Assessing Local Model Adequacy in Bayesian Hierarchical Models Using the Partitioned Deviance Information Criterion

Many diagnostic tools and goodness-of-fit measures, such as the Akaike information criterion (AIC) and the Bayesian deviance information criterion (DIC), are available to evaluate the overall adequacy of linear regression models. In addition, visually assessing adequacy in models has become an essential part of any regression analysis. In this paper, we focus on a spatial consideration of the local DIC measure for model selection and goodness-of-fit evaluation. We use a partitioning of the DIC into the local DIC, leverage, and deviance residuals to assess the local model fit and influence for both individual observations and groups of observations in a Bayesian framework. We use visualization of the local DIC and differences in local DIC between models to assist in model selection and to visualize the global and local impacts of adding covariates or model parameters. We demonstrate the utility of the local DIC in assessing model adequacy using HIV prevalence data from pregnant women in the Butare province of Rwanda during the period 1989-1993 using a range of linear model specifications, from global effects only to spatially varying coefficient models, and a set of covariates related to sexual behavior. Results of applying the diagnostic visualization approach include more refined model selection and greater understanding of the models as applied to the data.     

Accelerated cyclic oxidation testing protocols for thermal barrier coatings and alumina‐forming alloys and coatings

The oxide spallation resistance of oxide scales and ceramic thermal barrier coatings is a key design factor for developing high‐temperature alloy systems. Determination of the lifetimes of such alloy and coating systems is highly desirable. However, as improved systems are developed, lifetimes become so long that the time required to test a system to failure becomes prohibitive. Therefore, reliable protocols for accelerated testing and lifetime prediction are needed. This paper describes two attempts at developing such protocols. The first involves modification of the NASA COSP model to predict cyclic oxidation behavior of alloys and metallic coatings and the incorporation of acoustic emission data into this model. The second involves use of an indentation technique to induce spalling of thermal barrier coatings (TBCs) after short‐term thermal exposures. The first effort involves using the COSP Model, developed at NASA, as the basis for the prediction of oxide spallation. Acoustic emission measurements are used in an attempt to obtain critical parameters in the model from short‐time experiments for a variety of alloys and coatings which rely on alumina scales for oxidation resistance. The model is then used to predict the lives of these alloys and coatings when subjected to cyclic oxidation at 1100°C. A principal concern with ceramic thermal barrier coatings (TBCs) used in gas turbines is their loss of adhesion during service, leading to coating spallation. In this paper, an overview is given of an indentation test for brittle coatings on ductile substrates which is used to quantify decreases in interfacial toughness of TBC systems due to cyclic high‐temperature exposures. The indentation test involves penetration of the TBC and the oxide layer below it, inducing plastic straining in the underlying metal bond coat and superalloy substrate. The indentation strains cause an axisymmetric delamination of the TBC and oxide layers. Measurement of the extent of the delamination, coupled with finite‐element modeling, provides a measure of the adherence of the coating. Test results are presented tracking the loss of interfacial toughness for EBPVD TBC systems cyclically exposed at 1100°C.     

Making the Cape Floral Kingdom: The discovery and defence of indigenous flora at the Cape ca. 1890-1939

The colonial elite in the south-western Cape were historically aficionados of exotic flora and disdainful of the region's indigenous vegetation. This changed rapidly in the half century after ca. 1890 with the indigenization of botanical science and the emergence of a distinctive Cape botany, practised and patronized by the Cape Town patriciate. The botanists' re-imagining of the indigenous flora as the 'Cape Floral Kingdom', an ancient and endangered flora without equal anywhere in the world, served ideological and practical purposes for their sponsors. Floral nativism provided both a sense of identity for an emerging White settler nationalism and a justification for evicting the underclass from the commons and their conversion into a preserve for patrician leisure and contemplation. The political realignments of Union, however, left the Cape Town patriciate isolated and forced them to seek a broader popular audience among the urban middle classes of the region and United Kingdom. By the eve of the Second World War, identification with the indigenous Cape flora had become a mark of class, ethnic and regional identity for the old imperial urban, English-speaking middle class marooned in a new nation state governed by rural, Afrikaans republicanism.     

Selective filling of nanowells in nanowell arrays fabricated using polystyrene nanosphere lithography with cytochrome P450 enzymes

This work describes an original and simple technique for protein immobilization into nanowells, fabricated using nanopatterned array fabrication methods, while ensuring the protein retains normal biological activity. Nanosphere lithography was used to fabricate a nanowell array with nanowells 100?nm in diameter with a periodicity of 500?nm. The base of the nanowells was gold and the surrounding material was silicon dioxide. The different surface chemistries of these materials were used to attach two different self-assembled monolayers (SAM) with different affinities for the protein used here, cytochrome P450 (P450). The nanowell SAM, a methyl terminated thiol, had high affinity for the P450. The surrounding SAM, a polyethylene glycol silane, displayed very little affinity toward the P450 isozyme CYP2C9, as demonstrated by x-ray photoelectron spectroscopy and surface plasmon resonance. The regularity of the nanopatterned array was examined by scanning electron microscopy and atomic force microscopy. P450-mediated metabolism experiments of known substrates demonstrated that the nanowell bound P450 enzyme exceeded its normal activity, as compared to P450 solutions, when bound to the methyl terminated self-assembled monolayer. The nanopatterned array chips bearing P450 display long term stability and give reproducible results making them potentially useful for high-throughput screening assays or as nanoelectrode arrays.     

Competitive effects of natural organic matter: parametrization and verification of the three-component adsorption model COMPSORB

Natural organic matter (NOM) hinders adsorption of trace organic compounds on powdered activated carbon (PAC) via two dominant mechanisms: direct site competition and pore blockage. COMPSORB, a three-component model that incorporates these two competitive mechanisms, was developed in a previous study to describe the removal of trace contaminants in continuous-flow hybrid PAC adsorption/membrane filtration systems. Synthetic solutions containing two model compounds as surrogates for NOM were used in the original study to elucidate competitive effects and to verify the model. In the present study, a quantitative method to characterize the components of NOM that are responsible for competitive adsorption effects in natural water was developed to extend the application of COMPSORB to natural water systems. Using batch adsorption data, NOM was differentiated into two fictive fractions, representing the strongly competing and pore blocking components, and each was treated as a single compound. The equilibrium and kinetic parameters for these fictive compounds were calculated using simplified adsorption models. This parametrization procedure was carried out on two different natural waters, and the model was verified with experimental data obtained for atrazine removal from natural water in a PAC/membrane system. The model predicted the system performance reasonably well and highlighted the importance of considering both direct site competition and pore blockage effects of NOM in modeling these systems.     

AIR OXIDATION OF EASTERN OIL SHALES OF KENTUCKY. I. OXYGEN UPTAKE

The Devonian oil shale of Kentucky (Cleveland Member of the Ohio Shale) proves to be more susceptible to air oxidation than a high sulfur coal such as Western Kentucky No. 9, and much more susceptible than the Eocene Green River Formation shale of Colorado. The Mississippian oil shale (Sunbury Shale) is also readily air oxidized. Oxygen uptake per 100-grams organic carbon content over 10 hours at 30*C taken from plots of oxygen uptake vs. time is as follows: Ohio Shale, 650 cc; Sunbury Shale, 200 cc; Green River Formation shale, 50 cc; Ky No. 9 coal, 40 cc.

Special care in protecting samples from autoxidaion is required if good assays and analyses are to be obtained. The aging chacacteristics of eastern oil shales could potentially affect mining, transportation, crushing, screening, and stockpiling of feedstocks, particularly fines, for a commercial oil shale operation in Kentucky.     

Slumming in Utopia: Protest Construction and the Iconography of Urban America

This article examines the use of construction as a means of protest, particularly as it relates to the established symbolic imagery of traditional civic architecture and urbanism. The iconography of cities is divided. While the idealized image of official America symbolizes the aspirations of society, the image of the ghetto represents the failure of society. This article studies two projects which manipulate these images. The projects were built not by architects but by activists for various causes who coopted architecture as a tool for political demonstration. Their position outside of conventional architectural practice allowed them to challenge the habits of that practice. While the constructions were intended to protest specific social issues, they may also be viewed as general indictments of conventional urbanism and architectural representation.