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31.
Helle Svendsen Jacob Overgaard Dr. Marie Chevallier Eric Collet Prof. Bo B. Iversen Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(15):2780-2783
X‐ray vision : Single‐crystal XRD experiments (see picture) reveal the excited‐state structure of the photomagnetic heterobimetallic title complex. The system shows a decrease in all the iron–ligand bond lengths, suggesting that photoexcitation involves a ligand‐to‐metal charge transfer or a change in the superexchange coupling between the metal centers.
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Susanta Mitra Afshin Ghanbari-Siahkali Helle Kem Rehmeier Kristoffer Almdal 《Polymer Degradation and Stability》2006,91(1):81-93
An investigation on the time-dependent chemical degradation of ethylene-propylene diene rubber containing 5-ethylidene-2-norbornene as diene cured by peroxide crosslinking in the presence of a coagent in an acidic environment (20% Cr/H2SO4) has been made. Two types of rubber, with comparable monomer composition, but having significant differences in molar mass and levels of long chain branching were tested. Dicumyl peroxide and triallylcyanurate under similar conditions were used for curing the rubbers. The molecular mechanisms of chemical degradation at the surface were studied using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy, which demonstrate that several oxygenated species evolve during exposure. The primary process of degradation is hydrolytic attack on the crosslink sites, which is manifested by a decrease in crosslink density. The surface degradation is found to be strong enough to alter the bulk mechanical properties as observed by the change in retention in tensile strength, elongation at break, modulus at 50% elongation and, the change in micro-hardness. Retention in modulus at 50% elongation is found to follow a negative linear correlation with decrease in crosslink density. With higher molar mass and level of long chain branching more crosslinking occurs and thus comparatively more hydrolytic attack ensues. Scanning electron microscopy shows that the surface topography is significantly altered upon exposure and supports the notion of the dependence of degradation on the crosslinking density of the samples. Importantly, the coagent used in this study is shown to enhance the chemical degradation through formation of weaker sites for hydrolysis. The results also show that upon prolonged exposure the resulting oxygenated species tend to combine with each other. 相似文献
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Wilson SR Malerød H Petersen D Simic N Bobu MM Rise F Lundanes E Greibrokk T 《Journal of separation science》2006,29(4):582-589
There are several stages of the LC-SPE-NMR process that should be monitored closely to ensure an efficient isolation and concentration of the target analyte, for instance analyte break-through and compound transfer from the LC-SPE to the NMR probe. In this study, analyte break-through monitoring was performed with a UV detector and a mass spectrometer placed after the SPE unit. Easy break-through was a problem when attempting multiple trapping of various compounds using C18 SPE cartridges with the original commercial system. However, on lowering the flow rate over the SPE system and using SPE cartridges packed with porous carbon, the number of trappings possible increased five-fold. To increase control over the on-line SPE-NMR transfer, a gradient pump-UV system was used to elute compounds trapped on an SPE to an NMR probe. The analyte band was placed in the active volume of the probe by a stop-flow mechanism. The modified LC-SPE system was also coupled with off-line NMR analysis for determination of a degradation product of the insecticide monuron, present in the low ppm range. 相似文献
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J. Lindén T. Karlemo M. Karppinen T. Katila M. Lippmaa A. Nara L. Niinistö I. Tittonen K. Ullakko H. Yamauchi 《Hyperfine Interactions》1994,93(1):1635-1639
The rare-earth site of samples having the compositions (Fe,Cu)Sr2(Eu,Ce)
n
Cu2O4+2n+z (n=2 and 3) were studied by151Eu Mössbauer spectroscopy. The results obtained are compared with measurements of EuBa2Cu3O7– (123) and Bi2Sr2(Ca1–yEuy)Cu2O8+E
(2212) samples. The full quadrupole Hamiltonian of the 21.5-keV -transition was applied in analyzing the measured spectra. Simultaneous fitting of spectra recorded from crystallites oriented in various directions was used to determine the hyperfine parameters of then= 2 and 3 samples. Two different electric field gradients, not discernible in simple random crystallite measurements, were obtained for then=3 series. 相似文献
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Tine Jrgensen Helle Chris Nielsen Nageshwar Malhotra Jan Becher Mikael Begtrup 《Journal of heterocyclic chemistry》1992,29(7):1841-1845
Reactions of the diene 1-benzyloxy-2-methoxy-1,3-pentadiene-5-ol in intramolecular Diels-Alder reactions using maleic anhydride or fumaric acid ethyl ester is described. The new reactive diene is prepared starting from 3-methoxypyridine. The structure of the diene was elucidated by a NOE nmr experiment. 相似文献
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T. Harada I. Ohkubo M. Lippmaa Y. Matsumoto M. Sumiya H. Koinuma M. Oshima 《固体物理学:研究快报》2011,5(1):34-36
Ferromagnetic insulator Pr0.8Ca0.2Mn1–yCoy O3 (0 ≤ y ≤ 0.7) thin films were epitaxially grown by pulsed laser deposition on substrates of (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (100). To probe the ferromagnetic insulator state, the Co content dependences of the structural, magnetic, and transport properties were studied. Variation of lattice constant by the Co substitution is well reproduced considering that divalent and trivalent Co ions substitute for Mn ions at the perovskite B‐sites. For 0 ≤ y ≤ 0.3, the Curie temperature, saturation magnetization, and magnetoresistance increase with increasing Co content, retaining the insulating properties. Detailed analyses of transport and magnetic properties indicate the contribution of both double exchange and superexchange interactions to the appearance of the ferromagnetic insulating phase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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