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41.
Till Heinemann Matthias Springer Hermann Lienhart Stefan Kniesburges Carsten Othmer Stefan Becker 《Experiments in fluids》2014,55(5):1-11
Lift and drag of a passenger car are strongly influenced by the flow field around its rear end. The bluff body geometry produces a detached, transient flow which induces fluctuating forces on the body, affecting the rear axle, which may distress dynamic stability and comfort significantly. The investigations presented here deal with a 1:4 scale model of a simplified test car geometry that produces fluctuating lift and drag due to its strongly rounded rear geometry. To examine the influence of active flow control on this behavior, steady air jets were realized to exhaust from thin slots across the rear in three different configurations. Investigations were performed at $Re = 2.1 \times 10^{6}$ and included the capturing of effective integral lift and drag, velocity measurements in the surrounding flow field with Laser Doppler Anemometry, surface pressure measurements and surface oil flow visualization on the rear. The flow field was found to be dominated by two longitudinal vortices, developing from the detachment of the flow at the upper C-pillar positions, and a recirculating, transverse vortex above the rear window. With an air jet emerging from a slot across the surface right below the rear window section, tangentially directed upstream toward the roof section, total lift could be reduced by more than 7 %, with rear axle lift reduction of about 5 % and negligible drag affection ( $<$ 1 %). 相似文献
42.
Jan Brauer Elisabeth Quraishi Lisa Marie Kammer Prof. Till Opatz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):18168-18174
A simple visible light photochemical, nickel-catalyzed synthesis of ketones from carboxylic acid-derived precursors is presented. Hantzsch ester (HE) functions as a cheap, green and strong photoreductant to facilitate radical generation and also engages in the Ni-catalytic cycle to restore the reactive species. With this dual role, HE allows for the coupling of a large variety of radicals (1°,2°, benzylic, α-oxy & α-amino) with aroyl and alkanoyl moieties, a new feature in reactions of this type. With both precursors deriving from abundant carboxylic acids, this protocol is a welcome addition to the organic chemistry toolbox. The reaction proceeds under mild conditions without the need for toxic metal reagents or bases and shows a wide scope, including pharmaceuticals and complex molecular architectures. 相似文献
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A 2,6‐Bis(phenylamino)pyridinato Titanium Catalyst for the Highly Regioselective Hydroaminoalkylation of Styrenes and 1,3‐Butadienes 下载免费PDF全文
Jaika Dörfler Till Preuß Alexandra Schischko Dr. Marc Schmidtmann Prof. Dr. Sven Doye 《Angewandte Chemie (International ed. in English)》2014,53(30):7918-7922
The C? C bond forming catalytic hydroaminoalkylation of terminal alkenes, 1,3‐dienes, or styrenes allows a direct and highly atom efficient (100 %) synthesis of amines which can result in the formation of two regioisomers, the linear and the branched product. We present a new titanium catalyst with 2,6‐bis(phenylamino)pyridinato ligands for intermolecular hydroaminoalkylation reactions of styrenes and 1‐phenyl‐1,3‐butadienes that delivers the corresponding linear hydroaminoalkylation products with excellent regioselectivities. 相似文献
46.
Dr. Ilia Kochetygov Jocelyn Roth Dr. Jordi Espín Sophia Pache Dr. Anita Justin Till Schertenleib Dr. Nazanin Taheri Dr. Dmitry Chernyshov Prof. Wendy L. Queen 《Angewandte Chemie (International ed. in English)》2023,62(16):e202215595
The design of metal–organic frameworks (MOFs) having large pore sizes and volumes often requires the use of complex organic ligands, currently synthesized using costly and time-consuming palladium-catalyzed coupling chemistry. Thus, in the present work, a new strategy for ligand design is reported, where piperazine and dihydrophenazine units are used as substitutes for benzene rings, which are the basic building block of most MOF ligands. This chemistry, which is based on simple, nucleophilic aromatic substitution (SNAr) reactions, is used for the transition metal catalyst-free construction of 21 new, carboxylate-based ligands with varying sizes, shapes, and denticity and 15 linear di- and tetra-nitriles. Moreover, to demonstrate the utility of the ligands as building blocks, 16 new structurally diverse MOFs having surface areas up to 3100 m2 g−1 were also synthesized. 相似文献
47.
Ze Xu Yi-Xuan Liu Maryam Azadeh Hao-Cheng Thong Yuqi Jiang Fang-Zhou Yao Zhen-Xing Yue Zhong-Tai Zhang Zi-Long Tang Jing-Feng Li Heng Wang Till Frömling Ke Wang 《Angewandte Chemie (International ed. in English)》2023,62(9):e202216776
Recent advances in perovskite ferroelectrics have fostered a host of exciting sensors and actuators. Defect engineering provides critical control of the performance of ferroelectric materials, especially lead-free ones. However, it remains a challenge to quantitatively study the concentration of defects due to the complexity of measurement techniques. Here, a feasible approach to analyzing the A-site defect and electron in alkali metal niobate is demonstrated. The theoretical relationships among defect concentration, conductivity, and oxygen partial pressure can be established based on the defect chemistry equilibria. The type and concentration of defects are reflected through the conductivity variation with oxygen partial pressure. As a result, the variation of defect concentration gives rise to defect-driven interfacial polarization, which further leads to distinct properties of the ceramics. e.g., abnormal dielectric behavior. Furthermore, this study also suggests a strategy to manipulate defects and charges in perovskite oxides for performance optimization. 相似文献
48.
Sarah K. Wypysek Silvia P. Centeno Till Gronemann Dominik Wöll Walter Richtering 《Macromolecular bioscience》2023,23(8):2200456
Depending on their architectural and chemical design, microgels can selectively take up and release small molecules by changing the environmental properties, or capture and protect their cargo from the surrounding conditions. These outstanding properties make them promising candidates for use in biomedical applications as delivery or carrier systems. In this study, hollow anionic p(N-isopropylacrylamid-e-co-itaconic acid) microgels are synthesized and analyzed regarding their size, charge, and charge distribution. Furthermore, interactions between these microgels and the model protein cytochrome c are investigated as a function of pH. In this system, pH serves as a switch for the electrostatic interactions to alternate between no interaction, attraction, and repulsion. UV–vis spectroscopy is used to quantitatively study the encapsulation of cytochrome c and possible leakage. Additionally, fluorescence-lifetime images unravel the spatial distribution of the protein within the hollow microgels as a function of pH. These analyses show that cytochrome c mainly remains entrapped in the microgel, with pH controlling the localization of the protein – either in the microgel's cavity or in its network. This significantly differentiates these hollow microgels from microgels with similar chemical composition but without a solvent filled cavity. 相似文献
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Stephan Felder Dr. Sandra Dreisigacker Dr. Stefan Kehraus Edith Neu Prof. Dr. Gabriele Bierbaum Patrick R. Wright Prof. Dr. Dirk Menche Dr. Till F. Schäberle Prof. Dr. Gabriele M. König 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(28):9319-9324
Marine myxobacteria (Enhygromyxa, Plesiocystis, Pseudoenhygromyxa, Haliangium) are phylogenetically distant from their terrestrial counterparts. Salimabromide is the first natural product from the Plesiocystis/Enhygromyxa clade of obligatory marine myxobacteria. Salimabromide has a new tetracyclic carbon skeleton, comprising a brominated benzene ring, a furano lactone residue, and a cyclohexane ring, bridged by a seven‐membered cyclic moiety. The absolute configuration was deduced from experimental and calculated CD data. Salimabromide revealed antibiotic activity towards Arthrobacter cristallopoietes. 相似文献