Generalized Degrees of Freedom and Adaptive Model Selection in Linear Mixed-Effects Models

Linear mixed-effects models involve fixed effects, random effects and covariance structures, which require model selection to simplify a model and to enhance its interpretability and predictability. In this article, we develop, in the context of linear mixed-effects models, the generalized degrees of freedom and an adaptive model selection procedure defined by a data-driven model complexity penalty. Numerically, the procedure performs well against its competitors not only in selecting fixed effects but in selecting random effects and covariance structure as well. Theoretically, asymptotic optimality of the proposed methodology is established over a class of information criteria. The proposed methodology is applied to the BioCycle Study, to determine predictors of hormone levels among premenopausal women and to assess variation in hormone levels both between and within women across the menstrual cycle.     

Commentary: Measuring divergent thinking: Is there really one solution to the problem?

Commentary on an article by P. J. Silvia et al. (see record 2008-05954-001) which discusses the topic of divergent thinking. Although their findings appear reasonable, we have two key concerns with regard to these conclusions, 1) the strength of the available construct validity evidence, and 2) the substantive logic underlying the study. The next generation of measures should be applying a domain, strategy, process approach rather than the domain-free, output-based approach recommended by Silvia et al. (2008). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of Plate Wettability on Dispersed-Phase Holdup in a Pulsed Disc-and-Doughnut Solvent Extraction Column

The effect of plate wettability on the dispersed-phase holdup in a pulsed disc-and-doughnut solvent extraction column is presented. Teflon, nylon, and stainless steel plates have been used to simulate a change in the wetting characteristics of the plate material that can occur in an operating column due to ageing or deposits accumulating on the plate. Experimental holdup data have been measured over a range of operating conditions using a 1.0 m long glass column with an internal diameter of 72.5 mm containing alternating discs and doughnuts. The liquid-liquid system studied was tri-n-octylamine (TOA)-kerosene-water with sulphuric acid as the solute. Results show that there are noticeable changes in the characteristic velocity (determined from measured holdup) and operational regimes for the different plate materials, particularly at low pulsation intensities, when operating under dispersed aqueous conditions. Experimental holdup data from this study have also been compared to correlations from literature for predicting holdup. As none of these correlations for holdup incorporate plate wettability, a new correlation for predicting holdup has been proposed that incorporates the contact angle of the plate material to allow for changes in the wettability of the plate surface. This correlation is able to predict the holdup data from this study to within 10.5% for aqueous dispersed conditions.     

Precipitation study of CO2-loaded glycinate solution with the introduction of ethanol as an antisolvent

Focused beam reflectance measurement (FBRM) and ¹³C nuclear magnetic resonance (¹³C NMR) analysis were used to study the precipitation process of CO₂-loaded potassium glycinate (KGLY) solutions at different CO₂ loadings, during the addition of ethanol as an antisolvent at a rate of 10 mL·min⁻¹. The volume ratio of ethanol added to the KGLY solution (3.0 mol·L⁻¹, 340 mL) ranged from 0 to 3.0. Three solid-liquid-liquid phases were formed during the precipitation process. The FBRM results showed that the number of particles formed increased with CO₂ loading and ethanol addition for CO₂-unsaturated KGLY solutions, whilst for CO₂-saturated KGLY solution it first increased then decreased to a stable value with ethanol addition. ¹³C NMR spectroscopic analysis showed that the crystals precipitated from the CO₂-unsaturated KGLY solutions consisted of glycine only, and the quantity crystallised increased with CO₂ loading and ethanol addition. However, a complex mixture containing glycine, carbamate and potassium bicarbonate was precipitated from CO₂-saturated KGLY solution with the maximum precipitation percentages of 94.3%, 31.4% and 89.6%, respectively, at the ethanol volume fractions of 1.6, 2.5 and 2.3.     

Book reviews

This article describes the planning activity in Portugal in the middle of the twentieth century, notably the work of two exceptional planners, Etienne de Groër and Antão Almeida Garrett. The article moves from a first overview on the national context, to a focus on the two largest cities of Portugal, Lisbon, and Oporto. It was there that these two planners developed their most successful planning proposals. The planning activity of de Groër and Garrett is presented, first taken in isolation and then on a comparative basis. Issues addressed include the urban structure and the organization of the city, the street layout, and the system of zoning. It is argued that de Groër municipal plan for Lisbon and Garrett municipal plan for Oporto were able to leave a profound and lasting impact on these cities, being the most influential planning documents of the twentieth century in Lisbon and in Oporto.     

Hierarchical Bayesian inference in the visual cortex

Traditional views of visual processing suggest that early visual neurons in areas V1 and V2 are static spatiotemporal filters that extract local features from a visual scene. The extracted information is then channeled through a feedforward chain of modules in successively higher visual areas for further analysis. Recent electrophysiological recordings from early visual neurons in awake behaving monkeys reveal that there are many levels of complexity in the information processing of the early visual cortex, as seen in the long-latency responses of its neurons. These new findings suggest that activity in the early visual cortex is tightly coupled and highly interactive with the rest of the visual system. They lead us to propose a new theoretical setting based on the mathematical framework of hierarchical Bayesian inference for reasoning about the visual system. In this framework, the recurrent feedforward/feedback loops in the cortex serve to integrate top-down contextual priors and bottom-up observations so as to implement concurrent probabilistic inference along the visual hierarchy. We suggest that the algorithms of particle filtering and Bayesian-belief propagation might model these interactive cortical computations. We review some recent neurophysiological evidences that support the plausibility of these ideas.     

Influence of abilities on performance during practice: Effects of massed and distributed practice.

Prior research indicates that the influence of abilities on performance may change as a function of practice. The present research examined how learning styles influence the relationship between abilities and task performance. The styles examined were massed vs distributed practice. 209 Ss were asked to complete measures of spatial visualization and perceptual speed. They then practiced a complex skill acquisition task for 4 hrs under conditions that allowed them to pace their rate of practice. Analysis of several dependent measures revealed that perceptual speed contributed to task performance for 33 Ss who massed their practice, whereas spatial visualization contributed to performance for 61 Ss who distributed their practice. The implications of these findings for understanding the role of abilities in skill acquisition are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Kinetics of sulfur transfer from H2S to digenite (Cu2−xS) at 500°C

The kinetics of sulfur transfer from H₂S to cuprous sulfide (digenite) at 500°C has been established by the resistance relaxation technique. The resistance measurements have been carried out by the van der Pauw method, which uses a four probe configuration. The rate of the forward reaction decreases with the increase in the activity of sulfur in the sulfide (rate a _s ^–0.55 ) while the rate of the backward reaction is found to be nearly independent of the sulfur activity. Based on these results, the rate limiting step for sulfur transfer reaction to digenite is shown to be: H₂S (g) + 2e^– = S^2–(ad) + H₂(g).