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排序方式: 共有235条查询结果,搜索用时 31 毫秒
131.
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
132.
133.
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
134.
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
135.
Werner H. Gries 《Mikrochimica acta》1990,101(1-6):55-62
The non-standardized fitting of depth distributions of ion implanted analytes in solid matrices by arbitrarily chosen functions, as practiced at present, is unsatisfactory for the communication of results and is unacceptable for certification of ion implanted reference materials. Sampling theory applied to the nuclear slowing-down process of swift ions suggests that split Student-t functions should provide the mathematical representation sought. The exact shape and mathematical form of these functions are fully described and readily communicated by the use of five parameters (mode, two shape parameters and two scale parameters). A simple and fast fitting procedure is proposed.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday 相似文献
136.
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
137.
Barr DB Leng G Berger-Preiss E Hoppe HW Weerasekera G Gries W Gerling S Perez J Smith K Needham LL Angerer J 《Analytical and bioanalytical chemistry》2007,389(3):811-818
The objective of our study was to compare three vastly different analytical methods for measuring urinary metabolites of pyrethroid
and pyrethrum insecticides to determine whether they could produce comparable data and to determine if similar analytical
characteristics of the methods could be obtained by a secondary laboratory. This study was conducted as a part of a series
of validation studies undertaken by the German Research Foundation’s Committee on the Standardization of Analytical Methods
for Occupational and Environmental Medicine. We compared methods using different sample preparation methods (liquid–liquid
extraction and solid-phase extraction with and without chemical derivatization) and different analytical detection methods
(gas chromatography–mass spectrometry (single quadrupole), gas chromatography–high resolution mass spectrometry (magnetic
sector) in both electron impact ionization and negative chemical ionization modes, and high-performance liquid chromatography–tandem
mass spectrometry (triple quadrupole) with electrospray ionization). Our cross validation proved that similar analytical characteristics
could be obtained with any combination of sample preparation/analytical detection method and that all methods produced comparable
analytical results on unknown urine samples.
Cross-method comparison using unknown urine samples revealed reasonably good agreement for any combination of the methods
tested 相似文献
138.
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
139.
Anna V. Nomin Cdric Noel Thomas Gries Alexandre Nomin Valentin A. Milichko Thierry Belmonte 《Molecules (Basel, Switzerland)》2021,26(23)
Time-resolved optical emission spectroscopy of nanosecond-pulsed discharges ignited in liquid nitrogen between two bismuth electrodes is used to determine the main discharge parameters (electron temperature, electron density and optical thickness). Nineteen lines belonging to the Bi I system and seven to the Bi II system could be recorded by directly plunging the optical fibre into the liquid in close vicinity to the discharge. The lack of data for the Stark parameters to evaluate the broadening of the Bi I lines was solved by taking advantage of the time-resolved information supported by each line to determine them. The electron density was found to decrease exponentially from 6.5 ± 1.5 × 1016 cm−3 200 ns after ignition to 1.0 ± 0.5 × 1016 cm−3 after 1050 ns. The electron temperature was found to be 0.35 eV, close to the value given by Saha’s equation. 相似文献
140.
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