Microscopic projections

Microvilli are microscopic projections found on the luminal surface of the absorptive cells. Each absorptive cell may have literally thousands of microvilli forming the brush border. These structures increase the surface area for absorption another 20-fold. Together, these three anatomical adaptations of the intestinal mucosa — plicae circulares, villi, and microvilli — increase the surface area as much as 600-fold, which has a profound positive effect on the absorptive process. 

Although conventional soft lithography techniques can be used to fabricate nonspherical particles, the production rate is limited by the mold size, limiting mass production due to the increased complexity in parallel configuration setup, and a possible solution involves the combined use of a microfluidic device and microscope projection lithography, so that the fabrication process for nonspherical objects could be transformed into a continuous. ... 

Apparently N. A. Fuks [2] is correct in that the quantity r in Eq. (1.39) must not be considered the particle radius, but rather the radius of those sub-microscopic projections through which actual contact occurs between the particle and surface. Hence, in Chapter V we will be examining the influence of surface roughness and radius of curvature of the contacting bodies on the magnitude of adhesion. 

Corn [80] observed a fall in the adhesive force of fused glass particles to "Pyrex glass (mean height of microscopic projections 2159 db 127 A, 2921 127 A, 4826 127 A) with increasing microscopic roughness, and introduced a correction for roughness when determining the adhesive forces... 

The numerical values of and a, for a particular sample, which will depend on the kind of linear dimension chosen, cannot be calculated a priori except in the very simplest of cases. In practice one nearly always has to be satisfied with an approximate estimate of their values. For this purpose X is best taken as the mean projected diameter d, i.e. the diameter of a circle having the same area as the projected image of the particle, when viewed in a direction normal to the plane of greatest stability is determined microscopically, and it includes no contributions from the thickness of the particle, i.e. from the dimension normal to the plane of greatest stability. For perfect cubes and spheres, the value of the ratio x,/a ( = K, say) is of course equal to 6. For sand. Fair and Hatch found, with rounded particles 6T, with worn particles 6-4, and with sharp particles 7-7. For crushed quartz, Cartwright reports values of K ranging from 14 to 18, but since the specific surface was determined by nitrogen adsorption (p. 61) some internal surface was probably included. f... 

Most tests of the validity of the BET area have been carried out with finely divided solids, where independent evaluation of the surface area can be made from optical microscopic or, more often, electron microscopic observations of particle size, provided the size distribution is fairly narrow. As already explained (Section 1.10) the specific surface obtained in this way is related to the mean projected diameter through the equation... 

Microscope Methods In microscope methods of size analysis, direct measurements are made on enlarged images of the particles. In the simplest technique, linear measurements of particles are made by using a cahbrated scale on top of the particle image. Alternatively, the projected areas of the particles can be compared to areas of circles. 

The direct imaging magnetic sector mass analyzer (Fig. 3.19) has the unique property that all parts (lenses, electrostatic analyzer and magnetic sector field) of the secondary ion optics are stigmatic (comparable with light microscopes). This means that all points of the surface are simultaneously projected into the analyzer. 

For control or calibration purposes, film thickness can be determined by mounting a sectioned specimen and measuring the oxide film thickness directly on the screen of a projection microscope at a known magnification. Alternatively, the loss in weight of an anodised sample of known area may be found after the film has been stripped in a boiling solution made up as follows ... 

Fig. 11-2. The General Electric X-ray Microscope. The equipment uses x-ray shadow projection to magnify and reveal detailed internal structure of specimens opaque to electrons or light. (Courtesy of General Electric Company.)...

Their theory can also be regarded as the begiiming of micro-macro thinking in the written history of science in a philosophical manner, macroscopic properties are projected, but not transferred on a pttre hypothetical microscopic model (Weillbach, 1971). 

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