Precipitation sites

Gettering is a black art. It consists in forcing selected impurities (typically, transition metals) to diffuse toward unimportant regions of tlie device. This is often done by creating precipitation sites and perfoniiing heat treatments. The precipitation sites range from small oxygen complexes to layers such as an A1 silicide. The foniiation of such a... 

Morita etal. (2001) also examine the mechanics of nickel short-circuiting in Li/Na cells at ambient pressure. There is a process of linking local precipitation sites into chains, which extend into short circuits. 

Rainwater composition is determined by the atmospheric composition of the precipitation zone and by that of the zone of origin of the clouds and the winds that carry them to the precipitation site. It varies geographically and depends on the natural and anthropogenic input of gases and particles into the atmosphere, as well as on the atmospheric reactions that may transform them. Activity of the local biomes (see definition in Section 7.3) also affects rainwater composition as does the local weather, which in turn defines the amount of precipitation and therefore the concentration of components. 

Figure 8 Widmanstatten pattern in a poUshed and etched section of the IlD iron meteorite, Carbo. 10 cm field of view. The brownish tear shaped troilite nodule to the left has acted as precipitation site for kamacite (Geological Museum, University of Copenhagen, specimen 1990.143).

This information seems to preclude the present-day precipitation site as the major source of high radium values, so we are left with several alternatives (1) that the boundary between the freshwater zone and the transitional zone (hence the site of uranium accumulation) was once further west and that it has migrated eastward in the recent geologic past, or (2) that the source of radium is the high-Cl brine. 

Permeability in the vadose zone tends to be higher in finer sediments because flow occurs preferentially along grain surfaces rather than the centre of large pores. Finer sediments have more surfaces on which vadose flow can occur (Palmquist Johnson, 1962 Hillel, 1980 Jury et ai, 1991 Mozley Davis, 1996). If cementation is limited by the supply of Ca " and/or HCO3" to the precipitation site, vadose cements should occur preferentially in the finer sediments (Mozley Davis, 1996). 

As previously discussed, if cementation is limited by the supply of Ca and/or HCOj" to the precipitation site, and supply is limited by flow, phreatic... 

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