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Various Heights (various + height)
Selected AbstractsWindblown dust influenced by conventional and undercutter tillage within the Columbia Plateau, USA,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2009B. S. Sharratt Abstract Exceedance of the US Environmental Protection Agency national ambient air quality standard for PM10 (particulate matter ,10 µm in aerodynamic diameter) within the Columbia Plateau region of the Pacific Northwest US is largely caused by wind erosion of agricultural lands managed in a winter wheat,summer fallow rotation. Land management practices, therefore, are sought that will reduce erosion and PM10 emissions during the summer fallow phase of the rotation. Horizontal soil flux and PM10 concentrations above adjacent field plots (>2 ha), with plots subject to conventional or undercutter tillage during summer fallow, were measured using creep and saltation/suspension collectors and PM10 samplers installed at various heights above the soil surface. After wheat harvest in 2004 and 2005, the plots were either disked (conventional) or undercut with wide sweeps (undercutter) the following spring and then periodically rodweeded prior to sowing wheat in late summer. Soil erosion from the fallow plots was measured during six sampling periods over two years; erosion or PM10 loss was not observed during two periods due to the presence of a crust on the soil surface. For the remaining sampling periods, total surface soil loss from conventional and undercutter tillage ranged from 3 to 40 g m,2 and 1 to 27 g m,2 while PM10 loss from conventional and undercutter tillage ranged from 0·2 to 5·0 g m,2 and 0·1 to 3·3 g m,2, respectively. Undercutter tillage resulted in a 15% to 65% reduction in soil loss and 30% to 70% reduction in PM10 loss as compared with conventional tillage at our field sites. Therefore, based on our results at two sites over two years, undercutter tillage appears to be an effective management practice to reduce dust emissions from agricultural land subject to a winter wheat,summer fallow rotation within the Columbia Plateau. Copyright © 2009 John Wiley & Sons, Ltd. [source] Soil,pile,structure interaction under SH wave excitationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2003K. K. Koo Abstract A continuum model for the interaction analysis of a fully coupled soil,pile,structure system under seismic excitation is presented in this paper. Only horizontal shaking induced by harmonic SH waves is considered so that the soil,pile,structure system is under anti-plane deformation. The soil mass, pile and superstructure were all considered as elastic with hysteretic damping, while geometrically both pile and structures were simplified as a beam model. Buildings of various heights in Hong Kong designed to resist wind load were analysed using the present model. It was discovered that the acceleration of the piled-structures at ground level can, in general, be larger than that of a free-field shaking of the soil site, depending on the excitation frequency. For typical piled-structures in Hong Kong, the amplification factor of shaking at the ground level does not show simple trends with the number of storeys of the superstructure, the thickness and the stiffness of soil, and the stiffness of the superstructure if number of storeys is fixed. The effect of pile stiffness on the amplification factor of shaking is, however, insignificant. Thus, simply increasing the pile size or the superstructure stiffness does not necessarily improve the seismic resistance of the soil,pile,structure system; on the contrary, it may lead to excessive amplification of shaking for the whole system. Copyright © 2003 John Wiley & Sons, Ltd. [source] Monitoring bird migration with a fixed-beam radar and a thermal-imaging cameraJOURNAL OF FIELD ORNITHOLOGY, Issue 3 2006Sidney A. Gauthreaux Jr ABSTRACT Previous studies using thermal imaging cameras (TI) have used target size as an indicator of target altitude when radar was not available, but this approach may lead to errors if birds that differ greatly in size are actually flying at the same altitude. To overcome this potential difficulty and obtain more accurate measures of the flight altitudes and numbers of individual migrants, we have developed a technique that combines a vertically pointed stationary radar beam and a vertically pointed thermal imaging camera (VERTRAD/TI). The TI provides accurate counts of the birds passing through a fixed, circular sampling area in the TI display, and the radar provides accurate data on their flight altitudes. We analyzed samples of VERTRAD/TI video data collected during nocturnal fall migration in 2000 and 2003 and during the arrival of spring trans-Gulf migration during the daytime in 2003. We used a video peak store (VPS) to make time exposures of target tracks in the video record of the TI and developed criteria to distinguish birds, foraging bats, and insects based on characteristics of the tracks in the VPS images and the altitude of the targets. The TI worked equally well during daytime and nighttime observations and best when skies were clear, because thermal radiance from cloud heat often obscured targets. The VERTRAD/TI system, though costly, is a valuable tool for measuring accurate bird migration traffic rates (the number of birds crossing 1609.34 m [1 statute mile] of front per hour) for different altitudinal strata above 25 m. The technique can be used to estimate the potential risk of migrating birds colliding with man-made obstacles of various heights (e.g., communication and broadcast towers and wind turbines),a subject of increasing importance to conservation biologists. SINOPSIS Estudios previos, en donde no se ha hecho uso de radar, han utilizado cámaras infrarojas de imagen termal (CIT) y el tamaño de individuos como indicador, para detereminar la altura de vuelo. Sin embargo, este método puede dar origen a errores si las aves que vuelan a una misma altura varían en tamaño. Para subsanar esta dificultad y tomar medidas más exactas de la altura de vuelo y el número de individuos en una bandada, desarrollamos una técnica que combina un radar de rayos fijos con antena parabólica (RRF) con una cámara infraroja de imagen termal (RRT/CIT). El CIT provee de un conteo preciso de las aves pasando por un área circular fija de muestreo y el radar provee el dato preciso de la altura de vuelo. Utilizando una videograbadora digital, analizamos las muestras tomadas con la combinación RRT/CIT durante la migración otoñal noctura en el 2000 y el 2003 y durante la migración primaveral diurna del 2003, a través del Golfo de México. Utilizamos la cámara de video para hacer exposiciones en lapsos de tiempo en lo tomado por el CIT y desarrollamos criterios para distinguir entre aves, murciélagos e insectos, usando la huella dejada en el video y la altura del objeto. El CIT trabajo de forma eficiente tanto de dia como de noche, pero aún mejor cuando el cielo estaba despejado (cuando esta ausente la interferencia por la irradiación de calor de parte de las nubes). El sistema RRT/CIT, aunque costoso, es una herramienta valiosa para medir con presición las rutas migratorias y el número de aves moviéndose a diferente altura. Dicho sistema es de gran utilidad para determinar el riesgo de coliciones de aves migratorias con obstáculos construidos por el hombre a diferentes alturas (ej. torres de comunicación o turbinas de viento), asuntos de gran relevancia e importancia para la conservación de aves. [source] Diversity of canopy and understorey spiders in north-temperate hardwood forestsAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2009Maxim Larrivée Abstract 1,We characterized and compared diversity patterns of canopy and understorey spiders (Arachnida: Araneae) on sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.) in hardwood forests of southern Québec, Canada. 2,We sampled canopies of 45 sugar maple and 45 American beech trees and associated understorey saplings in mature protected forests near Montréal. Samples were obtained by beating the crown foliage at various heights and by beating saplings around each tree. 3,Eighty-two species were identified from 13 669 individuals. Forty-eight species and 3860 individuals and 72 species and 9809 individuals were collected from the canopy and the understorey, respectively. 4,Multivariate analyses (NMDS ordination and NPMANOVA) showed the composition of canopy and understorey assemblages differed significantly, and canopy assemblages differed between tree species. Rank-abundance distribution models fitted to the canopy and understorey data indicated that different mechanisms structure the assemblages in both habitats. Three abundant spider species were significantly more common in the canopy; ten species were collected significantly more often in the understorey. 5,The forest canopy was shown to be an important reservoir for spider diversity in north-temperate forests. [source] Crown development in a pioneer tree, Rhus trichocarpa, in relation to the structure and growth of individual branchesNEW PHYTOLOGIST, Issue 4 2006Noriyuki Osada Summary ,,Based on an allometric reconstruction, the structure and biomass-allocation patterns of branches and current-year shoots were investigated in branches of various heights in the pioneer tree Rhus trichocarpa, to evaluate how crown development is achieved and limited in association with height. Path analysis was conducted to explore the effects of light availability, basal height and size of individual branches on branch structure and growth. ,,Branch angle was affected by basal height, whereas branch mass was influenced primarily by light availability. This result suggests that branch structure is strongly constrained by basal height, and that trees mediate such constraints under different light environments. ,,Previous-year leaf area and light availability showed positive effects on current-year stem mass. In contrast, branch basal height and mass negatively affected current-year stem mass. Moreover, the length of stems of a given diameter decreased with increasing branch height. Therefore the cost of biomass investment for a unit growth in length is greater for branches of larger size and at upper positions. ,,Vertical growth rate in length decreased with increasing height. Height-dependent changes in stem allometry and angle influenced the reduction in vertical growth rate to a similar degree. [source] | |||||||||||||