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31.
We consider finite horizon Markov decision processes under performance measures that involve both the mean and the variance of the cumulative reward. We show that either randomized or history-based policies can improve performance. We prove that the complexity of computing a policy that maximizes the mean reward under a variance constraint is NP-hard for some cases, and strongly NP-hard for others. We finally offer pseudopolynomial exact and approximation algorithms. 相似文献
32.
Yang SM Shie JJ Fang JM Nandy SK Chang HY Lu SH Wang G 《The Journal of organic chemistry》2002,67(15):5208-5215
By the promotion of samarium diiodide, thiophene-2-carboxylate reacted with 2 equiv of ketones at the C-4 and C-5 positions to give diols such as 2 and 9. Because the intermediary organosamarium species were oxophilic but not too basic, the double hydroxyalkylations with various ketone substrates, including alkyl aryl ketones, acetylthiophenes, cyclohexanone, alpha-tetralone, and alpha-phenylacetophenones, were realized without complication of side reactions. The diol products underwent an acid-catalyzed dehydration to give dienes such as 3 and 10, which were treated with DDQ to give either polysubstituted thiophenes (e.g., 4 and 11) or benzothiophenes (e.g., 5, 13, and 14) depending on the reaction conditions. Oxidative annulations of 4,5-diarylthiophenes 11 and 4,5,6,7-tetraphenylbenzothiophenes 14 were carried out by photochemical or chemical methods to give the sulfur-containing polycyclic aromatic compounds, such as phenanthro[9,10-b]thiophene-2-carboxylate, piceno[13,14-b]thiophene-2-carboxylate, and tribenzo[fg,ij,rst]pentapheno[15,16-b]thiophene-2-carboxylates. This method is applicable to the preparation of polysubstituted thiophenes, benzothiophenes, and the related compounds possessing liquid crystalline, photochromic, and other functional properties. 相似文献
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As-Se-based chalcogenide glasses are IR transparent, and are an ideal braze for the ZnSe and ZnS. Interfacial reactions between As-Se and Zn were investigated using reaction couples As-50 at.% Se/Zn at 350°C, As-50 at.% Se/Zn at 370°C and As-60 at.% Se/Zn at 350°C. Cross-sections of reaction couples were analyzed by using optical microscopy and electron probe micro-analysis. Two phases were formed at the interface, and diffusion paths were glass/ZnSe/As2Zn3/Zn. Growth rates of the intermetallic layers were determined and at 350°C follow a parabolic law which indicates a diffusion-controlled mechanism. 相似文献
34.
Xi‐Rui Zeng Xiao‐Niu Fang Shie‐Ming Peng Hsiu‐Mei Lin 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(11):m497-m498
The crystal structure of the title compound, [Cu2(C2F3O2)2(C10H8N3O)2]·2CH3CN, contains discrete [Cu2(CF3COO)2(O‐dpa)2] molecules (O‐dpaH is di‐2‐pyridylamine 1‐oxide) which have imposed crystallographic twofold symmetry and an acetonitrile molecule of solvation. The O‐dpa− ligand is both bidentate and bridging, linking two Cu atoms with a separation of 3.4270 (11) Å. Each Cu atom is surrounded by four coordinated atoms that are almost coplanar, with dimensions Cu—N = 1.940 (2) and 1.984 (3) Å, and Cu—O = 1.912 (2) and 1.945 (2) Å. 相似文献
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Tetrakis(diethylamido)zirconium reacts with 2‐(dimethylamino)methyl pyrrole (DMAMP) and 2,5‐[bis(dimethylamino)methyl]pyrrole (BDMAMP) to give Zr(NEt)2(DMAMP)2 1 and Zr(NEt)3(BDMAMP) 2 , respectively. Both 1 and 2 have been characterized by 1H and 13C NMR spectroscopies and 1 has also been characterized by X‐ray crystallography. Complex 1 shows an agostic interaction between Zr and H(21A) in solid state that is not sustained in solution. Reacting 1 with 2 equivalents of trimethylsilyl chloride in toluene yields ZrCl2(DMAMP)2 3 in 75% yield which was characterized by 1H and 13C NMR spectroscopies. 相似文献
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