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Measurements have been carried out of the elastic constants of SrO in the virgin undoped state and of the changes produced in them by equilibrium doping with oxygen at ? 1200°C and oxygen partial pressure of 0.95 atm. The method used was Papadakis' pulse-echo overlap technique in conjunction with thermogravimetric analysis (T.G.A.) to determine mass and density changes due to oxygen doping.The values obtained for C11, C12 and C44 of the virgin crystal at 23°C are ;;.(These values are in very good agreement with those of Son and Bartels [2].)Values for and were found to be ?1.74% and ?0.86% respectively. Accurate valu could not be obtained because of sample size limitations after quenching. However, C12 was shown to definitely increase due to doping.Analysis of the results indicate that the elastic modulus changes can only be attributed to the formation of cation vacancies during doping. Analysis of the T.G.A. behavior indicates that this cation vacancy formation is probably associated with the presence of various tripositive cation and uninegative anion species depending upon the impurity concentrations of the sample. This implied impurity-controlled cation vacancy concentration is consistent with the earlier observed extrinsic nature of cation diffusion in SrO at 1200°C. 相似文献
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Frontispiece: Probing Transient Conformational States of Proteins by Solid‐State R1ρ Relaxation‐Dispersion NMR Spectroscopy
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Kehlet CT Sivertsen AC Bjerring M Reiss TO Khaneja N Glaser SJ Nielsen NC 《Journal of the American Chemical Society》2004,126(33):10202-10203
We present the first solid-state NMR experiments developed using optimal control theory. Taking heteronuclear dipolar recoupling in magic-angle-spinning NMR as an example, it proves possible to significantly improve the efficiency of the experiments while introducing robustness toward instrumental imperfections such as radio frequency inhomogeneity. The improvements are demonstrated by numerical simulations as well as practical experiments on a 13Calpha,15N-labeled powder of glycine. The experiments demonstrate a gain of 53% in the efficiency for 15N to 13Calpha coherence transfer relative to the typically double-cross-polarization experiments. 相似文献
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Probing Transient Conformational States of Proteins by Solid‐State R1ρ Relaxation‐Dispersion NMR Spectroscopy
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Dr. Peixiang Ma Jens D. Haller Jérémy Zajakala Dr. Pavel Macek Dr. Astrid C. Sivertsen Prof. Dr. Dieter Willbold Dr. Jérôme Boisbouvier Dr. Paul Schanda 《Angewandte Chemie (International ed. in English)》2014,53(17):4312-4317
The function of proteins depends on their ability to sample a variety of states differing in structure and free energy. Deciphering how the various thermally accessible conformations are connected, and understanding their structures and relative energies is crucial in rationalizing protein function. Many biomolecular reactions take place within microseconds to milliseconds, and this timescale is therefore of central functional importance. Here we show that R1ρ relaxation dispersion experiments in magic‐angle‐spinning solid‐state NMR spectroscopy make it possible to investigate the thermodynamics and kinetics of such exchange process, and gain insight into structural features of short‐lived states. 相似文献
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M Tollinger AC Sivertsen BH Meier M Ernst P Schanda 《Journal of the American Chemical Society》2012,134(36):14800-14807
We demonstrate that conformational exchange processes in proteins on microsecond-to-millisecond time scales can be detected and quantified by solid-state NMR spectroscopy. We show two independent approaches that measure the effect of conformational exchange on transverse relaxation parameters, namely Carr-Purcell-Meiboom-Gill relaxation-dispersion experiments and measurement of differential multiple-quantum coherence decay. Long coherence lifetimes, as required for these experiments, are achieved by the use of highly deuterated samples and fast magic-angle spinning. The usefulness of the approaches is demonstrated by application to microcrystalline ubiquitin. We detect a conformational exchange process in a region of the protein for which dynamics have also been observed in solution. Interestingly, quantitative analysis of the data reveals that the exchange process is more than 1 order of magnitude slower than in solution, and this points to the impact of the crystalline environment on free energy barriers. 相似文献
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Tse-An Yeh Chien-Li Lin John M. Sivertsen Jack H. Judy 《Journal of magnetism and magnetic materials》1993,120(1-3):314-318
Thin carbon protective coatings were deposited on rigid magnetic disks by rf diode sputtering using a mixture of argon and nitrogen gases. A continuous drag test with thin-film head sliders was used to evaluate the performance of carbon coatings. Results significantly show that the carbon-nitrogen coatings have better wear performance than pure argon-sputtered carbon coatings. In addition, an elasto-plastic analysis of the stress distribution strongly indicates that wear damage should more readily occur in carbon overcoats containing large graphite particles and that a durable carbon coating should have a higher percentage of sp3 bonding. 相似文献
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Chien-Li Lin Tse-An Yeh John M. Sivertsen Jack H. Judy 《Journal of magnetism and magnetic materials》1993,120(1-3):125-128
Recent investigations of the initiation of the wear process have identified the presence of wear features that result from specific inhomogeneities in phase and properties of a wear coat. To better understand the creation and formation of wear debris, detailed analysis of the sliding contact stress field is required in studying tribological reliability of the protective overcoats. Stress calculations by the finite element method were used to study the response of solid multilayered materials under sliding contact interaction, assuming Hertzian contact conditions. Numerical results are presented for both homogeneous and inhomogeneous protective overcoats. 相似文献