排序方式: 共有25条查询结果,搜索用时 250 毫秒
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Alves GA Amato S Anjos JC Appel JA Astorga J Bernard T Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Gay C Green DR Jedicke R Karchin PE Kwan S Lueking LJ de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review letters》1994,72(6):812-815
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Model studies of colloidal silica precipitation using biosilica extracts from<Emphasis Type="Italic"> Equisetum telmateia</Emphasis> 总被引:1,自引:0,他引:1
Structural materials containing silicon are produced in single celled organisms through to higher plants and animals. Hydrated amorphous silica is a colloidal mineral of infinite functionality that is formed into structures with microscopic and macroscopic form. Proteins and proteoglycans are suggested to play a critical role in the catalysis of silica polycondensation and in structure direction during the formation of these magnificent structures. This article extends knowledge on the effect of protein containing biosilica extracts from Equisetum telmateia on the kinetics of silica formation and structure regulation. Utilising potassium silicon catecholate as the source of soluble silicon, bioextracts obtained from plant silica by dissolution of the siliceous phase with aqueous HF following extensive acid digestion of the plant cell wall were found to modify the kinetic rate constants for the formation of small silicic acid oligomers under circumneutral pH conditions and to modify the solubility of silicic acid in solution. Addition of the bioextracts at ca. 1 wt% to the reaction medium reduced the sizes and range of sizes of the fundamental silica particles formed and led to the formation of crystalline polymorphs of silica under conditions of ca. neutral pH, room temperature and in the absence of multiply charged cations, conditions assumed to be relevant to the biological mineralization environment. The ability of biological organisms to regulate the formation of silica structures with prevention of crystallinity is discussed as are the implications of this study in terms of the generation of new materials with specific form and function for industrial application. 相似文献
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Andrew C. Kolbert Joseph G. Didier 《Journal of Polymer Science.Polymer Physics》1997,35(12):1955-1961
We report high-resolution solution-state NMR experiments on chain ends generated in ethylene–propylene copolymers by mechanical shearing in an extruder. The use of the higher resolution of the 13C-NMR spectrum, in a two-dimensional 1H-13C chemical shift correlation experiment, has allowed the complete resolution and assignment of the olefinic chain-end region of the 1H-NMR spectrum. Simultaneously, the assignments of the 13C olefinic resonances, previously identified [A. C. Kolbert, J. G. Didier, and L. Xu, Macromolecules, 29 , 8591 (1996)] are confirmed. An iterative method for calculating the average molecular weight, based on quantitative measurements of the olefinic 1H-NMR peak intensities is introduced and these results are compared with measurements from 13C-NMR and size exclusion chromatography and correlated to reduced viscosities. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1955–1961, 1997 相似文献
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Aitala EM Amato S Anjos JC Appel JA Ashery D Banerjee S Bediaga I Blaylock G Bracker SB Burchat PR Burnstein RA Carter T Carvalho HS Copty NK Costa I Cremaldi LM Darling C Denisenko K Fernandez A Gagnon P Gerzon S Gobel C Gounder K Halling AM Herrera G Hurvits G James C Kasper PA Kwan S Langs DC Leslie J Lundberg B MayTal-Beck S Meadows B de Mello Neto JR Milburn RH de Miranda JM Napier A Nguyen A d'Oliveira AB O'Shaughnessy K Peng KC Perera LP Purohit MV Quinn B Radeztsky S Rafatian A 《Physical review letters》1996,77(12):2384-2387
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Rabah Bey Jean-Pierre LohAC Mohand Moussaoui 《Journal de Mathématiques Pures et Appliquées》1999,78(10):1043
We deal here with a second order elliptic mixed problem which is posed in a regular open bounded domain of
. We study the regularity of its solution. We apply our results to the boundary stabilization of the wave equation. 相似文献
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Bizau J Esteva J Cubaynes D Wuilleumier FJ Blancard C La Fontaine AC Couillaud C Lachkar J Marmoret R Remond C Bruneau J Hitz D Ludwig P Delaunay M 《Physical review letters》2000,84(3):435-438
Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series. 相似文献