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31.
PD Dr. Michael Höpfner Stephan Borrmann Jörn Ungermann Robert Wagner 《Chemie in Unserer Zeit》2020,54(6):356-367
Ammonia (NH3) is the most important basic trace gas in the atmosphere. Due to its massively increasing anthropogenic production during the last 100 years, it strongly affects the global nitrogen budget. Its main sources are emissions due to agricultural activity. In the atmosphere, NH3 is a precursor for the formation of ammonium nitrate (AN) and ammonium sulfate (AS) aerosol particles, which are known as major constituents of fine particulate matter near the surface. By using data from the first high-altitude aircraft campaign in the Asian monsoon region as well as satellite observations, we could show that NH3 and AN particles are present up to altitudes of 18 km from the Mediterranean to the Western Pacific. From the emission regions in Northern India and Pakistan, strong convection during thunderstorms transports NH3 upwards where it contributes to the formation of AN particles. In contrast to previous assumptions, we could show with supporting laboratory experiments that the AN particles are present as solids instead of aqueous solution droplets. Crystallization can be induced by very small contaminations with AS. In contrast to aqueous droplets, solid AN particles are efficient ice nucleating particles at temperature below 230 K. As a consequence, these aerosols may considerably affect the formation and radiative properties of cirrus clouds, thus being of importance for the radiative budget of our atmosphere. 相似文献
32.
Hyunwook Jung Sina Stocker Christian Kunkel PD Dr. Harald Oberhofer Prof. Dr. Byungchan Han Prof. Dr. Karsten Reuter Dr. Johannes T. Margraf 《ChemSystemsChem》2020,2(4):e1900052
Machine learning (ML) models are increasingly used in combination with electronic structure calculations to predict molecular properties at a much lower computational cost in high-throughput settings. Such ML models require representations that encode the molecular structure, which are generally designed to respect the symmetries and invariances of the target property. However, size-extensivity is usually not guaranteed for so-called global representations. In this contribution, we show how extensivity can be built into global ML models using, e. g., the Many-Body Tensor Representation. Properties of extensive and non-extensive models for the atomization energy are systematically explored by training on small molecules and testing on small, medium and large molecules. Our results show that non-extensive models are only useful in the size-range of their training set, whereas extensive models provide reasonable predictions across large size differences. Remaining sources of error for extensive models are discussed. 相似文献
33.
Florian Kleemiss Erna K. Wieduwilt Dr. Emanuel Hupf Ming W. Shi Dr. Scott G. Stewart Prof. Dylan Jayatilaka Dr. Michael J. Turner Prof. Kunihisa Sugimoto Prof. Eiji Nishibori Prof. Dr. Tanja Schirmeister Dr. Thomas C. Schmidt Prof. Dr. Bernd Engels PD Dr. Simon Grabowsky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3407-3419
The crystal interaction density is generally assumed to be a suitable measure of the polarization of a low-molecular weight ligand inside an enzyme, but this approximation has seldomly been tested and has never been quantified before. In this study, we compare the crystal interaction density and the interaction electrostatic potential for a model compound of loxistatin acid (E64c) with those inside cathepsin B, in solution, and in vacuum. We apply QM/MM calculations and experimental quantum crystallography to show that the crystal interaction density is indeed very similar to the enzyme interaction density. Less than 0.1 e are shifted between these two environments in total. However, this difference has non-negligible consequences for derived properties. 相似文献
34.
Dr. Xiankang Zhong Dr. Matthias Schulz Dr. Chun-Hung Wu Dr. Martin Rabe Prof. Dr. Andreas Erbe PD Dr. Michael Rohwerder 《ChemElectroChem》2021,8(4):712-718
The oxygen reduction reaction (ORR) under ultrathin electrolyte layers is a key reaction in many processes, from atmospheric corrosion to energy conversion in fuel cells. However, the ORR current under ultrathin electrolyte layers is difficult to measure using conventional electrochemical methods. Hence, reliable data are scarce for the micrometer range and totally missing for the sub-micrometer range of the electrolyte layer thickness. Here, we report a novel hydrogen-permeation-based approach to measure the ORR current underneath thin and ultrathin electrolyte layers. By using a Kelvin-probe-based measurement of the potential, which results from dynamic equilibrium of oxygen reduction and hydrogen oxidation, and the corresponding hydrogen charging current density, the full current-potential relationship can be constructed. The results shed a new light on the nature of the limiting current density of ORR underneath ultrathin layers of electrolyte. 相似文献
35.
Michael Schöneich Tobias Lorenz Melanie Bawohl Tom Nilges PD Dr. Peer Schmidt 《无机化学与普通化学杂志》2010,636(11):2070-2070
36.
37.
Prof. Dr. Bikshandarkoil R. Srinivasan Santosh Y. Shetgaonkar PD Dr. Christian Näther 《无机化学与普通化学杂志》2011,637(1):130-136
The preparation, crystal structures, and thermal properties of [Ca(pyr)2(4‐nba)2]n ( 1 ) (pyr = pyrazole; 4‐nba = 4‐nitrobenzoate) {[Ca(H2O)2(3‐npth)] · H2O}n ( 2 ) (3‐npth = 3‐nitrophthalate), [Mg(H2O)5(3‐npth)] · 2H2O ( 3 ), and [Mg(H2O)4(2‐nba)2] ( 4 ) (2‐nba = 2‐nitrobenzoate) are reported. The anhydrous CaII compound 1 and the diaqua CaII‐3‐nitrophthalate monohydrate 2 are one‐dimensional coordination polymers containing a hexacoordinate CaII ion located on a center of inversion in 1 and a heptacoordinated CaII ion in 2 . In 1 , the 4‐nitrobenzoate moiety acts as a μ2‐bridging bidentate ligand, whereas the 3‐nitrophthalate anion exhibits a μ3‐bridging pentadentate coordination mode in 2 . The hexacoordinate MgII‐containing compounds 3 and 4 do not contain a [Mg(H2O)6]2+ unit and the central MgII ion is coordinated to at least one monodentate carboxylate unit namely the monodentate 3‐npth molecule in 3 and two trans monodentate 2‐nba molecules in 4 . Hydrogen bonding between the lattice water molecules results in the formation of a water dimer in 3 . A comparative study of 17 alkaline earth nitrocarboxylates is described. 相似文献
38.
39.
Hermann Sachdev PD Dr. 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2004,116(36):4800-4803
40.
E. P. Zemskov K. Kassner M. A. Tsyganov M. J.B. Hauser 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,72(3):457-465
Using a field-theoretic approach, we systematically generalize the usual semiclassical approximation for a harmonically trapped
ideal Bose gas in such a way that its range of applicability is essentially extended. With this we can analytically calculate
thermodynamic properties even for small particle numbers. In particular, it now becomes possible to determine the critical
temperature as well as the temperature dependence of both heat capacity and condensate fraction in low-dimensional traps,
where the standard semiclassical approximation is not even applicable. 相似文献