Direct microscopic measurement

Several devices are available commercially to measure mobihty. One of these (Zeta-Meter Inc., New York) allows direct microscopic measurement of individual particles. Another allows measurement in more concentrated suspensions (Numinco Instrument Corp., Monroeville, Pa.). The state of the charge can also be measured by a streaming-current detecdor (Waters Associates, Inc., Framingham, Mass.). For macromolecules, more elaborate devices such as the Tisehus moving-boundaiy apparatus are used. 

Whal is meant by the pore size ratings of commercially available membranes Pore size ratings of commercially available membranes are not indices of maximum pore opening diameters obtained from direct microscopic measurement or by particle passage methods. Ratings are almost always determined by indirect means based on theoretical considerations and on nondestructive test technology. 

The increase in liver weight associated with induction results from a combination of hepatocellular hyperplasia and hypertrophy. Hyperplasia is evidenced by an increased number of mitotic figures and hypertrophy by direct microscopic measurements of cell size and volume. 

The earliest test of diffraction based particle sizing instruments was published by Haden in 1938. He considered the Emmon Eriometer, the Bock Erythometer and Dr Pijper s blood cell tester. These instruments depended on near mono-disperse samples. The position of the diffraction rings was used to determine particle size. Haden compared these diffraction methods to direct microscopic measurements. He concluded that diffraction methods are satisfactory for measuring mean sizes and recommended specific instruments for different ty s of tests. 

There are a number of complications in the experimental measurement of the electrophoretic mobility of colloidal particles and its interpretation see Section V-6F. TTie experiment itself may involve a moving boundary type of apparatus, direct microscopic observation of the velocity of a particle in an applied field (the zeta-meter), or measurement of the conductivity of a colloidal suspension. 

So far, the existence of a well-defined entanglement length in dense polymer systems has been inferred indirectly from macroscopic experiments like measurements of the plateau modulus. However, its direct microscopic observation remained impossible. The difficulty in directly evaluating the entanglement... 

A comparison with the tube diameter derived from plateau moduli measurements on PEB-7 underlines this assertion. The coincidence of tube diameters determined macroscopically by application of the reptation model and direct microscopic results is far better than what could have been expected and strongly underlines the basic validity of the reptation approach. 

The measurement of contact angles for a sessile drop or bubble resting on or against a plane solid surface can be measured by direct microscopic examination. 

The point of zero charge is the pH at which net adsorption of potential determining ions on the oxide is zero. It is also termed the point of zero net proton charge (pznpc). It is obtained by potentiometic titration of the oxide in an indifferent electrolyte and is taken as the pH at which the titration curves obtained at several different electrolyte concentrations intersect (Fig. 10.5). It is, therefore, sometimes also termed the common point of intersection (cpi). The pzc of hematite has been determined directly by measuring the repulsive force between the (001) crystal surface and the (hematite) tip of a scanning atom force microscope, as a function of pH the pzc of 8.5-8.S was close to that found by potentiometic titration (Jordan and Eggleston, 1998). This technique has the potential to permit measurement of the pzc of individual crystal faces, but the authors stress that the precision must be improved. 

H3. Hayashi, H., LoGrippo, G. A., and Retry, M., Immunoglobulin levels in spinal fluid and saUva by direct immunochemical assay and microscopic measurements. Henry Ford Hosp. Med. J. 18,... 

Adatom diffusion, at least under the low temperature of field ion microscope measurements, almost always follows the direction of the surface channels. Thus adatoms on the W (112) and Rh (110) surfaces diffuse in one direction along the closely packed atomic rows of the surface channels. Such one-dimensional surface channel structures and random walks can be directly seen in the field ion images, and thus the diffusion anisotropy is observed directly through FIM images. Unfortunately, for smoother surfaces such as the W (110) and the fee (111), no atomic or surface channel structures can be seen in field ion images. But even in such cases, diffusion anisotropy can be established through a measurement of the two-dimensional displacement distributions, as discussed in the last section. Because of the anisotropy of a surface channel structure, the mean square displacements along any two directions will be different. In fact this is how diffusion anisotropy on the W (110) surface was initially found in an FIM observation.120... 

An increase in bacterial population would indicate a fermentation of some sort. However, measuring bacteria by plate count is cumbersome, and direct microscopic count in wine is difficult because of the similar appearances of bacteria and grape debris. 

With the Conti-Testor type of hardness tester manufactured by Wolpert, designed for the Theimert-Stoferle method, measurement of the scratch depth is automated. It is measured against a slide moving directly in front of the diamond point over the as yet undamaged surface. By this arrangement, errors occurring with microscope measurement can be avoided. 

Coulter Counter To avoid the tedium of direct microscopic counting, a Coulter counter can be employed. By using this technique, not only the cell number, but the cell size can be measured. The disadvantage of this technique is that it cannot distinguish between cells and any impure particles. The technique is also difficult to use with organisms in chains and is useless with mycelial organisms. 

The most important property characterizing a microporous membrane is the pore diameter (d). Some of the methods of measuring pore diameters are described in Chapter 7. Although microporous membranes are usually characterized by a single pore diameter value, most membranes actually contain a range of pore sizes. In ultrafiltration, the pore diameter quoted is usually an average value, but to confuse the issue, the pore diameter in microfiltration is usually defined in terms of the largest particle able to penetrate the membrane. This nominal pore diameter can be 5 to 10 times smaller than the apparent pore diameter based on direct microscopic examination of the membrane. 

Measuring the Soil Microbial Biomass 10.2.3.1 Direct Microscopic Counting... 

Enantiospecific addition of substituted ethylenes containing double bonds to Si dimers at silicon surfaces to form Si - C bonds via 2n + 2n addition reactions has been demonstrated by applying direct scanning probe microscopic measurements [90]. 

Fairs investigation of microscopic measurement consisted of two parts (1) Type of illumination for improving the resolution of the. microscope system, and (2) the development of a series of graticules for the direct comparison of the projected particle... 

The values of absolute values of (po and <70, since the calculation from film thickness by the DLVO-theory does not give an estimation whether the potential is positive or negative. However, the direct experimental measurements provide information which are the ions adsorbed at the interfaces electrolyte solution/air and non-ionic surfactant solution/air, and it is possible to determined the potential sign (see below). This is valid also for adsorption of ionic surfactants. 

FIGURE 4.2. A schematic of an atomic force microscope, comprising a piezo mbe, a cantilever, a sample or substrate to image and an optical lever using a laser and four-quadrant photodiode. A colloidal probe (radius 5 pm) is added to the end of the cantilever for direct force measurement. For imaging application, the probe is absent and the tip is rastered across the surface. 

Electrophoresis The most familiar electrokinetic experiment consists of setting up an electric field, E, in a solution containing charged particles and determining their velocity. The particle velocity, V, is measured by direct microscopic observation at the stagnation point (i.e., zero velocity point for electro-osmosis at the radius 0.707i c) in a capillaiy as shown in Figure 9.19. The zeta potential is then computed... 

The cell aspect ratio, which is characteristic for foam anisotropy, can be determined by microscopically measuring the linear cell dimensions on sections cut from different portions of a foam block. The results of such measurements can only be representative of the morphology of certain portions of a cellular structure. A statistical analysis of samples cut of different block portions and in different directions with respect to that of expansion is a very difficult task. 

---