Critical-state soil mechanics parameters and their variation for Vertisols in eastern Australia

Compression and shear tests were conducted on undisturbed samples from a range of Vertisols to determine the critical-state parameters, their variation, and the relationships between these parameters and the moisture content and density of the soil. The soils varied considerably in their characteristics, with the liquid limit ranging from 0.39 to 0.88, and were tested over a wide range of moisture contents, densities and saturations. The critical-state parameters describing compressional and shear properties varied with the moisture content, Atterberg limits and density of the soil, in contrast to saturated soils where these parameters are considered to be constants. It was found that the liquidity index (moisture content expressed as fractional distance between the liquid and plastic limits) explained the data significantly better than moisture content and also significantly better than did the suction. These data, therefore, supported suggestions that the Atterberg limits may serve as a useful basis for practical soil management guidelines. The measured parameters displayed considerable variation, demonstrating that any such guidelines need to be cast in terms of probabilities. The soil expanded when sheared if the normal stress during shear was less than about half the pre-consolidation stress and compressed when sheared if the normal stress during shear was more than about half the pre-consolidation stress. This behaviour was repeatable.     

Simulating soil deformation using a critical-state model: I. Laboratory tests

The paper examines the ability of a critical-state model to predict stresses and deformations of agricultural soil in a variety of laboratory shear and compression tests. The critical-state model used is a simple extension to the well-known Modified Cam Clay model. The extension provides a smoother transition from elastic to plastic behaviour and, amongst other things, introduces a capacity to model cyclic loading. The model is incorporated into a finite-element program. The model predictions are compared with: experimental observations of simple and direct shear tests with both constant normal stress and constant volume conditions; cyclic uniaxial compression tests; compaction tests in U-shaped and V-shaped boxes; and observations of some gross structural features caused by shear in direct-shear boxes. Predictions are made for both the compressing, strain-hardening and the expanding, strain-softening regimes of behaviour. In all cases the material properties for the model were obtained from tests other than those being used for the comparisons. The model predictions generally compare well with the various experimental results, although some numerical problems were encountered in strain-softening conditions. This demonstrates the versatility of the critical-state model for predicting fairly general stress and, deformation conditions in unsaturated soils using only five material-property constants. It also demonstrates that common laboratory strength and compression tests are adequate to measure the material properties.     

The effect of incorporation of cloxacillin in liposomes on treatment of experimental staphylococcal mastitis in mice

The effect of incorporation of cloxacillin in liposomes on the treatment of staphylococcal mastitis was assessed bacteriologically 18 h after treatment of experimental infections in mice caused by two strains of Staphylococcus aureus. Intramammary treatments were cloxacillin incorporated in liposomes, cloxacillin in combination with liposomes, empty liposomes, cloxacillin in saline and saline alone. In none of the experiments did entrapment of cloxacillin within liposomes enhance its antibacterial effects. Electron microscopic studies demonstrated the presence of liposomes in neutrophils which also contained staphylococci. The results support the hypothesis that intracellular staphylococci are metabolically dormant and therefore not susceptible to the action of inhibitors of cell wall synthesis such as cloxacillin.     

Monitoring of changes in tree and shrub layers in Wytham Woods (Oxfordshire), 1974-1991

In 1974–76 164 permanent 10x10 m plots were recorded atalternate intersections of a 100x100 m grid in Wytham Woods,Oxfordshire. Tree and shrub data were collected from all theplots in 1974–76, from 27 in 1984–85 and from allbut one in 1991–92. Changes in the structure and composition of the wood were assessedin terms of canopy cover, mean tree diameter, basal area andspecies occurrence. The wood has become more open (reduced canopycover) partly through management, partly through natural processessuch as windthrow and disease. The shrub cover has also declinedgreatly, probably because of increased deer browsing. Most standsare predominantly young growth and for the wood as a whole meantree diameter, basal area and tree height have increased. Theoverall composition of the wood has changed little, but therehas been a significant decline in mean woody species numberper plot from 5.8 to 4.1, mainly through declines in understoreyspecies and young oak (Quercus spp.). Elm (Ulmus spp.) coverhas been reduced by disease and birch (Betula spp.) sufferedpreferentially from windthrow. The results are used to indicate gains and losses in natureconservation terms for the wood as a whole. The strengths andweaknesses of this system may hold lessons for future woodlandmonitoring exercises.     

The Impact of Large Herbivores on the Conservation of Semi-natural Woods in the British Uplands

This review considers the history of woodland grazing and thegrazing ecology of large herbivores in the context of the conservationof semi-natural woods in the British uplands. The impact thatgrazing has on natural regeneration is frequently highlightedbut its effects on other vegetation, particularly the balancebetween bryophytes and higher plants are equally important.Grazing also influences both invertebrate and vertebrate populationsthrough its effect on vegetation structure. A low level of grazingby large herbivores in woodland provides a greater diversityin vegetation structure and species composition than eitherthe current prevalence of overgrazing or the absence of grazingin fenced woods. Low levels of grazing may also create conditionsfor the highest diversity of both plants and animals. The practicalproblems of managing woodland grazing are addressed in relationto conservation objectives for upland woods. Rotational grazing,seasonal grazing and reducing the overall levels of grazingin a wood are identified as possible management options. Furtherwork on these is however needed and topics for future researchare identified.     

Effect of herbage allowance on the efficiency of defoliation by the grazing animal

An experiment examining the relationship of daily herbage disappearance (DHD) and daily herbage allowance (DHA) is described. Cows with calves were grazed at three stocking rates on Kleingrass and Coastal Bermudagrass pastures. DHD and DHA were monitored at 14-d intervals. A significant positive linear relationship was noted between DHD and DHA ( P 0·25). Equations derived for Coastal Bermudagrass and Kleingrass were not significantly different and resulted in a combined equation Ŷ= 0·275X + 0·209 with an r² vaiue of 0·27. As DHA exceeded 6–9 kg DM per 100 kg live weight, efficiency of defoliation by the cows and calves declined.     

The Effects of Surgical Isolation and Application of Polypropylene Spiral Prostheses on Tracheal Blood Flow

Tracheal blood flow before and after division of the segmental tracheal blood supply with and without application of a polypropylene spiral prosthesis was measured in dogs by radiolabeled microsphere injection. Ischemia of the central part of the trachea, from the mid-cervical to mid-thoracic regions, was observed immediately after division of the segmental tracheal blood supply with and without polypropylene spiral prosthesis application. On day 3, tracheal blood flow was significantly decreased in the central part of the trachea with and without polypropylene spiral prosthesis application. On day 7, tracheal blood flow was significantly increased throughout the trachea, with no significant differences between animals with and without prosthesis application. There was no evidence of a collateral source of blood supply to the trachea. Surgical division of the segmental tracheal blood supply of the trachea. Surgical division of the segmental tracheal blood supply of the entire trachea is not recommended.     

Doppler sonographic measurements of arterial blood flow and their repeatability in the equine foot during weight bearing and non-weight bearing

In six normal adult horses, pulsed-wave Doppler sonographic inspections were made of the left and right lateral palmar proper digital artery (LPPDA) of each thoracic limb. Using a two-period, crossover design with repeated measures, each LPPDA was inspected on four occasions throughout the day over a 7 hour period and, on each occasion, with the limb weight bearing and non-weight bearing. In comparison with the observations made during weight bearing, there were significant increases (P<0.001) in blood-flow velocities when the limb was non-weight bearing. There was no relationship between blood velocities and the time of day, the order in which the inspections were made, resting heart rate, age of the horse, or hoof angle. In both weight bearing and nonweight bearing, the Doppler waveform demonstrated a systolic peak followed by at least two diastolic peaks and an end diastolic plateau. Horses that moved least during sonographic inspections had the lowest co-efficients variation.     

Changes in the Ground Flora of a Broadleaved Wood within a Clear Fell, Group Fells and a Coppiced Block

Changes in the ground flora, relative to undisturbed woodland,were measured in permanent (100 m² quadrats in a clear fell,group fells and a coppice area in Sheephouse Wood (Buckinghamshire)from 1984 to 1988. Species numbers rose rapidly in the clearand group fells to about twice that in the undisturbed woodland.Species indicative of higher light, moisture and nutrient conditionsappeared after felling or coppicing and the flora shifted fromone dominated by stress-tolerant species to a flora with morecompetitive and ruderal species. After two years, in both clearand group fells, the ground flora covered 90–100 per centof the quadrats (compared with 30–75 per cent in the undisturbedwoodland), but species richness started to decline. This wasprobably because of increased competition associated with thespread of grasses and rushes (Agrostis stolonifera, Deschampsiacespitosa, Holcus mollis and Juncus spp.). Species richnessdid not increase as much in the coppice area, and bramble (Rubusfruticosus), rather than grasses, became dominant. The subsequentdecline in species richness was more gradual in the coppicearea than in the clear fells. During this period there wereno significant changes in the species richness, total coveror species composition within the undisturbed woodland.