Locating two obnoxious facilities using the weighted maximin criterion

Given are a finite set of points P and a compact polygonal set S in R². The problem is to locate two new facilities in S, maximizing the minimum of all weighted distances between the points in P and the two new facilities, and the distance between the pair of new facilities. We present subquadratic algorithms.     

平面环状碳团簇的微波吸收特性

此文对平面环状碳团簇提出三类可能的结构和振转运动模型，计算其转动谱线与振转光谱的精细结构，所吸收的微波谱线一般在１－２０ＧＨＺ。     

平面微透镜的表面凸起现象分析

介绍了用离子交换法制得的平面微透镜的表面凸起现象,建立了分析这一现象的理论模型并给出了计算凸起程度的公式。平面微透镜的表面凸起有利于提高数值孔径和缩短交换时间,我们将它引入了平面微透镜阵列的设计和制作中并获得了良好的结果。     

数值模拟高能中子照相

 模拟了14 MeV中子在穿透样品后与闪烁体光纤的作用。对每根光纤中的能量沉积进行了计算，并转换成可见光(496 nm)光子数。在模拟实验中，分析了影响图像质量的因素。计算了散射中子本底与闪烁体和样品(聚乙烯)间距的关系。当间距为cm量级时，散射中子本底对图像的影响很小。计算表明系统对样品的甄别厚度与入射中子总数有关，在一定范围内近似与中子总数的对数成线性关系。通过模拟结果给出了理想平行中子束入射情况下系统的平面分辨率。     

[10]Paracyclophanediamides and their octadehydro derivatives: novel exotopic receptors with hydrogen-bonding sites on the bridge

2,9-Diaza-1,10-dioxo[10]paracyclophanes were prepared in short steps from the terephthaloyl chlorides via the corresponding 4,6-diyne derivatives, and the amide groups on the bridge endow the skeleton with the guest-binding properties as demonstrated by complexation with adrenaline by hydrogen bonds. The chiral auxiliaries on the bridge induce diastereomeric preference in terms of the planar chirality for the octadehydro derivative with a rigid diyne unit in crystal.     

Subcubic planar graphs of girth 7 are class I

We prove that planar graphs of maximum degree 3 and of girth at least 7 are 3-edge-colorable, extending the previous result for girth at least 8 by Kronk, Radlowski, and Franen from 1974.     

Ruthenium-catalyzed reduction of racemic tricarbonyl(η-aryl ketone)chromium complexes using transfer hydrogenation: A simple alternative to the resolution of planar chiral organometallics

Racemic planar chiral (η⁶-aryl ketone)Cr(CO)₃ complexes (aryl ketone = 1-indanone, 1-tetralone, 4-chromanone and thiochroman-4-one) were prepared by refluxing the aryl ketone with Cr(CO)₆ in a 10:1 mixture of dibutyl ether and THF. The reductions of the organometallic ketones by transfer hydrogenation in 2-propanol containing KOH and the catalyst precursor, generated from [RuCl₂(η⁶-benzene)]₂ and (−)-ephedrine, resulted in optically active syn-(R,S)-(η⁶-aryl alcohol)Cr(CO)₃ and (R)-(η⁶-aryl ketone)Cr(CO)₃ compounds in 31-97% ee. Reduction of racemic (η⁶-thiochroman-4-one)Cr(CO)₃ with the catalyst precursor generated from (+)-norephedrine, instead of (−)-ephedrine, inverted the configuration of the products obtained. Syn-(S,R)-(η⁶-thiochroman-4-ol)Cr(CO)₃ and (S)-(η⁶-thiochroman-4-one)-Cr(CO)₃ were isolated in 49% and >95% ee, respectively. The free aryl ketones were reduced using the same conditions as their respective chromium complexes, giving aryl alcohols in high ee (>95%). Reactions of non-rigid acetophenone, propriophenone and their tricarbonylchromium complexes resulted in moderate to low ee.     

含平面配位碳的过渡金属烃配合物MnHnC密度泛函理论研究

用密度泛函理论研究了含平面配位碳中心的过渡金属配合物MnHnC(n=4, M=Ni, Pd, Pt; n=5, M=Cu, Ag, Au)的结构和稳定性, 发现平面四配位碳满足八隅律规则, 而平面五配位碳与过渡金属配体形成部分离子键. 同时讨论了形成含两个或多个平面四配位碳中心的链状配合物M2n+2H2n+2Cn的可能性.     

Planar chiral ferrocene salen-type ligands featuring additional central and axial chirality

We report on novel chiral tridentate [NO₂]H₂ and tetradentate [N₂O₂]H₂ Schiff base ligands containing a planar chiral ferrocene moiety linked to hydroxyl-imine or diimine donors with central or axial chirality. Structurally, these ligands resemble half-salen and salen systems designed for stereoselective applications of their transition metal complexes in homogeneous catalysis. The modular synthesis involves diastereoselective metalation of chiral ferrocene or pentamethylferrocene acetals, followed by stereoconservative hydroxyalkylation and condensation with chiral hydroxyamines or diamines, respectively. In comparison to salen-type systems, an important advantage of these ligands is their tunable steric protection of the alkoxide donor site. A total of 18 different ligands varying in electronic and steric properties have been prepared and fully characterized by NMR, IR, mass spectroscopy and by single crystal structure analysis of nine precursors and representatives.