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Central Differences (central + difference)
Selected AbstractsInterpreting sustainable development and societal utility in Norwegian GMO assessmentsENVIRONMENTAL POLICY AND GOVERNANCE, Issue 4 2008G. Kristin Rosendal Abstract This article examines the process of assessing applications for genetically modified (GM) crops or plants for import or commercial planting in Norway. GMO legislation in Norway is closely linked to the EU through the Agreement on the European Economic Area (EEA), to which Norway is a party. A central difference with the EU processes emanates from specific clauses in the Norwegian Gene Technology Act on ,sustainable development' and ,societal utility', which provide a potentially wider leverage for Norwegian authorities to turn down the applications. Research material indicates evidence of an increasingly restrictive practice in the Norwegian evaluations, raising the question of how this can be explained in the face of increasing global acceptance of GMOs. A related question is to what extent and how this result is affected by the trends in the EU. An increasingly restrictive practice may be explained by changes in the access structure to the evaluating body, or it may be due to learning and a growing acceptance of the precautionary principle in this sector. Third, a higher number of rejections may largely be associated with the interest structure pertaining to GMOs in Norway. Final decisions are pending and there are uncertainties concerning how Norwegian authorities will apply the specific criteria of the Gene Technology Act. Copyright © 2008 John Wiley & Sons, Ltd and ERP Environment. [source] Susceptibility of a Northern Hardwood Forest to Exotic Earthworm InvasionCONSERVATION BIOLOGY, Issue 4 2005MICHAEL J. GUNDALE Acer saccharum; Bosque Nacional Ottawa; lombrices invasoras; Sylvania Wilderness Area; uso del suelo Abstract:,Numerous exotic earthworm species are colonizing northern hardwood forests of North America, where no native earthworms exist. Upon invasion, earthworms have been shown to alter the surface soil environment and plant populations and communities. We sought to identify land-use factors in the Ottawa National Forest (ONF), Michigan (U.S.A.), that contribute to earthworm invasion in forest dominated by sugar maple (Acer saccharum Marsh.) so that the susceptibility to additional colonization could be evaluated. We sampled earthworm communities in Sylvania Wilderness Area, a unique old-growth hardwood forest, and nonwilderness sites influenced by recreational fishing, recent timber harvesting, or roads. All the nonwilderness sites contained one to five species of exotic earthworms. In contrast, only 50% of wilderness sites contained exotic earthworms, all of a single species. Nonwilderness sites also had thinner litter and duff layers, higher soil C and N content, and higher nitrogen mineralization potentials than Sylvania sites. Two central differences between Sylvania and nonwilderness sites were that all nonwilderness sites were in close contact with roads and had a history of timber harvest, whereas these factors were not present in Sylvania Wilderness Area. Using average rates of colonization, we constructed two geographic information system models to estimate the percentage of sugar maple on the ONF falling within a theoretical 100-year invasion distance of roads and of second-growth sugar maple as relative indices of susceptibility to invasion. Both models indicated high susceptibility to invasion, with 91.7% and 98.9% of sugar maple habitat falling within a theoretical 100-year invasion distance of roads or historical harvests, respectively. Resumen:,Numerosas especies de lombrices exóticas están colonizando los bosques boreales, en los que previamente no existían lombrices terrestres nativas. Por encima de la invasión, se ha demostrado que las lombrices alteran el ambiente superficial del suelo, así como a las comunidades y poblaciones de plantas. Tratamos de identificar factores de uso del suelo en el Bosque Nacional Ottawa (BNO), Michigan, E. U. A., que contribuyen a la invasión de lombrices en bosques dominados por arces (Acer saccharum Marsh.), para poder evaluar la susceptibilidad a futuras invasiones. Muestreamos comunidades de lombrices en Sylvania Wilderness Area, un bosque maduro único, y en sitios no silvestres influenciados por pesca deportiva, cosecha reciente de madera o caminos. Todas las áreas no silvestres contenían 1 - 5 especies de lombrices exóticas. En contraste, solo 50% de los sitios silvestres contenían lombrices exóticas, todas de una sola especie. Los sitios no silvestres también tenían capas de hojarasca y de mantillo más delgadas, mayor contenido de C y N del suelo y mayor potencial de mineralización del nitrógeno que los sitios en Sylvania. Dos diferencias centrales entre Sylvania y los sitios no silvestres fueron que estos estaban en contacto cercano con caminos y tenían una historia de cosecha de madera, mientras que estos factores no estuvieron presentes en Sylvania Wilderness Area. Utilizando tasas promedio de colonización, construimos dos modelos de sistemas de información geográfica para estimar el porcentaje de arces en el BNO que queda a una distancia teórica de invasión en 100 años; con caminos y arce de crecimiento secundario como índices relativos de susceptibilidad a la invasión. Ambos modelos indicaron alta susceptibilidad a la invasión, con 91.7% y 98.9% del hábitat de arce dentro de la distancia teórica de invasión en 100 años o con cosechas históricas, respectivamente. [source] Rotating incompressible flow with a pressure Neumann conditionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2006Julio R. Claeyssen Abstract This work considers the internal flow of an incompressible viscous fluid contained in a rectangular duct subject to a rotation. A direct velocity,pressure algorithm in primitive variables with a Neumann condition for the pressure is employed. The spatial discretization is made with finite central differences on a staggered grid. The pressure and velocity fields are directly updated without any iteration. Numerical simulations with several Reynolds numbers and rotation rates were performed for ducts of aspect ratios 2:1 and 8:1. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical simulation of the unsteady flow over an elliptic cylinder at different orientationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2001H. M. Badr Abstract A numerical method is developed for investigating the two-dimensional unsteady viscous flow over an inclined elliptic cylinder placed in a uniform stream of infinite extent. The direction of the free stream is normal to the cylinder axis and the flow field unsteadiness arises from two effects, the first is due to the flow field development following the start of the motion and the second is due to vortex shedding in the wake region. The time-dependent flow is governed by the full conservation equations of mass and momentum with no boundary layer approximations. The parameters involved are the cylinder axis ratio, Reynolds number and the angle of attack. The investigation covers a Reynolds number range up to 5000. The minor,major axis ratio of the elliptic cylinder ranges between 0.5 and 0.6, and the angle of attack ranges between 0° and 90°. A series truncation method based on Fourier series is used to reduce the governing Navier,Stokes equations to two coupled infinite sets of second-order differential equations. These equations are approximated by retaining only a finite number of terms and are then solved by approximating the derivatives using central differences. The results reveal an unusual phenomenon of negative lift occurring shortly after the start of motion. Various comparisons are made with previous theoretical and experimental results, including flow visualizations, to validate the solution methodology. Copyright © 2001 John Wiley & Sons, Ltd. [source] A novel separable backward,central FDTD methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2006Wenhua Yu Abstract In this paper, we present a novel separable backward,central FDTD (SBC-FDTD) method in which the backward and central differences are used to discretize both time and spatial directive of the Maxwell's equations. For the type of problem in which the FDTD cell size in one direction is much smaller than those in the other directions, the time step in the proposed separable backward-central FDTD technique can be chosen based on the largest cell size instead of the smallest one used in the conventional Yee's FDTD. Compared to the alternating-direction implicit FDTD (ADI-FDTD), although the proposed approach is not unconditionally stable, it allows us to explicitly solve electric and magnetic fields in one direction. Both the numerical experiments and the stability property demonstrate that the proposed scheme is stable and accurate. A TE mode wave is used to validate the proposed technique. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 212,215, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21308 [source] | ||||||||||