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The mixing of the anaerobic digester contents significantly influences the efficiency of this operation; in particular, hydraulic dead zones are extremely detrimental to the reaction kinetics involved in anaerobic digestion. An analysis of the relative importance of thermal fluid movement in the digester to those caused by fluid inflow and outflow is presented. As an example, these principles are applied to a digester at the South Bend Wastewater Treatment Plant. Experimental measurements, which have general applicability for the measurement of digester mixing volume, confirm the theoretical conjectures. Various types of optimizations can be attempted on this mixing operation. One such optimization applied to gas lift mixers, as employed in the South Bend Treatment Plant, is illustrated. 相似文献
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Rates of single-copy DNA evolution in herons 总被引:2,自引:1,他引:1
DNA-DNA hybridization was used to discover the extent of single-copy DNA
similarity among 13 species of herons and one ibis. Genetic distances among
taxa were summarized as Tm values in a folded matrix. From this matrix,
trees with the same branching pattern were constructed by least squares
under one of two assumptions: (1) that sister branches are equal in length
and (2) that sister branches are not necessarily equal in length. The
residual sums of squares of these trees were compared by F-test to see
whether the branches of the tree built under assumption (2) fit the matrix
data significantly better than those of the tree built under assumption
(1). By this method the existence of different rates of DNA evolution in
different heron lineages was established. Bittern single-copy DNA has
evolved at a rate approximately 25% faster, and boat-billed heron
(Cochearius) and rufescent tiger heron (Tigrisoma lineatum) DNA has evolved
approximately 19% slower, than that of day and night herons. It appears
that the differences in rates of DNA evolution may increase proportionally
with genealogical distance.
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