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131.
Stereochemical effects in supramolecular self-assembly at surfaces: 1-D versus 2-D enantiomorphic ordering for PVBA and PEBA on Ag(111) 总被引:2,自引:0,他引:2
Barth JV Weckesser J Trimarchi G Vladimirova M De Vita A Cai C Brune H Günter P Kern K 《Journal of the American Chemical Society》2002,124(27):7991-8000
We present investigations on noncovalent bonding and supramolecular self-assembly of two related molecular building blocks at a noble metal surface: 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA) and 4-[(pyrid-4-yl-ethynyl)]benzoic acid (PEBA). These rigid, rodlike molecules comprising the same complementary moieties for hydrogen bond formation are comparable in shape and size. For PVBA, the ethenylene moiety accounts for two-dimensional (2-D) chirality upon confinement to a surface; PEBA is linear and thus 2-D achiral. Molecular films were deposited on a Ag(111) surface by organic molecular beam epitaxy and characterized by scanning tunneling microscopy. At low temperatures (around 150 K), both species form irregular networks of flat lying molecules linked via their endgroups in a diffusion-limited aggregation process. In the absence of kinetic limitations (adsorption or annealing at room temperature), hydrogen-bonded supramolecular assemblies form which are markedly different. With PVBA, enantiomorphic twin chains in two mirror-symmetric species running along a high-symmetry direction of the substrate lattice form by diastereoselective self-assembly of one enantiomer. The chirality signature is strictly correlated between neighboring twin chains. Enantiopure one-dimensional (1-D) supramolecular nanogratings with tunable periodicity evolve at intermediate coverages, reflecting chiral resolution in micrometer domains. In contrast, PEBA assembles in 2-D hydrogen-bonded islands, which are enantiomorphic because of the orientation of the supramolecular arrangements along low-symmetry directions of the substrate. Thus, for PVBA, chiral molecules form 1-D enantiomorphic supramolecular structures because of mesoscopic resolution of a 2-D chiral species, whereas with PEBA, the packing of an achiral species causes 2-D enantiomorphic arrangements. Model simulations of supramolecular ordering provide a deeper understanding of the stability of these systems. 相似文献
132.
133.
Wang Li Cai Jiwen Mao Zon-Wang Feng Xiao-Long Huang Jin-Wang 《Transition Metal Chemistry》2004,29(4):411-418
Four novel dinickel complexes, coordinated by mixed ligands of tren and racemic amino acids, namely [Ni2(tren)2(dl-alaninato)(H2O)]I3·2H2O (1), [Ni2(tren)2(dl-leucinato)(H2O)]I3·2.5H2O (2), [Ni2(tren)2(dl-phenylalaninato)(H2O)]I3·H2O (3), and {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}
n
(4), have been synthesized and structurally characterized by X-ray crystallography, FTIR, u.v. and e.s. spectra. They represent the first series of dinickel(II) complexes bridged by the unusual (N,O,O)-coordinated -amino acids. In complexes (1–3), one of the nickel(II) centers is coordinated by four N-atoms of the tren ligand, one O-atom of the carboxylate group of the amino acidato ligand and one H2O molecule. The other nickel(II) center is also coordinated by the four N-atoms of the tren ligand, one carboxylic O-atom and the amino N-atom of the amino acidato ligand, resulting in an asymmetric dinuclear core with chromophores of NiN4O2 and NiN5O. In the polymeric {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}
n
(4), the imidazole N-atom is also involved in ligation with nickel(II) and both nickel(II) centers have the same chromophore described as NiN5O. The Ni...Ni distances are in the 5.5199(10)–5.5807(15)Å range. Analyses of the magnetic properties of complexes (1), (3) and (4) show that a weak ferromagnetic interaction exists between the two nickel(II) centers. 相似文献
134.
135.
天然气水合物作为一种储量大、无污染的清洁能源近些年受到了广泛关注.近20年来,中国进行了较大范围的陆海域天然气水合物储层勘探与储量预测. 2017年,中国地质调查局牵头对南海神狐海域的天然气水合物进行了基于降压渗流原理的试验性开采.国内外已进行的水合物试采工程面临着气体产量低、出砂较多等问题,其最主要的原因之一是开发过程中沉积物内复杂多相渗流机理尚不明晰.本文综述了平行毛细管模型、Kozeny模型等广泛应用于天然气水合物开发渗流分析的理论模型,对比分析了水合物开发多尺度渗流过程模拟方法,简述了国内外含水合物沉积物渗透率测试、渗流过程中沉积物物性演变以及水合物开采室内模拟等方面的渗流实验进展,总结了矿场尺度的天然气水合物储层开采过程中产气数值模拟手段,展望了多相渗流模型、储层原位含水合物样品室内测试及结构与物性演化、矿场尺度数值模拟与水平井压裂技术等应用研究的未来方向与挑战. 相似文献
136.
Qiqin Cai Dingrong Yi Fumin Zou Zhaoyi Zhou Nan Li Feng Guo 《Entropy (Basel, Switzerland)》2022,24(9)
To scientifically and effectively evaluate the service capacity of expressway service areas (ESAs) and improve the management level of ESAs, we propose a method for the recognition of vehicles entering ESAs (VeESAs) and estimation of vehicle dwell times using electronic toll collection (ETC) data. First, the ETC data and their advantages are described in detail, and then the cleaning rules are designed according to the characteristics of the ETC data. Second, we established feature engineering according to the characteristics of VeESA and proposed the XGBoost-based VeESA recognition (VR-XGBoost) model. Studied the driving rules in depth, we constructed a kinematics-based vehicle dwell time estimation (K-VDTE) model. The field validation in Part A/B of Yangli ESA using real ETC transaction data demonstrates that the effectiveness of our proposal outperforms the current state-of-the-art. Specifically, in Part A and Part B, the recognition accuracies of VR-XGBoost are 95.9% and 97.4%, respectively, the mean absolute errors (MAEs) of dwell time are 52 and 14 s, respectively, and the root mean square errors (RMSEs) are 69 and 22 s, respectively. In addition, the confidence level of controlling the MAE of dwell time within 2 min is more than 97%. This work can effectively recognize the VeESA and accurately estimate the dwell time, which can provide a reference idea and theoretical basis for the service capacity evaluation and layout optimization of the ESA. 相似文献
137.
Lei Yang Xiaoyu Guo Xiaowei Song Deyuan Lu Wenjing Cai Zixiang Xiong 《Entropy (Basel, Switzerland)》2022,24(11)
This paper proposes an improved human-body-segmentation algorithm with attention-based feature fusion and a refined corner-based feature-point design with sub-pixel stereo matching for the anthropometric system. In the human-body-segmentation algorithm, four CBAMs are embedded in the four middle convolution layers of the backbone network (ResNet101) of PSPNet to achieve better feature fusion in space and channels, so as to improve accuracy. The common convolution in the residual blocks of ResNet101 is substituted by group convolution to reduce model parameters and computational cost, thereby optimizing efficiency. For the stereo-matching scheme, a corner-based feature point is designed to obtain the feature-point coordinates at sub-pixel level, so that precision is refined. A regional constraint is applied according to the characteristic of the checkerboard corner points, thereby reducing complexity. Experimental results demonstrated that the anthropometric system with the proposed CBAM-based human-body-segmentation algorithm and corner-based stereo-matching scheme can significantly outperform the state-of-the-art system in accuracy. It can also meet the national standards GB/T 2664-2017, GA 258-2009 and GB/T 2665-2017; and the textile industry standards FZ/T 73029-2019, FZ/T 73017-2014, FZ/T 73059-2017 and FZ/T 73022-2019. 相似文献
138.
GdTe_3 is a layered antiferromagnetic(AFM) metal with charge density wave(CDW).We grew monolayer(ML)GdTe_3 on graphene/6H-SiC(0001) substrates by molecular beam epitaxy.The electronic and magnetic structures are studied by scanning tunneling microscopy/spectroscopy,quasi-particle interference(QPI) and first-principles calculations.Strong evidence of CDW persisting at the two-dimensional(2D) limit is found.Band dispersions and partially gapped energy bands near the Fermi surface are revealed by the QPI patterns.By density functional theory +U calculations,AFM order with stripe pattern is found to be the magnetic ground state for ML GdTe_(3).These results provide fundamental understanding and pave the way for further investigation of GdTe_3 at the 2D limit. 相似文献
139.
Biao Mu Xianfang Wu Yunfei Niu Yan Chen Xinlun Cai Yanxiao Gong Zhenda Xie Xiaopeng Hu Shining Zhu 《中国光学快报(英文版)》2021,(6):28-32
Periodically poled lithium niobate on insulator[LNOI]ridge waveguides are desirable for high-efficiency nonlinear frequency conversions,and the fabrication proc... 相似文献
140.
Jia-Heng Cai Qi-Sheng Tian Xiao-Zhao Zhu Zhi-Hao Qu Wei He Dong-Ying Zhou Liang-Sheng Liao 《Molecules (Basel, Switzerland)》2022,27(17)
The effective reflective anode remains a highly desirable component for the fabrication of reliable top-emitting organic light-emitting diodes (TE-OLEDs) which have the potential to be integrated with complementary metal-oxide-semiconductor (CMOS) circuits for microdisplays. This work demonstrates a novel laminated anode consisting of a Cr/Al/Cr multilayer stack. Furthermore, we implement an ultra-thin titanium nitride (TiN) layer as a protective layer on the top of the Cr/Al/Cr composite anode, which creates a considerably reflective surface in the visible range, and meanwhile improves the chemical stability of the electrode against the atmosphere or alkali environment. Based on [2-(2-pyridinyl-N)phenyl-C](acetylacetonate)iridium(III) as green emitter and Mg/Ag as transparent cathode, our TE-OLED using the TiN-coated anode achieves the maximum current efficiency of 71.2 cd/A and the maximum power efficiency of 66.7 lm/W, which are 81% and 90% higher than those of the reference device without TiN, respectively. The good device performance shows that the Cr/Al/Cr/TiN could function as a promising reflective anode for the high-resolution microdisplays on CMOS circuits. 相似文献