Still exposure

In third-generation synchrotrons, the x-rays are generated in intense flashes of 100 picoseconds (ps) duration. If, dnring this time, an entire diffraction pattern is recorded, the time resolution equals 100 ps (Szebenyi et al. 1992 Srajer et al. 1996, Schotte et al. 2003). However, the traditional monochromatic oscillation diffraction method cannot be used since there is no way to rotate the crystal during this 100 ps timeframe to collect the integrated intensity of a Bragg reflection. Still exposures, therefore, have to be used. 

Figure 8.3 Single ciystal synchrotron X-ray diffraction patterns recorded from a variety of macromolecular crystals illustrating the variety of diffuse scattering features, (a) aPP, resolution limit 1.8A, wavelength 1.49A, 4.9° oscillation photograph. (b) RNAse, resolution limit 1.9 A, wavelength 1.488 A, still exposure.

The connnon tlnead to these designs is that a sample can be exposed to reaction conditions and then studied usmg surface science methods withont exposure to the ambient. The drawback to both of these designs is that the samples are still being analysed under UFIV conditions before and after the reaction under study. The need for in situ teclniiqnes is clear. 

Catalyst Durability. Automobile catalysts last for the life of the vehicle and still function well at the time the vehicle is scrapped. However, there is potential for decline in total catalytic performance from exposure to very high temperatures, accumulation of catalyst poisons, or loss of the active layer (29,64—68). 

The handling of the monomer presents a number of problems. The monomer will polymerise on storage even under an inert gas. Polymer deposition may be observed after standing for less than a day. Exposure to air, to water or to light will accelerate polymerisation. A number of phenolic materials are effective inhibitors, a typical example being 0.02% p-methoxyphenol. Exposure to light, air and water must, however, still be avoided. The monomer has an anaesthetic action and chronic toxic properties and care must therefore be taken in its handling. 

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

In nonindustrial settings, MCS substances are the cause of indoor air pollution and are the contaminants in air and water. Many of the chemicals which trigger MCS symptoms are known to be irritants or toxic to the nervous system. As an example, volatile organic compounds readily evaporate into the air at room temperature. Permitted airborne levels of such contaminants can still make ordinary people sick. When the human body is assaulted with levels of toxic chemicals that it cannot safely process, it is likely that at some point an individual will become ill. For some, the outcome could be cancer or reproductive damage. Others may become hypersensitive to these chemicals or develop other chronic disorders, while some people may not experience any noticeable health effects. Even where high levels of exposure occur, generally only a small percentage of people become chemically sensitive. 

---