75,389 research outputs found
GROUNDWATER PROTECTION POLICY AND AGRICULTURAL PRODUCTION: A RECURSIVE STOCHASTIC ANALYSIS
Contamination of groundwater by agricultural practices presents a dilemma between protecting a vital resource and maintaining a valuable part of the economy. Policies to balance these objectives are presented. In addition to an historical baseline, policies that ban certain pesticides, taxes and subsidies, and control cultural practices are also considered. A model is developed to reflect the current state of agriculture in Eastern Suffolk County. This model consists of a recursive programming component, which has input for it generated by a stochastic model of Colorado potato beetle pest dynamics and management strategies to control those pests. While income is reduced by banning pesticides, the reduction is small when compared with the improvement in environmental quality. Further efforts to reduce pesticide use resulted in a reduction in potato acreage and incomes, as well as yields. Analysis concludes that improvements in both farm income and environmental quality could be achieved through the adoption of subsidies for low-input conservation crops.Resource /Energy Economics and Policy,
Stationary device produces homogeneous mixture of fluids
Stationary device produces a homogeneous mixture of two or more one-phase or two-phase fluids. The device contains two concentric flow guides with helical passageways through which the fluids are forced into turbulent flow by the system pressure differential
Flux-tube Structure, Sum Rules and Beta-functions in SU(2)
Action and energy flux-tube profiles are computed, in SU(2) with
beta=2.4,2.5, for two quarks up to 1 fm apart and for which the colour fields
are in their ground state (A_1g) and the first (E_u) and higher (A'_1g) excited
gluonic states. When these profiles are integrated over all space, a scaling
comparison is made between the beta=2.4 and 2.5 data. Using sum rules, these
integrated forms also permit an estimate to be made of generalised
beta-functions giving b(2.4)=-0.312(15), b(2.5)=-0.323(9), f(2.4)=0.65(1) and
f(2.5)=0.68(1). When the profiles are integrated only over planes transverse to
the interquark line and assuming underlying string features, scaling
comparisons are again made near the centres of the interquark line for the
largest interquark distances. For the A'_{1g} case, some of the profiles
exhibit a 'dip-like' structure characteristic of the Isgur-Paton model.Comment: 3 pages, 6 eps figures. Presented at LATTICE9
Travelling gradients in interacting morphogen systems
Morphogen gradients are well known to play several important roles in development; however the mechanisms underlying the formation and maintenance of these gradients are often not well understood. In this work, we investigate whether the presence of a secondary morphogen can increase the robustness of the primary morphogen gradient to perturbation, thereby providing a more stable mechanism for development. We base our model around the interactions of Fibroblast Growth Factor 8 and retinoic acid, which have been shown to act as morphogens in many developmental systems. In particular, we investigate the formation of opposing gradients of these morphogens along the antero-posterior axis of vertebrate embryos, thereby controlling temporal and spatial aspects of axis segmentation and neuronal differentiation
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