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101.
Isotopically labelled (CH)x samples have been studied to probe the influence of nuclear spin diffusion on the relaxation mechanisms of polyacetylene. The results are discussed in terms of two spin species: those relaxing by direct interaction with solitons and those diffusing by mutual flip-flop towards this well relaxed core. Predictions are made for the time dependence of magnetization recovery and for the frequency dependence of long T1. 相似文献
102.
103.
Chester A. Mathis Rafael Gurvis Mark Knickelbein Kathleen D. Knierim Siu-Hong Mo John W. Root 《国际化学动力学杂志》1982,14(5):565-583
Results are reported from moderated nuclear recoil 18F experiments with the 273 K CHF3/C3F6/C2F6 system. Although the measurement sensitivity is only about ±12%, there is no evidence to support the occurrence of nonthermal F-to-HF reactions at 95 mol % C2F6 moderator concentration. 相似文献
104.
Abstract—Excitation of chloroplasts at low temperature (down to 4.2 K) by short laser flashes causes largely reversible absorption changes which are attributed to the photooxidation of P-700, the primary electron donor of Photosystem I. At temperatures below 100 K the dark re-reduction of P-700+ is biphasic. with half-times of about 122μs and 1.7 ms. The relative contribution of the two phases varies with temperature with the fast phase becoming dominant at the lowest temperatures (˜90% at 5 K). The results are interpreted in terms of tunnelling of the electron from one or two primary accepting sites back to P-700, a process which is largely dominant over the process of charge stabilisation. 相似文献
105.
Dr. Mathis Kreuzahler Prof. Dr. Gebhard Haberhauer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(4):e202103046
Metal catalysis has revolutionized synthetic chemistry, leading to entirely new, very efficient transformations, which enable access to complex functionalized molecules. One such new transformation method is the haloalkynylation reaction, in which both a halogen atom and an alkynyl unit are transferred to an unsaturated carbon-carbon bond. This minireview summarizes the development of metal-catalyzed haloalkynylation reactions since their beginning about a decade ago. So far, arynes, alkenes and alkynes have been used as unsaturated systems and the reactivities of these systems are summarized in individual chapters of the minireview. Especially, the last few years have witnessed a rapid development due to gold-catalyzed reactions. Here, we discuss how the choice of the catalytic system influences the regio- and stereoselectivity of the addition. 相似文献
106.
Dominik Denker Antonio Attili Michael Gauding Kai Niemietz Mathis Bode Heinz Pitsch 《Proceedings of the Combustion Institute》2021,38(2):2681-2689
The probabilty density function (PDF) of the mixture fraction is of integral importance to a large number of combustion models. Here, a novel modelling approach for the PDF of the mixture fraction is proposed which employs dissipation elements. While being restricted to the commonly used mean and variance of the mixture fraction, this model approach individually considers contributions of the laminar regions as well as the turbulent core and the turbulent/non-turbulent interface region. The later region poses a highly intermittent part of the flow which is of high relevance to the non-premixed combustion of pure hydrocarbon fuels. The model assumptions are justified by means of the gradient trajectory based analysis of high fidelity direct numerical simulation (DNS) datasets of two turbulent inert configurations and a turbulent non-premixed jet flame. The new dissipation element based model is validated against the DNS datasets and a comparison with the beta PDF is presented. 相似文献
107.
By grafting polystyryllithium (PSLi) or polyisoprenyllithium (PILi) onto the fullerene borne by the mono-adduct polystyrene (PS)-C60 (≈90%) obtained upon reacting the fullerene with azide-terminated PS, fairly well-defined palm-tree like polymers PSaC60(PSb)5 and block copolymers PSaC60(PI)5 could be obtained. In these architectures, 5 PS (PI) branches of equal length are connected to a PS trunk through a single fullerene molecule. 相似文献
108.
Phase separation that takes place during the formation of semi-interpenetrating polymer networks based on crosslinked polyurethane and linear polystyrene was studied by small-angle X-ray scattering and light scattering. The kinetics of the chemical reactions was followed by Fourier transform infrared spectroscopy. The occurrence of broad peaks in the X-ray scattering curves was interpreted in terms of distances between the urethane crosslinks. Small modulations on these curves were assigned to sphere-like structures with a diameter of around 5 nm which might be related to the urethane crosslink regions. Small modulations on the light-scattering curves at the beginning of styrene polymerization were assigned to spheres with diameters of around 4.5 μm, which can be related to the polystyrene-rich phase. These modulations disappear with time, which might indicate an increasing polydispersity of the domain sizes. The final morphology was found to depend on the time at which polymerization of styrene is initiated with respect to the time of gelation of polyurethane. 相似文献
109.
M. Plapp J.-F. Gouyet 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):267-282
We develop mean-field kinetic equations for a lattice gas model of a binary alloy with vacancies (ABv model) in which diffusion
takes place by a vacancy mechanism. These equations are applied to the study of phase separation of finite portions of an
unstable mixture immersed in a stable vapor. Due to a larger mobility of surface atoms, the most unstable modes of spinodal
decomposition are localized at the vapor-mixture interface. Simulations show checkerboard-like structures at the surface or
surface-directed spinodal waves. We determine the growth rates of bulk and surface modes by a linear stability analysis and
deduce the relation between the parameters of the model and the structure and length scale of the surface patterns. The thickness
of the surface patterns is related to the concentration fluctuations in the initial state.
Received 28 October 1998 相似文献
110.
Dr. Lucius Schmid Dr. Igor Fokin Mathis Brändlin Dorothee Wagner Prof. Dr. Inke Siewert Prof. Dr. Oliver S. Wenger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(72):e202202386
The activation of N2, CO2 or H2O to energy-rich products relies on multi-electron transfer reactions, and consequently it seems desirable to understand the basics of light-driven accumulation of multiple redox equivalents. Most of the previously reported molecular acceptors merely allow the storage of up to two electrons. We report on a terphenyl compound including two disulfide bridges, which undergoes four-electron reduction in two separate electrochemical steps, aided by a combination of potential compression and inversion. Under visible-light irradiation using the organic super-electron donor tetrakis(dimethylamino)ethylene, a cascade of light-induced reaction steps is observed, leading to the cleavage of both disulfide bonds. Whereas one of them undergoes extrusion of sulfur to result in a thiophene, the other disulfide is converted to a dithiolate. These insights seem relevant to enhance the current fundamental understanding of photochemical energy storage. 相似文献