Profile Effects in Early Bilingual Language and Literacy

Bilingual children's language and literacy is stronger in some domains than others. Reanalysis of data from a broad-scale study of monolingual English and bilingual Spanish-English learners in Miami provided a clear demonstration of "profile effects," where bilingual children perform at varying levels compared to monolinguals across different test types. The profile effects were strong and consistent across conditions of socioeconomic status, language in the home, and school setting (two way or English immersion). The profile effects indicated comparable performance of bilingual and monolingual children in basic reading tasks, but lower vocabulary scores for the bilinguals in both languages. Other test types showed intermediate scores in bilinguals, again with substantial consistency across groups. These profiles are interpreted as primarily due to the "distributed characteristic" of bilingual lexical knowledge, the tendency for bilingual individuals to know some words in one language but not the other and vice versa.

Animal Guts as Nonideal Chemical Reactors: Partial Mixing and Axial Variation in Absorption Kinetics

Animal guts have been idealized as axially uniform plug-flow reactors (PFRs) without significant axial mixing or as combinations in series of such PFRs with other reactor types. To relax these often unrealistic assumptions and to provide a means for relaxing others, I approximated an animal gut as a series of n continuously stirred tank reactors (CSTRs) and examined its performance as a Function of n. For the digestion problem of hydrolysis and absorption in series, I suggest as a first approximation that a tubular gut of length L and diameter D comprises n=L/D tanks in series. For n greater than or equal to 10, there is little difference between performance of the nCSTR model and an ideal PFR in the coupled tasks of hydrolysis and absorption. Relatively thinner and longer guts, characteristic of animals feeding on poorer forage, prove more efficient in both conversion and absorption by restricting axial mixing, in the same total volume, they also give a higher rate of absorption. I then asked how a fixed number of absorptive sites should be distributed among the n compartments. Absorption rate generally is maximized when absorbers are concentrated in the hindmost few compartments, but high food quality or suboptimal ingestion rates decrease the advantage of highly concentrated absorbers. This modeling approach connects gut function and structure at multiple scales and can be extended to include other nonideal reactor behaviors observed in real animals.