No description available.

Woody plants are encroaching into a karst savanna on the Edwards Plateau in central Texas, but their impact on hydrology is unclear because of high variability in soil depth and uncertainties about shallow and deep root contributions to water uptake, and water dynamics in rocky soil. The overall objectives of this study are to quantify contributions of shallow and deep roots to water uptake, and to quantify the impact of rock on soil hydraulic properties and water storage. A study was conducted in a karst savanna with ~50% woody cover to monitor spatial and temporal variations in soil moisture and root water uptake with neutron probe and time-domain reflectometry measurements. Bulk density was measured using gamma densitometry. Measurements were made to a depth of 1.6 m in a 25 m  25 m grid (5 m node spacing). The results showed that rock created high spatial variability in water storage. Water storage capacity in the measurement grid ranged from 185 to 401 mm, and coupled with heterogeneous distribution of trees led to high spatial variability in root water uptake. Most of the water uptake came from the upper 1 m of the soil profile, but 10% came from below 1.6 m. This indicated that roots had access to water stored within the bedrock, possibly in soil pockets. Statistical analysis showed that spatial distribution of θ was significantly correlated with rock distribution in the profile. Laboratory evaporation measurements showed that Small volume fractions of rock can increase evaporation from soils by slowing upward movement of water, thereby maintaining capillary connectivity to the surface for a longer period of time. Two simulation models, van Genuchten (VG) and Durner, were compared with the data from evaporation experiments. Results showed that the Durner model was more appropriate than the VG model for describing water retention and hydraulic conductivity of rocky soils.

No description available.

Thesis (M.Sc (Pharmaceutics))--North-West University, Potchefstroom Campus, 2009.

In Norway spruce there's a large natural variation in durability but knowledge about what is causing this variation is missing. In this thesis the focus were put into investigating how the water uptake ability was affected by the influence of heartwood versus sapwood and wood properties such as density and annual ring width. Liquid water permeability was checked trough a modified version of EN 927-5 and samples were also investigated trough the Mycologg Method. The wide grown wood with a coating system (a priming oil and alkyd or acrylate paint) absorbed less water than the narrow grown wood in the permeability test. The Mycologg test showed a clear difference between wide and narrow grown wood. Further research is necessary to examine the impact of wood properties when it comes to water uptake.

Thesis (M.Sc (Pharmaceutics))--North-West University, Potchefstroom Campus, 2009.

Thesis (M.Sc (Pharmaceutics))--North-West University, Potchefstroom Campus, 2009.

Various ammonium salts, urea, aqua ammonia, and anhydrous ammonia are important sources of nitrogen for the fertilization of agricultural crops. While ammonia and its compounds are useful as fertilizers, they can be, and often are, toxic to many plants (Willis and Rankin, 1930; Stout and Tolman, 1941; Raleigh, 1942; Stoll, 1954; Lorenz, 1955; Grogan and Zink, 1956; Allen, 1962; Cooke, 1962; Allred, 1963; Court et al, 1964; Hood and Ensminger, 1964). There are also products which have been designed to retard the oxidation of ammonia and its compounds (Go ring, 1962). It is therefore important that the effects of ammonia and its compounds on plants, plant growth and plant metabolism be fully understood.

Water-borne latex coatings represent a safer, more user-friendly, and environmentally responsible alternative to solvent-borne coatings, and are growing in popularity each year. However, these coatings often exhibit unfavorable performance when exposed to water for extended periods of time. This prolonged exposure often results in water uptake, which may give rise to other detrimental effects such as a decrease in modulus, blushing or water-whitening, reduced serviceable life, and softening of the film. In this study, various polymer composition latex design spaces are studied to develop an understanding of how water uptake can be modulated and minimized using common synthetic approaches. Factors including monomer selection, particle size, polymer molecular weight, crosslinking density, surfactant choice and particle stabilization, processing variables and Tg are considered. In addition, some formulation modifications including PVC, film thickness, and choice of coalescent package are explored to gain a more comprehensive understanding of final product performance. In quantifying the total water uptake of the films, gravimetric analysis tends to be the preferred method employed in the coatings industry. However, other analytical approaches can be used to better understand the effect that water has on the properties of the film. These methods may include differential scanning calorimetry, electrochemical impedance spectroscopy, immersion testing using dynamic mechanical analysis, and others. In the work, it has been shown that interparticle crosslinking, surfactant, and monomer selection can have an extreme influence on the water uptake of free films. Film samples exhibit a range of water uptake values from nearly 200% to less than 5% over a one-week soak in deionized water. It is thought that the surfactant may provide hydrophilic channels that allow water to v penetrate the film and form heterogeneous domains within the coating. These domains then grow and scatter light, leading to water-whitening and an increase in mass when compared to the dry film. Utilizing monomers with differing relative solubilities in water, such as methyl methacrylate and styrene, further allow control of this effect. Interparticle crosslinking via keto-hydrazide crosslinking, which is achieved during the film formation process, can also prevent the formation and growth of these large water domains, thus resulting in better performing films.

Sustainable polymeric materials put emphasis on mastering the whole life-cycle of polymeric materials. This includes the choice of raw materials, selection of synthesis and processing, environmental impact during long-term use followed by detailed knowledge about recycling and waste management.  Within this large efforts are put in the design and development of new biocomposites using renewable fibres instead of inert ones. The thesis deals with surface modifications of agricultural fibres and the design of biocomposites with optimal long-term properties balancing the potential risk for biodegradation.  The first part of this thesis involved surface modifications of oil palm fibres and production of biocomposites with PP as matrix. The chemical surface modifications of oil palm fibres explored propionylation, PPgMA grafting via solution modification and reactive blending and vinyltrimethoxy silanization as methods. All modified fibre/PP biocomposites showed improvements in the mechanical properties followed also by an improvement of water resistance. In comparison with unmodificed fibres/PP matrix the highest water resistance after the surface modifications of oil palm fibres were observed for silanization followed by PPgMA modified,  PPgMA blending and  propionylation. The second part aimed at producing fully biodegradable biocomposites and analysing the resulting properties with respect to potential risk for biodegradation. Sisal fibres were incorporated in PLA and PHBV and the resulting risk for biodegradation using a fungus, Aspergillus niger, monitored. Neat PLA and PHBV were compared with the corresponding biocomposites and already without fibres both polymers were notably biodegraded by Aspergillus niger. The degree of biodegradation of PLA and PHBV matrices was related to the extent of the growth on the material surfaces. Adding sisal fibres gave a substantial increase in the growth on the surfaces of the biocomposites. Correlating the type of surface modification of sisal fibres with degree of biodegradation, it was demonstrated that all chemically modified sisal/PLA biocomposites were less biodegraded than unmodified sisal biocomposites.  Propionylated sisal/PLA demonstrated the best resistance to biodegradation of all biocomposites while sisal/CA/PLA demonstrated high level of biodegradation after severe invasion by Aspergillus niger. In general, the biodegradation correlated strongly with the degree of water absorption and surface modifications that increase the hydrophobicity is a route to improve the resistance to biodegradation. Designing new biocomposites using renewable fibres and non-renewable and renewable matrices involve the balancing of the increase in mechanical properties, after improved adhesion between fibres and the polymer matrix, with the potential risk for biodegradation. / <p>QC 20130325</p>