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61.
6,7Li fast magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is used to study LiMn2O4 and Li3V2(PO4)3. The presence of paramagnetic transition metal centers in these materials has a profound effect on the resulting NMR spectra.
Lithium ion mobility has been studied by two-dimensional (2-D) exchange spectroscopy (EXSY) in Li3V2(PO4)3 but an absence of lithium ion exchange was observed for LiMn2O4. Several differences between the two materials are explored to explain these results. LiMn2O4 experiences a greater donation of electron spin density to the Li nucleus via the Fermi-contact interaction when compared
with Li3V2(PO4)3. This contributes to a greater hyperfine chemical shift and a larger dependence of chemical shift on temperature. The delocalized
electrons in LiMn2O4 cause temperature-independent T
1 relaxation rates and shorter relative T
2 values. The relative rates of ionic conductivity and spin–lattice or spin–spin relaxation in LiMn2O4 and Li3V2(PO4)3 are contrasted to illustrate the constraints on the use of 2-D EXSY to characterize ion dynamics in paramagnetic materials.
Authors' address: Gillian R. Goward, Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University,
1280 Main St. West, Hamilton, ON L8S 4M1, Canada 相似文献
62.
David J. Lowe Andrew V. Chapman Stuart Cook James J. C. Busfield 《Journal of Polymer Science.Polymer Physics》2011,49(22):1621-1627
Small strain Young's moduli of natural rubber (NR)/organoclay nanocomposites were estimated using the Guth–Gold, Halpin–Tsai (HT), and Krieger–Dougherty (KD) models, and compared with experimental measurements of NR vulcanizates containing organo‐montmorillonite (OM) or organo‐sepiolite (OS). To account for the effect on modulus of the NR matrix of the vulcanization‐active modifier in the organoclay, a matrix modulus correction (MMC) term was derived from the vulcanization parameters of the nanocomposites. The KD model gave a better empirical fit with the experimental data than the Guth–Gold model, with both giving good agreement with particle shape factors estimated from transmission electron microscope (TEM) images. The HT model gave the best fit with experiment for both types of nanocomposite, and use of the MMC term meant that the empirical shape factor was sufficiently close to that estimated from TEM images that the model could potentially be used to accurately predict the Young's moduli of NR/OM and NR/OS nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1621–1627, 2011 相似文献
63.
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65.
Sarah W. Kamau Chapman Paul O. Hassa Sabine Koch-Schneidemann Brigitte von Rechenberg Margarethe Hofmann-Amtenbrink Benedikt Steitz Alke Petri-Fink Heinrich Hofmann Michael O. Hottiger 《Journal of magnetism and magnetic materials》2008
Primary cell lines are more difficult to transfect when compared to immortalized/transformed cell lines, and hence new techniques are required to enhance the transfection efficiency in these cells. We isolated and established primary cultures of synoviocytes, chondrocytes, osteoblasts, melanocytes, macrophages, lung fibroblasts, and embryonic fibroblasts. These cells differed in several properties, and hence were a good representative sample of cells that would be targeted for expression and delivery of therapeutic genes in vivo. The efficiency of gene delivery in all these cells was enhanced using polyethylenimine-coated polyMAG magnetic nanoparticles, and the rates (17–84.2%) surpassed those previously achieved using other methods, especially in cells that are difficult to transfect. The application of permanent and pulsating magnetic fields significantly enhanced the transfection efficiencies in synoviocytes, chondrocytes, osteoblasts, melanocytes and lung fibroblasts, within 5 min of exposure to these magnetic fields. This is an added advantage for future in vivo applications, where rapid gene delivery is required before systemic clearance or filtration of the gene vectors occurs. 相似文献
66.
G. W. Pearce L. B. Norton und P. J. Chapman 《Fresenius' Journal of Analytical Chemistry》1938,112(5-6):235-236
Ohne Zusammenfassung 相似文献
67.
Laminar compressible flow in a tube 总被引:4,自引:0,他引:4
A two-dimensional solution for the velocity and pressure distributions in steady, laminar, isothermal flow of an ideal gas
in a long tube is obtained as a double perturbation expension in β, the radius to length ratio, and ε, the relative pressure drop. It is found that simple approximations estimate the exact
flow rate-pressure drop relationship accurately. 相似文献
68.
W. H. Bloemendal Thorpe Covelli A. C. Chapman H. D. Law R. Lobello Ch. Blarez G. Denigès E. Simonot A. Behre H. Frerichs und G. Rodenberg 《Fresenius' Journal of Analytical Chemistry》1911,50(4-5):328-331
Ohne Zusammenfassung 相似文献
69.
Ohne Zusammenfassung 相似文献
70.
A. Ch. Chapman V. Graham R. H. Carr H. B. Vickery G. W. Pucher F. Mach M. Popp J. Contzen O. Wagner W. Dörr und W. Preis 《Fresenius' Journal of Analytical Chemistry》1933,92(5-6):219-223
Ohne Zusammenfassung 相似文献