The relationship between structure and the hydraulic conductivity of soil

A random fractal matrix comprising a hierarchical aggregation of primary structural elements is used to capture the characteristics of a heterogeneous soil structure with a tortuous pore space. The influence of heterogeneity of both the solid matrix and the pore space, as well as the shape of the pore boundary, on the saturated and unsaturated hydraulic conductivity is studied. For such random structures, the fractal (Hausdorff) dimension alone is not enough to characterize the structure from the point of view of fluid flow and additional characterizations are introduced. The porosity, ρ_p, of the primary elements has a critical value, ρ_c. With probability 1, both the saturated and unsaturated conductivities are found to be dependent as a power law on the length scale, L, at which the measurement is made when ρ_p>ρ_c. When ρ_p<ρ_c, only the unsaturated conductivity is scaling in length scale, while the saturated conductivity becomes dominated, with probability close to 1, by the conductivity of the largest connecting pores in the structure, i.e. preferential pathways. The relationships between the parameters of the power laws and structure are derived and are found to depend on the fractal (Hausdorff) and spectral dimensions of the solid matrix, denoted d_m and respectively. A discussion of the importance of these results for the interpretation and extrapolation of measurements is presented, and the implications for variability and predictability of the hydraulic properties of soil is discussed.     

A Surgical Approach to the Ramus of the Mandible in Cattle and Horses Case Reports of a Bull and a Horse

A surgical approach to the ramus of the mandible was developed. Subperiosteal elevation of the masseter muscle from the ramus allowed reduction and plate fixation of ramus fractures in a bull and a horse. Results of follow-up examinations, 2 years after surgery, showed excellent functional and cosmetic results.     

Esophagotomy Closure in the Dog A Comparison of a Double-Layer Appositional and Two Single-Layer Appositional Techniques

Esophagotomies were performed on 36 dogs and closed with 3-0 polydioxanone in double-layer simple interrupted, single-layer simple interrupted, or single-layer simple continuous patterns. The operative time was shortest for single-layer simple continuous closure, followed by single-layer simple interrupted and double-layer simple interrupted, respectively. Three dogs with each suture pattern were euthanatized at hours 0 and 1, and days 4 and 28 after surgery. The esophagotomy incisions were subjected to bursting strength testing and examined microscopically. The bursting wall tension was higher for all three suture pattern groups at 28 days than at 0 and 1 hour. The double-layer closure had higher bursting wall tension than the single-layer closures at 0 hour and 4 days. Single-layer simple continuous closure had the lowest bursting wall tension for each time period. Single-layer simple interrupted closure had the highest bursting wall tension at 28 days. Microscopic examination revealed close approximation of tissue planes for the double-layer closure and mucosal ever-sion for the simple interrupted and simple continuous single-layer closures. Healing was superior histologically with the double-layer closure.     

Simultaneous Preservation of Soil Structural Properties and Phospholipid Profiles: A Comparison of Three Drying Techniques

There is a need to simultaneously preserve evidence of interactions between the biological community and soil structural properties of a soil in as near an intact (natural) state as possible.Three dehydration techniques were implemented and assessed for their ability to minimise disruption of both biological and physical properties of the same arable soil sample.Dehydration techniques applied until samples were at constant weight were i) air-drying at 20℃ (AD); ii)-80℃ freeze for 24 h,followed by freeze-drying (-80FD); and iii) liquid nitrogen snap freeze,followed by freeze-drying(LNFD) and were compared to a moist control.Physical structure was determined and quantified in three dimensions using X-ray computed tomography and microbial phenotypic community composition was assessed using phospholipid fatty acid (PLFA) profiling.This study confirms that any form of dehydration,when preparing soil for simultaneous biological and physical analysis,will alter the soil physical properties,and cause some change in apparent community structure.Freeze-drying (both the LNFD and -80FD treatments) was found to minimise disruption (when compared to the moist control soil) to both the soil physical properties and the community structure and is a preferable technique to air-drying which markedly alters the size and character of the pore network,as well as the phenotypic profile.The LNFD was the preferred treatment over the -80FD treatment as samples show low variability between replicates and a fast turn-around time between samples.Therefore snap freezing in liquid nitrogen,followed by freeze drying is the most appropriate form of dehydration when two sets of data,both physical and biological,need to be preserved simultaneously from a soil core.     

STUDIES ON SOIL COPPER

Adsorption isotherms were determined for the specific adsorption of copper by soils and soil constituents. Adsorption was found to conform to the Langmuir equation. The Langmuir constants, a (adsorption maximum) and b (bonding term), were calculated. Soils were found to have specific adsorption maxima at pH 5.5 of between 340 and 5780 μg g^?1, and a multiple regression analysis revealed that organic matter and free manganese oxides were the dominant constituents contributing towards specific adsorption. Adsorption maxima for soil constituents followed the order manganese oxides > organic matter > iron oxides > clay minerals, which supported the findings for whole soils. The cation exchange capacities (non-specific adsorption) of the test soils were found to be far greater than the specific adsorption maxima. However, evidence suggests that, for the relatively small amounts of copper normally present in soils, specific adsorption is the more important process in controlling the concentration of copper in the soil solution.     

The Effect of Epidural and General Anesthesia on the Healing of Colonic Anastomoses

Colonic anastomoses were performed on two groups of 13 dogs each. Epidural anesthesia and general anesthesia were performed in one group and general anesthesia only in the other. Intraoperatively, the epidural-general anesthesia dogs tended to bleed less, making the anastomosis less difficult. Histologic comparisons showed healing to be more advanced in the epidural-general anesthesia dogs compared to the general anesthesia dogs 24 hours and 7 days postoperatively. Differences were not noticed 14 and 28 days postoperatively. Bursting pressures were determined 24 hours after surgery. Differences between the groups were not noticed. Leakage occurred at 72% of the pressure determined to cause leakage in normal colons.