Phase-Field Modeling of the Coarsening in Multi-component Systems

A thermodynamically consistent method for the investigation of the coarsening behavior and in particular for the prediction of the secondary dendrite arm spacing (SDAS) in multi-component alloys is proposed which is based on the numerical simulation by means of a phase-field model. Existing variants of the phase-field model equations for multi-component systems were considered and their advantages and disadvantages were discussed. For the investigation of the coarsening behavior the variant described by the mixture composition and the entropy change was chosen. The method is applied to a high-alloy tool steel where it was found that elements such as C, Si, Mn decrease the SDAS whereas Cr increases. The resulting dependencies of the SDAS on alloy composition were compared to the analytical prediction of the coarsening model. For this aim the analytical model of the coarsening behavior in multi-component alloys [Rappaz and Boettinger, Acta Mater. 47 (1990)] was extended by taking into account the cross dependencies between the components in multi-component diffusion and the case of slow diffusion in the solid phase. The equilibrium parameters used in the phase-field model and in the analytical model were obtained from Thermo-Calc through global equilibrium calculations using the database TCFE7. The difference between both methods was found to be smaller than 2 pct in the investigated composition region.     

Phase-field modeling of the γ′-coarsening behavior in Ni-based superalloys

Microstructural changes during heat treatment of the Ni-based CMSX-4 and CMSX-6 superalloys have been investigated experimentally and simulated using a phase-field multi-component model incorporating elastic driving forces in the presence of a lattice misfit. Furthermore, a theoretical model of the coarsening of anisotropic particles is proposed for the prediction of the main kinetic parameters of the coarsening process. A comparison of the main characteristics of the microstructural evolution during non-directional γ′-coarsening, provided from both experiments and phase-field simulations, gives a good agreement of the coarsening kinetics of the CMSX-4 superalloy. However, for the CMSX-6 superalloy, phase-field simulation results and theoretical predictions are not entirely consistent with experimental results, and show that additional effects, for example, those caused by plastic deformation, might be a reason for the slow coarsening rate.     

Modeled infiltration rate distributions for U.S. housing

A set of 209 dwellings that represent 80% of U.S. housing stock is used to generate frequency distributions of residential infiltration rates. The set of homes is based on an analysis of the 1997 U.S. Department of Energy's Residential Energy Consumption Survey, which documents numerous housing characteristics including type, floor area, number of rooms, type of heating system, foundation type, and year of construction. The infiltration rate distributions are developed using the multizone network airflow model, CONTAM (CONTAMW 2.4 User Guide and Program Documentation, NISTIR 7251. National Institute of Standards and Technology.). In this work, 19 cities are selected to represent U.S. climatic conditions, and CONTAM simulations are performed for each of the 209 houses in these cities to calculate building air change rates for each hour over a year. Frequency distributions are then developed and presented nationally as well as based on house type and region. PRACTICAL IMPLICATIONS: These distributions will support indoor air quality, exposure, and energy analyses based on a truly representative collection of U.S. homes, which has previously not been possible. In addition, the methodology employed can be extended to other countries and other collections of buildings. For U.S.-specific analyses, these homes and their models, can be extended to include occupants, contaminant sources, and other building features to allow a wide range of studies to address other ventilation and indoor air quality issues.     

Optical inline analysis and monitoring of particle size and shape distributions for multiple applications: Scientific and industrial relevance

Particles occur in almost all processes in chemical and life sciences. The particle size and shape influence the process performance and product quality, and in turn they are influenced by the flow behavior of the particles during production. Monitoring and controlling such characteristics in multiphase systems to obtain sufficient qualities will greatly facilitate the achievement of reproducible and defined distributions. So far, obtaining this information inline has been challenging, because existing instruments lack measurement precision, being unable to process overlapping signals from different particle phases in highly concentrated multiphase systems. However, recent advances in photo-optics made it possible to monitor such features (particle size distribution (PSD), aspect ratio and particle concentration) with advanced image analysis (IA) in real-time. New analysis workflows as well as single feature extractions from the images using multiple image analysis algorithms allowed the precise real-time measurements of size, shape and concentration of particle collectives even separated from each other in three phase systems. The performances, advantages and drawbacks with other non-photo-optical methods for assessing the particle size distribution are compared and discussed.     

Relationships between cognitive and social functioning in preschool children.

Examined short-term longitudinal relationships between test measures of cognitive processes and ratings of classroom behaviors observed during free play. Ss were 64 35–57 mo old middle-class preschoolers, 34 boys and 30 girls. Magnification of the same covariation pattern over time was used as an index of reciprocal influences between cognitive and social functioning. Analyses differentiated between the static (individually stable) and linear-change components of social attributes. Verbal-conceptual processes covaried positively with the static measures of socially outgoing and task-oriented behaviors and with positive vs negative affective expressions in girls, but not in boys. A nonverbal cognitive measure did not so relate to the social measures. The linear-change components of certain social attributes exhibited consistent though limited relationships with the cognitive measures. The study yielded little evidence for reciprocity between the cognitive and social domains. Certain cognitive processes facilitated social adaptation, but social adaptation did not influence cognitive growth. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of pre‐freezing,puree content and pasteurisation regime on colour stability of strawberry nectar made from puree

BACKGROUND: Heat treatment during processing of strawberry products has been proposed to negatively affect colour stability. Moreover, the role of enzymes with respect to colour stability is ambiguous when consulting the existing literature. The aim of the present study was to investigate the impact of various processing parameters (pre‐freezing, puree content, pasteurisation temperature and heating time) on the colour stability and anthocyanin monomer and L ‐ascorbic acid contents of strawberry nectars made from puree. In addition, the effect of different enzyme activities on colour stability during storage of strawberry nectars was investigated. RESULTS: Pre‐freezing of strawberries before processing had a significant positive effect on the colour stability of nectars made from puree. No significant effect on colour stability was found for higher puree contents. Increasing both the pasteurisation temperature and the heating time had a significant positive effect on colour stability. Results showed that colour degradation during storage was mainly due to residual enzyme activities. The shelf‐life of strawberry nectar could be extended about fivefold by adding an enzyme inhibitor. CONCLUSION: The colour stability of strawberry nectar made from fresh puree may be improved to some extent by an appropriate pasteurisation regime. Enzymes play an important role in colour degradation during storage of the nectar. Inactivation of these enzyme activities, however, could not be achieved even after a heat treatment at 90 °C for 60 min. Copyright © 2008 Society of Chemical Industry