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排序方式: 共有163条查询结果,搜索用时 46 毫秒
61.
Deniz Zengel Pirmin Koch Bentolhoda Torkashvand Jan‐Dierk Grunwaldt Maria Casapu Olaf Deutschmann 《Angewandte Chemie (International ed. in English)》2020,59(34):14423-14428
Reducing greenhouse gas and pollutant emissions is one of the most stringent priorities of our society to minimize their dramatic effects on health and environment. Natural gas (NG) engines, in particular at lean conditions, emit less CO2 in comparison to combustion engines operated with liquid fuels but NG engines still require emission control devices for NOx removal. Using state‐of‐the‐art technologies for selective catalytic reduction (SCR) of NOx with NH3, we evaluated the interplay of the reducing agent NH3 and formaldehyde, which is always present in the exhaust of NG engines. Our results show that a significant amount of highly toxic hydrogen cyanide (HCN) is formed. All catalysts tested partially convert formaldehyde to HCOOH and CO. Additionally, they form secondary emissions of HCN due to catalytic reactions of formaldehyde and its oxidation intermediates with NH3. With the present components of the exhaust gas aftertreatment system the HCN emissions are not efficiently converted to non‐polluting gases. The development of more advanced catalyst formulations with improved oxidation activity is mandatory to solve this novel critical issue. 相似文献
62.
Peter Thumbs Timm T. Ensfelder Markus Hillmeier Mirko Wagner Matthias Heiss Constanze Scheel Alexander Schn Markus Müller Stylianos Michalakis Stefanie Kellner Thomas Carell 《Angewandte Chemie (International ed. in English)》2020,59(30):12352-12356
Queuosine (Q) is a hypermodified RNA nucleoside that is found in tRNAHis, tRNAAsn, tRNATyr, and tRNAAsp. It is located at the wobble position of the tRNA anticodon loop, where it can interact with U as well as C bases located at the respective position of the corresponding mRNA codons. In tRNATyr and tRNAAsp of higher eukaryotes, including humans, the Q base is for yet unknown reasons further modified by the addition of a galactose and a mannose sugar, respectively. The reason for this additional modification, and how the sugar modification is orchestrated with Q formation and insertion, is unknown. Here, we report a total synthesis of the hypermodified nucleoside galactosyl‐queuosine (galQ). The availability of the compound enabled us to study the absolute levels of the Q‐family nucleosides in six different organs of newborn and adult mice, and also in human cytosolic tRNA. Our synthesis now paves the way to a more detailed analysis of the biological function of the Q‐nucleoside family. 相似文献
63.
Ultrasonic attenuation and velocity have been measured close to and above the 105 K transition in flux-grown SrTiO3. The data are compared with data from Verneuil-grown SrTiO3. Larger exponents than expected are observed. The difference between relaxation times in the two samples is interpreted as being due to different impurity contents. 相似文献
64.
Using a scalar advection-reaction-diffusion equation with a cubic nonlinearity as a simple model problem, we investigate the effect of domain size on stability and bifurcations of steady states. We focus on two parameter regimes, namely, the regions where the steady state is convectively or absolutely unstable. In the convective-instability regime, the trivial stationary solution is asymptotically stable on any bounded domain but unstable on the real line. To measure the degree to which the trivial solution is stable, we estimate the distance of the trivial solution to the boundary of its basin of attraction: We show that this distance is exponentially small in the diameter of the domain for subcritical nonlinearities, while it is bounded away from zero uniformly in the domain size for supercritical nonlinearities. Lastly, at the onset of the absolute instability where the trivial steady state destabilizes on large bounded domains, we discuss bifurcations and amplitude scalings. 相似文献
65.
A scintillation counter telescope has been flown in the upper atmosphere at2.4g/cm2 from Bergen/Lüneburger Heide for the measurement of electrons and photons of the secondary cosmic radiation. The aim was to get the differential energy spectra of secondary photons in an energy range from 1 to 44 MeV and of secondary and return albedo electrons from 2 to 35 MeV for three different zenith angles (0 °, 90 ° and 180 °). The received photon spectrum is in good agreement to the results of other authors as well to lower as to higher energies. It has been shown, that the spectrum has a great anisotropy with a maximum of intensity around the horizon. The main reason therefore is the atmospheric deepness in the different directions. In this energy range we have found that the Bremsstrahlung of the return albedo electrons is the main reason for the photon flux and secondly the π0-decay. The measured electron spectra don't show any significant difference relative to the three zenith angles. These secondary electrons are produced isotropically in the upper atmosphere and they consist of a mixture of secondary and return albedo electrons. 相似文献
66.
The Newton map Nf of an entire function f turns the roots off into attracting fixed points. Let U be the immediate attractingbasin for such a fixed point of Nf. We study the behavior ofNf in a component V of \U. If V can be surrounded by an invariantcurve within U and satisfies the condition that for all z , Nf–1({z}) V is a finite set,then it is shown that V contains another immediate basin ofNf or a virtual immediate basin. 相似文献
67.
H. Scheel 《Isotopes in environmental and health studies》2013,49(9):330-332
Trace elements were determined in hippuran and the corresponding radiopharmaceutical preparation, labelled with 131I by using nondestructive radioactivation analysis. The presence of Cr, Hg, Au, Sb, Sc, Fe, Co, Na, Zn and Br in the above compounds has been proved and their concentrations determined 相似文献
68.
69.
Manuel Gentzen Dmitry E. Doronkin Thomas L. Sheppard Anna Zimina Haisheng Li Jelena Jelic Felix Studt Jan‐Dierk Grunwaldt Jrg Sauer Silke Behrens 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(44):15802-15806
The single‐step syngas‐to‐dimethyl ether (STD) process entails economic and technical advantages over the current industrial two‐step process. Pd/ZnO‐based catalysts have recently emerged as interesting alternatives to currently used Cu/ZnO/Al2O3 catalysts, but the nature of the active site(s), the reaction mechanism, and the role of Pd and ZnO in the solid catalyst are not well established. Now, Zn‐stabilized Pd colloids with a size of 2 nm served as the key building blocks for the methanol active component in bifunctional Pd/ZnO‐γ‐Al2O3 catalysts. The catalysts were characterized by combining high‐pressure operando X‐ray absorption spectroscopy and DFT calculations. The enhanced stability, longevity, and high dimethyl ether selectivity observed makes Pd/ZnO‐γ‐Al2O3 an effective alternative system for the STD process compared to Cu/ZnO/γ‐Al2O3. 相似文献
70.
W. Niehls M. Thiesen K. Scheel L. Sell A. Mahlke 《Analytical and bioanalytical chemistry》1897,36(1):178-179