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61.
Gabriele Bocelli Andrea Cantoni Franca Bigi Giovanni Sartori 《Journal of chemical crystallography》1992,22(6):691-694
The structure of the compound obtained by reaction of AlCl3-promotedm-xilene with 2,6-pyridine dicarbonyldichloride in dichloromethane has been investigated by X-ray diffraction methods. The compound is monoclinic, space groupP21/c,a=13.907(2),b=17.247(3),c=12.042(2) Å,=109.75(4)°. The structure was solved by direct methods and refined by full matrix least-squares to a finalR=6.37 for 3718 independent observed reflections [I>2(I)]. The structure of the compound enables an understanding of the chemical pathway of the synthesis process. 相似文献
62.
Raleigh W. Parrott II Christopher G. Hamaker Shawn R. Hitchcock 《Journal of heterocyclic chemistry》2008,45(3):873-878
A series of oxazolidines have been prepared by condensation of N‐isopropyl norephedrine with a variety of salicylaldehyde derivatives. Despite the stereochemical relationship of (1R,2S)‐norephedrine with (1R,2S)‐ephedrine, the resultant oxazolidines 12‐14 were determined to have a stronger stereochemical relationship with (1S,2S)‐pseudoephedrine based oxazolidines. The resultant oxazolidines were used as catalytic ligands in the addition of diethylzinc to several aldehydes. It was determined that the oxazolidine derivative 12 gave the highest yield and a moderate enantioselectivity. 相似文献
63.
Tesia V. Chciuk William R. Anderson Jr. Prof. Robert A. Flowers II 《Angewandte Chemie (International ed. in English)》2016,55(20):6033-6036
The relationship between proton‐donor affinity for SmII ions and the reduction of two substrates (anthracene and benzyl chloride) was examined. A combination of spectroscopic, thermochemical, and kinetic studies show that only those proton donors that coordinate or chelate strongly to SmII promote anthracene reduction through a PCET process. These studies demonstrate that the combination of SmII ions and water does not provide a unique reagent system for formal hydrogen atom transfer to substrates. 相似文献
64.
We present EQCM study for the electrochemical behavior of various 1-methyl-1'-alkylvilogen (C1CnV:n=1, 7-10, 12, 14,16, 18). In some viologens, we discussed the mechanism of CD-induced comproportionation reaction as well as electrodeposition pathway based on the EQCM and the spectroelectrochemical experimental results. 相似文献
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In computational intelligence, the term ‘memetic algorithm’ has come to be associated with the algorithmic pairing of a global search method with a local search method. In a sociological context, a ‘meme’ has been loosely defined as a unit of cultural information, the social analog of genes for individuals. Both of these definitions are inadequate, as ‘memetic algorithm’ is too specific, and ultimately a misnomer, as much as a ‘meme’ is defined too generally to be of scientific use. In this paper, we extend the notion of memes from a computational viewpoint and explore the purpose, definitions, design guidelines and architecture for effective memetic computing. Utilizing two conceptual case studies, we illustrate the power of high-order meme-based learning. With applications ranging from cognitive science to machine learning, memetic computing has the potential to provide much-needed stimulation to the field of computational intelligence by providing a framework for higher order learning. 相似文献
68.
Arthur Jaffe Christian D. Jäkel Roberto E. Martinez II 《Communications in Mathematical Physics》2014,329(1):1-28
We explore a framework for complex classical fields, appropriate for describing quantum field theories. Our fields are linear transformations on a Hilbert space, so they are more general than random variables for a probability measure. Our method generalizes Osterwalder and Schrader’s construction of Euclidean fields. We allow complex-valued classical fields in the case of quantum field theories that describe neutral particles. From an analytic point-of-view, the key to using our method is reflection positivity. We investigate conditions on the Fourier representation of the fields to ensure that reflection positivity holds. We also show how reflection positivity is preserved by various spacetime compactifications of ${\mathbb{R}^{d}}$ in different coordinate directions. 相似文献
69.
Many of the applications that seek to utilize shape memory alloys for their unique set of properties inevitably must deal, on some level, with the dimensional instability that is inherent to these materials under cyclic thermomechanical loading conditions. As a result, a better understanding of the transient and evolutionary behavior of a shape memory alloy is critical to both the successful design of useful actuation systems and development of accurate material models that can adequately capture the types of dimensional instability that can arise during component design. To this end, a set of experiments were conducted wherein the temperature cycling excursion was held fixed while the applied stress was varied. The results indicated that the extent of strain evolution produced under the initially applied stress has a significant impact on both the amount of transient that is observed as well as the rate of evolution observed under subsequent stress levels. In particular, lowering the applied stress to 50 MPa after cycling under an initial stress of 75 MPa did not stabilize the strain. However, lowering the applied stress to 50 MPa after cycling under an initial stress of 150 MPa produced a nearly saturated strain/temperature response. The thermomechanical observations are discussed in terms of the nature of strain evolution and its connection to the concept of a local/global minimization of the energy of the system, however, the exact mechanisms associated with these strain evolutions were not determined. 相似文献
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