Impact surface conditions

These techniques have very important applications to some of the micro-structural effects discussed previously in this chapter. For example, time-resolved measurements of the actual lattice strain at the impact surface will give direct information on rate of departure from ideal elastic impact conditions. Recall that the stress tensor depends on the elastic (lattice) strains (7.4). Measurements of the type described above give stress relaxation directly, without all of the interpretational assumptions required of elastic-precursor-decay studies. 

Mass concentration units for ambient measurements are mass (/xg) per unit volume (m ). Size classification involves the use of specially designed inlet configurations, e.g., PMjq sampling. To determine mass concentration, all the particles are removed from a known volume of air and their total mass is measured. This removal is accomplished by two techniques, filtration and impaction, described in Chapter 13. Mass measurements are made by pre-and postweighing of filters or impaction surfaces. To account for the absorption of water vapor, the filters are generally equilibrated at standard conditions T = 20°C and 50% relative humidity). 

Amongst the factors that will influence service performance are the effect of additives and impurities, temperature, detailed geometric size and shape, orientation and morphology, surface condition, energy and speed of any impacting blow, the shape of the impacting instrument, the environment, and strains in the article due to external loads. For this reason it is desirable, but not always feasible, to test prototype articles under conditions as close to service conditions as possible. 

Fig. 3.5. The experimental arrangement used for a typical compressed gas gun is shown. The apparatus is designed to impact a selected impactor upon a target material with precision on the alignment of the impacting surfaces. Velocity at the impact surface can be measured to an accuracy and precision of 0.1%. This loading produces the most precisely known condition of all shock-compression events.

If the fluid dynamic conditions of a droplet are within the spreading regime, i.e., below the threshold curve in the We-Oh map, liquid splashing and ejection from the impact surface can be eliminated. The corresponding threshold velocity can be written as ... 

The specific activation conditions required for an individual catalyst likely depend on the metal and support, but 300°C appears to be somewhat of a watershed temperature. Activation at temperatures above 300°C generally coincides with loss of Pt metal surface area due to sintering. The metal loading, dendrimer loading, and metahdendrimer ratios also impact activation conditions, suggesting that it may be necessary to optimize activation conditions for individual catalysts. Using temperatures at or near 300°C, supported pt,45,53,58,6i 45 pt Au, Pt-Cu,. and Ru ... 

Control of Friction/Impact Sparks. The ability of friction/impact sparks to ignite flammable atmospheres is dependent, among other factors, on the composition of the impacting surfaces. In particular, incendive sparks could be expected in any one of the following conditions ... 

The term lead-based paint hazard means any condition that causes exposure to lead from lead-contaminated dust, lead-contaminated soil, lead-contaminated paint that is deteriorated or present in accessible surfaces, friction surfaces, or impact surfaces that would result in adverse human health effects as established by the Administrator under this subchapter. 

Immediately after the Moon-forming impact, a rock-vapor atmosphere surrounded the Earth for a few thousand years and a stream atmosphere then surrounded the Earth for a few million years [54]. These violent surface conditions subsequently returned for thousands of year periods to the surface after asteroid impacts. One interesting effect is that an iron-rich asteroid may have transiently created a reducing atmosphere leading to the origin of life [55,56]. 

Seasonal-to-interannual variability in the global water cycle is largely determined by ocean and land processes and their impact on the atmosphere. The prediction of this variability relies on the persistence in surface conditions that tend to provide the atmosphere with consistent anomalies in fluxes over periods of weeks or months or even years. The time-scale of memory in the atmosphere is fairly short, but due to the atmosphere s connection to the land and ocean, each of which is characterized by a much longer memory, the climate system becomes complex in time... 

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