Refractory species

The most refractory species, A1 and Si, show little variation with size for particles larger than 0.08 ym. The concentrations of both species are very similar to the quantities determined by X-ray fluorescence analysis of bulk ash samples, indicated by the broken lines. The smaller particles contain very little of these major constitutents of the ash, most of... 

Similar plots of the data from higher temperature, nearly stoichiometric combustion. Figure 6, show substantially different trends. The refractory species, i.e., A1, Si, and Ca,show little variation with particle size. Comparison with Figure 5 suggests that this results from vaporization of small amounts of these species. The apparent decrease in the fine particle iron is caused by dilution with other major ash constitutents. Both sulfur and zinc concentrations increase as size decreases in spite of the larger amount of the other species in the fines. 

High temperature combustion at a nearly stoichiometric fuel-air ratio produced substantially different trends. While the behavior of sulfur and zinc did not change significantly, the fine particles contained large amounts of aluminum, silicon, and calcium. Iron made up a relatively small amount of the fine particles in this case. The difference between the two experiments is probably due to increased vaporization of the refractory species at higher combustion temperatures. The relative decrease in fine particle iron may result from dilution with silicon and, to a lesser extent, aluminum and calcium. 

Refractory species such as guinea pig seem to have fewer PPARa receptors in the liver, and observations suggest there are significant differences between rodents and humans in a number of aspects of the response. Recent studies in cynomologous monkeys treated with ciprofibrate have detected peroxisomal proliferation but only found slight changes in certain parameters [e.g., messenger RNA (mRNA) induction for acyl CoA oxidase] of minimal oxidative stress, and despite hypertrophy, cell proliferation was not detected. 

The data of Table I are derived from early time radiochemical data reported by Stevenson (5). The linearity of the radionuclide ratios was first pointed out in that report. The aerial filter samples were taken at successively later times, 1 and 2, below the reported cloud base, and 3, 4, and 5 in the cloud. The tabulated values of rA correspond to atom ratio of isotope A to an arbitrary refractory isotope normalized by dividing by the atom ratio in which the two species were formed. Refractory species include the isotopes of the rare earths Eu and Tb as well as 45Ca, 89Zr, Sc, and others produced by neutron reactions on stable isotopes. The tabulation has been limited to fission product species. However, the... 

The equation in this form states that in the samples analyzed the distribution of any radionuclide, A, can be expressed as a linear combination of the distribution of two species, a refractory and 137Cs. Therefore, we need to determine only refractory distribution, 137Cs distribution, and mass distribution with particle size and the distribution of all other isotopic species for which aA values are known and can be calculated. The refractory species used is 155Eu. It has a half-life of 1.811 years and two easily resolved gamma photopeaks so that its abundance as well as that of 137Cs can be determined readily by gamma spectrometry. 

As in the case of the land surface burst, complete characterization of the particle population requires only that particle mass, a volatile species, and a refractory species distribution with particle size be determined. All other isotopic distributions may be deduced from the istotope partition calculations described above. In the subsurface detonation, the earliest aerial cloud sample was obtained in the cloud 15 minutes after detonation. The early sample was, therefore, completely representative of the aerial cloud particle population. In Figure 5 the results of the size analysis on a weight basis are shown. Included for comparison is a size distribution for the early, local fallout material. The local fallout population and the aerial cloud population are separated completely from the time of their formation. 

The refractory species, of which 147Nd is typical, appear not to be associated at all with the late entering crystalline population. In the local fallout, 147Nd exhibits constant specific activity 1.05 X 109 atoms/ Mg, and in the early entering glass population the refractories appear on the basis of data obtained thus far to be primarily surface distributed. 

Based on the interisotopic ratios obtainable from the analysis of various early time gross particle samples from a given event, it is possible to relate the behavior of all isotopes to that of a single pair of isotopes—a volatile species and a refractory species. 

The distribution of the volatile species, the refractory species, and mass within the particle population can be determined by analysis of size separated fractions of early samples from the aerial cloud and close-in fallout. 

Figure 1. Correlation of the ratio 140Ba/"Mo with the ratio 156Eu/"Mo in a set of airborne-debris samples from a nuclear event. 156Eu has only refractory species for precursors the mass-99 chain exhibits volatile behavior, perhaps owing to the volatility of MoOs. The strong negative correlation indicates that 140Ba has at least some volatile precursors.

Asphaltenic sulfur is the most refractory specie in re-sids and the removal of metals, particularly nickel, correlates well with removal of asphaltenic sulfur. 

It should be emphasized that world-wide the treatment industry is based on comparatively few moderately permeable timbers. Problems can arise when there is commercial interest in using a timber that is somewhat less than ideal, perhaps because it is the main plantation species of that country (for example in the use of eucalypts and spruee). Although treatment of refractory species is not ideal, by drying to a low moisture eontent and with a high preservative loading in the surface layer, adequate serviee life may be achievable for certain end uses. 

One of the main effects of ion irradiation of frozen gases is the formation of molecular species not present in the original sample as indicated by the appearance of new absorption features in the IR spectra. As stated above, after irradiation of carbon bearing refractory species, complex residues are formed (IPHAC). These have been suggested to be analog materials to that of some planetary surfaces [22]. 

Aqua regia is an effective solvent for most base metal sulfates, sulfides, oxides, and carbonates. Some elements, however, form very stable diatomic oxides, referred to as refractory species. Aqua regia provides only a partial digestion for most rock-forming and refractory elements. Hydrofluoric acid can destroy silicate matrices completely to liberate trapped trace constituents. Basic solutions can dissolve tissue and many anionic forms of inorganic ions. Complex-ing solutions such as EDTA are used under conditions that dissolve specific ions (Perrin 1964). 

Refractory species (such as zirconium oxide) are incompletely atomized at the temperatures of a flame or a muffle furnace. If the radionuclide of interest may be in a refractory form, the material must be mixed with fusion reagents and melted at a high temperature. After cooling, the solidified melt is dissolved in a HNOj solution. Fusion mixtures that have been tested for many types of soil are listed in Table 4.2. Sample masses are limited by practical consideration of the final sample size, taking into consideration the large amounts of fusion reagents added to the sample. 

Glaze, W. H. Peyton, G. R. Huang, F. Y.j Burleson, J. L. Jones, P. C. "Oxidation of Water Supply Refractory Species by Ozone with Ultraviolet Radiation." Final Report, EPA-600/2-80-110, August, 1980. 

Transition-metal sulfide (TMS) catalysts play an important role in the petroleum industry. TMS are unique catalysts for the removal of heteroatoms (N, S, 0) in the presence of large amovmts of hydrogen (3). Hydrodesulfiirization (HDS) of petroleum feedstocks are commercially achieved with M0S2 or WS2 supported on alumina and promoted by Co or Ni, (3,4). Co-promoted catalysts are mainly used for HDS, whereas Ni-promoted catalysts are superior for HDN and hydrogenation reactions (5). Catal3rsts currently employed need to be improved to satisfy the imminent restrictions that require the removal of the most refractory species, mainly alkyl-substituted polyaromatic thiophenes. 

The reactivity (rate constants) of sulfur species differs strongly (Figures 6.8.5 and 6.8.6, Table 6.8.3). The most refractory species is the sterically hindered 4,6-dimethyldibenzothiophene (4,6-DMDBT), which is about an order of magnitude... 

For first-order reaction mixtures, the condition is k t 1/M. Here k is a characteristic rate constant for a moderately refractory species and M is the difference between the rate constants for two species whose reactivities are adjacent to each other (M k ). From Houalla et al. s HDS data " , k can be taken as the rate constant for the HDS of dibenzothiophene (DBT). And M can be estimated by the rate constants for the HDS of 4-methyl DBT and of 4,6-dimethyl DBT at 300°C and 10.5 MPa over a sulfided C0-M0/AI2O3 catalyst. The resulting region of validity is 3.87-10 t 161-10 h-g cat./cm feed. This is not stringent at all for the HDS of refiiactory middle distillates. However, if the regime of very long times t > /Sk) is of interest, one should use a discrete approach. 

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