Flow and Distribution of Fluid Phases Through Porous Plant Growth Media in Microgravity
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Limited understanding of the effects of reduced gravity on liquid and gaseous supply necessary for plant physiological functions hinders progress in plant research and crop production in space. Problems with controlling the plant environment have made it impossible to isolate microgravity as a variable of study. Over the last 10 years as much as 30 million dollars may have been spent on flight experiments with plants. Although a number of environmental factors such as light and air quality, and ventilation impact plant growth in microgravity, none have had such a limiting effect as control of water, air and nutrients in the root zone. Hydroponic culture systems are unsuitable for plant production in microgravity due to problems with water containment and liquid/gas phase separation.
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Application of X-Ray Computed Tomography for Characterization of Pore Structures in Geological Materials
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Nondestructive imaging methods such as X-Ray Computed Tomography (CT) yield high-resolution 3-D representations of pore space features and fluid distributions in porous materials. Steadily increasing computational capabilities and improved access to X-Ray CT facilities have contributed to a recent surge in microporous media research with objectives ranging from theoretical aspects of fluid and interfacial dynamics at the pore-scale to practical applications such as enhanced oil recovery and (D)NAPL transport and dissolution.

In recent years, significant efforts and resources have been devoted to improve CT technology, micro-scale analysis, and fluid dynamics simulations. However, the development of adequate image binarization methods for conversion of fuzzy grayscale CT volumes into a discrete form that permits quantitative characterization of pore space features and subsequent modeling of liquid distribution and flow processes seems to lack behind. We conducted a preliminary study on binarization and analysis techniques suitable for CT data of porous materials and found numerous methods for determining the separating grayscale threshold documented in literature, each of them yielding different results. Many of these methods that were originally developed for pattern recognition purposes were not previously applied, or are not thoroughly tested for application to X-Ray CT images of porous materials. Furthermore, access and availability of user friendly and sufficiently documented software for objective image binarization, analysis, and visualization is very limited. The objective of this project is to identify and refine locally adaptive thresholding methods applicable to porous materials. Advanced mathematical algorithms and lattice Boltzmann simulations are applied to determine pore space and transport properties and compare them to measured media properties.

NASA's Advanced Life Support program currently believes that particulate solid substrates are best suited to meet the short and long-term program needs. These needs include longevity and repeated use, repeated crops in the same substrate, eventual use of local Lunar or Martian materials, and recovery of roots for research purposes. Therefore, it is crucial that water, air and nutrient transport in small volumes of porous media be well understood. In particular, the ability to predict and tailor water and nutrient transport conditions in porous growth media under a variety of gravity conditions ranging from near weightlessness to reduced gravity environments such as the moon or mars is critical to the development of reliable experimental and production facilities.

Shrink-Swell Behavior and Hydraulic Properties of Clay Soils
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Some of the most productive agricultural soils contain appreciable amounts of active clay minerals and exhibit shrink-swell behavior in response to changes in soil water content and chemical composition of the soil solution. Associated changes in hydraulic and mechanical properties of such soils seriously hamper predictions of flow and transport processes. Hence fundamental understanding and predictions of clay-solute interactions at different scales is essential for development of agricultural and environmental management strategies. The research project is aimed at developing a new framework for predicting hydraulic properties of structurally active clay soils by building a comprehensive geometrical picture of the arrangement and evolution of clay fabric mixed with other textural constituents and linked to a physico-chemical model. Clay fabric is considered as an assembly of colloidal-size stacks of lamellae whose spatial organization and the spacing between individual clay sheets are functions of clay hydration state quantifiable via the disjoining pressure formalism. Silt and sand textural constituents are represented as rigid spheres interspaced by clay fabric in two basic configurations of "expansive" and "reductive" unit cells. Bulk media properties such as porosity and surface area provide constraints for the idealized geometry. A statistical upscaling scheme based on sand and silt particle size distributions and constrained by clay content, total porosity, and mass-volume - universal - relationships is employed to derive sample- and profile-scale liquid retention and hydraulic conductivity functions. At the profile-scale we consider effects of overburden on depth-dependent shrink-swell behavior, and formation of near-surface crack networks and their impact on surface intake properties. Experiments are designed to determine shrink-swell behavior and hydraulic properties of idealized clay-glass bead mixtures and several natural soils by using unconfined and confined measurement techniques. Direct microscopic observations of the spatial distribution of clay domains among sand and silt fractions (for different clay contents and ambient conditions) are used to test and refine key modeling assumptions. The project contributes to environmental management and agriculture by (1) elucidation of basic aspects of flow and transport processes in an evolving pore space; (2) development of physically based predictive models for hydraulic properties of swelling soils; and (3) provide new insights into salinity and sodicity management of agricultural clay soils. Furthermore, the results of this study enhance understanding of clay dispersion and surface sealing with consequent erosion hazards and enhanced colloidal-facilitated transport of agrochemicals.