Direct experimental evidence

Direct evidence for interdiffusion in compatible polymers does exist. Radio-metric studies [38,39] have demonstrated the presence of macromolecular diffusion. The diffusion coefficients were found to be of the order of 10 to 10 cm Vs, which Voyutskii [40] argues is completely adequate for the formation of an intrinsically strong interface between the polymers after a contact time of only a few seconds, as discussed above. Further work [41-43], using techniques of optical microscopy, including ultraviolet light employing luminescence analysis [43], has indicated that in compatible, non-polar polymers the interphase region where interdiffusion has occurred may be about 10 jxm deep but in cases where the solubility parameters, 8s, of the two polymers were appreciably different then no interdiffusion zone could be detected. 

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Because of the mentioned leveling effect of the solvent (or excess acid itself acting as such) the acidity cannot exceed that of its conjugate acid. In the case of water the limiting acidity is that of HsO. Proton-ated water, H30 (hydronium ion), was first postulated in 1907, and its preeminent role in acid-catalyzed reactions in aqueous media was first realized in the acid-base theory of Bronsted and Lowry. Direct experimental evidence for the hydronium ion in solution and in the... 

Surface Tension. Interfacial surface tension between fluid and filter media is considered to play a role in the adhesion of blood cells to synthetic fibers. Interfacial tension is a result of the interaction between the surface tension of the fluid and the filter media. Direct experimental evidence has shown that varying this interfacial tension influences the adhesion of blood cells to biomaterials. The viscosity of the blood product is important in the shear forces of the fluid to the attached cells viscosity of a red cell concentrate is at least 500 times that of a platelet concentrate. This has a considerable effect on the shear and flow rates through the filter. The surface stickiness plays a role in the critical shear force for detachment of adhered blood cells. 

Dall Asta and Motroni (44, 57) provided direct experimental evidence for the transalkylidenation mechanism in the case of cycloalkenes. With a catalyst system consisting of WOCI4, C2H6A1C12, and benzoyl peroxide they prepared a random copolymer of cyclooctene and cyclopentene, the cyclo-pentene double bond being labeled with 14C. The distribution of the radioactivity in the copolymer formed will depend on the site of ring opening. 

There is no direct experimental evidence for the intermediate 2.30 in the reaction sequence of Scheme 2-19. In the corresponding diazotization of 2-aminophenazine the proportion of the quinone diazide (isomer of 2.31) amounted to only 16%, but 30% unsubstituted phenazine was also found. The phenazine may have resulted from the overall redox reaction. 

On smooth Au surfaces, the adsorbed oxygen, which is only possible in molecular form [5], is not selective to form PO [6]. Therefore partial oxidation is contributed by oxygen adsorbed on Ti02. However, there are no direct experimental evidence whether O2 is adsorbed dissociatively or non-dissociatively. It is generally accepted that O2 adsorbs on Ti02 in a molecular form [7] and is activated at the Au/Ti02 interface [1]. 

Ertl and his colleagues in 1997 reported detailed STM data for the oxidation of CO at Pt(l 11) surfaces, with quantitative rates extracted from the atomically resolved surface events.27 The aim was to relate these to established macroscopic kinetic data, particularly since it had been shown that no surface reconstruction occurred and the reaction was considered to obey the Langmuir-Hinshelwood mechanism, where it is assumed that the product (C02) is formed by reaction between the two adsorbed reactants, in this case O(a) and CO(a). Nevertheless, it was well known that for many features of the CO oxidation reaction at Pt(lll) there is no mechanism that is consistent with all features of the kinetics the inherent problem is that in general a reaction mechanism cannot be uniquely established from kinetics because of the possible contribution of intermediates or complications for which there might be no direct experimental evidence. 

The experimental data also show that the crossover to the many-chain regime does not appear in the Q-window accessible to the method. Owing to this lack, the direct experimental evidence that the upturn has to be assigned to a single chain mode and does not result from a collective mode, is still missing. Nevertheless, assuming Dc c, and expressing Dg by DC/(Q/), from a simultaneous fit (c)/A = (6.0 0.5)c-1 and //A = 7.4 + 0.6 are derived. 

Considerations of the negative difference effect [see Section III(5(iv))] indicate the second case to be the likely one, but no direct experimental evidence has been obtained so far. 

Time-resolved in situ Small Angle Neutron Scattering (SANS) investigations have provided direct experimental evidence for the initial steps in the formation of the SBA-15 mesoporous material, prepared using the non-ionic tri-block copolymer Pluronic 123 and TEOS as silica precursor. Upon time, three steps take place during the cooperative self-assembly of the Pluronic micelles and the silica species. First, the hydrolysis of TEOS is completed, without modifications of the Pluronic spherical micelles. Then, when silica species begin to interact with the micelles, a transformation from spherical to cylindrical micelles takes place before the precipitation of the ordered SBA-15 material. Lastly, the precipitation occurs and hybrid cylindrical micelles assemble into the two-dimensional hexagonal structure of SBA-15. 

Fig. 4-11). Interestingly, the larger amounts of P2 protein that are in myelin of some species correlate with increased widths of the major dense lines as determined by X-ray diffraction, and there appears to be substantially more P2 in large sheaths than small ones [4]. The large variation in the amount and distribution of the protein from species to species and sheath to sheath raises so far unanswered questions about its function. Its similarities to cytoplasmic proteins in other cells, whose functions appear to involve solubilization and transport of fatty acids and retinoids, suggest that it might function similarly in myelin assembly or turnover, but there is currently no direct experimental evidence to support this hypothesis. 

Oxidative Alkoxylation of Nitrones to a-Alkoxy Nitrones and a-Alkoxy Substituted Nitroxyl Radicals The first direct experimental evidence of the possibility to carry out radical cation nucleophilic addition to nitrones with the formation of nitroxyl radicals has been cited in Section 2.4. Further, such a reaction route was referred to as inverted spin trapping this route is an alternative to a conventional spin trapping (508-512). Realization of either mechanism depends on the reaction conditions namely, on the strength of both nucleophile and oxidant. The use of strong oxidants in weak nucleophilic media tends to favour the radical cation mechanism... 

Direct experimental evidence for the trans elimination in E2 reactions has been obtained from deuterated -2-bromobutane (the deuterium atom occupies position 3). This compound on dehydrobromination forms trans and cis butene-2 in the ratio of 6 1... 

Perino, Science, 310,1797 (2005). Direct Experimental Evidence of a Growing Length Scale Accompanying the Glass Transition. 

The concentration dependence and non-linearity observed in do/pH curves indirectly show that it is not legitimate to ignore complexation. Direct experimental evidence, obtained with radiotracer methods (21,30,31), confirms the importance of complexation in the generation of surface charge do. Thus, we need to add the following equations to Equations 2 and 3, assuming for simplicity that the electrolyte is NaCl ... 

In the final analysis protein folding will be really understood only with the aid of much more extensive, direct experimental evidence. Speculative hypotheses can be useful, however, in suggesting potentially fruitful questions for experimental investigation. Probably the most important idea suggested by the above schema is that there are likely to be considerable systematic differences in the kinetics of folding between the various major structural categories of proteins. 

The first first direct experimental evidence for a roughening transition was reported in 1979. Several groups have studied the thermal behavior of the basal plane of a hexagonal close-packed He crystal. In a beautiful experiment Balibar and Casting obtained for this surface a roughening temperature of Tk 1.2K. 

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