A stress transformation approach to predicting the failure mode of wood

Summary A simple model, based on the use of transformations of second-order tensors, is presented in this paper to predict the failure mode of wood members stressed in various degrees of parallel-and perpendicular-to-grain tension and parallel-to-grain shear. This type of loading is indicative of structural wood members with cross grain or grain deviations in the vicinity of knots subjected to bending or tension. The model is based on the assumptions that failure is dictated by the presence of any of the aforementioned stresses that exceed the clear wood strength in that mode and that failure does not result from stress interactions. The magnitudes of the applied stresses are normalized relative to the wood strength in that mode. The ratio of applied stress to material strength that is greatest at any particular angle of load to grain is presumed to be the failure mode at that angle. To verify model predictions, optical and microscopic analyses of surfaces of failed specimens loaded in uniaxial tension at angles between 0° and 90° to grain were compared to previously obtained, or otherwise known, surfaces of specimens tested in tension and shear. Specimens tested at various angles to grain demonstrated failed surfaces very much like those associated with specimens loaded in the modes predicted by the model.     

Marking and retention of harlequin bug,Murgantia histrionica (Hahn) (Hemiptera: Pentatomidae), on pheromone-baited and unbaited plants

Harlequin bug (Murgantia histrionica) is an important pest of cole crops in the USA. The adults and nymphs feed on aboveground plant tissues by sucking cell contents and can seriously damage the host. Current insect control measures on cole crops target mainly lepidopteran pests, and the insecticides generally used do not control harlequin bug, so alternative management practices need to be explored. Previous research has established the existence of a male-produced pheromone attractive to both sexes and nymphs of M. histrionica. In this work, two systems of marking bugs were tested to verify if the mark affected fitness traits such as survival and host location. In a second phase, marked individuals were placed on trap host plants baited with synthetic pheromone lures to test whether migration rates were related to M. histrionica density on the trap plants and the presence of the attractants. Neither marking system affected the survival or orientation of the subjects compared to unmarked individuals. The pheromone lures significantly increased the attractiveness of the trap plants, but did not increase the retention time of the plants compared to unbaited plants. Emigration from the trap plants showed a constant rate and seemed unrelated to bug density on the plants. However, a mean peak density of ca. 36 bugs/plant was calculated. Beyond this number, density tended to decrease. These successful marking methods and retention time models support development of M. histrionica management with trap crops, by providing tentative control thresholds and decision rules.     

In vitro spasmolytic effect of aqueous extract of Calotropis procera on Guinea-pig trachea smooth muscle chain

The aqueous extract of Calotropis procera was evaluated for its spasmolytic effect using in vitro trachea smooth muscle chain of Guinea-pig. The extract (50, 100 and 200 microg/ml) showed a dose-dependent relaxant activity probably exhibited through the direct relaxant action on the smooth muscle.     

Landowner perceptions and the adoption of agroforestry practices in southern Ontario,Canada

A mail-out survey questionnaire was developed by the Agroforestry group at the University of Guelph to determine the level of awareness and interest in the adoption of agroforestry systems by landusers from four townships in Wellington County, Ontario. The questionnaire investigated: (1) the current level of knowledge regarding windbreaks, woodlots and plantations, intereropping, riparian plantations and silvipasture, (2) the present level of participation in each of these systems on-farm, (3) the perceived benefits and/or drawbacks of each of these initiatives with respect to total farm income, income diversity, land rehabilitation, land value/equity, soil/water conservation, labour intensity, overhead and return on the term of investment.The majority of respondents were familiar with conventional agroforestry systems such as windbreaks and woodlots/plantations (80%, 62% respectively), therefore the level of interest in the adoption of these practices was significant (74%, 66% respectively). Response rates were lower for silvipasture, riparian plantations and intercropping, most likely as result of the low level of familiarity with these practices (20%, 32%, 4% respectively). Respondents commented that agroforestry systems would have a neutral effect on farm income, and would increase land stewardship. In some cases, interested landusers indicated a willingness to participate in agroforestry systems even though they anticipated increases in overhead and labour intensity; however, this was only true if they held land stewardship as a priority. Landusers were more concerned with the economic aspects of agroforestry, as a determinant to the future adoptability of particular practices. Age, gender, farm operation and farm size were not correlated with the adoption of agroforestry systems.The success of agroforestry programs on farms in the study area is largely dependent on the attitudes and willingness of landusers to participate in non-traditional agricultural systems.     

Organic Matter Added to Bareroot Nursery Beds Influences Soil Properties and Morphology of Fraxinus pennsylvanica and Quercus rubra Seedlings

Bareroot hardwood seedling production involves intensive soil management. To increase soil organic matter (OM), nurseries commonly grow a cover crop for 1 year after every 1–2 year of seedling production. Raising soil OM levels can also be achieved through addition of soil amendments. We studied the influence of chicken manure (CM) and composted leaf, tree, and lawn trimmings (Cp) on soil properties and morphology of green ash (Fraxinus pennsylvanica Marsh.) and northern red oak (Quercus rubra L.) seedlings. CM was applied at 725, 1450, or 2900 kg ha⁻¹ (CM725, CM1450, and CM2900, respectively) and Cp was applied at 200 m³ ha⁻¹. Addition of CM and Cp significantly raised soil OM levels and altered soil chemical properties compared to the control (Ctrl). Root-collar diameter increased with addition of CM1450, CM2900, or Cp compared to CM725 or Ctrl plots for northern red oak, but was largest in soils amended with CM2900 for green ash. Conversely, height was greatest with addition of CM725 for northern red oak, but green ash seedlings were shorter in Ctrl plots than in all amendments except for CM725. Root volume of green ash and northern red oak seedlings was positively influenced by addition of CM or Cp. Seedling responses to nursery soil amendments vary with different forms and amounts of OM. Benefits to seedling growth through application of appropriate materials in the proper balance can improve seedling morphological quality and positively influence soil chemical properties.     

Strategies to promote healthier food purchases: a pilot supermarket intervention study

OBJECTIVE: To pilot the design and methodology for a large randomised controlled trial (RCT) of two interventions to promote healthier food purchasing: culturally appropriate nutrition education and price discounts. DESIGN: A 12-week, single-blind, pilot RCT. Effects on food purchases were measured using individualised electronic shopping data ('Shop 'N Go' system). Partial data were also collected on food expenditure at other (non-supermarket) retail outlets. SETTING: A supermarket in Wellington, New Zealand. PARTICIPANTS: Eligible customers were those who were the main household shoppers, shopped mainly at the participating store, and were registered to use the Shop 'N Go system. Ninety-seven supermarket customers (72% women; age 40 +/- 9.6 years, mean +/- standard deviation) were randomised to one of four intervention groups: price discounts, nutrition education, a combination of price discounts and nutrition education, or control (no intervention). RESULTS: There was a 98% follow-up rate of participants, with 85% of all reported supermarket purchases being captured via the electronic data collection system. The pilot did, however, demonstrate difficulty recruiting Maori, Pacific and low-income shoppers using the electronic register and mail-out. CONCLUSIONS: This pilot study showed that electronic sales data capture is a viable way to measure effects of study interventions on food purchases in supermarkets, and points to the feasibility of conducting a large-scale RCT to evaluate the effectiveness of price discounts and nutrition education. Recruitment strategies will, however, need to be modified for the main trial in order to ensure inclusion of all ethnic and socio-economic groups.     

Early growth and ecophysiological responses of Koa (Acacia koa A. Gray) seedlings to reduced water and phosphorus

Sites in need of restoration typically have one or more environmental factors that limit seedling establishment. Identifying ecophysiological responses to environmental stressors can provide important insights into mitigating measures that would allow seedlings to overcome such constraints to survival. Koa (Acacia koa A. Gray) is a nitrogen-fixing tree species endemic to Hawai?i that is highly valued in restoring degraded forest ecosystems, which are often limited in available water and phosphorus. This study examined how koa seedlings respond to conditions of reduced water (65 W) and no phosphorus (0P). After 17 weeks, seedlings subjected to 65 W or 0P accumulated less biomass, smaller root-collar diameters, and lower nitrogen and phosphorus contents. Combined reductions in water and P resulted in seedlings with increased root to shoot dry biomass and shorter shoots. Seedlings subjected to 65 W also had lower instantaneous rates of CO₂ assimilation, but higher instantaneous water-use efficiencies following irrigation, suggesting that koa responds to water deficits by decreasing water loss via reduced stomatal conductance. Seedlings subjected to 0P had similar rates of CO₂ assimilation relative to those grown with adequate P, suggesting that koa is able to employ strategies to avoid physiological impairment from conditions of inadequate P. Future research should assess whether subjecting koa seedlings to reduced water before planting on water-limited sites cues increased drought resistance and whether uptake and storage of P by seedlings in the nursery better supports growth following outplanting, particularly on sites with anticipated low plant-available water.

     

Exploring transformational outcomes from donor investments in agroforestry research for development

Agroforestry Systems - While many agroforestry research projects contribute to improving food security, livelihoods and management of natural resources, few have had a significant role in achieving...     

Putative human and avian risk factors for avian influenza virus infections in backyard poultry in Egypt

Highly pathogenic influenza A virus subtype H5N1 causes significant poultry mortality in the six countries where it is endemic and can also infect humans. Egypt has reported the third highest number of poultry outbreaks (n = 1084) globally. The objective of this cross-sectional study was to identify putative risk factors for H5N1 infections in backyard poultry in 16 villages in Damietta, El Gharbia, Fayoum, and Menofia governorates from 2010–2012. Cloacal and tracheal swabs and serum samples from domestic (n = 1242) and wild birds (n = 807) were tested for H5N1 via RT-PCR and hemagglutination inhibition, respectively. We measured poultry rearing practices with questionnaires (n = 306 households) and contact rates among domestic and wild bird species with scan sampling. Domestic birds (chickens, ducks, and geese, n = 51) in three governorates tested positive for H5N1 by PCR or serology. A regression model identified a significant correlation between H5N1 in poultry and the practice of disposing of dead poultry and poultry feces in the garbage (F = 15.7, p < 0.0001). In addition, contact between domestic and wild birds was more frequent in villages where we detected H5N1 in backyard flocks (F = 29.5, p < 0.0001).