Improvement of oxygen mass transfer estimation from oxygen concentration measurements in bubble column reactors

An original procedure has been established for estimating the overall volumetric mass transfer coefficient using the oxygen concentration curves resulting from the usual gassing-in and gassing-out method. This procedure was applied to experimental data obtained in a small scale bubble column using both tap water and a coalescence-inhibiting liquid mixture that represents the coalescence behavior of biological media. It is based on the analysis of the characteristics times of the system, including those of the hydrodynamics of the two phases, the sensor dynamics and the system inertia when the gas composition is modified. A numerical procedure was developed to estimate the characteristic time of the system inertia t_i, using the assumption that this inertia is nearly independent of superficial gas velocity U_G. The calculations confirmed that the optimized t_i value was nearly independent of U_G and of the coalescence behavior of the liquid phase. Additionally, the resulting K_La_L values for tap water were closer to the correlation of Shah et al. [1982. Design parameters estimations for bubble column reactors. A.I.Ch.E. Journal 28, 353-379] than those of other conventional models. Finally, the original procedure was also reported to reduce significantly the square sum deviation between the predicted and the measured oxygen response curves.     

Nuclear Magnetic Resonance Studies of Silicon Carbide Polytypes

The ²⁹Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon-13 chemical shifts obtained from spectra of the same polytypes are also tabulated.     

Capacitated, finish-to-order production planning with customer ordering day assignments

We examine the production and ordering fulfillment system of a firm offering a large variety of products to time-sensitive customers. The firm wants to combine a finish-to-order strategy with an existing customer ordering system. The finish-to-order policy guarantees significant inventory savings due to the large number of end-product offerings, but it may also increase setup costs due to a short delivery commitment. The ordering system assigns periodic ordering dates to customers, encourages them to place their orders only on these dates, and promises them the same short delivery time irrespective of their geographic locations. The ordering system facilitates a smooth capacity load as well as transportation economies by allowing shipments to each location once during each ordering cycle. We propose a formulation for the combinatorial problem of choosing an ordering-day assignment and a finish-to-order production schedule that minimizes setup costs and maintains a balanced capacity load. We examine a Lagrangian relaxation of this formulation and heuristic solutions based on our relaxation. Our numerical work demonstrates that our best heuristic differs from the optimal solution by 5% on average for small problems (with up to 10 products and 10 customers). Moreover, we show that the difference between the objective value of the relaxation and that of the best heuristic decreases significantly as the problem size increases, being as low as 4% on average for problems with 30 products and 30 customers.     

Mothers' supervision of their children's peer play: Relations with beliefs, perceptions, and knowledge.

Mothers (N?=?76) of 3- to 5-year-old children completed questionnaires assessing beliefs in the importance and modifiability (vs. innateness) of children's peer relationship skills, perceptions of their children's social competence with peers, and strategies they would use in response to children's peer interaction problems. A subsample of mothers (n?=?34) was observed supervising the play of their own children and a peer. Maternal perceptions of children's competence were negatively associated with the extent of mothers' involvement in children's play, whereas the quality of supervision was predicted by knowledge of socialization strategies and the interaction of beliefs and knowledge. Beliefs appeared to moderate the effects of maternal knowledge on mothers' behavior in that knowledge was associated with the quality of supervision only when mothers believed social skills were important and modifiable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Toward a unified theory of similarity and recognition.

A new theory of similarity, rooted in the detection and recognition literatures, is developed. The general recognition theory assumes that the perceptual effect of a stimulus is random but that on any single trial it can be represented as a point in a multidimensional space. Similarity is a function of the overlap of perceptual distributions. It is shown that the general recognition theory contains Euclidean distance models of similarity as a special case but that unlike them, it is not constrained by any distance axioms. Three experiments are reported that test the empirical validity of the theory. In these experiments the general recognition theory accounts for similarity data as well as the currently popular similarity theories do, and it accounts for identification data as well as the longstanding "champion" identification model does. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temperamental resistance to control increases the association between sleep problems and externalizing behavior development.

This study examined the moderating effects of temperamental resistance to control on the link between development of sleep problems and development of externalizing behaviors over a 5-year period. Resistance to control was assessed with mothers' retrospective reports of temperament in infancy, provided when children were 5 years of age. Sleep problems were assessed with mother reports on an annual basis from age 5 to age 9. Externalizing behaviors were assessed with teacher reports on an annual basis from age 5 to age 9. A cross-domain latent growth curve model indicated that sleep problem trajectories were positively associated with externalizing behavior trajectories only for children high in resistance to control. In addition, resistance to control was positively associated with initial (age 5) sleep problems and initial (age 5) externalizing behaviors. The authors speculate that the development of sleep problems promotes the development of behavior problems for resistant children, whose self-regulatory abilities are especially tenuous. Implications for prevention and treatment of conduct problems are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)