Mounting and Handling

Crystals of proteins, nucleic acids, viruses, and macromolecular complexes must be handled with considerable care because they are extremely fragile and contain a high proportion of solvent, principally water. Bernal and Crowfoot demonstrated in 1934 that diffraction patterns from protein crystals quickly degenerate upon dehydration in air. Thus it is essential 

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Reactors either have a thermal column or they do not. It is highly unlikely that a facility will install a thermal column for this application alone and therefore the cost of doing so is not relevant. Hence, only minimal funds are necessary for construction of a sample mounting and handling device. 

Surface analysis has an important role to play in the study of composites and fibers. Many surface analytical methods are available, but XPS is the most extensively used because surface chemical infonnation is essential. The two most important practical points are that samples be mounted and handled very carefully in the spectrometer and that the data be analyzed thoroughly. Complete problem solving cannot be achieved unless the surface analyst uses the full extent of information available (e.g., by careful curve re.soiution and by making use of valence band spectra). This chapter has given many examples of the type... 

Industrial, centrifugal elevators usually operate at speeds of about 75 m /min, and handle free-flowing, fine and loose materials having lump sizes of <50 mm. Sticky material can be a problem. Fine fluidizing materials often require perforations in the bottom of the buckets to vent entrapped air. Centrifugal elevator capacities range up to 370 m /h for a single row of buckets, and up to 1400 m /h for multiple rows of buckets. The buckets can be mounted on a belt or chain. 

Each photoelectrode was retested after mounting and current voltage plots obtained. All photoelectrodes decreased in performance and one became essentially inoperative. This is attributed to excessive handling during mounting which resulted in abrasion and deterioration of the deposit. The maximum power output of the individual mounted electrodes in the assembly varied from 5.TO mW to 0.13 mW. The maximum power obtained from the assembled converter was 27 mW. Under short circuit conditions the maximum power at 90.2 mA and 100 mV was 9 0 mW. The light intensity incident at the photocell was 92.5 mW/cm. ... 

Fig. 10. Arrangements of mechanical seals. A, Single seal. It is the most common and handles most applications. B, Inside mounted seal. It operates better because it has positive lubrication the entire seal is surrounded by fluid. C, Outside mounted seal. It is more easily accessible for maintenance and less of the seal is exposed to corrosive fluid.

The design of the equipment must therefore be as simple as possible. On the other hand, when using hot-cell units mounted with handling tongs, it may be favorable to use more automated systems in the production line. Systems like these can be run and controlled from steering panels outside the box unit. 

In this chapter, the results of past research are expanded because fiber cross sections were examined, rather than longitudinal views of fibers, and distributions of elements were obtained in addition to overall elemental spectra. Because the X-ray beam penetrates only a small distance into the surface of a sample (approximately 8-10 xm for a 25-kV excitation ), examination of a longitudinally mounted fiber produces elemental spectra of surface layers only. Such spectra may not be representative of the bulk of the fiber. In addition, this work improves upon past research in that the freeze-fracturing-freeze-drying EDS technique is suited to very small, fragile fiber samples (whether single fibers or small yam pieces), and is limited in size only in the operators ability to see and handle the samples. By using this procedure, compression of the fiber cross section and elemental redistribution are avoided. 

Other noise phenomena which may impair the performance of MCP s include switched on channels, hot spots , dead channels, and field emission from mounting hardware. Due to improved selection and production techniques, the incidence of dead channels and switched on channels is now relatively low. However, hot spots, producing relatively large numbers of spurious events, are a more common occurrence. Currently this effect is thought to be associated with dust or damage on the front surface of MCP s. Certainly our experiences suggest that, if care is taken with cleanliness and handling of MCP s, the occurrence of hot spots can be kept very low. 

For seawater analysis, it is possible to pump the sample directly from the sea to a shipboard analyser. The sample can then be de-gassed in-line and handled in a shipboard flow system. This possibility, and the main practical, physico-chemical and interpretative aspects, were discussed in relation to the in situ spectrophotometric determination of seawater pH [9]. The attractive features and applications of shipboard flow injection spectrophotometric determinations are discussed elsewhere [10,11]. A compact, shipboard flow analysis system incorporating a LTV photoreactor has also been reported for the determination of total phosphorus in estuarine and marine waters [12]. Another way to sample seawater is to use a towed torpedo-shaped "fish," deployed off the crane arm of a hydrographic winch at a distance of 5 m from the ship, connected to a deck mounted pump by appropriate tubing. Filtration can be incorporated in-line and the filtered sample collected or pumped directly to the flow analyser [13]. This approach (Fig. 8.1) minimises contamination and preconditions the sample, as demonstrated in the chemiluminometric determination of iron(II) in surface seawater. 

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