Phase contrast analysis

It will be assumed that the reader is familiar with the phase contrast method for the analysis of asbestos. If not, the equipment and procedures for the phase contrast analysis of asbestos have been described by the United States Public Health Service (1 ), National Institute for Occupational Safety and Health 2), (3), and by professional societies (4 ). 

C. Walling In the discussion at this session an interesting contradiction has arisen which needs to be resolved. Extensive data on liquid phase autoxidations near room temperature indicate that bimo-lecular interactions of peroxy radicals (particularly tertiary peroxy radicals ) are slow processes with appreciable activation energies. In contrast, analysis of high temperature gas-phase processes indicate fast interactions occurring at almost every collision. 

Phase contrast permits analysis of asbestos by morphology and by increased visibility of internal structure. Vegetable fiber, for example, will be more readily recognised since small differences in n is made more apparent. 

Phase contrast is often adequate for an accurate analysis of asbestos, especially if it is not necessary to determine the variety of asbestos present, or if interference from other fibers is not a problem. An experienced analyst is not likely to confuse chrysotile with other fibers u most cases. 

If fibers remain unidentified after examination by phase contrast, polarized light, compensators, or measurement of angle of extinction, the fibers can be removed from the membrane for dispersion stain analysis by ashing, particle picking, or dissolving the membrane. 

Figure 3.24 Two Fourier transformations during formation of a phase contrast image. (Reproduced with permission from J.P. Eberhart, Structural and Chemical Analysis of Materials, John Wiley Sons Ltd, Chichester. 1991 John Wiley Sons Ltd.)...

Figure 4.29 shows 120-nm wide and 10-nm thick Pt particles made by colloidal lithography on a 40-nm thick oxidized TEM membrane, i.e., with Si02 as the Pt support. Even though a thinner membrane 3delds better phase contrasts in TEM, atomic-scale resolution of particle-support boundary sites will normally require cross-sectional analysis. Using colloidal lithography, it is evident that a much narrower size distribution is obtained than by evaporation. 

Additional experiments that assess expression of a luciferase reporter gene at both the protein and mRNA levels also suggested an uncoupling of transcription from translation (Nothias et al., 1996). Injection of the reporter gene into the nucleus of a two-cell blastomere was followed by the rapid expression of both luciferase mRNA, as detected by a quantitative RT-PCR assay, and luciferase activity. In contrast, analysis of S-phase-arrested, one-cell embryos revealed that, while luciferase mRNA was readily detected at a time that corresponded to G2 of the one-... 

Miscibility of PI blends of different structures was reported by Hasegawa et al. [1991] using charge-transfer fluorescence spectra, dynamic mechanical analysis, and phase-contrast microscopy. These blends were BPDA/PDA PI with PMDA/PDA and PMDA/ODA PFs (BPDA = biphenyltetracarboxylic dianhydride PDA = p-phenylene diamine ODA = oxydianUine PMDA = pyromellitic dianhydride). Two patents issued virtually simultaneously noting the utility of miscible PI blends for gas separating membranes [Burgoyne et al., 1991 Kohn et al., 1991]. 

Optical microscopy on phase contrast mode allows observation of the different morphologies obtained for each PP/interfacial modifier/PA6 blend. By image analysis techniques, it is possible to carry out statistical field measurements not only of the mean number of particles on the dispersed phase but also of their preferential geometry, mean size, and size distribution. 

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