Oxygen-penetrability

A smooth coal pile surface, coupled with the gradual slope, minimi2es the differential wind pressures and consequent oxygen penetration. A 4-6 X 10 t lignite stockpile from the excavation for the Garrison Dam in North Dakota has been stable for many years as a result of this storage method. 

By using the unsteady-state model, the maximum oxygen penetration depth for highly packed immobilised cells has been reported to be in the range of 50-200 xm. 

The role which mobility of surface metal atoms play and the role of oxygen penetration into the lattice is only now beginning to be examined. 

Stations 23 and 24, located in the LSLE, have been subjected to hypoxic conditions since the 1980s. With depletion of oxygen in the bottom waters, the sediment oxygen penetration depth decreased, and Fe oxides, concentrated in the oxic sediment layer, were reductively dissolved and released adsorbed arsenic. Hence, the low oxygen levels during the last 25 years in the bottom waters is reflected in more reducing conditions in the sediment and increases in both dissolved and HA-extractable Fe and As. 

On storage in ambient air or immersion in H202 the Si-O-Si vibrational mode becomes detectable for electrochemically formed PS, without a significant change in the number of Si-Hx bonds, as shown in Fig. 6.15 [Th5]. This supports the assumption that oxygen penetrates the Si lattice and breaks the backbonds of the... 

The sediment oxygen penetration depth as a function of water coiumn depth in the Atlantic Ocean (open symbols) and Pacific Ocean (closed symbols). Source-. From Martin, W. R., and F. L. Sayles (2003). Treatise on Geochemistry, Elsevier. 

Table XVI shows two experiments which compared the same wine stored under different conditions (46). In both cases, the wine richer in anthocyanins is also that which is less colored. The mediation of tannins is not enough to explain the differences in color these can only be explained by a different structuring of the anthocyanin molecules. More specifically, the anthocyanin molecules will be reduced to colorless flavenes (14) during fermentation, which is a reductive process. The reoxidation occurs more rapidly in wooden casks which allow better oxygen penetration than metal storage tanks or large capacity casks. However, the flavenes themselves are relatively instable and can be irreversibly hydrolyzed into dihydrochalcones (16). This explains the lack of relationship between anthocyanin concentration and color, independent, of course, of the eventual appearance of free sulfur dioxide.

Contrary to H2S, the amount of S02 evolution remains constant with coal maturation. The peak temperature of S02 rises from about 350 C for the peat sample to about 650 C for the anthracite sample. This temperature increase with coal maturation could be due to a loss of inflammable volatile matter which accelerates the char oxidation, and a relative enrichment of the char in condensed aromatic nuclei more resistant to pyrolytic breakdown, as seen by PTP and Py-GC, but also to a reduction of the size of micropores during coalification which hampers oxygen penetration into the solid matrix. 

Beeck 393) as well as Bagg and Tompkins 395) has included oxygen as one of the gases in these investigations. As, however, oxygen penetrates easily into the surface layers of the adsorbents (Sec. VII,6), complications arise. 

The particularity of the natural conditions of the Black Sea lies in the fact that it the largest basin in the world with a permanent halocline and a two-layered structure of the waters. The intensive pycno- and halocline prevents the waters from vertical mixing and oxygen penetration to deeper layers even in the period of the development of the wintertime vertical convection. Therefore, the entire water column below a depth of 100-200 m represents an inanimate hydrogen sulphide zone, in which only anoxic processes take place. About 90% of the water volume does not participate in the processes of self-purification of the sea. 

At this time, some investigators consider that oxygen practically disappears at the density of nitrate maximum [14] or quite the contrary traces, that oxygen penetrates down into the hydrogen sulfide zone for 10-20 m [23]. In our opinion oxygen disappears at the level of onset of deep ammonia and dissolved Mn(II) and is consumed in reactions with these species. This situation appears stable from a hydrophysical point of view. 

In the case of an intensive laminar flame combustion, oxygen penetration to the surface, across the high-temperature reaction zone, is hindered due to the high rate of its reaction in the zone. A thermal decomposition of the polymer may be expected to take place under these conditions. Near the combustion limit, oxygen is able to penetrate the zone near the surface underneath the flame edge. However, its concentration (1-2 %) is insufficient for a profound oxidation of the condensed phase. The probability of oxygen penetration to the surface increases when the flame becomes turbulent and when the condensed phase decomposition products are less volatile... 

Fluorescence quantum-yield and lifetime measurements have established that oxygen penetrates micelles (Geiger and Turro, 1975). Entrance- and exit-rate constants have been determined for a cationic (CTAB) and an anionic (SLS) micelle system using I, S-dimethylnaphthalene as the fluorescing species (Hautala et al., 1973). Of general importance is that the solubility of oxygen is higher in the micelle than in the aqueous phase. 

Metallurgically, uranium metal may exist in three allotropic forms orthorhombic, tetragonal, or body-centered cubic (EPA 1991), and may be alloyed with other metals to alter its structural and physical properties to suit the application. Like aluminum metal powder, uranium metal powder is autopyrophoric and can burn spontaneously at room temperature in the presence of air, oxygen, and water. In the same manner, the surface of bulk metal, when first exposed to the atmosphere, rapidly oxidizes and produces a thin surface layer of UO2 which resists oxygen penetration and protects the inner metal from oxidation. 

Results. Figure 2 shows the results of the above calculations for the case of a spherical dodecane cloud burning in air. Here the local oxygen mass fraction, normalized by its ambient value, is plotted against the distance from the cloud center, measured in cloud radii, with as a parameter. Notice that when p = Q the cloud oflFers no resistance to oxygen penetration and the oxidizer mass fraction is at the ambient value every-... 

Whether the sediment is oxic or anoxic is also an important determinant of sedimentary N fluxes as well as the forms of N released. In sediments with significant organic matter deposition, oxygen does not generally penetrate far into the sediments such that reduced compounds like NH4 or N2 tend to dominate remineralization (e.g., Pedersen et ah, 1999). Similarly, efflux of NOs is also heavily dependent on oxygen penetration. 

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