microparticles approach
Doménech A Doménech-Carbó MT Vazquez de Agredos Pascual ML 《The journal of physical chemistry. B》2006,110(12):6027-6039
Combining a novel technique, the voltammetry of microparticles, with spectrometric, nuclear magnetic resonance, electron microscopy, and atomic force microscopy data, Maya Blue is detected in wall paintings of the Substructures A-3, A-5, and A-6, dated in the Early Classical period (440-450 a.c.), and the Substructure II-C, dated in the Late Preclassical period (150 b.C.), in the archaeological site of Calakmul (Campeche, Mexico), thus providing evidence on the use of the pigment 750 years prior to the date currently accepted. Electrochemical measurements, supported by spectrometric data, indicate that the presence of palygorskite-attached dehydroindigo, the oxidized form of indigo, contributes to the greenish color of Maya Blue. Enthalpy and entropy of attachment of such compounds to palygorskite are calculated from the temperature dependence of electrochemical data. Both attachment processes are endothermic, becoming thermodynamically spontaneous at moderate temperatures. Accordingly, ancient Mayas may modulate the hue of Maya Blue from turquoise to greenish blue by controlling the temperature during the crushing process. 相似文献
119.
In this paper, we study a quantum anti-Zeno effect (QAZE) purely induced by repetitive measurements for an artificial atom interacting with a structured bath. This bath can be artificially realized with coupled resonators in one dimension and possesses photonic band structure like Bloeh electron in a periodic potential. In the presence of repetitive measurements, the pure QAZE is discovered as the observable decay is not negligible even for the atomic energy level spacing outside of the energy band of the artificial bath. If there were no measurements, the decay would not happen outside of the band. In this sense, the enhanced decay is completely induced by measurements through the relaxation channels provided by the bath. Besides, we also discuss the controversial golden rule decay rates originated from the van Hove's singularities and the effects of the counter-rotating terms. 相似文献
120.
水上交通事故严重程度影响因素的识别对从根本上减少严重事故件数、降低事故危害和损失具有重要意义。在历史事故报告的基础上,构建并量化事故影响因素集,提出以极限学习机(ELM)为一般事故、严重事故的二分类器,以遗传算法(GA)为因素搜索算法的GA-ELM因素识别模型。对发生在我国水域的737件水上交通事故进行实证研究,并与以支持向量机(SVM)为分类器的GA-SVM模型进行对比分析。结果表明,GA-ELM模型识别出时段、人为致因、环境致因等9个事故严重程度影响因素,较GA-SVM模型结果更为精简,且分类精度较不做因素识别时分别提高8.2%、7.1%。此外,GA-ELM大大缩短运算时间。由此可见,GA-ELM可为水上交通事故严重程度影响因素识别提供一个较好的方法。 相似文献